Monitoring Period and Amplitude Changes in Classical Cepheids

NASA Astrophysics Data System (ADS)

Erickson, Mary; Engle, Scott G.; Wells, Mark

2017-06-01

Cepheid Variable Stars, which are located on the Instability Strip of the Hertzsprung-Russel Diagram, can be used as “standard candle” distance markers (Fiorentino 2007). This came about after the discovery of the Period-Luminosity Relationship (the Leavitt Law), and they have since become a cornerstone of the Cosmic Distance Scale and are helping to further refine the Hubble Constant. Cepheids will cross the Instability Strip, either in a “redward” (cooler) or “blueward” (hotter) direction depending on the stage in which the Cepheid is evolving (Neilson 2012). While Cepheids were originally believed to have regular periods, many are now known to have varying periods, dating back to Eddington (1919). Therefore, Cepheids must be closely monitored in order to deduce where these period variations are coming from - either from inside the star itself or from some outside source. Determining period changes in Cepheids can reveal important information (e.g. evolutionary states, potential companions, etc.).Photometric data were taken for two Cepheids from two different sources and analyzed. The Cepheids in question are AA Gem and BB Gem, both located in the Gemini constellation. Data for these two stars were taken from the All Sky Automated Survey (ASAS) and from the Robotically Controlled Telescope (RCT) at Kitt Peak National Observatory, on which Villanova has guaranteed access. ASAS observes automatically each clear night, and has done so for several years, making it an excellent source for obtaining Cepheid data. The RCT telescope also operates automatically, observing from a preset target list, and achieves a much higher precision than ASAS can. Multi-aperture photometry was performed on the AA Gem and BB Gem RCT images, in Astroimagej. The data were then separated into different seasons, and Fourier fits were applied to the light curves in Kephem (written by Andrej Prša and collaborators). These results were then analyzed via the Hertzsprung Method to find changes in the Cepheids’ times of maximum light (and thus periods).

Monitoring Period and Amplitude Changes in Classical Cepheids

NASA Astrophysics Data System (ADS)

Erickson, Mary; Engle, Scott G.; Wells, Mark

2017-01-01

Cepheid Variable Stars, which are located on the Instability Strip of the Hertzsprung-Russel Diagram, can be used as “standard candle” distance markers (Fiorentino 2007). This came about after the discovery of the Period-Luminosity Relationship (the Leavitt Law), and they have since become a cornerstone of the Cosmic Distance Scale and are helping to further refine the Hubble Constant. Cepheids will cross the Instability Strip, either in a “redward” (cooler) or “blueward” (hotter) direction depending on the stage in which the Cepheid is evolving (Neilson 2012). While Cepheids were originally believed to have regular periods, many are now known to have varying periods, dating back to Eddington (1919). Therefore, Cepheids must be closely monitored in order to deduce where these period variations are coming from - either from inside the star itself or from some outside source. Determining period changes in Cepheids can reveal important information (e.g. evolutionary states, potential companions, etc.).Photometric data were taken for two Cepheids from two different sources and analyzed. The Cepheids in question are AA Gem and BB Gem, both located in the Gemini constellation. Data for these two stars were taken from the All Sky Automated Survey (ASAS) and from the Robotically Controlled Telescope (RCT) at Kitt Peak National Observatory, on which Villanova has guaranteed access. ASAS observes automatically each clear night, and has done so for several years, making it an excellent source for obtaining Cepheid data. The RCT telescope also operates automatically, observing from a preset target list, and achieves a much higher precision than ASAS can. Multi-aperture photometry was performed on the AA Gem and BB Gem RCT images, in Astroimagej. The data were then separated into different seasons, and Fourier fits were applied to the light curves in Kephem (written by Andrej Prša and collaborators). These results were then analyzed via the Hertzsprung Method to find changes in the Cepheids’ times of maximum light (and thus periods).

The HST Key Project on the Extragalactic Distance Scale VI. The Cepheids in NGC925

NASA Technical Reports Server (NTRS)

Silbermann, N. A.; Harding, Paul; Madore, Barry F.; Kennicutt, Robert C., Jr.; Saha, Abhijit; Stetson, Peter; Freedman, Wendy L.; Mould, Jeremy R.; Graham, John A.; Hill, Robert J.;

KIC2569073, A second Cepheid in the Kepler FOV

NASA Astrophysics Data System (ADS)

Drury, Jason A.; Kuehn, Charles A.; Bellamy, Beau R.; Stello, Dennis; Bedding, Timothy R.

2015-09-01

One particularly interesting new variable discovered via Kepler's 200x200 pixel superstamp images is KIC2569073. With a period of 14.66 days and 0.04mag variability it is only the second Cepheid in the Kepler field, or a rotationally modulated variable. We discuss its classification as a Type II W Virginis Class Cepheid, and present the cycle-to-cycle period variations of this star, as well as the first direct observations of granulation noise within a Cepheid.

Extended Envelopes around Galactic Cepheids. III. Y Ophiuchi and α Persei from Near-Infrared Interferometry with CHARA/FLUOR

NASA Astrophysics Data System (ADS)

Mérand, Antoine; Aufdenberg, Jason P.; Kervella, Pierre; Foresto, Vincent Coudé du; ten Brummelaar, Theo A.; McAlister, Harold A.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.

2007-08-01

Unbiased angular diameter measurements are required for accurate distances to Cepheids using the interferometric Baade-Wesselink method (IBWM). The precision of this technique is currently limited by interferometric measurements at the 1.5% level. At this level, the center-to-limb darkening (CLD) and the presence of circumstellar envelopes (CSE) seem to be the two main sources of bias. The observations we performed aim at improving our knowledge of the interferometric visibility profile of Cepheids. In particular, we assess the systematic presence of CSE around Cepheids in order determine accurate distances with the IBWM free from CSE biased angular diameters. We observed a Cepheid (Y Oph) for which the pulsation is well resolved and a nonpulsating yellow supergiant (α Per) using long-baseline near-infrared interferometry. We interpreted these data using a simple CSE model we previously developed. We found that our observations of α Per do not provide evidence for a CSE. The measured CLD is explained by an hydrostatic photospheric model. Our observations of Y Oph, when compared to smaller baseline measurements, suggest that it is surrounded by a CSE with characteristics similar to CSEs found previously around other Cepheids. We have determined the distance to Y Oph to be d=491+/-18 pc. Additional evidence points toward the conclusion that most Cepheids are surrounded by faint CSEs, detected by near-infrared interferometry: after observing four Cepheids, all show evidence for a CSE. Our CSE nondetection around a nonpulsating supergiant in the instability strip, α Per, provides confidence in the detection technique and suggests a pulsation driven mass-loss mechanism for the Cepheids.

Ultra long period Cepheids: a primary standard candle out to the Hubble flow

NASA Astrophysics Data System (ADS)

Fiorentino, G.; Clementini, G.; Marconi, M.; Musella, I.; Saha, A.; Tosi, M.; Contreras Ramos, R.; Annibali, F.; Aloisi, A.; van der Marel, R.

2012-09-01

The cosmological distance ladder crucially depends on classical Cepheids (with P=3-80 days), which are primary distance indicators up to 33 Mpc. Within this volume, very few SNe Ia have been calibrated through classical Cepheids, with uncertainty related to the non-linearity and the metallicity dependence of their period-luminosity (PL) relation. Although a general consensus on these effects is still not achieved, classical Cepheids remain the most used primary distance indicators. A possible extension of these standard candles to further distances would be important. In this context, a very promising new tool is represented by the ultra-long period (ULP) Cepheids ( P≳80 days), recently identified in star-forming galaxies. Only a small number of ULP Cepheids have been discovered so far. Here we present and analyse the properties of an updated sample of 37 ULP Cepheids observed in galaxies within a very large metallicity range of 12+log(O/H) from ˜7.2 to 9.2 dex. We find that their location in the colour-magnitude ( V- I, V) diagram as well as their Wesenheit ( V- I) index-period (WP) relation suggests that they are the counterparts at high luminosity of the shorter-period ( P≲80 days) classical Cepheids. However, a complete pulsation and evolutionary theoretical scenario is needed to properly interpret the true nature of these objects. We do not confirm the flattening in the studied WP relation suggested by Bird et al. (Astrophys. J. 695:874, 2009). Using the whole sample, we find that ULP Cepheids lie around a WP relation similar to that of the LMC, although with a large spread (˜ 0.4 mag).

THE SECRET LIVES OF CEPHEIDS: EVOLUTION, MASS-LOSS, AND ULTRAVIOLET EMISSION OF THE LONG-PERIOD CLASSICAL CEPHEID

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neilson, Hilding R.; Engle, Scott G.; Guinan, Edward F.

The classical Cepheid l Carinae is an essential calibrator of the Cepheid Leavitt Law as a rare long-period Galactic Cepheid. Understanding the properties of this star will also constrain the physics and evolution of massive ( M ≥ 8 M {sub ⊙}) Cepheids. The challenge, however, is precisely measuring the star's pulsation period and its rate of period change. The former is important for calibrating the Leavitt Law and the latter for stellar evolution modeling. In this work, we combine previous time-series observations spanning more than a century with new observations to remeasure the pulsation period and compute the ratemore » of period change. We compare our new rate of period change with stellar evolution models to measure the properties of l Car, but find models and observations are, at best, marginally consistent. The results imply that l Car does not have significantly enhanced mass-loss rates like that measured for δ Cephei. We find that the mass of l Car is about 8–10 M {sub ⊙}. We present Hubble Space Telescope Cosmic Origins Spectrograph observations that also differ from measurements for δ Cep and β Dor. These measurements further add to the challenge of understanding the physics of Cepheids, but do hint at the possible relation between enhanced mass-loss and ultraviolet emission, perhaps both due to the strength of shocks propagating in the atmospheres of Cepheids.« less

Optical interferometry and Gaia parallaxes for a robust calibration of the Cepheid distance scale

NASA Astrophysics Data System (ADS)

Kervella, Pierre; Mérand, Antoine; Gallenne, Alexandre; Trahin, Boris; Borgniet, Simon; Pietrzynski, Grzegorz; Nardetto, Nicolas; Gieren, Wolfgang

2018-04-01

We present the modeling tool we developed to incorporate multi-technique observations of Cepheids in a single pulsation model: the Spectro-Photo-Interferometry of Pulsating Stars (SPIPS). The combination of angular diameters from optical interferometry, radial velocities and photometry with the coming Gaia DR2 parallaxes of nearby Galactic Cepheids will soon enable us to calibrate the projection factor of the classical Parallax-of-Pulsation method. This will extend its applicability to Cepheids too distant for accurate Gaia parallax measurements, and allow us to precisely calibrate the Leavitt law's zero point. As an example application, we present the SPIPS model of the long-period Cepheid RS Pup that provides a measurement of its projection factor, using the independent distance estimated from its light echoes.

Ultraviolet studies of Cepheids

NASA Technical Reports Server (NTRS)

Boehm-Vitense, Erika

1992-01-01

We discuss whether with new evolutionary tracks we still have a problem fitting the Cepheids and their evolved companions on the appropriate evolutionary tracks. We find that with the Bertelli et al. tracks with convective overshoot by one pressure scale height the problem is essentially removed, though somewhat more mixing would give a better fit. By using the results of recent nonlinear hydrodynamic calculations, we find that we also have no problem matching the observed pulsation periods of the Cepheids with those expected from their new evolutionary masses, provided that Cepheids with periods less than 9 days are overtone pulsators. We investigate possible mass loss of Cepheids from UV studies of the companion spectrum of S Mus and from the ultraviolet spectra of the long period Cepheid l Carinae. For S Mus with a period of 9.6 days we derive an upper limit for the mass loss of M less than 10(exp -9) solar mass, if a standard velocity law is assumed for the wind. For l Carinae with a period of 35.5 days we find a probable mass loss of M is approximately 10(exp -5+/-2) solar mass.

The Carnegie Hubble Program

NASA Technical Reports Server (NTRS)

Freedman, Wendy L.; Madore, Barry F.; Scowcroft, Vicky; Mnso, Andy; Persson, S. E.; Rigby, Jane; Sturch, Laura; Stetson, Peter

2011-01-01

We present an overview of and preliminary results from an ongoing comprehensive program that has a goal of determining the Hubble constant to a systematic accuracy of 2%. As part of this program, we are currently obtaining 3.6 micron data using the Infrared Array Camera (IRAC) on Spitzer, and the program is designed to include JWST in the future. We demonstrate that the mid-infrared period-luminosity relation for Cepheids at 3.6 microns is the most accurate means of measuring Cepheid distances to date. At 3.6 microns, it is possible to minimize the known remaining systematic uncertainties in the Cepheid extragalactic distance scale. We discuss the advantages of 3.6 micron observations in minimizing systematic effects in the Cepheid calibration of the Hubble constant including the absolute zero point, extinction corrections, and the effects of metallicity on the colors and magnitudes of Cepheids. We are undertaking three independent tests of the sensitivity of the mid-IR Cepheid Leavitt Law to metallicity, which when combined will allow a robust constraint on the effect. Finally, we are providing a new mid-IR Tully-Fisher relation for spiral galaxies.

Toward a renewed Galactic Cepheid distance scale from Gaia and optical interferometry

NASA Astrophysics Data System (ADS)

Kervella, Pierre; Mérand, Antoine; Gallenne, Alexandre; Trahin, Boris; Nardetto, Nicolas; Anderson, Richard I.; Breitfelder, Joanne; Szabados, Laszlo; Bond, Howard E.; Borgniet, Simon; Gieren, Wolfgang; Pietrzyński, Grzegorz

2017-09-01

Through an innovative combination of multiple observing techniques and modeling, we are assembling a comprehensive understanding of the pulsation and close environment of Cepheids. We developed the SPIPS modeling tool that combines all observables (radial velocimetry, photometry, angular diameters from interferometry) to derive the relevant physical parameters of the star (effective temperature, infrared excess, reddening, …) and the ratio of the distance and the projection factor d/p. We present the application of SPIPS to the long-period Cepheid RS Pup, for which we derive p = 1.25±0.06. The addition of this massive Cepheid consolidates the existing sample of p-factor measurements towards long-period pulsators. This allows us to conclude that p is constant or mildly variable around p = 1.29±0.04 (±3%) as a function of the pulsation period. The forthcoming Gaia DR2 will provide a considerable improvement in quantity and accuracy of the trigonometric parallaxes of Cepheids. From this sample, the SPIPS modeling tool will enable a robust calibration of the Cepheid distance scale.

Intrinsically variable stars

NASA Technical Reports Server (NTRS)

Bohm-Vitense, Erika; Querci, Monique

1987-01-01

The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.

X-Ray, UV and Optical Observations of Classical Cepheids: New Insights into Cepheid Evolution, and the Heating and Dynamics of Their Atmospheres

NASA Astrophysics Data System (ADS)

Engle, Scott G.; Guinan, Edward F.

2012-06-01

To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic origins spectrograph (COS) FUV-UV spectra of the bright, nearby Cepheids Polaris, δ Cep and β Dor. Previous studies made with the international ultraviolet explorer (IUE) showed a limited number of UV emission lines in Cepheids. The well-known problem presented by scattered light contamination in IUE spectra for bright stars, along with the excellent sensitivity & resolution combination offered by HST/COS, motivated this study, and the spectra obtained were much more rich and complex than we had ever anticipated. Numerous emission lines, indicating 10^4 K up to ~3 x 10^5 K plasmas, have been observed, showing Cepheids to have complex, dynamic outer atmospheres that also vary with the photospheric pulsation period. The FUV line emissions peak in the phase range φ ∼ 0.8-1.0 and vary by factors as large as 10x. A more complete picture of Cepheid outer atmospheres is accomplished when the HST/COS results are combined with X-ray observations that we have obtained of the same stars with XMM-Newton & Chandra. The Cepheids detected to date have X-ray luminosities of log Lx ~ 28.5-29.1 ergs/sec, and plasma temperatures in the 2-8 x 10^6 K range. Given the phase-timing of the enhanced emissions, the most plausible explanation is the formation of a pulsation-induced shocks that excite (and heat) the atmospheric plasmas surrounding the photosphere. A pulsation-driven α^2 equivalent dynamo mechanism is also a viable and interesting alternative. However, the tight phase-space of enhanced emission (peaking near 0.8-1.0 φ) favor the shock heating mechanism hypothesis.

Binary Cepheids From High-Angular Resolution

NASA Astrophysics Data System (ADS)

Gallenne, A.; Mérand, A.; Kervella, P.

2015-12-01

Optical interferometry is the only technique giving access to milli-arcsecond (mas) spatial resolution. This is a powerful and unique tool to detect the close orbiting companions of Cepheids, and offers an unique opportunity to make progress in resolving the Cepheid mass discrepancy. Our goal in studying binary Cepheids is to measure the astrometric position of the high-contrast companion, and then combine them with spectroscopic measurements to derive the orbital elements, distances, and dynamical masses. In the course of this program, we developed a new tool, CANDID, to search for high-contrast companions and set detection limits from interferometric observations

Recent progress in the theoretical modelling of Cepheids and RR Lyrae stars

NASA Astrophysics Data System (ADS)

Marconi, Marcella

2017-09-01

Cepheids and RR Lyrae are among the most important primary distance indicators to calibrate the extragalactic distance ladder and excellent stellar population tracers, for Population I and Population II, respectively. In this paper I first mention some recent theoretical studies of Cepheids and RR Lyrae obtained with different theoretical tools. Then I focus the attention on new results based on nonlinear convective pulsation models in the context of some international projects, including VMC@VISTA and the Gaia collaboration. The open problems for both Cepheids and RR Lyrae are briefly discussed together with some challenging future application.

Metallicity mapping of the Milky Way

NASA Astrophysics Data System (ADS)

Scowcroft, Vicky; Madore, Barry; Freedman, Wendy; Monson, Andy; Persson, Eric; Seibert, Mark; Rigby, Jane; Bersier, David; Stetson, Peter; Sturch, Laura

2011-05-01

We have discovered that the mid-infrared [3.6]-[4.5] colors of long-period Cepeids are dominated by a metallicity and temperature sensitive carbon monoxide feature that is squarely situated inside of the 4.5mu bandpass. The [3.6] photometry is unaffected by the CO and its PL relation can deliver distances to Cepheids that are individually good to ±4%. We will use the time-averaged 3.6um photometry of the 120 longest -period Galactic Cepheids to map the spiral structure of the Milky Way out to a radius 6 kpc around the solar neighborhood, and we will then use the [3.6]-[4.5] colors to derive spectroscopic-quality metallicities for each of these Cepheids. This will alow us to measure the radial gradient of metals in the galaxy and to explore its variance at fixed radius. For Cepheids with phased radial-velocity coverage we will for the first time apply the Baade-Wesselink methodology in the mid-infrared for determining the absolute luminosities (and distances) of these Cepheids. These determinations will greatly enhance the precision calibration of the slope, zero point and width of the Cepheid Period-Luminosity relation, well in advance of GAIA (whose nominal mission end is 2017). However, once GAIA has determined direct parallaxes to these same long-period Cepheids we will immediately be in a position to make the necessary intercomparisons and explore the physical consequences.

Circumstellar envelopes of Cepheids: a possible bias affecting the distance scale?

NASA Astrophysics Data System (ADS)

Kervella, Pierre; Gallenne, Alexandre; Mérand, Antoine

2013-02-01

Circumstellar envelopes (CSEs) have been detected around many Cepheids, first based on long-baseline interferometry, and now also using other observing techniques. These envelopes are particularly interesting for two reasons: their presence could impact the Cepheid distance scale, and they may be valuable tracers of stellar mass loss. Here we focus on their potential impact on the calibration of the Cepheid distance scale. We consider the photometric contribution of the envelopes in the visible, near-, and thermal-infrared domains. We conclude that the impact of CSEs on the apparent luminosities of Cepheids is negligible at visible wavelengths and generally weak (<5%) in the near-infrared (λ ~ 2 μm). In the thermal-infrared domain (λ ~ 8 μm), the flux contribution of the CSEs differs depending on the pulsation period: it is relatively weak (<15%) for stars with periods shorter than P ~ 10 days, but can reach ~ 30% for long-period Cepheids. We specifically discuss the long-period Galactic Cepheid RS Puppis, which exhibits a very large circumstellar, dusty envelope, and we conclude that this is not a representative case. Overall, the contribution of CSEs to the usual period-luminosity relations (from the visible to the K band) is mostly negligible. They could affect calibrations at longer wavelengths, although the presence of envelopes may have been partially taken into account in the existing empirical calibrations.

A Precision Determination of the Effect of Metallicity on Cepheid Absolute Magnitudes in VIJHK Bands from Magellanic Cloud Cepheids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wielgórski, Piotr; Pietrzyński, Grzegorz; Zgirski, Bartłomiej

Using high-quality observed period–luminosity ( P – L ) relations in both Magellanic Clouds in the VIJHK s bands and optical and near-infrared Wesenheit indices, we determine the effect of metallicity on Cepheid P – L relations by comparing the relative distance between the LMC and SMC as determined from the Cepheids to the difference in distance between the Clouds that has been derived with very high accuracy from late-type eclipsing binary systems. Within an uncertainty of 3%, which is dominated by the uncertainty on the mean difference in metallicity between the Cepheid populations in the LMC and SMC, wemore » find metallicity effects smaller than 2% in all bands and in the Wesenheit indices, consistent with a zero metallicity effect. This result is valid for the metallicity range from −0.35 dex to −0.75 dex corresponding to the mean [Fe/H] values for classical Cepheids in the LMC and SMC, respectively. Yet most Cepheids in galaxies beyond the Local Group and located in the less crowded outer regions of these galaxies do fall into this metallicity regime, making our result important for applications to determine the distances to spiral galaxies well beyond the Local Group. Our result supports previous findings that indicated a very small metallicity effect on the near-infrared absolute magnitudes of classical Cepheids, and resolves the dispute about the size and sign of the metallicity effect in the optical spectral range. It also resolves one of the most pressing problems in the quest toward a measurement of the Hubble constant with an accuracy of 1% from the Cepheid–supernova Ia method.« less

The Secret Lives of Cepheids: δ Cep—The Prototype of a New Class of Pulsating X-Ray Variable Stars

NASA Astrophysics Data System (ADS)

Engle, Scott G.; Guinan, Edward F.; Harper, Graham M.; Cuntz, Manfred; Remage Evans, Nancy; Neilson, Hilding R.; Fawzy, Diaa E.

2017-03-01

From our Secret Lives of Cepheids program, the prototype Classical Cepheid, δ Cep, is found to be an X-ray source with periodic pulsation-modulated X-ray variations. This finding complements our earlier reported phase-dependent FUV-UV emissions of the star that increase ˜10-20 times with highest fluxes at ˜ 0.90{--}0.95φ , just prior to maximum brightness. Previously δ Cep was found as potentially X-ray variable, using XMM-Newton observations. Additional phase-constrained data were secured with Chandra near X-ray emission peak, to determine if the emission and variability were pulsation-phase-specific to δ Cep and not transient or due to a possible coronally active, cool companion. The Chandra data were combined with prior XMM-Newton observations, and were found to very closely match the previously observed X-ray behavior. From the combined data set, a ˜4 increase in X-ray flux is measured, reaching a peak {L}{{X}} = 1.7 × 1029 erg s-1 near 0.45ϕ. The precise X-ray flux phasing with the star’s pulsation indicates that the emissions arise from the Cepheid and not from a companion. However, it is puzzling that the maximum X-ray flux occurs ˜0.5ϕ (˜3 days) later than the FUV-UV maximum. There are several other potential Cepheid X-ray detections with properties similar to δ Cep, and comparable X-ray variability is indicated for two other Cepheids: β Dor and V473 Lyr. X-ray generating mechanisms in δ Cep and other Cepheids are discussed. If additional Cepheids are confirmed to show phased X-ray variations, then δ Cep will be the prototype of a new class of pulsation-induced X-ray variables.

Lightcurves and Period Changes for Type II Cepheids in the Globular Cluster M13 (Abstract)

NASA Astrophysics Data System (ADS)

Smith, H. A.; Anderson, M.; Osborn, W.; Layden, A.; Kopacki, G.; Pritzl, B.; Kelley, A.; McBride, K.; Alexander, M.; Kuehn, C.; Kilian, A.; King, E.; Carbajal, D.; Lusting, R.; De Lee, N.

2015-12-01

(Abstract only) B, V, and Cousins I-band light curves have been observed for the type II Cepheids V1, V2, and V6 in the globular cluster M13. These are relatively short period, BL Her-type Cepheids, with periods of 1.5, 5.1, and 2.1 days, respectively. Additional observations of V2 have been obtained from early photographic plates in the Yerkes Observatory archive. Long term period changes of these Cepheids have been determined by combining recent photometry with earlier observations that now extend back for more than a century. The observed period changes for V1, V2, and V6 are compared with the predictions of stellar evolution theory, under the assumption that the progenitors of the Cepheids were stars that at one time were on the blue horizontal branch.

Spectroscopical Study of Faint Southern Cepheids with Southern African Large Telescope (salt). First Results.

NASA Astrophysics Data System (ADS)

Usenko, I. A.; Kniazev, A. Yu.; Kovtyukh, V. V.; Belik, S. I.; Berdnikov, L. N.

First Cepheids observations using echelle-spectrograph HRS fed by Southern African Large Telescope (SALT) were realized during 2016. All spectra have been obtained in the medium resoltion mode (R≍ 31000-41000) wth high S/N ratio near 50-220. All data were processed using package developed by authors based on the standard system of astronomical data reduction MIDAS. Using new echelle data we found the atmosphere parameters and chemical composition for 30 faint Cepheids of southern hemisphere, where for the most of theses stars these results we obtained for the first time. 28 stars are Cepheids after the first-dredge up stage, while ASAS 075842-25336.1 and ASAS 1131714-6605.0 having remarkable Li I 6707.8 Å absorption line and anomalous CNO and Na content could be consider as first crossing of the Cepheids instability strip.

Cepheid Masses and Isochrones

NASA Astrophysics Data System (ADS)

Evans, N. R.

Spectra of binary systems containing a Cepheid and a hot companion have been obtained with HST and IUE. Masses for 5 Cepheids are in agreement with evolutionary calculations using a moderate amount of convective overshoot. In another study of the HR diagram, half the systems with a Terminal Age Main Sequence (TAMS) companion do not match isochrones. Rotation in the companion is a possible explanation.

Period Variations for the Cepheid VZ Cyg

NASA Astrophysics Data System (ADS)

Sirorattanakul, Krittanon; Engle, Scott; Pepper, Joshua; Wells, Mark; Laney, Clifton D.; Rodriguez, Joseph E.; Stassun, Keivan G.

2017-12-01

The Cepheid Period-Luminosity law is a key rung on the extragalactic distance ladder. However, numerous Cepheids are known to undergo period variations. Monitoring, refining, and understanding these period variations allows us to better determine the parameters of the Cepheids themselves and of the instability strip in which they reside, and to test models of stellar evolution. VZ Cyg, a classical Cepheid pulsating at ˜4.864 days, has been observed for over 100 years. Combining data from literature observations, the Kilodegree Extremely Little Telescope (KELT) transit survey, and new targeted observations with the Robotically Controlled Telescope (RCT) at Kitt Peak, we find a period change rate of dP/dt = -0.0642 ± 0.0018 s yr-1. However, when only the recent observations are examined, we find a much higher period change rate of dP/dt = -0.0923 ± 0.0110 s yr-1. This higher rate could be due to an apparent long-term (P ≈ 26.5 years) cyclic period variation. The possible interpretations of this single Cepheid’s complex period variations underscore both the need to regularly monitor pulsating variables and the important benefits that photometric surveys such as KELT can have on the field. Further monitoring of this interesting example of Cepheid variability is recommended to confirm and better understand the possible cyclic period variations. Further, Cepheid timing analyses are necessary to fully understand their current behaviors and parameters, as well as their evolutionary histories.

The Araucaria Project: The Distances to the NGC 247 and WLM Galaxies From Cepheid Variables Discovered in a Wide-Field Imaging Survey

NASA Astrophysics Data System (ADS)

García, A.; Gieren, W.; Pietrzynski, G.

2009-05-01

Two different and extensive wide-field imaging surveys for Cepheid variables have been made in the Sculptor Group galaxy NGC 247 and in the Local Group Irregular galaxy WLM. We present the principal results obtained in this surveys in the context of the Araucaria project. We have discovered 60 Cepheids in WLM and 24 Cepheids in NGC 247. Our data define tight period-luminosity relations in V, I and the reddening-free Wesenheit magnitude W_I which are all extremely well fit by the corresponding slopes of the LMC Cepheid PL relation, suggesting no change of the PL relation slope down to a Cepheid metal abundance of about -1.0 dex, in agreement with other recent studies. We derive a true distance modulus to NGC 247 of 27.80+/-0.09 (r) +/-0.06 (s) mag from our data, in good agreement with the earlier 27.9+/-0.1 mag determination of Davidge (2006, ApJ, 641, 822) from TRGB I band magnitude. The true distance modulus to WLM derived from our data was 25.144+/-0.03 (r) +/-0.07 (s), in good agreement with the earlier 24.92+/-0.21determination of Lee, Freedman, & Madore (1993, ApJ, 417, 553) from Cepheid variables. Aditional information is available in The Araucaria Project homepage (http://ezzelino.ifa.hawaii.edu/ bresolin/Araucaria/index.html) and in the series of papers entitled: The Araucaria Project.

The secret lives of Cepheids: evolutionary changes and pulsation-induced shock heating in the prototype classical Cepheid δ Cep

DOE Office of Scientific and Technical Information (OSTI.GOV)

Engle, Scott G.; Guinan, Edward F.; Harper, Graham M.

Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well understood. In this, the first of several planned papers on program Cepheids, we report the current results for δ Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light-curve morphology, and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov et al. returns a small period change of dP/dt ≈–0.1006 ± 0.0002 s yr{sup -1}. There ismore » also evidence for a gradual light amplitude increase of ∼0.011 mag (V band) and ∼0.012 mag (B band) per decade over the last ∼50 years. In addition, Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, δ Cep is found to be a soft X-ray source (L {sub X} (0.3-2 keV) ≈4.5-13 × 10{sup 28} erg s{sup -1}) with peak flux at kT = 0.6-0.9 keV. The X-ray activity is found to vary, possibly in phase with the stellar pulsations. From 2010-2013, nine observations of δ Cep were carried out with HST-COS. The UV emissions are also variable and well phased with the stellar pulsations. Maximum UV line emissions occur near, or slightly before, maximum optical light, varying by as much as 20 times. This variability shows that pulsation-induced shock heating plays a significant role in Cepheid atmospheres, possibly in addition to a quiescent, magnetic heating. The results of this study show Cepheid atmospheres to be rather complex and dynamic.« less

Cepheid binaries with large mass ratios (M1/M2)

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage

1988-01-01

The IUE observations of 3 Cepheid systems (Polaris, FF Aql, and S Sge) are used to derive, or set limits on, the temperatures and masses of the companions. Light from the companions of FF Aql and S Sge from 1700 to 2000 A is consistent with an A5 to A7 main sequence companion for both Cepheids, with a mass of 1.8 solar mass. This mass for the companion of S Sge is smaller than required by the orbital mass function and an evolutionary mass of the Cepheid, suggesting that the companion may itself be a binary. For Polaris, the mass of the companion must be less than 1.8 solar mass.

VizieR Online Data Catalog: DIB 661.3nm in Cepheid spectra (Kashuba+, 2016)

NASA Astrophysics Data System (ADS)

Kashuba, S. V.; Andrievsky, S. M.; Chekhonadskikh, F. A.; Luck, R. E.; Kovtyukh, V. V.; Korotin, S. A.; Krelowski, J.; Galazutdinov, G. A.

2017-11-01

We used spectra of Northern hemisphere Cepheids obtained by REL - one of the co-authors of this paper, with the High Resolution Spectrograph of the Hobby-Eberly Telescope at the McDonald Observatory of the University of Texas at Austin (Texas, USA) with the resolving power of 30000, a typical signal-to-noise ratio of about 100, and wavelength range of 435-780nm. A total of 253 Cepheid spectra were used in the research. We performed an investigation of the 661.356 nm DIB profile in 253 spectra of 176 Cepheids. After removal of the blending YII line the EW of each DIB was calculated for each spectrum. (1 data file).

The Secret Lives of Cepheids: Evolution, Mass-Loss, and Ultraviolet Emission of the Long-period Classical Cepheid

NASA Astrophysics Data System (ADS)

Neilson, Hilding R.; Engle, Scott G.; Guinan, Edward F.; Bisol, Alexandra C.; Butterworth, Neil

2016-06-01

The classical Cepheid l Carinae is an essential calibrator of the Cepheid Leavitt Law as a rare long-period Galactic Cepheid. Understanding the properties of this star will also constrain the physics and evolution of massive (M ≥ 8 M ⊙) Cepheids. The challenge, however, is precisely measuring the star's pulsation period and its rate of period change. The former is important for calibrating the Leavitt Law and the latter for stellar evolution modeling. In this work, we combine previous time-series observations spanning more than a century with new observations to remeasure the pulsation period and compute the rate of period change. We compare our new rate of period change with stellar evolution models to measure the properties of l Car, but find models and observations are, at best, marginally consistent. The results imply that l Car does not have significantly enhanced mass-loss rates like that measured for δ Cephei. We find that the mass of l Car is about 8-10 M ⊙. We present Hubble Space Telescope Cosmic Origins Spectrograph observations that also differ from measurements for δ Cep and β Dor. These measurements further add to the challenge of understanding the physics of Cepheids, but do hint at the possible relation between enhanced mass-loss and ultraviolet emission, perhaps both due to the strength of shocks propagating in the atmospheres of Cepheids. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13019. This work is also based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), associated with program #060374.

The Near-infrared Optimal Distances Method Applied to Galactic Classical Cepheids Tightly Constrains Mid-infrared Period–Luminosity Relations

NASA Astrophysics Data System (ADS)

Wang, Shu; Chen, Xiaodian; de Grijs, Richard; Deng, Licai

2018-01-01

Classical Cepheids are well-known and widely used distance indicators. As distance and extinction are usually degenerate, it is important to develop suitable methods to robustly anchor the distance scale. Here, we introduce a near-infrared optimal distance method to determine both the extinction values of and distances to a large sample of 288 Galactic classical Cepheids. The overall uncertainty in the derived distances is less than 4.9%. We compare our newly determined distances to the Cepheids in our sample with previously published distances to the same Cepheids with Hubble Space Telescope parallax measurements and distances based on the IR surface brightness method, Wesenheit functions, and the main-sequence fitting method. The systematic deviations in the distances determined here with respect to those of previous publications is less than 1%–2%. Hence, we constructed Galactic mid-IR period–luminosity (PL) relations for classical Cepheids in the four Wide-Field Infrared Survey Explorer (WISE) bands (W1, W2, W3, and W4) and the four Spitzer Space Telescope bands ([3.6], [4.5], [5.8], and [8.0]). Based on our sample of hundreds of Cepheids, the WISE PL relations have been determined for the first time; their dispersion is approximately 0.10 mag. Using the currently most complete sample, our Spitzer PL relations represent a significant improvement in accuracy, especially in the [3.6] band which has the smallest dispersion (0.066 mag). In addition, the average mid-IR extinction curve for Cepheids has been obtained: {A}W1/{A}{K{{s}}}≈ 0.560, {A}W2/{A}{K{{s}}}≈ 0.479, {A}W3/{A}{K{{s}}}≈ 0.507, {A}W4/{A}{K{{s}}}≈ 0.406, {A}[3.6]/{A}{K{{s}}}≈ 0.481, {A}[4.5]/{A}{K{{s}}}≈ 0.469, {A}[5.8]/{A}{K{{s}}}≈ 0.427, and {A}[8.0]/{A}{K{{s}}}≈ 0.427 {mag}.

New Cepheid variables in the Crux-Centaurus region

NASA Technical Reports Server (NTRS)

Grayzeck, E. J.

1978-01-01

Two star fields in the southern Milky Way, between galactic longitudes of approximately 294 and 320 deg, have been searched for new variables. At least three long-period (periods greater than 9 days) classical Cepheids have been tentatively identified, as well as one Virginis star. The resultant distribution of Cepheids along the Milky Way in the Crux-Centaurus region indicates a concentration of spiral tracers near a longitude of about 307 deg.

ANS ultraviolet observations of dwarf Cepheids

NASA Astrophysics Data System (ADS)

Sturch, C. R.; Wu, C.-C.

1983-03-01

Ultraviolet observations of three dwarf Cepheids (VZ Cnc, SX Phe, and AI Vel) are presented. The UV light curves are consistent with those in the visual region. When compared to standard stars, all three dwarf Cepheids exhibit flux deficiencies at the shortest observed wavelengths. The most extreme deficiencies appear for SX Phe; these may be related to the other properties previously noted for this star, including low metallicity, high space motion, and low luminosity.

VizieR Online Data Catalog: OGLE-II. Cepheids in IC 1613 (Udalski+, 2001)

NASA Astrophysics Data System (ADS)

Udalski, A.; Wyrzykowski, L.; Pietrzynski, G.; Szewczyk, O.; Szymanski, M.; Kubiak, M.; Soszynski, I.; Zebrun, K.

2003-01-01

We present results of the search for Cepheids in the galaxy IC 1613 carried out as a sub-project of the OGLE-II microlensing survey. 138 Cepheids were found in the 14.2'x14.2' region in the center of the galaxy. We present light curves, VI photometry and basic data for all these objects, as well as color-magnitude diagram of the observed field. (4 data files).

Optical Gravitational Lensing Experiment Cepheids Have Lower Amplitudes in the Small Magellanic Cloud than in the Large Magellanic Cloud.

PubMed

Paczyński; Pindor

2000-04-20

We selected Cepheids from the Optical Gravitational Lensing Experiment database for the Magellanic Clouds in the period range of 101.1

Constraining the intermediate-mass range of the Initial Mass Function using Galactic Cepheids

NASA Astrophysics Data System (ADS)

Mor, R.; Figueras, F.; Robin, A. C.; Lemasle, B.

2015-05-01

Aims. To use the Besançon Galaxy Model (Robin A.C. et al., 2003) and the most complete observational catalogues of Galactic Cepheids to constrain the intermediate-mass range of the Initial Mass Function (IMF) in the Milky Way Galactic thin disc. Methods. We have optimized the flexibility of the new Besançon Galaxy Model (Czekaj et al., 2014) to simulate magnitude and distance complete samples of young intermediate mass stars assuming different IMFs and Star Formation Histories (SFH). Comparing the simulated synthetic catalogues with the observational data, we studied which IMF reproduces better the observational number of Cepheids in the Galactic thin disc. We analysed three different IMFs: (1) Salpeter, (2) Kroupa-Haywood and (3) Haywood-Robin, all of them with a decreasing SFH from Aumer and Binney, 2009. Results. For the first time the Besançon Galaxy Model is used to characterize the Galactic Cepheids. We find that for most of the cases the Salpeter IMF overestimates the number of observed Cepheids and Haywood-Robin IMF underestimates it. The Kroupa-Haywood IMF, with a slope α=3.2, is the one that best reproduces the observed Cepheids. From the comparison of the predicted and observed number of Cepheids up to V=12, we point that the model might underestimate the scale-height of the young population. The effects of the variation of the model ingredients need to be quantified. Conclusions. In agreement with Kroupa and Weidner (2003), our study shows that the Salpeter IMF (α=2.35) overestimates the star counts in the range 4 ≤ M/M_{⊙} ≤ 10 and supports the idea that the slope of the intermediate and massive stars IMF is steeper than the Salpeter IMF.

STScI-PRC96-21b DISTANCE MEASUREMENTS TO A TYPE-IA SUPERNOVA BEARING GALAXY

NASA Technical Reports Server (NTRS)

2002-01-01

This Hubble Space Telescope image shows NGC 4639, a spiral galaxy located 78 million light-years away in the Virgo cluster of galaxies. The blue dots in the galaxy's outlying regions indicate the presence of young stars. Among them are young, bright stars called Cepheids, which are used as reliable milepost markers to obtain accurate distances to nearby galaxies. Astronomers measure the brightness of Cepheids to calculate the distance to a galaxy. Allan Sandage's team used Cepheids to measure the distance to NGC 4639, the farthest galaxy to which Cepheid distance has been calculated. After using Cepheids to calculate the distance to NGC 4639, the team compared the results to the peak brightness measurements of SN 1990N, a type Ia supernova located in the galaxy. Then they compared those numbers with the peak brightness of supernovae similarly calibrated in nearby galaxies. The team then determined that type Ia supernovae are reliable secondary distance markers, and can be used to determine distances to galaxies several hundred times farther away than Cepheids. An accurate value for the Hubble Constant depends on Cepheids and secondary distance methods. The color image was made from separate exposures taken in the visible and near-infrared regions of the spectrum with the Wide Field Planetary Camera 2. Credit: A. Sandage (Carnegie Observatories), A. Saha (Space Telescope Science Institute), G.A. Tammann, and L. Labhardt (Astronomical Institute, University Basel), F.D. Macchetto and N. Panagia (Space Telescope Science Institute/ European Space Agency), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo.

Araucaria Project: Pulsating stars in binary systems and as distance indicators

NASA Astrophysics Data System (ADS)

Pilecki, Bogumił; Gieren, Wolfgang; Pietrzyński, Grzegorz; Smolec, Radosław

2017-09-01

Pulsating stars, like Cepheids or RR Lyrae stars, are ones of the most important distance indicators. They are also key objects for testing the predictions of stellar evolution and stellar pulsation theory. In the Araucaria Project we have studied these objects since 2002, measuring distances to the galaxies in the Local Group and beyond. In 2010 we have for the first time confirmed spectroscopically the existence of a classical Cepheid in an eclipsing binary system. This has opened an opportunity to study in great details and with high accuracy (better than 1%) the physical parameters of these very important objects. First dynamical mass determination (Mcep = 4.16 ± 0.03 M⊙) let us solve the long-standing mass discrepancy problem. Since then we have measured masses for 6 classical Cepheids in binary systems and determined projection factors for three of them. One of the analyzed systems was confirmed to consist of two first-overtone Cepheids. Type II Cepheids are recently becoming more important as distance indicators and astrophysics laboratory, although our knowledge of these stars is quite limited. Their evolutionary status is also not well understood and observational constraints are needed to confirm the current theories. We are presenting here our first results of the spectroscopic analysis of 4 of these systems. The masses of type II Cepheids seem consistent with the expected 0.5 - 0.6 M⊙. We also present first results of the fully modeled pulsator originally classified as peculiar W Vir star. The mass of this star is 1.51 ± 0.09 M⊙ and the p-factor 1.3 ± 0.03. It was eventually found not to belong to any typical Cepheid group.

THE ARAUCARIA PROJECT: THE DISTANCE TO THE SCULPTOR GALAXY NGC 247 FROM NEAR-INFRARED PHOTOMETRY OF CEPHEID VARIABLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gieren, Wolfgang; Pietrzynski, Grzegorz; Szewczyk, Olaf

2009-08-01

We have obtained deep near-infrared images in J and K filters of four fields in the Sculptor Group spiral galaxy NGC 247 with the ESO VLT and Infrared Spectrometer and Array Camera. For a sample of 10 Cepheids in these fields, previously discovered by GarcIa-Varela et al. from optical wide-field images, we have determined mean J and K magnitudes and have constructed the period-luminosity (PL) relations in these bands. Using the near-infrared PL relations together with those in the optical V and I bands, we have determined a true distance modulus for NGC 247 of 27.64 mag, with a randommore » uncertainty of {+-}2% and a systematic uncertainty of {approx}4% which is dominated by the effect of unresolved stars on the Cepheid photometry. The mean reddening affecting the NGC 247 Cepheids of E(B - V) = 0.18 {+-} 0.02 mag is mostly produced in the host galaxy itself and is significantly higher than what was found in the previous optical Cepheid studies in NGC 247 of our own group, and Madore et al., leading to a 7% decrease in the previous optical Cepheid distance. As in other studies of our project, the distance modulus of NGC 247 we report is tied to an assumed Large Magellanic Cloud distance modulus of 18.50. Comparison with other distance measurements to NGC 247 shows that the present IR-based Cepheid distance is the most accurate among these determinations. With a distance of 3.4 Mpc, NGC 247 is about 1.5 Mpc more distant than NGC 55 and NGC 300, two other Sculptor Group spirals analyzed before with the same technique by our group.« less

On the impact of helium abundance on the Cepheid period-luminosity and Wesenheit relations and the distance ladder

NASA Astrophysics Data System (ADS)

Carini, R.; Brocato, E.; Raimondo, G.; Marconi, M.

2017-08-01

This work analyses the effect of the helium content on synthetic period-luminosity relations (PLRs) and period-Wesenheit relations (PWRs) of Cepheids and the systematic uncertainties on the derived distances that a hidden population of He-enhanced Cepheids may generate. We use new stellar and pulsation models to build a homogeneous and consistent framework to derive the Cepheid features. The Cepheid populations expected in synthetic colour-magnitude diagrams of young stellar systems (from 20 to 250 Myr) are computed in several photometric bands for Y = 0.25 and 0.35, at a fixed metallicity (Z = 0.008). The PLRs appear to be very similar in the two cases, with negligible effects (few per cent) on distances, while PWRs differ somewhat, with systematic uncertainties in deriving distances as high as ˜ 7 per cent at log P < 1.5. Statistical effects due to the number of variables used to determine the relations contribute to a distance systematic error of the order of few percent, with values decreasing from optical to near-infrared bands. The empirical PWRs derived from multiwavelength data sets for the Large Magellanic Cloud (LMC) is in a very good agreement with our theoretical PWRs obtained with a standard He content, supporting the evidence that LMC Cepheids do not show any He effect.

Spectroscopic analysis of Cepheid variables with 2D radiation-hydrodynamic simulations

NASA Astrophysics Data System (ADS)

Vasilyev, Valeriy

2018-06-01

The analysis of chemical enrichment history of dwarf galaxies allows to derive constraints on their formation and evolution. In this context, Cepheids play a very important role, as these periodically variable stars provide a means to obtain accurate distances. Besides, chemical composition of Cepheids can provide a strong constraint on the chemical evolution of the system. Standard spectroscopic analysis of Cepheids is based on using one-dimensional (1D) hydrostatic model atmospheres, with convection parametrised using the mixing-length theory. However, this quasi-static approach has theoretically not been validated. In my talk, I will discuss the validity of the quasi-static approximation in spectroscopy of short-periodic Cepheids. I will show the results obtained using a 2D time-dependent envelope model of a pulsating star computed with the radiation-hydrodynamics code CO5BOLD. I will then describe the impact of new models on the spectroscopic diagnostic of the effective temperature, surface gravity, microturbulent velocity, and metallicity. One of the interesting findings of my work is that 1D model atmospheres provide unbiased estimates of stellar parameters and abundances of Cepheid variables for certain phases of their pulsations. Convective inhomogeneities, however, also introduce biases. I will then discuss how these results can be used in a wider parameter space of pulsating stars and present an outlook for the future studies.

On an apparent discrepancy between pulsation and evolution masses for Cepheids.

NASA Technical Reports Server (NTRS)

Iben, I., Jr.; Tuggle, R. S.

1972-01-01

Results of new theoretical pulsation calculations in the linear nonadiabatic approximation are presented. Emphasis is placed on the location of blue edges (the borderline between stability and instability against pulsation) for pulsation in the fundamental mode. The results of evolutionary calculations for the helium-burning phase are introduced, and a theoretical period-luminosity relationship is obtained for Cepheids that lie on the blue edge of the instability strip. The theoretical results are then compared with current estimates of the intrinsic bulk properties of 13 Cepheids, and it is shown how theoretical and observational properties may be reconciled without assuming significant mass loss or the necessity of major adjustments in the theory. Finally, it is argued that the required revision in Cepheid luminosities lies within the observational uncertainties.

New Classical Cepheids in the Inner Part of the Northern Galactic Disk, and Their Kinematics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanioka, Satoshi; Matsunaga, Noriyuki; Fukue, Kei

2017-06-20

The characteristics of the inner Galaxy remain obscured by significant dust extinction, hence infrared surveys are useful for finding young Cepheids whose distances and ages can be accurately determined. A near-infrared photometric and spectroscopic survey was carried out and three classical Cepheids were unveiled in the inner disk, around 20° and 30° in Galactic longitude. The targets feature small Galactocentric distances, 3–5 kpc, and their velocities are important, as they may be under the environmental influence of the Galactic bar. While one of the Cepheids has a radial velocity consistent with the Galactic rotation, the other two are moving significantlymore » slower. We also compare their kinematics with that of high-mass star-forming regions with measured parallactic distances.« less

Intrinsic B-V color for galactic cepheids and some comments on the Sandage-Tammann relationship

NASA Technical Reports Server (NTRS)

Kelsall, T.

1972-01-01

Transformations are found for converting the b-y color excesses for Cepheids given by Williams (1966) and Kelsall (1971) into B-V excesses. The combination of these results with the E(B-V)'s determined by Sandage and Tammann (1971) gives precise data for eighty-eight galactic Cepheids. The period-color and period-color-(amplitude defect) relationships, that are germane to the LogP intervals 0.4 to 1.4 and 0.4 to 1.3, respectively, are found.

An independent Cepheid distance scale: Current status

NASA Technical Reports Server (NTRS)

Barnes, T. G., III

1980-01-01

An independent distance scale for Cepheid variables is discussed. The apparent magnitude and the visual surface brightness, inferred from an appropriate color index, are used to determine the angular diameter variation of the Cepheid. When combined with the linear displacement curve obtained from the integrated radial velocity curve, the distance and linear radius are determined. The attractiveness of the method is its complete independence of all other stellar distance scales, even though a number of practical difficulties currently exist in implementing the technique.

Cepheids as Cosmology Tools

NASA Image and Video Library

2012-10-03

This graph illustrates the Cepheid period-luminosity relationship, used to calculate the size, age and expansion rate of the universe. The data shown are from NASA Spitzer Space Telescope which has made the most precise measurements yet.

Type II Cepheids and Related Variables

NASA Astrophysics Data System (ADS)

Schmidt, Edward G.

2008-08-01

While type II Cepheids have considerable potential to contribute to our knowledge of a number of areas of astrophysics, their usefulness is compromised by the relatively small number of such stars known. I have undertaken a project to identify more of them in two large area sky surveys, and to determine some of the basic properties of the stars which are confirmed as type II Cepheids. In the course of this project a significant number of small amplitude stars which appear to be closely related to the type II Cepheids have been identified. The nature of these objects is also being investigated. The photometry portion of the project is complete and spectra were obtained for about half of the stars with the GCAM spectrograph on the 2.1-m telescope. This proposal requests time to obtain spectra for about 2/3 of the remaining stars.

Ultraviolet Observations of Three Dwarf Cepheids

NASA Astrophysics Data System (ADS)

Sturch, Conrad R.

Ultraviolet observations of three dwarf Cepheids (VZ Cnc, SX Phe, and AI Vel) have been obtained with the ANS. Analysis of these observations (Sturch and WU 1982) reveals that the flux distributions observed for each of these objects exhibit UV deficiencies which increase monotonically with decreasing wavelengths. The largest UV deficiencies are noted for SX Phe which has been identified with group of dwarf Cepheids with low metallicity and low luminosity, two attributes that are expected to have opposite effects on the UV flux distribution. It is proposed to obtain low dispersion IUE spectra of the three stars throughout each of their light cycles. Such observations will identify spectral features responsible for the flux deficiencies and will provide data necessary for a detailed comparison with model atmospheres. Knowledge of atmospheric parameters will lead to a better understanding of the evolutionary status of dwarf Cepheids.

Opacity, metallicity, and Cepheid period ratios in the galaxy and Magellanic Clouds

NASA Technical Reports Server (NTRS)

Simon, Norman R.; Kanbur, Shashi M.

1994-01-01

Linear pulsation calculations are employed to reproduce the bump Cepheid resonance (P(sub 2)/P(sub 0) = 0.5 at P(sub 0) approximately equal to 10 days) and to model, individually, the P(sub 1)/P(sub 0) period ratios for the dozen known Galactic beat Cepheids. Convection is ignored. The results point to a range of metallicity among the Cepheids, perhaps as large as 0.01 approximately less than Z approximately less than 0.02, with no evidence for any star exceeding Z = 0.02. We find masses and luminosities which range from M approximately less than 4 solar mass, log(base 10) approximately less than 3.0 at P(sub 0) approximately equal to 3 days to M approximately less than 6 solar mass, log(base 10) L approximately greater than 3.5 at P(sub 0) approximately equal to 10 days. Similar parameters are indicated for the P(sub 0) approximately equal to 10 days Cepheids in the LMC and SMC, provided that the resonance for these stars occurs at a slightly longer period, P(sub 0) days, as has been suggested in the literature. Our calculations were performed mainly using OPAL opacities, but also with new opacities from the Opacity project (OP). Only small differences were found between the OPAL results and those from OP. Finally, some suggestions are made for possible future work, including evolution and pulsation calculations, and more precise observations of Cepheids in the Magellanic Clouds.

Empirical Calibration of the P-Factor for Cepheid Radii Determined Using the IR Baade-Wesselink Method

NASA Astrophysics Data System (ADS)

Joner, Michael D.; Laney, C. D.

2012-05-01

We have used 41 galactic Cepheids for which parallax or cluster/association distances are available, and for which pulsation parallaxes can be calculated, to calibrate the p-factor to be used in K-band Baade-Wesselink radius calculations. Our sample includes the 10 Cepheids from Benedict et al. (2007), and three additional Cepheids with Hipparcos parallaxes derived from van Leeuwen et al. (2007). Turner and Burke (2002) list cluster distances for 33 Cepheids for which radii have been or (in a few cases) can be calculated. Revised cluster distances from Turner (2010), Turner and Majaess (2008, 2012), and Majaess and Turner (2011, 2012a, 2012b) have been used where possible. Radii have been calculated using the methods described in Laney and Stobie (1995) and converted to K-band absolute magnitudes using the methods described in van Leeuwen et al. (2007), Feast et al. (2008), and Laney and Joner (2009). The resulting pulsation parallaxes have been used to estimate the p-factor for each Cepheid. These new results stand in contradiction to those derived by Storm et al. (2011), but are in good agreement with theoretical predictions by Nardetto et al. (2009) and with interferometric estimates of the p-factor, as summarized in Groenewegen (2007). We acknowledge the Brigham Young University College of Physical and Mathematical Sciences for continued support of research done using the facilities and personnel at the West Mountain Observatory. This support is connected with NSF/AST grant #0618209.

The Secret Lives of Cepheids: Evolutionary Changes and Pulsation-induced Shock Heating in the Prototype Classical Cepheid δ Cep

NASA Astrophysics Data System (ADS)

Engle, Scott G.; Guinan, Edward F.; Harper, Graham M.; Neilson, Hilding R.; Remage Evans, Nancy

2014-10-01

Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well understood. In this, the first of several planned papers on program Cepheids, we report the current results for δ Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light-curve morphology, and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov et al. returns a small period change of dP/dt ≈-0.1006 ± 0.0002 s yr-1. There is also evidence for a gradual light amplitude increase of ~0.011 mag (V band) and ~0.012 mag (B band) per decade over the last ~50 years. In addition, Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, δ Cep is found to be a soft X-ray source (L X (0.3-2 keV) ≈4.5-13 × 1028 erg s-1) with peak flux at kT = 0.6-0.9 keV. The X-ray activity is found to vary, possibly in phase with the stellar pulsations. From 2010-2013, nine observations of δ Cep were carried out with HST-COS. The UV emissions are also variable and well phased with the stellar pulsations. Maximum UV line emissions occur near, or slightly before, maximum optical light, varying by as much as 20 times. This variability shows that pulsation-induced shock heating plays a significant role in Cepheid atmospheres, possibly in addition to a quiescent, magnetic heating. The results of this study show Cepheid atmospheres to be rather complex and dynamic. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #11726, #12302, and #13019. This work is also based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).

The Araucaria Project. The Distance to the Sculptor Group Galaxy NGC 7793 from Near-infrared Photometry of Cepheid Variables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zgirski, Bartlomiej; Pietrzyński, Grzegorz; Wielgorski, Piotr

Following the earlier discovery of classical Cepheid variables in the Sculptor Group spiral galaxy NGC 7793 from an optical wide-field imaging survey, we have performed deep near-infrared J - and K -band follow-up photometry of a subsample of these Cepheids to derive the distance to this galaxy with a higher accuracy than what was possible from optical photometry alone, by minimizing the effects of reddening and metallicity on the distance result. Combining our new near-infrared period–luminosity relations with previous optical photometry, we obtain a true distance modulus to NGC 7793 of (27.66 ± 0.04) mag (statistical) ±0.07 mag (systematic), i.e.,more » a distance of (3.40 ± 0.17) Mpc. We also determine the mean reddening affecting the Cepheids to be E(B − V) = (0.08 ± 0.02) mag, demonstrating that there is significant dust extinction intrinsic to the galaxy in addition to the small foreground extinction. A comparison of the new, improved Cepheid distance to earlier distance determinations of NGC 7793 from the Tully–Fisher and TRGB methods is in agreement within the reported uncertainties of these previous measurements.« less

A New Threshold of Precision, 30 micro-arcsecond Parallaxes and Beyond

NASA Astrophysics Data System (ADS)

Riess, Adam

2017-08-01

The star formation histories of our nearest neighbors, M31 and theLMC, have been the subjects of intensive study but the 3% to 5%uncertainty in their distance limits knowledge of the ages of theirstructures to 0.6 to 1.0 Gyr. Two recent developments make it possibleto reach the previously unimaginable precision in distance of 1%. Thefirst is the development of DASH, which allows HST and WFC3 to slewtens of arcminutes between exposures within an orbit under gyrocontrol with enough precision to efficiently observe widelydistributed Cepheids.The second is the arrival of parallaxmeasurements from Gaia which are calibrating the individual distancesof long period Cepheids in the Milky Way to 2%. However, bandpass andzeropoint differences between ground and space observations wouldcompromise the precision of the Gaia parallaxes when building aCepheid bridge to our neighbors. We propose to dash around the LMC andM31 with WFC3 to rapidly collect 3 band photometry of over 70 longperiod Cepheids using the same photometric system as a calibration setof Cepheids in the Milky Way. These will nullify otherwise systematicerrors to extend the precision of Gaia beyond the Milky Way and clockthe formation of structures in M31 and the LMC to 100 Myr.

The Araucaria Project. The Distance to the Sculptor Group Galaxy NGC 7793 from Near-infrared Photometry of Cepheid Variables

NASA Astrophysics Data System (ADS)

Zgirski, Bartlomiej; Gieren, Wolfgang; Pietrzyński, Grzegorz; Karczmarek, Paulina; Gorski, Marek; Wielgorski, Piotr; Narloch, Weronika; Graczyk, Dariusz; Kudritzki, Rolf-Peter; Bresolin, Fabio

2017-10-01

Following the earlier discovery of classical Cepheid variables in the Sculptor Group spiral galaxy NGC 7793 from an optical wide-field imaging survey, we have performed deep near-infrared J- and K-band follow-up photometry of a subsample of these Cepheids to derive the distance to this galaxy with a higher accuracy than what was possible from optical photometry alone, by minimizing the effects of reddening and metallicity on the distance result. Combining our new near-infrared period-luminosity relations with previous optical photometry, we obtain a true distance modulus to NGC 7793 of (27.66 ± 0.04) mag (statistical) ±0.07 mag (systematic), I.e., a distance of (3.40 ± 0.17) Mpc. We also determine the mean reddening affecting the Cepheids to be E(B - V) = (0.08 ± 0.02) mag, demonstrating that there is significant dust extinction intrinsic to the galaxy in addition to the small foreground extinction. A comparison of the new, improved Cepheid distance to earlier distance determinations of NGC 7793 from the Tully-Fisher and TRGB methods is in agreement within the reported uncertainties of these previous measurements.

Variable stars in the Pegasus dwarf galaxy (DDO 216)

NASA Technical Reports Server (NTRS)

Hoessel, J. G.; Abbott, Mark J.; Saha, A.; Mossman, Amy E.; Danielson, G. Edward

1990-01-01

Observations obtained over a period of five years of the resolved stars in the Pegasus dwarf irregular galaxy (DDO 216) have been searched for variable stars. Thirty-one variables were found, and periods established for 12. Two of these variable stars are clearly eclipsing variables, seven are very likely Cepheid variables, and the remaining three are probable Cepheids. The period-luminosity relation for the Cepheids indicates a distance modulus for Pegasus of m - M = 26.22 + or - 0.20. This places Pegasus very near the zero-velocity surface of the Local Group.

Galactic bulge population II Cepheids in the VVV survey: period-luminosity relations and a distance to the Galactic centre

NASA Astrophysics Data System (ADS)

Bhardwaj, A.; Rejkuba, M.; Minniti, D.; Surot, F.; Valenti, E.; Zoccali, M.; Gonzalez, O. A.; Romaniello, M.; Kanbur, S. M.; Singh, H. P.

2017-09-01

Context. Multiple stellar populations of different ages and metallicities reside in the Galactic bulge that trace its structure and provide clues to its formation and evolution. Aims: We present the near-infrared observations of population II Cepheids in the Galactic bulge from VISTA Variables in the Vía Láctea (VVV) survey. The JHKs photometry together with optical data from Optical Gravitational Lensing Experiment (OGLE) survey provide an independent estimate of the distance to the Galactic centre. The old, metal-poor and low-mass population II Cepheids are also investigated as useful tracers for the structure of the Galactic bulge. Methods: We identify 340 population II Cepheids in the VVV survey Galactic bulge catalogue based on their match with the OGLE-III Catalogue. The single-epoch JH and multi-epoch Ks observations complement the accurate periods and optical (VI) mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our Ks-band period-luminosity relation, Ks = -2.189(0.056) [log (P)-1] + 11.187(0.032), is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. Results: We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes, and extinction for 264 Galactic bulge population II Cepheids that have good-quality Ks-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic centre, R0 = 8.34 ± 0.03(stat.) ± 0.41(syst.), which changes by with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial distribution, similar to metal-poor RR Lyrae variables. We do not find evidence of the inclined bar as traced by the metal-rich red-clump stars. Conclusions: Population II Cepheid and RR Lyrae variables follow similar period-luminosity relations and trace the same metal-poor old population in the Galactic bulge. The number density for population II Cepheids is more limited as compared to abundant RR Lyraes but they are bright and exhibit a wide range in period that provides a robust period-luminosity relation for an accurate estimate of the distance to the Galactic centre. The full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A100

Hubble Space Telescope Snapshot Survey for Resolved Companions of Galactic Cepheids

NASA Astrophysics Data System (ADS)

Evans, Nancy Remage; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Tingle, Evan; Karovska, Margarita; Pillitteri, Ignazio

2016-05-01

We have conducted an imaging survey with the Hubble Space Telescope Wide Field Camera 3 (WFC3) of 70 Galactic Cepheids, typically within 1 kpc, with the aim of finding resolved physical companions. The WFC3 field typically covers the 0.1 pc area where companions are expected. In this paper, we identify 39 Cepheids having candidate companions, based on their positions in color-magnitude diagrams, and having separations ⩾ 5'' from the Cepheids. We use follow-up observations of 14 of these candidates with XMM-Newton, and of one of them with ROSAT, to separate X-ray-active young stars (probable physical companions) from field stars (chance alignments). Our preliminary estimate, based on the optical and X-ray observations, is that only 3% of the Cepheids in the sample have wide companions. Our survey easily detects resolved main-sequence companions as faint as spectral type K. Thus the fact that the two most probable companions (those of FF Aql and RV Sco) are earlier than type K is not simply a function of the detection limit. We find no physical companions having separations larger than 4000 au in the X-ray survey. Two Cepheids are exceptions in that they do have young companions at significantly larger separations (δ Cep and S Nor), but both belong to a cluster or a loose association, so our working model is that they are not gravitationally bound binary members, but rather cluster/association members. All of these properties provide constraints on both star formation and subsequent dynamical evolution. The low frequency of true physical companions at separations > 5'' is confirmed by examination of the subset of the nearest Cepheids and also the density of the fields. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

ON THE DISTANCE OF THE MAGELLANIC CLOUDS USING CEPHEID NIR AND OPTICAL-NIR PERIOD-WESENHEIT RELATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inno, L.; Bono, G.; Buonanno, R.

2013-02-10

We present the largest near-infrared (NIR) data sets, JHKs, ever collected for classical Cepheids in the Magellanic Clouds (MCs). We selected fundamental (FU) and first overtone (FO) pulsators, and found 4150 (2571 FU, 1579 FO) Cepheids for Small Magellanic Cloud (SMC) and 3042 (1840 FU, 1202 FO) for Large Magellanic Cloud (LMC). Current sample is 2-3 times larger than any sample used in previous investigations with NIR photometry. We also discuss optical VI photometry from OGLE-III. NIR and optical-NIR Period-Wesenheit (PW) relations are linear over the entire period range (0.0 < log P {sub FU} {<=} 1.65) and their slopesmore » are, within the intrinsic dispersions, common between the MCs. These are consistent with recent results from pulsation models and observations suggesting that the PW relations are minimally affected by the metal content. The new FU and FO PW relations were calibrated using a sample of Galactic Cepheids with distances based on trigonometric parallaxes and Cepheid pulsation models. By using FU Cepheids we found a true distance moduli of 18.45 {+-} 0.02(random) {+-} 0.10(systematic) mag (LMC) and 18.93 {+-} 0.02(random) {+-} 0.10(systematic) mag (SMC). These estimates are the weighted mean over 10 PW relations and the systematic errors account for uncertainties in the zero point and in the reddening law. We found similar distances using FO Cepheids (18.60 {+-} 0.03(random) {+-} 0.10(systematic) mag (LMC) and 19.12 {+-} 0.03(random) {+-} 0.10(systematic) mag (SMC)). These new MC distances lead to the relative distance, {Delta}{mu} = 0.48 {+-} 0.03 mag (FU, log P = 1) and {Delta}{mu} = 0.52 {+-} 0.03 mag (FO, log P = 0.5), which agrees quite well with previous estimates based on robust distance indicators.« less

Anchoring the Distance Scale via X-Ray/Infrared Data for Cepheid Clusters: SU Cas

NASA Astrophysics Data System (ADS)

Majaess, D.; Turner, D. G.; Gallo, L.; Gieren, W.; Bonatto, C.; Lane, D. J.; Balam, D.; Berdnikov, L.

2012-07-01

New X-ray (XMM-Newton) and JHKs (Observatoire du Mont-Mégantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J - H) = 0.08 ± 0.02 and d = 405 ± 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d=414+/- 5(\\sigma _{\\bar{x}}) +/- 10 (\\sigma) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (δ Cep, ζ Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H 0.

The Carnegie Hubble Program: The Distance and Structure of the SMC as Revealed by Mid-Infrared Observations of Cepheids

NASA Technical Reports Server (NTRS)

Scowcroft, Victoria; Freedman, Wendy L.; Madore, Barry F.; Monson, Andy; Persson, S. E.; Rich, Jeff; Seibert, Mark; Rigby, Jane R.

2016-01-01

Using Spitzer observations of classical Cepheids we have measured the true average distance modulus of the Small Magellanic Cloud (SMC) to be18.96 +/- 0.01 stat +/- 0.03sys mag (corresponding to 62+/- 0.3kpc), which is 0.48 +/- 0.01 mag more distant than the LMC. This is in agreement with previous results from Cepheid observations, as well as with measurements from other indicators such as RR Lyrae stars and the tip of the red giant branch. Utilizing the properties of the mid-infrared Leavitt Law we measured precise distances to individual Cepheids in the SMC, and have confirmed that the galaxy is tilted and elongated such that its eastern side is up to20 kpc closer than its western side. This is in agreement with the results from red clump stars and dynamical simulations of the Magellanic Clouds and Stream.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Edward G., E-mail: eschmidt1@unl.edu

We have obtained VR photometry of 447 Cepheid variable star candidates with declinations north of -14 Degree-Sign 30', most of which were identified using the Northern Sky Variability Survey (NSVS) data archive. Periods and other photometric properties were derived from the combination of our data with the NSVS data. Atmospheric parameters were determined for 81 of these stars from low-resolution spectra. The identification of type II Cepheids based on the data presented in all four papers in this series is discussed. On the basis of spectra, 30 type II Cepheids were identified while 53 variables were identified as cool, mainmore » sequence stars and 283 as red giants following the definitions in Paper III. An additional 30 type II Cepheids were identified on the basis of light curves. The present classifications are compared with those from the Machine-learned All Sky Automated Survey Classification Catalog for 174 stars in common.« less

Secret Lives of Cepheids: beta Dor as a Test of Cepheid X-ray Heating Mechanisms

NASA Astrophysics Data System (ADS)

Engle, Scott

2017-09-01

We propose two 40 ksec phase-constrained ACIS-I observations of the 9.8 day Cepheid beta Dor. This will fill its uncharted 0.9-0.2 phase gap to confirm and define (Lx, kT) its pulsation-driven X-ray variations and help identify the mechanism (shocks, magnetic fields, turbulent dynamos) responsible, in complement to our recent confirmation of pulsation-induced X-ray variations from delta Cep (Engle et al. 2017). Beta Dor has different properties than delta Cep (P = 9.8/5.4d; R = 61/44Rsun), and the proposed visits are crucial to combine with existing X-ray and FUV data and test the X-ray heating mechanisms. This program is the culmination of several years of work, and the resulting nearly complete phase coverage of beta Dor makes this Cepheid the timeliest and most promising target.

Hydrodynamic models of a cepheid atmosphere. Ph.D. Thesis - Maryland Univ., College Park

NASA Technical Reports Server (NTRS)

Karp, A. H.

1974-01-01

A method for including the solution of the transfer equation in a standard Henyey type hydrodynamic code was developed. This modified Henyey method was used in an implicit hydrodynamic code to compute deep envelope models of a classical Cepheid with a period of 12(d) including radiative transfer effects in the optically thin zones. It was found that the velocity gradients in the atmosphere are not responsible for the large microturbulent velocities observed in Cepheids but may be responsible for the occurrence of supersonic microturbulence. It was found that the splitting of the cores of the strong lines is due to shock induced temperature inversions in the line forming region. The adopted light, color, and velocity curves were used to study three methods frequently used to determine the mean radii of Cepheids. It is concluded that an accuracy of 10% is possible only if high quality observations are used.

The Secret Lives of Cepheids: Searching for Evolutionary Changes Using Photoelectric Photometry

NASA Astrophysics Data System (ADS)

Toce, Michael; Guinan, Edward F.; Engle, Scott G.; Wasatonic, Richard P.

2016-01-01

Classical Cepheids are pulsating, yellow supergiants and one of the most important classes of variable stars. They have a direct linear relationship between their period and luminosity and thus serve as crucial "standard candles" for determining the cosmic distance scale and measuring the Hubble Constant. Also, Cepheids play a fundamental role in the calibration of Type Ia supernovae, indicating that the expansion of the Universe is accelerating, and also infer the existence of dark energy. Studies of changes in their pulsation periods and amplitudes reveal evolutionary changes too subtle to detect directly, and understanding these various characteristics of Cepheids is critical to their use as high-precision standard candles. To this end, the Villanova Secret Lives of Cepheids (SLiC) program was created as a comprehensive study of Cepheid behavior, evolution, pulsations, atmospheres, heating dynamics, shocks and winds. As part of the SLiC program, ground-based photometry is being carried out of small sample of bright Cepheids. The observations are being made using the 14-inch reflector telescope at Villanova Campus Observatory. Mounted on the telescope is a SBIG photoelectric photometer equipped with standard Johnson UBVRI filters. Photometry is being carried out of the following stars along with their spectral type, period, and visual mag: X Cyg (F7Ib, ~16.39d, 6.47mag), DT Cyg (F7.5Ib, ~2.5d, 5.82mag), S Sge (G5Ibv, ~8.38d, 5.36mag), FF Aql (F6Ib, ~4.47d, 5.38mag), Eta Aql (F6Iab, ~7.18d,3.80mag), and Delta Cep (F5Iab, ~5.37d, 3.75mag). The primary scientific objectives are to obtain light curves to investigate possible evolutionary changes from small variations in luminosity, light amplitude and pulsation period. Special emphasis was placed on the classical Cepheid X Cyg due to recent changes in pulsation period, shown by Szabados via a phase jump in X Cyg's O-C (observed - calculated). X Cyg holds priority in our observations as we attempt to affirm or deny this pulsation period change. We combined the Villanova photometry with complementary B, V and Near-IR photometry conducted from nearby Allentown by Wasatonic.

Metal-poor Type II Cepheids with Periods Less Than Three Days

NASA Astrophysics Data System (ADS)

Kovtyukh, V.; Wallerstein, G.; Yegorova, I.; Andrievsky, S.; Korotin, S.; Saviane, I.; Belik, S.; Davis, C. E.; Farrell, E. M.

2018-05-01

We have analyzed 10 high-resolution spectra of Type II Cepheids with periods less than 3 days. We find that they clearly separate into two groups: those with near or slightly below solar metallicities, and those with [Fe/H] between ‑1.5 and ‑2.0. While the former are usually called BL Her stars, we suggest that the latter be called UY Eri stars. The UY Eri subclass appears to be similar to the short period variables in globular clusters of the Galactic Halo. Globular clusters with [Fe/H] > ‑1.0 almost never have Type II Cepheids.

Cepheids Geometrical Distances Using Space Interferometry

NASA Astrophysics Data System (ADS)

Marengo, M.; Karovska, M.; Sasselov, D. D.; Sanchez, M.

2004-05-01

A space based interferometer with a sub-milliarcsecond resolution in the UV-optical will provide a new avenue for the calibration of primary distance indicators with unprecedented accuracy, by allowing very accurate and stable measurements of Cepheids pulsation amplitudes at wavelengths not accessible from the ground. Sasselov & Karovska (1994) have shown that interferometers allow very accurate measurements of Cepheids distances by using a ``geometric'' variant of the Baade-Wesselink method. This method has been succesfully applied to derive distances and radii of nearby Cepheids using ground-based near-IR and optical interferometers, within a 15% accuracy level. Our study shows that the main source of error in these measurements is due to the perturbing effects of the Earth atmosphere, which is the limiting factor in the interferometer stability. A space interferometer will not suffer from this intrinsic limitations, and can potentially lead to improve astronomical distance measurements by an order of magnitude in precision. We discuss here the technical requirements that a space based facility will need to carry out this project, allowing distance measurements within a few percent accuracy level. We will finally discuss how a sub-milliarcsecond resolution will allow the direct distance determination for hundreds of galactic sources, and provide a substantial improvement in the zero-point of the Cepheid distance scale.

The Carnegie Hubble Program: The Leavitt Law at 3.6 microns and 4.5 microns in the Large Magellanic Cloud

NASA Technical Reports Server (NTRS)

Scowcroft, Victoria; Freedman, Wendy L.; Madore, Barry F.; Monson, Andrew J.; Persson, S. E.; Seibert, Mark; Rigby, Jane R.; Sturch, Laura

2011-01-01

The Carnegie Hubble Program (CHP) is designed to improve the extragalactic distance scale using data from the post-cryogenic era of Spitzer. The ultimate goal is a determination of the Hubble constant to an accuracy of 2%. This paper is the first in a series on the Cepheid population of the Large Magellanic Cloud, and focuses on the period-luminosity relations (Leavitt laws) that will be used, in conjunction with observations of Milky Way Cepheids, to set the slope and zero-point of the Cepheid distance scale in the mid-infrared. To this end, we have obtained uniformly-sampled light curves for 85 LMC Cepheids, having periods between 6 and 140 days. Period- luminosity and period-color relations are presented in the 3.6 micron and 4.5 micron bands. We demonstrate that the 3.6 micron band is a superb distance indicator. The cyclical variation of the [3.6]-[4.5] color has been measured for the first time. We attribute the amplitude and phase of the color curves to the dissociation and recombination of CO molecules in the Cepheid s atmosphere. The CO affects only the 4.5 micron flux making it a potential metallicity indicator.

Observations of classical cepheids

NASA Technical Reports Server (NTRS)

Pel, J. W.

1980-01-01

The observations of classical Cepheids are reviewed. The main progress that has been made is summarized and some of the problems yet to be solved are discussed. The problems include color excesses, calibration of color, duplicity, ultraviolet colors, temperature-color relations, mass discrepancies, and radius determination.

Mass and p-factor of the Type II Cepheid OGLE-LMC-T2CEP-098 in a Binary System

NASA Astrophysics Data System (ADS)

Pilecki, Bogumił; Gieren, Wolfgang; Smolec, Radosław; Pietrzyński, Grzegorz; Thompson, Ian B.; Anderson, Richard I.; Bono, Giuseppe; Soszyński, Igor; Kervella, Pierre; Nardetto, Nicolas; Taormina, Mónica; Stȩpień, Kazimierz; Wielgórski, Piotr

2017-06-01

We present the results of a study of the type II Cepheid (P puls = 4.974 days) in the eclipsing binary system OGLE-LMC-T2CEP-098 (P orb = 397.2 days). The Cepheid belongs to the peculiar W Vir group, for which the evolutionary status is virtually unknown. It is the first single-lined system with a pulsating component analyzed using the method developed by Pilecki et al. We show that the presence of a pulsator makes it possible to derive accurate physical parameters of the stars even if radial velocities can be measured for only one of the components. We have used four different methods to limit and estimate the physical parameters, eventually obtaining precise results by combining pulsation theory with the spectroscopic and photometric solutions. The Cepheid radius, mass, and temperature are 25.3+/- 0.2 {R}⊙ , 1.51+/- 0.09 {M}⊙ , and 5300+/- 100 {{K}}, respectively, while its companion has a similar size (26.3 {R}⊙ ), but is more massive (6.8 {M}⊙ ) and hotter (9500 K). Our best estimate for the p-factor of the Cepheid is 1.30+/- 0.03. The mass, position on the period-luminosity diagram, and pulsation amplitude indicate that the pulsating component is very similar to the Anomalous Cepheids, although it has a much longer period and is redder in color. The very unusual combination of the components suggest that the system has passed through a mass-transfer phase in its evolution. More complicated internal structure would then explain its peculiarity. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

New Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55

NASA Astrophysics Data System (ADS)

Lohr, M. E.; Negueruela, I.; Tabernero, H. M.; Clark, J. S.; Lewis, F.; Roche, P.

2018-05-01

As part of a wider investigation of evolved massive stars in Galactic open clusters, we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51, Berkeley 55 and NGC 6603. Using new multi-epoch photometry, we confirm that Be 51 #162 and Be 55 #107 are bona fide Cepheids, with pulsation periods of 9.83±0.01 d and 5.850±0.005 d respectively, while NGC 6603 star W2249 does not show significant photometric variability. Using the period-luminosity relationship for Cepheid variables, we determine a distance to Be 51 of 5.3^{+1.0}_{-0.8} kpc and an age of 44^{+9}_{-8} Myr, placing it in a sparsely-attested region of the Perseus arm. For Be 55, we find a distance of 2.2±0.3 kpc and age of 63^{+12}_{-11} Myr, locating the cluster in the Local arm. Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222, these represent an important increase in the number of young, massive Cepheids known in Galactic open clusters. We also consider new Gaia (data release 2) parallaxes and proper motions for members of Be 51 and Be 55; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters, but the well-constrained proper motion measurements furnish further confirmation of cluster membership. However, future final Gaia parallaxes for such objects should provide valuable independent distance measurements, improving the calibration of the period-luminosity relationship, with implications for the distance ladder out to cosmological scales.

Brief Report: High Sensitivity and Specificity of the Cepheid Xpert HIV-1 Qualitative Point-of-Care Test Among Newborns in Botswana.

PubMed

Ibrahim, Maryanne; Moyo, Sikhulile; Mohammed, Terence; Mupfumi, Lucy; Gaseitsiwe, Simani; Maswabi, Kenneth; Ajibola, Gbolahan; Gelman, Rebecca; Batlang, Oganne; Sakoi, Maureen; Auletta-Young, Chloe; Makhema, Joseph; Lockman, Shahin; Shapiro, Roger L

2017-08-15

HIV point-of-care (POC) testing allows for early infant HIV diagnosis and treatment, but POC accuracy at birth and in the setting of antiretroviral prophylaxis for the prevention of mother-to-child HIV transmission is unknown. We evaluated the Cepheid Xpert HIV-1 Qual POC test against the Roche Taqman HIV-1 DNA polymerase chain reaction (PCR) platform using dried blood spots from 15 HIV-infected and 75 HIV-exposed uninfected newborns. These infants were screened for HIV at <96 hours of life at 5 hospital maternity wards in Botswana; all infants received postexposure antiretroviral prophylaxis with single-dose nevirapine and zidovudine, and most mothers received 3-drug antiretroviral therapy in pregnancy and at delivery. Fourteen of the 15 PCR positive samples tested positive by Cepheid POC, yielding a sensitivity of 93.3% (95% confidence interval: 68.1 to 99.8). Baseline viral load among positive infants ranged from <40 to >10,000,000 copies/mL, with a median of 2403 copies/mL. The HIV RNA for the infant with false-negative POC testing was 1661 copies/mL. Of note, 2 infants with low HIV RNA (<40 and 272 copies/mL) were correctly identified as HIV positive by Cepheid POC. All the 75 PCR-negative samples tested negative by Cepheid POC, yielding a specificity of 100% (95% confidence interval: 96.1 to 100). Our study demonstrates high sensitivity and specificity for the Cepheid POC assay in the first week of life despite early infection and antiretroviral prophylaxis. This platform may be a useful approach for adding early infant HIV diagnosis to current testing programs.

Identification of Cepheid Variables in ASAS Data (Poster abstract)

NASA Astrophysics Data System (ADS)

Johnson, J.; Larsen, K.

2014-06-01

(Abstract only) Cepheid variables are well-known to be important to astronomers, as their period-luminosity relationship is used to determine the distances to galaxies. The unambiguous identification of newly discovered Cepheid variables in large photometric data sets is therefore of significance. A data set of 3,548 candidate Cepheid variable stars in the ASAS data was provided by Patrick Wils (through Doug Welch). A computer program had originally identified these candidates; however, Wils investigated a small subset of the data by hand and discovered that the vast majority of these stars were misidentified. The most common misidentification was of BY Draconis stars (rotating spotted K and M dwarfs). In a companion piece, Swenton and Larsen sought out the most likely Cepheid candidates in the data; the work discussed here is instead focused on looking at stars that had properties that were clearly different from Cepheids, more specifically properties likely to be seen in BY Dra stars. We are sorting the spreadsheet stars by characteristics in order to find as many BY Dra variables as possible (since they seem to be the most commonly misidentified stars). These characteristics include newly available infrared photometry (2MASS), proper motion (PPMXL), and X-Ray emission (ROTSE) data (for which we received helpful guidance from Sebastian Otero) as well as VSX information. The first 103 stars to be studied are those with the smallest range in magnitude (less than or equal to 0.1). An analysis of their light curves and other available data is being undertaken in order to determine whether or not they are indeed BY Dra-type variables. In doing so the goal is to be able to submit and publish the correct identifications for these stars to the International Variable Star Index (VSX) and the JAAVSO.

Nonlinear convective pulsation models of type II Cepheids

NASA Astrophysics Data System (ADS)

Smolec, Radoslaw

2015-08-01

We present a grid of nonlinear convective pulsation models of type-II Cepheids: BL Her stars, W Vir stars and RV Tau stars. The models cover a wide range of masses, luminosities, effective temperatures and chemical compositions. The most interesting result is detection of deterministic chaos in the models. Different routes to chaos are detected (period doubling, intermittent route) as well as variety of phenomena intrinsic to chaotic dynamics (periodic islands within chaotic bands, crisis bifurcation, type-I and type-III intermittency). Some of the phenomena (period doubling in BL Her and in RV Tau stars, irregular pulsation of RV Tau stars) are well known in the pulsation of type-II Cepheids. Prospects of discovering the other are briefly discussed. Transition from BL Her type pulsation through W Vir type till RV Tau type is analysed. In the most luminous models a dynamical instability is detected, which indicates that pulsation driven mass loss is important process occurring in type-II Cepheids.

The orbit of the Cepheid AW Per

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage; Welch, Douglas L.

1988-01-01

An orbit for the classical Cepheid AW Per was derived. Phase residuals from the light curve are consistent with the light-time effect from the orbit. The companion was studied using IUE spectra. The flux distribution from 1300 to 1700 A is unusual, probably an extreme PbSi star, comparable to a B7V or B8V star. The flux of the composite spectrum from 1200 A through V is well matched by F7Ib and B8V standard stars with Delta M(sub upsilon) = 3(m) multiplied by 1. The mass function from the orbit indicates that the mass of the Cepheid must be greater that 4.7 solar mass if it is the more massive component. A B7V to B8V companion is compatible with the 1 sigma lower limit (3.5 solar mass) from the mass function. This implies that the Cepheid has the same mass, but the large magnitude difference rules this out. It is likely that the companion is itself a binary.

New Parallaxes of Galactic Cepheids from Spatially Scanning the Hubble Space Telescope: Implications for the Hubble Constant

NASA Astrophysics Data System (ADS)

Riess, Adam G.; Casertano, Stefano; Yuan, Wenlong; Macri, Lucas; Anderson, Jay; MacKenty, John W.; Bowers, J. Bradley; Clubb, Kelsey I.; Filippenko, Alexei V.; Jones, David O.; Tucker, Brad E.

2018-03-01

We present new measurements of the parallax of seven long-period (≥10 days) Milky Way (MW) Cepheid variables (SS CMa, XY Car, VY Car, VX Per, WZ Sgr, X Pup, and S Vul) using one-dimensional astrometric measurements from spatial scanning of Wide-Field Camera 3 on the Hubble Space Telescope (HST). The observations were obtained at ∼6 month intervals over 4 years. The distances are 1.7–3.6 kpc, with a mean precision of 45 μas (signal-to-noise ratio (S/N) ≈ 10) and a best precision of 29 μas (S/N = 14). The accuracy of the parallaxes is demonstrated through independent analyses of >100 reference stars. This raises to 10 the number of long-period Cepheids with significant parallax measurements, 8 obtained from this program. We also present high-precision mean F555W, F814W, and F160W magnitudes of these Cepheids, allowing a direct, zeropoint-independent comparison to >1800 extragalactic Cepheids in the hosts of 19 SNe Ia. This sample addresses two outstanding systematic uncertainties affecting prior comparisons of MW and extragalactic Cepheids used to calibrate the Hubble constant (H 0): their dissimilarity of periods and photometric systems. Comparing the new parallaxes to their predicted values derived from reversing the distance ladder gives a ratio (or independent scale for H 0) of 1.037 ± 0.036, consistent with no change and inconsistent at the 3.5σ level with a ratio of 0.91 needed to match the value predicted by Planck cosmic microwave background data in concert with ΛCDM. Using these data instead to augment the Riess et al. measurement of H 0 improves the precision to 2.3%, yielding 73.48 ± 1.66 km s‑1 Mpc‑1, and the tension with Planck + ΛCDM increases to 3.7σ. The future combination of Gaia parallaxes and HST spatial scanning photometry of 50 MW Cepheids can support a <1% calibration of H 0.

Observational calibration of the projection factor of Cepheids. I. The type II Cepheid κ Pavonis

NASA Astrophysics Data System (ADS)

Breitfelder, J.; Kervella, P.; Mérand, A.; Gallenne, A.; Szabados, L.; Anderson, R. I.; Willson, M.; Le Bouquin, J.-B.

2015-04-01

Context. The distance of pulsating stars, in particular Cepheids, are commonly measured using the parallax of pulsation technique. The different versions of this technique combine measurements of the linear diameter variation (from spectroscopy) and the angular diameter variation (from photometry or interferometry) amplitudes, to retrieve the distance in a quasi-geometrical way. However, the linear diameter amplitude is directly proportional to the projection factor (hereafter p-factor), which is used to convert spectroscopic radial velocities (i.e., disk integrated) into pulsating (i.e., photospheric) velocities. The value of the p-factor and its possible dependence on the pulsation period are still widely debated. Aims: Our goal is to measure an observational value of the p-factor of the type-II Cepheid κ Pavonis. Methods: The parallax of the type-II Cepheid κ Pav was measured with an accuracy of 5% using HST/FGS. We used this parallax as a starting point to derive the p-factor of κ Pav, using the SPIPS technique (Spectro-Photo-Interferometry of Pulsating Stars), which is a robust version of the parallax-of-pulsation method that employs radial velocity, interferometric and photometric data. We applied this technique to a combination of new VLTI/PIONIER optical interferometric angular diameters, new CORALIE and HARPS radial velocities, as well as multi-colour photometry and radial velocities from the literature. Results: We obtain a value of p = 1.26 ± 0.07 for the p-factor of κ Pav. This result agrees with several of the recently derived Period-p-factor relationships from the literature, as well as previous observational determinations for Cepheids. Conclusions: Individual estimates of the p-factor are fundamental to calibrating the parallax of pulsation distances of Cepheids. Together with previous observational estimates, the projection factor we obtain points to a weak dependence of the p-factor on period. Based on observations realized with ESO facilities at Paranal Observatory under program IDs 091.D-0020 and 093.D-0316.Based on observations collected at ESO La Silla Observatory using the Coralie spectrograph mounted to the Swiss 1.2 m Euler telescope, under program CNTAC2014A-5.

VizieR Online Data Catalog: Type II Cepheid and RR Lyrae variables (Feast+, 2008)

NASA Astrophysics Data System (ADS)

Feast, M. W.; Laney, C. D.; Kinman, T. D.; van Leeuwen, F.; Whitelock, P. A.

2008-10-01

Infrared and optical absolute magnitudes are derived for the type II Cepheids kappa Pav and VY Pyx using revised Hipparcos parallaxes and for kappa Pav, V553 Cen and SW Tau from pulsational parallaxes. Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorily and are combined in deriving absolute magnitudes. Phase-corrected J, H and Ks mags are given for 142 Hipparcos RR Lyraes based on Two-Micron All-Sky Survey observations. Pulsation and trigonometrical parallaxes for classical Cepheids are compared to establish the best value for the projection factor (p) used in pulsational analyses. (3 data files).

Cepheid temperature and the Blazhko effect

NASA Technical Reports Server (NTRS)

Teays, Terry

1995-01-01

Two separate research projects were covered under this contract. The first project was to study the temperatures of Cepheid variable stars, while the second was a study of the Blazhko effect in RR Larae, both of them using IUE data. They will be reported on separately, in what follows.

Exploring the η Aquila System: Another Cepheid Parallax and Further Evidence for a Tertiary

NASA Astrophysics Data System (ADS)

Benedict, George Frederick; Barnes, Thomas G.; Evans, Nancy; Cochran, William; McArthur, Barbara E.; Harrison, Thomas E.

2018-01-01

We report progress towards a re-analysis of Hubble Space Telescope Fine Guidance Sensor astrometric data, originally acquired to determine a parallax for and absolute magnitudes of the classical Cepheid, η Aquila. This object was not included in past Cepheid Period-Luminosity Relation (PLR) work (Benedict et al. 2007, AJ, 133, 1810), because we had an insufficient number of epochs with which to establish a suspected and complicating companion orbit. Our new investigation is considerably aided by including a significant number of radial velocity measures (RV) from six sources, including new, high-quality Hobby-Eberly Telescope spectra. We first derive a 12 Fourier coefficient description of the Cepheid pulsation, solving for velocity offsets required to bring the six RV data sets into coincidence. We next model the RV residuals to that fit with an orbit. The resulting orbit has very high eccentricity. The astrometric residuals show only a very small perturbation, consistent with a prediction from the spectroscopic orbit. We finally include that orbit in a combined astrometry and radial velocity model. This modeling, similar to that presented in Benedict and Harrison (2017, AJ, 153, 258) yields a parallax, allowing inclusion of η Aquila in a PLR. It also establishes a Cepheid/companion mass ratio for the early-type star companion identified in IUE spectra (Evans 1991, ApJ, 372, 597).

An Extremely Low Mid-infrared Extinction Law toward the Galactic Center and 4% Distance Precision to 55 Classical Cepheids

NASA Astrophysics Data System (ADS)

Chen, Xiaodian; Wang, Shu; Deng, Licai; de Grijs, Richard

2018-06-01

Distances and extinction values are usually degenerate. To refine the distance to the general Galactic Center region, a carefully determined extinction law (taking into account the prevailing systematic errors) is urgently needed. We collected data for 55 classical Cepheids projected toward the Galactic Center region to derive the near- to mid-infrared extinction law using three different approaches. The relative extinction values obtained are {A}J/{A}{K{{s}}}=3.005,{A}H/{A}{K{{s}}}=1.717, {A}[3.6]/{A}{K{{s}}}=0.478,{A}[4.5]/{A}{K{{s}}}=0.341, {A}[5.8]/{A}{K{{s}}}=0.234,{A}[8.0]/{A}{K{{s}}} =0.321,{A}W1/{A}{K{{s}}}=0.506, and {A}W2/{A}{K{{s}}}=0.340. We also calculated the corresponding systematic errors. Compared with previous work, we report an extremely low and steep mid-infrared extinction law. Using a seven-passband “optimal distance” method, we improve the mean distance precision to our sample of 55 Cepheids to 4%. Based on four confirmed Galactic Center Cepheids, a solar Galactocentric distance of R 0 = 8.10 ± 0.19 ± 0.22 kpc is determined, featuring an uncertainty that is close to the limiting distance accuracy (2.8%) for Galactic Center Cepheids.

A 2.4% DETERMINATION OF THE LOCAL VALUE OF THE HUBBLE CONSTANT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riess, Adam G.; Scolnic, Dan; Jones, David O.

We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new near-infrared (NIR) observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on ∼300 SNe Ia at z < 0.15. All 19 hosts as well as the megamaser system NGC 4258more » have been observed with WFC3 in the optical and NIR, thus nullifying cross-instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC 4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST -based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (i) megamasers in NGC 4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes measured with HST /FGS, HST /WFC3 spatial scanning and/or Hipparcos , and (iv) 2 DEBs in M31. The Hubble constant from each is 72.25 ± 2.51, 72.04 ± 2.67, 76.18 ± 2.37, and 74.50 ± 3.27 km s{sup 1} Mpc{sup 1}, respectively. Our best estimate of H {sub 0} = 73.24 ± 1.74 km s{sup 1} Mpc{sup 1} combines the anchors NGC 4258, MW, and LMC, yielding a 2.4% determination (all quoted uncertainties include fully propagated statistical and systematic components). This value is 3.4 σ higher than 66.93 ± 0.62 km s{sup 1} Mpc{sup 1} predicted by ΛCDM with 3 neutrino flavors having a mass of 0.06 eV and the new Planck data, but the discrepancy reduces to 2.1 σ relative to the prediction of 69.3 ± 0.7 km s{sup 1} Mpc{sup 1} based on the comparably precise combination of WMAP +ACT+SPT+BAO observations, suggesting that systematic uncertainties in CMB radiation measurements may play a role in the tension. If we take the conflict between Planck high-redshift measurements and our local determination of H {sub 0} at face value, one plausible explanation could involve an additional source of dark radiation in the early universe in the range of Δ N {sub eff} ≈ 0.4–1. We anticipate further significant improvements in H {sub 0} from upcoming parallax measurements of long-period MW Cepheids.« less

A 2.4% Determination of the Local Value of the Hubble Constant

NASA Astrophysics Data System (ADS)

Riess, Adam G.; Macri, Lucas M.; Hoffmann, Samantha L.; Scolnic, Dan; Casertano, Stefano; Filippenko, Alexei V.; Tucker, Brad E.; Reid, Mark J.; Jones, David O.; Silverman, Jeffrey M.; Chornock, Ryan; Challis, Peter; Yuan, Wenlong; Brown, Peter J.; Foley, Ryan J.

2016-07-01

We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new near-infrared (NIR) observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on ˜300 SNe Ia at z < 0.15. All 19 hosts as well as the megamaser system NGC 4258 have been observed with WFC3 in the optical and NIR, thus nullifying cross-instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC 4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (I) megamasers in NGC 4258, (II) 8 DEBs in the LMC, (III) 15 MW Cepheids with parallaxes measured with HST/FGS, HST/WFC3 spatial scanning and/or Hipparcos, and (IV) 2 DEBs in M31. The Hubble constant from each is 72.25 ± 2.51, 72.04 ± 2.67, 76.18 ± 2.37, and 74.50 ± 3.27 km s-1 Mpc-1, respectively. Our best estimate of H 0 = 73.24 ± 1.74 km s-1 Mpc-1 combines the anchors NGC 4258, MW, and LMC, yielding a 2.4% determination (all quoted uncertainties include fully propagated statistical and systematic components). This value is 3.4σ higher than 66.93 ± 0.62 km s-1 Mpc-1 predicted by ΛCDM with 3 neutrino flavors having a mass of 0.06 eV and the new Planck data, but the discrepancy reduces to 2.1σ relative to the prediction of 69.3 ± 0.7 km s-1 Mpc-1 based on the comparably precise combination of WMAP+ACT+SPT+BAO observations, suggesting that systematic uncertainties in CMB radiation measurements may play a role in the tension. If we take the conflict between Planck high-redshift measurements and our local determination of H 0 at face value, one plausible explanation could involve an additional source of dark radiation in the early universe in the range of ΔN eff ≈ 0.4-1. We anticipate further significant improvements in H 0 from upcoming parallax measurements of long-period MW Cepheids. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, C.G.

Starting with the initial understanding that pulsation in variable stars is caused by the heat engine of Hydrogen and Helium ionization in their atmospheres (A.S. Eddington in Cox 1980) it was soon realized that non-linear effects were responsible for the detailed features on their light and velocity curves. With the advent of the computer we were able to solve the coupled set of hydrodynamics and radiation diffusion equations to model these non-linear features. This paper describes some recent model results for long period (LP) Cepheids in an attempt to get another handle on Cepheid masses. Section II discusses these resultsmore » and Section III considers the implications of these model results on the problem of the Cepheid mass discrepancy.« less

VizieR Online Data Catalog: Cepheid radial velocity amplitude modulations (Anderson, 2014)

NASA Astrophysics Data System (ADS)

Anderson, R. I.

2014-06-01

A total of 983 radial velocity measurements of the four Cepheids QZ Nor (125), V335 Pup (95), l Car (324), and RS Pup (439) are provided. The measurements are based on observations carried out between April 2011 and February 2014 that were obtained using the Coralie spectrograph, mounted to the Swiss 1.2m Euler telescope located at La Silla Observatory, Chile. For each Cepheid, a table with the barycentric Julian date of observation, radial velocity, and the measurement uncertainty are provided. In addition, a table containing the identifiers, coordinates, and pulsation periods used to phase-fold the data (see the figures in the article) is provided. (5 data files).

Observing campaign on 5 variables in Cygnus

NASA Astrophysics Data System (ADS)

Waagen, Elizabeth O.

2015-10-01

Dr. George Wallerstein (University of Washington) has requested AAVSO assistance in monitoring 5 variable stars in Cygnus now through December 2015. He is working to complete the radial velocity curves for these stars, and needs optical light curves for correlation with the spectra he will be obtaining. Wallerstein writes: "I need to know the time of max or min so I can assign a phase to each spectrum. Most classical Cepheids are quite regular so once a time of max or min can be established I can derive the phase of each observation even if my obs are several cycles away from the established max or min. MZ Cyg is a type II Cepheid and they are less regular than their type I cousins." SZ Cyg, X Cyg, VX Cyg, and TX Cyg are all classical Cepheids. V and visual observations are requested. These are long-period Cepheids, so nightly observations are sufficient. Finder charts with sequence may be created using the AAVSO Variable Star Plotter (https://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details.

Subtle flickering in Cepheids: Kepler and MOST

NASA Astrophysics Data System (ADS)

Evans, Nancy Remage; Szabó, Robert; Szabados, Laszlo; Derekas, Aliz; Matthews, Jaymie M.; Cameron, Chris; the MOST Team

2014-02-01

Fundamental mode classical Cepheids have light curves which repeat accurately enough that we can watch them evolve (change period). The new level of accuracy and quantity of data with the Kepler and MOST satellites probes this further. An intriguing result was found in the long time-series of Kepler data for V1154 Cyg the one classical Cepheid (fundamental mode, P = 4.9 d) in the field, which has short term changes in period (~=20 minutes), correlated for ~=10 cycles (period jitter). To follow this up, we obtained a month long series of observations of the fundamental mode Cepheid RT Aur and the first overtone pulsator SZ Tau. RT Aur shows the traditional strict repetition of the light curve, with the Fourier amplitude ratio R 1/R 2 remaining nearly constant. The light curve of SZ Tau, on the other hand, fluctuates in amplitude ratio at the level of approximately 50%. Furthermore prewhitening the RT Aur data with 10 frequencies reduces the Fourier spectrum to noise. For SZ Tau, considerable power is left after this prewhitening in a complicated variety of frequencies.

A spectro-interferometric view of l Carinae's modulated pulsations

NASA Astrophysics Data System (ADS)

Anderson, Richard I.; Mérand, Antoine; Kervella, Pierre; Breitfelder, Joanne; Eyer, Laurent; Gallenne, Alexandre

Classical Cepheids are radially pulsating stars that enable important tests of stellar evolution and play a crucial role in the calibration of the local Hubble constant. l Carinae is a particularly well-known distance calibrator, being the closest long-period (P ~ 35.5 d) Cepheid and subtending the largest angular diameter. We have carried out an unprecedented observing program to investigate whether recently discovered cycle-to-cycle changes (modulations) of l Carinae's radial velocity (RV) variability are mirrored by its variability in angular size. To this end, we have secured a fully contemporaneous dataset of high-precision RVs and high-precision angular diameters. Here we provide a concise summary of our project and report preliminary results. We confirm the modulated nature of the RV variability and find tentative evidence of cycle-to-cycle differences in l Car's maximal angular diameter. Our analysis is exploring the limits of state-of-the-art instrumentation and reveals additional complexity in the pulsations of Cepheids. If confirmed, our result suggests a previously unknown pulsation cycle dependence of projection factors required for determining Cepheid distances via the Baade-Wesselink technique.

The atmosphere, the p-factor and the bright visible circumstellar environment of the prototype of classical Cepheids δ Cep

NASA Astrophysics Data System (ADS)

Nardetto, Nicolas; Poretti, Ennio; Mérand, Antoine; Anderson, Richard I.; Fokin, Andrei; Fouqué, Pascal; Gallenne, Alexandre; Gieren, Wolfgang; Graczyk, Dariusz; Kervella, Pierre; Mathias, Philippe; Mourard, Denis; Neilson, Hilding; Pietrzynski, Grzegorz; Pilecki, Bogumil; Rainer, Monica; Storm, Jesper

2017-09-01

Even ≃ 16000 cycles after its discovery by John Goodricke in 1783, δ Cep, the prototype of classical Cepheids, is still studied intensively in order to better understand its atmospheric dynamical structure and its environment. Using HARPS-N spectroscopic measurements, we have measured the atmospheric velocity gradient of δ Cep for the first time and we confirm the decomposition of the projection factor, a subtle physical quantity limiting the Baade-Wesselink (BW) method of distance determination. This decomposition clarifies the physics behind the projection factor and will be useful to interpret the hundreds of p-factors that will come out from the next Gaia release. Besides, VEGA/CHARA interferometric observations of the star revealed a bright visible circumstellar environment contributing to about 7% to the total flux. Better understanding the physics of the pulsation and the environment of Cepheids is necessary to improve the BW method of distance determination, a robust tool to reach Cepheids in the MilkyWay, and beyond, in the Local Group.

The binary system containing the classical Cepheid T Mon

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage; Lyons, Ronald W.

1994-01-01

Several new results are presented for the binary system containing the 27(sup d) classical Cepheid T Mon. New radial velocities for the Cepheid have been obtained, which confirm the decreasing orbital motion at the current epoch. The spectral type of the companion (B9.8 V) has been determined from an International Ultraviolet Explorer (IUE) low resolution spectrum. An IUE high resolution spectrum has been measured to search for the velocity of the companion. A velocity signal at +36 km/s on JD 2,446,105.21 has been tentatively identified as the velocity of the companion, but confirmation of this velocity would be very valuable. Results based on this tentative identification of the velocity are that the companion does not have a high projected rotation velocity, that the companion is unlikely to be a short period binary, and that the gamma velocity of the system is between 20 and 36 km/s. The luminosity and temperature of both the Cepheid and the companion are well determined from the satellite and ground-based observations and the Cepheid PLC relation. However, the companion is above the ZAMS in the H-R diagram, which is inconsistent with the large luminosity difference between the two stars. High rotation for the companion (viewed pole-on) is a possible explanation. The lower limit to the mass function (from the lower limits to the orbital period and amplitude) requires a very high eccentricity for the system for reasonable estimates for the masses of the two stars.

DISCOVERY OF A PAIR OF CLASSICAL CEPHEIDS IN AN INVISIBLE CLUSTER BEYOND THE GALACTIC BULGE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dékány, I.; Palma, T.; Minniti, D.

2015-01-20

We report the discovery of a pair of extremely reddened classical Cepheid variable stars located in the Galactic plane behind the bulge, using near-infrared (NIR) time-series photometry from the VISTA Variables in the Vía Láctea Survey. This is the first time that such objects have ever been found in the opposite side of the Galactic plane. The Cepheids have almost identical periods, apparent brightnesses, and colors. From the NIR Leavitt law, we determine their distances with ∼1.5% precision and ∼8% accuracy. We find that they have a same total extinction of A(V)≃32 mag, and are located at the same heliocentricmore » distance of 〈d〉=11.4±0.9 kpc, and less than 1 pc from the true Galactic plane. Their similar periods indicate that the Cepheids are also coeval, with an age of ∼48±3 Myr, according to theoretical models. They are separated by an angular distance of only 18.″3, corresponding to a projected separation of ∼1 pc. Their position coincides with the expected location of the Far 3 kpc Arm behind the bulge. Such a tight pair of similar classical Cepheids indicates the presence of an underlying young open cluster that is both hidden behind heavy extinction and disguised by the dense stellar field of the bulge. All our attempts to directly detect this “invisible cluster” have failed, and deeper observations are needed. (letters)« less

Spectroscopic studies of yellow supergiants in the Cepheid instability strip

NASA Astrophysics Data System (ADS)

Usenko, I. A.

2017-04-01

High-resolution spectra of nine yellow nonvariable supergiants (NVSs) located within the canonical Cepheid instability strip from Sandage and Tammann (1969) ( α Aqr, ɛ Leo, μ Per, ω Gem, BD+60 2532, HD 172365, HD 187299, HD 190113, and HD 200102) were taken with the 1-m Zeiss and 6-m BTA telescopes at the Special Astrophysical Observatory of the Russian Academy of Sciences in the 1990s. These have been used to determine the atmospheric parameters, chemical composition, radial velocities, reddenings, luminosities, distances, and radii. The spectroscopic estimates of T eff and the luminosities determined from the Hipparcos parallaxes have shown eight of the nine program NVSs on the T eff-log( L/ L ⊙) diagram to be outside the canonical Cepheid instability strip. When the edges of the Cepheid instability strip from Bono et al. (2000) are used, out of the NVSs from the list on the diagram one is within the Cepheid instability strip but closer to the red edge, two are at the red edge, three are beyond the red edge, two are at the blue edge, and one is beyond the blue edge. The evolutionary masses of the objects have been estimated. The abundances of α-elements, r- and s-process elements for all program objects have turned out to be nearly solar. The CNO, Na, Mg, and Al abundance estimates have shown that eight of the nine NVSs from the list have already passed the first dredge-up. Judging by the abundances of the key elements and its position on the T eff-log( L/ L ⊙) diagram, the lithium-rich supergiant HD 172365 is at the post-main-sequence evolutionary stage of gravitational helium core contraction and moves toward the first crossing of the Cepheid instability strip. The star ɛ Leo should be assigned to bright supergiants, while HD 187299 and HD 190113 may have already passed the second dredge-up and move to the asymptotic branch.

Investigating light curve modulation via kernel smoothing. I. Application to 53 fundamental mode and first-overtone Cepheids in the LMC

NASA Astrophysics Data System (ADS)

Süveges, Maria; Anderson, Richard I.

2018-03-01

Context. Recent studies have revealed a hitherto unknown complexity of Cepheid pulsations by discovering irregular modulated variability using photometry, radial velocities, and interferometry. Aim. We aim to perform a statistically rigorous search and characterization of such phenomena in continuous time, applying it to 53 classical Cepheids from the OGLE-III catalog. Methods: We have used local kernel regression to search for both period and amplitude modulations simultaneously in continuous time and to investigate their detectability. We determined confidence intervals using parametric and non-parametric bootstrap sampling to estimate significance, and investigated multi-periodicity using a modified pre-whitening approach that relies on time-dependent light curve parameters. Results: We find a wide variety of period and amplitude modulations and confirm that first overtone pulsators are less stable than fundamental mode Cepheids. Significant temporal variations in period are more frequently detected than those in amplitude. We find a range of modulation intensities, suggesting that both amplitude and period modulations are ubiquitous among Cepheids. Over the 12-year baseline offered by OGLE-III, we find that period changes are often nonlinear, sometimes cyclic, suggesting physical origins beyond secular evolution. Our method detects modulations (period and amplitude) more efficiently than conventional methods that are reliant on certain features in the Fourier spectrum, and pre-whitens time series more accurately than using constant light curve parameters, removing spurious secondary peaks effectively. Conclusions: Period and amplitude modulations appear to be ubiquitous among Cepheids. Current detectability is limited by observational cadence and photometric precision: detection of amplitude modulation below 3 mmag requires space-based facilities. Recent and ongoing space missions (K2, BRITE, MOST, CoRoT) as well as upcoming ones (TESS, PLATO) will significantly improve detectability of fast modulations, such as cycle-to-cycle variations, by providing high-cadence high-precision photometry. High-quality long-term ground-based photometric time series will remain crucial to study longer-term modulations and to disentangle random fluctuations from secular evolution.

The HST Key Project on the Extragalactic Distance Scale

NASA Astrophysics Data System (ADS)

Freedman, W. L.

1994-12-01

One of the major unresolved problems in observational cosmology is the determination of the Hubble Constant, (H_0). The Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale aims to provide a measure of H_0 to an accuracy of 10%. Historically the route to H_0 has been plagued by systematic errors; hence there is no quick and easy route to a believeable value of H_0. Achieving plausible error limits of 10% requires careful attention to eliminating potential sources of systematic error. The strategy adopted by the Key Project team is threefold: First, to discover Cepheids in spiral galaxies located in the field and in small groups that are suitable for the calibration of several independent secondary methods. Second, to make direct Cepheid measurements of 3 spiral galaxies in the Virgo cluster and 2 members of the Fornax cluster. Third, to provide a check on the the Cepheid distance scale via independent distance estimates to nearby galaxies, and in addition, to undertake an empirical test of the sensitivity of the zero point of the Cepheid PL relation to heavy-element abundances. First results from the HST Key Project will be presented. We have now determined Cepheid distances to 4 galaxies using the HST: these are the nearby galaxies M81 and M101, the edge-on galaxy NGC 925, and the face-on spiral galaxy M100 in the Virgo cluster. Recently we have measured a Cepheid distance for M100 of 17 +/- 2 Mpc, which yields a value of H_0 = 80 +/- 17 km/sec/Mpc. This work was carried out in collaboration with the other members of the HST Key Project team, R. Kennicutt, J. Mould, F. Bresolin, S. Faber, L. Ferrarese, H. Ford, J. Graham, J. Gunn, M. Han, P. Harding, J. Hoessel, R. Hill, J. Huchra, S. Hughes, G. Illingworth, D. Kelson, B. Madore, R. Phelps, A. Saha, N. Silbermann, P. Stetson, and A. Turner.

Spectroscopic properties of a two-dimensional time-dependent Cepheid model. I. Description and validation of the model

NASA Astrophysics Data System (ADS)

Vasilyev, V.; Ludwig, H.-G.; Freytag, B.; Lemasle, B.; Marconi, M.

2017-10-01

Context. Standard spectroscopic analyses of Cepheid variables are based on hydrostatic one-dimensional model atmospheres, with convection treated using various formulations of mixing-length theory. Aims: This paper aims to carry out an investigation of the validity of the quasi-static approximation in the context of pulsating stars. We check the adequacy of a two-dimensional time-dependent model of a Cepheid-like variable with focus on its spectroscopic properties. Methods: With the radiation-hydrodynamics code CO5BOLD, we construct a two-dimensional time-dependent envelope model of a Cepheid with Teff = 5600 K, log g = 2.0, solar metallicity, and a 2.8-day pulsation period. Subsequently, we perform extensive spectral syntheses of a set of artificial iron lines in local thermodynamic equilibrium. The set of lines allows us to systematically study effects of line strength, ionization stage, and excitation potential. Results: We evaluate the microturbulent velocity, line asymmetry, projection factor, and Doppler shifts. The microturbulent velocity, averaged over all lines, depends on the pulsational phase and varies between 1.5 and 2.7 km s-1. The derived projection factor lies between 1.23 and 1.27, which agrees with observational results. The mean Doppler shift is non-zero and negative, -1 km s-1, after averaging over several full periods and lines. This residual line-of-sight velocity (related to the "K-term") is primarily caused by horizontal inhomogeneities, and consequently we interpret it as the familiar convective blueshift ubiquitously present in non-pulsating late-type stars. Limited statistics prevent firm conclusions on the line asymmetries. Conclusions: Our two-dimensional model provides a reasonably accurate representation of the spectroscopic properties of a short-period Cepheid-like variable star. Some properties are primarily controlled by convective inhomogeneities rather than by the Cepheid-defining pulsations. Extended multi-dimensional modelling offers new insight into the nature of pulsating stars.

The Araucaria Project: The Distance to the Local Group Galaxy NGC 6822 from Cepheid Variables Discovered in a Wide-Field Imaging Survey

NASA Astrophysics Data System (ADS)

Pietrzyński, Grzegorz; Gieren, Wolfgang; Udalski, Andrzej; Bresolin, Fabio; Kudritzki, Rolf-Peter; Soszyński, Igor; Szymański, Michał; Kubiak, Marcin

2004-12-01

We have obtained mosaic images of NGC 6822 in the V and I bands on 77 nights. From these data, we have conducted an extensive search for Cepheid variables over the entire field of the galaxy, and we have found 116 such variables with periods ranging from 1.7 to 124 days. We used the long-period (>5.6 days) Cepheids to establish the period-luminosity (PL) relations in V, I, and in the reddening-independent Wesenheit index, which are all very tightly defined. Fitting the OGLE LMC slopes in the various bands to our data, we have derived distance values for NGC 6822 in V, I, and WI, which agree very well among themselves. Our adopted best distance value from the reddening-free Wesenheit index is 23.34+/-0.04 (statistical) +/-0.05 (systematic) mag. This value agrees within the combined 1 σ uncertainties with a previous distance value derived for NGC 6822 by McAlary and coworkers from near-IR photometry of nine Cepheids, but our new value is significantly more accurate. We compare the slopes of the Cepheid PL relation in V and I as determined in the five best-observed nearby galaxies, which span a metallicity range from -1.0 to -0.3 dex, and find the data consistent with no metallicity dependence of the PL relation slope in this range. Comparing the magnitudes of 10 day Cepheids with the I-band magnitudes of the tip of the red giant branch in the same set of galaxies, there is no evidence either for a significant variation of the PL zero points in V and I. The available data limit such a zero-point variation to less than 0.03 mag in the considered low-metallicity regime. Based on observations obtained with the 1.3 m telescope at the Las Campanas Observatory.

Nonlinear Modeling of Radial Stellar Pulsations

NASA Astrophysics Data System (ADS)

Smolec, R.

2009-09-01

In this thesis, I present the results of my work concerning the nonlinear modeling of radial stellar pulsations. I will focus on classical Cepheids, particularly on the double-mode phenomenon. History of nonlinear modeling of radial stellar pulsations begins in the sixties of the previous century. At the beginning convection was disregarded in model equations. Qualitatively, almost all features of the radial pulsators were successfully modeled with purely radiative hydrocodes. Among problems that remained, the most disturbing was modeling of the double-mode phenomenon. This long-standing problem seemed to be finally solved with the inclusion of turbulent convection into the model equations (Kollath et al. 1998, Feuchtinger 1998). Although dynamical aspects of the double-mode behaviour were extensively studied, its origin, particularly the specific role played by convection, remained obscure. To study this and other problems of radial stellar pulsations, I implemented the convection into pulsation hydrocodes. The codes adopt the Kuhfuss (1986) convection model. In other codes, particularly in the Florida-Budapest hydrocode (e.g. Kollath et al. 2002), used in comput! ation of most of the published double-mode models, different approximations concerning e.g. eddy-viscous terms or treatment of convectively stable regions are adopted. Particularly the neglect of negative buoyancy effects in the Florida-Budapest code and its consequences, were never discussed in the literature. These consequences are severe. Concerning the single-mode pulsators, neglect of negative buoyancy leads to smaller pulsation amplitudes, in comparison to amplitudes computed with code including these effects. Particularly, neglect of negative buoyancy reduces the amplitude of the fundamental mode very strong. This property of the Florida-Budapest models is crucial in bringing up the stable non-resonant double-mode Cepheid pulsation involving fundamental and first overtone modes (F/1O). Such pulsation is not observed in models computed including negative buoyancy. As the neglect of negative buoyancy is physically not correct, so are the double-mode Cepheid models computed with the Florida-Budapest hydrocode. Extensive search for F/1O double-mode Cepheid pulsation with the codes including negative buoyancy effects yielded null result. Some resonant double-mode F/1O Cepheid models were found, but their occurrence was restricted to a very narrow domain in the Hertzsprung-Russel diagram. Model computations intended to model the double-overtone (1O/2O) Cepheids in the Large Magellanic Cloud, also revealed some stable double-mode pulsations, however, restricted to a narrow period range. Resonances are most likely conductive in bringing up the double-mode behaviour observed in these models. However, majority of the double-overtone LMC Cepheids cannot be reproduced with our codes. Hence, the modeling of double-overtone Cepheids with convective hydrocodes is not satisfactory, either. Double-mode pulsation still lacks satisfactory explanation, and problem of its modeling remains open.

A Cepheid Distance to NGC 4603 in the Centaurus Cluster

NASA Technical Reports Server (NTRS)

Madore, B.; Newman, J.; Zepf, S.; Davis, M.; Freedman, W.; Madore, B.; Stetson, P.; Silbermann, N.; Phelps, R.

1999-01-01

In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling 6 orbits) in the F814W filter.

Separation in 5 Msun Binaries

NASA Astrophysics Data System (ADS)

Evans, Nancy R.; Bond, H. E.; Schaefer, G.; Mason, B. D.; Karovska, M.; Tingle, E.

2013-01-01

Cepheids (5 Msun stars) provide an excellent sample for determining the binary properties of fairly massive stars. International Ultraviolet Explorer (IUE) observations of Cepheids brighter than 8th magnitude resulted in a list of ALL companions more massive than 2.0 Msun uniformly sensitive to all separations. Hubble Space Telescope Wide Field Camera 3 (WFC3) has resolved three of these binaries (Eta Aql, S Nor, and V659 Cen). Combining these separations with orbital data in the literature, we derive an unbiased distribution of binary separations for a sample of 18 Cepheids, and also a distribution of mass ratios. The distribution of orbital periods shows that the 5 Msun binaries prefer shorter periods than 1 Msun stars, reflecting differences in star formation processes.

THE VVV SURVEY REVEALS CLASSICAL CEPHEIDS TRACING A YOUNG AND THIN STELLAR DISK ACROSS THE GALAXY’S BULGE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dékány, I.; Minniti, D.; Majaess, D.

2015-10-20

Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy’s evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the lastmore » 100 million years.« less

VizieR Online Data Catalog: BVIc light curves of 57 Cepheids (Berdnikov+,

NASA Astrophysics Data System (ADS)

Berdnikov, L. N.; Kniazev, A. Yu.; Sefako, R.; Kravtsov, V. V.; Zhujko, S. V.

2014-04-01

In 2008-2013, we obtained 11333 CCD BV Ic frames for 57 Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South AfricanAstronomicalObservatory (SAAO, South Africa) and the 40-cm telescope of the Cerro Armazones Astronomical Observatory of the Universidad Catolica del Norte (OCA, Chile) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented. Comparison of our light curves with those constructed from photoelectric observations shows that the differences between their mean magnitudes exceed 0.05mag in 20% of the cases. This suggests the necessity of performing CCD observations for all Cepheids. (2 data files).

CCD BVI c observations of Cepheids

NASA Astrophysics Data System (ADS)

Berdnikov, L. N.; Kniazev, A. Yu.; Sefako, R.; Kravtsov, V. V.; Zhujko, S. V.

2014-02-01

In 2008-2013, we obtained 11333 CCD BVI c frames for 57 Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) and the 40-cm telescope of the Cerro Armazones Astronomical Observatory of the Universidad Católica del Norte (OCA, Chile) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented. Comparison of our light curves with those constructed from photoelectric observations shows that the differences between their mean magnitudes exceed 0ṃ05 in 20% of the cases. This suggests the necessity of performing CCD observations for all Cepheids.

On Distance Scale Bias due to Stellar Multiplicity and Associations

NASA Astrophysics Data System (ADS)

Anderson, Richard I.; Riess, Adam

2018-01-01

The Cepheid Period-luminosity relation (Leavitt Law) provides the most accurate footing for the cosmic distance scale (CDS). Recently, evidence has been presented that the value of the Hubble constant H0 measured via the cosmic distance scale differs by 3.4σ from the value inferred using Planck data assuming ΛCDM cosmology (Riess et al. 2016). This exciting result may point to missing physics in the cosmological model; however, before such a claim can be made, careful analyses must address possible systematics involved in the calibration of the CDS.A frequently made claim in the literature is that companion stars or cluster membership of Cepheids may bias the calibration of the CDS. To evaluate this claim, we have carried out the first detailed study of the impact of Cepheid multiplicity and cluster membership on the determination of H0. Using deep HST imaging of M31 we directly measured the mean photometric bias due to cluster companions on Cepheid-based distances. Together with the empirical determination of the frequency with which Cepheids appear in clusters we quantify the combined H0 bias from close associations to be approximately 0.3% (0.20 km s-1 Mpc-1) for the passbands commonly used. Thus, we demonstrate that stellar associations cannot explain the aforementioned discrepancy observed in H0 and do not prevent achieving the community goal of measuring H0 with an accuracy of 1%. We emphasize the subtle, but important, difference between systematics relevant for calibrating the Leavitt Law (achieving a better understanding of stellar physics) and for accurately calibrating the CDS (measuring H0).

Evaluation of the Cepheid® Xpert®C. difficile binary toxin (BT) diagnostic assay.

PubMed

McGovern, Alan M; Androga, Grace O; Moono, Peter; Collins, Deirdre A; Foster, Niki F; Chang, Barbara J; Riley, Thomas V

2018-06-01

Strains of Clostridium difficile producing only binary toxin (CDT) are found commonly in animals but not humans. However, human diagnostic tests rarely look for CDT. The Cepheid Xpert C. difficile BT assay detects CDT with equal sensitivity (≥92%) in human and animal faecal samples. Copyright © 2018 Elsevier Ltd. All rights reserved.

75 FR 36432 - Termination of Declarations Justifying Emergency Use Authorizations of Certain In Vitro...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-25

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The Carnegie Chicago Hubble Program: The Mid-Infrared Colours of Cepheids and the Effect of Metallicity on the CO Band-Head at 4.6 Micron

NASA Technical Reports Server (NTRS)

Scowcroft, Victoria; Seibert, Mark; Freedman, Wendy L.; Beaton, Rachael L.; Madore, Barry F.; Monson, Andrew J.; Rich, Jeffery A.; Rigby, Jane R.

2016-01-01

We compare mid-infrared (IR) 3.6 and 4.5 micron Warm Spitzer observations for Cepheids in the Milky Way and the Large and Small Magellanic Clouds. Using models, we explore in detail the effect of the CO rotation-vibration band-head at 4.6 micron on the mid-IR photometry. We confirm the temperature sensitivity of the CO band-head at 4.6 micron and find no evidence for an effect at 3.6 micron. We compare the ([3.6]-[4.5]) period-colour relations in the MW, LMC and SMC. The slopes of the period-colour relations for the three galaxies are in good agreement, but there is a trend in zero-point with metallicity, with the lowest metallicity Cepheids having redder mid-IR colours. Finally, we present a colour-[Fe/H] relation based on published spectroscopic metallicities. This empirical relation, calibrated to the metallicity system of Genovali et al., demonstrates that the ([3.6]-[4.5]) colour provides a reliable metallicity indicator for Cepheids, with a precision comparable to current spectroscopic determinations.

An application of Bayesian statistics to the extragalactic Cepheid distance scale

NASA Astrophysics Data System (ADS)

Barnes, Thomas G., III; Moffett, Thomas J.; Jefferys, W. H.; Forestell, Amy D.

2004-05-01

We have determined quasi-geometric distances to the Magellanic Clouds, M31 and M33. Our analysis uses a Bayesian statistical method to provide mathematically rigorous and objective solutions for individual Cepheids. We combine the individual distances with a hierarchial Bayesian model to determine the galactic distances. We obtain distance moduli 18.87 ± 0.07 mag (LMC, 12 stars), 19.14 ± 0.10 (SMC, 8 stars), 23.83 ± 0.35 mag (M33, 1 star) and 25.2 ± 0.6 mag (M31, 1 star) - all uncorrected for metallicity. The M31 and M33 distances are very preliminary. If the Pl relations of the LMC, SMC, and Galaxy are identical, our results exclude the metallicity effect in the V, (V - R) surface brightness method predicted by Hindsley and Bell (1989) at the 5σ level. Alternately, if Hindsley & Bell's prediction is adopted as true, we find a metallicity effect intrinsic to the Cepheid PL relation requiring a correction Δ(V - Mv) = (0.36 ± 0.07)Δ[A/H] mag. The latter has the opposite sign to other observational estimates of the Cepheid metallicity effect.

Homing in on Polaris: A 7 M⊙ first-overtone Cepheid entering the instability strip for the first time

NASA Astrophysics Data System (ADS)

Anderson, Richard I.

2018-04-01

A recently presented HST/FGS parallax measurement of the Polaris system has been interpreted as evidence for the Cepheid Polaris Aa to be pulsating in the second overtone. An age discrepancy between components A and B has been noted and discussed in terms of a stellar merger. Here I show that the new parallax of Polaris is consistent with a simpler interpretation of Polaris as a 7 M⊙, first-overtone, classical Cepheid near the hot boundary of the first instability strip crossing. This picture is anchored to rates of period change, the period-luminosity relation, the location in color-magnitude space, the interferometrically determined radius, spectroscopic N/C and N/O enhancements, and a dynamical mass measurement. The detailed agreement between models and data corroborates the physical association between the Cepheid and its visual companion as well as the accuracy of the HST parallax. The age discrepancy between components A and B is confirmed and requires further analysis, for example to investigate the possibility of stellar mergers in an evaporating birth cluster of which the Polaris triple system would be the remaining core.

The Influential Effect of Blending, Bump, Changing Period, and Eclipsing Cepheids on the Leavitt Law

NASA Astrophysics Data System (ADS)

García-Varela, A.; Muñoz, J. R.; Sabogal, B. E.; Vargas Domínguez, S.; Martínez, J.

2016-06-01

The investigation of the nonlinearity of the Leavitt law (LL) is a topic that began more than seven decades ago, when some of the studies in this field found that the LL has a break at about 10 days. The goal of this work is to investigate a possible statistical cause of this nonlinearity. By applying linear regressions to OGLE-II and OGLE-IV data, we find that to obtain the LL by using linear regression, robust techniques to deal with influential points and/or outliers are needed instead of the ordinary least-squares regression traditionally used. In particular, by using M- and MM-regressions we establish firmly and without doubt the linearity of the LL in the Large Magellanic Cloud, without rejecting or excluding Cepheid data from the analysis. This implies that light curves of Cepheids suggesting blending, bumps, eclipses, or period changes do not affect the LL for this galaxy. For the Small Magellanic Cloud, when including Cepheids of this kind, it is not possible to find an adequate model, probably because of the geometry of the galaxy. In that case, a possible influence of these stars could exist.

Cepheid variables in the flared outer disk of our galaxy.

PubMed

Feast, Michael W; Menzies, John W; Matsunaga, Noriyuki; Whitelock, Patricia A

2014-05-15

Flaring and warping of the disk of the Milky Way have been inferred from observations of atomic hydrogen but stars associated with flaring have not hitherto been reported. In the area beyond the Galactic centre the stars are largely hidden from view by dust, and the kinematic distances of the gas cannot be estimated. Thirty-two possible Cepheid stars (young pulsating variable stars) in the direction of the Galactic bulge were recently identified. With their well-calibrated period-luminosity relationships, Cepheid stars are useful distance indicators. When observations of these stars are made in two colours, so that their distance and reddening can be determined simultaneously, the problems of dust obscuration are minimized. Here we report that five of the candidates are classical Cepheid stars. These five stars are distributed from approximately one to two kiloparsecs above and below the plane of the Galaxy, at radial distances of about 13 to 22 kiloparsecs from the centre. The presence of these relatively young (less than 130 million years old) stars so far from the Galactic plane is puzzling, unless they are in the flared outer disk. If so, they may be associated with the outer molecular arm.

Gaia DR1 Evidence of Disrupting the Perseus Arm

NASA Astrophysics Data System (ADS)

Baba, Junichi; Kawata, Daisuke; Matsunaga, Noriyuki; Grand, Robert J. J.; Hunt, Jason A. S.

2018-02-01

We have discovered a clear sign of the disruption phase of the Perseus arm in the Milky Way using Cepheid variables, taking advantage of the accurately measured distances of Cepheids and the proper motions from Gaia Data Release 1. Both the Galactocentric radial and rotation velocities of 77 Cepheids within 1.5 kpc of the Perseus arm are correlated with their distances from the locus of the Perseus arm, as the trailing side is rotating faster and moving inward compared to the leading side. We also found a negative vertex deviation for the Cepheids on the trailing side, ‑27.°6 ± 2.°4, in contrast to the positive vertex deviation in the solar neighborhood. This is, to our knowledge, the first direct evidence that the vertex deviation around the Perseus arm is affected by the spiral arm. We compared these observational trends with our N-body/hydrodynamics simulations based on a static density-wave spiral scenario and with those based on a transient dynamic spiral scenario. Although our comparisons are limited to qualitative trends, they strongly favor the conclusion that the Perseus arm is in the disruption phase of a transient arm.

Variable Stars in the Draco Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Harris, H. C.; Silberman, N. A.; Smith, H. A.

A new survey of the variable stars in the Draco dwarf spheroidal galaxy updates the pioneering study of this galaxy by Baade and Swope (1961). Our improved data, taken in BVI filters with CCD cameras on three telescopes at more than 80 epochs, allow us to investigate the known variables and to discover new, mostly low-amplitude variables. Approximately 300 variables are found and classified, more than double the number of variables analyzed previously. Most are RR Lyraes, with a small fraction of Anomalous Cepheids. This large sample of variables provides a unique opportunity to study the properties of these stars in a single system. This paper discusses the census of RR Lyraes, including RRc-type, double-mode, and Blazhko-effect RR Lyraes, as well as Anomalous Cepheids, and Type II Cepheids in Draco.

The Development of Early Pulsation Theory, or, How Cepheids Are Like Steam Engines

NASA Astrophysics Data System (ADS)

Stanley, M.

2012-06-01

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A. S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. Surprisingly, the pulsation theory not only depended on novel developments in stellar physics, but the theory also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.

Gaia Data Release 1. Testing parallaxes with local Cepheids and RR Lyrae stars

NASA Astrophysics Data System (ADS)

Gaia Collaboration; Clementini, G.; Eyer, L.; Ripepi, V.; Marconi, M.; Muraveva, T.; Garofalo, A.; Sarro, L. M.; Palmer, M.; Luri, X.; Molinaro, R.; Rimoldini, L.; Szabados, L.; Musella, I.; Anderson, R. I.; Prusti, T.; de Bruijne, J. H. J.; Brown, A. G. A.; Vallenari, A.; Babusiaux, C.; Bailer-Jones, C. A. L.; Bastian, U.; Biermann, M.; Evans, D. W.; Jansen, F.; Jordi, C.; Klioner, S. A.; Lammers, U.; Lindegren, L.; Mignard, F.; Panem, C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; Valette, V.; van Leeuwen, F.; Walton, N. A.; Aerts, C.; Arenou, F.; Cropper, M.; Drimmel, R.; Høg, E.; Katz, D.; Lattanzi, M. G.; O'Mullane, W.; Grebel, E. K.; Holland, A. D.; Huc, C.; Passot, X.; Perryman, M.; Bramante, L.; Cacciari, C.; Castañeda, J.; Chaoul, L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra, R.; Hernández, J.; Jean-Antoine-Piccolo, A.; Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Ordóñez-Blanco, D.; Panuzzo, P.; Portell, J.; Richards, P. J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thévenin, F.; Torra, J.; Els, S. G.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Lock, T.; Mercier, E.; Altmann, M.; Andrae, R.; Astraatmadja, T. L.; Bellas-Velidis, I.; Benson, K.; Berthier, J.; Blomme, R.; Busso, G.; Carry, B.; Cellino, A.; Cowell, S.; Creevey, O.; Cuypers, J.; Davidson, M.; De Ridder, J.; de Torres, A.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.; Frémat, Y.; García-Torres, M.; Gosset, E.; Halbwachs, J.-L.; Hambly, N. C.; Harrison, D. L.; Hauser, M.; Hestroffer, D.; Hodgkin, S. T.; Huckle, H. E.; Hutton, A.; Jasniewicz, G.; Jordan, S.; Kontizas, M.; Korn, A. J.; Lanzafame, A. C.; Manteiga, M.; Moitinho, A.; Muinonen, K.; Osinde, J.; Pancino, E.; Pauwels, T.; Petit, J.-M.; Recio-Blanco, A.; Robin, A. C.; Siopis, C.; Smith, M.; Smith, K. W.; Sozzetti, A.; Thuillot, W.; van Reeven, W.; Viala, Y.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aguado, J. J.; Allan, P. M.; Allasia, W.; Altavilla, G.; Álvarez, M. A.; Alves, J.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.; Antoja, T.; Antón, S.; Arcay, B.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.; Barache, C.; Barata, C.; Barbier, A.; Barblan, F.; Barrado y Navascués, D.; Barros, M.; Barstow, M. A.; Becciani, U.; Bellazzini, M.; Bello García, A.; Belokurov, V.; Bendjoya, P.; Berihuete, A.; Bianchi, L.; Bienaymé, O.; Billebaud, F.; Blagorodnova, N.; Blanco-Cuaresma, S.; Boch, T.; Bombrun, A.; Borrachero, R.; Bouquillon, S.; Bourda, G.; Bragaglia, A.; Breddels, M. A.; Brouillet, N.; Brüsemeister, T.; Bucciarelli, B.; Burgess, P.; Burgon, R.; Burlacu, A.; Busonero, D.; Buzzi, R.; Caffau, E.; Cambras, J.; Campbell, H.; Cancelliere, R.; Cantat-Gaudin, T.; Carlucci, T.; Carrasco, J. M.; Castellani, M.; Charlot, P.; Charnas, J.; Chiavassa, A.; Clotet, M.; Cocozza, G.; Collins, R. S.; Costigan, G.; Crifo, F.; Cross, N. J. G.; Crosta, M.; Crowley, C.; Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; De Cat, P.; de Felice, F.; de Laverny, P.; De Luise, F.; De March, R.; de Souza, R.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.; Delgado, H. E.; Di Matteo, P.; Diakite, S.; Distefano, E.; Dolding, C.; Dos Anjos, S.; Drazinos, P.; Durán, J.; Dzigan, Y.; Edvardsson, B.; Enke, H.; Evans, N. W.; Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Falcão, A. J.; Farràs Casas, M.; Federici, L.; Fedorets, G.; Fernández-Hernández, J.; Fernique, P.; Fienga, A.; Figueras, F.; Filippi, F.; Findeisen, K.; Fonti, A.; Fouesneau, M.; Fraile, E.; Fraser, M.; Fuchs, J.; Gai, M.; Galleti, S.; Galluccio, L.; Garabato, D.; García-Sedano, F.; Garralda, N.; Gavras, P.; Gerssen, J.; Geyer, R.; Gilmore, G.; Girona, S.; Giuffrida, G.; Gomes, M.; González-Marcos, A.; González-Núñez, J.; González-Vidal, J. J.; Granvik, M.; Guerrier, A.; Guillout, P.; Guiraud, J.; Gúrpide, A.; Gutiérrez-Sánchez, R.; Guy, L. P.; Haigron, R.; Hatzidimitriou, D.; Haywood, M.; Heiter, U.; Helmi, A.; Hobbs, D.; Hofmann, W.; Holl, B.; Holland, G.; Hunt, J. A. S.; Hypki, A.; Icardi, V.; Irwin, M.; Jevardat de Fombelle, G.; Jofré, P.; Jonker, P. G.; Jorissen, A.; Julbe, F.; Karampelas, A.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, E.; Koposov, S. E.; Kordopatis, G.; Koubsky, P.; Krone-Martins, A.; Kudryashova, M.; Bachchan, R. K.; Lacoste-Seris, F.; Lanza, A. F.; Lavigne, J.-B.; Le Poncin-Lafitte, C.; Lebreton, Y.; Lebzelter, T.; Leccia, S.; Leclerc, N.; Lecoeur-Taibi, I.; Lemaitre, V.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.; Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; Löffler, W.; López, M.; Lorenz, D.; MacDonald, I.; Magalhães Fernandes, T.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant, J. M.; Marinoni, S.; Marrese, P. M.; Marschalkó, G.; Marshall, D. J.; Martín-Fleitas, J. M.; Martino, M.; Mary, N.; Matijevič, G.; McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Miranda, B. M. H.; Molina, D.; Molinaro, M.; Molnár, L.; Moniez, M.; Montegriffo, P.; Mor, R.; Mora, A.; Morbidelli, R.; Morel, T.; Morgenthaler, S.; Morris, D.; Mulone, A. F.; Narbonne, J.; Nelemans, G.; Nicastro, L.; Noval, L.; Ordénovic, C.; Ordieres-Meré, J.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler, F.; Palacin, H.; Palaversa, L.; Parsons, P.; Pecoraro, M.; Pedrosa, R.; Pentikäinen, H.; Pichon, B.; Piersimoni, A. M.; Pineau, F.-X.; Plachy, E.; Plum, G.; Poujoulet, E.; Prša, A.; Pulone, L.; Ragaini, S.; Rago, S.; Rambaux, N.; Ramos-Lerate, M.; Ranalli, P.; Rauw, G.; Read, A.; Regibo, S.; Reylé, C.; Ribeiro, R. A.; Riva, A.; Rixon, G.; Roelens, M.; Romero-Gómez, M.; Rowell, N.; Royer, F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann, J.; Salgado, J.; Salguero, E.; Sarasso, M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol, M.; Segovia, J. C.; Segransan, D.; Shih, I.-C.; Smareglia, R.; Smart, R. L.; Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.; Steidelmüller, H.; Stephenson, C. A.; Stoev, H.; Suess, F. F.; Süveges, M.; Surdej, J.; Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.; Terrett, D.; Tingley, B.; Trager, S. C.; Turon, C.; Ulla, A.; Utrilla, E.; Valentini, G.; van Elteren, A.; Van Hemelryck, E.; van Leeuwen, M.; Varadi, M.; Vecchiato, A.; Veljanoski, J.; Via, T.; Vicente, D.; Vogt, S.; Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Weingrill, K.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Zucker, S.; Zurbach, C.; Zwitter, T.; Alecu, A.; Allen, M.; Allende Prieto, C.; Amorim, A.; Anglada-Escudé, G.; Arsenijevic, V.; Azaz, S.; Balm, P.; Beck, M.; Bernstein, H.-H.; Bigot, L.; Bijaoui, A.; Blasco, C.; Bonfigli, M.; Bono, G.; Boudreault, S.; Bressan, A.; Brown, S.; Brunet, P.-M.; Bunclark, P.; Buonanno, R.; Butkevich, A. G.; Carret, C.; Carrion, C.; Chemin, L.; Chéreau, F.; Corcione, L.; Darmigny, E.; de Boer, K. S.; de Teodoro, P.; de Zeeuw, P. T.; Delle Luche, C.; Domingues, C. D.; Dubath, P.; Fodor, F.; Frézouls, B.; Fries, A.; Fustes, D.; Fyfe, D.; Gallardo, E.; Gallegos, J.; Gardiol, D.; Gebran, M.; Gomboc, A.; Gómez, A.; Grux, E.; Gueguen, A.; Heyrovsky, A.; Hoar, J.; Iannicola, G.; Isasi Parache, Y.; Janotto, A.-M.; Joliet, E.; Jonckheere, A.; Keil, R.; Kim, D.-W.; Klagyivik, P.; Klar, J.; Knude, J.; Kochukhov, O.; Kolka, I.; Kos, J.; Kutka, A.; Lainey, V.; LeBouquin, D.; Liu, C.; Loreggia, D.; Makarov, V. V.; Marseille, M. G.; Martayan, C.; Martinez-Rubi, O.; Massart, B.; Meynadier, F.; Mignot, S.; Munari, U.; Nguyen, A.-T.; Nordlander, T.; O'Flaherty, K. S.; Ocvirk, P.; Olias Sanz, A.; Ortiz, P.; Osorio, J.; Oszkiewicz, D.; Ouzounis, A.; Park, P.; Pasquato, E.; Peltzer, C.; Peralta, J.; Péturaud, F.; Pieniluoma, T.; Pigozzi, E.; Poels, J.; Prat, G.; Prod'homme, T.; Raison, F.; Rebordao, J. M.; Risquez, D.; Rocca-Volmerange, B.; Rosen, S.; Ruiz-Fuertes, M. I.; Russo, F.; Serraller Vizcaino, I.; Short, A.; Siebert, A.; Silva, H.; Sinachopoulos, D.; Slezak, E.; Soffel, M.; Sosnowska, D.; Straižys, V.; ter Linden, M.; Terrell, D.; Theil, S.; Tiede, C.; Troisi, L.; Tsalmantza, P.; Tur, D.; Vaccari, M.; Vachier, F.; Valles, P.; Van Hamme, W.; Veltz, L.; Virtanen, J.; Wallut, J.-M.; Wichmann, R.; Wilkinson, M. I.; Ziaeepour, H.; Zschocke, S.

2017-09-01

Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims: In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, which involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity (PL), period-Wesenheit (PW) relations for classical and Type II Cepheids and infrared PL, PL-metallicity (PLZ), and optical luminosity-metallicity (MV-[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS. Methods: Classical Cepheids were carefully selected in order to discard known or suspected binary systems. The final sample comprises 102 fundamental mode pulsators with periods ranging from 1.68 to 51.66 days (of which 33 with σϖ/ϖ< 0.5). The Type II Cepheids include a total of 26 W Virginis and BL Herculis stars spanning the period range from 1.16 to 30.00 days (of which only 7 with σϖ/ϖ< 0.5). The RR Lyrae stars include 200 sources with pulsation period ranging from 0.27 to 0.80 days (of which 112 with σϖ/ϖ< 0.5). The new relations were computed using multi-band (V,I,J,Ks) photometry and spectroscopic metal abundances available in the literature, and by applying three alternative approaches: (I) linear least-squares fitting of the absolute magnitudes inferred from direct transformation of the TGAS parallaxes; (II) adopting astrometry-based luminosities; and (III) using a Bayesian fitting approach. The last two methods work in parallax space where parallaxes are used directly, thus maintaining symmetrical errors and allowing negative parallaxes to be used. The TGAS-based PL,PW,PLZ, and MV- [Fe/H] relations are discussed by comparing the distance to the Large Magellanic Cloud provided by different types of pulsating stars and alternative fitting methods. Results: Good agreement is found from direct comparison of the parallaxes of RR Lyrae stars for which both TGAS and HST measurements are available. Similarly, very good agreement is found between the TGAS values and the parallaxes inferred from the absolute magnitudes of Cepheids and RR Lyrae stars analysed with the Baade-Wesselink method. TGAS values also compare favourably with the parallaxes inferred by theoretical model fitting of the multi-band light curves for two of the three classical Cepheids and one RR Lyrae star, which were analysed with this technique in our samples. The K-band PL relations show the significant improvement of the TGAS parallaxes for Cepheids and RR Lyrae stars with respect to the Hipparcos measurements. This is particularly true for the RR Lyrae stars for which improvement in quality and statistics is impressive. Conclusions: TGAS parallaxes bring a significant added value to the previous Hipparcos estimates. The relations presented in this paper represent the first Gaia-calibrated relations and form a work-in-progress milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia Data Release 2 (DR2) in 2018. Full Tables A.1-A.3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A79

Einstein observations of three classical Cepheids

NASA Technical Reports Server (NTRS)

Bohm-Vitense, E.; Parsons, S. B.

1983-01-01

We have looked for X-ray emission from the classical Cepheids delta Cep, beta Dor, and zeta Gem during phases when the latter two stars show emission in low excitation chromospheric lines. No X-ray flux was detected except possibly from zeta Gem at phase 0.26. Derived upper limits are in line with emission flux or upper limits obtained for other F and G supergiants.

A test of Gaia Data Release 1 parallaxes: implications for the local distance scale

NASA Astrophysics Data System (ADS)

Casertano, Stefano; Riess, Adam G.; Bucciarelli, Beatrice; Lattanzi, Mario G.

2017-03-01

Aims: We present a comparison of Gaia Data Release 1 (DR1) parallaxes with photometric parallaxes for a sample of 212 Galactic Cepheids at a median distance of 2 kpc, and explore their implications on the distance scale and the local value of the Hubble constant H0. Methods: The Cepheid distances are estimated from a recent calibration of the near-infrared period-luminosity (P-L) relation. The comparison is carried out in parallax space, where the DR1 parallax errors, with a median value of half the median parallax, are expected to be well-behaved. Results: With the exception of one outlier, the DR1 parallaxes are in very good global agreement with the predictions from a well-established P-L relation, with a possible indication that the published errors may be conservatively overestimated by about 20%. This confirms that the quality of DR1 parallaxes for the Cepheids in our sample is well within their stated errors. We find that the parallaxes of 9 Cepheids brighter than G = 6 may be systematically underestimated. If interpreted as an independent calibration of the Cepheid luminosities and assumed to be otherwise free of systematic uncertainties, DR1 parallaxes are in very good agreement (within 0.3%) with the current estimate of the local Hubble constant, and in conflict at the level of 2.5σ (3.5σ if the errors are scaled) with the value inferred from Planck cosmic microwave background data used in conjunction with ΛCDM. We also test for a zeropoint error in Gaia parallaxes and find none to a precision of 20 μas. We caution however that with this early release, the complete systematic properties of the measurements may not be fully understood at the statistical level of the Cepheid sample mean, a level an order of magnitude below the individual uncertainties. The early results from DR1 demonstrate again the enormous impact that the full mission will likely have on fundamental questions in astrophysics and cosmology.

Pulsating Star Mystery Solved

NASA Astrophysics Data System (ADS)

2010-11-01

By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. Up to now astronomers had two incompatible theoretical predictions of Cepheid masses. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations. The new results, from a team led by Grzegorz Pietrzyński (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the 25 November 2010 edition of the journal Nature. Grzegorz Pietrzyński introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct." Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun [1]. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe [2]. Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20-30% less than predictions from the theory of the evolution of stars. This embarrassing discrepancy has been known since the 1960s. To resolve this mystery, astronomers needed to find a double star containing a Cepheid where the orbit happened to be seen edge-on from Earth. In these cases, known as eclipsing binaries, the brightness of the two stars dims as one component passes in front of the other, and again when it passes behind the other star. In such pairs astronomers can determine the masses of the stars to high accuracy [3]. Unfortunately neither Cepheids nor eclipsing binaries are common, so the chance of finding such an unusual pair seemed very low. None are known in the Milky Way. Wolfgang Gieren, another member of the team, takes up the story: "Very recently we actually found the double star system we had hoped for among the stars of the Large Magellanic Cloud. It contains a Cepheid variable star pulsating every 3.8 days. The other star is slightly bigger and cooler, and the two stars orbit each other in 310 days. The true binary nature of the object was immediately confirmed when we observed it with the HARPS spectrograph on La Silla." The observers carefully measured the brightness variations of this rare object, known as OGLE-LMC-CEP0227 [4], as the two stars orbited and passed in front of one another. They also used HARPS and other spectrographs to measure the motions of the stars towards and away from the Earth - both the orbital motion of both stars and the in-and-out motion of the surface of the Cepheid as it swelled and contracted. This very complete and detailed data allowed the observers to determine the orbital motion, sizes and masses of the two stars with very high accuracy - far surpassing what had been done before for a Cepheid. The mass of the Cepheid is now known to about 1% and agrees exactly with predictions from the theory of stellar pulsation. However, the larger mass predicted by stellar evolution theory was shown to be significantly in error. The much-improved mass estimate is only one outcome of this work, and the team hopes to find other examples of these remarkably useful pairs of stars to exploit the method further. They also believe that from such binary systems they will eventually be able to pin down the distance to the Large Magellanic Cloud to 1%, which would mean an extremely important improvement of the cosmic distance scale. Notes [1] The first Cepheid variables were spotted in the 18th century and the brightest ones can easily be seen to vary from night to night with the unaided eye. They take their name from the star Delta Cephei in the constellation of Cepheus (the King), which was first seen to vary by John Goodricke in England in 1784. Remarkably, Goodricke was also the first to explain the light variations of another kind of variable star, eclipsing binaries. In this case two stars are in orbit around each other and pass in front of each other for part of their orbits and so the total brightness of the pair drops. The very rare object studied by the current team is both a Cepheid and an eclipsing binary. Classical Cepheids are massive stars, distinct from similar pulsating stars of lower mass that do not share the same evolutionary history. [2] The period luminosity relation for Cepheids, discovered by Henrietta Leavitt in 1908, was used by Edwin Hubble to make the first estimates of the distance to what we now know to be galaxies. More recently Cepheids have been observed with the Hubble Space Telescope and with the ESO VLT on Paranal to make highly accurate distance estimates to many nearby galaxies. [3] In particular, astronomers can determine the masses of the stars to high accuracy if both stars happen to have a similar brightness and therefore the spectral lines belonging to each of the two stars can be seen in the observed spectrum of the two stars together, as is the case for this object. This allows the accurate measurement of the motions of both stars towards and away from Earth as they orbit, using the Doppler effect. [4] The name OGLE-LMC-CEP0227 arises because the star was first discovered to be a variable during the OGLE search for gravitational microlensing. More details about OGLE are available at: http://ogle.astrouw.edu.pl/. More information This research was presented in a paper to appear in the journal Nature on 25 November 2010. The team is composed of G. Pietrzyński (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), I. B. Thompson (Carnegie Observatories, USA), W. Gieren (Universidad de Concepción, Chile), D. Graczyk (Universidad de Concepción, Chile), G. Bono (INAF-Osservatorio Astronomico di Roma, Universita' di Roma, Italy), A. Udalski (Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), I. Soszyński (Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), D. Minniti (Pontificia Universidad Católica de Chile) and B. Pilecki (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland). ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Investigating light curve modulation via kernel smoothing. II. New additional modes in single-mode OGLE classical Cepheids

NASA Astrophysics Data System (ADS)

Süveges, Maria; Anderson, Richard I.

2018-04-01

Detailed knowledge of the variability of classical Cepheids, in particular their modulations and mode composition, provides crucial insight into stellar structure and pulsation. However, tiny modulations of the dominant radial-mode pulsation were recently found to be very frequent, possibly ubiquitous in Cepheids, which makes secondary modes difficult to detect and analyse, since these modulations can easily mask the potentially weak secondary modes. The aim of this study is to re-investigate the secondary mode content in the sample of OGLE-III and -IV single-mode classical Cepheids using kernel regression with adaptive kernel width for pre-whitening, instead of using a constant-parameter model. This leads to a more precise removal of the modulated dominant pulsation, and enables a more complete survey of secondary modes with frequencies outside a narrow range around the primary. Our analysis reveals that significant secondary modes occur more frequently among first overtone Cepheids than previously thought. The mode composition appears significantly different in the Large and Small Magellanic Clouds, suggesting a possible dependence on chemical composition. In addition to the formerly identified non-radial mode at P2 ≈ 0.6…0.65P1 (0.62-mode), and a cluster of modes with near-primary frequency, we find two more candidate non-radial modes. One is a numerous group of secondary modes with P2 ≈ 1.25P1, which may represent the fundamental of the 0.62-mode, supposed to be the first harmonic of an l ∈ {7, 8, 9} non-radial mode. The other new mode is at P2 ≈ 1.46P1, possibly analogous to a similar, rare mode recently discovered among first overtone RR Lyrae stars.

Large Magellanic Cloud Near-infrared Synoptic Survey. IV. Leavitt Laws for Type II Cepheid Variables

NASA Astrophysics Data System (ADS)

Bhardwaj, Anupam; Macri, Lucas M.; Rejkuba, Marina; Kanbur, Shashi M.; Ngeow, Chow-Choong; Singh, Harinder P.

2017-04-01

We present time-series observations of Population II Cepheids in the Large Magellanic Cloud at near-infrared (JHK s ) wavelengths. Our sample consists of 81 variables with accurate periods and optical (VI) magnitudes from the OGLE survey, covering various subtypes of pulsators (BL Herculis, W Virginis, and RV Tauri). We generate light-curve templates using high-quality I-band data in the LMC from OGLE and K s -band data in the Galactic bulge from VISTA Variables in Via Láctea survey and use them to obtain robust mean magnitudes. We derive period-luminosity (P-L) relations in the near-infrared and Period-Wesenheit (P-W) relations by combining optical and near-infrared data. Our P-L and P-W relations are consistent with published work when excluding long-period RV Tauris. We find that Pop II Cepheids and RR Lyraes follow the same P-L relations in the LMC. Therefore, we use trigonometric parallax from the Gaia DR1 for VY Pyx and the Hubble Space Telescope parallaxes for k Pav and 5 RR Lyrae variables to obtain an absolute calibration of the Galactic K s -band P-L relation, resulting in a distance modulus to the LMC of {μ }{LMC}=18.54+/- 0.08 mag. We update the mean magnitudes of Pop II Cepheids in Galactic globular clusters using our light-curve templates and obtain distance estimates to those systems, anchored to a precise late-type eclipsing binary distance to the LMC. We find that the distances to these globular clusters based on Pop II Cepheids are consistent (within 2σ ) with estimates based on the {M}V-[{Fe}/{{H}}] relation for horizontal branch stars.

Discovery Of An Infrared Bow Shock Associated With Delta Cephei

NASA Astrophysics Data System (ADS)

Remage Evans, Nancy; Marengo, M.; Barmby, P.; Matthews, L. D.; Bono, G.; Welch, D. L.; Romaniello, M.; Huelsman, D.; Su, K. Y. L.; Fazio, G.

2010-05-01

We have obtained Spitzer Infrared Array Camera (IRAC) and Multiband Infrared Photometer for Spitzer (MIPS) observations of a sample of classical Cepheids both to derive infrared Leavitt Laws (Period-Luminosity Relations) and to look for evidence of mass loss in the spectral energy distributions. The MIPS 24 and 70 micron images of Delta Cep were particularly striking, since they show an arc of emission offset about an arcmin from Delta Cep. The emission is shaped like a bow shock and is aligned with the space motion of the Cepheid, implying it is physically related to the star. Bow shock structures of this kind can be formed when ram pressure of the ambient ISM balances the wind from a mass-losing star, raising the intriguing possibility that delta Cep is undergoing mass-loss during the Cepheid phase. Circumstellar emission is not a general feature of our Cepheid observations, but 2 unusual circumstances may make it visible around Delta Cep. If the Cepheid was already surrounded by interstellar matter, mass loss from the star could have created the bow shock. Second, Delta Cep has a physical companion 40" to the South, HD 213317, itself a binary. This B7-8 III-IV star is hot enough that it may produce infrared emission by heating dust within the ejected material. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. P. B. and D. W. both acknowledge research support through Discovery Grants from the Natural Sciences and Engineering Research Council of Canada. N. R. E. acknowledges support from the Chandra X-Ray Center grant NAS8-03060.

The Cepheids of NGC 1866: a precise benchmark for the extragalactic distance scale and stellar evolution from modern UBVI photometry

NASA Astrophysics Data System (ADS)

Musella, I.; Marconi, M.; Stetson, P. B.; Raimondo, G.; Brocato, E.; Molinaro, R.; Ripepi, V.; Carini, R.; Coppola, G.; Walker, A. R.; Welch, D. L.

2016-04-01

We present the analysis of multiband time series data for a sample of 24 Cepheids in the field of the Large Magellanic Cloud cluster NGC 1866. Very accurate BVI Very Large Telescope photometry is combined with archival UBVI data, covering a large temporal window, to obtain precise mean magnitudes and periods with typical errors of 1-2 per cent and of 1 ppm, respectively. These results represent the first accurate and homogeneous data set for a substantial sample of Cepheid variables belonging to a cluster and hence sharing common distance, age and original chemical composition. Comparisons of the resulting multiband period-luminosity and Wesenheit relations to both empirical and theoretical results for the Large Magellanic Cloud are presented and discussed to derive the distance of the cluster and to constrain the mass-luminosity relation of the Cepheids. The adopted theoretical scenario is also tested by comparison with independent calibrations of the Cepheid Wesenheit zero-point based on trigonometric parallaxes and Baade-Wesselink techniques. Our analysis suggests that a mild overshooting and/or a moderate mass-loss can affect intermediate-mass stellar evolution in this cluster and gives a distance modulus of 18.50 ± 0.01 mag. The obtained V,I colour-magnitude diagram is also analysed and compared with both synthetic models and theoretical isochrones for a range of ages and metallicities and for different efficiencies of core overshooting. As a result, we find that the age of NGC 1866 is about 140 Myr, assuming Z = 0.008 and the mild efficiency of overshooting suggested by the comparison with the pulsation models.

The Hubble Space Telescope Extragalactic Distance Scale Key Project. 1: The discovery of Cepheids and a new distance to M81

NASA Technical Reports Server (NTRS)

Freedman, Wendy L.; Hughes, Shaun M.; Madore, Barry F.; Mould, Jeremy R.; Lee, Myung Gyoon; Stetson, Peter; Kennicutt, Robert C.; Turner, Anne; Ferrarese, Laura; Ford, Holland

1994-01-01

We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I magnitude system using a ground-based calibration. Apparent period-luminosity relations at V and I were constructed, from which apparent distance moduli were measured with respect to assumed values of mu(sub 0) = 18.50 mag and E(B - V) = 0.10 mag for the Large Magellanic Cloud. The difference in the apparent V and I moduli yields a measure of the difference in the total mean extinction between the M81 and the LMC Cepheid samples. A low total mean extinction to the M81 sample of E(B - V) = 0.03 +/- 0.05 mag is obtained. The true distance modulus to M81 is determined to be 27.80 +/- 0.20 mag, corresponding to a distance of 3.63 +/- 0.34 Mpc. These data illustrate that with an optimal (power-law) sampling strategy, the HST provides a powerful tool for the discovery of extragalactic Cepheids and their application to the distance scale. M81 is the first calibrating galaxy in the target sample of the HST Key Project on the Extragalactic Distance Scale, the ultimate aim of which is to provide a value of the Hubble constant to 10% accuracy.

Extended envelopes around Galactic Cepheids. IV. T Monocerotis and X Sagittarii from mid-infrared interferometry with VLTI/MIDI

NASA Astrophysics Data System (ADS)

Gallenne, A.; Mérand, A.; Kervella, P.; Chesneau, O.; Breitfelder, J.; Gieren, W.

2013-10-01

Aims: We study the close environment of nearby Cepheids using high spatial resolution observations in the mid-infrared with the VLTI/MIDI instrument, a two-beam interferometric recombiner. Methods: We obtained spectra and visibilities for the classical Cepheids X Sgr and T Mon. We fitted the MIDI measurements, supplemented by B,V,J,H,K literature photometry, with the numerical transfer code DUSTY to determine the dust shell parameters. We used a typical dust composition for circumstellar environments. Results: We detect an extended dusty environment in the spectra and visibilities for both stars, although T Mon might suffer from thermal background contamination. We attribute this to the presence of a circumstellar envelope (CSE) surrounding the Cepheids. This is optically thin for X Sgr (τ0.55 μm = 0.008), while it appears to be thicker for T Mon (τ0.55 μm = 0.15). They are located at about 15-20 stellar radii. Following our previous work, we derived a likely period-excess relation in the VISIR PAH1 filter, f8.6 μm[%]= 0.81(±0.04)P[day]. We argue that the impact of CSEs on the mid-IR period-luminosity (P - L) relation cannot be negligible because they can bias the Cepheid brightness by up to about 30%. For the K-band P - L relation, the CSE contribution seems to be lower (<5%), but the sample needs to be enlarged to firmly conclude that the impact of the CSEs is negligible in this band. Based on observations made with ESO telescopes at Paranal observatory under program ID 082.D-0066Table 3 is only available in electronic form at http://www.aanda.org

Light curves for bump Cepheids computed with a dynamically zoned pulsation code

NASA Technical Reports Server (NTRS)

Adams, T. F.; Castor, J. I.; Davis, C. G.

1980-01-01

The dynamically zoned pulsation code developed by Castor, Davis, and Davison was used to recalculate the Goddard model and to calculate three other Cepheid models with the same period (9.8 days). This family of models shows how the bumps and other features of the light and velocity curves change as the mass is varied at constant period. The use of a code that is capable of producing reliable light curves demonstrates that the light and velocity curves for 9.8 day Cepheid models with standard homogeneous compositions do not show bumps like those that are observed unless the mass is significantly lower than the 'evolutionary mass.' The light and velocity curves for the Goddard model presented here are similar to those computed independently by Fischel, Sparks, and Karp. They should be useful as standards for future investigators.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Edward G.; Hemen, Brian; Rogalla, Danielle

We have obtained VR photometry of 282 Cepheid variable star candidates from the northern part of the All Sky Automated Survey (ASAS). These together with data from the ASAS and the Northern Sky Variability Survey (NSVS) were used to redetermine the periods of the stars. We divided the stars into four groups based on location in a plot of mean color, (V-R), versus period. Two of the groups fell within the region of the diagram containing known type II Cepheids and yielded 14 new highly probable type II Cepheids. The properties of the remaining stars in these two groups aremore » discussed but their nature remains uncertain. Unexplained differences exist between the sample of stars studied here and a previous sample drawn from the NSVS by Akerlof et al. This suggests serious biases in the identification of variables in different surveys.« less

Performance Characteristics of the Cepheid Xpert vanA Assay for Rapid Identification of Patients at High Risk for Carriage of Vancomycin-Resistant Enterococci

PubMed Central

Gilhuley, Kathleen; Cianciminio-Bordelon, Diane; Tang, Yi-Wei

2012-01-01

We compared the performance characteristics of culture and the Cepheid Xpert vanA assay for routine surveillance of vancomycin-resistant enterococci (VRE) from rectal swabs in patients at high risk for VRE carriage. The Cepheid Xpert vanA assay had a limit of detection of 100 CFU/ml and correctly detected 101 well-characterized clinical VRE isolates with no cross-reactivity in 27 non-VRE and related culture isolates. The clinical sensitivity, specificity, positive predictive value, and negative predictive value of the Xpert vanA PCR assay were 100%, 96.9%, 91.3%, and 100%, respectively, when tested on 300 consecutively collected rectal swabs. This assay provides excellent predictive values for prompt identification of VRE-colonized patients in hospitals with relatively high rates of VRE carriage. PMID:22972822

VizieR Online Data Catalog: Neutron-capture elements abundances in Cepheids (da Silva+ 2016)

NASA Astrophysics Data System (ADS)

da Silva, R.; Lemasle, B.; Bono, G.; Genovali, K.; McWilliam, A.; Cristallo, S.; Bergemann, M.; Buonanno, R.; Fabrizio, M.; Ferraro, I.; Francois, P.; Iannicola, G.; Inno, L.; Laney, C. D.; Kudritzki, R.-P.; Matsunaga, N.; Nonino, M.; Primas, F.; Przybilla, N.; Romaniello, M.; Thevenin, F.; Urbaneja, M. A.

2015-11-01

The abundances of Fe, Y, La, Ce, Nd, and Eu for our sample of 73 Cepheids plus data available in the literature for other 362 Cepheids are shown. We first show the abundances derived based on individual spectra for the 73 stars, then the averaged values, and finally the data from the literature. The original abundances available in the literature were rescaled according to the zero-point differences listed in Table 5. The priority was given in the following order: we first adopt the abundances provided by our group, this study (TS) and Lemasle et al. (2013A&A...558A..31L, LEM), and then those provided by the other studies, Luck & Lambert (2011AJ....142..136L, LIII), and Luck et al. (2011AJ....142...51L, LII). (4 data files).

ESA's Hipparcos satellite revises the scale of the cosmos

NASA Astrophysics Data System (ADS)

1997-02-01

This ruler relies on the brightnesses of winking stars called Cepheids, but the distances of the nearest examples, which calibrate the ruler, could only be estimated. Direct measurements by Hipparcos imply that the Cepheids are more luminous and more distant than previously imagined. The brightnesses of Cepheids seen in other galaxies are used as a guide to their distances. All of these galaxies may now be judged to lie farther away. At the same time the Hipparcos Cepheid scale drastically reduces the ages of the oldest stars, to about 11 billion years. By a tentative interpretation the Universe is perhaps 12 billion years old. Michael Feast from the University of Cape Town, South Africa, announces his conclusion about the Cepheids at a meeting devoted to Hipparcos at the Royal Astronomical Society in London today (14 February 1997). It will provoke much comment and controversy, because the scale and age of the Universe is the touchiest issue in cosmology. The best hope for confirming or modifying the result now rests with studies using Hipparcos data on other kinds of variable stars. An investigation of the variables called Miras, by Floor van Leeuwen of Royal Greenwich Observatory, Cambridge, and his colleagues, is described at the same London meeting. Full scientific reports on both the Cepheids and Miras have been accepted for publication in a leading journal, the Monthly Notices of the Royal Astronomical Society. European teams of scientists and engineers conceived and launched the unique Hipparcos satellite, which operated from 1989 to 1993. Hipparcos fixed precise positions in the sky of 120,000 stars (Hipparcos Catalogue) and logged a million more with a little less accuracy (Tycho Catalogue). Since 1993 the largest computations in the history of astronomy have reconciled the observations, to achieve a hundredfold improvement in the accuracy of star positions compared with previous surveys. Slight seasonal shifts in stellar positions as the Earth orbits the Sun, called parallaxes, give the first direct measurements of the distances of large numbers of stars. With the overall calculations completed, the harvest of scientific discoveries has begun. Among those delighted with the immediate irruption into cosmology, from this spacecraft made in Europe, is ESA's director of science, Roger Bonnet. "When supporters of the Hipparcos project argued their case," Bonnet recalls, "they were competing with astrophysical missions with more obvious glamour. But they promised remarkable consequences for all branches of astronomy. And already we see that even the teams using the Hubble Space Telescope will benefit from a verdict from Hipparcos on the distance scale that underpins all their reckonings of the expansion of the Universe." The pulse-rates of the stars Cepheid stars alternately squeeze themselves and relax, like a beating heart. They wax and wane rhythmically in brightness, every few days or weeks, at a rate that depends on their luminosity. Henrietta Leavitt at the Harvard College Observatory discovered in the early years of this century that bigger and more brilliant Cepheids vary with a longer period, according to a strict rule. It allows astronomers to gauge relative distances simply by taking the pulse-rates of the Cepheids and measuring their apparent brightnesses. Nearby Cepheids are typically 1000-2000 light-years away. They are too far for even Hipparcos to obtain very exact distance measurements, but by taking twenty-six examples and comparing them, Michael Feast and his colleague Robin Catchpole of RGO Cambridge arrive at consistent statistics. These define the relationship between the period and the luminosity, needed to judge the distances of Cepheids. The zero point is for an imaginary Cepheid pulsating once a day. This would be a star 300 times more luminous than the Sun, according to the Hipparcos data. The slowest Cepheid in the sample, l Carinae, has a period of 36 days and is equivalent to 18,000 suns. Applied to existing data on Cepheids seen in nearby galaxies, the Hipparcos result increases their distances. It pushes the Large Magellanic Cloud away, from 163,000 light-years, the previously accepted value, to 179,000 light-years with the Hipparcos Cepheid corrections, an increase of 10 per cent. Feast and Catchpole feed this result back to our own Milky Way Galaxy, and into calculations of the age of globular clusters, which harbour some of the oldest stars of the Universe. The reckoning involves another kind of variable star, the RR Lyraes, and the Hipparcos investigators arrive at an age of 11 billion years for the oldest stars. Other estimates of the oldest stars assigned to them an age of 14.6 billion years. This seemed, absurdly, to leave them older than the Universe. A team of astronomers using the Hubble Space Telescope recently declared the Universe to be only 9-12 billion years old. The Hipparcos Cepheid result increases that Hubble-inferred cosmic lifespan to 10-13 billion years. "I hope we've cured a nonsensical contradiction that was a headache for cosmologists," Michael Feast says. "We judge the Universe to be a little bigger and therefore a little older, by about a billion years. The oldest stars seem to be much younger than supposed, by about 4 billion years. If we can settle on an age of the Universe at, say, 12 billion years then everything will fit nicely." Feast and Catchpole have also cleared up a mystery about the nearest and most familiar Cepheid variable. This is Polaris, the Pole Star. Imperceptibly to the human eye, its brightness varies at a relatively high rate, every 3 days. That should make it, by the Cepheid rule, a feebler star than it appears to be. Hipparcos fixes the distance of Polaris at 430 light-years, and the researchers conclude that Polaris pulsates with an overtone, at a rate 40 per cent faster than expected for a Cepheid of its size and luminosity. Several other Cepheids gauged by Hipparcos also exhibit overtones. Were these not recognized as fast pulsators they would give false impressions in the Cepheid distance scale. The miraculous stars Another famous variable star pulsates at more than twice the frequency that theorists would expect. This is Mira, the prototype of the class of stars investigated by Floor van Leeuwen and his colleagues, using the Hipparcos data. To an unaided eye, Omicron Ceti appears and disappears in a cycle of 11 months. In the 17th Century astronomers named it Mira, the miraculous star. Astrophysicists today interpret Mira as a senile star slightly more massive than the Sun. It has swollen into a red giant and started oscillating, as a prelude to greater instabilities that will in due course fling the outer layers of the star into space. Hipparcos fixes Mira's distance at 420 light-years. Other astronomers have gauged the apparent width of the star, as seen from the ground, so the Hipparcos team can compute the diameter of Mira as 650 million kilometres -- somewhat wider than the orbit of Mars. If the Sun were in Mira's state it would swallow up the Earth and all of the inner planets. Astronomers knew that Mira was big, but the Hipparcos result confirms that it is too large to be oscillating in a simple fashion. Again its variation is an overtone, and the same is true of some other variable stars of the same type, known collectively as the Miras. The sixteen Miras in the survey are mostly 300-1000 light-years away, at distances more comfortably within the grasp of Hipparcos parallaxes. Before Hipparcos, there was only one fairly good measurement of a Mira distance, for the star R Leonis. Even in that case, Hipparcos adjusts the distance from 390 to 330 light-years. Patricia Whitelock of the South African Astronomical Observatory played a prominent part in the Mira study. In preparation for the Hipparcos data, observations of selected Miras from South Africa and Russia, with infrared instruments, assessed the extent to which they are dimmed by dust. Taking this effect into account, as well as the occurrence of overtones, the team arrives at a cosmic distance scale. As with the Cepheids, they can deduce distances by comparing the brightness of a Mira with its period of variation. Applied to the Large Magellanic Cloud, where Miras have been detected, the Hipparcos Mira scale puts the galaxy at 166,000 or 171,000 light-years, depending on the method of calculation preferred. This result is intermediate between the commonly accepted distance to the Large Magellanic Cloud and the new result from the Hipparcos Cepheid scale. "Frankly the Cepheids are at the limit of the useful range of Hipparcos, for distance measurements," comments Floor van Leeuwen. "And as for the Miras, ours is the very first attempt to gauge the absolute distance to another galaxy via parallax measurements on this type of star. So I think we should be grateful to Hipparcos, that our earliest answers are in the right ballpark and in fairly good agreement, without being hasty in drawing cosmological conclusions." Only the beginning Michael Perryman, ESA's project scientist for Hipparcos, anticipates a warm debate among astronomers. Should the Hipparcos Cepheid results be taken at face value, with all their implications for the size and age of the Universe? He remains confident that the issue will be settled by other results quarried from the Hipparcos data. Further Hipparcos studies of variable stars, including the RR Lyraes, are in progress. Also relevant to the distance scale are differing quantities of heavy elements present in stars of different ages, which can affect their luminosities. Any remaining confusion on this point will be dispelled by mainstream Hipparcos research devoted to the basic astrophysics of stars of different ages of origin, and at different stages of their life cycles. "Until Hipparcos, the cosmic distance scale rested on well-informed guesses," Michael Perryman says. "The distances we now have, for stars of many kinds, provide for the very first time a firm foundation from which to gauge the distances of galaxies. The work has only just begun. If it should turn out that the Cepheids have given the final answer straight away, that might be surprising. But there will be no reason for astonishment when Hipparcos's direct measurements of stellar distances lead to a revised scale for the Universe." The Hipparcos Cepheid scale is due to be debated in London today and in Seattle on 17 February, when Michael Feast will speak at the annual meeting the American Association for the Advancement of Science. It will also be one of the hot topics at ESA's Hipparcos Symposium in Venice,13-16 May. The Venice meeting will celebrate the release of the Hipparcos and Tycho Catalogues to the world-wide astronomical community. It will also offer the first overview of results obtained by the groups who have had early access to the data, by virtue of their contributions to the Hipparcos mission. The subjects range from the Solar System and the Sun's neighbours among the stars, through special stars and the shape and behaviour of the Milky Way Galaxy, to the link between the starry sky of Hipparcos and the wide Universe of galaxies and quasars. Further notifications about the Venice Symposium will be distributed to the press in due course. Meanwhile information about Hipparcos is accessible on the World Wide Web: http://astro.estec.esa.nl/Hipparcos/hipparcos.html

Evaluation of the Cepheid Xpert MTB/RIF assay for direct detection of Mycobacterium tuberculosis complex in respiratory specimens.

PubMed

Marlowe, Elizabeth M; Novak-Weekley, Susan M; Cumpio, Joven; Sharp, Susan E; Momeny, Michelle A; Babst, Anna; Carlson, Jonathan S; Kawamura, Masae; Pandori, Mark

2011-04-01

A total of 217 specimens submitted for routine smear and culture from three different sites within the western United States were used to evaluate the GeneXpert MTB/RIF assay (for research use only) (Cepheid, Sunnyvale, CA). Overall agreement compared to culture was 89% (98% for smear positives and 72% for smear negatives) for detection of Mycobacterium tuberculosis.

Evaluation of the Cepheid Xpert MTB/RIF Assay for Direct Detection of Mycobacterium tuberculosis Complex in Respiratory Specimens▿

PubMed Central

Marlowe, Elizabeth M.; Novak-Weekley, Susan M.; Cumpio, Joven; Sharp, Susan E.; Momeny, Michelle A.; Babst, Anna; Carlson, Jonathan S.; Kawamura, Masae; Pandori, Mark

2011-01-01

A total of 217 specimens submitted for routine smear and culture from three different sites within the western United States were used to evaluate the GeneXpert MTB/RIF assay (for research use only) (Cepheid, Sunnyvale, CA). Overall agreement compared to culture was 89% (98% for smear positives and 72% for smear negatives) for detection of Mycobacterium tuberculosis. PMID:21289151

The orbit and companion of the Cepheid S Sge - A probable triple system

NASA Technical Reports Server (NTRS)

Evans, Nancy R.; Welch, Douglas L.; Slovak, Mark H.; Barnes, Thomas G., III; Moffett, Thomas J.

1993-01-01

New radial velocities for the classical Cepheid S Sge have been obtained and combined with previous observations to derive a new orbit. The revised orbital elements are: gamma, -10.3 +/- 0.4 km/s; K, 15.5 +/- 0.2 km/s; e, 0.23 +/- 0.02; omega, 203.1 +/- 4.2 deg; T0, 39902.3 +/- 6.6 JD; P, 675.79 +/- 0.18 days; f(m), 0.239 +/- 0.010 solar masses; a sin i, 0.935 AU = 139.9 +/- 2.0 x 10 exp 6 km; s.e., 1.2 km/s. The revised elements differ very little from the orbit determined by Herbig and Moore (1952). We have also obtained low resolution IUE spectra to search for the companion. The IUE spectra show excess flux at 1800 A when compared with spectra of the single Cepheid Delta Cep at the same (B-V)0. The spectral type of the companion determined from this flux excess is A7 V to F0 V. However, the mass of such a companion (1.7 to 1.5 solar masses) is smaller than the minimum mass (2.8 solar masses) required by the mass function and an evolutionary mass of the Cepheid. We infer that the companion is itself a short period binary.

V1334 Cyg: A Triple System Containing a Classical Cepheid

NASA Astrophysics Data System (ADS)

Evans, N. R.

2000-05-01

HR 8157 = ADS 14859 = HD 203156 = V1334 Cyg was recognized a hundred years ago to be a marginally resolved visual binary. Millis (1969, Lowell Obs Bull, 7, 113) discovered that the brightest star in the system is a low amplitude classical Cepheid with a pulsation period of 3.3 days. Early radial velocity observations by Abt and Levy (1970, PASP, 82, 334) differed from scattered radial velocity observations in the first half of the century implying that in addition to the long period system, the Cepheid is also a member of a short period binary. We have observed Cepheid V1334 Cyg A for nearly 30 years. From this radial velocity data we have derived an orbit with a period of 5 years. The orbit provides limits on the mass of the companion (V1334 Cyg C) of 3.1 to 4.4 solar masses. We have used an IUE high resolution spectrum to conclude that the hottest star in the system (V1334 Cyg B) which dominates the spectrum in the ultraviolet is the wide companion since the velocity is very near the systemic velocity. Financial support was supplied through a Natural Sciences and Engineering Research Council, Canada (NSERC) grant and HST Grant GO-07478.01-96A, and from the Chandra Science Center NASA Contract NAS8-39073.

VizieR Online Data Catalog: Improved reddenings for 59 Galactic Cepheids (Madore+, 2017)

NASA Astrophysics Data System (ADS)

Madore, B. F.; Freedman, W. L.; Moak, S.

2018-01-01

We have used a published compilation of absolute magnitudes measured in seven bands, based on distances and reddenings independently determined for 59 Galactic Cepheids (Fouque+ 2007, J/A+A/476/73), with overtone and suspected overtone pulsators omitted. Where available, HST parallaxes have been adopted for these stars, followed by Infrared Surface Brightness (IRSB) determinations and then Interferometric Baade-Wesselink applications and, finally, revised Hipparcos parallaxes. (1 data file).

X-Ray Detection of the Cluster Containing the Cepheid S Mus

NASA Astrophysics Data System (ADS)

Evans, Nancy Remage; Pillitteri, Ignazio; Wolk, Scott; Guinan, Edward; Engle, Scott; Bond, Howard E.; Schaefer, Gail H.; Karovska, Margarita; DePasquale, Joseph; Tingle, Evan

2014-04-01

The galactic Cepheid S Muscae has recently been added to the important list of Cepheids linked to open clusters, in this case the sparse young cluster ASCC 69. Low-mass members of a young cluster are expected to have rapid rotation and X-ray activity, making X-ray emission an excellent way to discriminate them from old field stars. We have made an XMM-Newton observation centered on S Mus and identified a population of X-ray sources whose near-IR Two Micron All Sky Survey counterparts lie at locations in the J, (J - K) color-magnitude diagram consistent with cluster membership at the distance of S Mus. Their median energy and X-ray luminosity are consistent with young cluster members as distinct from field stars. These strengthen the association of S Mus with the young cluster, making it a potential Leavitt law (period-luminosity relation) calibrator.

The development of early pulsation theory, or, how Cepheids are like steam engines"

NASA Astrophysics Data System (ADS)

Stanley, Matthew

2011-05-01

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A.S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. These theoretical models relied on highly speculative physics, but nonetheless returned very impressive results despite attacks from figures such as James Jeans. Surprisingly, the pulsation theory not only depended on developments in stellar physics, but also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.

Classical Cepheid luminosities from binary companions

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage

1991-01-01

Luminosities for the classical Cepheids Eta Aql, W Sgr, and SU Cas are determined from IUE spectra of their binary companions. Spectral types of the companions are determined from the spectra by comparison with the spectra of standard stars. The absolute magnitude inferred from these spectral types is used to determine the absolute magnitude of the Cepheid, either directly or from the magnitude difference between the two stars. For the temperature range of the companions (A0 V), distinctions of a quarter of a spectral subclass can be made in the comparison between the companions and standard stars. The absolute magnitudes for Eta Aql and W Sgr agree well with the period-luminosity-color relation of Feast and Walker (1987). Random errors are estimated to be 0.3 mag. SU Cas, however, is overluminous for pulsation in the fundamental mode, implying that it is pulsating in an overtone.

Absorption line profiles in a companion spectrum of a mass losing cool supergiant

NASA Technical Reports Server (NTRS)

Rodrigues, Liliya L.; Boehm-Vitense, Erika

1990-01-01

Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculated absorption line profiles that would be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star wind and for different orbital phases of the binary. Bowen and Wilson find theoretically that stellar pulsations drive mass loss. We therefore apply our calculations to the Cepheid binary S Muscae which has a B5V companion. We find an upper limit for the Cepheid mass loss of M less than or equal to 7 x 10(exp -10) solar mass per year provided that the stellar wind of the companion does not influence the Cepheid wind at large distances.

VizieR Online Data Catalog: Gaia DR1 and OGLE variable stars (Udalski+, 2016)

NASA Astrophysics Data System (ADS)

Udalski, A.; Soszynski, I.; Skowron, D. M.; Skowron, J.; Pietrukowicz, P.; Mroz, P.; Poleski, R.; Szymanski, M. K.; Kozlowski, S.; Wyrzykowski, L.; Ulaczyk, K.; Pawlak, M.

2018-04-01

To assess the Gaia dataset of Cepheids and RR Lyr stars presented in the Gaia DR1 (Clementini et al., 2016A&A...595A.133C, Cat. I/337) we cross-identified the sample of 3194 variable stars presented on the final Gaia pipeline list (599 Cepheid and 2595 RR Lyr candidates) with the OGLE detected objects using RA/DEC coordinates provided within Gaia DR1. (4 data files).

Discovery of Cepheids in NGC 5253: Absolute peak brightness of SN Ia 1895B and SN Ia 1972E and the value of H(sub 0)

NASA Technical Reports Server (NTRS)

Saha, A.; Sandage, Allan; Labhardt, Lukas; Schwengeler, Hans; Tammann, G. A.; Panagia, N.; Macchetto, F. D.

1995-01-01

Observations of the Hubble Space Telescope (HST) between 1993 May 31 and 1993 July 19 in 20 epochs in the F555W passband and five epochs in the F785LP passband have led to the discovery of 14 Cepheids in the Amorphous galaxy NGC 5253. The apparent V distance modulus is (m-M)(sub AV) = 28.08 +/- 0.10 determined from the 12 Cepheids with normal amplitudes. The distance modulus using the F785LP data is consistent with the V value to within the errors. Five methods used to determine the internal reddening are consistent with zero differential reddening, accurate to a level of E(B-V) less than 0.05 mag, over the region occupied by Cepheids and the two supernovae (SNe) produced by NGC 5253. The apparent magnitudes at maximum for the two SNe in NGC 5253 are adopted as B(sub max) = 8.33 +/- 0.2 mag for SN 1895B, and B(sub max) = 8.56 +/- 0.1 and V(sub max) = 8.60 +/- 0.1 for SN 1972E which is a prototype SN of Type Ia. The apparent magnitude system used by Walker (1923) for SN 1859B has been corrected to the modern B scale and zero point to determine its adopted B(sub max) value.

NO EVIDENCE FOR CLASSICAL CEPHEIDS AND A NEW DWARF GALAXY BEHIND THE GALACTIC DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pietrukowicz, P.; Udalski, A.; Szymański, M. K.

2015-11-10

Based on data from the ongoing OGLE Galaxy Variability Survey (OGLE GVS), we have verified observed properties of stars detected by the near-infrared VVV survey in a direction near the Galactic plane at longitude l ≈ −27° and recently tentatively classified as classical Cepheids belonging to, hence claimed, a dwarf galaxy at a distance of about 90 kpc from the Galactic Center. Three of four stars are detected in the OGLE GVS I-band images. We show that two of the objects are not variable at all, and the third one with a period of 5.695 days and a nearly sinusoidalmore » light curve of an amplitude of 0.5 mag cannot be a classical Cepheid and is very likely a spotted object. These results together with a very unusual shape of the K{sub s}-band light curve of the fourth star indicate that it is very likely that none of them is a Cepheid and, thus there is no evidence for a background dwarf galaxy. Our observations show that great care must be taken when classifying objects by their low-amplitude close-to-sinusoidal near-infrared light curves, especially with a small number of measurements. We also provide a sample of high-amplitude spotted stars with periods of a few days that can mimic pulsations and even eclipses.« less

Place in History and Astrophysics as the Pole Star and the Nearest Cepheid

NASA Astrophysics Data System (ADS)

Guinan, Edward F.

2012-05-01

Over ten centuries ago years, precession moved the Earth's North Celestial Pole (NCP) near the direction of alpha Ursae Minoris - now known as Polaris. Since that time Polaris has served as an important navigation star. By 2100 (at closest approach) Polaris moves within 0.5 deg of the NCP. Because of its brightness ( 2nd mag) and fixed place in the sky, Polaris is frequently referenced in literature, folklore, and pop culture. For example, in the Arctic, Polaris is known to the Inuit (among other names) as Nuuttuittuq ("never moves"), while the Yup'ik Eskimo refer to Polaris as Agyarrlak ("major star"). But Polaris, as the nearest Classical Cepheid (and also member of a multiple star system) is astrophysically important and interesting in its own right. Primarily this is because Polaris' physical properties can be precisely determined. Its distance provides a luminosity, pulsation mode and calibration for the Leavitt Law (Period-Luminosity relation). But, Polaris has been found to be full of surprises and puzzles. Over the last century Polaris has been undergoing rapid, large changes in its pulsation period (increasing at over 4 sec/yr.) as well as in its light and radial velocity variations. Noteworthy, during the early-1990s, Polaris nearly stopped pulsating and thus almost ceased being a Cepheid! Surprisingly Polaris (and other Cepheids) recently have been discovered to have significant mass-loss, and to display X-ray and FUV-line emission variations in phase with their pulsations. In this introductory talk Polaris' place in history and in the field of astronomy will be briefly discussed along with the important role it plays in the broader understanding of Cepheid structure and evolution. This research is, in part, supported by NASA Grants HST-GO11726.01 and NNX08AX37G, which we gratefully acknowledge.

Distances to M101, NGC 2403, and NGC 2366 via Long Period Variables

NASA Astrophysics Data System (ADS)

Jurcevic, J. S.

1998-12-01

A new method of measuring accurately extra-Galactic distances has been developed based on the relationship between the luminosity of red supergiant variable (RSV) stars at optical wavelengths and their period of luminosity variation. This period-luminosity (PL) relationship has been calibrated in the broadband optical R and I-bands with RSVs from the Galactic Perseus OB1 association, the Large Magellanic Cloud, and M33. To verify the effectiveness of these RSV PL relations, the distances to the galaxies M101, NGC 2403, and NGC 2366 were determined. These galaxies were chosen because they had existing Cepheid based distances to use as a comparison between the two methods. These galaxies also span a range of metallicity to investigate any metallicity effects. Ground-based photometry of the galaxies in the R-band was obtained over four years to discover red variable stars with periods in the range 100--1200 days. The number of RSVs discovered in M101, NGC 2403, and NGC 2366 was 42, 61, and 20, respectively. By assuming a distance modulus for the Large Magellanic Cloud of 18.5 +/- 0.1 mag, single epoch I-band photometry of the RSVs was used to construct random phase PL relations resulting in distance moduli for M101, NGC 2403, and NGC 2366 of 29.40 +/- 0.16, 27.67 +/- 0.16, and 27.86 +/- 0.20 mag, respectively. These distances have been corrected for extinction by assuming values of E(B - V) = 0.10, 0.04, and 0.04 mag, respectively. These distances agree quite well with those found via recent Cepheid based measurements. In particular, the RSV distance modulus to M101 is very close to the HST Key Project Cepheid modulus of 29.34 +/- 0.17 mag (Kelson {et al. } 1996). These results show that RSVs, at optical wavelengths, provide a new method for measuring distances with a precision comparable to that of Cepheids with the advantages of being more luminous and more abundant than Cepheids.

Polaris: Mass and Multiplicity

DTIC Science & Technology

2006-01-01

NW, Washington, D.C. 20392-5420, USA Abstract. Polaris, the nearest and brightest classical Cepheid, is a member of at least a triple system. It...has a wide (18′′) physical companion, the F-type dwarf Polaris B. Polaris itself is a single-lined spectroscopic binary with an orbital period of ∼30...orbit, the Hipparcos parallax, and our measurement of the separation (0′′.176 ± 0′′.002), we find a preliminary mass of 5.0 ± 1.5 M for the Cepheid and

Rapid Detection of Staphylococcus aureus and Methicillin-Resistant S. aureus (MRSA) in Wound Specimens and Blood Cultures: Multicenter Preclinical Evaluation of the Cepheid Xpert MRSA/SA Skin and Soft Tissue and Blood Culture Assays▿

PubMed Central

Wolk, D. M.; Struelens, M. J.; Pancholi, P.; Davis, T.; Della-Latta, P.; Fuller, D.; Picton, E.; Dickenson, R.; Denis, O.; Johnson, D.; Chapin, K.

2009-01-01

A multicenter preclinical evaluation was conducted to evaluate the performance of two Cepheid Xpert assays for detection of methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus. Sensitivity was 97.1% and 98.3% for MRSA in wound and blood culture specimens, respectively. Sensitivity was 100% for S. aureus from both specimen types. PMID:19144803

OB Stars and Cepheids From the Gaia TGAS Catalogue: Test of their Distances and Proper Motions

NASA Astrophysics Data System (ADS)

Bobylev, Vadim V.; Bajkova, Anisa T.

2017-12-01

We consider young distant stars from the Gaia TGAS catalog. These are 250 classical Cepheids and 244 OB stars located at distances up to 4 kpc from the Sun. These stars are used to determine the Galactic rotation parameters using both trigonometric parallaxes and proper motions of the TGAS stars. In this case the considered stars have relative parallax errors less than 200%. Following the well-known statistical approach, we assume that the kinematic parameters found from the line-of-sight velocities Vr are less dependent on errors of distances than the found from the velocity components Vl. From values of the first derivative of the Galactic rotation angular velocity '0, found from the analysis of velocities Vr and Vl separately, the scale factor of distances is determined.We found that from the sample of Cepheids the scale of distances of the TGAS should be reduced by 3%, and from the sample of OB stars, on the contrary, the scale should be increased by 9%.

NEW EVIDENCE SUPPORTING MEMBERSHIP FOR TW NOR IN LYNGA 6 AND THE CENTAURUS SPIRAL ARM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majaess, Daniel; Turner, David; Moni Bidin, Christian

2011-11-10

The putative association between the 10{sub .}{sup d}8 classical Cepheid TW Nor and the open cluster Lynga 6 has generated considerable debate in the literature. New JHK{sub s} photometry in tandem with existing radial velocities for Lynga 6 stars implies cluster membership for TW Nor and establishes the variable as a high-weight calibrator for classical Cepheid relations. Fundamental mean parameters determined for Lynga 6 are: d = 1.91 {+-} 0.10 kpc, E(J - H) = 0.38 {+-} 0.02, and log {tau} = 7.9 {+-} 0.1. The Benedict et al./Turner Galactic VI{sub c} Wesenheit function was revised using TW Nor's newmore » parameters: W{sub VI,0} (- 3.37 {+-} 0.08)log P{sub 0} - 2.48 {+-} 0.08. TW Nor/Lynga 6 lie beyond the Sagittarius-Carina spiral arm and occupy the Centaurus arm, along with innumerable young Cepheids and clusters (e.g., VW Cen and VVV CL070).« less

On geometric distance determination to the Cepheid RS Puppis from its light echoes

NASA Astrophysics Data System (ADS)

Bond, H. E.; Sparks, W. B.

2009-02-01

Context: The luminous Galactic Cepheid RS Puppis is unique in being surrounded by a dust nebula illuminated by the variable light of the Cepheid. In a recent paper in this journal, Kervella et al. (2008) report a very precise geometric distance to RS Pup, based on measured phase lags of the light variations of individual knots in the reflection nebula. Aims: In this commentary, we examine the validity of the distance measurement, as well as the reality of the spatial structure of the nebula determined by Feast (2008) based upon the phase lags of the knots. Methods: Kervella et al. assumed that the illuminated dust knots lie, on average, in the plane of the sky (otherwise it is not possible to derive a geometric distance from direct imaging of light echoes). We consider the biasing introduced by the high efficiency of forward scattering. Results: We conclude that most of the knots are in fact likely to lie in front of the plane of the sky, thus invalidating the Kervella et al. result. We also show that the flat equatorial disk structure determined by Feast is unlikely; instead, the morphology of the nebula is more probably bipolar, with a significant tilt of its axis with respect to the plane of the sky. Conclusions: Although the Kervella et al. distance result is invalidated, we show that high-resolution polarimetric imaging has the potential to yield a valid geometric distance to this important Cepheid.

VI-band follow-up observations of ultra-long-period Cepheid candidates in M31

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngeow, Chow-Choong; Yang, Michael Ting-Chang; Lin, Chi-Sheng

2015-02-01

The ultra-long-period Cepheids (ULPCs) are classical Cepheids with pulsation periods exceeding ≈80 days. The intrinsic brightness of ULPCs are ∼1 to ∼3 mag brighter than their shorter period counterparts. This makes them attractive in future distance scale work to derive distances beyond the limit set by the shorter period Cepheids. We have initiated a program to search for ULPCs in M31, using the single-band data taken from the Palomar Transient Factory, and identified eight possible candidates. In this work, we presented the VI-band follow-up observations of these eight candidates. Based on our VI-band light curves of these candidates and theirmore » locations in the color–magnitude diagram and the Period–Wesenheit diagram, we verify two candidates as being truly ULPCs. The six other candidates are most likely other kinds of long-period variables. With the two confirmed M31 ULPCs, we tested the applicability of ULPCs in distance scale work by deriving the distance modulus of M31. It was found to be μ{sub M31,ULPC}=24.30±0.76 mag. The large error in the derived distance modulus, together with the large intrinsic dispersion of the Period–Wesenheit (PW) relation and the small number of ULPCs in a given host galaxy, means that the question of the suitability of ULPCs as standard candles is still open. Further work is needed to enlarge the sample of calibrating ULPCs and reduce the intrinsic dispersion of the PW relation before re-considering ULPCs as suitable distance indicators.« less

The MOST Accurate Photometry for Cepheid Modes

NASA Astrophysics Data System (ADS)

Evans, Nancy Remage; Szabo, Robert; Szabados, Laszlo; Derekas, Aliz; Kiss, Laszlo; Matthews, Jaymie; Cameron, Chris

2014-06-01

Fundamental mode classical Cepheids have famously repeatable light curves and periods steady enough that we can watch them evolve (change period). Overtone pulsators, on theother hand often have period changes too large to be explained by evolution, at least during the longest (second and third) passages through the instability strip. We obtained a month long series of observations with the MOST satellite of the fundamental mode Cepheid RT Aur and the first overtone pulsator SZ Tau. RT Aur shows the traditional strict repetition of the light curve, with the Fourier amplitude ratio R1/R2 remaining constant (varying by only a percent). The light curve of SZ Tau, on the other hand, fluctuates in amplitude ratio at the level of approximately 50\\%. Furthermore prewhitening the RT Aur data with 10 frequencies reduces the Fourier spectrum to noise. For SZ Tau, considerable power is left after this prewhitening in a complicated variety of frequencies. Financial Support was provided by CXC NASA Contract NAS8-03060 (NRE), ESTEC Contract No. 4000106398/12/NL/KML (LS), European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 269194(IRSES/ASK) (RS, AD).

Observations of Cepheids with the MOST satellite: contrast between pulsation modes

NASA Astrophysics Data System (ADS)

Evans, N. R.; Szabó, R.; Derekas, A.; Szabados, L.; Cameron, C.; Matthews, J. M.; Sasselov, D.; Kuschnig, R.; Rowe, J. F.; Guenther, D. B.; Moffat, A. F. J.; Rucinski, S. M.; Weiss, W. W.

2015-02-01

The quantity and quality of satellite photometric data strings is revealing details in Cepheid variation at very low levels. Specifically, we observed a Cepheid pulsating in the fundamental mode and one pulsating in the first overtone with the Canadian MOST (Microvariability and Oscillations of Stars) satellite. The 3.7-d period fundamental mode pulsator (RT Aur) has a light curve that repeats precisely, and can be modelled by a Fourier series very accurately. The overtone pulsator (SZ Tau, 3.1 d period) on the other hand shows light-curve variation from cycle to cycle which we characterize by the variations in the Fourier parameters. We present arguments that we are seeing instability in the pulsation cycle of the overtone pulsator, and that this is also a characteristic of the O - C curves of overtone pulsators. On the other hand, deviations from cycle to cycle as a function of pulsation phase follow a similar pattern in both stars, increasing after minimum radius. In summary, pulsation in the overtone pulsator is less stable than that of the fundamental mode pulsator at both long and short time-scales.

New calibrators for the Cepheid period-luminosity relation

NASA Technical Reports Server (NTRS)

Evans, Nancy R.

1992-01-01

IUE spectra of six Cepheids have been used to determine their absolute magnitudes from the spectral types of their binary companions. The stars observed are U Aql, V659 Cen, Y Lac, S Nor, V350 Sgr, and V636 Sco. The absolute magnitude for V659 Cen is more uncertain than for the others because its reddening is poorly determined and the spectral type is hotter than those of the others. In addition, a reddening law with extra absorption in the 2200 A region is necessary, although this has a negligible effect on the absolute magnitude. For the other Cepheids, and also Eta Aql and W Sgr, the standard deviation from the Feast and Walker period-luminosity-color (PLC) relation is 0.37 mag, confirming the previously estimated internal uncertainty. The absolute magnitudes for S Nor from the binary companion and from cluster membership are very similar. The preliminary PLC zero point is less than 2 sigma (+0.21 mag) different from that of Feast and Walker. The same narrowing of the instability strip at low luminosities found by Fernie is seen.

Variable stars in the dwarf galaxy GR 8 (DDO 155)

NASA Technical Reports Server (NTRS)

Tolstoy, Eline; Saha, A.; Hoessel, John G.; Danielson, G. Edward

1995-01-01

Observations of the resolved stars in dwarf galaxy GR 8, obtained over the period 1980 February to 1994 March, are presented. Thirty-four separate epochs were searched for variable stars, and a total of six were found, of which one has Cepheid characteristics. After correction for Galactic extinction this single Cepheid yields a distance modulus of m - M = 26.75 +/- 0.35. This corresponds to a distance of 2.24 Mpc, placing GR 8 near the Local Group (LG) zero-velocity surface. The other five variable stars are very red, and possibly have long periods of order 100 days or more.

[Evaluation of an Xpert EV (Cepheid®) molecular diagnostic technique for enteroviral meningitis].

PubMed

Alonso Pérez, Natalia; Sagastizabal Cardelus, Belén; Prieto Tato, Luis Manuel; Guillén Martín, Sara; González Torralba, Ana; García Bermejo, Isabel; Ramos Amador, José Tomás

2017-10-01

Polymerase chain reaction (PCR) assays have shown to be useful and quick for the diagnosis of enterovirus in aseptic meningitis. The aim of our study was to analyse the changes in clinical practice after the introduction of a real-time polymerase chain reaction (RT-PCR) technique using the Xpert EV (Cepheid ® ) assay for the qualitative detection of enterovirus RNA in cerebrospinal fluid specimens from children with suspected viral meningitis. A retrospective study was performed in children older than 1year, diagnosed with enterovirus meningitis in a third level hospital from November 2006 to February 2013. The first period, before the availability of Xpert EV (Cepheid ® ) (Group1, November 2006-August 2010) was compared with the later period (Group2, September 2010-February 2013). Clinical characteristics, the mean length of stay, and the cost per inpatient cases, were compared between the 2periods. Forty-one patients (60.9% male) were included, with a median age of 64 months (interquartile range 28-96). Twenty-six patients (63.4%) were included in Group2. There were non-statistically significant differences in the epidemiological, disease severity, and laboratory characteristics between both periods of study. A significant difference was observed in the mean length of stay, with it being shorter in Group2 (48hours vs 40.5hours, P=.039), and a significant lower inpatient cost per case (€779.77 vs €656.05, P<.05). Xpert EV (Cepheid ® ) assay was useful for decreasing the length of hospital stay and the costs associated with hospitalisation in children with enterovirus meningitis. Copyright © 2016 Asociación Española de Pediatría. Publicado por Elsevier España, S.L.U. All rights reserved.

Revisiting the Abundance Gradient in the Maser Host Galaxy NGC 4258

NASA Astrophysics Data System (ADS)

Bresolin, Fabio

2011-03-01

New spectroscopic observations of 36 H II regions in NGC 4258 obtained with the Gemini telescope are combined with existing data from the literature to measure the radial oxygen abundance gradient in this galaxy. The [O III]λ4363 auroral line was detected in four of the outermost targets (17-22 kpc from the galaxy center), allowing a determination of the electron temperature Te of the ionized gas. From the use of different calibrations of the R 23 abundance indicator, an oxygen abundance gradient of approximately -0.012 ± 0.002 dex kpc-1 is derived. Such a shallow gradient, combined with the difference in the distance moduli measured from the Cepheid period-luminosity relation by Macri et al. between two distinct fields in NGC 4258, would yield an unrealistically strong effect of metallicity on the Cepheid distances. This strengthens the suggestion that systematic biases might affect the Cepheid distance of the outer field. Evidence for a similar effect in the differential study of M33 by Scowcroft et al. is presented. A revision of the transformation between strong-line and Te -based abundances in Cepheid-host galaxies is discussed. In the Te abundance scale, the oxygen abundance of the inner field of NGC 4258 is found to be comparable with the LMC value. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

The binary companion of the classical Cepheid AW Per

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage

1989-01-01

An analysis of IUE spectra of the companion of AW Per shows it to be an extreme BpSi/HeW star with a spectral type of B7 V to B8 V. The flux of the composite spectrum from 1200 A through V is found to be well matched by F7 Ib and B8 V standard stars with Delta M(V) = 3.1 mag. The results suggest that the mass of the Cepheid must be greater than 4.7 solar masses. The flux distribution of the star and the mass limits from the orbit are consistent with a companion that is itself a binary.

Revised device labeling for the Cepheid Xpert MTB/RIF assay for detecting Mycobacterium tuberculosis.

PubMed

2015-02-27

The Food and Drug Administration (FDA) has cleared the Xpert MTB/RIF Assay (Cepheid; Sunnyvale, California) with an expanded intended use that includes testing of either one or two sputum specimens as an alternative to examination of serial acid-fast stained sputum smears to aid in the decision of whether continued airborne infection isolation (AII) is warranted for patients with suspected pulmonary tuberculosis. This change reflects the outcome of a recent multicenter international study demonstrating that negative Xpert MTB/RIF Assay results from either one or two sputum specimens are highly predictive of the results of two or three negative acid-fast sputum smears.

Chandra Observation of Polaris: Census of Low-Mass Companions

NASA Astrophysics Data System (ADS)

Evans, Nancy Remage; Wolk, Scott; Guinan, Edward; Engle, Scott; Schlegel, Eric; Mason, Brian; Karovska, Margarita; Spitzbart, Bradley

2009-09-01

We have observed Polaris = HD 8890 with Chandra ACIS-I for 10 ksec and found an X-ray source at the location of the Cepheid Polaris A = Aa + Ab with log L_X = 28.89 ergs s^{-1} and a kT = 0.6 keV. Either the F7 Ib supergiant or the F6 V spectroscopic companion could produce a spectrum this soft. Polaris B is not an X-ray source, which is consistent with its early F spectral type. However, this shows that it does not itself have a lower mass companion. Two resolved low mass stars ``C and D" are not physical companions based on the lack of X-rays (indicating an older age than the Cepheid) and inconsistent motion. In addition, a possible more distant companion is identified, and also less plausible one. Thus, this observation provides a complete census of companions down to masses as small as an order of magnitude less than the Cepheid and nearly 15 mag fainter within the surrounding 0.1 pc.Funding for this work was provided by Chandra grant GO6-7011A Chandra X-ray Center NASA Contract NAS8-39073

VizieR Online Data Catalog: >20yrs of HST obs. of Cepheids in SNIa host gal. (Hoffmann+, 2016)

NASA Astrophysics Data System (ADS)

Hoffmann, S. L.; Macri, L. M.; Riess, A. G.; Yuan, W.; Casertano, S.; Foley, R. J.; Filippenko, A. V.; Tucker, B. E.; Chornock, R.; Silverman, J. M.; Welch, D. L.; Goobar, A.; Amanullah, R.

2017-01-01

HST observations of Cepheid variables (both archival or newly obtained) span more than two decades (1994-2016; see table 1). The earliest Cepheid observations we analyzed were obtained with the Wide Field and Planetary Camera 2 (WFPC2) as part of the initial efforts to measure H0 with HST (Freedman+ 2001ApJ...553...47F; Sandage+ 2006ApJ...653..843S) and were later used by Freedman+ (2012ApJ...758...24F) to reach beyond the LMC for the Carnegie Hubble Project. We also re-analyzed observations obtained in previous phases of our project (Riess+ 2009, J/ApJS/183/109; 2011, J/ApJ/730/119) with the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) and/or the Wide Field Camera 3 (WFC3) Ultraviolet and Visible Channel (UVIS). Finally, we obtained new observations of nine SN Ia hosts using WFC3. We obtained the majority of our optical images with these modern cameras, 113 and 132 unique epochs with ACS and WFC3, respectively, while WFPC2 contributes a smaller fraction with 67 epochs. (6 data files).

Erratum: The Extragalactic Distance Scale Key Project. III. The Discovery of Cepheids and a New Distance to M101 Using the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Kelson, Daniel D; Illingworth, Garth D.; Freedman, Wendy F.; Graham, John A.; Hill, Robert; Madore, Barry F.; Saha, Abhijit; Stetson, Peter B.; Kennicutt, Robert C., Jr.; Mould, Jeremy R.; Hughes, Shaun M.; Ferrarese, Laura; Phelps, Randy; Turner, Anne; Cook, Kem H.; Ford, Holland; Hoessel, John G.; Huchra, John

1997-03-01

In the paper ``The Extragalactic Distance Scale Key Project. III. The Discovery of Cepheids and a New Distance to M101 Using the Hubble Space Telescope'' by Daniel D. Kelson, Garth D. Illingworth, Wendy F. Freedman, John A. Graham, Robert Hill, Barry F. Madore, Abhijit Saha, Peter B. Stetson, Robert C. Kennicutt, Jr., Jeremy R. Mould, Shaun M. Hughes, Laura Ferrarese, Randy Phelps, Anne Turner, Kem H. Cook, Holland Ford, John G. Hoessel, and John Huchra (ApJ, 463, 26 [1996]), two of the tables are in error. The magnitudes in Tables B1 and B2, in Appendix B, are ordered incorrectly. As a result, the Julian dates are not associated with their correct Cepheid magnitudes. We have now corrected these data, and updated versions of the tables are available on the World Wide Web. The tables are available in ASCII format at our Key Project site (http://www.ipac.caltech.edu/H0kp/) and will appear in volume 7 of the AAS CDROM. PostScript and paper copies are also available from the first author (http://www.ucolick.org/~kelson/H0/home.html or kelson@ucolick.org).

Discovering Cepheid and RR Lyrae Stars: Pan-STARRS Science Archive @ STScI and Robotically Controlled Telescopes

NASA Astrophysics Data System (ADS)

Johnson, Elizabeth; Strolger, Louis-Gregory; Engle, Scott G.; Anderson, Richard I.; Rest, Armin; Calamida, Annalisa; Dosovitz Fox, Ori; Laney, David

2017-01-01

Cepheid and RR Lyrae stars are an integral part of the cosmic distance ladder and are also useful for studying galactic structure and stellar ages. This project aims to greatly expand the number of known periodic variables in our galaxy by identifying candidates in the PanSTARRS-1 3pi catalog, and carrying out systematically targeted characterization with robotically controlled telescopes. Candidate targets are selected from available detection tables based on color and variability indices and are then fully vetted using robotic telescopes: the RCT 1.3 meter (Kitt Peak National Observatory) and RATIR 1.5 meter (Mexico). Here we present work to develop a full, semi-automated prescription for candidate selection, targeted follow-up photometry, cataloging, and classification, which allows the review of approximately 25 variable candidates every two weeks. We make comparisons of our sample selection and purity from a similar study based on Pan-STARRS data (Hernitschek et al. 2016), as well as candidates identified in Gaia DR1. The goal, through continued observation and analysis, is to identify at least 10,000 new variables, hundreds of which will be new Cepheid and RR Lyrae stars.

Spectroscopic properties of a two-dimensional time-dependent Cepheid model. II. Determination of stellar parameters and abundances

NASA Astrophysics Data System (ADS)

Vasilyev, V.; Ludwig, H.-G.; Freytag, B.; Lemasle, B.; Marconi, M.

2018-03-01

Context. Standard spectroscopic analyses of variable stars are based on hydrostatic 1D model atmospheres. This quasi-static approach has not been theoretically validated. Aim. We aim at investigating the validity of the quasi-static approximation for Cepheid variables. We focus on the spectroscopic determination of the effective temperature Teff, surface gravity log g, microturbulent velocity ξt, and a generic metal abundance log A, here taken as iron. Methods: We calculated a grid of 1D hydrostatic plane-parallel models covering the ranges in effective temperature and gravity that are encountered during the evolution of a 2D time-dependent envelope model of a Cepheid computed with the radiation-hydrodynamics code CO5BOLD. We performed 1D spectral syntheses for artificial iron lines in local thermodynamic equilibrium by varying the microturbulent velocity and abundance. We fit the resulting equivalent widths to corresponding values obtained from our dynamical model for 150 instances in time, covering six pulsational cycles. In addition, we considered 99 instances during the initial non-pulsating stage of the temporal evolution of the 2D model. In the most general case, we treated Teff, log g, ξt, and log A as free parameters, and in two more limited cases, we fixed Teff and log g by independent constraints. We argue analytically that our approach of fitting equivalent widths is closely related to current standard procedures focusing on line-by-line abundances. Results: For the four-parametric case, the stellar parameters are typically underestimated and exhibit a bias in the iron abundance of ≈-0.2 dex. To avoid biases of this type, it is favorable to restrict the spectroscopic analysis to photometric phases ϕph ≈ 0.3…0.65 using additional information to fix the effective temperature and surface gravity. Conclusions: Hydrostatic 1D model atmospheres can provide unbiased estimates of stellar parameters and abundances of Cepheid variables for particular phases of their pulsations. We identified convective inhomogeneities as the main driver behind potential biases. To obtain a complete view on the effects when determining stellar parameters with 1D models, multidimensional Cepheid atmosphere models are necessary for variables of longer period than investigated here.

VEGA/CHARA interferometric observations of Cepheids. I. A resolved structure around the prototype classical Cepheid δ Cep in the visible spectral range

NASA Astrophysics Data System (ADS)

Nardetto, N.; Mérand, A.; Mourard, D.; Storm, J.; Gieren, W.; Fouqué, P.; Gallenne, A.; Graczyk, D.; Kervella, P.; Neilson, H.; Pietrzynski, G.; Pilecki, B.; Breitfelder, J.; Berio, P.; Challouf, M.; Clausse, J.-M.; Ligi, R.; Mathias, P.; Meilland, A.; Perraut, K.; Poretti, E.; Rainer, M.; Spang, A.; Stee, P.; Tallon-Bosc, I.; ten Brummelaar, T.

2016-09-01

Context. The B-W method is used to determine the distance of Cepheids and consists in combining the angular size variations of the star, as derived from infrared surface-brightness relations or interferometry, with its linear size variation, as deduced from visible spectroscopy using the projection factor. The underlying assumption is that the photospheres probed in the infrared and in the visible are located at the same layer in the star whatever the pulsation phase. While many Cepheids have been intensively observed by infrared beam combiners, only a few have been observed in the visible. Aims: This paper is part of a project to observe Cepheids in the visible with interferometry as a counterpart to infrared observations already in hand. Methods: Observations of δ Cep itself were secured with the VEGA/CHARA instrument over the full pulsation cycle of the star. Results: These visible interferometric data are consistent in first approximation with a quasi-hydrostatic model of pulsation surrounded by a static circumstellar environment (CSE) with a size of θCSE = 8.9 ± 3.0 mas and a relative flux contribution of fCSE = 0.07 ± 0.01. A model of visible nebula (a background source filling the field of view of the interferometer) with the same relative flux contribution is also consistent with our data at small spatial frequencies. However, in both cases, we find discrepancies in the squared visibilities at high spatial frequencies (maximum 2σ) with two different regimes over the pulsation cycle of the star, φ = 0.0 - 0.8 and φ = 0.8-1.0. We provide several hypotheses to explain these discrepancies, but more observations and theoretical investigations are necessary before a firm conclusion can be drawn. Conclusions: For the first time we have been able to detect in the visible domain a resolved structure around δ Cep. We have also shown that a simple model cannot explain the observations, and more work will be necessary in the future, both on observations and modelling. The data are available on the Jean-Marie Mariotti Center OiDB service (http://oidb.jmmc.fr) and at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/593/A45

The period-luminosity and period-radius relations of Type II and anomalous Cepheids in the Large and Small Magellanic Clouds

NASA Astrophysics Data System (ADS)

Groenewegen, M. A. T.; Jurkovic, M. I.

2017-07-01

Context. Type II Cepheids (T2Cs) and anomalous Cepheids (ACs) are pulsating stars that follow separate period-luminosity relations. Aims: We study the period-luminosity (PL) and period-radius (PR) relations for T2Cs and ACs in the Magellanic Clouds. Methods: In an accompanying paper we determined the luminosities and effective temperatures for the 335 T2Cs and ACs in the LMC and SMC discovered in the OGLE-III survey, by constructing the spectral energy distribution (SED) and fitting this with model atmospheres and a dust radiative transfer model (in the case of dust excess). Building on these results we studied the PL and PR relations of these sources. Using existing pulsation models for RR Lyrae and classical Cepheids we derive the period-luminosity-mass-temperature-metallicity relations and then estimate the pulsation mass. Results: The PL relation for the T2Cs does not appear to depend on metallicity and is Mbol = + 0.12-1.78log P (for P < 50 days), excluding the dusty RV Tau stars. Relations for fundamental and first overtone LMC ACs are also presented. The PR relation for T2C also shows little or no dependence on metallicity or period. Our preferred relation combines SMC and LMC stars and all T2C subclasses and is log R = 0.846 + 0.521log P. Relations for fundamental and first overtone LMC ACs are also presented. The pulsation masses from the RR Lyrae and classical Cepheid pulsation models agree well for the short period T2Cs, the BL Her subtype, and ACs, and are consistent with estimates in the literature, I.e. MBLH 0.49M⊙ and MAC 1.3M⊙, respectively. The masses of the W Vir appear similar to the BL Her. The situation for the pWVir and RV Tau stars is less clear. For many RV Tau the masses are in conflict with the standard picture of (single-star) post-AGB evolution, where the masses are either too large (≳1 M⊙) or too small (≲0.4 M⊙). Full Table 3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/A29

Spectroscopic studies of three Cepheids with high positive pulsation period increments: SZ Cas, BY Cas, and RU Sct

NASA Astrophysics Data System (ADS)

Usenko, I. A.; Klochkova, V. G.

2015-07-01

Three high-resolution spectra have been taken at different times with the 6-m SAO RAS telescope (LYNX and PFES spectrographs) for three Cepheids exhibiting high positive period increments: the small-amplitude (DCEPS) SZ Cas and BY Cas and the classical (DCEP) RU Sct. SZ Cas and RU Sct are members of the Galactic open clusters χ and h Per and Trump 35, respectively. Analysis of the spectra has shown that the interstellar Na I D1 and D2 lines in all objects are considerably stronger than the atmospheric ones and are redshifted in SZ Cas and BY Cas and blushifted in RU Sct. The core of the H α absorption line in BY Cas has an asymmetric knifelike shape, while RU Sct exhibits an intense emission in the blue wing of this line. Such phenomena are observed in long-period Cepheids and bright hypergiants with an extended envelope. In this case, the strong Mg Ib 5183.62 Å and Ba II 5853.67, 6141.713, and 6496.90 Å lines with low χlow in SZ Cas and RU Sct also show characteristic knifelike profiles with an asymmetry in the red region, while the Ba II 4934.095 Å line shows similar profiles in the blue one. The absorption lines of neutral atoms and singly ionized metals with different lowerlevel excitation potentials exhibit different degrees of asymmetry: from a pronounced one with secondary components in BY Cas (similar to those in the small-amplitude Cepheid BG Cru pulsating in the first overtone and having an envelope) to its insignificance or virtual absence in SZ Cas and RU Sct. Analysis of the secular changes in mean T eff determined from photometric color indices and spectra over the last 55 years for these stars has revealed periodic fluctuations of 200 K for SZ Cas and BY Cas and 500 K for RU Sct. For SZ Cas and RU Sct, T eff determined in some years from some color indices show much lower values, which together with the temperature fluctuations can be associated with mass loss and dust formation. Based on these facts, we hypothesize the existence of circumstellar envelopes around all three Cepheids. We have determined the atmospheric parameters and chemical composition of the program Cepheids. An appreciable carbon underabundance, a nitrogen overabundance (the result was obtained only for BY Cas), a nearly solar oxygen abundance, a sodium overabundance, and solar magnesium and aluminum abundances have been revealed in all stars, suggesting that these yellow supergiants has already passed the first dredge-up. The abundances of the Fe-peak elements, a-elements, and r- and s-process elements are nearly solar. [Fe/H] = -0.05 dex for SZ Cas and [Fe/H]= +0.05 dex for RU Sct can be used to estimate the metallicities of the open clusters χ and h Per and Trump 35, respectively.

Quantitative results of stellar evolution and pulsation theories.

NASA Technical Reports Server (NTRS)

Fricke, K.; Stobie, R. S.; Strittmatter, P. A.

1971-01-01

The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

VizieR Online Data Catalog: 5yr radial velocity measurements of 19 Cepheids (Anderson+, 2016)

NASA Astrophysics Data System (ADS)

Anderson, R. I.; Casertano, S.; Riess, A. G.; Melis, C.; Holl, B.; Semaan, T.; Papics, P. I.; Blanco-Cuaresma, S.; Eyer, L.; Mowlavi, N.; Palaversa, L.; Roelens, M.

2016-11-01

We here present a detailed investigation of spectroscopic binarity of the 19 Cepheids for which HST/WFC3 spatial scan parallaxes are being recorded (Riess+ 2014ApJ...785..161R; Casertano+ 2016ApJ...825...11C). We have secured time-series observations from three different high-resolution echelle spectrographs: Coralie (R~60000) at the Swiss 1.2m Euler telescope located at La Silla Observatory, Chile; Hermes (R~85000) at the Flemish 1.2m Mercator telescope located at the Roque de los Muchachos Observatory on La Palma, Canary Islands, Spain; Hamilton (R~60000) at the 3m Shane telescope located at Lick Observatory, California, USA. (8 data files).

Uncertainties in the interstellar extinction curve and the Cepheid distance to M101

NASA Astrophysics Data System (ADS)

Nataf, David M.

2015-05-01

I revisit the Cepheid-distance determination to the nearby spiral galaxy M101 (Pinwheel Galaxy) of Shappee & Stanek, in light of several recent investigations questioning the shape of the interstellar extinction curve at λ ≈ 8000 Å (i.e. the I band). I find that the relatively steep extinction ratio AI/E(V - I) = 1.1450 from Fitzpatrick & Massa is slightly favoured relative to AI/E(V - I) = 1.2899 from Fitzpatrick and significantly favoured relative the historically canonical value of AI/E(V - I) = 1.4695, from Cardelli et al. The steeper extinction curves, with lower values of AI/E(V - I), yield fits with reduced scatter, metallicity dependences to the dereddened Cepheid luminosities that are closer to values inferred in the Local Group, and that are less sensitive to the choice of reddening cut imposed in the sample selection. The increase in distance modulus to M101 when using the preferred extinction curve is Δμ ˜ 0.06 mag, resulting in the estimate of the distance modulus to M101 relative to the LMC is ΔμLMC ≈ 10.72 ± 0.03 (stat). The best-fitting metallicity dependence is dMI/d{[O/H]} ≈ (-0.38 ± 0.14 (stat)) mag dex-1.

Discovery of a Group of Receding, Variable Halo Stars toward Norma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakrabarti, Sukanya; Sargent, Benjamin; Lipnicky, Andrew

2017-08-01

We present results from spectroscopic observations of a trio of Cepheid candidates identified from K {sub s} -band light curves toward Norma. The spectra show that these stars are moving with a large and similar radial velocity—the heliocentric velocities are 171 ± 32 km s{sup −1}, 164 ± 37 km s{sup −1}, and 173 ± 20 km s{sup −1}. The average radial velocity is ∼169 km s{sup −1}, which is large and distinct from typical stars in the Galaxy’s stellar disk. Given the radial velocities and associated 1 σ error, we find that the combined probability that these three starsmore » are foreground Milky Way disk stars is ∼7 × 10{sup −4}%, and the probability that these are large-amplitude spotted stars in a binary is ∼10{sup −5}%. These objects at l ∼ 333° and b ∼ −1° are therefore associated with the stellar halo. The identification of these sources as Type I Cepheids is not certain, and thus the distances of these sources are not yet well established. Assuming the 3.6 μ m period–luminosity relation of Type I Cepheids gives a distance of ∼78 kpc for these sources.« less

The Critical Importance of Russell's Diagram

NASA Astrophysics Data System (ADS)

Gingerich, O.

2013-04-01

The idea of dwarf and giants stars, but not the nomenclature, was first established by Eijnar Hertzsprung in 1905; his first diagrams in support appeared in 1911. In 1913 Henry Norris Russell could demonstrate the effect far more strikingly because he measured the parallaxes of many stars at Cambridge, and could plot absolute magnitude against spectral type for many points. The general concept of dwarf and giant stars was essential in the galactic structure work of Harlow Shapley, Russell's first graduate student. In order to calibrate the period-luminosity relation of Cepheid variables, he was obliged to fall back on statistical parallax using only 11 Cepheids, a very sparse sample. Here the insight provided by the Russell diagram became critical. The presence of yellow K giant stars in globular clusters credentialed his calibration of the period-luminosity relation by showing that the calibrated luminosity of the Cepheids was comparable to the luminosity of the K giants. It is well known that in 1920 Shapley did not believe in the cosmological distances of Heber Curtis' spiral nebulae. It is not so well known that in 1920 Curtis' plot of the period-luminosity relation suggests that he didn't believe it was a physical relation and also he failed to appreciate the significance of the Russell diagram for understanding the large size of the Milky Way.

Resolved stars in nearby galaxies: Ground-based photometry of M81

NASA Technical Reports Server (NTRS)

Madore, Barry F.; Freedman, Wendy L.; Lee, Myung G.

1993-01-01

Using the Canada-France-Hawaii Telescope (CFHT) we have obtained three closely spaced epochs of calibrated Blue Violet Red Infrared (BVRI) CCD imaging of two fields in M81, each known to contain a thirty-day Cepheid. Calibrated BVRI photometry of the brightest stars in these fields is presented. The slope of the luminosity function from the brightest 3-4 mag of the main-sequence blue plume is consistent with similar determinations of the apparent luminosity function in other resolved galaxies, thereby removing the one potential deviation from universality noted by Freedman in a photographic study of luminosity functions in nearby resolved galaxies. Under the assumption that the two Cepheids are representative, a reddening-law fit to the multiwavelength BVRI period-luminosity moduli give a true distance modulus of (m-M)sub 0 = 27.79 mag for M81, corresponding to a linear distance of 3.6 Mpc. An error analysis shows that the derived true distance modulus has a random error of +/- 0.28 mag (due to the photometric uncertainties in the BVRI data), with a systematic uncertainty of +/- 0.10 mag (accounting for the combined effects of unknown phasing of the data points, and the unknown positioning of these particular stars within the Cepheid instabiliy strip).

Extended envelopes around Galactic Cepheids. I. ℓ Carinae from near and mid-infrared interferometry with the VLTI

NASA Astrophysics Data System (ADS)

Kervella, P.; Mérand, A.; Perrin, G.; Coudé du Foresto, V.

2006-03-01

We present the results of long-baseline interferometric observations of the bright southern Cepheid ℓ Carinae in the infrared N (8-13 μm) and K (2.0-2.4 μm) bands, using the MIDI and VINCI instruments of the VLT Interferometer. We resolve in the N band a large circumstellar envelope (CSE) that we model with a Gaussian of 3 Rstar (≈500 R⊙ ≈ 2-3 AU) half width at half maximum. The signature of this envelope is also detected in our K band data as a deviation from a single limb darkened disk visibility function. The superimposition of a Gaussian CSE on the limb darkened disk model of the Cepheid star results in a significantly better fit of our VINCI data. The extracted CSE parameters in the K band are a half width at half maximum of 2 Rstar, comparable to the N band model, and a total brightness of 4% of the stellar photosphere. A possibility is that this CSE is linked to the relatively large mass loss rate of ℓ Car. Though its physical nature cannot be determined from our data, we discuss an analogy with the molecular envelopes of RV Tauri, red supergiants and Miras.

Carnegie Hubble Program: A Mid-Infrared Calibration of the Hubble Constant

NASA Technical Reports Server (NTRS)

Freedman, Wendy L.; Madore, Barry F.; Scowcroft, Victoria; Burns, Chris; Monson, Andy; Persson, S. Eric; Seibert, Mark; Rigby, Jane

2012-01-01

Using a mid-infrared calibration of the Cepheid distance scale based on recent observations at 3.6 micrometers with the Spitzer Space Telescope, we have obtained a new, high-accuracy calibration of the Hubble constant. We have established the mid-IR zero point of the Leavitt law (the Cepheid period-luminosity relation) using time-averaged 3.6 micrometers data for 10 high-metallicity, MilkyWay Cepheids having independently measured trigonometric parallaxes. We have adopted the slope of the PL relation using time-averaged 3.6micrometers data for 80 long-period Large Magellanic Cloud (LMC) Cepheids falling in the period range 0.8 < log(P) < 1.8.We find a new reddening-corrected distance to the LMC of 18.477 +/- 0.033 (systematic) mag. We re-examine the systematic uncertainties in H(sub 0), also taking into account new data over the past decade. In combination with the new Spitzer calibration, the systematic uncertainty in H(sub 0) over that obtained by the Hubble Space Telescope Key Project has decreased by over a factor of three. Applying the Spitzer calibration to the Key Project sample, we find a value of H(sub 0) = 74.3 with a systematic uncertainty of +/-2.1 (systematic) kilometers per second Mpc(sup -1), corresponding to a 2.8% systematic uncertainty in the Hubble constant. This result, in combination with WMAP7measurements of the cosmic microwave background anisotropies and assuming a flat universe, yields a value of the equation of state for dark energy, w(sub 0) = -1.09 +/- 0.10. Alternatively, relaxing the constraints on flatness and the numbers of relativistic species, and combining our results with those of WMAP7, Type Ia supernovae and baryon acoustic oscillations yield w(sub 0) = -1.08 +/- 0.10 and a value of N(sub eff) = 4.13 +/- 0.67, mildly consistent with the existence of a fourth neutrino species.

A blinded determination of H0 from low-redshift Type Ia supernovae, calibrated by Cepheid variables

NASA Astrophysics Data System (ADS)

Zhang, Bonnie R.; Childress, Michael J.; Davis, Tamara M.; Karpenka, Natallia V.; Lidman, Chris; Schmidt, Brian P.; Smith, Mathew

2017-10-01

Presently, a >3σ tension exists between values of the Hubble constant H0 derived from analysis of fluctuations in the cosmic microwave background by Planck, and local measurements of the expansion using calibrators of Type Ia supernovae (SNe Ia). We perform a blinded re-analysis of Riess et al. (2011) to measure H0 from low-redshift SNe Ia, calibrated by Cepheid variables and geometric distances including to NGC 4258. This paper is a demonstration of techniques to be applied to the Riess et al. (2016) data. Our end-to-end analysis starts from available Harvard -Smithsonian Center for Astrophysics (CfA3) and Lick Observatory Supernova Search (LOSS) photometries, providing an independent validation of Riess et al. (2011). We obscure the value of H0 throughout our analysis and the first stage of the referee process, because calibration of SNe Ia requires a series of often subtle choices, and the potential for results to be affected by human bias is significant. Our analysis departs from that of Riess et al. (2011) by incorporating the covariance matrix method adopted in Supernova Legacy Survey and Joint Lightcurve Analysis to quantify SN Ia systematics, and by including a simultaneous fit of all SN Ia and Cepheid data. We find H_0 = 72.5 ± 3.1 ({stat}) ± 0.77 ({sys}) km s-1 Mpc-1with a three-galaxy (NGC 4258+LMC+MW) anchor. The relative uncertainties are 4.3 per cent statistical, 1.1 per cent systematic, and 4.4 per cent total, larger than in Riess et al. (2011) (3.3 per cent total) and the Efstathiou (2014) re-analysis (3.4 per cent total). Our error budget for H0 is dominated by statistical errors due to the small size of the SN sample, whilst the systematic contribution is dominated by variation in the Cepheid fits, and for the SNe Ia, uncertainties in the host galaxy mass dependence and Malmquist bias.

Determining H {sub 0} with Bayesian hyper-parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cardona, Wilmar; Kunz, Martin; Pettorino, Valeria, E-mail: wilmar.cardona@unige.ch, E-mail: Martin.Kunz@unige.ch, E-mail: valeria.pettorino@thphys.uni-heidelberg.de

We re-analyse recent Cepheid data to estimate the Hubble parameter H {sub 0} by using Bayesian hyper-parameters (HPs). We consider the two data sets from Riess et al. 2011 and 2016 (labelled R11 and R16, with R11 containing less than half the data of R16) and include the available anchor distances (megamaser system NGC4258, detached eclipsing binary distances to LMC and M31, and MW Cepheids with parallaxes), use a weak metallicity prior and no period cut for Cepheids. We find that part of the R11 data is down-weighted by the HPs but that R16 is mostly consistent with expectations formore » a Gaussian distribution, meaning that there is no need to down-weight the R16 data set. For R16, we find a value of H {sub 0} = 73.75 ± 2.11 km s{sup −1} Mpc{sup −1} if we use HPs for all data points (including Cepheid stars, supernovae type Ia, and the available anchor distances), which is about 2.6 σ larger than the Planck 2015 value of H {sub 0} = 67.81 ± 0.92 km s{sup −1} Mpc{sup −1} and about 3.1 σ larger than the updated Planck 2016 value 66.93 ± 0.62 km s{sup −1} Mpc{sup −1}. If we perfom a standard χ{sup 2} analysis as in R16, we find H {sub 0} = 73.46 ± 1.40 (stat) km s{sup −1} Mpc{sup −1}. We test the effect of different assumptions, and find that the choice of anchor distances affects the final value significantly. If we exclude the Milky Way from the anchors, then the value of H {sub 0} decreases. We find however no evident reason to exclude the MW data. The HP method used here avoids subjective rejection criteria for outliers and offers a way to test datasets for unknown systematics.« less

Geometry of the Large Magellanic Cloud Using Multi- wavelength Photometry of Classical Cepheids

NASA Astrophysics Data System (ADS)

Deb, Sukanta; Ngeow, Chow-Choong; Kanbur, Shashi M.; Singh, Harinder P.; Wysocki, Daniel; Kumar, Subhash

2018-05-01

We determine the geometrical and viewing angle parameters of the Large Magellanic Cloud (LMC) using the Leavitt law based on a sample of more than 3500 common classical Cepheids (FU and FO) in optical (V, I), near-infrared (JHKs) and mid-infrared ([3.6] μm and [4.5] μm) photometric bands. Statistical reddening and distance modulus free from the effect of reddening to each of the individual Cepheids are obtained using the simultaneous multi-band fit to the apparent distance moduli from the analysis of the resulting Leavitt laws in these seven photometric bands. A reddening map of the LMC obtained from the analysis shows good agreement with the other maps available in the literature. Extinction free distance measurements along with the information of the equatorial coordinates (α, δ) for individual stars are used to obtain the corresponding Cartesian coordinates with respect to the plane of the sky. By fitting a plane solution of the form z = f(x, y) to the observed three dimensional distribution, the following viewing angle parameters of the LMC are obtained: inclination angle i = 25°.110 ± 0°.365, position angle of line of nodes θlon = 154°.702 ± 1°.378. On the other hand, modelling the observed three dimensional distribution of the Cepheids as a triaxial ellipsoid, the following values of the geometrical axes ratios of the LMC are obtained: 1.000 ± 0.003: 1.151 ± 0.003: 1.890 ± 0.014 with the viewing angle parameters: inclination angle of i = 11°.920 ± 0°.315 with respect to the longest axis from the line of sight and position angle of line of nodes θlon = 128°.871 ± 0°.569. The position angles are measured eastwards from north.

HST Snapshot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441

NASA Technical Reports Server (NTRS)

Pritzl, Barton J.; Smith, Horace A.; Stetson, Peter B.; Catelan, Marcio; Sweigart, Allen V.; Layden, Andrew C.; Rich, R. Michael

2003-01-01

We present the results of a Hubble Space Telescope snapshot program to survey the inner region of the metal-rich globular cluster NGC 6441 for its variable stars. A total of 57 variable stars was found including 38 RR Lyrae stars, 6 Population II Cepheids, and 12 long period variables. Twenty-four of the RR Lyrae stars and all of the Population II Cepheids were previously undiscovered in ground-based surveys. Of the RR Lyrae stars observed in h s survey, 26 are pulsating in the fundamental mode with a mean period of 0.753 d and 12 are first-overtone mode pulsators with a mean period of 0.365 d. These values match up very well with those found in ground-based surveys. Combining all the available data for NGC 6441, we find mean periods of 0.759 d and 0.375 d for the RRab and RRc stars, respectively. We also find that the RR Lyrae in this survey are located in the same regions of a period-amplitude diagram as those found in ground-based surveys. The overall ratio of RRc to total RR Lyrae is 0.33. Although NGC 6441 is a metal-rich globular cluster and would, on that ground, be expected either to have few RR Lyrae stars, or to be an Oosterhoff type I system, its RR Lyrae more closely resemble those in Oosterhoff type II globular clusters. However, even compared to typical Oosterhoff type II systems, the mean period of its RRab stars is unusually long. We also derived I-band period-luminosity relations for the RR Lyrae stars. Of the six Population II Cepheids, five are of W Virginis type and one is a BL Herculis variable star. This makes NGC 6441, along with NGC 6388, the most metal-rich globular cluster known to contain these types of variable stars. Another variable, V118, may also be a Population II Cepheid given its long period and its separation in magnitude from the RR Lyrae stars. We examine the period-luminosity relation for these Population II Cepheids and compare it to those in other globular clusters and in the Large Magellanic Cloud. We argue that there does not appear to be a change in the period-luminosity relation slope between the BL Herculis and W Virginis stars, but that a change of slope does occur when the RV Tauri stars are added to the period-luminosity relation.

Monitoring Cepheid variables using the new BYU Observation Deck Robotic Telescopes

NASA Astrophysics Data System (ADS)

Bugg, Adam Garth; Hintz, Eric G.; Joner, Michael D.

2018-01-01

In January 2017 work was completed on the new observation deck of the Eyring Science Center on the Brigham Young University campus. This deck was designed with pedestals to currently hold up to 5 robotic telescope systems. One of the first test projects was to monitor a sample of Classical Cepheid variables to watch for changes in the light curves. Starting with a sample of stars which had previously been monitored spectroscopically using the Dominion Astrophysical Observatory 1.2-m telescope, we collected photometric data in the H-alpha/H-beta system detailed in Joner & Hintz (2015). We will present a preliminary analysis of this data and the abilities of the new deck to monitor these type of objects.

Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) survey

NASA Astrophysics Data System (ADS)

Ripepi, V.; Moretti, M. I.; Clementini, G.; Marconi, M.; Cioni, M. R.; Marquette, J. B.; Tisserand, P.

2012-09-01

The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting K S -band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build K S -band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the K-band period luminosity ( PLK S ), the period-luminosity-color ( PLC) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC K S -band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of ˜0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of ˜0.01 mag). The average K S magnitudes derived for both types of variables were used to derive PLK S relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.

Accurate PCR Detection of Influenza A/B and Respiratory Syncytial Viruses by Use of Cepheid Xpert Flu+RSV Xpress Assay in Point-of-Care Settings: Comparison to Prodesse ProFlu.

PubMed

Cohen, Daniel M; Kline, Jennifer; May, Larissa S; Harnett, Glenn Eric; Gibson, Jane; Liang, Stephen Y; Rafique, Zubaid; Rodriguez, Carina A; McGann, Kevin M; Gaydos, Charlotte A; Mayne, Donna; Phillips, David; Cohen, Jason

2018-02-01

The Xpert Flu+RSV Xpress Assay is a fast, automated in vitro diagnostic test for qualitative detection and differentiation of influenza A and B viruses and respiratory syncytial virus (RSV) performed on the Cepheid GeneXpert Xpress System. The objective of this study was to establish performance characteristics of the Xpert Flu+RSV Xpress Assay compared to those of the Prodesse ProFlu+ real-time reverse transcription-PCR (RT-PCR) assay (ProFlu+) for the detection of influenza A and B viruses as well as RSV in a Clinical Laboratory Improvement Amendments (CLIA)-waived (CW) setting. Overall, the assay, using fresh and frozen nasopharyngeal (NP) swabs, demonstrated high concordance with results of the ProFlu+ assay in the combined CW and non-CW settings with positive percent agreements (PPA) (100%, 100%, and 97.1%) and negative percent agreements (NPA) (95.2%, 99.5%, and 99.6%) for influenza A and B viruses and RSV, respectively. In conclusion, this multicenter study using the Cepheid Xpert Flu+RSV Xpress Assay demonstrated high sensitivities and specificities for influenza A and B viruses and RSV in ∼60 min for use at the point-of-care in the CW setting. Copyright © 2018 American Society for Microbiology.

Validation of the Cepheid GeneXpert for Detecting Ebola Virus in Semen.

PubMed

Loftis, Amy James; Quellie, Saturday; Chason, Kelly; Sumo, Emmanuel; Toukolon, Mason; Otieno, Yonnie; Ellerbrok, Heinzfried; Hobbs, Marcia M; Hoover, David; Dube, Karine; Wohl, David A; Fischer, William A

2017-02-01

Ebola virus (EBOV) RNA persistence in semen, reported sexual transmission, and sporadic clusters at the end of the 2013-2016 epidemic have prompted recommendations that male survivors refrain from unprotected sex unless their semen is confirmed to be EBOV free. However, there is no fully validated assay for EBOV detection in fluids other than blood. The Cepheid Xpert Ebola assay for EBOV RNA detection was validated for whole semen and blood using samples obtained from uninfected donors and spiked with inactivated EBOV. The validation procedure incorporated standards from Clinical and Laboratory Standards Institute and Good Clinical Laboratory Practices guidelines for evaluating molecular devices for use in infectious disease testing. The assay produced limits of detection of 1000 copies/mL in semen and 275 copies/mL in blood. Limits of detection for both semen and blood increased with longer intervals between collection and testing, with acceptable results obtained up to 72 hours after specimen collection. The Cepheid Xpert Ebola assay is accurate and precise for detecting EBOV in whole semen. A validated assay for EBOV RNA detection in semen informs the care of male survivors of Ebola, as well as recommendations for public health. © The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.

New Results on Cepheid Masses

NASA Astrophysics Data System (ADS)

Evans, N. R.; Bohm-Vitense, E.; Carpenter, K.; Robinson, R.; Beck-Winchatz, B.

1996-12-01

Masses for Cepheid variable stars can be measured by combining the orbital velocity amplitude for the Cepheid (from a ground-based orbit) with the orbital velocity amplitude of a hot main sequence companion (observed in the ultraviolet from satellites such as IUE and HST) and the mass of the companion (inferred from from the ultraviolet energy distribution). Observations of 5 binary systems are now completed or in progress with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. Recently completed observations of U Aql lead to a mass of 5.1 +/- 1.1 Msun . We will discuss the results for S Mus, V350 Sgr, U Aql, and Y Car, and the constraints they place on stellar evolution calculations. As would be expected, some of the B companions have high rotational velocities, decreasing the accuracy with which their orbital velocities can be measured. The preliminary conclusion from the 4 HST targets and SU Cyg (mass from IUE observations) is that a weighted mean indicates no convective overshoot but the mode (which reflects the HST results better) agrees with the modest overshoot used in the Geneva evolutionary calculations. Financial Support was provided by a NASA grant GO-4541-01 to EB--V and GO-4541.02 to KGC, a grant from the Natural Sciences and Engineering Council, Canada to NRE, from the AXAF Science Center NASA Contract NAS8-39073.

Searching for Low-mass Companions of Cepheids, Part II

NASA Astrophysics Data System (ADS)

Remage Evans, Nancy; Tingle, E.; Bond, H. E.; Schaefer, G. H.; Mason, B.; Karovska, M.; Wolk, S.; Pillitteri, I.; DePasquale, J.; Guinan, E.; Engle, S.

2012-01-01

The formation of a binary/multiple system is an effective way to manipulate angular momentum during the star-formation process. The properties of binary systems (separations and mass ratios) are thus the ``fingerprints" of the process. Low mass companions are the most difficult to identify particularly for massive stars. We are conducting a snapshot survey of the nearest Cepheids (5 Msun stars) using the Hubble Space Telescope Wide Field Camera 3 (WFC3) to discover possible resolved low mass companions. The color-magnitude combination is the first approach to identifying probable physical companions. The distributions of mass and separation for these stars will be discussed. Financial suppoet was provided by Hubble grant GO-12215.01-A and the Chandra X-ray Center NASA contract NAS8-03060.

Dedicated System for Observation of Polaris

NASA Astrophysics Data System (ADS)

Gavin, Andrew

2018-01-01

Polaris, the North Star, has been known to be a Cepheid variable star for over 150 years (Seidel, 1852). Special interest has been given to Polaris’ variations because of its changing period and periods of cessation (D. Turner et al, 2005). The continuous monitoring of Polaris’ brightness provides us with insights on the behaviors of Cepheid variable stars that are undergoing transformations. Since its inception in 2004, the Polaris project has been somewhat of a white whale for PARI and the numerous interns that have worked on the project. The primary goal of this project is the production of a continuous light curve of Polaris through an automated system. Along with providing a continuous light curve of Polaris, this system will be able to produce an archive of data on the seeing conditions of the PARI site.

CORS BAADE-WESSELINK DISTANCE TO THE LMC NGC 1866 BLUE POPULOUS CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molinaro, R.; Ripepi, V.; Marconi, M.

2012-03-20

We used optical, near-infrared photometry, and radial velocity data for a sample of 11 Cepheids belonging to the young LMC blue populous cluster NGC 1866 to estimate their radii and distances on the basis of the CORS Baade-Wesselink method. This technique, based on an accurate calibration of surface brightness as a function of (U - B), (V - K) colors, allows us to estimate, simultaneously, the linear radius and the angular diameter of Cepheid variables, and consequently to derive their distance. A rigorous error estimate on radii and distances was derived by using Monte Carlo simulations. Our analysis gives amore » distance modulus for NGC 1866 of 18.51 {+-} 0.03 mag, which is in agreement with several independent results.« less

Bias Properties of Extragalactic Distance Indicators. VIII. H0 from Distance-limited Luminosity Class and Morphological Type-Specific Luminosity Functions for SB, SBC, and SC Galaxies Calibrated Using Cepheids

NASA Astrophysics Data System (ADS)

Sandage, Allan

1999-12-01

Relative, reduced to absolute, magnitude distributions are obtained for Sb, Sbc, and Sc galaxies in the flux-limited Revised Shapley-Ames Catalog (RSA2) for each van den Bergh luminosity class (L), within each Hubble type (T). The method to isolate bias-free subsets of the total sample is via Spaenhauer diagrams, as in previous papers of this series. The distance-limited type and class-specific luminosity functions are normalized to numbers of galaxies per unit volume (105 Mpc3), rather than being left as relative functions, as in Paper V. The functions are calculated using kinematic absolute magnitudes, based on an arbitrary trial value of H0=50. Gaussian fits to the individual normalized functions are listed for each T and L subclass. As in Paper V, the data can be freed from the T and L dependencies by applying a correction of 0.23T+0.5L to the individual absolute magnitudes. Here, T=3 for Sb, 4 for Sbc, and 5 for Sc galaxies, and the L values range from 1 to 6 as the luminosity class changes from I to III-IV. The total luminosity function, obtained by combining the volume-normalized Sb, Sbc, and Sc individual luminosity functions, each corrected for the T and L dependencies, has an rms dispersion of 0.67 mag, similar to much of the Tully-Fisher parameter space. Absolute calibration of the trial kinematic absolute magnitudes is made using 27 galaxies with known T and L that also have Cepheid distances. This permits the systematic correction to the H0=50 kinematic absolute magnitudes of 0.22+/-0.12 mag, givingH0=55+/-3(internal) km s-1 Mpc-1 . The Cepheid distances are based on the Madore/Freedman Cepheid period-luminosity (PL) zero point that requires (m-M)0=18.50 for the LMC. Using the modern LMC modulus of (m-M)0=18.58 requires a 4% decrease in H0, giving a final value of H0=53+/-7 (external) by this method. These values of H0, based here on the method of luminosity functions, are in good agreement with (1) H0=55+/-5 by Theureau and coworkers from their bias-corrected Tully-Fisher method of ``normalized distances'' for field galaxies; (2) H0=56+/-4 from the method through the Virgo Cluster, as corrected to the global kinematic frame (Tammann and coworkers); and (3) H0=58+/-5 from Cepheid-calibrated Type Ia supernovae (Saha and coworkers). Our value here also disagrees with the final value from the NASA ``Key Project'' group value of H0=70+/-7. Analysis of the total flux-limited sample of Sb, Sbc, and Sc galaxies in the RSA2 by the present method, but uncorrected for selection bias, would give an incorrect value of H0=71 using the same Cepheid calibration. The effect of the bias is pernicious at the 30% level; either it must be corrected by the methods in the papers of this series, or the data must be restricted to the distance-limited subset of any sample, as is done here.

Observational calibration of the projection factor of Cepheids. IV. Period-projection factor relation of Galactic and Magellanic Cloud Cepheids

NASA Astrophysics Data System (ADS)

Gallenne, A.; Kervella, P.; Mérand, A.; Pietrzyński, G.; Gieren, W.; Nardetto, N.; Trahin, B.

2017-11-01

Context. The Baade-Wesselink (BW) method, which combines linear and angular diameter variations, is the most common method to determine the distances to pulsating stars. However, the projection factor, p-factor, used to convert radial velocities into pulsation velocities, is still poorly calibrated. This parameter is critical on the use of this technique, and often leads to 5-10% uncertainties on the derived distances. Aims: We focus on empirically measuring the p-factor of a homogeneous sample of 29 LMC and 10 SMC Cepheids for which an accurate average distances were estimated from eclipsing binary systems. Methods: We used the SPIPS algorithm, which is an implementation of the BW technique. Unlike other conventional methods, SPIPS combines all observables, i.e. radial velocities, multi-band photometry and interferometry into a consistent physical modelling to estimate the parameters of the stars. The large number and their redundancy insure its robustness and improves the statistical precision. Results: We successfully estimated the p-factor of several Magellanic Cloud Cepheids. Combined with our previous Galactic results, we find the following P-p relation: -0.08± 0.04(log P-1.18) + 1.24± 0.02. We find no evidence of a metallicity dependent p-factor. We also derive a new calibration of the period-radius relation, log R = 0.684± 0.007(log P-0.517) + 1.489± 0.002, with an intrinsic dispersion of 0.020. We detect an infrared excess for all stars at 3.6 μm and 4.5 μm, which might be the signature of circumstellar dust. We measure a mean offset of Δm3.6 = 0.057 ± 0.006 mag and Δm4.5 = 0.065 ± 0.008 mag. Conclusions: We provide a new P-p relation based on a multi-wavelength fit that can be used for the distance scale calibration from the BW method. The dispersion is due to the LMC and SMC width we took into account because individual Cepheids distances are unknown. The new P-R relation has a small intrinsic dispersion: 4.5% in radius. This precision will allow us to accurately apply the BW method to nearby galaxies. Finally, the infrared excesses we detect again raise the issue of using mid-IR wavelengths to derive period-luminosity relation and to calibrate the Hubble constant. These IR excesses might be the signature of circumstellar dust, and are never taken into account when applying the BW method at those wavelengths. Our measured offsets may give an average bias of 2.8% on the distances derived through mid-IR P-L relations.

A search for the binary companion of Polaris

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage

1988-01-01

Polaris has a spectroscopic orbit determined from an extensive series of observations as well as a more uncertain astrometric orbit. The determination of its mass and evolutionary state is of considerable interest because it is a low-amplitude classical Cepheid with unusual period and amplitude variations. In this study, IUE spectra are investigated to search for light from the companion. The spectra of Polaris from 1600 A to 3200 A are a good match for nonvariable supergiants of similar spectral type. The lack of any excess flux at the shortest wavelengths implies that a main-sequence companion must be later than A8 V. Although this is the most likely companion, the ultraviolet observations cannot rule out a white dwarf 15,000 K or cooler. Both these companions are consistent with either an evolutionary mass or a smaller pulsation mass for the Cepheid.

Searching For Low-mass Companions Of Cepheids

NASA Astrophysics Data System (ADS)

Remage Evans, Nancy; Bond, H.; Schaefer, G.; Karovska, M.; Mason, B.; DePasquale, J.; Pillitteri, I.; Guinan, E.; Engle, S.

2011-05-01

The role played by binary and multiple stars in star formation is receiving a great deal of attention, both theoretically and observationally. Two questions under discussion are how wide physical companions can be and how frequently massive stars have low mass companions. An important new observational tool is the development of high resolution imaging, both from space and from the ground (Adaptive Optics and interferometry). We are conducting a snapshot survey of the nearest Cepheids using the Hubble Space Telescope Wide Field Camera 3 (WFC3). The aim is to discover possible resolved low mass companions. Results from this survey will be discussed, including images of Eta Aql. X-ray luminosity can confirm or refute that putative low mass companions are young enough to be physical companions. This project tests the reality of both wide and low mass companions of these intermediate-mass stars.

Period Changes of Type II Cepheids in the Globular Cluster M5

NASA Astrophysics Data System (ADS)

Randall, Jill M.; Rabidoux, K.; Smith, H. A.; De Lee, N.; Pritzl, B.; Osborn, W.

2007-05-01

The observed period changes of a pulsating variable star can, in principle, provide a sensitive test of the movement of the variable through the instability strip of the HR diagram. We revisit the long term period behavior of variables V42 and V84 in M5, making use of new BVI light curves of these type II Cepheids. V42 has shown a small decrease in period since 1889. The period changes of V84 are more difficult to ascertain, with possible short term changes in the observed phase of maximum light. The observed period changes, in both cases based upon observations spanning more than a century, are consistent with the earlier determinations of Coutts Clement & Sawyer Hogg (1977, JRASC, 71, 281). (This research is supported by the College of Science of the Florida Institute of Technology.)

Spectro-Interferometry Studies of Velocity-Related Phenomena at the Surface of Stars: Pulsation and Rotation

NASA Astrophysics Data System (ADS)

Mérand, Antoine; Patru, Fabien; Aufdenberg, Jason

We illustrate here two applications of spectro-interferometry to the study of velocity fields at the surface of stars: pulsation and rotation. Stellar pulsation has been resolved spectroscopically for a long time, and interferometry has resolved stellar diameters variations due to pulsation. Combining the two provides unique insights to the study of Cepheids, in particular regarding the structure of the photosphere or investigating the infamous projection factor which biases distances measured by the Baade-Wesselink method. On the other hand, resolving the surface velocity field of rotating stars offers a unique opportunity to potentially study differential rotation in other cases than for the Sun. We also present the model we have implemented recently, as well as two applications to VLTI/AMBER Data: the pulsation of Cepheids and the rotation of intermediate mass main sequence stars.

VizieR Online Data Catalog: BVI photometry of LMC bar variables (Di Fabrizio+, 2005)

NASA Astrophysics Data System (ADS)

di Fabrizio, L.; Clementini, G.; Maio, M.; Bragaglia, A.; Carretta, E.; Gratton, R.; Montegriffo, P.; Zoccali, M.

2005-01-01

We present the Johnson-Cousins B,V and I time series data obtained for 162 variable stars (135 RR Lyrae, 4 candidate Anomalous Cepheids, 11 Classical Cepheids, 11 eclipsing binaries and 1 delta Scuti star) in two 13x13 square arcmin areas close to the bar of the Large Magellanic Cloud. The photometric observations presented in this paper were carried out at the 1.54m Danish telescope located in La Silla, Chile, on the nights 4-7 January 1999, UT, and 23-24 January 2001, UT, respectively. In the paper we give coordinates, finding charts, periods, epochs, amplitudes, and mean quantities (intensity- and magnitude-averaged luminosities) of the variables with full coverage of the light variations, along with a discussion of the pulsation properties of the RR Lyrae stars in the sample. (8 data files).

Successful off-label use of the Cepheid Xpert GBS in a late-onset neonatal meningitis by Streptococcus agalactiae.

PubMed

Savini, Vincenzo; Marrollo, Roberta; Coclite, Eleonora; Fusilli, Paola; D'Incecco, Carmine; Fazii, Paolo

2014-01-01

We report the case of a late-onset neonatal meningitis by Streptococcus agalactiae (group B Streptococcus - GBS) that was diagnosed with a latex agglutination assay (on cerebrospinal fluid, CSF), as well as by using, for the first time, Xpert GBS (Cepheid, US) on CSF. Due to empirical antibiotics given before sampling, both CSF and blood culture were negative, so the abovementioned diagnostics was crucial. Moreover, the Xpert GBS assay, performed according to an off-label, modified protocol (the system is designed for GBS-carriage intrapartum screening, based on a completely automated real time-Polymerase Chain Reaction) quickly detected the organism's genome target. Although further investigation on this test's performace on CSF is required, then, we trust it may be a promising, quick and precise diagnostic method for infections in newborns.

High-precision infra-red stellar interferometry

NASA Astrophysics Data System (ADS)

Lane, Benjamin F.

2003-08-01

This dissertation describes work performed at the Palomar Testbed Interferometer (PTI) during 1998 2002. Using PTI, we developed a method to measure stellar angular diameters in the 1 3 milli-arcsecond range with a precision of better than 5%. Such diameter measurements were used to measure the mass-radius relations of several lower main sequence stars and hence verify model predictions for these stars. In addition, by measuring the changes in Cepheid angular diameters during the pulsational cycle and applying a Baade-Wesselink analysis we are able to derive the distances to two galactic Cepheids (η Aql & ζ Gem) with a precision of ˜10%; such distance determinations provide an independent calibration of the Cepheid period- luminosity relations that underpin current estimates of cosmic distance scales. Second, we used PTI and the adaptive optics facility at the Keck Telescope on Mauna Kea to resolve the low mass binary systems BY Dra and GJ 569B, resulting in dynamical mass determinations for these systems. GJ 569B most likely contains at least one sub-stellar component, and as such represents the first dynamical mass determination of a brown dwarf. Finally, a new observing technique, dual star phase referencing, was developed and demonstrated at PTI. Phase referencing allows interferometric observations of stars previously too faint to observe, and is a prerequisite for large-scale interferometric astrometry programs such as the one planned for the Keck Interferometer; interferometric astrometry is a promising technique for the study of extra-solar planetary systems, particularly ones with long-period planets.

Campaign for a New Eclipsing Cepheid

NASA Astrophysics Data System (ADS)

Henden, Arne; Welch, Doug; Terrell, Dirk

2007-06-01

ASAS 182611+1212.6, discovered by Pojmanski et al. during the ASAS survey, independently discovered by Antipin at al. on Moscow archive plates, and found in the NSVS (Wozniak et al. 2004, AJ 127, 2436), was initially classified as a typical Type II Cepheid with a period of 4.1523 days. However, scatter in the light curve indicated possible multiperiodic behavior. After 3 years of CCD observations by Antipin, the system was seen to exhibit eclipses of period 51.38 days and amplitude about 0.3 mag (primary) and possibly about 0.2 mag (secondary). This is the first known glactic eclipsing binary Cepheid. The AAVSO is conducting a campaign to study this star via high-precision, multicolor photometry obtained over several eclipse cycles. Observers are requested to obtain multicolor photometry with a S/N=100 or better on every image. Time resolution of one hour is adequate, so cycling through the filters need not be rushed. Apply transformation coefficients when possible. For calculating ephemerides, the pulsational maximum occurred on HJD 2453196.529 with a period of 4.1523 days; the eclipse primary minimum occurred on HJD 2453571.36 with a period of 51.38 days. The next primary eclipse will occur around July 9, but these eclipses are several days wide. A finding chart may be found at http://www.aavso.org/observing/charts/vsp (enter ASAS182612 for its name, or use the coordinates) with suitable comparison stars marked. Report/upload observations to the AAVSO.

Near-IR Period-Luminosity Relations for variable stars in ω Centauri

NASA Astrophysics Data System (ADS)

Navarrete, C.; Catelan, M.; Contreras Ramos, R.; Gran, F.; Alonso-García, J.; Dékány, I.

2014-10-01

We report on an extensive time-series study of the globular cluster ω Centauri (NGC 5139), obtained in the framework of the VVV Templates project (Catelan et al. 2013, arXiv: 1310.1996). This cluster was chosen for this project due to its large variable star content. A total of 42 and 100 epochs of the cluster in J and K_{S}, respectively, were taken using VIRCAM@VISTA, and PSF photometry was performed to derive light curves for 270 pulsating stars (RRab, RRc, type II Cepheids and SX Phoenicis) with an unprecedented phase coverage in the near-IR. Period-Luminosity (PL) relations in both bands were derived using Fourier fitted magnitudes for RR Lyrae and Type II Cepheids, while weighted-average magnitudes were used for SX Phe stars. Using the PL relation for RRab stars derived by Dékány et al. (2013, ApJ, 776, 19L) in the VISTA K_{S} system, we determine a distance modulus of (m-M)_{0} = 13.78 ± 0.04 mag, in good agreement with Del Principe et al. (2006, ApJ, 652, 362). From Type II Cepheids we derived a value of (m-M)_{0} = 13.67 ± 0.07 mag, similar to what was found by Matsunaga et al. (2006, MNRAS, 370, 1979). For SX Phe stars, we use the derived periods and magnitudes to infer their pulsation modes, and we confirm that at least 12 of them are fundamental-mode pulsators (Olech et al. 2005, MNRAS, 363, 40).

Variable Stars in Large Magellanic Cloud Globular Clusters. II. NGC 1786

NASA Astrophysics Data System (ADS)

Kuehn, Charles A.; Smith, Horace A.; Catelan, Márcio; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura

2012-12-01

This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series B-V photometric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binaries, 3 Delta Scuti/SX Phoenicis variables, and 2 variables of undetermined type. Photometric parameters for these variables are presented. We present physical properties for some of the RR Lyrae stars, derived from Fourier analysis of their light curves. We discuss several different indicators of Oosterhoff type which indicate that the Oosterhoff classification of NGC 1786 is not as clear cut as what is seen in most globular clusters. Based on observations taken with the SMARTS 1.3 m telescope operated by the SMARTS Consortium and observations taken at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

[Detection of Staphylococcus aureus resistant to methicillin (MRSA) by molecular biology (Cepheid GeneXpert IL, GeneOhm BD, Roche LightCycler, Hyplex Evigene I2A) versus screening by culture: Economic and practical strategy for the laboratory].

PubMed

Laudat, P; Demondion, E; Jouannet, C; Charron, J; Chillou, C; Salaun, V; Mankikian, B

2012-06-01

Patients admitted in cardiac surgery and cardiac ICU at the Clinic Saint-Gatien (Tours) are screened for MRSA at the entrance by nasal swab and culture on blood agar and selective chromogenic medium made by addition of cefoxitin: BBL CHROMagar MRSA-II BD (result obtained at Day +1). We wanted to assess the molecular biology techniques available to obtain a result at day 0 for the majority of patients and to define an economic and practical strategy for the laboratory. We studied four molecular biology techniques: Cepheid GeneXpert (Cepheid) GeneOhm (BD), LightCycler (Roche) and Hyplex (I2A). Upon reception, nasal swabs were treated by culture, considered as reference, and one of the techniques of molecular biology, according to the manufacturer's notice. We conducted four studies between April 2008 and February 2009 to obtain a significant sample for each of them. By screening we mean a method that allows us to exclude MRSA carriage for patients waiting for surgery, and not to change patient management: for example, lack of isolation measures specific to entrance, no modification of antibiotic prophylaxis during surgery and no isolation measures in the immediate postoperative period. The criteria we considered for this evaluation were: (1) technician time: time to perform one or a series of sample(s) n=10 or more (about 2h for all techniques except GeneXpert 75min), level of skilled competences (no specific training for GeneXpert); (2) results: turnaround time (all molecular biology techniques), ease of reading and results interpretations (no specialized training required for GeneXpert), failure or not (12% of failure of internal controls for GeneOhm); (3) economic: cost for one or a series of sample(s) (n=10 or more), if we considered X as the reference culture cost (10 X Hyplex and LightCycler, 20 X and 40 X for GeneXpert GeneOhm); (4) NPV: 100% for GeneXpert and LightCycler. At same sensitivity, no technique, including culture, can solve alone our problem, which is: (1) get results at day 0 for batch of samples (n<10): all molecular biology techniques; (2) beyond 10 samples: LightCycler (Roche) automated or Hyplex (I2A) manual; (3) when the result at day 1 is sufficient, the use of chromogenic agar with a reading of less than 18h as BBL CHROMagar MRSA II (BD) remains the most economical; (4) to be sure that a patient admitted at Day 0, even at night's emergency, is not carrier of MRSA: only Cepheid GeneXpert technology (IL). Furthermore, Cepheid GeneXpert (IL) allows performing several tests in parallel. The rapidity of this system can help control the transmission and make better use of antibiotics. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

The Milky Way, the Local Group & the IR Tully-Fisher Diagram

NASA Technical Reports Server (NTRS)

Malhotra, S.; Spergel, D.; Rhoads, J.; Li, J.

1996-01-01

Using the near infrared fluxes of local group galaxies derived from Cosmic Background Explorer/Diffuse Infrared Background Experiment band maps and published Cepheid distances, we construct Tully-Fisher diagrams for the Local Group.

Comparative pulsation calculations with OP and OPAL opacities

NASA Technical Reports Server (NTRS)

Kanbur, Shashi M.; Simon, Norman R.

1994-01-01

Comparative linear nonadiabatic pulsation calculations are presented using the OPAL and Opacity Project opacities. The two sets of opacities include effects due to intermediate coupling and fine structure as well as new abundances. We used two mass luminosity (M-L) relations, one standard (BIT), and one employing substantial convective core overshoot (COV). The two sets of opacities cannot be differentiated on the basis of the stellar pulsation calculations presented here. The BIT relation can model the beat and bump Cepheids with masses between 4 and 7 solar mass, while if the overshoot relation is used, masses between 2 and 6 solar mass are required. In the RR Lyrae regime, we find the inferred masses of globular cluster RRd stars to be little influenced by the choice of OPAL or OP. Finally, the limited modeling we have done is not able to constrain the Cepheid M-L relation based upon period ratios observed in the beat and bump stars.

Evaluation of the Cepheid Xpert MTB/RIF assay

PubMed Central

Shinnick, Thomas M; Starks, Angela M; Alexander, Heather L; Castro, Kenneth G

2018-01-01

The lack of capacity to provide laboratory confirmation of a diagnosis of tuberculosis disease (TB) is contributing to enormous gaps in the ability to find, treat and follow TB patients. WHO estimates that globally only about 57% of the notified new cases of pulmonary TB in 2012 and about 19% of rifampicin-resistant TB cases were laboratory confirmed. The Cepheid Xpert® MTB/RIF assay has been credited with revolutionizing laboratory testing to aid in the diagnosis of TB and rifampicin-resistant TB. This semi-automated test can detect both the causative agent of TB and mutations that confer rifampicin resistance from clinical specimens within 2 h after starting the test. In this article, we review the performance of the test, its pathway to regulatory approval and endorsement, guidelines for its use and lessons learned from the implementation of the test in low-burden, high-resource countries and in high-burden, low-resource countries. PMID:25373876

VizieR Online Data Catalog: LMC NIR Synoptic Survey. II. Wesenheit relations (Bhardwaj+, 2016)

NASA Astrophysics Data System (ADS)

Bhardwaj, A.; Kanbur, S. M.; Macri, L. M.; Singh, H. P.; Ngeow, C.-C.; Wagner-Kaiser, R.; Sarajedini, A.

2018-03-01

We make use of NIR mean magnitudes for 775 fundamental-mode and 474 first-overtone Cepheids in the LMC from Macri et al. 2015, J/AJ/149/117 (Paper I). These magnitudes are based on observations from a synoptic survey (average of 16 epochs) of the central region of the LMC using the CPAPIR camera at the Cerro Tololo Interamerican Observatory 1.5-m telescope between 2006 and 2007. Most of these Cepheid variables were previously studied in the optical V and I bands by the third phase of the Optical Gravitational Lensing Experiment (OGLE-III) survey (Soszynski et al. 2008, J/AcA/58/163; Ulaczyk et al. 2013, J/AcA/63/159). The V and I band mean magnitudes are also compiled in Paper I. The calibration into the 2MASS photometric system, extinction corrections, and the adopted reddening law are discussed in detail in Paper I. (4 data files).

Astrophysical tests of modified gravity: Constraints from distance indicators in the nearby universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Bhuvnesh; Vikram, Vinu; Sakstein, Jeremy

2013-12-10

We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators—cepheids, tip of the red giant branch (TRGB) stars, and water masers—operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered (in opposite directions) over a range of chameleon gravity theory parameters well below the sensitivity of cosmological probes. Using published data, we havemore » compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. We use a comparable set of screened galaxies as a control sample. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background field value), we obtain constraints on both the chameleon and symmetron screening scenarios. In particular we show that f(R) models with background field values f {sub R0} above 5 × 10{sup –7} are ruled out at the 95% confidence level. We also compare TRGB and maser distances to the galaxy NGC 4258 as a second test for larger field values. While there are several approximations and caveats in our study, our analysis demonstrates the power of gravity tests in the local universe. We discuss the prospects for additional improved tests with future observations.« less

The occurrence of binary evolution pulsators in classical instability strip of RR Lyrae and Cepheid variables

NASA Astrophysics Data System (ADS)

Karczmarek, P.; Wiktorowicz, G.; Iłkiewicz, K.; Smolec, R.; Stępień, K.; Pietrzyński, G.; Gieren, W.; Belczynski, K.

2017-04-01

Single star evolution does not allow extremely low-mass stars to cross the classical instability strip (IS) during the Hubble time. However, within binary evolution framework low-mass stars can appear inside the IS once the mass transfer (MT) is taken into account. Triggered by a discovery of low-mass (0.26 M⊙) RR Lyrae-like variable in a binary system, OGLE-BLG-RRLYR-02792, we investigate the occurrence of similar binary components in the IS, which set up a new class of low-mass pulsators. They are referred to as binary evolution pulsators (BEPs) to underline the interaction between components, which is crucial for substantial mass-loss prior to the IS entrance. We simulate a population of 500 000 metal-rich binaries and report that 28 143 components of binary systems experience severe MT (losing up to 90 per cent of mass), followed by at least one IS crossing in luminosity range of RR Lyrae (RRL) or Cepheid variables. A half of these systems enter the IS before the age of 4 Gyr. BEPs display a variety of physical and orbital parameters, with the most important being the BEP mass in range 0.2-0.8 M⊙, and the orbital period in range 10-2 500 d. Based on the light curve only, BEPs can be misclassified as genuine classical pulsators, and as such they would contaminate genuine RRL and classical Cepheid variables at levels of 0.8 and 5 per cent, respectively. We state that the majority of BEPs will remain undetected and we discuss relevant detection limitations.

``But I am constant as the North Star*'' - The Return of Polaris as a Low Amplitude Classical Cepheid

NASA Astrophysics Data System (ADS)

Davis, J. J.; Tracey, J. C.; Engle, S. G.; Guinan, E. F.

2002-12-01

* Julius Caesar, William Shakespeare Polaris ( ≈ +2.0 mag; B-V = +0.60; F7 Ib) is a low amplitude Classical Cepheid with a pulsation period of P = 3.97 days. Polaris is one of the nearest (dHipparcos = 132 +/- 8 pc) and brightest Cepheid. This Cepheid (Polaris A) is the luminous member of the multiple star system (ADS 1477). Over the last century amazing changing have been occurring for this famous star. The pulsation period has been increasing a rate of dP/dt = +3.2 sec/yr while the light amplitude has decreased from ~0.12 mag (1900s) to ~0.02 mag (early1990s). A recent summary and thorough discussion of Polaris's interesting properties are given by Evans et al. (2002, ApJ, 567, 1121). We have been carrying out photoelectric photometry of Polaris starting in early 2002. This photometry is a continuation of the work done on Polaris by Kamper and Fernie. Our observations were made to obtain new epochal light curves and accurate times of maximum light. We secured well defined 450 nm and 550 nm light curves from which we extracted accurate measures of light amplitudes of 0.033 +/- 0.004 mag and 0.028 +/- 0.003 mag, respectively. These light amplitudes are slightly larger than those observed during the early 1990s. So it appears that the century long decrease in the light amplitude has halted (or paused). Our time of maximum light was combined with previous timings and reaffirms the increase in period of +3.2 sec/yr. These observations lend strong support to overtone nature of Polaris's pulsations, whose transition from moderate to low amplitude pulsator will be discussed in more detail in this poster. In addition to the long-term secular increase in the Polaris's pulsation period, an analysis of the O-Cs indicates +/-0.25 day cyclic oscillations in the apparent period with time scale of 11-12 years. The nature of these period oscillations is being investigated and will be discussed. We gratefully acknowledge the support for this research from NSF/RUI Grant AST 00-71260 and by the Undergraduate Summer Research Assistance Program Grant from Delaware Space Grant Consortium.

The Dynamical Challenges of the Polaris Multiple System

NASA Astrophysics Data System (ADS)

Turner, David G.; Usenko, I. A.; Miroshnichenko, A. S.; Klochkova, V. G.; Panchuk, V. E.; Yang, S. L.

2006-06-01

The hierarchal triple system formed by the bright, nearby Cepheid Polaris, its visual companion (ADS 1477B), and recently resolved spectroscopic companion (ADS 1477Ab) at first sight seems well understood in terms of its astrometric properties: a parallax implying a distance of 132 +-8 pc (Hipparcos), and residuals implying an orbital inclination of 50 degrees (Wielen et al. 2000). But the recent optical detection of ADS 1477Ab by Evans et al. (2005) with the Hubble Space Telescope can be used to place independent constraints on the orbital properties of the system, once it is combined with the parameters of the spectroscopic orbit. To that end, existing radial velocity data for Polaris over the past 120 years, including previously-unpublished and recent observations obtained over the past two decades, have been collected, reanalyzed, and examined in order to improve the orbital parameters for the spectroscopic binary. There are small discrepancies in the data that may be linked to different sets of spectral lines and wavelength coverage used to infer the photospheric motion of the Cepheid, or to the inevitable problems of establishing reliable systemic velocities for a pulsating star. But the primary discrepancies lie in the implied properties of the Polaris system from the orbital solution, which seem to confirm the parallax of Polaris but not the orbital inclination, which may be edge-on. The results also conflict directly with other features of Polaris that are inferred from its other Cepheid characteristics: decreasing light amplitude, rapid period increase, location near the center of the instability strip, and possible membership in the Pleiades moving group. Such discrepancies are numerous enough to raise suspicions that there may be a fourth star in the system, although its detection may defy observers.

The VMC Survey - XIII. Type II Cepheids in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Ripepi, V.; Moretti, M. I.; Marconi, M.; Clementini, G.; Cioni, M.-R. L.; de Grijs, R.; Emerson, J. P.; Groenewegen, M. A. T.; Ivanov, V. D.; Muraveva, T.; Piatti, A. E.; Subramanian, S.

2015-01-01

The VISTA (Visible and Infrared Survey Telescope for Astronomy) survey of the Magellanic Clouds System (VMC) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near-complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III (Optical Gravitational Lensing Experiment) survey. We present J and Ks light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW Vir) and 27 RV Tau variables. We complement our near-infrared photometry with the V magnitudes from the OGLE III survey, allowing us to build a variety of period-luminosity (PL), period-luminosity-colour (PLC) and period-Wesenheit (PW) relationships, including any combination of the V, J, Ks filters and valid for BL Her and W Vir classes. These relationships were calibrated in terms of the LMC distance modulus, while an independent absolute calibration of the PL(Ks) and the PW(Ks, V) was derived on the basis of distances obtained from Hubble Space Telescope parallaxes and Baade-Wesselink technique. When applied to the LMC and to the Galactic globular clusters hosting T2CEPs, these relations seem to show that (1) the two Population II standard candles RR Lyrae and T2CEPs give results in excellent agreement with each other; (2) there is a discrepancy of ˜0.1 mag between Population II standard candles and classical Cepheids when the distances are gauged in a similar way for all the quoted pulsators. However, given the uncertainties, this discrepancy is within the formal 1σ uncertainties.

The VMC Survey. XIX. Classical Cepheids in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Ripepi, V.; Marconi, M.; Moretti, M. I.; Clementini, G.; Cioni, M.-R. L.; de Grijs, R.; Emerson, J. P.; Groenewegen, M. A. T.; Ivanov, V. D.; Piatti, A. E.

2016-06-01

The “VISTA near-infrared YJK s survey of the Magellanic Clouds System” (VMC) is collecting deep K s-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, K s light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involving the V, J, K s bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near-infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V, K s) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of Δμ = 0.55 ± 0.04 mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are μ SMC = 19.01 ± 0.05 mag and μ SMC = 19.04 ± 0.06 mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.

The VMC survey - XXIII. Model fitting of light and radial velocity curves of Small Magellanic Cloud classical Cepheids

NASA Astrophysics Data System (ADS)

Marconi, M.; Molinaro, R.; Ripepi, V.; Cioni, M.-R. L.; Clementini, G.; Moretti, M. I.; Ragosta, F.; de Grijs, R.; Groenewegen, M. A. T.; Ivanov, V. D.

2017-04-01

We present the results of the χ2 minimization model fitting technique applied to optical and near-infrared photometric and radial velocity data for a sample of nine fundamental and three first overtone classical Cepheids in the Small Magellanic Cloud (SMC). The near-infrared photometry (JK filters) was obtained by the European Southern Observatory (ESO) public survey 'VISTA near-infrared Y, J, Ks survey of the Magellanic Clouds system' (VMC). For each pulsator, isoperiodic model sequences have been computed by adopting a non-linear convective hydrodynamical code in order to reproduce the multifilter light and (when available) radial velocity curve amplitudes and morphological details. The inferred individual distances provide an intrinsic mean value for the SMC distance modulus of 19.01 mag and a standard deviation of 0.08 mag, in agreement with the literature. Moreover, the intrinsic masses and luminosities of the best-fitting model show that all these pulsators are brighter than the canonical evolutionary mass-luminosity relation (MLR), suggesting a significant efficiency of core overshooting and/or mass-loss. Assuming that the inferred deviation from the canonical MLR is only due to mass-loss, we derive the expected distribution of percentage mass-loss as a function of both the pulsation period and the canonical stellar mass. Finally, a good agreement is found between the predicted mean radii and current period-radius (PR) relations in the SMC available in the literature. The results of this investigation support the predictive capabilities of the adopted theoretical scenario and pave the way for the application to other extensive data bases at various chemical compositions, including the VMC Large Magellanic Cloud pulsators and Galactic Cepheids with Gaia parallaxes.

Testing iSpec for the determination of atmospheric parameters and abundances of δ Cephei and RR Lyrae

NASA Astrophysics Data System (ADS)

Blanco-Cuaresma, S.; Anderson, R. I.; Eyer, L.; Mowlavi, N.

2017-03-01

Classical Cepheids and RR Lyrae stars are radially pulsating stars where the spectral type varies according to pulsation phase. Several studies used synthesis and the equivalent width method to determine the variations of effective temperature, surface gravity and metallicity for classical Cepheids and RR Lyrae stars (Luck and Andrievsky 2004; Kovtyukh et al. 2005; Andrievsky et al 2005; Luck et al 2008; Takeda et al. 2013; Fossati et al. 2014). We evaluated the applicability of iSpec (Blanco-Cuaresma et al. 2014 - http://www.blancocuaresma.com/s/), which has been extensively used with non-pulsating FGK stars, and derived atmospheric parameters as a function of phase for δ Cephei and RR Lyrae (the two prototypes stars for each class). The results showed that when we apply a non-adapted traditional spectroscopic method to pulsating stars, derived gravities do not seem to follow a physically logical evolution. Nevertheless, metallicity is globally stable and effective temperature variations globally agree with expectations from the radius variations indicated by the radial velocity variability. Max/min values and average results agree with the literature. In terms of broadening parameters, macroturbulent and projected rotation velocities are very difficult to disentangle even if their profiles are not exactly the same. Individual chemical abundances as function of phase are stable as it was expected (the chemical composition of the star should not vary). We plan to use this information to identify absorption lines that are reliable and stable (less affected by blending) during the whole pulsating cycle. This new line selection may help to improve the determination of atmospheric parameters and it could allow us to be more confident in the study of other less known Cepheids and RR Lyrae stars.

Evaluation of the Cepheid Xpert Flu Assay for rapid identification and differentiation of influenza A, influenza A 2009 H1N1, and influenza B viruses.

PubMed

Novak-Weekley, S M; Marlowe, E M; Poulter, M; Dwyer, D; Speers, D; Rawlinson, W; Baleriola, C; Robinson, C C

2012-05-01

The Xpert Flu Assay cartridge is a next-generation nucleic acid amplification system that provides multiplexed PCR detection of the influenza A, influenza A 2009 H1N1, and influenza B viruses in approximately 70 min with minimal hands-on time. Six laboratories participated in a clinical trial comparing the results of the new Cepheid Xpert Flu Assay to those of culture or real-time PCR with archived and prospectively collected nasal aspirate-wash (NA-W) specimens and nasopharyngeal (NP) swabs from children and adults. Discrepant results were resolved by DNA sequence analysis. After discrepant-result analysis, the sensitivities of the Xpert Flu Assay for prospective NA-W specimens containing the influenza A, influenza A 2009 H1N1, and influenza B viruses compared to those of culture were 90.0%, 100%, and 100%, respectively, while the sensitivities of the assay for prospective NP swabs compared to those of culture were 100%, 100%, and 100%, respectively. The sensitivities of the Xpert Flu Assay for archived NA-W specimens compared to those of Gen-Probe ProFlu+ PCR for the influenza A, influenza A 2009 H1N1, and influenza B viruses were 99.4%, 98.4%, and 100%, respectively, while the sensitivities of the Xpert Flu Assay for archived NP swabs compared to those of ProFlu+ were 98.1%, 100%, and 93.8%, respectively. The sensitivities of the Xpert Flu Assay with archived NP specimens compared to those of culture for the three targets were 97.5%, 100%, and 93.8%, respectively. We conclude that the Cepheid Xpert Flu Assay is an accurate and rapid method that is suitable for on-demand testing for influenza viral infection.

H0 revisited

NASA Astrophysics Data System (ADS)

Efstathiou, George

2014-05-01

I reanalyse the Riess et al. (hereafter R11) Cepheid data using the revised geometric maser distance to NGC 4258 of Humphreys et al. (hereafter H13). I explore different outlier rejection criteria designed to give a reduced χ2 of unity and compare the results with the R11 rejection algorithm, which produces a reduced χ2 that is substantially less than unity and, in some cases, leads to underestimates of the errors on parameters. I show that there are sub-luminous low-metallicity Cepheids in the R11 sample that skew the global fits of the period-luminosity relation. This has a small but non-negligible impact on the global fits using NGC 4258 as a distance scale anchor, but adds a poorly constrained source of systematic error when using the Large Magellanic Cloud as an anchor. I also show that the small Milky Way Cepheid sample with accurate parallax measurements leads to a distance to NGC 4258 that is in tension with the maser distance. I conclude that H0 based on the NGC 4258 maser distance is H0 = 70.6 ± 3.3 km s-1 Mpc-1, compatible within 1σ with the recent determination from Planck for the base six-parameter Λ cold dark matter cosmology. If the H-band period-luminosity relation is assumed to be independent of metallicity and the three distance anchors are combined, I find H0 = 72.5 ± 2.5 km s-1 Mpc-1, which differs by 1.9σ from the Planck value. The differences between the Planck results and these estimates of H0 are not large enough to provide compelling evidence for new physics at this stage.

The Carnegie Hubble Program: The Infrared Leavitt Law in IC 1613

NASA Technical Reports Server (NTRS)

Scowcroft, Victoria; Freedman, Wendy L.; Madore, Barry F.; Monson, Andrew J.; Persson, S. E.; Seibert, Mark; Rigby, Jane R.; Melbourne, Jason

2013-01-01

We have observed the dwarf galaxy IC 1613 at multiple epochs in the midinfrared using Spitzer and the in the near-infrared using the new FourStar near-IR camera on Magellan. We have constructed Cepheid period luminosity relations in the J, H, Ks, [3.6] and [4.5] bands and have used the run of their apparent distance moduli as a function of wavelength to derive the line of sight reddening and distance to IC 1613. Using a nineband fit, we find E(BV ) = 0.050.01 mag and an extinction corrected distance modulus of 0 = 24.29 0.03statistical 0.03systematic mag. By comparing our multiband and [3.6] distance moduli to results from the tip of the red giant branch and red clump distance indicators, we find that metallicity has no measurable effect on Cepheid distances at 3.6 m in the metallicity range 1.0 [Fe/H] 0.2, hence derivations of the Hubble constant at this wavelength require no correction for metallicity.

Cepheid Period-Luminosity Relation and Kinematics Based on the Revised Hipparcos Catalogue

NASA Astrophysics Data System (ADS)

Zhang, H.; Shen, M.; Zhu, Z.

2011-12-01

The revised Hipparcos catalogue was released by van Leeuwen in 2007. The revised parallaxes of the classical Cepheids yield the zero-point of the period-luminosity relation ρ=-1.37± 0.07 in the optical BV bands, which is 0.06mag fainter than that given by Feast & Catchpole from the old Hipparcos data. Moreover, we discuss the kinematic parameters of the Galaxy based on an axisymmetric model. The Oort constants are A=17.42± 1.17km s-1kpc-1, B=-12.46± 0.86km s-1kpc-1, and the peculiar motion of the Sun is (12.58±1.09,14.52± 1.06, 8.98±0.98)km s-1. Using a dynamical model for an assumed elliptical disk, a weak elliptical potential of the disk is found with eccentricity ɛ(R0)=0.067± 0.036 and the direction of minor axis φb=31.7°± 14.5°.

Pulsating stars and the distance scale

NASA Astrophysics Data System (ADS)

Macri, Lucas

2017-09-01

I present an overview of the latest results from the SH0ES project, which obtained homogeneous Hubble Space Telescope (HST) photometry in the optical and near-infrared for ˜ 3500 and ˜ 2300 Cepheids, respectively, across 19 supernova hosts and 4 calibrators to determine the value of H0 with a total uncertainty of 2.4%. I discuss the current 3.4σ "tension" between this local measurement and predictions of H0 based on observations of the CMB and the assumption of "standard" ΛCDM. I review ongoing efforts to reach σ(H0) = 1%, including recent advances on the absolute calibration of Milky Way Cepheid period-luminosity relations (PLRs) using a novel astrometric technique with HST. Lastly, I highlight recent results from another collaboration on the development of new statistical techniques to detect, classify and phase extragalactic Miras using noisy and sparsely-sampled observations. I present preliminary Mira PLRs at various wavelengths based on the application of these techniques to a survey of M33.

Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements

NASA Astrophysics Data System (ADS)

Breitfelder, J.; Mérand, A.; Kervella, P.; Gallenne, A.; Szabados, L.; Anderson, R. I.; Le Bouquin, J.-B.

2016-03-01

Context. The distance to pulsating stars is classically estimated using the parallax-of-pulsation (PoP) method, which combines spectroscopic radial velocity (RV) measurements and angular diameter (AD) estimates to derive the distance of the star. A particularly important application of this method is the determination of Cepheid distances in view of the calibration of their distance scale. However, the conversion of radial to pulsational velocities in the PoP method relies on a poorly calibrated parameter, the projection factor (p-factor). Aims: We aim to measure empirically the value of the p-factors of a homogeneous sample of nine bright Galactic Cepheids for which trigonometric parallaxes were measured with the Hubble Space Telescope (HST) Fine Guidance Sensor. Methods: We use the SPIPS algorithm, a robust implementation of the PoP method that combines photometry, interferometry, and radial velocity measurements in a global modeling of the pulsation of the star. We obtained new interferometric angular diameter measurements using the PIONIER instrument at the Very Large Telescope Interferometer (VLTI), completed by data from the literature. Using the known distance as an input, we derive the value of the p-factor of the nine stars of our sample and study its dependence with the pulsation period. Results: We find the following p-factors: p = 1.20 ± 0.12 for RT Aur, p = 1.48 ± 0.18 for T Vul, p = 1.14 ± 0.10 for FF Aql, p = 1.31 ± 0.19 for Y Sgr, p = 1.39 ± 0.09 for X Sgr, p = 1.35 ± 0.13 for W Sgr, p = 1.36 ± 0.08 for β Dor, p = 1.41 ± 0.10 for ζ Gem, and p = 1.23 ± 0.12 for ℓ Car. Conclusions: The values of the p-factors that we obtain are consistently close to p = 1.324 ± 0.024. We observe some dispersion around this average value, but the observed distribution is statistically consistent with a constant value of the p-factor as a function of the pulsation period (χ2 = 0.669). The error budget of our determination of the p-factor values is presently dominated by the uncertainty on the parallax, a limitation that will soon be waived by Gaia. Based on observations carried out with ESO facilities at Paranal Observatory under program 093.D-0316, 094.D-0773 and 094.D-0584.

Cepheid Calibration of the Peak Brightness of SNe Ia.. 9; SN 1989B in NGC 3627

NASA Technical Reports Server (NTRS)

Saha, A.; Sandage, Allan; Tammann, G. A.; Labhardt, Lukas; Macchetto, F. D.; Panagia, N.

1999-01-01

Repeated imaging observations have been made of NGC 3627 with the Hubble Space Telescope in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F8141,V band. The galaxy hosted the prototypical, "Branch normal", type la supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 days to 3.85 days. The de-reddened distance modulus is determined to be (m - M)(sub 0) = 30.22 +/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. The photometric data of Wells et al. (1994), combined with the Cepheid data for NGC 3627 give MB(max) = -19.36 +/- 0.18 and M(sub V)(max) = -19.34 +/- 0.16 for SN 1989B. Combined with the previous six calibrations in this program, plus two additional calibrations determined by others gives the mean absolute magnitudes at maximum of (M(sub B)) = -19.48 +/- 0.07 for "Brunch normal" SNe Ia at this interim stage in the calibration program. Using the argument by Wells et al. (1994) that SN 1989B here is virtually identical in decay rate and colors at maximum with SN 198ON in NGC 1316 in the Fornax cluster, and that such identity means nearly identical absolute magnitude, it follows that the difference in the distance modulus of NGC 3627 and NGC 1316 is 1.62 +/- 0.03 mag. Thus the NGC 3627 modulus implies that (m - M)(sub 0) = 31.84 for NGC 1316. The second parameter correlations of M(max) of blue SNe la with decay rate, color at maximum, and Hubble type are re-investigated. The dependence of (M(max)) on decay rate is non-linear, showing a minimum for decay rates between 1.0 less than ADelta(sub m)15 less than 1.6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe la with decay-rate data and the current eight calibrating SNe la for the correlation with decay rate as well as color gives H(sub 0) = 60 +/- 2 (internal) km/s Mpc, in both B and V. The same value to within 4% is obtained if only the SNe la in spirals (without second parameter corrections) are considered. The correlation of SNe la color at maximum with M(max) cannot be due to internal absorption because the slope coefficients in B, V, and I with the change in magnitude are far from or even opposite to the canonical reddening values. The color effect must be intrinsic to the supernova physics. "Absorption" corrections of distant blue SNe la will lead to incorrect values of H(sub 0). The Cepheid distances used in this series are insensitive to metallicity differences. The zeropoint of the P-L relation is based on an assumed LMC modulus of (m - M)(sub 0) = 18.50. As this may have to be increased by 0(sup m).06 to 0(sup m).08, all distances in this paper will follow and Ho will decrease by 3 - 4%.

Chandra Observation of Polaris: Census of Low-mass Companions

NASA Astrophysics Data System (ADS)

Evans, Nancy Remage; Guinan, Edward; Engle, Scott; Wolk, Scott J.; Schlegel, Eric; Mason, Brian D.; Karovska, Margarita; Spitzbart, Bradley

2010-05-01

We have observed Cepheid Polaris (α UMi A: F7 Ib [Aa] + F6 V [Ab]) with Chandra ACIS-I for 10 ks. An X-ray source was found at the location of Polaris with log LX = 28.89 erg s-1 (0.3-8 keV) and kT = 0.6 keV. A spectrum this soft could come from either the supergiant or the dwarf, as shown by comparable coronal stars. Two resolved low-mass visual companions, "C" and "D," are not physical members of the system based on the lack of X-rays (indicating an age older than the Cepheid) and inconsistent proper motions. Polaris B is not an X-ray source, consistent with its early F spectral type, and probably does not have a lower mass companion itself. A possible more distant member is identified, and an additional less plausible one. This provides a complete census of companions out to 0.1 pc covering a mass ratio range of an order of magnitude and a ΔV of nearly 15 mag. Based on observations made with the NASA Chandra Satellite.

August gamma Cepheids (523-AGC)

NASA Astrophysics Data System (ADS)

Roggemans, Paul

2018-02-01

Favorable weather conditions between 19 August and 5 September 2017 enabled the CAMS BeNeLux network to collect 3189 orbits. A radiant concentration was spotted which was identified as the August gamma Cepheids (523-AGC). An independent search on a selection from all available meteor orbit lists coming from the suspect radiant area and velocity range was made. This resulted in 283 similar orbits, radiating from R.A. 358.4° and Decl. +76.2° with a geocentric velocity of 43.7 km/s in a time lapse between 146° and 165° in solar longitude with best activity at 155.7°. The orbital elements match perfectly with previously published results. There is no indication for any periodicity in the shower displays from year to year. The AGC-meteors are remarkably rich in bright meteors and rather deficient in faint meteors. Being detected independently from orbital data collected by different video networks, confirmed by 283 orbits with a medium threshold D criterion DD < 0.08 and 125 orbits with a high threshold of DD < 0.04, this minor shower could be considered to be listed as an established meteor shower.

Type II Cepheids: evidence for Na-O anticorrelation for BL Her type stars?

NASA Astrophysics Data System (ADS)

Kovtyukh, V.; Yegorova, I.; Andrievsky, S.; Korotin, S.; Saviane, I.; Lemasle, B.; Chekhonadskikh, F.; Belik, S.

2018-06-01

The chemical composition of 28 Population II Cepheids and one RR Lyrae variable has been studied using high-resolution spectra. The chemical composition of W Vir variable stars (with periods longer than 8 d) is typical for the halo and thick disc stars. However, the chemical composition of BL Her variables (with periods of 0.8-4 d) is drastically different, although it does not differ essentially from that of the stars belonging to globular clusters. In particular, the sodium overabundance ([Na/Fe] ≈ 0.4) is reported for most of these stars, and the Na-O anticorrelation is also possible. The evolutionary tracks for BL Her variables (with a progenitor mass value of 0.8 solar masses) indicate that mostly helium-overabundant stars (Y = 0.30-0.35) can fall into the instability strip region. We suppose that it is the helium overabundance that accounts not only for the existence of BL Her variable stars but also for the observed abnormalities in the chemical composition of this small group of pulsating variables.

Reducing the H0 and σ8 tensions with dark matter-neutrino interactions

NASA Astrophysics Data System (ADS)

Di Valentino, Eleonora; Bœhm, Céline; Hivon, Eric; Bouchet, François R.

2018-02-01

The introduction of dark matter-neutrino interactions modifies the cosmic microwave background (CMB) angular power spectrum at all scales, thus affecting the reconstruction of the cosmological parameters. Such interactions can lead to a slight increase of the value of H0 and a slight decrease of S8≡σ8√{Ωm/0.3 } , which can help reduce somewhat the tension between the CMB and weak lensing or Cepheids data sets. Here we show that it is impossible to solve both tensions simultaneously. While the 2015 Planck temperature and low multipole polarization data combined with the Cepheids data sets prefer large values of the Hubble rate (up to H0=72.1-1.7+1.5 km /s /Mpc , when Neff is free to vary), the σ8 parameter remains too large to reduce the σ8 tension. Adding high multipole Planck polarization data does not help since this data shows a strong preference for low values of H0, thus worsening current tensions, even though they also prefer smaller value of σ8.

VizieR Online Data Catalog: LMC NIR survey. IV. Type II Cepheid variables (Bhardwaj+, 2017)

NASA Astrophysics Data System (ADS)

Bhardwaj, A.; Macri, L. M.; Rejkuba, M.; Kanbur, S. M.; Ngeow, C.-C.; Singh, H. P.

2018-05-01

This paper is the fourth in a series of articles based on observations obtained by the Large Magellanic Cloud Near-infrared Synoptic Survey (LMCNISS; Macri et al. 2015, J/AJ/149/117, hereafter Paper I). In Paper I we carried out a time-series survey of 18 deg2 in the central region of the LMC at JHKs wavelengths using the 1.5 m telescope at the Cerro Tololo Inter-American Observatory and the CPAPIR camera. Observations were carried out in queue mode by the SMARTS consortium during 32 nights from 2006 November to 2007 November. The survey products include measurements for more than 3.5x106 sources, including ~1500 Classical Cepheids. We cross-matched the LMCNISS catalog (Paper I) against OGLE-III (Soszynski et al. 2008, J/AcA/58/293) and identified 81 T2Cs with periods ranging from 1 to 68 days; 70 of these have JHKs measurements, while the remaining 11 only have data in J and/or H band. The sample consists of 16 BLH, 31 WVI, 12 PWV, and 22 RVT stars. (4 data files).

VizieR Online Data Catalog: OGLE: Gaia South Ecliptic Pole Field (Soszynski+, 2012)

NASA Astrophysics Data System (ADS)

Soszynski, I.; Udalski, A.; Poleski, R.; Kozlowski, S.; Wyrzykowski, L.; Pietrukowicz, P.; Szymanski, M. K.; Kubiak, M.; Pietrzynski, G.; Ulaczyk, K.; Skowron, J.

2013-03-01

We present a comprehensive analysis of the Gaia South Ecliptic Pole (GSEP) field, 5.3 square degrees area around the South Ecliptic Pole on the outskirts of the LMC, based on the data collected during the fourth phase of the Optical Gravitational Lensing Experiment, OGLE-IV. The GSEP field will be observed during the commissioning phase of the ESA Gaia space mission for testing and calibrating the Gaia instruments. We provide the photometric maps of the GSEP region containing the mean VI photometry of all detected stellar objects and their equatorial coordinates. We show the quality and completeness of the OGLE-IV photometry and color-magnitude diagrams of this region. We conducted an extensive search for variable stars in the GSEP field leading to the discovery of 6789 variable stars. In this sample we found 132 classical Cepheids, 686 RR Lyr type stars, 2819 long-period, and 1377 eclipsing variables. Several objects deserving special attention were also selected, including a new classical Cepheid in a binary eclipsing system. (9 data files).

Distance and absolute magnitudes of the brightest stars in the dwarf galaxy Sextans A

NASA Technical Reports Server (NTRS)

Sandage, A.; Carlson, G.

1982-01-01

In an attempt to improve present bright star calibration, data were gathered for the brightest red and blue stars and the Cepheids in the Im V dwarf galaxy, Sextans A. On the basis of a magnitude sequence measured to V and B values of about 22 and 23, respectively, the mean magnitudes of the three brightest blue stars are V=17.98 and B=17.88. The three brightest red supergiants have V=18.09 and B=20.14. The periods and magnitudes measured for five Cepheids yield an apparent blue distance modulus of 25.67 + or - 0.2, via the P-L relation, and the mean absolute magnitudes of V=-7.56 and B=-5.53 for the red supergiants provide additional calibration of the brightest red stars as distance indicators. If Sextans A were placed at the distance of the Virgo cluster, it would appear to have a surface brightness of 23.5 mag/sq arcec. This, together with the large angular diameter, would make such a galaxy easily discoverable in the Virgo cluster by means of ground-based surveys.

Investigations of the Local supercluster velocity field. II. A study using Tolman-Bondi solution and galaxies with accurate distances from the Cepheid PL-relation

NASA Astrophysics Data System (ADS)

Ekholm, T.; Lanoix, P.; Teerikorpi, P.; Paturel, G.; Fouqué, P.

1999-11-01

A sample of 32 galaxies with accurate distance moduli from the Cepheid PL-relation (Lanoix \\cite{Lanoix99}) has been used to study the dynamical behaviour of the Local (Virgo) supercluster. We used analytical Tolman-Bondi (TB) solutions for a spherically symmetric density excess embedded in the Einstein-deSitter universe (q_0=0.5). Using 12 galaxies within Theta =30degr from the centre we found a mass estimate of 1.62M_virial for the Virgo cluster. This agrees with the finding of Teerikorpi et al. (\\cite{Teerikorpi92}) that TB-estimate may be larger than virial mass estimate from Tully & Shaya (\\cite{Tully84}). Our conclusions do not critically depend on our primary choice of the global H_0=57 km s-1 Mpc{-1} established from SNe Ia (Lanoix \\cite{Lanoix99}). The remaining galaxies outside Virgo region do not disagree with this value. Finally, we also found a TB-solution with the H_0 and q_0 cited yielding exactly one virial mass for the Virgo cluster.

Binary Cepheids: Separations and Mass Ratios in 5 M ⊙ Binaries

NASA Astrophysics Data System (ADS)

Evans, Nancy Evans; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Karovska, Margarita; Tingle, Evan

2013-10-01

Deriving the distribution of binary parameters for a particular class of stars over the full range of orbital separations usually requires the combination of results from many different observing techniques (radial velocities, interferometry, astrometry, photometry, direct imaging), each with selection biases. However, Cepheids—cool, evolved stars of ~5 M ⊙—are a special case because ultraviolet (UV) spectra will immediately reveal any companion star hotter than early type A, regardless of the orbital separation. We have used International Ultraviolet Explorer UV spectra of a complete sample of all 76 Cepheids brighter than V = 8 to create a list of all 18 Cepheids with companions more massive than 2.0 M ⊙. Orbital periods of many of these binaries are available from radial-velocity studies, or can be estimated for longer-period systems from detected velocity variability. In an imaging survey with the Hubble Space Telescope Wide Field Camera 3, we resolved three of the companions (those of η Aql, S Nor, and V659 Cen), allowing us to make estimates of the periods out to the long-period end of the distribution. Combining these separations with orbital data in the literature, we derive an unbiased distribution of binary separations, orbital periods, and mass ratios. The distribution of orbital periods shows that the 5 M ⊙ binaries have systematically shorter periods than do 1 M ⊙ stars. Our data also suggest that the distribution of mass ratios depends on both binary separation and system multiplicity. The distribution of mass ratios as a function of orbital separation, however, does not depend on whether a system is a binary or a triple. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained by the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

The EPOCH Project. I. Periodic variable stars in the EROS-2 LMC database

NASA Astrophysics Data System (ADS)

Kim, Dae-Won; Protopapas, Pavlos; Bailer-Jones, Coryn A. L.; Byun, Yong-Ik; Chang, Seo-Won; Marquette, Jean-Baptiste; Shin, Min-Su

2014-06-01

The EPOCH (EROS-2 periodic variable star classification using machine learning) project aims to detect periodic variable stars in the EROS-2 light curve database. In this paper, we present the first result of the classification of periodic variable stars in the EROS-2 LMC database. To classify these variables, we first built a training set by compiling known variables in the Large Magellanic Cloud area from the OGLE and MACHO surveys. We crossmatched these variables with the EROS-2 sources and extracted 22 variability features from 28 392 light curves of the corresponding EROS-2 sources. We then used the random forest method to classify the EROS-2 sources in the training set. We designed the model to separate not only δ Scuti stars, RR Lyraes, Cepheids, eclipsing binaries, and long-period variables, the superclasses, but also their subclasses, such as RRab, RRc, RRd, and RRe for RR Lyraes, and similarly for the other variable types. The model trained using only the superclasses shows 99% recall and precision, while the model trained on all subclasses shows 87% recall and precision. We applied the trained model to the entire EROS-2 LMC database, which contains about 29 million sources, and found 117 234 periodic variable candidates. Out of these 117 234 periodic variables, 55 285 have not been discovered by either OGLE or MACHO variability studies. This set comprises 1906 δ Scuti stars, 6607 RR Lyraes, 638 Cepheids, 178 Type II Cepheids, 34 562 eclipsing binaries, and 11 394 long-period variables. catalog of these EROS-2 LMC periodic variable stars is available at http://stardb.yonsei.ac.kr and at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/566/A43

The Carina Project. I. Bright Variable Stars

NASA Astrophysics Data System (ADS)

Dall'Ora, M.; Ripepi, V.; Caputo, F.; Castellani, V.; Bono, G.; Smith, H. A.; Brocato, E.; Buonanno, R.; Castellani, M.; Corsi, C. E.; Marconi, M.; Monelli, M.; Nonino, M.; Pulone, L.; Walker, A. R.

2003-07-01

We present new BV time series data of the Carina dwarf spheroidal galaxy (dSph). Current data cover an area of ~0.3 deg2 around the center of the galaxy and allow us to identify 92 variables. Among them 75 are RR Lyrae stars, 15 are bona fide anomalous Cepheids, one might be a Galactic field RR Lyrae star, and one is located along the Carina red giant branch. Expanding upon the seminal photographic investigation by Saha, Monet, & Seitzer we supply, for the first time, accurate estimates of their pulsation parameters (periods, amplitudes, mean magnitudes, and colors) on the basis of CCD photometry. Approximately 50% of both RR Lyrae stars and anomalous Cepheids are new identifications. Among the RR Lyrae sample, six objects are new candidate double-mode (RRd) variables. On the basis of their pulsation properties we estimate that two variables (V158, V182) are about 50% more massive than typical RR Lyrae stars, while the bulk of the anomalous Cepheids are roughly a factor of 2 more massive than fundamental-mode (RRab) RR Lyrae stars. This finding supports the evidence that these objects are intermediate-mass stars during central He-burning phases. We adopted three different approaches to estimate the Carina distance modulus, namely, the first-overtone blue edge method, the period-luminosity-amplitude relation, and the period-luminosity-color relation. We found DM=20.19+/-0.12, a result that agrees quite well with similar estimates based on different distance indicators. The data for Carina, together with data available in the literature, strongly support the conclusion that dSph's can barely be classified into the classical Oosterhoff dichotomy. The mean period of RRab's in Carina resembles that found for Oosterhoff type II clusters, whereas the ratio between first-overtone (RRc) pulsators and the total number of RR Lyrae stars is quite similar to that found in Oosterhoff type I clusters. Based on observations collected at the European Southern Observatory, La Silla, Chile, on Osservatorio Astronomico di Capodimonte guaranteed time.

Measuring the Hubble constant with Type Ia supernovae as near-infrared standard candles

NASA Astrophysics Data System (ADS)

Dhawan, Suhail; Jha, Saurabh W.; Leibundgut, Bruno

2018-01-01

The most precise local measurements of H0 rely on observations of Type Ia supernovae (SNe Ia) coupled with Cepheid distances to SN Ia host galaxies. Recent results have shown tension comparing H0 to the value inferred from CMB observations assuming ΛCDM, making it important to check for potential systematic uncertainties in either approach. To date, precise local H0 measurements have used SN Ia distances based on optical photometry, with corrections for light curve shape and colour. Here, we analyse SNe Ia as standard candles in the near-infrared (NIR), where luminosity variations in the supernovae and extinction by dust are both reduced relative to the optical. From a combined fit to 9 nearby calibrator SNe with host Cepheid distances from Riess et al. (2016) and 27 SNe in the Hubble flow, we estimate the absolute peak J magnitude MJ = -18.524 ± 0.041 mag and H0 = 72.8 ± 1.6 (statistical) ±2.7 (systematic) km s-1 Mpc-1. The 2.2% statistical uncertainty demonstrates that the NIR provides a compelling avenue to measuring SN Ia distances, and for our sample the intrinsic (unmodeled) peak J magnitude scatter is just 0.10 mag, even without light curve shape or colour corrections. Our results do not vary significantly with different sample selection criteria, though photometric calibration in the NIR may be a dominant systematic uncertainty. Our findings suggest that tension in the competing H0 distance ladders is likely not a result of supernova systematics that could be expected to vary between optical and NIR wavelengths, like dust extinction. We anticipate further improvements in H0 with a larger calibrator sample of SNe Ia with Cepheid distances, more Hubble flow SNe Ia with NIR light curves, and better use of the full NIR photometric data set beyond simply the peak J-band magnitude.

THE VMC SURVEY. XIX. CLASSICAL CEPHEIDS IN THE SMALL MAGELLANIC CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ripepi, V.; Marconi, M.; Moretti, M. I.

2016-06-01

The “VISTA near-infrared YJK {sub s}  survey of the Magellanic Clouds System” (VMC) is collecting deep K {sub s}-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y , J , K {sub s} light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period–luminosity (PL), period–luminosity–color (PLC), and period–Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involvingmore » the V , J , K {sub s} bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near–infrared PL, PW, and PLC relations for SO pulsators to date. We used PW( V , K {sub s}) to estimate the relative SMC–LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of Δ μ  = 0.55 ± 0.04 mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are μ {sub SMC} = 19.01 ± 0.05 mag and μ {sub SMC} = 19.04 ± 0.06 mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.« less

The tip of the Red Giant Branch as a Distance Indicator for Resolved Galaxies: II. Computer Simulations

NASA Technical Reports Server (NTRS)

Madore, B. F.; Freedman, W. L.

1994-01-01

Based on both empirical data for nearby galaxies, and on computer simulations, we show that measuring the position of the tip of the first-ascent red-giant branch (TRGB) provides a means of obtaining the distances to nearby galaxies with a precision and accuracy comparable to using Cepheids and/or RR Lyrae variables.

Trajectories of Cepheid variable stars in the Galactic nuclear bulge

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki

2012-06-01

The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, 10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, 25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

Galaxy distances and deviations from universal expansion; Proceedings of the NATO Advanced Research Workshop, Kona, HI, Jan. 13-17, 1986

NASA Astrophysics Data System (ADS)

Madore, Barry F.; Tully, R. Brent

A collection of papers on galaxy distances and deviations from universal expansion is presented. Individual topics addressed include: new results on the distance scale and the Hubble constant, Magellanic Clouds and the distance scale, CCD observations of Cepheids in nearby galaxies, distances using A supergiant stars, infrared calibration of the Cepheid distance scale, two stepping stones to the Hubble constant, physical models of supernovae and the distance scale, 21 cm line widths and distances of spiral galaxies, infrared color-luminosity relations for field galaxies, minimizing the scatter in the Tully-Fisher relation, photometry of galaxies and the local peculiar motion, elliptical galaxies and nonuniformities in the Hubble flow, and large-scale anisotropy in the Hubble flow. Also discussed are: improved distance indicator for elliptical galaxies, anisotropy of galaxies detected by IRAS, the local gravitational field, measurements of the CBR, measure of cosmological times, ages from nuclear cosmochronology, extragalactic gas at high redshift, supercluster infall models, Virgo infall and the mass density of the universe, dynamics of superclusters and Omega(0), distribution of galaxies versus dark matter, peculiar velocities and galaxy formation, cosmological shells and blast waves.

Pulsating star products from the Palomar Transient Factory: Ultra-long period Cepheids in M31 and RR Lyrae in Kepler field

NASA Astrophysics Data System (ADS)

Ngeow, Chow-Choong

2017-09-01

The Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF), are wide-field synoptic sky surveys aimed to detect transients. Even though the main science goal for PTF/iPTF is to detect various types of transients, the synoptic nature of the surveys can also be used for the study of variable stars. In this proceedings contribution, I will first give a brief introduction to PTF/iPTF, followed by the two pulsating stars studies using the PTF/iPTF data: the Ultra-Long Period Cepheids (ULPC) in M31 and the RR Lyrae in the Kepler field. For the formal study, we searched the M31's ULPC using PTF imaging data, and follow up the candidates with other telescopes. Our finding revealed that there are only two ULPC in M31. I will give a brief implication of our finding in distance scale studies. For the latter study, I will present our work on the derivation of metallicity-light curve relation in native PTF/iPTF R-band using the RRab stars in the Kepler field.

Emission lines in the long period Cepheid l Carinae

NASA Technical Reports Server (NTRS)

Boehm-Vitense, Erika; Love, Stanley G.

1991-01-01

For the Cepheid (l) Carinae with a pulsation period of 35.5 days we have studied the emission line fluxes as a function of pulsational phase in order to find out whether we see chromosphere and transition layer emission or whether we see emission due to an outward moving shock. All emission lines show a steep increase in flux shortly before maximum light suggestive of a shock moving through the surface layers. The large ratio of the C IV to C II line fluxes shows that these are not transition layer lines. During maximum light the large ratio of the C IV to C II line fluxes also suggests that we see emission from a shock with velocities greater than 100 km/sec such that C IV emission can be excited. With such velocities mass outflow appears possible. The variations seen in the Mg II line profiles show that there is an internal absorption over a broad velocity band independent of the pulsational phase. We attribute this absorption to a circumstellar 'shell'. This 'shell' appears to be seen also as spatially extended emission in the O I line at 1300 angstrom, which is probably excited by resonance with Ly beta.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cacciari, C.; Clementini, G.

Attention is given to the folowing topics: population I and II variable stars; LP variables, the sun, and mass determination; and predegenerate and degenerate variables. Particular papers are presented on alternative evolutionary approaches to the absolute magnitude of the RR Lyrae variables; the evolution of the Cepheid stars; nonradial pulsations in rapidly rotating Delta Scuti stars; dynamical models of dust shells around Mira variables; and pulsations of central stars of planetary nebulae.

Determining accurate distances to nearby galaxies

NASA Astrophysics Data System (ADS)

Bonanos, Alceste Zoe

2005-11-01

Determining accurate distances to nearby or distant galaxies is a very simple conceptually, yet complicated in practice, task. Presently, distances to nearby galaxies are only known to an accuracy of 10-15%. The current anchor galaxy of the extragalactic distance scale is the Large Magellanic Cloud, which has large (10-15%) systematic uncertainties associated with it, because of its morphology, its non-uniform reddening and the unknown metallicity dependence of the Cepheid period-luminosity relation. This work aims to determine accurate distances to some nearby galaxies, and subsequently help reduce the error in the extragalactic distance scale and the Hubble constant H 0 . In particular, this work presents the first distance determination of the DIRECT Project to M33 with detached eclipsing binaries. DIRECT aims to obtain a new anchor galaxy for the extragalactic distance scale by measuring direct, accurate (to 5%) distances to two Local Group galaxies, M31 and M33, with detached eclipsing binaries. It involves a massive variability survey of these galaxies and subsequent photometric and spectroscopic follow-up of the detached binaries discovered. In this work, I also present a catalog of variable stars discovered in one of the DIRECT fields, M31Y, which includes 41 eclipsing binaries. Additionally, we derive the distance to the Draco Dwarf Spheroidal galaxy, with ~100 RR Lyrae found in our first CCD variability study of this galaxy. A "hybrid" method of discovering Cepheids with ground-based telescopes is described next. It involves applying the image subtraction technique on the images obtained from ground-based telescopes and then following them up with the Hubble Space Telescope to derive Cepheid period-luminosity distances. By re-analyzing ESO Very Large Telescope data on M83 (NGC 5236), we demonstrate that this method is much more powerful for detecting variability, especially in crowded fields. I finally present photometry for the Wolf-Rayet binary WR 20a, which confirmed that the system consists of two extremely massive stars and refined the values of the masses. It is the most massive binary known with an accurate mass determination.

Post-AGB Stars in Nearby Galaxies as Calibrators for HST

NASA Technical Reports Server (NTRS)

Bond, Howard E.

2003-01-01

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program under Grant NAG 5-6821. The Principal Investigator is Howard E. Bond (Space Telescope Science Institute). STScI Postdoctoral Associates Laura K. Fullton (1998), David Alves (1998-2001), and Michael Siegel (2001) were partially supported by this grant. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic- giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The argument is that, in old populations, the stars that are evolving through the PAGB region of the HR diagram arise from only a single main-sequence turnoff mass. In addition, theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, PAGB stars of these spectral types are very easily identified. because of their large Balmer jumps, which are due to their very low surface gravities. Our approach is first to identify PAGB stars in Milky Way globular clusters and in other Local Group galaxies, which are at known distances, and thus to measure accurate absolute magnitudes for the PAGB stars. With this Milky Way and Local Group luminosity calibration, we will then be in a position to find PAGB stars in more distant galaxies from the ground, and ultimately from the Hubble Space Telescope. and thus derive distances. These PAGB stars are, as noted above, the visually brightest members of Population II, and hence will allow distance measurements to galaxies that do not contain Cepheids, such as elliptical galaxies, as well as distances to spirals using PAGB stars in their halos. Moreover, the method is entirely independent of Cepheids. and thus provides a direct test of the Cepheid distance scale. The program will also provide information on the evolutionary lifetimes of PAGB stars.

The Hubble Space Telescope extragalactic distance scale key project. 2: Photometry of WFC images of M81

NASA Technical Reports Server (NTRS)

Hughes, Shaun M. G.; Stetson, Peter B.; Turner, Anne; Kennicutt, Robert C., Jr.; Hill, Robert; Lee, Myung Gyoon; Freedman, Wendy L.; Mould, Jeremy R.; Madore, Barry F.; Ferrarese, Laura

1994-01-01

The Extragalactic Distance Scale (H(sub o)) Key Project for Hubble Space Telescope (HST) aims to employ the Cepheid period-luminosity (P-L) relation to measure galaxy distances out as far as the Virgo Cluster. The vital steps in this program are (1) to obtain precise photometry of stellar images from the Wide Field Camera (WFC) exposures of selected galaxies, and (2) to calibrate this photometry to obtain reliable distances to these galaxies from the Cepheid P-L relation. We have used the DAOPHOT II and ALLFRAME programs to determine 28 instrumental magnitudes -- 22 of F555W (of about V) and six of F785LP (of about I) -- of all stars brighter than V of about 25 in each of two 2.56 arcmin x 2.56 arcmin WFC fields of M81. The reductions use a varying point-spread function to account for the field effects in the WFC optics and yield instrumental magnitudes with single epoch precision ranging from 0.09 to 0.24 mag, at V of about 21.8 to 23.8 -- the magnitude range of the 30 Cepheids that we have now identified in M81. For brighter stars (V of about 22), single epoch magnitudes are precise to 0.09 mag. The photometric calibration onto the Johnson V and Kron-Cousins I systems was determined from independent ground-based CCD observing at the Canada-France-Hawaii Telescope (CFHT) 3.6 m (confirmed by the Kitt Peak National Observatory (KPNO) 4.0 m) and from the Palomar 5.0 m (using the wide-field COSMIC camera) and 1.5 m telescopes. Secondary standards, taken from the COSMIC and CFHT frames, were established in each of the WFC fields in V and I, allowing a direct transformation from ALLFRAME magnitudes to calibrated V and I magnitudes, giving mean V of about 23 magnitudes accurate to of about +/- 0.1 mag. The stellar populations in M81 have been analyzed in terms of the luminosity functions and color magnitude diagrams (CMD) derived from these data, from which we identify numerous supergiants, and a CMD morphology similar to M33.

Mode identification in Beta Cephei stars

NASA Technical Reports Server (NTRS)

Aizenmen, M. L.; Lesh, J. R.

1980-01-01

The essential observational characteristics related to mode identification are summarized. Major emphasis is placed on the following: both light and velocity amplitudes; typical periods in both light and radial velocity; the light curve for Beta Cephei stars in comparison to the classical Cepheids and RR Lyrae stars; the van Hoof effect with respect to the radial velocity curves in many Beta Cephei stars; and the line profiles of many Beta Cephei stars.

Smallpox and pan-Orthodox Virus Detection by Real-Time 3’-Minor Groove Binder TaqMan Assays Oil the Roche LightCycler and the Cepheid Smart Cycler Platforms

DTIC Science & Technology

2003-11-08

Bacillus anthracis BA0068 Ames Sterne SPS 97.13.213 Bacillus cereus Bacillus coagulans Bacillus licheniformis Bacillus macerans Bacillus ...megaterium Bacillus polymyxa Bacillus sphaericus Bacillus stearothermophilus Bacillus subtilis subsp. niger Bacillus thuringiensis Bacillus popilliae...varicella- zoster virus, and Bacillus anthracis DNA by LightCycler polymerase chain reaction after autoclaving:

Binary Cepheids: Separations and Mass Ratios in 5 Solar Mass Binaries

DTIC Science & Technology

2013-10-01

astrometry, photometry , direct imaging), each with selection biases. However, Cepheids—cool, evolved stars of∼5M—are a special case because ultraviolet...detected velocity variability. In an imaging survey with the Hubble Space Telescope Wide Field Camera 3, we resolved three of the companions (those...1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and

OXYGEN ABUNDANCES IN CEPHEIDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luck, R. E.; Andrievsky, S. M.; Korotin, S. N.

2013-07-01

Oxygen abundances in later-type stars, and intermediate-mass stars in particular, are usually determined from the [O I] line at 630.0 nm, and to a lesser extent, from the O I triplet at 615.7 nm. The near-IR triplets at 777.4 nm and 844.6 nm are strong in these stars and generally do not suffer from severe blending with other species. However, these latter two triplets suffer from strong non-local thermodynamic equilibrium (NLTE) effects and thus see limited use in abundance analyses. In this paper, we derive oxygen abundances in a large sample of Cepheids using the near-IR triplets from an NLTEmore » analysis, and compare those abundances to values derived from a local thermodynamic equilibrium (LTE) analysis of the [O I] 630.0 nm line and the O I 615.7 nm triplet as well as LTE abundances for the 777.4 nm triplet. All of these lines suffer from line strength problems making them sensitive to either measurement complications (weak lines) or to line saturation difficulties (strong lines). Upon this realization, the LTE results for the [O I] lines and the O I 615.7 nm triplet are in adequate agreement with the abundance from the NLTE analysis of the near-IR triplets.« less

Image-Subtraction Photometry of Variable Stars in the Globular Clusters NGC 6388 and NGC 6441

NASA Technical Reports Server (NTRS)

Corwin, Michael T.; Sumerel, Andrew N.; Pritzl, Barton J.; Smith, Horace A.; Catelan, M.; Sweigart, Allen V.; Stetson, Peter B.

2006-01-01

We have applied Alard's image subtraction method (ISIS v2.1) to the observations of the globular clusters NGC 6388 and NGC 6441 previously analyzed using standard photometric techniques (DAOPHOT, ALLFRAME). In this reanalysis of observations obtained at CTIO, besides recovering the variables previously detected on the basis of our ground-based images, we have also been able to recover most of the RR Lyrae variables previously detected only in the analysis of Hubble Space Telescope WFPC2 observations of the inner region of NGC 6441. In addition, we report five possible new variables not found in the analysis of the EST observations of NGC 6441. This dramatically illustrates the capabilities of image subtraction techniques applied to ground-based data to recover variables in extremely crowded fields. We have also detected twelve new variables and six possible variables in NGC 6388 not found in our previous groundbased studies. Revised mean periods for RRab stars in NGC 6388 and NGC 6441 are 0.676 day and 0.756 day, respectively. These values are among the largest known for any galactic globular cluster. Additional probable type II Cepheids were identified in NGC 6388, confirming its status as a metal-rich globular cluster rich in Cepheids.

The Dusty Disc of NGC 247

NASA Astrophysics Data System (ADS)

2011-03-01

This image of NGC 247, taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile, reveals the fine details of this highly inclined spiral galaxy and its rich backdrop. Astronomers say this highly tilted orientation, when viewed from Earth, explains why the distance to this prominent galaxy was previously overestimated. The spiral galaxy NGC 247 is one of the closest spiral galaxies of the southern sky. In this new view from the Wide Field Imager on the MPG/ESO 2.2-metre telescope in Chile large numbers of the galaxy's component stars are clearly resolved and many glowing pink clouds of hydrogen, marking regions of active star formation, can be made out in the loose and ragged spiral arms. NGC 247 is part of the Sculptor Group, a collection of galaxies associated with the Sculptor Galaxy (NGC 253, also shown in eso0902 and eso1025). This is the nearest group of galaxies to our Local Group, which includes the Milky Way, but putting a precise value on such celestial distances is inherently difficult. To measure the distance from the Earth to a nearby galaxy, astronomers have to rely on a type of variable star called a Cepheid to act as a distance marker. Cepheids are very luminous stars, whose brightness varies at regular intervals. The time taken for the star to brighten and fade can be plugged into a simple mathematical relation that gives its intrinsic brightness. When compared with the measured brightness this gives the distance. However, this method isn't foolproof, as astronomers think this period-luminosity relationship depends on the composition of the Cepheid. Another problem arises from the fact that some of the light from a Cepheid may be absorbed by dust en route to Earth, making it appear fainter, and therefore further away than it really is. This is a particular problem for NGC 247 with its highly inclined orientation, as the line of sight to the Cepheids passes through the galaxy's dusty disc. However, a team of astronomers is currently looking into the factors that influence these celestial distance markers in a study called the Araucaria Project [1]. The team has already reported that NGC 247 is more than a million light-years closer to the Milky Way than was previously thought, bringing its distance down to just over 11 million light-years. Apart from the main galaxy itself, this view also reveals numerous galaxies shining far beyond NGC 247. In the upper right of the picture three prominent spirals form a line and still further out, far behind them, many more galaxies can be seen, some shining right through the disc of NGC 247. This colour image was created from a large number of monochrome exposures taken through blue, yellow/green and red filters taken over many years. In addition exposures through a filter that isolates the glow from hydrogen gas have also been included and coloured red. The total exposure times per filter were 20 hours, 19 hours, 25 minutes and 35 minutes, respectively. Notes [1] The Araucaria Project is a collaboration between astronomers from institutions in Chile, the United States and Europe. ESO's Very Large Telescope provided data for the project. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

ON THE EVOLUTIONARY AND PULSATION MASS OF CLASSICAL CEPHEIDS. III. THE CASE OF THE ECLIPSING BINARY CEPHEID CEP0227 IN THE LARGE MAGELLANIC CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prada Moroni, P. G.; Gennaro, M.; Bono, G.

2012-04-20

We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass and age) of the eclipsing binary system-CEP0227-in the Large Magellanic Cloud (LMC). We computed several sets of evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were also constructed either by neglecting or by including a moderate convective core overshooting ({beta}{sub ov} = 0.2) during central hydrogen-burning phases. Sets of models were also constructed either by neglecting or by assuming a canonical ({eta} = 0.4, 0.8) or an enhanced ({eta} = 4) mass-loss rate. The most probable solutions weremore » computed in three different planes: luminosity-temperature, mass-radius, and gravity-temperature. By using the Bayes factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting ({beta}{sub ov} = 0.2) and a canonical mass-loss rate ({eta} = 0.4) give stellar masses for the primary (Cepheid)-M = 4.14{sup +0.04}{sub -0.05} M{sub Sun }-and for the secondary-M = 4.15{sup +0.04}{sub -0.05} M{sub Sun }-that agree at the 1% level with dynamical measurements. Moreover, we found ages for the two components and for the combined system-t = 151{sup +4}{sub -3} Myr-that agree at the 5% level. The solutions based on evolutionary models that neglect the mass loss attain similar parameters, while those ones based on models that either account for an enhanced mass loss or neglect convective core overshooting have lower Bayes factors and larger confidence intervals. The dependence on the mass-loss rate might be the consequence of the crude approximation we use to mimic this phenomenon. By using the isochrone of the most probable solution and a Gaussian prior on the LMC distance, we found a true distance modulus-18.53{sup +0.02}{sub -0.02} mag-and a reddening value-E(B - V) = 0.142{sup +0.005}{sub -0.010} mag-that agree quite well with similar estimates in the literature.« less

A Search for Galactic Red Supergiant Variables Beyond the Solar Circle

NASA Astrophysics Data System (ADS)

Alves, David; MacConnell, Jack; Wing, Robert; Bond, Howard E.; Zurek, David; Hoard, Donald W.

2000-02-01

The Galactic rotation curve outside of the Solar circle is particularly difficult to ascertain, yet of critical importance for characterizing the distribution of mass in the Galaxy. We propose to identify a new and large sample of stellar kinematic tracers beyond the Solar circle, in the form of red supergiant variables (RSVs; spectral type M0-M5, luminosity class Ia-Ib). RSVs are ideal tracers of the heavily extincted outer Galactic disk, because (1) they are the intrinsically most luminous Pop I standard candles in the near-infrared, (2) they are more common than the classically employed Cepheids, and (3) they exhibit a period-luminosity relation of comparable precision to that of Cepheids. With the CTIO 0.9m in queue mode, we will derive the pulsation periods of our RSV candidates, allowing us to identify the most distant RSVs for further study. In addition, follow- up observations to obtain accurate, phase-weighted (``(gamma)'') radial velocities (a prerequisite for determining the Galactic rotation curve with RSVs) cannot be planned without period information. We have preselected RSV candidates from a catalog of ~1500 red supergiants in the Galactic plane, originally identified on objective-prism plates. Spectral types and luminosity classes have been determined from 8-color Wing photometry and medium-resolution spectra. The pulsation periods are expected to be 100 to 1000 days, and thus we request long-term status.

Prospective comparison of RT-PCR/ESI-MS to Prodesse ProFlu Plus and Cepheid GenXpert for the detection of Influenza A and B viruses.

PubMed

Hardick, Justin; Dugas, Andrea; Goheen, Joshua; Rothman, Richard; Gaydos, Charlotte

2015-03-01

RT-PCR/ESI-MS has previously demonstrated the capability to detect and identify respiratory viral pathogens in nasopharyngeal swabs. This study expands on previous research by performing a prospective evaluation of RT-PCR/ESI-MS to detect and identify Influenza A and B viruses compared to Prodesse ProFlu Plus and combined ProFlu Plus and Cepheid Xpert Flu. ProFlu Plus was also used as a gold standard for comparison for respiratory syncytial virus detection. Using ProFlu Plus as a gold standard, RT-PCR/ESI-MS had sensitivity and specificity of 82.1% (23/28) and 100% (258/258), respectively, for Influenza A, 100% (16/16) and 99.6% (269/270), respectively for Influenza B, and 88.6% (39/44) and 99.6% (241/242) for any Influenza virus. Using matching results from ProFlu Plus and Xpert Flu as a gold standard, RT-PCR/ESI-MS had 85.2% (23/27) and 100% (259/259) sensitivity and specificity respectively for Influenza A, 100% (14/14) and 99.6% (270/272), respectively for Influenza B virus. Overall, RT-PCR/ESI-MS was not as sensitive as the combined gold standard of ProFlu Plus and Xpert Flu, although it has the capability of detecting other respiratory viruses. Copyright © 2015 Elsevier B.V. All rights reserved.

Karl Schwarzschild Lecture: The Ups and Downs of the Hubble Constant (With 12 Figures)

NASA Astrophysics Data System (ADS)

Tammann, G. Andreas

2006-01-01

A brief history of the determination of the Hubble constant H_0 is given. Early attempts following Lemaitre (1927) gave much too high values due to errors of the magnitude scale, Malmquist bias and calibration problems. By 1962 most authors agreed that 75< H_0 <130. After 1975 a dichotomy arose with values near 100 and others around 55. The former came from apparent-magnitude-limited samples and were affected by Malmquist bias. New distance indicators were introduced; they were sometimes claimed to yield high values of H_0, but the most recent data lead to H_0 in the 60's, yet with remaining difficulties as to the zero-point of the respective distance indicators. SNe Ia with their large range and very small luminosity dispersion (avoiding Malmquist bias) offer a unique opportunity to determine the large-scale value of H_0. Their maximum luminosity can be well calibrated from 10 SNe Ia in local parent galaxies whose Cepheids have been observed with HST. An unforeseen difficulty - affecting all Cepheid distances - is that their P-L relation varies from galaxy to galaxy, presumably in function of metallicity. A proposed solution is summarized here. The conclusion is that H_0 = 63.2 +/- 1.3 (random) +/- 5.3 (systematic) on all scales. The expansion age becomes then (with Omega_m=0.3, Omega_Lambda=0.7) 15.1 Gyr.

A Probabilistic Approach to Fitting Period–luminosity Relations and Validating Gaia Parallaxes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sesar, Branimir; Fouesneau, Morgan; Bailer-Jones, Coryn A. L.

Pulsating stars, such as Cepheids, Miras, and RR Lyrae stars, are important distance indicators and calibrators of the “cosmic distance ladder,” and yet their period–luminosity–metallicity (PLZ) relations are still constrained using simple statistical methods that cannot take full advantage of available data. To enable optimal usage of data provided by the Gaia mission, we present a probabilistic approach that simultaneously constrains parameters of PLZ relations and uncertainties in Gaia parallax measurements. We demonstrate this approach by constraining PLZ relations of type ab RR Lyrae stars in near-infrared W 1 and W 2 bands, using Tycho- Gaia Astrometric Solution (TGAS) parallaxmore » measurements for a sample of ≈100 type ab RR Lyrae stars located within 2.5 kpc of the Sun. The fitted PLZ relations are consistent with previous studies, and in combination with other data, deliver distances precise to 6% (once various sources of uncertainty are taken into account). To a precision of 0.05 mas (1 σ ), we do not find a statistically significant offset in TGAS parallaxes for this sample of distant RR Lyrae stars (median parallax of 0.8 mas and distance of 1.4 kpc). With only minor modifications, our probabilistic approach can be used to constrain PLZ relations of other pulsating stars, and we intend to apply it to Cepheid and Mira stars in the near future.« less

ASTRONOMY: The Distance to the Large Magellanic Cloud.

PubMed

Cole, A A

2000-08-18

The Large Magellanic Cloud (LMC), a satellite of the Milky Way, is an important yardstick by which most intergalactic distances are measured. But as Cole explains in this Perspective, how far away the LMC is remains a matter of dispute, with far reaching implications in cosmology. But observations of Cepheids and of eclipsing binaries, two types of stars that allow absolute luminosity and thus absolute distances to be determined, are promising to resolve this important issue in the not too distant future.

Pulsating stars in the VMC survey

NASA Astrophysics Data System (ADS)

Cioni, Maria-Rosa L.; Ripepi, Vincenzo; Clementini, Gisella; Groenewegen, Martin A. T.; Moretti, Maria I.; Muraveva, Tatiana; Subramanian, Smitha

2017-09-01

The VISTA survey of the Magellanic Clouds system (VMC) began observations in 2009 and since then, it has collected multi-epoch data at Ks and in addition multi-band data in Y and J for a wide range of stellar populations across the Magellanic system. Among them are pulsating variable stars: Cepheids, RR Lyrae, and asymptotic giant branch stars that represent useful tracers of the host system geometry. Based on observations made with VISTA at ESO under programme ID 179.B-2003.

Analytical and clinical performance characteristics of the Abbott RealTime MTB RIF/INH Resistance, an assay for the detection of rifampicin and isoniazid resistant Mycobacterium tuberculosis in pulmonary specimens.

PubMed

Kostera, Joshua; Leckie, Gregor; Tang, Ning; Lampinen, John; Szostak, Magdalena; Abravaya, Klara; Wang, Hong

2016-12-01

Clinical management of drug-resistant tuberculosis patients continues to present significant challenges to global health. To tackle these challenges, the Abbott RealTime MTB RIF/INH Resistance assay was developed to accelerate the diagnosis of rifampicin and/or isoniazid resistant tuberculosis to within a day. This article summarizes the performance of the Abbott RealTime MTB RIF/INH Resistance assay; including reliability, analytical sensitivity, and clinical sensitivity/specificity as compared to Cepheid GeneXpert MTB/RIF version 1.0 and Hain MTBDRplus version 2.0. The limit of detection (LOD) of the Abbott RealTime MTB RIF/INH Resistance assay was determined to be 32 colony forming units/milliliter (cfu/mL) using the Mycobacterium tuberculosis (MTB) strain H37Rv cell line. For rifampicin resistance detection, the Abbott RealTime MTB RIF/INH Resistance assay demonstrated statistically equivalent clinical sensitivity and specificity as compared to Cepheid GeneXpert MTB/RIF. For isoniazid resistance detection, the assay demonstrated statistically equivalent clinical sensitivity and specificity as compared to Hain MTBDRplus. The performance data presented herein demonstrate that the Abbott RealTime MTB RIF/INH Resistance assay is a sensitive, robust, and reliable test for realtime simultaneous detection of first line anti-tuberculosis antibiotics rifampicin and isoniazid in patient specimens. Copyright © 2016 The Author. Published by Elsevier Ltd.. All rights reserved.

NGC 6067: a young and massive open cluster with high metallicity

NASA Astrophysics Data System (ADS)

Alonso-Santiago, J.; Negueruela, I.; Marco, A.; Tabernero, H. M.; González-Fernández, C.; Castro, N.

2017-08-01

NGC 6067 is a young open cluster hosting the largest population of evolved stars among known Milky Way clusters in the 50-150 Ma age range. It thus represents the best laboratory in our Galaxy to constrain the evolutionary tracks of 5-7 M⊙ stars. We have used high-resolution spectra of a large sample of bright cluster members (45), combined with archival photometry, to obtain accurate parameters for the cluster as well as stellar atmospheric parameters. We derive a distance of 1.78 ± 0.12 kpc, an age of 90 ± 20 Ma and a tidal radius of 14.8^{+6.8}_{-3.2} arcmin. We estimate an initial mass above 5700 M⊙, for a present-day evolved population of two Cepheids, two A supergiants and 12 red giants with masses ≈6 M⊙. We also determine chemical abundances of Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y and Ba for the red clump stars. We find a supersolar metallicity, [Fe/H] = +0.19 ± 0.05, and a homogeneous chemical composition, consistent with the Galactic metallicity gradient. The presence of a Li-rich red giant, star 276 with A(Li) = 2.41, is also detected. An overabundance of Ba is found, supporting the enhanced s-process. The ratio of yellow to red giants is much smaller than 1, in agreement with models with moderate overshooting, but the properties of the cluster Cepheids do not seem consistent with current Padova models for supersolar metallicity.

Variable stars in Local Group Galaxies - II. Sculptor dSph

NASA Astrophysics Data System (ADS)

Martínez-Vázquez, C. E.; Stetson, P. B.; Monelli, M.; Bernard, E. J.; Fiorentino, G.; Gallart, C.; Bono, G.; Cassisi, S.; Dall'Ora, M.; Ferraro, I.; Iannicola, G.; Walker, A. R.

2016-11-01

We present the identification of 634 variable stars in the Milky Way dwarf spheroidal (dSph) satellite Sculptor based on archival ground-based optical observations spanning ˜24 yr and covering ˜2.5 deg2. We employed the same methodologies as the `Homogeneous Photometry' series published by Stetson. In particular, we have identified and characterized one of the largest (536) RR Lyrae samples so far in a Milky Way dSph satellite. We have also detected four Anomalous Cepheids, 23 SX Phoenicis stars, five eclipsing binaries, three field variable stars, three peculiar variable stars located above the horizontal branch - near to the locus of BL Herculis - that we are unable to classify properly. Additionally, we identify 37 long period variables plus 23 probable variable stars, for which the current data do not allow us to determine the period. We report positions and finding charts for all the variable stars, and basic properties (period, amplitude, mean magnitude) and light curves for 574 of them. We discuss the properties of the RR Lyrae stars in the Bailey diagram, which supports the coexistence of subpopulations with different chemical compositions. We estimate the mean mass of Anomalous Cepheids (˜1.5 M⊙) and SX Phoenicis stars (˜1 M⊙). We discuss in detail the nature of the former. The connections between the properties of the different families of variable stars are discussed in the context of the star formation history of the Sculptor dSph galaxy.

[Implementation of vanA and vanB genes by PCR technique research interest in system (Xpert vanA/vanB CepheidR) closed in a laboratory of microbiology in managing an outbreak to Enterococcus faecium resistant glycopeptide (EfRG)].

PubMed

Dekeyser, S; Beclin, E; Descamps, D

2011-04-01

The closed system PCR for the rapid detection of vanA and vanB genes (Xpert vanA/vanB Cepheid(®)) was evaluated in our laboratory, to improve the rapidity of the response and thus the management of patients and isolation measures during two GRE outbreaks. From March to December2009, 565 samples were analysed by PCR associated to bacterial culture initially for all samples for 2months (n = 75), and thereafter for PCR-positive samples only. In this study, sensitivity and negative predictive values of the PCR were 100%. Specificity was evaluated in the presence and absence of outbreak: 69.3 and 76.8% respectively. The variability of false positive rates between units were lower in nonepidemic than during epidemic phase. The global false positive rate was 23.9%. This easy-to-use technology provides rapid results… four samples are tested in 1h versus 72h for culture. Despite its reagent cost, it represents an important hospital diagnostic tool: improvement of the management of cohorting areas and patient transfer between units, adaptation of isolation measures and treatments. However, culture remains necessary to confirm any positive result obtained by PCR and for epidemiological surveillance. Copyright © 2010 Elsevier Masson SAS. All rights reserved.

Properties of the Open Cluster Tombaugh 1 from High-resolution Spectroscopy and uvbyCaHβ Photometry

NASA Astrophysics Data System (ADS)

Sales Silva, João V.; Carraro, Giovanni; Anthony-Twarog, Barbara J.; Moni Bidin, Christian; Costa, Edgardo; Twarog, Bruce A.

2016-01-01

Open clusters can be the key to deepening our knowledge on various issues involving the structure and evolution of the Galactic disk and details of stellar evolution because a cluster’s properties are applicable to all its members. However, the number of open clusters with detailed analysis from high-resolution spectroscopy or precision photometry imposes severe limitations on studies of these objects. To expand the number of open clusters with well-defined chemical abundances and fundamental parameters, we investigate the poorly studied, anticenter open cluster Tombaugh 1. Using precision uvbyCaHβ photometry and high-resolution spectroscopy, we derive the cluster’s reddening, obtain photometric metallicity estimates, and, for the first time, present a detailed abundance analysis of 10 potential cluster stars (nine clump stars and one Cepheid). Using the radial position from the cluster center and multiple color indices, we have isolated a sample of unevolved, probable single-star members of Tombaugh 1. From 51 stars, the cluster reddening is found to be E(b-y) = 0.221 ± 0.006 or E(B-V) = 0.303 ± 0.008, where the errors refer to the internal standard errors of the mean. The weighted photometric metallicity from m1 and hk is [Fe/H] = -0.10 ± 0.02, while a match to the Victoria-Regina Strömgren isochrones leads to an age of 0.95 ± 0.10 Gyr and an apparent modulus of (m-M) = 13.10 ± 0.10. Radial velocities identify six giants as probable cluster members, and the elemental abundances of Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Y, Ba, Ce, and Nd have been derived for both the cluster and the field stars. Tombaugh 1 appears to be a typical inner thin disk, intermediate-age open cluster of slightly subsolar metallicity, located just beyond the solar circle, with solar elemental abundance ratios except for the heavy s-process elements, which are a factor of two above solar. Its metallicity is consistent with a steep metallicity gradient in the galactocentric region between 9.5 and 12 kpc. Our study also shows that Cepheid XZ CMa is not a member of Tombaugh 1 and reveals that this Cepheid presents signs of barium enrichment, making it a probable binary star. Based on observations carried out at Las Campanas Observatory (program ID: CN2009B-042) and Cerro Tololo Inter-American Observatory.

A Picture-perfect Pure-disc Galaxy

NASA Astrophysics Data System (ADS)

2011-02-01

The bright galaxy NGC 3621, captured here using the Wide Field Imager on the 2.2-metre telescope at ESO's La Silla Observatory in Chile, appears to be a fine example of a classical spiral. But it is in fact rather unusual: it does not have a central bulge and is therefore described as a pure-disc galaxy. NGC 3621 is a spiral galaxy about 22 million light-years away in the constellation of Hydra (The Sea Snake). It is comparatively bright and can be seen well in moderate-sized telescopes. This picture was taken using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile. The data were selected from the ESO archive by Joe DePasquale as part of the Hidden Treasures competition [1]. Joe's picture of NGC 3621 was ranked fifth in the competition. This galaxy has a flat pancake shape, indicating that it hasn't yet come face to face with another galaxy as such a galactic collision would have disturbed the thin disc of stars, creating a small bulge in its centre. Most astronomers think that galaxies grow by merging with other galaxies, in a process called hierarchical galaxy formation. Over time, this should create large bulges in the centres of spirals. Recent research, however, has suggested that bulgeless, or pure-disc, spiral galaxies like NGC 3621 are actually fairly common. This galaxy is of further interest to astronomers because its relative proximity allows them to study a wide range of astronomical objects within it, including stellar nurseries, dust clouds, and pulsating stars called Cepheid variables, which astronomers use as distance markers in the Universe [2]. In the late 1990s, NGC 3621 was one of 18 galaxies selected for a Key Project of the Hubble Space Telescope: to observe Cepheid variables and measure the rate of expansion of the Universe to a higher accuracy than had been possible before. In the successful project, 69 Cepheid variables were observed in this galaxy alone. Multiple monochrome images taken through four different colour filters were combined to make this picture. Images taken through a blue filter have been coloured blue in the final picture, images through a yellow-green filter are shown as green and images through a red filter as dark orange. In addition images taken through a filter that isolates the glow of hydrogen gas have been coloured red. The total exposure times per filter were 30, 40, 40 and 40 minutes respectively. Notes [1] ESO's Hidden Treasures 2010 competition gave amateur astronomers the opportunity to search through ESO's vast archives of astronomical data, hoping to find a well-hidden gem that needed polishing by the entrants. Participants submitted nearly 100 entries and ten skilled people were awarded some extremely attractive prizes, including an all expenses paid trip for the overall winner to ESO's Very Large Telescope (VLT) on Cerro Paranal, in Chile, the world's most advanced optical telescope. The ten winners submitted a total of 20 images that were ranked as the highest entries in the competition out of the near 100 images. [2] Cepheid variables are very luminous stars - up to 30 000 times brighter than our Sun - whose brightness varies at regular intervals over several days, weeks or months. The period of this variation in luminosity is related to the star's true brightness, known as its absolute magnitude. By knowing the absolute magnitude of the star, and measuring how bright it appears, astronomers can easily calculate its distance from Earth. Cepheid variables are therefore vital for establishing the scale of the Universe. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Obituary: Theodore Siegumfeldt Jacobsen, 1901-2003

NASA Astrophysics Data System (ADS)

Kraft, Robert Paul; Wallerstein, George

2003-12-01

Theodor Jacobsen, oldest member of the American Astronomical Society, died in Seattle on 17 July 2003 at the age of 102. His astronomical career, which began in the 1920's, coincided with the rise of astronomy in the University of Washington from a one-man activity within mathematics to today's major astronomical department of more than 30 faculty and other research personnel. Born on 6 February 1901 in Copenhagen, Denmark, he immigrated with his parents, brother and three sisters to the USA in 1917. Even while he was still in Denmark, his interest in astronomy was sparked at age 7 by a gift from his parents of a two-inch telescope. As early as 1921, in the midst of his undergraduate studies in chemistry at Stanford, he wrote to Director W. W. Campbell of Lick Observatory, inquiring how he should prepare for a career in astronomy and whether one could make a living at it. Campbell encouraged him to learn as much physics and mathematics as possible with the outcome that, on completion of his BA degree at Stanford, Jacobsen became a University of California Berkeley graduate student and was appointed a Lick Observatory fellow in the period 1923 to 1926. Following completion of his PhD thesis, entitled ``A Redetermination of the Radial Velocity Curves of Certain Cepheid Variable Stars" (LOB, 379, 1926), he was appointed as ``assistant" at Lick, a position roughly equivalent to that of ``instructor" in a modern University environment. Inquiries concerning whether Lick could recommend ``a promising young man to take over teaching some astronomy and math" from then President Spencer of the University of Washington were received by Lick's acting director Robert Aitken in 1928. They were looking for a Berkeley PhD, said Spencer, and Aitken responded with an enthusiastic recommendation of Theodor Jacobsen, who then took up his duties in Seattle with the beginning of the fall term 1928. Jacobsen succeeded H. Zanstra (of Zanstra mechanism fame) in the Dept. of Mathematics, but it was not until 1948 that astronomy was split off from mathematics, at which time Jacobsen became chair and sole member of the new Astronomy Department. During the World War II years, he taught navigation to the recruits who moved on to become naval officers. In the postwar years, he taught elementary astronomy, as well as more advanced courses in practical astronomy, the kinds of subjects found in Smart's "Spherical Astronomy" text including celestial mechanics and observational work using the UW Observatory transit instrument. He chaired the Astronomy Department until 1965 when the Department began to undergo its modern expansion; he formally retired in 1971. Jacobsen's post-thesis research continued to center on the determination of radial velocities of cepheids as well as binary stars and he maintained connections on a modest scale with the Dominion Astrophysical Observatory in Victoria, B.C. In this era of emphasis on galaxy evolution and cosmology, it is easy to forget that in the 1920s, there was still controversy over the nature of cepheids---were they pulsating stars or merely some form of odd binary? Jacobsen's extremely accurate radial velocity curves of these stars, when combined with then newly emerging accurate light curves, did much to bolster the pulsation hypothesis. According to astronomers currently working in the field, Jacobsen's 1926 velocity curves, obtained with the then state-of-the-art Mills spectrograph attached to the Lick 36-inch refractor, attained an impressive accuracy in the gamma velocities of these cepheids of about 100 m/s! His last paper on cepheid velocities was a joint publication in 1992, written when Jacobsen was more than 90 years old. He also was a major contributor to the study of the ``level effect," a term applied to the fact that during the pulsation cycle, the radial velocity curves differ depending upon the spectral line formation depth within the cepheid atmospheres. The effect was recognized as a result of the passage of a running wave, again a manifestation of the pulsation phenomenon in cepheids. Although the astronomy of stars was Jacobsen's main focus, he was a man of many interests. He had a love of the mountains, especially the nearby Cascade Range. He was especially fond of one-day hiking trips around and on the flanks of Mt Rainier, although he never attempted the strenuous climb to the summit. But some of the lesser summits of the Cascade range were among his trophies: Mt Hood in the late 40s, and Mt St. Helens in the 30s when because of its graceful symmetry, it was known as the ``Fujiyama of the West." He was also an accomplished pianist, his tastes running from Beethoven to the early romantics such as Schubert and Chopin. In many ways, his pianistic philosophy paralleled his personal attitudes about doing astronomy. For him, precision and clarity took precedence over lofty grand strategies. He was happy to make what he called modest additions to astronomical research, standing as it were, ``on the shoulders of others." Along with this, he would lament over, for example, how difficult it was to make the last movement of Beethoven's Op.27, No.2 clear---to make it effective, he would say, you have to pay attention to the details, just as doing good astronomy meant paying attention to the details. Jacobsen married Evelyn Brandt a well-known Seattle piano teacher. They kept Welsh Corgi dogs, which they named for various famous astronomers. Theodor and Evelyn played together at facing grand pianos, sometimes works for duo piano, sometimes piano concertos with the orchestral part in piano transcription. All this came to an end in 1993 when Evelyn died after 40 years of marriage. They had no children. Jacobsen remained interested in classical astronomy---that of the Greeks and Arabs---as a kind of hobby during his entire life. But it surprised some members of the UW astronomy faculty when they found, on visiting Jacobsen in his home in the mid-90s, an extensive manuscript that he had composed using modern mathematics to rederive the laws of planetary motions as conceived by the ancients using far more primitive means. With the help of these and other colleagues, he was able to publish, at the age of 98, a UW Press book entitled ``Planetary Systems from the Ancient Greeks to Kepler."

Prospective and retrospective evaluation of the Cepheid Xpert® Flu/RSV XC assay for rapid detection of influenza A, influenza B, and respiratory syncytial virus.

PubMed

Salez, Nicolas; Nougairede, Antoine; Ninove, Laetitia; Zandotti, Christine; de Lamballerie, Xavier; Charrel, Remi N

2015-04-01

A total of 281 clinical specimens (nasal swabs and nasopharyngeal aspirates) were tested with the Xpert® Flu/RSV XC. The results were compared to those obtained with the real-time retro transcriptase-polymerase chain reaction assays routinely used in our laboratory. The Xpert® Flu/RSV XC showed sensitivity/specificity of 97.8%/100% and 97.9%/100% for flu and respiratory syncytial virus, respectively. Copyright © 2015 Elsevier Inc. All rights reserved.

Petersen diagram revolution

NASA Astrophysics Data System (ADS)

Smolec, Radoslaw; Dziembowski, Wojciech; Moskalik, Pawel; Netzel, Henryka; Prudil, Zdenek; Skarka, Marek; Soszynski, Igor

2017-09-01

Over the recent years, the Petersen diagram for classical pulsators, Cepheids and RR Lyr stars, populated with a few hundreds of new multiperiodic variables. We review our analyses of the OGLE data, which resulted in a significant extension of the known, and in the discovery of a few new and distinct forms of multiperiodic pulsation. The showcase includes not only radial mode pulsators, but also radial-non-radial pulsators and stars with significant modulation observed on top of the beat pulsation. First theoretical models explaining the new forms of stellar variability are briefly discussed.

VizieR Online Data Catalog: Distances of Gaia DR1 TGAS sources (Astraatmadja+, 2016)

NASA Astrophysics Data System (ADS)

Astraatmadja, T. L.; Bailer-Jones, C. A. L.

2016-09-01

This is a catalogue of distances and their asymmetric uncertainties inferred from the parallaxes published in the Gaia DR1 catalogue. Two priors are used: The exponentially decreasing space density and the Milky Way prior. For the exponentially decreasing space density prior, two scale lengths are used: 110pc and 1350pc. The former is based on a fitting of the true distance distribution of a subset of the GUMS catalogue (Robin et al., 2012, Cat. VI/137) which are limited to V<11. This is the magnitude at which Tycho-2 is 99% complete. The latter is based on the same procedure but limited to G=20.7, which is the expected limiting magnitude of Gaia. For the Milky Way prior, the parameters are described in the paper. We report the mode of the posterior PDF, the median, the 90% credible interval, and a standard deviation in distance which are calculated by scaling the 90% into 68.3%. The Cepheids data used for the validation of the results are included here as well. They are taken from Groenewegen (2013, Cat. J/A+A/550/A70) and cross-matched with Hipparcos and/or Tycho by making a Simbad query of each Cepheids and finding the corresponding Hipparcos and/or Tyho identifier. The distances are inferred either by neglecting the systematic uncertainties of 0.3mas (Gaia Collaboration et al., 2016, Cat. I/337) for reasons described in the paper, or by adding a systematic uncertainties of 0.3mas in quadrature with the random parallax uncertainties. We provide both results here. (4 data files).

Survey of non-linear hydrodynamic models of type-II Cepheids

NASA Astrophysics Data System (ADS)

Smolec, R.

2016-03-01

We present a grid of non-linear convective type-II Cepheid models. The dense model grids are computed for 0.6 M⊙ and a range of metallicities ([Fe/H] = -2.0, -1.5, -1.0), and for 0.8 M⊙ ([Fe/H] = -1.5). Two sets of convective parameters are considered. The models cover the full temperature extent of the classical instability strip, but are limited in luminosity; for the most luminous models, violent pulsation leads to the decoupling of the outermost model shell. Hence, our survey reaches only the shortest period RV Tau domain. In the Hertzsprung-Russell diagram, we detect two domains in which period-doubled pulsation is possible. The first extends through the BL Her domain and low-luminosity W Vir domain (pulsation periods ˜2-6.5 d). The second domain extends at higher luminosities (W Vir domain; periods >9.5 d). Some models within these domains display period-4 pulsation. We also detect very narrow domains (˜10 K wide) in which modulation of pulsation is possible. Another interesting phenomenon we detect is double-mode pulsation in the fundamental mode and in the fourth radial overtone. Fourth overtone is a surface mode, trapped in the outer model layers. Single-mode pulsation in the fourth overtone is also possible on the hot side of the classical instability strip. The origin of the above phenomena is discussed. In particular, the role of resonances in driving different pulsation dynamics as well as in shaping the morphology of the radius variation curves is analysed.

New variable stars discovered in the fields of three Galactic open clusters using the VVV survey

NASA Astrophysics Data System (ADS)

Palma, T.; Minniti, D.; Dékány, I.; Clariá, J. J.; Alonso-García, J.; Gramajo, L. V.; Ramírez Alegría, S.; Bonatto, C.

2016-11-01

This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the J-, H- and Ks- bands obtained from the Vista Variables in the Vía Láctea (VVV) Survey. We performed in each cluster field a variability search using Stetson's variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study, 157 in total in three different known OCs, are classified based on their light curve shapes, periods, amplitudes and their location in the corresponding color-magnitude (J -Ks ,Ks) and color-color (H -Ks , J - H) diagrams. We found 5 possible Cepheid stars which, based on the period-luminosity relation, are very likely type II Cepheids located behind the bulge. Among the newly discovered variables, there are eclipsing binaries, δ Scuti, as well as background RR Lyrae stars. Using the new version of the Wilson & Devinney code as well as the "Physics Of Eclipsing Binaries" (PHOEBE) code, we analyzed some of the best eclipsing binaries we discovered. Our results show that these studied systems turn out to be ranging from detached to double-contact binaries, with low eccentricities and high inclinations of approximately 80°. Their surface temperatures range between 3500 K and 8000 K.

A COMPREHENSIVE, WIDE-FIELD STUDY OF PULSATING STARS IN THE CARINA DWARF SPHEROIDAL GALAXY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vivas, A. Katherina; Mateo, Mario, E-mail: akvivas@cida.ve, E-mail: mmateo@umich.edu

2013-12-01

We report the detection of 388 pulsating variable stars (and some additional miscellaneous variables) in the Carina dwarf spheroidal galaxy over an area covering the full visible extent of the galaxy and extending a few times beyond its photometric (King) tidal radius along the direction of its major axis. Included in this total are 340 newly discovered dwarf Cepheids (DCs), which are mostly located ∼2.5 mag below the horizontal branch and have very short periods (<0.1 days), typical of their class and consistent with their location on the upper part of the extended main sequence of the younger populations ofmore » the galaxy. Several extra-tidal DCs were found in our survey up to a distance of ∼1° from the center of Carina. Our sample also includes RR Lyrae stars and anomalous Cepheids, some of which were found outside the galaxy's tidal radius as well. This supports past works that suggest that Carina is undergoing tidal disruption. We use the period-luminosity relationship for DCs to estimate a distance modulus of μ{sub 0} = 20.17 ± 0.10 mag, in very good agreement with the estimate from RR Lyrae stars. We find some important differences in the properties of the DCs of Carina and those in Fornax and the LMC, the only extragalactic samples of DCs currently known. These differences may reflect a metallicity spread, depth along the line of sight, and/or different evolutionary paths of the DC stars.« less

Comparison of Cepheid Xpert Flu/RSV XC and BioFire FilmArray for Detection of Influenza A, Influenza B, and Respiratory Syncytial Virus.

PubMed

Wahrenbrock, Mark G; Matushek, Scott; Boonlayangoor, Sue; Tesic, Vera; Beavis, Kathleen G; Charnot-Katsikas, Angella

2016-07-01

The Xpert Flu/RSV XC was compared to the FilmArray respiratory panel for detection of influenza (Flu) A, Flu B, and respiratory syncytial virus (RSV), using 128 nasopharyngeal swabs. Positive agreements were 100% for Flu A and RSV and 92.3% for Flu B. The Xpert may be useful in clinical situations when extensive testing is not required and may serve an important role in laboratories already performing broader respiratory panel testing. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Interpretation of OAO-2 ultraviolet light curves of beta Doradus

NASA Technical Reports Server (NTRS)

Hutchinson, J. L.; Lillie, C. F.; Hill, S. J.

1975-01-01

Middle-ultraviolet light curves of beta Doradus, obtained by OAO-2, are presented along with other evidence indicating that the small additional bumps observed on the rising branches of these curves have their origin in shock-wave phenomena in the upper atmosphere of this classical Cepheid. A simple piston-driven spherical hydrodynamic model of the atmosphere is developed to explain the bumps, and the calculations are compared with observations. The model is found to be consistent with the shapes of the light curves as well as with measurements of the H-alpha radial velocities.

Variable stars in the Leo A dwarf galaxy (DDO 69)

NASA Technical Reports Server (NTRS)

Hoessel, John G.; Saha, A.; Krist, John; Danielson, G. Edward

1994-01-01

Observations of the Leo A dwarf galaxy, obtained over the period from 1980 to 1991 are reported. Forty two separate Charge Coupled Devices (CCD) frames were searched for variable stars. A total of 14 suspected variables were found, 9 had sufficient coverage for period determination, and 5 had Cepheid light curves. Four of these stars fit well on a P-L relation and yield a distance modulus, after correction for Galactic foreground extinction, of m-M = 26.74. This corresponds to a distance of 2.2 Mpc, placing Leo A near the Local Group zero-velocity surface.

Characterizing the Norma Overdensity

NASA Astrophysics Data System (ADS)

Sargent, Benjamin; Chakrabarti, Sukanya; Boyer, Martha; Angeloni, Rodolfo; Sarajedini, Ata; Guhathakurta, Raja

2018-05-01

We recently discovered receding, clustered Cepheid candidates towards the Norma constellation that may mark a new dwarf galaxy of the Milky Way. If this dwarf galaxy is confirmed, this would be a breakthrough in near-field cosmology, as it would represent the first dwarf galaxy that was predicted by a dynamical analysis to be subsequently discovered. Underlying the search for this dwarf galaxy is the hope that one could characterize dark-matter dominated dwarf galaxies from analysis of disturbances in Galactic disks, i.e., Galactoseismology. At b 1, it would also be the closest dwarf galaxy to the Galactic plane. Aside from its expected distinct kinematics, another signature of a dwarf galaxy is an excess of stars in the CMD. When we correct for extinction the VVV photometry of the area where we saw the Cepheid candidates and subtract out a control field (i.e. a Galactic background field), we see an excess of stars that may correspond to red-clump stars at a distance of 80 kpc. However, we used the Bonifacio et al. (2000) extinction prescription that is known to be inaccurate close to the Galactic plane. Majewski et al. (2011) have shown that the combination of NIR and MIR colors, namely H-4.5 micron or K_s - 3.6 micron, can produce a far better extinction correction than prior extinction maps. To extinction correct the VVV data, we need Spitzer data that is complete down to 17 mag in 4.5 um. Deep MIR data are crucial for us to do the extinction correction properly, and Spitzer is the only instrument that can enable this effort. By appropriately correcting the VVV and F2 photometry for extinction following Majewski et al. (2011), we should be able to separate the stellar populations of the expected dwarf galaxy candidate.

Evaluation of Cepheid's Xpert MTB/Rif test on pleural fluid in the diagnosis of pleural tuberculosis in a high prevalence HIV/TB setting.

PubMed

Lusiba, John K; Nakiyingi, Lydia; Kirenga, Bruce J; Kiragga, Agnes; Lukande, Robert; Nsereko, Maria; Ssengooba, Willy; Katamba, Achilles; Worodria, William; Joloba, Moses L; Mayanja-Kizza, Harriet

2014-01-01

Diagnosis of pleural tuberculosis (TB) using routinely available diagnostic methods is challenging due to the paucibacillary nature of the disease. Histopathology and pleural tissue TB culture involves an invasive procedure which requires expertise and appropriate equipment, both often unavailable in many health units. Xpert MTB/Rif test has been widely evaluated in sputum specimens but data on its performance in pleural TB is scarce. We evaluated the accuracy of Cepheid's Xpert MTB/Rif test on pleural fluid in the diagnosis of pleural TB in Uganda. Consenting adult patients with exudative pleural effusions underwent pleural biopsy and the tissue obtained subjected to Lowenstein-Jensen and mycobacterial growth indicator tube MTB cultures and histopathology. Pleural fluid for Xpert MTB/Rif testing was also collected. Data on socio-demographic characteristics, clinical symptoms, HIV status and CD4 count were also collected. Sensitivity, specificity, positive and negative predictive values of Xpert MTB/Rif test on pleural fluid in pleural TB diagnosis were calculated using pleural tissue MTB culture and/or histopathology as the reference standard. Of the 116 participants [female 50%, mean age 34 (SD ±13], 87/116 (75%) had pleural TB confirmed on pleural tissue culture and/or histopathology. The Xpert MTB/Rif test identified 25 (28.7%) of the 87 confirmed pleural TB cases. The sensitivity and specificity of Xpert MTB/Rif test were 28.7% and 96.6% respectively while the positive and negative predictive values were 96.1% and 31.1% respectively. Xpert MTB/Rif test on pleural fluid does not accurately diagnose pleural TB and therefore cannot be used as an initial evaluation test in patients with suspected pleural TB. New, rapid and accurate tests for the diagnosis of pleural TB are still warranted.

Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the δ Scuti stars AI Velorum and β Cassiopeiae

NASA Astrophysics Data System (ADS)

Guiglion, G.; Nardetto, N.; Mathias, P.; Domiciano de Souza, A.; Poretti, E.; Rainer, M.; Fokin, A.; Mourard, D.; Gieren, W.

2013-02-01

Aims: The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. The key parameter of this method is the projection factor used to convert the radial velocity into the pulsation velocity. Our analysis was aimed at deriving for the first time the projection factor of δ Scuti stars, using high-resolution spectra of the high-amplitude pulsator AI Vel and of the fast rotator β Cas. Methods: The geometric component of the projection factor (i.e. p0) was calculated using a limb-darkening model of the intensity distribution for AI Vel, and a fast-rotator model for β Cas. Then, using SOPHIE/OHP data for β Cas and HARPS/ESO data for AI Vel, we compared the radial velocity curves of several spectral lines forming at different levels in the atmosphere and derived the velocity gradient associated to the spectral-line-forming regions in the atmosphere of the star. This velocity gradient was used to derive a dynamical projection factor p. Results: We find a flat velocity gradient for both stars and finally p = p0 = 1.44 for AI Vel and p = p0 = 1.41 for β Cas. By comparing Cepheids and δ Scuti stars, these results bring valuable insights into the dynamical structure of pulsating star atmospheres. They suggest that the period-projection factor relation derived for Cepheids is also applicable to δ Scuti stars pulsating in a dominant radial mode. This work uses observations made with the HARPS instrument at the 3.6 m telescope (La Silla, Chile) in the framework of the LP185.D-0056 and with the SOPHIE instrument at OHP (France).

Variable Stars In the Unusual, Metal-Rich Globular Cluster

NASA Technical Reports Server (NTRS)

Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.; Oegerle, William R. (Technical Monitor)

2002-01-01

We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6388 using time-series BV photometry. Twenty-eight new variables were found in this survey, increasing the total number of variables found near NGC 6388 to approx. 57. A significant number of the variables are RR Lyrae (approx. 14), most of which are probable cluster members. The periods of the fundamental mode RR Lyrae are shown to be unusually long compared to metal-rich field stars. The existence of these long period RRab stars suggests that the horizontal branch of NGC 6388 is unusually bright. This implies that the metallicity-luminosity relationship for RR Lyrae stars is not universal if the RR Lyrae in NGC 6388 are indeed metal-rich. We consider the alternative possibility that the stars in NGC 6388 may span a range in [Fe/H]. Four candidate Population II Cepheids were also found. If they are members of the cluster, NGC 6388 would be the most metal-rich globular cluster to contain Population II Cepheids. The mean V magnitude of the RR Lyrae is found to be 16.85 +/- 0.05 resulting in a distance of 9.0 to 10.3 kpc, for a range of assumed values of (M(sub V)) for RR Lyrae. We determine the reddening of the cluster to be E(B - V) = 0.40 +/- 0.03 mag, with differential reddening across the face of the cluster. We discuss the difficulty in determining the Oosterhoff classification of NGC 6388 and NGC 6441 due to the unusual nature of their RR Lyrae, and address evolutionary constraints on a recent suggestion that they are of Oosterhoff type II.

Multicenter Evaluation of the Cepheid Xpert Methicillin-Resistant Staphylococcus aureus (MRSA) Test as a Rapid Screening Method for Detection of MRSA in Nares▿

PubMed Central

Wolk, D. M.; Picton, E.; Johnson, D.; Davis, T.; Pancholi, P.; Ginocchio, C. C.; Finegold, S.; Welch, D. F.; de Boer, M.; Fuller, D.; Solomon, M. C.; Rogers, B.; Mehta, M. S.; Peterson, L. R.

2009-01-01

The first U.S. multicenter clinical trial to assess the performance of the Cepheid Xpert MRSA assay (Xpert MRSA) was conducted. The assay is a qualitative test designed for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) directly from nares swabs. This novel test combines integrated nucleic acid extraction and automated real-time PCR for the detection of a MRSA-specific signature sequence. A total of 1,077 nares specimens were collected from seven geographically distinct health care sites across the United States with prevalence rates ranging from 5.2% to 44%. Nares specimens were tested by (i) the Xpert MRSA assay, (ii) direct culture on CHROMagar MRSA medium (direct CM culture), and (iii) broth-enriched culture (Trypticase soy broth with 6.5% sodium chloride) followed by plating onto CHROMagar MRSA medium (broth-enriched CM culture). When direct CM culture was designated the reference method, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the Xpert MRSA assay were 94.3%, 93.2%, 73.0%, and 98.8%, respectively. When broth-enriched CM culture was used as the reference method, the clinical sensitivity, specificity, PPV, and NPV of the Xpert MRSA assay were 86.3%, 94.9%, 80.5%, and 96.6%, respectively. The BD GeneOhm MRSA (BDGO) assay was performed as a comparative molecular method. No statistical performance differences were observed between the Xpert MRSA and BDGO assays when they were compared to culture methods. From this large-scale, multicenter clinical comparison, we conclude that the Xpert MRSA assay is a simple, rapid, and accurate method for performing active surveillance for MRSA in a variety of health care populations. PMID:19129414

Comparative Evaluation of the Diagnostic Performance of the Prototype Cepheid GeneXpert Ebola Assay

PubMed Central

Jansen van Vuren, Petrus; Grobbelaar, Antoinette; Storm, Nadia; Conteh, Ousman; Konneh, Kelfala; Kamara, Abdul; Sanne, Ian

2015-01-01

The Ebola virus disease (EVD) outbreak in West Africa has highlighted an urgent need for point-of-care (POC) assays for the diagnosis of this devastating disease in resource-limited African countries. The diagnostic performance characteristics of a prototype Cepheid GeneXpert Ebola POC used to detect Ebola virus (EBOV) in stored serum and plasma samples collected from suspected EVD cases in Sierra Leone in 2014 and 2015 was evaluated. The GeneXpert Ebola POC is a self-contained single-cartridge automated system that targets the glycoprotein (GP) and nucleoprotein (NP) genes of EBOV and yields results within 90 min. Results from 281 patient samples were compared to the results of a TaqMan real-time reverse transcription-PCR (RT-PCR) targeting the polymerase gene and performed on two real-time PCR machines. Agreement between the three platforms was 100% at cycle threshold (CT) values of ≤34.99, but discordant results were noted between CT values of 35 and 45.The diagnostic sensitivity of the three platforms was 100% in 91 patient samples that were confirmed to be infectious by virus isolation. All three molecular platforms detected viral EBOV RNA in additional samples that did not contain viable EBOV. The analytical sensitivity of the GeneXpert Ebola POC for the detection of NP was higher, and comparable to that of polymerase gene detection, than that for the detection of GP when using a titrated laboratory stock of EBOV. There was no detectable cross-reactivity with other hemorrhagic fever viruses or arboviruses. The GeneXpert Ebola POC offers an easy to operate and sensitive diagnostic tool that can be used for the rapid screening of suspected EVD cases in treatment or in holding centers during EVD outbreaks. PMID:26637383

A two-column formalism for time-dependent modelling of stellar convection. I. Description of the method

NASA Astrophysics Data System (ADS)

Stökl, A.

2008-11-01

Context: In spite of all the advances in multi-dimensional hydrodynamics, investigations of stellar evolution and stellar pulsations still depend on one-dimensional computations. This paper devises an alternative to the mixing-length theory or turbulence models usually adopted in modelling convective transport in such studies. Aims: The present work attempts to develop a time-dependent description of convection, which reflects the essential physics of convection and that is only moderately dependent on numerical parameters and far less time consuming than existing multi-dimensional hydrodynamics computations. Methods: Assuming that the most extensive convective patterns generate the majority of convective transport, the convective velocity field is described using two parallel, radial columns to represent up- and downstream flows. Horizontal exchange, in the form of fluid flow and radiation, over their connecting interface couples the two columns and allows a simple circulating motion. The main parameters of this convective description have straightforward geometrical meanings, namely the diameter of the columns (corresponding to the size of the convective cells) and the ratio of the cross-section between up- and downdrafts. For this geometrical setup, the time-dependent solution of the equations of radiation hydrodynamics is computed from an implicit scheme that has the advantage of being unaffected by the Courant-Friedrichs-Lewy time-step limit. This implementation is part of the TAPIR-Code (short for The adaptive, implicit RHD-Code). Results: To demonstrate the approach, results for convection zones in Cepheids are presented. The convective energy transport and convective velocities agree with expectations for Cepheids and the scheme reproduces both the kinetic energy flux and convective overshoot. A study of the parameter influence shows that the type of solution derived for these stars is in fact fairly robust with respect to the constitutive numerical parameters.

The VMC survey - XXV. The 3D structure of the Small Magellanic Cloud from Classical Cepheids

NASA Astrophysics Data System (ADS)

Ripepi, Vincenzo; Cioni, Maria-Rosa L.; Moretti, Maria Ida; Marconi, Marcella; Bekki, Kenji; Clementini, Gisella; de Grijs, Richard; Emerson, Jim; Groenewegen, Martin A. T.; Ivanov, Valentin D.; Molinaro, Roberto; Muraveva, Tatiana; Oliveira, Joana M.; Piatti, Andrés E.; Subramanian, Smitha; van Loon, Jacco Th.

2017-11-01

The VISTA near-infrared YJKs survey of the Magellanic System (VMC) is collecting deep Ks-band time-series photometry of pulsating stars hosted by the two Magellanic Clouds and their connecting bridge. Here, we present Y, J, Ks light curves for a sample of 717 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with our previous results and V magnitude from literature, allowed us to construct a variety of period-luminosity and period-Wesenheit relationships, valid for Fundamental, First and Second Overtone pulsators. These relations provide accurate individual distances to CCs in the SMC over an area of more than 40 deg2. Adopting literature relations, we estimated ages and metallicities for the majority of the investigated pulsators, finding that (i) the age distribution is bimodal, with two peaks at 120 ± 10 and 220 ± 10 Myr; (i) the more metal-rich CCs appear to be located closer to the centre of the galaxy. Our results show that the three-dimensional distribution of the CCs in the SMC is not planar but heavily elongated for more than 25-30 kpc approximately in the east/north-east towards south-west direction. The young and old CCs in the SMC show a different geometric distribution. Our data support the current theoretical scenario predicting a close encounter or a direct collision between the Clouds some 200 Myr ago and confirm the presence of a Counter-Bridge predicted by some models. The high-precision three-dimensional distribution of young stars presented in this paper provides a new test bed for future models exploring the formation and evolution of the Magellanic System.

The Hubble Constant to 1%: Physics beyond LambdaCDM

NASA Astrophysics Data System (ADS)

Riess, Adam

2017-08-01

By steadily advancing the precision and accuracy of the Hubble constant, we now see 3.4-sigma evidence for a deviation from the standard LambdaCDM model and thus the exciting chance of discovering new fundamental physics such as exotic dark energy, a new relativistic particle, dark matter interactions, or a small curvature, to name a few possibilities. We propose a coordinated program to accomplish three goals with one set of observations: (1) improve the precision of the best route to H_0 with HST observations of Cepheids in the hosts of 11 SNe Ia, lowering the uncertainty to 1.3% to reach the discovery threshold of 5-sigma and begin resolving the underlying source of the deviation; (2) continue testing the quality of Cepheid distances, so far the most accurate and reliable indicators in the near Universe, using the tip of the red giant branch (TRGB); and (3) use oxygen-rich Miras to confirm the present tension with the CMB and establish a future route available to JWST. We can achieve all three goals with one dataset and take the penultimate step to reach 1% precision in H_0 after Gaia. With its long-pass filter and NIR capability, we can collect these data with WFC3 many times faster than previously possible while overcoming the extinction and metallicity effects that challenged the first generation of H_0 measurements. Our results will complement the leverage available at high redshift from other cosmological tools such as BAO, the CMB, and SNe Ia, and will provide a 40% improvement on the WFIRST measurements of dark energy. Reaching this precision will be a fitting legacy for the telescope charged to resolve decades of uncertainty regarding the Hubble constant.

A new estimate of the Hubble constant using the Virgo cluster distance

NASA Astrophysics Data System (ADS)

Visvanathan, N.

The Hubble constant, which defines the size and age of the universe, remains substantially uncertain. Attention is presently given to an improved distance to the Virgo Cluster obtained by means of the 1.05-micron luminosity-H I width relation of spirals. In order to improve the absolute calibration of the relation, accurate distances to the nearby SMC, LMC, N6822, SEX A and N300 galaxies have also been obtained, on the basis of the near-IR P-L relation of the Cepheids. A value for the global Hubble constant of 67 + or 4 km/sec per Mpc is obtained.

Spectrum synthesis of the Type Ia supernovae SN 1992A and SN 1981B

NASA Technical Reports Server (NTRS)

Nugent, Peter; Baron, E.; Hauschildt, Peter H.; Branch, David

1995-01-01

We present non-local thermodynamic equilibrium (non-LTE) synthetic spectra for the Type Ia supernovae SN 1992A and SN 1981B, near maximum light. At this epoch both supernovae were observed from the UV through the optical. This wide spectral coverage is essential for determining the density structure of a SN Ia. Our fits are in good agreement with observation and provide some insight as to the differences between these supernovae. We also discuss the application of the expanding photosphere method to SNe Ia which gives a distance that is independent of those based on the decay of Ni-56 and Cepheid variable stars.

Constraining the axion-photon coupling with massive stars.

PubMed

Friedland, Alexander; Giannotti, Maurizio; Wise, Michael

2013-02-08

We point out that stars in the mass window ~8-12M([circumpunct]) can serve as sensitive probes of the axion-photon interaction, g(Aγγ). Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually eliminate the blue loop phase of the evolution. This would contradict observational data, since the blue loops are required, e.g., to account for the existence of Cepheid stars. Using the MESA stellar evolution code, modified to include the extra cooling, we conservatively find g(Aγγ)

Advances in stellar evolution; Proceedings of the Workshop on Stellar Ecology, Marciana Marina, Italy, June 23-29, 1996

NASA Astrophysics Data System (ADS)

Rood, R. T.; Renzini, A.

1997-01-01

The present volume on stellar evolution discusses fundamentals of stellar evolution and star clusters, variable stars, AGB stars and planetary nebulae, white dwarfs, binary star evolution, and stars in galaxies. Attention is given to the stellar population in the Galactic bulge, a photometric study of NGC 458, and HST observations of high-density globular clusters. Other topics addressed include the Cepheid instability strip in external galaxies, Hyades cluster white dwarfs and the initial-final mass relation, element diffusion in novae, mass function of the stars in the solar neighborhood, synthetic spectral indices for elliptical galaxies, and stars at the Galactic center.

John Goodricke, Edward Pigott, and Their Study of Variable Stars

NASA Astrophysics Data System (ADS)

French, Linda M.

2012-06-01

John Goodricke and Edward Pigott, working in York, England, between 1781 and 1786, determined the periods of variation of eclipsing binaries such as Algol and Beta Lyrae and speculated that the eclipses of Algol might be caused by a "dark body," perhaps even a planet. They also determined the periods of variation of the first two known Cepheid variables, the stars whose period-luminosity relation today enables astronomers to determine distances to distant galaxies. Goodricke holds special interest because he was completely deaf and because he died at the age of 21. The lives and work of these two astronomers are described.

VizieR Online Data Catalog: l Car radial velocity curves (Anderson, 2016)

NASA Astrophysics Data System (ADS)

Anderson, R. I.

2018-02-01

Line-of-sight (radial) velocities of the long-period classical Cepheid l Carinae were measured from 925 high-quality optical spectra recorded using the fiber-fed high-resolution (R~60,000) Coralie spectrograph located at the Euler telescope at La Silla Observatory, Chile. The data were taken between 2014 and 2016. This is the full version of Tab. 2 presented partially in the paper. Line shape parameters (depth, width, asymmetry) are listed for the computed cross-correlation profiles (CCFs). Radial velocities were determined using different techniques (Gaussian, bi-Gaussian) and measured on CCFs computed using three different numerical masks (G2, weak lines, strong lines). (1 data file).

A spectroscopic investigation of the eclipsing binary Epsilon Aurigae

NASA Technical Reports Server (NTRS)

Balachandran, Suchitra

1991-01-01

The objectives were to examine, in detail, the spectra of the eclipsing binary Epsilon Aurigae taken with the IUE satellite telescope during the 1982 to 1984 eclipse. All of the low resolution spectra were analyzed and UV light curves are presented. The primary findings are as follows: (1) a constant eclipse depth from 1600 A to longer wavelengths and a sharp drop in the eclipse depth from 1600 to 1200 A; (2) the absence of large amplitude fluctuations in the UV as expected from a Cepheid primary; and (3) equal ingress and egress times in contradiction to that interpreted from visible light curves. The effects of these findings on the eclipse geometry are being studied.

Estrellas variables en campos de cúmulos abiertos galácticos detectadas en el relevamiento VVV

NASA Astrophysics Data System (ADS)

Palma, T.; Dékany, I.; Clariá, J. J.; Minniti, D.; Alonso-García, J. A.; Ramírez Alegría, S.; Bonatto, C.

2016-08-01

The present project constitutes a massive search for variable stars in the field of open clusters projected on highly reddened regions of the galactic disk and bulge. This search is being performed using -, - and -band observations of the near-infrared variability Survey Vista variables in the Via Lactea. We present the first results obtained in four open clusters projected on the Galactic bulge. The new variables discovered in the current work, 182 in total, are classified on the basis of their light curves and their locations in the corresponding color-magnitude diagrams. Among the newly discovered variable stars, Cepheids, RR Lyrae, Scuti, eclipsing binaries and other types have been found.

Optical and Infrared Photometry of SN 2005df

NASA Astrophysics Data System (ADS)

Krisciunas, Kevin; Suntzeff, Nicholas B.; Espinoza, Juan; Gonzalez, David; Miranda, Alberto; Sanhueza, Pedro

2017-12-01

We present optical BVRI and near-infrared YJHK_s photometry of the normal Type Ia supernova 2005df, obtained with the CTIO 1.3-m and 0.9-m telescopes. The B- and V-band photometry, S-corrected to the filter prescriptions of Bessell(1990), matches the corresponding photometry from the ANU published by Milne et al. (2010). The R-band photometry from CTIO and ANU matches well without any corrections. A combination of V-band and near-IR photometry shows that SN 2005df is unreddened in its host galaxy. Spectropolarimetry of this supernova was obtained with the VLT, and the distance to the host galaxy is being determined from observations of Cepheids using the Hubble Space Telescope.

VizieR Online Data Catalog: NGC 6822 Cepheids JHKs light curves (Feast+, 2012)

NASA Astrophysics Data System (ADS)

Feast, M. W.; Whitelock, P. A.; Menzies, J. W.; Matsunaga, N.

2013-03-01

Our survey of NGC 6822 is confined to the optical bar which is aligned nearly north-south. We used the Japanese-South African IRSF (InfraRed Survey Facility) telescope equipped with the SIRIUS camera, which permits simultaneous imaging in the J, H and Ks bands. We defined three overlapping fields, with field 1 centred at RA=19:44:56 and DE=-14:48:06 (2000.0). Fields 2 and 3 are centred 6.7 arcmin north and south, respectively, from field 1. The three fields, approximately 7.8 arcmin2, were observed in JHKs at 19, 18 and 16 epochs, respectively, over a period of 3.5yr. (2 data files).

Hubble Space Telescope Trigonometric Parallax of Polaris B, Companion of the Nearest Cepheid

NASA Astrophysics Data System (ADS)

Bond, Howard E.; Nelan, Edmund P.; Remage Evans, Nancy; Schaefer, Gail H.; Harmer, Dianne

2018-01-01

Polaris, the nearest and brightest Cepheid, is a potential anchor point for the Leavitt period–luminosity relation. However, its distance is a matter of contention, with recent advocacy for a parallax of ∼10 mas, in contrast with the Hipparcos measurement of 7.54 ± 0.11 mas. We report an independent trigonometric parallax determination, using the Fine Guidance Sensors (FGS) on the Hubble Space Telescope. Polaris itself is too bright for FGS, so we measured its eighth-magnitude companion Polaris B, relative to a network of background reference stars. We converted the FGS relative parallax to absolute, using estimated distances to the reference stars from ground-based photometry and spectral classification. Our result, 6.26 ± 0.24 mas, is even smaller than that found by Hipparcos. We note other objects for which Hipparcos appears to have overestimated parallaxes, including the well-established case of the Pleiades. We consider possible sources of systematic error in the FGS parallax, but find no evidence they are significant. If our “long” distance is correct, the high luminosity of Polaris indicates that it is pulsating in the second overtone of its fundamental mode. Our results raise several puzzles, including a long pulsation period for Polaris compared to second-overtone pulsators in the Magellanic Clouds, and a conflict between the isochrone age of Polaris B (∼2.1 Gyr) and the much younger age of Polaris A. We discuss possibilities that B is not a physical companion of A, in spite of the strong evidence that it is, or that one of the stars is a merger remnant. These issues may be resolved when Gaia provides parallaxes for both stars. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained by the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

John Goodricke, Edward Pigott, and Their Study of Variable Stars

NASA Astrophysics Data System (ADS)

French, Linda M.

2011-05-01

John Goodricke (1764-1786) and Edward Pigott (1753-1825) are credited with determining the first accurate periods for several important variable stars. Goodricke's name is associated with the determination of the period of the eclipsing binary Algol (Beta Persei); for this he was awarded the Copley Prize of the Royal Society of London. He also determined the periods of the contact binary Beta Lyrae and of Delta Cephei, the prototype Cepheid variable. Around the same time, Edward Pigott obtained the period of Eta Aquilae, another Cepheid. In actuality, the two collaborated on all these observations; today we would call them co-discoverers. Goodricke is the better known of the two, in part because he won the Copley Medal, in part because of his tragically short life, and in part because he was deaf. Edward Pigott was the more experienced observer, having worked with his father Nathaniel on determining the longitudes of several cities on the Continent. Evidence shows, however, that Goodricke had some astronomical experience while a student at the Warrington Academy. The journals of the two show that they developed a partnership that made the most of both their talents over the brief time (less than five years) they worked together before Goodricke's death. Today, the two are remembered as having suggested eclipses as the cause for the periodic dimming of Algol. This explanation is accepted today as the correct one. In their day, however, most eminent astronomers believed that starspots were a more likely cause for the dimming. By the time of John Goodricke's death, he seems to have accepted that explanation as well. A study of the work of Goodricke and Pigott contains many lessons for today's observers of variable stars. This work was supported by an AAS Small Research Grant and by the Pollack Award of the Dudley Observatory.

Detection of methicillin-resistant Staphylococcus aureus by a duplex droplet digital PCR assay.

PubMed

Kelley, Kashonda; Cosman, Angela; Belgrader, Phillip; Chapman, Brenda; Sullivan, Donna C

2013-07-01

Health care-associated infections with methicillin-resistant Staphylococcus aureus (MRSA) contribute to significant hospitalization costs. We report here a droplet digital PCR (ddPCR) assay, which is a next-generation emulsion-based endpoint PCR assay for high-precision MRSA analysis. Reference cultures of MRSA, methicillin-susceptible S. aureus (MSSA), and confounders were included as controls. Copan swabs were used to sample cultures and collect specimens for analysis from patients at a large teaching hospital. Swab extraction and cell lysis were accomplished using magnetic-driven agitation of silica beads. Quantitative PCR (qPCR) (Roche Light Cycler 480) and ddPCR (Bio-Rad QX100 droplet digital PCR system) assays were used to detect genes for the staphylococcal protein SA0140 (SA) and the methicillin resistance (mecA) gene employing standard TaqMan chemistries. Both qPCR and ddPCR assays correctly identified culture controls for MRSA (76), MSSA (12), and confounder organisms (36) with 100% sensitivity and specificity. Analysis of the clinical samples (211 negative and 186 positive) collected during a study of MRSA nasal carriage allowed direct comparison of the qPCR and ddPCR assays to the Cepheid MRSA GeneXpert assay. A total of 397 clinical samples were examined in this study. Cepheid MRSA GeneXpert values were used to define negative and positive samples. Both the qPCR and ddPCR assays were in good agreement with the reference assay. The sensitivities for the qPCR and ddPCR assays were 96.8% (95% confidence interval [CI], 93.1 to 98.5%) and 96.8% (95% CI, 93.1 to 98.5%), respectively. Both the qPCR and ddPCR assays had specificities of 91.9% (95% CI, 87.5 to 94.9%) for qPCR and 91.0% (95% CI, 86.4 to 94.2%) for ddPCR technology.

Is there a concordance value for H0?

NASA Astrophysics Data System (ADS)

Luković, Vladimir V.; D'Agostino, Rocco; Vittorio, Nicola

2016-11-01

Context. We test the theoretical predictions of several cosmological models against different observables to compare the indirect estimates of the current expansion rate of the Universe determined from model fitting with the direct measurements based on Cepheids data published recently. Aims: We perform a statistical analysis of type Ia supernova (SN Ia), Hubble parameter, and baryon acoustic oscillation data. A joint analysis of these datasets allows us to better constrain cosmological parameters, but also to break the degeneracy that appears in the distance modulus definition between H0 and the absolute B-band magnitude of SN Ia, M0. Methods: From the theoretical side, we considered spatially flat and curvature-free ΛCDM, wCDM, and inhomogeneous Lemaître-Tolman-Bondi (LTB) models. To analyse SN Ia we took into account the distributions of SN Ia intrinsic parameters. Results: For the ΛCDM model we find that Ωm = 0.35 ± 0.02, H0 = (67.8 ± 1.0) km s-1 Mpc-1, while the corrected SN absolute magnitude has a normal distribution N(19.13,0.11). The wCDM model provides the same value for Ωm, while H0 = (66.5 ± 1.8) km s-1 Mpc-1 and w = -0.93 ± 0.07. When an inhomogeneous LTB model is considered, the combined fit provides H0 = (64.2 ± 1.9) km s-1 Mpc-1. Conclusions: Both the Akaike information criterion and the Bayes factor analysis cannot clearly distinguish between ΛCDM and wCDM cosmologies, while they clearly disfavour the LTB model. For the ΛCDM, our joint analysis of the SN Ia, the Hubble parameter, and the baryon acoustic oscillation datasets provides H0 values that are consistent with cosmic microwave background (CMB)-only Planck measurements, but they differ by 2.5σ from the value based on Cepheids data.

Evaluation of Cepheid's Xpert MTB/RIF Test on Pleural Fluid in the Diagnosis of Pleural Tuberculosis in a High Prevalence HIV/TB Setting

PubMed Central

Kirenga, Bruce J.; Kiragga, Agnes; Lukande, Robert; Nsereko, Maria; Ssengooba, Willy; Katamba, Achilles; Worodria, William; Joloba, Moses L.; Mayanja-Kizza, Harriet

2014-01-01

Background Diagnosis of pleural tuberculosis (TB) using routinely available diagnostic methods is challenging due to the paucibacillary nature of the disease. Histopathology and pleural tissue TB culture involves an invasive procedure which requires expertise and appropriate equipment, both often unavailable in many health units. Xpert MTB/Rif test has been widely evaluated in sputum specimens but data on its performance in pleural TB is scarce. We evaluated the accuracy of Cepheid's Xpert MTB/Rif test on pleural fluid in the diagnosis of pleural TB in Uganda. Methods Consenting adult patients with exudative pleural effusions underwent pleural biopsy and the tissue obtained subjected to Lowenstein-Jensen and mycobacterial growth indicator tube MTB cultures and histopathology. Pleural fluid for Xpert MTB/Rif testing was also collected. Data on socio-demographic characteristics, clinical symptoms, HIV status and CD4 count were also collected. Sensitivity, specificity, positive and negative predictive values of Xpert MTB/Rif test on pleural fluid in pleural TB diagnosis were calculated using pleural tissue MTB culture and/or histopathology as the reference standard. Results Of the 116 participants [female 50%, mean age 34 (SD ±13], 87/116 (75%) had pleural TB confirmed on pleural tissue culture and/or histopathology. The Xpert MTB/Rif test identified 25 (28.7%) of the 87 confirmed pleural TB cases. The sensitivity and specificity of Xpert MTB/Rif test were 28.7% and 96.6% respectively while the positive and negative predictive values were 96.1% and 31.1% respectively. Conclusion Xpert MTB/Rif test on pleural fluid does not accurately diagnose pleural TB and therefore cannot be used as an initial evaluation test in patients with suspected pleural TB. New, rapid and accurate tests for the diagnosis of pleural TB are still warranted. PMID:25051491

The Optical Gravitational Lensing Experiment. Gaia South Ecliptic Pole Field as Seen by OGLE-IV

NASA Astrophysics Data System (ADS)

Soszyński, I.; Udalski, A.; Poleski, R.; Kozłowski, S.; Wyrzykowski, Ł.; Pietrukowicz, P.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Ulaczyk, K.; Skowron, J.

2012-09-01

We present a comprehensive analysis of the Gaia South Ecliptic Pole (GSEP) field, 5.3 square degrees area around the South Ecliptic Pole on the outskirts of the LMC, based on the data collected during the fourth phase of the Optical Gravitational Lensing Experiment, OGLE-IV. The GSEP field will be observed during the commissioning phase of the ESA Gaia space mission for testing and calibrating the Gaia instruments. We provide the photometric maps of the GSEP region containing the mean VI photometry of all detected stellar objects and their equatorial coordinates. We show the quality and completeness of the OGLE-IV photometry and color-magnitude diagrams of this region. We conducted an extensive search for variable stars in the GSEP field leading to the discovery of 6789 variable stars. In this sample we found 132 classical Cepheids, 686 RR Lyr type stars, 2819 long-period, and 1377 eclipsing variables. Several objects deserving special attention were also selected, including a new classical Cepheid in a binary eclipsing system. To provide empirical data for the Gaia Science Alert system we also conducted a search for optical transients. We discovered two firm type Ia supernovae and nine additional supernova candidates. To facilitate future Gaia supernovae detections we prepared a list of more than 1900 galaxies to redshift about 0.1 located in the GSEP field. Finally, we present the results of astrometric study of the GSEP field. With the 26 months time base of the presented here OGLE-IV data, proper motions of stars could be detected with the accuracy reaching 2 mas/yr. Astrometry allowed to distinguish galactic foreground variable stars detected in the GSEP field from LMC objects and to discover about 50 high proper motion stars (proper motion ≥ 100 mas/yr). Among them three new nearby white dwarfs were found. All data presented in this paper are available to the astronomical community from the OGLE Internet archive.

Persistent C II absorption in the normal type Ia supernova 2002fk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cartier, Régis; Zelaya, Paula; Hamuy, Mario

2014-07-01

We present well-sampled UBVRIJHK photometry of SN 2002fk starting 12 days before maximum light through 122 days after peak brightness, along with a series of 15 optical spectra from –4 to +95 days since maximum. Our observations show the presence of C II lines in the early-time spectra of SN 2002fk, expanding at 11,000 km s{sup –1} and persisting until 8 days past maximum light with a velocity of ∼9000 km s{sup –1}. SN 2002fk is characterized by a small velocity gradient of v-dot {sub Si} {sub II}=26 km s{sup –1} day{sup –1}, possibly caused by an off-center explosion withmore » the ignition region oriented toward the observer. The connection between the viewing angle of an off-center explosion and the presence of C II in the early-time spectrum suggests that the observation of C II could be also due to a viewing angle effect. Adopting the Cepheid distance to NGC 1309 we provide the first H {sub 0} value based on near-infrared (near-IR) measurements of a Type Ia supernova (SN) between 63.0 ± 0.8 (±3.4 systematic) and 66.7 ± 1.0 (±3.5 systematic) km s{sup –1} Mpc{sup –1}, depending on the absolute magnitude/decline rate relationship adopted. It appears that the near-IR yields somewhat lower (6%-9%) H {sub 0} values than the optical. It is essential to further examine this issue by (1) expanding the sample of high-quality near-IR light curves of SNe in the Hubble flow, and (2) increasing the number of nearby SNe with near-IR SN light curves and precise Cepheid distances, which affords the promise to deliver a more precise determination of H {sub 0}.« less

Eclipsing Binaries in the OGLE Variable Star Catalogs. V. Long-Period EB-Type Light Curve Systems in the Small Magellanic Cloud and the PLC-β Relation

NASA Astrophysics Data System (ADS)

Rucinski, Slavek M.; Maceroni, Carla

2001-01-01

Thirty-eight long-period (P>10 days) apparently contact binary stars discovered by the OGLE-II project in the SMC show EB-type light curves and an ``inverted'' period-color relation with longer orbital periods for redder systems. The strong light variations between eclipses can be explained within a semidetached model in which ellipsoidal variations of a large, evolved, Roche lobe-filling component dominates over eclipse effects in the systemic light changes. The model requires further spectroscopic and color-curve support before it can be fully accepted. It is noted that the dominant role of the Roche lobe-filling component in the total systemic luminosity can explain the new period-luminosity-color (PLC) relation, which has been established for the long-period EB (LP-EB) systems. We call it the PLC-β relation, to distinguish it from the Cepheid relation. Two versions of the PLC-β relation-based on the (B-V)0 or (V-I)0 color indices-have been calibrated for 33 systems with (V-I)0>0.25 spanning the orbital period range of 11 to 181 days (it was found that blue systems with (V-I)0<=0.25 do not follow the same calibration). The relations can provide maximum-light, absolute-magnitude estimates accurate to ɛMV~=0.35 mag within the approximate range -3

The Carnegie-Chicago Hubble Program. I. An Independent Approach to the Extragalactic Distance Scale Using Only Population II Distance Indicators

NASA Astrophysics Data System (ADS)

Beaton, Rachael L.; Freedman, Wendy L.; Madore, Barry F.; Bono, Giuseppe; Carlson, Erika K.; Clementini, Gisella; Durbin, Meredith J.; Garofalo, Alessia; Hatt, Dylan; Jang, In Sung; Kollmeier, Juna A.; Lee, Myung Gyoon; Monson, Andrew J.; Rich, Jeffrey A.; Scowcroft, Victoria; Seibert, Mark; Sturch, Laura; Yang, Soung-Chul

2016-12-01

We present an overview of the Carnegie-Chicago Hubble Program, an ongoing program to obtain a 3% measurement of the Hubble constant (H 0) using alternative methods to the traditional Cepheid distance scale. We aim to establish a completely independent route to H 0 using RR Lyrae variables, the tip of the red giant branch (TRGB), and Type Ia supernovae (SNe Ia). This alternative distance ladder can be applied to galaxies of any Hubble type, of any inclination, and, using old stars in low-density environments, is robust to the degenerate effects of metallicity and interstellar extinction. Given the relatively small number of SNe Ia host galaxies with independently measured distances, these properties provide a great systematic advantage in the measurement of H 0 via the distance ladder. Initially, the accuracy of our value of H 0 will be set by the five Galactic RR Lyrae calibrators with Hubble Space Telescope Fine-Guidance Sensor parallaxes. With Gaia, both the RR Lyrae zero-point and TRGB method will be independently calibrated, the former with at least an order of magnitude more calibrators and the latter directly through parallax measurement of tip red giants. As the first end-to-end “distance ladder” completely independent of both Cepheid variables and the Large Magellanic Cloud, this path to H 0 will allow for the high-precision comparison at each rung of the traditional distance ladder that is necessary to understand tensions between this and other routes to H 0. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #13472 and #13691.

New Evidence for Mass Loss from δ Cephei from H I 21 cm Line Observations

NASA Astrophysics Data System (ADS)

Matthews, L. D.; Marengo, M.; Evans, N. R.; Bono, G.

2012-01-01

Recently published Spitzer Space Telescope observations of the classical Cepheid archetype δ Cephei revealed an extended dusty nebula surrounding this star and its hot companion HD 213307. At far-infrared wavelengths, the emission resembles a bow shock aligned with the direction of space motion of the star, indicating that δ Cephei is undergoing mass loss through a stellar wind. Here we report H I 21 cm line observations with the Very Large Array (VLA) to search for neutral atomic hydrogen associated with this wind. Our VLA data reveal a spatially extended H I nebula (~13' or 1 pc across) surrounding the position of δ Cephei. The nebula has a head-tail morphology, consistent with circumstellar ejecta shaped by the interaction between a stellar wind and the interstellar medium (ISM). We directly measure a mass of circumstellar atomic hydrogen M_H I ≈ 0.07 M_{⊙}, although the total H I mass may be larger, depending on the fraction of circumstellar material that is hidden by Galactic contamination within our band or that is present on angular scales too large to be detected by the VLA. It appears that the bulk of the circumstellar gas has originated directly from the star, although it may be augmented by material swept from the surrounding ISM. The H I data are consistent with a stellar wind with an outflow velocity V o = 35.6 ± 1.2 km s-1 and a mass-loss rate of {\\dot{M}}≈ (1.0+/- 0.8)× 10^{-6} M_{⊙} yr-1. We have computed theoretical evolutionary tracks that include mass loss across the instability strip and show that a mass-loss rate of this magnitude, sustained over the preceding Cepheid lifetime of δ Cephei, could be sufficient to resolve a significant fraction of the discrepancy between the pulsation and evolutionary masses for this star.

Pulsating star research and the Gaia revolution

NASA Astrophysics Data System (ADS)

Eyer, Laurent; Clementini, Gisella; Guy, Leanne P.; Rimoldini, Lorenzo; Glass, Florian; Audard, Marc; Holl, Berry; Charnas, Jonathan; Cuypers, Jan; Ridder, Joris De; Evans, Dafydd W.; de Fombelle, Gregory Jevardat; Lanzafame, Alessandro; Lecoeur-Taibi, Isabelle; Mowlavi, Nami; Nienartowicz, Krzysztof; Riello, Marco; Ripepi, Vincenzo; Sarro, Luis; Süveges, Maria

2017-09-01

In this article we present an overview of the ESA Gaia mission and of the unprecedented impact that Gaia will have on the field of variable star research. We summarise the contents and impact of the first Gaia data release on the description of variability phenomena, with particular emphasis on pulsating star research. The Tycho-Gaia astrometric solution, although limited to 2.1 million stars, has been used in many studies related to pulsating stars. Furthermore a set of 3,194 Cepheids and RR Lyrae stars with their times series have been released. Finally we present the plans for the ongoing study of variable phenomena with Gaia and highlight some of the possible impacts of the second data release on variable, and specifically, pulsating stars.

Enhancements of Bayesian Blocks; Application to Large Light Curve Databases

NASA Technical Reports Server (NTRS)

Scargle, Jeff

2015-01-01

Bayesian Blocks are optimal piecewise linear representations (step function fits) of light-curves. The simple algorithm implementing this idea, using dynamic programming, has been extended to include more data modes and fitness metrics, multivariate analysis, and data on the circle (Studies in Astronomical Time Series Analysis. VI. Bayesian Block Representations, Scargle, Norris, Jackson and Chiang 2013, ApJ, 764, 167), as well as new results on background subtraction and refinement of the procedure for precise timing of transient events in sparse data. Example demonstrations will include exploratory analysis of the Kepler light curve archive in a search for "star-tickling" signals from extraterrestrial civilizations. (The Cepheid Galactic Internet, Learned, Kudritzki, Pakvasa1, and Zee, 2008, arXiv: 0809.0339; Walkowicz et al., in progress).

The Barnes-Evans color-surface brightness relation: A preliminary theoretical interpretation

NASA Technical Reports Server (NTRS)

Shipman, H. L.

1980-01-01

Model atmosphere calculations are used to assess whether an empirically derived relation between V-R and surface brightness is independent of a variety of stellar paramters, including surface gravity. This relationship is used in a variety of applications, including the determination of the distances of Cepheid variables using a method based on the Beade-Wesselink method. It is concluded that the use of a main sequence relation between V-R color and surface brightness in determining radii of giant stars is subject to systematic errors that are smaller than 10% in the determination of a radius or distance for temperature cooler than 12,000 K. The error in white dwarf radii determined from a main sequence color surface brightness relation is roughly 10%.

Times of Maximum Light: The Passband Dependence

NASA Astrophysics Data System (ADS)

Joner, M. D.; Laney, C. D.

2004-05-01

We present UBVRIJHK light curves for the dwarf Cepheid variable star AD Canis Minoris. These data are part of a larger project to determine absolute magnitudes for this class of stars. Our figures clearly show changes in the times of maximum light, the amplitude, and the light curve morphology that are dependent on the passband used in the observation. Note that when data from a variety of passbands are used in studies that require a period analysis or that search for small changes in the pulsational period, it is easy to introduce significant systematic errors into the results. We thank the Brigham Young University Department of Physics and Astronmy for continued support of our research. We also acknowledge the South African Astronomical Observatory for time granted to this project.

Galactic Astronomy in the Ultraviolet

NASA Astrophysics Data System (ADS)

Rastorguev, A. S.; Sachkov, M. E.; Zabolotskikh, M. V.

2017-12-01

We propose a number of prospective observational programs for the ultraviolet space observatory WSO-UV, which seem to be of great importance to modern galactic astronomy. The programs include the search for binary Cepheids; the search and detailed photometric study and the analysis of radial distribution of UV-bright stars in globular clusters ("blue stragglers", blue horizontal-branch stars, RR Lyrae variables, white dwarfs, and stars with UV excesses); the investigation of stellar content and kinematics of young open clusters and associations; the study of spectral energy distribution in hot stars, including calculation of the extinction curves in the UV, optical and NIR; and accurate definition of the relations between the UV-colors and effective temperature. The high angular resolution of the observatory allows accurate astrometric measurements of stellar proper motions and their kinematic analysis.

Evidence for Pulsation-Driven Mass Loss from δ Cephei

NASA Astrophysics Data System (ADS)

Marengo, M.; Evans, N. R.; Matthews, L. D.; Bono, G.; Barmby, P.; Welch, D. L.; Romaniello, M.; Su, K. Y. L.; Fazio, G. G.; Huelsman, D.

We found the first direct evidence that the Cepheid class namesake, δ Cephei, is currently losing mass. These observations are based on data obtained with the Spitzer Space Telescope in the infrared, and with the Very Large Array in the radio. We found that δ Cephei is associated with a vast circumstellar structure, reminiscent of a bow shock. This structure is created as the wind from the star interacts with the local interstellar medium. We measure an outflow velocity of ≈ 35. 5 km s- 1 and a mass loss rate of ≈ 10- 7-10- 6 M ⊙ year- 1. The very low dust content of the outflow suggests that the wind is possibly pulsation-driven, rather than dust-driven as common for other classes of evolved stars.

Laboratory demonstration of Stellar Intensity Interferometry using a software correlator

NASA Astrophysics Data System (ADS)

Matthews, Nolan; Kieda, David

2017-06-01

In this talk I will present measurements of the spatial coherence function of laboratory thermal (black-body) sources using Hanbury-Brown and Twiss interferometry with a digital off-line correlator. Correlations in the intensity fluctuations of a thermal source, such as a star, allow retrieval of the second order coherence function which can be used to perform high resolution imaging and source geometry characterization. We also demonstrate that intensity fluctuations between orthogonal polarization states are uncorrelated but can be used to reduce systematic noise. The work performed here can readily be applied to existing and future Imaging Air-Cherenkov telescopes to measure spatial properties of stellar sources. Some possible candidates for astronomy applications include close binary star systems, fast rotators, Cepheid variables, and potentially even exoplanet characterization.

Stellar pulsations in beyond Horndeski gravity theories

NASA Astrophysics Data System (ADS)

Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya

2017-03-01

Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

Robust high-contrast companion detection from interferometric observations. The CANDID algorithm and an application to six binary Cepheids

NASA Astrophysics Data System (ADS)

Gallenne, A.; Mérand, A.; Kervella, P.; Monnier, J. D.; Schaefer, G. H.; Baron, F.; Breitfelder, J.; Le Bouquin, J. B.; Roettenbacher, R. M.; Gieren, W.; Pietrzyński, G.; McAlister, H.; ten Brummelaar, T.; Sturmann, J.; Sturmann, L.; Turner, N.; Ridgway, S.; Kraus, S.

2015-07-01

Context. Long-baseline interferometry is an important technique to spatially resolve binary or multiple systems in close orbits. By combining several telescopes together and spectrally dispersing the light, it is possible to detect faint components around bright stars in a few hours of observations. Aims: We provide a rigorous and detailed method to search for high-contrast companions around stars, determine the detection level, and estimate the dynamic range from interferometric observations. Methods: We developed the code CANDID (Companion Analysis and Non-Detection in Interferometric Data), a set of Python tools that allows us to search systematically for point-source, high-contrast companions and estimate the detection limit using all interferometric observables, i.e., the squared visibilities, closure phases and bispectrum amplitudes. The search procedure is made on a N × N grid of fit, whose minimum needed resolution is estimated a posteriori. It includes a tool to estimate the detection level of the companion in the number of sigmas. The code CANDID also incorporates a robust method to set a 3σ detection limit on the flux ratio, which is based on an analytical injection of a fake companion at each point in the grid. Our injection method also allows us to analytically remove a detected component to 1) search for a second companion; and 2) set an unbiased detection limit. Results: We used CANDID to search for the companions around the binary Cepheids V1334 Cyg, AX Cir, RT Aur, AW Per, SU Cas, and T Vul. First, we showed that our previous discoveries of the components orbiting V1334 Cyg and AX Cir were detected at >25σ and >13σ, respectively. The astrometric positions and flux ratios provided by CANDID for these two stars are in good agreement with our previously published values. The companion around AW Per is detected at more than 15σ with a flux ratio of f = 1.22 ± 0.30%, and it is located at ρ = 32.16 ± 0.29 mas and PA = 67.1 ± 0.3°. We made a possible detection of the companion orbiting RT Aur with f = 0.22 ± 0.11%, and at ρ = 2.10 ± 0.23 mas and PA = -136 ± 6°. It was detected at 3.8σ using the closure phases only, and so more observations are needed to confirm the dectection. No companions were detected around SU Cas and T Vul. We also set the detection limit for possible undetected companions around these stars. We found that there is no companion with a spectral type earlier than B7V, A5V, F0V, B9V, A0V, and B9V orbiting the Cepheids V1334 Cyg, AX Cir, RT Aur, AW Per, SU Cas, and T Vul, respectively. This work also demonstrates the capabilities of the MIRC and PIONIER instruments, which can reach a dynamic range of 1:200, depending on the angular distance of the companion and the (u,v) plane coverage. In the future, we plan to work on improving the sensitivity limits for realistic data through better handling of the correlations. The current version of the code is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A68

The performance of Luminex ARIES® Flu A/B & RSV and Cepheid Xpert® Flu/RSV XC for the detection of influenza A, influenza B, and respiratory syncytial virus in prospective patient samples.

PubMed

McMullen, Phillip; Boonlayangoor, Sue; Charnot-Katsikas, Angella; Beavis, Kathleen G; Tesic, Vera

2017-10-01

The demand for rapid, accurate viral testing has increased the number of assays available for the detection of viral pathogens. One of the newest FDA cleared platforms is the Luminex ARIES ® Flu A/B & RSV, which is a fully automated, real-time PCR-based assay used for detection of influenza A, influenza B, and respiratory syncytial virus (RSV). We sought to compare the performance of Luminex ARIES ® Flu A/B & RSV assay to the Cepheid Xpert ® Flu/RSV XC assay for rapid Flu and RSV testing. A series of consecutive nasopharyngeal specimens received in the clinical microbiology laboratory during peak influenza season at a major academic center in Chicago, IL, were prospectively tested, using both the ARIES ® Flu A/B & RSV and Xpert ® Flu/RSV XC assays, side by side. Discrepant results were tested on the BioFire FilmArray ® Respiratory Panel for resolution. A total of 143 consecutive nasopharyngeal specimens, obtained from patients ranging from six months to ninety-three years in age were received between January 1st, 2017 and March 21st, 2017. There was 96.6% agreement between the two assays for detection influenza A, 100% agreement for detection influenza B and RSV, and 98.9% agreement for negative results. The Xpert ® Flu/RSV XC performed with an average turn-around time of approximately 60min, compared to the ARIES ® Flu A/B & RSV of approximately 120min. Both assays were equally easy to perform, with a similar amount of hands-on technologist time for each platform. Overall, these results indicate that both tests are comparable in terms of result agreement and technical ease-of-use. The Xpert ® Flu/RSV XC assay did produce results with less turn-around-time, approximately 60min quicker than the ARIES ® Flu A/B & RSV. Copyright © 2017 Elsevier B.V. All rights reserved.

Distances to Nearby Galaxies via Long Period Variables

NASA Astrophysics Data System (ADS)

Jurcevic, John S.

A new method of measuring extra-Galactic distances has been developed based on the relationship between the luminosity of red supergiant variable (RSV) stars at optical wavelengths and the period of their luminosity variation. This period-luminosity (PL) relationship has been calibrated with RSVs from the Galactic Perseus OB1 association, the Large Magellanic Cloud, and M33 in the broadband optical R and I-bands, in a narrow part of the I-band at 8250 Å, and in the infrared K-band. By using these RSV PL relations, the distances to a sample of nearby galaxies (M101, NGC 2403, and NGC 2366) were determined. These galaxies were chosen because they had existing Cepheid based distances which allowed for a comparison between the two methods and provided a means of verifying the effectiveness of the RSV PL relation. The galaxies were also chosen to span a range of metallicity to allow an investigation of any effects due to metallicity differences. Photometry in the R-band was obtained over a period of three years for the galaxies with a coverage of 20, 17, and 13 epochs for M101, NGC 2403, and NGC 2366, respectively. By looking for red variable stars with periods in the range 100-1200 days the total number of RSVs discovered in the three galaxies was 123. Assuming a distance modulus for the Large Magellanic Cloud of 18.5 +/- 0.1 mag, single epoch I-band photometry of the RSVs was used to construct random phase PL relations resulting in distance moduli for M101, NGC 2403, and NGC 2366 of 29.40 +/- 0.16, 27.67 +/- 0.16, and 27.86 +/- 0.20 mag, respectively. Similarly, PL relations were also found using phase averaged R-band magnitudes which produced distance moduli of 29.09 +/- 0.16, 27.56 +/- 0.16, and 27.76 +/- 0.21 mag, respectively. These distances have been corrected for extinction by assuming values of E(B - V) = 0.10, 0.04, and 0.04 mag. The distances derived agree with those found via Cepheids which indicates that RSVs provide a very useful new method for measuring distances.

Time Domain Astronomy with the Harvard Plates: from Cepheids to DASCH

NASA Astrophysics Data System (ADS)

Grindlay, Jonathan E.

2014-06-01

The ~500,000 Harvard glass plate photographic negatives are the world’s largest and most complete (full sky; 107y time span) database for Time Domain Astronomy (TDA) on days-months-decades to century timescales. With plate fields of view ranging from 3o - 30o exposed quasi-randomly full sky from 1885 - 1992, any object is observed ~1000 - 3000 times, with limiting magnitudes ranging from B =12-18. I briefly review some of the colorful history of this massive plate-taking project and a few of the pivotal discoveries (e.g. the “Leavitt Law” for the Cepheid Period-Luminosity relation) made by visual studies of the plates by the true TDA pioneers, the likely <300 different visual users of the plates. I then describe our Digital Access to a Sky Century @ Harvard (DASCH) project to fully digitize and reduce this wealth of data 1 Pb) and provide it on spinning disk to the full astronomical community and public. Using the full-sky APASS catalog giving BVR magnitudes (for V ~9-17) as well as GSC2.3.2 for both fainter and brighter stars, DASCH does spatially resolved (0.25o -0.6o bins) photometric calibrations to derive B magnitudes with rm 0.1mag over the full plate and over the (typically) ~6-8 different principal plate series (telescopes and plate scales) covering any given object, along with ~0.3-1 arcsec astrometry (depending on plate scale) for each stellar object averaged over ~1year. The high speed/precision scanner, plate processing, and analysis pipeline have now enabled the first data releases (DR1-DR3) of 12 to cover full sky and already enabled a wealth of new discoveries. I describe a few examples, such as: K2III giants with decadal variations; a new class of Symbiotic novae; ~50-100y recurrence times for black hole X-ray binary outbursts; and QPOs from 3C273. The DASCH data are increasingly available 15% now; 100% in 3.5y) for TDA on largely unexplored timescales. We are grateful to NSF for support with grants AST-0407380, AST-0909073 and AST-1313370.

The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

NASA Astrophysics Data System (ADS)

Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

2018-01-01

Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr, while RR Lyrae can have delay-times < 10 Gyrs. These observations cannot be explained by models using mass and metallicity alone. In future projects, I will apply the DTD technique to constrain the supergiant and pre-supernova evolutionary models.

A Detailed Survey of Pulsating Variables in Five Globular Clusters (Abstract)

NASA Astrophysics Data System (ADS)

Murphy, B. W.

2016-12-01

(Abstract only) Globular clusters are ideal laboratories for conducting a stellar census. Of particular interest are pulsating variables, which provide astronomers with a tool to probe the properties of the stars and the cluster. We observed each of five globular clusters hundreds to thousands of times over a time span ranging from 2 to 4 years in B, V, and I filters using the SARA 0.6-meter telescope located at Cerro Tololo Interamerican Observatory and the 0.9-meter telescope located at Kitt Peak, Arizona. The images were analyzed using difference image analysis to identify and produce light curves of all variables found in each cluster. In total we identified 377 variables with 140 of these being newly discovered increasing the number of known variables stars in these clusters by 60%. Of the total we have identified 319 RR Lyrae variables (193 RR0, 18 RR01, 101 RR1, 7 RR2), 9 SX Phe stars, 5 Cepheid variables, 11 eclipsing variables, and 33 long period variables. For IC4499 we identified 64 RR0, 18 RR01, 14 RR1, 4 RR2, 1 SX Phe, 1 eclipsing binary, and 2 long period variables. For NGC4833 we identified 10 RR0, 7 RR1, 3 RR2, 6 SX Phe, 5 eclipsing binaries, and 9 long period variables. For NGC6171 (M107) we identified 14 RR0, 7 RR1, and 1 SX Phe. For NGC6402 (M14) we identified 55 RR0, 57 RR1, 1 RR2, 1 SX Phe, 6 Cepheids, 1 eclipsing binary, and 15 long period variables. For NGC6584 we identified 50 RR0, 16 RR1, 4 eclipsing binaries, and 7 long period variables. From our extensive data set we were able to obtain sufficient temporal and complete phase coverage of the RR Lyrae variables. This has allowed us not only to properly classify each of the RR Lyrae variables but also to use Fourier decomposition of the B, V, and I light curves to further analyze the properties of the variable stars and hence the physical properties of each globular cluster.

Hubble Watches Super Star Create Holiday Light Show

NASA Image and Video Library

2017-12-08

This festive NASA Hubble Space Telescope image resembles a holiday wreath made of sparkling lights. The bright southern hemisphere star RS Puppis, at the center of the image, is swaddled in a gossamer cocoon of reflective dust illuminated by the glittering star. The super star is ten times more massive than our sun and 200 times larger. RS Puppis rhythmically brightens and dims over a six-week cycle. It is one of the most luminous in the class of so-called Cepheid variable stars. Its average intrinsic brightness is 15,000 times greater than our sun’s luminosity. The nebula flickers in brightness as pulses of light from the Cepheid propagate outwards. Hubble took a series of photos of light flashes rippling across the nebula in a phenomenon known as a "light echo." Even though light travels through space fast enough to span the gap between Earth and the moon in a little over a second, the nebula is so large that reflected light can actually be photographed traversing the nebula. By observing the fluctuation of light in RS Puppis itself, as well as recording the faint reflections of light pulses moving across the nebula, astronomers are able to measure these light echoes and pin down a very accurate distance. The distance to RS Puppis has been narrowed down to 6,500 light-years (with a margin of error of only one percent). The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. Acknowledgment: H. Bond (STScI and Pennsylvania State University) NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

On the Radial Abundance Gradients of Europium and Oxygen of Stars Inside the Disk of a Simulated Milky Way

NASA Astrophysics Data System (ADS)

Ruiz-Rocha, Krystal; Montes, Gabriela; Ramirez-Ruiz, Enrico

2017-01-01

Studies of galaxy evolution and formation through simulations and observations have yielded valuable insight into the life of stars. Abundance gradients, in particular, provide useful information about the element assembly history in the Milky Way. To study these gradients we use data from a simulation titled Eris which has been constructed with the goal of reproducing the properties of the Milky Way, to find the gradients of stars located in the disk that have been enriched by Supernovae and Neutron Star Mergers. We compare these gradients to the observations acquired from looking at Cepheids and field stars in the disk of our Milky Way. We also aim to understand whether radial metallicity gradients can be used to differentiate between Neutron Star Merger versus Type II Supernovae enrichment.

Xpert Flu for point-of-care diagnosis of human influenza in industrialized countries.

PubMed

Salez, Nicolas; Nougairede, Antoine; Ninove, Laetitia; Zandotti, Christine; de Lamballerie, Xavier; Charrel, Rémi N

2014-05-01

Respiratory infections, particularly those caused by influenza viruses, represent the third-most important cause of death in the world due to infectious diseases. Nevertheless, despite the enormous publicity attracted by epidemics due to these viruses, laboratory diagnosis, documentation and recording of respiratory diseases is still unsatisfactory. Available diagnostic tests capable of providing results rapidly are either limited and insufficiently sensitive or highly sensitive and specific but insufficiently rapid. Considerable investment and research efforts have been made towards the development of new diagnostics for influenza A and B viruses and the Xpert(®) Flu assay (Cepheid(®), CA, USA) has emerged as one of the most promising. In this article, we review current knowledge of the Xpert Flu test, discuss its potential value as a point-of-care test and outline the potential leads for future development.

Variable Stars with the Kepler Space Telescope

NASA Astrophysics Data System (ADS)

Molnár, L.; Szabó, R.; Plachy, E.

2016-12-01

The Kepler space telescope has revolutionized our knowledge about exoplanets and stars and is continuing to do so in the K2 mission. The exquisite photometric precision, together with the long, uninterrupted observations opened up a new way to investigate the structure and evolution of stars. Asteroseismology, the study of stellar oscillations, allowed us to investigate solar-like stars, and to peer into the insides of red giants and massive stars. But many discoveries have been made about classical variable stars, too, ranging from pulsators like Cepheids and RR Lyraes to eclipsing binary stars and cataclysmic variables, and even supernovae. In this review, which is far from an exhaustive summary of all results obtained with Kepler, we collected some of the most interesting discoveries, and ponder on the role for amateur observers in this golden era of stellar astrophysics.

Stellar pulsations in beyond Horndeski gravity theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya, E-mail: sakstein@physics.upenn.edu, E-mail: mka1g13@soton.ac.uk, E-mail: kazuya.koyama@port.ac.uk

Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify themore » best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.« less

Population of the lower part of the instability strip: Delta Scuti stars and dwarf Cepheids (or AI Velorum)

NASA Technical Reports Server (NTRS)

Auvergne, M.; Baglin, A.; Lecontel, J. M.; Valtier, J. C.

1980-01-01

Some of the properties of the atmospheric variations in delta Scuti stars were investigated with emphasis on the amplitude and the shape of both light curves and radial velocity curves. It is shown that these curves are small and rapidly variable in the case of dwarf Scuti stars; for the evolved stars the situation is more complex. The relation between variables and nonvariables, and also the results on abundances in the atmospheres of these stars were surveyed with respect to the hydrodynamics of their envelopes. The abundance anomalies of Am stars were qualitatively examined. The coexistence of abundance anomalies and variability among giants were also studied. Attempts were made to relate the variability to the hydrogen ionization zone in an envelope deprived of helium. Specific results are reported.

Radio Astronomers Set New Standard for Accurate Cosmic Distance Measurement

NASA Astrophysics Data System (ADS)

1999-06-01

A team of radio astronomers has used the National Science Foundation's Very Long Baseline Array (VLBA) to make the most accurate measurement ever made of the distance to a faraway galaxy. Their direct measurement calls into question the precision of distance determinations made by other techniques, including those announced last week by a team using the Hubble Space Telescope. The radio astronomers measured a distance of 23.5 million light-years to a galaxy called NGC 4258 in Ursa Major. "Ours is a direct measurement, using geometry, and is independent of all other methods of determining cosmic distances," said Jim Herrnstein, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. The team says their measurement is accurate to within less than a million light-years, or four percent. The galaxy is also known as Messier 106 and is visible with amateur telescopes. Herrnstein, along with James Moran and Lincoln Greenhill of the Harvard- Smithsonian Center for Astrophysics; Phillip Diamond, of the Merlin radio telescope facility at Jodrell Bank and the University of Manchester in England; Makato Inoue and Naomasa Nakai of Japan's Nobeyama Radio Observatory; Mikato Miyoshi of Japan's National Astronomical Observatory; Christian Henkel of Germany's Max Planck Institute for Radio Astronomy; and Adam Riess of the University of California at Berkeley, announced their findings at the American Astronomical Society's meeting in Chicago. "This is an incredible achievement to measure the distance to another galaxy with this precision," said Miller Goss, NRAO's Director of VLA/VLBA Operations. "This is the first time such a great distance has been measured this accurately. It took painstaking work on the part of the observing team, and it took a radio telescope the size of the Earth -- the VLBA -- to make it possible," Goss said. "Astronomers have sought to determine the Hubble Constant, the rate of expansion of the universe, for decades. This will in turn lead to an estimate of the age of the universe. In order to do this, you need an unambiguous, absolute distance to another galaxy. We are pleased that the NSF's VLBA has for the first time determined such a distance, and thus provided the calibration standard astronomers have always sought in their quest for accurate distances beyond the Milky Way," said Morris Aizenman, Executive Officer of the National Science Foundation's (NSF) Division of Astronomical Sciences. "For astronomers, this measurement is the golden meter stick in the glass case," Aizenman added. The international team of astronomers used the VLBA to measure directly the motion of gas orbiting what is generally agreed to be a supermassive black hole at the heart of NGC 4258. The orbiting gas forms a warped disk, nearly two light-years in diameter, surrounding the black hole. The gas in the disk includes water vapor, which, in parts of the disk, acts as a natural amplifier of microwave radio emission. The regions that amplify radio emission are called masers, and work in a manner similar to the way a laser amplifies light emission. Determining the distance to NGC 4258 required measuring motions of extremely small shifts in position of these masers as they rotate around the black hole. This is equivalent to measuring an angle one ten-thousandth the width of a human hair held at arm's length. "The VLBA is the only instrument in the world that could do this," said Moran. "This work is the culmination of a 20-year effort at the Harvard Smithsonian Center for Astrophysics to measure distances to cosmic masers," said Irwin Shapiro, Director of that institution. Collection of the data for the NGC 4258 project was begun in 1994 and was part of Herrnstein's Ph.D dissertation at Harvard University. Previous observations with the VLBA allowed the scientists to measure the speed at which the gas is orbiting the black hole, some 39 million times more massive than the Sun. They did this by observing the amount of change in the wavelength of the radio waves caused by the Doppler effect. The gas is orbiting at a speed of more than two million miles per hour. The orbiting disk of gas is almost edge-on as viewed from Earth. The astronomers obtained the orbital speeds and the positions of the masers in the disk by measuring the Doppler Shift of the masers at the disk's sides, where the gas is moving almost directly away from the Earth on one side and toward the Earth on the other. Measurements of the different orbital speeds at different distances from the black hole, made in 1994, allowed them to determine the mass of the black hole. These measurements required the great resolving power, or ability to see fine detail, of the VLBA. This picture of an orbiting disk was confirmed by measurement of centrifugal acceleration, according to the scientists. The newest observations were focused on maser "spots" on the near edge of the disk, where orbital motion shifts their position in the sky, though by an extremely small amount. The VLBA, however, was able to detect this extremely small movement, called "proper motion" by astronomers. This motion was detected by observing the galaxy at 4- to 8-month intervals over more than three years. "By knowing the speed at which the gas is orbiting and then measuring its motion across the sky, we can use plain old trigonometry to calculate the distance," Greenhill said. He added, however, that "you need a bit of luck to be able to do this. So far, we know of only 22 galaxies with water masers in their nuclear regions that also are relatively nearby. Then, the geometry of the disk, relative to Earth, has to be right to allow us to make such a measurement" The VLBA measurement of NGC 4258's distance differs significantly from the distance to that galaxy determined through HST observations of Cepheid variable stars. Using such stars, a team of astronomers led by University of California-Berkeley scientist Eyal Maoz has made preliminary and as-yet unpublished estimates of the distance to NGC 4258 as either 27 or 29 million light-years, depending on assumptions about the characteristics of this type of star in that galaxy. Other Cepheid-based galaxy distances were used to calculate the expansion rate of the universe, called the Hubble Constant, announced by a team of HST observers last week. "This difference could mean that there may be more uncertainty in Cepheid-determined distances than people have realized," said Moran. "Providing this directly-determined distance to one galaxy -- a distance that can serve as a milestone -- should be helpful in determining distances to other galaxies, and thus the Hubble Constant and the size and age of the universe" The VLBA is a system of ten radio-telescope antennas, each 25 meters (82 feet) in diameter, stretching some 5,000 miles from Mauna Kea in Hawaii to St. Croix in the U.S. Virgin Islands. Operated from NRAO's Array Operations Center in Socorro, NM, the VLBA offers astronomers the greatest resolving power of any telescope anywhere. The NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Background information: Determining Cosmic Distances Determining cosmic distances obviously is vital to understanding the size of the universe. In turn, knowing the size of the universe is an important step in determining its age. "The size puts a limit on how much expansion could have occurred since the Big Bang, and thus tells us something about the age," said Moran. However, determining cosmic distances has proven to be a particularly thorny problem for astronomers. In the third century, B.C., the Greek astronomer Aristarchus devised a method of using trigonometry to determine the relative distances of the Moon and Sun, but in practice his method was difficult to use. Though a great first step, he missed the mark by a factor of 20. It wasn't until 1761 that trigonometric methods produced a relatively accurate distance to Venus, thus calibrating the size of the Solar System. The first accurate distance to another star was determined trigonometrically by Friedrich Wilhelm Bessel in 1838. Traditional trigonometric methods of measuring celestial distances require extremely accurate measurement of an object's position in the sky. By measuring the apparent shift in an object's position, called parallax, caused by the Earth's journey around the Sun, the distance to the object can be calculated. Until recent years, such measurements were limited by the atmosphere's degrading effect on optical observations. Recently, the Hipparcos satellite has measured stellar distances accurate to within 10 percent out to about 300 light-years. Beyond the range of parallax measurements, astronomers were forced to use indirect methods of estimating distances. Many of these methods make presumptions about the intrinsic brightness of objects, then estimate the distance by measuring how much fainter they appear on Earth. The faintness is presumed to be caused by the distance, according to the inverse-square law (doubling of the distance reduces brightness by a factor of four). Thus, stars of a particular spectral class are all presumed to be of the same intrinsic brightness. Such techniques have been used to estimate distances of stars out to about 25,000 light-years, still not far enough to estimate distance beyond our own Milky Way Galaxy. Early in the 20th Century, Henrietta Leavitt, of Harvard College Observatory, discovered that variable-brightness stars known as Cepheid variables showed a useful property -- the longer their pulsation periods, the brighter they are intrinsically. Once the absolute distance to a few Cepheids was determined, these stars were used to measure distances beyond the Milky Way. In the 1920s, Edwin Hubble used Cepheid-variable distance determinations to show that, contrary to then-prevalent opinion, many "nebulae" were, in fact, other galaxies far distant from our own. Distances determined using Cepheid variables, along with measurements of the Doppler shift of other galaxies' light, allowed Hubble to discover the expansion of the universe, the basis of the Big Bang theory. The Cepheid technique still is one of the building blocks of the extragalactic distance scale. However, because of absorption of light by interstellar dust and subtle differences among the stars themselves, this technique is subject to considerable uncertainty. Similarly, techniques that use a specific type of supernova (Type Ia) presumed to be of uniform intrinsic brightness, while able to make distance estimates farther than the Cepheid technique, still are subject to uncertainties. The NSF's VLBA, with resolving power hundreds of times better than even the Hubble Space Telescope, has allowed direct trigonometric techniques to be applied in measuring much greater distances than ever before. The VLBA measured the expansion of the shell of exploding debris from the supernova SN 1993J in the galaxy M81, 11 million light- years away. This information, combined with optical observations that measured the speed of the expanding debris by the Doppler shift of its emitted spectral lines, allowed a trigonometric calculation of the distance to M81. Now, with the VLBA's direct measurement of motions in the gas disk surrounding NGC 4258, trigonometric measurement, not subject to the vagaries of dust absorption and other uncertaintities in an object's brightness, has been extended to a distance of more than 23 million light-years.

Detection of periodicity based on independence tests - III. Phase distance correlation periodogram

NASA Astrophysics Data System (ADS)

Zucker, Shay

2018-02-01

I present the Phase Distance Correlation (PDC) periodogram - a new periodicity metric, based on the Distance Correlation concept of Gábor Székely. For each trial period, PDC calculates the distance correlation between the data samples and their phases. PDC requires adaptation of the Székely's distance correlation to circular variables (phases). The resulting periodicity metric is best suited to sparse data sets, and it performs better than other methods for sawtooth-like periodicities. These include Cepheid and RR-Lyrae light curves, as well as radial velocity curves of eccentric spectroscopic binaries. The performance of the PDC periodogram in other contexts is almost as good as that of the Generalized Lomb-Scargle periodogram. The concept of phase distance correlation can be adapted also to astrometric data, and it has the potential to be suitable also for large evenly spaced data sets, after some algorithmic perfection.

Type Ia supernovae as standard candles

NASA Technical Reports Server (NTRS)

Branch, David; Miller, Douglas L.

1993-01-01

The distribution of absolute blue magnitudes among Type Ia supernovae (SNs Ia) is studied. Supernovae were used with well determined apparent magnitudes at maximum light and parent galaxies with relative distances determined by the Tully-Fisher or Dn - sigma techniques. The mean absolute blue magnitude is given and the observational dispersion is only sigma(MB) 0.36, comparable to the expected combined errors in distance, apparent magnitude, and extinction. The mean (B-V) color at maximum light is 0.03 +/- 0.04, with a dispersion sigma(B-V) = 0.20. The Cepheid-based distance to IC 4182, the parent galaxy of the normal and unextinguished Type Ia SN 1937C, leads to a Hubble constant of H(0) + 51 +/- 12 km/s Mpc. The existence of a few SNs Ia that appear to have been reddened and dimmed by dust in their parent galaxies does not seriously compromise the use of SNs Ia as distance indicators.

Evaluation of the Xpert Flu test and comparison with in-house real-time RT-PCR assays for detection of influenza virus from 2008 to 2011 in Marseille, France.

PubMed

Salez, N; Ninove, L; Thirion, L; Gazin, C; Zandotti, C; de Lamballerie, X; Charrel, R N

2012-04-01

Rapid documentation of respiratory specimens can have an impact on the management of patients and their relatives in terms of preventive and curative measures. We compared the results of the Xpert(®) Flu assay (Cepheid) with three real-time RT-PCR assays using 127 nasopharyngeal samples, of which 75 were positive for influenza A (with 52 identified as A/H1N1-2009) and 52 were positive for influenza B. The Xpert(®) Flu assay presented a quasi-absence of non-interpretable tests, and showed sensitivity and specificity of 100% and 100% for Flu A, 98.4% and 100% for A/H1N1-2009, and 80.7% and 100% for Flu B. © 2012 The Authors. Clinical Microbiology and Infection © 2012 European Society of Clinical Microbiology and Infectious Diseases.

All-Sky Census of Variable Stars from the ATLAS Survey

NASA Astrophysics Data System (ADS)

Heinze, Aren Nathaniel; Tonry, John; Denneau, Larry; Stalder, Brian

2018-01-01

The Asteroid Terrestrial-Impact Last Alert Survey uses two custom-built 0.5 meter telescopes to scan the whole accessible sky down to magnitude 19.5 every two nights, with a cadence optimized to detect small asteroids on their 'final plunge' toward impact with Earth. This cadence is also well suited to the detection of variable stars with a huge range of periods and properties, while ATLAS' use of two filters provides additional scientific depth. From the first two years of ATLAS data we have constructed a catalog of several hundred thousand variable objects with periods from one hour to hundreds of days. These include RR Lyrae stars, Cepheids, eclipsing binaries, spotted stars, ellipsoidal variables, Miras; and other objects both regular and irregular. We describe the construction of this catalog, including our multi-step confirmation process for genuine variables; some big-picture scientific conclusions; and prospects for more detailed results.

Variable Stars in the Field of the Hydra II Ultra-Faint Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Vivas, Anna Katherina; Olsen, Knut A.; Blum, Robert D.; Nidever, David L.; Walker, Alistair R.; Martin, Nicolas; Besla, Gurtina; Gallart, Carme; Van Der Marel, Roeland P.; Majewski, Steven R.; Munoz, Ricardo; Kaleida, Catherine C.; Saha, Abhijit; Conn, Blair; Jin, Shoko

2016-06-01

We searched for variable stars in Hydra II, one of the recently discovered ultra-faint dwarf satellites of the Milky Way, using gri time-series obtained with the Dark Energy Camera (DECam) at Cerro Tololo Inter-American Observatory, Chile. We discovered one RR Lyrae star in the galaxy which was used to derive a distance of 154±8 kpc to this system and to re-calculate its absolute magnitude and half-light radius.A comparison with other RR Lyrae stars in ultra-faint systems indicates similar pulsational properties among them, which are different to those found among halo field stars and those in the largest of the Milky Way satellites. We also report the discovery of 31 additional short period variables in the field of view (RR Lyrae, SX Phe, eclipsing binaries, and a likely anomalous cepheid) which are likely not related with Hydra II.

Pulsating stars in ω Centauri. Near-IR properties and period-luminosity relations

NASA Astrophysics Data System (ADS)

Navarrete, Camila; Catelan, Márcio; Contreras Ramos, Rodrigo; Alonso-García, Javier; Gran, Felipe; Dékány, István; Minniti, Dante

2017-09-01

ω Centauri (NGC 5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of ω Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete J and KS near-IR catalog of variable stars in the field of ω Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands.

Measuring cosmological parameters

PubMed Central

Freedman, Wendy L.

1998-01-01

In this review, the status of measurements of the matter density (Ωm), the vacuum energy density or cosmological constant (ΩΛ), the Hubble constant (H0), and the ages of the oldest measured objects (t0) are summarized. Three independent types of methods for measuring the Hubble constant are considered: the measurement of time delays in multiply imaged quasars, the Sunyaev–Zel’dovich effect in clusters, and Cepheid-based extragalactic distances. Many recent independent dynamical measurements are yielding a low value for the matter density (Ωm ≈ 0.2–0.3). A wide range of Hubble constant measurements appear to be converging in the range of 60–80 km/sec per megaparsec. Areas where future improvements are likely to be made soon are highlighted—in particular, measurements of anisotropies in the cosmic microwave background. Particular attention is paid to sources of systematic error and the assumptions that underlie many of the measurement methods. PMID:9419315

HARPS-N high spectral resolution observations of Cepheids I. The Baade-Wesselink projection factor of δ Cep revisited

NASA Astrophysics Data System (ADS)

Nardetto, N.; Poretti, E.; Rainer, M.; Fokin, A.; Mathias, P.; Anderson, R. I.; Gallenne, A.; Gieren, W.; Graczyk, D.; Kervella, P.; Mérand, A.; Mourard, D.; Neilson, H.; Pietrzynski, G.; Pilecki, B.; Storm, J.

2017-01-01

Context. The projection factor p is the key quantity used in the Baade-Wesselink (BW) method for distance determination; it converts radial velocities into pulsation velocities. Several methods are used to determine p, such as geometrical and hydrodynamical models or the inverse BW approach when the distance is known. Aims: We analyze new HARPS-N spectra of δ Cep to measure its cycle-averaged atmospheric velocity gradient in order to better constrain the projection factor. Methods: We first apply the inverse BW method to derive p directly from observations. The projection factor can be divided into three subconcepts: (1) a geometrical effect (p0); (2) the velocity gradient within the atmosphere (fgrad); and (3) the relative motion of the optical pulsating photosphere with respect to the corresponding mass elements (fo-g). We then measure the fgrad value of δ Cep for the first time. Results: When the HARPS-N mean cross-correlated line-profiles are fitted with a Gaussian profile, the projection factor is pcc-g = 1.239 ± 0.034(stat.) ± 0.023(syst.). When we consider the different amplitudes of the radial velocity curves that are associated with 17 selected spectral lines, we measure projection factors ranging from 1.273 to 1.329. We find a relation between fgrad and the line depth measured when the Cepheid is at minimum radius. This relation is consistent with that obtained from our best hydrodynamical model of δ Cep and with our projection factor decomposition. Using the observational values of p and fgrad found for the 17 spectral lines, we derive a semi-theoretical value of fo-g. We alternatively obtain fo-g = 0.975 ± 0.002 or 1.006 ± 0.002 assuming models using radiative transfer in plane-parallel or spherically symmetric geometries, respectively. Conclusions: The new HARPS-N observations of δ Cep are consistent with our decomposition of the projection factor. The next step will be to measure p0 directly from the next generation of visible interferometers. With these values in hand, it will be possible to derive fo-g directly from observations. Table A.1 is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A73

Polarimetric measures of selected variable stars

NASA Astrophysics Data System (ADS)

Elias, N. M., II; Koch, R. H.; Pfeiffer, R. J.

2008-10-01

Aims: The purpose of this paper is to summarize and interpret unpublished optical polarimetry for numerous program stars that were observed over the past decades at the Flower and Cook Observatory (FCO), University of Pennsylvania. We also make the individual calibrated measures available for long-term comparisons with new data. Methods: We employ three techniques to search for intrinsic variability within each dataset. First, when the observations for a given star and filter are numerous enough and when a period has been determined previously via photometry or spectroscopy, the polarimetric measures are plotted versus phase. If a statistically significant pattern appears, we attribute it to intrinsic variability. Second, we compare means of the FCO data to means from other workers. If they are statistically different, we conclude that the object exhibits long-term intrinsic variability. Third, we calculate the standard deviation for each program star and filter and compare it to the standard deviation estimated from comparable polarimetric standards. If the standard deviation of the program star is at least three times the value estimated from the polarimetric standards, the former is considered intrinsically variable. All of these statements are strengthened when variability appears in multiple filters. Results: We confirm the existence of an electron-scattering cloud at L1 in the β Per system, and find that LY Aur and HR 8281 possess scattering envelopes. Intrinsic polarization was detected for Nova Cas 1993 as early as day +3. We detected polarization variability near the primary eclipse of 32 Cyg. There is marginal evidence for polarization variability of the β Cepheid type star γ Peg. The other objects of this class exhibited no variability. All but one of the β Cepheid objects (ES Vul) fall on a tight linear relationship between linear polarization and E(B-V), in spite of the fact that the stars lay along different lines of sight. This dependence falls slightly below the classical upper limit of Serkowski, Mathewson, and Ford. The table, which contains the polarization observations of the program stars discussed in this paper, is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/489/911

WetLab-2: Tools for Conducting On-Orbit Quantitative Real-Time Gene Expression Analysis on ISS

NASA Technical Reports Server (NTRS)

Parra, Macarena; Almeida, Eduardo; Boone, Travis; Jung, Jimmy; Schonfeld, Julie

2014-01-01

The objective of NASA Ames Research Centers WetLab-2 Project is to place on the ISS a research platform capable of conducting gene expression analysis via quantitative real-time PCR (qRT-PCR) of biological specimens sampled or cultured on orbit. The project has selected a Commercial-Off-The-Shelf (COTS) qRT-PCR system, the Cepheid SmartCycler and will fly it in its COTS configuration. The SmartCycler has a number of advantages including modular design (16 independent PCR modules), low power consumption, rapid ramp times and the ability to detect up to four separate fluorescent channels at one time enabling multiplex assays that can be used for normalization and to study multiple genes of interest in each module. The team is currently working with Cepheid to enable the downlink of data from the ISS to the ground and provide uplink capabilities for programming, commanding, monitoring, and instrument maintenance. The project has adapted commercial technology to design a module that can lyse cells and extract RNA of sufficient quality and quantity for use in qRT-PCR reactions while using a housekeeping gene to normalize RNA concentration and integrity. The WetLab-2 system is capable of processing multiple sample types ranging from microbial cultures to animal tissues dissected on-orbit. The ability to conduct qRT-PCR on-orbit eliminates the confounding effects on gene expression of reentry stresses and shock acting on live cells and organisms or the concern of RNA degradation of fixed samples. The system can be used to validate terrestrial analyses of samples returned from ISS by providing on-orbit gene expression benchmarking prior to sample return. The ability to get on orbit data will provide investigators with the opportunity to adjust experiment parameters for subsequent trials based on the real-time data analysis without need for sample return and re-flight. Researchers will also be able to sample multigenerational changes in organisms. Finally, the system can be used for analysis of air, surface, water, and clinical samples to monitor environmental contaminants and crew health. The verification flight of the instrument is scheduled to launch on SpaceX-7 in June 2015.

Development Status of the WetLab-2 Project: New Tools for On-orbit Real-time Quantitative Gene Expression.

NASA Technical Reports Server (NTRS)

Jung, Jimmy; Parra, Macarena P.; Almeida, Eduardo; Boone, Travis; Chinn, Tori; Ricco, Antonio; Souza, Kenneth; Hyde, Liz; Rukhsana, Yousuf; Richey, C. Scott

2013-01-01

The primary objective of NASA Ames Research Centers WetLab-2 Project is to place on the ISS a research platform to facilitate gene expression analysis via quantitative real-time PCR (qRT-PCR) of biological specimens grown or cultured on orbit. The WetLab-2 equipment will be capable of processing multiple sample types ranging from microbial cultures to animal tissues dissected on-orbit. In addition to the logistical benefits of in-situ sample processing and analysis, conducting qRT-PCR on-orbit eliminates the confounding effects on gene expression of reentry stresses and shock acting on live cells and organisms. The system can also validate terrestrial analyses of samples returned from ISS by providing quantitative on-orbit gene expression benchmarking prior to sample return. The ability to get on orbit data will provide investigators with the opportunity to adjust experimental parameters for subsequent trials based on the real-time data analysis without need for sample return and re-flight. Finally, WetLab-2 can be used for analysis of air, surface, water, and clinical samples to monitor environmental contaminants and crew health. The verification flight of the instrument is scheduled to launch on SpaceX-5 in Aug. 2014.Progress to date: The WetLab-2 project completed a thorough study of commercially available qRT-PCR systems and performed a downselect based on both scientific and engineering requirements. The selected instrument, the Cepheid SmartCycler, has advantages including modular design (16 independent PCR modules), low power consumption, and rapid ramp times. The SmartCycler has multiplex capabilities, assaying up to four genes of interest in each of the 16 modules. The WetLab-2 team is currently working with Cepheid to modify the unit for housing within an EXPRESS rack locker on the ISS. This will enable the downlink of data to the ground and provide uplink capabilities for programming, commanding, monitoring, and instrument maintenance. The project is currently designing a module that will lyse the cells and extract RNA of sufficient quality for use in qRT-PCR reactions while using a housekeeping gene to normalize RNA concentration and integrity. Current testing focuses on two promising commercial products and chemistries that allow for RNA extraction with minimal complexity and crew time.

HUBBLE SPACE TELESCOPE ON TRACK FOR MEASURING THE EXPANSION RATE OF THE UNIVERSE

NASA Technical Reports Server (NTRS)

2002-01-01

Two international teams of astronomers, using NASA's Hubble Space Telescope, are reporting major progress in converging on an accurate measurement of the Universe's rate of expansion -- a value which has been debated for over half a century. These new results yield ranges for the age of the Universe from 9-12 billion years, and 11-14 billion years, respectively. The goal of the project is to measure the Hubble Constant to ten percent accuracy. The Hubble Space Telescope Key Project team, an international group of over 20 astronomers, is led by Wendy Freedman of Carnegie Observatories, Pasadena, CA, Robert Kennicutt, University of Arizona, Tucson, AZ, and Jeremy Mould, Mount Stromlo and Siding Springs Observatory, Australia. The group's interim results, announced at a meeting held at the Space Telescope Science Institute (STScI) in Baltimore, Maryland, are consistent with their preliminary result, announced in 1994, of 80 kilometers per second per megaparsec (km/sec/Mpc), based on observations of a galaxy in the Virgo cluster. 'We have five different ways of measuring the Hubble Constant with HST,' said Dr. Freedman. 'The results are coming in between 68 and 78 km/sec/Mpc.' (For example, at an expansion rate of 75 km/sec/Mpc, galaxies appear to be receding from us at a rate of 162,000 miles per hour for every 3.26 million light-years farther out we look). Two months ago, a second team, led by Allan Sandage, also of the Carnegie Observatories, Abhijit Saha, STScI, Gustav Tammann and Lukas Labhardt, Astronomical Institute, University of Basel, Duccio Macchetto and Nino Panagia, STScI/European Space Agency, reported a slower expansion rate of 57 km/sec/Mpc. The value of the Hubble Constant allows astronomers to calculate the expansion age of the Universe, the time elapsed since the Big Bang. Astronomers have been arguing recently whether the time since the Big Bang is consistent with the ages of the oldest stars. The ages are calculated from combining the expansion rate with an estimate of how much matter is in space. The younger age values from each team assume the Universe is at a critical density where it contains just enough matter to expand indefinitely. The higher age estimates are calculated based on a low density of matter in space. (See 'Science Background' for more information on the expanding Universe.) 'A point of great interest is whether the age of the Universe arrived at this way is really older than the independently derived ages of the oldest stars,' said Saha, an investigator on both Hubble teams. 'The numbers lean on the side that the stellar ages are a little lower, or that the hypothesis that we live in a critical density universe needs to be questioned,' said Saha. 'As further results accumulate over the next few years, we hope to tighten the constraints on these issues.' THE OBSERVATIONS The Key Project team is midway along in their three-year program to derive the expansion rate of the Universe based on precise distance measurements to galaxies. They have now measured Cepheid distances to a dozen galaxies, and are about halfway through their overall program. The Key Project team also presented a preliminary estimate of the distance to the Fornax cluster of galaxies. The estimate was obtained through the detection and measurement with the Hubble Space Telescope of pulsating stars known as Cepheid variables found in the Fornax cluster. The Fornax cluster is measured to be approximately as far away as the Virgo cluster of galaxies -- about 60 million light-years. The Key Project team member who led this effort, Caltech astronomer Barry Madore said, 'This cluster allows us to make independent estimates of the expansion rate of the Universe using a number of different techniques. All of these methods are now in excellent agreement. With Fornax we are now at turning point in this field.' The team is measuring Cepheid distances to the Virgo and Fornax clusters of galaxies as a complementary test. Their strategy is to compare and contrast expansion numbers from a variety of distance indicators. The Key Project team is systematically looking into a variety of methods for measuring distances. They are using Cepheids in a large sample to tie into five or six 'secondary methods'. One such secondary method relates the total luminosity of a galaxy to the rate at which the galaxy is spinning, the Tully-Fisher relation. Another secondary method makes use of a special class of exploding star known as a type Ia supernova. This phase of the Hubble Constant research will be completed within another two years. In contrast, the Sandage team focused on a single secondary distance indicator, one of the same indicators also used by the Key Project team, the type Ia supernova. Sandage maintains that these stars are 'standard bombs' according to theory. He suggests that when they explode they all reach exactly the same intrinsic brightness. This would make them extremely reliable 'standard candles,' (objects with a well-known intrinsic brightness) visible 1,000 times farther away than Cepheids. Since they are intrinsically brighter than any other standard candle, they offer the opportunity for an accurate measurement of the Universe's overall expansion by looking out the farthest. Although both teams are still in disagreement over the precise rate at which the Universe is expanding and on how old it is, they are optimistic that their estimates will continue to converge with further observations and analysis. * * * * Members of the Key Project team include W. Freedman (Carnegie Observatories), R. Kennicutt (University of Arizona), J. Mould (Mount Stromlo and Siding Springs Observatories, Australia), L. Ferrarese (Johns Hopkins University), H. Ford (Johns Hopkins University), J. Graham (Department of Terrestrial Magnetism), M. Han (University of Wisconsin), P. Harding (University of Arizona), J. Hoessel (University of Wisconsin), J. Huchra (Smithsonian/Harvard University), S. Hughes (Royal Greenwich Observatory, Cambridge), G. Illingworth (University of California, Santa Cruz), B.F. Madore (IPAC/Caltech), R. Phelps (Carnegie Observatories), A. Saha (Space Telescope Science Institute), N. Silbermann (IPAC), P. Stetson (Dominion Astrophysical Observatory), and S. Sakai (IPAC). Members of the Sandage team include A. Sandage (Carnegie Observatories), A. Saha (Space Telescope Science Institute), G.A. Tammann, and L. Labhardt (Astronomical Institute, University of Basel), F.D. Macchetto and N. Panagia (Space Telescope Science Institute/European Space Agency).

Chaos in the Music of the Spheres

NASA Astrophysics Data System (ADS)

Buchler, J. Robert; Kolláth, Zoltan; Cadmus, Robert

2002-07-01

The light curves (time series of the radiated energy) of most large amplitude, pulsating stars such as the well known Cepheid stars are regular. However, a smaller group of variable stars that are located next to them in the Hertzsprung-Russell diagram undergoes irregular light variations and exhibits irregular radial velocities as well. The mechanism behind this irregular behavior was a long standing mystery. A flow reconstruction technique based on the observed lightcurves of six separate stars shows that their underlying dynamics is chaotic and low dimensional (d = 4). Furthermore, we present evidence that the physical mechanism behind the behavior is the nonlinear interaction of just two pulsation eigenmodes. In a generalized Shil'nikov scenario, the pulsation energy alternates continuously, but irregularly between a lower frequency mode that is linearly unstable and thus growing, and a stable overtone that gets entrained through a low order resonance (2:1), but that wants to decay. The flow reconstruction from the stellar light curve thus yields interesting physical insight into the pulsation mechanism.

The impact of large-scale, long-term optical surveys on pulsating star research

NASA Astrophysics Data System (ADS)

Soszyński, Igor

2017-09-01

The era of large-scale photometric variability surveys began a quarter of a century ago, when three microlensing projects - EROS, MACHO, and OGLE - started their operation. These surveys initiated a revolution in the field of variable stars and in the next years they inspired many new observational projects. Large-scale optical surveys multiplied the number of variable stars known in the Universe. The huge, homogeneous and complete catalogs of pulsating stars, such as Cepheids, RR Lyrae stars, or long-period variables, offer an unprecedented opportunity to calibrate and test the accuracy of various distance indicators, to trace the three-dimensional structure of the Milky Way and other galaxies, to discover exotic types of intrinsically variable stars, or to study previously unknown features and behaviors of pulsators. We present historical and recent findings on various types of pulsating stars obtained from the optical large-scale surveys, with particular emphasis on the OGLE project which currently offers the largest photometric database among surveys for stellar variability.

Impact of Distance Determinations on Galactic Structure. I. Young and Intermediate-Age Tracers

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki; Bono, Giuseppe; Chen, Xiaodian; de Grijs, Richard; Inno, Laura; Nishiyama, Shogo

2018-06-01

Here we discuss impacts of distance determinations on the Galactic disk traced by relatively young objects. The Galactic disk, ˜40 kpc in diameter, is a cross-road of studies on the methods of measuring distances, interstellar extinction, evolution of galaxies, and other subjects of interest in astronomy. A proper treatment of interstellar extinction is, for example, crucial for estimating distances to stars in the disk outside the small range of the solar neighborhood. We'll review the current status of relevant studies and discuss some new approaches to the extinction law. When the extinction law is reasonably constrained, distance indicators found in today and future surveys are telling us stellar distribution and more throughout the Galactic disk. Among several useful distance indicators, the focus of this review is Cepheids and open clusters (especially contact binaries in clusters). These tracers are particularly useful for addressing the metallicity gradient of the Galactic disk, an important feature for which comparison between observations and theoretical models can reveal the evolution of the disk.

Period-luminosity relations for red supergiant variables - II. The distance to M101

NASA Astrophysics Data System (ADS)

Jurcevic, J. S.; Pierce, M. J.; Jacoby, G. H.

2000-04-01

We report the discovery of 42 red supergiant variables (RSVs) in the late-type spiral galaxy M101. Periods for the luminosity variation of these RSVs were determined from 20 epochs of ground-based CCD photometry in the Kron-Cousins R band obtained with the KPNO 2.1-m and WIYN 3.5-m telescopes over a span of three years. The periods found were in the range 200-1300days. Using the relationship between the RSV periods and their luminosity in the Kron-Cousins I band, we estimate a reddening-corrected distance modulus to M101 of 29.40+/-0.16mag (based on a distance modulus of 18.5+/-0.1mag for the Large Magellanic Cloud). This distance is consistent with the Hubble Space Telescope Key Project Cepheid distances of 29.34+/-0.17mag for the outer field of M101 and 29.21+/-0.17mag for the inner field.

The Optical Gravitational Lensing Experiment. The Catalog of Stellar Proper Motions toward the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Poleski, R.; Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Ulaczyk, K.

2012-03-01

We present a catalog of over 6.2 million stars with measured proper motions. All these stars are observed in the direction of the Magellanic Clouds within the brightness range 12

Element-abundance inhomogeneity of interstellar matter as it follows from the chemical composition of the O-type supergiants HDE 226868 (Cyg X-1) and *alpha; Cam

NASA Astrophysics Data System (ADS)

Bochkarev, N. G.; Karitskaya, E. A.; Shimanskii, V. V.; Galazutdinov, G. A.

2013-10-01

By means of synthetic spectrum modeling with non-LTE effects, we determined element abundances in the atmospheres of two O supergiants with similar physical characteristics: HDE 226868 (the optical component of Cyg X-1) and α Cam. These objects are situated at the distance about 2.5 kpc from each other. HDE 226868 has higher abundances compared to α Cam. The differences of Al, S, Zn, and averaged CNO abundances are within 0.15-0.30 dex. This is in a good qualitative agreement with the inhomogeneity of the heavy-element distribution over the Galactic disk derived by Luck et al. (2006) from Cepheids. This finding confirms the inhomogeneity of chemical-element distribution on the scale of 2 kpc and is in agreement with the concept of interstellar-matter superclouds preserving their intrinsic particularities on a time scale in excess of 1 Gyr.

Spectroscopy of chromospheric lines of giants in the globular cluster

NASA Technical Reports Server (NTRS)

Dupree, A. K.; Hartmann, Lee; Smith, Graeme H.; Rodgers, A. W.; Roberts, W. H.; Zucker, D. B.

1994-01-01

Spectroscopic observations of chromospheric transitions (Mg II, H-alpha, and Ca II K) from two red giants (A31 and A59) in the globular cluster NGC 6572 were made with the Goddard High Resolution Spectrograph on the Hubble Space Telescope and the coude spectrograph of the 1.9 m telescope at the Mount Stromlo Observatory. These measurements give evidence for chromospheric activity and outward motions within the atmospheres. The surface flux of the Mg II emission is comparable to that in disk population giants of similar (B-V) color. The Mg II profiles are asymmetric, which is most likely caused by absorption in an expanding stellar atmosphere and/or by possible interstellar features. Notches are found in the core of the H-alpha line of A59, which are similar to those found in Cepheids. This suggests that shocks are present in the atmosphere of A59 and indicates that hydrodynamic phenomena are influencing the levvel of chromospheric emission and producing upper atmospheric motions which may lead to mass loss.

A Detailed Study of the Variable Stars in Five Galactic Globular Clusters: IC4499, NGC4833, NGC6171 (M107), NGC6402 (M14), and NGC6584

NASA Astrophysics Data System (ADS)

Murphy, Brian W.; Darragh, Andrew; Hettinger, Paul; Hibshman, Adam; Johnson, Elliott W.; Liu, Z. J.; Pajkos, Michael A.; Stephenson, Hunter R.; Vondersaar, John R.; Conroy, Kyle E.; McCombs, Thayne A.; Reinhardt, Erik D.; Toddy, Joseph

2015-08-01

We present the results of an extensive study intended to search for and properly classify the variable stars in five galactic globular clusters. Each of the five clusters was observed hundreds to thousands of times over a time span ranging from 2 to 4 years using the SARA 0.6m located at Cerro Tololo Interamerican Observatory. The images were analyzed using the image subtract method of Alard (2000) to identify and produce light curves of all variables found in each cluster. In total we identified 373 variables with 140 of these being newly discovered increasing the number of known variables stars in these clusters by 60%. Of the total we have identified 312 RR Lyrae variables (187 RR0, 18 RR01, 99 RR1, 8 RR2), 9 SX Phe stars, 6 Cepheid variables, 11 eclipsing variables, and 35 long period variables. For IC4499 we identified 64 RR0, 18 RR01, 14 RR1, 4 RR2, 1 SX Phe, 1 eclipsing binary, and 2 long period variables. For NGC4833 we identified 10 RR0, 7 RR1, 2 RR2, 6 SX Phe, 5 eclipsing binaries, and 9 long period variables. For NGC6171 (M107) we identified 13 RR0, 7 RR1, and 1 SX Phe. For NGC6402 (M14) we identified 52 RR0, 56 RR1, 1 RR2, 1 SX Phe, 6 Cepheids, 1 eclipsing binary, and 15 long period variables. For NGC6584 we identified 48 RR0, 15 RR1, 1 RR2, 5 eclipsing binaries, and 9 long period variables. Using the RR Lyrae variables we found the mean V magnitude of the horizontal branch to be VHB = ⟨V ⟩RR = 17.63, 15.51, 15.72, 17.13, and 16.37 magnitudes for IC4499, NGC4833, NGC6171 (M107), NGC6402 (M14), and NGC6584, respectively. From our extensive data set we were able to obtain sufficient temporal and complete phase coverage of the RR Lyrae variables. This has allowed us not only to properly classify each of the RR Lyrae variables but also to use Fourier decomposition of the light curves to further analyze the properties of the variable stars and hence physical properties of each clusters. In this poster we will give the temperature, radius, stellar mass, metallicity, and helium abundance of the set of RR Lyrae variable stars found in each of the five globular clusters.

A Portrait of One Hundred Thousand and One Galaxies

NASA Astrophysics Data System (ADS)

2002-08-01

Rich and Inspiring Experience with NGC 300 Images from the ESO Science Data Archive Summary A series of wide-field images centred on the nearby spiral galaxy NGC 300 , obtained with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory , have been combined into a magnificent colour photo. These images have been used by different groups of astronomers for various kinds of scientific investigations, ranging from individual stars and nebulae in NGC 300, to distant galaxies and other objects in the background. This material provides an interesting demonstration of the multiple use of astronomical data, now facilitated by the establishment of extensively documented data archives, like the ESO Science Data Archive that now is growing rapidly and already contains over 15 Terabyte. Based on the concept of Astronomical Virtual Observatories (AVOs) , the use of archival data sets is on the rise and provides a large number of scientists with excellent opportunities for front-line investigations without having to wait for precious observing time. In addition to presenting a magnificent astronomical photo, the present account also illustrates this important new tool of the modern science of astronomy and astrophysics. PR Photo 18a/02 : WFI colour image of spiral galaxy NGC 300 (full field) . PR Photo 18b/02 : Cepheid stars in NGC 300 PR Photo 18c/02 : H-alpha image of NGC 300 PR Photo 18d/02 : Distant cluster of galaxies CL0053-37 in the NGC 300 field PR Photo 18e/02 : Dark matter distribution in CL0053-37 PR Photo 18f/02 : Distant, reddened cluster of galaxies in the NGC 300 field PR Photo 18g/02 : Distant galaxies, seen through the outskirts of NGC 300 PR Photo 18h/02 : "The View Beyond" ESO PR Photo 18a/02 ESO PR Photo 18a/02 [Preview - JPEG: 400 x 412 pix - 112k] [Normal - JPEG: 1200 x 1237 pix - 1.7M] [Hi-Res - JPEG: 4000 x 4123 pix - 20.3M] Caption : PR Photo 18a/02 is a reproduction of a colour-composite image of the nearby spiral galaxy NGC 300 and the surrounding sky field, obtained in 1999 and 2000 with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory. See the text for details about the many different uses of this photo. Smaller areas in this large field are shown in Photos 18b-h/02 , cf. below. The High-Res version of this image has been compressed by a factor 4 (2 x 2 pixel rebinning) to reduce it to a reasonably transportable size. Technical information about this and the other photos is available at the end of this communication. Located some 7 million light-years away, the spiral galaxy NGC 300 [1] is a beautiful representative of its class, a Milky-Way-like member of the prominent Sculptor group of galaxies in the southern constellation of that name. NGC 300 is a big object in the sky - being so close, it extends over an angle of almost 25 arcmin, only slightly less than the size of the full moon. It is also relative bright, even a small pair of binoculars will unveil this magnificent spiral galaxy as a hazy glowing patch on a dark sky background. The comparatively small distance of NGC 300 and its face-on orientation provide astronomers with a wonderful opportunity to study in great detail its structure as well as its various stellar populations and interstellar medium. It was exactly for this purpose that some images of NGC 300 were obtained with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory. This advanced 67-million pixel digital camera has already produced many impressive pictures, some of which are displayed in the WFI Photo Gallery [2]. With its large field of view, 34 x 34 arcmin 2 , the WFI is optimally suited to show the full extent of the spiral galaxy NGC 300 and its immediate surroundings in the sky, cf. PR Photo 18a/02 . NGC 300 and "Virtual Astronomy" In addition to being a beautiful sight in its own right, the present WFI-image of NGC 300 is also a most instructive showcase of how astronomers with very different research projects nowadays can make effective use of the same observations for their programmes . The idea to exploit one and the same data set is not new, but thanks to rapid technological developments it has recently developed into a very powerful tool for the astronomers in their continued quest to understand the Universe. This kind of work has now become very efficient with the advent of a fully searchable data archive from which observational data can then - after the expiry of a nominal one-year proprietary period for the observers - be made available to other astronomers. The ESO Science Data Archive was established some years ago and now encompasses more than 15 Terabyte [3]. Normally, the identification of specific data sets in such a large archive would be a very difficult and time-consuming task. However, effective projects and software "tools" like ASTROVIRTEL and Querator now allow the users quickly to "filter" large amounts of data and extract those of their specific interest. Indeed, "Archival Astronomy" has already led to many important discoveries, cf. the ASTROVIRTEL list of publications. There is no doubt that "Virtual Astronomical Observatories" will play an increasingly important role in the future, cf. ESO PR 26/01. The present wide-field images of NGC 300 provide an impressive demonstration of the enormous potential of this innovative approach. Some of the ways they were used are explained below. Cepheids in NGC 300 and the cosmic distance scale ESO PR Photo 18b/02 ESO PR Photo 18b/02 [Preview - JPEG: 468 x 400 pix - 112k] [Full-Res - JPEG: 1258 x 1083 pix - 1.6M] Caption : PR Photo 18b/02 shows some of the Cepheid type stars in the spiral galaxy NGC 300 (at the centre of the markers), as they were identified by Wolfgang Gieren and collaborators during the research programme for which the WFI images of NGC 300 were first obtained. In this area of NGC 300, there is also a huge cloud of ionized hydrogen (a "HII shell"). It measures about 2000 light-years in diameter, thus dwarfing even the enormous Tarantula Nebula in the LMC, also photographed with the WFI (cf. ESO PR Photos 14a-g/02 ). The largest versions ("normal" or "full-res") of this and the following photos are shown with their original pixel size, demonstrating the incredible amount of detail visible on one WFI image. Technical information about this photo is available below. In 1999, Wolfgang Gieren (Universidad de Concepcion, Chile) and his colleagues started a search for Cepheid-type variable stars in NGC 300. These stars constitute a key element in the measurement of distances in the Universe. It has been known since many years that the pulsation period of a Cepheid-type star depends on its intrinsic brightness (its "luminosity"). Thus, once its period has been measured, the astronomers can calculate its luminosity. By comparing this to the star's apparent brightness in the sky, and applying the well-known diminution of light with the second power of the distance, they can obtain the distance to the star. This fundamental method has allowed some of the most reliable measurements of distances in the Universe and has been essential for all kinds of astrophysics, from the closest stars to the remotest galaxies. Previous to Gieren's new project, only about a dozen Cepheids were known in NGC 300. However, by regularly obtaining wide-field WFI exposures of NGC 300 from July 1999 through January 2000 and carefully monitoring the apparent brightness of its brighter stars during that period, the astronomers detected more than 100 additional Cepheids . The brightness variations (in astronomical terminology: "light curves") could be determined with excellent precision from the WFI data. They showed that the pulsation periods of these Cepheids range from about 5 to 115 days. Some of these Cepheids are identified on PR Photo 18b/02 , in the middle of a very crowded field in NGC 300. When fully studied, these unique observational data will yield a new and very accurate distance to NGC 300, making this galaxy a future cornerstone in the calibration of the cosmic distance scale . Moreover, they will also allow to understand in more detail how the brightness of a Cepheid-type star depends on its chemical composition, currently a major uncertainty in the application of the Cepheid method to the calibration of the extragalactic distance scale. Indeed, the effect of the abundance of different elements on the luminosity of a Cepheid can be especially well measured in NGC 300 due to the existence of large variations of these abundances in the stars located in the disk of this galaxy. Gieren and his group, in collaboration with astronomers Fabio Bresolin and Rolf Kudritzki (Institute of Astronomy, Hawaii, USA) are currently measuring the variations of these chemical abundances in stars in the disk of NGC 300, by means of spectra of about 60 blue supergiant stars, obtained with the FORS multi-mode instruments at the ESO Very Large Telescope (VLT) on Paranal. These stars, that are among the optically brightest in NGC 300, were first identified in the WFI images of this galaxy obtained in different colours - the same that were used to produce PR Photo 18a/02 . The nature of those stars was later spectroscopically confirmed at the VLT. As an important byproduct of these measurements, the luminosities of the blue supergiant stars in NGC 300 will themselves be calibrated (as a new cosmic "standard candle"), taking advantage of their stellar wind properties that can be measured from the VLT spectra. The WFI Cepheid observations in NGC 300, as well as the VLT blue supergiant star observations, form part of a large research project recently initiated by Gieren and his group that is concerned with the improvement of various stellar distance indicators in nearby galaxies (the "ARAUCARIA" project ). Clues on star formation history in NGC 300 ESO PR Photo 18c/02 ESO PR Photo 18c/02 [Preview - JPEG: 440 x 400 pix - 63k] [Normal - JPEG: 1200 x 1091 pix - 664k] [Full-Res - JPEG: 5515 x 5014 pix - 14.3M] Caption : PR Photo 18c/02 displays NGC 300, as seen through a narrow optical filter (H-alpha) in the red light of hydrogen atoms. A population of intrinsically bright and young stars turned "on" just a few million years ago. Their radiation and strong stellar winds have shaped many of the clouds of ionized hydrogen gas ("HII shells") seen in this photo. The "rings" near some of the bright stars are caused by internal reflections in the telescope. Technical information about this photo is available below.. But there is much more to discover on these WFI images of NGC 300! The WFI images obtained in several broad and narrow band filters from the ultraviolet to the near-infrared spectral region (U, B, V, R, I and H-alpha) allow a detailed study of groups of heavy, hot stars (known as "OB associations") and a large number of huge clouds of ionized hydrogen ("HII shells") in this galaxy. Corresponding studies have been carried out by Gieren's group, resulting in the discovery of an amazing number of OB associations, including a number of giant associations. These investigations, taken together with the observed distribution of the pulsation periods of the Cepheids, allow to better understand the history of star formation in NGC 300. For example, three distinct peaks in the number distribution of the pulsation periods of the Cepheids seem to indicate that there have been at least three different bursts of star formation within the past 100 million years. The large number of OB associations and HII shells ( PR Photo 18c/02 ) furthermore indicate the presence of a numerous, very young stellar population in NGC 300, aged only a few million years. Dark matter and the observed shapes of distant galaxies In early 2002, Thomas Erben and Mischa Schirmer from the "Institut für Astrophysik and extraterrestrische Forschung" ( IAEF , Universität Bonn, Germany), in the course of their ASTROVIRTEL programme, identified and retrieved all available broad-band and H-alpha images of NGC 300 available in the ESO Science Data Archive. Most of these have been observed for the project by Gieren and his colleagues, described above. However, the scientific interest of the German astronomers was very different from that of their colleagues and they were not at all concerned about the main object in the field, NGC 300. In a very different approach, they instead wanted to study those images to measure the amount of dark matter in the Universe, by means of the weak gravitational lensing effect produced by distant galaxy clusters. Various observations, ranging from the measurement of internal motions ("rotation curves") in spiral galaxies to the presence of hot X-ray gas in clusters of galaxies and the motion of galaxies in those clusters, indicate that there is about ten times more matter in the Universe than what is observed in the form of stars, gas and galaxies ("luminous matter"). As this additional matter does not emit light at any wavelengths, it is commonly referred to as "dark" matter - its true nature is yet entirely unclear. Insight into the distribution of dark matter in the Universe can be gained by looking at the shapes of images of very remote galaxies, billions of light-years away, cf. ESO PR 24/00. Light from such distant objects travels vast distances through space before arriving here on Earth, and whenever it passes heavy clusters of galaxies, it is bent a little due to the associated gravitational field. Thus, in long-exposure, high-quality images, this "weak lensing" effect can be perceived as a coherent pattern of distortion of the images of background galaxies. Gravitational lensing in the NGC 300 field ESO PR Photo 18d/02 ESO PR Photo 18d/02 [Preview - JPEG: 400 x 495 pix - 82k] [Full-Res - JPEG: 1304 x 1615 pix - 3.2M] Caption : PR Photo 18d/02 shows the distant cluster of galaxies CL0053-37 , as imaged on the WFI photo of the NGC 300 sky field. The elongated distribution of the cluster galaxies, as well as the presence of two large, early-type elliptical galaxies indicate that this cluster is still in the process of formation. Some of the galaxies appear to be merging. From the measured redshift ( z = 0.1625), a distance of about 2.1 billion light-years is deduced. Technical information about this photo is available below. ESO PR Photo 18e/02 ESO PR Photo 18e/02 [Preview - JPEG: 400 x 567 pix - 89k] [Normal - JPEG: 723 x 1024 pix - 424k] Caption : PR Photo 18e/02 is a "map" of the dark matter distribution (black contours) in the cluster of galaxies CL0053-37 (shown in PR Photo 18d/02 ), as obtained from the weak lensing effects detected in the WFI images, and the X-ray flux (green contours) taken from the All-Sky Survey carried out by the ROSAT satellite observatory. The distribution of galaxies resembles the elongated, dark-matter profile. Because of ROSAT's limited image sharpness (low "angular resolution"), it cannot be entirely ruled out that the observed X-ray emission is due to an active nucleus of a galaxy in CL0053-37, or even a foreground stellar binary system in NGC 300. The WFI NGC 300 images appeared promising for gravitational lensing research because of the exceptionally long total exposure time. Although the large foreground galaxy NGC 300 would block the light of tens of thousands of galaxies in the background, a huge number of others would still be visible in the outskirts of this sky field, making a search for clusters of galaxies and associated lensing effects quite feasible. To ensure the best possible image sharpness in the combined image, and thus to obtain the most reliable measurements of the shapes of the background objects, only red (R-band) images obtained under the best seeing conditions were combined. In order to provide additional information about the colours of these faint objects, a similar approach was adopted for images in the other bands as well. The German astronomers indeed measured a significant lensing effect for one of the galaxy clusters in the field ( CL0053-37 , see PR Photo 18d/02 ); the images of background galaxies around this cluster were noticeably distorted in the direction tangential to the cluster center. Based on the measured degree of distortion, a map of the distribution of (dark) matter in this direction was constructed ( PR Photo 18e/02 ). The separation of unlensed foreground (bluer) and lensed background galaxies (redder) greatly profited from the photometric measurements done by Gieren's group in the course of their work on the Cepheids in NGC 300. Assuming that the lensed background galaxies lie at a mean redshift of 1.0, i.e. a distance of 8 billion light-years, a mass of about 2 x 10 14 solar masses was obtained for the CL0053-37 cluster. This lensing analysis in the NGC 300 field is part of the Garching-Bonn Deep Survey (GaBoDS) , a weak gravitational lensing survey led by Peter Schneider (IAEF). GaBoDS is based on exposures made with the WFI and until now a sky area of more than 12 square degrees has been imaged during very good seeing conditions. Once complete, this investigation will allow more insight into the distribution and cosmological evolution of galaxy cluster masses, which in turn provide very useful information about the structure and history of the Universe. One hundred thousand galaxies ESO PR Photo 18f/02 ESO PR Photo 18f/02 [Preview - JPEG: 400 x 526 pix - 93k] [Full-Res - JPEG: 756 x 994 pix - 1.0M] Caption : PR Photo 18f/02 shows a group of galaxies , seen on the NGC 300 images. They are all quite red and their similar colours indicate that they must be about equally distant. They probably constitute a distant cluster, now in the stage of formation. Technical information about this photo is available below. ESO PR Photo 18g/02 ESO PR Photo 18g/02 [Preview - JPEG: 469 x 400 pix - xxk] [Full-Res - JPEG: 1055 x 899 pix - 968k] Caption : PR Photo 18g/02 shows an area in the outer regions of NGC 300. Disks of spiral galaxies are usually quite "thin" (some hundred light-years), as compared to their radial extent (tens of thousands of light-years across). In areas where only small amounts of dust are present, it is possible to see much more distant galaxies right through the disk of NGC 300 , as demonstrated by this image. Technical information about this photo is available below. ESO PR Photo 18h/02 ESO PR Photo 18h/02 [Preview - JPEG: 451 x 400 pix - 89k] [Normal - JPEG: 902 x 800 pix - 856k] [Full-Res - JPEG: 2439 x 2163 pix - 6.0M] Caption : PR Photo 18h/02 is an astronomers' joy ride to infinity. Such a rarely seen view of our universe imparts a feeling of the vast distances in space. In the upper half of the image, the outer region of NGC 300 is resolved into innumerable stars, while in the lower half, myriads of galaxies - a thousand times more distant - catch the eye. In reality, many of them are very similar to NGC 300, they are just much more remote. In addition to allowing a detailed investigation of dark matter and lensing effects in this field, the present, very "deep" colour image of NGC 300 invites to perform a closer inspection of the background galaxy population itself . No less than about 100,000 galaxies of all types are visible in this amazing image. Three known quasars ([ICS96] 005342.1-375947, [ICS96] 005236.1-374352, [ICS96] 005336.9-380354) with redshifts 2.25, 2.35 and 2.75, respectively, happen to lie inside this sky field, together with many interacting galaxies, some of which feature tidal tails. There are also several groups of highly reddened galaxies - probably distant clusters in formation, cf. PR Photo 18f/02 . Others are seen right through the outer regions of NGC 300, cf. PR Photo 18g/02 . More detailed investigations of the numerous galaxies in this field are now underway. From the nearby spiral galaxy NGC 300 to objects in the young Universe, it is all there, truly an astronomical treasure trove, cf. PR Photo 18h/02 ! Notes [1]: "NGC" means "New General Catalogue" (of nebulae and clusters) that was published in 1888 by J.L.E. Dreyer in the "Memoirs of the Royal Astronomical Society". [2]: Other colour composite images from the Wide-Field Imager at the MPG/ESO 2.2-m telescope at the La Silla Observatory are available at the ESO Outreach website at http://www.eso.org/esopia"bltxt">Tarantula Nebula in the LMC, cf. ESO PR Photos 14a-g/02. [3]: 1 Terabyte = 10 12 byte = 1000 Gigabyte = 1 million million byte. Technical information about the photos PR Photo 18a/02 and all cutouts were made from 110 WFI images obtained in the B-band (total exposure time 11.0 hours, rendered as blue), 105 images in the V-band (10.4 hours, green), 42 images in the R-band (4.2 hours, red) and 21 images through a H-alpha filter (5.1 hours, red). In total, 278 images of NGC 300 have been assembled to produce this colour image, together with about as many calibration images (biases, darks and flats). 150 GB of hard disk space were needed to store all uncompressed raw data, and about 1 TB of temporary files was produced during the extensive data reduction. Parallel processing of all data sets took about two weeks on a four-processor Sun Enterprise 450 workstation. The final colour image was assembled in Adobe Photoshop. To better show all details, the overall brightness of NGC 300 was reduced as compared to the outskirts of the field. The (red) "rings" near some of the bright stars originate from the H-alpha frames - they are caused by internal reflections in the telescope. The images were prepared by Mischa Schirmer at the Institut für Astrophysik und Extraterrestrische Forschung der Universität Bonn (IAEF) by means of a software pipeline specialised for reduction of multiple CCD wide-field imaging camera data. The raw data were extracted from the public sector of the ESO Science Data Archive. The extensive observations were performed at the ESO La Silla Observatory by Wolfgang Gieren, Pascal Fouque, Frederic Pont, Hermann Boehnhardt and La Silla staff, during 34 nights between July 1999 and January 2000. Some additional observations taken during the second half of 2000 were retrieved by Mischa Schirmer and Thomas Erben from the ESO archive. CD-ROM with full-scale NGC 300 image soon available PR Photo 18a/02 has been compressed by a factor 4 (2 x 2 rebinning). For PR Photos 18b-h/02 , the largest-size versions of the images are shown at the original scale (1 pixel = 0.238 arcsec). A full-resolution TIFF-version (approx. 8000 x 8000 pix; 200 Mb) of PR Photo 18a/02 will shortly be made available by ESO on a special CD-ROM, together with some other WFI images of the same size. An announcement will follow in due time.

The Chemical Composition and Period Change Rate of the Anomalous Cepheid V19 in NGC 54661.

NASA Astrophysics Data System (ADS)

McCarthy, James K.; Nemec, James M.

1997-06-01

A detailed model atmosphere and chemical composition analysis has been made of the brightest known anomalous Cepheid, V19 in the globular cluster NGC 5466. Our study is based on 30 minute CCD echelle spectrograms (4300 <= λ <= 6630 Å) acquired in 1995 and 1996 with the HIRES spectrograph on the 10 m Keck-I telescope. New CCD photometric observations from 1992 to 1996 suggest that V19 was near minimum light at the time each spectrum was acquired, a conclusion that is also supported by spectral analyses using Kurucz model atmospheres. The line widths in the HIRES spectra are quite narrow, with v sin i <= 18 km s-1. Given that V19 is the first anomalous Cepheid (AC) to be observed at such high spectroscopic resolution, the rotational velocity is significant in view of the hypothesis that ACs are coalesced binaries. The upper limit on v sin i for V19 appears to contradict this hypothesis, unless sin i is very small. Radial velocities derived from each HIRES spectrogram, vr = +111.0 +/- 0.1 km s-1 in 1995 August and vr = +110.9 +/- 0.2 km s-1 in 1996 June, are smaller than would be expected at minimum light based on previous, though much less precise, radial velocity measurements. The lack of a detectable change in vr over 311 days, if reinforced by continued monitoring, would also call into question the evolutionary scenario that explains V19 as the result of mass transfer in a close binary system presently composed of an AC plus a white dwarf, unless the orbit is in the plane of the sky. The atmospheric parameters of V19 at the time of the 1995 HIRES observation (φ = 0.51 +/- 0.03) are estimated to have been Teff = 6450 +/- 50 K, log g = 2.55 +/- 0.15 dex, and microturbulence ξ = 2.5 +/- 0.2 km s-1, in agreement with photometric light-cycle measurements near minimum light. The spectroscopic estimates are based on theoretical line profile fits to the observed wings of the H I Balmer lines Hγ, Hβ, and Hα, together with an investigation of the ionization equilibria of Fe I:Fe II and Mg I:Mg II, taking into account the effects of non-LTE. Adopting these atmospheric parameters and a distance modulus for NGC 5466 of (m - M)0 = 16.01 +/- 0.10 gives a spectroscopic mass estimate for V19 of 1.66+0.7-0.5 \\Mscrsolar, which is significantly larger than the mass of the main-sequence turnoff stars in NGC 5466. Equivalent width measurements of 26 Fe II lines give an iron abundance of [Fe/H] = -1.92 +/- 0.05 dex. This value is consistent with previous determinations of the mean metallicity for NGC 5466 from integrated spectra and from lower S/N echelle spectroscopy of individual red giant stars, to within the quoted uncertainties. The absence of the strongest lines of Zn I suggests a possible underabundance of this element. No evidence is found for strong s-process enrichment, with [Ba/H] = -2.45 +/- 0.13 dex from four Ba II lines, consistent with our upper limits [La/H] <= -1.93, [Ce/H] <= -1.69, and [Nd/H] <= -1.75, based on the marginal detections or absences of the strongest La II, Ce II, and Nd II lines in the spectral regions recorded. Calcium is enhanced with respect to iron, with [Ca/Fe] = +0.22 dex derived from 16 Ca I lines and 56 Fe I lines, under the assumption of LTE; other α-elements (e.g., Mg, Si, S, and Ti) are also enhanced relative to iron. In general, the abundance ratios to iron closely match the normal, well-established pattern for metal-poor stars. This result further constrains evolutionary models attempting to explain anomalous Cepheid stars like V19 as the result of coalescence or mass transfer in an evolved binary system; unlike the velocity evidence, this abundance constraint applies regardless of inclination. Finally, the rate of change of V19's pulsation period was investigated using photometry of new CCD frames taken in 1995 and 1996 with the Dominion Astrophysical Observatory 1.8 m telescope and taken in 1996 with the Hale 5 m telescope at Palomar Observatory. This new photometry was combined with unpublished 1992 and 1993 data (courtesy of M. Corwin) and all earlier photometry available from the literature. If the period is assumed to be constant, then the new O-C diagram suggests a revised period of P = 0d.821307. However, if the O-C data are fitted allowing P to change linearly with time, then the derived period change rate, β = dP/dt = -0d.28 +/- 0d.19 Myr-1, would imply that V19 is evolving toward hotter temperature, and its pulsation period at the present epoch (1996; JD = 2,450,250) is instead P = 0d.8213010 +/- 0d.0000003. In either case, the residuals in the O-C diagram suggest a possible long-term (Porb ~ 10,000 day) binary motion. Any such companion would be far too distant to have contributed to the mass of V19 through Roche lobe overflow. Based in part on observations obtained at the 200 inch (5 m) Hale Telescope at Palomar Observatory, which is operated by the California Institute of Technology in scientific partnership with Cornell University and the Jet Propulsion Laboratory. Based in part on observations made at the Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada

Eighteenth-Century Observations of Algol: The First Suggestion of an Exoplanet?

NASA Astrophysics Data System (ADS)

French, Linda M.

2017-10-01

In November of 1782, 18-year old John Goodricke of York, England, was amazed to observe the star Algol (Beta Persei) dim by more than one magnitude and then return to full brightness over a period of seven hours. Goodricke and his mentor, Edward Pigott, speculated that the dimming could only have been caused by a "dark body" passing in front of Algol. Over the succeeding months, the two were able to refine the period between what we now know to be eclipses to 2.87 days. They would determine the periods of other variable stars, including the first two Cepheid variables known. Yet in their lifetime, their suggestion that Algol's variation was due to an eclipse was not accepted. Most astronomers believed the variations were due to spots on the surface of a single star. Only a century later, with the advent of astronomical spectroscopy, was Algol's true nature revealed. Goodricke and Pigott's work is one of the first studies of stellar variation; their methods and occasional pitfalls are ones to which modern astronomers can relate.

A New Measurement of the Expansion Rate of the Universe, Evidence of New Physics?

NASA Astrophysics Data System (ADS)

Riess, Adam

2018-01-01

The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was possible with the first generations of Hubble Telescope instruments. A streamlined distance ladder constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provide 2.4% precision and offer the means to do even better. By steadily improving the precision and accuracy of the Hubble constant, we now see evidence for significant deviations from the standard model, referred to as LambdaCDM, and thus the exciting chance, if true, of discovering new fundamental physics such as exotic dark energy, a new relativistic particle, or a small curvature to name a few possibilities. I will review recent and expected progress in the near term.

The Hubble Constant from Supernovae

NASA Astrophysics Data System (ADS)

Saha, Abhijit; Macri, Lucas M.

The decades-long quest to obtain a precise and accurate measurement of the local expansion rate of the universe (the Hubble Constant or H0) has greatly benefited from the use of supernovae (SNe). Starting from humble beginnings (dispersions of ˜ 0.5 mag in the Hubble flow in the late 1960s/early 1970s), the increasingly more sophisticated understanding, classification, and analysis of these events turned type Ia SNe into the premiere choice for a secondary distance indicator by the early 1990s. While some systematic uncertainties specific to SNe and to Cepheid-based distances to the calibrating host galaxies still contribute to the H0 error budget, the major emphasis over the past two decades has been on reducing the statistical uncertainty by obtaining ever-larger samples of distances to SN hosts. Building on early efforts with the first-generation instruments on the Hubble Space Telescope, recent observations with the latest instruments on this facility have reduced the estimated total uncertainty on H0 to 2.4 % and shown a path to reach a 1 % measurement by the end of the decade, aided by Gaia and the James Webb Space Telescope.

The Non-Axisymmetric Milky Way

NASA Technical Reports Server (NTRS)

Spergel, David N.

1996-01-01

The Dwek et al. model represents the current state-of-the-art model for the stellar structure of our Galaxy. The improvements we have made to this model take a number of forms: (1) the construction of a more detailed dust model so that we can extend our modeling to the galactic plane; (2) simultaneous fits to the bulge and the disk; (3) the construction of the first self-consistent model for a galactic bar; and (4) the development and application of algorithms for constructing nonparametric bar models. The improved Galaxy model has enabled a number of exciting science projects. In Zhao et al., we show that the number and duration of microlensing events seen by the OGLE and MACHO collaborations towards the bulge were consistent with the predictions of our bar model. In Malhotra et al., we constructed an infrared Tully-Fisher (TF) relation for the local group. We found the tightest TF relation ever seen in any band and in any group of galaxies. The tightness of the correlation places strong constraints on galaxy formation models and provides a independent check of the Cepheid distance scale.

A Modern Update and Usage of Historical Variable Star Catalogs

NASA Astrophysics Data System (ADS)

Pagnotta, Ashley; Graur, Or; Murray, Zachary; Kruk, Julia; Christie-Dervaux, Lucien; Chen, Dong Yi

2015-01-01

One of the earliest modern variable star catalogs was constructed by Henrietta Swan Leavitt during her tenure at the Harvard College Observatory (HCO) in the early 1900s. Originally published in 1908, Leavitt's catalog listed 1777 variables in the Magellanic Clouds (MCs). The construction and analysis of this catalog allowed her to subsequently discover the Cepheid period-luminosity relationship, now known as the Leavitt Law. The MC variable star catalogs were updated and expanded by Cecilia Payne-Gaposchkin in 1966 and 1971. Although newer studies of the MC variables have been performed since then, the new information has not always been correlated with the old due to a lack of modern descriptors of the stars listed in the Harvard MC catalogs. We will discuss the history of MC variable star catalogs, especially those compiled using the HCO plates, as well as our modernized version of the Leavitt and Payne-Gaposchkin catalogs. Our modern catalog can be used in conjunction with the archival plates (primarily via the Digital Access to a Sky Century @ Harvard scanning project) to study the secular behavior of the MC variable stars over the past century.

First Hubble Space Telescope observations of the brightest stars in the Virgo galaxy M100 = NGC 4321

NASA Technical Reports Server (NTRS)

Freedman, Wendy L.; Madore, Barry F.; Stetson, Peter B.; Hughes, Shaun M. G.; Holtzman, Jon A.; Mould, Jeremy R.; Trauger, John T.; Gallagher, John S., III; Ballester, Gilda E.; Burrows, Christopher J.

1994-01-01

As part of both the Early Release Observations from the Hubble Space Telescope (HST) and the Key Project on the Extragalactic Distance Scale, we have obtained multiwavelength BVR Wide Field/Planetary Camera-2 (WFPC2) images for the face-on Virgo cluster spiral galaxy M100 = NGC 4321. We report here preliminary results from those observations, in the form of a color-magnitude diagram for approximately 11,500 stars down to V approximately 27 mag and a luminosity function for the brightest blue stars which is found to have a slope of 0.7, in excellent agreement with previous results obtained for significantly nearer galaxies. With the increased resolution now available using WFPC2, the number of galaxies in which we can directly measure Population I stars and thereby quantify the recent evolution, as well as test stellar evolution theory, has dramatically increased by at least a factor of 100. Finally, we find that the stars are present in M100 at the colors and luminosities expected for the brightest Cepheid variables in galaxies.

Le premier ciel de Gaia

NASA Astrophysics Data System (ADS)

Turon, Catherine; Arenou, Frederic

2016-11-01

On 14 September 2016, the first data release of the ESA's Gaia mission has been published. Based on raw data collected between 25 July 2014 and 16 Septembre 2015, i.e. only over the first 14 months of mission, this first "Gaia sky" includes the accurate positions and Gaia magnitudes of more than a billion objects: it is already the largest all-sky survey to date even though the incomplete scanning of some areas of the sky is reflected by some artefacts that will gradually fade out as more data are collected. In addition, for a subset of two million stars in common between Gaia and the Hipparcos and Tycho-2 catalogues, positions, parallaxes and proper motions have been obtained with an accuracy 3 times better than those of Hipparcos and for 20 times more stars. Finally, light curves of about 3200 RR Lyrae and Cepheid variable stars have been obtained from the repeated observations of the Ecliptic Poles made during the first month of Gaia operations. A first glance at the quality of the data is presented here, as well as some remarks about the use of this very preliminary Gaia catalogue.

Quantifying the line-of-sight mass distributions for time-delay lenses with stellar masses

NASA Astrophysics Data System (ADS)

Rusu, Cristian; Fassnacht, Chris; Treu, Tommaso; Suyu, Sherry; Auger, Matt; Koopmans, Leon; Marshall, Phil; Wong, Kenneth; Collett, Thomas; Agnello, Adriano; Blandford, Roger; Courbin, Frederic; Hilbert, Stefan; Meylan, Georges; Sluse, Dominique

2014-12-01

Measuring cosmological parameters with a realistic account of systematic uncertainties is currently one of the principal challenges of physical cosmology. Building on our recent successes with two gravitationally lensed systems, we have started a program to achieve accurate cosmographic measurements from five gravitationally lensed quasars. We aim at measuring H_0 with an accuracy better than 4%, comparable to but independent from measurements by current BAO, SN or Cepheid programs. The largest current contributor to the error budget in our sample is uncertainty about the line-of-sight mass distribution and environment of the lens systems. In this proposal, we request wide-field u-band imaging of the only lens in our sample without already available Spitzer/IRCA observations, B1608+656. The proposed observations are critical for reducing these uncertainties by providing accurate redshifts and in particular stellar masses for galaxies in the light cones of the target lens system. This will establish lensing as a powerful and independent tool for determining cosmography, in preparation for the hundreds of time-delay lenses that will be discovered by future surveys.

Stellar complexes in spiral arms of galaxies

NASA Astrophysics Data System (ADS)

Efremov, Yu. N.

The history of the introduction and development of the star complexes conception is briefly described. These large groups of stars were picked out and named as such ones in our Galaxy with argumentation and evidence for their physical unity (using the Cepheid variables the distances and ages of which are easy determined from their periods); anyway earlier the complexes were noted along the spiral arms of the Andromeda galaxy, but were not recognized as a new kind of star group. The chains of complexes along the spiral arms are observed quite rarely; their origin is explained by magneto- gravitational or purely gravitational instability developing along the arm. It is not clear why these chains are quite a rare phenomenon - and more so why sometimes the regular chain of complexes are observed in one arm only. Probably intergalactic magnetic field participated in formation of such chains. Apart from the complexes located along the arms, there are isolated giant complexes known (up to 700 pc in diameter) which look like super-gigantic but rather rarefied globular clusters. Until now only two of these formations are studied, in NGC 6946 and M51.

Two Cepheid variables in the Fornax dwarf galaxy

NASA Technical Reports Server (NTRS)

Light, R. M.; Armandroff, T. E.; Zinn, R.

1986-01-01

Two fields surrounding globular clusters 2 and 3 in the Fornax dwarf spheroidal galaxy have been searched for short-period variable stars that are brighter than the horizontal branch. This survey confirmed as variable the two suspected suprahorizontal-branch variables discovered by Buonanno et al. (1985) in their photometry of the clusters. The observations show that the star in cluster 2 is a W Virginis variable of 14.4 day period. It is the first W Vir variable to be found in a dwarf spheroidal galaxy, and its proximity to the center of cluster 2 suggests that it is a cluster member. The other star appears to be an anomalous Cephpeid of 0.78 day period. It lies outside or very near the boundary of cluster 3, and is therefore probably a member of the field population of Fornax. Although no other suprahorizontal-branch variables were discovered in the survey, it did confirm as variable two of the RR Lyrae candidates of Buonanno et al., which appeared at the survey limit. The implications of these observations for the understanding of the stellar content at Fornax are discussed.

THE TAIWANESE-AMERICAN OCCULTATION SURVEY PROJECT STELLAR VARIABILITY. II. DETECTION OF 15 VARIABLE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mondal, S.; Lin, C. C.; Chen, W. P.

2010-05-15

The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data-covering timescales from a fraction of a second to a few hundred days-are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (R.A. = 17{sup h}30{sup m}6.{sup s}7, decl. = 27{sup 0}17'30'', J2000), which had beenmore » observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 deg{sup 2} field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the light curves, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, {delta} Scuti, SX Phonencis, semi-regular, and eclipsing binaries.« less

Modern Geometric Methods of Distance Determination

NASA Astrophysics Data System (ADS)

Thévenin, Frédéric; Falanga, Maurizio; Kuo, Cheng Yu; Pietrzyński, Grzegorz; Yamaguchi, Masaki

2017-11-01

Building a 3D picture of the Universe at any distance is one of the major challenges in astronomy, from the nearby Solar System to distant Quasars and galaxies. This goal has forced astronomers to develop techniques to estimate or to measure the distance of point sources on the sky. While most distance estimates used since the beginning of the 20th century are based on our understanding of the physics of objects of the Universe: stars, galaxies, QSOs, the direct measures of distances are based on the geometric methods as developed in ancient Greece: the parallax, which has been applied to stars for the first time in the mid-19th century. In this review, different techniques of geometrical astrometry applied to various stellar and cosmological (Megamaser) objects are presented. They consist in parallax measurements from ground based equipment or from space missions, but also in the study of binary stars or, as we shall see, of binary systems in distant extragalactic sources using radio telescopes. The Gaia mission will be presented in the context of stellar physics and galactic structure, because this key space mission in astronomy will bring a breakthrough in our understanding of stars, galaxies and the Universe in their nature and evolution with time. Measuring the distance to a star is the starting point for an unbiased description of its physics and the estimate of its fundamental parameters like its age. Applying these studies to candles such as the Cepheids will impact our large distance studies and calibration of other candles. The text is constructed as follows: introducing the parallax concept and measurement, we shall present briefly the Gaia satellite which will be the future base catalogue of stellar astronomy in the near future. Cepheids will be discussed just after to demonstrate the state of the art in distance measurements in the Universe with these variable stars, with the objective of 1% of error in distances that could be applied to our closest galaxy the LMC, and better constrain the distances of large sub-structures around the Milky Way. Then exciting objects like X-Ray binaries will be presented in two parts corresponding to "low" or "high" mass stars with compact objects observed with X-ray satellites. We shall demonstrate the capability of these objects to have their distances measured with high accuracy with not only helps in the study of these objects but could also help to measure the distance of the structure they belong. For cosmological objects and large distances of megaparsecs, we shall present what has been developed for more than 20 years in the geometric distance measurements of MegaMasers, the ultimate goal being the estimation of the H0 parameter.

Smallpox and pan-Orthopox Virus Detection by Real-Time 3′-Minor Groove Binder TaqMan Assays on the Roche LightCycler and the Cepheid Smart Cycler Platforms

PubMed Central

Kulesh, David A.; Baker, Robert O.; Loveless, Bonnie M.; Norwood, David; Zwiers, Susan H.; Mucker, Eric; Hartmann, Chris; Herrera, Rafael; Miller, David; Christensen, Deanna; Wasieloski, Leonard P.; Huggins, John; Jahrling, Peter B.

2004-01-01

We designed, optimized, and extensively tested several sensitive and specific real-time PCR assays for rapid detection of both smallpox and pan-orthopox virus DNAs. The assays are based on TaqMan 3′-minor groove binder chemistry and were performed on both the rapid-cycling Roche LightCycler and the Cepheid Smart Cycler platforms. The hemagglutinin (HA) J7R, B9R, and B10R genes were used as targets for the variola virus-specific assays, and the HA and DNA polymerase-E9L genes were used as targets for the pan-orthopox virus assays. The five orthopox virus assays were tested against a panel of orthopox virus DNAs (both genomic and cloned) at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). The results indicated that each assay was capable of detecting both the appropriate cloned gene and genomic DNA. The assays showed no cross-reactivity to the 78 DNAs in the USAMRIID bacterial cross-reactivity panel. The limit of detection (LOD) of each assay was determined to be between 12 and 25 copies of target DNA. The assays were also run against a blind panel of DNAs at the Centers for Disease Control and Prevention (CDC) on both the LightCycler and the Smart Cycler. The panel consisted of eight different variola virus isolates, five non-variola virus orthopox virus isolates, two varicella-zoster virus isolates, and one herpes simplex virus isolate. Each sample was tested in triplicate at 2.5 ng, 25 pg, 250 fg, and 2.5 fg, which represent 1.24 × 107, 1.24 × 105, 1.24 × 103, and 1.24 × 101 genome equivalents, respectively. The results indicated that each of the five assays was 100% specific (no false positives) when tested against both the USAMRIID panels and the CDC blind panel. With the CDC blind panel, the LightCycler was capable of detecting 96.2% of the orthopox virus DNAs and 93.8% of the variola virus DNAs. The Smart Cycler was capable of detecting 92.3% of the orthopox virus DNAs and between 75 and 93.8% of the variola virus DNAs. However, all five assays had nearly 100% sensitivity on both machines with samples above the LOD (>12 gene copies). These real-time PCR assays represent a battery of tests to screen for and confirm the presence of variola virus DNA. The early detection of a smallpox outbreak is crucial whether the incident is an act of bioterrorism or an accidental occurrence. PMID:14766823

Smallpox and pan-orthopox virus detection by real-time 3'-minor groove binder TaqMan assays on the roche LightCycler and the Cepheid smart Cycler platforms.

PubMed

Kulesh, David A; Baker, Robert O; Loveless, Bonnie M; Norwood, David; Zwiers, Susan H; Mucker, Eric; Hartmann, Chris; Herrera, Rafael; Miller, David; Christensen, Deanna; Wasieloski, Leonard P; Huggins, John; Jahrling, Peter B

2004-02-01

We designed, optimized, and extensively tested several sensitive and specific real-time PCR assays for rapid detection of both smallpox and pan-orthopox virus DNAs. The assays are based on TaqMan 3'-minor groove binder chemistry and were performed on both the rapid-cycling Roche LightCycler and the Cepheid Smart Cycler platforms. The hemagglutinin (HA) J7R, B9R, and B10R genes were used as targets for the variola virus-specific assays, and the HA and DNA polymerase-E9L genes were used as targets for the pan-orthopox virus assays. The five orthopox virus assays were tested against a panel of orthopox virus DNAs (both genomic and cloned) at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). The results indicated that each assay was capable of detecting both the appropriate cloned gene and genomic DNA. The assays showed no cross-reactivity to the 78 DNAs in the USAMRIID bacterial cross-reactivity panel. The limit of detection (LOD) of each assay was determined to be between 12 and 25 copies of target DNA. The assays were also run against a blind panel of DNAs at the Centers for Disease Control and Prevention (CDC) on both the LightCycler and the Smart Cycler. The panel consisted of eight different variola virus isolates, five non-variola virus orthopox virus isolates, two varicella-zoster virus isolates, and one herpes simplex virus isolate. Each sample was tested in triplicate at 2.5 ng, 25 pg, 250 fg, and 2.5 fg, which represent 1.24 x 10(7), 1.24 x 10(5), 1.24 x 10(3), and 1.24 x 10(1) genome equivalents, respectively. The results indicated that each of the five assays was 100% specific (no false positives) when tested against both the USAMRIID panels and the CDC blind panel. With the CDC blind panel, the LightCycler was capable of detecting 96.2% of the orthopox virus DNAs and 93.8% of the variola virus DNAs. The Smart Cycler was capable of detecting 92.3% of the orthopox virus DNAs and between 75 and 93.8% of the variola virus DNAs. However, all five assays had nearly 100% sensitivity on both machines with samples above the LOD (>12 gene copies). These real-time PCR assays represent a battery of tests to screen for and confirm the presence of variola virus DNA. The early detection of a smallpox outbreak is crucial whether the incident is an act of bioterrorism or an accidental occurrence.

Imaging Variable Stars with HST

NASA Astrophysics Data System (ADS)

Karovska, Margarita

2011-05-01

The Hubble Space Telescope (HST) observations of astronomical sources, ranging from objects in our solar system to objects in the early Universe, have revolutionized our knowledge of the Universe its origins and contents.I will highlight results from HST observations of variable stars obtained during the past twenty or so years. Multiwavelength observations of numerous variable stars and stellar systems were obtained using the superb HST imaging capabilities and its unprecedented angular resolution, especially in the UV and optical. The HST provided the first detailed images probing the structure of variable stars including their atmospheres and circumstellar environments. AAVSO observations and light curves have been critical for scheduling of many of these observations and provided important information and context for understanding of the imaging results of many variable sources. I will describe the scientific results from the imaging observations of variable stars including AGBs, Miras, Cepheids, semi-regular variables (including supergiants and giants), YSOs and interacting stellar systems with a variable stellar components. These results have led to an unprecedented understanding of the spatial and temporal characteristics of these objects and their place in the stellar evolutionary chains, and in the larger context of the dynamic evolving Universe.

Imaging Variable Stars with HST

NASA Astrophysics Data System (ADS)

Karovska, M.

2012-06-01

(Abstract only) The Hubble Space Telescope (HST) observations of astronomical sources, ranging from objects in our solar system to objects in the early Universe, have revolutionized our knowledge of the Universe its origins and contents. I highlight results from HST observations of variable stars obtained during the past twenty or so years. Multiwavelength observations of numerous variable stars and stellar systems were obtained using the superb HST imaging capabilities and its unprecedented angular resolution, especially in the UV and optical. The HST provided the first detailed images probing the structure of variable stars including their atmospheres and circumstellar environments. AAVSO observations and light curves have been critical for scheduling of many of these observations and provided important information and context for understanding of the imaging results of many variable sources. I describe the scientific results from the imaging observations of variable stars including AGBs, Miras, Cepheids, semiregular variables (including supergiants and giants), YSOs and interacting stellar systems with a variable stellar components. These results have led to an unprecedented understanding of the spatial and temporal characteristics of these objects and their place in the stellar evolutionary chains, and in the larger context of the dynamic evolving Universe.

Comparison of Xpert Flu rapid nucleic acid testing with rapid antigen testing for the diagnosis of influenza A and B.

PubMed

DiMaio, Michael A; Sahoo, Malaya K; Waggoner, Jesse; Pinsky, Benjamin A

2012-12-01

Influenza infections are associated with thousands of hospital admissions and deaths each year. Rapid detection of influenza is important for prompt initiation of antiviral therapy and appropriate patient triage. In this study the Cepheid Xpert Flu assay was compared with two rapid antigen tests, BinaxNOW Influenza A & B and BD Directigen EZ Flu A+B, as well as direct fluorescent antibody testing for the rapid detection of influenza A and B. Using real-time, hydrolysis probe-based, reverse transcriptase PCR as the reference method, influenza A sensitivity was 97.3% for Xpert Flu, 95.9% for direct fluorescent antibody testing, 62.2% for BinaxNOW, and 71.6% for BD Directigen. Influenza B sensitivity was 100% for Xpert Flu and direct fluorescent antibody testing, 54.5% for BinaxNOW, and 48.5% for BD Directigen. Specificity for influenza A was 100% for Xpert Flu, BinaxNOW, and BD Directigen, and 99.2% for direct fluorescent antibody testing. All methods demonstrated 100% specificity for influenza B. These findings support the use of the Xpert Flu assay in settings requiring urgent diagnosis of influenza A and B. Copyright © 2012 Elsevier B.V. All rights reserved.

Detailed opacity calculations for stellar models

NASA Astrophysics Data System (ADS)

Pain, Jean-Christophe; Gilleron, Franck

2016-10-01

We present a state of the art of precise spectral opacity calculations illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments of hot dense plasmas produced by ultra-high-intensity laser interaction. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. Focus is put on iron, due to its crucial role in the understanding of asteroseismic observations of Beta Cephei-type and Slowly Pulsating B stars, as well as in the Sun. For instance, in Beta Cephei-type stars (which should not be confused with Cepheid variables), the iron-group opacity peak excites acoustic modes through the kappa-mechanism. A particular attention is paid to the higher-than-predicted iron opacity measured on Sandia's Z facility at solar interior conditions (boundary of the convective zone). We discuss some theoretical aspects such as orbital relaxation, electron collisional broadening, ionic Stark effect, oscillator-strength sum rules, photo-ionization, or the ``filling-the-gap'' effect of highly excited states.

An independent determination of the local Hubble constant

NASA Astrophysics Data System (ADS)

Fernández Arenas, David; Terlevich, Elena; Terlevich, Roberto; Melnick, Jorge; Chávez, Ricardo; Bresolin, Fabio; Telles, Eduardo; Plionis, Manolis; Basilakos, Spyros

2018-02-01

The relationship between the integrated H β line luminosity and the velocity dispersion of the ionized gas of H II galaxies and giant H II regions represents an exciting standard candle that presently can be used up to redshifts z ˜ 4. Locally it is used to obtain precise measurements of the Hubble constant by combining the slope of the relation obtained from nearby (z ≤ 0.2) H II galaxies with the zero-point determined from giant H II regions belonging to an `anchor sample' of galaxies for which accurate redshift-independent distance moduli are available. We present new data for 36 giant H II regions in 13 galaxies of the anchor sample that includes the megamaser galaxy NGC 4258. Our data are the result of the first 4 yr of observation of our primary sample of 130 giant H II regions in 73 galaxies with Cepheid determined distances. Our best estimate of the Hubble parameter is 71.0 ± 2.8(random) ± 2.1(systematic) km s- 1Mpc- 1. This result is the product of an independent approach and, although at present less precise than the latest SNIa results, it is amenable to substantial improvement.

VizieR Online Data Catalog: OGLE Magellanic Clouds anomalous Cepheids (Soszynski+, 2015)

NASA Astrophysics Data System (ADS)

Soszynski, I.; Udalski, A.; Szymanski, M. K.; Pietrzynski, G.; Wyrzykowski, L.; Ulaczyk, K.; Poleski, R.; Pietrukowicz, P.; Kozlowski, S.; Skowron, J.; Mroz, P.; Pawlak, M.

2016-06-01

Time-series I and V-band photometry of the Magellanic Clouds was obtained in the years 2010-2015 using the 32-chip mosaic CCD camera mounted at the focus of the 1.3-m Warsaw Telescope located at Las Campanas Observatory in Chile. The observatory is operated by the Carnegie Institution for Science. The OGLE- IV camera has a total field of view of 1.4 square degrees and pixel scale of 0.26". The OGLE-IV fields cover approximately 650 square degrees in both Clouds and a region between both galaxies, the so-called Magellanic Bridge. For each field we obtained from 90 (in sparse regions far from the centers of the Magellanic Clouds) to over 750 observing points (in the densest fields) in the Cousins I-band and from several to over 260 points in the Johnson V-band. Data reduction of the OGLE images was performed using the Difference Image Analysis technique (Alard and Lupton 1998ApJ...503..325A, Wozniak 2000). Detailed descriptions of the instrumentation, photometric reductions and astrometric calibrations of the OGLE-IV data are provided by Udalski et al. (2015, Cat. J/AcA/50/421). (8 data files).

Model for Spiral Galaxys Rotation Curves

NASA Astrophysics Data System (ADS)

Hodge, John

2003-11-01

A model of spiral galaxy dynamics is proposed. An expression describing the rotation velocity of particles v in a galaxy as a function of the distance from the center r (RC) is developed. The resulting, intrinsic RC of a galaxy is Keplerian in the inner bulge and rising in the disk region without modifying the Newtonian gravitational potential (MOND) and without unknown dark matter. The v^2 is linearly related to r of the galaxy in part of the rapidly rising region of the HI RC (RRRC) and to r^2 in another part of the RRRC. The r to discontinuities in the surface brightness versus r curve is related to the 21 cm line width, the measured mass of the central supermassive black hole (SBH), and the maximum v^2 in the RRRC. The distance to spiral galaxies can be calculated from these relationships that tightly correlates with the distance calculated using Cepheid variables. Differing results in measuring the mass of the SBH from differing measurement procedures are explained. This model is consistent with previously unexplained data, has predicted new relationships, and suggests a new model of the universe. Full text: http://web.infoave.net/ ˜scjh.

Constructing a cosmological model-independent Hubble diagram of type Ia supernovae with cosmic chronometers

NASA Astrophysics Data System (ADS)

Li, Zhengxiang; Gonzalez, J. E.; Yu, Hongwei; Zhu, Zong-Hong; Alcaniz, J. S.

2016-02-01

We apply two methods, i.e., the Gaussian processes and the nonparametric smoothing procedure, to reconstruct the Hubble parameter H (z ) as a function of redshift from 15 measurements of the expansion rate obtained from age estimates of passively evolving galaxies. These reconstructions enable us to derive the luminosity distance to a certain redshift z , calibrate the light-curve fitting parameters accounting for the (unknown) intrinsic magnitude of type Ia supernova (SNe Ia), and construct cosmological model-independent Hubble diagrams of SNe Ia. In order to test the compatibility between the reconstructed functions of H (z ), we perform a statistical analysis considering the latest SNe Ia sample, the so-called joint light-curve compilation. We find that, for the Gaussian processes, the reconstructed functions of Hubble parameter versus redshift, and thus the following analysis on SNe Ia calibrations and cosmological implications, are sensitive to prior mean functions. However, for the nonparametric smoothing method, the reconstructed functions are not dependent on initial guess models, and consistently require high values of H0, which are in excellent agreement with recent measurements of this quantity from Cepheids and other local distance indicators.

Gaia DR1 documentation Chapter 6: Variability

NASA Astrophysics Data System (ADS)

Eyer, L.; Rimoldini, L.; Guy, L.; Holl, B.; Clementini, G.; Cuypers, J.; Mowlavi, N.; Lecoeur-Taïbi, I.; De Ridder, J.; Charnas, J.; Nienartowicz, K.

2017-12-01

This chapter describes the photometric variability processing of the Gaia DR1 data. Coordination Unit 7 is responsible for the variability analysis of over a billion celestial sources. In particular the definition, design, development, validation and provision of a software package for the data processing of photometrically variable objects. Data Processing Centre Geneva (DPCG) responsibilities cover all issues related to the computational part of the CU7 analysis. These span: hardware provisioning, including selection, deployment and optimisation of suitable hardware, choosing and developing software architecture, defining data and scientific workflows as well as operational activities such as configuration management, data import, time series reconstruction, storage and processing handling, visualisation and data export. CU7/DPCG is also responsible for interaction with other DPCs and CUs, software and programming training for the CU7 members, scientific software quality control and management of software and data lifecycle. Details about the specific data treatment steps of the Gaia DR1 data products are found in Eyer et al. (2017) and are not repeated here. The variability content of the Gaia DR1 focusses on a subsample of Cepheids and RR Lyrae stars around the South ecliptic pole, showcasing the performance of the Gaia photometry with respect to variable objects.

AUTOCLASSIFICATION OF THE VARIABLE 3XMM SOURCES USING THE RANDOM FOREST MACHINE LEARNING ALGORITHM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farrell, Sean A.; Murphy, Tara; Lo, Kitty K., E-mail: s.farrell@physics.usyd.edu.au

In the current era of large surveys and massive data sets, autoclassification of astrophysical sources using intelligent algorithms is becoming increasingly important. In this paper we present the catalog of variable sources in the Third XMM-Newton Serendipitous Source catalog (3XMM) autoclassified using the Random Forest machine learning algorithm. We used a sample of manually classified variable sources from the second data release of the XMM-Newton catalogs (2XMMi-DR2) to train the classifier, obtaining an accuracy of ∼92%. We also evaluated the effectiveness of identifying spurious detections using a sample of spurious sources, achieving an accuracy of ∼95%. Manual investigation of amore » random sample of classified sources confirmed these accuracy levels and showed that the Random Forest machine learning algorithm is highly effective at automatically classifying 3XMM sources. Here we present the catalog of classified 3XMM variable sources. We also present three previously unidentified unusual sources that were flagged as outlier sources by the algorithm: a new candidate supergiant fast X-ray transient, a 400 s X-ray pulsar, and an eclipsing 5 hr binary system coincident with a known Cepheid.« less

Globular Cluster Variable Stars—Atlas and Coordinate Improvement using AAVSOnet Telescopes (Abstract)

NASA Astrophysics Data System (ADS)

Welch, D.; Henden, A.; Bell, T.; Suen, C.; Fare, I.; Sills, A.

2015-12-01

(Abstract only) The variable stars of globular clusters have played and continue to play a significant role in our understanding of certain classes of variable stars. Since all stars associated with a cluster have the same age, metallicity, distance and usually very similar (if not identical reddenings), such variables can produce uniquely powerful constraints on where certain types of pulsation behaviors are excited. Advanced amateur astronomers are increasingly well-positioned to provide long-term CCD monitoring of globular cluster variable star but are hampered by a long history of poor or inaccessible finder charts and coordinates. Many of variable-rich clusters have published photographic finder charts taken in relatively poor seeing with blue-sensitive photographic plates. While useful signal-to-noise ratios are relatively straightforward to achieve for RR Lyrae, Type 2 Cepheids, and red giant variables, correct identification remains a difficult issue—particularly when images are taken at V or longer wavelengths. We describe the project and report its progress using the OC61, TMO61, and SRO telescopes of AAVSOnet after the first year of image acquisition and demonstrate several of the data products being developed for globular cluster variables.

Variability Survey of ω Centauri in the Near-IR: Period-Luminosity Relations

NASA Astrophysics Data System (ADS)

Navarrete, Camila; Catelan, Márcio; Contreras Ramos, Rodrigo; Gran, Felipe; Alonso-García, Javier; Dékány, István

2015-08-01

ω Centauri (NGC 5139) is by far the most massive globular star cluster in the Milky Way, and has even been suggested to be the remnant of a dwarf galaxy. As such, it contains a large number of variable stars of different classes. Here we report on a deep, wide-field, near-infrared variability survey of omega Cen, carried out by our team using ESO's 4.1m VISTA telescope. Our time-series data comprise 42 and 100 epochs in J and Ks, respectively. This unique dataset has allowed us to derive complete light curves for hundreds of variable stars in the cluster, and thereby perform a detailed analysis of the near-infrared period-luminosity (PL) relations for different variability classes, including type II Cepheids, SX Phoenicis, and RR Lyrae stars. In this contribution, in addition to describing our survey and presenting the derived light curves, we present the resulting PL relations for each of these variability classes, including the first calibration of this sort for the SX Phoenicis stars. Based on these relations, we also provide an updated (pulsational) distance modulus for omega Cen, compare with results based on independent techniques, and discuss possible sources of systematic errors.

Cool neutral hydrogen in the direction of an anonymous OB association

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bania, T.M.

1983-08-01

H I self-absorption is seen in the direction l = 55./sup 0/6 probably physically associated with an anonymous OB association which has the Cepheid GY Sagittae as a member. The cool H I is in two clouds at least 15 pc in diameter located 3.25 kpc from the Sun. If their temperature is approx. =50 K, the cloud masses are approx. =10/sup 3/ M/sub sun/. The neutral atomic hydrogen clouds are probably warm envelopes surrounding cold molecular cloud cores because CO observations in this region show two molecular clouds nearly coincident with the absorbing H i gas. Since the OBmore » association is only approx. =10/sup 7/ years old, these clouds are likely to be part of the original cloud complex from which the stellar cluster formed. The H i clouds are part of the larger Arecibo survey of self-absorption which suggests that many of the Arecibo clouds are associated with heretofore unidentified star clusters. Even if this is generally not the case, the Arecibo objects have accurate kinematic distances and thus provide a new sample of cool H I clouds whose thermodynamic properties can be studied.« less

Scalar potential model (SPM) of redshift and discrete redshift

NASA Astrophysics Data System (ADS)

Hodge, John

2005-11-01

On the galactic scale the universe is inhomogeneous and redshift z is occasionally less than zero. Several differences among galaxy types suggest that spiral galaxies are Sources and that early type galaxies are Sinks of a scalar potential field (SPF). The morphology-radius and intragalactic medium cluster observations support a cell structure of galaxies. The SPF causes the mass expected by Newtonian mechanics to measure less in Source galaxies and more in Sink galaxies. The cell structure allows the universe to be bounded and flat without collapsing. An equation is derived relating z of particle photons and the distance D to galaxies. The calculated z has a correlation coefficient of 0.88 with the measured z for a sample of 32 spiral galaxies with a Cepheid based D. The equation is consistent with z <0 observations of close galaxies. At low cosmological distances, the equation reduces to z ~ KD, where K is a constant, positive value. The model qualitatively suggests the discrete variations in z, which was reported by W. G. Tifft, 1997, ApJ 485, 465 and others, are consistent with the SPM. Full text: http://web.infoave.net/ scjh.

Precision Distances with the Tip of the Red Giant Branch Method

NASA Astrophysics Data System (ADS)

Beaton, Rachael Lynn; Carnegie-Chicago Hubble Program Team

2018-01-01

The Carnegie-Chicago Hubble Program aims to construct a distance ladder that utilizes old stellar populations in the outskirts of galaxies to produce a high precision measurement of the Hubble Constant that is independent of Cepheids. The CCHP uses the tip of the red giant branch (TRGB) method, which is a statistical measurement technique that utilizes the termination of the red giant branch. Two innovations combine to make the TRGB a competitive route to the Hubble Constant (i) the large-scale measurement of trigonometric parallax by the Gaia mission and (ii) the development of both precise and accurate means of determining the TRGB in both nearby (~1 Mpc) and distant (~20 Mpc) galaxies. Here I will summarize our progress in developing these standardized techniques, focusing on both our edge-detection algorithm and our field selection strategy. Using these methods, the CCHP has determined equally precise (~2%) distances to galaxies in the Local Group (< 1 Mpc) and across the Local Volume (< 20 Mpc). The TRGB is, thus, an incredibly powerful and straightforward means to determine distances to galaxies of any Hubble Type and, thus, has enormous potential for putting any number of astrophyiscal phenomena on absolute units.

Quantitative Spectroscopy of Supergiants in the Local Group Dwarf Galaxy IC 1613: Metallicity and Distance

NASA Astrophysics Data System (ADS)

Berger, Travis A.; Kudritzki, Rolf-Peter; Urbaneja, Miguel A.; Bresolin, Fabio; Gieren, Wolfgang; Pietrzyński, Grzegorz; Przybilla, Norbert

2018-06-01

We present a spectral analysis of 21 blue supergiant stars of spectral types late B to early A within the Local Group dwarf galaxy IC 1613, based on VLT Focal Reducer and Low Dispersion Spectrograph 2 low-resolution spectra. Combining our results with studies of early B-type blue supergiants, we report a wide bimodal distribution of metallicities with two peaks around [Z] ∼ ‑0.50 dex and [Z] ∼ ‑0.85 dex. The bimodal distribution correlates with spatial location, when compared with column densities of neutral hydrogen in IC 1613. While the low [Z] objects appear in regions of relatively high ISM H I column densities or close to them, the high [Z] supergiants are found in the central H I hole that is almost devoid of hydrogen. This suggests there are varied chemical evolution histories for the young stellar populations in IC 1613. Utilizing the flux-weighted gravity–luminosity relation, we determine IC 1613's distance modulus as m ‑ M = 24.39 ± 0.11 mag. This value is in agreement within previous distance measurements using the near-infrared period–luminosity relationship of Cepheids and the tip of the red giant branch.

Classification of ROTSE Variable Stars using Machine Learning

NASA Astrophysics Data System (ADS)

Wozniak, P. R.; Akerlof, C.; Amrose, S.; Brumby, S.; Casperson, D.; Gisler, G.; Kehoe, R.; Lee, B.; Marshall, S.; McGowan, K. E.; McKay, T.; Perkins, S.; Priedhorsky, W.; Rykoff, E.; Smith, D. A.; Theiler, J.; Vestrand, W. T.; Wren, J.; ROTSE Collaboration

2001-12-01

We evaluate several Machine Learning algorithms as potential tools for automated classification of variable stars. Using the ROTSE sample of ~1800 variables from a pilot study of 5% of the whole sky, we compare the effectiveness of a supervised technique (Support Vector Machines, SVM) versus unsupervised methods (K-means and Autoclass). There are 8 types of variables in the sample: RR Lyr AB, RR Lyr C, Delta Scuti, Cepheids, detached eclipsing binaries, contact binaries, Miras and LPVs. Preliminary results suggest a very high ( ~95%) efficiency of SVM in isolating a few best defined classes against the rest of the sample, and good accuracy ( ~70-75%) for all classes considered simultaneously. This includes some degeneracies, irreducible with the information at hand. Supervised methods naturally outperform unsupervised methods, in terms of final error rate, but unsupervised methods offer many advantages for large sets of unlabeled data. Therefore, both types of methods should be considered as promising tools for mining vast variability surveys. We project that there are more than 30,000 periodic variables in the ROTSE-I data base covering the entire local sky between V=10 and 15.5 mag. This sample size is already stretching the time capabilities of human analysts.

New Self-lensing Models of the Small Magellanic Cloud: Can Gravitational Microlensing Detect Extragalactic Exoplanets?

NASA Astrophysics Data System (ADS)

Mróz, Przemek; Poleski, Radosław

2018-04-01

We use three-dimensional distributions of classical Cepheids and RR Lyrae stars in the Small Magellanic Cloud (SMC) to model the stellar density distribution of a young and old stellar population in that galaxy. We use these models to estimate the microlensing self-lensing optical depth to the SMC, which is in excellent agreement with the observations. Our models are consistent with the total stellar mass of the SMC of about 1.0× {10}9 {M}ȯ under the assumption that all microlensing events toward this galaxy are caused by self-lensing. We also calculate the expected event rates and estimate that future large-scale surveys, like the Large Synoptic Survey Telescope (LSST), will be able to detect up to a few dozen microlensing events in the SMC annually. If the planet frequency in the SMC is similar to that in the Milky Way, a few extragalactic planets can be detected over the course of the LSST survey, provided significant changes in the SMC observing strategy are devised. A relatively small investment of LSST resources can give us a unique probe of the population of extragalactic exoplanets.

Reliability of the Xpert HPV assay to detect high-risk human papillomavirus DNA in a colposcopy referral population.

PubMed

Castle, Philip E; Smith, Katherine M; Davis, Thomas E; Schmeler, Kathleen M; Ferris, Daron G; Savage, Ashlyn H; Gray, Jermaine E; Stoler, Mark H; Wright, Thomas C; Ferenczy, Alex; Einstein, Mark H

2015-01-01

The Xpert HPV Assay (Xpert; Cepheid, Sunnyvale, CA) was developed for the multianalytic GeneXpert platform. In a colposcopy referral population of 708 women living in the United States, two cervical specimens, A and B, were collected, and both were tested by the Xpert assay for high-risk human papillomavirus (hrHPV) DNA, permitting an evaluation of its test reliability. Specimen B was also tested by Hybrid Capture 2 (hc2; Qiagen, Germantown, MD) and the cobas HPV Test (cobas; Roche Molecular Systems, Pleasanton, CA). The κ and percent agreement for any hrHPV for the two Xpert results were 0.88 and 94.5%, respectively. There was no statistical difference in testing positive on both specimens by Xpert (P = .62). The sensitivity for detection of cervical intraepithelial neoplasia grade 2 or more severe (CIN2+) was 89.0% using specimen A and 90.4% using specimen B for Xpert, 90.4% for cobas, and 81.6% for hc2. The Xpert assay was sensitive and reliable for the detection of hrHPV and the identification of women with CIN2+. Copyright© by the American Society for Clinical Pathology.

Feasibility of using microbiology diagnostic tests of moderate or high complexity at the point - of - care in a delivery suite.

PubMed

Gray, J W; Milner, P J; Edwards, E H; Daniels, J P; Khan, K S

2012-07-01

Point-of-care testing (POCT) is one of the fastest growing sectors of laboratory diagnostics. Most tests in routine use are haematology or biochemistry tests that are of low complexity. Microbiology POCT has been constrained by a lack of tests that are both accurate and of low complexity. We describe our experience of the practical issues around using more complex POCT for detection of Group B streptococci (GBS) in swabs from labouring women. We evaluated two tests for their feasibility in POCT: an optical immune assay (Biostar OIA Strep B, Inverness Medical, Princetown, NJ) and a PCR (IDI-Strep B, Cepheid, Sunnyvale, CA), which have been categorised as being of moderate and high complexity, respectively. A total of 12 unqualified midwifery assistants (MA) were trained to undertake testing on the delivery suite. A systematic approach to the introduction and management of POC testing was used. Modelling showed that the probability of test results being available within a clinically useful timescale was high. However, in the clinical setting, we found it impossible to maintain reliable availability of trained testers. Implementation of more complex POC testing is technically feasible, but it is expensive, and may be difficult to achieve in a busy delivery suite.

Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

NASA Astrophysics Data System (ADS)

Britavskiy, Nikolay; Pancino, Elena; Romano, Donatella; Tsymbal, Vadim

2015-08-01

We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a Least Squares Deconvolution (LSD) of the line profiles in order to analyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (± 1 km/s) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 km/s even with a low number of high-resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Cacciari, C.; Clementini, C.

2016-05-01

We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a least squares deconvolution (LSD) of the line profiles in order to an- alyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (+- 2 kms^-1) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 kms^-1 even with a low number of high- resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

Cosmological Constraints from the Redshift Dependence of the Alcock–Paczynski Effect: Dynamical Dark Energy

NASA Astrophysics Data System (ADS)

Li, Xiao-Dong; Sabiu, Cristiano G.; Park, Changbom; Wang, Yuting; Zhao, Gong-bo; Park, Hyunbae; Shafieloo, Arman; Kim, Juhan; Hong, Sungwook E.

2018-04-01

We perform an anisotropic clustering analysis of 1,133,326 galaxies from the Sloan Digital Sky Survey (SDSS-III) Baryon Oscillation Spectroscopic Survey Data Release 12 covering the redshift range 0.15 < z < 0.69. The geometrical distortions of the galaxy positions, caused by incorrect assumptions in the cosmological model, are captured in the anisotropic two-point correlation function on scales of 6–40 h ‑1 Mpc. The redshift evolution of this anisotropic clustering is used to place constraints on the cosmological parameters. We improve the methodology of Li et al. to enable efficient exploration of high-dimensional cosmological parameter spaces, and apply it to the Chevallier–Polarski–Linder parameterization of dark energy, w = w 0 + w a z/(1 + z). In combination with data on the cosmic microwave background, baryon acoustic oscillations, Type Ia supernovae, and H 0 from Cepheids, we obtain Ω m = 0.301 ± 0.008, w 0 = ‑1.042 ± 0.067, and w a = ‑0.07 ± 0.29 (68.3% CL). Adding our new Alcock–Paczynski measurements to the aforementioned results reduces the error bars by ∼30%–40% and improves the dark-energy figure of merit by a factor of ∼2. We check the robustness of the results using realistic mock galaxy catalogs.

Hubble 2006: Science Year in Review

NASA Technical Reports Server (NTRS)

Brown, R.

2007-01-01

The 10 science articles selected for this years annual science report exemplify the range of Hubble research from the Solar System, across our Milky Way, and on to distant galaxies. The objects of study include a new feature on Jupiter, binaries in the Kuiper Belt, Cepheid variable stars, the Orion Nebula, distant transiting planets, lensing galaxies, active galactic nuclei, red-and-dead galaxies, and galactic outflows and jets. Each narrative strives to construct the readers understanding of the topics and issues, and to place the latest research in historical, as well as scientific, context. These essays reveal trends in the practice of astronomy. More powerful computers are permitting astronomers to study ever larger data sets, enabling the discovery of subtle effects and rare objects. (Two investigations created mosaic images that are among the largest produced to date.) Multiwavelength data sets from ground-based telescopes, as well as other great observatories Spitzer and Chandraare increasingly important for holistic interpretations of Hubble results. This yearbook also presents profiles of 12 individuals who work with Hubble, or Hubble data, on a daily basis. They are representative of the many students, scientists, engineers, and other professions who are proudly associated with Hubble. Their stories collectively communicate the excitement and reward of careers related to space science and technology.

Multiband Fourier Analysis and Interstellar Reddening of the Variable Stars in the Globular Cluster NGC 6402 (M14)

NASA Astrophysics Data System (ADS)

Weinschenk, Sedrick; Murphy, Brian; Villiger, Nathan J.

2018-01-01

We present a detailed study of the variable stars in the globular cluster NGC 6402 (M14). Approximately 1500 B and V band images were collected from July 2016 to August 2017 using the SARA Consortium Jacobus Kaptyen 1-meter telescope located in the Canary Islands. Using difference image analysis, we were able to identify 145 probable variable stars, confirming the 133 previously known variables and adding 12 new variables. The variables consisted of 117 RR Lyrae stars, 18 long period variables, 2 eclipsing variables, 6 Cepheid variables, and 2 SX Phoenix variables. Of the RR Lyrae variables 55 were of fundamental mode RR0 stars, of which 18 exhibited the Blazhko effect, 57 were of 1st overtone RR1, of which 7 appear to exhibit the Blazhko effect, 1 2nd overtone RR2, and 2 double mode variables. We found an average period of 0.59016 days for RR0 stars and 0.30294 days for RR1 stars. Using the multiband light curves of both the RR0 and RR1 variables we found an average E(B-V) of 0.604 with a scatter of 0.15 magnitudes. Using Fourier decomposition of the RR Lyrae light curves we also determined the metallicity and distance of the NGC 6402.

Non-LTE spectral analysis and model constraints on SN 1993J

NASA Technical Reports Server (NTRS)

Baron, E.; Hauschildt, P. H.; Branch, D.; Austin, S.; Garnavich, P.; Ann, Hong Bae; Wagner, R. M.; Filippenko, A. V.; Matheson, T.; Liebert, James

1995-01-01

We present non-Local Thermodynamic Equilibrium (LTE) synthetic spectra for a time series of observations of SN 1993J obtained on 1993 March 30-31, April 7, April 13-15, and June 13 UT. The spectra are dominated by hydrogen Balmer lines; neutral helium lines, which have been nonthermally excited; and Fe II features. The density profile evolves from an extremely steep 'brick wall' structure with an equivalent power-law index of about 50 on March 30 to a more typical SN II profile with a power law index of about 10. The early spectra are well fitted by a solar composition of metals, although an enhanced abundance of helium is required in order to fit the neutral helium lines. By June 13, the photosphere has receded deep into the helium layer, although there appears to be a layer of hydrogen at higher velocity. The distance is estimated for each epoch. While consistent results are found for spectra obtained in the month of April, the spread in distances from March to June is quite large. Our value for April is mu = 28.0 +/- 0.3 mag, consistent with the recent Cepheid distance to the host galaxy M81. We also compare our results to other implementations of the expanding photosphere method.

Estimating Distances from Parallaxes. III. Distances of Two Million Stars in the Gaia DR1 Catalogue

NASA Astrophysics Data System (ADS)

Astraatmadja, Tri L.; Bailer-Jones, Coryn A. L.

2016-12-01

We infer distances and their asymmetric uncertainties for two million stars using the parallaxes published in the Gaia DR1 (GDR1) catalogue. We do this with two distance priors: A minimalist, isotropic prior assuming an exponentially decreasing space density with increasing distance, and an anisotropic prior derived from the observability of stars in a Milky Way model. We validate our results by comparing our distance estimates for 105 Cepheids which have more precise, independently estimated distances. For this sample we find that the Milky Way prior performs better (the rms of the scaled residuals is 0.40) than the exponentially decreasing space density prior (rms is 0.57), although for distances beyond 2 kpc the Milky Way prior performs worse, with a bias in the scaled residuals of -0.36 (versus -0.07 for the exponentially decreasing space density prior). We do not attempt to include the photometric data in GDR1 due to the lack of reliable color information. Our distance catalog is available at http://www.mpia.de/homes/calj/tgas_distances/main.html as well as at CDS. This should only be used to give individual distances. Combining data or testing models should be done with the original parallaxes, and attention paid to correlated and systematic uncertainties.

Modernizing Pickles - A Tool for Planning and Scheduling HST Astrometry

NASA Astrophysics Data System (ADS)

Juarez, Aaron; McArthur, B.; Benedict, G. F.

2007-12-01

Pickles is a Macintosh program written in C that was developed as a tool for determining pointings and rolls of the Hubble Space Telescope (HST) to place targets and astrometric reference stars in the Fine Guidance Sensor (FGS) field of regard ("pickles"). The program was developed in the late 1980s and runs under the "Classic” System. Ongoing HST astrometry projects require that this code be ported to the Intel-Mac OSX, because the Classic System is now unsupported. Pickles is a vital part of HST astrometry research. It graphically aids the investigator to determine where, when, and how the HST/FGS combination can observe an object and associated astrometric reference stars. Presently, Pickles can extract and display star positions from Guide Star Catalogs, such as the ACRS, SAO, and AGK3 catalogs via CD-ROMs. Future improvements will provide access to these catalogs and others through the internet. As an example of the past utility of Pickles, we highlight the recent determination of parallaxes for ten galactic Cepheids to determine an improved solar-metallicity Period-Luminosity relation. Support for this work was provided by NASA through grants GO-10989, -11210, and -11211 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Interferometry in the era of time-domain astronomy

NASA Astrophysics Data System (ADS)

Schaefer, Gail H.; Cassan, Arnaud; Gallenne, Alexandre; Roettenbacher, Rachael M.; Schneider, Jean

2018-04-01

The physical nature of time variable objects is often inferred from photometric light-curves and spectroscopic variations. Long-baseline optical interferometry has the power to resolve the spatial structure of time variable sources directly in order to measure their physical properties and test the physics of the underlying models. Recent interferometric studies of variable objects include measuring the angular expansion and spatial structure during the early stages of novae outbursts, studying the transits and tidal distortions of the components in eclipsing and interacting binaries, measuring the radial pulsations in Cepheid variables, monitoring changes in the circumstellar discs around rapidly rotating massive stars, and imaging starspots. Future applications include measuring the image size and centroid displacements in gravitational microlensing events, and imaging the transits of exoplanets. Ongoing and upcoming photometric surveys will dramatically increase the number of time-variable objects detected each year, providing many potential targets to observe interferometrically. For short-lived transient events, it is critical for interferometric arrays to have the flexibility to respond rapidly to targets of opportunity and optimize the selection of baselines and beam combiners to provide the necessary resolution and sensitivity to resolve the source as its brightness and size change. We discuss the science opportunities made possible by resolving variable sources using long baseline optical interferometry.

A Theoretical Probe for Excitation Mechanisms of Sun-like and Mira-like Oscillations of Stars

NASA Astrophysics Data System (ADS)

Xiong, Da-run; Deng, Li-cai

2013-01-01

The linear nonadiabatic oscillations for evolutionary models of 0.6- 3M8 stars are calculated by using a nonlocal and time-dependent convection theory. The results show that in the HR diagram the pulsation-unstable low- temperature stars on the right side of instability strip can be divided into two groups. One group indicates the Sun-like oscillation stars composed of the main- sequence dwarfs, sub-giants and red giants (RGs) of low and intermediate lu- minosities, which are unstable in the intermediate- and high-order (n ≥ 12) p- modes, and stable in the low-order (n ≤ 5) p-modes. Another group indicates the Mira-like stars composed of the bright RGs and asymptotic giant branch (AGB) stars, which are just contrary to Sun-like stars, unstable in low-order (n ≤ 5) p-modes and stable in the intermediate- and high-order (n ≥ 12) p-modes. The oscillations for the red edge of Cepheid (δ Scuti) instability strip, Sun-like and Mira-like stars can be explained uniformly by the coupling between convection and oscillation (CCO). For the low-temperature stars on the right side of in- stability strip, CCO is the dominant excitation and damping mechanism of the oscillations of low- and intermediate-order p-modes, and the turbulent stochas- tic excitation becomes important only for the high-order p-modes of Sun-like oscillations.

Clustering of Local Group Distances: Publication Bias or Correlated Measurements? V. Galactic Rotation Constants

NASA Astrophysics Data System (ADS)

de Grijs, Richard; Bono, Giuseppe

2017-10-01

As part of an extensive data mining effort, we have compiled a database of 162 Galactic rotation speed measurements at R 0 (the solar Galactocentric distance), {{{\\Theta }}}0. Published between 1927 and 2017 June, this represents the most comprehensive set of {{{\\Theta }}}0 values since the 1985 meta-analysis that led to the last revision of the International Astronomical Union’s recommended Galactic rotation constants. Although we do not find any compelling evidence for the presence of “publication bias” in recent decades, we find clear differences among the {{{\\Theta }}}0 values and the {{{\\Theta }}}0/{R}0 ratios resulting from the use of different tracer populations. Specifically, young tracers (including OB and supergiant stars, masers, Cepheid variables, H II regions, and young open clusters), as well as kinematic measurements of Sgr A* near the Galactic Center, imply a significantly larger Galactic rotation speed at the solar circle and a higher {{{\\Theta }}}0/{R}0 ratio (i.e., {{{\\Theta }}}0=247+/- 3 km s‑1 and {{{\\Theta }}}0/{R}0=29.81+/- 0.32 km s‑1 kpc‑1 statistical uncertainties only) than any of the tracers dominating the Galaxy’s mass budget (i.e., field stars and the H I/CO distributions). Using the latter to be most representative of the bulk of the Galaxy’s matter distribution, we arrive at an updated set of Galactic rotation constants,

Absolute Distances to Nearby Type Ia Supernovae via Light Curve Fitting Methods

NASA Astrophysics Data System (ADS)

Vinkó, J.; Ordasi, A.; Szalai, T.; Sárneczky, K.; Bányai, E.; Bíró, I. B.; Borkovits, T.; Hegedüs, T.; Hodosán, G.; Kelemen, J.; Klagyivik, P.; Kriskovics, L.; Kun, E.; Marion, G. H.; Marschalkó, G.; Molnár, L.; Nagy, A. P.; Pál, A.; Silverman, J. M.; Szakáts, R.; Szegedi-Elek, E.; Székely, P.; Szing, A.; Vida, K.; Wheeler, J. C.

2018-06-01

We present a comparative study of absolute distances to a sample of very nearby, bright Type Ia supernovae (SNe) derived from high cadence, high signal-to-noise, multi-band photometric data. Our sample consists of four SNe: 2012cg, 2012ht, 2013dy and 2014J. We present new homogeneous, high-cadence photometric data in Johnson–Cousins BVRI and Sloan g‧r‧i‧z‧ bands taken from two sites (Piszkesteto and Baja, Hungary), and the light curves are analyzed with publicly available light curve fitters (MLCS2k2, SNooPy2 and SALT2.4). When comparing the best-fit parameters provided by the different codes, it is found that the distance moduli of moderately reddened SNe Ia agree within ≲0.2 mag, and the agreement is even better (≲0.1 mag) for the highest signal-to-noise BVRI data. For the highly reddened SN 2014J the dispersion of the inferred distance moduli is slightly higher. These SN-based distances are in good agreement with the Cepheid distances to their host galaxies. We conclude that the current state-of-the-art light curve fitters for Type Ia SNe can provide consistent absolute distance moduli having less than ∼0.1–0.2 mag uncertainty for nearby SNe. Still, there is room for future improvements to reach the desired ∼0.05 mag accuracy in the absolute distance modulus.

A NEW CENSUS OF THE VARIABLE STAR POPULATION IN THE GLOBULAR CLUSTER NGC 2419

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Criscienzo, M.; Greco, C.; Ripepi, V.

We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two {delta} Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification. The pulsation properties of the RR Lyrae variables are close to those of Oosterhoff type II clusters, consistentmore » with the low metal abundance and the cluster horizontal branch morphology, disfavoring (but not totally ruling out) an extragalactic hypothesis for the origin of NGC 2419. The observed properties of RR Lyrae and SX Phoenicis stars are used to estimate the cluster reddening and distance, using a number of different methods. Our final value is {mu}{sub 0} (NGC 2419) = 19.71 {+-} 0.08 mag (D = 87.5 {+-} 3.3 kpc), with E(B - V) = 0.08 {+-} 0.01 mag, [Fe/H] = -2.1 dex on the Zinn and West metallicity scale, and a value of M{sub V} that sets {mu}{sub 0} (LMC) = 18.52 mag. This value is in good agreement with the most recent literature estimates of the distance to NGC 2419.« less

Rifampicin Resistance and Multidrug-Resistant Tuberculosis Detection Using Xpert MTB/RIF in Wuhan, China: A Retrospective Study.

PubMed

Huang, Hai; Zhang, Yanlin; Li, Sheng; Wang, Jun; Chen, Jun; Pan, Zhiyun; Gan, Hui

2018-06-01

The Xpert MTB/RIF test (Cepheid, Sunnyvale, CA) can simultaneously detect the Mycobacterium tuberculosis (MTB) complex DNA and rifampicin (RFP) resistance and can rapidly determine RFP resistance and predict multidrug-resistant tuberculosis (MDR-TB). In this study, we analyzed clinical examination results of a hospital specializing in TB treatment in Wuhan, Hubei, China, and examined the use of traditional culture and drug-sensitive test (DST) results as a gold standard to assess the diagnosis value of the Xpert MTB/RIF test in RFP resistance and MDR-TB. A total of 2,910 specimens were received in the Mycobacteriology Laboratory, Wuhan Pulmonary Hospital, for Xpert MTB/RIF testing between December 2013 and December 2014. After the results were reviewed by exclusion criteria, 1,066 Xpert test results were eligible for our study. We then compared the Xpert test results with sputum acid-fast bacilli staining, cultures, and DST results. In total, Xpert correctly identified 96.71% (147/152) RFP-resistant TB and 98.25% (898/914) RFP-sensitive TB specimens. Of the 147 RFP-resistant TB specimens detected by Xpert, 122 MDR-TB (82.99%) were identified by traditional culture and DST techniques. Xpert can simultaneously detect MTB and RFP resistance with high sensitivity and specificity. Thus, Xpert testing aids in saving a considerable amount of time in the diagnosis and treatment of MDR-TB.

Prospective and Retrospective Evaluation of the Performance of the FDA-Approved Cepheid Xpert Flu/RSV XC Assay.

PubMed

Arbefeville, Sophie; Thonen-Kerr, Elizabeth; Ferrieri, Patricia

2017-11-08

Rapid and accurate detection of respiratory viruses is important in patient care and in guiding therapy and infection prevention policy. Rapid viral antigen assays are simple to perform and provide results within 15 to 30 minutes but are limited by their modest-to-moderate sensitivity. Molecular assays are more sensitive and specific but require more technical time and expertise and are more expensive. We verified the performance of the Xpert Flu/RSV XC assay prospectively, using patient respiratory samples from the 2014-2015 respiratory season, and, retrospectively, with frozen patient samples from the previous respiratory season. A total of 60 specimens were assayed on the Xpert Flu/RSV XC assay and by the GenMark Diagnostics eSensor Respiratory Viral Panel. The sensitivity of the Xpert Flu/RSV XC for Flu A was 100% (23/23), for Flu B, 80% (8/10), and for respiratory syncytial virus (RSV), 94.1% (16/17), compared to the reference assay (GenMark). The specificity was 100%. Eight specimens were positive for viruses other than Flu A/B or RSV, and this did not interfere with detection of targets in the Xpert assay. We demonstrated that the performance of the Xpert Flu/RSV XC was comparable to the more comprehensive molecular respiratory assay. © American Society for Clinical Pathology, 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Utilizing the AAVSO's Variable Star Index (VSX) In Undergraduate Research Projects

NASA Astrophysics Data System (ADS)

Larsen, Kristine

2016-01-01

Among the many important services that the American Association of Variable Star Observers (AAVSO) provides to the astronomical community is the Variable Star Index (VSX - https://www.aavso.org/vsx/). This online catalog of variable stars is the repository of data on over 334,000 variable stars, including information on spectral type, range of magnitude, period, and type of variable, among other properties. A number of these stars were identified as being variable through automated telescope surveys, such as ASAS (All Sky Automated Survey). The computer code of this survey classified newly discovered variables as best it could, but a significant number of false classifications have been noted. The reclassification of ASAS variables in the VSX data, as well as a closer look at variables identified as miscellaneous type in VSX, are two of many projects that can be undertaken by interested undergraduates. In doing so, students learn about the physical properties of various types of variable stars as well as statistical analysis and computer software, especially the VStar variable star data visualization and analysis tool that is available to the astronomical community free of charge on the AAVSO website (https://www.aavso.org/vstar-overview). Two such projects are described in this presentation, the first to identify BY Draconis variables erroneously classified as Cepheids in ASAS data, and the second to identify SRD semiregular variables misidentified as "miscellaneous" in VSX.

Utilizing the AAVSO's Variable Star Index (VSX) in Undergraduate Research Projects (Poster abstract)

NASA Astrophysics Data System (ADS)

Larsen, K.

2016-12-01

(Abstract only) Among the many important services that the American Association of Variable Star Observers (AAVSO) provides to the astronomical community is the Variable Star Index (VSX; https://www.aavso.org/vsx/). This online catalog of variable stars is the repository of data on over 334,000 variable stars, including information on spectral type, range of magnitude, period, and type of variable, among other properties. A number of these stars were identified as being variable through automated telescope surveys, such as ASAS (All Sky Automated Survey). The computer code of this survey classified newly discovered variables as best it could, but a significant number of false classifications have been noted. The reclassification of ASAS variables in the VSX data, as well as a closer look at variables identified as miscellaneous type in VSX, are two of many projects that can be undertaken by interested undergraduates. In doing so, students learn about the physical properties of various types of variable stars as well as statistical analysis and computer software, especially the vstar variable star data visualization and analysis tool that is available to the astronomical community free of charge on the AAVSO website (https://www.aavso.org/vstar-overview). Three such projects are described in this presentation, to identify BY Draconis variables misidentified as Cepheids or "miscellaneous", and SRD semiregular variables and ELL (rotating ellipsoidal) variables misidentified as "miscellaneous", in ASAS data and VSX.

Three year evaluation of Xpert MTB/RIF in a low prevalence tuberculosis setting: A Scottish perspective.

PubMed

Parcell, Benjamin J; Jarchow-MacDonald, Anna A; Seagar, Amie-Louise; Laurenson, Ian F; Prescott, Gordon J; Lockhart, Michael

2017-05-01

Xpert MTB/RIF (Cepheid) is a rapid molecular assay shown to be sensitive and specific for pulmonary tuberculosis (TB) diagnosis in highly endemic countries. We evaluated its diagnostic performance in a low TB prevalence setting, examined rifampicin resistance detection and quantitative capabilities predicting graded auramine microscopy and time to positivity (TTP) of culture. Xpert MTB/RIF was used to test respiratory samples over a 3 year period. Samples underwent graded auramine microscopy, solid/liquid culture, in-house IS6110 real-time PCR, and GenoType MTBDRplus (HAIN Lifescience) to determine rifampicin and/or isoniazid resistance. A total of 2103 Xpert MTB/RIF tests were performed. Compared to culture sensitivity was 95.8%, specificity 99.5%, positive predictive value (PPV) 82.1%, and negative predictive value (NPV) 99.9%. A positive correlation was found between auramine microscopy grade and Xpert MTB/RIF assay load. We found a clear reduction in the median TTP as Xpert MTB/RIF assay load increased. Rifampicin resistance was detected. Xpert MTB/RIF was rapid and accurate in diagnosing pulmonary TB in a low prevalence area. Rapid results will influence infection prevention and control and treatment measures. The excellent NPV obtained suggests further work should be carried out to assess its role in replacing microscopy. Copyright © 2017 The British Infection Association. Published by Elsevier Ltd. All rights reserved.

Robust Period Estimation Using Mutual Information for Multiband Light Curves in the Synoptic Survey Era

NASA Astrophysics Data System (ADS)

Huijse, Pablo; Estévez, Pablo A.; Förster, Francisco; Daniel, Scott F.; Connolly, Andrew J.; Protopapas, Pavlos; Carrasco, Rodrigo; Príncipe, José C.

2018-05-01

The Large Synoptic Survey Telescope (LSST) will produce an unprecedented amount of light curves using six optical bands. Robust and efficient methods that can aggregate data from multidimensional sparsely sampled time-series are needed. In this paper we present a new method for light curve period estimation based on quadratic mutual information (QMI). The proposed method does not assume a particular model for the light curve nor its underlying probability density and it is robust to non-Gaussian noise and outliers. By combining the QMI from several bands the true period can be estimated even when no single-band QMI yields the period. Period recovery performance as a function of average magnitude and sample size is measured using 30,000 synthetic multiband light curves of RR Lyrae and Cepheid variables generated by the LSST Operations and Catalog simulators. The results show that aggregating information from several bands is highly beneficial in LSST sparsely sampled time-series, obtaining an absolute increase in period recovery rate up to 50%. We also show that the QMI is more robust to noise and light curve length (sample size) than the multiband generalizations of the Lomb–Scargle and AoV periodograms, recovering the true period in 10%–30% more cases than its competitors. A python package containing efficient Cython implementations of the QMI and other methods is provided.

Revisiting the radial abundance gradients of nitrogen and oxygen of the Milky Way

NASA Astrophysics Data System (ADS)

Esteban, C.; García-Rojas, J.

2018-05-01

We present spectra obtained with the 10.4 m Gran Telescopio Canarias telescope of 13 Galactic H II regions, most of them of very low ionisation degree. The objects are located along the Galactic disc, with RG from 5.7 to 16.1 kpc. We determine Te([N II]) for all of them. We obtain - for the first time - a radial abundance gradient of N that is independent on the ionisation correction factor. The radial distribution of the N/O ratio is almost flat, indicating that the bulk of N is not formed by standard secondary processes. We have made a reassessment of the radial O abundance gradient combining our results with previous similar ones by Esteban et al. (2017); producing a homogeneous dataset of 35 H II regions with direct determinations of the electron temperature. We report the possible presence of a flattening or drop of the O abundance in the inner part of the Galactic disc. This result confirms previous findings from metallicity distributions based on Cepheids and red giants. Finally, we find that the scatter of the N and O abundances of H II regions with respect to the gradient fittings is not substantially larger than the observational uncertainties, indicating that both chemical elements seem to be well mixed in the interstellar gas at a given distance along the Galactic disc

Performance of the Xpert HIV-1 Viral Load Assay: a Systematic Review and Meta-analysis

PubMed Central

Nash, Madlen; Huddart, Sophie; Badar, Sayema; Baliga, Shrikala; Saravu, Kavitha

2018-01-01

ABSTRACT Viral load (VL) is the preferred treatment-monitoring approach for HIV-positive patients. However, more rapid, near-patient, and low-complexity assays are needed to scale up VL testing. The Xpert HIV-1 VL assay (Cepheid, Sunnyvale, CA) is a new, automated molecular test, and it can leverage the GeneXpert systems that are being used widely for tuberculosis diagnosis. We systematically reviewed the evidence on the performance of this new tool in comparison to established reference standards. A total of 12 articles (13 studies) in which HIV patient VLs were compared between Xpert HIV VL assay and a reference standard VL assay were identified. Study quality was generally high, but substantial variability was observed in the number and type of agreement measures reported. Correlation coefficients between Xpert and reference assays were high, with a pooled Pearson correlation (n = 8) of 0.94 (95% confidence interval [CI], 0.89, 0.97) and Spearman correlation (n = 3) of 0.96 (95% CI, 0.86, 0.99). Bland-Altman metrics (n = 11) all were within 0.35 log copies/ml of perfect agreement. Overall, Xpert HIV-1 VL performed well compared to current reference tests. The minimal training and infrastructure requirements for the Xpert HIV-1 VL assay make it attractive for use in resource-constrained settings, where point-of-care VL testing is most needed. PMID:29386266

Performance of the Xpert HIV-1 Viral Load Assay: a Systematic Review and Meta-analysis.

PubMed

Nash, Madlen; Huddart, Sophie; Badar, Sayema; Baliga, Shrikala; Saravu, Kavitha; Pai, Madhukar

2018-04-01

Viral load (VL) is the preferred treatment-monitoring approach for HIV-positive patients. However, more rapid, near-patient, and low-complexity assays are needed to scale up VL testing. The Xpert HIV-1 VL assay (Cepheid, Sunnyvale, CA) is a new, automated molecular test, and it can leverage the GeneXpert systems that are being used widely for tuberculosis diagnosis. We systematically reviewed the evidence on the performance of this new tool in comparison to established reference standards. A total of 12 articles (13 studies) in which HIV patient VLs were compared between Xpert HIV VL assay and a reference standard VL assay were identified. Study quality was generally high, but substantial variability was observed in the number and type of agreement measures reported. Correlation coefficients between Xpert and reference assays were high, with a pooled Pearson correlation ( n = 8) of 0.94 (95% confidence interval [CI], 0.89, 0.97) and Spearman correlation ( n = 3) of 0.96 (95% CI, 0.86, 0.99). Bland-Altman metrics ( n = 11) all were within 0.35 log copies/ml of perfect agreement. Overall, Xpert HIV-1 VL performed well compared to current reference tests. The minimal training and infrastructure requirements for the Xpert HIV-1 VL assay make it attractive for use in resource-constrained settings, where point-of-care VL testing is most needed. Copyright © 2018 Nash et al.

Validation of Clinical Testing for Warfarin Sensitivity

PubMed Central

Langley, Michael R.; Booker, Jessica K.; Evans, James P.; McLeod, Howard L.; Weck, Karen E.

2009-01-01

Responses to warfarin (Coumadin) anticoagulation therapy are affected by genetic variability in both the CYP2C9 and VKORC1 genes. Validation of pharmacogenetic testing for warfarin responses includes demonstration of analytical validity of testing platforms and of the clinical validity of testing. We compared four platforms for determining the relevant single nucleotide polymorphisms (SNPs) in both CYP2C9 and VKORC1 that are associated with warfarin sensitivity (Third Wave Invader Plus, ParagonDx/Cepheid Smart Cycler, Idaho Technology LightCycler, and AutoGenomics Infiniti). Each method was examined for accuracy, cost, and turnaround time. All genotyping methods demonstrated greater than 95% accuracy for identifying the relevant SNPs (CYP2C9 *2 and *3; VKORC1 −1639 or 1173). The ParagonDx and Idaho Technology assays had the shortest turnaround and hands-on times. The Third Wave assay was readily scalable to higher test volumes but had the longest hands-on time. The AutoGenomics assay interrogated the largest number of SNPs but had the longest turnaround time. Four published warfarin-dosing algorithms (Washington University, UCSF, Louisville, and Newcastle) were compared for accuracy for predicting warfarin dose in a retrospective analysis of a local patient population on long-term, stable warfarin therapy. The predicted doses from both the Washington University and UCSF algorithms demonstrated the best correlation with actual warfarin doses. PMID:19324988

Validation of clinical testing for warfarin sensitivity: comparison of CYP2C9-VKORC1 genotyping assays and warfarin-dosing algorithms.

PubMed

Langley, Michael R; Booker, Jessica K; Evans, James P; McLeod, Howard L; Weck, Karen E

2009-05-01

Responses to warfarin (Coumadin) anticoagulation therapy are affected by genetic variability in both the CYP2C9 and VKORC1 genes. Validation of pharmacogenetic testing for warfarin responses includes demonstration of analytical validity of testing platforms and of the clinical validity of testing. We compared four platforms for determining the relevant single nucleotide polymorphisms (SNPs) in both CYP2C9 and VKORC1 that are associated with warfarin sensitivity (Third Wave Invader Plus, ParagonDx/Cepheid Smart Cycler, Idaho Technology LightCycler, and AutoGenomics Infiniti). Each method was examined for accuracy, cost, and turnaround time. All genotyping methods demonstrated greater than 95% accuracy for identifying the relevant SNPs (CYP2C9 *2 and *3; VKORC1 -1639 or 1173). The ParagonDx and Idaho Technology assays had the shortest turnaround and hands-on times. The Third Wave assay was readily scalable to higher test volumes but had the longest hands-on time. The AutoGenomics assay interrogated the largest number of SNPs but had the longest turnaround time. Four published warfarin-dosing algorithms (Washington University, UCSF, Louisville, and Newcastle) were compared for accuracy for predicting warfarin dose in a retrospective analysis of a local patient population on long-term, stable warfarin therapy. The predicted doses from both the Washington University and UCSF algorithms demonstrated the best correlation with actual warfarin doses.

PULSATION PERIOD VARIATIONS IN THE RRc LYRAE STAR KIC 5520878

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hippke, Michael; Learned, John G.; Zee, A.

Learned et al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among variable stars using photometric data from themore » Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have found two such regimes of long and short pulse durations. The sequence of period lengths, expressed as time series data, is strongly autocorrelated, with correlation coefficients of prime numbers being significantly higher (p = 99.8%). Our analysis of this candidate star shows that the prime number oddity originates from two simultaneous pulsation periods and is likely of natural origin. Simple physical models elucidate the frequency content and asymmetries of the KIC 5520878 light curve. Despite this SETI null result, we encourage testing of other archival and future time-series photometry for signs of modulated stars. This can be done as a by-product to the standard analysis, and can even be partly automated.« less

VizieR Online Data Catalog: Spectroscopic and photometric properties of Tombaugh 1 (Sales+, 2016)

NASA Astrophysics Data System (ADS)

Sales Silva, J. V.; Carraro, G.; Anthony-Twarog, B. J.; Moni Bidin, C.; Costa, E.; Twarog, B. A.

2018-03-01

Photometry for Tombaugh 1 was secured in 2010 December during a five-night run using the Cerro Tololo Inter-American Observatory 1.0 m telescope operated by the SMARTS consortium (http://www.astro.yale.edu/smarts). The telescope is equipped with an STA 4064x4064 CCD camera (http://www.astronomy.ohio-state.edu/Y4KCam/detector) with 15 μm pixels, yielding a scale of 0.289"/pixel and a field of view (FOV) of 20'x20' at the Cassegrain focus of the telescope. Over the night of 2010 January 5, we observed 10 potential cluster stars (nine clump stars and one Cepheid; see Section 4.1) with the Inamori-Magellan Areal Camera & Spectrograph (IMACS; Dressler et al. 2006SPIE.6269E..0FD) attached to the Magellan telescope (6.5 m) located at Las Campanas, Chile. The spectra were obtained using the Multi-Object Echelle (MOE) mode with two exposures, one of 900 s and the other of 1200 s. Our spectra have a resolution of R~20000, while the spectral coverage depends on the location of the star on the multislit mask, but it generally goes from 4200 to 9100 Å. The detector consists of a mosaic with eight CCDs with gaps of about 0.93 mm between the CCDs, causing small gaps in stellar spectra. (7 data files).

STELLAR ARCHEOLOGY IN THE GALACTIC HALO WITH ULTRA-FAINT DWARFS. VII. HERCULES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella, E-mail: ilaria@na.astro.it, E-mail: ripepi@na.astro.it, E-mail: marcella@na.astro.it

2012-09-10

We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, (P{sub ab}) = 0.68 days ({sigma} = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability.more » The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 {+-} 0.15 dex, E(B - V) = 0.09 {+-} 0.02 mag, and (m - M){sub 0} = 20.6 {+-} 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V {approx} 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' Multiplication-Sign 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68.« less

The Araucaria Project: The Distance to the Fornax Dwarf Galaxy from Near-infrared Photometry of RR Lyrae Stars

NASA Astrophysics Data System (ADS)

Karczmarek, Paulina; Pietrzyński, Grzegorz; Górski, Marek; Gieren, Wolfgang; Bersier, David

2017-12-01

We have obtained single-phase near-infrared (NIR) magnitudes in the J and K bands for 77 RR Lyrae (RRL) stars in the Fornax Dwarf Spheroidal Galaxy. We have used different theoretical and empirical NIR period-luminosity-metallicity calibrations for RRL stars to derive their absolute magnitudes, and found a true, reddening-corrected distance modulus of 20.818+/- 0.015{{(statistical)}}+/- 0.116{{(systematic)}} mag. This value is in excellent agreement with the results obtained within the Araucaria Project from the NIR photometry of red clump stars (20.858 ± 0.013 mag), the tip of the red giant branch (20.84+/- 0.04+/- 0.14 mag), as well as with other independent distance determinations to this galaxy. The effect of metallicity and reddening is substantially reduced in the NIR domain, making this method a robust tool for accurate distance determination at the 5% level. This precision is expected to reach the level of 3% once the zero points of distance calibrations are refined thanks to the Gaia mission. NIR period-luminosity-metallicity relations of RRL stars are particularly useful for distance determinations to galaxies and globular clusters up to 300 kpc, that lack young standard candles, like Cepheids. Based on data collected with the VLT/HAWK-I instrument at ESO Paranal Observatory, Chile, as a part of programme 082.D-0123(B).

Clustering of local group distances: Publication bias or correlated measurements? II. M31 and beyond

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Grijs, Richard; Bono, Giuseppe

2014-07-01

The accuracy of extragalactic distance measurements ultimately depends on robust, high-precision determinations of the distances to the galaxies in the local volume. Following our detailed study addressing possible publication bias in the published distance determinations to the Large Magellanic Cloud (LMC), here we extend our distance range of interest to include published distance moduli to M31 and M33, as well as to a number of their well-known dwarf galaxy companions. We aim at reaching consensus on the best, most homogeneous, and internally most consistent set of Local Group distance moduli to adopt for future, more general use based on themore » largest set of distance determinations to individual Local Group galaxies available to date. Based on a careful, statistically weighted combination of the main stellar population tracers (Cepheids, RR Lyrae variables, and the magnitude of the tip of the red-giant branch), we derive a recommended distance modulus to M31 of (m−M){sub 0}{sup M31}=24.46±0.10 mag—adopting as our calibration an LMC distance modulus of (m−M){sub 0}{sup LMC}=18.50 mag—and a fully internally consistent set of benchmark distances to key galaxies in the local volume, enabling us to establish a robust and unbiased, near-field extragalactic distance ladder.« less

Spectroscopic and photometric oscillatory envelope variability during the S Doradus outburst of the luminous blue variable R71

NASA Astrophysics Data System (ADS)

Mehner, A.; Baade, D.; Groh, J. H.; Rivinius, T.; Hambsch, F.-J.; Bartlett, E. S.; Asmus, D.; Agliozzo, C.; Szeifert, T.; Stahl, O.

2017-12-01

Context. Luminous blue variables (LBVs) are evolved massive stars that exhibit instabilities that are not yet understood. Stars can lose several solar masses during this evolutionary phase. The LBV phenomenon is thus critical to our understanding of the evolution of the most massive stars. Aims: The LBV R71 in the Large Magellanic Cloud is presently undergoing an S Doradus outburst, which started in 2005. To better understand the LBV phenomenon, we determine the fundamental stellar parameters of R71 during its quiescence phase. In addition, we analyze multiwavelength spectra and photometry obtained during the current outburst. Methods: We analyzed pre-outburst CASPEC spectra from 1984-1997, EMMI spectra in 2000, UVES spectra in 2002, and FEROS spectra from 2005 with the radiative transfer code CMFGEN to determine the fundamental stellar parameters of the star. A spectroscopic monitoring program with VLT X-shooter since 2012 secured visual to near-infrared spectra throughout the current outburst, which is well-covered by ASAS and AAVSO photometry. Mid-infrared images and radio data were also obtained. Results: During quiescence, R71 has an effective temperature of Teff = 15 500 K and a luminosity of log(L∗/L⊙) = 5.78. We determine its mass-loss rate to 4.0 × 10-6M⊙ yr-1. We present the spectral energy distribution of R71 from the near-ultraviolet to the mid-infrared during its present outburst. Semi-regular oscillatory variability in the light curve of the star is observed during the current outburst. Absorption lines develop a second blue component on a timescale of twice that length. The variability may consist of one (quasi-)periodic component with P 425/850 d with additional variations superimposed. Conclusions: R71 is a classical LBV, but this star is at the lower luminosity end of this group. Mid-infrared observations suggest that we are witnessing dust formation and grain evolution. During its current S Doradus outburst, R71 occupies a region in the HR diagram at the high-luminosity extension of the Cepheid instability strip and exhibits similar irregular variations as RV Tau variables. LBVs do not pass the Cepheid instability strip because of core evolution, but they develop comparable cool, low-mass, extended atmospheres in which convective instabilities may occur. As in the case of RV Tau variables, the occurrence of double absorption lines with an apparent regular cycle may be due to shocks within the atmosphere and period doubling may explain the factor of two in the lengths of the photometric and spectroscopic cycles. Based on observations collected at ESO's Very Large Telescope under Prog-IDs: 69.D-0390(D), 289.D-5040(A), 290.D-5032(A), 091.D-0116(A, B), 092.D-0024(A), 094.D-0266(A, B, C), 096.D-0043(A, B, C), 097.D-0006(A, B), 598.D-0005(A, B) and at the MPG/ESO 2.2-m Telescope under Prog-IDs: 076.D-0609(A), 078.D-0790(B), 086.D-0997(A, B), 087.D-0946(A), 089.D-0975(A), 094.A-9029(D), 096.A-9039(A), 097.D-0612(A, B), 098.D-0071(A).

Diagnosis of Clostridium difficile-associated disease: examination of multiple algorithms using toxin EIA, glutamate dehydrogenase EIA and loop-mediated isothermal amplification.

PubMed

Bamber, A I; Fitzsimmons, K; Cunniffe, J G; Beasor, C C; Mackintosh, C A; Hobbs, G

2012-01-01

The laboratory diagnosis of Clostridium difficile infection (CDI) needs to be accurate and timely to ensure optimal patient management, infection control and reliable surveillance. Three methods are evaluated using 810 consecutive stool samples against toxigenic culture: CDT TOX A/B Premier enzyme immunoassay (EIA) kit (Meridian Bioscience, Europe), Premier EIA for C. difficile glutamate dehydrogenase (GDH) (Meridian Bioscience, Europe) and the Illumigene kit (Meridian Bioscience, Europe), both individually and within combined testing algorithms. The study revealed that the CDT TOX A/B Premier EIA gave rise to false-positive and false-negative results and demonstrated poor sensitivity (56.47%), compared to Premier EIA for C. difficile GDH (97.65%), suggesting this GDH EIA can be a useful negative screening method. Results for the Illumigene assay alone showed sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) of 91.57%, 98.07%, 99.03% and 84.44%, respectively. A two-stage algorithm using Premier EIA for C. difficile GDH/Illumigene assay yielded superior results compared with other testing algorithms (91.57%, 98.07%, 99.03% and 84.44%, respectively), mirroring the Illumigene performance. However, Illumigene is approximately half the cost of current polymerase chain reaction (PCR) methods, has a rapid turnaround time and requires no specialised skill base, making it an attractive alternative to assays such as the Xpert C. difficile assay (Cepheid, Sunnyvale, CA). A three-stage algorithm offered no improvement and would hamper workflow.

Self-oscillation

NASA Astrophysics Data System (ADS)

Jenkins, Alejandro

2013-04-01

Physicists are very familiar with forced and parametric resonance, but usually not with self-oscillation, a property of certain dynamical systems that gives rise to a great variety of vibrations, both useful and destructive. In a self-oscillator, the driving force is controlled by the oscillation itself so that it acts in phase with the velocity, causing a negative damping that feeds energy into the vibration: no external rate needs to be adjusted to the resonant frequency. The famous collapse of the Tacoma Narrows bridge in 1940, often attributed by introductory physics texts to forced resonance, was actually a self-oscillation, as was the swaying of the London Millennium Footbridge in 2000. Clocks are self-oscillators, as are bowed and wind musical instruments. The heart is a “relaxation oscillator”, i.e., a non-sinusoidal self-oscillator whose period is determined by sudden, nonlinear switching at thresholds. We review the general criterion that determines whether a linear system can self-oscillate. We then describe the limiting cycles of the simplest nonlinear self-oscillators, as well as the ability of two or more coupled self-oscillators to become spontaneously synchronized (“entrained”). We characterize the operation of motors as self-oscillation and prove a theorem about their limit efficiency, of which Carnot’s theorem for heat engines appears as a special case. We briefly discuss how self-oscillation applies to servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business cycle, among other applications. Our emphasis throughout is on the energetics of self-oscillation, often neglected by the literature on nonlinear dynamical systems.

A pilot evaluation of whole blood finger-prick sampling for point-of-care HIV viral load measurement: the UNICORN study.

PubMed

Fidler, Sarah; Lewis, Heather; Meyerowitz, Jodi; Kuldanek, Kristin; Thornhill, John; Muir, David; Bonnissent, Alice; Timson, Georgina; Frater, John

2017-10-20

There is a global need for HIV viral load point-of-care (PoC) assays to monitor patients receiving antiretroviral therapy. UNICORN was the first study of an off-label protocol using whole blood finger-prick samples tested with and without a simple three minute spin using a clinic-room microcentrifuge. Two PoC assays were evaluated in 40 HIV-positive participants, 20 with detectable and 20 with undetectable plasma viral load (pVL) (<20 copies/ml). Using 100 µl finger-prick blood samples, the Cepheid Xpert HIV-1 Viral Load and HIV-1 Qual cartridges were compared with laboratory pVL assessment (TaqMan, Roche). For participants with undetectable viraemia by TaqMan, there was poor concordance without centrifugation with the TaqMan platform with only 40% 'undetectable' using Xpert VL and 25% 'not detected' using the Qual assay. After a 3 minute spin, 100% of samples were undetectable using either assay, showing full concordance with the TaqMan assay. Defining a lower limit of detection of 1000 copies/ml when including a spin, there was 100% concordance with the TaqMan platform with strong correlation (rho 0.95 and 0.94; p < 0.0001 for both assays). When including a simple microcentrifugation step, finger-prick PoC testing was a quick and accurate approach for assessing HIV viraemia, with excellent concordance with validated laboratory approaches.

Chlamydia and Gonorrhea in HIV-Infected Pregnant Women and Infant HIV Transmission.

PubMed

Adachi, Kristina; Klausner, Jeffrey D; Bristow, Claire C; Xu, Jiahong; Ank, Bonnie; Morgado, Mariza G; Watts, D Heather; Weir, Fred; Persing, David; Mofenson, Lynne M; Veloso, Valdilea G; Pilotto, Jose Henrique; Joao, Esau; Nielsen-Saines, Karin

2015-10-01

Sexually transmitted infections (STIs) such as Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) can lead to adverse pregnancy and neonatal outcomes. The prevalence of STIs and its association with HIV mother-to-child transmission (MTCT) were evaluated in a substudy analysis from a randomized, multicenter clinical trial. Urine samples from HIV-infected pregnant women collected at the time of labor and delivery were tested using polymerase chain reaction testing for the detection of CT and NG (Xpert CT/NG; Cepheid, Sunnyvale, CA). Infant HIV infection was determined by HIV DNA polymerase chain reaction at 3 months. Of the 1373 urine specimens, 249 (18.1%) were positive for CT and 63 (4.6%) for NG; 35 (2.5%) had both CT and NG detected. Among 117 cases of HIV MTCT (8.5% transmission), the lowest transmission rate occurred among infants born to CT- and NG-uninfected mothers (8.1%) as compared with those infected with only CT (10.7%) and both CT and NG (14.3%; P = 0.04). Infants born to CT-infected mothers had almost a 1.5-fold increased risk for HIV acquisition (odds ratio, 1.47; 95% confidence interval, 0.9-2.3; P = 0.09). This cohort of HIV-infected pregnant women is at high risk for infection with CT and NG. Analysis suggests that STIs may predispose to an increased HIV MTCT risk in this high-risk cohort of HIV-infected women.

Accuracy of a rapid real-time polymerase chain reaction assay for diagnosis of group B Streptococcus colonization in a cohort of HIV-infected pregnant women.

PubMed

Gouvea, Maria Isabel S; Joao, Esau C; Teixeira, Maria de Lourdes B; Read, Jennifer S; Fracalanzza, Sergio E L; Souza, Claudia T V; Souza, Maria José de; Torres Filho, Helio M; Leite, Cassiana C F; do Brasil, Pedro E A A

2017-05-01

There are limited data regarding Xpert performance to detect Group B Streptococcus (GBS) in HIV-infected pregnant women. We evaluated the accuracy of a rapid real-time polymerase chain reaction (PCR) test in a cohort of HIV-infected women. At 35-37 weeks of pregnancy, a pair of combined rectovaginal swabs were collected for two GBS assays in a cohort of sequentially included HIV-infected women in Rio de Janeiro: (1) culture; and (2) real-time PCR assay [GeneXpert GBS (Cepheid, Sunnyvale, CA)]. Using culture as the reference, sensitivity, specificity, positive and negative-likelihood ratios were estimated. From June 2012 to February 2015, 337 pregnant women met inclusion criteria. One woman was later excluded, due to failure to obtain a result in the index test; 336 were included in the analyses. The GBS colonization rate was 19.04%. Sensitivity and specificity of the GeneXpert GBS assay were 85.94% (95% CI: 75.38-92.42) and 94.85% (95% CI: 91.55-96.91), respectively. Positive and negative predictive values were 79.71% (95% CI: 68.78-87.51) and 96.63% (95% CI: 93.72-98.22), respectively. GeneXpert GBS is an acceptable test for the identification of GBS colonization in HIV-infected pregnant women and represents a reasonable option to detect GBS colonization in settings where culture is not feasible.

The H0 tension in light of vacuum dynamics in the universe

NASA Astrophysics Data System (ADS)

Solà, Joan; Gómez-Valent, Adrià; de Cruz Pérez, Javier

2017-11-01

Despite the outstanding achievements of modern cosmology, the classical dispute on the precise value of H0, which is the first ever parameter of modern cosmology and one of the prime parameters in the field, still goes on and on after over half a century of measurements. Recently the dispute came to the spotlight with renewed strength owing to the significant tension (at > 3 σ c.l.) between the latest Planck determination obtained from the CMB anisotropies and the local (distance ladder) measurement from the Hubble Space Telescope (HST), based on Cepheids. In this work, we investigate the impact of the running vacuum model (RVM) and related models on such a controversy. For the RVM, the vacuum energy density ρΛ carries a mild dependence on the cosmic expansion rate, i.e. ρΛ (H), which allows to ameliorate the fit quality to the overall SNIa + BAO + H (z) + LSS + CMB cosmological observations as compared to the concordance ΛCDM model. By letting the RVM to deviate from the vacuum option, the equation of state w = - 1 continues to be favored by the overall fit. Vacuum dynamics also predicts the following: i) the CMB range of values for H0 is more favored than the local ones, and ii) smaller values for σ8 (0). As a result, a better account for the LSS structure formation data is achieved as compared to the ΛCDM, which is based on a rigid (i.e. non-dynamical) Λ term.

Chlamydia and Gonorrhea in HIV-infected Pregnant Women and Infant HIV Transmission

PubMed Central

Adachi, Kristina; Klausner, Jeffrey D.; Bristow, Claire C.; Xu, Jiahong; Ank, Bonnie; Morgado, Mariza G; Watts, D. Heather; Weir, Fred; Persing, David; Mofenson, Lynne M.; Veloso, Valdilea G.; Pilotto, Jose Henrique; Joao, Esau; Nielsen-Saines, Karin

2015-01-01

BACKGROUND Sexually transmitted infections (STIs) such as Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) can lead to adverse pregnancy and neonatal outcomes. STI prevalence and its association with HIV mother-to-child transmission (MTCT) were evaluated in a sub-study analysis from a randomized, multi-center clinical trial. METHODOLOGY Urine samples from HIV-infected pregnant women collected at the time of labor and delivery were tested using polymerase chain reaction (PCR) testing for the detection of CT and NG (Xpert® CT/NG, Cepheid, Sunnyvale, CA). Infant HIV infection was determined by HIV DNA PCR at 3 months. RESULTS Of the 1373 urine specimens, 249 (18.1%) were positive for CT and 63 (4.6%) for NG; 35 (2.5%) had both CT and NG detected. Among 117 cases of HIV MTCT (8.5% transmission) the lowest transmission rate occurred among infants born to CT and NG uninfected mothers (8.1%) as compared to those infected with only CT (10.7%) and both CT and NG (14.3%), (p = 0.04). Infants born to CT-infected mothers had almost a 1.5-fold increased risk for HIV acquisition (OR 1.47, 95% CI 0.9–2.3, p=0.09). CONCLUSION This cohort of HIV-infected pregnant women are at high risk for infection with CT and NG. Analysis suggests that STIs may predispose to an increased HIV MTCT risk in this high risk cohort of HIV-infected women. PMID:26372927

A Near-infrared Period–Luminosity Relation for Miras in NGC 4258, an Anchor for a New Distance Ladder

NASA Astrophysics Data System (ADS)

Huang, Caroline D.; Riess, Adam G.; Hoffmann, Samantha L.; Klein, Christopher; Bloom, Joshua; Yuan, Wenlong; Macri, Lucas M.; Jones, David O.; Whitelock, Patricia A.; Casertano, Stefano; Anderson, Richard I.

2018-04-01

We present year-long, near-infrared (NIR) Hubble Space Telescope (HST) WFC3 observations of Mira variables in the water megamaser host galaxy NGC 4258. Miras are asymptotic giant branch variables that can be divided into oxygen- (O-) and carbon- (C-) rich subclasses. Oxygen-rich Miras follow a tight (scatter ∼0.14 mag) period–luminosity relation (PLR) in the NIR and can be used to measure extragalactic distances. The water megamaser in NGC 4258 gives a geometric distance to the galaxy accurate to 2.6% that can serve to calibrate the Mira PLR. We develop criteria for detecting and classifying O-rich Miras with optical and NIR data as well as NIR data alone. In total, we discover 438 Mira candidates that we classify with high confidence as O-rich. Our most stringent criteria produce a sample of 139 Mira candidates that we use to measure a PLR. We use the OGLE-III sample of O-rich Miras in the Large Magellanic Cloud to obtain a relative distance modulus, μ 4258 ‑ μ LMC = 10.95 ± 0.01 (statistical) ±0.06 (systematic) mag, that is statistically consistent with the relative distance determined using Cepheids. These results demonstrate the feasibility of discovering and characterizing Miras using the NIR with the HST and the upcoming James Webb Space Telescope and using those Miras to measure extragalactic distances and determine the Hubble constant.

Clinical value of polymerase chain reaction in detecting group B streptococcus during labor.

PubMed

Koppes, Dorothea Maria; Vriends, Antonius Arnoldus Cornelis Maria; van Rijn, Michiel; van Heesewijk, Antonine Dimphne

2017-06-01

To reduce the intrapartum use of antibiotics in women with prolonged rupture of the membranes (PROM) by restriction of antibiotics to women who are colonized with group B streptococci (GBS), as identified with the Cepheid Gene Xpert polymerase chain reaction (PCR) for detecting GBS. We conducted a randomized controlled trial among full-term delivering women with PROM. Fifty-four women were enrolled, based on a power calculation with a significance level of 5% and a power of 95%. Twenty-seven women received the standard treatment (rectovaginal swab [RVS] for bacterial culture and antibiotics). For another 27 women PCR was performed on the RVS and antibiotics were used only when the PCR was positive. The primary outcome was reduction in antibiotic use, defined as the percentage of women who received antibiotics during labor. 54 Women were enrolled in the study between 1 May and 18 November 2014. There were no significant differences in baseline characteristics. In total, 10 of the 54 women were GBS positive (18.5%). Of those 10 women, three were identified on bacterial culture and seven on PCR. In the bacterial culture group all the women received antibiotics. In the PCR group 10 women (37%) received antibiotics (P = 0.002). Two false-positive PCR tests were identified. There were no false-negative PCR tests. Real-time identification of GBS on PCR reduces the intrapartum use of antibiotics in women with PROM. © 2017 Japan Society of Obstetrics and Gynecology.

The Baade-Wesselink projection factor of the δ-Scuti stars AI Vel and β Cas

NASA Astrophysics Data System (ADS)

Guiglion, G.; Nardetto, N.; Domiciano de Souza, A.; Mathias, P.; Mourard, D.; Poretti, E.

2012-12-01

The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. After determining the angular diameter and the linear radius variations, the distance is derived by a simple ratio. The linear radius variation is measured by integrating the pulsation velocity (hereafter V_{puls}) over one pulsating cycle. However, from observations we have only access to the radial velocity (V_{rad}) because of the projection along the line-of-sight. The projection factor, used to convert the radial velocity into the pulsation velocity, is defined by: p = V_{puls} / V_{rad}. We aim to derive the projection factor for two δ-Scuti stars, the high amplitude pulsator AI Vel and the fast rotator β Cas. The geometric component of the projection factor is derived using a limb-darkening model of the intensity distribution of AI Vel, and a fast rotator model for β Cas. Then, by comparing the radial velocity curves of several spectral lines forming at different levels in the atmosphere, we derive directly the velocity gradient (in a part of the atmosphere of the star) using SOPHIE/OHP data for β Cas and HARPS/ESO data for AI Vel, which is used to derive a dynamical projection factor for both stars. We find p = 1.44 ± 0.05 for AI Vel and p = 1.41 ± 0.25 for β Cas. By comparing Cepheids and δ-Scuti stars, these results bring valuable insights into the dynamical structure of pulsating star atmospheres.

The Far-Field Hubble Constant

NASA Astrophysics Data System (ADS)

Lauer, Tod

1995-07-01

We request deep, near-IR (F814W) WFPC2 images of five nearby Brightest Cluster Galaxies (BCG) to calibrate the BCG Hubble diagram by the Surface Brightness Fluctuation (SBF) method. Lauer & Postman (1992) show that the BCG Hubble diagram measured out to 15,000 km s^-1 is highly linear. Calibration of the Hubble diagram zeropoint by SBF will thus yield an accurate far-field measure of H_0 based on the entire volume within 15,000 km s^-1, thus circumventing any strong biases caused by local peculiar velocity fields. This method of reaching the far field is contrasted with those using distance ratios between Virgo and Coma, or any other limited sample of clusters. HST is required as the ground-based SBF method is limited to <3,000 km s^-1. The high spatial resolution of HST allows precise measurement of the SBF signal at large distances, and allows easy recognition of globular clusters, background galaxies, and dust clouds in the BCG images that must be removed prior to SBF detection. The proposing team developed the SBF method, the first BCG Hubble diagram based on a full-sky, volume-limited BCG sample, played major roles in the calibration of WFPC and WFPC2, and are conducting observations of local galaxies that will validate the SBF zeropoint (through GTO programs). This work uses the SBF method to tie both the Cepheid and Local Group giant-branch distances generated by HST to the large scale Hubble flow, which is most accurately traced by BCGs.

Near-infrared variability study of the central 2.3 arcmin × 2.3 arcmin of the Galactic Centre - I. Catalogue of variable sources

NASA Astrophysics Data System (ADS)

Dong, Hui; Schödel, Rainer; Williams, Benjamin F.; Nogueras-Lara, Francisco; Gallego-Cano, Eulalia; Gallego-Calvente, Teresa; Wang, Q. Daniel; Morris, Mark R.; Do, Tuan; Ghez, Andrea

2017-09-01

We used 4-yr baseline Hubble Space Telescope/Wide Field Camera 3 IR observations of the Galactic Centre in the F153M band (1.53 μm) to identify variable stars in the central ∼2.3 arcmin × 2.3 arcmin field. We classified 3845 long-term (periods from months to years) and 76 short-term (periods of a few days or less) variables among a total sample of 33 070 stars. For 36 of the latter ones, we also derived their periods (<3 d). Our catalogue not only confirms bright long period variables and massive eclipsing binaries identified in previous works but also contains many newly recognized dim variable stars. For example, we found δ Scuti and RR Lyrae stars towards the Galactic Centre for the first time, as well as one BL Her star (period < 1.3 d). We cross-correlated our catalogue with previous spectroscopic studies and found that 319 variables have well-defined stellar types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant branch stars. We used colours and magnitudes to infer the probable variable types for those stars without accurately measured periods or spectroscopic information. We conclude that the majority of unclassified variables could potentially be eclipsing/ellipsoidal binaries and Type II Cepheids. Our source catalogue will be valuable for future studies aimed at constraining the distance, star formation history and massive binary fraction of the Milky Way nuclear star cluster.

Clinical Evaluation of the Cepheid Xpert TV Assay for Detection of Trichomonas vaginalis with Prospectively Collected Specimens from Men and Women

PubMed Central

Gaydos, C. A.; Davis, T.; Marrazzo, J.; Furgerson, D.; Taylor, S. N.; Smith, B.; Bachmann, L. H.; Ackerman, R.; Spurrell, T.; Ferris, D.; Burnham, C.-A. D.; Reno, H.; Lebed, J.; Eisenberg, D.; Kerndt, P.; Philip, S.; Jordan, J.; Quigley, N.

2017-01-01

ABSTRACT Trichomoniasis is the most prevalent curable sexually transmitted disease (STD). It has been associated with preterm birth and the acquisition and transmission of HIV. Recently, nucleic acid amplification tests (NAAT) have been FDA cleared in the United States for detection of Trichomonas vaginalis in specimens from both women and men. This study reports the results of a multicenter study recently conducted using the Xpert TV (T. vaginalis) assay to test specimens from both men and women. On-demand results were available in as little as 40 min for positive specimens. A total of 1,867 women and 4,791 men were eligible for inclusion in the analysis. In women, the performance of the Xpert TV assay was compared to the patient infected status (PIS) derived from the results of InPouch TV broth culture and Aptima NAAT for T. vaginalis. The diagnostic sensitivities and specificities of the Xpert TV assay for the combined female specimens (urine samples, self-collected vaginal swabs, and endocervical swabs) ranged from 99.5 to 100% and 99.4 to 99.9%, respectively. For male urine samples, the diagnostic sensitivity and specificity were 97.2% and 99.9%, respectively, compared to PIS results derived from the results of broth culture for T. vaginalis and bidirectional gene sequencing of amplicons. Excellent performance characteristics were seen using both female and male specimens. The ease of using the Xpert TV assay should result in opportunities for enhanced screening for T. vaginalis in both men and women and, hopefully, improved control of this infection. PMID:29167292

An evaluation of false-positive rifampicin resistance on the Xpert MTB/RIF.

PubMed

Cayci, Yeliz Tanriverdi; Bilgin, Kemal; Coban, Ahmet Yilmaz; Birinci, Asuman; Durupınar, Belma

2017-11-01

Mycobacterium tuberculosis (MTB) is one of the most significant causes of mortality and morbidity. Early diagnose is important especially in multiple drug resistant tuberculosis to avoid transmission. Traditional techniques requires at least one to three weeks for diagnosis of tuberculosis. Diagnostic delays with multiple drug resistant tuberculosis are associated with worse clinical outcomes and increased transmission The Xpert MTB/RIF assay is one of the new diagnostic device for the diagnosis of tuberculosis and rapid detection of rifampicin resistance. We assessed the performance of Xpert MTB/RIF assay for detecting rifampicin resistance using phenotypic drug susceptibility tests as automated BD MGIT 960. Total of 2136 specimens were included in the study. Xpert MTB/RIF testing was performed on samples, using version 4 cartridges, according to the manufacturer's recommendations. The MTBC culture and first-line phenotypic DST were performed in automated BD MGIT 960 (Becton & Dickinson, USA) according to the recommendations of the manufacturer. Agar proportion was used in the case of inconsistency for rifampicin resistance. Thirty-four samples (19 respiratory and 15 nonrespiratory samples) were determined as positive for M. tuberculosis complex by Xpert MTB/RIF (Cepheid GeneXpert® System, USA). Xpert MTB/RIF assay detected 4/34 (11.7%) specimens as rifampicin resistant. One of the rifampicin resistant isolates was determined susceptible in MGIT 960 automated system. This isolate was also tested with agar proportion method and found susceptible to rifampicin. The Xpert MTB/RIF assay can be used as first-line assay for the detection of M. tuberculosis. However, microbiologists must be aware of the limitations of the assay.

A Closer Look at the Alpha Persei Coronal Conundrum

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.

2017-03-01

A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, the mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV) coronal-proxy Si IV unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multifaceted program tested that premise. Ground-based optical coronography and near-UV imaging with Hubble Space Telescope (HST) Wide-Field Camera 3 searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si IV emissions of α Per, in a deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as part of the joint program, are aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution—a well-separated companion—has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.

The Catalina Surveys Southern periodic variable star catalogue

NASA Astrophysics Data System (ADS)

Drake, A. J.; Djorgovski, S. G.; Catelan, M.; Graham, M. J.; Mahabal, A. A.; Larson, S.; Christensen, E.; Torrealba, G.; Beshore, E.; McNaught, R. H.; Garradd, G.; Belokurov, V.; Koposov, S. E.

2017-08-01

Here, we present the results from our analysis of 6 yr of optical photometry taken by the Siding Spring Survey (SSS). This completes a search for periodic variable stars within the 30 000 deg2 of the sky covered by the Catalina Surveys. The current analysis covers 81 million sources with declinations between -20° and -75° with median magnitudes in the range 11 < V < 19.5. We find approximately 34 000 new periodic variable stars in addition to the ˜9000 RR Lyrae that we previously discovered in SSS data. This brings the total number of periodic variables identified in Catalina data to ˜110 000. The new SSS periodic variable stars mainly consist of eclipsing binaries, RR Lyrae, LPVs, RS CVn stars, δ Scutis, and Anomalous Cepheids. By cross-matching these variable stars with those from prior surveys, we find that ˜90 per cent of the sources are new discoveries and recover ˜95 per cent of the known periodic variables in the survey region. For the known sources, we find excellent agreement between our catalogue and prior values of luminosity, period, and amplitude. However, we find many variable stars that had previously been misclassified. Examining the distribution of RR Lyrae, we find a population associated with the Large Magellanic Cloud (LMC) that extends more than 20° from its centre confirming recent evidence for the existence of a very extended stellar halo in the LMC. By combining SSS photometry with Dark Energy Survey data, we identify additional LMC halo RR Lyrae, thus confirming the significance of the population.

Comparison of Diagnostic Algorithms for Detecting Toxigenic Clostridium difficile in Routine Practice at a Tertiary Referral Hospital in Korea.

PubMed

Moon, Hee-Won; Kim, Hyeong Nyeon; Hur, Mina; Shim, Hee Sook; Kim, Heejung; Yun, Yeo-Min

2016-01-01

Since every single test has some limitations for detecting toxigenic Clostridium difficile, multistep algorithms are recommended. This study aimed to compare the current, representative diagnostic algorithms for detecting toxigenic C. difficile, using VIDAS C. difficile toxin A&B (toxin ELFA), VIDAS C. difficile GDH (GDH ELFA, bioMérieux, Marcy-l'Etoile, France), and Xpert C. difficile (Cepheid, Sunnyvale, California, USA). In 271 consecutive stool samples, toxigenic culture, toxin ELFA, GDH ELFA, and Xpert C. difficile were performed. We simulated two algorithms: screening by GDH ELFA and confirmation by Xpert C. difficile (GDH + Xpert) and combined algorithm of GDH ELFA, toxin ELFA, and Xpert C. difficile (GDH + Toxin + Xpert). The performance of each assay and algorithm was assessed. The agreement of Xpert C. difficile and two algorithms (GDH + Xpert and GDH+ Toxin + Xpert) with toxigenic culture were strong (Kappa, 0.848, 0.857, and 0.868, respectively). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of algorithms (GDH + Xpert and GDH + Toxin + Xpert) were 96.7%, 95.8%, 85.0%, 98.1%, and 94.5%, 95.8%, 82.3%, 98.5%, respectively. There were no significant differences between Xpert C. difficile and two algorithms in sensitivity, specificity, PPV and NPV. The performances of both algorithms for detecting toxigenic C. difficile were comparable to that of Xpert C. difficile. Either algorithm would be useful in clinical laboratories and can be optimized in the diagnostic workflow of C. difficile depending on costs, test volume, and clinical needs.

Blue large-amplitude pulsators as a new class of variable stars

NASA Astrophysics Data System (ADS)

Pietrukowicz, Paweł; Dziembowski, Wojciech A.; Latour, Marilyn; Angeloni, Rodolfo; Poleski, Radosław; di Mille, Francesco; Soszyński, Igor; Udalski, Andrzej; Szymański, Michał K.; Wyrzykowski, Łukasz; Kozłowski, Szymon; Skowron, Jan; Skowron, Dorota; Mróz, Przemek; Pawlak, Michał; Ulaczyk, Krzysztof

2017-08-01

Regular intrinsic brightness variations observed in many stars are caused by pulsations. These pulsations provide information on the global and structural parameters of the star. The pulsation periods range from seconds to years, depending on the compactness of the star and properties of the matter that forms its outer layers. Here, we report the discovery of more than a dozen previously unknown short-period variable stars: blue large-amplitude pulsators. These objects show very regular brightness variations with periods in the range of 20-40 min and amplitudes of 0.2-0.4 mag in the optical passbands. The phased light curves have a characteristic sawtooth shape, similar to the shape of classical Cepheids and RR Lyrae-type stars pulsating in the fundamental mode. The objects are significantly bluer than main-sequence stars observed in the same fields, which indicates that all of them are hot stars. Follow-up spectroscopy confirms a high surface temperature of about 30,000 K. Temperature and colour changes over the cycle prove the pulsational nature of the variables. However, large-amplitude pulsations at such short periods are not observed in any known type of stars, including hot objects. Long-term photometric observations show that the variable stars are very stable over time. Derived rates of period change are of the order of 10-7 per year and, in most cases, they are positive. According to pulsation theory, such large-amplitude oscillations may occur in evolved low-mass stars that have inflated helium-enriched envelopes. The evolutionary path that could lead to such stellar configurations remains unknown.

The Spiral Arm Segments of the Galaxy within 3 kpc from the Sun: A Statistical Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griv, Evgeny; Jiang, Ing-Guey; Hou, Li-Gang, E-mail: griv@bgu.ac.il

As can be reasonably expected, upcoming large-scale APOGEE, GAIA, GALAH, LAMOST, and WEAVE stellar spectroscopic surveys will yield rather noisy Galactic distributions of stars. In view of the possibility of employing these surveys, our aim is to present a statistical method to extract information about the spiral structure of the Galaxy from currently available data, and to demonstrate the effectiveness of this method. The model differs from previous works studying how objects are distributed in space in its calculation of the statistical significance of the hypothesis that some of the objects are actually concentrated in a spiral. A statistical analysismore » of the distribution of cold dust clumps within molecular clouds, H ii regions, Cepheid stars, and open clusters in the nearby Galactic disk within 3 kpc from the Sun is carried out. As an application of the method, we obtain distances between the Sun and the centers of the neighboring Sagittarius arm segment, the Orion arm segment in which the Sun is located, and the Perseus arm segment. Pitch angles of the logarithmic spiral segments and their widths are also estimated. The hypothesis that the collected objects accidentally form spirals is refuted with almost 100% statistical confidence. We show that these four independent distributions of young objects lead to essentially the same results. We also demonstrate that our newly deduced values of the mean distances and pitch angles for the segments are not too far from those found recently by Reid et al. using VLBI-based trigonometric parallaxes of massive star-forming regions.« less

Variable Stars in the Field of the Hydra II Ultra-faint Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Vivas, A. Katherina; Olsen, Knut; Blum, Robert; Nidever, David L.; Walker, Alistair R.; Martin, Nicolas F.; Besla, Gurtina; Gallart, Carme; van der Marel, Roeland P.; Majewski, Steven R.; Kaleida, Catherine C.; Muñoz, Ricardo R.; Saha, Abhijit; Conn, Blair C.; Jin, Shoko

2016-05-01

We report the discovery of one RR Lyrae star in the ultra-faint satellite galaxy Hydra II based on time series photometry in the g, r and I bands obtained with the Dark Energy Camera at Cerro Tololo Inter-American Observatory, Chile. The association of the RR Lyrae star discovered here with Hydra II is clear because is located at 42\\prime\\prime from the center of the dwarf, well within its half-light radius of 102\\prime\\prime . The RR Lyrae star has a mean magnitude of I=21.30+/- 0.04 which is too faint to be a field halo star. This magnitude translates to a heliocentric distance of 151 ± 8 kpc for Hydra II; this value is ˜ 13% larger than the estimate from the discovery paper based on the average magnitude of several blue horizontal branch star candidates. The new distance implies a slightly larger half-light radius of {76}-10+12 pc and a brighter absolute magnitude of {M}V=-5.1+/- 0.3, which keeps this object within the realm of the dwarf galaxies. A comparison with other RR Lyrae stars in ultra-faint systems indicates similar pulsational properties among them, which are different to those found among halo field stars and those in the largest of the Milky Way satellites. We also report the discovery of 31 additional short period variables in the field of view (RR Lyrae, SX Phe, eclipsing binaries, and a likely anomalous cepheid) which are likely not related with Hydra II.

THE CURIOUS CASE OF THE ALPHA PERSEI CORONA: A DWARF IN SUPERGIANT'S CLOTHING?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayres, Thomas R., E-mail: Thomas.Ayres@Colorado.edu

2011-09-10

Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290-1430 A far-ultraviolet (FUV) spectrum of {alpha} Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si IV 1400 A doubletmore » (T {approx} 8 x 10{sup 4} K), are very weak, as are the chromospheric C II 1335 A multiplet (T {approx} 3 x 10{sup 4} K) and O I 1305 A triplet. In fact, the Si IV features of {alpha} Per are not only narrower than those of later, G-type supergiants of similar L{sub X}/L{sub bol}, but are also fainter (in L{sub SiIV}/L{sub bol}) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on {alpha} Per finds the X-ray centroid offset from the stellar position by 9'', at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star.« less

Calibration of the Tip of the Red Giant Branch Distance Method in IR

NASA Astrophysics Data System (ADS)

Sakai, Shoko

1999-02-01

We propose to investigate the feasibility of the tip of the red giant branch (TRGB) as a distance indicator in IR wavelength. The TRGB has been shown both observationally and theoretically to be an excellent distance indicator in I-band, mainly because of its insensitivity to both metallicity and age. Its accuracy is comparable to that of the Cepheid variable stars. The TRGB method in I-band is currently calibrated by Galactic globular clusters whose distances have been measured with RR Lyrae variables. The main objective of this proposal is to calibrate this method in IR by obtaining JHK photometry for a number of Galactic globular clusters. This is motivated by two related scientific goals: (1) It will be possible in the future to obtain direct distances to galaxies even in Coma cluster using the NGST, but only if the TRGB method has been calibrated accurately in IR filters. If the method is proven reliable, then it can be a powerful tool to map out the density and velocity fields of the local Universe in three dimensions. (2) A considerable amount of effort has been spent on obtaining accurate, direct distances to nearby galaxies. However, this has been difficult for a number of galaxies, including IC 342, because they are located at very low Galactic latitude. These galaxies could potentially have a tremendous effect on the dynamics of the Local Group, depending on their distances. Using the calibrated IR TRGB method, we could solve this uncertainty by measuring their distances directly.

Educating astrometry and celestial mechanics students for the 21st century

NASA Astrophysics Data System (ADS)

van Altena, W. F.; Stavinschi, M.

2008-07-01

Astrometry and Celestial Mechanics have entered a new era with the advent of Micro-arcsecond positions, parallaxes and proper motions. Cutting-edge science topics will be addressed that were far beyond our grasp only a few years ago. It will be possible to determine definitive distances to Cepheid variables, the center of our Galaxy, the Magellanic Clouds and other Local Group members. We will measure the orbital parameters of dwarf galaxies that are merging with the Milky Way, define the kinematics, dynamics and structure of our Galaxy and search for evidence of the Dark Matter that makes up most of the mass in the universe. Stellar masses will be determined routinely to 1% accuracy and we will be able to make full orbit solutions and mass determinations for Extrasolar planetary systems. If we are to take advantage of Micro-arcsecond astrometry, we need to reformulate our study of reference frames, systems and the equations of motion in the context of special and general relativity. Methods also need to be developed to statistically analyze our data and calibrate our instruments to levels beyond current standards. As a consequence, our curricula must be drastically revised to meet the needs of students in the 21st Century. With the above considerations in mind, we developed a syllabus for an introductory one-semester course in Astrometry and Celestial Mechanics. This course gives broad introductions to most topics in our fields and a base of knowledge from which a student can elect areas for self-study or attendance at centers where advanced courses, workshops or internships are available.

Laboratory Diagnosis and Susceptibility Testing for Mycobacterium tuberculosis.

PubMed

Procop, Gary W

2016-12-01

The laboratory, which utilizes some of the most sophisticated and rapidly changing technologies, plays a critical role in the diagnosis of tuberculosis. Some of these tools are being employed in resource-challenged countries for the rapid detection and characterization of Mycobacterium tuberculosis. Foremost, the laboratory defines appropriate specimen criteria for optimal test performance. The direct detection of mycobacteria in the clinical specimen, predominantly done by acid-fast staining, may eventually be replaced by rapid-cycle PCR. The widespread use of the Xpert MTB/RIF (Cepheid) assay, which detects both M. tuberculosis and key genetic determinants of rifampin resistance, is important for the early detection of multidrug-resistant strains. Culture, using both broth and solid media, remains the standard for establishing the laboratory-based diagnosis of tuberculosis. Cultured isolates are identified far less commonly by traditional biochemical profiling and more commonly by molecular methods, such as DNA probes and broad-range PCR with DNA sequencing. Non-nucleic acid-based methods of identification, such as high-performance liquid chromatography and, more recently, matrix-assisted laser desorption/ionization-time of flight mass spectrometry, may also be used for identification. Cultured isolates of M. tuberculosis should be submitted for susceptibility testing according to standard guidelines. The use of broth-based susceptibility testing is recommended to significantly decrease the time to result. Cultured isolates may also be submitted for strain typing for epidemiologic purposes. The use of massive parallel sequencing, also known as next-generation sequencing, promises to continue to this molecular revolution in mycobacteriology, as whole-genome sequencing provides identification, susceptibility, and typing information simultaneously.

Evaluation of a Rapid and Completely Automated Real-Time Reverse Transcriptase PCR Assay for Diagnosis of Enteroviral Meningitis▿

PubMed Central

Nolte, Frederick S.; Rogers, Beverly B.; Tang, Yi-Wei; Oberste, M. Steven; Robinson, Christine C.; Kehl, K. Sue; Rand, Kenneth A.; Rotbart, Harley A.; Romero, Jose R.; Nyquist, Ann-Christine; Persing, David H.

2011-01-01

Nucleic acid amplification tests (NAATs) for enterovirus RNA in cerebrospinal fluid (CSF) have emerged as the new gold standard for diagnosis of enteroviral meningitis, and their use can improve the management and decrease the costs for caring for children with enteroviral meningitis. The Xpert EV assay (Cepheid, Sunnyvale, CA) is a rapid, fully automated real-time PCR test for the detection of enterovirus RNA that was approved by the U.S. Food and Drug Administration for in vitro diagnostic use in March 2007. In this multicenter trial we established the clinical performance characteristics of the Xpert EV assay in patients presenting with meningitis symptoms relative to clinical truth. Clinical truth for enteroviral meningitis was defined as clinical evidence of meningitis, the absence of another detectable pathogen in CSF, and detection of enterovirus in CSF either by two reference NAATs or by viral culture. A total of 199 prospectively and 235 retrospectively collected specimens were eligible for inclusion in this study. The overall prevalence of enteroviral meningitis was 26.04%. The Xpert EV assay had a sensitivity of 94.69% (90% confidence interval [CI] = 89.79 to 97.66%), specificity of 100% (90% CI = 99.07 to 100%), positive predictive value of 100%, negative predictive value of 98.17, and an accuracy of 98.62% relative to clinical truth. The Xpert EV assay demonstrated a high degree of accuracy for diagnosis of enteroviral meningitis. The simplicity and on-demand capability of the Xpert EV assay should prove to be a valuable adjunct to the evaluation of suspected meningitis cases. PMID:21159942

Evaluation of a rapid and completely automated real-time reverse transcriptase PCR assay for diagnosis of enteroviral meningitis.

PubMed

Nolte, Frederick S; Rogers, Beverly B; Tang, Yi-Wei; Oberste, M Steven; Robinson, Christine C; Kehl, K Sue; Rand, Kenneth A; Rotbart, Harley A; Romero, Jose R; Nyquist, Ann-Christine; Persing, David H

2011-02-01

Nucleic acid amplification tests (NAATs) for enterovirus RNA in cerebrospinal fluid (CSF) have emerged as the new gold standard for diagnosis of enteroviral meningitis, and their use can improve the management and decrease the costs for caring for children with enteroviral meningitis. The Xpert EV assay (Cepheid, Sunnyvale, CA) is a rapid, fully automated real-time PCR test for the detection of enterovirus RNA that was approved by the U.S. Food and Drug Administration for in vitro diagnostic use in March 2007. In this multicenter trial we established the clinical performance characteristics of the Xpert EV assay in patients presenting with meningitis symptoms relative to clinical truth. Clinical truth for enteroviral meningitis was defined as clinical evidence of meningitis, the absence of another detectable pathogen in CSF, and detection of enterovirus in CSF either by two reference NAATs or by viral culture. A total of 199 prospectively and 235 retrospectively collected specimens were eligible for inclusion in this study. The overall prevalence of enteroviral meningitis was 26.04%. The Xpert EV assay had a sensitivity of 94.69% (90% confidence interval [CI] = 89.79 to 97.66%), specificity of 100% (90% CI = 99.07 to 100%), positive predictive value of 100%, negative predictive value of 98.17, and an accuracy of 98.62% relative to clinical truth. The Xpert EV assay demonstrated a high degree of accuracy for diagnosis of enteroviral meningitis. The simplicity and on-demand capability of the Xpert EV assay should prove to be a valuable adjunct to the evaluation of suspected meningitis cases.

A new method of measuring centre-of-mass velocities of radially pulsating stars from high-resolution spectroscopy

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Fossati, L.

2018-03-01

We present a radial velocity analysis of 20 solar neighbourhood RR Lyrae and three Population II Cepheid variables. We obtained high-resolution, moderate-to-high signal-to-noise ratio spectra for most stars; these spectra covered different pulsation phases for each star. To estimate the gamma (centre-of-mass) velocities of the programme stars, we use two independent methods. The first, `classic' method is based on RR Lyrae radial velocity curve templates. The second method is based on the analysis of absorption-line profile asymmetry to determine both pulsational and gamma velocities. This second method is based on the least-squares deconvolution (LSD) technique applied to analyse the line asymmetry that occurs in the spectra. We obtain measurements of the pulsation component of the radial velocity with an accuracy of ±3.5 km s-1. The gamma velocity was determined with an accuracy of ±10 km s-1, even for those stars having a small number of spectra. The main advantage of this method is the possibility of obtaining an estimation of gamma velocity even from one spectroscopic observation with uncertain pulsation phase. A detailed investigation of LSD profile asymmetry shows that the projection factor p varies as a function of the pulsation phase - this is a key parameter, which converts observed spectral line radial velocity variations into photospheric pulsation velocities. As a by-product of our study, we present 41 densely spaced synthetic grids of LSD profile bisectors based on atmospheric models of RR Lyr covering all pulsation phases.

Cracking the Conundrum of F-supergiant Coronae

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.

2018-02-01

Chandra X-ray and HST far-ultraviolet (FUV) observations of three early-F supergiants have shed new light on a previous puzzle involving a prominent member of the class: α Persei (HD 20902: F5 Ib). The warm supergiant is a moderately strong, hard coronal (T∼ {10}7 K) X-ray source, but has 10 times weaker “subcoronal” Si IV 1393 Å (T∼ 8× {10}4 K) emissions than early-G supergiants of similar high-energy properties. The α Per X-ray excess was speculatively ascribed to a close-in hyperactive G-dwarf companion, which could have escaped previous notice, lost in the glare of the bright star. However, a subsequent dedicated multi-wavelength imaging campaign failed to find any evidence for a resolved secondary. The origin of the α Per high-energy dichotomy then devolved to (1) an unresolved companion or (2) intrinsic coronal behavior. Exploring the second possibility, the present program has found that early-F supergiants do appear to belong to a distinct coronal class, characterized by elevated X-ray/FUV ratios, although sharing some similarities with Cepheid variables in their transitory X-ray “high states.” Remarkably, the early-F supergiants now are seen to align with the low-activity end of the X-ray/FUV sequence defined by late-type dwarfs, suggesting that the disjoint behavior relative to the G supergiants might be attributed to thinner outer atmospheres on the F types, as in dwarfs, but in this case perhaps caused by a weakened “ionization valve” effect due to overly warm photospheres.

Detection of Norovirus by BD MAX™, Xpert® Norovirus, and xTAG® Gastrointestinal Pathogen Panel in stool and vomit samples.

PubMed

McHugh, Martin P; Guerendiain, Daniel; Hardie, Alison; Kenicer, Juliet; MacKenzie, Laura; Templeton, Kate E

2018-06-08

Norovirus is a leading cause of infectious gastroenteritis, characterized by outbreaks of diarrhoea and vomiting in closed settings. Nucleic acid amplification tests allow rapid and sensitive laboratory diagnosis of norovirus, with a number of commercial platforms now available. Evaluate the performance of the Becton Dickinson BD-MAX™System, Cepheid Xpert® Norovirus Assay, and Luminex xTAG® Gastrointestinal Pathogen Panel (GPP) for norovirus detection in stool. Assess the performance of the Xpert® Norovirus Assay and BD-MAX™ in vomit samples. 163 diarrhoeal stool samples were tested on four diagnostic systems (laboratory-defined real time RT-PCR (assigned as gold standard), BD MAX™, Xpert® Norovirus Assay, and xTAG® GPP). A further 70 vomit samples were tested on the Xpert and BD MAX platforms. In stool, sensitivity and specificity of the BD-MAX™ was 96.8% and 100%, for Xpert® Norovirus Assay was 91.9% and 100%, and for xTAG® GPP was 79.0% and 87.1%. In vomit samples positive and negative percent agreement was 95.6% and 92.0%, between the BD-MAX™ and Xpert® Norovirus. The BD-MAX™ System with user defined settings and the Xpert® Norovirus Assay showed acceptable sensitivity and specificity for detection of norovirus from stool and vomit. The xTAG GPP assay was less reliable for norovirus detection but can detect a number of other clinically useful enteropathogens. Clinical laboratories must consider skill mix, budget, and sample throughput to determine the best fit for their service. Copyright © 2018 Elsevier B.V. All rights reserved.

Clustering of local group distances: publication bias or correlated measurements? I. The large Magellanic cloud

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Grijs, Richard; Wicker, James E.; Bono, Giuseppe

2014-05-01

The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly—and with a small spread—around the 'canonical' distance modulus, (m – M){sub 0} = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available tomore » date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m – M){sub 0} = 18.49 ± 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent.« less

Obituary: David Stanley Evans, 1916-2004

NASA Astrophysics Data System (ADS)

Bash, Frank N.

2005-12-01

David Stanley Evans died on 14 November 2004 in Austin, Texas. He was a noted observational astronomer whose career was divided between South Africa and Texas. He also used the extensive historical collections at the University of Texas to write several books on the history of astronomy. He was born in Cardiff, Wales on 28 January 1916. David received his BA degree in mathematics in 1937 from Kings College, Cambridge. He became a PhD student at Cambridge Observatory in 1937, and was one of Sir Arthur Eddington's last surviving students. He received his PhD degree in 1941 with a dissertation entitled, "The Formation of the Balmer Series of Hydrogen in Stellar Atmospheres." He was a conscientious objector to war and, thus, spent the war years at Oxford working with physicist Kurt Mendelssohn on medical problems, involving cadavers, relating to the war. During these years, David was scientific editor of "Discovery", and he was editor of "The Observatory". David left England in 1946 in order to take up the position of Second Assistant at the Radcliffe Observatory, Pretoria, South Africa. He and H. Knox Shaw were the entire staff after R. O. Redman left, and they aluminized and installed the mirrors in the 74-inch telescope. His notable scientific contribution was to use lunar occultations to measure stellar angular diameters during the 1950s. He succeeded in determining the angular diameter of Antares and determined that Arcturus was not circular but had an elliptical shape. The elliptical shape was later shown to be an instrumental artifact, but the utility of using lunar occultations to measure stellar diameters and stellar multiplicity was conclusively demonstrated. T. Gold presented David's paper on lunar occultation angular diameters at the January 1953 meeting of the Royal Astronomical Society. For the rest of his life, David resented Gold's remarks, because he felt that he had been ridiculed. By 1953, David Evans was Chief Assistant at the Royal Observatory headquartered in Cape Town, South Africa. David had designed and built a Newtonian spectrograph for the 74-inch Radcliffe Telescope with which he measured the first southern galaxy redshifts. David and his family spent 1965-66 in Austin, Texas, where he was a National Science Foundation Senior Visiting Scientist at the University of Texas and McDonald Observatory. They moved permanently to Austin in 1968 and David became a Professor of Astronomy and Associate Director of McDonald Observatory at the University of Texas at Austin. At McDonald Observatory, R. E. Nather had devised a high-speed photometer capable of measuring millisecond time-scale changes in brightness and with Brian Warner, he invented "high-speed astronomy". This instrument caused Evans to revive his occultation program and, over the next twenty years, he produced the major part of the angular diameters of late-type stars with his students and collaborators. In addition, David and collaborators used the extensive collections of the University of Texas to write "Herschel at the Cape". David was also involved in observing the occultation of ? Sco by Jupiter in 1972 and in observing, during a solar eclipse in 1973, the gravitational deflections in the positions of stars whose light passes near to the Sun. The eclipse was observed from Mauritania, and the observations confirmed Einstein's prediction again. David Evans and his students studied late-type stars that have large star-spots and others that flare. In addition, they studied stars whose lunar occultation observations had revealed them to be double or even more than two stars. David Evans's major scientific contribution was an application of his stellar angular diameters to deduce the surface brightness of stars with the result that with suitable color indices one could use photometry to deduce the angular diameter of stars. This is applicable to stars which can never be occulted by the Moon, and its application to Cepheid variable stars has yielded their distances. This relation between angular diameters and a V-R color index is called the Barnes-Evans Relation. Tom Barnes gives most of the credit to Evans, but said that David insisted that the authors be listed in alphabetical order. This work was greeted with initial skepticism but it stimulated an enormous amount of interest and has been used to measure distances to 100 Cepheid variable stars in our galaxy. The method gives a distance to one of them, Delta Cephei, that agrees closely with recently measured parallaxes using HST. The Barnes-Evans method yields distances which are accurate to a few percent and is applicable to Cepheids in nearby galaxies. Before coming to Texas, David Evans had never given a large lecture course at a university, and his efforts met with mixed success especially in introductory classes for freshmen facing a "science requirement." David had considerably more success supervising PhD dissertations. He was supervisor for four. He was promoted to the position of Jack S. Josey Centennial Professor of Astronomy in 1984, which is the position he held until his retirement in 1986. He was awarded the Gill Medal of the Astronomical Society of South Africa in 1988. David Evans had a remarkable facility for language, especially English. He was an author of eight books including a 1966 edition of "Teach Yourself Astronomy", which was an introduction to astronomy and an inspiration to a number of currently active astronomers. He also loved history, especially of Southern Hemisphere astronomy but also of the McDonald Observatory. In fact, David continued to be very active after retirement and when he died he had completed a book (with Karen Winget) on the eclipse expedition to Mauritania, which is not yet printed.

The Globular Cluster NGC 6402 (M14). II. Variable Stars

NASA Astrophysics Data System (ADS)

Contreras Peña, C.; Catelan, M.; Grundahl, F.; Stephens, A. W.; Smith, H. A.

2018-03-01

We present time-series BVI photometry for the Galactic globular cluster NGC 6402 (M14). The data consist of ∼137 images per filter, obtained using the 0.9 and 1.0 m SMARTS telescopes at the Cerro Tololo Inter-American Observatory. The images were obtained during two observing runs in 2006–2007. The image-subtraction package ISIS, along with DAOPHOT II/ALLFRAME, was used to perform crowded-field photometry and search for variable stars. We identified 130 variables, eight of which are new discoveries. The variable star population is comprised of 56 ab-type RR Lyrae stars, 54 c-type RR Lyrae, 6 type II Cepheids, 1 W UMa star, 1 detached eclipsing binary, and 12 long-period variables. We provide Fourier decomposition parameters for the RR Lyrae, and discuss the physical parameters and photometric metallicity derived therefrom. The M14 distance modulus is also discussed, based on different approaches for the calibration of the absolute magnitudes of RR Lyrae stars. The possible presence of second-overtone RR Lyrae in M14 is critically addressed, with our results arguing against this possibility. By considering all of the RR Lyrae stars as members of the cluster, we derive < {P}ab > =0.589 {{d}}{{a}}{{y}}{{s}}. This, together with the position of the RR Lyrae stars of both Bailey types in the period–amplitude diagram, suggests an Oosterhoff-intermediate classification for the cluster. Such an intermediate Oosterhoff type is much more commonly found in nearby extragalactic systems, and we critically discuss several other possible indications that may point to an extragalactic origin for this cluster. Based on observations obtained with the 0.9 m and 1 m telescopes at the Cerro Tololo Inter-American Observatory, Chile, operated by the SMARTS consortium.

SSET: Spatially-scanned Spectra of Exoplanet Transits

NASA Astrophysics Data System (ADS)

McCullough, Peter R.; Berta, Z. K.; Howard, A. W.; MacKenty, J. W.; WFC3 Team

2012-01-01

Spatial scanning is expected to have some advantages over staring-mode observations with the HST WFC3 instrument, especially for very bright stars, i.e. those that intrinsically can provide the highest sensitivity observations. We analyze 1.1-1.7 micron spectra of a transit of the super-Earth GJ1214b obtained 2011-4-18 during re-commissioning of a technique for spatially scanning the Hubble Space Telescope. These are the first data of this type obtained with the HST instrument WFC3. Results are directly compared to staring-mode observations with the same instrument of the same target by Berta et al. (2011). We also describe a case study of the sub-Neptune-sized planet HD 97658b in terms of proposed observations and what they may reveal of that planet. We also summarize publicly-available descriptions of additional HST programs that use the spatial-scanning technique (Table 1). Table 1 HST program, Title, Investigators, Scanned Targets 12181 The Atmospheric Structure of Giant Hot Exoplanets, Deming, L. D. et al., HD 209458 and HD 189733 12325 Photometry with Spatial Scans, MacKenty, J. W., & McCullough, P. R., GJ1214 12336 Scan Enabled Photometry, MacKenty, J. W., McCullough, P. R., & Deustua, S., Vega and other calibration stars 12449 Atmospheric Composition of the ExoNeptune HAT-P-11, Deming, L. D., et al., HAT-P-11 12473 An Optical Transmission Spectral Survey of hot-Jupiter Exoplanetary Atmospheres, Sing, D. K. et al., WASP-31, HAT-P-1 12495 Near-IR Spectroscopy of the Hottest Known Exoplanet, WASP-33b, Deming, L. D. et al., WASP-33 12679 Luminosity-Distance Standards from Gaia and HST, Riess, A., et al., Milky Way Cepheids 12713 Spatial Scanned L-flat Validation Pathfinder, McCullough and MacKenty, nearly identical double stars

Rolling Out Xpert® MTB/RIF for TB Detection in HIV-Infected Populations:An Opportunity for Systems Strengthening.

PubMed

Pathmanathan, Ishani; Date, Anand; Coggin, William L; Nkengasong, John; Piatek, Amy S; Alexander, Heather

2017-03-31

To eliminate preventable deaths, disease and suffering due to tuberculosis (TB), improved diagnostic capacity is critical. The Cepheid Xpert ® MTB/RIF assay is recommended by the World Health Organization as the initial diagnostic test for people with suspected HIV-associated TB. However, despite high expectations, its scale-up in real-world settings has faced challenges, often due to the systems that support it. In this commentary we discuss needs and opportunities for systems strengthening to support widespread scale-up of Xpert ® MTB/RIF as they relate to each step within the TB diagnostic cascade, from finding presumptive patients, to collecting, transporting and testing sputum specimens, to reporting and receiving results, to initiating and monitoring treatment and, ultimately, to ensuring successful and timely treatment and cure. Investments in evidence-based interventions at each step along the cascade and within the system as a whole will augment not only the utility of Xpert ® MTB/RIF, but also the successful implementation of future diagnostic tests. Xpert ® MTB/RIF will only improve patient outcomes if optimally implemented within the context of strong TB programs and systems. Roll-out of this technology to people living with HIV and others in resource-limited settings offers the opportunity to leverage current TB and HIV laboratory, diagnostic and programmatic investments, while also addressing challenges and strengthening coordination between laboratory systems, laboratory-program interfaces, and TB-HIV program interfaces. If successful, the benefits of this tool could extend beyond progress towards global End TB Strategy goals, to improve system-wide capacity for global disease detection and control.

SN 2012fr: Ultraviolet, Optical, and Near-infrared Light Curves of a Type Ia Supernova Observed within a Day of Explosion

DOE PAGES

Contreras, Carlos; Phillips, M. M.; Burns, Christopher R.; ...

2018-05-18

We present detailed ultraviolet, optical, and near-infrared light curves of the Type Ia supernova (SN) 2012fr, which exploded in the Fornax cluster member NGC 1365. These precise high-cadence light curves provide a dense coverage of the flux evolution from -12 to +140 days with respect to the epoch of B-band maximum (more » $${t}_{{B}_{\\max }}$$). Supplementary imaging at the earliest epochs reveals an initial slow and nearly linear rise in luminosity with a duration of ~2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of 56 Ni mixing in the ejecta. From our analysis of the light curves, we conclude that: (i) the explosion occurred < 22 hr before the first detection of the supernova, (ii) the rise time to peak bolometric (λ >1800) luminosity was 16.5 ± 0.6 days, (iii) the supernova suffered little or no host-galaxy dust reddening, (iv) the peak luminosity in both the optical and near-infrared was consistent with the bright end of normal Type Ia diversity, and (v) 0.60 ± 0.15 M ⊙ of 56Ni was synthesized in the explosion. Despite its normal luminosity, SN 2012fr displayed unusually prevalent high-velocity Ca ii and Si ii absorption features, and a nearly constant photospheric velocity of the Si ii λ6355 line at ~12,000 km s -1 that began ~5 days before $${t}_{{B}_{\\max }}$$. We also highlight some of the other peculiarities in the early phase photometry and the spectral evolution. SN 2012fr also adds to a growing number of Type Ia supernovae that are hosted by galaxies with direct Cepheid distance measurements.« less

Evaluation of the performance of C. DIFF QUIK CHEK COMPLETE and its usefulness in a hospital setting with a high prevalence of Clostridium difficile infection.

PubMed

Chung, Hae-Sun; Lee, Miae

2017-01-01

Rapid and accurate diagnosis of Clostridium difficile infection (CDI) is crucial for patient care, infection control, and efficient surveillance. We evaluated C. DIFF QUIK CHEK COMPLETE (QCC; TechLab), which detects glutamate dehydrogenase (GDH) antigen (QCC-Ag) and toxin A/B (QCC-Tox) simultaneously, and compared it to the laboratory diagnostics for CDI currently in use in a tertiary hospital setting with a high prevalence of CDI. QCC, RIDASCREEN C. difficile toxin A/B assay (Toxin EIA; R-Biopharm AG), chromID C. difficile agar (bioMérieux) culture (ChromID culture), and Xpert C. difficile PCR assay (Xpert PCR; Cepheid) were performed according to the manufacturers' instructions. Performances of the assays were compared against that of Xpert PCR as a reference. Of the 231 loose stool specimens, 83 (35.9%) were positive by Xpert PCR. The sensitivity, specificity, and positive and negative predictive values were 97.6%, 93.9%, 90.0%, and 98.6%, respectively, for QCC-Ag and 55.4%, 100%, 100%, and 80.0%, respectively, for QCC-Tox. The median threshold cycle values of the QCC-Tox(+) specimens were lower than those of the QCC-Tox(-) specimens. Results of QCC as an initial screening test were confirmed in 81.0% (187/231) of samples; these specimens did not require further testing. QCC is a rapid, easy, and cost-effective method that would be a useful first-line screening assay for laboratory diagnosis of CDI in a tertiary hospital with a high prevalence of CDI. A two-step algorithm using QCC as an initial screening tool, followed by Xpert PCR as a confirmatory test, is a practical and cost-effective approach. Copyright © 2016 American Federation for Medical Research.

LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX

NASA Astrophysics Data System (ADS)

Prieto, J. L.; Stanek, K. Z.; Kochanek, C. S.; Weisz, D. R.; Baruffolo, A.; Bechtold, J.; Burwitz, V.; De Santis, C.; Gallozzi, S.; Garnavich, P. M.; Giallongo, E.; Hill, J. M.; Pogge, R. W.; Ragazzoni, R.; Speziali, R.; Thompson, D. J.; Wagner, R. M.

2008-01-01

In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV ~ - 7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 271 days, and the light curve is well fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed of two yellow supergiants (V - Isimeq 1 mag, Teffsimeq 4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however, note a second example. The SMC F0 supergiant R47 is a bright (MV ~ - 7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well fit as a contact binary with a 181 day period. We propose that these systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage. We also discuss the possibility of this variable being a long-period Cepheid. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

Clinical Evaluation of the Cepheid Xpert TV Assay for Detection of Trichomonas vaginalis with Prospectively Collected Specimens from Men and Women.

PubMed

Schwebke, Jane R; Gaydos, C A; Davis, T; Marrazzo, J; Furgerson, D; Taylor, S N; Smith, B; Bachmann, L H; Ackerman, R; Spurrell, T; Ferris, D; Burnham, C A; Reno, H; Lebed, J; Eisenberg, D; Kerndt, P; Philip, S; Jordan, J; Quigley, N

2018-02-01

Trichomoniasis is the most prevalent curable sexually transmitted disease (STD). It has been associated with preterm birth and the acquisition and transmission of HIV. Recently, nucleic acid amplification tests (NAAT) have been FDA cleared in the United States for detection of Trichomonas vaginalis in specimens from both women and men. This study reports the results of a multicenter study recently conducted using the Xpert TV ( T. vaginalis ) assay to test specimens from both men and women. On-demand results were available in as little as 40 min for positive specimens. A total of 1,867 women and 4,791 men were eligible for inclusion in the analysis. In women, the performance of the Xpert TV assay was compared to the patient infected status (PIS) derived from the results of InPouch TV broth culture and Aptima NAAT for T. vaginalis The diagnostic sensitivities and specificities of the Xpert TV assay for the combined female specimens (urine samples, self-collected vaginal swabs, and endocervical swabs) ranged from 99.5 to 100% and 99.4 to 99.9%, respectively. For male urine samples, the diagnostic sensitivity and specificity were 97.2% and 99.9%, respectively, compared to PIS results derived from the results of broth culture for T. vaginalis and bidirectional gene sequencing of amplicons. Excellent performance characteristics were seen using both female and male specimens. The ease of using the Xpert TV assay should result in opportunities for enhanced screening for T. vaginalis in both men and women and, hopefully, improved control of this infection. Copyright © 2018 Schwebke et al.

Interstellar extinction curve variations towards the inner Milky Way: a challenge to observational cosmology

NASA Astrophysics Data System (ADS)

Nataf, David M.; Gonzalez, Oscar A.; Casagrande, Luca; Zasowski, Gail; Wegg, Christopher; Wolf, Christian; Kunder, Andrea; Alonso-Garcia, Javier; Minniti, Dante; Rejkuba, Marina; Saito, Roberto K.; Valenti, Elena; Zoccali, Manuela; Poleski, Radosław; Pietrzyński, Grzegorz; Skowron, Jan; Soszyński, Igor; Szymański, Michał K.; Udalski, Andrzej; Ulaczyk, Krzysztof; Wyrzykowski, Łukasz

2016-03-01

We investigate interstellar extinction curve variations towards ˜4 deg2 of the inner Milky Way in VIJKs photometry from the OGLE-III (third phase of the Optical Gravitational Lensing Experiment) and VVV (VISTA Variables in the Via Lactea) surveys, with supporting evidence from diffuse interstellar bands and F435W, F625W photometry. We obtain independent measurements towards ˜2000 sightlines of AI, E(V - I), E(I - J) and E(J - Ks), with median precision and accuracy of 2 per cent. We find that the variations in the extinction ratios AI/E(V - I), E(I - J)/E(V - I) and E(J - Ks)/E(V - I) are large (exceeding 20 per cent), significant and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve have at least two degrees of freedom, and not one (e.g. RV), which we confirm with a principal component analysis. We derive a median value of = 13.44, which is ˜60 per cent higher than the `standard' value. We show that the Wesenheit magnitude WI = I - 1.61(I - J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of Type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ˜100 per cent and lack sensitivity to extinction curve variations.

Non-Local Thermodynamic Equilibrium Spectrum Synthesis of Type IA Supernovae

NASA Astrophysics Data System (ADS)

Nugent, Peter Edward

1997-09-01

Type Ia supernovae (SNe Ia) are valuable distance indicators for cosmology and the elements they eject are are important for nucleosynthesis. They appear to be thermonuclear disruptions of carbon-oxygen white dwarfs that accrete from companion stars until they approach the Chandrasekbar mass, and there is a suspicion that the propagation of the nuclear burning front involves a transition from a deflagration to a detonation. Detailed modeling of the atmospheres and spectra of SNe Ia is needed to advance our understanding of SNe Ia. Comparison of synthetic and observed spectra provides information on the temperature, density, velocity, and composition of the ejected matter and thus constrain hydrodynamical models. In addition, the expanding photosphere method yields distances to individual events that are independent of distances based on the decay of 56Ni in SNe Ia and of Cepheid variable stars in the parent galaxies. This thesis is broken down into 4 major sections, each highlighting a different way with which to use spectrum synthesis to analyze SNe Ia. Chapters 2 and 3 look at normal SNe Ia and their potential use as distance indicators using SEAM. Chapter 4 examines spectral correlations with luminosity in SNe Ia and provides a plausible explanation for these correlations via spectrum synthesis. In Chapter 5 the spectra of various hydrodynamical models are calculated in an effort to answer the question of which current progenitor/explosion model is the most plausible for a SN Ia. Finally, we look at the importance of NLTE calculations and line identifications in Chapter 6. Also included are two appendices which contain more technical information concerning γ-ray deposition and the thermalization parameter.

Meatal Swabs Contain Less Cellular Material and Are Associated with a Decrease in Gram Stain Smear Quality Compared to Urethral Swabs in Men.

PubMed

Jordan, Stephen J; Schwebke, Jane R; Aaron, Kristal J; Van Der Pol, Barbara; Hook, Edward W

2017-07-01

Urethral swabs are the samples of choice for point-of-care Gram stain testing to diagnose Neisseria gonorrhoeae infection and nongonococcal urethritis (NGU) in men. As an alternative to urethral swabs, meatal swabs have been recommended for the collection of urethral discharge to diagnose N. gonorrhoeae and Chlamydia trachomatis infection in certain populations by nucleic acid amplification testing (NAAT), as they involve a less invasive collection method. However, as meatal swabs could be sampling a reduced surface area and result in fewer collected epithelial cells compared to urethral swabs, the adequacy of meatal swab specimens to collect sufficient cellular material for Gram stain testing remains unknown. We enrolled 66 men who underwent either urethral or meatal swabbing and compared the cellular content and Gram stain failure rate. We measured the difference in swab cellular content using the Cepheid Xpert CT/NG sample adequacy control crossing threshold (SAC CT ) and determined the failure rate of Gram stain smears (GSS) due to insufficient cellular material. In the absence of discharge, meatal smears were associated with a significant reduction in cellular content ( P = 0.0118), which corresponded with a GSS failure rate significantly higher than that for urethral swabs (45% versus 3%, respectively; P < 0.0001). When discharge was present, there was no difference among results from urethral and meatal swabs. Therefore, if GSS testing is being considered for point-of-care diagnosis of N. gonorrhoeae infection or NGU in men, meatal swabs should be avoided in the absence of a visible discharge. Copyright © 2017 American Society for Microbiology.

A Closer Look at the Alpha Persei Coronal Conundrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayres, Thomas R., E-mail: Thomas.Ayres@Colorado.edu

2017-03-01

A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, the mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV) coronal-proxy Si iv unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multifaceted program tested that premise. Ground-based optical coronography and near-UV imaging with Hubble Space Telescope ( HST ) Wide-Field Camera 3 searched formore » any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si iv emissions of α Per, in a deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as part of the joint program, are aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution—a well-separated companion—has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.« less

A longitudinal evaluation of performance of automated BCR-ABL1 quantitation using cartridge-based detection system.

PubMed

Enjeti, Anoop; Granter, Neil; Ashraf, Asma; Fletcher, Linda; Branford, Susan; Rowlings, Philip; Dooley, Susan

2015-10-01

An automated cartridge-based detection system (GeneXpert; Cepheid) is being widely adopted in low throughput laboratories for monitoring BCR-ABL1 transcript in chronic myelogenous leukaemia. This Australian study evaluated the longitudinal performance specific characteristics of the automated system.The automated cartridge-based system was compared prospectively with the manual qRT-PCR-based reference method at SA Pathology, Adelaide, over a period of 2.5 years. A conversion factor determination was followed by four re-validations. Peripheral blood samples (n = 129) with international scale (IS) values within detectable range were selected for assessment. The mean bias, proportion of results within specified fold difference (2-, 3- and 5-fold), the concordance rate of major molecular remission (MMR) and concordance across a range of IS values on paired samples were evaluated.The initial conversion factor for the automated system was determined as 0.43. Except for the second re-validation, where a negative bias of 1.9-fold was detected, all other biases fell within desirable limits. A cartridge-specific conversion factor and efficiency value was introduced and the conversion factor was confirmed to be stable in subsequent re-validation cycles. Concordance with the reference method/laboratory at >0.1-≤10 IS was 78.2% and at ≤0.001 was 80%, compared to 86.8% in the >0.01-≤0.1 IS range. The overall and MMR concordance were 85.7% and 94% respectively, for samples that fell within ± 5-fold of the reference laboratory value over the entire period of study.Conversion factor and performance specific characteristics for the automated system were longitudinally stable in the clinically relevant range, following introduction by the manufacturer of lot specific efficiency values.

Observing Planetary Nebulae with JWST and Extremely Large Telescopes

NASA Astrophysics Data System (ADS)

Sahai, Raghvendra

2015-01-01

Most stars in the Universe that leave the main sequence in a Hubble time will end their lives evolving through the Planetary Nebula (PN) evolutionary phase. The heavy mass loss which occurs during the preceding AGB phase is important across astrophysics, dramatically changing the course of stellar evolution, dominantly contributing to the dust content of the interstellar medium, and influencing its chemical composition. The evolution from the AGB phase to the PN phases remains poorly understood, especially the dramatic transformation that occurs in the morphology of the mass-ejecta as AGB stars and their round circumstellar envelopes evolve into mostly PNe, the majority of which deviate strongly from spherical symmetry. In addition, although the PN [OIII] luminosity function (PNLF) has been used as a standard candle (on par with distance indicators such as Cepheids), we do not understand why it works. It has been argued that the resolution of these issues may be linked to binarity and associated processes such as mass transfer and common envelope evolution.Thus, understanding the formation and evolution of PNe is of wide astrophysical importance. PNe have long been known to emit across a very large span of wavelengths, from the radio to X-rays. Extensive use of space-based observatories at X-ray (Chandra/ XMM-Newton), optical (HST) and far-infrared (Spitzer, Herschel) wavelengths in recent years has produced significant new advances in our knowledge of these objects. Given the expected advent of the James Webb Space Telescope in the near future, and ground-based Extremely Large Telescope(s) somewhat later, this talk will focus on future high-angular-resolution, high-sensitivity observations at near and mid-IR wavelengths with these facilities that can help in addressing the major unsolved problems in the study of PNe.

The Enigmatic Local Hubble Flow: Probing the Nearby Peculiar Velocity Field with Consistent Distances to Neighboring Galaxies.

NASA Astrophysics Data System (ADS)

Mendez, B.; Davis, M.; Newman, J.; Madore, B. F.; Freedman, W. L.; Moustakas, J.

2002-12-01

The properties of the velocity field in the local volume (cz < 550 km s-1) have been difficult to constrain due to a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distribution of galaxies in the 1.2 Jy IRAS redshift survey, predict a quadrupolar flow pattern locally with strong infall at the poles of the local Supergalactic plane. In an attempt to resolve this discrepency, we probe the local velocity field and begin to establish a consistent set of galactic distances. We have obtained images of nearby galaxies in I, V, and B bands from the W.M. Keck Observatory and in F814W and F555W filters from the Hubble Space Telescope. Where these galaxies are well resolved into stars we can use the Tip of the Red Giant Branch (TRGB) as a distance indicator. Using a maximum likelihood analysis to quantitatively measure the I magnitude of the TRGB we determine precise distances to several nearby galaxies. We supplement that dataset with published distances to local galaxies measured using Cepheids, Surface Brightness Fluctuations, and the TRGB. With these data we find that the amplitude of the local flow is roughly half that expected in linear theory and N-body simulations; thus the enigma of cold local flows persists. This work was supported in part by NASA through a grant from the Space Telescope Science Institute and a Predoctoral Fellowship for Minorities from the Ford Foundation.

Variability survey of brightest stars in selected OB associations

NASA Astrophysics Data System (ADS)

Laur, Jaan; Kolka, Indrek; Eenmäe, Tõnis; Tuvikene, Taavi; Leedjärv, Laurits

2017-02-01

Context. The stellar evolution theory of massive stars remains uncalibrated with high-precision photometric observational data mainly due to a small number of luminous stars that are monitored from space. Automated all-sky surveys have revealed numerous variable stars but most of the luminous stars are often overexposed. Targeted campaigns can improve the time base of photometric data for those objects. Aims: The aim of this investigation is to study the variability of luminous stars at different timescales in young open clusters and OB associations. Methods: We monitored 22 open clusters and associations from 2011 to 2013 using a 0.25-m telescope. Variable stars were detected by comparing the overall light-curve scatter with measurement uncertainties. Variability was analysed by the light curve feature extraction tool FATS. Periods of pulsating stars were determined using the discrete Fourier transform code SigSpec. We then classified the variable stars based on their pulsation periods and available spectral information. Results: We obtained light curves for more than 20 000 sources of which 354 were found to be variable. Amongst them we find 80 eclipsing binaries, 31 α Cyg, 13 β Cep, 62 Be, 16 slowly pulsating B, 7 Cepheid, 1 γ Doradus, 3 Wolf-Rayet and 63 late-type variable stars. Up to 55% of these stars are potential new discoveries as they are not present in the Variable Star Index (VSX) database. We find the cluster membership fraction for variable stars to be 13% with an upper limit of 35%. Variable star catalogue (Tables A.1-A.10) and light curves are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A108

A complex approach to the blue-loop problem

NASA Astrophysics Data System (ADS)

Ostrowski, Jakub; Daszynska-Daszkiewicz, Jadwiga

2015-08-01

The problem of the blue loops during the core helium burning, outstanding for almost fifty years, is one of the most difficult and poorly understood problems in stellar astrophysics. Most of the work focused on the blue loops done so far has been performed with old stellar evolution codes and with limited computational resources. In the end the obtained conclusions were based on a small sample of models and could not have taken into account more advanced effects and interactions between them.The emergence of the blue loops depends on many details of the evolution calculations, in particular on chemical composition, opacity, mixing processes etc. The non-linear interactions between these factors contribute to the statement that in most cases it is hard to predict without a precise stellar modeling whether a loop will emerge or not. The high sensitivity of the blue loops to even small changes of the internal structure of a star yields one more issue: a sensitivity to numerical problems, which are common in calculations of stellar models on advanced stages of the evolution.To tackle this problem we used a modern stellar evolution code MESA. We calculated a large grid of evolutionary tracks (about 8000 models) with masses in the range of 3.0 - 25.0 solar masses from the zero age main sequence to the depletion of helium in the core. In order to make a comparative analysis, we varied metallicity, helium abundance and different mixing parameters resulting from convective overshooting, rotation etc.The better understanding of the properties of the blue loops is crucial for our knowledge of the population of blue supergiants or pulsating variables such as Cepheids, α-Cygni or Slowly Pulsating B-type supergiants. In case of more massive models it is also of great importance for studies of the progenitors of supernovae.

THE EFFECT OF THE {sup 14}N(p, {gamma}){sup 15}O REACTION ON THE BLUE LOOPS IN INTERMEDIATE-MASS STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halabi, Ghina M.; El Eid, Mounib F.; Champagne, Arthur

2012-12-10

We present stellar evolutionary sequences of stars in the mass range 5-12 M{sub Sun }, having solar-like initial composition. The stellar models are obtained using updated input physics, including recent rates of thermonuclear reactions. We investigate the effects of a modification of the {sup 14}N(p, {gamma}){sup 15}O reaction rate, as suggested by recent evaluations, on the formation and extension of the blue loops encountered during the evolution of the stars in the above mass range. We find that a reduced {sup 14}N(p, {gamma}){sup 15}O rate, as described in the text, has a striking impact on the physical conditions of burningmore » and mixing during shell hydrogen burning when the blue loops are formed. In particular, we find that the efficiency of shell hydrogen burning is crucial for the formation of an extended blue loop. We show that a significantly reduced {sup 14}N(p, {gamma}){sup 15}O rate affects severely the extension of the blue loops and the time spent by the star in the blue part of the Hertzsprung-Russell diagram in the mass range 5-7 M{sub Sun} if the treatment of convection is based on the Schwarzschild criterion only. In this case, envelope overshooting helps to restore well-extended blue loops as supported by the observations of the Cepheid stars. If core overshooting is included during the core hydrogen and core helium burning phases, the loop formation and its properties depend on how this overshooting is treated for a given stellar mass range, as well as on its efficiency.« less

The EB factory project. I. A fast, neural-net-based, general purpose light curve classifier optimized for eclipsing binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paegert, Martin; Stassun, Keivan G.; Burger, Dan M.

2014-08-01

We describe a new neural-net-based light curve classifier and provide it with documentation as a ready-to-use tool for the community. While optimized for identification and classification of eclipsing binary stars, the classifier is general purpose, and has been developed for speed in the context of upcoming massive surveys such as the Large Synoptic Survey Telescope. A challenge for classifiers in the context of neural-net training and massive data sets is to minimize the number of parameters required to describe each light curve. We show that a simple and fast geometric representation that encodes the overall light curve shape, together withmore » a chi-square parameter to capture higher-order morphology information results in efficient yet robust light curve classification, especially for eclipsing binaries. Testing the classifier on the ASAS light curve database, we achieve a retrieval rate of 98% and a false-positive rate of 2% for eclipsing binaries. We achieve similarly high retrieval rates for most other periodic variable-star classes, including RR Lyrae, Mira, and delta Scuti. However, the classifier currently has difficulty discriminating between different sub-classes of eclipsing binaries, and suffers a relatively low (∼60%) retrieval rate for multi-mode delta Cepheid stars. We find that it is imperative to train the classifier's neural network with exemplars that include the full range of light curve quality to which the classifier will be expected to perform; the classifier performs well on noisy light curves only when trained with noisy exemplars. The classifier source code, ancillary programs, a trained neural net, and a guide for use, are provided.« less

Dwarf spheroidal satellites of M31. I. Variable stars and stellar populations in Andromeda XIX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cusano, Felice; Clementini, Gisella; Garofalo, Alessia

We present B, V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.'2) of Andromeda's dwarf spheroidal companions, which we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23' × 23' area centered on And XIX and present the deepest color-magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V ∼ 26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which extends to the blue to significantly populate the classicalmore » instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and three of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ((P {sub ab}) = 0.62 days, σ = 0.03 days) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average luminosity of the RR Lyrae stars ((V(RR)) = 25.34 mag, σ = 0.10 mag), we determine a distance modulus of (m – M){sub 0} = 24.52 ± 0.23 mag in a scale where the distance to the Large Magellanic Cloud (LMC) is 18.5 ± 0.1 mag. The ACs follow a well-defined Period-Wesenheit (PW) relation that appears to be in very good agreement with the PW relationship defined by the ACs in the LMC.« less

Education and Outreach with the Northwest Indiana Robotic Telescope

NASA Astrophysics Data System (ADS)

Rengstorf, Adam W.; Slavin, S. D.

2011-01-01

The Northwest Indiana Robotic (NIRo) Telescope is being used to completely revise the introductory astronomy laboratory experiments at Purdue University Calumet (PUC). The NIRo telescope is a new 20-inch RC telescope. It was dedicated in Aug 2010, is designed to be operated remotely and/or robotically, and is located 30 miles south of PUC's campus in rural Lake county, IN. A suite of laboratory experiments is being developed and piloted during the 2010-2011 academic year. Lab experiments will progress from introductions to instruments and software, through simple data visualization and analysis, to developing and submitting an observing plan to complete multi-week laboratories. Experiments for both the solar system course and the stars & galaxies are being developed. Students in the solar system course will request and analyze images for such experiments as recreating Aristarchus’ relative size & distance calculations, establishing an observing strategy to monitor the Galilean satellites & determine Jupiter's mass, an ongoing `asteroid hunt', Martian retrograde motion, and Venusian phases. The stars & galaxies course will complete labs on galaxy morphology, eclipsing binaries, building an HR-diagram, cluster aging, and distances to Cepheid variables. The main outreach component is the development of a primary education program. In conjunction with the PUC School of Education and area middle-school science teachers, we are in the process of identifying the subset of laboratory ideas best suited to the State of Indiana Earth & Space Science teaching standards from grades 6 - 8. These laboratories are being developed into finished data products, curricula, and learning modules appropriate for the middle school classroom. The middle school classroom will be able to request observations and retrieve reduced images via an internet portal, currently in development. This project has been funded by NSF award #DUE-0736592.

The tip of the red giant branch as a distance indicator for resolved galaxies. 2: Computer simulations

NASA Technical Reports Server (NTRS)

Madore, Barry F.; Freedman, Wendy L.

1995-01-01

Based on both empirical data for the nearby galaxies, and on computer simulations, we show that measuring the position of the tip of the first-ascent red-giant branch provides a means of obtaining the distances to nearby galaxies with a precision and accuracy comparable to using Cepheids and/or RR Lyrae variables. We present an analysis of synthetic I vs (V-I) color magnitude diagrams of Population 2 systems to investigate the use of the observed discontinuity in the I-band luminosity function as a primary distance indicator. In the simulations we quantify the effects (1) signal to noise, (2) crowding, (3) population size, and (4) non-giant-branch-star contamination, on the method adopted for detecting the discontinuity,, measuring its luminosity, and estimating its uncertainity. We discuss sources of systematic error in the context of observable parameters, such as the signal-to-noise ratio and/or surface brightness. The simulations are then scaled to observed color-magnitude diagrams. It is concluded, that from the ground the tip of the red-giant-branch method can be sucessfully used to determine distances accurate to +/- 10% for galaxies out to 3 Mpc (mu approximately 27.5 mag); and from space a factor of four further in distance (mu approximately 30.6 mag) can be reached using HST. This method can be applied whereever a metal-poor population (-2.0 less than Z less than -0.7) of red-giant stars is detected (whose age is in the range 7-17 Gyr), whether that population resides in the halo of a spiral galaxy, the extended outer disk of a dwarf irregular, or in the outer periphery of an elliptical galaxy.

Rapid MRSA PCR on respiratory specimens from ventilated patients with suspected pneumonia: a tool to facilitate antimicrobial stewardship.

PubMed

Trevino, S E; Pence, M A; Marschall, J; Kollef, M H; Babcock, H M; Burnham, C-A D

2017-05-01

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of pneumonia in ventilated patients. Our objective was to evaluate the GeneXpert MRSA/SA SSTI Assay (Xpert MRSA/SA) (Cepheid, Sunnyvale, CA) for use in lower respiratory tract (LRT) specimens for rapid MRSA detection and to determine the potentially saved antibiotic-days if a culture-based identification method was replaced by this assay. Remnant LRT samples from ventilated patients submitted to the microbiology laboratory for routine culture were tested using conventional culture and Xpert MRSA/SA. One hundred of 310 LRT specimens met the inclusion criteria. Ten samples were positive for MRSA by Xpert MRSA/SA, while six were positive by routine culture methods. Xpert MRSA/SA correctly identified 5/6 positive and 89/94 negative MRSA specimens, for a sensitivity of 83.3%, specificity of 94.7%, positive predictive value of 45.6%, and negative predictive value of 98.9%. The assay also correctly detected 3/3 positive and 90/97 negative methicillin-susceptible S. aureus (MSSA) specimens, for a sensitivity of 100%, specificity of 92.8%, positive predictive value of 30%, and negative predictive value of 100%. A total of 748 vancomycin and 305 linezolid antibiotic-days were associated with the enrolled specimens. Vancomycin and linezolid utilization could decrease by 68.4% and 83%, respectively, if discontinued 1 day after negative polymerase chain reaction (PCR) results. The Xpert MRSA/SA SSTI rapid MRSA PCR assay performed well in respiratory samples from ventilated patients with suspected pneumonia and has the potential to facilitate stewardship efforts such as reducing empiric vancomycin and linezolid therapy.

A Second Ladder: Testing for Bias in the Type Ia Distance Scale with SBF

NASA Astrophysics Data System (ADS)

Milne, Peter

2016-10-01

We propose obtaining Surface Brightness Fluctuation (SBF) distances to the hosts galaxies of 20 nearby type Ia supernovae (SNe Ia), resulting in a sample of 29 SNe Ia in 27 galaxies when combined with HST-SBF distances from the literature. This sample can then be compared with the existing 18 SN Ia distances from Cepheids. Through these comparisons, we will determine if there are any discrepancies between the SBF distance scale, which is extended into the Hubble flow using early-type galaxies, and the SNIa distance scale, for which local calibrators are scarce and host galaxy types and SN environments are heterogenous. Since recent measurements of UV-optical colors suggest that SN Ia properties do depend on galaxy type and environment, it is essential that SNe Ia in all galaxy types are included when extending SN Ia distances to the distant Hubble flow. Since the conclusion that universal expansion is accelerating was originally based on SNe Ia distances, and because recent measurements of UV-optical colors suggest that SN Ia properties do depend on galaxy type and environment, it is essential to measure the same types of SNe in the same types of galaxies. To meet this goal, we propose to measure high-precision SBF distances to all early-type galaxies that have hosted SNIa within 80 Mpc. We will therefore be able to distinguish between systematic offsets in the derived Hubble constant between galaxies and/or SNe of different types and correct for them. SBF is the only distance measurement technique with statistical uncertainties comparable to SN Ia that can be applied to the early-type of galaxies in which the majority of the high-redshift SNIa occur.

Clostridium difficile rates in asymptomatic and symptomatic hospitalized patients using nucleic acid testing.

PubMed

Truong, Cynthia; Schroeder, Lee F; Gaur, Rajiv; Anikst, Victoria Emma; Komo, Ikuko; Watters, Colleen; McCalley, Erin; Kulik, Carole; Pickham, David; Lee, Nancy J; Banaei, Niaz

2017-04-01

The Clostridium difficile rate in symptomatic patients represents both those with C. difficile infection (CDI) and those with colonization. To predict the extent of CDI overdiagnosis, we compared the asymptomatic colonization rate to the symptomatic positivity rate in hospitalized patients using nucleic acid testing. Between July 2014 and April 2015, formed stool samples were collected from asymptomatic patients after admission to 3 hospital wards at the Stanford Hospital. Stool samples from symptomatic patients with suspected CDI in the same wards were collected for testing per provider order. The GeneXpert C. difficile tcdB polymerase chain reaction (PCR) assay (Cepheid, Sunnyvale, CA, USA) was performed on all stool samples and PCR cycle threshold was used as a measure of genomic equivalents. Chart review was performed to obtain clinical history and medication exposure. We found an asymptomatic C. difficile carriage rate of 11.8% (43/365) (95% confidence interval [CI], 8.5-15.1%) and a positivity rate in symptomatic patients of 15.4% (54/351) (95% CI, 11.6-19.2%; P=0.19). The median PCR cycle thresholds was not significantly different between asymptomatic carriers and symptomatic positives (29.5 versus 27.3; P=0.07). Among asymptomatic patients, 11.6% (5/43) of carriers and 8.4% (27/322; P=0.56) of noncarriers subsequently became symptomatic CDI suspects within the same hospitalization. Single and multivariate analysis did not identify any demographic or clinical factors as being significantly associated with C. difficile carriage. Asymptomatic C. difficile carriage rate was similar to symptomatic positivity rate. This suggests the majority of PCR-positive results in symptomatic patients are likely due to C. difficile colonization. Disease-specific biomarkers are needed to accurately diagnose patients with C. difficile disease. Copyright © 2017 Elsevier Inc. All rights reserved.

Near-IR period-luminosity relations for pulsating stars in ω Centauri (NGC 5139)

NASA Astrophysics Data System (ADS)

Navarrete, C.; Catelan, M.; Contreras Ramos, R.; Alonso-García, J.; Gran, F.; Dékány, I.; Minniti, D.

2017-08-01

Aims: The globular cluster ω Centauri (NGC 5139) hosts hundreds of pulsating variable stars of different types, thus representing a treasure trove for studies of their corresponding period-luminosity (PL) relations. Our goal in this study is to obtain the PL relations for RR Lyrae and SX Phoenicis stars in the field of the cluster, based on high-quality, well-sampled light curves in the near-infrared (IR). Methods: Observations were carried out using the VISTA InfraRed CAMera (VIRCAM) mounted on the Visible and Infrared Survey Telescope for Astronomy (VISTA). A total of 42 epochs in J and 100 epochs in KS were obtained, spanning 352 days. Point-spread function photometry was performed using DoPhot and DAOPHOT crowded-field photometry packages in the outer and inner regions of the cluster, respectively. Results: Based on the comprehensive catalog of near-IR light curves thus secured, PL relations were obtained for the different types of pulsators in the cluster, both in the J and KS bands. This includes the first PL relations in the near-IR for fundamental-mode SX Phoenicis stars. The near-IR magnitudes and periods of Type II Cepheids and RR Lyrae stars were used to derive an updated true distance modulus to the cluster, with a resulting value of (m - M)0 = 13.708 ± 0.035 ± 0.10 mag, where the error bars correspond to the adopted statistical and systematic errors, respectively. Adding the errors in quadrature, this is equivalent to a heliocentric distance of 5.52 ± 0.27 kpc. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, with the VISTA telescope (project ID 087.D-0472, PI R. Angeloni).

Stellar Populations and Nearby Galaxies with the LSST

NASA Astrophysics Data System (ADS)

Saha, Abhijit; Olsen, K.; Monet, D. G.; LSST Stellar Populations Collaboration

2009-01-01

The LSST will produce a multi-color map and photometric object catalog of half the sky to r=27.6 (AB mag; 5-sigma). Time-space sampling of each field spanning ten years will allow variability, proper motion and parallax measurements for objects brighter than r=24.7. As part of providing an unprecedented map of the Galaxy, the accurate multi-band photometry will permit photometric parallaxes, chemical abundances and a handle on ages via colors at turn-off for main-sequence (MS) stars at all distances within the Galaxy as well as in the Magellanic Clouds, and dwarf satellites of the Milky Way. This will support comprehensive studies of star formation histories and chemical evolution for field stars. The structures of the Clouds and dwarf spheroidals will be traced with the MS stars, to equivalent surface densities fainter than 35 mag/square arc-second. With geometric parallax accuracy of 1 milli-arc-sec, comparable to HIPPARCOS but reaching more than 10 magnitudes fainter, a robust complete sample of solar neighborhood stars will be obtained. The LSST time sampling will identify and characterize variable stars of all types, from time scales of 1 hr to several years, a feast for variable star astrophysics. The combination of wide coverage, multi-band photometry, time sampling and parallax taken together will address several key problems: e.g. fine tuning the extragalactic distance scale by examining properties of RR Lyraes and Cepheids as a function of parent populations, extending the faint end of the galaxy luminosity function by discovering them using star count density enhancements on degree scales tracing, and indentifying inter-galactic stars through novae and Long Period Variables.

SN 2012fr: Ultraviolet, Optical, and Near-infrared Light Curves of a Type Ia Supernova Observed within a Day of Explosion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contreras, Carlos; Phillips, M. M.; Burns, Christopher R.

We present detailed ultraviolet, optical, and near-infrared light curves of the Type Ia supernova (SN) 2012fr, which exploded in the Fornax cluster member NGC 1365. These precise high-cadence light curves provide a dense coverage of the flux evolution from -12 to +140 days with respect to the epoch of B-band maximum (more » $${t}_{{B}_{\\max }}$$). Supplementary imaging at the earliest epochs reveals an initial slow and nearly linear rise in luminosity with a duration of ~2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of 56 Ni mixing in the ejecta. From our analysis of the light curves, we conclude that: (i) the explosion occurred < 22 hr before the first detection of the supernova, (ii) the rise time to peak bolometric (λ >1800) luminosity was 16.5 ± 0.6 days, (iii) the supernova suffered little or no host-galaxy dust reddening, (iv) the peak luminosity in both the optical and near-infrared was consistent with the bright end of normal Type Ia diversity, and (v) 0.60 ± 0.15 M ⊙ of 56Ni was synthesized in the explosion. Despite its normal luminosity, SN 2012fr displayed unusually prevalent high-velocity Ca ii and Si ii absorption features, and a nearly constant photospheric velocity of the Si ii λ6355 line at ~12,000 km s -1 that began ~5 days before $${t}_{{B}_{\\max }}$$. We also highlight some of the other peculiarities in the early phase photometry and the spectral evolution. SN 2012fr also adds to a growing number of Type Ia supernovae that are hosted by galaxies with direct Cepheid distance measurements.« less

Impact of a rapid molecular test for positive blood cultures from neonatal intensive care patients on clinical management: a retrospective audit.

PubMed

Koh, L L; O'Rourke, S; Brennan, M; Clooney, L; Cafferkey, M; McCallion, N; Drew, R J

2018-05-01

Both Staphylococcus aureus and coagulase negative Staphylococci are common causes of late-onset neonatal sepsis in the neonatal intensive care unit (NICU), usually relating to intravascular access device infections. This project aimed to review the impact on antimicrobial treatment and clinical outcome in the NICU setting, of the introduction of the Xpert MRSA/SA BC test (Cepheid, USA) for the identification of staphylococci in blood cultures. A retrospective audit was carried out of the pre- and post-intervention periods; the intervention was the introduction of the Xpert MRSA/SA BC test. In total, 88 neonates had positive blood cultures with Staphylococcus spp., comprising 42 neonates in the pre-intervention and 46 in the post-intervention groups. The pre-intervention group had a higher birth weight (1.541 kg vs. 1.219 kg, p = 0.05) and higher platelet count (288 vs. 224 × 10 9 /L, p = 0.05). There was a trend towards a shorter duration of antimicrobial therapy in term infants and in the length of admission; however, this was not statistically significant (p = 0.2). All of the nine infants post-intervention with significant bacteraemia (S. aureus =3, CoNS =6) were changed to the optimal antimicrobial at the time the result was available. This study shows that the introduction of the Xpert MRSA/SA BC test can lead to a reduction in the length of admission and duration of antimicrobials in term infants; however, the difference was not statistically significant. All nine infants with clinically significant bacteraemia were treated with the appropriate antimicrobial when the Xpert MRSA/SA BC test result was available.

The Carnegie–Chicago Hubble Program. III. The Distance to NGC 1365 via the Tip of the Red Giant Branch

NASA Astrophysics Data System (ADS)

Jang, In Sung; Hatt, Dylan; Beaton, Rachael L.; Lee, Myung Gyoon; Freedman, Wendy L.; Madore, Barry F.; Hoyt, Taylor J.; Monson, Andrew J.; Rich, Jeffrey A.; Scowcroft, Victoria; Seibert, Mark

2018-01-01

The Carnegie–Chicago Hubble Program (CCHP) seeks to anchor the distance scale of Type Ia supernovae via the Tip of the Red Giant Branch (TRGB) method. Based on deep Hubble Space Telescope ACS/WFC imaging, we present an analysis of the TRGB for the metal-poor halo of NGC 1365, a giant spiral galaxy in the Fornax cluster that was host to the Type Ia supernova SN 2012fr. We have measured the extinction-corrected TRGB magnitude of NGC 1365 to be F814W = 27.34 ± 0.03stat ± 0.04sys mag. In advance of future direct calibration by Gaia, we adopt a provisional I-band TRGB luminosity set at the Large Magellanic Cloud and find a true distance modulus μ 0 = 31.29 ± 0.04stat ± 0.06sys mag or D = 18.1 ± 0.3stat ± 0.5sys Mpc. This measurement is in excellent agreement with recent Cepheid-based distances to NGC 1365 and reveals no significant difference in the distances derived from stars of Populations I and II for this galaxy. We revisit the error budget for the CCHP path to the Hubble constant based on the analysis presented here, i.e., that for one of the most distant Type Ia supernova hosts within our Program, and find that a 2.5% measurement is feasible with the current sample of galaxies and TRGB absolute calibration. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13691.

PERIOD–COLOR AND AMPLITUDE–COLOR RELATIONS AT MAXIMUM AND MINIMUM LIGHT FOR RR LYRAE STARS IN THE SDSS STRIPE 82 REGION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngeow, Chow-Choong; Kanbur, Shashi M.; Schrecengost, Zachariah

Investigation of period–color (PC) and amplitude–color (AC) relations at the maximum and minimum light can be used to probe the interaction of the hydrogen ionization front (HIF) with the photosphere and the radiation hydrodynamics of the outer envelopes of Cepheids and RR Lyraes. For example, theoretical calculations indicated that such interactions would occur at minimum light for RR Lyrae and result in a flatter PC relation. In the past, the PC and AC relations have been investigated by using either the ( V − R ){sub MACHO} or ( V − I ) colors. In this work, we extend previousmore » work to other bands by analyzing the RR Lyraes in the Sloan Digital Sky Survey Stripe 82 Region. Multi-epoch data are available for RR Lyraes located within the footprint of the Stripe 82 Region in five ( ugriz ) bands. We present the PC and AC relations at maximum and minimum light in four colors: ( u − g ){sub 0}, ( g − r ){sub 0}, ( r − i ){sub 0}, and ( i − z ){sub 0}, after they are corrected for extinction. We found that the PC and AC relations for this sample of RR Lyraes show a complex nature in the form of flat, linear or quadratic relations. Furthermore, the PC relations at minimum light for fundamental mode RR Lyrae stars are separated according to the Oosterhoff type, especially in the ( g − r ){sub 0} and ( r − i ){sub 0} colors. If only considering the results from linear regressions, our results are quantitatively consistent with the theory of HIF-photosphere interaction for both fundamental and first overtone RR Lyraes.« less

Rapid Detection of Mycobacterium tuberculosis and Rifampin Resistance by Use of On-Demand, Near-Patient Technology▿ † ‡

PubMed Central

Helb, Danica; Jones, Martin; Story, Elizabeth; Boehme, Catharina; Wallace, Ellen; Ho, Ken; Kop, JoAnn; Owens, Michelle R.; Rodgers, Richard; Banada, Padmapriya; Safi, Hassan; Blakemore, Robert; Lan, N. T. Ngoc; Jones-López, Edward C.; Levi, Michael; Burday, Michele; Ayakaka, Irene; Mugerwa, Roy D.; McMillan, Bill; Winn-Deen, Emily; Christel, Lee; Dailey, Peter; Perkins, Mark D.; Persing, David H.; Alland, David

2010-01-01

Current nucleic acid amplification methods to detect Mycobacterium tuberculosis are complex, labor-intensive, and technically challenging. We developed and performed the first analysis of the Cepheid Gene Xpert System's MTB/RIF assay, an integrated hands-free sputum-processing and real-time PCR system with rapid on-demand, near-patient technology, to simultaneously detect M. tuberculosis and rifampin resistance. Analytic tests of M. tuberculosis DNA demonstrated a limit of detection (LOD) of 4.5 genomes per reaction. Studies using sputum spiked with known numbers of M. tuberculosis CFU predicted a clinical LOD of 131 CFU/ml. Killing studies showed that the assay's buffer decreased M. tuberculosis viability by at least 8 logs, substantially reducing biohazards. Tests of 23 different commonly occurring rifampin resistance mutations demonstrated that all 23 (100%) would be identified as rifampin resistant. An analysis of 20 nontuberculosis mycobacteria species confirmed high assay specificity. A small clinical validation study of 107 clinical sputum samples from suspected tuberculosis cases in Vietnam detected 29/29 (100%) smear-positive culture-positive cases and 33/39 (84.6%) or 38/53 (71.7%) smear-negative culture-positive cases, as determined by growth on solid medium or on both solid and liquid media, respectively. M. tuberculosis was not detected in 25/25 (100%) of the culture-negative samples. A study of 64 smear-positive culture-positive sputa from retreatment tuberculosis cases in Uganda detected 63/64 (98.4%) culture-positive cases and 9/9 (100%) cases of rifampin resistance. Rifampin resistance was excluded in 54/55 (98.2%) susceptible cases. Specificity rose to 100% after correcting for a conventional susceptibility test error. In conclusion, this highly sensitive and simple-to-use system can detect M. tuberculosis directly from sputum in less than 2 h. PMID:19864480

Clarifying the Hubble constant tension with a Bayesian hierarchical model of the local distance ladder

NASA Astrophysics Data System (ADS)

Feeney, Stephen M.; Mortlock, Daniel J.; Dalmasso, Niccolò

2018-05-01

Estimates of the Hubble constant, H0, from the local distance ladder and from the cosmic microwave background (CMB) are discrepant at the ˜3σ level, indicating a potential issue with the standard Λ cold dark matter (ΛCDM) cosmology. A probabilistic (i.e. Bayesian) interpretation of this tension requires a model comparison calculation, which in turn depends strongly on the tails of the H0 likelihoods. Evaluating the tails of the local H0 likelihood requires the use of non-Gaussian distributions to faithfully represent anchor likelihoods and outliers, and simultaneous fitting of the complete distance-ladder data set to ensure correct uncertainty propagation. We have hence developed a Bayesian hierarchical model of the full distance ladder that does not rely on Gaussian distributions and allows outliers to be modelled without arbitrary data cuts. Marginalizing over the full ˜3000-parameter joint posterior distribution, we find H0 = (72.72 ± 1.67) km s-1 Mpc-1 when applied to the outlier-cleaned Riess et al. data, and (73.15 ± 1.78) km s-1 Mpc-1 with supernova outliers reintroduced (the pre-cut Cepheid data set is not available). Using our precise evaluation of the tails of the H0 likelihood, we apply Bayesian model comparison to assess the evidence for deviation from ΛCDM given the distance-ladder and CMB data. The odds against ΛCDM are at worst ˜10:1 when considering the Planck 2015 XIII data, regardless of outlier treatment, considerably less dramatic than naïvely implied by the 2.8σ discrepancy. These odds become ˜60:1 when an approximation to the more-discrepant Planck Intermediate XLVI likelihood is included.

On the radial oxygen distribution in the Galactic disc

NASA Astrophysics Data System (ADS)

Mishurov, Yu. N.; Tkachenko, R. V.

2018-01-01

The binned oxygen distribution, derived using new Cepheid observations, demonstrates wriggling radial pattern with different gradients in various ranges of Galactic radius, in particular a plateau distribution within 7 ≲ r ≲ 9 kpc (for the solar distance r⊙ = 7.9 kpc) where the mean Galactic abundance is about 0.2 dex higher than the solar one. Our modelling of oxygen synthesis in the Galactic disc is based on the refine theory that takes into account the combined effect of corotation resonance and turbulent diffusion on the disc enrichment. The theory fits to observations best of all if the time-scale (t_f=-f/\\dot{f}) of gas infall rate f(r, t) (where r and t are the Galactocentric radius and time, respectively) on to the disc is tf ∼ 2-3 Gyr whereas the fit is the worst if tf ∼ 6 Gyr (the last means that the high rate of gas infall at present epoch ∼1.5 M⊙ yr-1 does not satisfy the observed oxygen radial distribution). For inside-out scenario, further studies are necessary. Using the derived mean masses of newly synthesized oxygen ejected per core-collapsed supernova and theoretical oxygen yields, we compute the initial upper masses, mU, of stars that can explode as core-collapsed supernovae. Our estimates show that if tf ∼ 2 Gyr in the framework of rotating stars, their mU are no more than 24 M⊙, but if tf ∼ 3 Gyr in model of rotating stars or in the case of non-rotating star mU can be as high as 40-50 M⊙ like Wolf-Rayet stars that are considered as candidates for Types Ib/c supernovae.

Patterns of Extragenital Chlamydia and Gonorrhea in Women and Men Who Have Sex With Men Reporting a History of Receptive Anal Intercourse.

PubMed

Danby, Claire S; Cosentino, Lisa A; Rabe, Lorna K; Priest, Carol L; Damare, Khrystine C; Macio, Ingrid S; Meyn, Leslie A; Wiesenfeld, Harold C; Hillier, Sharon L

2016-02-01

Screening for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) in men who have sex with men is risk based. Despite high frequencies of oral and receptive anal intercourse (RAI) among women, extragenital screening is not recommended. Women (n = 175) and men who have sex with men (n = 224) primarily recruited from a sexually transmitted infection clinic reporting a lifetime history of RAI completed a structured questionnaire and clinician-collected swab samples from the rectum, pharynx, vagina (women), and urine (men). CT and GC were detected using 2 commercial nucleic acid amplification tests (Aptima Combo 2; Hologic, Inc, Bedford, MA; Xpert CT/NG, Cepheid Innovation, Sunnyvale, CA). The median age of the population was 26 years, 62% were white, and 88% were enrolled from a sexually transmitted disease clinic. Men were more likely than women to have GC (22.8% vs. 3.4%) and CT (21.9% vs. 12.6%). In men versus women, GC was detected in 16.5% versus 2.3% of pharyngeal swabs, 11.6% versus 2.3% of rectal swabs, and 5.4% versus 2.9% of urine samples or vaginal swabs. C. trachomatis was detected in 2.2% versus 1.7% of pharyngeal swabs, 17.4% versus 11.4% of rectal swabs, and 4.5% versus 10.3% for urogenital sites in men versus women. Overall 79.6% of CT and 76.5% of GC in men and 18.2% of CT and 16.7% of GC in women were detected only in the pharynx or rectum. Reliance on urogenital screening alone misses most of GC and CT in men and more than 15% of infections in women reporting RAI.

Investigations of the Local Supercluster velocity field. III. Tracing the backside infall with distance moduli from the direct Tully-Fisher relation

NASA Astrophysics Data System (ADS)

Ekholm, T.; Lanoix, P.; Teerikorpi, P.; Fouqué, P.; Paturel, G.

2000-03-01

We have extended the discussion of Paper II (Ekholm et al. \\cite{Ekholm99a}) to cover also the backside of the Local Supercluster (LSC) by using 96 galaxies within Theta <30degr from the adopted centre of LSC and with distance moduli from the direct B-band Tully-Fisher relation. In order to minimize the influence of the Malmquist bias we required log Vmax>2.1 and sigma B_T<0.2mag. We found out that if RVirgo<20 Mpc this sample fails to follow the expected dynamical pattern from the Tolman-Bondi (TB) model. When we compared our results with the Virgo core galaxies given by Federspiel et al. (\\cite{Federspiel98}) we were able to constrain the distance to Virgo: RVirgo=20-24 Mpc. When analyzing the TB-behaviour of the sample as seen from the origin of the metric as well as that with distances from the extragalactic Cepheid PL-relation we found additional support to the estimate RVirgo= 21 Mpc given in Paper II. Using a two-component mass-model we found a Virgo mass estimate MVirgo=(1.5 - 2)x Mvirial, where Mvirial=9.375*E14Msun for RVirgo= 21 Mpc. This estimate agrees with the conclusion in Paper I (Teerikorpi et al. \\cite{Teerikorpi92}). Our results indicate that the density distribution of luminous matter is shallower than that of the total gravitating matter when q0<= 0.5. The preferred exponent in the density power law, alpha ~2.5, agrees with recent theoretical work on the universal density profile of dark matter clustering in an Einstein-deSitter universe (Tittley & Couchman \\cite{Tittley99}).

Precision Photometry of Long Period Variable Stars: Flares and Bumps in the Night (Poster abstract)

NASA Astrophysics Data System (ADS)

Mais, D.

2015-06-01

(Abstract only) Mira variable stars are a broad class of stars, which encompass spectroscopic classes of type M, S, and C. These stars are closely related in terms of their long term variability, position on the Hertzsprung-Russell diagram their intermediate mass (from ~0.8 to ~8 solar mass) and the fact that class M evolves into the S and C type stars as certain stages of shell burning around the core proceeds. Recently, evidence has accumulated to suggest that Mira variables may go through flare up stages which result in brightening on the order of several tenths of a magnitude or more and may last hours to days in length. Very little is known about these events, indeed it is not clear that these events are real. In order to address the reality of these events, we established an automated acquisition/analysis of a group of 108 Mira variables in order to obtain the densest coverage of the periods to better constrain the potential flare-ups. Telescope control scripts were put in place along with real time analysis. This allowed for unattended acquisition of data on every clear night, all night long, in the V, R, and I photometric bands. In addition, during the course of the night multiple determinations are often obtained for a given star. The light curves of many of the program stars show a Cepheid-like bump phenomenon, however these appear on the ascending part of the light curve. In general, these bumps appear in longer period Mira's (>350 days). Bumps are not obvious or easily seen in VISUAL data records, although slope changes during rising phase are seen in some cases. So far, greater than 100,000 magnitude determinations have been obtained, many closely spaced in time. This should help to further constrain the potential occurrences of flare-up events.

The Carina Project. VI. The Helium-burning Variable Stars

NASA Astrophysics Data System (ADS)

Coppola, G.; Stetson, P. B.; Marconi, M.; Bono, G.; Ripepi, V.; Fabrizio, M.; Dall'Ora, M.; Musella, I.; Buonanno, R.; Ferraro, I.; Fiorentino, G.; Iannicola, G.; Monelli, M.; Nonino, M.; Pulone, L.; Thévenin, F.; Walker, A. R.

2013-09-01

We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, 4 are Anomalous Cepheids (ACs), and 2 are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dwarf spheroidal galaxies and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We use the BV Period-Wesenheit (PW) relation of RRLs together with evolutionary prescriptions and find a true distance modulus of 20.09 ± 0.07 (intrinsic) ± 0.1 (statistical) mag that agrees quite well with similar estimates available in the literature. We identified four peculiar variables. Taking into account their position in the Bailey diagram and in the BV PW relation, two of them (V14 and V149) appear to be candidate ACs, while two (V158 and V182) might be peculiar RRLs. In particular, the variable V158 has a period and a V-band amplitude very similar to the low-mass RRL—RRLR-02792—recently identified by Pietrzyński et al. in the Galactic bulge. Based on images collected with the MOSAICII camera available at the CTIO 4 m Blanco telescope, La Serena (2003B-0051, 2004B-0227, and 2005B-0092; PI: A. R. Walker) and in part with the WFI available at the 2.2 m MPG/ESO telescope (A064.L-0327) and with images obtained from the ESO/ST-ECF Science Archive Facility.

SN 2012fr: Ultraviolet, Optical, and Near-infrared Light Curves of a Type Ia Supernova Observed within a Day of Explosion

NASA Astrophysics Data System (ADS)

Contreras, Carlos; Phillips, M. M.; Burns, Christopher R.; Piro, Anthony L.; Shappee, B. J.; Stritzinger, Maximilian D.; Baltay, C.; Brown, Peter J.; Conseil, Emmanuel; Klotz, Alain; Nugent, Peter E.; Turpin, Damien; Parker, Stu; Rabinowitz, D.; Hsiao, Eric Y.; Morrell, Nidia; Campillay, Abdo; Castellón, Sergio; Corco, Carlos; González, Consuelo; Krisciunas, Kevin; Serón, Jacqueline; Tucker, Brad E.; Walker, E. S.; Baron, E.; Cain, C.; Childress, Michael J.; Folatelli, Gastón; Freedman, Wendy L.; Hamuy, Mario; Hoeflich, P.; Persson, S. E.; Scalzo, Richard; Schmidt, Brian; Suntzeff, Nicholas B.

2018-05-01

We present detailed ultraviolet, optical, and near-infrared light curves of the Type Ia supernova (SN) 2012fr, which exploded in the Fornax cluster member NGC 1365. These precise high-cadence light curves provide a dense coverage of the flux evolution from ‑12 to +140 days with respect to the epoch of B-band maximum ({t}{B\\max }). Supplementary imaging at the earliest epochs reveals an initial slow and nearly linear rise in luminosity with a duration of ∼2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of 56Ni mixing in the ejecta. From our analysis of the light curves, we conclude that: (i) the explosion occurred <22 hr before the first detection of the supernova, (ii) the rise time to peak bolometric (λ > 1800 Å) luminosity was 16.5 ± 0.6 days, (iii) the supernova suffered little or no host-galaxy dust reddening, (iv) the peak luminosity in both the optical and near-infrared was consistent with the bright end of normal Type Ia diversity, and (v) 0.60 ± 0.15 M ⊙ of 56Ni was synthesized in the explosion. Despite its normal luminosity, SN 2012fr displayed unusually prevalent high-velocity Ca II and Si II absorption features, and a nearly constant photospheric velocity of the Si II λ6355 line at ∼12,000 {km} {{{s}}}-1 that began ∼5 days before {t}{B\\max }. We also highlight some of the other peculiarities in the early phase photometry and the spectral evolution. SN 2012fr also adds to a growing number of Type Ia supernovae that are hosted by galaxies with direct Cepheid distance measurements. This paper includes data gathered with the 6.5 m Magellan Baade Telescope, located at Las Campanas Observatory, Chile.

[Value of polymerase chain reaction in serum for the diagnosis of enteroviral meningitis].

PubMed

Marque Juillet, S; Lion, M; Pilmis, B; Tomini, E; Dommergues, M-A; Laporte, S; Foucaud, P

2013-06-01

Enteroviruses (EV) are a common cause of aseptic meningitis in children. Virological diagnosis of EV meningitis is currently based on the detection of the viral genome in the cerebrospinal fluid (CSF). This study attempted to determine the correlation and the temporality of the polymerase chain reaction (PCR) assay in serum and CSF and to evaluate the possibility of diagnosing EV infection only on the serum PCR. The EV genome was sought by RT real-time PCR (Smart Cycler EV Primer and Probe Set(®), Cepheid) in CSF and serum, collected at the same time, for all children who underwent a lumbar puncture for suspected meningitis, between 1 June and 31 July 2010 at the Versailles Hospital. Forty-four patients were included in the study. EV infection was documented for 22 of them. In 10 patients, the EV genome was detected in CSF only; in 3 patients in serum only, and in 9 patients in both. Among patients with acute EV neurological infection, viremic children were significantly younger (1.6 months versus 5.8 years; P<0.001). Viremia was detected when the serum was sampled within 30 h after the beginning of symptoms. These results confirm previous reports of early and transient viremia in young children. This preliminary study shows the limits and added value of EV PCR in serum. It suggests that in some children and under certain conditions (age >3 months, clinical and biological compatibility with a viral infection, no previous antibiotic therapy, time from symptom onset to blood sampling <30 h, PCR in serum analyzed within 3h), PCR in serum, when positive, is a possible alternative. Therefore, it may be possible to diagnose EV infection without performing a lumbar puncture in a limited number of young children (11.4% of our suspected cases). This study needs to be reinforced by a multicenter study with a broader panel of patients. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

VizieR Online Data Catalog: Gaia DR1 (Gaia Collaboration, 2016)

NASA Astrophysics Data System (ADS)

Gaia Collaboration

2016-06-01

Gaia DR1 is based on observations collected between 25 July 2014 and 16 September 2015. Gaia DR1 contains positions (RA,DE) and G magnitudes for all sources with acceptable formal standard errors on positions. Positions and individual uncertainties are computed using a generic prior and Bayes' rule (detailed description in "Gaia astrometry for stars with too few observations. A Bayesian approach", Michalik et al., 2015A&A...583A..68M). The five-parameter astrometric solution - positions, parallaxes, and proper motions - for stars in common between the Tycho-2 Catalogue and Gaia is contained in Gaia DR1. This part of Gaia DR1 is based on the Tycho-Gaia Astrometric Solution (paper with detailed description (Michalik et al., 2015A&A...574A.115M); paper describing theory and background (Michalik et al., 2014A&A...571A..85M); paper describing quasar extension (Michalik & Lindegren, 2016A&A...586A..26M)). At the beginning of the routine phase, for a period of 4 weeks, a special scanning mode repeatedly covering the ecliptic poles on every spin was executed for calibration purposes. Photometric data of selected RR Lyrae and Cepheid variable stars based on these high-cadence measurements are contained in Gaia DR1. Positions (RA,DE) and G magnitudes for 2152 ICRF quasars (F. Mignard et al., 2016, A&A, in press.). The Gaia Archive DR1 data is available at archives.esac.esa.int/gaia. Tgas and Gaia Sources can be downloaded as VOTables, FITS or CSV at http://cdn.gea.esac.esa.int/Gaia/ If you use public Gaia DR1 data in your paper, please take note of our guide on how to acknowledge and cite Gaia DR1: http://gaia.esac.esa.int/documentation/GDR1/Miscellaneous/\\ seccreditandcitationinstructions.html (9 data files).

Do adjunct tuberculosis tests, when combined with Xpert MTB/RIF, improve accuracy and the cost of diagnosis in a resource-poor setting?

PubMed Central

Theron, Grant; Pooran, Anil; Peter, Jonny; van Zyl-Smit, Richard; Mishra, Hridesh Kumar; Meldau, Richard; Calligaro, Greg; Allwood, Brian; Sharma, Surendra Kumar; Dawson, Rod; Dheda, Keertan

2017-01-01

Information regarding the utility of adjunct diagnostic tests in combination with Xpert MTB/RIF (Cepheid, Sunnyvale, CA, USA) is limited. We hypothesised adjunct tests could enhance accuracy and/or reduce the cost of tuberculosis (TB) diagnosis prior to MTB/RIF testing, and rule-in or rule-out TB in MTB/RIF-negative individuals. We assessed the accuracy and/or laboratory-associated cost of diagnosis of smear microscopy, chest radiography (CXR) and interferon-γ release assays (IGRAs; T-SPOT-TB (Oxford Immunotec, Oxford, UK) and QuantiFERON-TB Gold In-Tube (Cellestis, Chadstone, Australia)) combined with MTB/RIF for TB in 480 patients in South Africa. When conducted prior to MTB/RIF: 1) smear microscopy followed by MTB/RIF (if smear negative) had the lowest cost of diagnosis of any strategy investigated; 2) a combination of smear microscopy, CXR (if smear negative) and MTB/RIF (if imaging compatible with active TB) did not further reduce the cost per TB case diagnosed; and 3) a normal CXR ruled out TB in 18% of patients (57 out of 324; negative predictive value (NPV) 100%). When downstream adjunct tests were applied to MTB/RIF-negative individuals, radiology ruled out TB in 24% (56 out of 234; NPV 100%), smear microscopy ruled in TB in 21% (seven out of 24) of culture-positive individuals and IGRAs were not useful in either context. In resource-poor settings, smear microscopy combined with MTB/RIF had the highest accuracy and lowest cost of diagnosis compared to either technique alone. In MTB/RIF-negative individuals, CXR has poor rule-in value but can reliably rule out TB in approximately one in four cases. These data inform upon the programmatic utility of MTB/RIF in high-burden settings. PMID:22075479

Evaluation of the Xpert MTB/RIF Performance on Tissues: Potential Impact on Airborne Infection Isolation at a Tertiary Cancer Care Center.

PubMed

McMillen, Tracy; Usiak, Shauna C; Chen, Liang Hua; Gomez, Luz; Ntiamoah, Peter; Hameed, Meera R; Budvytiene, Indre; Banaei, Niaz; Kamboj, Mini; Babady, N Esther

2018-04-01

OBJECTIVES In this study, we sought to evaluate the performance of the Xpert MTB/RIF (Cepheid) assay for the detection of Mycobacterium tuberculosis (MTB) complex DNA on fresh and formalin-fixed, paraffin-embedded (FFPE) tissue specimens from oncology patients in an area with a low prevalence of tuberculosis. We also aimed to retrospectively assess the potential impact of Xpert MTB/RIF on the duration of airborne infection isolation (AII). SETTING A 473-bed, tertiary-care cancer center in New York City. DESIGN A total of 203 tissue samples (101 FFPE and 102 fresh) were tested using Xpert MTB/RIF, including 133 pulmonary tissue samples (65.5%) and 70 extrapulmonary tissue samples (34.5%). Acid-fast bacilli (AFB) culture was used as the diagnostic gold standard. The limit of detection (LOD) and reproducibility were also evaluated for both samples types using contrived specimens. The potential impact of the Xpert MTB PCR assay on tissue samples from AII patients on AII duration was retrospectively assessed. RESULTS Using the Xpert MTB/RIF for fresh tissue specimens, the sensitivity was 50% (95% CI, 1.3%-98.7%) and the specificity was 99% (95% CI, 94.5%-99.9%). For FFPE tissue specimens, the sensitivity was 100% (95% CI, 63.1%-100%) and the specificity was 98.3% (95% CI, 95.5%-100%. The LOD was 103 colony-forming units (CFU)/mL for both fresh and FFPE tissue specimens, and the Xpert MTB/RIF was 100% reproducible at concentrations 10 times that of the LOD. With an expected turnaround time of 24 hours, the Xpert MTB PCR could decrease the duration of AII from a median of 8 days to a median of 1 day. CONCLUSIONS The Xpert MTB/RIF assay offers a valid option for ruling out Mycobacterium tuberculosis complex (MTBC) on tissue samples from oncology patients and for minimizing AII resource utilization. Infect Control Hosp Epidemiol 2018;39:462-466.

Analytical Performance Characteristics of the Cepheid GeneXpert Ebola Assay for the Detection of Ebola Virus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinsky, Benjamin A.; Sahoo, Malaya K.; Sandlund, Johanna

The recently developed Xpert® Ebola Assay is a novel nucleic acid amplification test for simplified detection of Ebola virus (EBOV) in whole blood and buccal swab samples. The assay targets sequences in two EBOV genes, lowering the risk for new variants to escape detection in the test. The objective of this report is to present analytical characteristics of the Xpert® Ebola Assay on whole blood samples. Our study evaluated the assay’s analytical sensitivity, analytical specificity, inclusivity and exclusivity performance in whole blood specimens. EBOV RNA, inactivated EBOV, and infectious EBOV were used as targets. The dynamic range of the assay,more » the inactivation of virus, and specimen stability were also evaluated. The lower limit of detection (LoD) for the assay using inactivated virus was estimated to be 73 copies/mL (95% CI: 51–97 copies/mL). The LoD for infectious virus was estimated to be 1 plaque-forming unit/mL, and for RNA to be 232 copies/mL (95% CI 163–302 copies/mL). The assay correctly identified five different Ebola viruses, Yambuku-Mayinga, Makona-C07, Yambuku-Ecran, Gabon-Ilembe, and Kikwit-956210, and correctly excluded all non-EBOV isolates tested. The conditions used by Xpert® Ebola for inactivation of infectious virus reduced EBOV titer by ≥6 logs. In conclusion, we found the Xpert® Ebola Assay to have high analytical sensitivity and specificity for the detection of EBOV in whole blood. It offers ease of use, fast turnaround time, and remote monitoring. The test has an efficient viral inactivation protocol, fulfills inclusivity and exclusivity criteria, and has specimen stability characteristics consistent with the need for decentralized testing. The simplicity of the assay should enable testing in a wide variety of laboratory settings, including remote laboratories that are not capable of performing highly complex nucleic acid amplification tests, and during outbreaks where time to detection is critical.« less

Centennial History of the Carnegie Institution of Washington

NASA Astrophysics Data System (ADS)

Sandage, Allan

2013-01-01

Foreword Richard A. Meserve; Acknowledgements; Prologue; Part I. Before the Beginning (1542-1904): 1. A telegram; 2. The origin of a name; 3. Three observatories for Mount Wilson before the real one; 4. The creation of the Carnegie Institution and its initial Astronomy Advisory Committee; Part II. Creation of the Observatory and the First Scientific Results: 5. The instruments of detection: solar telescopes, coelostats, spectrographs and spectra; 6. Snow, hale, frost and gale: just the right people to study storms on the sun; 7. Tower telescopes and magnetic fields and cycles; 8. Pioneers of peering: the scientific staff in the early years (1904-9); 9. Solar physics: the intermediate years (1910-30); 10. Yet more solar physics: motions on the surface, clocks in the gravity field and the reality of prominences; Part III. The Beginning of Nighttime Sidereal Astronomy at Mount Wilson: 11. The coming of the 60-inch and 100-inch reflectors; 12. Life on the mountain; 13. Anatomy of an observatory; Part IV. Preparation for an Understanding of Stellar Evolution and Galactic Structure: 14. Galactic structure in the raw; 15. Spectral classification and the invention of spectroscopic parallaxes; 16. Radial velocity; 17. Globular star clusters and the galactocentric revolution; 18. Galactic rotation: Stromberg, Lindblad and Oort; 19. The Carnegie Meridian Astrometry Department at the Dudley Observatory; 20. Absolute magnitudes from direct parallaxes and stellar motions; 21. Threads leading to the population concept that became the fabric of evolution; Part V. Physics of the Stars and the Interstellar Medium: 22. Five problems in astrophysics; 23. Long-term research associates and short-term visitors; 24. Interstellar gas, instruments and the spiral arms of the galaxy; Part VI. Observational Cosmology and the Code of Stellar Evolution: 25. Observational cosmology I: galaxy classification and the discovery of cepheids; 26. Observational cosmology II: the expansion of the universe and the search for the curvature of space; 27. Down more corridors of time; 28. The observational approach to stellar evolution; Epilogue; Abbreviations; Notes; Bibliography; Index.

Centennial History of the Carnegie Institution of Washington

NASA Astrophysics Data System (ADS)

Sandage, Allan

2005-03-01

Foreword Richard A. Meserve; Acknowledgements; Prologue; Part I. Before the Beginning (1542-1904): 1. A telegram; 2. The origin of a name; 3. Three observatories for Mount Wilson before the real one; 4. The creation of the Carnegie Institution and its initial Astronomy Advisory Committee; Part II. Creation of the Observatory and the First Scientific Results: 5. The instruments of detection: solar telescopes, coelostats, spectrographs and spectra; 6. Snow, hale, frost and gale: just the right people to study storms on the sun; 7. Tower telescopes and magnetic fields and cycles; 8. Pioneers of peering: the scientific staff in the early years (1904-9); 9. Solar physics: the intermediate years (1910-30); 10. Yet more solar physics: motions on the surface, clocks in the gravity field and the reality of prominences; Part III. The Beginning of Nighttime Sidereal Astronomy at Mount Wilson: 11. The coming of the 60-inch and 100-inch reflectors; 12. Life on the mountain; 13. Anatomy of an observatory; Part IV. Preparation for an Understanding of Stellar Evolution and Galactic Structure: 14. Galactic structure in the raw; 15. Spectral classification and the invention of spectroscopic parallaxes; 16. Radial velocity; 17. Globular star clusters and the galactocentric revolution; 18. Galactic rotation: Stromberg, Lindblad and Oort; 19. The Carnegie Meridian Astrometry Department at the Dudley Observatory; 20. Absolute magnitudes from direct parallaxes and stellar motions; 21. Threads leading to the population concept that became the fabric of evolution; Part V. Physics of the Stars and the Interstellar Medium: 22. Five problems in astrophysics; 23. Long-term research associates and short-term visitors; 24. Interstellar gas, instruments and the spiral arms of the galaxy; Part VI. Observational Cosmology and the Code of Stellar Evolution: 25. Observational cosmology I: galaxy classification and the discovery of cepheids; 26. Observational cosmology II: the expansion of the universe and the search for the curvature of space; 27. Down more corridors of time; 28. The observational approach to stellar evolution; Epilogue; Abbreviations; Notes; Bibliography; Index.

Treatment initiation among persons diagnosed with drug resistant tuberculosis in Johannesburg, South Africa

PubMed Central

Schnippel, Kathryn; Govathson, Caroline; Sineke, Tembeka; Black, Andrew; Long, Lawrence; Berhanu, Rebecca; Rosen, Sydney

2017-01-01

Background In South Africa, roughly half of the drug-resistant TB cases diagnosed are reported to have been started on treatment. We determined the proportion of persons diagnosed with rifampicin resistant (RR-) TB who initiated treatment in Johannesburg after the introduction of decentralized RR-TB care in 2011. Methods We retrospectively matched adult patients diagnosed with laboratory-confirmed RR-TB in Johannesburg from 07/2011-06/2012 with records of patients initiating RR-TB treatment at one of the city’s four public sector treatment sites (one centralized, three decentralized). Patients were followed from date of diagnosis until the earliest of RR-TB treatment initiation, death, or 6 months’ follow-up. We report diagnostic methods and outcomes, proportions initiating treatment, and median time from diagnosis to treatment initiation. Results 594 patients were enrolled (median age 34 (IQR 29–42), 287 (48.3%) female). Diagnosis was by GenoType MTBDRplus (Hain-Life-Science) line probe assay (LPA) (281, 47.3%), Xpert MTB/RIF (Cepheid) (258, 43.4%), or phenotypic drug susceptibility testing (DST) (30, 5.1%) with 25 (4.2%) missing a diagnosis method. 320 patients (53.8%) had multi-drug resistant TB, 158 (26.6%) rifampicin resistant TB by Xpert MTB/RIF, 102 (17.2%) rifampicin mono-resistance, and 14 (2.4%) extensively drug-resistant TB. 256/594 (43.0%) patients initiated treatment, representing 70.7% of those who were referred for treatment (362/594). 338/594 patients (57.0%) did not initiate treatment, including 104 (17.5%) who died before treatment was started. The median time from sputum collection to treatment initiation was 33 days (IQR 12–52). Conclusion Despite decentralized RR-TB treatment, fewer than half the patients diagnosed in Johannesburg initiated appropriate treatment. Offering treatment at decentralized sites alone is not sufficient; improvements in linking patients diagnosed with RR-TB to effective treatment is essential. PMID:28746344

Evaluation of Seegene Allplex Respiratory Panel 1 kit for the detection of influenza virus and human respiratory syncytial virus.

PubMed

Gimferrer, Laura; Andrés, Cristina; Rando, Ariadna; Piñana, Maria; Codina, Maria Gema; Martin, Maria Del Carmen; Fuentes, Francisco; Rubio, Susana; Alcubilla, Pilar; Pumarola, Tomàs; Antón, Andrés

2018-05-25

Influenza (FLUV) and human respiratory syncytial (HRSV) viruses are etiological agents of respiratory infections that cause a significant morbidity and mortality worldwide. A rapid and accurate diagnosis of these respiratory viruses is essential for an appropriate patient management. Molecular tests are the best detection option due to their high sensitivity and specificity. Seegene's Allplex™ Respiratory Panel 1 (Allplex RP1) is a real-time one-step RT-PCR assay for the simultaneous detection of FLUAV, FLUBV, HRSV-A and HRSV-B. In addition, it allows the determination of FLUAV subtype (H1, H3 and H1pdm09). This study aims to evaluate Allplex RP1 as a rapid molecular test for the detection of FLUAV, FLUBV, HRSV-A and HRSV-B viruses. The Allplex RP1 assay will be compared with other two commercial molecular assays, Prodesse ProFlu+ and ProFAST+ (Hologic, Madison, WI, USA), and GeneXpert Flu/RSV XC (Cepheid, USA). Allplex RP1, ProFlu+ and GeneXpert tests showed 95%, 91% and 96% of accuracy; and 94%, 88% and 95% of sensitivity, respectively. Moreover, Allplex RP1 showed a FLUAV subtype sensitivity of 91% and 88% for FLUAV-H1pdm09 and FLUAV-H3 respectively, and ProFAST+ assay showed sensitivities of 100% for both targets. The three assays showed a 100% of specificity and PPV, while the NPV were 84%, 73% and 86% for Allplex RP1, Prodesse and GeneXpert, respectively. In this study, Seegene's Allplex RP1 assay showed to be highly sensitive, specific, and suitable for detection of FLUV and HRSV, including FLUAV subtyping. In addition, it is also a hands-on-time saving assay due to the automated nucleic acid extraction and PCR setup. Copyright © 2018. Published by Elsevier B.V.

Clostridium difficile Testing in the Clinical Laboratory by Use of Multiple Testing Algorithms ▿

PubMed Central

Novak-Weekley, Susan M.; Marlowe, Elizabeth M.; Miller, John M.; Cumpio, Joven; Nomura, Jim H.; Vance, Paula H.; Weissfeld, Alice

2010-01-01

The incidence of Clostridium difficile infection (CDI) has risen almost 3-fold in the United States over the past decade, emphasizing the need for rapid and accurate tests for CDI. The Cepheid Xpert C. difficile assay is an integrated, closed, nucleic acid amplification system that automates sample preparation and real-time PCR detection of the toxin B gene (tcdB). A total of 432 stool specimens from symptomatic patients were tested by a glutamate dehydrogenase (GDH) assay, a toxin A and B enzyme immunoassay (EIA), the Xpert C. difficile assay, and a cell culture cytotoxicity neutralization assay (CCCN). The results of these methods, used individually and in combination, were compared to those of toxigenic culture. Results for the Xpert C. difficile assay alone showed a sensitivity, specificity, positive predictive value, and negative predictive value (NPV) of 94.4, 96.3, 84.0, and 98.8%, while the EIA alone gave corresponding values of 58.3, 94.7, 68.9, and 91.9%, respectively. An algorithm using the GDH assay and the EIA (plus the CCCN if the EIA was negative) showed corresponding values of 83.1, 96.7, 83.1, and 96.1%. The Xpert C. difficile assay was statistically superior to the EIA (P, <0.001 by Fisher's exact test) and to the GDH-EIA-CCCN algorithm (P, 0.0363). Combining the GDH and Xpert C. difficile assays lowered both the sensitivity and the NPV of the Xpert assay. The GDH-EIA-CCCN procedure required, on average, 2 days to complete testing on GDH-positive results, while testing by the Xpert C. difficile assay was completed, on average, in less than 1 h. Xpert C. difficile testing yielded the highest sensitivity and NPV, in the least amount of time, of the individual- and multiple-test algorithms evaluated in this study. PMID:20071552

Use of Cepheid Xpert Carba-R® for Rapid Detection of Carbapenemase-Producing Bacteria in Abdominal Septic Patients Admitted to Intensive Care Unit.

PubMed

Cortegiani, Andrea; Russotto, Vincenzo; Graziano, Giorgio; Geraci, Daniela; Saporito, Laura; Cocorullo, Gianfranco; Raineri, Santi Maurizio; Mammina, Caterina; Giarratano, Antonino

2016-01-01

Early institution of effective antibiotic therapy and source control are pivotal to improve survival of abdominal septic patients. Xpert® Carba-R is a real time polymerase chain reaction assay for rapid detection and differentiation of five genes (blaKPC, blaVIM, blaOXA-48, blaIMP-1, blaNDM) responsible for carbapenem resistance. We performed an observational study investigating the clinical usefulness and applicability of Xpert® Carba-R to detect carbapenem resistance in abdominal septic patients admitted to intensive care unit. We compared the results of Xpert® Carba-R with standard microbiological culture. We collected a set of two rectal/stomia swabs and two swabs from abdominal drainage fluid for each patient. We included 20 patients for a total of 45 comparisons between the two methods. In our clinical setting, the overall performance of Xpert® Carba-R for detection of carbapenem resistance in the presence of genes detectable and non-detectable by the method was: sensitivity 50% (95% CI 24.6-75.3); specificity 93.1% (95% CI 77.2-99.1); positive predictive value (PPV) 80% (95% CI 44.4-97.5); negative predictive value (NPV) 77.1% (95% CI 56.9-89.6). The inter-rater agreement was 0.47 (SE 0.14; 95% CI 0.20-0.74). When considering the only 5 mechanisms of resistance detected by both methods, the overall diagnostic performance was: sensitivity 100% (95% CI 69.1-100), specificity 94.2 (95% CI 80.8-99.3), PPV 83.3 (95% CI 59.6-97.9) and NPV 100% (95% CI 89.4-100). The inter-rater agreement was 0.88 (SE 0.08; 95% CI 0.71-1). Xpert® Carba-R may be considered an additional diagnostic tool for early diagnosis of carbapenem resistance in abdominal septic patients. Clinicians should be aware of their epidemiology before its introduction in the diagnostic protocol of their intensive care units.