Extinction in the Star Cluster SAI 113 and Galactic Structure in Carina

NASA Astrophysics Data System (ADS)

Carraro, Giovanni; Turner, David G.; Majaess, Daniel J.; Baume, Gustavo L.; Gamen, Roberto; Molina Lera, José A.

2017-04-01

Photometric CCD UB VI C photometry obtained for 4860 stars surrounding the embedded southern cluster SAI 113 (Skiff 8) is used to examine the reddening in the field and derive the distance to the cluster and nearby van Genderen 1. Spectroscopic color excesses for bright cluster stars, photometric reddenings for A3 dwarfs, and dereddening of cluster stars imply that the reddening and extinction laws match results derived for other young clusters in Carina: {E}U-B/{E}B-V≃ 0.64 and {R}V≃ 4. SAI 113 displays features that may be linked to a history of dynamical interactions among member stars: possible circumstellar reddening and rapid rotation of late B-type members, ringlike features in star density, and a compact core, with most stars distributed randomly across the field. The group van Genderen 1 resembles a stellar asterism, with potential members distributed randomly across the field. Distances of 3.90 ± 0.19 kpc and 2.49 ± 0.09 kpc are derived for SAI 113 and van Genderen 1, respectively, with variable reddenings {E}B-V ranging from 0.84 to 1.29 and 0.23 to 1.28. The SRC variables CK Car and EV Car may be outlying members of van Genderen 1, thereby of use for calibrating the period-luminosity relation for pulsating M supergiants. More importantly, the anomalous reddening and extinction evident in Carina and nearby regions of the Galactic plane in the fourth quadrant impact the mapping of spiral structure from young open clusters. The distribution of spiral arms in the fourth quadrant may be significantly different from how it is often portrayed.

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 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.

VizieR Online Data Catalog: VI photometry and spectroscopy in h+{chi} Per (Currie+, 2010)

NASA Astrophysics Data System (ADS)

Currie, T.; Hernandez, J.; Irwin, J.; Kenyon, S. J.; Tokarz, S.; Balog, Z.; Bragg, A.; Berlind, P.; Calkins, M.

2010-04-01

Optical VI photometry of h and {chi} Persei were taken with the Mosaic Imager at the 4m Mayall telescope at the Kitt Peak National Observatory on 2006 October 13-16 and 27-30. We acquired low-resolution optical spectroscopy of Two Micron All Sky Survey (2MASS)-detected stars within 1deg2 of the cluster centers. For faint stars, we used the multiobject, fiber-fed spectrograph Hectospec on the 6.5m MMT. Brighter stars were observed with the fiber-fed spectrograph Hydra on the 3.5m WIYN telescope at Kitt Peak National Observatory and single-slit FAST spectrograph on the 1.5m Tillinghast telescope at the Fred Lawrence Whipple Observatory. (4 data files).

Analysis of Neckel and Chini standard stars in the UBVRI photometric system

NASA Astrophysics Data System (ADS)

Oriol, R.

1992-12-01

This paper studies the list of 60 faint standard stars of Neckel and Chini (1980) in the UBVRI Johnson photometric system. We have re-reduced the standard stars using our own method of reduction from a large number of selected observations made at the Observatorio Astronomico Nacional and at the Centro Astronomico Hispano-Aleman, both at Calar Alto, Spain, and at the Observatorio del Roque de los Muchachos, La Palma Island, Spain. The reduction method used is explained and the results are given for the four colors used: (B-V), (U-B), (V-R), and (V-I), together with the V magnitude, that is, we have corrected many standard stars for each color and magnitude. These results are supported with graphs where residual color is plotted against corresponding color (or magnitude). Finally, our (V-R) and (V-I) results are compared to those of Taylor et al. (1989), with a good correspondence.

A PROFILE ANALYSIS OF RAMAN-SCATTERED O VI BANDS AT 6825 Å AND 7082 Å IN SANDULEAK’S STAR

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

Heo, Jeong-Eun; Lee, Hee-Won; Angeloni, Rodolfo

2016-12-20

We present a detailed modeling of the two broad bands observed at 6825 and 7082 Å in Sanduleak’s star, a controversial object in the Large Magellanic Cloud. These bands are known to originate from Raman scattering of O vi  λ λ 1032 and 1038 photons with atomic hydrogen and are only observed in bona fide symbiotic stars. Our high-resolution spectrum obtained with the Magellan Inamori Kyocera Echelle spectrograph at the Magellan-Clay Telescope reveals, quite surprisingly, that the profiles of the two bands look very different: while the Raman 6825 Å band shows a single broad profile with a redward extendedmore » bump, the Raman 7082 Å band exhibits a distinct triple-peak profile. Our model suggests that the O vi emission nebula can be decomposed into a red, blue, and central emission region from an accretion disk, a bipolar outflow, and a further compact, optically thick region. We also perform Monte Carlo simulations with the aim of fitting the observed flux ratio F (6825)/ F (7082) ∼ 4.5, which indicates that the neutral region in Sanduleak’s star is characterized by the column density N{sub Hi} ∼ 1 × 10{sup 23} cm{sup −2}.« less

Pre-main sequence stars with disks in the Eagle Nebula observed in scattered light

NASA Astrophysics Data System (ADS)

Guarcello, M. G.; Damiani, F.; Micela, G.; Peres, G.; Prisinzano, L.; Sciortino, S.

2010-10-01

Context. NGC 6611 and its parental cloud, the Eagle Nebula (M 16), are well-studied star-forming regions, thanks to their large content of both OB stars and stars with disks and the observed ongoing star formation. In our previous studies of the Eagle Nebula, we identified 834 disk-bearing stars associated with the cloud, after detecting their excesses in NIR bands from J band to 8.0 μ m. Aims: In this paper, we study in detail the nature of a subsample of disk-bearing stars that show peculiar characteristics. They appear older than the other members in the V vs. V-I diagram, and/or they have one or more IRAC colors at pure photospheric values, despite showing NIR excesses, when optical and infrared colors are compared. Methods: We confirm the membership of these stars to M 16 by a spectroscopic analysis. The physical properties of these stars with disks are studied by comparing their spectral energy distributions (SEDs) with the SEDs predicted by models of T Tauri stars with disks and envelopes. Results: We show that the age of these stars estimated from the V vs. V-I diagram is unreliable since their V-I colors are altered by the light scattered by the disk into the line of sight. Only in a few cases their SEDs are compatible with models with excesses in V band caused by optical veiling. Candidate members with disks and photospheric IRAC colors are selected by the used NIR disk diagnostic, which is sensitive to moderate excesses, such as those produced by disks with low masses. In 1/3 of these cases, scattering of stellar flux by the disks can also be invoked. Conclusions: The photospheric light scattered by the disk grains into the line of sight can affect the derivation of physical parameters of Class II stars from photometric optical and NIR data. Besides, the disks diagnostic we defined are useful for selecting stars with disks, even those with moderate excesses or whose optical colors are altered by veiling or photospheric scattered light. Table with the data of the stars 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/521/A18

The Extent of Chemically Enriched Gas around Star-forming Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Johnson, Sean D.; Chen, Hsiao-Wen; Mulchaey, John S.; Schaye, Joop; Straka, Lorrie A.

2017-11-01

Supernova driven winds are often invoked to remove chemically enriched gas from dwarf galaxies to match their low observed metallicities. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circumgalactic medium, CGM) and pollute the intergalactic medium (IGM). Here, we present a survey of the CGM and IGM around 18 star-forming field dwarfs with stellar masses of {log} {M}* /{M}⊙ ≈ 8{--}9 at z≈ 0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than that of the host virial radius, {R}{{h}}. Ten are probed in the surrounding IGM at d/{R}{{h}}=1{--}3. The absorption measurements include neutral hydrogen, the dominant silicon ions for diffuse cool gas (T ˜ 104 K; Si II, Si III, and Si IV), moderately ionized carbon (C IV), and highly ionized oxygen (O VI). Metal absorption from the CGM of the dwarfs is less common and ≈ 4× weaker compared to massive star-forming galaxies, though O VI absorption is still common. None of the dwarfs probed at d/{R}{{h}}=1{--}3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM of the dwarfs accounts for only 2%-6% of the expected silicon budget from the yields of supernovae associated with past star formation. The highly ionized O VI accounts for ≈8% of the oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of ≲0.2, the highly ionized CGM may represent a significant metal reservoir even for dwarfs not expected to maintain gravitationally shock heated hot halos.

Chromospherically active stars. VI - HD 136901 = UV CrB: A massive ellipsoidal K giant single-lined spectroscopic binary

NASA Technical Reports Server (NTRS)

Fekel, Francis C.; Kirkpatrick, J. Davy; Yang, Xinxing; Strassmeier, Klaus G.

1989-01-01

The variable star HD 136901 = UV CrB is a chromospherically active K2 III single-lined spectroscopic binary with an orbital period of 18.665 days. It has modest-strength Ca H and K emission and UV features, while H-alpha is a strong absorption feature containing little or no emission. The inclination of the system is 53 + or - 12 deg. The v sin i of the primary is 42 + or - 2 km/s, resulting in a minimum radius of 15.5 + or - 0.8 solar. When compared with the Roche lobe radius, this results in a mass ratio of 2.90 or larger. Additional constraints indicate that the secondary has a mass between 0.85 and 1.25 solar. Thus, the mass of the primary is at least 2.5 solar and probably is in the range 2.5-4 solar.

Highly ionized atoms observed with Copernicus. [stellar O lines

NASA Technical Reports Server (NTRS)

York, D. G.

1974-01-01

Based on high-resolution observations using the Princeton satellite/spectrometer on Copernicus the O VI doublet is discussed in detail, in conjunction with data for the resonance lines of N V, Si IV, and S IV reported in five stars. The temperature, density, and the possible extent of the O VI producing region are discussed. The ratio N(S IV)/N(O VI) is used to derive a lower limit to the temperature in the O VI producing region. In near pressure equilibrium with normal interstellar clouds and H II regions minimum densities are found to be consistent with a hot plasma.

VizieR Online Data Catalog: OGLE II. VI photometry of Galactic Bulge (Udalski+, 2002)

NASA Astrophysics Data System (ADS)

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

2003-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive (2 data files).

First detection of bromine and antimony in hot stars

NASA Astrophysics Data System (ADS)

Werner, K.; Rauch, T.; Knörzer, M.; Kruk, J. W.

2018-06-01

Bromine (Z = 35) and antimony (Z = 51) are extremely difficult to detect in stars. In very few instances, weak and mostly uncertain identifications of Br I, Br II, and Sb II in relatively cool, chemically peculiar stars were successful. Adopted solar abundance values rely on meteoritic determinations. Here, we announce the first identification of these species in far-ultraviolet spectra of hot stars (with effective temperatures of 49 500-70 000 K), namely in helium-rich (spectral type DO) white dwarfs. We identify the Br VI resonance line at 945.96 Å. A previous claim of Br detection based on this line is incorrect because its wavelength position is inaccurate by about 7 Å in atomic databases. Taking advantage of precise laboratory measurements, we identify this line as well as two other, subordinate Br VI lines. Antimony is detected by the Sb V resonance doublet at 1104.23/1225.98 Å as well as two subordinate Sb VI lines. A model-atmosphere analysis reveals strongly oversolar Br and Sb abundances that are caused by radiative-levitation dominated atomic diffusion. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer.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 NAS5-26666.

The Epoch of the First Star Formation in the Closest Metal-Poor Blue Compact Dwarf Galaxy UGC 4483

NASA Astrophysics Data System (ADS)

Aloisi, Alessandra

2017-08-01

Metal-poor Blue Compact Dwarf (BCD) galaxies have been interpreted as nearby galaxies in formation. This view has been challenged by HST detection of Red Giant Branch (RGB) stars in all metal-poor BCDs where an RGB tip (TRGB, brightest RGB phase) has been searched for, impling the presence of stars at least 1 Gyr old. Due to the age-metallicity degeneracy, the RGB color provides little insight into the exact star formation history (SFH) beyond 1 Gyr. So, the first SF epoch may have occurred anywhere between 13 and 1 Gyr ago. To resolve this, it is necessary to reach features in the color-magnitude diagram (CMD) that are much fainter than the TRGB. Here we propose new WFC3/UVIS observations (with ACS/WFC in parallel) of the closest metal-poor BCD, UGC 4483. These data will yield an I vs. V-I CMD that goes 4 mag deeper than the TRGB allowing to detect red clump (RC) and horizontal branch (HB) stars. Variable stars of RR Lyrae type will also be detected. With their mere presence, these variables will indisputably prove the existence of a population at least 10 Gyr old. Apparent mag and width of RC, HB and RGB will independently constrain age and metallicity of the old/evolved stars, the presence of multiple SF episodes, their duration and metallicity spread. This deep crowded-field photometric project is only possible with HST. Due to UGC 4483 location in CVZ, it can be done in half the number of orbits that it would otherwise take. Since UGC 4483 is so close, it may be the only BCD for which these questions can be answered in the near future. It provides our best chance for learning about the true cosmological age and evolutionary state of these enigmatic galaxies.

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

Stellar Laboratories: New GeV and Ge VI Oscillator Strengths and their Validation in the Hot White Dwarf RE0503-289

NASA Technical Reports Server (NTRS)

Rauch, T.; Werner, K.; Biemont, E.; Quinet, P.; Kruk, J. W.

2013-01-01

State-of-the-art spectral analysis of hot stars by means of non-LTE model-atmosphere techniques has arrived at a high level of sophistication. The analysis of high-resolution and high-S/N spectra, however, is strongly restricted by the lack of reliable atomic data for highly ionized species from intermediate-mass metals to trans-iron elements. Especially data for the latter has only been sparsely calculated. Many of their lines are identified in spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable determination of their abundances establishes crucial constraints for AGB nucleosynthesis simulations and, thus, for stellar evolutionary theory. Aims. In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified. Individual abundance determinations are hampered by the lack of reliable oscillator strengths. Most of these identified lines stem from Ge V. In addition, we identified Ge VI lines for the first time. We calculated Ge V and Ge VI oscillator strengths in order to reproduce the observed spectrum. Methods. We newly calculated Ge V and Ge VI oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our non-LTE stellar-atmosphere models for the analysis of the Ge IV-VI spectrum exhibited in high-resolution and high-S/N FUV (FUSE) and UV (ORFEUS/BEFS, IUE) observations of RE 0503-289. Results. In the UV spectrum of RE 0503-289, we identify four Ge IV, 37 Ge V, and seven Ge VI lines. Most of these lines are identified for the first time in any star. We can reproduce almost all Ge IV, GeV, and Ge VI lines in the observed spectrum of RE 0503-289 (T(sub eff) = 70 kK, log g = 7.5) at log Ge = -3.8 +/- 0.3 (mass fraction, about 650 times solar). The Ge IV/V/VI ionization equilibrium, that is a very sensitive T(sub eff) indicator, is reproduced well. Conclusions. Reliable measurements and calculations of atomic data are a prerequisite for stellar-atmosphere modeling. Our oscillator-strength calculations have allowed, for the first time, Ge V and Ge VI lines to be successfully reproduced in a white dwarf s (RE 0503-289) spectrum and to determine its photospheric Ge abundance.

The Optical Gravitational Lensing Experiment. BVI Maps of Dense Stellar Regions. III. The Galactic Bulge

NASA Astrophysics Data System (ADS)

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

2002-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive.

Coronal gas in the galaxy. II. A statistical analysis of O VI absorptions

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

Jenkins, E.B.

Results from the survey of interstellar O VI by Jenkins and by Jenkins and Meloy are analyzed to synthesize a global description of the properties of the coronal gas. Tests for correlations of column densities or velocities with properties of the target stars showed no evidence for a circumstellar origin for the absorption lines. An overall average density n (O VI) =2.8 x 10/sup -8/ cm/sup -3/ was found in the galactic plane, with a decrease which approximately follows exp (-z/300 pc) away from the plane.Fluctuations in column densities over various lines of sight suggest that existence of six hotmore » gas regions kpc/sup -/1, randomly distributed in space, each with an O VI column density of about 10/sup 13/ cm/sup -2/. These regions account for an average density n (O VI) =2.1 x 10/sup -8/ cm/sup -3/; the remaining 7 x 10/sup -9/ cm/sup -3/ is produced by more sparsely distributed but thicker parcels of hot gas which are seen toward 10% of the stars. The statistics of radial velocity centroids and widths support the interpretation of distinct domains; each region has an internal velocity dispersion consistent with a Doppler broadening of a plasma at T> or approx. =2 x 10/sup 5/ K (near the characteristic temperature for a maximum concentration of O VI in collisional equilibrium), while the regions themselves move about with a dispersion of radial velocities equal to 26 km s/sup -1/. Systematic motions of gas away from the galactic plane could not be seen, however.Excursions from the normal O VI per unit distance have no perceptible anicorrelation with deviations in reddening by cool interstellar coulds: a fact which suggests that the average filling factor of O VI gas is less than 20% if coronal gas really displaces the cooler material and does not have large variations in density and temperature.« less

Ultraviolet observations of alpha Aurigae from Copernicus

NASA Technical Reports Server (NTRS)

Dupree, A. K.

1975-01-01

Emission lines of L-alpha (1215.67 A) and O VI (1031.94 A) were detected in the spectroscopic binary alpha Aur (Capella) with the Princeton experiment on Copernicus. Temperatures of the emitting regions are inferred to be in excess of 300,000 K. The temperature and emission measure are consistent with a variable source of soft X-rays. If the emission is attributed to the primary star (G5 III), the atmosphere is expanding with velocities of about 20-100 km/s. Such expansion can lead to material within the binary system. The density of interstellar hydrogen inferred from absorption of stellar L-alpha appears to be approximately 0.01 hydrogen atoms per cu cm.

Galactic and Circumgalactic O VI and its Impact on the Cosmological Metal and Baryon Budgets at 2 < z <~ 3.5

NASA Astrophysics Data System (ADS)

Lehner, N.; O'Meara, J. M.; Fox, A. J.; Howk, J. C.; Prochaska, J. X.; Burns, V.; Armstrong, A. A.

2014-06-01

We present the first results from our NASA Keck Observatory Database of Ionized Absorbers toward Quasars (KODIAQ) survey which aims to characterize the properties of the highly ionized gas of galaxies and their circumgalactic medium (CGM) at 2 < z < 4. We select absorbers optically thick at the Lyman limit (τLL > 1, log N_{H\\,\\scriptsize{I}} \\textgreater 17.3) as probes of these galaxies and their CGM where both transitions of the O VI doublet have little contamination from the Lyα, β forests. We found 20 absorbers that satisfy these rules: 7 Lyman limit systems (LLSs), 8 super-LLSs (SLLSs) and 5 damped Lyα (DLAs). The O VI detection rate is 100% for the DLAs, 71% for the LLSs, and 63% for the SLLSs. When O VI is detected, log \\langle N_{O\\,\\scriptsize{VI}} \\rangle = 14.9 +/- 0.3, an average O VI column density substantially larger and with a smaller dispersion than found in blind O VI surveys at similar redshifts. Strong O VI absorption is therefore nearly ubiquitous in the CGM of z ~ 2-3 galaxies. The total velocity widths of the O VI profiles are also large (200 \\le \\Delta v_{O\\,\\scriptsize{VI}} \\le 400 km s-1). These properties are quite similar to those seen for O VI in low-z star-forming galaxies, and therefore we hypothesize that these strong CGM O VI absorbers (with τLL > 1) at 2 < z <~ 3.5 also probe outflows of star-forming galaxies. The LLSs and SLLSs with no O VI absorption have properties consistent with those seen in cosmological simulations tracing cold streams feeding galaxies. When the highly ionized (Si IV and O VI) gas is taken into account, we determine that the τLL > 1 absorbers could contain as much as 3%-14% of the cosmic baryon budget at z ~ 2-3, only second to the Lyα forest. We conservatively show that 5%-20% of the metals ever produced at z ~ 2-3 are in form of highly ionized metals ejected in the CGM of galaxies. We dedicate this paper and the KODIAQ project to the memory and families of Wal Sargent and Arthur M. Wolfe. Without the vision and terrific efforts of these two scientists, this survey would not exist. Their careers have greatly inspired and influenced our own, and we hope that their work continues to flourish with this archival data set.

Indexes of temporal myocardial repolarization dispersion and sudden cardiac death in heart failure: any difference?

PubMed

Piccirillo, Gianfranco; Rossi, Pietro; Mitra, Marilena; Quaglione, Raffaele; Dell'Armi, Annalaura; Di Barba, Daniele; Maisto, Damiana; Lizio, Andrea; Barillà, Francesco; Magrì, Damiano

2013-03-01

The QT variability index, calculated between Q- and the T-wave end (QTend VI), is an index of temporal myocardial repolarization lability associated with sudden cardiac death (SCD) in chronic heart failure (CHF). Little is known about temporal variability in the other two temporal myocardial repolarization descriptors obtained from Q-Tpeak and Tpeak -Tend intervals. We therefore investigated differences between these indexes in patients with CHF who died suddenly and in those who survived with a left ventricular ejection fraction (LVEF) ≤35% or >35%. We selected 127 ECG and systolic blood pressure (SPB) recordings from outpatients with CHF all of whom had been followed up for 30 months. We calculated RR and SPB variability by power spectral analysis and QTend VI, QTpeak VI, Tpeak Tend VI. We then subdivided data patients into three groups SCD, LVEF ≤ 35%, and LVEF > 35%. The LVEF was higher in the SCD than in the LVEF ≤ 35% group, whereas no difference was found between the SCD and LVEF > 35% groups. QTend VI, QTpeak VI, and Tpeak Tend VI were higher in the SCD and LVEF ≤ 35% groups than in the LVEF > 35% group. Multivariate analysis detected a negative relationship between all repolarization variability indexes, low frequency obtained from RR intervals and LVEF. Our data show that variability in the first (QTpeak VI) and second halves of the QT interval (Tpeak -Tend VI) significantly contributes to the QTend VI in patients with CHF. Further studies should investigate whether these indexes might help stratify the risk of SCD in patients with a moderately depressed LVEF. ©2012, Wiley Periodicals, Inc.

Hourly variations in O VI P Cygni profiles of hot stars

NASA Technical Reports Server (NTRS)

York, D. G.; Vidal-Madjar, A.; Laurent, C.; Bonnet, R.

1977-01-01

Significant changes in the ultraviolet absorption profiles are reported in the spectra of Delta Ori A, Iota Ori, and Zeta Pup. The present data show changes in count rates in excess of 30 per cent at velocities more negative than -900 km/s, if these data are interpreted as being dominated by O VI absorption in stellar winds. The time scales range from 1 to 6 hours.

VizieR Online Data Catalog: CaII in extragalactic red giants (Tolstoy+, 2001)

NASA Astrophysics Data System (ADS)

Tolstoy, E.; Irwin, M. J.; Cole, A. A.; Pasquini, L.; Gilmozzi, R.; Gallagher, J. S.

2002-01-01

Spectroscopic abundance determinations for stars spanning a Hubble time in age are necessary in order to determine unambiguously the evolutionary histories of galaxies. Using FORS1 in multi-object spectroscopy mode on ANTU (UT1) at the ESO VLT on Paranal, we have obtained near-infrared spectra from which we have measured the equivalent widths of the two strongest Ca II triplet lines to determine metal abundances for a sample of red giant branch stars, selected from ESO NTT optical (I, V-I) photometry of three nearby Local Group galaxies: the Sculptor dwarf spheroidal, the Fornax dwarf spheroidal and the dwarf irregular NGC 6822. The summed equivalent width of the two strongest lines in the Ca II triplet absorption-line feature, centred at 8500{AA}, can be readily converted into an [Fe/H] abundance using the previously established calibrations by Armandroff & Da Costa (1991AJ....101.1329A) and Rutledge, Hesser & Stetson (1997, Cat. ). We have measured metallicities for 37 stars in Sculptor, 32 stars in Fornax and 23 stars in NGC 6822, yielding more precise estimates of the metallicity distribution functions for these galaxies than it is possible to obtain photometrically. In the case of NGC 6822, this is the first direct measurement of the abundances of the intermediate-age and old stellar populations. We find metallicity spreads in each galaxy which are broadly consistent with the photometric width of the red giant branch, although the abundances of individual stars do not always appear to correspond to their colour. This is almost certainly predominantly due to a highly variable star formation rate with time in these galaxies, which results in a non-uniform, non-globular-cluster-like evolution of the Ca/Fe ratio. (6 data files).

The extent of chemically enriched gas around star-forming dwarf galaxies

NASA Astrophysics Data System (ADS)

Johnson, Sean

2018-01-01

Supernovae driven winds are often invoked to remove chemically enriched gas from galaxies to match the low metallicities of dwarf galaxies. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circum-galactic medium or CGM) and pollute the intergalactic medium (IGM). I will present a survey of the CGM and IGM around 18 star-forming field dwarf galaxies with stellar masses of log M*/M⊙ ≈ 8 ‑ 9 at z ≈ 0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than the host virial radius, Rh. Ten are probed at d/Rh = 1 ‑ 3 to study the surrounding IGM. The absorption measurements include neutral hydrogen (H I), the dominant silicon ions for diffuse cool gas (T ∼ 104 K; Si II, Si III, and Si IV), more highly ionized carbon (C IV), and highly ionized oxygen (O VI). The metal absorption from the CGM of the dwarf galaxies is less common and ≈ 4× weaker compared to massive star-forming galaxies though O VI absorption is still common. None of the dwarfs probed at d/Rh = 1 ‑ 3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM accounts for only 2 ‑ 6% of the expected silicon budget. CGM absorption from O VI can account for ≈ 8% of the expected oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of 0.2, this highly ionized phase of the CGM may represent a significant metal reservoir even for dwarf galaxies not expected to maintain gravitationally shock heated hot halos.

An Extensive Census of Hubble Space Telescope Counterparts to Chandra X-Ray Sources in the Globular Cluster 47 Tucanae. I. Astrometry and Photometry

NASA Astrophysics Data System (ADS)

Edmonds, Peter D.; Gilliland, Ronald L.; Heinke, Craig O.; Grindlay, Jonathan E.

2003-10-01

We report in this study of 47 Tucanae the largest number of optical identifications of X-ray sources yet obtained in a single globular cluster. Using deep Chandra ACIS-I imaging and extensive Hubble Space Telescope studies with Wide Field Planetary Camera 2 (WFPC2; including a 120 orbit program giving superb V and I images), we have detected optical counterparts to at least 22 cataclysmic variables (CVs) and 29 chromospherically active binaries (BY Dra and RS CVn systems) in 47 Tuc. These identifications are all based on tight astrometric matches between X-ray sources and objects with unusual (non-main-sequence [non-MS]) optical colors and/or optical variability. Several other CVs and active binaries have likely been found, but these have marginal significance because of larger offsets between the X-ray and optical positions, or colors and variability that are not statistically convincing. These less secure optical identifications are not subsequently discussed in detail. In the U versus U-V color-magnitude diagram (CMD), where the U band corresponds to either F336W or F300W, the CVs all show evidence for blue colors compared with the MS, but most of them fall close to the main sequence in the V versus V-I CMD, showing that the secondary stars dominate the optical light. The X-ray-detected active binaries have magnitude offsets above the MS (in both the U versus U-V or V versus V-I CMDs) that are indistinguishable from those of the much larger sample of optical variables (eclipsing and contact binaries and BY Dra variables) detected in the recent WFPC2 studies of Albrow et al. We also present the results of a new, deeper search for optical companions to millisecond pulsars (MSPs). One possible optical companion to an MSP (47 Tuc T) was found, adding to the two optical companions already known. Finally, we study several blue stars with periodic variability from Albrow et al. that show little or no evidence for X-ray emission. The optical colors of these objects differ from those of 47 Tuc (and field) CVs. An accompanying paper will present time series results for these optical identifications and will discuss X-ray-to-optical flux ratios, spatial distributions, and an overall interpretation of the results. Based on observations with the NASA/ESA Hubble Space Telescope obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

High-resolution spectra of stars in globular clusters. VI - Oxygen-deficient red giant stars in M13

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

Brown, J.A.; Wallerstein, G.; Oke, J.B.

From high-resolution, high signal-to-noise spectra, abundances of carbon, nitrogen, and oxygen and the C-12/C-13 ratio for five red giants in M13, including star II-67, which has previously been reported to be deficient in oxygen have been determined. Three of the five stars exhibit substantial oxygen deficiencies; O/Fe values range from +0.5 to less than about 0.3. The sum of the CNO nuclides is the same for all stars, which is interpreted as evidence that mixing of CNO-cycled material into the envelope is the cause of the variations in oxygen abundance. 41 refs.

A Monte Carlo Study of Flux Ratios of Raman Scattered O VI Features at 6825 and 7082 Å in Symbiotic Stars

NASA Astrophysics Data System (ADS)

Lee, Young-Min; Lee, Dae-Sub; Chang, Seok-Jun; Heo, Jeong-Eun; Lee, Hee-Won; Hwang, Narae; Park, Byeong-Gon; Lee, Ho-Gyu

2016-12-01

Symbiotic stars are regarded as wide binary systems consisting of a hot white dwarf and a mass losing giant. They exhibit unique spectral features at 6825 and 7082 Å, which are formed via Raman scattering of O VI λλ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of O VI λ1032 and λ1038 line photons and compute the flux ratio F(6825)/F(7082) of these Raman scattered O VI features formed in neutral regions with a simple geometric shape as a function of H I column density N H I . In cylindrical and spherical neutral regions with the O VI source embedded inside, the flux ratio F(6825)/F(7082) shows an overall decrease from 3 to 1 as N H I increases in the range {10}22{--24} {{cm}}-2. In cases of slab geometry and other geometries with the O VI source outside the H I region, Rayleigh escape operates to lower the flux ratio considerably. For moderate values of {N}{{H}{{I}}}˜ {10}23 {{cm}}-2 the flux ratio behaves in a complicated way to exhibit a broad bump with a peak value of 3.5 in the case of a sphere geometry. We find that the ratio of Raman conversion efficiencies of O VI λλ 1032, 1038 ranges from 0.8 to 3.5. Our high resolution spectra of “D” type HM Sge and “S” type AG Dra obtained with the Canada-France-Hawaii Telescope show that the flux ratio F(6825)/F(7082) of AG Dra is significantly smaller than that of HM Sge, implying that “S” type symbiotics are characterized by higher N H I than “D” type symbiotics.

Stellar laboratories . IX. New Se v, Sr iv-vii, Te vi, and I vi oscillator strengths and the Se, Sr, Te, and I abundances in the hot white dwarfs G191-B2B and RE 0503-289

NASA Astrophysics Data System (ADS)

Rauch, T.; Quinet, P.; Knörzer, M.; Hoyer, D.; Werner, K.; Kruk, J. W.; Demleitner, M.

2017-10-01

Context. To analyze spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model-atmosphere techniques are mandatory. Reliable atomic data is crucial for the calculation of such model atmospheres. Aims: We aim to calculate new Sr iv-vii oscillator strengths to identify for the first time Sr spectral lines in hot white dwarf (WD) stars and to determine the photospheric Sr abundances. To measure the abundances of Se, Te, and I in hot WDs, we aim to compute new Se v, Te vi, and I vi oscillator strengths. Methods: To consider radiative and collisional bound-bound transitions of Se v, Sr iv - vii, Te vi, and I vi in our NLTE atmosphere models, we calculated oscillator strengths for these ions. Results: We newly identified four Se v, 23 Sr v, 1 Te vi, and three I vi lines in the ultraviolet (UV) spectrum of RE 0503-289. We measured a photospheric Sr abundance of 6.5+ 3.8-2.4× 10-4 (mass fraction, 9500-23 800 times solar). We determined the abundances of Se (1.6+ 0.9-0.6× 10-3, 8000-20 000), Te (2.5+ 1.5-0.9× 10-4, 11 000-28 000), and I (1.4+ 0.8-0.5× 10-5, 2700-6700). No Se, Sr, Te, and I line was found in the UV spectra of G191-B2B and we could determine only upper abundance limits of approximately 100 times solar. Conclusions: All identified Se v, Sr v, Te vi, and I vi lines in the UV spectrum of RE 0503-289 were simultaneously well reproduced with our newly calculated oscillator strengths. 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 NAS5-26666. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. Full Tables A.15 to A.21 are only available via the German Astrophysical Virtual Observatory (GAVO) service TOSS (http://dc.g-vo.org/TOSS).

Stellar laboratories: new Ge V and Ge VI oscillator strengths and their validation in the hot white dwarf RE 0503-289

NASA Astrophysics Data System (ADS)

Rauch, T.; Werner, K.; Biémont, É.; Quinet, P.; Kruk, J. W.

2012-10-01

Context. State-of-the-art spectral analysis of hot stars by means of non-LTE model-atmosphere techniques has arrived at a high level of sophistication. The analysis of high-resolution and high-S/N spectra, however, is strongly restricted by the lack of reliable atomic data for highly ionized species from intermediate-mass metals to trans-iron elements. Especially data for the latter has only been sparsely calculated. Many of their lines are identified in spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable determination of their abundances establishes crucial constraints for AGB nucleosynthesis simulations and, thus, for stellar evolutionary theory. Aims: In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified. Individual abundance determinations are hampered by the lack of reliable oscillator strengths. Most of these identified lines stem from Ge V. In addition, we identified Ge VI lines for the first time. We calculated Ge V and Ge VI oscillator strengths in order to reproduce the observed spectrum. Methods: We newly calculated Ge V and Ge VI oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our non-LTE stellar-atmosphere models for the analysis of the Ge iv-vi spectrum exhibited in high-resolution and high-S/N FUV (FUSE) and UV (ORFEUS/BEFS, IUE) observations of RE 0503-289. Results: In the UV spectrum of RE 0503-289, we identify four Ge IV, 37 Ge V, and seven Ge VI lines. Most of these lines are identified for the first time in any star. We can reproduce almost all Ge IV, Ge V, and Ge VI lines in the observed spectrum of RE 0503-289 (Teff = 70 kK, log g = 7.5) at log Ge = -3.8 ± 0.3 (mass fraction, about 650 times solar). The Ge iv/v/vi ionization equilibrium, that is a very sensitive Teff indicator, is reproduced well. Conclusions: Reliable measurements and calculations of atomic data are a prerequisite for stellar-atmosphere modeling. Our oscillator-strength calculations have allowed, for the first time, Ge V and Ge VI lines to be successfully reproduced in a white dwarf's (RE 0503-289) spectrum and to determine its photospheric Ge abundance. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer.Figures 4-6 and Tables 1, 3 are available in electronic form at http://www.aanda.orgTables 2 and 4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A55

Multicolor CCD Photometry of the Open Cluster IC361

DTIC Science & Technology

2010-01-01

journal Volume 19 Numbers 1/2 2010 Contents V. Straizys, A. Kazlauskas. Young stars in the Camelopardalis dust and molecular clouds. VI. YSOs...Vilnius + I system for 7250 stars down to 1= 19.6 mag has been obtained in the 20’ x 26’ field of the open cluster IC 361 in Camelopardalis . The catalog...1= 19.6 mag has been obtained in the 20’ x 26’ field of the open cluster IC 361 in Camelopardalis . The catalog of 1420 stars down to V ~ 18.5 mag

Pulsation, binarity and close frequency spacing in $delta Scuti ta$ Scuti stars: BQ and BW Cancri. Results of the STEPHI VI campaign in Praesepe Cluster

NASA Astrophysics Data System (ADS)

Alvarez, M.; Hernandez, M. M.; Michel, E.; Jiang, S. Y.; Belmonte, J. A.; Chevreton, M.; Massacrier, G.; Liu, Y. Y.; Li, Z. P.; Goupil, M. J.; Cortes, T. Roca; Mangeney, A.; Dolez, N.; Valtier, J. C.; Vidal, I.; Sperl, M.; Talon, S.

1998-12-01

New pulsation modes in two delta Scuti stars of Praesepe cluster, BQ and BW Cnc, have been detected during the STEPHI VI campaign in 1995. In particular, 3 frequencies for BQ Cnc and 9 frequencies for BW Cnc have been found above a 99% confidence level. The possibility of the presence of a g-mode present in BQ Cnc is discussed, considering its binarity. The effect of mutual interference between very close detected frequencies in BW Cnc during the observations, is also considered. This last effect reveals the necessity of long-period observing runs, in order to avoid its influence in the final number of detected modes. In such situation, studies of secular amplitude changes can be strongly affected.

Impaired Behavior Regulation under Conditions of Concurrent Variable Schedules of Reinforcement in Children with ADHD

ERIC Educational Resources Information Center

Taylor, David; Lincoln, Alan J.; Foster, Sharon L.

2010-01-01

Objective: To bridge theory of response inhibition and learning in children with ADHD. Method: Thirty ADHD and 30 non-ADHD children (ages 9-12) were compared under concurrent variable interval (VI-15 sec., VI-30 sec. and VI- 45 sec.) reinforcement schedules that required the child to switch between the three schedules under conditions of…

Preference as a Function of Active Interresponse Times: A Test of the Active Time Model

ERIC Educational Resources Information Center

Misak, Paul; Cleaveland, J. Mark

2011-01-01

In this article, we describe a test of the active time model for concurrent variable interval (VI) choice. The active time model (ATM) suggests that the time since the most recent response is one of the variables controlling choice in concurrent VI VI schedules of reinforcement. In our experiment, pigeons were trained in a multiple concurrent…

ORFEUS spectroscopy of the O BT VI lines in symbiotic stars and the Raman scattering process

NASA Astrophysics Data System (ADS)

Schmid, H. M.; Krautter, J.; Appenzeller, I.; Barnstedt, J.; Dumm, T.; Fromm, A.; Gölz, M.; Grewing, M.; Gringel, W.; Haas, C.; Hopfensitz, W.; Kappelmann, N.; Krämer, G.; Lindenberger, A.; Mandel, H.; Mürset, U.; Schild, H.; Schmutz, W.; Widmann, H.

1999-08-01

We present orfeus spectra of the O vi lambda lambda 1032,1038 emission lines in the symbiotic stars AG Dra, V1016 Cyg, RR Tel, CD-43(deg) 14304, AG Peg and Z And. The O vi emission lines can convert into broad and highly polarized emission lines at lambda 6825 and lambda 7082 in a Raman scattering process by neutral hydrogen. From a comparison of direct and Raman scattered radiation we extract new information on the scattering geometry in symbiotic systems. The nebular O vi emission lines are in all objects redshifted by about +40 km s(-1) . This can be explained as a radiative line transfer effect in a slowly expanding emission region. A comparable redshift is measured in the Raman scattered O vi lines. In AG Peg the O vi emissions show beside a narrow nebular line a broad component from a fast stellar wind outflow. Many interstellar absorption lines of molecular hydrogen are detected, particularly near the O vi lambda 1038 component. With model calculations we investigate their impact on the O vi lines. From the dereddened line fluxes of the direct and Raman scattered O vi lines we derive the scattering efficiency, which is defined as photon flux ratio N_Raman/N_O VI. The efficiencies derived for RR Tel, V1016 Cyg and Z And indicate that about 30% of the released O vi lambda 1032 photons interact with the neutral scattering region. The efficiencies for AG Dra and CD-43(deg14304) are much higher, which may suggest that the O vi nebulosity is embedded in a H(0) -region. The D-type system RR Tel shows strong line profile differences between the direct O vi emission, which is single-peaked, and the Raman scattered emission, which is double-peaked. This indicates that the neutral scattering region in RR Tel ``sees'' different O vi line profiles, implying that the O vi nebulosity is far from spherically symmetric. In a tentative model we suggest for RR Tel an O vi flow pattern where material streams from the cool giant towards the hot component, which further accelerates the gas radially. For the S-type systems AG Dra, CD-43(deg14304) and Z And the line profile differences between the direct and the Raman scattered O vi emissions are less pronounced. This may suggest that the O vi profiles depend less on the emission direction than in the D-type system RR Tel. For AG Peg we detect for the first time the Raman scattered emission at lambda 6825. The Raman line shows a narrow, nebular component as the O vi line, but no equivalent emission to the broad O vi wind component. The higher conversion efficiency for the narrow component indicates that the nebular O vi emission is significantly closer to the cool giant than the hot, mass losing component, and strongly supports previous colliding wind models for this object. Based on observations taken during the orfeus-spas i and orfeus-spas ii space shuttle missions, and ground based data collected at the ESO 2.2m and 3.6m telescopes at La Silla, Chile, and the 4.2m William Herschel Telescope at La Palma, Canary Islands. ESO observations were granted for the programs 52.7-040 and 58.D-0866.

Photometry of occultation candidate stars. I - Uranus 1985 and Saturn 1985-1991

NASA Technical Reports Server (NTRS)

French, L. M.; Morales, G.; Dalton, A. S.; Klavetter, J. J.; Conner, S. R.

1985-01-01

Photometric observations of five stars to be occulted by the rings around Uranus are presented. The four stars to be occulted by Saturn or its rings during the period 1985-1991 were also observed. The observations were carried out with a CCD detector attached to the Kitt Peak McGraw-Hill 1.30-m telescope. Landolt standards of widely ranging V-I color indices were used to determine the extinction coefficients, transformation coefficients, and zero points of the stars. Mean extinction coefficients are given for each night of observation. K magnitudes for each star were estimated on the basis of the results of Johnson (1967). The complete photometric data set is given in a series of tables.

Pulsar and CV Observations

NASA Astrophysics Data System (ADS)

Malina, R. F.

PSR_0656+14: Measurement of surface thermal emission from neutron stars (NS) is essential to theories regarding the condensed matter state equation, the thermal evolution of NS, and of NS atmospheres. We propose to conduct 50 Ang band FUV photometric observations of PSR B0656+14, an X-ray, SXR and EUV bright isolated NS with an optical counterpart. FUV photometry will provide critical characterization of the NS's surface thermal radiation. Higher energy observations may be effected by poorly established effects including magnetized atmospheres, chemical compositions, temperature gradients and gravitational effects. Optical observations may be subject to non-thermal effects. V3885 Sgr: V3885 Sgr is one of the brightest nonmagnetic cataclysmic variables. We propose to observe V3885 Sgr for 5 to 6 contiguous FUSE orbits, achieving a S/N of about 12 at full resolution even at the troughs of the source's O VI absorption lines in each spectrum (assuming 2000 sec visibility per orbit). The primary purpose of the observations is to use the source as a bright continuum against which to study local interstellar absorption lines. Although observed on Malina's Co-I Program, the data will be analyzed in collaboration with members of the O VI Project.

NASA Astrophysics Data System (ADS)

Morisset, C.; Delgado-Inglada, G.; Torres-Peimbert, S.

2014-04-01

Most - if not all - planetary nebulae exhibit a complex structure, far from the spherical shape. The reasons for this dramatic change in symmetry, that occurs in early stage of the development of the nebula, remain controversial. The same physics operates in a variety of stars, from young (winds from young stars and/or high mass stars) to old (novae, symbiotic stars). The aim of the APN series of conferences has been to offer the opportunity to anyone involved in the study of asymmetric planetary nebulae (and related objects) to discuss the latest results obtained in this field. The APN VI conference was organized by the Instituto de Astronomia (UNAM) and took place on Riviera Maya, Quintana Roo, México, 4-8 Nov. 2013

X-ray emission at low-mass end of the MS - Results from an extensive Einstein Observatory survey

NASA Technical Reports Server (NTRS)

Barbera, M.; Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Rosner, R.

1992-01-01

The 0.16-4.0 keV X-ray emission from K and M stars of luminosity classes IV, V, and VI within 25 parsec of the sun was measured using all available Einstein Observatory IPC data and a critical compilation of catalogued optical data. Fifty four of 88 stars were detected, 70 of 138 M stars with Mv less than 13.4 (corresponding to M6) and 15 or 31 fainter M stars. The surveyed stars were grouped, on the basis of U, V, W space velocity components, into old-disk, young-disk, and halo population stars. Then, a subsample was selected which is statistically representative of the population of K and M stars in the solar neighborhood, on the basis of which unbiased Maximum Likelihood X-ray luminosity functions were constructed for K, early M, and late M stars. The investigation revealed a decrease of X-ray luminosity with increasing stellar age in the range of ages of disk population stars.

VizieR Online Data Catalog: NGC 6802 dwarf cluster members and non-members (Tang+, 2017)

NASA Astrophysics Data System (ADS)

Tang, B.; Geisler, D.; Friel, E.; Villanova, S.; Smiljanic, R.; Casey, A. R.; Randich, S.; Magrini, L.; San, Roman I.; Munoz, C.; Cohen, R. E.; Mauro, F.; Bragaglia, A.; Donati, P.; Tautvaisiene, G.; Drazdauskas, A.; Zenoviene, R.; Snaith, O.; Sousa, S.; Adibekyan, V.; Costado, M. T.; Blanco-Cuaresma, S.; Jimenez-Esteban, F.; Carraro, G.; Zwitter, T.; Francois, P.; Jofre, P.; Sordo, R.; Gilmore, G.; Flaccomio, E.; Koposov, S.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Bayo, A.; Damiani, F.; Franciosini, E.; Hourihane, A.; Lardo, C.; Lewis, J.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sacco, G.; Worley, C. C.; Zaggia, S.

2016-11-01

The dwarf stars in NGC 6802 observed by GIRAFFE spectrograph are separated into four tables: 1. cluster members in the lower main sequence; 2. cluster members in the upper main sequence; 3. non-member dwarfs in the lower main sequence; 4. non-member dwarfs in the upper main sequence. The star coordinates, V band magnitude, V-I color, and radial velocity are given. (4 data files).

The influence of conjugation variables on the design and immunogenicity of a glycoconjugate vaccine against Salmonella Typhi

PubMed Central

Arcuri, M.; Di Benedetto, R.; Cunningham, A. F.; Saul, A.; MacLennan, C. A.

2017-01-01

In recent years there have been major efforts to develop glycoconjugate vaccines based on the Vi polysaccharide that will protect against Salmonella enterica Typhi infections, particularly typhoid fever, which remains a major public health concern in low-income countries. The design of glycoconjugate vaccines influences the immune responses they elicit. Here we systematically test the response in mice to Vi glycoconjugates that differ in Vi chain length (full-length and fragmented), carrier protein, conjugation chemistry, saccharide to protein ratio and size. We show that the length of Vi chains, but not the ultimate size of the conjugate, has an impact on the anti-Vi IgG immune response induced. Full-length Vi conjugates, independent of the carrier protein, induce peak IgG responses rapidly after just one immunization, and secondary immunization does not enhance the magnitude of these responses. Fragmented Vi linked to CRM197 and diphtheria toxoid, but not to tetanus toxoid, gives lower anti-Vi antibody responses after the first immunization than full-length Vi conjugates, but antibody titres are similar to those induced by full-length Vi conjugates following a second dose. The chemistry to conjugate Vi to the carrier protein, the linker used, and the saccharide to protein ratio do not significantly alter the response. We conclude that Vi length and carrier protein are the variables that influence the anti-Vi IgG response to immunization the most, while other parameters are of lesser importance. PMID:29287062

Zodiacal Exoplanets in Time (ZEIT). VI. A Three-planet System in the Hyades Cluster Including an Earth-sized Planet

NASA Astrophysics Data System (ADS)

Mann, Andrew W.; Vanderburg, Andrew; Rizzuto, Aaron C.; Kraus, Adam L.; Berlind, Perry; Bieryla, Allyson; Calkins, Michael L.; Esquerdo, Gilbert A.; Latham, David W.; Mace, Gregory N.; Morris, Nathan R.; Quinn, Samuel N.; Sokal, Kimberly R.; Stefanik, Robert P.

2018-01-01

Planets in young clusters are powerful probes of the evolution of planetary systems. Here we report the discovery of three planets transiting EPIC 247589423, a late-K dwarf in the Hyades (≃800 Myr) cluster, and robust detection limits for additional planets in the system. The planets were identified from their K2 light curves as part of our survey of young clusters and star-forming regions. The smallest planet has a radius comparable to Earth ({0.99}-0.04+0.06{R}\\oplus ), making it one of the few Earth-sized planets with a known, young age. The two larger planets are likely a mini-Neptune and a super-Earth, with radii of {2.91}-0.10+0.11{R}\\oplus and {1.45}-0.08+0.11{R}\\oplus , respectively. The predicted radial velocity signals from these planets are between 0.4 and 2 m s-1, achievable with modern precision RV spectrographs. Because the target star is bright (V = 11.2) and has relatively low-amplitude stellar variability for a young star (2-6 mmag), EPIC 247589423 hosts the best known planets in a young open cluster for precise radial velocity follow-up, enabling a robust test of earlier claims that young planets are less dense than their older counterparts.

Empirical ionization fractions in the winds and the determination of mass-loss rates for early-type stars

NASA Technical Reports Server (NTRS)

Lamers, H. J. G. L. M.; Gathier, R.; Snow, T. P.

1980-01-01

From a study of the UV lines in the spectra of 25 stars from 04 to B1, the empirical relations between the mean density in the wind and the ionization fractions of O VI, N V, Si IV, and the excited C III (2p 3P0) level were derived. Using these empirical relations, a simple relation was derived between the mass-loss rate and the column density of any of these four ions. This relation can be used for a simple determination of the mass-loss rate from O4 to B1 stars.

Feeding the fire: tracing the mass-loading of 107 K galactic outflows with O VI absorption

NASA Astrophysics Data System (ADS)

Chisholm, J.; Bordoloi, R.; Rigby, J. R.; Bayliss, M.

2018-02-01

Galactic outflows regulate the amount of gas galaxies convert into stars. However, it is difficult to measure the mass outflows remove because they span a large range of temperatures and phases. Here, we study the rest-frame ultraviolet spectrum of a lensed galaxy at z ˜ 2.9 with prominent interstellar absorption lines from O I, tracing neutral gas, up to O VI, tracing transitional phase gas. The O VI profile mimics weak low-ionization profiles at low velocities, and strong saturated profiles at high velocities. These trends indicate that O VI gas is co-spatial with the low-ionization gas. Further, at velocities blueward of -200 km s-1 the column density of the low-ionization outflow rapidly drops while the O VI column density rises, suggesting that O VI is created as the low-ionization gas is destroyed. Photoionization models do not reproduce the observed O VI, but adequately match the low-ionization gas, indicating that the phases have different formation mechanisms. Photoionized outflows are more massive than O VI outflows for most of the observed velocities, although the O VI mass outflow rate exceeds the photoionized outflow at velocities above the galaxy's escape velocity. Therefore, most gas capable of escaping the galaxy is in a hot outflow phase. We suggest that the O VI absorption is a temporary by-product of conduction transferring mass from the photoionized phase to an unobserved hot wind, and discuss how this mass-loading impacts the observed circum-galactic medium.

A Handbook of Descriptive and Practical Astronomy

NASA Astrophysics Data System (ADS)

Chambers, George Frederick

2010-06-01

Book I. A Sketch of the Solar System: 1. The sun; 2. The planets; 3. Vulcan; 4. Mercury; 5. Venus; 6. The earth; 7. The moon; 8. Mars; 9. The minor planets; 10. Jupiter; 11. Saturn; 12. Uranus; 13. Neptune; Book II. Eclipses and their Associated Phenomena: 1. General outlines; 2. Eclipses of the sun; 3. The total eclipse of the sun of July 28, 1851; 4. The annular eclipse of the sun of March 14-15, 1858; 5. The total eclipse of the sun of July 18, 1860; 6. Historical notices; 7. Eclipses of the moon; 8. Suggestions for observing annular eclipses of the sun; 9. Transits of the inferior planets; 10. Occultations; Book III. The Tides: 1. Introduction; 2. Local disturbing influences; Book IV. Miscellaneous Astronomical Phenomena: 1. Variation in the obliquity of the ecliptic; 2. Aberration; 3. Refraction; Book V. Comets: 1. General remarks; 2. Periodic comets; 3. Remarkable comets; 4. Cometary statistics; 5. Historical notices; Book VI. Chronological Astronomy: 1. What time is; 2. Hours; 3. Means of measuring time; 4. The Dominical or Sunday letter; 5. Tables for the conversion of time; Book VII. The Starry Heavens: 1. The Pole-Star; 2. Double stars; 3. Variable stars; 4. Clusters and nebulae; 5. The Milky Way; 6. The constellations; Book VIII. Astronomical Instruments: 1. Telescopes; 2. Telescope stands; 3. The equatorial; 4. The transit instrument; 5. Other astronomical instruments; 6. History of the telescope; Book IX. A Sketch of the History of Astronomy; Book X. Meteoric Astronomy: 1. Classification of the subject; 2. The origin of aërolites; 3. Shooting stars; Appendices; Index.

THE DISCOVERY OF A RARE WO-TYPE WOLF-RAYET STAR IN THE LARGE MAGELLANIC CLOUD

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

Neugent, Kathryn F.; Massey, Philip; Morrell, Nidia, E-mail: kneugent@lowell.edu, E-mail: phil.massey@lowell.edu, E-mail: nmorrell@lco.cl

While observing OB stars within the most crowded regions of the Large Magellanic Cloud, we happened upon a new Wolf-Rayet (WR) star in Lucke-Hodge 41, the rich OB association that contains S Doradus and numerous other massive stars. At first glance the spectrum resembled that of a WC4 star, but closer examination showed strong O VI {lambda}{lambda}3811, 34 lines, leading us to classify it as a WO4. This is only the second known WO in the LMC, and the first known WO4 (the other being a WO3). This rarity is to be expected due to these stars' short lifespans asmore » they represent the most advanced evolutionary stage in a massive star's lifetime before exploding as supernovae. This discovery shows that while the majority of WRs within the LMC have been discovered, there may be a few WRs left to be found.« less

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

VizieR Online Data Catalog: AAVSO International Variable Star Index VSX (Watson+, 2006-2014)

NASA Astrophysics Data System (ADS)

Watson, C.; Henden, A. A.; Price, A.

2017-05-01

This file contains Galactic stars known or suspected to be variable. It lists all stars that have an entry in the AAVSO International Variable Star Index (VSX; http://www.aavso.org/vsx). The database consisted initially of the General Catalogue of Variable Stars (GCVS) and the New Catalogue of Suspected Variables (NSV) and was then supplemented with a large number of variable star catalogues, as well as individual variable star discoveries or variables found in the literature. Effort has also been invested to update the entries with the latest information regarding position, type and period and to remove duplicates. The VSX database is being continually updated and maintained. For historical reasons some objects outside of the Galaxy have been included. (3 data files).

VizieR Online Data Catalog: AAVSO International Variable Star Index VSX (Watson+, 2006-2014)

NASA Astrophysics Data System (ADS)

Watson, C.; Henden, A. A.; Price, A.

2018-05-01

This file contains Galactic stars known or suspected to be variable. It lists all stars that have an entry in the AAVSO International Variable Star Index (VSX; http://www.aavso.org/vsx). The database consisted initially of the General Catalogue of Variable Stars (GCVS) and the New Catalogue of Suspected Variables (NSV) and was then supplemented with a large number of variable star catalogues, as well as individual variable star discoveries or variables found in the literature. Effort has also been invested to update the entries with the latest information regarding position, type and period and to remove duplicates. The VSX database is being continually updated and maintained. For historical reasons some objects outside of the Galaxy have been included. (3 data files).

A SYSTEMATIC SEARCH FOR COROTATING INTERACTION REGIONS IN APPARENTLY SINGLE GALACTIC WOLF-RAYET STARS. II. A GLOBAL VIEW OF THE WIND VARIABILITY

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

Chene, A.-N.; St-Louis, N., E-mail: achene@astro-udec.cl, E-mail: stlouis@astro.umontreal.ca

This study is the second part of a survey searching for large-scale spectroscopic variability in apparently single Wolf-Rayet (WR) stars. In a previous paper (Paper I), we described and characterized the spectroscopic variability level of 25 WR stars observable from the northern hemisphere and found 3 new candidates presenting large-scale wind variability, potentially originating from large-scale structures named corotating interaction regions (CIRs). In this second paper, we discuss an additional 39 stars observable from the southern hemisphere. For each star in our sample, we obtained 4-5 high-resolution spectra with a signal-to-noise ratio of {approx}100 and determined its variability level usingmore » the approach described in Paper I. In total, 10 new stars are found to show large-scale spectral variability of which 7 present CIR-type changes (WR 8, WR 44, WR55, WR 58, WR 61, WR 63, WR 100). Of the remaining stars, 20 were found to show small-amplitude changes and 9 were found to show no spectral variability as far as can be concluded from the data on hand. Also, we discuss the spectroscopic variability level of all single galactic WR stars that are brighter than v {approx} 12.5, and some WR stars with 12.5 < v {<=} 13.5, i.e., all the stars presented in our two papers and four more stars for which spectra have already been published in the literature. We find that 23/68 stars (33.8%) present large-scale variability, but only 12/54 stars ({approx}22.1%) are potentially of CIR type. Also, we find that 31/68 stars (45.6%) only show small-scale variability, most likely due to clumping in the wind. Finally, no spectral variability is detected based on the data on hand for 14/68 (20.6%) stars. Interestingly, the variability with the highest amplitude also has the widest mean velocity dispersion.« less

Human Methadone Self-Administration and the Generalized Matching Law

ERIC Educational Resources Information Center

Spiga, Ralph; Maxwell, R. Stockton; Meisch, Richard A.; Grabowski, John

2005-01-01

The present study examined whether in humans the generalized matching law described the relation between relative responding and relative drug intake by humans under concurrent variable interval variable interval (conc VI VI) schedules of drug reinforcement. Methadone-maintained patients, stabilized on 80 mg per day of methadone, were recruited…

Reduction of hexavalent chromium in water samples acidified for preservation

USGS Publications Warehouse

Stollenwerk, K.G.; Grove, D.B.

1985-01-01

Reduction of hexavalent chromium, Cr(VI), in water samples, preserved by standard techniques, was investigated. The standard preservation technique for water samples that are to be analyzed for Cr(VI) consists of filtration through a 0.45-??m membrane, acidification to a pH < 2, and storage in plastic bottles. Batch experiments were conducted to evaluate the effect of H+ concentration, NO2, temperature, and dissolved organic carbon (DOC) on the reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) to Cr(III) increased with increasing NO2, DOC, H+, and temperature. Reduction of Cr(VI) by organic matter occurred in some samples even though the samples were unacidified. Reduction of Cr(VI) is inhibited to an extent by storing the sample at 4??C. Stability of Cr(VI) in water is variable and depends on the other constituents present in the sample. Water samples collected for the determination of Cr(VI) should be filtered (0.45-??m membrane), refrigerated, and analyzed as quickly as possible. Water samples should not be acidified. Measurement of total Cr in addition to Cr(VI) can serve as a check for Cr(VI) reduction. If total Cr is greater than Cr(VI), the possibility that Cr(VI) reduction has occurred needs to be considered.The rate of reduction of Cr(VI) to Cr(III) increased with increasing NO//2, DOC, H** plus , and temperature. Reduction of Cr(VI) by organic matter occurred in some samples even though the samples were unacidified. Reduction of Cr(VI) is inhibited to an extent by storing the sample at 4 degree C. Stability of Cr(VI) in water is variable and depends on the other constituents present in the sample. Water samples collected for the determination of Cr(VI) should be filtered (0. 45- mu m membrane), refrigerated, and analyzed as quickly as possible. Water samples should not be acidified. Measurement of total Cr in addition to Cr(VI) can serve as a check for Cr(VI) reduction. If total Cr is greater than Cr(VI), the possibility that Cr(VI) reduction has occurred needs to be considered.

CASBaH: the Multiphase Circumgalactic Medium During the Decline of Cosmic Star Formation

NASA Astrophysics Data System (ADS)

Burchett, Joseph N.; Tripp, Todd; Prochaska, Jason; Werk, Jessica; Willmer, Christopher; Ford, Amanda Brady; Howk, Chris

2018-01-01

The COS Absorption Survey of Baryon Harbors (CASBaH) comprises high-S/N spectra of nine z > 0.9 QSOs with coverage from the far-ultraviolet to the optical. These sightlines access the rich suite of rest-frame extreme-ultraviolet (600 - 1000 Angstroms) spectral transitions, such as Ne VIII, Mg X, and O II/III/IV, in addition to those more well studied at longer wavelengths (O VI, C III, Mg II). We have undertaken a large ground-based spectroscopic follow-up campaign to identify galaxies projected near the QSO sightlines and leverage the myriad diagnostics within the QSO spectra to study the circumgalactic medium (CGM) at 0.2 < z < 1 over the crucial epoch when star formation activity in the Universe was in sharp decline. We will present results from this multiwavelength study characterizing the CGM across multiple ionization states, focusing on the O VI and Ne VIII-probed warm-hot (105-106 K) gas within the halos of our galaxy sample.

Raman-scattered O VI λ1032 and He II λ1025 and Bipolar Outflow in the Symbiotic Star V455 Sco

NASA Astrophysics Data System (ADS)

Heo, Jeong-Eun; Angeloni, Rodolfo; Di Mille, Francesco; Palma, Tali; Chang, Seok-Jun; Hong, Chae-Lin; Lee, Hee-Won

2016-07-01

Raman-scattering by atomic hydrogen is a unique spectroscopic process that may probe the mass transfer and mass loss phenomena in symbiotic stars(SSs). In the optical high- resolution spectra of the S-type SS V455 Sco, we note the presence of two Raman-scattered features, one at around 6825 Å with a triple-peak profile formed from Raman-scattering of O VI λ1032 and the other Raman-scattered He II λ1025 at around 6545 Å. Adopting an accretion flow model with additional contribution from a collimated bipolar outflow, we propose that the blue and central peaks are contributed from the accretion flow and the bipolar flow is responsible for the remaining red peak. With the absence of [N II] λ6548, the Raman-scattered He II λ1025 at around 6545 Å is immersed in the broad Ha wings that appear to be formed by Raman-scattering of far-UV continuum near Lyman series.

IRAS variables as galactic structure tracers - Classification of the bright variables

NASA Technical Reports Server (NTRS)

Allen, L. E.; Kleinmann, S. G.; Weinberg, M. D.

1993-01-01

The characteristics of the 'bright infrared variables' (BIRVs), a sample consisting of the 300 brightest stars in the IRAS Point Source Catalog with IRAS variability index VAR of 98 or greater, are investigated with the purpose of establishing which of IRAS variables are AGB stars (e.g., oxygen-rich Miras and carbon stars, as was assumed by Weinberg (1992)). Results of the analysis of optical, infrared, and microwave spectroscopy of these stars indicate that, out of 88 stars in the BIRV sample identified with cataloged variables, 86 can be classified as Miras. Results of a similar analysis performed for a color-selected sample of stars, using the color limits employed by Habing (1988) to select AGB stars, showed that, out of 52 percent of classified stars, 38 percent are non-AGB stars, including H II regions, planetary nebulae, supergiants, and young stellar objects, indicating that studies using color-selected samples are subject to misinterpretation.

The Mass and Absorption Columns of Galactic Gaseous Halos

NASA Astrophysics Data System (ADS)

Qu, Zhijie; Bregman, Joel N.

2018-01-01

The gaseous halo surrounding the galaxy is a reservoir for the gas on the galaxy disk, supplying materials for the star formation. We developed a gaseous halo model connecting the galactic disk and the gaseous halo by assuming the star formation rate is equal to the radiative cooling rate. Besides the single-phase collisional gaseous halo, we also consider the photoionization effect and a time-independent cooling model that assumes the mass cooling rate is constant over all temperatures. The photoionization dominates the low mass galaxy and the outskirts of the massive galaxy due to the low-temperature or low-density nature. The multi-phase cooling model dominates the denser region within the cooling radius, where the efficient radiative cooling must be included. Applying these two improvements, our model can reproduce the most of observed high ionization state ions (i.e., O VI, O VII, Ne VIII and Mg X). Our models show that the O VI column density is almost a constant of around 10^14 cm^-2 over a wide stellar mass from M_\\star ~10^8 M_Sun to 10^11 M_Sun, which is constant with current observations. This model also implies the O VI is photoionized for the galaxy with a halo mass <~ 3 * 10^11 M_Sun, while for more massive galaxies, the O VI is from the cooling-down medium from higher temperature materials (collisional ionized). As higher ionization states, Mg X and Ne VIII are also consistent with observations with the column density of 10^13.5 - 10^14.0 cm^-2, however, the absorber-galaxy pair sample is few to constrain the connection with the galaxy. Based on our calculation, such a gaseous halo cannot close the census of baryonic materials in the galaxy, which shows the same tendency as the baryonic fraction function of the EAGLE simulation. Finally, our model predicts plateaus of the Ne VIII and the Mg X column densities above the sub-L^* galaxy, and the possibly detectable O VII and O VIII column densities for low-mass galaxies, which help to determine the required detection limit for the future observations and missions.

Elemental abundance analyses with coadded DAO spectrograms. VI - The mercury-manganese stars Nu Cancri, Iota Coronae Borealis and HR 8349

NASA Technical Reports Server (NTRS)

Adelman, Saul J.

1989-01-01

The elemental abundances of three mercury-manganese stars, Nu Cancri, Iota Coronae Borealis, and HR 8349, were found to be consistent with previous analyses of this series. As Iota CrB is a double-lined spectroscopic binary with a small velocity amplitude for most of its period, its study required determining whether the observed lines were produced in the primary or secondary or both. The derived abundances and effective termperatures were used along with those of mercury-manganese stars previously analyzed in order to extend the study of probable correlations between abundances, with the effective temperature and surface gravity in accordance with radiative diffusion explanations.

Globular cluster photometry with the Hubble Space Telescope. I - Description of the method and analysis of the core of 47 Tuc

NASA Technical Reports Server (NTRS)

Guhathakurta, Puragra; Yanny, Brian; Schneider, Donald P.; Bahcall, John N.

1992-01-01

Accurate photometry for individual post-main-sequence stars in the core of the Galactic globular cluster 47 Tuc is presented and analyzed using an empirical point spread function model and Monte Carlo simulations. A V vs. V-I color-magnitude diagrams is constructed which shows several distinct stellar types, including RGB and HB stars. Twenty-four blue straggler stars are detected in 47 Tuc, more concentrated toward the center of the cluster than the giants. This supports the hypothesis is that the stragglers are either coalesced stars or members of binary systems that are more massive than single stars. The radial profile of the projected stellar density is flat in the central region of 47 Tuc with a core radius of 23 +/- 2 arcsec. No signature of a collapsed core is evident. The observed radial cumulative distribution of stars rules out the presence of a massive compact object in the center.

Added-values of high spatiotemporal remote sensing data in crop yield estimation

NASA Astrophysics Data System (ADS)

Gao, F.; Anderson, M. C.

2017-12-01

Timely and accurate estimation of crop yield before harvest is critical for food market and administrative planning. Remote sensing derived parameters have been used for estimating crop yield by using either empirical or crop growth models. The uses of remote sensing vegetation index (VI) in crop yield modeling have been typically evaluated at regional and country scales using coarse spatial resolution (a few hundred to kilo-meters) data or assessed over a small region at field level using moderate resolution spatial resolution data (10-100m). Both data sources have shown great potential in capturing spatial and temporal variability in crop yield. However, the added value of data with both high spatial and temporal resolution data has not been evaluated due to the lack of such data source with routine, global coverage. In recent years, more moderate resolution data have become freely available and data fusion approaches that combine data acquired from different spatial and temporal resolutions have been developed. These make the monitoring crop condition and estimating crop yield at field scale become possible. Here we investigate the added value of the high spatial and temporal VI for describing variability of crop yield. The explanatory ability of crop yield based on high spatial and temporal resolution remote sensing data was evaluated in a rain-fed agricultural area in the U.S. Corn Belt. Results show that the fused Landsat-MODIS (high spatial and temporal) VI explains yield variability better than single data source (Landsat or MODIS alone), with EVI2 performing slightly better than NDVI. The maximum VI describes yield variability better than cumulative VI. Even though VI is effective in explaining yield variability within season, the inter-annual variability is more complex and need additional information (e.g. weather, water use and management). Our findings augment the importance of high spatiotemporal remote sensing data and supports new moderate resolution satellite missions for agricultural applications.

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.

US residential building air exchange rates: new perspectives to improve decision making at vapor intrusion sites.

PubMed

Reichman, Rivka; Shirazi, Elham; Colliver, Donald G; Pennell, Kelly G

2017-02-22

Vapor intrusion (VI) is well-known to be difficult to characterize because indoor air (IA) concentrations exhibit considerable temporal and spatial variability in homes throughout impacted communities. To overcome this and other limitations, most VI science has focused on subsurface processes; however there is a need to understand the role of aboveground processes, especially building operation, in the context of VI exposure risks. This tutorial review focuses on building air exchange rates (AERs) and provides a review of literature related building AERs to inform decision making at VI sites. Commonly referenced AER values used by VI regulators and practitioners do not account for the variability in AER values that have been published in indoor air quality studies. The information presented herein highlights that seasonal differences, short-term weather conditions, home age and air conditioning status, which are well known to influence AERs, are also likely to influence IA concentrations at VI sites. Results of a 3D VI model in combination with relevant AER values reveal that IA concentrations can vary more than one order of magnitude due to air conditioning status and one order of magnitude due to house age. Collectively, the data presented strongly support the need to consider AERs when making decisions at VI sites.

A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. VII. NGC 1502

NASA Astrophysics Data System (ADS)

Michalska, G.; Pigulski, A.; Stęlicki, M.; Narwid, A.

2009-12-01

We present results of variability search in the field of the young open cluster NGC 1502. Eight variable stars were discovered. Of six other stars in the observed field that were suspected for variability, we confirm variability of two, including one β Cep star, NGC 1502-26. The remaining four suspects were found to be constant in our photometry. In addition, UBVIC photometry of the well-known massive eclipsing binary SZ Cam was obtained. The new variable stars include: two eclipsing binaries of which one is a relatively bright detached system with an EA-type light curve, an α2 CVn-type variable, an SPB candidate, a field RR Lyr star and three other variables showing variability of unknown origin. The variability of two of them is probably related to their emission in Hα, which has been measured by means of the α index obtained for 57 stars brighter than V≍16 mag in the central part of the observed field. Four other non-variable stars with emission in Hα were also found. Additionally, we provide VIC photometry for stars down to V=17 mag and UB photometry for about 50 brightest stars in the observed field. We also show that the 10 Myr isochrone fits very well the observed color-magnitude diagram if a distance of 1 kpc and mean reddening, E(V-IC)=0.9 mag are adopted.

Variable Star and Exoplanet Section of the Czech Astronomical Society

NASA Astrophysics Data System (ADS)

Brát, L.; Zejda, M.

2010-12-01

We present activities of Czech variable star observers organized in the Variable Star and Exoplanet Section of the Czech Astronomical Society. We work in four observing projects: B.R.N.O. - eclipsing binaries, MEDUZA - intrinsic variable stars, TRESCA - transiting exoplanets and candidates, HERO - objects of high energy astrophysics. Detailed information together with O-C gate (database of eclipsing binaries minima timings) and OEJV (Open European Journal on Variable stars) are available on our internet portal http://var.astro.cz.

Radiation-driven winds of hot stars. VI - Analytical solutions for wind models including the finite cone angle effect

NASA Technical Reports Server (NTRS)

Kudritzki, R. P.; Pauldrach, A.; Puls, J.; Abbott, D. C.

1989-01-01

Analytical solutions for radiation-driven winds of hot stars including the important finite cone angle effect (see Pauldrach et al., 1986; Friend and Abbott, 1986) are derived which approximate the detailed numerical solutions of the exact wind equation of motion very well. They allow a detailed discussion of the finite cone angle effect and provide for given line force parameters k, alpha, delta definite formulas for mass-loss rate M and terminal velocity v-alpha as function of stellar parameters.

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.

Periodic and Aperiodic Variability in the Molecular Cloud ρ Ophiuchus

NASA Astrophysics Data System (ADS)

Parks, J. Robert; Plavchan, Peter; White, Russel J.; Gee, Alan H.

2014-03-01

Presented are the results of a near-IR photometric survey of 1678 stars in the direction of the ρ Ophiuchus (ρ Oph) star forming region using data from the 2MASS Calibration Database. For each target in this sample, up to 1584 individual J-, H-, and Ks -band photometric measurements with a cadence of ~1 day are obtained over three observing seasons spanning ~2.5 yr it is the most intensive survey of stars in this region to date. This survey identifies 101 variable stars with ΔKs -band amplitudes from 0.044 to 2.31 mag and Δ(J - Ks ) color amplitudes ranging from 0.053 to 1.47 mag. Of the 72 young ρ Oph star cluster members included in this survey, 79% are variable; in addition, 22 variable stars are identified as candidate members. Based on the temporal behavior of the Ks time-series, the variability is distinguished as either periodic, long time-scale or irregular. This temporal behavior coupled with the behavior of stellar colors is used to assign a dominant variability mechanism. A new period-searching algorithm finds periodic signals in 32 variable stars with periods between 0.49 to 92 days. The chief mechanism driving the periodic variability for 18 stars is rotational modulation of cool starspots while 3 periodically vary due to accretion-induced hot spots. The time-series for six variable stars contains discrete periodic "eclipse-like" features with periods ranging from 3 to 8 days. These features may be asymmetries in the circumstellar disk, potentially sustained or driven by a proto-planet at or near the co-rotation radius. Aperiodic, long time-scale variations in stellar flux are identified in the time-series for 31 variable stars with time-scales ranging from 64 to 790 days. The chief mechanism driving long time-scale variability is variable extinction or mass accretion rates. The majority of the variable stars (40) exhibit sporadic, aperiodic variability over no discernable time-scale. No chief variability mechanism could be identified for these variable stars.

Mythical Maia, ultrashort and 53 PSC variables. Lecture 4

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

Cox, A.N.

1983-03-14

Moving down the main sequence from the ..beta.. Cephei variables, we come to later B-type stars. The suspicion of variability for these stars goes back to Vogel in 1891 who studied the radial velocities of Vega. Since that time there have been numerous studies of Vega (Wisniewski and Johnson 1979, Fernie 1981) and other B and early A stars which hint at variability in both radial velocity and light. Since Struve (1955) discussed these stars 28 years ago, they have been called the Maia stars after the Pleiades star that he thought was the prototype. The uncertainty in their actualmore » variability has led Breger (1980) to call them the mythical Maia variables.« less

The Mass and Absorption Columns of Galactic Gaseous Halos

NASA Astrophysics Data System (ADS)

Qu, Zhijie; Bregman, Joel N.

2018-03-01

The galactic gaseous halo is a gas reservoir for the interstellar medium in the galaxy disk, supplying materials for star formation. We developed a gaseous halo model connecting the galaxy disk and the gaseous halo by assuming that the star formation rate on the disk is balanced by the radiative cooling rate of the gaseous halo, including stellar feedback. In addition to a single-temperature gaseous halo in collisional ionization equilibrium, we also consider the photoionization effect and a steady-state cooling model. Photoionization is important for modifying the ion distribution in low-mass galaxies and in the outskirts of massive galaxies due to the low densities. The multiphase cooling model dominates the region within the cooling radius, where t cooling = t Hubble. Our model reproduces most of the observed high ionization state ions for a wide range of galaxy masses (i.e., O VI, O VII, Ne VIII, Mg X, and O VIII). We find that the O VI column density has a narrow range around ≈1014 cm‑2 for halo masses from M ⋆ ≈ 3 × 1010 M ⊙ to 6 × 1012 M ⊙, which is consistent with some but not all observational studies. For galaxies with halo masses ≲3 × 1011 M ⊙, photoionization produces most of the O VI, while for more massive galaxies, the O VI is from the medium that is cooling from higher temperatures. Fitting the Galactic (Milky-Way) O VII and O VIII suggests a gaseous halo model where the metallicity is ≈0.55 Z ⊙ and the gaseous halo has a maximum temperature of ≈1.9 × 106 K. This gaseous halo model does not close the census of baryonic material within R 200.

R associations. VI - The reddening law in dust clouds and the nature of early-type emission stars in nebulosity from a study of five associations

NASA Technical Reports Server (NTRS)

Herbst, W.; Warner, J. W.; Miller, D. P.; Herzog, A.

1982-01-01

Positions, identification charts, UBVRIKLMN photometry and spectral types are given for stars, illuminating reflection nebulae that are visible on the POSS prints, which have been identified in five associations. With a ratio of total to selective extinction of 4.2, the reddening law applicable to the dust clouds in which the stars are embedded is steeper than normal. The five associations exhibit 18 early-type stars with circumstellar shells, of which those with spectral types earlier than B5 characteristically have weak IR excesses, in contrast to the strong excesses indicative of circumstellar dust, of later-type stars. Color-magnitude charts show a distribution lying above the ZAMS by up to about 2 mag for both the circumstellar shell stars and those classified as rapid rotators. It is suggested that (1) rapid rotation accounts for the scatter in the color-magnitude diagram, and (2) many of the nebulous early-type emission-line stars are rapid rotators rather than pre-main sequence objects.

Olive fruits and vacuum impregnation, an interesting combination for dietetic iron enrichment.

PubMed

Zunin, Paola; Turrini, Federica; Leardi, Riccardo; Boggia, Raffaella

2017-02-01

In this study vacuum impregnation (VI) was employed for the iron enrichment of olive fruits, which are very interesting as food vehicle for VI mineral supplementation for the porosity of their pulp. NaFeEDTA was chosen for olives fortification since it prevents iron from binding with compounds that could hinder it from being efficiently absorbed and since it causes few organoleptic problems. In order to improve the efficiency of the VI process, several parameters of the whole process were studied by design of experiment techniques. First of all D-optimal design was employed for a preliminary screening of the most significant process variables and showed that the concentration of VI solution was by far the most significant process variable, though its time in contact with olives was also significant. A factorial design was then applied to the remaining variables and it showed that the speed of the addition of VI solution was also significant. Finally, the application of a face centered composite design to the three selected variables allowed to detect processing conditions leading to final iron contents of 1.5-3 mg/g, corresponding to an introduction of 10-15 mg Fe with four or five fortified olive fruits. No effect on olive taste was observed at these concentrations. The results showed that olive fruits were the most interesting vehicles for the supplementation of both iron and other minerals.

X-ray variability of Pleiades late-type stars as observed with the ROSAT-PSPC

NASA Astrophysics Data System (ADS)

Marino, A.; Micela, G.; Peres, G.; Sciortino, S.

2003-08-01

We present a comprehensive analysis of X-ray variability of the late-type (dF7-dM) Pleiades stars, detected in all ROSAT-PSPC observations; X-ray variations on short (hours) and medium (months) time scales have been explored. We have grouped the stars in two samples: 89 observations of 42 distinct dF7-dK2 stars and 108 observations of 61 dK3-dM stars. The Kolmogorov-Smirnov test applied on all X-ray photon time series show that the percentage of cases of significant variability is quite similar on both samples, suggesting that the presence of variability does not depend on mass for the time scales and mass range explored. The comparison between the Time X-ray Amplitude Distribution functions (XAD) of the set of dF7-dK2 and of the dK3-dM show that, on short time scales, dK3-dM stars show larger variations than dF7-dK2. A subsample of eleven dF7-dK2 and eleven dK3-dM Pleiades stars allows the study of variability on longer time scales: we found that variability on medium - long time scales is relatively more common among dF7-dK2 stars than among dK3-dM ones. For both dF7-dK2 Pleiades stars and dF7-dK2 field stars, the variability on short time scales depends on Lx while this dependence has not been observed among dK3-dM stars. It may be that the variability among dK3-dM stars is dominated by flares that have a similar luminosity distribution for stars of different Lx, while flaring distribution in dF7-dK2 stars may depend on X-ray luminosity. The lowest mass stars show significant rapid variability (flares?) and no evidence of rotation modulation or cycles. On the contrary, dF7-dK2 Pleiades stars show both rapid variability and variations on longer time scales, likely associated with rotational modulation or cycles.

Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram

NASA Technical Reports Server (NTRS)

Grillmair, C. J.; Lauer, T. R.; Worthey, G.; Faber, S. M.; Freedman, W. L.; Madore, B. F.; Ajhar, E. A.; Baum, W. A.; Holtzman, J. A.; Lynds, C. R.;

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.

Variable Star Observing in Hungary

NASA Astrophysics Data System (ADS)

Mizser, Attila

1986-12-01

Astronomy and variable star observing has a long history in Hungary, dating back to the private observatories erected by the Hungarian nobility in the late 19th Century. The first organized network of amateur variable star observers, the Variable Star Section of the new Hungarian Astronomical Association, was organized around the Urania Observatory in Budapest in 1948. Other groups, dedicated to various types of variables, have since been organized.

Molecular Cloud Evolution VI. Measuring cloud ages

NASA Astrophysics Data System (ADS)

Vázquez-Semadeni, Enrique; Zamora-Avilés, Manuel; Galván-Madrid, Roberto; Forbrich, Jan

2018-06-01

In previous contributions, we have presented an analytical model describing the evolution of molecular clouds (MCs) undergoing hierarchical gravitational contraction. The cloud's evolution is characterized by an initial increase in its mass, density, and star formation rate (SFR) and efficiency (SFE) as it contracts, followed by a decrease of these quantities as newly formed massive stars begin to disrupt the cloud. The main parameter of the model is the maximum mass reached by the cloud during its evolution. Thus, specifying the instantaneous mass and some other variable completely determines the cloud's evolutionary stage. We apply the model to interpret the observed scatter in SFEs of the cloud sample compiled by Lada et al. as an evolutionary effect so that, although clouds such as California and Orion A have similar masses, they are in very different evolutionary stages, causing their very different observed SFRs and SFEs. The model predicts that the California cloud will eventually reach a significantly larger total mass than the Orion A cloud. Next, we apply the model to derive estimated ages of the clouds since the time when approximately 25% of their mass had become molecular. We find ages from ˜1.5 to 27 Myr, with the most inactive clouds being the youngest. Further predictions of the model are that clouds with very low SFEs should have massive atomic envelopes constituting the majority of their gravitational mass, and that low-mass clouds (M ˜ 103-104M⊙) end their lives with a mini-burst of star formation, reaching SFRs ˜300-500 M⊙ Myr-1. By this time, they have contracted to become compact (˜1 pc) massive star-forming clumps, in general embedded within larger GMCs.

Chromium (VI) biosorption by Saccharomyces cerevisiae subjected to chemical and thermal treatments.

PubMed

De Rossi, Andrea; Rigon, Magali Rejane; Zaparoli, Munise; Braido, Rafael Dalmas; Colla, Luciane Maria; Dotto, Guilherme Luiz; Piccin, Jeferson Steffanello

2018-05-28

The potential of chemically and thermally treated Saccharomyces cerevisiae as biosorbents for chromium (VI) was investigated in this work. The presence of this toxic metal in industrial effluents is harmful to the environment, so, it is important to develop environmental friendly methods for Cr(VI) removal from these effluents. Biosorption using microorganisms such as S. cerevisiae is a viable treatment option because this biomass is easily available as a residue of fermentation industries. In this study, the affecting variables on Cr(VI) biosorption were studied by constructing biosorption isotherms, using lyophilized yeast subjected to chemical and thermal treatments. S. cerevisiae was able to remove 99.66% of Cr(VI) from effluents by biosorption. The significant variables affecting biosorption were pH, initial Cr(VI) concentration, and contact time. The biosorption isotherms were represented by the Freundlich model for the untreated biomass, BET model for the chemically treated biomass, and Langmuir model for the heat-treated biomass. Thermal treatment increased the biosorption affinity of the biomass for chromium, while the chemical treatment facilitated the formation of a multilayer.

Intervening O vi Quasar Absorption Systems at Low Redshift: A Significant Baryon Reservoir.

PubMed

Tripp; Savage; Jenkins

2000-05-01

Far-UV echelle spectroscopy of the radio-quiet QSO H1821+643 (zem=0.297), obtained with the Space Telescope Imaging Spectrograph (STIS) at approximately 7 km s-1 resolution, reveals four definite O vi absorption-line systems and one probable O vi absorber at 0.15

The FUSE Survey of 0 VI in the Galactic Halo

NASA Technical Reports Server (NTRS)

Sonneborn, George; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Jenkins, E. B.; Moos, H. W.; Shull, J. M.

2003-01-01

This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

Four new Delta Scuti stars

NASA Technical Reports Server (NTRS)

Schutt, R. L.

1991-01-01

Four new Delta Scuti stars are reported. Power, modified into amplitude, spectra, and light curves are used to determine periodicities. A complete frequency analysis is not performed due to the lack of a sufficient time base in the data. These new variables help verify the many predictions that Delta Scuti stars probably exist in prolific numbers as small amplitude variables. Two of these stars, HR 4344 and HD 107513, are possibly Am stars. If so, they are among the minority of variable stars which are also Am stars.

The MACHO Project LMC Variable Star Inventory. VI. The Second Overtone Mode of Cepheid Pulsation from First/Second Overtone Beat Cepheids

NASA Astrophysics Data System (ADS)

Alcock, C.; Allsman, R. A.; Alves, D.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Griest, K.; Lehner, M. J.; Marshall, S. L.; Minniti, D.; Peterson, B. A.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Rorabeck, A.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D. L.; MACHO Collaboration

1999-01-01

MACHO Project photometry of 45 LMC first and second overtone (FO and SO, respectively) beat Cepheids that pulsate in the FO and SO has been analyzed to determine the light-curve characteristics for the SO mode of Cepheid pulsation. We predict that singly periodic SO Cepheids will have nearly sinusoidal light curves; that we will only be able to discern SO Cepheids from fundamental (F) and FO Cepheids for P<~1.4 days; and that the SO distribution will overlap the short-period edge of the LMC FO Cepheid period-luminosity relation (when both are plotted as a function of photometric period). We also report the discovery of one SO Cepheid candidate, MACHO*05:03:39.6-70:04:32, with a photometric period of 0.775961+/-0.000019 days and an instrumental amplitude of 0.047+/-0.009 mag in V.

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.

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.

The Beginning of Variable star astronomy in Hungary

NASA Astrophysics Data System (ADS)

Zsoldos, Endre

Variable star astronomy began in Hungary as elsewhere: new objects have been recognized in the sky. Comets appeared in 16th - 17th century chronicles. The first mention of the new star of 1572 seems to be the "Prognosticon" of Wilhelm Misocacus, printed in 1578. New stars were discussed in the 17th century by Jesuits as well as Protestants. The work of Jacob Schnitzler is especially interesting from this point. The Cartesians dealt with new stars with less enthusiasm, they hardly mentioned them. The beginning of the 19th century saw the development of science in Hungarian, variable stars, however, were left out. The birth of variable star astronomy might be linked to the Ógyalla Observatory, originally a private observatory of Miklós Konkoly Thege. The 1885 supernova in the Andromeda Nebula were observed there, as well as the spectra of a few interesting variable stars. Theoretical astrophysics also has its beginnings in Ógyalla through the work of Radó Kövesligethy. Professional variable star astronomy started here in the early 20th century through the work of Antal Tass

Comparing Pleasure and Pain: The Fundamental Mathematical Equivalence of Reward Gain and Shock Reduction under Variable Interval Schedules

ERIC Educational Resources Information Center

Mallpress, Dave E. W.; Fawcett, Tim W.; McNamara, John M.; Houston, Alasdair I.

2012-01-01

The relationship between positive and negative reinforcement and the symmetry of Thorndike's law of effect are unresolved issues in operant psychology. Here we show that, for a given pattern of responding on variable interval (VI) schedules with the same programmed rate of food rewards (positive reinforcement VI) or electric shocks (negative…

Fluorescent excitation of Fe 2, Mn 2, Ti 2, N 1 lines by V 4, N 5, O 6: Emission lines in the spectra of symbiotic stars and Seyfert galaxies

NASA Technical Reports Server (NTRS)

Gilra, D. P.

1984-01-01

Analysis of the published IUE and ground based high resolution spectra of symbiotic stars, particularly RR Tel, shows that the dominant excitation mechanism of Fe II, Mn II, Ti II, and N I lines is the selective fluorescent excitation of some levels by the strong C IV, N V, and O VI emission lines. The same mechanism should work for the excitation of Fe II lines in the spectra of Seyfert galaxies and Q60's whose emission spectra are quite similar to those of symbiotic stars. The similarities and differences between the fluroescent excitation mechanism reported herein and the Bowen's mechanism is analyzed.

Examining the infrared variable star population discovered in the Small Magellanic Cloud using the SAGE-SMC survey

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

Polsdofer, Elizabeth; Marengo, M.; Seale, J.

2015-02-01

We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud” (SAGE-SMC) and the “Spitzer Survey of the Small Magellanic Cloud” (S{sup 3}MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer’s InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 μm bands, and the Multiband Imaging Photometer for Spitzer 24 μm band. Anmore » error-weighted flux difference between each pair of three epochs (“variability index”) is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ∼2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.« less

Unsignaled Delay of Reinforcement, Relative Time, and Resistance to Change

ERIC Educational Resources Information Center

Shahan, Timothy A.; Lattal, Kennon A.

2005-01-01

Two experiments with pigeons examined the effects of unsignaled, nonresetting delays of reinforcement on responding maintained by different reinforcement rates. In Experiment 1, 3-s unsignaled delays were introduced into each component of a multiple variable-interval (VI) 15-s VI 90-s VI 540-s schedule. When considered as a proportion of the…

The panchromatic Hubble Andromeda Treasury. VI. The reliability of far-ultraviolet flux as a star formation tracer on subkiloparsec scales

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

Simones, Jacob E.; Skillman, Evan D.; Weisz, Daniel R.

We have used optical observations of resolved stars from the Panchromatic Hubble Andromeda Treasury to measure the recent (<500 Myr) star formation histories (SFHs) of 33 far-UV (FUV)-bright regions in M31. The region areas ranged from ∼10{sup 4} to 10{sup 6} pc{sup 2}, which allowed us to test the reliability of FUV flux as a tracer of recent star formation on subkiloparsec scales. The star formation rates (SFRs) derived from the extinction-corrected observed FUV fluxes were, on average, consistent with the 100 Myr mean SFRs of the SFHs to within the 1σ scatter. Overall, the scatter was larger than themore » uncertainties in the SFRs and particularly evident among the smallest regions. The scatter was consistent with an even combination of discrete sampling of the initial mass function and high variability in the SFHs. This result demonstrates the importance of satisfying both the full-IMF and the constant-SFR assumptions for obtaining precise SFR estimates from FUV flux. Assuming a robust FUV extinction correction, we estimate that a factor of 2.5 uncertainty can be expected in FUV-based SFRs for regions smaller than 10{sup 5} pc{sup 2} or a few hundred parsecs. We also examined ages and masses derived from UV flux under the common assumption that the regions are simple stellar populations (SSPs). The SFHs showed that most of the regions are not SSPs, and the age and mass estimates were correspondingly discrepant from the SFHs. For those regions with SSP-like SFHs, we found mean discrepancies of 10 Myr in age and a factor of 3-4 in mass. It was not possible to distinguish the SSP-like regions from the others based on integrated FUV flux.« less

On the temperature and the interstellar nature of coronal gas observed by Copernicus

NASA Technical Reports Server (NTRS)

York, D. G.

1977-01-01

More detailed scans of ions expected in interstellar absorption at temperatures of 100,000 to 1 million K have been made with Copernicus in five stars: Alpha Vir, Beta Cen, Lambda Sco, Mu Col, and HD 28497. Preliminary data show that the absorption due to O VI is stationary compared with the velocities of stellar absorption in the spectrum of the spectroscopic binary Lambda Sco, thus demonstrating its nonstellar nature. Ionization temperatures interpreted using steady-state or time-dependent assumptions yield values of 280,000 to 700,000 K. There is some evidence that a range of temperatures consistent with this spread may in fact exist in Alpha Vir. For this limited sample of data, there is no clear evidence for a generic association of low-column-density H2 and the O VI absorption. It is concluded that the O VI absorption refers to regions with temperatures exceeding 250,000 K. The only UV diagnostic for the gas appears to be the O VI features, though C IV may be useful in some cases.

X-ray emission at the low-mass end - Results from an extensive Einstein Observatory survey

NASA Technical Reports Server (NTRS)

Barbera, M.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.; Rosner, R.

1993-01-01

We have used available IPC data and a critical compilation of cataloged optical data to measure the 0.16-3.5 keV X-ray emission from 88 K and 169 M stars of luminosity classes IV, V, and VI within 25 pc from the Sun. The IPC detected 54 out of the 88 K stars, 70 out of the 138 M stars with M(v) less than 13.4, and 15 out of the 31 fainter M stars. We have identified a subsample of surveyed stars that is statistically representative of the population of K and M stars in the solar neighborhood. On the basis of this subsample (1) we have shown the occurrence of a drop in the level of X-ray emission for M stars later than approximately M5; (2) we have built unbiased maximum likelihood X-ray luminosity functions for the K, early M, and late M stars; (3) we have confirmed, both for K and M stars, the decrease of X-ray luminosity with increasing stellar age in the range of ages of disk population stars: and (4) we have shown that no obvious correlation is present between X-ray and bolometric luminosities in the entire representative samples of K and M stars, but only within flare stars which also seem to mark a saturation in X-ray luminosity level.

Variability search in M 31 using principal component analysis and the Hubble Source Catalogue

NASA Astrophysics Data System (ADS)

Moretti, M. I.; Hatzidimitriou, D.; Karampelas, A.; Sokolovsky, K. V.; Bonanos, A. Z.; Gavras, P.; Yang, M.

2018-06-01

Principal component analysis (PCA) is being extensively used in Astronomy but not yet exhaustively exploited for variability search. The aim of this work is to investigate the effectiveness of using the PCA as a method to search for variable stars in large photometric data sets. We apply PCA to variability indices computed for light curves of 18 152 stars in three fields in M 31 extracted from the Hubble Source Catalogue. The projection of the data into the principal components is used as a stellar variability detection and classification tool, capable of distinguishing between RR Lyrae stars, long-period variables (LPVs) and non-variables. This projection recovered more than 90 per cent of the known variables and revealed 38 previously unknown variable stars (about 30 per cent more), all LPVs except for one object of uncertain variability type. We conclude that this methodology can indeed successfully identify candidate variable stars.

Variable Stars in the Field of TrES-3b (Abstract)

NASA Astrophysics Data System (ADS)

Aadland, E.

2018-06-01

(Abstract only) The star field around the exoplanet TrES-3b has potential for finding unknown variable stars. The field was observed over several nights using Minnesota State University Moorheadís Feder Observatory. A light curve for each star was created and are being evaluated for variability and periodicity. A python program is in development to help complete the analysis by automating some of the process. Several stars in the field appear to be variable and are being further analyzed to determine a period and to classify the type of variable.

CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I. Time resolved X-ray spectral analysis during optical dips and accretion bursts in stars with disks

NASA Astrophysics Data System (ADS)

Guarcello, M. G.; Flaccomio, E.; Micela, G.; Argiroffi, C.; Sciortino, S.; Venuti, L.; Stauffer, J.; Rebull, L.; Cody, A. M.

2017-06-01

Context. Pre-main sequence stars are variable sources. The main mechanisms responsible for their variability are variable extinction, unsteady accretion, and rotational modulation of both hot and dark photospheric spots and X-ray-active regions. In stars with disks, this variability is related to the morphology of the inner circumstellar region (≤0.1 AU) and that of the photosphere and corona, all impossible to be spatially resolved with present-day techniques. This has been the main motivation for the Coordinated Synoptic Investigation of NGC 2264, a set of simultaneous observations of NGC 2264 with 15 different telescopes. Aims: In this paper, we focus on the stars with disks. We analyze the X-ray spectral properties extracted during optical bursts and dips in order to unveil the nature of these phenomena. Stars without disks are studied in a companion paper. Methods: We analyze simultaneous CoRoT and Chandra/ACIS-I observations to search for coherent optical and X-ray flux variability in stars with disks. Then, stars are analyzed in two different samples. In stars with variable extinction, we look for a simultaneous increase of optical extinction and X-ray absorption during the optical dips; in stars with accretion bursts, we search for soft X-ray emission and increasing X-ray absorption during the bursts. Results: We find evidence for coherent optical and X-ray flux variability among the stars with variable extinction. In 9 of the 24 stars with optical dips, we observe a simultaneous increase of X-ray absorption and optical extinction. In seven dips, it is possible to calculate the NH/AV ratio in order to infer the composition of the obscuring material. In 5 of the 20 stars with optical accretion bursts, we observe increasing soft X-ray emission during the bursts that we associate to the emission of accreting gas. It is not surprising that these properties are not observed in all the stars with dips and bursts, since favorable geometric configurations are required. Conclusions: The observed variable absorption during the dips is mainly due to dust-free material in accretion streams. In stars with accretion bursts, we observe, on average, a larger soft X-ray spectral component not observed in non-accreting stars.

VizieR Online Data Catalog: HST FGS-1r parallaxes for 8 metal-poor stars (Chaboyer+, 2017)

NASA Astrophysics Data System (ADS)

Chaboyer, B.; McArthur, B. E.; O'Malley, E.; Benedict, G. F.; Feiden, G. A.; Harrison, T. E.; McWilliam, A.; Nelan, E. P.; Patterson, R. J.; Sarajedini, A.

2017-08-01

Each program star was observed with the HST Advanced Camera for Surveys-Wide Field Camera (ACS/WFC) in the F606W and F814W filters. The CTE-corrected ACS/WFC images for the program stars were retrieved from MAST. These instrumental magnitudes were corrected for exposure time, matched to form colors, and calibrated to the VEGAMag and ground-based VI systems using the Sirianni+ (2005PASP..117.1049S) photometric transformations. Ground based photometry for all of our program stars were obtained using the New Mexico State University (NMSU) 1m telescope, the MDM 1.3m telescope, and the SMARTS 0.9m telescope. See appendix A1 for further details. We used HST FGS-1r, a two-axis interferometer, to make the astrometric observations. Eighty-nine orbits of HST astrometric observations were made between 2008 December and 2013 June. Every orbit contained several observations of the target and surrounding reference stars. (4 data files).

VISTA variables in the Sagittarius dwarf spheroidal galaxy: pulsation-versus dust-driven winds on the giant branches

NASA Astrophysics Data System (ADS)

McDonald, I.; Zijlstra, A. A.; Sloan, G. C.; Kerins, E.; Lagadec, E.; Minniti, D.

2014-04-01

Variability is examined in over 2.6 million stars covering 11 square degrees of the core of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) from Visible and Infrared Survey Telescope for Astronomy Z-band observations. Generally, pulsation on the Sgr dSph giant branches appears to be excited by the internal κ mechanism. Pulsation amplitudes appear identical between red and asymptotic (red giant branch/asymptotic giant branch) giant stars, and between unreddened carbon and oxygen-rich stars at the same luminosity. The lack of correlation between infrared excess and variability among oxygen-rich stars indicates that pulsations do not contribute significantly to wind driving in oxygen-rich stars in the Sgr dSph, though the low amplitudes of these stars mean this may not apply elsewhere. The dust-enshrouded carbon stars have the highest amplitudes of the stars we observe. Only in these stars does an external κ-mechanism-driven pulsation seem likely, caused by variations in their more opaque carbon-rich molecules or dust. This may allow pulsation driving of winds to be effective in carbon stars. Variability can be simplified to a power law (A ∝ L/T2), as in other systems. In total, we identify 3026 variable stars (with rms variability of δZ ≳ 0.015 mag), of which 176 are long-period variables associable with the upper giant branches of the Sgr dSph. We also identify 324 candidate RR Lyrae variables in the Sgr dSph and 340 in the outer Galactic bulge.

Higher Education Advocate. Volume VI, Number 1-12.

ERIC Educational Resources Information Center

Wechsler, Harold, Ed.

1989-01-01

Twelve issues of the National Education Association's (NEA) newsletter for NEA members in higher education focus on the following subjects: (1) NEA endorsement of Dukakis candidacy, and organizing at Southern Illinois University; (2) Dukakis STARS plan: a solid solution, and the Dukakis advantage; (3) the 100th Congress: praise from NEA, and the…

Variable Stars in M13. II.The Red Variables and the Globular Cluster Period-Luminosity Relation

NASA Astrophysics Data System (ADS)

Osborn, W.; Layden, A.; Kopacki, G.; Smith, H.; Anderson, M.; Kelly, A.; McBride, K.; Pritzl, B.

2017-06-01

New CCD observations have been combined with archival data to investigate the nature of the red variables in the globular cluster M13. Mean magnitudes, colors and variation ranges on the UBVIC system have been determined for the 17 cataloged red variables. 15 of the stars are irregular or semi-regular variables that lie at the top of the red giant branch in the color-magnitude diagram. Two stars are not, including one with a well-defined period and a light curve shape indicating it is an ellipsoidal or eclipsing variable. All stars redder than (V-IC)0=1.38 mag vary, with the amplitudes being larger with increased stellar luminosity and with bluer filter passband. Searches of the data for periodicities yielded typical variability cycle times ranging from 30 d up to 92 d for the most luminous star. Several stars have evidence of multiple periods. The stars' period-luminosity diagram compared to those from microlensing survey data shows that most M13 red variables are overtone pulsators. Comparison with the diagrams for other globular clusters shows a correlation between red variable luminosity and cluster metallicity.

Dynamical Asteroseismology: towards improving the theories of stellar structure and (tidal) evolution

NASA Astrophysics Data System (ADS)

Tkachenko, Andrew

2017-10-01

The potential of the dynamical asteroseismology, the research area that builds upon the synergies between the asteroseismology and binary stars research fields, is discussed in this manuscript. We touch upon the following topics: i) the mass discrepancy observed in intermediate-to high-mass main-sequence and evolved binaries as well as in the low mass systems that are still in the pre-main sequence phase of their evolution; ii) the rotationally induced mixing in high-mass stars, in particular how the most recent theoretical predictions and spectroscopic findings compare to the results of asteroseismic investigations; iii) internal gravity waves and their potential role in the evolution of binary star systems and surface nitrogen enrichment in high-mass stars; iv) the tidal evolution theory, in particular how its predictions of spin-orbit synchronisation and orbital circularisation compare to the present-day high-quality observations; v) the tidally-induced pulsations and their role in the angular momentum transport within binary star systems; vi) the scaling relations between fundamental and seismic properties of stars across the entire HR-diagram.

The Clusters AgeS Experiment (CASE). Variable stars in the field of the globular cluster NGC 362

NASA Astrophysics Data System (ADS)

Rozyczka, M.; Thompson, I. B.; Narloch, W.; Pych, W.; Schwarzenberg-Czerny, A.

2016-09-01

The field of the globular cluster NGC 362 was monitored between 1997 and 2015 in a search for variable stars. BV light curves were obtained for 151 periodic or likely periodic variable stars, over a hundred of which are new detections. Twelve newly detected variable stars are proper-motion members of the cluster: two SX Phe and two RR Lyr pulsators, one contact binary, three detached or semi-detached eclipsing binaries, and four spotted variable stars. The most interesting objects among these are the binary blue straggler V20 with an asymmetric light curve, and the 8.1 d semidetached binary V24 located on the red giant branch of NGC 362, which is a Chandra X-ray source. We also provide substantial new data for 24 previously known variable stars.

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.

Variable Stars Observed in the Galactic Disk by AST3-1 from Dome A, Antarctica

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

Wang, Lingzhi; Ma, Bin; Hu, Yi

AST3-1 is the second-generation wide-field optical photometric telescope dedicated to time-domain astronomy at Dome A, Antarctica. Here, we present the results of an i -band images survey from AST3-1 toward one Galactic disk field. Based on time-series photometry of 92,583 stars, 560 variable stars were detected with i magnitude ≤16.5 mag during eight days of observations; 339 of these are previously unknown variables. We tentatively classify the 560 variables as 285 eclipsing binaries (EW, EB, and EA), 27 pulsating variable stars ( δ Scuti, γ Doradus, δ Cephei variable, and RR Lyrae stars), and 248 other types of variables (unclassifiedmore » periodic, multiperiodic, and aperiodic variable stars). Of the eclipsing binaries, 34 show O’Connell effects. One of the aperiodic variables shows a plateau light curve and another variable shows a secondary maximum after peak brightness. We also detected a complex binary system with an RS CVn-like light-curve morphology; this object is being followed-up spectroscopically using the Gemini South telescope.« less

Effects of rotation and tidal distortions on the shapes of radial velocity curves of polytropic models of pulsating variable stars

NASA Astrophysics Data System (ADS)

Kumar, Tarun; Lal, Arvind Kumar; Pathania, Ankush

2018-06-01

Anharmonic oscillations of rotating stars have been studied by various authors in literature to explain the observed features of certain variable stars. However, there is no study available in literature that has discussed the combined effect of rotation and tidal distortions on the anharmonic oscillations of stars. In this paper, we have created a model to determine the effect of rotation and tidal distortions on the anharmonic radial oscillations associated with various polytropic models of pulsating variable stars. For this study we have used the theory of Rosseland to obtain the anharmonic pulsation equation for rotationally and tidally distorted polytropicmodels of pulsating variable stars. The main objective of this study is to investigate the effect of rotation and tidal distortions on the shapes of the radial velocity curves for rotationally and tidally distorted polytropic models of pulsating variable stars. The results of the present study show that the rotational effects cause more deviations in the shapes of radial velocity curves of pulsating variable stars as compared to tidal effects.

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.

Baryonic Content in the Warm-Hot IGM at Low Redshift

NASA Technical Reports Server (NTRS)

Sonneborn, George; Shull, M.; Danforth, C.; Moos, W.

2007-01-01

Baryons are 4.5% of the universe's mass/energy density; only 10% of these are in stars, galaxies, and clusters. At low-redshift 90% of baryons are in the IGM, 30% in Ly-alpha forest, but most are in hot gas (10(exp 5-7) K) produced by shocks during structure formation. O VI 1032-38 A are the best tracers of this gas. The distribution of O VI absorbers observed by FUSE rises as N(sup -2+/-0.2, down to 10(exp 13)/sq cm. Integrated to logN=13, 7% of baryons reside in the O VI-bearing IGM at 10% solar metallicity, T approx. 10(exp 5.5) K. At redshift z<0.1 metals have been transported less than 800/h kpc from L* galaxies and 200/h kpc from 0.1 L* galaxies. The steepness of dN/dz means that low-N absorbers contribute an equal mass of hot IGM as higher N gas. The total mass of O VI-bearing gas in the IGM depends on determining the turnover in dN/dz at low N(O VI). Future observations by FUSE are needed to reach lower N and to reduce the uncertainty in the dN/dz power law.

Increased mortality risk among the visually impaired: the roles of mental well-being and preventive care practices.

PubMed

Zheng, D Diane; Christ, Sharon L; Lam, Byron L; Arheart, Kristopher L; Galor, Anat; Lee, David J

2012-05-14

Mechanisms by which visual impairment (VI) increases mortality risk are poorly understood. We estimated the direct and indirect effects of self-rated VI on risk of mortality through mental well-being and preventive care practice mechanisms. Using complete data from 12,987 adult participants of the 2000 Medical Expenditure Panel Survey with mortality linkage through 2006, we undertook structural equation modeling using two latent variables representing mental well-being and poor preventive care to examine multiple effect pathways of self-rated VI on all-cause mortality. Generalized linear structural equation modeling was used to simultaneously estimate pathways including the latent variables and Cox regression model, with adjustment for controls and the complex sample survey design. VI increased the risk of mortality directly after adjusting for mental well-being and other covariates (hazard ratio [HR] = 1.25 [95% confidence interval: 1.01, 1.55]). Poor preventive care practices were unrelated to VI and to mortality. Mental well-being decreased mortality risk (HR = 0.68 [0.64, 0.74], P < 0.001). VI adversely affected mental well-being (β = -0.54 [-0.65, -0.43]; P < 0.001). VI also increased mortality risk indirectly through mental well-being (HR = 1.23 [1.16, 1.30]). The total effect of VI on mortality including its influence through mental well-being was HR 1.53 [1.24, 1.90]. Similar but slightly stronger patterns of association were found when examining cardiovascular disease-related mortality, but not cancer-related mortality. VI increases the risk of mortality directly and indirectly through its adverse impact on mental well-being. Prevention of disabling ocular conditions remains a public health priority along with more aggressive diagnosis and treatment of depression and other mental health conditions in those living with VI.

Félix de Roy: a life of variable stars

NASA Astrophysics Data System (ADS)

Shears, J.

2011-08-01

Félix de Roy (1883-1942), an internationally recognised amateur astronomer, made significant contributions to variable star research. As an active observer, he made some 91,000 visual estimates of a number of different variable stars. A Belgian national, he took refuge in England during World War I. While there, de Roy became well enough known to serve later as Director of the BAA Variable Star Section for seventeen years. Through this office, and his connections with other organisations around the world, he encouraged others to pursue the observation of variable stars. Not merely content to accumulate observational data, de Roy also analysed the data and published numerous papers.

On the phase form of a deformation quantization with separation of variables

NASA Astrophysics Data System (ADS)

Karabegov, Alexander

2016-06-01

Given a star product with separation of variables on a pseudo-Kähler manifold, we obtain a new formal (1, 1)-form from its classifying form and call it the phase form of the star product. The cohomology class of a star product with separation of variables equals the class of its phase form. We show that the phase forms can be arbitrary and they bijectively parametrize the star products with separation of variables. We also describe the action of a change of the formal parameter on a star product with separation of variables, its formal Berezin transform, classifying form, phase form, and canonical trace density.

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.

Clustering high-dimensional mixed data to uncover sub-phenotypes: joint analysis of phenotypic and genotypic data.

PubMed

McParland, D; Phillips, C M; Brennan, L; Roche, H M; Gormley, I C

2017-12-10

The LIPGENE-SU.VI.MAX study, like many others, recorded high-dimensional continuous phenotypic data and categorical genotypic data. LIPGENE-SU.VI.MAX focuses on the need to account for both phenotypic and genetic factors when studying the metabolic syndrome (MetS), a complex disorder that can lead to higher risk of type 2 diabetes and cardiovascular disease. Interest lies in clustering the LIPGENE-SU.VI.MAX participants into homogeneous groups or sub-phenotypes, by jointly considering their phenotypic and genotypic data, and in determining which variables are discriminatory. A novel latent variable model that elegantly accommodates high dimensional, mixed data is developed to cluster LIPGENE-SU.VI.MAX participants using a Bayesian finite mixture model. A computationally efficient variable selection algorithm is incorporated, estimation is via a Gibbs sampling algorithm and an approximate BIC-MCMC criterion is developed to select the optimal model. Two clusters or sub-phenotypes ('healthy' and 'at risk') are uncovered. A small subset of variables is deemed discriminatory, which notably includes phenotypic and genotypic variables, highlighting the need to jointly consider both factors. Further, 7 years after the LIPGENE-SU.VI.MAX data were collected, participants underwent further analysis to diagnose presence or absence of the MetS. The two uncovered sub-phenotypes strongly correspond to the 7-year follow-up disease classification, highlighting the role of phenotypic and genotypic factors in the MetS and emphasising the potential utility of the clustering approach in early screening. Additionally, the ability of the proposed approach to define the uncertainty in sub-phenotype membership at the participant level is synonymous with the concepts of precision medicine and nutrition. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

The UK Infrared Telescope M33 monitoring project - IV. Variable red giant stars across the galactic disc

NASA Astrophysics Data System (ADS)

Javadi, Atefeh; Saberi, Maryam; van Loon, Jacco Th.; Khosroshahi, Habib; Golabatooni, Najmeh; Mirtorabi, Mohammad Taghi

2015-03-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope, of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. In this fourth paper of the series, we present a search for variable red giant stars in an almost square degree region comprising most of the galaxy's disc, carried out with the WFCAM (Wide Field CAMera) instrument in the K band. These data, taken during the period 2005-2007, were complemented by J- and H-band images. Photometry was obtained for 403 734 stars in this region; of these, 4643 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. The variable stars are concentrated towards the centre of M33, more so than low-mass, less-evolved red giants. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. Most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey. The photometric catalogue is made publicly available at the Centre de Données astronomiques de Strasbourg.

The UK Infrared Telescope M33 monitoring project - I. Variable red giant stars in the central square kiloparsec

NASA Astrophysics Data System (ADS)

Javadi, Atefeh; van Loon, Jacco Th.; Mirtorabi, Mohammad Taghi

2011-02-01

We have conducted a near-infrared monitoring campaign at the UK Infrared Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive data set was obtained in the K band with the UIST instrument for the central 4 × 4 arcmin2 (1 kpc2) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18 398 stars in this region; of these, 812 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the variability survey and the photometric catalogue - which is made publicly available at the Centre de Données astronomiques de Strasbourg - and discuss the properties of the variable stars. The most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey.

Hot HB Stars in Globular Clusters - Physical Parameters and Consequences for Theory. VI. The Second Parameter Pair M3 and M13

NASA Technical Reports Server (NTRS)

Moehler, S.; Landsman, W. B.; Sweigart, A. V.; Grundahl, F.

2002-01-01

We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M13 and M3, which form a famous second parameter pair. From the spectra we derived - for the first time in M13 - atmospheric parameters (effective temperature and surface gravity) as well as abundances of helium, magnesium, and iron. Consistent with analyses of hot HB stars in other globular clusters we find evidence for helium depletion and iron enrichment in stars hotter than about 12,000 K in both M3 and M13. Accounting for the iron enrichment substantially improves the agreement with canonical evolutionary models, although the derived gravities and masses are still somewhat too low. This remaining discrepancy may be an indication that scaled-solar metal-rich model atmospheres do not adequately represent the highly non-solar abundance ratios found in blue HB stars with radiative levitation. We discuss the effects of an enhancement in the envelope helium abundance on the atmospheric parameters of the blue HB stars, as might be caused by deep mixing on the red giant branch or primordial pollution from an earlier generation of intermediate mass asymptotic giant branch stars.

General catalogue of variable stars: Version GCVS 5.1

NASA Astrophysics Data System (ADS)

Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N.

2017-01-01

Work aimed at compiling detailed catalogs of variable stars in the Galaxy, which has been carried out continuously by Moscow variable-star researchers since 1946 on behalf of the International Astronomical Union, has entered the stage of the publication of the 5th, completely electronic edition of the General Catalogue of Variable Stars (GCVS). This paper describes the requirements for the contents of the 5th edition and the current state of the catalog in its new version, GCVS 5.1. The complete revision of information for variable stars in the constellation Carina and the compilation of the 81st Name-list of Variable Stars are considered as examples of work on the 5th edition. The GCVS 5.1 is freely accessible on the Internet. We recommend the present paper as a unified reference to the 5th edition of the GCVS.

Basic properties and variability

NASA Technical Reports Server (NTRS)

Querci, Francois R.

1987-01-01

Giant and supergiant M, S, and C stars are discussed in this survey of research. Basic properties as determined by spectra, chemical composition, photometry, or variability type are discussed. Space motions and space distributions of cool giants are described. Distribution of these stars in our galaxy and those nearby is discussed. Mira variables in particular are surveyed with emphasis on the following topics: (1) phase lag phenomenon; (2) Mira light curves; (3) variations in color indices; (4) determination of multiple periods; (5) correlations between quantities such as period length, light-curve shape, infrared (IR) excess, and visible and IR color diagram; (6) semiregular (SR) variables and different time scales in SR light variations; (7) irregular variable Lb and Lc stars; (8) different time-scale light variations; (9) hydrogen-deficient carbon (HdC) stars, in particular RCB stars; and (10) irreversible changes and rapid evolution in red variable stars.

New Variable Stars in the KP2001 Catalog from the Data Base of the Northern Sky Variability Survey

NASA Astrophysics Data System (ADS)

Petrosyan, G. V.

2018-03-01

The optical variability of stars in the KP2001 catalog is studied. Monitor data from the automatic Northern Sky Variability Survey (NSVS) are used for this purpose. Of the 257 objects that were studied, 5 are Mira Ceti variables (mirids), 33 are semiregular (SR), and 108 are irregular variables (Ir). The light curves of the other objects show no noticeable signs of variability. For the first time, 11 stars are assigned to the semiregular and 105 stars to the irregular variables. Of the irregular variables, the light curves of two, No. 8 and No. 194, are distinct and are similar to the curves for eclipsing variables. The periods and amplitudes of the mirids and semiregular variables are determined using the "VStar" program package from AAVSO. The absolute stellar magnitudes M K and distances are also estimated, along with the mass loss for the mirids. The behavior of stars from KP2001 in 2MASS and WISE color diagrams is examined.

Near-infrared Variability in the Orion Nebula Cluster

NASA Astrophysics Data System (ADS)

Rice, Thomas S.; Reipurth, Bo; Wolk, Scott J.; Vaz, Luiz Paulo; Cross, N. J. G.

2015-10-01

Using UKIRT on Mauna Kea, we have carried out a new near-infrared J, H, K monitoring survey of almost a square degree of the star-forming Orion Nebula Cluster with observations on 120 nights over three observing seasons, spanning a total of 894 days. We monitored ˜15,000 stars down to J≈ 20 using the WFCAM instrument, and have extracted 1203 significantly variable stars from our data. By studying variability in young stellar objects (YSOs) in the H - K, K color-magnitude diagram, we are able to distinguish between physical mechanisms of variability. Many variables show color behavior indicating either dust-extinction or disk/accretion activity, but we find that when monitored for longer periods of time, a number of stars shift between these two variability mechanisms. Further, we show that the intrinsic timescale of disk/accretion variability in young stars is longer than that of dust-extinction variability. We confirm that variability amplitude is statistically correlated with evolutionary class in all bands and colors. Our investigations of these 1203 variables have revealed 73 periodic AA Tau type variables, many large-amplitude and long-period (P\\gt 15 days) YSOs, including three stars showing widely spaced periodic brightening events consistent with circumbinary disk activity, and four new eclipsing binaries. These phenomena and others indicate the activity of long-term disk/accretion variability processes taking place in young stars. We have made the light curves and associated data for these 1203 variables available online.

Investigation of Structure in the Light Curves of a Sample of Newly Discovered Long Period Variable Stars

NASA Astrophysics Data System (ADS)

Craine, E. R.; Culver, R. B.; Eykholt, R.; Flurchick, K. M.; Kraus, A. L.; Tucker, R. A.; Walker, D. K.

2015-09-01

Long period variable stars exhibit hump structures, and possibly flares, in their light curves. While the existence of humps is not controversial, the presence of flaring activity is less clear. Mining of a sky survey database of new variable star discoveries (the first MOTESS-GNAT Variable Star Catalog (MG1-VSC)) has led to identification of 47 such stars for which there are sufficient data to explore the presence of anomalous light curve features. We find a number of hump structures, and see one possible flare, suggesting that they are rare events. We present light curves and measured parameters for these stars, and a population statistical analysis.

A Binary Nature of the Marginal CP Star Sigma Sculptoris

NASA Astrophysics Data System (ADS)

Janík, Jan; Krtička, Jiří; Mikulášek, Zdeněk; Zverko, Juraj; Pintado, Olga; Paunzen, Ernst; Prvák, Milan; Skalický, Jan; Zejda, Miloslav; Adam, Christian

2018-05-01

The A2 V star σ Scl was suspected of being a low-amplitude rotating variable of the Ap-type star by several authors. Aiming to decide whether the star is a variable chemically peculiar (CP) star, we searched for the photometric and spectroscopic variability, and determined chemical abundances of σ Scl. The possible variability was tested using several types of periodograms applied to the photometry from Long-Term Photometry of Variables project (LTPV) and Hipparcos. Sixty spectrograms of high signal-to-noise (S/N) were obtained and used for chemical analysis of the stellar atmosphere and for looking for spectral variability that is symptomatic for the CP stars. We did not find any signs of the light variability or prominent chemical peculiarity, that is specific for the CP stars. The only exception is the abundance of scandium, which is significantly lower than the solar one and yttrium and barium, which are strongly overabundant. As a by-product of the analysis, and with the addition of 29 further spectra, we found that σ Scl is a single-lined spectroscopic binary with orbital period of 46.877(8) d. We argue that σ Scl is not an Ap star, but rather a marginal Am star in SB1 system. The spectral energy distribution of the binary reveals infrared excess due to circumstellar material.

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.

Construction of the Database for Pulsating Variable Stars

NASA Astrophysics Data System (ADS)

Chen, Bing-Qiu; Yang, Ming; Jiang, Bi-Wei

2012-01-01

A database for pulsating variable stars is constructed to favor the study of variable stars in China. The database includes about 230,000 variable stars in the Galactic bulge, LMC and SMC observed in an about 10 yr period by the MACHO(MAssive Compact Halo Objects) and OGLE(Optical Gravitational Lensing Experiment) projects. The software used for the construction is LAMP, i.e., Linux+Apache+MySQL+PHP. A web page is provided for searching the photometric data and light curves in the database through the right ascension and declination of an object. Because of the flexibility of this database, more up-to-date data of variable stars can be incorporated into the database conveniently.

General Catalogue of Variable Stars: Current Status and New Name-Lists

NASA Astrophysics Data System (ADS)

Samus, N. N.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Durlevich, O. V.

2010-12-01

A short history of variable-star catalogs is presented. After the second World War, the International Astronomical Union asked astronomers of the Soviet Union to become responsible for variable-star catalogs. Currently, the catalog is kept electronically and is a joint project of the Institute of Astronomy (Russian Academy of Sciences) and Sternberg Astronomical Institute (Moscow University). We review recent trends in the field of variable-star catalogs, discuss problems and new prospects related to modern large-scale automatic photometric sky surveys, outline the subject of discussions on the future of the variable-star catalogs in the profile commissions of the IAU, and call for suggestions from the astronomical community.

Cataclysmic Variable Stars

NASA Astrophysics Data System (ADS)

Hellier, Coel

2001-01-01

Cataclysmic variable stars are the most variable stars in the night sky, fluctuating in brightness continually on timescales from seconds to hours to weeks to years. The changes can be recorded using amateur telescopes, yet are also the subject of intensive study by professional astronomers. That study has led to an understanding of cataclysmic variables as binary stars, orbiting so closely that material transfers from one star to the other. The resulting process of accretion is one of the most important in astrophysics. This book presents the first account of cataclysmic variables at an introductory level. Assuming no previous knowledge of the field, it explains the basic principles underlying the variability, while providing an extensive compilation of cataclysmic variable light curves. Aimed at amateur astronomers, undergraduates, and researchers, the main text is accessible to those with no mathematical background, while supplementary boxes present technical details and equations.

New Variable Stars found in the NSVS Database (2)

NASA Astrophysics Data System (ADS)

Nicholson, Martin; Sutherland, Jane

2006-01-01

In 2004 and 2005 a search for variable stars not listed in the General Catalogue of Variable Stars or in Sinbad was conducted by members of the Remote Astronomical Society in the publicly available data of the Northern Sky Variability Survey (NSVS, Wozniak et al., 2004). NSVS fields were searched for candidates with both a sufficient number of observations to allow valid analysis and also with a significantly higher magnitude scatter than normal for stars of their magnitude.

Chromium Biosorption from Cr(VI) Aqueous Solutions by Cupressus lusitanica Bark: Kinetics, Equilibrium and Thermodynamic Studies.

PubMed

Netzahuatl-Muñoz, Alma Rosa; Cristiani-Urbina, María del Carmen; Cristiani-Urbina, Eliseo

2015-01-01

The present study investigated the kinetics, equilibrium and thermodynamics of chromium (Cr) ion biosorption from Cr(VI) aqueous solutions by Cupressus lusitanica bark (CLB). CLB total Cr biosorption capacity strongly depended on operating variables such as initial Cr(VI) concentration and contact time: as these variables rose, total Cr biosorption capacity increased significantly. Total Cr biosorption rate also increased with rising solution temperature. The pseudo-second-order model described the total Cr biosorption kinetic data best. Langmuir´s model fitted the experimental equilibrium biosorption data of total Cr best and predicted a maximum total Cr biosorption capacity of 305.4 mg g(-1). Total Cr biosorption by CLB is an endothermic and non-spontaneous process as indicated by the thermodynamic parameters. Results from the present kinetic, equilibrium and thermodynamic studies suggest that CLB biosorbs Cr ions from Cr(VI) aqueous solutions predominantly by a chemical sorption phenomenon. Low cost, availability, renewable nature, and effective total Cr biosorption make CLB a highly attractive and efficient method to remediate Cr(VI)-contaminated water and wastewater.

Chromium Biosorption from Cr(VI) Aqueous Solutions by Cupressus lusitanica Bark: Kinetics, Equilibrium and Thermodynamic Studies

PubMed Central

Netzahuatl-Muñoz, Alma Rosa; Cristiani-Urbina, María del Carmen; Cristiani-Urbina, Eliseo

2015-01-01

The present study investigated the kinetics, equilibrium and thermodynamics of chromium (Cr) ion biosorption from Cr(VI) aqueous solutions by Cupressus lusitanica bark (CLB). CLB total Cr biosorption capacity strongly depended on operating variables such as initial Cr(VI) concentration and contact time: as these variables rose, total Cr biosorption capacity increased significantly. Total Cr biosorption rate also increased with rising solution temperature. The pseudo-second-order model described the total Cr biosorption kinetic data best. Langmuir´s model fitted the experimental equilibrium biosorption data of total Cr best and predicted a maximum total Cr biosorption capacity of 305.4 mg g-1. Total Cr biosorption by CLB is an endothermic and non-spontaneous process as indicated by the thermodynamic parameters. Results from the present kinetic, equilibrium and thermodynamic studies suggest that CLB biosorbs Cr ions from Cr(VI) aqueous solutions predominantly by a chemical sorption phenomenon. Low cost, availability, renewable nature, and effective total Cr biosorption make CLB a highly attractive and efficient method to remediate Cr(VI)-contaminated water and wastewater. PMID:26352933

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.

British variable star associations, 1848-1908

NASA Astrophysics Data System (ADS)

Toone, J.

2010-06-01

The study of variable stars lagged some distance behind solar system, positional (double star) and deep sky research until the middle part of the 19th century. Then, following F. W. A. Argelander's pioneering work in the 1840s, there was a striking increase in variable star research, particularly in Europe. The transformation was to such an extent that in the second half of the 19th century there were three attempts at forming variable star associations within Great Britain. The first in 1863 was the ASOVS, which never got off the ground. The second in 1883 was the LAS VSS, which was successfully launched but had somewhat limited achievements. The third launched in 1890 was the BAA VSS which was eventually both a resounding and lasting success. This paper is an outline history of these three associations up to a position of one hundred years ago (1908). [A summary version of this paper was presented at the joint meeting of the American Association of Variable Star Observers (AAVSO) and British Astronomical Association Variable Star Section (BAA VSS) held at Cambridge, UK, on 2008 April 11.

A Photometric Variability Survey of Field K and M Dwarf Stars with HATNet

NASA Astrophysics Data System (ADS)

Hartman, J. D.; Bakos, G. Á.; Noyes, R. W.; Sipőcz, B.; Kovács, G.; Mazeh, T.; Shporer, A.; Pál, A.

2011-05-01

Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broadband photometric variability of a sample of 27, 560 field K and M dwarfs selected by color and proper motion (V - K >~ 3.0, μ > 30 mas yr-1, plus additional cuts in J - H versus H - KS and on the reduced proper motion). We search the light curves for periodic variations and for large-amplitude, long-duration flare events. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries (EBs), as secure variable star detections that are not obvious blends. We estimate that a further ~26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including five of the EBs, have previously been identified as variables or are blended with previously identified variables. One of the newly identified EBs is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M 1 = M 2 = 0.258 ± 0.008 M sun and R 1 = R 2 = 0.289 ± 0.007 R sun. The radii of the component stars are larger than theoretical expectations if the system is older than ~200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs, finding that many of the well-established relations for F, G, and K dwarfs continue into the M dwarf regime. We find that the fraction of stars that is variable with peak-to-peak amplitudes greater than 0.01 mag increases exponentially with the V - KS color such that approximately half of field dwarfs in the solar neighborhood with M <~ 0.2 M sun are variable at this level. Our data hint at a change in the rotation-activity-age connection for stars with M <~ 0.25 M sun.

The History of Variable Stars: A Fresh Look

NASA Astrophysics Data System (ADS)

Hatch, R. A.

2012-06-01

(Abstract only) For historians of astronomy, variable stars are important for a simple reason - stars change. But good evidence suggests this is a very modern idea. Over the millennia, our species has viewed stars as eternal and unchanging, forever fixed in time and space - indeed, the Celestial Dance was a celebration of order, reason, and stability. But everything changed in the period between Copernicus and Newton. According to tradition, two New Stars announced the birth of the New Science. Blazing across the celestial stage, Tycho's Star (1572) and Kepler's Star (1604) appeared dramatically - and just as unexpectedly - disappeared forever. But variable stars were different. Mira Ceti, the oldest, brightest, and most controversial variable star, was important because it appeared and disappeared again and again. Mira was important because it did not go away. The purpose of this essay is to take a fresh look at the history of variable stars. In re-thinking the traditional narrative, I begin with the first sightings of David Fabricius (1596) and his contemporaries - particularly Hevelius (1662) and Boulliau (1667) - to new traditions that unfolded from Newton and Maupertuis to Herschel (1780) and Pigott (1805). The essay concludes with important 19th-century developments, particularly by Argelander (1838), Pickering (1888), and Lockyer (1890). Across three centuries, variable stars prompted astronomers to re-think all the ways that stars were no longer "fixed." New strategies were needed. Astronomers needed to organize, to make continuous observations, to track changing magnitudes, and to explain stellar phases. Importantly - as Mira suggested from the outset - these challenges called for an army of observers with the discipline of Spartans. But recruiting that army required a strategy, a set of theories with shared expectations. Observation and theory worked hand-in-hand. In presenting new historical evidence from neglected printed sources and unpublished manuscripts, this essay aims to offer a fresh look at the history of variable stars.

A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. IX. NGC 457

NASA Astrophysics Data System (ADS)

Moździerski, D.; Pigulski, A.; Kopacki, G.; Kołaczkowski, Z.; Stęślicki, M.

2014-06-01

We present results of a BVIC variability survey in the young open cluster NGC 457 based on observations obtained during three separate runs spanning almost 20 years. In total, we found 79 variable stars, of which 66 are new. The BVIC photometry was transformed to the standard system and used to derive cluster parameters by means of isochrone fitting. The cluster is about 20 Myr old, the mean reddening amounts to about 0.48 mag in terms of the color excess E(B-V). Depending on the metallicity, the isochrone fitting yields a distance between 2.3 kpc and 2.9 kpc, which locates the cluster in the Perseus arm of the Galaxy. Using the complementary Hα photometry carried out in two seasons separated by over 10 years, we find that the cluster is very rich in Be stars. In total, 15 stars in the observed field of which 14 are cluster members showed Hα in emission either during our observations or in the past. Most of the Be stars vary in brightness on different time scales including short-period variability related most likely to g-mode pulsations. A single-epoch spectrum of NGC 457-6 shows that this Be star is presently in the shell phase. The inventory of variable stars in the observed field consists of a single β Cep-type star, NGC 457-8, 13 Be stars, 21 slowly pulsating B stars, seven δ Sct stars, one γ Dor star, 16 unclassified periodic stars, 8 eclipsing systems and a dozen of stars with irregular variability, of which six are also B-type stars. As many as 45 variable stars are of spectral type B which is the largest number in all open clusters presented in this series of papers. The most interesting is the discovery of a large group of slowly pulsating B stars which occupy the cluster main sequence in the range between V=11 mag and 14.5 mag, corresponding to spectral types B3 to B8. They all have very low amplitudes and about half show pulsations with frequencies higher than 3 d-1. We argue that these are most likely fast-rotating slowly pulsating B stars, observed also in other open clusters.

Zeta Pegasi: An SPB Variable Star

NASA Technical Reports Server (NTRS)

Goebel, John H.

2007-01-01

Broadband photometric observations of the bright star Zeta Pegasi are presented that display brightness variability of 488.2 +/- 6.6 micromag (ppm) range with a period of 22.952 +/- 0.804 hr (f approx. equals 1.04566 c/d). The variation is monosinusoidal, so the star is recommended for membership in the class of small-amplitude Slowly Pulsating B-Stars (SPB) variables oscillating in a non-radial g-mode.

The influence of electrode type on electrocoagulation process for removal of chromium (VI) metal in plating industrial wastewater

NASA Astrophysics Data System (ADS)

Prasetyaningrum, Aji; Jos, Bakti; Dharmawan, Yudhy; Prabowo, Bilal T.; Fathurrazan, Muh.; Fyrouzabadi

2018-05-01

Chromium (VI) is one of the major metallic pollutants in plating industrial wastewater. Cr(VI) is one of toxic metal that cause serious threat to human health and the environment because its non-biodegradable. Among the technologies for removing these pollutants, electrocoagulation can be considered as an effective method. This method have some advantages such as less amount of produced sludge and high efficiency in removal of pollutants.This research intended to study the effects of type of electrode on the degree of Cr(VI) removal from wastewater of plating industry using electrocoagulation method. This laboratory research conducted with 3 types of electrode (aluminum, stainless and combination of both electrode). Synthetic chromium wastewater was prepared at the initial concentration of 100 mg L-1. The process was conducted at pH 3. The electricity current was setting at 3 Ampere. The variable of time of electrocoagulation at 1 and 2 hours. After performing the process on electrochemical cells, samples analyzed by the UV-Vis spectrophotometer regarding amount of Cr(VI) metals. The results showed that aluminium was the best performance electrode at variable of 2 hours with 26% of reduction of Cr(VI)metal content in plating industrial waste water.

Discovering new variable stars at Key Stage 3

NASA Astrophysics Data System (ADS)

Chubb, Katy; Hood, Rosie; Wilson, Thomas; Holdship, Jonathan; Hutton, Sarah

2017-05-01

Details of the London pilot of the ‘Discovery Project’ are presented, where university-based astronomers were given the chance to pass on some real and applied knowledge of astronomy to a group of selected secondary school pupils. It was aimed at students in Key Stage 3 of their education, allowing them to be involved in real astronomical research at an early stage of their education, the chance to become the official discoverer of a new variable star, and to be listed in the International Variable Star Index database (The International Variable Star Index, Version 1.1, American Association of Variable Star Observers (AAVSO), 2016, http://aavso.org/vsx), all while learning and practising research-level skills. Future plans are discussed.

IUE observations of variability in winds from hot stars

NASA Technical Reports Server (NTRS)

Grady, C. A.; Snow, T. P., Jr.

1981-01-01

Observations of variability in stellar winds or envelopes provide an important probe of their dynamics. For this purpose a number of O, B, Be, and Wolf-Rayet stars were repeatedly observed with the IUE satellite in high resolution mode. In the course of analysis, instrumental and data handling effects were found to introduce spurious variability in many of the spectra. software was developed to partially compensate for these effects, but limitations remain on the type of variability that can be identified from IUE spectra. With these contraints, preliminary results of multiple observations of two OB stars, one Wolf-Rayet star, and a Be star are discussed.

ViLLaGEs: opto-mechanical design of an on-sky visible-light MEMS-based AO system

NASA Astrophysics Data System (ADS)

Grigsby, Bryant; Lockwood, Chris; Baumann, Brian; Gavel, Don; Johnson, Jess; Ammons, S. Mark; Dillon, Daren; Morzinski, Katie; Reinig, Marc; Palmer, Dave; Severson, Scott; Gates, Elinor

2008-07-01

Visible Light Laser Guidestar Experiments (ViLLaGEs) is a new Micro-Electro Mechanical Systems (MEMS) based visible-wavelength adaptive optics (AO) testbed on the Nickel 1-meter telescope at Lick Observatory. Closed loop Natural Guide Star (NGS) experiments were successfully carried out during engineering during the fall of 2007. This is a major evolutionary step, signaling the movement of AO technologies into visible light with a MEMS mirror. With on-sky Strehls in I-band of greater than 20% during second light tests, the science possibilities have become evident. Described here is the advanced engineering used in the design and construction of the ViLLaGEs system, comparing it to the LickAO infrared system, and a discussion of Nickel dome infrastructural improvements necessary for this system. A significant portion of the engineering discussion revolves around the sizable effort that went towards eliminating flexure. Then, we detail upgrades to ViLLaGEs to make it a facility class instrument. These upgrades will focus on Nyquist sampling the diffraction limited point spread function during open loop operations, motorization and automation for technician level alignments, adding dithering capabilities and changes for near infrared science.

Variable Star Discoveries for Research Education at the Phillips Academy Observatory

NASA Astrophysics Data System (ADS)

Odden, Caroline; Yoon, Seokjun; Zhu, Emily; Little, John; Taylor, Isabel; Kim, Ji Seok; Briggs, John W.

2014-06-01

The discovery and publication of unknown variable stars by high school students is a highly engaging activity in a new hands-on research course developed at Phillips Academy in Andover, Massachusetts. Students use MPO Canopus software to recognize candidate variable stars in image series typically recorded for asteroid rotation studies. Follow-up observations are made using the 16-inch DFM telescopes at the Phillips Academy Observatory and at the HUT Observatory near Eagle, Colorado, as well as with a remote-access 20-inch at New Mexico Skies Observatory near Mayhill, New Mexico. The Catalina Sky Survey can provide additional photometric measurements. Confirmed variables, with light curves and periods, are submitted to the International Variable Star Index and Journal of the American Association of Variable Star Observers. Asteroid rotation studies are published in Minor Planet Bulletin.

Short-term variability and mass loss in Be stars. II. Physical taxonomy of photometric variability observed by the Kepler spacecraft

NASA Astrophysics Data System (ADS)

Rivinius, Th.; Baade, D.; Carciofi, A. C.

2016-09-01

Context. Classical Be stars have been established as pulsating stars. Space-based photometric monitoring missions contributed significantly to that result. However, whether Be stars are just rapidly rotating SPB or β Cep stars, or whether they have to be understood differently, remains debated in the view of their highly complex power spectra. Aims: Kepler data of three known Be stars are re-visited to establish their pulsational nature and assess the properties of additional, non-pulsational variations. The three program stars turned out to be one inactive Be star, one active, continuously outbursting Be star, and one Be star transiting from a non-outbursting into an outbursting phase, thus forming an excellent sample to distill properties of Be stars in the various phases of their life-cycle. Methods: The Kepler data was first cleaned from any long-term variability with Lomb-Scargle based pre-whitening. Then a Lomb-Scargle analysis of the remaining short-term variations was compared to a wavelet analysis of the cleaned data. This offers a new view on the variability, as it enables us to see the temporal evolution of the variability and phase relations between supposed beating phenomena, which are typically not visualized in a Lomb-Scargle analysis. Results: The short-term photometric variability of Be stars must be disentangled into a stellar and a circumstellar part. The stellar part is on the whole not different from what is seen in non-Be stars. However, some of the observed phenomena might be to be due to resonant mode coupling, a mechanism not typically considered for B-type stars. Short-term circumstellar variability comes in the form of either a group of relatively well-defined, short-lived frequencies during outbursts, which are called Štefl frequencies, and broad bumps in the power spectra, indicating aperiodic variability on a time scale similar to typical low-order g-mode pulsation frequencies, rather than true periodicity. Conclusions: From a stellar pulsation perspective, Be stars are rapidly rotating SPB stars, that is they pulsate in low order g-modes, even if the rapid rotation can project the observed frequencies into the traditional high-order p-mode regime above about 4 c/d. However, when a circumstellar disk is present, Be star power spectra are complicated by both cyclic, or periodic, and aperiodic circumstellar phenomena, possibly even dominating the power spectrum.

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.

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.

VizieR Online Data Catalog: VI photometry of Berkeley 66 (Guarnieri+ 1997)

NASA Astrophysics Data System (ADS)

Guarnieri, M. D.; Carraro, G.

1996-06-01

A colour magnitude diagram (CMD) extending to V=~19mag is given for 444 stars in the region of the galactic cluster Berkeley 66. The V and I photometry of a nearby field is also reported. This object appears very faint, highly contaminated by foreground stars and very reddened. The apparent distance modulus (m-M) and the colour excess EV-I are guessed to be 17.5 and 1.1, respectively, with an uncertainty of at least 30%. Adopting these values the comparison of the CMD with theoretical isochrones from the Padova group provides an age around 1.0Gyr. (1 data file).

The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

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

Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.

We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10{sup 4} < M{sub *} < 10{sup 9} M{sub ☉}). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted 'true fossils' identified by Bovill and Ricotti show that only two (Hercules and Leo IV) indicate star formation quenchedmore » by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).« less

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

NASA Astrophysics Data System (ADS)

Dahn, Conard C.; Harris, Hugh C.; Subasavage, John P.; Ables, Harold D.; Canzian, Blaise J.; Guetter, Harry H.; Harris, Fred H.; Henden, Arne H.; Leggett, S. K.; Levine, Stephen E.; Luginbuhl, Christian B.; Monet, Alice B.; Monet, David G.; Munn, Jeffrey A.; Pier, Jeffrey R.; Stone, Ronald C.; Vrba, Frederick J.; Walker, Richard L.; Tilleman, Trudy M.

2017-10-01

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK s near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.

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.

VStar: Variable star data visualization and analysis tool

NASA Astrophysics Data System (ADS)

VStar Team

2014-07-01

VStar is a multi-platform, easy-to-use variable star data visualization and analysis tool. Data for a star can be read from the AAVSO (American Association of Variable Star Observers) database or from CSV and TSV files. VStar displays light curves and phase plots, can produce a mean curve, and analyzes time-frequency with Weighted Wavelet Z-Transform. It offers tools for period analysis, filtering, and other functions.

VSOP: the variable star one-shot project. I. Project presentation and first data release

NASA Astrophysics Data System (ADS)

Dall, T. H.; Foellmi, C.; Pritchard, J.; Lo Curto, G.; Allende Prieto, C.; Bruntt, H.; Amado, P. J.; Arentoft, T.; Baes, M.; Depagne, E.; Fernandez, M.; Ivanov, V.; Koesterke, L.; Monaco, L.; O'Brien, K.; Sarro, L. M.; Saviane, I.; Scharwächter, J.; Schmidtobreick, L.; Schütz, O.; Seifahrt, A.; Selman, F.; Stefanon, M.; Sterzik, M.

2007-08-01

Context: About 500 new variable stars enter the General Catalogue of Variable Stars (GCVS) every year. Most of them however lack spectroscopic observations, which remains critical for a correct assignement of the variability type and for the understanding of the object. Aims: The Variable Star One-shot Project (VSOP) is aimed at (1) providing the variability type and spectral type of all unstudied variable stars, (2) process, publish, and make the data available as automatically as possible, and (3) generate serendipitous discoveries. This first paper describes the project itself, the acquisition of the data, the dataflow, the spectroscopic analysis and the on-line availability of the fully calibrated and reduced data. We also present the results on the 221 stars observed during the first semester of the project. Methods: We used the high-resolution echelle spectrographs HARPS and FEROS in the ESO La Silla Observatory (Chile) to survey known variable stars. Once reduced by the dedicated pipelines, the radial velocities are determined from cross correlation with synthetic template spectra, and the spectral types are determined by an automatic minimum distance matching to synthetic spectra, with traditional manual spectral typing cross-checks. The variability types are determined by manually evaluating the available light curves and the spectroscopy. In the future, a new automatic classifier, currently being developed by members of the VSOP team, based on these spectroscopic data and on the photometric classifier developed for the COROT and Gaia space missions, will be used. Results: We confirm or revise spectral types of 221 variable stars from the GCVS. We identify 26 previously unknown multiple systems, among them several visual binaries with spectroscopic binary individual components. We present new individual results for the multiple systems V349 Vel and BC Gru, for the composite spectrum star V4385 Sgr, for the T Tauri star V1045 Sco, and for DM Boo which we re-classify as a BY Draconis variable. The complete data release can be accessed via the VSOP web site. Based on data obtained at the La Silla Observatory, European Southern Observatory, under program ID 077.D-0085.

The abundance, distribution, and physical nature of highly ionized oxygen O VI, O VII, and O VIII in IllustrisTNG

NASA Astrophysics Data System (ADS)

Nelson, Dylan; Kauffmann, Guinevere; Pillepich, Annalisa; Genel, Shy; Springel, Volker; Pakmor, Rüdiger; Hernquist, Lars; Weinberger, Rainer; Torrey, Paul; Vogelsberger, Mark; Marinacci, Federico

2018-06-01

We explore the abundance, spatial distribution, and physical properties of the O VI, O VII, and O VIII ions of oxygen in circumgalactic and intergalactic media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume cosmological magnetohydrodynamical simulations. Modelling the ionization states of simulated oxygen, we find good agreement with observations of the low-redshift O VI column density distribution function (CDDF), and present its evolution for all three ions from z = 0 to z = 4. Producing mock quasar absorption line spectral surveys, we show that the IllustrisTNG simulations are fully consistent with constraints on the O VI content of the CGM from COS-haloes and other low-redshift observations, producing columns as high as observed. We measure the total amount of mass and average column densities of each ion using hundreds of thousands of simulated galaxies spanning 10^{11} < {M}_halo/ M⊙<1015 corresponding to 109 < M⋆/ M⊙<1012 in stellar mass. Stacked radial profiles of O VI are computed in 3D number density and 2D projected column density, decomposing into 1-halo and 2-halo terms. Relating halo O VI to properties of the central galaxy, we find a correlation between the (g - r) colour of a galaxy and the total amount of O VI in its CGM. In comparison to the COS-Haloes finding, this leads to a dichotomy of columns around star-forming versus passive galaxies at fixed stellar (or halo) mass. We demonstrate that this correlation is a direct result of black hole feedback associated with quenching and represents a causal consequence of galactic-scale baryonic feedback impacting the physical state of the circumgalactic medium.

A Catalog of Eclipsing Binaries and Variable Stars Observed with ASTEP 400 from Dome C, Antarctica

NASA Astrophysics Data System (ADS)

Chapellier, E.; Mékarnia, D.; Abe, L.; Guillot, T.; Agabi, K.; Rivet, J.-P.; Schmider, F.-X.; Crouzet, N.; Aristidi, E.

2016-10-01

We used the large photometric database of the ASTEP program, whose primary goal was to detect exoplanets in the southern hemisphere from Antarctica, to search for eclipsing binaries (EcBs) and variable stars. 673 EcBs and 1166 variable stars were detected, including 31 previously known stars. The resulting online catalogs give the identification, the classification, the period, and the depth or semi-amplitude of each star. Data and light curves for each object are available at http://astep-vo.oca.eu.

Deep and wide photometry of two open clusters NGC 1245 and NGC 2506: dynamical evolution and halo

NASA Astrophysics Data System (ADS)

Lee, S. H.; Kang, Y.-W.; Ann, H. B.

2013-06-01

We studied the structure of two old open clusters, NGC 1245 and NGC 2506, from a wide and deep VI photometry data acquired using the CFH12K CCD camera at Canada-France-Hawaii Telescope. We devised a new method for assigning cluster membership probability to individual stars using both spatial positions and positions in the colour-magnitude diagram. From analyses of the luminosity functions at several cluster-centric radii and the radial surface density profiles derived from stars with different luminosity ranges, we found that the two clusters are dynamically relaxed to drive significant mass segregation and evaporation of some fraction of low-mass stars. There seems to be a signature of tidal tail in NGC 1245 but the signal is too low to be confirmed.

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.

Observation and modelling of main-sequence star chromospheres - XII. Two-component model chromospheres for five active dM1e stars

NASA Astrophysics Data System (ADS)

Houdebine, E. R.

2009-08-01

We aim to constrain the Hα, CaII H and CaII K profiles from quiescent and active regions on active dM1e stars. A preliminary analysis of all the data available for dM1e stars shows that the Hα/CaII equivalent width (EW) ratio varies by up to a factor of 7 for different stars in our sample. We find that spectroscopic binaries have a significantly smaller ratio than single dM1e stars. We also find that the pre-main-sequence stars Gl 616.2, GJ 1264 and Gl 803 have a ratio lower than main-sequence single dM1e stars. These differences imply that different chromospheric structures are present on different stars, notably the temperature minimum must decrease with an increasing Hα/CaII EW ratio. For these reasons, it is impossible to reproduce all observations with only one grid of model chromospheres. We show that the grid of model chromospheres of Paper VI is adequate to describe the physical conditions that prevail in the chromospheres of spectroscopic binaries and pre-main-sequence M1e stars, but not for the conditions in single dM1e stars. One or more additional grids of model chromospheres will be necessary to reproduce all observations. We use the method developed in Paper XI in this series, in order to build two-component model chromospheres for five M1e field stars: FF And A, FF And B, GJ 1264, AU Mic and Gl 815A. Our solutions provide an exact match of the Hα and the mean CaII H & K EWs within measurement uncertainties. We compare the theoretical profiles and the observed profiles of Hα and the CaII H & K resonance lines. On the one hand, our fits to the CaII lines are reasonably good. On the other hand, our models tend to produce Hα profiles with a central absorption that is too deep. This suggests that the column mass at the transition region for plages is underestimated, but this would imply that the contrast factor between quiescent and active regions in the CaII lines is larger than 5. We find that, except in the cases of FF And A and AU Mic, the total Hα profile is dominated by the contributions from plage regions. The Hα profiles in quiescent regions are typically filled in or slightly in emission. We also find that, as in the case of the less active dM1 stars, CaII emission in dM1e stars is generally dominated by the contribution from plage regions. We find plage filling factors typically in the range 10 to 60 per cent. These are on average (40 per cent) slightly larger than those derived for the less active dM1 stars (30 per cent). Our modelling shows that the grid of model chromospheres of Paper VI is adequate for only a subset of dM1e stars. Physical conditions that prevail in the chromospheres of dM1e stars are very different from one star to another. For this reason, this study demonstrates the critical need for several improved grids of model chromospheres as well as higher signal-to-noise ratio data. Based on observations collected at Observatoire de Haute Provence, France, and at the European Southern Observatory, Chile. E-mail: eric_houdebine@yahoo.fr

On the origin of the warm-hot absorbers in the Milky Way's halo

NASA Astrophysics Data System (ADS)

Marasco, A.; Marinacci, F.; Fraternali, F.

2013-08-01

Disc galaxies like the Milky Way are expected to be surrounded by massive coronae of hot plasma that may contain a significant fraction of the so-called missing baryons. We investigate whether the local (|vLSR| < 400 km s-1) warm-hot absorption features observed towards extra-Galactic sources or halo stars are consistent with being produced by the cooling of the Milky Way's corona. In our scheme, cooling occurs at the interface between the disc and the corona and it is triggered by positive supernova feedback. We combine hydrodynamical simulations with a dynamical 3D model of the galactic fountain to predict the all-sky distribution of this cooling material, and we compare it with the observed distribution of detections for different `warm' (Si III, Si IV, C II, C IV) and `hot' (O VI) ionized species. The model reproduces the position-velocity distribution and the column densities of the vast majority of warm absorbers and about half of O VI absorbers. We conclude that the warm-hot gas responsible for most of the detections lies within a few kiloparsec from the Galactic plane, where high-metallicity material from the disc mixes efficiently with the hot corona. This process provides an accretion of a few M⊙ yr- 1 of fresh gas that can easily feed the star formation in the disc of the Galaxy. The remaining O VI detections are likely to be a different population of absorbers, located in the outskirts of the Galactic corona and/or in the circumgalactic medium of nearby galaxies.

Variable Star Catalogs: Their Past, Present and Future

NASA Astrophysics Data System (ADS)

Samus, N. N.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Durlevich, O. V.

2010-02-01

After the second World War, the International Astronomical Union made astronomers of the Soviet Union responsible for variable-star catalogues. This work has been continued ever since the first edition of the General Catalogue of Variable Stars compiled by the team headed by P. P. Parenago and B. V. Kukarkin and published in 1948. Currently, the catalogue work is a joint project of the Institute of Astronomy (Russian Academy of Sciences) and Sternberg Astronomical Institute (Moscow University). This paper is a brief review of recent trends in the field of variable-star catalogues. We discuss problems as well as new prospects related to modern large-scale automatic photometric sky surveys, and outline the state of discussions on the future of the variable-star catalogues in the profile commissions of the IAU.

First Detection of Krypton and Xenon in a White Dwarf

NASA Astrophysics Data System (ADS)

Werner, Klaus; Rauch, Thomas; Ringat, Ellen; Kruk, Jeffrey W.

2012-07-01

We report on the first detection of the noble gases krypton (Z = 36) and xenon (54) in a white dwarf. About 20 Kr VI- VII and Xe VI- VII lines were discovered in the ultraviolet spectrum of the hot DO-type white dwarf RE 0503-289. The observations, performed with the Far Ultraviolet Spectroscopic Explorer, also reveal highly ionized photospheric lines from other trans-iron group elements, namely Ga (31), Ge (32), As (33), Se (34), Mo (42), Sn (50), Te (52), and I (53), from which gallium and molybdenum are new discoveries in white dwarfs, too. For Kr and Xe, we performed an NLTE analysis and derived mass fractions of log Kr = -4.3 ± 0.5 and log Xe = -4.2 ± 0.6, corresponding to an enrichment by factors of 450 and 3800, respectively, relative to the Sun. The origin of the large overabundances is unclear. We discuss the roles of neutron-capture nucleosynthesis in the precursor star and radiation-driven diffusion. It is possible that diffusion is insignificant and that the observed metal abundances constrain the evolutionary history of the star. Its hydrogen deficiency may be the consequence of a late helium-shell flash or a binary white dwarf merger.

The Pan-STARRS 1 Medium Deep Field Variable Star Catalog

NASA Astrophysics Data System (ADS)

Flewelling, Heather

2015-01-01

We present the first Pan-STARRS 1 Medium Deep Field Variable Star Catalog (PS1-MDF-VSC). The Pan-STARRS 1 (PS1) telescope is a 1.8 meter survey telescope with a 1.4 Gigapixel camera, located in Haleakala, Hawaii. The Medium Deep survey, which consists of 10 fields located uniformly across the sky, totalling 70 square degrees, is observed each night, in 2-3 filters per field, with 8 exposures per filter, resulting in 3000-4000 data points per star over a time span of 3.5 years. To find the variables, we select the stars with > 200 detections, between 16th and 21st magnitude. There are approximately 500k stars that fit this criteria, they then go through a lomb-scargle fitting routine to determine periodicity. After a periodicity cut, the ~400 candidates are classified by eye into different types of variable stars. We have identified several hundred variable stars, with periods ranging between a few minutes to a few days, and about half are not previously identified in the literature. We compare our results to the stripe 82 variable catalog, which overlaps part of the sky with the PS1 catalog.

The Pan-STARRS 1 Medium Deep Field Variable Star Catalog

NASA Astrophysics Data System (ADS)

Flewelling, Heather

2015-08-01

We present the first Pan-STARRS 1 Medium Deep Field Variable Star Catalog (PS1-MDF-VSC). The Pan-STARRS 1 (PS1) telescope is a 1.8 meter survey telescope with a 1.4 Gigapixel camera, located in Haleakala, Hawaii. The Medium Deep survey, which consists of 10 fields located uniformly across the sky, totalling 70 square degrees, is observed each night, in 2-3 filters per field, with 8 exposures per filter, resulting in 3000-4000 data points per star over a time span of 3.5 years. To find the variables, we select the stars with > 200 detections, between 16th and 21st magnitude. There are approximately 500k stars that fit this criteria, they then go through a lomb-scargle fitting routine to determine periodicity. After a periodicity cut, the ~400 candidates are classified by eye into different types of variable stars. We have identified several hundred variable stars, with periods ranging between a few minutes to a few days, and about half are not previously identified in the literature. We compare our results to the stripe 82 variable catalog, which overlaps part of the sky with the PS1 catalog.

Sisian, Zorats Karer, Tsits Karer, Karahunge ...

NASA Astrophysics Data System (ADS)

Martirosyan, Hamlet

2015-07-01

The Sisian or Zorats Karer megalithic monument is located in the RA Syunik region, 3 km away from the town of Sisian. There are holes between 4-5 cm in diamater in 85 out of 223 stones that are currently upright, each between 0.5-3 m in height. This pre-historic monument was a worship center, as well as an observatory where the Sun, planets and stars rising and setting were observed between VI-IV millennia B.C. The literal meaning of the construction's original name Sisian means "rising (stones)", and the name Zorats Karer means "stones of the stars" or "stones of the gods". The data from Mesopotamian cuneiform sources and Armenian medieval manuscripts show that the stars (constellations) were considered as personifications of certain gods. In the Zorats Karer worship center, via observations of the rising of a given star, the moment of the respective god's rising from the underground and his influence spreading over the Earth was defined.

More Unusual Light Curves from Kepler

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-03-01

Twenty-three new objects have been added to the growing collection of stars observed to have unusual dips in their light curves. A recent study examines these stars and the potential causes of their strange behavior.An Influx of DataThe primary Kepler mission provided light curves for over 100,000 stars, and its continuation K2 is observing another 20,000 stars every three months. As we enter an era where these enormous photometric data sets become commonplace Gaia will obtain photometry for millions of stars, and LSST billions its crucial that we understand the different categories of variability observed in these stars.The authors find three different types of light curves among their 23 unusual stars. Scallop-shell curves (top) show many undulations; persistent flux-dip class curves (middle) have discrete triangularly shaped flux dips; transient, narrow dip class curves (bottom) have only one dip that is variable in depth. The authors speculate a common cause for the scallop-shell and persistent flux-dip stars, and a different cause for the transient flux-dip stars. [Stauffer et al. 2017]After filtering out the stars with planets, those in binary systems, those with circumstellar disks, and those with starspots, a number of oddities remain: a menagerie of stars with periodic variability that cant be accounted for in these categories. Some of these stars are now famous (for instance, Boyajians star); some are lesser known. But by continuing to build up this sample of stars with unusual light curves, we have a better chance of understanding the sources of variability.Building the MenagerieTo this end, a team of scientists led by John Stauffer (Spitzer Science Center at Caltech) has recently hunted for more additions to this sample in the K2 data set. In particular, they searched through the light curves from stars in the Oph and Upper Scorpius star-forming region a data set that makes up the largest collection of high-quality light curves for low-mass, pre-main-sequence stars ever obtained.In these light curves, Stauffer and collaborators found a set of 23 very low-mass, mid-to-late-type M dwarfs with unusual variability in their light curves. The variability is consistent with the stars rotation period where measured which suggests that whatever causes the dips in the light curve, its orbiting at the same rate as the star spins.Causes of Variability?These plots show how the properties of these 23 stars compare to those of the rest of the stars in their cluster (click for a closer look!). For all but the rotation rate, they are typical. But the stars with scallop-shaped light curves have among the shortest periods in Upper Sco, with somenear the theoretical break-up for stars of their age. [Stauffer et al. 2017]The authors categorize the 23 stars into two main groups.The first group consists of 19 stars with short periods; more than half of them rotate within a factor of two of their predicted breakup period! Many of these show sudden changes in their light-curve morphology, often after a stellar flare. The authors propose that the variability in these light curves might be caused by warm coronal gas clouds that are organized into a structured toroidal shape around the star.The second group consists of the remaining four stars, which have slightly longer periods. The light curves show a single short-duration flux dip with highly variable depth and shape superposed on normal, spotted-star light curves. The authors best guess for these four stars is that there are clouds of dusty debris circling the star, possibly orbiting a close-in planet or resulting from a recent collisional event.Stauffer and collaborators are currently developing more detailed models for these stars based on the possible variability scenarios. The next step, they state, is to determine if the gas in these structures have properties necessary to generate the light-curve features we see.CitationJohn Stauffer et al 2017 AJ 153 152. doi:10.3847/1538-3881/aa5eb9

Photometric Variations of Solar-type Stars: Results of the Cloudcroft Survey

NASA Technical Reports Server (NTRS)

Giampapa, M. S.

1984-01-01

The results of a synoptic program to search for the occurrence of photometric variability in solar type stars as seen in continuum band photometry are summarized. The survey disclosed the existence of photometric variability in solar type stars that is related to the presence of spots on the stellar surface. The observed variability detected in solar type stars is at enhanced levels compared to that observed for the Sun.

The ASAS-SN Catalog of Variable Stars I: The Serendipitous Survey

NASA Astrophysics Data System (ADS)

Jayasinghe, T.; Kochanek, C. S.; Stanek, K. Z.; Shappee, B. J.; Holoien, T. W.-S.; Thompson, Todd A.; Prieto, J. L.; Dong, Subo; Pawlak, M.; Shields, J. V.; Pojmanski, G.; Otero, S.; Britt, C. A.; Will, D.

2018-04-01

The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to routinely monitor the whole sky with a cadence of ˜2 - 3 days down to V≲ 17 mag. ASAS-SN has monitored the whole sky since 2014, collecting ˜100 - 500 epochs of observations per field. The V-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. We present a catalog of 66,533 bright, new variable stars discovered during our search for supernovae, including 27,753 periodic variables and 38,780 irregular variables. V-band light curves for the ASAS-SN variables are available through the ASAS-SN variable stars database (https://asas-sn.osu.edu/variables). The database will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey.

Photometric Variability of the Be Star Population

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

Labadie-Bartz, Jonathan; Pepper, Joshua; McSwain, M. Virginia

2017-06-01

Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10more » years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.« less

Spectral Properties and Variability of BIS objects

NASA Astrophysics Data System (ADS)

Gaudenzi, S.; Nesci, R.; Rossi, C.; Sclavi, S.; Gigoyan, K. S.; Mickaelian, A. M.

2017-10-01

Through the analysis and interpretation of newly obtained and of literature data we have clarified the nature of poorly investigated IRAS point sources classified as late type stars, belonging to the Byurakan IRAS Stars catalog. From medium resolution spectroscopy of 95 stars we have strongly revised 47 spectral types and newly classified 31 sources. Nine stars are of G or K types, four are N carbon stars in the Asymptotic Giant Branch, the others being M-type stars. From literature and new photometric observations we have studied their variability behaviour. For the regular variables we determined distances, absolute magnitudes and mass loss rates. For the other stars we estimated the distances, ranging between 1.3 and 10 kpc with a median of 2.8 kpc from the galactic plane, indicating that BIS stars mostly belong to the halo population.

Observations of red-giant variable stars by Aboriginal Australians

NASA Astrophysics Data System (ADS)

Hamacher, Duane W.

2018-04-01

Aboriginal Australians carefully observe the properties and positions of stars, including both overt and subtle changes in their brightness, for subsistence and social application. These observations are encoded in oral tradition. I examine two Aboriginal oral traditions from South Australia that describe the periodic changing brightness in three pulsating, red-giant variable stars: Betelgeuse (Alpha Orionis), Aldebaran (Alpha Tauri), and Antares (Alpha Scorpii). The Australian Aboriginal accounts stand as the only known descriptions of pulsating variable stars in any Indigenous oral tradition in the world. Researchers examining these oral traditions over the last century, including anthropologists and astronomers, missed the description of these stars as being variable in nature as the ethnographic record contained several misidentifications of stars and celestial objects. Arguably, ethnographers working on Indigenous Knowledge Systems should have academic training in both the natural and social sciences.

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.

Optical photometric variable stars towards the Galactic H II region NGC 2282

NASA Astrophysics Data System (ADS)

Dutta, Somnath; Mondal, Soumen; Joshi, Santosh; Jose, Jessy; Das, Ramkrishna; Ghosh, Supriyo

2018-05-01

We report here CCD I-band time series photometry of a young (2-5 Myr) cluster NGC 2282, in order to identify and understand the variability of pre-main-sequence (PMS) stars. The I-band photometry, down to ˜20.5 mag, enables us to probe the variability towards the lower mass end (˜0.1 M⊙) of PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H α emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H α emission, near-IR (NIR)/mid-IR (MIR) excess or both and are candidate members of the cluster. Out of 62 variables, 41 are periodic variables, with a rotation rate ranging from 0.2-7 d. The period distribution exhibits a median period at ˜1 d, as in many young clusters (e.g. NGC 2264, ONC, etc.), but it follows a unimodal distribution, unlike others that have bimodality, with slow rotators peaking at ˜6-8 d. To investigate the rotation-disc and variability-disc connection, we derived the NIR excess from Δ(I - K) and the MIR excess from Spitzer [3.6]-[4.5] μm data. No conclusive evidence of slow rotation with the presence of discs around stars and fast rotation for discless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with IR excess is found for all variables.

Time Resolved X-Ray Spectral Analysis of Class II YSOs in NGC 2264 During Optical Dips and Bursts

NASA Astrophysics Data System (ADS)

Guarcello, Mario Giuseppe; Flaccomio, Ettore; Micela, Giuseppina; Argiroffi, Costanza; Venuti, Laura

2016-07-01

Pre-Main Sequence stars are variable sources. The main mechanisms responsible for their variability are variable extinction, unsteady accretion, and rotational modulation of both hot and dark photospheric spots and X-ray active regions. In stars with disks this variability is thus related to the morphology of the inner circumstellar region (<0.1 AU) and that of photosphere and corona, all impossible to be spatially resolved with present day techniques. This has been the main motivations of the Coordinated Synoptic Investigation of NGC2264, a set of simultaneous observations of NGC2264 with 15 different telescopes.We analyze the X-ray spectral properties of stars with disks extracted during optical bursts and dips in order to unveil the nature of these phenomena. Stars are analyzed in two different samples. In stars with variable extinction a simultaneous increase of optical extinction and X-ray absorption is searched during the optical dips; in stars with accretion bursts we search for soft X-ray emission and increasing X-ray absorption during the bursts. In 9/33 stars with variable extinction we observe simultaneous increase of X-ray absorption and optical extinction. In seven dips it is possible to calculate the NH/AV ratio in order to infer the composition of the obscuring material. In 5/27 stars with optical accretion bursts, we observe soft X-ray emission during the bursts that we associate to the emission of accreting gas. It is not surprising that these properties are not observed in all the stars with dips and bursts since favorable geometric configurations are required. The observed variable absorption during the dips is mainly due to dust-free material in accretion streams. In stars with accretion bursts we observe in average a larger soft X-ray spectral component not observed in non accreting stars. This indicates that this soft X-ray emission arises from the accretion shocks.

A CCD search of short period variable stars in six selected fields. (Italian Title: Ricerca CCD di variabili a breve periodo in sei campi selezionati)

NASA Astrophysics Data System (ADS)

Valentini, S.

2013-12-01

A search of variable stars was carried out, using a new software specifically created by the author, on a series of images acquired at the Astronomical Observatory of Santa Lucia di Stroncone (Terni, Italy) between October 2010 and March 2012. This research, named Fast Variable Stars Survey (FVSS), arose from the idea to verify if the log files pr oduced by the software Astrometrica (H. Raab), could be used as a basis for rapid detection of short-period variable stars. The r esults obtained showed that the idea is very valid, so that the new software has allowed the identification and the correct determination of the period of thirty-two new variable stars in the six stellar fields subjected to analysis.

A New Binary Star System of EW Type in Draco: GSC 03905-01870

NASA Astrophysics Data System (ADS)

Barquin, S.

2018-05-01

Discovery of a new binary star system (GSC 03905-01870 = USNO-B1.0 1431-0327922 = UCAC4 716-059522) in the Draco constellation is presented. It was discovered during a search for previously unreported eclipsing binary stars through the ASAS-SN database. The shape of the light curve and its characteristics (period of 0.428988+-0.000001 d, amplitude of 0.34+-0.02 V Mag, primary minimum epoch HJD 2457994.2756+-0.0002) indicates that the new variable star is an eclipsing binary of W Ursae Majoris type. I registered this variable star in The International Variable Star Index (VSX), its AAVSO UID is 000-BMP-891.

Statistical Analysis of Main and Interaction Effects on Cu(II) and Cr(VI) Decontamination by Nitrogen-Doped Magnetic Graphene Oxide

NASA Astrophysics Data System (ADS)

Hu, Xinjiang; Wang, Hui; Liu, Yunguo

2016-10-01

A nitrogen-doped magnetic graphene oxide (NMGO) was synthesized and applied as an adsorbent to remove Cu(II) and Cr(VI) ions from aqueous solutions. The individual and combined effects of various factors (A: pH, B: temperature, C: initial concentration of metal ions, D: CaCl2, and E: humic acid [HA]) on the adsorption were analyzed by a 25-1 fractional factorial design (FFD). The results from this study indicated that the NMGO had higher adsorption capacities for Cu(II) ions than for Cr(VI) ions under most conditions, and the five selected variables affected the two adsorption processes to different extents. A, AC, and C were the very important factors and interactions for Cu(II) adsorption. For Cr(VI) adsorption, A, B, C, AB, and BC were found to be very important influencing variables. The solution pH (A) was the most important influencing factor for removal of both the ions. The main effects of A-E on the removal of Cu(II) were positive. For Cr(VI) adsorption, the main effects of A and D were negative, while B, C, and E were observed to have positive effects. The maximum adsorption capacities for Cu(II) and Cr(VI) ions over NMGO were 146.365 and 72.978 mg/g, respectively, under optimal process conditions.

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

A Method to Estimate the Masses of Asymptotic Giant Branch Variable Stars

NASA Astrophysics Data System (ADS)

Takeuti, Mine; Nakagawa, Akiharu; Kurayama, Tomoharu; Honma, Mareki

2013-06-01

AGB variable stars are at the transient phase between low and high mass-loss rates; estimating the masses of these stars is necessary to study the evolutionary processes and mass-loss processes during the AGB stage. We applied the pulsation constant theoretically derived by Xiong and Deng (2007 MNRAS, 378, 1270) to 15 galactic AGB stars in order to estimate their masses. We found that using the pulsation constant is effective to estimate the mass of a star pulsating with two different pulsation modes, such as S Crt and RX Boo, which provides mass estimates comparable to theoretical results of AGB star evolution. We also extended the use of the pulsation constant to single-mode variables, and analyzed the properties of AGB stars related to their masses.

Construction of Database for Pulsating Variable Stars

NASA Astrophysics Data System (ADS)

Chen, B. Q.; Yang, M.; Jiang, B. W.

2011-07-01

A database for the pulsating variable stars is constructed for Chinese astronomers to study the variable stars conveniently. The database includes about 230000 variable stars in the Galactic bulge, LMC and SMC observed by the MACHO (MAssive Compact Halo Objects) and OGLE (Optical Gravitational Lensing Experiment) projects at present. The software used for the construction is LAMP, i.e., Linux+Apache+MySQL+PHP. A web page is provided to search the photometric data and the light curve in the database through the right ascension and declination of the object. More data will be incorporated into the database.

The millimagnitude variability of the HgMn star φ Phe

NASA Astrophysics Data System (ADS)

Prvák, M.; Krtička, J.; Korhonen, H.

2018-01-01

The horizontally inhomogeneous chemical composition of the atmospheres of the chemically peculiar stars causes wavelength redistribution of the spectral energy in areas with increased abundance of heavier elements. Due to the rotation of the star, this usually leads to strictly periodic photometric variability in some spectral regions. We used abundance maps of the HgMn star φ Phe (HD 11753), obtained by means of the Doppler imaging, to model its photometric variability. Comparing the light curves derived from abundance maps obtained at different times, we also study how the time evolution of the surface spots affects this variability.

Remote sensing-based characterization of land management and biophysical factors in grassland

NASA Astrophysics Data System (ADS)

Ramspott, Matthew E.

Land use and management are important factors influencing ecosystem functions, including the cycling of carbon (C) in plant/soil systems. Information about land use and management, needed to prioritize conservation efforts in managed grasslands of the Central Great Plains, can be obtained using remote sensing techniques, but this process is complex in grasslands because of the subtle class differences, large within-class variability, and complex seasonal changes in canopy spectral characteristics. In this study, time-series of remotely sensed data were used to derive vegetation index (VI) and image texture measures. The utility of these measures for classification of five managed grassland types was assessed using ANOVA and stepwise discriminant analysis methods. Image texture was found to improve the accuracy of classification by ˜13% over the use of VI alone. The optimal timing of data acquisition for classification with VI was found to be in April/May and in October; optimal timing for acquisition of texture was in June. Remotely sensed VI have been commonly used to model photosynthetic capacity and net primary production in ecosystems. Since VI theoretically assume canopy conditions of uniform geometry and greenness, seasonally variable management-induced changes in the grassland canopy can potentially influence the VI response and therefore the strength and stability of the model. This study examined the seasonal and inter-annual stability of the relationship between VI and photosynthetic capacity under both idealized and realized conditions. With regression analysis, the relationship between VI and field-measured estimates of photosynthetic capacity was established and evaluated. This work identified two types of management activity strongly influencing the stability of this relationship: (1) Conservation management, in which the vegetation is neither hayed nor grazed, results in accumulation of senescent canopy material and leads to lower than expected VI response; (2) Heavy grazing management leads to elevated levels of forb (non-grass species) cover in the canopy coupled with low photosynthetic capacity and high levels of bare ground, resulting in higher than expected VI response. When sites exhibiting these characteristics were removed, the relationship between VI and photosynthetic capacity was found to be stable seasonally and between years.

Long-term integrating samplers for indoor air and sub slab soil gas at VI sites

EPA Science Inventory

Vapor intrusion (VI) site assessments are plagued by substantial spatial and temporal variability that makes exposure and risk assessment difficult. Most risk-based decision making for volatile organic compound (VOC) exposure in the indoor environment is based on health benchmark...

Observing variable stars at the University of Athens Observatory

NASA Astrophysics Data System (ADS)

Gazeas, K.; Manimanis, V. N.; Niarchos, P. G.

In 1999 the University of Athens installed a 0.4-m Cassegrain telescope (CCT-16, by DFM Engineering) on the roof of the Department of Astrophysics, Astronomy and Mechanics, equipped with a ST-8 CCD camera and Bessel UBVRI filters. Although the telescope was built for educational purposes, we found it can be a perfect research instrument, as we can obtain fine quality light curves of bright variable stars, even from a place close to the city center. Light curves of the δ Scuti star V1162 Ori and of the sdB star PG 1336-018 are presented, showing the ability of a 40-cm telescope to detect negligible luminosity fluctuations of relatively bright variable stars. To date, we succeed in making photometry of stars down to 15th magnitude with satisfactory results. We expect to achieve even better results in the future, as our methods still improve, and as the large number of relatively bright stars gives us the chance to study various fields of CCD photometry of variables.

Large amplitude change in spot-induced rotational modulation of the Kepler Ap star KIC 2569073

NASA Astrophysics Data System (ADS)

Drury, Jason A.; Murphy, Simon J.; Derekas, Aliz; Sódor, Ádám; Stello, Dennis; Kuehn, Charles A.; Bedding, Timothy R.; Bognár, Zsófia; Szigeti, László; Szakáts, Róbert; Sárneczky, Krisztián; Molnár, László

2017-11-01

An investigation of the 200 × 200 pixel `superstamp' images of the centres of the open clusters NGC 6791 and NGC 6819 allows for the identification and study of many variable stars that were not included in the Kepler target list. KIC 2569073 (V = 14.22), is a particularly interesting variable Ap star that we discovered in the NGC 6791 superstamp. With a rotational period of 14.67 d and 0.034 mag variability, it has one of the largest peak-to-peak variations of any known Ap star. Colour photometry reveals an antiphase correlation between the B band, and the V, R and I bands. This Ap star is a rotational variable, also known as an α2 CVn star, and is one of only a handful of Ap stars observed by Kepler. While no change in spot period or amplitude is observed within the 4 yr Kepler time series, the amplitude shows a large increase compared to ground-based photometry obtained two decades ago.

A study about the photometric variability in the M42 region

NASA Astrophysics Data System (ADS)

Lima, G. H. R. A.; Vaz, L. P. R.; Reipurth, B.

2003-08-01

The M42 region in Orion is one of the most active regarding stellar formation in the neighborhood of the solar system. At a distance of 450pc, it gives us an excellent oportunity to study star formation processes. By studying 22 films of this region, covering an area of 5 by 5 degrees, taken in almost regular intervals through 2.5 years by ESO 1m Schimdt Telescope, in La Silla, Chile, we seek to discover variable stars among the young stars. These films were digitalized by the SuperCOSMOS (the most precise scientific scanner today) team, and each film were exposed for 30 minutes. Our knowledge about the variability of low-mass young variable stars were outdated, and were based on old photographic plates, which were studied by the so called blink comparators and Iris photometers. Now we developed a process to study these data and identify possible candidate stars to be constants or variables, and developed some softwares based on this process. We also used some softwares supplied by the SuperCosmos team to help our analysis of the dataset. After identifying the stars, which we, definitively, can consider variables, we will study more deeply these ones in hope to obtain more data about the formation process. We expect to detect thousands of new variables within our data as also the light curves for each star detected.

Time-Series Photometry of Variable Stars in the Globular Cluster NGC 288

NASA Astrophysics Data System (ADS)

Lee, Dong-Joo; Koo, Jae-Rim; Hong, Kyeongsoo; Kim, Seung-Lee; Lee, Jae Woo; Lee, Chung-Uk; Jeon, Young-Beom; Kim, Yun-Hak; Lim, Beomdu; Ryu, Yoon-Hyun; Cha, Sang-Mok; Lee, Yongseok; Kim, Dong-Jin; Park, Byeong-Gon; Kim, Chun-Hwey

2016-12-01

We present the results of BV time-series photometry of the globular cluster NGC 288. Observations were carried out to search for variable stars using the Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes and a 4k pre-science CCD camera during a test observation from August to December, 2014. We found a new SX Phe star and confirmed twelve previously known variable stars in NGC 288. For the semi-regular variable star V1, we newly determined a period of 37.3 days from light curves spanning 137 days. The light-curve solution of the eclipsing binary V10 indicates that the system is probably a detached system. The pulsation properties of nine SX Phe stars were examined by applying multiple frequency analysis to their light curves. We derived a new Period-Luminosity (P-L) relation, < M_{V} rangle = -2.476(±0.300) log P - 0.354(±0.385), from six SX Phe stars showing the fundamental mode. Additionally, the period ratios of three SX Phe stars that probably have a double-radial mode were investigated; P_{FO}/P_{F} = 0.779 for V5, P_{TO}/P_{FO} = 0.685 for V9, P_{SO}/P_{FO} = 0.811 for V11. This paper is the first contribution in a series assessing the detections and properties of variable stars in six southern globular clusters with the KMTNet system.

Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory. VI; The Second Parameter Pair M 3 and M 13

NASA Technical Reports Server (NTRS)

Moehler, S.; Landsman, W. B.; Sweigart, A. V.; Grundahl, F.

2003-01-01

We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M 13 and M 3, which form a famous "second parameter" pair. F rom the spectra and Stromgren photometry we derived - for the first time in M 13 - atmospheric parameters (effective temperature and surface gravity). For stars with Stromgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric parameters derived from Stromgren photometry and those derived from Balmer line profile fits. However, for cooler stars there is a disagreement in the parameters derived by the two methods, for which we have no satisfactory explanation. Stars hotter than 12,000 K show evidence for helium depletion and iron enrichment, both in M 3 and M 13. Accounting for the iron enrichment substantially improves the agreement with canonical evolutionary models, although the derived gravities and masses are still somewhat too low. This remaining discrepancy may be an indication that scaled-solar metal-rich model atmospheres do not adequately represent the highly non-solar abundance ratios found in blue HB stars affected by diffusion. We discuss the effects of an enhancement in the envelope helium abundance on the atmospheric parameters of the blue HB stars, as might be caused by deep mixing on the red giant branch or primordial pollution from an earlier generation of intermediate mass asymptotic giant branch stars. Key words. Stars: atmospheres - Stars: evolution - Stars: horizontal branch - Globular clusters: individual: M 3 - Globular clusters: individual: M 13

A near-infrared interferometric survey of debris-disc stars. VI. Extending the exozodiacal light survey with CHARA/JouFLU

NASA Astrophysics Data System (ADS)

Nuñez, P. D.; Scott, N. J.; Mennesson, B.; Absil, O.; Augereau, J.-C.; Bryden, G.; ten Brummelaar, T.; Ertel, S.; Coudé du Foresto, V.; Ridgway, S. T.; Sturmann, J.; Sturmann, L.; Turner, N. J.; Turner, N. H.

2017-12-01

We report the results of high-angular-resolution observations that search for exozodiacal light in a sample of main sequence stars and sub-giants. Using the "jouvence" of the fiber linked unit for optical recombination (JouFLU) at the center for high angular resolution astronomy (CHARA) telescope array, we have observed a total of 44 stars. Out of the 44 stars, 33 are new stars added to the initial, previously published survey of 42 stars performed at CHARA with the fiber linked unit for optical recombination (FLUOR). Since the start of the survey extension, we have detected a K-band circumstellar excess for six new stars at the 1% level or higher, four of which are known or candidate binaries, and two for which the excess could be attributed to exozodiacal dust. We have also performed follow-up observations of 11 of the stars observed in the previously published survey and found generally consistent results. We do however detect a significantly larger excess on three of these follow-up targets: Altair, υ And and κ CrB. Interestingly, the last two are known exoplanet host stars. We perform a statistical analysis of the JouFLU and FLUOR samples combined, which yields an overall exozodi detection rate of . We also find that the K-band excess in FGK-type stars correlates with the existence of an outer reservoir of cold (≲100 K) dust at the 99% confidence level, while the same cannot be said for A-type stars.

The American Association of Variable Star Observers: Serving the Research Community in 2010 and Beyond

NASA Astrophysics Data System (ADS)

Templeton, Matthew R.; Henden, A. A.; Davis, K.; Kinne, R.; Watson, C.; Saladyga, M.; Waagen, E.; Beck, S.; Menali, G.; Price, A.; Turner, R.

2010-05-01

The American Association of Variable Star Observers (AAVSO) holds the largest single online database of variable star data in the world, collected from thousands of amateur and professional observers during the past century. One of our core missions is to preserve and distribute these data to the research community in service to the science of variable star astronomy. But as an organization, the AAVSO is much more than a data archive. Our services to the research community include: monitoring for and announcement of major astronomical events like novae and supernovae; organization and management of observing campaigns; support for satellite and other TOO observing programs by the professional community; creation of comparison star sequences and generation of charts for the observer community; and observational and other support for the amateur, professional, and educator communities in all things related to variable stars. As we begin a new century of variable star astronomy we invite you to take advantage of the services the AAVSO can provide, and to become a part of our organization yourselves. In this poster, we highlight some of the most important services the AAVSO can provide to the professional research community, as well as suggest ways in which your research may be enhanced with support from the AAVSO.

Multimode delta Scuti stars in the open cluster NGC 7062

NASA Astrophysics Data System (ADS)

Freyhammer, L. M.; Arentoft, T.; Sterken, C.

2001-03-01

The central field of NGC 7062 was observed intensively with the main goal of finding delta Scuti stars suitable for use in asteroseismological tests of stellar structure and evolution theory. BV time series photometry was obtained for this northern open cluster, which has a large population of stars inside the delta Scuti instability strip, making it a probable host of several such variables. We report findings of 15 pulsating stars, including at least 13 delta Scuti stars. Ten variables oscillate in two or more frequencies. Only one of these variables was known before, for which we detected 9 frequencies. Five probable variables are mentioned, and period analysis is given for all 20 stars. Based on observations obtained at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisíca de Canarias.

High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability

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

Chojnowski, S. Drew; Holtzman, Jon A.; Wisniewski, John P.

2017-04-01

We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance ofmore » the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.« less

Application of plasma electrolysis method for simultaneous phenol and Cr(VI) wastewater degradation using Na2SO4 electrolyte

NASA Astrophysics Data System (ADS)

Harianti, Aulia Rahmi; Saksono, Nelson

2017-11-01

Phenol and Cr (VI) are two types of wastewater known as dangerous and difficult to degrade. Through this study, phenol and Cr (VI) metal wastewater were degraded simultaneously using plasma electrolysis method by reactive species, •OH and H•. The variation of anode depth and position of plasma formation as independent variables correlated with yield of hydroxyl radical, percentage of phenol and Cr (VI) degradation, and specific energy. Within 30 minutes, phenol was degraded to 98.4% and Cr (VI) was degraded to 93.35% with 171.05 kJ/mmol in specific energy, and 174.53 ppm in COD. The optimum condition was obtained in anodic plasma and 1.5 cm in anode depth. The highest degradation percentage of phenol and Cr (VI) were 99.79% and 97.33% achieved during 180 minutes of plasma electrolysis process.

Documentation for the machine-readable version of the catalogue of 20457 Star positions obtained by photography in the declination zone -48 deg to -54 deg (1950)

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1983-01-01

The machine readable catalog, as it is distributed from the Astronomical Data Center, is described. Some minor reformatting of the magnetic tape version is received to decrease the record size and conserve space; the data content is identical to the sample shown in Table VI of the source reference.

Image-Subtraction Photometry of Variable Stars in the Field of the Globular Cluster NGC 6934

NASA Astrophysics Data System (ADS)

Kaluzny, J.; Olech, A.; Stanek, K. Z.

2001-03-01

We present CCD BVI photometry of 85 variable stars from the field of the globular cluster NGC 6934. The photometry was obtained with the image subtraction package ISIS. 35 variables are new identifications: 24 RRab stars, five RRc stars, two eclipsing binaries of W UMa-type, one SX Phe star, and three variables of other types. Both detected contact binaries are foreground stars. The SX Phe variable belongs most likely to the group of cluster blue stragglers. Large number of newly found RR Lyr variables in this cluster, as well as in other clusters recently observed by us, indicates that total RR Lyr population identified up to date in nearby galactic globular clusters is significantly (>30%) incomplete. Fourier decomposition of the light curves of RR Lyr variables was used to estimate the basic properties of these stars. From the analysis of RRc variables we obtain a mean mass of M=0.63 Msolar, luminosity logL/Lsolar=1.72, effective temperature Teff=7300 and helium abundance Y=0.27. The mean values of the absolute magnitude, metallicity (on Zinn's scale) and effective temperature for RRab variables are MV=0.81, [Fe/H]=-1.53 and Teff=6450, respectively. From the B-V color at minimum light of the RRab variables we obtained the color excess to NGC 6934 equal to E(B-V)=0.09+/-0.01. Different calibrations of absolute magnitudes of RRab and RRc available in literature were used to estimate apparent distance modulus of the cluster: (m-M)V=16.09+/-0.06. We note a likely error in the zero point of the HST-based V-band photometry of NGC 6934 recently presented by Piotto et al. Among analyzed sample of RR Lyr stars we have detected a short period and low amplitude variable which possibly belongs to the group of second overtone pulsators (RRe subtype variables). The BVI photometry of all variables is available electronically via anonymous ftp. The complete set of the CCD frames is available upon request. Based on observations obtained with the 1.2 m Telescope at the F. L. Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics.

A seven-year northern sky survey of Ap stars for rapid variability

NASA Technical Reports Server (NTRS)

Nelson, Matthew J.; Kreidl, Tobias J.

1993-01-01

A high-speed photometric survey of 120 Ap stars in the northern sky, has been conducted, between 1985 and 1991, in order to search for rapid variability. Stars of spectral types, namely from B8 to F4, have been selected for the survey. The selected pulsational variable stars occupy the hotter regions of the instability strip of the Hertzsprung-Russel diagram. Noted is the absence of pulsations in the hotter B8-A3 Ap stars; this does not, however, preclude the existence of pulsations, since HD 218495 was recently discovered to be a rapidly oscillating Ap (roAp) star. The primary result of this study is that various combinations of photometric indices, while pointing towards roAp stars having the characteristic signatures of cool, SrCrEu stars, still fail to isolate the roAp phenomenon from similar nonpulsating Ap stars. Color-magnitude and color-color diagrams are presented in order to complete this survey.

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA

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

Wang Lingzhi; Macri, Lucas M.; Krisciunas, Kevin

Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night. We present high-cadence time-series aperture photometry of 10,000 stars with i < 14.5 mag located in a 23 deg{sup 2} region centered on the south celestial pole. The photometry was obtained with one of the CSTAR telescopes during 128 days of the 2008 Antarctic winter. We used this photometric data set to derive site statistics for Dome A and to search for variable stars. Thanks to the nearlymore » uninterrupted synoptic coverage, we found six times as many variables as previous surveys with similar magnitude limits. We detected 157 variable stars, of which 55% were unclassified, 27% were likely binaries, and 17% were likely pulsating stars. The latter category includes {delta} Scuti, {gamma} Doradus, and RR Lyrae variables. One variable may be a transiting exoplanet.« less

Variable Stars in the Field of V729 Aql

NASA Astrophysics Data System (ADS)

Cagaš, P.

2017-04-01

Wide field instruments can be used to acquire light curves of tens or even hundreds of variable stars per night, which increases the probability of new discoveries of interesting variable stars and generally increases the efficiency of observations. At the same time, wide field instruments produce a large amount of data, which must be processed using advanced software. The traditional approach, typically used by amateur astronomers, requires an unacceptable amount of time needed to process each data set. New functionality, built into SIPS software package, can shorten the time needed to obtain light curves by several orders of magnitude. Also, newly introduced SILICUPS software is intended for post-processing of stored light curves. It can be used to visualize observations from many nights, to find variable star periods, evaluate types of variability, etc. This work provides an overview of tools used to process data from the large field of view around the variable star V729 Aql. and demonstrates the results.

Velocity fields and spectrum peculiarities in Beta Cephei stars

NASA Technical Reports Server (NTRS)

Lesh, J. R.

1980-01-01

The acquisition of short wavelength spectra of Beta Cephei variable stars from the International Ultraviolet Explorer is reported. A total of 122 images of 10 variable stars and 3 comparison stars were obtained. All of the images were observed in the high dispersion mode through a small aperture. The development of image processing methods is also briefly discussed.

The ASAS-SN catalogue of variable stars I: The Serendipitous Survey

NASA Astrophysics Data System (ADS)

Jayasinghe, T.; Kochanek, C. S.; Stanek, K. Z.; Shappee, B. J.; Holoien, T. W.-S.; Thompson, Toda A.; Prieto, J. L.; Dong, Subo; Pawlak, M.; Shields, J. V.; Pojmanski, G.; Otero, S.; Britt, C. A.; Will, D.

2018-07-01

The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to routinely monitor the whole sky with a cadence of ˜2-3 d down to V ≲ 17 mag. ASAS-SN has monitored the whole sky since 2014, collecting ˜100-500 epochs of observations per field. The V-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. We present a catalogue of 66 179 bright, new variable stars discovered during our search for supernovae, including 27 479 periodic variables and 38 700 irregular variables. V-band light curves for the ASAS-SN variables are available through the ASAS-SN variable stars data base (https://asas-sn.osu.edu/variables). The data base will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey.

Skysurvey Results of RotseIIID Data

NASA Astrophysics Data System (ADS)

Bilir, Cansu; Varol Keskin, MR..

2016-07-01

The aim of this thesis is to find variable stars from the ROTSEIIID fields data files. In order to determine the variable stars, a simple but effective software, that works seamlessly, has been developed. Robotic Optical Transient Search Experiment (ROTSE) is a worldwide project with four robotic telescopes, established in order to follow the optical afterglow radiation of the Gamma-Ray Bursts (GRB). In this study, the observations of the fields obtained from the ROTSEIIID Telescope located in the TÜBİTAK (Scientific and Technological Research Council of Turkey) National Observatory were used. ROTSEIIID creates a calibrated object list (cobj) from the observations gathered automatically. The different values of each star (RA, DEC, Pixel Coordinates, M, MERR, Flags etc.) can be found in this generated list. In this thesis these values are extracted from data files. A php programme was developed in order to extract time series data of every star in a field. It also searches period, and if found, calculates phases for this data. The goal of this study is to determine the variable stars, especially unknown variables. Ds9 and fv programs are used for dealing with FITS files. Also flowchart of program is given in this thesis. In addition Debil (for finding some parameters of detached eclipsing binary stars) and Gnuplot (for drawing graphics) are used by php program. Using gnuplot, magnitude-time and period-time graphics of each star are plotted. The searching program is used for some different fields of RotseIIID data files. On the basis of the results of this research, 42 variable stars found and 14 of them are listed end of the thesis with their light curves. The data used in this thesis will be studied more detailed and research results of new/unknown variable stars will be published along the Msc thesis. We are still studying on the data of new variable stars which were discovered by this research and the results will be published in near future...

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.

Infrared Studies of the Variability and Mass Loss of Dusty Asymptotic Giant Branch Stars in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Sargent, Benjamin; Groenewegen, M. A. T.

2018-01-01

The asymptotic giant branch (AGB) phase is one of the last phases of a star's life. AGB stars lose mass in an outflow in which dust condenses and is pushed away from the star. Extreme AGB stars are so named because their very red colors suggest very large amounts of dust, which in turn suggests extremely high mass loss rates. AGB stars also vary in brightness, and studies show that extreme AGB stars tend to have longer periods than other AGB stars and are more likely to be fundamental mode pulsators than other AGB stars. Extreme AGB stars are difficult to study, as their colors are so red due to their copious amounts of circumstellar dust that they are often not detected at optical wavelengths. Therefore, they must be observed at infrared wavelengths to explore their variability. Using the Spitzer Space Telescope, my team and I have observed a sample of extreme AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) over Cycles 9 through 12 during the Warm Spitzer mission. For each cycle, we typically observed a set of extreme AGB stars at both 3.6 and 4.5 microns wavelength approximately monthly for most of a year. These observations reveal a wide range of variability properties. I present results from our analysis of the data obtained from these Spitzer variability programs, including light curve analyses and comparison to period-luminosity diagrams. Funding is acknowledged from JPL RSA # 1561703.

VizieR Online Data Catalog: Mira stars discovered in LAMOST DR4 (Yao+, 2017)

NASA Astrophysics Data System (ADS)

Yao, Y.; Liu, C.; Deng, L.; de Grijs, R.; Matsunaga, N.

2017-10-01

By the end of 2016 March, the wide-field Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) DR4 catalog had accumulated 7681185 spectra (R=1800), of which 6898298 were of stars. We compiled a photometrically confirmed sample of Mira variables from the Kiso Wide-Field Camera (KWFC) Intensive Survey of the Galactic Plane (KISOGP; Matsunaga 2017, arXiv:1705.08567), the American Association of Variable Star Observers (AAVSO) International Database Variable Star Index (VSX; Watson 2006, B/vsx, version 2017-05-02; we selected stars of variability type "M"), and the SIMBAD Astronomical Database. We first cross-matched the KISOGP and VSX Miras with the LAMOST DR4 catalog. Finally, we cross-matched the DR4 catalog with the SIMBAD database. See section 2. (1 data file).

Highly ionized gas in the Gum nebula and elsewhere - A comparison of IUE and Copernicus satellite results

NASA Technical Reports Server (NTRS)

Edgar, Richard J.; Savage, Blair D.

1992-01-01

The data from six high-dispersion IUE echelle spectra are averaged in order to obtain an interstellar absorption line spectrum with an S/N of about 30 and a resolution of about 25 km/s. The interstellar lines of C IV and Si IV are very strong and broad and N V is detected. The profiles for these species and Al III are compared to the Copernicus satellite profiles for O VI. The high ionization lines toward HD 64760 are much stronger and broader than those recorded toward Zeta Pup and Gamma super 2 Vel, the two exciting stars of the Gum nebula. The profiles for Al III and Si IV are similar and considerably narrower than the O VI profile. An origin in photoionized Gum nebula gas is suggested as the most likely explanation for Al III and Si IV. The C IV profile has a high positive velocity wing extending to approximately +80 km/s, which is similar in appearance to the positive velocity portion of the O VI profile. It is inferred that a substantial part of the observed C IV has an origin in the collisionally ionized gas most likely rsponsible for the O VI.

THE BERLIN EXOPLANET SEARCH TELESCOPE II CATALOG OF VARIABLE STARS. I. CHARACTERIZATION OF THREE SOUTHERN TARGET FIELDS

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

Fruth, T.; Cabrera, J.; Csizmadia, Sz.

2013-11-01

A photometric survey of three southern target fields with BEST II yielded the detection of 2406 previously unknown variable stars and an additional 617 stars with suspected variability. This study presents a catalog including their coordinates, magnitudes, light curves, ephemerides, amplitudes, and type of variability. In addition, the variability of 17 known objects is confirmed, thus validating the results. The catalog contains a number of known and new variables that are of interest for further astrophysical investigations, in order to, e.g., search for additional bodies in eclipsing binary systems, or to test stellar interior models. Altogether, 209,070 stars were monitoredmore » with BEST II during a total of 128 nights in 2009/2010. The overall variability fraction of 1.2%-1.5% in these target fields is well comparable to similar ground-based photometric surveys. Within the main magnitude range of R in [11, 17], we identify 0.67(3)% of all stars to be eclipsing binaries, which indicates a completeness of about one third for this particular type in comparison to space surveys.« less

Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals.

PubMed

Joe-Wong, Claresta; Brown, Gordon E; Maher, Kate

2017-09-05

Hexavalent chromium is a water-soluble pollutant, the mobility of which can be controlled by reduction of Cr(VI) to less soluble, environmentally benign Cr(III). Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(VI), but the kinetics and pathways of Cr(VI) reduction by such clay minerals are poorly understood. We reacted aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich nontronite. The effects of ionic strength, pH, total Fe content, and the fraction of reduced structural Fe(II) [Fe(II)/Fe(total)] were examined. The last variable had the largest effect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction varies by more than 3 orders of magnitude with Fe(II)/Fe(total) and is described by a linear free energy relationship. Under all conditions examined, Cr and Fe K-edge X-ray absorption near-edge structure spectra show that the main Cr-bearing product is a Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI). This study helps to quantify our understanding of the kinetics of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) behavior in subsurface environments.

Investigation of equilibrium and kinetics of Cr(VI) adsorption by dried Bacillus cereus using response surface methodology.

PubMed

Yang, Kai; Zhang, Jing; Yang, Tao; Wang, Hongyu

2016-01-01

In this study, response surface methodology (RSM) based on three-variable-five-level central composite rotatable design was used to analyze the effects of combined and individual operating parameters (biomass dose, initial concentration of Cr(VI) and pH) on the Cr(VI) adsorption capacity of dried Bacillus cereus. A quadratic polynomial equation was obtained to predict the adsorbed Cr(VI) amount. Analysis of variance showed that the effect of biomass dose was the key factor in the removal of Cr(VI). The maximum adsorbed Cr(VI) amount (30.93 mg g(-1)) was found at 165.30 mg L(-1), 2.96, and 3.01 g L(-1) for initial Cr(VI) concentration, pH, and biosorbent dosage, respectively. The surface chemical functional groups and microstructure of unloaded and Cr(VI)-loaded dried Bacillus cereus were identified by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. Besides, the results gained from these studies indicated that Langmuir isotherm and the second-order rate expression were suitable for the removal of Cr(VI) from wastewater. The results revealed RSM was an effective method for optimizing biosorption process, and dried Bacillus cereus had a remarkable performance on the removal of Cr(VI) from wastewater.

The First Pan-Starrs Medium Deep Field Variable Star Catalog

NASA Astrophysics Data System (ADS)

Flewelling, Heather

2013-01-01

We present the first Pan-Starrs 1 Medium Deep Field Variable Star Catalog (PS1-MDF-VSC). The Pan-Starrs 1 (PS1) telescope is a 1.8 meter survey telescope with a 1.4 Gigapixel camera, and is located in Haleakala, Hawaii. The Medium Deep survey, which consists of 10 fields located uniformly across the sky, totalling 70 square degrees, is observed each night, in 2-3 filters per field, with 8 exposures per filter. We have located and classified several hundred periodic variable stars within the Medium Deep fields, and we present the first catalog listing the properties of these variable stars.

The Pan-STARRS 1 Medium Deep Field Variable Star Catalog

NASA Astrophysics Data System (ADS)

Flewelling, Heather

2016-01-01

We present the first Pan-STARRS 1 Medium Deep Field Variable Star Catalog (PS1-MDF-VSC). The Pan-STARRS 1 (PS1) telescope is a 1.8 meter survey telescope with a 1.4 Gigapixel camera, located in Haleakala, Hawaii. The Medium Deep survey, which consists of 10 fields located uniformly across the sky, totaling 70 square degrees, is observed each night, in 2-3 filters per field, with 8 exposures per filter, resulting in 3000-4000 data points per star over a time span of 3.5 years. To find the variables, we select objects with > 200 detections, and remove those flagged as saturated. No other cuts are used. There are approximately 2.4 million objects that fit this criteria, with magnitudes between 13th and 24th. These objects are then passed through a lomb-scargle fitting routine to determine periodicity. After a periodicity cut, the candidates are classified by eye into different types of variable stars. We have identified several thousand periodic variable stars, with periods ranging between a few minutes to a few days. We compare our findings to the variable star catalogs within Vizier and AAVSO. In particular, for field MD02, we recover all the variables that are faint in Vizier, and we find good agreement with the periods reported in Vizier.

Caroline Furness and the Evolution of Visual Variable Star Observing

NASA Astrophysics Data System (ADS)

Larsen, Kristine

2017-01-01

An Introduction to the Study of Variable Stars by Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, was published in October 2015. Issued in honor of the fiftieth anniversary of the founding of Vassar College, the work was meant to fill a void in the literature, namely as both an introduction to the topic of variable stars as well as a manual explaining how they should be observed and the resulting data analyzed. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World’s Fair in Chicago. The book covers the relevant history of and background on types of variable stars, star charts, catalogs, and the magnitude scale, then describes observing techniques, including visual, photographic, and photoelectric photometry. The work finishes with a discussion of light curves and patterns of variability, with a special emphasis on eclipsing binaries and long period variables. Furness’s work is therefore a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. Furness’s book and its reception in the scientific community are analyzed, and parallels with (and departures from) the current advice given by the AAVSO to beginning variable star observers today are highlighted.

Revisiting Caroline Furness's An Introduction to the Study of Variable Stars on its Centenary (Poster abstract)

NASA Astrophysics Data System (ADS)

Larsen, K.

2016-06-01

(Abstract only) A century and one month ago (October 1915) Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, published An Introduction to the Study of Variable Stars. Issued in honor of the fiftieth anniversary of the founding of Vassar College, the work was meant to fill a void in the literature, namely as both an introduction to the topic of variable stars and as a manual explaining how they should be observed and the resulting data analyzed. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World's Fair in Chicago. The book covers the relevant history of and background on types of variable stars, star charts, catalogs, and the magnitude scale, then describes observing techniques, including visual, photographic, and photoelectric photometry. The work finishes with a discussion of light curves and patterns of variability, with a special emphasis on eclipsing binaries and long period variables. Furness's work is a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. This presentation will analyze both Furness's book and its reception in the scientific community, and draw parallels to current advice given to beginning variable star observers.

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.

The RECONS Hunt for Intriguing Binaries in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Bean, J. L.; Henry, T. J.; Jao, W. C.; Subasavage, J. P.

2001-12-01

As part of an effort to characterize the Sun's neighbors, photometric research was carried out on two samples of low-mass stars known or suspected to lie within 25 parsecs of the Sun. Quality filtered optical photometric data (UBVRI) from published research were merged with recently released infrared data (JHK) from the Two Micron All Sky Survey (2MASS) to create comprehensive long baseline V-I or V-K colors for more than 1400 stars. These were then combined with parallaxes from the NStars Database to create color-absolute magnitude diagrams. The results of this research include increasing the breadth of the NStars Database by adding photometric data for over 1400 stars, and identifying intriguing multiple systems (close spectroscopic binaries, BY Dra types, RS CVn systems) as well as white dwarfs and evolved stars in the solar neighborhood. More than two dozen objects have been identified as probable new multiple systems from their positions above the main sequence. Additional investigations for these intriguing systems are planned, including observations made with the GSU CHARA Array to resolve very close binary systems. This research is a continuation of the work done by RECONS (Research Consortium on Nearby Stars) based at Georgia Sate U., Johns Hopkins U., and U. Virginia, and NASA's Nearby Stars Project (NStars).

Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

NASA Astrophysics Data System (ADS)

Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

2014-02-01

The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

Hubble Tarantula Treasury Project - VI. Identification of Pre-Main-Sequence Stars using Machine Learning techniques

NASA Astrophysics Data System (ADS)

Ksoll, Victor F.; Gouliermis, Dimitrios A.; Klessen, Ralf S.; Grebel, Eva K.; Sabbi, Elena; Anderson, Jay; Lennon, Daniel J.; Cignoni, Michele; de Marchi, Guido; Smith, Linda J.; Tosi, Monica; van der Marel, Roeland P.

2018-05-01

The Hubble Tarantula Treasury Project (HTTP) has provided an unprecedented photometric coverage of the entire star-burst region of 30 Doradus down to the half Solar mass limit. We use the deep stellar catalogue of HTTP to identify all the pre-main-sequence (PMS) stars of the region, i.e., stars that have not started their lives on the main-sequence yet. The photometric distinction of these stars from the more evolved populations is not a trivial task due to several factors that alter their colour-magnitude diagram positions. The identification of PMS stars requires, thus, sophisticated statistical methods. We employ Machine Learning Classification techniques on the HTTP survey of more than 800,000 sources to identify the PMS stellar content of the observed field. Our methodology consists of 1) carefully selecting the most probable low-mass PMS stellar population of the star-forming cluster NGC2070, 2) using this sample to train classification algorithms to build a predictive model for PMS stars, and 3) applying this model in order to identify the most probable PMS content across the entire Tarantula Nebula. We employ Decision Tree, Random Forest and Support Vector Machine classifiers to categorise the stars as PMS and Non-PMS. The Random Forest and Support Vector Machine provided the most accurate models, predicting about 20,000 sources with a candidateship probability higher than 50 percent, and almost 10,000 PMS candidates with a probability higher than 95 percent. This is the richest and most accurate photometric catalogue of extragalactic PMS candidates across the extent of a whole star-forming complex.

Pulsating B and Be stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Diago, P. D.; Gutiérrez-Soto, J.; Fabregat, J.; Martayan, C.

2008-03-01

Context: Stellar pulsations in main-sequence B-type stars are driven by the κ-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the SMC is lower than Z = 0.005, it constitutes a very suitable object to test these predictions. Aims: The main objective is to investigate the existence of B-type pulsators at low metallicities, searching for short-term periodic variability in absorption-line B and Be stars in the SMC. The analysis has been performed in a sample of 313 B and Be stars with fundamental astrophysical parameters accurately determined from high-resolution spectroscopy. Methods: Photometric light curves of the MACHO project have been analyzed using standard Fourier techniques and linear and non-linear least squares fitting methods. The position of the pulsating stars in the HR diagram has been used to ascertain their nature and to map the instability regions in the SMC. Results: We have detected 9 absorption-line B stars showing short-period variability, two among them being multiperiodic. One star is most likely a β Cephei variable and the remaining 8 are SPB stars. The SPB instability strip in the SMC is shifted towards higher temperatures than the Galaxy. In the Be star sample, 32 stars are short-period variables, 20 among them multiperiodic. 4.9% of B stars and 25.3% of Be stars are pulsating stars. Conclusions: β Cephei and SPB stars do exist at the SMC metallicity. The fractions of SPB stars and pulsating Be stars in the SMC are lower than in the Galaxy. The fraction of pulsating Be stars in the SMC is much higher than the fraction of pulsating absorption-line B stars, as in the Galaxy.

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.

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

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

Dahn, Conard C.; Harris, Hugh C.; Subasavage, John P.

2017-10-01

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson–Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK{sub s} near-infrared photometry, a sample of absolute magnitude versus color and color versusmore » color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.« less

The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster NGC 6362

NASA Astrophysics Data System (ADS)

Kaluzny, J.; Thompson, I. B.; Rozyczka, M.; Pych, W.; Narloch, W.

2014-12-01

The field of the globular cluster NGC 6362 was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for 69 periodic variable stars including 34 known RR Lyr stars, 10 known objects of other types and 25 newly detected variable stars. Among the latter we identified 18 proper-motion members of the cluster: seven detached eclipsing binaries (DEBs), six SX Phe stars, two W UMa binaries, two spotted red giants, and a very interesting eclipsing binary composed of two red giants - the first example of such a system found in a globular cluster. Five of the DEBs are located at the turnoff region, and the remaining two are redward of the lower main sequence. Eighty-four objects from the central 9×9 arcmin2 of the cluster were found in the region of cluster blue stragglers. Of these 70 are proper motion (PM) members of NGC 6362 (including all SX Phe and two W UMa stars), and five are field stars. The remaining nine objects lacking PM information are located at the very core of the cluster, and as such they are likely genuine blue stragglers.

A Search for Circumstellar Gas-Disk Variability in F-type Stars

NASA Astrophysics Data System (ADS)

Adkins, Ally; Montgomery, Sharon Lynn; Welsh, Barry

2018-01-01

Over the past six years, short-term (night-to-night) variability in the CaII K-line (3933Å) absorption has been detected towards 22 rapidly-rotating A-type stars, all but four of them discovered by us. Most of these stars are young (age < 100 million years) and possess dusty debris disks as evidenced by their infrared excesses. The variability is thought to be due to kilometer-sized planetesimals (i.e., exocomets) that release gas during their catastrophic in-falls towards their central star. To expand the relatively small number of systems showing this type of variability, we conducted a search amongst nearby, rapidly-rotating, F-type stars. Here, we present high signal-to-noise, medium-resolution spectral observations of the CaII K-line absorption (R≈60,000) recorded towards seven F-type stars. Six of these stars were observed multiple times over the course of our seven-night run on the 2.1-meter Otto Struve Telescope (McDonald Observatory) during June 2017. The appearance or absence of similar short-lived, Doppler-shifted absorption in F-type stars serves as a test of our understanding of the underlying phenomena.

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.

EMG biofeedback: the effects of CRF, FR, VR, FI, and VI schedules of reinforcement on the acquisition and extinction of increases in forearm muscle tension.

PubMed

Cohen, S L; Richardson, J; Klebez, J; Febbo, S; Tucker, D

2001-09-01

Biofeedback was used to increase forearm-muscle tension. Feedback was delivered under continuous reinforcement (CRF), variable interval (VI), fixed interval (FI), variable ratio (VR), and fixed ratio (FR) schedules of reinforcement when college students increased their muscle tension (electromyograph, EMG) above a high threshold. There were three daily sessions of feedback, and Session 3 was immediately followed by a session without feedback (extinction). The CRF schedule resulted in the highest EMG, closely followed by the FR and VR schedules, and the lowest EMG scores were produced by the FI and VI schedules. Similarly, the CRF schedule resulted in the greatest amount of time-above-threshold and the VI and FI schedules produced the lowest time-above-threshold. The highest response rates were generated by the FR schedule, followed by the VR schedule. The CRF schedule produced relatively low response rates, comparable to the rates under the VI and FI schedules. Some of the data are consistent with the partial-reinforcement-extinction effect. The present data suggest that different schedules of feedback should be considered in muscle-strengthening-contexts such as during the rehabilitation of muscles following brain damage or peripheral nervous-system injury.

Amplitude Variability in gamma Dor and delta Sct Stars Observed by Kepler

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

Guzik, Joyce Ann; Kosak, Mary Katherine; Bradley, Paul Andrew

2015-08-17

The NASA Kepler spacecraft data revealed a large number of new multimode nonradially pulsating gamma Dor and delta Sct variable stars. The Kepler high-precision long time-series photometry makes it possible to study amplitude variations of the frequencies, and recent literature on amplitude and frequency variations in nonradially pulsating variables is summarized. Several methods are applied to study amplitude variability in about a dozen gamma Doradus or delta Scuti candidate variable stars observed for several quarters as part of the Kepler Guest Observer program. The magnitude and timescale of the amplitude variations are discussed, along with the presence or absence ofmore » correlations between amplitude variations for different frequencies of a given star. Proposed causes of amplitude spectrum variability that will require further investigation are also discussed.« less

Overview of the observations of symbiotic stars

NASA Technical Reports Server (NTRS)

Viotti, Roberto

1993-01-01

The term Symbiotic stars commonly denotes variable stars whose optical spectra simultaneously present a cool absorption spectrum (typically TiO absorption bands) and emission lines of high ionization energy. This term is now used for the category of variable stars with composite spectrum. The main spectral features of these objects are: (1) the presence of the red continuum typical of a cool star, (2) the rich emission line spectrum, and (3) the UV excess, frequently with the Balmer continuum in emission. In addition to the peculiar spectrum, the very irregular photometric and spectroscopic variability is the major feature of the symbiotic stars. Moreover, the light curve is basic to identify the different phases of activity in a symbiotic star. The physical mechanisms that cause the symbiotic phenomenon and its variety are the focus of this paper. An astronomical phenomenon characterized by a composite stellar spectrum with two apparently conflicting features, and large variability has been observed. Our research set out to find the origin of this behavior and, in particular, to identify and measure the physical mechanism(s) responsible for the observed phenomena.

HST/COS detection of a Ne VIII absorber towards PG 1407+265: an unambiguous tracer of collisionally ionized hot gas?

NASA Astrophysics Data System (ADS)

Hussain, T.; Muzahid, S.; Narayanan, A.; Srianand, R.; Wakker, B. P.; Charlton, J. C.; Pathak, A.

2015-01-01

We report the detection of Ne VIII in a zabs = 0.599 61 absorber towards the QSO PG1407+265 (zem= 0.94). Besides Ne VIII, absorption from H I Lyman series lines (H I λ1025-λ915), several other low (C II, N II, O II and S II), intermediate (C III, N III, N IV, O III, S IV and S V) and high (S VI, O VI and Ne VIII) ionization metal lines are detected. Disparity in the absorption line kinematics between different ions implies that the absorbing gas comprises of multiple ionization phases. The low and the intermediate ions (except S V) trace a compact (˜410 pc), metal-rich (Z ˜ Z⊙) and overdense (log nH ˜ -2.6) photoionized region that sustained star formation for a prolonged period. The high ions, Ne VIII and O VI, can be explained as arising in a low density (-5.3 ≤ log nH ≤ -5.0), metal-rich (Z ≳ Z⊙) and diffuse (˜180 kpc) photoionized gas. The S V, S VI and C IV [detected in the Faint Object Spectrograph (FOS) spectrum] require an intermediate photoionization phase with -4.2 < log nH < -3.5. Alternatively, a pure collisional ionization model, as used to explain the previous known Ne VIII absorbers, with 5.65 < log T < 5.72, can reproduce the S VI, O VI and Ne VIII column densities simultaneously in a single phase. However, even such models require an intermediate phase to reproduce any observable S V and/or C IV. Therefore, we conclude that when multiple phases are present, the presence of Ne VIII is not necessarily an unambiguous indication of collisionally ionized hot gas.

Gaia luminosities of pulsating A-F stars in the Kepler field

NASA Astrophysics Data System (ADS)

Balona, L. A.

2018-06-01

All stars in the Kepler field brighter than 12.5 magnitude have been classified according to variability type. A catalogue of δ Scuti and γ Doradus stars is presented. The problem of low frequencies in δ Sct stars, which occurs in over 98 percent of these stars, is discussed. Gaia DR2 parallaxes were used to obtain precise luminosities, enabling the instability strips of the two classes of variable to be precisely defined. Surprisingly, it turns out that the instability region of the γ Dor stars is entirely within the δ Sct instability strip. Thus γDor stars should not be considered a separate class of variable. The observed red and blue edges of the instability strip do not agree with recent model calculations. Stellar pulsation occurs in less than half of the stars in the instability region and arguments are presented to show that this cannot be explained by assuming pulsation at a level too low to be detected. Precise Gaia DR2 luminosities of high-amplitude δ Sct stars (HADS) show that most of these are normal δ Sct stars and not transition objects. It is argued that current ideas on A star envelopes need to be revised.

New Variable Stars found in the NSVS Database

NASA Astrophysics Data System (ADS)

Nicholson, Martin; Sutherland, Jane; Sutherland, Charles

2005-12-01

A search for previously unreported variable stars was conducted by members of the Remote Astronomical Society in the publicly available data of the Northern Sky Variability Survey (NSVS, Wozniak et al., 2004). NSVS fields were searched for candidates with both a sufficient number of observations to allow valid analysis and also with a significantly higher magnitude scatter than normal for stars of their magnitude.

Deformation quantization with separation of variables of an endomorphism bundle

NASA Astrophysics Data System (ADS)

Karabegov, Alexander

2014-01-01

Given a holomorphic Hermitian vector bundle E and a star-product with separation of variables on a pseudo-Kähler manifold, we construct a star product on the sections of the endomorphism bundle of the dual bundle E∗ which also has the appropriately generalized property of separation of variables. For this star product we prove a generalization of Gammelgaard's graph-theoretic formula.

Box-Behnken methodology for Cr (VI) and leather dyes removal by an eco-friendly biosorbent: F. vesiculosus.

PubMed

Cobas, M; Sanromán, M A; Pazos, M

2014-05-01

This study focused on leather industrial effluents treatment by biosorption using Fucus vesiculosus as low-cost adsorbent. These effluents are yellowish-brown color and high concentration of Cr (VI). Therefore, biosorption process was optimized using response surface methodology based on Box-Behnken design operating with a simulated leather effluent obtained by mixture of Cr (VI) solution and four leather dyes. The key variables selected were initial solution pH, biomass dosage and CaCl2 concentration in the pretreatment stage. The statistical analysis shows that pH has a negligible effect, being the biomass dosage and CaCl2 concentration the most significant variables. At optimal conditions, 98% of Cr (VI) and 88% of dyes removal can be achieved. Freundlich fitted better to the obtained equilibrium data for all studied systems than Temkin, Langmuir or D-R models. In addition, the use of the final biosorbent as support-substrate to grown of enzyme producer fungi, Pleurotus ostreatus, was also demonstrated. Copyright © 2014 Elsevier Ltd. All rights reserved.

Be Star Hα Line Profile Variability

NASA Astrophysics Data System (ADS)

Austin, S. J.; Dunlap, B.; Franklin, M.; Hoggard, T.; Hoskins, J. S.

2004-12-01

The monitoring of the spectroscopic variability of Be stars is crucial for testing Be star models. Motivated by this, a Be star monitoring project was developed for undergraduate student research involvement. We have been obtaining 0.8 Angstrom/pixel resolution Hα line profiles for several bright Be stars since 2003 June. These spectra were acquired using the UCA Fiber Fed Spectrograph used at the UCA Observatory and the Nubbin Ridge Observatory in Royal, AR. H-α line profiles, velocities, and variability are shown for Delta Sco, Chi Oph, Eta PsA, 48 Lib, and Upsilon Sgr (HD181615). Funding has been provided by the UCA University Research Council and the Arkansas Space Grant Consortium.

A census of variability in globular cluster M 68 (NGC 4590)

NASA Astrophysics Data System (ADS)

Kains, N.; Arellano Ferro, A.; Figuera Jaimes, R.; Bramich, D. M.; Skottfelt, J.; Jørgensen, U. G.; Tsapras, Y.; Street, R. A.; Browne, P.; Dominik, M.; Horne, K.; Hundertmark, M.; Ipatov, S.; Snodgrass, C.; Steele, I. A.; Lcogt/Robonet Consortium; Alsubai, K. A.; Bozza, V.; Calchi Novati, S.; Ciceri, S.; D'Ago, G.; Galianni, P.; Gu, S.-H.; Harpsøe, K.; Hinse, T. C.; Juncher, D.; Korhonen, H.; Mancini, L.; Popovas, A.; Rabus, M.; Rahvar, S.; Southworth, J.; Surdej, J.; Vilela, C.; Wang, X.-B.; Wertz, O.; Mindstep Consortium

2015-06-01

Aims: We analyse 20 nights of CCD observations in the V and I bands of the globular cluster M 68 (NGC 4590) and use them to detect variable objects. We also obtained electron-multiplying CCD (EMCCD) observations for this cluster in order to explore its core with unprecedented spatial resolution from the ground. Methods: We reduced our data using difference image analysis to achieve the best possible photometry in the crowded field of the cluster. In doing so, we show that when dealing with identical networked telescopes, a reference image from any telescope may be used to reduce data from any other telescope, which facilitates the analysis significantly. We then used our light curves to estimate the properties of the RR Lyrae (RRL) stars in M 68 through Fourier decomposition and empirical relations. The variable star properties then allowed us to derive the cluster's metallicity and distance. Results: M 68 had 45 previously confirmed variables, including 42 RRL and 2 SX Phoenicis (SX Phe) stars. In this paper we determine new periods and search for new variables, especially in the core of the cluster where our method performs particularly well. We detect 4 additional SX Phe stars and confirm the variability of another star, bringing the total number of confirmed variable stars in this cluster to 50. We also used archival data stretching back to 1951 to derive period changes for some of the single-mode RRL stars, and analyse the significant number of double-mode RRL stars in M 68. Furthermore, we find evidence for double-mode pulsation in one of the SX Phe stars in this cluster. Using the different classes of variables, we derived values for the metallicity of the cluster of [Fe/H] = -2.07 ± 0.06 on the ZW scale, or -2.20 ± 0.10 on the UVES scale, and found true distance moduli μ0 = 15.00 ± 0.11 mag (using RR0 stars), 15.00 ± 0.05 mag (using RR1 stars), 14.97 ± 0.11 mag (using SX Phe stars), and 15.00 ± 0.07 mag (using the MV -[Fe/H] relation for RRL stars), corresponding to physical distances of 10.00 ± 0.49, 9.99 ± 0.21, 9.84 ± 0.50, and 10.00 ± 0.30 kpc, respectively. Thanks to the first use of difference image analysis on time-series observations of M 68, we are now confident that we have a complete census of the RRL stars in this cluster. The full Table 2 is only 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/578/A128

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First Detection of Krypton and Xenon in a White Dwarf

NASA Technical Reports Server (NTRS)

Werner, Klaus; Rauch, Thomas; Ringat, Ellen; Kruk, Jeffrey W.

2012-01-01

We report on the first detection of the noble gases krypton (Z = 36) and xenon (54) in a white dwarf. About 20 KrVI-VII and Xe VI-VII lines were discovered in the ultraviolet spectrum of the hot DO-type white dwarf RE 0503-289. The observations, performed with the Far Ultraviolet Spectroscopic Explorer, also reveal highly ionized photospheric lines from other trans-iron group elements, namely Ga (31), Ge (32), As (33), Se (34), Mo (42), Sn (50), Te (52), and I (53), from which gallium and molybdenum are new discoveries in white dwarfs, too. For Kr and Xe, we performed an NLTE analysis and derived mass fractions of log Kr = -4.3 plus or minus 0.5 and log Xe = -4.2 plus or minus 0.6, corresponding to an enrichment by factors of 450 and 3800, respectively, relative to the Sun. The origin of the large overabundances is unclear. We discuss the roles of neutron-capture nucleosynthesis in the-precursor star and radiation-driven diffusion. It is possible that diffusion is insignificant and thaI the observed metal abundances constrain the evolutionary history of the star. Its hydrogen deficiency may be the consequence of a late helium-shell nash or a binary white dwarf merger.

Chromospheric activity of periodic variable stars (including eclipsing binaries) observed in DR2 LAMOST stellar spectral survey

NASA Astrophysics Data System (ADS)

Zhang, Liyun; Lu, Hongpeng; Han, Xianming L.; Jiang, Linyan; Li, Zhongmu; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Cao, Zihuang

2018-05-01

The LAMOST spectral survey provides a rich databases for studying stellar spectroscopic properties and chromospheric activity. We cross-matched a total of 105,287 periodic variable stars from several photometric surveys and databases (CSS, LINEAR, Kepler, a recently updated eclipsing star catalogue, ASAS, NSVS, some part of SuperWASP survey, variable stars from the Tsinghua University-NAOC Transient Survey, and other objects from some new references) with four million stellar spectra published in the LAMOST data release 2 (DR2). We found 15,955 spectra for 11,469 stars (including 5398 eclipsing binaries). We calculated their equivalent widths (EWs) of their Hα, Hβ, Hγ, Hδ and Caii H lines. Using the Hα line EW, we found 447 spectra with emission above continuum for a total of 316 stars (178 eclipsing binaries). We identified 86 active stars (including 44 eclipsing binaries) with repeated LAMOST spectra. A total of 68 stars (including 34 eclipsing binaries) show chromospheric activity variability. We also found LAMOST spectra of 12 cataclysmic variables, five of which show chromospheric activity variability. We also made photometric follow-up studies of three short period targets (DY CVn, HAT-192-0001481, and LAMOST J164933.24+141255.0) using the Xinglong 60-cm telescope and the SARA 90-cm and 1-m telescopes, and obtained new BVRI CCD light curves. We analyzed these light curves and obtained orbital and starspot parameters. We detected the first flare event with a huge brightness increase of more than about 1.5 magnitudes in R filter in LAMOST J164933.24+141255.0.

Hereditary motor and sensory neuropathy type VI with optic atrophy.

PubMed

Voo, Irene; Allf, Bryan E; Udar, Nitin; Silva-Garcia, Rosamaria; Vance, Jeffrey; Small, Kent W

2003-10-01

To present the detailed clinical findings of a large family with hereditary motor and sensory neuropathy type VI (HMSN VI), a syndrome featuring optic atrophy. Observational case series. A detailed history was obtained and physical examination was made of the extended family of the proband for evidence of neurologic dysfunction. The OPA1 gene was screened for mutations by direct DNA sequencing. Twelve of 97 family members examined are affected with signs of HMSN VI. Three other members have either optic atrophy or peripheral neuropathy, thus allowing an appreciation of the full clinical spectrum of disease. No mutations were found in the OPA1 gene. This family demonstrates the variable expressivity of this disorder as well as incomplete penetrance. This is the largest known family with HMSN VI. No association was found with changes in the OPA1 gene.

Smearing model and restoration of star image under conditions of variable angular velocity and long exposure time.

PubMed

Sun, Ting; Xing, Fei; You, Zheng; Wang, Xiaochu; Li, Bin

2014-03-10

The star tracker is one of the most promising attitude measurement devices widely used in spacecraft for its high accuracy. High dynamic performance is becoming its major restriction, and requires immediate focus and promotion. A star image restoration approach based on the motion degradation model of variable angular velocity is proposed in this paper. This method can overcome the problem of energy dispersion and signal to noise ratio (SNR) decrease resulting from the smearing of the star spot, thus preventing failed extraction and decreased star centroid accuracy. Simulations and laboratory experiments are conducted to verify the proposed methods. The restoration results demonstrate that the described method can recover the star spot from a long motion trail to the shape of Gaussian distribution under the conditions of variable angular velocity and long exposure time. The energy of the star spot can be concentrated to ensure high SNR and high position accuracy. These features are crucial to the subsequent star extraction and the whole performance of the star tracker.

A precursive study of the time-domain survey of the Galactic Anti-center using the Nanshan 1-meter telescope with variable stars detected

NASA Astrophysics Data System (ADS)

Ma, Shu-Guo; Esamdin, Ali; Ma, Lu; Niu, Hu-Biao; Fu, Jian-Ning; Zhang, Yu; Liu, Jin-Zhong; Yang, Tao-Zhi; Song, Fang-Fang; Pu, Guang-Xin

2018-04-01

Following the LAMOST Spectroscopic Survey and the Xuyi's Photometric Survey of the Galactic Anti-center, we plan to carry out a time-domain survey of the Galactic Anti-center (TDS-GAC) to study variable stars by using the Nanshan 1-meter telescope. Before the beginning of TDS-GAC, a precursive sky survey (PSS) has been executed. The goal of the PSS is to optimize the observation strategy of TDS-GAC and to detect some strong transient events, as well as to find some short time-scale variable stars of different types. By observing a discontinuous sky area of 15.03 deg2 with the standard Johnson-Cousin-Bessel V filter, 48 variable stars are found and the time series are analyzed. Based on the behaviors of the light curves, 28 eclipsing binary stars, 10 RR Lyraes, 3 periodic pulsating variables of other types have been classified. The rest 7 variables stay unclassified with deficient data. In addition, the observation strategy of TD-GAC is described, and the pipeline of data reduction is tested.

Eight to 14 μm spectral monitoring of long period variable stars with GLADYS.

NASA Astrophysics Data System (ADS)

Levan, P. D.; Sloan, G.; Grasdalen, G.

The authors describe an ongoing program of spectral monitoring of long period variable stars using GLADYS, a long slit prism spectrometer that employs a 58x62 pixel Si:Ga detector array. The goal is to compare the equivalent widths of the SiC emission features in carbon-rich circumstellar shells, and the silicate emission features in oxygen-rich circumstellar stars, obtained over different phases of the continuum variability cycle. Spectra of long period variables and low amplitude variables recently obtained on the Wyoming Infrared Observatory 2.3 m telescope are presented.

Pre-main sequence variables in young cluster Stock 18

NASA Astrophysics Data System (ADS)

Sinha, Tirthendu; Sharma, Saurabh; Pandey, Rakesh; Pandey, Anil Kumar

2018-04-01

We have carried out multi-epoch deep I band photometry of the open cluster Stock 18 to search for variable stars in star forming regions. In the present study, we identified 65 periodic and 217 non-periodic variable stars. The periods of most of the periodic variables are between 2 hours to 15 days and their magnitude varies between 0.05 to 0.6 mag. We have derived spectral energy distributions for 48 probable pre-main sequence variables. Their average age and mass are 2.7 ± 0.3 Myrs and 2.7 ± 0.2 Mo, respectively.

ZZ Canis Minoris as a symbiotic star

NASA Technical Reports Server (NTRS)

Bopp, B. W.

1984-01-01

The H-aplha and Na I D-line regions of the M6 giant star ZZ Canis Minoris (ZZ CMi) were observed with the Kitt Peak coude feed telescope and a CCD detector. It is shown that ZZ CMi has similar spectroscopic and photoproperties to the symbiotic star EG And. The data are used to argue for the classification of ZZ CMi as a symbiotic star despite its current listing in the General Catalog of Variable Stars (GCVS) as a semi-regular variable. The infrared magnitudes of ZZ CMi and the known symbiotic stars are compared in a table.

RR Lyrae in the UMi dSph Galaxy

NASA Astrophysics Data System (ADS)

Kuehn, Charles; Kinemuchi, Karen; Jeffery, Elizabeth; Grabowski, Kathleen; Nemec, James; Herrera, Daniel

2018-01-01

Over the past two years we have obtained observations of the Ursa Minor dwarf spheroidal galaxy with the goal of completing an updated catalog of the variable stars in the dwarf galaxy. In addition to finding new variable stars, this updated catalog will allow us to look at period changes in the variables and to determine stellar characteristic for the RR Lyrae stars in the dSph. We will compare the RR Lyrae stellar characteristics to other RR Lyrae stars found in the Local Group dSph galaxies; these comparisons can give us insights to the near-field cosmology of the Local Group. In this poster we present our updated catalog of RR Lyrae stars in the UMi dSph; the updated catalog includes Fourier decomposition parameters, metallicities, and other physical properties for the RR Lyrae stars.

The Optical Gravitational Lensing Experiment. Catalog of RR Lyr Stars in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

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

2003-06-01

We present the catalog of RR Lyr stars discovered in a 4.5 square degrees area in the central parts of the Large Magellanic Cloud (LMC). Presented sample contains 7612 objects, including 5455 fundamental mode pulsators (RRab), 1655 first-overtone (RRc), 272 second-overtone (RRe) and 230 double-mode RR Lyr stars (RRd). Additionally we attach alist of several dozen other short-period pulsating variables. The catalog data include astrometry, periods, BVI photometry, amplitudes, and parameters of the Fourier decomposition of the I-band light curve of each object. We present density map of RR Lyr stars in the observed fields which shows that the variables are strongly concentrated toward the LMC center. The modal values of the period distribution for RRab, RRc and RRe stars are 0.573, 0.339 and 0.276 days, respectively. The period-luminosity diagrams for BVI magnitudes and for extinction insensitive index W_I are constructed. We provide the log P-I, log P-V and log P-W_I relations for RRab, RRc and RRe stars. The mean observed V-band magnitudes of RR Lyr stars in the LMC are 19.36 mag and 19.31 mag for ab and c types, respectively, while the extinction free values are 18.91 mag and 18.89 mag. We found a large number of RR Lyr stars pulsating in two modes closely spaced in the power spectrum. These stars are believed to exhibit non-radial pulsating modes. We discovered three stars which simultaneously reveal RR Lyr-type and eclipsing-type variability. If any of these objects were an eclipsing binary system containing RR Lyr star, then for the first time the direct determination of the mass of RR Lyr variable would be possible. We provide a list of six LMC star clusters which contain RR Lyr stars. The richest cluster, NGC 1835, hosts 84 RR Lyr variables. The period distribution of these stars suggests that NGC1835 shares features of Oosterhoff type I and type II groups. All presented data, including individual BVI observations and finding charts are available from the OGLE Internet archive.

A SPECTROPOLARIMETRIC TEST OF THE STRUCTURE OF THE INTRINSIC ABSORBERS IN THE QUASAR HS 1603+3820

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

Misawa, Toru; Kawabata, Koji S.; Eracleous, Michael

We report the results of a spectropolarimetric observation of the C VI 'mini-broad' absorption line (mini-BAL) in the quasar HS 1603+3820 (z {sub em} = 2.542). The observations were carried out with the FOCAS instrument on the Subaru Telescope and yielded an extremely high polarization sensitivity of {delta}p{approx} 0.1%, at a resolving power of R {approx} 1500. HS 1603+3820 has been the target of a high-resolution spectroscopic monitoring campaign for more than four years, aimed at studying its highly variable C VI mini-BAL profile. Using the monitoring observations in an earlier paper, we were able to narrow down the causesmore » of the variability to the following two scenarios: (1) scattering material of variable optical depth redirecting photons around the absorber and (2) a variable, highly ionized screen between the continuum source and the absorber which modulates the UV continuum incident on the absorber. The observations presented here provide a crucial test of the scattering scenario and lead us to disfavor it because (1) the polarization level is very small (p {approx} 0.6%) throughout the spectrum and (2) the polarization level does not increase across the mini-BAL trough. Thus, the variable screen scenario emerges as our favored explanation of the C VI mini-BAL variability. Our conclusion is bolstered by recent X-ray observations of nearby mini-BAL quasars, which show a rapidly variable soft X-ray continuum that appears to be the result of transmission through an ionized absorber of variable ionization parameter and optical depth.« less

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.

The TAROT Suspected Variable Star Catalog

NASA Astrophysics Data System (ADS)

Damerdji, Y.; Klotz, A.; Boër, M.

2007-04-01

TAROT (Télescope à Action Rapide pour les Objets Transitoires) is a robotic observatory designed to observe very early optical transients of gamma-ray bursts (GRBs). As GRBs do not often occur, we use TAROT for various other celestial targets spread over the sky. For every field observed by TAROT, we computed the magnitudes of every star. From this work, we found 1175 new variable stars brighter than 17 mag. We selected the best variable star candidates and compiled them in the TSVSC1 (TAROT Suspected Variable Star Catalog, ver. 1), which also contains Fourier-series coefficients that fit the light curves. Based on observations collected with the TAROT instrument at the Calern Observatory, France. Complementary observations were carried out with the T80 telescope at the Observatoire de Haute-Provence, France. Additional material described in § 5 is available in electronic format at the CDS at http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/AJ/.

An ultraviolet study of B[e] stars: evidence for pulsations, luminous blue variable type variations and processes in envelopes

NASA Astrophysics Data System (ADS)

Krtičková, I.; Krtička, J.

2018-06-01

Stars that exhibit a B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including the presence of Balmer lines in emission, forbidden lines and strong infrared excess due to dust. Observations of emission lines indicate illumination by an ultraviolet ionizing source, which is key to understanding the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from the Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and the correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including light absorption by the disc, pulsations, luminous blue variable type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is present not only in the disc but also above its plane. The flux and line variability is consistent with a two-component model of a circumstellar environment composed of a dense disc and an ionized envelope. Observations of B[e] supergiants show that many of these stars have nearly the same luminosity, about 1.9 × 105 L⊙, and similar effective temperatures.

Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades

NASA Astrophysics Data System (ADS)

White, T. R.; Pope, B. J. S.; Antoci, V.; Pápics, P. I.; Aerts, C.; Gies, D. R.; Gordon, K.; Huber, D.; Schaefer, G. H.; Aigrain, S.; Albrecht, S.; Barclay, T.; Barentsen, G.; Beck, P. G.; Bedding, T. R.; Fredslund Andersen, M.; Grundahl, F.; Howell, S. B.; Ireland, M. J.; Murphy, S. J.; Nielsen, M. B.; Silva Aguirre, V.; Tuthill, P. G.

2017-11-01

The most powerful tests of stellar models come from the brightest stars in the sky, for which complementary techniques, such as astrometry, asteroseismology, spectroscopy and interferometry, can be combined. The K2 mission is providing a unique opportunity to obtain high-precision photometric time series for bright stars along the ecliptic. However, bright targets require a large number of pixels to capture the entirety of the stellar flux, and CCD saturation, as well as restrictions on data storage and bandwidth, limit the number and brightness of stars that can be observed. To overcome this, we have developed a new photometric technique, which we call halo photometry, to observe very bright stars using a limited number of pixels. Halo photometry is simple, fast and does not require extensive pixel allocation, and will allow us to use K2 and other photometric missions, such as TESS, to observe very bright stars for asteroseismology and to search for transiting exoplanets. We apply this method to the seven brightest stars in the Pleiades open cluster. Each star exhibits variability; six of the stars show what are most likely slowly pulsating B-star pulsations, with amplitudes ranging from 20 to 2000 ppm. For the star Maia, we demonstrate the utility of combining K2 photometry with spectroscopy and interferometry to show that it is not a `Maia variable', and to establish that its variability is caused by rotational modulation of a large chemical spot on a 10 d time-scale.

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.

Combinations of Response-Dependent and Response-Independent Schedule-Correlated Stimulus Presentation in an Observing Procedure

ERIC Educational Resources Information Center

DeFulio, Anthony; Hackenberg, Timothy D.

2008-01-01

Pigeons pecked a response key on a variable-interval (VI) schedule, in which responses produced food every 40 s, on average. These VI periods, or components, alternated in irregular fashion with extinction components in which food was unavailable. Pecks on a second (observing) key briefly produced exteroceptive stimuli (houselight flashes)…

Synergies between exoplanet surveys and variable star research

NASA Astrophysics Data System (ADS)

Kovacs, Geza

2017-09-01

With the discovery of the first transiting extrasolar planetary system back in 1999, a great number of projects started to hunt for other similar systems. Because the incidence rate of such systems was unknown and the length of the shallow transit events is only a few percent of the orbital period, the goal was to monitor continuously as many stars as possible for at least a period of a few months. Small aperture, large field of view automated telescope systems have been installed with a parallel development of new data reduction and analysis methods, leading to better than 1% per data point precision for thousands of stars. With the successful launch of the photometric satellites CoRoT and Kepler, the precision increased further by one-two orders of magnitude. Millions of stars have been analyzed and searched for transits. In the history of variable star astronomy this is the biggest undertaking so far, resulting in photometric time series inventories immensely valuable for the whole field. In this review we briefly discuss the methods of data analysis that were inspired by the main science driver of these surveys and highlight some of the most interesting variable star results that impact the field of variable star astronomy.

Locating the Accretion Footprint on a Herbig Ae Star: MWC 480

NASA Technical Reports Server (NTRS)

Grady, C. A.; Hamaguchi, K.; Schneider, G.; Stecklum, B.; Woodgate, B. E.; McCleary, J. E.; Williger, G. M.; Sitko, M. L.; Menard, F.; Henning, Th.;

The Bulgarian Contribution to the Study of variable stars on observational data from the Kepler mission

NASA Astrophysics Data System (ADS)

Kjurkchieva, D. P.; Dimitrov, D. P.; Radeva, V. S.; Vasileva, D. L.; Atanasova, T. V.; Stateva, I. V.; Petrov, N. I.; Iliev, I. Kh.

2018-02-01

This review paper presents the results of investigations of variable stars obtained by Bulgarian astronomers based on observations of Kepler mission. The main contributions are: determination of orbits and global parameters of more than 100 binary stars; creation of the largest catalog of eccentric stars; identification of sixty new binaries with eccentricity over 0.5; discovery of 19 heartbeat stars; detailed investigation of the spot and flare activity of several binary stars; asteroseismic study of three pulsating stars; detection of deep transits of WD 1145+017 due to its disentangling planet system. The paper illustrates not only scientific significance but also educational and social impact of the work on these tasks.

Report on the Photometric Observations of the Variable Stars DH Pegasi, DY Pegasi, and RZ Cephei

NASA Astrophysics Data System (ADS)

Abu-Sharkh, I.; Fang, S.; Mehta, S.; Pham, D.

2014-12-01

We report 872 observations on two RR Lyrae variable stars, DH Pegasi and RZ Cephei, and on one SX Phoenicis variable, DY Pegasi. This paper discusses the methodology of our measurements, the light curves, magnitudes, epochs, and epoch prediction of the above stars. We also derived the period of DY Pegasi. All measurements and analyses are compared with prior publications and known values from multiple databases.

Searching for Variable Stars in the SDSS Calibration Fields (Abstract)

NASA Astrophysics Data System (ADS)

Smith, J. A.; Butner, M.; Tucker, D.; Allam, S.

2018-06-01

(Abstract only) We are searching the Sloan Digital Sky Survey (SDSS) calibration fields for variable stars. This long neglected data set, taken with a 0.5-m telescope, contains nearly 200,000 stars in more than 100 fields which were observed over the course of 8+ years during the observing portion of the SDSS-I and SDSS-II surveys. During the course of the survey, each field was visited from 10 to several thousand times, so our initial pass is just to identify potential variable stars. Our initial "quick-look" effort shows several thousand potential candidates and includes at least one nearby supernova. We present our plans for a follow-up observational program for further identification of variable types and period determinations.

A survey for pulsations in A-type stars using SuperWASP

NASA Astrophysics Data System (ADS)

Holdsworth, Daniel L.

2015-12-01

"It is sound judgement to hope that in the not too distant future we shall be competent to understand so simple a thing as a star." - Sir Arthur Stanley Eddington, The Internal Constitution of Stars, 1926 A survey of A-type stars is conducted with the SuperWASP archive in the search for pulsationally variable stars. Over 1.5 million stars are selected based on their (J-H) colour. Periodograms are calculated for light curves which have been extracted from the archive and cleaned of spurious points. Peaks which have amplitudes greater than 0.5 millimagnitude are identified in the periodograms. In total, 202 656 stars are identified to show variability in the range 5-300 c/d. Spectroscopic follow-up was obtained for 38 stars which showed high-frequency pulsations between 60 and 235 c/d, and a further object with variability at 636 c/d. In this sample, 13 were identified to be normal A-type δ Sct stars, 14 to be pulsating metallic-lined Am stars, 11 to be rapidly oscillating Ap (roAp) stars, and one to be a subdwarf B variable star. The spectra were used not only to classify the stars, but to determine an effective temperature through Balmer line fitting. Hybrid stars have been identified in this study, which show pulsations in both the high- and low-overtone domains; an observation not predicted by theory. These stars are prime targets to perform follow-up observations, as a confirmed detection of this phenomenon will have significant impact on the theory of pulsations in A-type stars. The detected number of roAp stars has expanded the known number of this pulsator class by 22 per cent. Within these results both the hottest and coolest roAp star have been identified. Further to this, one object, KIC 7582608, was observed by the Kepler telescope for 4 yr, enabling a detailed frequency analysis. This analysis has identified significant frequency variations in this star, leading to the hypothesis that this is the first close binary star of its type. The observational results presented in this thesis are able to present new challenges to the theory of pulsations in A-type stars, with potentially having the effect of further delaying the full understanding of 'so simple a thing as a star'.

VizieR Online Data Catalog: Abundances of 8 RR Lyrae subclass C variable stars (Govea+, 2014)

NASA Astrophysics Data System (ADS)

Govea, J.; Gomez, T.; Preston, G. W.; Sneden, C.

2016-02-01

We chose 10 candidate RR Lyrae variable stars of subclass c (RRc) stars for spectroscopic observation. Many of these stars were first identified as RRc variables by the All Sky Automated Survey (ASAS) of Pojmanski 2003 (cat. II/264). The target star list included ASAS 144154-0324.7 and ASAS 204440-2402.7. But our spectroscopic study suggest that these two stars are probably W UMa binaries instead of RR Lyrae stars Our spectra were obtained with the echelle spectrograph of the du Pont 2.5m telescope at the Las Campanas Observatory. Four observing runs during 2009-2010 were partly devoted to this project. The spectrograph was used with the 1.5*4'' entrance slit, which translates to a resolving power of R=λ/Δλ~27000 at the MgI b lines near 5180Å. The total continuous wavelength coverage of the spectra was 3500-9000Å. (6 data files).

The IUE Mega Campaign: Wind Variability and Rotation in Early-Type Stars

NASA Technical Reports Server (NTRS)

Massa, D.; Fullerton, A. W.; Nichols, J. S.; Owocki, S. P.; Prinja, R. K.; St-Louis, N.; Willis, A. J.; Altner, B.; Bolton, C. T.; Cassinelli, J. P.;

Upscaling of U (VI) desorption and transport from decimeter‐scale heterogeneity to plume‐scale modeling

USGS Publications Warehouse

Curtis, Gary P.; Kohler, Matthias; Kannappan, Ramakrishnan; Briggs, Martin A.; Day-Lewis, Frederick D.

2015-01-01

Scientifically defensible predictions of field scale U(VI) transport in groundwater requires an understanding of key processes at multiple scales. These scales range from smaller than the sediment grain scale (less than 10 μm) to as large as the field scale which can extend over several kilometers. The key processes that need to be considered include both geochemical reactions in solution and at sediment surfaces as well as physical transport processes including advection, dispersion, and pore-scale diffusion. The research summarized in this report includes both experimental and modeling results in batch, column and tracer tests. The objectives of this research were to: (1) quantify the rates of U(VI) desorption from sediments acquired from a uranium contaminated aquifer in batch experiments;(2) quantify rates of U(VI) desorption in column experiments with variable chemical conditions, and(3) quantify nonreactive tracer and U(VI) transport in field tests.

Hearing Color

NASA Astrophysics Data System (ADS)

Bieryla, Allyson; Diaz Merced, Wanda; Davis, Daniel

2018-06-01

In astronomy, the relationship between color and temperature is an important concept. This concept can be demonstrated in a laboratory or seen at telescope when observing stars. A blind/visually-impaired (B/VI) person would not be able to engage in the same observational demonstrations that are typically done to explain this concept. We’ve developed a tool for B/VI students to participate in these types of observational activities. Using an arduino compatible micro controller with and RGB light sensor, we are able to convert filtered light into sound. The device will produce different timbres for different wavelengths of light, which can then be used to distinguish the temperature of an object. The device is handheld, easy to program and inexpensive to reproduce (< $50). It is also fitted to mount on a telescope for observing. The design schematic and code will be open source and available for download.

Variable Circumstellar Disks of Classical Be Stars in Clusters

NASA Astrophysics Data System (ADS)

Gerhartz, C.; Bjorkman, K. S.; Bjorkman, J. E.; Wisniewski, J. P.

2016-11-01

Circumstellar disks are common among many stars, at most spectral types, and at different stages of their lifetimes. Among the near-main-sequence classical Be stars, there is growing evidence that these disks form, dissipate, and reform on timescales that differ from star to star. Using data obtained with the Large Monolithic Imager (LMI) at the Lowell Observatory Discovery Channel Telescope (DCT), along with additional complementary data obtained at the University of Toledo Ritter Observatory (RO), we have begun a long-term monitoring project of a well-studied set of galactic star clusters that are known to contain Be stars. Our goal is to develop a statistically significant sample of variable circumstellar disk systems over multiple timescales. With a robust multi-epoch study we can determine the relative fraction of Be stars that exhibit disk-loss or disk-renewal phases, and investigate the range of timescales over which these events occur. A larger sample will improve our understanding of the prevalence and nature of the disk variability, and may provide insight about underlying physical mechanisms.

Assessment of the effect of visual impairment on mortality through multiple health pathways: structural equation modeling.

PubMed

Christ, Sharon L; Lee, David J; Lam, Byron L; Zheng, D Diane; Arheart, Kristopher L

2008-08-01

To estimate the direct effects of self-reported visual impairment (VI) on health, disability, and mortality and to estimate the indirect effects of VI on mortality through health and disability mediators. The National Health Interview Survey (NHIS) is a population-based annual survey designed to be representative of the U.S. civilian noninstitutionalized population. The National Death Index of 135,581 NHIS adult participants, 18 years of age and older, from 1986 to 1996 provided the mortality linkage through 2002. A generalized linear structural equation model (GSEM) with latent variable was used to estimate the results of a system of equations with various outcomes. Standard errors and test statistics were corrected for weighting, clustering, and stratification. VI affects mortality, when direct adjustment was made for the covariates. Severe VI increases the hazard rate by a factor of 1.28 (95% CI: 1.07-1.53) compared with no VI, and some VI increases the hazard by a factor of 1.13 (95% CI: 1.07-1.20). VI also affects mortality indirectly through self-rated health and disability. The total effects (direct effects plus mediated effects) on the hazard of mortality of severe VI and some VI relative to no VI are hazard ratio (HR) 1.54 (95% CI: 1.28-1.86) and HR 1.23 (95% CI: 1.16-1.31), respectively. In addition to the direct link between VI and mortality, the effects of VI on general health and disability contribute to an increased risk of death. Ignoring the latter may lead to an underestimation of the substantive impact of VI on mortality.

Wide-Field Variability Survey of the Globular Cluster M 79 and a New Period-Luminosity Relation for SX Phe Stars

NASA Astrophysics Data System (ADS)

Kopacki, G.

2015-03-01

We present the results of a search for variable stars in a 26×39 arcmin2 field around globular cluster M 79 (NGC 1904). The search was made by means of an extended version of image subtraction, which allows us to analyze in a uniform manner CCD frames obtained with different telescopes and cameras of different sizes and resolutions. The search resulted in finding 20 new variable stars, among which 13 are cluster members. The members include one new RR Lyr star of subtype c, three SX Phe stars, and nine variable red giants. We also show that V7 is a W Vir star with a period of 13.985 d. Revised mean periods of RRab and RRc stars, ab=0.71 d and c=0.34 d, respectively, and relative percentage of RRc stars, Nc/(Nab+Nc)=45% confirm that M 79 belongs to the Oosterhoff II group of globular clusters. The mean V magnitude of the horizontal branch of M 79 based on ten RR Lyr stars has been estimated to be VHB=RR=16.11±0.03 mag. In one RRc star, V9, light changes with three close frequencies were detected, indicating excitation of nonradial modes. An SX Phe star, V18, is a double-mode pulsator with two radial modes excited, fundamental and first overtone. Moreover, we have discovered two SX Phe or δ Sct stars and one W UMa type system, all likely field objects. We also studied the period-luminosity relation for SX Phe stars. Using 62 fundamental and fundamentalized periods of radial double-mode and high-amplitude SX Phe stars known in Galactic globular clusters, we have derived the slope and zero point of this relation to be, -3.3±0.27 and 2.68±0.03 mag (at log(P/d)=-1.24), respectively.

A photometric study of Be stars located in the seismology fields of COROT

NASA Astrophysics Data System (ADS)

Gutiérrez-Soto, J.; Fabregat, J.; Suso, J.; Lanzara, M.; Garrido, R.; Hubert, A.-M.; Floquet, M.

2007-12-01

Context: In preparation for the COROT mission, an exhaustive photometric study of Be stars located in the seismology fields of the mission has been performed. The very precise and long-time-spanned photometric observations gathered by the COROT satellite will give important clues on the origin of the Be phenomenon. Aims: The aim of this work is to find short-period variable Be stars located in the seismology fields of COROT, and to study and characterise their pulsational properties. Methods: Light curves obtained at the Observatorio de Sierra Nevada, together with data from Hipparcos and ASAS-3 for a total of 84 Be stars, were analysed in order to search for short-term variations. We applied standard Fourier techniques and non-linear least-square fitting to the time series. Results: We found 7 multiperiodic, 21 mono-periodic and 26 non-variable Be stars. Short-term variability was detected in 74% of early-type Be stars and in 31% of mid- to late-type Be stars. We show that non-radial pulsations are more frequent among Be stars than in slow-rotating B stars of the same spectral range. Appendix A is only available in electronic form at http://www.aanda.org

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.

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs. Variable star searches and new discoveries

NASA Astrophysics Data System (ADS)

Figuera Jaimes, R.; Bramich, D. M.; Skottfelt, J.; Kains, N.; Jørgensen, U. G.; Horne, K.; Dominik, M.; Alsubai, K. A.; Bozza, V.; Calchi Novati, S.; Ciceri, S.; D'Ago, G.; Galianni, P.; Gu, S.-H.; Harpsøe, K. B. W.; Haugbølle, T.; Hinse, T. C.; Hundertmark, M.; Juncher, D.; Korhonen, H.; Mancini, L.; Popovas, A.; Rabus, M.; Rahvar, S.; Scarpetta, G.; Schmidt, R. W.; Snodgrass, C.; Southworth, J.; Starkey, D.; Street, R. A.; Surdej, J.; Wang, X.-B.; Wertz, O.

2016-04-01

Aims: We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. Methods: Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. Results: The light curves of 12 541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center. Based on data collected by the MiNDSTEp team with the Danish 1.54m telescope at ESO's La Silla observatory in Chile.Full Table 1 is only available at 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/588/A128

ROTSE All-Sky Surveys for Variable Stars. I. Test Fields

NASA Astrophysics Data System (ADS)

Akerlof, C.; Amrose, S.; Balsano, R.; Bloch, J.; Casperson, D.; Fletcher, S.; Gisler, G.; Hills, J.; Kehoe, R.; Lee, B.; Marshall, S.; McKay, T.; Pawl, A.; Schaefer, J.; Szymanski, J.; Wren, J.

2000-04-01

The Robotic Optical Transient Search Experiment I (ROTSE-I) experiment has generated CCD photometry for the entire northern sky in two epochs nightly since 1998 March. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering roughly 2000 deg2, we identify 1781 periodic variable stars with mean magnitudes between mv=10.0 and mv=15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars.

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.

Exploración del catálogo de objetos en emisión H de Henize y All Sky Automated Survey: nuevas variables y tipos espectrales

NASA Astrophysics Data System (ADS)

Jaque Arancibia, M.; Barbá, R. H.; Collado, A.; Gamen, R.; Arias, J. I.

2016-08-01

Large astronomical surveys allow us to do systematic studies of stellar populations with significant statistical weight. In this study, we have cross-correlated the Henize's (1976) catalog of stellar sources with H emission-line with “The All Sky Automated Survey'' database. After the positional cross-matching we have found that 1402 of 1926 H sources have ASAS light-curves. From that number, more than 50 (723 sources) are periodic variables with amplitude larger than 0.05 magnitudes, while 276 sources show photometric variations without a clear periodicity. Variable stars that we have found are of many different types, among them Miras, eclipsing binaries, bursting stars, etc. Also, only 133 stars are known previously as variable sources in ASAS catalogue, and 93 of them were studied previously in detail. In order to characterize the nature of the sources, we have started a medium-resolution spectroscopic survey of the unstudied variable emission-line objects using the 2.15-m Jorge Sahade Telescope at Complejo Astronómico El Leoncito (Argentina). At the moment, we have observed a set of 67 blue stars selected using 2MASS colors, being almost all of them Be-type stars. This set of bright new variable Be-type stars is ideal for follow-up monitoring for the study of the Be-phenomenon.

THE AGE OF THE LOCAL INTERSTELLAR BUBBLE

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

Abt, Helmut A., E-mail: abt@noao.edu

2011-05-15

The Local Interstellar Bubble is an irregular region from 50 to 150 pc from the Sun in which the interstellar gas density is 10{sup -2}-10{sup -3} of that outside the bubble and the interstellar temperature is 10{sup 6} K. Evidently most of the gas was swept out by one or more supernovae. I explored the stellar contents and ages of the region from visual double stars, spectroscopic doubles, single stars, open clusters, emission regions, X-ray stars, planetary nebulae, and pulsars. The bubble has three sub-regions. The region toward the galactic center has stars as early as O9.5 V and withmore » ages of 2-4 M yr. It also has a pulsar (PSRJ1856-3754) with a spin-down age of 3.76 Myr. That pulsar is likely to be the remnant of the supernova that drove away most of the gas. The central lobe has stars as early as B7 V and therefore an age of about 160 Myr or less. The Pleiades lobe has stars as early as B3 and therefore an age of about 50 Myr. There are no obvious pulsars that resulted from the supernovae that cleared out those areas. As found previously by Welsh and Lallement, the bubble has five B stars along its perimeter that show high-temperature ions of O VI and C II along their lines of sight, confirming its high interstellar temperature.« less

Optical Monitoring of Young Stellar Objects

NASA Astrophysics Data System (ADS)

Kar, Aman; Jang-Condell, Hannah; Kasper, David; Findlay, Joseph; Kobulnicky, Henry A.

2018-06-01

Observing Young Stellar Objects (YSOs) for variability in different wavelengths enables us to understand the evolution and structure of the protoplanetary disks around stars. The stars observed in this project are known YSOs that show variability in the Infrared. Targets were selected from the Spitzer Space Telescope Young Stellar Object Variability (YSOVAR) Program, which monitored star-forming regions in the mid-infrared. The goal of our project is to investigate any correlation between the variability in the infrared versus the optical. Infrared variability of YSOs is associated with the heating of the protoplanetary disk while accretion signatures are observed in the H-alpha region. We used the University of Wyoming’s Red Buttes Observatory to monitor these stars for signs of accretion using an H-alpha narrowband filter and the Johnson-Cousins filter set, over the Summer of 2017. We perform relative photometry and inspect for an image-to-image variation by observing these targets for a period of four months every two to three nights. The study helps us better understand the link between accretion and H-alpha activity and establish a disk-star connection.

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.

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.

An investigation of the photometric variability of confirmed and candidate Galactic Be stars using ASAS-3 data

NASA Astrophysics Data System (ADS)

Bernhard, Klaus; Otero, Sebastián; Hümmerich, Stefan; Kaltcheva, Nadejda; Paunzen, Ernst; Bohlsen, Terry

2018-05-01

We present an investigation of a large sample of confirmed (N=233) and candidate (N=54) Galactic classical Be stars (mean V magnitude range of 6.4 to 12.6 mag), with the main aim of characterizing their photometric variability. Our sample stars were preselected among early-type variables using light curve morphology criteria. Spectroscopic information was gleaned from the literature, and archival and newly-acquired spectra. Photometric variability was analyzed using archival ASAS-3 time series data. To enable a comparison of results, we have largely adopted the methodology of Labadie-Bartz et al. (2017), who carried out a similar investigation based on KELT data. Complex photometric variations were established in most stars: outbursts on different time-scales (in 73±5 % of stars), long-term variations (36±6 %), periodic variations on intermediate time-scales (1±1 %) and short-term periodic variations (6±3 %). 24±6 % of the outbursting stars exhibit (semi)periodic outbursts. We close the apparent void of rare outbursters reported by Labadie-Bartz et al. (2017), and show that Be stars with infrequent outbursts are not rare. While we do not find a significant difference in the percentage of stars showing outbursts among early-type, mid-type and late-type Be stars, we show that early-type Be stars exhibit much more frequent outbursts. We have measured rising and falling times for well-covered and well-defined outbursts. Nearly all outburst events are characterized by falling times that exceed the rising times. No differences were found between early-, mid- and late-type stars; a single non-linear function adequately describes the ratio of falling time to rising time across all spectral subtypes, with the ratio being larger for short events.

Value of Conditioned Reinforcers as a Function of Temporal Context

ERIC Educational Resources Information Center

O'Daly, Matthew; Meyer, Steven; Fantino, Edmund

2005-01-01

In two experiments, pigeons were trained on a multiple-chain schedule, in which the initial link for one chain was a variable-interval (VI) 100s schedule and for the other chain a VI 10s schedule. The terminal links were both fixed-time 30s schedules signaled by differently colored stimuli. Following training, the pigeons had their preference for…

Prevalence and risk factors of vision impairment among children of employees of Telecom, Italy.

PubMed

Nucci, Carlo; Cofini, Vincenza; Mancino, Raffaele; Ricci, Federico; Martucci, Alessio; Cecilia, Maria Rosita; Ciciarelli, Vincenzo; Zazzara, Francesca; Cedrone, Claudio; di Orio, Ferdinando

2016-06-10

To define the prevalence, causes, and risk factors of vision impairment (VI) in children. In this study, relatives of Association for Supplemental Health Insurance to the Employees of Telecom members aged 5-16 years were examined in all Italian regions. A standardized record card was used to collect data on medical history; keratometry; objective refraction; uncorrected, presenting, and best-corrected visual acuity (VA); examination of the pupils, adnexa, and anterior segment; direct ophthalmoscopy; posterior segment and fundus examination; and assessment for ocular pathology. Binocular and monocular VI were defined by a VA <5/10 (or <20/40). The campaign included 17,508 children, 12,798 of whom (73.1%) were examined (and 12,740 on whom all VA data were gathered). The prevalence of uncorrected, presenting, and best-corrected VI in the better eye was 9.0%, 2.51%, and 0.10%, respectively. The following variables were associated with presenting VI: age 10-16 years, family history of myopia, female sex, family history of keratoconus, and hypertension. Myopia is the main cause of VI (82.6%). A total of 96% of children with presenting VI had correctable VI. Correctable VI because of myopia is an important public health problem in school-age children in Italy.

The discovery of low-mass pre-main-sequence stars in Cepheus OB3b

NASA Astrophysics Data System (ADS)

Pozzo, M.; Naylor, T.; Jeffries, R. D.; Drew, J. E.

2003-05-01

We report the discovery of a low-mass pre-main-sequence (PMS) stellar population in the younger subgroup of the Cepheus OB3 association, Cep OB3b, using UBVI CCD photometry and follow-up spectroscopy. The optical survey covers approximately 1300 arcmin2 on the sky and gives a global photometric and astrometric catalogue for more than 7000 objects. The location of a PMS population is well defined in a V versus (V-I) colour-magnitude diagram. Multifibre spectroscopic results for optically selected PMS candidates confirm the T Tauri nature for 10 objects, with equal numbers of classical TTS (CTTS) and weak-line TTS (WTTS). There are six other objects that we classify as possible PMS stars. The newly discovered TTS stars have masses in the range ~0.9-3.0 Msolar and ages from <1 to nearly 10 Myr, based on the Siess, Dufour & Forestini isochrones. Their location close to the O and B stars of the association (especially the O7n star) demonstrates that low-mass star formation is indeed possible in such an apparently hostile environment dominated by early-type stars and that the latter must have been less effective in eroding the circumstellar discs of their lower-mass siblings compared with other OB associations (e.g. λ-Ori). We attribute this to the nature of the local environment, speculating that the bulk of molecular material, which shielded low-mass stars from the ionizing radiation of their early-type siblings, has only recently been removed.

The 3.5 micron light curves of long period variable stars. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Strecker, D. W.

1973-01-01

Infrared observations at an effective wavelength of 3.5 microns of a selected group of long period variable (LPV) stars are presented. Mira type and semiregular stars of M, S, and C spectral classifications were monitored throughout the full cycle of variability. Although the variable infrared radiation does not exactly repeat in intensity or time, the regularity is sufficient to produce mean 3.5 micron light curves. The 3.5 micron maximum radiation lags the visual maximum by about one-seventh of a cycle, while the minimum 3.5 micron intensity occurs nearly one-half cycle after infrared maximum. In some stars, there are inflections or humps on the ascending portion of the 3.5 micron light curve which may also be seen in the visual variations.

Empirical mass-loss rates for 25 O and early B stars, derived from Copernicus observations

NASA Technical Reports Server (NTRS)

Gathier, R.; Lamers, H. J. G. L. M.; Snow, T. P.

1981-01-01

Ultraviolet line profiles are fitted with theoretical line profiles in the cases of 25 stars covering a spectral type range from O4 to B1, including all luminosity classes. Ion column densities are compared for the determination of wind ionization, and it is found that the O VI/N V ratio is dependent on the mean density of the wind and not on effective temperature value, while the Si IV/N V ratio is temperature-dependent. The column densities are used to derive a mass-loss rate parameter that is empirically correlated against the mass-loss rate by means of standard stars with well-determined rates from IR or radio data. The empirical mass-loss rates obtained are compared with those derived by others and found to vary by as much as a factor of 10, which is shown to be due to uncertainties or errors in the ionization fractions of models used for wind ionization balance prediction.

Distribution and Kinematics of O VI in the Galactic Halo

NASA Astrophysics Data System (ADS)

Savage, B. D.; Sembach, K. R.; Wakker, B. P.; Richter, P.; Meade, M.; Jenkins, E. B.; Shull, J. M.; Moos, H. W.; Sonneborn, G.

2003-05-01

Far-Ultraviolet Spectroscopic Explorer (FUSE) spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI λλ1031.93, 1037.62 absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km s-1 reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T~3×105 K in the Milky Way thick disk/halo. The integrated column density, log[N(O VI) cm-2], ranges from 13.85 to 14.78 with an average value of 14.38 and a standard deviation of 0.18. Large irregularities in the gas distribution are found to be similar over angular scales extending from <1° to 180°, implying a considerable amount of small- and large-scale structure in the absorbing gas. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI midplane density of n0(O VI)=1.7×10-8 cm-3, a scale height of ~2.3 kpc, and a ~0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low- and intermediate-velocity H I, Hα emission from the warm ionized gas at ~104 K, and hot X-ray-emitting gas at ~106 K. The O VI has an average velocity dispersion, b~60 km s-1, and standard deviation of 15 km s-1. Thermal broadening alone cannot explain the large observed profile widths. The average O VI absorption velocities toward high-latitude objects (|b|>45deg) range from -46 to 82 km s-1, with a high-latitude sample average of 0 km s-1 and a standard deviation of 21 km s-1. High positive velocity O VI absorbing wings extending from ~100 to ~250 km s-1 observed along 21 lines of sight may be tracing the flow of O VI into the halo. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the north. If a fountain flow dominates, a mass flow rate of approximately 1.4 Msolar yr-1 of cooling hot gas to each side of the Galactic plane with an average density of 10-3 cm-3 is required to explain the average value of log[N(O VI)sin|b|] observed in the southern Galactic hemisphere. Such a flow rate is comparable to that estimated for the Galactic intermediate-velocity clouds.

Transits, Spots, and Eclipses: The Sunís Role in Pedagogy and Outreach (Abstract)

NASA Astrophysics Data System (ADS)

Larsen, K.

2018-06-01

(Abstract only) While most people observe variable stars at night, the observers of the AAVSO Solar Section make a single observation per day, but only if it is sunny, because our variable is the Sun itself. While the Sun can play an important role in astronomy outreach and pedagogy in general, as demonstrated by the recent 2017 eclipse, it can also serve as an ambassador for variable stars. This talk will examine how our sun can be used as a tool to explain several types of variable star behaviors, including transits, spots, and eclipses.

Influence of spatial and temporal variability of subsurface soil moisture and temperature on vapour intrusion

NASA Astrophysics Data System (ADS)

Bekele, Dawit N.; Naidu, Ravi; Chadalavada, Sreenivasulu

2014-05-01

A comprehensive field study was conducted at a site contaminated with chlorinated solvents, mainly trichloroethylene (TCE), to investigate the influence of subsurface soil moisture and temperature on vapour intrusion (VI) into built structures. Existing approaches to predict the risk of VI intrusion into buildings assume homogeneous or discrete layers in the vadose zone through which TCE migrates from an underlying source zone. In reality, the subsurface of the majority of contaminated sites will be subject to significant variations in moisture and temperature. Detailed site-specific data were measured contemporaneously to evaluate the impact of spatial and temporal variability of subsurface soil properties on VI exposure assessment. The results revealed that indoor air vapour concentrations would be affected by spatial and temporal variability of subsurface soil moisture and temperature. The monthly monitoring of soil-gas concentrations over a period of one year at a depth of 3 m across the study site demonstrated significant variation in TCE vapour concentrations, which ranged from 480 to 629,308 μg/m3. Soil-gas wells at 1 m depth exhibited high seasonal variability in TCE vapour concentrations with a coefficient of variation 1.02 in comparison with values of 0.88 and 0.74 in 2 m and 3 m wells, respectively. Contour plots of the soil-gas TCE plume during wet and dry seasons showed that the plume moved across the site, hence locations of soil-gas monitoring wells for human risk assessment is a site specific decision. Subsurface soil-gas vapour plume characterisation at the study site demonstrates that assessment for VI is greatly influenced by subsurface soil properties such as temperature and moisture that fluctuate with the seasons of the year.

Searching for δ Scuti-type pulsation and characterising northern pre-main-sequence field stars

NASA Astrophysics Data System (ADS)

Díaz-Fraile, D.; Rodríguez, E.; Amado, P. J.

2014-08-01

Context. Pre-main-sequence (PMS) stars are objects evolving from the birthline to the zero-age main sequence (ZAMS). Given a mass range near the ZAMS, the temperatures and luminosities of PMS and main-sequence stars are very similar. Moreover, their evolutionary tracks intersect one another causing some ambiguity in the determination of their evolutionary status. In this context, the detection and study of pulsations in PMS stars is crucial for differentiating between both types of stars by obtaining information of their interiors via asteroseismic techniques. Aims: A photometric variability study of a sample of northern field stars, which previously classified as either PMS or Herbig Ae/Be objects, has been undertaken with the purpose of detecting δ Scuti-type pulsations. Determination of physical parameters for these stars has also been carried out to locate them on the Hertzsprung-Russell diagram and check the instability strip for this type of pulsators. Methods: Multichannel photomultiplier and CCD time series photometry in the uvby Strömgren and BVI Johnson bands were obtained during four consecutive years from 2007 to 2010. The light curves have been analysed, and a variability criterion has been established. Among the objects classified as variable stars, we have selected those which present periodicities above 4 d-1, which was established as the lowest limit for δ Scuti-type pulsations in this investigation. Finally, these variable stars have been placed in a colour-magnitude diagram using the physical parameters derived with the collected uvbyβ Strömgren-Crawford photometry. Results: Five PMS δ Scuti- and three probable β Cephei-type stars have been detected. Two additional PMS δ Scuti stars are also confirmed in this work. Moreover, three new δ Scuti- and two γ Doradus-type stars have been detected among the main-sequence objects used as comparison or check stars.

A Spectropolarimetric Test of the Structure of the Intrinsic Absorbers in the Quasar HS 1603+3820

NASA Astrophysics Data System (ADS)

Misawa, Toru; Kawabata, Koji S.; Eracleous, Michael; Charlton, Jane C.; Kashikawa, Nobunari

2010-08-01

We report the results of a spectropolarimetric observation of the C VI "mini-broad" absorption line (mini-BAL) in the quasar HS 1603+3820 (z em = 2.542). The observations were carried out with the FOCAS instrument on the Subaru Telescope and yielded an extremely high polarization sensitivity of δp~ 0.1%, at a resolving power of R ~ 1500. HS 1603+3820 has been the target of a high-resolution spectroscopic monitoring campaign for more than four years, aimed at studying its highly variable C VI mini-BAL profile. Using the monitoring observations in an earlier paper, we were able to narrow down the causes of the variability to the following two scenarios: (1) scattering material of variable optical depth redirecting photons around the absorber and (2) a variable, highly ionized screen between the continuum source and the absorber which modulates the UV continuum incident on the absorber. The observations presented here provide a crucial test of the scattering scenario and lead us to disfavor it because (1) the polarization level is very small (p ~ 0.6%) throughout the spectrum and (2) the polarization level does not increase across the mini-BAL trough. Thus, the variable screen scenario emerges as our favored explanation of the C VI mini-BAL variability. Our conclusion is bolstered by recent X-ray observations of nearby mini-BAL quasars, which show a rapidly variable soft X-ray continuum that appears to be the result of transmission through an ionized absorber of variable ionization parameter and optical depth. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Variability of Massive Young Stellar Objects in Cygnus-X

NASA Astrophysics Data System (ADS)

Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

2013-01-01

Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

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.

Variable stars in the Galactic center, as revealed by the VVV Survey

NASA Astrophysics Data System (ADS)

Molina, Claudio Navarro; Borissova, Jura; Catelan, Márcio; Kurtev, Radostin; Medina, Nicolás

2017-09-01

A variability search has been performed in the Galactic center, using the nearinfrared images from the Vista Variables in the Vía Láctea (VVV) Survey. Light curves contain 89 epochs in the KS band. A total of 353 variable stars were found, of which only 47 are already present in the literature.

A Study of Nonthermal X-Ray and Radio Emission from the O Star 9 Sgr

NASA Technical Reports Server (NTRS)

Waldron, Wayne L.; Corcoran, Michael F.; Drake, Stephen A.

1999-01-01

The observed X-ray and highly variable nonthermal radio emission from OB stars has eluded explanation for more than 18 years. The most favorable model of X-ray production in these stars (shocks) predicts both nonthermal radio and X-ray emission. The nonthermal X-ray emission should occur above 2 keV and the variability of this X-ray component should also be comparable to the observed radio variability. To test this scenario, we proposed an ASC/VLA monitoring program to observe the OB star, 9 Sgr, a well known nonthermal, variable radio source and a strong X-ray source. We requested 625 ks ASCA observations with a temporal spacing of approximately 4 days which corresponds to the time required for a density disturbance to propagate to the 6 cm radio free-free photosphere. The X-ray observations were coordinated with 5 multi-wavelength VLA observations. These observations represent the first systematic attempt to investigate the relationship between the X-ray and radio emission in OB stars.

New Galactic Candidate Luminous Blue Variables and Wolf-Rayet Stars

NASA Astrophysics Data System (ADS)

Stringfellow, Guy S.; Gvaramadze, Vasilii V.; Beletsky, Yuri; Kniazev, Alexei Y.

2012-04-01

We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 μm) and GLIMPSE (8 μm) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of this class.

Weak metal lines in optical high-resolution Very Large Telescope and Keck spectra of "cool" PG 1159 stars

NASA Astrophysics Data System (ADS)

Werner, K.; Rauch, T.

2014-09-01

PG 1159 stars are very hot (effective temperatures Teff = 75 000-200 000 K), hydrogen-deficient (pre-) white dwarfs. They probably are the result of a late helium-shell flash that laid bare the He, C, and O rich intershell matter of the progenitor Asymptotic Giant Branch (AGB) star. Their chemical surface composition thus allows to conclude on details of AGB-star nucleosynthesis. Due to their very high effective temperatures, detailed spectral analyses are usually completely reliant on ultraviolet observations, except for some species in the hottest PG 1159 stars (Teff ≳ 130 000 K), which do exhibit highly excited lines from the CNO elements and neon (C iv, N v, O vi, Ne vii-viii) in optical spectra. Particularly problematic are, however, the coolest members of the PG 1159 class that exclusively show C iv lines in the optical. Access to the nitrogen abundance is important to decide which of the late-thermal pulse evolutionary scenarios was experienced by a particular star, while a high oxygen abundance is an important marker that the star could pulsate. In the present paper, we investigate high-resolution high signal-to-noise optical spectra of three "cool" PG 1159 stars (PG 0122+200, PG 2131+066, MCT 0130-1937, Teff = 80 000-95 000 K). With the help of non-LTE model atmospheres and synthetic spectra, we are able to identify a large number of weak CNO lines (C iii, N iv, O iii-v) that were not detected before in these stars. They allow abundance determinations and enable us to constrain the effective temperature to high precision through ionization equilibria without the requirement to access the ultraviolet spectral range.

A search for stars of very low metal abundance. VI. Detailed abundances of 313 metal-poor stars

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

Roederer, Ian U.; Preston, George W.; Thompson, Ian B.

2014-06-01

We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10 yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coudé Spectrograph on the Harlan J. Smith Telescope atmore » McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by ≈0.25 dex for red giants and ≈0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] ≤–3.5, 84 stars with [Fe/H] ≤–3.0, and 210 stars with [Fe/H] ≤–2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] ≤–2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.« less

Discovery of a Gas Giant Planet in Microlensing Event Ogle-2014-BLG-1760

NASA Technical Reports Server (NTRS)

Bhattacharya, A.; Bennett, D. P.; Bond, I. A.; Sumi, T.; Udalski, A.; Street, R.; Tsapras, Y.; Abe, F.; Freeman, M.; Fukui, A.

2016-01-01

We present the analysis of the planetary microlensing event OGLE-2014-BLG-1760, which shows a strong light-curve signal due to the presence of a Jupiter mass ratio planet. One unusual feature of this event is that the source star is quite blue, with V-I = 1.48 +/- 0.08. This is marginally consistent with a source star in the Galactic bulge, but it could possibly indicate a young source star on the far side of the disk. Assuming a bulge source, we perform a Bayesian analysis assuming a standard Galactic model, and this indicates that the planetary system resides in or near the Galactic bulge at D(sub L) = 6.9 +/- 1.1 kpc. It also indicates a host-star mass of M(sub *) = 0.51(sup + 0.44/sub -0.28) M(sub theta), a planet mass of m(sub p ) = 0.56(sup +0.34/sub -0.26) M(sub J), and a projected star-planet separation of a(perpendicular) = 1.75(sup +0.33/sub -0.34) au. The lens-source relative proper motion is micro(sub rel) = 6.5 +/- 1.1mas per yr. The lens (and stellar host star) is estimated to be very faint compared to the source star, so it is most likely that it can be detected only when the lens and source stars start to separate. Due to the relatively high relative proper motion, the lens and source will be resolved to about approximately 46 mas in 6-8 yr after the peak magnification. So, by 2020-2022, we can hope to detect the lens star with deep, high-resolution images.

Bulge RR Lyrae stars in the VVV tile b201

NASA Astrophysics Data System (ADS)

Gran, F.; Minniti, D.; Saito, R. K.; Navarrete, C.; Dékány, I.; McDonald, I.; Contreras Ramos, R.; Catelan, M.

2015-03-01

Context. The VISTA Variables in the Vía Láctea (VVV) Survey is one of the six ESO public surveys currently ongoing at the VISTA telescope on Cerro Paranal, Chile. VVV uses near-IR (ZYJHKs) filters that at present provide photometry to a depth of Ks ~ 17.0 mag in up to 36 epochs spanning over four years, and aim at discovering more than 106 variable sources as well as trace the structure of the Galactic bulge and part of the southern disk. Aims: A variability search was performed to find RR Lyrae variable stars. The low stellar density of the VVV tile b201, which is centered at (ℓ,b) ~ (-9°, -9°), makes it suitable to search for variable stars. Previous studies have identified some RR Lyrae stars using optical bands that served to test our search procedure. The main goal is to measure the reddening, interstellar extinction, and distances of the RR Lyrae stars and to study their distribution on the Milky Way bulge. Methods: For each star in the tile with more than 25 epochs (~90% of the objects down to Ks ~ 17.0 mag), the standard deviation and χ2 test were calculated to identify variable candidates. Periods were determined using the analysis of variance. Objects with periods in the RR Lyrae range of 0.2 ≤ P ≤ 1.2 days were selected as candidate RR Lyrae. They were individually examined to exclude false positives. Results: A total of 1.5 sq deg were analyzed, and we found 39 RR Lyr stars, 27 of which belong to the ab-type and 12 to the c-type. Our analysis recovers all the previously identified RR Lyrae variables in the field and discovers 29 new RR Lyr stars. The reddening and extinction toward all the RRab stars in this tile were derived, and distance estimations were obtained through the period-luminosity relation. Despite the limited amount of RR Lyrae stars studied, our results are consistent with a spheroidal or central distribution around ~8.1 and ~8.5 kpc. for either the Cardelli or Nishiyama extinction law. Our analysis does not reveal a stream-like structure. Nevertheless, a larger area must be analyzed to definitively rule out streams. Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002.

Automated classification of periodic variable stars detected by the wide-field infrared survey explorer

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

Masci, Frank J.; Grillmair, Carl J.; Cutri, Roc M.

2014-07-01

We describe a methodology to classify periodic variable stars identified using photometric time-series measurements constructed from the Wide-field Infrared Survey Explorer (WISE) full-mission single-exposure Source Databases. This will assist in the future construction of a WISE Variable Source Database that assigns variables to specific science classes as constrained by the WISE observing cadence with statistically meaningful classification probabilities. We have analyzed the WISE light curves of 8273 variable stars identified in previous optical variability surveys (MACHO, GCVS, and ASAS) and show that Fourier decomposition techniques can be extended into the mid-IR to assist with their classification. Combined with other periodicmore » light-curve features, this sample is then used to train a machine-learned classifier based on the random forest (RF) method. Consistent with previous classification studies of variable stars in general, the RF machine-learned classifier is superior to other methods in terms of accuracy, robustness against outliers, and relative immunity to features that carry little or redundant class information. For the three most common classes identified by WISE: Algols, RR Lyrae, and W Ursae Majoris type variables, we obtain classification efficiencies of 80.7%, 82.7%, and 84.5% respectively using cross-validation analyses, with 95% confidence intervals of approximately ±2%. These accuracies are achieved at purity (or reliability) levels of 88.5%, 96.2%, and 87.8% respectively, similar to that achieved in previous automated classification studies of periodic variable stars.« less

A search for T Tauri stars and related objects: Archival photometry of candidate variables in V733 Cep field

NASA Astrophysics Data System (ADS)

Jurdana-Šepić, R.; Poljančić Beljan, I.

Searching for T Tauri stars or related early type variables we carried out a BVRI photometric measurements of five candidates with positions within the field of the pre-main sequence object V733 Cephei (Persson's star) located in the dark cloud L1216 near to Cepheus OB3 Association: VES 946, VES 950, NSV 14333, NSV 25966 and V385 Cep. Their magnitudes are determined on the plates from Asiago Observatory historical photographic archive exposed 1971 - 1978. We provide finding charts for program stars and comparison sequence stars, magnitude estimations, magnitude mean values and BVR_cI_c light curves of program stars.

Determining Hβ Color Indices for 23 δ Scuti Variable Stars

NASA Astrophysics Data System (ADS)

Bush, Tabitha C.; Hintz, E. G.; Shreeve, D. K.; Jorgenson, K.

2010-01-01

Color index is a fundamental characteristic in the study of δ Scuti variable stars. The then comprehensive catalog of δ Scutis compiled by Rodriguez et al. (Rodriguez, E. Lopez Gonzalez, M. J., & Lopez de Coca, P. 2000, A&AS, 144, 469) contains 636 δ Scuti stars and several characteristics of these stars, including Hβ color index. Of the 417 stars in this catalog brighter than 13th magnitude, about 20% of them are missing Hβ color index values. We present 23 of these previously unpublished values, calculated from a calibration relation using spectroscopic observations obtained at the Dominion Astrophysical Observatory of 167 δ Scuti stars north of -01 degrees declination and brighter than 13th magnitude.

Aerospace video imaging systems for rangeland management

NASA Technical Reports Server (NTRS)

Everitt, J. H.; Escobar, D. E.; Richardson, A. J.; Lulla, K.

1990-01-01

This paper presents an overview on the application of airborne video imagery (VI) for assessment of rangeland resources. Multispectral black-and-white video with visible/NIR sensitivity; color-IR, normal color, and black-and-white MIR; and thermal IR video have been used to detect or distinguish among many rangeland and other natural resource variables such as heavy grazing, drought-stressed grass, phytomass levels, burned areas, soil salinity, plant communities and species, and gopher and ant mounds. The digitization and computer processing of VI have also been demonstrated. VI does not have the detailed resolution of film, but these results have shown that it has considerable potential as an applied remote sensing tool for rangeland management. In the future, spaceborne VI may provide additional data for monitoring and management of rangelands.

GORGONA - the characteristic of the software system.

NASA Astrophysics Data System (ADS)

Artim, M.; Zejda, M.

A description of the new software system is given. The GORGONA system is established to the processing, making and administration of archives of periodic variable stars observations, observers and observed variable stars.

Long-term variability of T Tauri stars using WASP

NASA Astrophysics Data System (ADS)

Rigon, Laura; Scholz, Alexander; Anderson, David; West, Richard

2017-03-01

We present a reference study of the long-term optical variability of young stars using data from the WASP project. Our primary sample is a group of well-studied classical T Tauri stars (CTTSs), mostly in Taurus-Auriga. WASP light curves cover time-scales of up to 7 yr and typically contain 10 000-30 000 data points. We quantify the variability as a function of time-scale using the time-dependent standard deviation 'pooled sigma'. We find that the overwhelming majority of CTTSs have a low-level variability with σ < 0.3 mag dominated by time-scales of a few weeks, consistent with rotational modulation. Thus, for most young stars, monitoring over a month is sufficient to constrain the total amount of variability over time-scales of up to a decade. The fraction of stars with a strong optical variability (σ > 0.3 mag) is 21 per cent in our sample and 21 per cent in an unbiased control sample. An even smaller fraction (13 per cent in our sample, 6 per cent in the control) show evidence for an increase in variability amplitude as a function of time-scale from weeks to months or years. The presence of long-term variability correlates with the spectral slope at 3-5 μm, which is an indicator of inner disc geometry, and with the U-B band slope, which is an accretion diagnostics. This shows that the long-term variations in CTTSs are predominantly driven by processes in the inner disc and in the accretion zone. Four of the stars with long-term variations show periods of 20-60 d, significantly longer than the rotation periods and stable over months to years. One possible explanation is cyclic changes in the interaction between the disc and the stellar magnetic field.

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

Inter-Longitude Astronomy (ILA) Project: Current Highlights And Perspectives. I. Magnetic vs. Non-Magnetic Interacting Binary Stars

NASA Astrophysics Data System (ADS)

Andronov, I. L.; Antoniuk, K. A.; Baklanov, A. V.; Breus, V. V.; Burwitz, V.; Chinarova, L. L.; Chochol, D.; Dubovsky, P. A.; Han, W.; Hegedus, T.; Henden, A.; Hric, L.; Chun-Hwey, Kim; Yonggi, Kim; Kolesnikov, S. V.; Kudzej, I.; Liakos, A.; Niarchos, P. G.; Oksanen, A.; Patkos, L.; Petrik, K.; Pit', N. V.; Shakhovskoy, N. M.; Virnina, N. A.; Yoon, J.; Zola, S.

2010-12-01

We present a review of highlights of our photometric and photo-polarimetric monitoring and mathematical modeling of interacting binary stars of different types classical, asynchronous, intermedi ate polars with 25 timescales corresponding to differ ent physical mechanisms and their combinations (part "Polar"); negative and positive superhumpers in nova- like and dwarf novae stars ("Superhumper"); symbiotic ("Symbiosis"); eclipsing variables with and without ev idence for a current mass transfer ("Eclipser") with a special emphasis on systems with a direct impact of the stream into the gainor star's atmosphere, which we propose to call "Impactors", or V361 Lyr-type stars. Other parts of the ILA project are "Stellar Bell" (pul sating variables of different types and periods - M, SR, RV Tau, RR Lyr, Delta Sct) and "New Variable".

Further observations of the lambda 10830 He line in stars and their significance as a measure of stellar activity

NASA Technical Reports Server (NTRS)

Zirin, H.

1975-01-01

Measurements of the lambda 1030 He line in 198 stars are given along with data on other features in that spectral range. Nearly 80% of all G and K stars show some lambda 10830; of these, half are variable and 1/4 show emission. It was confirmed that lambda 10830 is not found in M stars, is weak in F stars, and is particularly strong in close binaries. The line is found in emission in extremely late M and S stars, along with P gamma, but P gamma is not in emission in G and K stars with lambda 10830 emissions. Variable He emission and Ti I emission are found in the RV Tauri variables R Scuti and U Mon. In R Aqr the Fe XIII coronal line lambda 10747 and a line at lambda 11012 which may be singlet He or La II are found, as well as lambda 10830 and P gamma. The nature of coronas or hot chromospheres in the various stars is discussed. It was concluded that the lambda 10830 intensity must be more or less proportional to the energy deposited in the chromosphere corona by non-thermal processes.

A VLA 3.6 centimeter survey of N-type carbon stars

NASA Technical Reports Server (NTRS)

Luttermoser, Donald G.; Brown, Alexander

1992-01-01

The results are presented of a VLA-continuum survey of 7 N-type carbon stars at 3.6 cm. Evidence exists for hot plasma around such stars; the IUE satellite detected emission lines of singly ionized metals in the optically brightest carbon stars, which in solar-type stars indicate the existence of a chromosphere. In the past, these emission lines were used to constrain the lower portion of the archetypical chromospheric model of N-type carbon stars, that of TX Psc. Five of the survey stars are semiregular (1 SRa and 4 SRb) variables and two are irregular (Lb) variables. Upper limits of about 0.07 mJy are set of the SRb and Lb variables and the lone SRa (V Hya) was detected with a flux of 0.22 mJy. The upper limits for the six stars that are not detected indicate that the temperature in their winds is less than 10,000 K. Various scenarios for the emission from V Hya are proposed, and it is suggested that the radio continuum is shock-related (either due to pulsation or the suspected bipolar jet) and not due to a supposed accretion disk around an unseen companion.

LUMINOSITY DISCREPANCY IN THE EQUAL-MASS, PRE-MAIN-SEQUENCE ECLIPSING BINARY PAR 1802: NON-COEVALITY OR TIDAL HEATING?

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

Gomez Maqueo Chew, Yilen; Stassun, Keivan G.; Hebb, Leslie

Parenago 1802, a member of the {approx}1 Myr Orion Nebula Cluster, is a double-lined, detached eclipsing binary in a 4.674 day orbit, with equal-mass components (M{sub 2}/M{sub 1} = 0.985 {+-} 0.029). Here we present extensive VI{sub C} JHK{sub S} light curves (LCs) spanning {approx}15 yr, as well as a Keck/High Resolution Echelle Spectrometer (HIRES) optical spectrum. The LCs evince a third light source that is variable with a period of 0.73 days, and is also manifested in the high-resolution spectrum, strongly indicating the presence of a third star in the system, probably a rapidly rotating Classical T Tauri star.more » We incorporate this third light into our radial velocity and LC modeling of the eclipsing pair, measuring accurate masses (M{sub 1} = 0.391 {+-} 0.032 and M{sub 2} = 0.385 {+-} 0.032 M{sub Sun }), radii (R{sub 1} = 1.73 {+-} 0.02 and R{sub 2} = 1.62 {+-} 0.02 R{sub Sun }), and temperature ratio (T{sub eff,1}/T{sub eff,2} = 1.0924 {+-} 0.0017). Thus, the radii of the eclipsing stars differ by 6.9% {+-} 0.8%, the temperatures differ by 9.2% {+-} 0.2%, and consequently the luminosities differ by 62% {+-} 3%, despite having masses equal to within 3%. This could be indicative of an age difference of {approx}3 Multiplication-Sign 10{sup 5} yr between the two eclipsing stars, perhaps a vestige of the binary formation history. We find that the eclipsing pair is in an orbit that has not yet fully circularized, e = 0.0166 {+-} 0.003. In addition, we measure the rotation rate of the eclipsing stars to be 4.629 {+-} 0.006 days; they rotate slightly faster than their 4.674 day orbit. The non-zero eccentricity and super-synchronous rotation suggest that the eclipsing pair should be tidally interacting, so we calculate the tidal history of the system according to different tidal evolution theories. We find that tidal heating effects can explain the observed luminosity difference of the eclipsing pair, providing an alternative to the previously suggested age difference.« less

ASAS 095221-4329.8 und ASAS 123034-7703.9 - zwei R-CrB-Stern-Kandidaten aus der ASAS-Datenbank

NASA Astrophysics Data System (ADS)

Huemmerich, Stefan

2011-04-01

During an examination of ASAS Misc-type objects, the stars ASAS 095221-4329.8 GSC 07706-00560, 09:52:21.38 -43:29:40.5) and ASAS 123034-7703.9 (GSC 09416-00380, 12:30:34.22 -77:03:52.7) - both of which show semi-regular variability - were found to exhibit significant obscuration events in their V-band lightcurves. Both stars are likely to be red giants undergoing fading events, possibly of DY Per-type. However, spectroscopy of both stars is needed for a conclusive classification. The corresponding entries in the International Variable Star Index (VSX) have been revised accordingly; variability type was set to "RCB:".

A heavy-metal home

NASA Image and Video Library

2016-05-30

This 10.5-billion-year-old globular cluster, NGC 6496, is home to heavy-metal stars of a celestial kind! The stars comprising this spectacular spherical cluster are enriched with much higher proportions of metals — elements heavier than hydrogen and helium, are in astronomy curiously known as metals — than stars found in similar clusters. A handful of these high-metallicity stars are also variable stars, meaning that their brightness fluctuates over time. NGC 6496 hosts a selection of long-period variables — giant pulsating stars whose brightness can take up to, and even over, a thousand days to change — and short-period eclipsing binaries, which dim when eclipsed by a stellar companion. The nature of the variability of these stars can reveal important information about their mass, radius, luminosity, temperature, composition, and evolution, providing astronomers with measurements that would be difficult or even impossible to obtain through other methods. NGC 6496 was discovered in 1826 by Scottish astronomer James Dunlop. The cluster resides at about 35 000 light-years away in the southern constellation of Scorpius (The Scorpion).

Variable Circumstellar Disks of “Classical” Be Stars

NASA Astrophysics Data System (ADS)

Gerhartz, Cody; Bjorkman, K. S.; Wisniewski, J. P.

2013-06-01

Circumstellar disks are common among many stars, all spectral types, and at different stages of their lifetimes. Among the near-main sequence “Classical” Be stars, there is growing evidence that these disks can form, dissipate, and reform, on timescales that are differ from case to case. We present data for a subset of cases where observations have been obtained throughout the different phases of the disk cycle. Using data obtained with the SpeX instrument at the NASA IRTF, we examine the IR spectral line variability of these stars to better understand the timescales and the physical mechanisms involved. The primary focus in this study are the V/R variations that are observed in the sample. The second stage of our project is to examine a sample of star clusters known to contain Be stars, with the goal to develop a more statistically significant sample of variable circumstellar disk systems. With a robust multi-epoch study we can determine whether these Be stars exhibit disk-loss or disk-renewal phases. The larger sample will enable a better understanding of the prevalence of these disk events.

VI photometry of the galactic cluster Berkeley 66

NASA Astrophysics Data System (ADS)

Guarnieri, M. D.; Carraro, G.

1997-03-01

A colour magnitude diagram (CMD) extending to V ~= 19 mag is given for 444 stars in the region of the galactic cluster Berkeley 66. The V and I photometry of a nearby field is also reported. This object appears very faint, highly contaminated by foreground stars and very reddened. The apparent distance modulus (m-M) and the colour excess E_{V-I} are guessed to be 17.5 and 1.1, respectively, with an uncertainty of at least 30%. Adopting these values the comparison of the CMD with theoretical isochrones from the Padova group provides an age around 1.0 Gyr. Based on observations carried out at Pino Torinese Observatory, Torino, Italy. Table 2 is available only in electronic form at the CDS via anonymous ftp 130.79.128.5.

Instabilities in Interacting Binary Stars

NASA Astrophysics Data System (ADS)

Andronov, I. L.; Andrych, K. D.; Antoniuk, K. A.; Baklanov, A. V.; Beringer, P.; Breus, V. V.; Burwitz, V.; Chinarova, L. L.; Chochol, D.; Cook, L. M.; Cook, M.; Dubovský, P.; Godlowski, W.; Hegedüs, T.; Hoňková, K.; Hric, L.; Jeon, Y.-B.; Juryšek, J.; Kim, C.-H.; Kim, Y.; Kim, Y.-H.; Kolesnikov, S. V.; Kudashkina, L. S.; Kusakin, A. V.; Marsakova, V. I.; Mason, P. A.; Mašek, M.; Mishevskiy, N.; Nelson, R. H.; Oksanen, A.; Parimucha, S.; Park, J.-W.; Petrík, K.; Quiñones, C.; Reinsch, K.; Robertson, J. W.; Sergey, I. M.; Szpanko, M.; Tkachenko, M. G.; Tkachuk, L. G.; Traulsen, I.; Tremko, J.; Tsehmeystrenko, V. S.; Yoon, J.-N.; Zola, S.; Shakhovskoy, N. M.

2017-07-01

The types of instability in the interacting binary stars are briefly reviewed. The project “Inter-Longitude Astronomy” is a series of smaller projects on concrete stars or groups of stars. It has no special funds, and is supported from resources and grants of participating organizations, when informal working groups are created. This “ILA” project is in some kind similar and complementary to other projects like WET, CBA, UkrVO, VSOLJ, BRNO, MEDUZA, AstroStatistics, where many of us collaborate. Totally we studied 1900+ variable stars of different types, including newly discovered variables. The characteristic timescale is from seconds to decades and (extrapolating) even more. The monitoring of the first star of our sample AM Her was initiated by Prof. V.P. Tsesevich (1907-1983). Since more than 358 ADS papers were published. In this short review, we present some highlights of our photometric and photo-polarimetric monitoring and mathematical modeling of interacting binary stars of different types: classical (AM Her, QQ Vul, V808 Aur = CSS 081231:071126+440405, FL Cet), asynchronous (BY Cam, V1432 Aql), intermediate (V405 Aql, BG CMi, MU Cam, V1343 Her, FO Aqr, AO Psc, RXJ 2123, 2133, 0636, 0704) polars and magnetic dwarf novae (DO Dra) with 25 timescales corresponding to different physical mechanisms and their combinations (part “Polar”); negative and positive superhumpers in nova-like (TT Ari, MV Lyr, V603 Aql, V795 Her) and many dwarf novae stars (“Superhumper”); eclipsing “non-magnetic” cataclysmic variables(BH Lyn, DW UMa, EM Cyg; PX And); symbiotic systems (“Symbiosis”); super-soft sources (SSS, QR And); spotted (and not spotted) eclipsing variables with (and without) evidence for a current mass transfer (“Eclipser”) with a special emphasis on systems with a direct impact of the stream into the gainer star's atmosphere, which we propose to call “Impactor” (short from “Extreme Direct Impactor”), or V361 Lyr-type stars. Other parts of the ILA project are “Stellar Bell” (interesting pulsating variables of different types and periods - M, SR, RV Tau, RR Lyr, Delta Sct with changes of characteristics) and “Novice”(=“New Variable”) discoveries and classification based on special own observations and data mining with a subsequent monitoring for searching and studying possible multiple components of variability. Special mathematical methods have been developed to create a set of complementary software for statistically optimal modeling of variable stars of different types.

Hubble Friday - Heavy Metal Stars

NASA Image and Video Library

2017-12-08

Hubble rocks out with heavy metal stars! This 10.5-billion-year-old globular cluster, NGC 6496, is home to heavy-metal stars of a celestial kind! The stars comprising this spectacular spherical cluster are enriched with much higher proportions of metals — elements heavier than hydrogen and helium are curiously known as metals in astronomy — than stars found in similar clusters. A handful of these high-metallicity stars are also variable stars, meaning that their brightness fluctuates over time. NGC 6496 hosts a selection of long-period variables — giant pulsating stars whose brightness can take up to, and even over, a thousand days to change — and short-period eclipsing binaries, which dim when eclipsed by a stellar companion. The nature of the variability of these stars can reveal important information about their mass, radius, luminosity, temperature, composition, and evolution, providing astronomers with measurements that would be difficult or even impossible to obtain through other methods. NGC 6496 was discovered in 1826 by Scottish astronomer James Dunlop. The cluster resides at about 35,000 light-years away in the southern constellation of Scorpius (The Scorpion). Image credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt Text credit: European Space Agency Read more: go.nasa.gov/1U2wqGW

Kepler's first view of O-star variability: K2 data of five O stars in Campaign 0 as a proof of concept for O-star asteroseismology

NASA Astrophysics Data System (ADS)

Buysschaert, B.; Aerts, C.; Bloemen, S.; Debosscher, J.; Neiner, C.; Briquet, M.; Vos, J.; Pápics, P. I.; Manick, R.; Schmid, V. S.; Van Winckel, H.; Tkachenko, A.

2015-10-01

We present high-precision photometric light curves of five O-type stars observed with the refurbished Kepler satellite during its Campaign 0. For one of the stars, we also assembled high-resolution ground-based spectroscopy with the HERMES spectrograph attached to the 1.2 m Mercator telescope. The stars EPIC 202060097 (O9.5V) and EPIC 202060098 (O7V) exhibit monoperiodic variability due to rotational modulation with an amplitude of 5.6 and 9.3 mmag and a rotation period of 2.63 and 5.03 d, respectively. EPIC 202060091 (O9V) and EPIC 202060093 (O9V:pe) reveal variability at low frequency but the cause is unclear. EPIC 202060092 (O9V:p) is discovered to be a spectroscopic binary with at least one multiperiodic β Cep-type pulsator whose detected mode frequencies occur in the range [0.11, 6.99] d-1 and have amplitudes between 0.8 and 2.0 mmag. Its pulsation spectrum is shown to be fully compatible with the ones predicted by core-hydrogen burning O-star models. Despite the short duration of some 33 d and the limited data quality with a precision near 100 μmag of these first K2 data, the diversity of possible causes for O-star variability already revealed from campaigns of similar duration by the MOST and CoRoT satellites is confirmed with Kepler. We provide an overview of O-star space photometry and give arguments why future K2 monitoring during Campaigns 11 and 13 at short cadence, accompanied by time-resolved high-precision high-resolution spectroscopy, opens up the possibility of in-depth O-star seismology.

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.

Long-term Photometric Variability in Kepler Full-frame Images: Magnetic Cycles of Sun–like Stars

NASA Astrophysics Data System (ADS)

Montet, Benjamin T.; Tovar, Guadalupe; Foreman-Mackey, Daniel

2017-12-01

Photometry from the Kepler mission is optimized to detect small, short-duration signals like planet transits at the expense of long-term trends. This long-term variability can be recovered in photometry from the full-frame images (FFIs), a set of calibration data collected approximately monthly during the Kepler mission. Here we present f3, an open-source package to perform photometry on the Kepler FFIs in order to detect changes in the brightness of stars in the Kepler field of view over long time baselines. We apply this package to a sample of 4000 Sun–like stars with measured rotation periods. We find that ≈10% of these targets have long-term variability in their observed flux. For the majority of targets, we find that the luminosity variations are either correlated or anticorrelated with the short-term variability due to starspots on the stellar surface. We find a transition between anticorrelated (starspot-dominated) variability and correlated (facula-dominated) variability between rotation periods of 15 and 25 days, suggesting the transition between the two modes is complete for stars at the age of the Sun. We also identify a sample of stars with apparently complete cycles, as well as a collection of short-period binaries with extreme photometric variation over the Kepler mission.

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.

Engaging Generation Now, Inspiring Generation Next

NASA Astrophysics Data System (ADS)

Simonsen, Mike; Gay, P.

2008-05-01

In 2008, the Education and Public Outreach Committee of the American Association of Variable Star Observers (AAVSO) initiated several new strategies for disseminating accurate, stimulating, engaging information on general astronomy and variable star science to thousands of students, parents, and amateur astronomers each year through astronomy clubs, societies, and star party events. We are initiating contact with astronomy clubs and organizations to offer qualified speakers from the AAVSO Speakers Bureau for their meetings and activities. The current roster of speakers include, professional astronomers, doctors, engineers, teachers and some of the world's leading variable star observers. Request information is available on the AAVSO website. For organizations and individuals unable to engage one of our speakers due to time, distance or financial constraints, we have made PowerPoint presentations used in previous talks available free for download from the same web pages. Thousands of amateur astronomers and their children attend star parties each year. As an extension of our speakers’ bureau, our goal is to have an AAVSO representative at each of the major star parties each year giving an enthusiastic talk on variable stars or related astronomical subject and supplying inspirational printed materials on astronomy and amateur contributions to science. The nation's largest astronomy clubs have monthly newsletters they distribute to their membership. Newsletter editors are constantly in need of quality, interesting content to fill out their issues each month. We are offering a `writers’ bureau’ service to newsletter editors, similar to the news wire services used by newspapers. We will supply up to a half dozen articles on astronomy and variable star science each month for editors to use at their discretion in their publications. Our goal is to provide information, inspiration and encourage participation among amateur astronomers and their kids, our next generation of astronomers.

Anomalous double-mode RR Lyrae stars in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Soszyński, I.; Smolec, R.; Dziembowski, W. A.; Udalski, A.; Szymański, M. K.; Wyrzykowski, Ł.; Ulaczyk, K.; Poleski, R.; Pietrukowicz, P.; Kozłowski, S.; Skowron, D.; Skowron, J.; Mróz, P.; Pawlak, M.

2016-12-01

We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars has been extracted from the latest edition of the Optical Gravitational Lensing Experiment collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The P1O/PF period ratios of our anomalous RRd stars are within a range of 0.725-0.738, while `classical' double-mode RR Lyrae variables have period ratios in the range of 0.742-0.748. In contrast to the typical RRd stars, in the majority of the anomalous pulsators, the F-mode amplitudes are higher than the 1O-mode amplitudes. The light curves associated with the F-mode in the anomalous RRd stars show different morphology than the light curves of, both, regular RRd stars and single-mode RRab stars. Most of the anomalous double-mode stars show long-term modulations of the amplitudes (Blazhko-like effect). Translating the period ratios into the abundance parameter, Z, we find for our stars Z ∈ (0.002, 0.005) - an order of magnitude higher values than typical for RR Lyrae stars. The mass range of the RRd stars inferred from the WI versus PF diagram is (0.55-0.75) M⊙. These parameters cannot be accounted for with single star evolution assuming a Reimers-like mass-loss. Much greater mass-loss caused by interaction with other stars is postulated. We blame the peculiar pulsation properties of our stars to the parametric resonance instability of the 1O-mode to excitation of the F- and 2O-modes as with the inferred parameters of the stars 2ω1O ≈ ωF + ω2O.

Probing the Reverse Shock in an Oxygen-Rich Supernova Remnant

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Gaetz, Terrance J.

2003-01-01

The aim of this proposal was to examine the O VI emission at three positions around the X-ray bright ring of the remnant in order to investigate the relation between the O VI emission, the X-ray O VII and O VIII emission, and the optical [O III] emission, and how these vary around the rim of the remnant. So far, only one Far Ultraviolet Spectroscopic Explorer (FUSE) pointing at the remnant has been performed, together with the background pointing needed to subtract the diffuse scattered light from nearby O stars. The data were recalibrated using the CalFUSE calibration pipeline, but the emission is faint enough that hand processing will be needed for this pointing to optimize the extraction. Rereduction of the data is underway. A postdoctoral fellow has also been hired, and in part she will assist with the analysis.

An upper limit on interstellar C IV in the spectrum of gamma-2 Velorum

NASA Technical Reports Server (NTRS)

Lengyel-Frey, D.; Stecher, T. P.; West, D. K.

1975-01-01

An upper limit on the column density of C IV along the line of sight to gamma-2 Vel is derived from upper limits placed on the equivalent widths of the interstellar C IV doublet with rest wavelengths at 1548.20 A and 1550.77 A. A lower limit of 250,000 K is calculated for the electron temperature of O VI emitting regions by combining the C IV results with a measurement of the column density of interstellar O VI for the same star and using calculations for the relative ionization of some abundant elements as a function of electron temperature in a low-density plasma. Since gamma-2 Vel is in the central part of the Gum Nebula, the high temperature suggested by these results is shown to support the idea that a high-temperature phase of the interstellar medium, possibly maintained by supernova explosions, may exist.-

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

Serendipitous discovery of an irregular and a semi-regular type variable in the field of BY Draconis

NASA Astrophysics Data System (ADS)

Messina, S.; Marino, G.; Rodonò, M.; Cutispoto, G.

2000-12-01

We present new evidence of the optical variability of two red giant stars: HD 172468 and HK Dra, based on photometric and spectroscopic observations. These stars had been included as check stars in our photometric monitoring program of BY Dra and turned out to be variable. HD 172468, whereas almost constant for most of the time, suddenly started to drop in brightness to such a low level to become undetectable. We suspect that such an abrupt event may be an ``obscurational'' minimum, that is typical of eruptive RCB stars, or may be due to the variable extinction by circumstellar dust in a young Orion type object. HK Dra, already known as an irregular variable, is characterised by periodic flux modulation with season-to-season changes of the photometric period, as inferred from a periodogram analysis. It also shows changes of the light curve peak-to-peak amplitude and shape. Such a behaviour in giant stars is commonly found among semi-regular giants (SR) at the Asymptotic Giant Branch (AGB). Our radial velocity measurements rule out that HK Dra may be a close binary system.

Implications of the Large O VI Columns around Low-redshift L ∗ Galaxies

NASA Astrophysics Data System (ADS)

McQuinn, Matthew; Werk, Jessica K.

2018-01-01

Observations reveal massive amounts of O VI around star-forming L * galaxies, with covering fractions of near unity extending to the host halo’s virial radius. This O VI absorption is typically kinematically centered upon photoionized gas, with line widths that are suprathermal and kinematically offset from the galaxy. We discuss various scenarios and whether they could result in the observed phenomenology (cooling gas flows, boundary layers, shocks, virialized gas). If collisionally ionized, as we argue is most probable, the O VI observations require that the circumgalactic medium (CGM) of L * galaxies holds nearly all of the associated baryons within a virial radius (∼ {10}11 {M}ȯ ) and hosts massive flows of cooling gas with ≈ 30[{nT}/30 {{cm}}-3 {{K}}] {M}ȯ {{yr}}-1, which must be largely prevented from accreting onto the host galaxy. Cooling and feedback energetics considerations require 10< {nT}< 100 cm‑3 K for the warm and hot halo gases. We argue that virialized gas, boundary layers, hot winds, and shocks are unlikely to directly account for the bulk of the O VI. Furthermore, we show that there is a robust constraint on the number density of many of the photoionized ∼ {10}4 {{K}} absorption systems that yields upper bounds in the range n< (0.1-3) × {10}-3(Z/0.3) cm‑3, suggesting that the dominant pressure in some photoionized clouds is nonthermal. This constraint is in accordance with the low densities inferred from more complex photoionization modeling. The large amount of cooling gas that is inferred could re-form these clouds in a fraction of the halo dynamical time, and it requires much of the feedback energy available from supernovae to be dissipated in the CGM.

The Subaru/XMM-Newton Deep Survey (SXDS). V. Optically Faint Variable Object Survey

NASA Astrophysics Data System (ADS)

Morokuma, Tomoki; Doi, Mamoru; Yasuda, Naoki; Akiyama, Masayuki; Sekiguchi, Kazuhiro; Furusawa, Hisanori; Ueda, Yoshihiro; Totani, Tomonori; Oda, Takeshi; Nagao, Tohru; Kashikawa, Nobunari; Murayama, Takashi; Ouchi, Masami; Watson, Mike G.; Richmond, Michael W.; Lidman, Christopher; Perlmutter, Saul; Spadafora, Anthony L.; Aldering, Greg; Wang, Lifan; Hook, Isobel M.; Knop, Rob A.

2008-03-01

We present our survey for optically faint variable objects using multiepoch (8-10 epochs over 2-4 years) i'-band imaging data obtained with Subaru Suprime-Cam over 0.918 deg2 in the Subaru/XMM-Newton Deep Field (SXDF). We found 1040 optically variable objects by image subtraction for all the combinations of images at different epochs. This is the first statistical sample of variable objects at depths achieved with 8-10 m class telescopes or the Hubble Space Telescope. The detection limit for variable components is i'vari ~ 25.5 mag. These variable objects were classified into variable stars, supernovae (SNe), and active galactic nuclei (AGNs), based on the optical morphologies, magnitudes, colors, and optical-mid-infrared colors of the host objects, spatial offsets of variable components from the host objects, and light curves. Detection completeness was examined by simulating light curves for periodic and irregular variability. We detected optical variability for 36% +/- 2% (51% +/- 3% for a bright sample with i' < 24.4 mag) of X-ray sources in the field. Number densities of variable objects as functions of time intervals Δ t and variable component magnitudes i'vari are obtained. Number densities of variable stars, SNe, and AGNs are 120, 489, and 579 objects deg-2, respectively. Bimodal distributions of variable stars in the color-magnitude diagrams indicate that the variable star sample consists of bright (V ~ 22 mag) blue variable stars of the halo population and faint (V ~ 23.5 mag) red variable stars of the disk population. There are a few candidates of RR Lyrae providing a possible number density of ~10-2 kpc-3 at a distance of >150 kpc from the Galactic center. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based on observations (program GN-2002B-Q-30) 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 (US), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

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Unsupervised classification of variable stars

NASA Astrophysics Data System (ADS)

Valenzuela, Lucas; Pichara, Karim

2018-03-01

During the past 10 years, a considerable amount of effort has been made to develop algorithms for automatic classification of variable stars. That has been primarily achieved by applying machine learning methods to photometric data sets where objects are represented as light curves. Classifiers require training sets to learn the underlying patterns that allow the separation among classes. Unfortunately, building training sets is an expensive process that demands a lot of human efforts. Every time data come from new surveys; the only available training instances are the ones that have a cross-match with previously labelled objects, consequently generating insufficient training sets compared with the large amounts of unlabelled sources. In this work, we present an algorithm that performs unsupervised classification of variable stars, relying only on the similarity among light curves. We tackle the unsupervised classification problem by proposing an untraditional approach. Instead of trying to match classes of stars with clusters found by a clustering algorithm, we propose a query-based method where astronomers can find groups of variable stars ranked by similarity. We also develop a fast similarity function specific for light curves, based on a novel data structure that allows scaling the search over the entire data set of unlabelled objects. Experiments show that our unsupervised model achieves high accuracy in the classification of different types of variable stars and that the proposed algorithm scales up to massive amounts of light curves.

Eclipsing binary stars in the era of massive surveys First results and future prospects

NASA Astrophysics Data System (ADS)

Papageorgiou, Athanasios; Catelan, Márcio; Ramos, Rodrigo Contreras; Drake, Andrew J.

2017-09-01

Our thinking about eclipsing binary stars has undergone a tremendous change in the last decade. Eclipsing binary stars are one of nature's best laboratories for determining the fundamental physical properties of stars and thus for testing the predictions of theoretical models. Some of the largest ongoing variable star surveys include the Catalina Real-time Transient Survey (CRTS) and the VISTA Variables in the Vía Láctea survey (VVV). They both contain a large amount of photometric data and plenty of information about eclipsing binaries that wait to be extracted and exploited. Here we briefly describe our efforts in this direction.

Strengths use as a secret of happiness: Another dimension of visually impaired individuals' psychological state.

PubMed

Matsuguma, Shinichiro; Kawashima, Motoko; Negishi, Kazuno; Sano, Fumiya; Mimura, Masaru; Tsubota, Kazuo

2018-01-01

It is well recognized that visual impairments (VI) worsen individuals' mental condition. However, little is known about the positive aspects including subjective happiness, positive emotions, and strengths. Therefore, the purpose of this study was to investigate the positive aspects of persons with VI including their subjective happiness, positive emotions, and strengths use. Positive aspects of persons with VI were measured using the Subjective Happiness Scale (SHS), the Scale of Positive and Negative Experience-Balance (SPANE-B), and the Strengths Use Scale (SUS). A cross-sectional analysis was utilized to examine personal information in a Tokyo sample (N = 44). We used a simple regression analysis and found significant relationships between the SHS or SPANE-B and SUS; on the contrary, VI-related variables were not correlated with them. A multiple regression analysis confirmed that SUS was a significant factor associated with both the SHS and SPANE-B. Strengths use might be a possible protective factor from the negative effects of VI.

Stochastic simulation of uranium migration at the Hanford 300 Area.

PubMed

Hammond, Glenn E; Lichtner, Peter C; Rockhold, Mark L

2011-03-01

This work focuses on the quantification of groundwater flow and subsequent U(VI) transport uncertainty due to heterogeneity in the sediment permeability at the Hanford 300 Area. U(VI) migration at the site is simulated with multiple realizations of stochastically-generated high resolution permeability fields and comparisons are made of cumulative water and U(VI) flux to the Columbia River. The massively parallel reactive flow and transport code PFLOTRAN is employed utilizing 40,960 processor cores on DOE's petascale Jaguar supercomputer to simultaneously execute 10 transient, variably-saturated groundwater flow and U(VI) transport simulations within 3D heterogeneous permeability fields using the code's multi-realization simulation capability. Simulation results demonstrate that the cumulative U(VI) flux to the Columbia River is less responsive to fine scale heterogeneity in permeability and more sensitive to the distribution of permeability within the river hyporheic zone and mean permeability of larger-scale geologic structures at the site. Copyright © 2010 Elsevier B.V. All rights reserved.

Upscaling of U(VI) Desorption and Transport from Decimeter-Scale Heterogeneity to Plume-Scale Modeling

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

Curtis, Gary P.; Kohler, Matthias; Kannappan, Ramakrishnan

2015-02-24

Scientifically defensible predictions of field scale U(VI) transport in groundwater requires an understanding of key processes at multiple scales. These scales range from smaller than the sediment grain scale (less than 10 μm) to as large as the field scale which can extend over several kilometers. The key processes that need to be considered include both geochemical reactions in solution and at sediment surfaces as well as physical transport processes including advection, dispersion, and pore-scale diffusion. The research summarized in this report includes both experimental and modeling results in batch, column and tracer tests. The objectives of this research weremore » to: (1) quantify the rates of U(VI) desorption from sediments acquired from a uranium contaminated aquifer in batch experiments;(2) quantify rates of U(VI) desorption in column experiments with variable chemical conditions, and(3) quantify nonreactive tracer and U(VI) transport in field tests.« less

Digital Archiving: Where the Past Lives Again

NASA Astrophysics Data System (ADS)

Paxson, K. B.

2012-06-01

The process of digital archiving for variable star data by manual entry with an Excel spreadsheet is described. Excel-based tools including a Step Magnitude Calculator and a Julian Date Calculator for variable star observations where magnitudes and Julian dates have not been reduced are presented. Variable star data in the literature and the AAVSO International Database prior to 1911 are presented and reviewed, with recent archiving work being highlighted. Digitization using optical character recognition software conversion is also demonstrated, with editing and formatting suggestions for the OCR-converted text.

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.

Discovery of a Wolf-Rayet Star through Detection of Its Photometric Variability

NASA Astrophysics Data System (ADS)

Littlefield, Colin; Garnavich, Peter; Marion, G. H. Howie; Vinkó, József; McClelland, Colin; Rettig, Terrence; Wheeler, J. Craig

2012-06-01

We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 Å, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 Å line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocular Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B - V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 ± 0.3 kpc.

The occurrence of non-pulsating stars in the γ Dor and δ Sct pulsation instability regions: Results from Kepler quarter 14–17 data

DOE PAGES

Guzik, J. A.; Bradley, P. A.; Jackiewicz, J.; ...

2015-04-21

In this study, the high precision long time-series photometry of the NASA Kepler spacecraft provides an excellent means to discover and characterize variability in main-sequence stars, and to make progress in interpreting the pulsations to derive stellar interior structure and test stellar models. For stars of spectral types A–F, the Kepler data revealed a number of surprises, such as more hybrid pulsating Sct and Dor pulsators than expected, pulsators lying outside of the instability regions predicted by theory, and stars that were expected to pulsate, but showed no variability. In our 2013 Astronomical Review article, we discussed the statistics ofmore » variability for 633 faint (Kepler magnitude 14–16) spectral type A–F stars observed by Kepler during Quarters 6–13 (June 2010–June 2012).« less

The occurrence of non-pulsating stars in the γ Dor and δ Sct pulsation instability regions: Results from Kepler quarter 14–17 data

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

Guzik, J. A.; Bradley, P. A.; Jackiewicz, J.

In this study, the high precision long time-series photometry of the NASA Kepler spacecraft provides an excellent means to discover and characterize variability in main-sequence stars, and to make progress in interpreting the pulsations to derive stellar interior structure and test stellar models. For stars of spectral types A–F, the Kepler data revealed a number of surprises, such as more hybrid pulsating Sct and Dor pulsators than expected, pulsators lying outside of the instability regions predicted by theory, and stars that were expected to pulsate, but showed no variability. In our 2013 Astronomical Review article, we discussed the statistics ofmore » variability for 633 faint (Kepler magnitude 14–16) spectral type A–F stars observed by Kepler during Quarters 6–13 (June 2010–June 2012).« less

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.

Probing me Reverse Shock in an Oxygen-Rich Supernova Remnant

NASA Technical Reports Server (NTRS)

Gaetz, Terrance; Sonneborn, George (Technical Monitor)

2004-01-01

The aim of this project is to examine the O VI emission at three positions around the X- ray bright ring of the remnant in order to investigate the relation between the O VI emission, the X-ray O VII and O VIII emission, and the optical [OIII} emission, and how these vary around the rim of the remnant. All three pointings and the background pointing have now been observed; the archive notification for the most recent dataset was Oct 30, 2003. After reprocessing and screening, the net exposure time for the SE exposure is only 54 percent of the approved time (15 kilosec). for the SE exposure, the available statistics are not good enough for analysis. A request for reobservation to make up for the lost time in the SE pointing has been approved. Broad O VI 1032 and O VI 1038 emission is detected with velocity width of at least 800 km/s, and possibly exceeding 1000 km/s. The Flanagan et al. analysis of the Chandra grating data show bulk velocities in the X-ray gas of order +/- 1000 km/s. In the region of the FUSE E0lO2-SE pointing, the Chandra data indicate both blue-shifted and red-shifted emission. Analysis of the velocity structure of the O VI emission will provide additional constraints on the kinematics of the gas: is it emission from a tilted expanding barrel, or a more symmetric expansion? The O VI fluxes are also needed to assess whether the O VI is radiation from recombining O VII or instead fiom cooler gas ionizing toward O VII. The emission is faint, however, which complicates the analysis. Because the lines are so broad, absorption by intervening H2, CII, and foreground OVI must be considered. A number of stars in the SMC have been observed which provide information on foreground OVI absorption. The initial analyses have concentrated on the Li1F channel since the guidance is based on that channel. The Li2F channel is being examined exposure by exposure to see if any of the data can be used to improve the signal to noise in the Li1F data.

Time-dependent Models of Magnetospheric Accretion onto Young Stars

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

Robinson, C. E.; Espaillat, C. C.; Owen, J. E.

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that ifmore » the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.« less

The MACHO Project Large Magellanic Cloud Variable-Star Inventory. IX. Frequency Analysis of the First-Overtone RR Lyrae Stars and the Indication for Nonradial Pulsations

NASA Astrophysics Data System (ADS)

Alcock, C.; Allsman, R.; Alves, D. R.; Axelrod, T.; Becker, A.; Bennett, D.; Clement, C.; Cook, K. H.; Drake, A.; Freeman, K.; Geha, M.; Griest, K.; Kovács, G.; Kurtz, D. W.; Lehner, M.; Marshall, S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.; Quinn, P.; Rodgers, A.; Rowe, J.; Stubbs, C.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D. L.

2000-10-01

More than 1300 variables classified provisionally as first-overtone RR Lyrae pulsators in the MACHO variable-star database of the Large Magellanic Cloud (LMC) have been subjected to standard frequency analysis. Based on the remnant power in the prewhitened spectra, we found 70% of the total population to be monoperiodic. The remaining 30% (411 stars) are classified as one of nine types according to their frequency spectra. Several types of RR Lyrae pulsational behavior are clearly identified here for the first time. Together with the earlier discovered double-mode (fundamental and first-overtone) variables, this study increased the number of known double-mode stars in the LMC to 181. During the total 6.5 yr time span of the data, 10% of the stars showed strong period changes. The size, and in general also the patterns of the period changes, exclude a simple evolutionary explanation. We also discovered two additional types of multifrequency pulsators with low occurrence rates of 2% for each. In the first type, there remains one closely spaced component after prewhitening by the main pulsation frequency. In the second type, the number of remnant components is two; they are also closely spaced, and are symmetric in their frequency spacing relative to the central component. This latter type of variables are associated with their relatives among the fundamental pulsators, known as Blazhko variables. Their high frequency (~20%) among the fundamental-mode variables versus the low occurrence rate of their first-overtone counterparts makes it more difficult to explain the Blazhko phenomenon by any theory depending mainly on the role of aspect angle or magnetic field. None of the current theoretical models are able to explain the observed close frequency components without invoking nonradial pulsation components in these stars.

News and Views: Kleopatra a pile of rubble, shedding moons; Did plasma flow falter to stretch solar minimum? Amateurs hit 20 million variable-star observations; Climate maths; Planetary priorities; New roles in BGA

NASA Astrophysics Data System (ADS)

2011-04-01

Metallic asteroid 216 Kleopatra is shaped like a dog's bone and has two tiny moons - which came from the asteroid itself - according to a team of astronomers from France and the US, who also measured its surprisingly low density and concluded that it is a collection of rubble. The recent solar minimum was longer and lower than expected, with a low polar field and an unusually large number of days with no sunspots visible. Models of the magnetic field and plasma flow within the Sun suggest that fast, then slow meridional flow could account for this pattern. Variable stars are a significant scientific target for amateur astronomers. The American Association of Variable Star Observers runs the world's largest database of variable star observations, from volunteers, and reached 20 million observations in February.

Multiple stellar populations in Magellanic Cloud clusters - VI. A survey of multiple sequences and Be stars in young clusters

NASA Astrophysics Data System (ADS)

Milone, A. P.; Marino, A. F.; Di Criscienzo, M.; D'Antona, F.; Bedin, L. R.; Da Costa, G.; Piotto, G.; Tailo, M.; Dotter, A.; Angeloni, R.; Anderson, J.; Jerjen, H.; Li, C.; Dupree, A.; Granata, V.; Lagioia, E. P.; Mackey, A. D.; Nardiello, D.; Vesperini, E.

2018-06-01

The split main sequences (MSs) and extended MS turnoffs (eMSTOs) detected in a few young clusters have demonstrated that these stellar systems host multiple populations differing in a number of properties such as rotation and, possibly, age. We analyse Hubble Space Telescope photometry for 13 clusters with ages between ˜40 and ˜1000 Myr and of different masses. Our goal is to investigate for the first time the occurrence of multiple populations in a large sample of young clusters. We find that all the clusters exhibit the eMSTO phenomenon and that MS stars more massive than ˜1.6 M_{⊙} define a blue and a red MS, with the latter hosting the majority of MS stars. The comparison between the observations and isochrones suggests that the blue MSs are made of slow-rotating stars, while the red MSs host stars with rotational velocities close to the breakup value. About half of the bright MS stars in the youngest clusters are H α emitters. These Be stars populate the red MS and the reddest part of the eMSTO, thus supporting the idea that the red MS is made of fast rotators. We conclude that the split MS and the eMSTO are a common feature of young clusters in both Magellanic Clouds. The phenomena of a split MS and an eMSTO occur for stars that are more massive than a specific threshold, which is independent of the host-cluster mass. As a by-product, we report the serendipitous discovery of a young Small Magellanic Cloud cluster, GALFOR 1.

Amateur-Professional Collaborations in the AAVSO

NASA Astrophysics Data System (ADS)

Hawkins, G.; Mattei, J. A.; Waagen, E. O.

2000-05-01

The AAVSO coordinates, collects, evaluates, and archives variable star observations made largely by amateur astronomers around the world, and publishes and disseminates these observations to researchers and educators worldwide. Its electronic database of nearly 10 million visual variable star observations contributed by 6,000 amateur astronomers in over 40 countries since 1911 is the world's largest and longest-running. The AAVSO has a long history of collaborations between its amateur astronomer observers and professional astronomers. Many of the over 275 requests received yearly from astronomers for AAVSO data and services result in collaborative projects - particularly in multiwavelength observations of variable stars using ground-based telescopes and/or satellites - to help schedule observing runs; provide sumultaneous optical coverage of observing targets and immediate notification of their activity during particular satellite observations; correlate multiwavelength data; and analyze long-term variable star behavior. Among the more dramatic collaborations AAVSO observers have participated in are numerous multi-satellite observing runs on specific variable stars triggered in response to real-time alerts to stellar activity from AAVSO observers; and the variable star observations made during the Astro-2 mission, in which real-time observations by AAVSO observers directed shuttle astronauts to observing targets, and resulted in seminal new information about the cataclysmic variable Z Camelopardalis. The AAVSO is embarking on an exciting new collaboration with Gamma-Ray astronomers at NASA/Marshall Space Flight Center. The AAVSO and the MSFC Gamma-Ray Burst Team have established a Gamma-Ray Burst Network, in which participating AAVSO observers will be alerted immediately via pagers and email to the detection of gamma-ray bursts and will use their own CCD-equipped telescopes to search for the optical counterpart. We gratefully acknowledge partial funding of this network by NASA. Contact the AAVSO at aavso@aavso.org or http://www.aavso.org.

Temporary vs. Permanent Sub-slab Ports: A Comparative ...

EPA Pesticide Factsheets

Vapor intrusion (VI) is the migration of subsurface vapors, including radon and volatile organic compounds (VOCs), from the subsurface to indoor air. The VI exposure pathway extends from the contaminant source, which can be impacted soil, non-aqueous phase liquid, or contaminated groundwater, to indoor air-exposure points. Therefore, contaminated matrices may include groundwater, soil, soil gas, and indoor air. VOC contaminants of concern typically include halogenated solvents such as trichloroethene, tetrachloroethene, and chloroform, as well as petroleum hydrocarbons, such as the aromatic VOCs benzene, toluene, and xylenes. Radon is a colorless radioactive gas that is released by radioactive decay of radionuclides in rock and soil that migrate into homes through VI in a similar fashion to VOCs. This project focused on the performance of permanent versus temporary sub-slab sampling ports for the determination of VI of halogenated VOCs and radon into an unoccupied house. VOC and radon concentrations measured simultaneously in soil gas using collocated temporary and permanent ports appeared to be independent of the type of port. The variability between collocated temporary and permanent ports was much less than the spatial variability between different locations within a single residential duplex. The agreement of the majority of VOC and radon concentrations, 0–36% relative percent difference, and 2–19% relative standard deviation respectively, of each sub-sl

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.

Near-infrared variability study of the central 2.3 × 2.3 arcmin2 of the Galactic Centre - II. Identification of RR Lyrae stars in the Milky Way nuclear star cluster

NASA Astrophysics Data System (ADS)

Dong, Hui; Schödel, Rainer; Williams, Benjamin F.; Nogueras-Lara, Francisco; Gallego-Cano, Eulalia; Gallego-Calvente, Teresa; Wang, Q. Daniel; Rich, R. Michael; Morris, Mark R.; Do, Tuan; Ghez, Andrea

2017-11-01

Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K ≥ 15) stellar population in the Milky Way's nuclear star cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analysed HST/WFC3/IR observations of the central 2.3 × 2.3 arcmin2 of the Milky Way and found 21 variable stars with periods between 0.2 and 1 d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as 4 RRc stars, 4 RRab stars, 3 RRab candidates and 10 binaries. Especially, the four RRab stars show sawtooth light curves and fall exactly on to the Oosterhoff I division in the Bailey diagram. Compared to the RRab stars reported by Minniti et al., our new RRab stars have higher extinction (AK > 1.8) and should be closer to the Galactic Centre. The extinction and distance of one RRab stars match those for the Milky Way's nuclear star cluster given in previous works. We perform simulations and find that after correcting for incompleteness, there could be not more than 40 RRab stars within the Milky Way's nuclear star cluster and in our field of view. Through comparing with the known globular clusters of the Milky Way, we estimate that if there exists an old, metal-poor (-1.5 < [Fe/H] < -1) stellar population in the Milky Way nuclear star cluster on a scale of 5 × 5 pc, then it contributes at most 4.7 × 105 M⊙, I.e. ˜18 per cent of the stellar mass.

OPTICAL SPECTROSCOPY OF X-RAY-SELECTED YOUNG STARS IN THE CARINA NEBULA

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

Vaidya, Kaushar; Chen, Wen-Ping; Lee, Hsu-Tai

We present low-resolution optical spectra for 29 X-ray sources identified as either massive star candidates or low-mass pre-main-sequence (PMS) star candidates in the clusters Trumpler 16 and Trumpler 14 of the Carina Nebula. Spectra of two more objects (one with an X-ray counterpart, and one with no X-ray counterpart), not originally our targets, but found close (∼3″) to two of our targets, are presented as well. Twenty early-type stars, including an O8 star, seven B1–B2 stars, two B3 stars, a B5 star, and nine emission-line stars, are identified. Eleven T Tauri stars, including eight classical T Tauri stars (CTTSs) and threemore » weak-lined T Tauri stars, are identified. The early-type stars in our sample are more reddened compared to the previously known OB stars of the region. The Chandra hardness ratios of our T Tauri stars are found to be consistent with the Chandra hardness ratios of T Tauri stars of the Orion Nebula Cluster. Most early-type stars are found to be nonvariable in X-ray emission, except the B2 star J104518.81–594217.9, the B3 star J104507.84–594134.0, and the Ae star J104424.76–594555.0, which are possible X-ray variables. J104452.20–594155.1, a CTTS, is among the brightest and the hardest X-ray sources in our sample, appears to be a variable, and shows a strong X-ray flare. The mean optical and near-infrared photometric variability in the V and K{sub s} bands, of all sources, is found to be ∼0.04 and 0.05 mag, respectively. The T Tauri stars show significantly larger mean variation, ∼0.1 mag, in the K{sub s} band. The addition of one O star and seven B1–B2 stars reported here contributes to an 11% increase of the known OB population in the observed field. The 11 T Tauri stars are the first ever confirmed low-mass PMS stars in the Carina Nebula region.« less

Hands-On Astrophysics: Variable Stars in Math, Science, and Computer Education

NASA Astrophysics Data System (ADS)

Mattei, J. A.; Percy, J. R.

1999-12-01

Hands-On Astrophysics (HOA): Variable Stars in Math, Science, and Computer Education, is a project recently developed by the American Association of Variable Star Observers (AAVSO) with funds from the National Science Foundation. HOA uses the unique methods and the international database of the AAVSO to develop and integrate students' math and science skills through variable star observation and analysis. It can provide an understanding of basic astronomy concepts, as well as interdisciplinary connections. Most of all, it motivates the user by exposing them to the excitement of doing real science with real data. Project materials include: a database of 600,000 variable star observations; VSTAR (a data plotting and analysis program), and other user friendly software; 31 slides and 14 prints of five constellations; 45 variable star finder charts; an instructional videotape in three 15-minute segments; and a 560-page student's and teacher's manual. These materials support the National Standards for Science and Math education by directly involving the students in the scientific process. Hands-On Astrophysics is designed to be flexible. It is organized so that it can be used at many levels, in many contexts: for classroom use from high school to college level, or for individual projects. In addition, communication and support can be found through the AAVSO home page on the World Wide Web: http://www.aavso.org. The HOA materials can be ordered through this web site or from the AAVSO, 25 Birch Street Cambridge, MA 02138, USA. We gratefully acknowledge the education grant ESI-9154091 from the National Science Foundation which funded the development of this project.

MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

NASA Astrophysics Data System (ADS)

Lii, Patrick; Romanova, Marina; Lovelace, Richard

2014-01-01

Accreting magnetized stars may be in the propeller regime of disc accretion in which the angular velocity of the stellar magnetosphere exceeds that of the inner disc. In these systems, the stellar magnetosphere acts as a centrifugal barrier and inhibits matter accretion onto the rapidly rotating star. Instead, the matter accreting through the disc accumulates at the disc-magnetosphere interface where it picks up angular momentum and is ejected from the system as a wide-angled outflow which gradually collimates at larger distances from the star. If the ejection rate is lower than the accretion rate, the matter will accumulate at the boundary faster than it can be ejected; in this case, accretion onto the star proceeds through an episodic accretion instability in which the episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion of matter onto the star. In addition to the matter dominated wind component, the propeller outflow also exhibits a well-collimated, magnetically-dominated Poynting jet which transports energy and angular momentum away from the star. The propeller mechanism may explain some of the weakly-collimated jets and winds observed around some T Tauri stars as well as the episodic variability present in their light curves. It may also explain some of the quasi-periodic variability observed in cataclysmic variables, millisecond pulsars and other magnetized stars.

X ray emission from Wolf-Rayet stars with recurrent dust formation

NASA Technical Reports Server (NTRS)

Rawley, Gayle L.

1993-01-01

We were granted a ROSAT observation of the Wolf-Rayet star WR 137 (equals HD 192641) to test a proposed mechanism for producing the infrared variability reported by Williams et al. (1987). These studies showed one clear infrared outburst preceded by what may be the dimming of a previous outburst. The recurrent dust formation model was put forward by Williams et al. (1990) to account for similar variability seen in WR 140, which varies in both the infrared and X-ray bands. The detected X-ray flux from WR 140 was observed to decrease from its normally high (for Wolf-Rayet stars) level as the infrared flux increased. Observation of two apparently-periodic infrared outbursts led to the hypothesis that WR 140 had an O star companion in an eccentric orbit, and that the increase in infrared flux came from a dust formation episode triggered by the compression of the O star and Wolf-Rayet star winds. The absorption of the X-rays by the increased material explained the decrease in flux at those wavelengths. If the infrared variability in WR 137 were caused by a similar interaction of the Wolf-Rayet star with a companion, we might expect that WR 137 would show corresponding X-ray variability and an X-ray luminosity somewhat higher than typical WC stars, as well as a phase-dependent non-thermal X-ray spectrum. Our goals in this study were to obtain luminosity estimates from our counting rates for comparison with previous observations of WR 137 and other WC class stars, especially WR 140; to compare the luminosity with the IR lightcurve; and to characterize the spectral shape of the X-ray emission, including the column density.

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.

Spectral monitoring of AB Aur

NASA Astrophysics Data System (ADS)

Rodríguez Díaz, L. F.; Oostra, B.

2017-07-01

The Astronomical Observatory of the Universidad de los Andes in Bogotá, Colombia, did a spectral monitoring during 2014 and 2015 to AB Aurigae, the brightest Herbig Ae/be star in the northern hemisphere. The aim of this project is applying spectral techniques, in order to identify specific features that could help us not only to understand how this star is forming, but also to establish a pattern to explain general star formation processes. We have recorded 19 legible spectra with a resolving power of R = 11,0000, using a 40 cm Meade telescope with an eShel spectrograph, coupled by a 50-micron optical fiber. We looked for the prominent absorption lines, the Sodium doublet at 5890Å and 5896Å, respectively and Magnesium II at 4481Å; to measure radial velocities of the star, but, we did not find a constant value. Instead, it ranges from 15 km/s to 32 km/s. This variability could be explained by means of an oscillation or pulsation of the external layers of the star. Other variabilities are observed in some emission lines: Hα, Hβ, He I at 5876Å and Fe II at 5018Å. It seems this phenomenon could be typical in stars that are forming and have a circumstellar disk around themselves. This variability is associated with the nonhomogeneous surface of the star and the interaction that it has with its disk. Results of this interaction could be seen also in the stellar wind ejected by the star. More data are required in order to look for a possible period in the changes of radial velocity of the star, the same for the variability of He I and Fe II, and phenomena present in Hα. We plan to take new data in January of 2017.

Asteroseismology of hybrid δ Scuti-γ Doradus pulsating stars

NASA Astrophysics Data System (ADS)

Sánchez Arias, J. P.; Córsico, A. H.; Althaus, L. G.

2017-01-01

Context. Hybrid δ Scuti-γ Doradus pulsating stars show acoustic (p) oscillation modes typical of δ Scuti variable stars, and gravity (g) pulsation modes characteristic of γ Doradus variable stars simultaneously excited. Observations from space missions such as MOST, CoRoT, and Kepler have revealed a large number of hybrid δ Scuti-γ Doradus pulsators, thus paving the way for an exciting new channel of asteroseismic studies. Aims: We perform detailed asteroseismological modelling of five hybrid δ Scuti-γ Doradus stars. Methods: A grid-based modeling approach was employed to sound the internal structure of the target stars using stellar models ranging from the zero-age main sequence to the terminal-age main sequence, varying parameters such as stellar mass, effective temperature, metallicity and core overshooting. Their adiabatic radial (ℓ = 0) and non-radial (ℓ = 1,2,3) p and g mode periods were computed. Two model-fitting procedures were used to search for asteroseismological models that best reproduce the observed pulsation spectra of each target star. Results: We derive the fundamental parameters and the evolutionary status of five hybrid δ Scuti-γ Doradus variable stars recently observed by the CoRoT and Kepler space missions: CoRoT 105733033, CoRoT 100866999, KIC 11145123, KIC 9244992, and HD 49434. The asteroseismological model for each star results from different criteria of model selection, in which we take full advantage of the richness of periods that characterises the pulsation spectra for this kind of star.

Variable Circumstellar Disks of “Classical” Be Stars, Part 2

NASA Astrophysics Data System (ADS)

Gerhartz, Cody; Davidson, J. W.; Bjorkman, K. S.; Wisniewski, J. P.

2014-01-01

Circumstellar disks are common among many stars, all spectral types, and at different stages of their lifetimes. Among the near-main sequence “Classical” Be stars, there is growing evidence that these disks can form, dissipate, and reform, on timescales that are differ from case to case. We present data for a subset of cases where observations have been obtained throughout the different phases of the disk cycle. Using data obtained with the SpeX instrument at the NASA IRTF, we examine the IR spectral line variability of these stars to better understand the timescales and the physical mechanisms involved. The primary focus in this study are the V/R variations that are observed in the sample. A complete run of all double-peaked velocity profiles in the sample is now complete. The second stage of our project is to examine a sample of star clusters known to contain Be stars, with the goal to develop a more statistically significant sample of variable circumstellar disk systems. With a robust multi-epoch study we can determine whether these Be stars exhibit disk-loss or disk-renewal phases. The larger sample will enable an understanding of the prevalence of these disk events.

Extreme Variables in Star Forming Regions

NASA Astrophysics Data System (ADS)

Contreras Peña, Carlos Eduardo

2015-01-01

The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution. The original classification of eruptive variables divides them in two separate subclasses known as FU Orionis stars (FUors) and EX Lupi stars (EXors). In this classical view FUors are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths. Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables, show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables. However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to far-infrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV. We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data releases of the UKIDSS Galactic Plane Survey. We find 71 stars with ΔK > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded from the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| < 1° yields 816 high amplitude variables, which include known variables of different classes such as high mass X-ray binaries, Novae and eclipsing binaries among others. Remarkably, 65% of the sample are found concentrated towards areas of star formation, similar to the results from GPS. In both surveys, sources in SFRs show spectral energy distributions (SEDs) that support classification as YSOs. This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow-up allows us to confirm the pre-main sequence nature of several GPS and VVV Objects. Most objects in both samples show spectroscopic signatures that can be attributed to YSOs undergoing high states of accretion, such as veiling of photospheric features and CO emission, or show FUor-like spectra. We also find a large fraction of objects with 2.12 μm H2 emission that can be explained as arising from shock-excited emission caused by molecular outflows. Whether these molecular outflows are related to outbursts events cannot be confirmed from our data. Adding the GPS and VVV spectroscopic results, we find that between 6 and 14 objects are new additions to the FUor class from their close resemblance to the near-infrared spectra of FUors, and at least 23 more objects are new additions to the eruptive variable class. For most of these we are unable to classify them into any of the original definitions for this variable class. In any case, we are adding up to 37 new stars to the eruptive variable class which would double the current number of known objects. We note that most objects are found to be deeply embedded optically invisible stars, thus increasing the number of objects belonging to this subclass by a much larger factor. In general, objects in our samples which are found to be likely eruptive variable stars show a mixture of characteristics that can be attributed to both of the optically-defined classes. This agrees well with the recent discoveries in the literature. Finally, we are able to derive a first rough estimate on the incidence of episodic accretion among class I YSOs in the star-forming complex G305. We find that ~9% of such objects are in a state of high accretion. This number is in agreement with previous theoretical and observational estimates among class I YSOs.

Revised coordinates of variable stars in Cassiopeia

NASA Astrophysics Data System (ADS)

Nesci, R.

2018-02-01

The identification of the variable stars published on IBVS 3573 has ben revised on the basis of the original (unpublished) finding charts. Cross check with the 2MASS catalog has been made to get more accurate coordinates and to confirm their nature from their , colors. The Mira stars, given their known periods, could be used with the astrometric parallaxes of the forthcoming Gaia catalog to improve the Period-Luminosity relation.

Ubiquitous time variability of integrated stellar populations.

PubMed

Conroy, Charlie; van Dokkum, Pieter G; Choi, Jieun

2015-11-26

Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

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).

STELLAR ARCHAEOLOGY IN THE GALACTIC HALO WITH THE ULTRA-FAINT DWARFS. VI. URSA MAJOR II

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

Dall'Ora, M.; Ripepi, Vincenzo; Marconi, Marcella

2012-06-10

We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf satellite Ursa Major II (UMa II), spanning the magnitude range from V {approx} 15 to V {approx} 23.5 mag and extending over an 18 Multiplication-Sign 18 arcmin{sup 2} area centered on the Galaxy. Our photometry goes down to about 2 mag below the Galaxy's main-sequence turnoff that we detected at V {approx} 21.5 mag. We have discovered a bona fide RR Lyrae variable star in UMa II, which we use to estimate a conservative dereddened distance modulus for the galaxy of (m - M){sub 0} = 17.70more » {+-} 0.04 {+-} 0.12 mag, where the first error accounts for the uncertainties of the calibrated photometry, and the second reflects our lack of information on the metallicity of the star. The corresponding distance to UMa II is 34.7{sup +0.6}{sub -0.7}({sup +2.0}{sub -1.9}) kpc. Our photometry shows evidence of a spread in the Galaxy's subgiant branch, compatible with a spread in metal abundance in the range between Z = 0.0001 and Z = 0.001. Based on our estimate of the distance, a comparison of the fiducial lines of the Galactic globular clusters M68 and M5 ([Fe/H] = -2.27 {+-} 0.04 dex and -1.33 {+-} 0.02 dex, respectively), with the position on the CMD of spectroscopically confirmed Galaxy members, may suggest the existence of stellar populations of different metal abundance/age in the central region of UMa II.« less

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

Searching for Variable Stars in the Field of Dolidze 35 (Abstract)

NASA Astrophysics Data System (ADS)

Welch, J.; Smith, J. A.

2018-06-01

(Abstract only) We are conducting a study of the open cluster Dolidze-35. We have a data set which contains several nights and spans four years. One step of our survey is to search these data to identify candidate local standards and potential variable stars. We present early results of the variable search effort.

Frequency Analysis of the RRc Variables of the MACHO Database for the LMC

NASA Astrophysics Data System (ADS)

Kovács, G.; Alcock, C.; Allsman, R.; Alves, D.; Axelrod, T.; Becker, A.; Bennett, D.; Clement, C.; Cook, K. H.; Drake, A.; Freeman, K.; Geha, M.; Griest, K.; Kurtz, D. W.; Lehner, M.; Marshall, S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.; Quinn, P.; Rodgers, A.; Rowe, J.; Stubbs, C.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D. L.; MACHO Collaboration

We present the first massive frequency analysis of the 1200 first overtone RR Lyrae stars in the Large Magellanic Cloud observed in the first 4.3 yr of the MACHO project. Besides the many new double-mode variables, we also discovered stars with closely spaced frequencies. These variables are most probably nonradial pulsators.

Measuring the rotation periods of 4-10 Myr T-Tauri stars in the Orion OB1 association

NASA Astrophysics Data System (ADS)

Karim, Md Tanveer; Stassun, Keivan; Briceno, Cesar; Vivas, Kathy; Raetz, Stefanie; Calvet, Nuria; Mateu, Cecilia; Downes, Juan Jose; Hernandez, Jesus; Neuhäuser, Ralph; Mugrauer, Markus; Takahashi, Hidenori; Tachihara, Kengo; Chini, Rolf; YETI

2016-01-01

Most existing studies of young stellar populations have focused on the youngest (< 2-3 Myr) T-Tauri stars, which are usually associated with their natal gas and hence easier to identify. In contrast, older T-Tauri stars (~ 4-10 Myr), being more difficult to find, have been less studied, even though they hold key insight to understanding evolution of lower-mass (0.1-2 M⊙) stars and of protoplanetary discs. We present a study of photometric variability of 1974 confirmed 4-10 Myr old T-Tauri stars in the Orion OB1 association using optical time-series from three different surveys: the Centro de Investigaciones de Astronomía-Quest Equatorial Survey Team (CIDA-QUEST), the Young Exoplanet Transit Initiative (YETI) and from a Kitt Peak National Observatory (KPNO) campaign. We investigated stellar rotation periods according to the type of stars (Classical or Weak-lined T-Tauri stars) and their locations, to look for population-wide trends. We detected 563 periodic variables and 1411 non-periodic variables by investigating the light curves of these stars. We find that ~ 30% of Weak-line T-Tauri stars (WTTS) and ~ 20% of Classical T-Tauri stars (CTTS) are periodic. Though we did not find any noticeable difference in rotation period between CTTS and WTTS, our study does show a change in the overall rotation periods of stars 4-10 Myr old, consistent with predictions of angular momentum evolution models, an important constraint for theoretical models for an age range for which no similar data existed.

VizieR Online Data Catalog: Stellar parameters of KIC planet-host stars (Bastien+, 2014)

NASA Astrophysics Data System (ADS)

Bastien, F. A.; Stassun, K. G.; Pepper, J.

2017-07-01

We draw our bright KOI sample from the NASA Exoplanet Archive (NEA; Akeson et al. 2013PASP..125..989A) accessed on 2014 January 7. We restrict the sample to stars with 6650 K>Teff>4500 K, the Teff range for which F8 is calibrated. We exclude 28 stars with overall range of photometric variability >10 ppt (parts per thousand), as phenomena in the light curves of such chromospherically active stars can boost the measured F8 and thus result in an erroneous F8-based log g. These excluded stars (10% of the sample) are cooler than average for the overall sample, as expected given their large variability. Our sample after applying these cuts contains 289 stars (407 KOIs). (1 data file).

Dermoscopic nevus patterns in skin of colour: a prospective, cross-sectional, morphological study in individuals with skin type V and VI.

PubMed

Lallas, A; Reggiani, C; Argenziano, G; Kyrgidis, A; Bakos, R; Masiero, N C M S; Scheibe, A B; Cabo, H; Ozdemir, F; Sortino-Rachou, A M; Turk, B Gerceker; Moscarella, E; Longo, C; Zalaudek, I

2014-11-01

Most of the knowledge on the prevailing dermoscopic patterns of acquired melanocytic nevi (AMV) is based on studies in Caucasians, while little research focuses on the dermoscopic variability in nevi in skin of colour. To analyse the prevalent dermoscopic nevus patterns in subjects with a skin type (ST) V and VI. Prospective, cross-sectional, morphological study was conducted in six clinics with enrolment of consecutive individuals with a ST V or VI. Digital dermoscopic images of selected representative AMN were assessed for dermoscopic colours, morphological patterns and pigment distribution. Analysis of 300 nevi from subjects with ST V and VI revealed significant differences in the nevus pattern between these two groups. The majority of nevi in ST V revealed a reticular pattern, whereas persons with ST VI more frequently exhibited a structureless pattern. Black, blue and grey were more frequent in ST VI, whereas the vast majority of nevi in ST V individuals showed dark brown colour. Our study provides new insights into the nevus pattern in individuals with a dark pigmentary trait, which may aid the diagnosis and management of nevi in this patients group. © 2013 European Academy of Dermatology and Venereology.

The Search for New Luminous Blue Variable Stars: Near-Infrared Spectroscopy of Stars With 24 micron Shells

NASA Astrophysics Data System (ADS)

Stringfellow, Guy; Gvaramadze, Vasilii

2010-02-01

Luminous Blue Variable (LBV) stars represent an extremely rare class of very luminous and massive stars. Only about a dozen confirmed Galactic LBV stars are known to date, which precludes us from determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. The known LBV stars each have their own unique properties, so new discoveries add insight into the properties and evolutionary status of LBVs and massive stars; even one new discovery of objects of this type could provide break-through results in the understanding of the intermediate stages of massive star evolution. We have culled a prime sample of possible LBV candidates from the Spitzer 24 (micron) archival data. All have circumstellar nebulae, rings, and shells (typical of LBVs and related stars) surrounding reddened central stars. Spectroscopic followup of about two dozen optically visible central stars associated with the shells from this sample showed that they are either candidate LBVs, late WN-type Wolf-Rayet stars or blue supergiants. We propose infrared spectroscopic observations of the central stars for a large fraction (23 stars) of our northern sample to determine their nature and discover additional LBV candidates. These stars have no plausible optical counterparts, so infrared spectra are needed. This program requires two nights of Hale time using TripleSpec.

Advective removal of intraparticle uranium from contaminated vadose zone sediments, Hanford, U.S.

PubMed

Ilton, Eugene S; Qafoku, Nikolla P; Liu, Chongxuan; Moore, Dean A; Zachara, John M

2008-03-01

A column study on U(VI)-contaminated vadose zone sediments from the Hanford Site, WA, was performed to investigate U(VI) release kinetics with water advection and variable geochemical conditions. The sediments were collected from an area adjacent to and below tank BX-102 that was contaminated as a result of a radioactive tank waste overfill event. The primary reservoir for U(VI) in the sediments are micrometer-size precipitates composed of nanocrystallite aggregates of a Na-U-Silicate phase, most likely Na-boltwoodite, that nucleated and grew within microfractures of the plagioclase component of sand-sized granitic clasts. Two sediment samples, with different U(VI) concentrations and intraparticle mass transfer properties, were leached with advective flows of three different solutions. The influent solutions were all calcite-saturated and in equilibrium with atmospheric CO2. One solution was prepared from DI water, the second was a synthetic groundwater (SGW) with elevated Na that mimicked groundwater at the Hanford site, and the third was the same SGW but with both elevated Na and Si. The latter two solutions were employed, in part, to test the effect of saturation state on U(VI) release. For both sediments, and all three electrolytes, there was an initial rapid release of U(VI) to the advecting solution followed by slower near steady-state release. U(VI)aq concentrations increased during subsequent stop-flow events. The electrolytes with elevated Na and Si depressed U(VL)aq concentrations in effluent solutions. Effluent U(VI)aq concentrations for both sediments and all three electrolytes were simulated reasonably well by a three domain model (the advecting fluid, fractures, and matrix) that coupled U(VI) dissolution, intraparticle U(VI)aq diffusion, and interparticle advection, where diffusion and dissolution properties were parameterized in a previous batch study.

Confirming LBV Candidates Through Variability: A Photometric and Spectroscopic Monitoring Study

NASA Astrophysics Data System (ADS)

Stringfellow, Guy; Gvaramadze, Vasilii

2012-02-01

Luminous Blue Variable (LBV) stars represent an extremely rare class of very luminous, massive stars. About a dozen confirmed Galactic LBV stars are known, which precludes determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. Several catalogues of nebulae - rings and shells typical of LBVs - derived from the GLIMPSE and MIPSGAL surveys have recently been published. We conducted a near-IR spectral survey of a large subset of central stars residing within these nebulae and have identified nearly two dozen new candidate LBVs (cLBVs) based on spectral similarity alone; they remain cLBVs until 1-3 mag variability is demonstrated, securing their LBV nature. This marks a significant advancement in the study of massive stars, far outweighing the return from many studies searching for LBVs and WRs the past several decades. Using SMARTS 16 new cLBVs, 3 confirmed LBVs, and 2 previously known cLBVs will undergo photometric IR-monitoring, with 6 new cLBVs monitored spectroscopically (already being photometrically monitored elsewhere).

Confirming LBV Candidates Through Variability: A Photometric and Spectroscopic Monitoring Study

NASA Astrophysics Data System (ADS)

Stringfellow, Guy; Gvaramadze, Vasilii

2011-08-01

Luminous Blue Variable (LBV) stars represent an extremely rare class of very luminous, massive stars. About a dozen confirmed Galactic LBV stars are known, which precludes determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. Several catalogues of nebulae - rings and shells typical of LBVs - derived from the GLIMPSE and MIPSGAL surveys have recently been published. We conducted a near-IR spectral survey of a large subset of central stars residing within these nebulae and have identified nearly two dozen new candidate LBVs (cLBVs) based on spectral similarity alone; they remain cLBVs until 1-3 mag variability is demonstrated, securing their LBV nature. This marks a significant advancement in the study of massive stars, far outweighing the return from many studies searching for LBVs and WRs the past several decades. Using SMARTS 16 new cLBVs, 3 confirmed LBVs, and 2 previously known cLBVs will undergo photometric IR-monitoring, with 6 new cLBVs monitored spectroscopically (already being photometrically monitored elsewhere).

A remarkable oxygen-rich asymptotic giant branch variable in the Sagittarius Dwarf Irregular Galaxy

NASA Astrophysics Data System (ADS)

Whitelock, Patricia A.; Menzies, John W.; Feast, Michael W.; Marigo, Paola

2018-01-01

We report and discuss JHKS photometry for Sgr dIG, a very metal-deficient galaxy in the Local Group, obtained over 3.5 years with the Infrared Survey Facility in South Africa. Three large amplitude asymptotic giant branch variables are identified. One is an oxygen-rich star that has a pulsation period of 950 d, which was until recently undergoing hot bottom burning, with Mbol ∼ -6.7. It is surprising to find a variable of this sort in Sgr dIG, given their rarity in other dwarf irregulars. Despite its long period the star is relatively blue and is fainter, at all wavelengths shorter than 4.5 μm, than anticipated from period-luminosity relations that describe hot bottom burning stars. A comparison with models suggests it had a main-sequence mass Mi ∼ 5 M⊙ and that it is now near the end of its asymptotic giant branch evolution. The other two periodic variables are carbon stars with periods of 670 and 503 d (Mbol ∼ -5.7 and -5.3). They are very similar to other such stars found on the asymptotic giant branch of metal-deficient Local Group galaxies and a comparison with models suggests Mi ∼ 3 M⊙. We compare the number of asymptotic giant branch variables in Sgr dIG to those in NGC 6822 and IC 1613, and suggest that the differences may be due to the high specific star formation rate and low metallicity of Sgr dIG.

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.

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.

VizieR Online Data Catalog: Early-type EBs with intermediate orbital periods (Moe+, 2015)

NASA Astrophysics Data System (ADS)

Moe, M.; Di Stefano, R.

2017-09-01

In this study, we select the NB~96000 systems in the OGLE-I catalog (Udalski et al. 2008AcA....58...89U) with mean magnitudes 16.0

Iron abundance in the hot DA white dwarfs Feige 24 and G191 B2B

NASA Technical Reports Server (NTRS)

Vennes, Stephane; Chayer, Pierre; Thorstensen, John R.; Bowyer, Stuart; Shipman, Harry L.

1992-01-01

Attention is given to model calculations of the far- and extreme-UV line spectra of highly ionized Fe species (Fe IV, Fe V, and Fe VI) for hot high-gravity H-rich stars. A spectral analysis of 31 hr of exposure of the DA white dwarf Feige 24 with IUE in the echelle mode reveals the presence of Fe with an abundance relative to H by number of (5-10) x 10 exp -6 with an uncertainty dominated by the determination of stellar parameters. An analysis of IUE data from the white dwarf G191 B2B results in a similar Fe abundance if this star shares similar atmospheric parameters (Teff, g) with Feige 24. Fe is thus the second most abundant photospheric element in hot DA white dwarfs.

Radial velocity variability and stellar properties of FGK stars in the cores of NGC 2516 and NGC 2422

NASA Astrophysics Data System (ADS)

Bailey, John I.; Mateo, Mario; White, Russel J.; Shectman, Stephen A.; Crane, Jeffrey D.

2018-04-01

We present multi-epoch high-dispersion optical spectra obtained with the Michigan/Magellan Fibre System of 126 and 125 Sun-like stars in the young clusters NGC 2516 (141 Myr) and NGC 2422 (73 Myr). We determine stellar properties including radial velocity (RV), Teff, [Fe/H], [α/Fe] and the line-of-sight rotation rate, vrsin (i), from these spectra. Our median RV precision of 80 m s-1 on individual epochs that span a temporal baseline of 1.1 yr enables us to investigate membership and stellar binarity, and to search for sub-stellar companions. We determine membership probabilities and RV variability probabilities for our sample along with candidate companion orbital periods for a select subset of stars. In NGC 2516, we identified 81 RV members, 27 spectroscopic binaries (17 previously identified as photometric binaries) and 16 other stars that show significant RV variability after accounting for average stellar jitter at the 74 m s-1 level. In NGC 2422, we identify 57 members, 11 spectroscopic binaries and three other stars that show significant RV variability after accounting for an average jitter of 138 m s-1. We use Monte Carlo simulations to verify our stellar jitter measurements, determine the proportion of exoplanets and stellar companions to which we are sensitive, and estimate companion-mass limits for our targets. We also report mean cluster metallicity, velocity and velocity dispersion based on our member targets. We identify 58 non-member stars as RV variables, 24 of which have RV amplitudes that imply stellar or brown-dwarf mass companions. Finally, we note the discovery of a separate RV clustering of stars in our NGC 2422 sample.

Observing Globular Cluster RR Lyrae Variables with the BYU West Mountain Observatory

NASA Astrophysics Data System (ADS)

Jeffery, E. J.; Joner, M. D.

2016-06-01

We have utilized the 0.9-meter telescope of the Brigham Young University West Mountain Observatory to secure data on six northern hemisphere globular clusters. Here we present representative observations of RR Lyrae stars located in these clusters, including light curves. We compare light curves produced using both DAOPHOT and ISIS software packages. Light curve fitting is done with FITLC. We find that for well-separated stars, DAOPHOT and ISIS provide comparable results. However, for stars within the cluster core, ISIS provides superior results. These improved techniques will allow us to better measure the properties of cluster variable stars.

Modeling biosorption of Cr(VI) onto Ulva compressa L. from aqueous solutions.

PubMed

Aid, Asma; Amokrane, Samira; Nibou, Djamel; Mekatel, Elhadj; Trari, Mohamed; Hulea, Vasile

2018-01-01

The marine biomass Ulva compressa L. (ECL) was used as a low-cost biosorbent for the removal of Cr(VI) from contaminated aqueous solutions. The operating variables were optimized: pH ∼ 2, initial concentration of 25 mg/L, solid/liquid ratio of 6 g/L and a temperature of 50 °C, leading to an uptake elimination of 96%. A full factorial experimental design technique enabled us to obtain a mathematical model describing the Cr(VI) biosorption and to study the main effects and interactions among operational parameters. The equilibrium isotherm was analyzed by the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models; it has been found that the adsorption process follows well the Langmuir model. Kinetic studies showed that the pseudo-second order model describes suitably the experimental data. The thermodynamic parameters indicated an endothermic heat and a spontaneity of the Cr(VI) biosorption onto ECL.

RR Lyrae variables in M33: two new fields and an analysis of the galaxy's population

NASA Astrophysics Data System (ADS)

Tanakul, Nahathai; Yang, Soung-Chul; Sarajedini, Ata

2017-06-01

We present a re-analysis of M33 RR Lyrae variables in four different fields: two inner disc fields and two outer disc fields. These are located at 8.5, 8.7, 36 and 46 arcmin from the centre of M33, respectively. We identify 48 new RR Lyrae variable stars and refine the light-curve properties of 51 previously identified variables. From the light curves, we calculate reddenings and metallicities for each star. Using data in this paper and previously published material, we are able to construct a radial density profile for the RR Lyrae stars in M33. This profile, when plotted in log space, has a slope of ˜-2.0 ± 0.15 which agrees with the radial distribution of halo stars in the Milky Way and M31. This suggests that the majority of M33 RR Lyrae variables observed so far belong to the halo. We also examine the RR Lyrae specific frequency and absolute magnitude relation in M33 and find good agreement with previous studies.

Ionization and thermal equilibrium models for O star winds based on time-independent radiation-driven wind theory

NASA Technical Reports Server (NTRS)

Drew, J. E.

1989-01-01

Ab initio ionization and thermal equilibrium models are calculated for the winds of O stars using the results of steady state radiation-driven wind theory to determine the input parameters. Self-consistent methods are used for the roles of H, He, and the most abundant heavy elements in both the statistical and the thermal equilibrium. The model grid was chosen to encompass all O spectral subtypes and the full range of luminosity classes. Results of earlier modeling of O star winds by Klein and Castor (1978) are reproduced and used to motivate improvements in the treatment of the hydrogen equilibrium. The wind temperature profile is revealed to be sensitive to gross changes in the heavy element abundances, but insensitive to other factors considered such as the mass-loss rate and velocity law. The reduced wind temperatures obtained in observing the luminosity dependence of the Si IV lambda 1397 wind absorption profile are shown to eliminate any prospect of explaining the observed O VI lambda 1036 line profiles in terms of time-independent radiation-driven wind theory.

Lights and shadows: multi-wavelength analysis of young stellar objects and their protoplanetary discs

NASA Astrophysics Data System (ADS)

Rigon, Laura

2016-03-01

Stars form from the collapse of molecular clouds and evolve in an environment rich in gas and dust before becoming Main Sequence stars. During this phase, characterised by the presence of a protoplanetary disc, stars manifest changes in the structure and luminosity. This thesis performs a multi-wavelength analysis, from optical to mm range, on a sample of young stars (YSOs), mainly Classical T Tauri (CTTS). The purpose is to study optical and infrared variability and its relation with the protoplanetary disc. Longer wavelength, in the mm range, are used instead to investigate the evolution of the disc, in terms of dust growth. In optical, an F-test on a sample of 39 CTTS reveals that 67% of the stars are variable. The variability, quantified through pooled sigma, is visible both in magnitude amplitudes and changes over time. Time series analysis applied on the more variable stars finds the presence of quasi periodicity, with periods longer than two weeks, interpreted either as eclipsing material in the disc happening on a non-regular basis, or as a consequence of star-disc interaction via magnetic field lines. The variability of YSOs is confirmed also in infrared, even if with lower amplitude. No strong correlations are found between optical and infrared variability, which implies a different cause or a time shift in the two events. By using a toy model to explore their origin, I find that infrared variations are likely to stem from emissions in the inner disc. The evolution of discs in terms of dust growth is confirmed in most discs by the analysis of the slope of the spectral energy distribution (SED), after correcting for wind emission and optical depth effects. However, the comparison with a radiative transfer model highlights that a number of disc parameters, in particular disc masses and temperature, dust size distribution and composition, can also affect the slope of the SED.

The Sproul 24-Inch Refractor: Entering A New Century of Research

NASA Astrophysics Data System (ADS)

Augensen, H. J.; Heintz, W. D.; Schultz, M. R.; Hassel, G. E., Jr.; Inoue, S.; Howanski, R.; Fanning, T.

1999-05-01

The Sproul Observatory, located in Swarthmore, Pennsylvania, has been in operation since 1912. Its major research instrument is a 24-inch, f/18 refracting telescope with lenses made by Brashear. The research conducted during the 20th century concentrated on obtaining parallaxes of nearby stars and also on the exploration of visual double and multiple star systems. The Sproul plate vault contains some 90,000 plates, from which 1500 stellar parallaxes, or about 10% of the current parallax database, have been extracted. Heintz made 54,000 observations (including those made with other telescopes) of double stars over 43 years (47,500 by micrometer, 6500 by photography), resulting in the calculation of 500 orbits and 900 newly discovered double stars. Photographic observations ceased in 1994. In 1998 the refractor was fitted with an Apogee AP-6 CCD camera, which contains a Kodak KAF 1000 chip with 1024 x 1024 pixel array, and gives a 0.45 arcseconds per pixel image scale and 8 x 8 arcminute field of view at the focal plane. The camera is operated using PMIS software. A filter wheel constructed by ISI Systems and attached to the camera contains 5-mm thick B, V, and R filters. The Sproul telescope has now been given a new task: the study of variable stars. Currently under investigation are RV Tauri and semiregular variables, SX Phoenicis stars, and also stars which are suspected of being variable, taken from the New Catalogue of Stars Suspected of Variability of Light, Nauka Publishing, Moscow 1982. Thus far, the most convincing cases for variability are NSV 656 (irregular?), 1098 (large amplitude, probably Mira type), 1470 (short P, eclipsing?), and 13514 (P 105d?). This work has been supported by a Provost Grant from Swarthmore College and by the Howard Hughes Medical Institute-Supported Summer Research in Science Program.

SpecDB: The AAVSO’s Public Repository for Spectra of Variable Stars

NASA Astrophysics Data System (ADS)

Kafka, Stella; Weaver, John; Silvis, George; Beck, Sara

2018-01-01

SpecDB is the American Association of Variable Star Observers (AAVSO) spectral database. Accessible to any astronomer with the capability to perform spectroscopy, SpecDB provides an unprecedented scientific opportunity for amateur and professional astronomers around the globe. Backed by the Variable Star Index, one of the most utilized variable star catalogs, SpecDB is expected to become one of the world leading databases of its kind. Once verified by a team of expert spectroscopists, an observer can upload spectra of variable stars target easily and efficiently. Uploaded spectra can then be searched for, previewed, and downloaded for inclusion in publications. Close community development and involvement will ensure a user-friendly and versatile database, compatible with the needs of 21st century astrophysics. Observations of 1D spectra are submitted as FITS files. All spectra are required to be preprocessed for wavelength calibration and dark subtraction; Bias and flat are strongly recommended. First time observers are required to submit a spectrum of a standard (non-variable) star to be checked for errors in technique or equipment. Regardless of user validation, FITS headers must include several value cards detailing the observation, as well as information regarding the observer, equipment, and observing site in accordance with existing AAVSO records. This enforces consistency and provides necessary details for follow up analysis. Requirements are provided to users in a comprehensive guidebook and accompanying technical manual. Upon submission, FITS headers are automatically checked for errors and any anomalies are immediately fed back to the user. Successful candidates can then submit at will, including multiple simultaneous submissions. All published observations can be searched and interactively previewed. Community involvement will be enhanced by an associated forum where users can discuss observation techniques and suggest improvements to the database.

A UV-to-MIR monitoring of DR Tau: Exploring how water vapor in the planet formation region is affected by stellar accretion variability

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

Banzatti, A.; Meyer, M. R.; Manara, C. F.

2014-01-01

Young stars are known to show variability due to non-steady mass accretion rate from their circumstellar disks. Accretion flares can produce strong energetic irradiation and heating that may affect the disk in the planet formation region, close to the central star. During an extreme accretion outburst in the young star EX Lupi, the prototype of EXor variables, remarkable changes in molecular gas emission from ∼1 AU in the disk have recently been observed. Here, we focus on water vapor and explore how it is affected by variable accretion luminosity in T Tauri stars. We monitored a young highly variable solar-massmore » star, DR Tau, using simultaneously two high/medium-resolution spectrographs at the European Southern Observatory Very Large Telescope: VISIR at 12.4 μm to observe water lines from the disk and X-shooter covering from 0.3 to 2.5 μm to constrain the stellar accretion. Three epochs spanning timescales from several days to several weeks were obtained. The accretion luminosity was estimated to change within a factor of ∼2 and no change in water emission was detected at a significant level. In comparison with EX Lupi and EXor outbursts, DR Tau suggests that the less long-lived and weaker variability phenomena typical of T Tauri stars may leave water at planet-forming radii in the disk mostly unaffected. We propose that these systems may provide evidence for two processes that act over different timescales: ultraviolet photochemistry in the disk atmosphere (faster) and heating of the deeper disk layers (slower).« less

Massive stars: flare activity due to infalls of comet-like bodies

NASA Astrophysics Data System (ADS)

Ibadov, Subhon; Ibodov, Firuz S.

2015-01-01

Passages of comet-like bodies through the atmosphere/chromosphere of massive stars at velocities more than 600 km/s will be accompanied, due to aerodynamic effects as crushing and flattening, by impulse generation of hot plasma within a relatively very thin layer near the stellar surface/photosphere as well as ``blast'' shock wave, i.e., impact-generated photospheric stellar/solar flares. Observational manifestations of such high-temperature phenomena will be eruption of the explosive layer's hot plasma, on materials of the star and ``exploding'' comet nuclei, into the circumstellar environment and variable anomalies in chemical abundances of metal atoms/ions like Fe, Si etc. Interferometric and spectroscopic observations/monitoring of young massive stars with dense protoplanetary discs are of interest for massive stars physics/evolution, including identification of mechanisms for massive stars variability.

Spectrophotometry of peculiar B and A stars. XVIII - The helium rich variable stars HR 1890, Sigma Orionis E, and HD 37776

NASA Technical Reports Server (NTRS)

Adelman, S. J.; Pyper, D. M.

1985-01-01

Optical region spectrophotometry at 3300-7850 A has been obtained for three helium rich stars, HR 1890, Sigma Ori E, and HD 37776, of the Orion OB1 Association. New uvby-beta photometry of HR 1890 and HD 37776 as well as published data are also used to investigate the variability of these stars. A new period of 1.53862 days was determined for HD 37776. For all three stars H-beta varies in antiphase with strong He I lines. The spectrophotometric bandpass containing the strong He I line at 4471 A varies in phase with the R index of Pedersen and Thomsen (1977). Evidence is found for weak absorption features which appear to be an extension of the 5200 A feature seen in cooler CP stars.

DISCOVERY OF A WOLF-RAYET STAR THROUGH DETECTION OF ITS PHOTOMETRIC VARIABILITY

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

Littlefield, Colin; Garnavich, Peter; McClelland, Colin

We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 A, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 A line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocularmore » Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B - V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 {+-} 0.3 kpc.« less

MONET, HET and SALT and asteroseismological observations and theory in Göttingen

NASA Astrophysics Data System (ADS)

Schuh, S.; Hessman, F. V.; Dreizler, S.; Kollatschny, W.; Glatzel, W.

2007-06-01

The Göttingen stellar astrophysics group, headed by Stefan Dreizler, conducts research on extrasolar planets and their host stars, on lower-main sequence stars, and on evolved compact objects, in particular hot white dwarfs (including PG 1159 objects, magnetic WDs and cataclysmic variables), and subdwarf B stars. In addition to sophisticated NLTE spectral analyses of these stars, which draw on the extensive stellar atmosphere modelling experience of the group, we actively develop and apply a variety of photometric monitoring and time-resolved spectroscopic techniques to address time-dependent phenomena. With the new instrumentational developments described below, we plan to continue the study of variable white dwarfs (GW Vir, DB and ZZ Ceti variables) and in particular sdB EC 14026 and PG 1617 pulsators which already constitute a main focus, partly within the Whole Earth Telescope (WET/DARC), http://www.physics.udel.edu/~jlp/darc/) collaboration, on a new level. Additional interest is directed towards strange mode instabilities in Wolf Rayet stars.

Delta Scuti Variables

NASA Astrophysics Data System (ADS)

Handler, Gerald

2009-09-01

We review recent research on Delta Scuti stars from an observer's viewpoint. First, some signposts helping to find the way through the Delta Scuti jungle are placed. Then, some problems in studying individual pulsators in the framework of asteroseismology are given before a view on how the study of these variables has benefited (or not) from past and present high-precision asteroseismic space missions is presented. Some possible pitfalls in the analysis of data with a large dynamical range in pulsational amplitudes are pointed out, and a strategy to optimize the outcome of asteroseismic studies of Delta Scuti stars is suggested. We continue with some views on ``hybrid'' pulsators and interesting individual High Amplitude Delta Scuti stars, and then take a look on Delta Scuti stars in stellar systems of several different kinds. Recent results on pre-main sequence Delta Scuti stars are discussed as are questions related to the instability strip of these variables. Finally, some remarkable new theoretical results are highlighted before, instead of a set of classical conclusions, questions to be solved in the future, are raised.

Variable stars around selected open clusters in the VVV area: Young Stellar Objects

NASA Astrophysics Data System (ADS)

Medina, Nicolas; Borissova, Jura; Bayo, Amelia; Kurtev, Radostin; Lucas, Philip

2017-09-01

Time-varying phenomena are one of the most substantial sources of astrophysical information, and led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search and analyze variable sources in the near infrared Ks band, using the data from the Vista Variables in the Vía Láctea (VVV) ESO Public Survey ([5, 8]). One of our main goals is to investigate the Young Stellar Objects (YSOs) in the Galactic star forming regions, looking for: •Variability. •New pre-main sequence star clusters. Here we present the newly discovered YSOs within some selected stellar clusters in our Galaxy.

An Undergraduate Research Experience on Studying Variable Stars

NASA Astrophysics Data System (ADS)

Amaral, A.; Percy, J. R.

2016-06-01

We describe and evaluate a summer undergraduate research project and experience by one of us (AA), under the supervision of the other (JP). The aim of the project was to sample current approaches to analyzing variable star data, and topics related to the study of Mira variable stars and their astrophysical importance. This project was done through the Summer Undergraduate Research Program (SURP) in astronomy at the University of Toronto. SURP allowed undergraduate students to explore and learn about many topics within astronomy and astrophysics, from instrumentation to cosmology. SURP introduced students to key skills which are essential for students hoping to pursue graduate studies in any scientific field. Variable stars proved to be an excellent topic for a research project. For beginners to independent research, it introduces key concepts in research such as critical thinking and problem solving, while illuminating previously learned topics in stellar physics. The focus of this summer project was to compare observations with structural and evolutionary models, including modelling the random walk behavior exhibited in the (O-C) diagrams of most Mira stars. We found that the random walk could be modelled by using random fluctuations of the period. This explanation agreed well with observations.

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. VI. Luminosities and Mass-loss Rates on Population Scales

NASA Astrophysics Data System (ADS)

Riebel, D.; Srinivasan, S.; Sargent, B.; Meixner, M.

2012-07-01

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ~30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 × 10-5 M ⊙ yr-1, equivalent to a total mass injection rate (including the gas) into the ISM of ~6 × 10-3 M ⊙ yr-1. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K s band as a function of J - K s color, BC_{K_{s}} = -0.40(J-K_{s})^2 + 1.83(J-K_{s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (\\dot{M}_{d}) from C-rich AGB stars, such as log \\dot{M_{d}} = ({-18.90}/({(K_{s}-[8.0])+3.37}))-5.93. We find that a larger fraction of AGB stars exhibiting the "long-secondary period" phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

Cosmic stellar relics in the Galactic halo

NASA Astrophysics Data System (ADS)

Salvadori, Stefania; Schneider, Raffaella; Ferrara, Andrea

2007-10-01

We study the stellar population history and chemical evolution of the Milky Way (MW) in a hierarchical Λ cold dark matter model for structure formation. Using a Monte Carlo method based on the semi-analytical extended Press & Schechter formalism, we develop a new code GALAXY MERGER TREE AND EVOLUTION (GAMETE) to reconstruct the merger tree of the Galaxy and follow the evolution of gas and stars along the hierarchical tree. Our approach allows us to compare the observational properties of the MW with model results, exploring different properties of primordial stars, such as their initial mass function and the critical metallicity for low-mass star formation, Zcr. In particular, by matching our predictions to the metallicity distribution function (MDF) of metal-poor stars in the Galactic halo we find that: (i) a strong supernova (SN) feedback is required to reproduce the observed properties of the MW; (ii) stars with [Fe/H] < -2.5 form in haloes accreting Galactic medium (GM) enriched by earlier SN explosions; (iii) the fiducial model (Zcr = 10-4Zsolar, mPopIII = 200 Msolar) provides an overall good fit to the MDF, but cannot account for the two hyper-metal-poor (HMP) stars with [Fe/H] < -5 the latter can be accommodated if Zcr <= 10-6 Zsolar but such model overpopulates the `metallicity desert', that is, the range -5.3 < [Fe/H] < -4 in which no stars have been detected; (iv) the current non-detection of metal-free stars robustly constrains either Zcr > 0 or the masses of the first stars mPopIII > 0.9 Msolar (v) the statistical impact of truly second-generation stars, that is, stars forming out of gas polluted only by metal-free stars, is negligible in current samples; and (vi) independent of Zcr, 60 per cent of metals in the GM are ejected through winds by haloes with masses M < 6 × 109 Msolar, thus showing that low-mass haloes are the dominant population contributing to cosmic metal enrichment. We discuss the limitations of our study and comparison with previous work.

Murmur intensity in small-breed dogs with myxomatous mitral valve disease reflects disease severity.

PubMed

Ljungvall, I; Rishniw, M; Porciello, F; Ferasin, L; Ohad, D G

2014-11-01

To determine whether murmur intensity in small-breed dogs with myxomatous mitral valve disease reflects clinical and echocardiographic disease severity. Retrospective multi-investigator study. Records of adult dogs Ä20 kg with myxomatous mitral valve disease were examined. Murmur intensity and location were recorded and compared with echocardiographic variables and functional disease status. Murmur intensities in consecutive categories were compared for prevalences of congestive heart failure, pulmonary hypertension and cardiac remodelling. 578 dogs [107 with "soft" (30 Grade I/VI and 77 II/VI), 161 with "moderate" (Grade III/VI), 160 with "loud" (Grade IV/VI) and 150 with "thrilling" (Grade V/VI or VI/VI) murmurs] were studied. No dogs with soft murmurs had congestive heart failure, and 90% had no remodelling. However, 56% of dogs with "moderate", 29% of dogs with "loud" and 8% of dogs with "thrilling" murmurs and subclinical myxomatous mitral valve disease also had no remodelling. Probability of a dog having congestive heart failure or pulmonary hypertension increased with increasing murmur intensity. A 4-level murmur grading scheme separated clinically meaningful outcomes in small-breed dogs with myxomatous mitral valve disease. Soft murmurs in small-breed dogs are strongly indicative of subclinical heart disease. Thrilling murmurs are associated with more severe disease. Other murmurs are less informative on an individual basis. © 2014 British Small Animal Veterinary Association.

Discovery of White Dwarfs in the Globular Clusters M13 and M22 Using HST ACS Photometric Data

NASA Astrophysics Data System (ADS)

Cho, Dong-Hwan; Yoon, Tae Seog; Lee, Sang-Gak; Sung, Hyun-Il

2015-12-01

A search for hot and bright white dwarfs (WDs) in the Milky Way globular clusters M13 (NGC 6205) and M22 (NGC 6656) is carried out using the deep and homogeneous VI photometric catalog of Anderson et al. and and Sarajedini et al., based on data taken with the ACS/WFC aboard the Hubble Space Telescope (HST). V versus V-I color-magnitude diagrams (CMDs) of M13 and M22 are constructed and numerous spurious detections are rejected according to their photometric quality parameters qfit(V) and qfit(I). In the case of M13, further radial restriction is applied to reject central stars with higher photometric errors due to central crowding. From each resultant V versus V-I CMD, sixteen and thirteen WD candidates are identified in M13 and M22, respectively. They are identified as stellar objects in the accompanying ACS/WFC images and are found to be randomly distributed across the central regions of M13 and M22. Their positions in the CMDs are in the bright part of the DA WD cooling sequences indicating that they are true WDs. In order to confirm their nature, follow-up spectroscopic observations are needed.

Use of the AAVSO's International Variable Star Index (VSX) in an Undergraduate Astronomy Course Capstone Project

NASA Astrophysics Data System (ADS)

Larsen, Kristine

2017-06-01

The author discusses a capstone project that utilizes the AAVSO's International Variable Star Index (VSX), ASAS light curves and phase plots, and the SIMBAD astronomical data repository in a laboratory-based undergraduate Stellar and Galactic Astronomy course.

A New Catalog of Variable Stars in the Field of the Open Cluster M37

NASA Astrophysics Data System (ADS)

Chang, S.-W.; Byun, Y.-I.; Hartman, J. D.

2015-07-01

We present a comprehensive re-analysis of stellar photometric variability in the field of the open cluster M37 following the application of a new photometry and de-trending method to the MMT/Megacam image archive. This new analysis allows a rare opportunity to explore photometric variability over a broad range of timescales, from minutes to a month. The intent of this work is to examine the entire sample of more than 30,000 objects for periodic, aperiodic, and sporadic behaviors in their light curves. We show a modified version of the fast χ2 periodogram algorithm (Fχ2) and change-point analysis as tools for detecting and assessing the significance of periodic and non-periodic variations. The benefits of our new photometry and analysis methods are evident. A total of 2,306 stars exhibit convincing variations that are induced by flares, pulsations, eclipses, starspots, and unknown causes in some cases. This represents a 60% increase in the number of variables known in this field. Moreover, 30 of the previously identified variables are found to be false positives resulting from time-dependent systematic effects. The new catalog includes 61 eclipsing binary systems, 92 multiperiodic variable stars, 132 aperiodic variables, and 436 flare stars, as well as several hundreds of rotating variables. Based on extended and improved catalog of variables, we investigate the basic properties (e.g., period, amplitude, type) of all variables. The catalog can be accessed through the web interface (http://stardb.yonsei.ac.kr/).

Linear solvation energy relationships (LSER): 'rules of thumb' for Vi/100, π*, Βm, and αm estimation and use in aquatic toxicology

USGS Publications Warehouse

Hickey, James P.

1996-01-01

This chapter provides a listing of the increasing variety of organic moieties and heteroatom group for which Linear Solvation Energy Relationship (LSER) values are available, and the LSER variable estimation rules. The listings include values for typical nitrogen-, sulfur- and phosphorus-containing moieties, and general organosilicon and organotin groups. The contributions by an ion pair situation to the LSER values are also offered in Table 1, allowing estimation of parameters for salts and zwitterions. The guidelines permit quick estimation of values for the four primary LSER variables Vi/100, π*, Βm, and αm by summing the contribtuions from its components. The use of guidelines and Table 1 significantly simplifies computation of values for the LSER variables for most possible organic comppounds in the environment, including the larger compounds of environmental and biological interest.

Binarity and Variable Stars in the Open Cluster NGC 2126

NASA Astrophysics Data System (ADS)

Chehlaeh, Nareemas; Mkrtichian, David; Kim, Seung-Lee; Lampens, Patricia; Komonjinda, Siramas; Kusakin, Anatoly; Glazunova, Ljudmila

2018-04-01

We present the results of an analysis of photometric time-series observations for NGC 2126 acquired at the Thai National Observatory (TNO) in Thailand and the Mount Lemmon Optical Astronomy Observatory (LOAO) in USA during the years 2004, 2013 and 2015. The main purpose is to search for new variable stars and to study the light curves of binary systems as well as the oscillation spectra of pulsating stars. NGC 2126 is an intermediate-age open cluster which has a population of stars inside the δ Scuti instability strip. Several variable stars are reported including three eclipsing binary stars, one of which is an eclipsing binary star with a pulsating component (V551 Aur). The Wilson-Devinney technique was used to analyze its light curves and to determine a new set of the system’s parameters. A frequency analysis of the eclipse-subtracted light curve was also performed. Eclipsing binaries which are members of open clusters are capable of delivering strong constraints on the cluster’s properties which are in turn useful for a pulsational analysis of their pulsating components. Therefore, high-resolution, high-quality spectra will be needed to derive accurate component radial velocities of the faint eclipsing binaries which are located in the field of NGC 2126. The new Devasthal Optical Telescope, suitably equipped, could in principle do this.

Fourier Decomposition and Properties of the Variable Stars in the Globular Cluster NGC 4833

NASA Astrophysics Data System (ADS)

Reed, Hunter M.; Pajkos, Michael A.; Murphy, Brian W.; Darragh, Andrew

2016-01-01

Globular clusters provide an ideal setting to study stellar evolution of stars of similar composition and age. RR Lyrae stars found in globular clusters have a variety of uses in probing the physical characteristics of the stellar population itself and its evolution. Building upon our previous study, we focus on the RR Lyrae stars in the globular cluster NGC 4833. From March through June 2014, we used the Southeastern Association for Research in Astronomy 0.6-meter telescope located at CTIO to collect nearly 1,500 images of NGC 4833 in the B, V, R, and I bands. Using difference image analysis we identified 40 variable stars. Of these, 20 were RR Lyrae stars with 10 being of type RR0, 7 of type RR1, and 3 of type RR2. Additionally, 6 SX Phe, 5 eclipsing binaries, and 9 long period variables were identified. The average period of the type RR0, RR1, and RR2 type variables were 0.69597 days, 0.39547 days, and 0.30654 days, respectively. The periods of the RR Lyrae stars and ratio of N1/(N0+N1) of 0.41 is indicative of an Oosterhoff Type II cluster. The observations of the RR Lyrae stars were of very high quality and phase coverage allowing us to perform Fourier decomposition of their light curves. From this Fourier decomposition we were able to determine the physical characteristics of the RR Lyrae stars. We found the mean iron abundance to be [Fe/H]JKZW = -1.87 ± 0.06, the mean apparent V-magnitude RR0 and RR1 type variables to be VRR = 15.51 ± 0.11, a mean absolute V-magnitude of MV = 0.636 ± 0.053; and an effective temperature for RR0's and RR1's of log10Teff = 3.797 and log10Teff = 3.855, respectively. The multi-band photometry allowed us to determine the reddening of the cluster, E(B-V) = 0.342 ± 0.021, which resulted in a distance of D(kpc) = 5.91 ± 0.31 to NGC 4833.

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).

Results from the Rothney Astrophysical Observatory Variable Star Search Program: Background, Procedure, and Results from RAO Field 1

NASA Astrophysics Data System (ADS)

Williams, Michael D.; Milone, E. F.

2013-12-01

We describe a variable star search program and present the fully reduced results of a search in a 19 square degree (4.4 × 4.4) field centered on J2000 RA = 22:03:24, DEC= +18:54:32. The search was carried out with the Baker-Nunn Patrol Camera located at the Rothney Astrophysical Observatory in the foothills of the Canadian Rockies. A total of 26,271 stars were detected in the field, over a range of about 11-15 (instrumental) magnitudes. Our image processing made use of the IRAF version of the DAOPHOT aperture photometry routine and we used the ANOVA method to search for periodic variations in the light curves. We formally detected periodic variability in 35 stars, that we tentatively classify according to light curve characteristics: 6 EA (Algol), 5 EB (?? Lyrae), 19 EW (W UMa), and 5 RR (RR Lyrae) stars. Eleven of the detected variable stars have been reported previously in the literature. The eclipsing binary light curves have been analyzed with a package of light curve modeling programs and 25 have yielded converged solutions. Ten of these are of systems that are detached, 3 semi-detached, 10 overcontact, and 2 are of systems that appear to be in marginal contact. We discuss these results as well as the advantages and disadvantages of the instrument and of the program.

FFT Deconvultion of Be Star Hα Line Profiles

NASA Astrophysics Data System (ADS)

Austin, S. J.

2005-12-01

We have been monitoring the spectroscopic variability of Be stars using the UCA Fiber Fed Spectrograph. The spectra are 0.8 Angstrom/pixel resolution of the Hα line. The observed line profiles are a convolution of the actual profile and the instrumental profile. A Fast Fourier Transform (FFT) method has been used to deconvolve the observed profiles, given the instrument profile obtained by observing the narrow lines from the HgNe wavelength calibration lamp. The long-term monitoring of the spectroscopic variability of Be stars is crucial for testing the various Be star models. Deconvolved H-α line profiles, velocities, and variability are shown for gamma Cas, delta Sco, chi Oph, eta PsA, 48 Lib, and upsilon Sgr (HD181615). Funding has been provided by the UCA University Research Council and the Arkansas Space Grant Consortium.

Globular cluster photometry with the Hubble Space Telescope. 3: Blue stragglers and variable stars in the core of M3

NASA Technical Reports Server (NTRS)

Guhathakurta, Puragra; Yanny, Brian; Bahcall, John N.; Schneider, Donald P.

1994-01-01

This paper describes Hubble Space Telescope (HST)/Planetary Camera-I images of the core of the dense globular cluster M3 (NGC 5272). Stellar photometry in the F555W (V) and F785LP (I) bands, with a 1-sigma photometric accuracy of about 0.1 mag, has been used to construct color-magnitude diagrams of about 4700 stars above the main-sequence turnoff within r less than or approximately equal to 1 min of the cluster center. We have also analyzed archival HST F336W (U) images of M3 obtained by the Wide Field/Planetary Camera-I Instrument Definition Team. The UVI data are used to identify 28 blue straggler (BS) stars within the central 0.29 sq. arcmin. The specific frequency of BSs in this region of M3, N(sub BS)/N(sub V less than (V(HB)+2)) = 0.094 +/- 0.019, is about a factor of 2 - 3 higher than that found by Bolte et al. in a recent ground-based study of the same region, but comparable to that seen in the sparse outer parts of the same cluster and in HST observations of the core of the higher density cluster 47 Tuc. The BSs in M3 are slightly more centrally concentrated than red giant branch stars while horizontal branch stars are somewhat less concentrated red giants. The radial distribution of V-selected subgiant and turnoff stars is well fit by a King model with a core radius r(sub core) = 28 arcmin +/- 2 arcmin (90% confidence limits), which corresponds to 1.4 pc. Red giant and horizontal branch stars selected in the ultraviolet data (U less than 18) have a somewhat more compact distribution (r(sub core) = 22.5 arcmin). The HST U data consist of 17 exposures acquired over a span of three days. We have used these data to isolate 40 variable stars for which relative astrometry, brightnesses, colors, and light curves are presented. A Kolmogorov-Smirnov test indicates that, typically, the variability for each star is significant at the 95% level. We identify two variable BS candidates (probably of the SX Phe type), out of a sample of approximately 25 BSs in which variability could have been detected. Most of the variables are RR Lyrae stars on the horizontal branch. All of them have periods P greater than or approximately equal 8 h.

Interrogation of duplicitous stars with an APT

NASA Technical Reports Server (NTRS)

Bopp, Bernard W.

1992-01-01

Preliminary results from intensive spectroscopic and APT monitoring of two interacting binary systems are presented. Both V644 Mon (Be + K:) and HD 37453 (F5 II + B) show complex, composite, and variable spectral. APT observations extending over three years show both stars to vary by 0.1-0.2 mag in V. The photometric variability of V644 Mon appears to be irregular, though there is some evidence for periodic behavior in the 50-60 day range. HD 37453 has an orbital period of 66.75 days; the best-fit photometric period is not quite half this value, indicating the star is an ellipsoidal variable.

The OGLE Collection of Variable Stars. Over 450 000 Eclipsing and Ellipsoidal Binary Systems Toward the Galactic Bulge

NASA Astrophysics Data System (ADS)

Soszyński, I.; Pawlak, M.; Pietrukowicz, P.; Udalski, A.; Szymański, M. K.; Wyrzykowski, Ł.; Ulaczyk, K.; Poleski, R.; Kozłowski, S.; Skowron, D. M.; Skowron, J.; Mróz, P.; Hamanowicz, A.

2016-12-01

We present a collection of 450 598 eclipsing and ellipsoidal binary systems detected in the OGLE fields toward the Galactic bulge. The collection consists of binary systems of all types: detached, semi-detached, and contact eclipsing binaries, RS CVn stars, cataclysmic variables, HW Vir binaries, double periodic variables, and even planetary transits. For all stars we provide the I- and V-band time-series photometry obtained during the OGLE-II, OGLE-III, and OGLE-IV surveys. We discuss methods used to identify binary systems in the OGLE data and present several objects of particular interest.

The detection of X-ray variability in O stars

NASA Technical Reports Server (NTRS)

Snow, T. P., Jr.; Cash, W.; Grady, C. A.

1981-01-01

Seven O stars known to have strong, and sometimes variable, stellar winds have been observed repeatedly with the Imaging Proportional Counter on the Einstein Observatory, in a program designed to determine whether the X-ray fluxes from these stars are variable. In three cases, definite changes were seen, either on a time scale of a year (Iota Ori and Delta Ori) or five days (15 Mon). In two of these cases, the X-ray spectrum was harder when the overall flux was higher, indicating that some of the fluctuations may take place in a hot (approximately 10 to the 7th K) emitting region at the bottom of the winds.

Spectral and Photometric Data of Be Star, EM Cep

NASA Astrophysics Data System (ADS)

Kochiashvili, Nino; Natsvilishvili, Rezo; Kochiashvili, Ia; Vardosanidze, Manana; Beradze, Sopia; Pannicke, Anna

The subject of investigation in this project is a Be spectral type giant variable star EM Cep. It was established that the star has a double nature: 1. when emission lines are seen in its spectrum and 2. when only absorption lines are observable and emission lines are not seen. This means that the star is not always in Be state. Be state continues existing during a few months. EM Cep shows flare activity too. The causes of photometric and spectral variability are to be established. The existence of different mechanisms, which provokes Be phenomenon, is possible. The character of light curves' variability gives us possibility to propose that it is not excluded that the star could be a short-period Cepheid of λ Eri type. However, we do not have sufficient data to exclude its binarity. On the basis of the observations carried out at Abastumani observatory, the light curve with two minima and two maxima were revealed, but these data, too accord with the half-period - we can also consider a light curve with one minimum and one maximum. Both cases suggest a good agreement with the characters of variability. For the case of binarity in Abastumani observatory, a set of orbital elements by using the Wilson-Devinney code is already obtained. The elements correspond to the model of acceptable, real close binary star. However, notwithstanding this situation, the true nature of the star is not established for the moment. To solve this problem, we need to get high-resolution spectral data, when by using radial velocity curves, it would be possible to answer the question of binarity of the star. It is not excluded to reveal spectral lines of the second component in case of binarity of the star. Since 2014, we have renewed UBVRI photometric observations of EM Cep in Abastumani using a 48-cm telescope with CCD device. Spectral observations are made in Azerbaijan, Shamakhy Observatory. Our German Colleagues have been observing the star since March of 2017 at the Observatory of the Jena University. We plan to carry out a joint analysis of the observations of the three observatories to explain the observational peculiarities of the star.

Precise time series photometry for the Kepler-2.0 mission

NASA Astrophysics Data System (ADS)

Aigrain, S.; Hodgkin, S. T.; Irwin, M. J.; Lewis, J. R.; Roberts, S. J.

2015-03-01

The recently approved NASA K2 mission has the potential to multiply by an order of magnitude the number of short-period transiting planets found by Kepler around bright and low-mass stars, and to revolutionize our understanding of stellar variability in open clusters. However, the data processing is made more challenging by the reduced pointing accuracy of the satellite, which has only two functioning reaction wheels. We present a new method to extract precise light curves from K2 data, combining list-driven, soft-edged aperture photometry with a star-by-star correction of systematic effects associated with the drift in the roll angle of the satellite about its boresight. The systematics are modelled simultaneously with the stars' intrinsic variability using a semiparametric Gaussian process model. We test this method on a week of data collected during an engineering test in 2014 January, perform checks to verify that our method does not alter intrinsic variability signals, and compute the precision as a function of magnitude on long-cadence (30 min) and planetary transit (2.5 h) time-scales. In both cases, we reach photometric precisions close to the precision reached during the nominal Kepler mission for stars fainter than 12th magnitude, and between 40 and 80 parts per million for brighter stars. These results confirm the bright prospects for planet detection and characterization, asteroseismology and stellar variability studies with K2. Finally, we perform a basic transit search on the light curves, detecting two bona fide transit-like events, seven detached eclipsing binaries and 13 classical variables.

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way

NASA Astrophysics Data System (ADS)

Bensby, T.; Feltzing, S.; Gould, A.; Yee, J. C.; Johnson, J. A.; Asplund, M.; Meléndez, J.; Lucatello, S.; Howes, L. M.; McWilliam, A.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Poleski, R.; Wyrzykowski, Ł.; Ulaczyk, K.; Kozłowski, S.; Pietrukowicz, P.; Skowron, J.; Mróz, P.; Pawlak, M.; Abe, F.; Asakura, Y.; Bhattacharya, A.; Bond, I. A.; Bennett, D. P.; Hirao, Y.; Nagakane, M.; Koshimoto, N.; Sumi, T.; Suzuki, D.; Tristram, P. J.

2017-09-01

We present a detailed elemental abundance study of 90 F and G dwarf, turn-off, and subgiant stars in the Galactic bulge. Based on high-resolution spectra acquired during gravitational microlensing events, stellar ages and abundances for 11 elements (Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Zn, Y and Ba) have been determined. Four main findings are presented: (1) a wide metallicity distribution with distinct peaks at [Fe/H] = -1.09, -0.63, -0.20, + 0.12, + 0.41; (2) ahigh fraction of intermediate-age to young stars where at [Fe/H] > 0 more than 35% are younger than 8 Gyr, and for [Fe/H] ≲ -0.5 most stars are 10 Gyr or older; (3) several episodes of significant star formation in the bulge has been identified: 3, 6, 8, and 11 Gyr ago; (4) tentatively the "knee" in the α-element abundance trends of the sub-solar metallicity bulge is located at a slightly higher [Fe/H] than in the local thick disk. These findings show that the Galactic bulge has complex age and abundance properties that appear to be tightly connected to the main Galactic stellar populations. In particular, the peaks in the metallicity distribution, the star formation episodes, and the abundance trends, show similarities with the properties of the Galactic thin and thick disks. At the same time, the star formation rate appears to have been slightly faster in the bulge than in the local thick disk, which most likely is an indication of the denser stellar environment closer to the Galactic centre. There are also additional components not seen outside the bulge region, and that most likely can be associated with the Galactic bar. Our results strengthen the observational evidence that support the idea of a secular origin for the Galactic bulge, formed out of the other main Galactic stellar populations present in the central regions of our Galaxy. Additionally, our analysis of this enlarged sample suggests that the (V-I)0 colour of the bulge red clump should be revised to 1.09. Based on data obtained with the European Southern Observatory telescopes (Proposal ID:s 87.B-0600, 88.B-0349, 89.B-0047, 90.B-0204, 91.B-0289, 92.B-0626, 93.B-0700, 94.B-0282), the Magellan Clay telescope at the Las Campanas observatory, and the Keck I telescope at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.Full Tables A.1 and A.2 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/A89

The impact of knowledge transfer on the detection of venous invasion in colorectal cancer.

PubMed

Kirsch, Richard; Assarzadegan, Naziheh; Messenger, David E; Juda, Ari; Riddell, Robert H; Pollett, Aaron; Streutker, Catherine J; Divaris, Dimitrios X; Newell, Ken J; Price, Russell G; Smith, Sharyn; Al-Haddad, Sahar; Parfitt, Jeremy R; Driman, David K

2017-09-01

Venous invasion (VI) is an independent predictor of hematogenous metastasis and mortality in colorectal cancer (CRC) yet remains widely underreported. Its detection may require recognition of subtle morphologic clues, which at times are only unmasked with an elastin stain. This study evaluates the impact of a knowledge transfer initiative (KTI) on VI detection in a "real-world" pathology practice setting. Following participation in an interobserver variability study of VI detection (Kirsch et al, 2013), 12 participants received educational materials highlighting key issues in VI detection. Eighteen months later, participants were invited to submit pathology reports from all CRC resections signed out 18 months prior to and 18 months following the KTI (n = 266 and n = 244, respectively). Nine pathologists participated. Reports were reviewed for VI and other established prognostic factors. Numbers of elastin stains and tumor-containing blocks were also recorded. Comparative analyses were adjusted for baseline differences in tumor, lymph node, and metastasis stage; tumor location; use of neoadjuvant therapy; and number of tumor-containing blocks. VI detection increased significantly post-KTI versus pre-KTI (39.3% versus 18.4%, adjusted odds ratio [OR] 2.86 [1.91-4.28], P < .001). Increased VI detection post-KTI was observed in both stage II (31.8% versus 12.5%, adjusted OR 3.27 [1.45-7.42], P = .004) and stage III CRC (62.4% versus 28.2%, adjusted OR 4.23 [2.37-7.55], P < .001). All pathologists demonstrated increased VI detection post-KTI. Use of elastin stains was significantly higher post-KTI versus pre-KTI (61.5% versus 5.3% of cases respectively, P < .001). This study demonstrates the effectiveness of knowledge transfer in increasing VI detection in routine pathology practice. Copyright © 2017 Elsevier Inc. All rights reserved.

VizieR Online Data Catalog: Variable Stars in the Galactic Center (Dong+, 2017)

NASA Astrophysics Data System (ADS)

Dong, H.; Schodel, R.; William, B. F.; Nogueras-Lara, F.; Gallego-Cano, E.; Gallego-Calvente, T.; Wang, Q. D.; Morris, R. M.; Do, T.; Ghez, A.

2017-06-01

We use the 'DOLPHOT' to detect sources and extract photometry from the HST WFC3/IR observations at the F127M and F135M bands of the Galactic Centre from 2010 to 2014. The F153M observations, which are used to identify variable stars, include 290 dithered exposures from six HST programs. The detailed description of the HST dataset are given in Table 1 of the paper. We identified 33070 sources. Their F127M and F153M magnitudes, as well as their uncertainties, are given in Table 3. For each star, we used the least chi square method to identify whether it is variable or not. The output from the least chi square method are chi2y and chi2d, which are calculated from all the 290 dithered exposures and the exposures in March and April, 2014, respectively, to examine whether the star varies among years and/or days. In order to reduce the potential variation among dithered exposures, which could be potentially introduced by instrument effects, we also bin the dithered exposures and use the least chi square method to calculate chi2y,b and chi2{d,b}. We classify stars with chi2y>3 and chi2y,b>2 are variables among years and stars with chi2d>3 and chi2d,b>2 are variables among days. The detailed description about the data analysis is given in the paper. In Table 4, we gives the magnitudes of sources in individual dithered exposures, as well as the photometric uncertainties and the quality control parameters provided by 'DOLPHOT', such as signal-to-noise ratio, sharpness^2, crowd and flag. We also cross-correlated our variables with previous variable studies taken by ground-based telescopes in Table 8 and spectroscopic observations in Table 9. (4 data files).

Monitoring solar-type stars for luminosity variations

NASA Technical Reports Server (NTRS)

Lockwood, G. W.; Skiff, B. A.

1988-01-01

Since 1984, researchers have made more than 1500 differential photometric b (471 nm) and y (551 nm) measurements of three dozen solar-like lower main sequence stars whose chromospheric activity was previosly studied by O. C. Wilson. Here, researchers describe their methodology and the statistical tests used to distinguish intrinsic stellar variability from observational and instrument errors. The incidence of detected variability among the program and comparison stars is summarized. Among the 100 plus pairs of stars measured differentially, only a dozen were found that were unusually constant, with peak-to-peak amplitudes of seasonal mean brightness smaller than 0.3 percent (0.003 mag) over a two-to-three-year interval.

Chromospherically active stars. IV - HD 178450 = V478 Lyr: An early-type BY Draconis type binary

NASA Technical Reports Server (NTRS)

Fekel, Francis C.

1988-01-01

It is shown that the variable star HD 178450 = V478 Lyr is a chromospherically active G8 V single-lined spectroscopic binary with a period of 2.130514 days. This star is characterized by strong UV emission features and a filled-in H-alpha absorption line which is variable in strength. Classified as an early-type BY Draconis system, it is similar to the BY Dra star HD 175742 = V775 Her. The unseen secondary of HD 178450 has a mass of about 0.3 solar masses and is believed to be an M2-M3 dwarf.

A survey for red varibles INT he LMC - II

NASA Astrophysics Data System (ADS)

Reid, Neill; Glass, I. S.; Catchpole, R. M.

1988-05-01

Infrared photometry of a sample of 126 variables drawn from a 16 sq deg area of the northern LMC is presented. Most of these stars were previously unknown and the majority prove the be long period red-giant variables. Most of the latter stars fall within two groups in the /K(0), log(P)/ diagram, the lower luminosity ones being Miras which obey a definite period-luminosity relation. Using the latter stars as distance estimators is discussed. The /M(bol), P/ diagram is compared with the theoretical tracks calculated by Wood, Bessell & Fox (1983), and it is found that the distribution of stars is probably consistent with a lull in star formation in the LMC from about 10 to the 9th - 2 x 10 to the 8th yr ago, although this conclusion depends strongly on the luminosity at which stars of different initial mass enter the thermally pulsing AGB.

Photometric Studies of Stars in the Vicinity of Cyg OB7

NASA Astrophysics Data System (ADS)

Melikian, N. D.; Gomez, J.

2017-12-01

Results of BVRI photometric studies of 131 stars in the stellar association Cyg OB7 are presented. Observational data were obtained with the 2.6-m telescope at the Byurakan Observatory during 2000, 2002, 2004, and 2011 using the ByuFOSC-2 and SCORPIO spectral cameras. Observations made in 2007 on the 182-cm telescope (Asiago, Italy) at the Padova Astronomical Observatory with the AFOSC (Asiago Faint Object Spectrograph and Camera) detector system are also used. Variations with amplitudes ranging from 0m.2 to 2m.16 are detected in 42 of the stars. Variability is observed for the first time in 31 of the 42 stars. The brightness of 32 of the stars was essentially unchanged during the time of our measurements. All of the 42 variables lie very close to the T Tau type stars on a two-color diagram.

Four New Binary Stars in the Field of CL Aurigae. II

NASA Astrophysics Data System (ADS)

Kim, Chun-Hwey; Lee, Jae Woo; Duck, Hyun Kim; Andronov, Ivan L.

2010-12-01

We report on a discovery of four new variable stars (USNO-B1.0 1234-0103195, 1235- 0097170, 1236-0100293 and 1236-0100092) in the field of CL Aur. The stars are classified as eclipsing binary stars with orbital periods of 0.5137413(23) (EW type), 0.8698365(26) (EA) and 4.0055842(40) (EA with a significant orbital eccentricity), respectively. The fourth star (USNO-B1.0 1236-0100092) showed only one partial ascending branch of the light curves, although 22 nights were covered at the 61-cm telescope at the Sobaeksan Optical Astronomy Observatory (SOAO) in Korea. Fourteen minima timings for these stars are published separately. In an addition to the original discovery paper (Kim et al. 2010), we discuss methodological problems and present results of mathematical modeling of the light curves using other methods, i.e. trigonometric polynomial fits and the newly developed fit "NAV" ("New Algol Variable").

BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. IV. THE CENTRAL STARS OF HaTr 4 AND Hf 2-2

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

Hillwig, Todd C.; Schaub, S. C.; Bond, Howard E.

We explore the photometrically variable central stars of the planetary nebulae HaTr 4 and Hf 2-2. Both have been classified as close binary star systems previously based on their light curves alone. Here, we present additional arguments and data confirming the identification of both as close binaries with an irradiated cool companion to the hot central star. We include updated light curves, orbital periods, and preliminary binary modeling for both systems. We also identify for the first time the central star of HaTr 4 as an eclipsing binary. Neither system has been well studied in the past, but we utilizemore » the small amount of existing data to limit possible binary parameters, including system inclination. These parameters are then compared to nebular parameters to further our knowledge of the relationship between binary central stars of planetary nebulae and nebular shaping and ejection.« less

Star Products with Separation of Variables Admitting a Smooth Extension

NASA Astrophysics Data System (ADS)

Karabegov, Alexander

2012-08-01

Given a complex manifold M with an open dense subset Ω endowed with a pseudo-Kähler form ω which cannot be smoothly extended to a larger open subset, we consider various examples where the corresponding Kähler-Poisson structure and a star product with separation of variables on (Ω, ω) admit smooth extensions to M. We give a simple criterion of the existence of a smooth extension of a star product and apply it to these examples.

Line profile variation in delta-Orionis A, l-Orionis A, and 15 Monocerotis

NASA Technical Reports Server (NTRS)

Grady, C. A.; Snow, T. P.; Cash, W. C.

1984-01-01

The results of a monitoring program with IUE and Einstein are presented for three stars, delta-Ori A, l-Ori A, and 15 Mon. Line profile variability is observed in the UV profiles accessible to IUE and the relation between the variation in the different ions suggests that the ionization level is varying in the winds of these stars. This is consistent with Einstein observations of soft X-ray variability for two of the stars.

Use of the AAVSO's International Variable Star Index (VSX) in an Undergraduate Astronomy Course Capstone Project (Abstract)

NASA Astrophysics Data System (ADS)

Larsen, K.

2017-12-01

(Abstract only) The author discusses a capstone project that utilizes the AAVSO's International Variable Star Index (VSX), ASAS light curves and phase plots, and the SIMBAD astronomical data repository in a laboratory-based undergraduate Stellar and Galactic Astronomy course.

Microfabricated gas chromatograph for on-site determinations of TCE in indoor air arising from vapor intrusion. 2. Spatial/temporal monitoring.

PubMed

Kim, Sun Kyu; Burris, David R; Bryant-Genevier, Jonathan; Gorder, Kyle A; Dettenmaier, Erik M; Zellers, Edward T

2012-06-05

We demonstrate the use of two prototype Si-microfabricated gas chromatographs (μGC) for continuous, short-term measurements of indoor trichloroethylene (TCE) vapor concentrations related to the investigation of TCE vapor intrusion (VI) in two houses. In the first house, with documented TCE VI, temporal variations in TCE air concentrations were monitored continuously for up to 48 h near the primary VI entry location under different levels of induced differential pressure (relative to the subslab). Concentrations ranged from 0.23 to 27 ppb by volume (1.2-150 μg/m(3)), and concentration trends agreed closely with those determined from concurrent reference samples. The sensitivity and temporal resolution of the measurements were sufficiently high to detect transient fluctuations in concentration resulting from short-term changes in variables affecting the extent of VI. Spatial monitoring showed a decreasing TCE concentration gradient with increasing distance from the primary VI entry location. In the second house, with no TCE VI, spatial profiles derived from the μGC prototype data revealed an intentionally hidden source of TCE within a closet, demonstrating the capability for locating non-VI sources. Concentrations measured in this house ranged from 0.51 to 56 ppb (2.7-300 μg/m(3)), in good agreement with reference method values. This first field demonstration of μGC technology for automated, near-real-time, selective VOC monitoring at low- or subppb levels augurs well for its use in short- and long-term on-site analysis of indoor air in support of VI assessments.

Temporal variability of indoor air concentrations under natural conditions in a house overlying a dilute chlorinated solvent groundwater plume.

PubMed

Holton, Chase; Luo, Hong; Dahlen, Paul; Gorder, Kyle; Dettenmaier, Erik; Johnson, Paul C

2013-01-01

Current vapor intrusion (VI) pathway assessment heavily weights concentrations from infrequent (monthly-seasonal) 24 h indoor air samples. This study collected a long-term and high-frequency data set that can be used to assess indoor air sampling strategies for answering key pathway assessment questions like: "Is VI occurring?", and "Will VI impacts exceed thresholds of concern?". Indoor air sampling was conducted for 2.5 years at 2-4 h intervals in a house overlying a dilute chlorinated solvent plume (10-50 μg/L TCE). Indoor air concentrations varied by 3 orders of magnitude (<0.01-10 ppbv TCE) with two recurring behaviors. The VI-active behavior, which was prevalent in fall, winter, and spring involved time-varying impacts intermixed with sporadic periods of inactivity; the VI-dormant behavior, which was prevalent in the summer, involved long periods of inactivity with sporadic VI impacts. These data were used to study outcomes of three simple sparse data sampling plans; the probabilities of false-negative and false-positive decisions were dependent on the ratio of the (action level/true mean of the data), the number of exceedances needed, and the sampling strategy. The analysis also suggested a significant potential for poor characterization of long-term mean concentrations with sparse sampling plans. The results point to a need for additional dense data sets and further investigation into the robustness of possible VI assessment paradigms. As this is the first data set of its kind, it is unknown if the results are representative of other VI-sites.

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

Downes, R.A.

Galactic plane ultraviolet-excess (uv-excess) objects covering about 1000 square degrees of sky were surveyed. Photographic plates were obtained with both uv and blue filters, to select the uv-excess candidates, which were then observed spectroscopically to determine their classification. Most of the objects selected were nearby early-type stars with low interstellar reddening; however, a collection of hot white dwarfs, subdwarf O (sdO) stars, subdwarf B (sdB) stars, and cataclysmic variables was also found. Photoelectric photometry was obtained for these stars and a statistical analysis was performed to determine the space densities and scale heights for the four classes of objects. Severalmore » interesting objects (or class of objects) were discovered, and data for some of these stars are presented. Among the peculiar objects found are an emission-line white dwarf similar to the pulsating PG 1159 stars, a Population II Wolf-Rayet star, a previously catalogued object with a strong Fe II emission-line spectrum, and a new class of object, resembling the sdB stars, that shows variable strength H..cap alpha.. absorption, with the H..cap alpha.. line sometimes completely filled in.« less

Unravelling the Role of the SW Sextantis Stars in the Evolution of Cataclysmic Variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Steeghs, D.; Rodriguez-Gil, P.; Gansicke, B.; Marsh Warwick, T. R.; Araujo-Betancor, S.; Long, K.

2006-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of 33 SW Sex stars, and request here Gemini/GMOS-N time to obtain orbital phase-resolved spectroscopy if one of them enters a low state. These data will be used to accurately measure the mass ratio, white dwarf temperature, and distance of the system, eventually providing the first detailed system parameters for any SW Sex star.

VizieR Online Data Catalog: Radial velocities in M3, M13, and M92 (Kamann+, 2014)

NASA Astrophysics Data System (ADS)

Kamann, S.; Wisotzki, L.; Roth, M. M.; Gerssen, J.; Husser, T.-O.; Sandin, C.; Weilbacher, P.

2014-04-01

Radial velocity data are presented for three Galactic globular clusters, M3, M13, and M92. The provided catalogues include several hundreds of stars in each cluster that cover a wide range of distances to the cluster centres. Besides the measured radial velocities, the catalogues contain measurement uncertainties, identifiers, world coordinates and variability information for each star. The velocities for stars near the centres of the clusters were obtained using PMAS integral field spectroscopy (IFS). Note that in order to facilitate future variability studies, for each star the individual velocity measurements are provided instead of a single combined velocity. The PMAS data are complemented with velocities reported in various literature studies for stars at larger distances to the centres. (6 data files).

Photometry Using Kepler "Superstamps" of Open Clusters NGC 6791 & NGC 6819

NASA Astrophysics Data System (ADS)

Kuehn, Charles A.; Drury, Jason A.; Bellamy, Beau R.; Stello, Dennis; Bedding, Timothy R.; Reed, Mike; Quick, Breanna

2015-09-01

The Kepler space telescope has proven to be a gold mine for the study of variable stars. Usually, Kepler only reads out a handful of pixels around each pre-selected target star, omitting a large number of stars in the Kepler field. Fortunately, for the open clusters NGC 6791 and NGC 6819, Kepler also read out larger "superstamps" which contained complete images of the central region of each cluster. These cluster images can be used to study additional stars in the open clusters that were not originally on Kepler's target list. We discuss our work on using two photometric techniques to analyze these superstamps and present sample results from this project to demonstrate the value of this technique for a wide variety of variable stars.

The Diffuse Interstellar Cloud Experiment: a high-resolution far-ultraviolet spectrograph.

PubMed

Schindhelm, Eric; Beasley, Matthew; Burgh, Eric B; Green, James C

2012-03-01

We have designed, assembled, and launched a sounding rocket payload to perform high-resolution far-ultraviolet spectroscopy. The instrument is functionally a Cassegrain telescope followed by a modified Rowland spectrograph. The spectrograph was designed to achieve a resolving power (R=λ/δλ) of 60,000 in a compact package by adding a magnifying secondary optic. This is enabled by using a holographically ruled grating to minimize aberrations induced by the second optic. We designed the instrument to observe two stars on opposing sides of a nearby hot/cold gas interface. Obtaining spectra of the O VI doublet in absorption toward these stars can provide new insight into the processes governing hot gas in the local interstellar medium. Here we present the optical design and alignment of the telescope and spectrograph, as well as flight results. © 2012 Optical Society of America

High-precision photometry by telescope defocussing - VI. WASP-24, WASP-25 and WASP-26

NASA Astrophysics Data System (ADS)

Southworth, John; Hinse, T. C.; Burgdorf, M.; Calchi Novati, S.; Dominik, M.; Galianni, P.; Gerner, T.; Giannini, E.; Gu, S.-H.; Hundertmark, M.; Jørgensen, U. G.; Juncher, D.; Kerins, E.; Mancini, L.; Rabus, M.; Ricci, D.; Schäfer, S.; Skottfelt, J.; Tregloan-Reed, J.; Wang, X.-B.; Wertz, O.; Alsubai, K. A.; Andersen, J. M.; Bozza, V.; Bramich, D. M.; Browne, P.; Ciceri, S.; D'Ago, G.; Damerdji, Y.; Diehl, C.; Dodds, P.; Elyiv, A.; Fang, X.-S.; Finet, F.; Figuera Jaimes, R.; Hardis, S.; Harpsøe, K.; Jessen-Hansen, J.; Kains, N.; Kjeldsen, H.; Korhonen, H.; Liebig, C.; Lund, M. N.; Lundkvist, M.; Mathiasen, M.; Penny, M. T.; Popovas, A.; Prof., S.; Rahvar, S.; Sahu, K.; Scarpetta, G.; Schmidt, R. W.; Schönebeck, F.; Snodgrass, C.; Street, R. A.; Surdej, J.; Tsapras, Y.; Vilela, C.

2014-10-01

We present time series photometric observations of 13 transits in the planetary systems WASP-24, WASP-25 and WASP-26. All three systems have orbital obliquity measurements, WASP-24 and WASP-26 have been observed with Spitzer, and WASP-25 was previously comparatively neglected. Our light curves were obtained using the telescope-defocussing method and have scatters of 0.5-1.2 mmag relative to their best-fitting geometric models. We use these data to measure the physical properties and orbital ephemerides of the systems to high precision, finding that our improved measurements are in good agreement with previous studies. High-resolution Lucky Imaging observations of all three targets show no evidence for faint stars close enough to contaminate our photometry. We confirm the eclipsing nature of the star closest to WASP-24 and present the detection of a detached eclipsing binary within 4.25 arcmin of WASP-26.

Visual Spectroscopy of R Scuti (Poster abstract)

NASA Astrophysics Data System (ADS)

Undreiu, L.; Chapman, A.

2015-06-01

(Abstract only) We are currently conducting a visual spectral analysis of the brightest known RV Tauri variable star, R Scuti. The goal of our undergraduate research project is to investigate this variable star's erratic nature by collecting spectra at different times in its cycle. Starting in late June of 2014 and proceeding into the following four months, we have monitored the alterations in the spectral characteristics that accompany the progression of R Sct's irregular cycle. During this time, we were given the opportunity to document the star's most recent descent from maximum brightness V~5 to a relatively deep minimum of V~7.5. Analysis of the data taken during the star's period of declining magnitude has provided us with several interesting findings that concur with the observations of more technically sophisticated studies. Following their collection, we compared our observations and findings with archived material in the hopes of facilitating a better understanding of the physical state of RV Tauri stars and the perplexing nature of their evolution. Although identification of the elements in the star's bright phase proved to be challenging, documenting clear absorption features in its fainter stage was far less difficult. As previously reported in similar studies, we identified prominent TiO molecular absorption bands near R Sct's faintest state, typical of mid-M spectral type stars. In addition to these TiO absorption lines, we report the presence of many more metallic lines in the spectral profiles obtained near star's minimum. Supportive of previously published hypotheses regarding the causation of its variability, we observed significant variation in the star's spectral characteristics throughout different phases of its cycle. We are hopeful that our observations will make a meaningful contribution to existing databases and help advance our collective understanding of RV Tauri stars and their evolutionary significance.

Identification and period investigation of pulsation variable star UY Camelopardalis, an RR Lyrae star in binary system

NASA Astrophysics Data System (ADS)

Li, Lin-Jia; Qian, Sheng-Bang; Voloshina, Irina; Metlov, Vladimir G.; Zhu, Li-Ying; Liao, Wen-Ping

2018-06-01

We present photometric measurements of the short period variable star UY Cam, which has been classified as a δ Scuti or c-type RR Lyrae (RRc) variable in different catalogs. Based on the analyses on Fourier coefficients and (NUV - V)0, we find that UY Cam is probably an RRc star. We obtain 58 new times of light maximum for UY Cam based on several sky surveys and our observations. Combining these with the times of light maximum in literature, a total of 154 times of light maximum are used to analyze the O - C diagram of UY Cam. The results show that the O - C pattern can be described by a downward parabolic component with a rate of -6.86 ± 0.47 × 10-11 d d-1, and a cyclic variation with a period of 65.7 ± 2.4 yr. We suppose these components are caused by the stellar evolution and the light travel time effect (LiTE) of a companion in elliptical orbit, respectively. By calculation, the minimum mass of the potential companion is about 0.17 M⊙, and its mass should be less than or equal to the pulsation primary star when the inclination i > 22.5°D. Therefore, the companion should be a low-mass star, like a late-type main-sequence star or a white dwarf. Due to the unique property of UY Cam, we suggest that more observations and studies on UY Cam and other RRc stars are needed to check the nature of these stars, including the pulsations and binarities.

High-resolution spectroscopy and abundance analysis of δ Scuti stars near the γ Doradus instability strip

NASA Astrophysics Data System (ADS)

Kahraman Aliçavuş, F.; Niemczura, E.; Polińska, M.; Hełminiak, K. G.; Lampens, P.; Molenda-Żakowicz, J.; Ukita, N.; Kambe, E.

2017-10-01

δ Scuti stars are remarkable objects for asteroseismology. In spite of decades of investigations, there are still important questions about these pulsating stars to be answered, such as their positions in log Teff-log g diagram, or the dependence of the pulsation modes on atmospheric parameters and rotation. Therefore, we performed a detailed spectroscopic study of 41 δ Scuti stars. The selected objects are located near the γ Doradus instability strip to make a reliable comparison between both types of variables. Spectral classification, stellar atmospheric parameters (Teff, log g, ξ) and v sin I values were determined. The spectral types and luminosity classes of stars were found to be A1-F5 and III-V, respectively. The Teff ranges from 6600 to 9400 K, whereas the obtained log g values are from 3.4 to 4.3. The v sin I values were found between 10 and 222 km s-1. The derived chemical abundances of δ Scuti stars were compared to those of the non-pulsating stars and γ Doradus variables. It turned out that both δ Scuti and γ Doradus variables have similar abundance patterns, which are slightly different from the non-pulsating stars. These chemical differences can help us to understand why there are non-pulsating stars in classical instability strip. Effects of the obtained parameters on pulsation period and amplitude were examined. It appears that the pulsation period decreases with increasing Teff. No significant correlations were found between pulsation period, amplitude and v sin I.

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.

VizieR Online Data Catalog: HST VI Photometry of Six LMC Old Globular Clusters (Olsen+ 1998)

NASA Astrophysics Data System (ADS)

Olsen, K. A. G.; Hodge, P. W.; Mateo, M.; Olszewski, E. W.; Schommer, R. A.; Suntzeff, N. B.; Walker, A. R.

1998-11-01

The following tables contain the results of photometry performed on Hubble Space Telescope WFPC2 images of the Large Magellanic Cloud globular clusters NGC 1754, 1835, 1898, 1916, 2005, and 2019. The magnitudes reported here were measured from Planetary Camera F555W and F814W images using DoPHOT (Schechter, Mateo, & Saha 1993) and afterwards transformed to Johnson V/Kron-Cousins I using equation 9 of Holtzman et al. (1995PASP..107.1065H). We carried out photometry on both long (1500 sec combined in F555W, 1800 sec in F814W) and short (40 sec combined in F555W, 60 sec in F814W) exposures. Where the short exposure photometry produced smaller errors, we report those magnitudes in place of those measured from the long exposures. For each star, we give an integer identifier, its x and y pixel position as measured in the F555W PC image, its V and I magnitude, the photometric errors reported by DoPHOT, both the V and I DoPHOT object types (multiplied by 10 if the reported magnitude was measured in the short exposure frame), and a flag if the star was removed during our procedure for statistical field star subtraction. Summary of data reduction and assessment of photometric accuracy: Cosmic ray rejection, correction for the y-dependent CTE effect (Holtzman et al. 1995a), geometric distortion correction, and bad pixel flagging were applied to the images before performing photometry. For the photometry, we used version 2.5 of DoPHOT, modified by Eric Deutsch to handle floating-point images. We found that there were insufficient numbers of bright, isolated stars in the PC frames for producing aperture corrections. Aperture corrections as a function of position in the frame were instead derived using WFPC2 point spread functions kindly provided by Peter Stetson. As these artificially generated aperture corrections agree well with ones derived from isolated stars in the WF chips, we trust that they are reliable to better than 0.05 mag. In agreement with the report of Whitmore & Heyer (1997), we found an offset in mean magnitudes between the short- and long-exposure photometry. We corrected for this effect by adjusting the short-exposure magnitudes to match, on average, those of the long exposures. Finally, we merged the short- and long- exposure lists of photometry as described above and transformed the magnitudes from the WFPC2 system to Johnson V/Kron-Cousins I, applying the Holtzman et al. (1995PASP..107.1065H) zero points. Statistical field star subtraction was performed using color-magnitude diagrams of the field stars produced from the combined WF frames. Completeness and random and systematic errors in the photometry were extensively modelled through artificial star tests. Crowding causes the completeness to be a strong function of position in the frame, with detection being most difficult near the cluster centers. In addition, we found that crowding introduces systematic errors in the photometry, generally <0.05 mag, that depend on the V-I and V of the star. Fortunately, these errors are well-understood. However, unknown errors in the zero points may persist at the ~0.05 mag level. (5 data files).

VizieR Online Data Catalog: HST VI Photometry of Six LMC Old Globular Clusters (Olsen+ 1998)

NASA Astrophysics Data System (ADS)

Olsen, K. A. G.; Hodge, P. W.; Mateo, M.; Olszewski, E. W.; Schommer, R. A.; Suntzeff, N. B.; Walker, A. R.

1998-11-01

The following tables contain the results of photometry performed on Hubble Space Telescope WFPC2 images of the Large Magellanic Cloud globular clusters NGC 1754, 1835, 1898, 1916, 2005, and 2019. The magnitudes reported here were measured from Planetary Camera F555W and F814W images using DoPHOT (Schechter, Mateo, & Saha 1993) and afterwards transformed to Johnson V/Kron-Cousins I using equation 9 of Holtzman et al. (1995PASP..107.1065H). We carried out photometry on both long (1500 sec combined in F555W, 1800 sec in F814W) and short (40 sec combined in F555W, 60 sec in F814W) exposures. Where the short exposure photometry produced smaller errors, we report those magnitudes in place of those measured from the long exposures. For each star, we give an integer identifier, its x and y pixel position as measured in the F555W PC image, its V and I magnitude, the photometric errors reported by DoPHOT, both the V and I DoPHOT object types (multiplied by 10 if the reported magnitude was measured in the short exposure frame), and a flag if the star was removed during our procedure for statistical field star subtraction. Summary of data reduction and assessment of photometric accuracy: Cosmic ray rejection, correction for the y-dependent CTE effect (Holtzman et al. 1995a), geometric distortion correction, and bad pixel flagging were applied to the images before performing photometry. For the photometry, we used version 2.5 of DoPHOT, modified by Eric Deutsch to handle floating-point images. We found that there were insufficient numbers of bright, isolated stars in the PC frames for producing aperture corrections. Aperture corrections as a function of position in the frame were instead derived using WFPC2 point spread functions kindly provided by Peter Stetson. As these artificially generated aperture corrections agree well with ones derived from isolated stars in the WF chips, we trust that they are reliable to better than 0.05 mag. In agreement with the report of Whitmore & Heyer (1997), we found an offset in mean magnitudes between the short- and long-exposure photometry. We corrected for this effect by adjusting the short-exposure magnitudes to match, on average, those of the long exposures. Finally, we merged the short- and long- exposure lists of photometry as described above and transformed the magnitudes from the WFPC2 system to Johnson V/Kron-Cousins I, applying the Holtzman et al. (1995PASP..107.1065H) zero points. Statistical field star subtraction was performed using color-magnitude diagrams of the field stars produced from the combined WF frames. Completeness and random and systematic errors in the photometry were extensively modelled through artificial star tests. Crowding causes the completeness to be a strong function of position in the frame, with detection being most difficult near the cluster centers. In addition, we found that crowding introduces systematic errors in the photometry, generally <0.05 mag, that depend on the V-I and V of the star. Fortunately, these errors are well-understood. However, unknown errors in the zero points may persist at the ~0.05 mag level. (6 data files).

The All Sky Automated Survey. The Catalog of Bright Variable Stars in the I-band, South of Declination +28o

NASA Astrophysics Data System (ADS)

Sitek, M.; Pojmański, G.

2014-06-01

This paper presents the results of our extensive search for the bright variable stars in approximately 30 000 square degrees of the south sky in the I-band data collected by 9o×9o camera of the All Sky Automated Survey between 2002 and 2009. Lists of over 27 000 variable stars brighter than 9 mag at maximum light, with amplitudes ranging from 0.02 mag to 7 mag and variability time-scales from hours to years, as well as corresponding light curves are provided. Automated classification algorithm based on stellar properties (period, Fourier coefficients, 2MASS J, H, K, colors, ASAS V-band data) was used to roughly classify objects. Despite low spatial resolution of the ASAS data (≍15'') we cross-identified all objects with other available data sources. Coordinates of the most probable 2MASS counterparts are provided. 27 705 stars brighter than I=9 mag were found to be variable, of which 7842 objects were detected to be variable for the first time. Brief statistics and discussion of the presented data is provided. All the photometric data is available over the Internet at http://www.astrouw.edu.pl/ gp/asas/AsasBrightI.html

The Dirigible: A Catalyst for Resource Exploitation in Remote Areas?

DTIC Science & Technology

1985-04-01

ir’ship (26’.: 13). .. Hybrid . A he ,vi er than air vehiLile which Lomb nes.’-. s.tar~ it (gas) anrid cly ,mi L (pro~pel 1er s, jet e, g ines ) li ft...another test with a hybrid airship (8:.33). TABLE 1. - Airships Rejected p The three remaining airships will be discussed next. All arc? hybrid LTAs...heavy-lift markets. (Drawing at Appendix 3.) The Cyclo-Crane is a hybrid aircraft utilizing aerostatic lift from a helium filled centerbody to support

Influence of aging and chronic heart failure on temporal dispersion of myocardial repolarization

PubMed Central

Piccirillo, Gianfranco; Moscucci, Federica; Pascucci, Matteo; Pappadà, Maria Antonella; D’Alessandro, Gaetana; Rossi, Pietro; Quaglione, Raffaele; Di Barba, Daniele; Barillà, Francesco; Magrì, Damiano

2013-01-01

Background and purpose: QT and Tpeak-Tend (Te) intervals are associated with sudden cardiac death in patients with chronic heart failure (CHF). We studied age-dependent influence on short-term temporal dispersion of these two variables in patients with postischemic CHF. Method: We grouped 75 CHF and 53 healthy control subjects into three age subsets: ≤50 years, >50 years and ≤65 years, and >65 years. We then calculated the following indices: QT and Te variability index (QTVI and TeVI), the ratio between the short-term variability (STV) of QT or Te, and the STV of resting rate (RR) (QT/RR STV and Te/RR STV). Results: In all different age subgroups, patients with CHF showed a higher level of QTVI than age-matched control subjects (≤50 years: P < 0.0001; >50 years and ≤65 years: P < 0.05; >65 years: P < 0.05). Patients with CHF < 50 years old also had all repolarization variability indices higher than normal age-matched controls (TeVI, P < 0.05; QT/RR STV, P < 0.05; Te/RR STV, P < 0.05), whereas we did not find any difference between the two older classes of subjects. Both QTVI (r2: 0.178, P < 0.05) and TeVI (r2: 0.433, P < 0.001) were positively related to age in normal subjects, even if the first correlation was weaker than the second one. Conclusion: Our data showed that QTVI could be used in all ages to evaluate repolarization temporal liability, whereas the other indices are deeply influenced by age. Probably, the age-dependent increase in QTVI was more influenced by a reduction of RR variability reported in older normal subjects. PMID:23662051

Influence of aging and chronic heart failure on temporal dispersion of myocardial repolarization.

PubMed

Piccirillo, Gianfranco; Moscucci, Federica; Pascucci, Matteo; Pappadà, Maria Antonella; D'Alessandro, Gaetana; Rossi, Pietro; Quaglione, Raffaele; Di Barba, Daniele; Barillà, Francesco; Magrì, Damiano

2013-01-01

QT and T(peak)-T(end) (Te) intervals are associated with sudden cardiac death in patients with chronic heart failure (CHF). We studied age-dependent influence on short-term temporal dispersion of these two variables in patients with postischemic CHF. We grouped 75 CHF and 53 healthy control subjects into three age subsets: ≤ 50 years, >50 years and ≤ 65 years, and >65 years. We then calculated the following indices: QT and Te variability index (QTVI and TeVI), the ratio between the short-term variability (STV) of QT or Te, and the STV of resting rate (RR) (QT/RR STV and Te/RR STV). In all different age subgroups, patients with CHF showed a higher level of QTVI than age-matched control subjects (≤ 50 years: P < 0.0001; >50 years and ≤ 65 years: P < 0.05; >65 years: P < 0.05). Patients with CHF < 50 years old also had all repolarization variability indices higher than normal age-matched controls (TeVI, P < 0.05; QT/RR STV, P < 0.05; Te/RR STV, P < 0.05), whereas we did not find any difference between the two older classes of subjects. Both QTVI (r²: 0.178, P < 0.05) and TeVI (r²: 0.433, P < 0.001) were positively related to age in normal subjects, even if the first correlation was weaker than the second one. Our data showed that QTVI could be used in all ages to evaluate repolarization temporal liability, whereas the other indices are deeply influenced by age. Probably, the age-dependent increase in QTVI was more influenced by a reduction of RR variability reported in older normal subjects.

The All Sky Automated Survey. Catalog of Variable Stars. IV. 18^h-24^h Quarter of the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Pojmanski, G.; Maciejewski, G.

2005-03-01

In this paper we present the fourth part of the photometric data from the 9 arcdeg x 9 arcdeg ASAS camera monitoring the whole southern hemisphere in V-band. Preliminary list (based on observations obtained since January 2001) of variable stars located between RA 18^h and 24^h is released. 10311 stars brighter than V=15 mag were found to be variable (1641 eclipsing, 1116 regularly pulsating, 938 Mira-type and 6616 other stars). Light curves have been classified using the automated algorithm taking into account periods, amplitudes, Fourier coefficients of the light curves, 2MASS colors and IRAS infrared fluxes. Basic photometric properties are presented in the tables and some examples of thumbnail light curves are printed for reference. All photometric data are available over the Internet at http://www.astrouw.edu.pl/~gp/asas/asas.html or http://archive.princeton.edu/~asas

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

The All Sky Automated Survey. The Catalog of Variable Stars. II. 6^h-12^h Quarter of the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Pojmanski, G.

2003-12-01

This paper describes the second part of the photometric data from the 9 arcdeg times 9 arcdeg ASAS camera monitoring the whole southern hemisphere in the V-band. Preliminary list of variable stars based on observations obtained since January 2001 is presented. Over 2800000 stars brighter than V=15 mag on 18000 frames were analyzed and 11357 were found to be variable (2685 eclipsing, 907 regularly pulsating, 521 Mira and 7244 other, mostly SR, IRR and LPV stars). Periodic light curves have been classified using the automated algorithm, which now takes into account IRAS infrared fluxes. Basic photometric properties are presented in the tables and some examples of thumbnail light curves are printed for reference. All photometric data are available over the INTERNET at http://www.astrouw.edu.pl/~gp/asas/asas.html or http://archive.princeton.edu/~asas.

The All Sky Automated Survey. Catalog of Variable Stars. III. 12h-18h Quarter of the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Pojmanski, G.; Maciejewski, G.

2004-06-01

This paper describes the third part of the photometric data from the 9 arcdeg x 9arcdeg ASAS camera monitoring the whole southern hemisphere in V-band. Preliminary list of variable stars based on observations obtained since January 2001 is presented. Over 3200000 stars brighter than V=15 mag on 18000 frames were analyzed and 10453 were found to be variable (1718 eclipsing, 731 regularly pulsating, 849 Mira and 7155 other stars). Light curves have been classified using the improved automated algorithm, which now takes into account 2MASS colors and IRAS infrared fluxes. Basic photometric properties are presented in the tables and some examples of thumbnail light curves are printed for reference. All photometric data are available over the INTERNET at http://www.astrouw.edu.pl/\\gp/asas/asas.html or http://archive.princeton.edu/\\asas.

Infinitesimal Deformations of a Formal Symplectic Groupoid

NASA Astrophysics Data System (ADS)

Karabegov, Alexander

2011-09-01

Given a formal symplectic groupoid G over a Poisson manifold ( M, π 0), we define a new object, an infinitesimal deformation of G, which can be thought of as a formal symplectic groupoid over the manifold M equipped with an infinitesimal deformation {π_0 + \\varepsilon π_1} of the Poisson bivector field π 0. To any pair of natural star products {(ast,tildeast)} having the same formal symplectic groupoid G we relate an infinitesimal deformation of G. We call it the deformation groupoid of the pair {(ast,tildeast)} . To each star product with separation of variables {ast} on a Kähler-Poisson manifold M we relate another star product with separation of variables {hatast} on M. We build an algorithm for calculating the principal symbols of the components of the logarithm of the formal Berezin transform of a star product with separation of variables {ast} . This algorithm is based upon the deformation groupoid of the pair {(ast,hatast)}.

The SpaceInn-SISMA Database: Characterization of a Large Sample of Variable and Active Stars by Means of Harps Spectra

NASA Astrophysics Data System (ADS)

Rainer, M.; Poretti, E.; Mistò, A.; Panzera, M. R.; Molinaro, M.; Cepparo, F.; Roth, M.; Michel, E.; Monteiro, M. J. P. F. G.

2016-12-01

We created a large database of physical parameters and variability indicators by fully reducing and analyzing the large number of spectra taken to complement the asteroseismic observations of the COnvection, ROtation and planetary Transits (CoRoT) satellite. 7103 spectra of 261 stars obtained with the ESO echelle spectrograph HARPS have been stored in the VO-compliant database Spectroscopic Indicators in a SeisMic Archive (SISMA), along with the CoRoT photometric data of the 72 CoRoT asteroseismic targets. The remaining stars belong to the same variable classes of the CoRoT targets and were observed to better characterize the properties of such classes. Several useful variability indicators (mean line profiles, indices of differential rotation, activity and emission lines) together with v\\sin I and radial-velocity measurements have been extracted from the spectra. The atmospheric parameters {T}{eff},{log}g, and [Fe/H] have been computed following a homogeneous procedure. As a result, we fully characterize a sample of new and known variable stars by computing several spectroscopic indicators, also providing some cases of simultaneous photometry and spectroscopy.

On the period determination of ASAS eclipsing binaries

NASA Astrophysics Data System (ADS)

Mayangsari, L.; Priyatikanto, R.; Putra, M.

2014-03-01

Variable stars, or particularly eclipsing binaries, are very essential astronomical occurrence. Surveys are the backbone of astronomy, and many discoveries of variable stars are the results of surveys. All-Sky Automated Survey (ASAS) is one of the observing projects whose ultimate goal is photometric monitoring of variable stars. Since its first light in 1997, ASAS has collected 50,099 variable stars, with 11,076 eclipsing binaries among them. In the present work we focus on the period determination of the eclipsing binaries. Since the number of data points in each ASAS eclipsing binary light curve is sparse, period determination of any system is a not straightforward process. For 30 samples of such systems we compare the implementation of Lomb-Scargle algorithm which is an Fast Fourier Transform (FFT) basis and Phase Dispersion Minimization (PDM) method which is non-FFT basis to determine their period. It is demonstrated that PDM gives better performance at handling eclipsing detached (ED) systems whose variability are non-sinusoidal. More over, using semi-automatic recipes, we get better period solution and satisfactorily improve 53% of the selected object's light curves, but failed against another 7% of selected objects. In addition, we also highlight 4 interesting objects for further investigation.

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.

New SX Phoenicis Variables in the Globular Cluster NGC 4833

NASA Astrophysics Data System (ADS)

Darragh, A. N.; Murphy, B. W.

2012-07-01

We report the discovery of 6 SX Phoenicis stars in the southern globular cluster NGC 4833. Images were obtained from January through June 2011 with the Southeastern Association for Research in Astronomy 0.6 meter telescope located at Cerro Tololo Interamerican Observatory. The ISIS image subtraction method was used to search for variable stars in the cluster. We confirmed 17 previously cataloged variables and have identified 10 new variables. Of the total number of confirmed variables in our 10×10 arcmin^2 field, we classified 10 RRab variables, with a mean period of 0.69591 days, 7 RRc, with a mean period of 0.39555 days, 2 possible RRe variables with a mean period of 0.30950 days, a W Ursae Majoris contact binary, an Algol-type binary, and the 6 SX Phoenicis stars with a mean period of 0.05847 days. The periods, relative numbers of RRab and RRc variables, and Bailey diagram are indicative of the cluster being of the Oosterhoff type II. We present the phased-light curves, periods of previously known variables and the periods and classifications of the newly discovered variables, and their location on the color-magnitude diagram.

Yes, Aboriginal Australians can and did discover the variability of Betelgeuse

NASA Astrophysics Data System (ADS)

Schaefer, Bradley E.

2018-04-01

Recently, a widely publicized claim has been made that the Aboriginal Australians discovered the variability of the red star Betelgeuse in the modern Orion, plus the variability of two other prominent red stars: Aldebaran and Antares. This result has excited the usual healthy skepticism, with questions about whether any untrained peoples can discover the variability and whether such a discovery is likely to be placed into lore and transmitted for long periods of time. Here, I am offering an independent evaluation, based on broad experience with naked-eye sky viewing and astro-history. I find that it is easy for inexperienced observers to detect the variability of Betelgeuse over its range in brightness from V = 0.0 to V = 1.3, for example in noticing from season-to-season that the star varies from significantly brighter than Procyon to being greatly fainter than Procyon. Further, indigenous peoples in the Southern Hemisphere inevitably kept watch on the prominent red star, so it is inevitable that the variability of Betelgeuse was discovered many times over during the last 65 millennia. The processes of placing this discovery into a cultural context (in this case, put into morality stories) and the faithful transmission for many millennia is confidently known for the Aboriginal Australians in particular. So this shows that the whole claim for a changing Betelgeuse in the Aboriginal Australian lore is both plausible and likely. Given that the discovery and transmission is easily possible, the real proof is that the Aboriginal lore gives an unambiguous statement that these stars do indeed vary in brightness, as collected by many ethnographers over a century ago from many Aboriginal groups. So I strongly conclude that the Aboriginal Australians could and did discover the variability of Betelgeuse, Aldebaran, and Antares.

Investigating the Spectroscopic Variability of Magentically Active M Dwarfs In SDSS.

NASA Astrophysics Data System (ADS)

Ventura, Jean-Paul; Schmidt, Sarah J.; Cruz, Kelle; Rice, Emily; Cid, Aurora

2018-01-01

Magnetic activity, a wide range of observable phenomena produced in the outer atmospheres of stars is, currently, not well understood for M dwarfs. In higher mass stars, magnetic activity is powered by a dynamo process involving the differential rotation of a star’s inner regions. This process generates a magnetic field, heats up regions in the chromosphere and produces Hα emission line radiation from collisional excitation. Using spectroscopic data from the Sloan Digital Sky Survey (SDSS), I compare Hα emission line strengths for a subsample of 12,000 photometric variability selected M dwarfs from Pan-STARRS1 with those of a known non-variable sample. Presumably, the photometric variability originates from the occurrence of star spots at the stellar surface, which are the result of an intense magnetic field and associated chromospheric heating. We proceed with this work in order to test whether the photometric variability of the sample correlates with chromospheric Hα emission features. If not, we explore alternate reasons for that photometric variability (e.g. binarity or transiting planetary companions)

Detection of a weak maser emission pedestal associated with the SiO maser. [in variable late stars

NASA Technical Reports Server (NTRS)

Snyder, L. E.; Dickinson, D. F.; Brown, L. W.; Buhl, D.

1978-01-01

Results are reported for high-spectral-resolution observations of the v = 1, J = 1-0 SiO maser sources at 43,122.027 MHz (6.95 mm wavelength) associated with the variable stars Omega Cet, NML Tau, VY CMa, R Leo, W Hya, VX Sgr, NML Cyg, and R Cas. A weak underlying maser emission pedestal is clearly observed in the spectra of all but NML Cyg and R Cas. The data indicate that the underlying pedestal of SiO emission appears to originate in a shell-like region around the star, has a thermal appearance even though it must be due to weak maser emission, and appears to be part of the spectral signature of SiO maser emission from late-type stars. It is found that the center velocities of the pedestals may be used to determine stellar radial velocities. Observations of large-scale time variations in the intensity of the Ori A SiO maser and the detection of weak maser pedestals associated with each of the two strong emission-feature groups in Orion are also discussed. It is suggested that the Orion molecular cloud might contain two late-type long-period variable stars that may be semiregular variables.

Aperture Fever and the Quality of AAVSO Visual Estimates: mu Cephei as an Example

NASA Astrophysics Data System (ADS)

Turner, D. G.

2014-06-01

(Abstract only) At the limits of human vision the eye can reach precisions of 10% or better in brightness estimates for stars. So why did the quality of AAVSO visual estimates suddenly drop to 50% or worse for many stars following World War II? Possibly it is a consequence of viewing variable stars through ever-larger aperture instruments than was the case previously, a time when many variables were observed without optical aid. An example is provided by the bright red supergiant variable mu Cephei, a star that has the potential to be a calibrating object for the extragalactic distance scale if its low-amplitude brightness variations are better defined. It appears to be a member of the open cluster Trumpler 37, so its distance and luminosity can be established provided one can pinpoint the amount of interstellar extinction between us and it. mu Cep appears to be a double-mode pulsator, as suggested previously in the literature, but with periods of roughly 700 and 1,000 days it is unexciting to observe and its red color presents a variety of calibration problems. Improving quality control for such variable stars is an issue important not only to the AAVSO, but also to science in general.

Confirming LBV Candidates Through Variability: A Photometric and Spectroscopic Monitoring Study

NASA Astrophysics Data System (ADS)

Stringfellow, Guy; Gvaramadze, Vasilii

2013-02-01

Luminous Blue Variable (LBV) stars represent an extremely rare class of luminous massive stars with high mass loss rates. The paucity ( 12) of confirmed Galactic LBV precludes determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. We've been conducting an optical/near-IR spectral survey of a large subset of central stars residing within newly discovered it Spitzer nebulae and have identified over two dozen new candidate LBVs (cLBVs) based on spectral similarity alone; confirming them as bona fide LBVs requires demonstrating 1-3 mag photometric and spectroscopic variability. This marks a significant advancement in the study of massive stars, far outweighing the return from many studies searching for LBVs and WRs the past several decades. Monitoring from semesters 2011B-2012A already has confirmed one new cLBV as a bona fide LBV. We propose to continue optical-IR photometric monitoring of these cLBVS with the 1.3m. Chiron, replacing the RC spectrograph on the 1.5m, now allows high-resolution optical spectroscopic monitoring of bright cLBVs, 11 of which are proposed herein. Spectra are important for understanding the physics driving photometric variability, properties of the wind, and allow analysis of line profiles.

VizieR Online Data Catalog: JHK lightcurves of red giants in the SMC (Takayama+, 2015)

NASA Astrophysics Data System (ADS)

Takayama, M.; Wood, P. R.; Ita, Y.

2017-11-01

This is JHK light curves of 7 oxygen rich stars and 14 carbon stars which show the variability of prominent long secondary periods (LSPs). Those stars are cross-identified with OGLE LSP variables in the Small Magellanic Cloud (Soszynski et al. 2011, J/AcA/61/217). A long-term multiband near-IR photometric survey for variable stars in the Large and Small Magellanic Clouds has been carried out at the South African Astronomical Observatory at Sutherland (Ita et al., in preparation). The SIRIUS camera attached to the IRSF 1.4 m telescope was used for this survey and more than 10 yr of observations in the near-IR bands J(1.25 μm), H(1.63 μm) and KS(2.14 μm) band were obtained. In this work, we select the SMC stars from the SIRIUS data base. We obtained the V- and I-band time series of SMC red giants from the OGLE project (Soszynski et al. 2011, J/AcA/61/217). (2 data files).

Variable Stars in Large Magellanic Cloud Globular Clusters. III. Reticulum

NASA Astrophysics Data System (ADS)

Kuehn, Charles A.; Dame, Kyra; Smith, Horace A.; Catelan, Márcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura

2013-06-01

This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. The primary goal of this series is to look at how the characteristics and behavior of RR Lyrae stars in Oosterhoff-intermediate systems compare to those of their counterparts in Oosterhoff-I/II systems. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We found a total of 32 variables stars (22 RRab, 4 RRc, and 6 RRd stars) in our field of view. We present photometric parameters and light curves for these stars. We also present physical properties, derived from Fourier analysis of light curves, for some of the RR Lyrae stars. We discuss the Oosterhoff classification of Reticulum and use our results to re-derive the distance modulus and age of the cluster. 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).

K2 Variable Catalogue: Variable stars and eclipsing binaries in K2 campaigns 1 and 0

NASA Astrophysics Data System (ADS)

Armstrong, D. J.; Kirk, J.; Lam, K. W. F.; McCormac, J.; Walker, S. R.; Brown, D. J. A.; Osborn, H. P.; Pollacco, D. L.; Spake, J.

2015-07-01

Aims: We have created a catalogue of variable stars found from a search of the publicly available K2 mission data from Campaigns 1 and 0. This catalogue provides the identifiers of 8395 variable stars, including 199 candidate eclipsing binaries with periods up to 60 d and 3871 periodic or quasi-periodic objects, with periods up to 20 d for Campaign 1 and 15 d for Campaign 0. Methods: Lightcurves are extracted and detrended from the available data. These are searched using a combination of algorithmic and human classification, leading to a classifier for each object as an eclipsing binary, sinusoidal periodic, quasi periodic, or aperiodic variable. The source of the variability is not identified, but could arise in the non-eclipsing binary cases from pulsation or stellar activity. Each object is cross-matched against variable star related guest observer proposals to the K2 mission, which specifies the variable type in some cases. The detrended lightcurves are also compared to lightcurves currently publicly available. Results: The resulting catalogue gives the ID, type, period, semi-amplitude, and range of the variation seen. We also make available the detrended lightcurves for each object. The catalogue is available at http://deneb.astro.warwick.ac.uk/phrlbj/k2varcat/ 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/579/A19

Exploring the SDSS Dataset with Linked Scatter Plots: I. EMP, CEMP, and CV Stars

NASA Technical Reports Server (NTRS)

Carbon, Duane F.; Henze, Christopher; Nelson, Bron C.

2017-01-01

We present the results of a search for EMP, CEMP, and cataclysmic variable stars using a new exploration tool based on linked scatter plots (LSPs). Our approach is especially designed to work with very large spectrum data sets such as the SDSS, LAMOST, RAVE, and Gaia data sets and can be applied to stellar, galaxy, and quasar spectra. As a demonstration, we conduct a search for EMP, CEMP, and cataclysmic variable stars in the SDSS DR10 data set. We first created a 3326-dimensional phase space containing nearly 2 billion measures of the strengths of over 1600 spectral features in 569,738 SDSS stars. These measures capture essentially all the stellar atomic and molecular species visible at the resolution of SDSS spectra. We show how LSPs can be used to quickly isolate and examine interesting portions of this phase space. To illustrate, we use LSPs coupled with cuts in selected portions of phase space to extract EMP stars, C-rich EMP stars, and CV stars. We present identifications for 59 previously unrecognized candidate EMP stars and 11 previously unrecognized candidate CEMP stars. We also call attention to 2 candidate He II emission CV stars found by the LSP approach that have not yet been discussed in the literature.

Exploring the SDSS Dataset with Linked Scatter Plots: I. EMP, CEMP, and CV Stars.

PubMed

Carbon, Duane F; Henze, Christopher; Nelson, Bron C

2017-02-01

We present the results of a search for EMP, CEMP, and cataclysmic variable stars using a new exploration tool based on linked scatter plots (LSPs). Our approach is especially designed to work with very large spectrum data sets such as the SDSS, LAMOST, RAVE, and Gaia data sets and can be applied to stellar, galaxy, and quasar spectra. As a demonstration, we conduct a search for EMP, CEMP, and cataclysmic variable stars in the SDSS DR10 data set. We first created a 3326-dimensional phase space containing nearly 2 billion measures of the strengths of over 1600 spectral features in 569,738 SDSS stars. These measures capture essentially all the stellar atomic and molecular species visible at the resolution of SDSS spectra. We show how LSPs can be used to quickly isolate and examine interesting portions of this phase space. To illustrate, we use LSPs coupled with cuts in selected portions of phase space to extract EMP stars, C-rich EMP stars, and CV stars. We present identifications for 59 previously unrecognized candidate EMP stars and 11 previously unrecognized candidate CEMP stars. We also call attention to 2 candidate He II emission CV stars found by the LSP approach that have not yet been discussed in the literature.

Exploring the SDSS Dataset with Linked Scatter Plots: I. EMP, CEMP, and CV Stars

PubMed Central

Carbon, Duane F.; Henze, Christopher; Nelson, Bron C.

2017-01-01

We present the results of a search for EMP, CEMP, and cataclysmic variable stars using a new exploration tool based on linked scatter plots (LSPs). Our approach is especially designed to work with very large spectrum data sets such as the SDSS, LAMOST, RAVE, and Gaia data sets and can be applied to stellar, galaxy, and quasar spectra. As a demonstration, we conduct a search for EMP, CEMP, and cataclysmic variable stars in the SDSS DR10 data set. We first created a 3326-dimensional phase space containing nearly 2 billion measures of the strengths of over 1600 spectral features in 569,738 SDSS stars. These measures capture essentially all the stellar atomic and molecular species visible at the resolution of SDSS spectra. We show how LSPs can be used to quickly isolate and examine interesting portions of this phase space. To illustrate, we use LSPs coupled with cuts in selected portions of phase space to extract EMP stars, C-rich EMP stars, and CV stars. We present identifications for 59 previously unrecognized candidate EMP stars and 11 previously unrecognized candidate CEMP stars. We also call attention to 2 candidate He II emission CV stars found by the LSP approach that have not yet been discussed in the literature. PMID:28684884

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.

Variable Stars and Constant Commitments: The Stellar Career of Dorrit Hoffleit

NASA Astrophysics Data System (ADS)

Larsen, Kristine

2011-05-01

Astronomer, educator, and science historian Dorrit Hoffleit (1907-2007) was widely respected by the amateur and professional astronomical community as a mentor and an ardent supporter of independent research. Her more than 600 catalogues, books, articles, book reviews, and news columns cover myriad aspects of astronomy, from variable stars and stellar properties to meteor showers, quasars, and rocketry. She also made important contributions to the history of astronomy. Hoffleit worked at the Harvard College Observatory from 1927-1956, where she discovered over 1200 variable stars. When Director Harlow Shapley retired from Harvard, Hoffleit gave up her tenured position and moved to Yale University, where she was placed in charge of the Yale Catalog of Bright Stars. At the same time, she was offered a position as director of the Maria Mitchell Observatory on Nantucket Island in Massachusetts. Hoffleit split her dual positions into six-month stints and remained director at the Mitchell Observatory for 21 years, developing a summer research program that engaged more than 100 undergraduate students (all but three of them women) in variable star research. Up until shortly before her death, she continued to work tirelessly on selected projects, and she was in high demand as a collaborator with colleagues at Yale and elsewhere. She was especially devoted to the American Association of Variable Star Observers (AAVSO) in part because it brought together amateur and professional astronomers in collaboration. She served on the organization's council for 23 years and as its president from 1961-1963. In 2002, the AAVS0 published her autobiography, Misfortunes as Blessings in Disguise, in which Hoffleit explains how she always felt blessed by the opportunities in her life, even those which initially seemed misfortunes, and above all else valued creativity, flexibility, collegiality, and intellectual freedom in her professional life.

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.

A disk asymmetry in motion around the B[e] star MWC158

NASA Astrophysics Data System (ADS)

Kluska, J.; Benisty, M.; Soulez, F.; Berger, J.-P.; Le Bouquin, J.-B.; Malbet, F.; Lazareff, B.; Thiébaut, E.

2016-06-01

Context. MWC158 is a star with the B[e] phenomenon that shows strong spectrophotometric variability (in lines and in UV and visible continuum) attributed to phases of shell ejection. The evolutionary stage of this star was never clearly determined. Previous interferometric, spectropolarimetric and spectro-interferometric studies suggest a disk morphology for its environment. Aims: We investigate the origin of the variability within the inner astronomical unit of the central star using near-infrared interferometric observations with PIONIER at the VLTI over a two-year period. Methods: We performed an image reconstruction of the circumstellar environment using the SPARCO method. We discovered that the morphology of the circumstellar environment could vary on timescales of weeks or days. We carried out a parametric fit of the data with a model consisting of a star, a disk and a bright spot that represents a brighter emission in the disk. Results: We detect strong morphological changes in the first astronomical unit around the star, that happen on a timescale of few months. We cannot account for such variability well with a binary model. Our parametric model fits the data well and allows us to extract the location of the asymmetry for different epochs. Conclusions: For the first time, we detect a morphological variability in the environment of MWC158. This variability is reproduced by a model of a disk and a bright spot. The locations of the bright spot suggest that it is located in the disk, but its precise motion is not determined. The origin of the asymmetry in the disk is complex and may be related to asymmetric shell ejections. Based on observations performed with PIONIER mounted on the ESO Very Large Telescope interferometer (programmes: 089.C-0211, 190.C-0963).

Active Learning to Overcome Sample Selection Bias: Application to Photometric Variable Star Classification

NASA Astrophysics Data System (ADS)

Richards, Joseph W.; Starr, Dan L.; Brink, Henrik; Miller, Adam A.; Bloom, Joshua S.; Butler, Nathaniel R.; James, J. Berian; Long, James P.; Rice, John

2012-01-01

Despite the great promise of machine-learning algorithms to classify and predict astrophysical parameters for the vast numbers of astrophysical sources and transients observed in large-scale surveys, the peculiarities of the training data often manifest as strongly biased predictions on the data of interest. Typically, training sets are derived from historical surveys of brighter, more nearby objects than those from more extensive, deeper surveys (testing data). This sample selection bias can cause catastrophic errors in predictions on the testing data because (1) standard assumptions for machine-learned model selection procedures break down and (2) dense regions of testing space might be completely devoid of training data. We explore possible remedies to sample selection bias, including importance weighting, co-training, and active learning (AL). We argue that AL—where the data whose inclusion in the training set would most improve predictions on the testing set are queried for manual follow-up—is an effective approach and is appropriate for many astronomical applications. For a variable star classification problem on a well-studied set of stars from Hipparcos and Optical Gravitational Lensing Experiment, AL is the optimal method in terms of error rate on the testing data, beating the off-the-shelf classifier by 3.4% and the other proposed methods by at least 3.0%. To aid with manual labeling of variable stars, we developed a Web interface which allows for easy light curve visualization and querying of external databases. Finally, we apply AL to classify variable stars in the All Sky Automated Survey, finding dramatic improvement in our agreement with the ASAS Catalog of Variable Stars, from 65.5% to 79.5%, and a significant increase in the classifier's average confidence for the testing set, from 14.6% to 42.9%, after a few AL iterations.

Photometric and spectral evolution of the symbiotic eclipsing variable V1329 Cygni at a late stage of its nova-like outburst

NASA Astrophysics Data System (ADS)

Arkhipova, V. P.; Esipov, V. F.; Ikonnikova, N. P.; Komissarova, G. V.

2015-03-01

The photoelectric UBV observations of the peculiar symbiotic star V1329 Cyg performed at the Crimean Station of the SAI-MSU during 245 nights over the period 2003-2014 are presented. The star's light curves since 1973 from the Crimean observations are shown. The brightness decline after its outburst over the last 40 years was . The phase color curves at phases 0.2 and 0.8 have maxima. Their qualitative interpretation in terms of the model of interacting winds in symbiotic binary star systems is proposed. The orbital period of the binary system has been redetermined. The spectroscopic observations at the 125-cm telescope of the Crimean Station from 1994 to 2014 have confirmed the change in the system's emission spectrum with orbital phase. The HI, He I, and Fe II line fluxes clearly trace the orbital motion. The Balmer hydrogen lines as well as the continuum at λ6000 and the V-band flux change by a factor of ˜3.5 from minimum to maximum light. The neutral helium lines change by a factor of 5. The high-excitation He II, [FeVII], [Ca VII] lines and the Raman O VI λ6825 line have shown changes in the fluxes by a factor of ˜2-3 weakly correlating with the orbital phase. The equivalent widths of the HI and He I lines are maximal at the star's maximum light and have distinct minima at phases 0.2 and 0.8, while the equivalent widths of the He II, [FeVII], and [CaVII] lines are minimal in the range of phases 0.2-0.8. The question about the location of the permitted and forbidden line emission zones in the binary system V1329 Cyg is discussed. The evolution of the emission spectrum for V1329 Cyg from 1980 to 2014 has been studied on the basis of new and archival data. A gradual decrease in the absolute fluxes of the nebular emission lines has been detected. The [O III] and [Fe VII] lines have weakened significantly. However, the [Fe X] λ6375 Å line has appeared and gradually strengthened, suggesting an increase in the degree of gas ionization in the line formation zone.

Four Star School Awards: Key Factors that Predict High Performance among Indiana School Corporations

ERIC Educational Resources Information Center

Veracco, Lawrence H.

2009-01-01

The purpose of this study was to analyze the Four Star status of Indiana school corporations in order to determine if certain variables currently existing among school corporations could be predictive of Four Star status. Differences in Four Star status were examined with respect to school corporation size, school corporation average teacher…

Wolf-Rayet stars

NASA Technical Reports Server (NTRS)

Abbott, David C.; Conti, Peter S.

1987-01-01

The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.

Primordial main equence binary stars in the globular cluster M71

NASA Technical Reports Server (NTRS)

Yan, Lin; Mateo, Mario

1994-01-01

We report the identification of five short-period variables near the center of the metal-rich globular cluster M71. Our observations consist of multiepoch VI charge coupled device (CCD) images centered on the cluster and covering a 6.3 min x 6.3 min field. Four of these variables are contact eclipsing binaries with periods between 0.35 and 0.41 days; one is a detached or semidetached eclipsing binary with a period of 0.56 days. Two of the variables were first identified as possible eclipsing binaries in an earlier survey by Hodder et al. (1992). We have used a variety of arguments to conclude that all five binary stars are probable members of M71, a result that is consistent with the low number (0.15) of short-period field binaries expected along this line of sight. Based on a simple model of how contact binaries evolve from initially detached binaries, we have determined a lower limit of 1.3% on the frequency of primordial binaries in M71 with initial orbital periods in the range 2.5 - 5 days. This implies that the overall primordial binary frequency, f, is 22(sup +26)(sub -12)% assuming df/d log P = const ( the 'flat' distribution), or f = 57(sup +15)(sub -8)% for df/d log P = 0.032 log P + const as observed for G-dwarf binaries in the solar neighborhood (the 'sloped' distribution). Both estimates of f correspond to binaries with initial periods shorter than 800 yr since any longer-period binaries would have been disrupted over the lifetime of the cluster. Our short-period binary frequency is in excellent agreement with the observed frequency of red-giant binaries observed in globulars if we adopt the flat distribution. For the sloped distribution, our results significantly overestimate the number of red-giant binaries. All of the short-period M71 binaries lie within 1 mag of the luminosity of the cluster turnoff in the color-magnitude diagram despite the fact we should have easily detected similar eclipsing binaries 2 - 2.5 mag fainter than this. We discuss the implications of this on our estimates of the binary frequency in M71 and on the formation of blue stragglers.

Calibrating the pixel-level Kepler imaging data with a causal data-driven model

NASA Astrophysics Data System (ADS)

Wang, Dun; Foreman-Mackey, Daniel; Hogg, David W.; Schölkopf, Bernhard

2015-01-01

In general, astronomical observations are affected by several kinds of noise, each with it's own causal source; there is photon noise, stochastic source variability, and residuals coming from imperfect calibration of the detector or telescope. In particular, the precision of NASA Kepler photometry for exoplanet science—the most precise photometric measurements of stars ever made—appears to be limited by unknown or untracked variations in spacecraft pointing and temperature, and unmodeled stellar variability. Here we present the Causal Pixel Model (CPM) for Kepler data, a data-driven model intended to capture variability but preserve transit signals. The CPM works at the pixel level (not the photometric measurement level); it can capture more fine-grained information about the variation of the spacecraft than is available in the pixel-summed aperture photometry. The basic idea is that CPM predicts each target pixel value from a large number of pixels of other stars sharing the instrument variabilities while not containing any information on possible transits at the target star. In addition, we use the target star's future and past (auto-regression). By appropriately separating the data into training and test sets, we ensure that information about any transit will be perfectly isolated from the fitting of the model. The method has four hyper-parameters (the number of predictor stars, the auto-regressive window size, and two L2-regularization amplitudes for model components), which we set by cross-validation. We determine a generic set of hyper-parameters that works well on most of the stars with 11≤V≤12 mag and apply the method to a corresponding set of target stars with known planet transits. We find that we can consistently outperform (for the purposes of exoplanet detection) the Kepler Pre-search Data Conditioning (PDC) method for exoplanet discovery, often improving the SNR by a factor of two. While we have not yet exhaustively tested the method at other magnitudes, we expect that it should be generally applicable, with positive consequences for subsequent exoplanet detection or stellar variability (in which case we must exclude the autoregressive part to preserve intrinsic variability).

The effective temperature of the white-dwarf star and ZZ Ceti candidate Wolf 485A

NASA Technical Reports Server (NTRS)

Digel, S. W.; Shipman, H. L.

1984-01-01

Previous multichannel observations of W485A (WD 1327-08) have placed it in the instability strip, the effective temperature range 11,000-13,000 K. In the instability strip, most of the stars (the ZZ Ceti stars) are variable, but W485A has not been detected to be variable. In this paper, high-resolution spectra of W485A and improved hydrogen-line broadening routines are used in the ATLAS model-atmospheres program to find the temperature of W485A; the estimate of effective temperature most consistent with the other data on the star is 14,600 K, outside the instability strip.

THE TAIWAN-AMERICAN OCCULTATION SURVEY PROJECT STELLAR VARIABILITY. I. DETECTION OF LOW-AMPLITUDE {delta} SCUTI STARS

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

Kim, D.-W.; Protopapas, P.; Alcock, C.

2010-02-15

We analyzed data accumulated during 2005 and 2006 by the Taiwan-American Occultation Survey (TAOS) in order to detect short-period variable stars (periods of {approx}<1 hr) such as {delta} Scuti. TAOS is designed for the detection of stellar occultation by small-size Kuiper Belt Objects and is operating four 50 cm telescopes at an effective cadence of 5 Hz. The four telescopes simultaneously monitor the same patch of the sky in order to reduce false positives. To detect short-period variables, we used the fast Fourier transform algorithm (FFT) in as much as the data points in TAOS light curves are evenly spaced.more » Using FFT, we found 41 short-period variables with amplitudes smaller than a few hundredths of a magnitude and periods of about an hour, which suggest that they are low-amplitude {delta} Scuti stars. The light curves of TAOS {delta} Scuti stars are accessible online at the Time Series Center Web site (http://timemachine.iic.harvard.edu)« less

The two variables in the triple system HR 6469 = V819 Her: One eclipsing, one spotted

NASA Technical Reports Server (NTRS)

Van Hamme, Walter V.; Hall, Douglas S.; Hargrove, Adam W.; Henry, Gregory W.; Wasson, Rick; Barksdale, William S.; Chang, Sandy; Fried, Robert E.; Green, Charles L.; Lines, Helen C.

1994-01-01

A complete BV light curve, from 14 nights of good data obtained with the Vanderbilt University-Tennessee State University (VU-TSU) automatic telescope, are presented and solved with the Wilson-Devinney program. Third light is evaluated, with the companion star brighter by 0.58(sup m) in V and 0.11(sup m) in B. The eclipses are partial. Inferred color indices yield F2 V and F8 V for the eclipsing pair and G8 IV-III for the distant companion star. After removing the variability due to eclipses, we study the residual variability of the G8 IV-III star over the ten years 1982 to 1992. Each yearly light curve is fit with a two-spot model. Three relatively long-lived spots are identified, with rotation periods of 85.9(sup d), 85.9(sup d), and 86.1(sup d). The weak and intermittent variability is understood because the G8 IV-III star has a Rossby number at the threshold for the onset of heavy spottedness.

Variables en la región central del cúmulo globular NGC 3201: descomposición de Fourier de las curvas de luz de las RR Lyrae y análisis de la relación período-luminosidad de las SX Phoenicis

NASA Astrophysics Data System (ADS)

Ahumada, J. A.; Arellano Ferro, A.; Calderón, J. H.; Kains, N.

2015-08-01

We present CCD time-series observations of the central region of the globular cluster NGC 3201, collected from CASLEO in March 2013, with the aim of performing the Fourier decomposition of the light curves of the RR Lyrae variables. This procedure, applied to the RRab-type stars, gave a mean value [Fe/H], for the cluster metallicity, and 5.00 0.22 kpc, for the cluster distance. The values found from two RRc stars are consistent with those derived previously. Because of differential reddening across the cluster field, individual reddenings for the RRab stars were estimated from their curves, resulting in an average value . An investigation of the light curves of stars in the blue straggler region led to the discovery of three new SX Phoenicis variables. The period-luminosity relation of the SX Phoenicis was used for an independent determination of the distance to the cluster and of the individual reddenings of these variables.

Ultraviolet spectroscopy of the brightest supergiants in M31 and M33

NASA Technical Reports Server (NTRS)

Humphreys, R. M.; Blaha, C.; Dodorico, S.; Gull, T. R.; Benevenuti, P.

1983-01-01

Ultraviolet spectroscopy from the IUE, in combination with groundbased visual and infrared photometry, are to determine the energy distributions of the luminous blue variables, the Hubble-Sandage variables, in M31 and M33. The observed energy distributions, especially in the ultraviolet, show that these stars are suffering interstellar reddening. When corrected for interstellar extinction, the integrated energy distributions yield the total luminosities and black body temperatures of the stars. The resulting bolometric magnitudes and temperatures confirm that these peculiar stars are indeed very luminous, hot stars. They occupy the same regions of the sub B01 vs. log T sub e diagram as do eta Car, P Cyg and S Dor in our galaxy and the LMC. Many of the Hubble-Sandage variables have excess infrared radiation which is attributed to free-free emission from their extended atmospheres. Rough mass loss estimates from the infrared excess yield rates of 0.00001 M sub annual/yr. The ultraviolet spectra of the H-S variables are also compared with similar spectra of eta Car, P Cyg and S For.

Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, B[e] Supergiants, and the Warm Hypergiants: How to Tell Them Apart

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

Humphreys, Roberta M.; Gordon, Michael S.; Hahn, David

In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe ii emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission linesmore » of [O i] and [Fe ii] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [O i] emission lines in their spectra. Some LBVs have [Fe ii] emission lines, but not all. Their SEDs show free–free emission in the near-infrared but no evidence for warm dust . Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe ii] and [O i] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.« less

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.

Longitudinal validity of abdominal adiposity assessment by regional bioelectrical impedance.

PubMed

Alvero-Cruz, José Ramón; García-Romero, Jerónimo C; Carrillo de Albornoz-Gil, Margarita; Jiménez, Manuel; Correas-Gomez, Lorena; Peñaloza, Piero; López-Fernández, Iván; Carnero, Elvis A

2018-03-20

The main goal of this study was to analyze the longitudinal agreement between changes in trunk and abdominal adiposity variables assessed by DXA and portable bioimpedance device (ViScan). A total of 44 women, enrolled in a 4-month exercise intervention, were included in this analysis. Trunk/abdominal compartments were assessed by ViScan and DXA. Adjusted correlations for age and FM at first assessment (pre) were utilized to perform concurrent validation among methods and completed with an agreement analysis. We observed significant differences between the changes detected by DXA and ViScan for %TFM (difference = -1.41%; p < 0.05), and proportional bias (Kendall's Tau = 0.53; p < 0.0001). Changes in abdominal adiposity were similar (difference = -0.1037 z-score units, p = 0.53), although there was proportional bias (Kendall's Tau = -0.24, p < 0.022). ViScan has a limited capability to evaluated changes in trunk and abdominal adiposity, at least for clinical purposes in adult women.

In Search of Stellar Music: Finding Pulsators for the TESS Mission

NASA Astrophysics Data System (ADS)

Richey-Yowell, Tyler; Pepper, Joshua; KELT Collaboration

2017-01-01

The Transiting Exoplanet Survey Satellite (TESS) will search for small transiting exoplanets orbiting bright stars. One of the additional mission objectives is to observe oscillating variable stars to precisely measure these stars’ masses, radii, and internal structures. Since TESS can observe only a limited number of stars with high enough cadence to detect these oscillations, it is necessary to identify candidates that will yield the most valuable results. Using data from the Kilodegree Extremely Little Telescope (KELT), we searched for bright stars showing oscillations to be included as TESS targets. We found 2,108 variable stars with B-V < 0.5 and P < 5 days. Further analysis will be carried out to establish final candidates. This project was funded by the National Science Foundation grant PHY-1359195 to the Lehigh University REU program.

Nova-like variables

NASA Technical Reports Server (NTRS)

Ladous, Constanze

1993-01-01

On grounds of different observable characteristics five classes of nova-like objects are distinguished: the UX Ursae Majoris stars, the antidwarf novae, the DQ Herculis stars, the AM Herculis stars, and the AM Canum Venaticorum stars. Some objects have not been classified specifically. Nova-like stars share most observable features with dwarf novae, except for the outburst behavior. The understanding is that dwarf novae, UX Ursae Majoris stars, and anti-dwarf novae are basically the same sort of objects. The difference between them is that in UX Ursae Majoris stars the mass transfer through the accretion disc always is high so the disc is stationary all the time; in anti-dwarf novae for some reason the mass transfer occasionally drops considerably for some time, and in dwarf novae it is low enough for the disc to undergo semiperiodic changes between high and low accretion events. DQ Herculis stars are believed to possess weakly magnetic white dwarfs which disrupt the inner disc at some distance from the central star; the rotation of the white dwarf can be seen as an additional photometric period. In AM Herculis stars, a strongly magnetic white dwarf entirely prevents the formation of an accretion disk and at the same time locks the rotation of the white dwarf to the binary orbit. Finally, AM Canum Venaticorum stars are believed to be cataclysmic variables that consist of two white dwarf components.

Nearby Hot Stars May Change Our View of Distant Sources

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

As if it werent enough that quasars distant and bright nuclei of galaxies twinkle of their own accord due to internal processes, nature also provides another complication: these distant radio sources can also appear to twinkle because of intervening material between them and us. A new study has identified a possible source for the material getting in the way.Unexplained VariabilityA Spitzer infrared view of the Helix nebula, which contains ionized streamers of gas extending radially outward from the central star. [NASA/JPL-Caltech/Univ. of Ariz.]Distant quasars occasionally display extreme scintillation, twinkling with variability timescales shorter than a day. This intra-day variability is much greater than we can account for with standard models of the interstellar medium lying between the quasar and us. So what could cause this extreme scattering instead?The first clue to this mystery came from the discovery of strong variability in the radio source PKS 1322110. In setting up follow-up observations of this object, Mark Walker (Manly Astrophysics, Australia) and collaborators noticed that, in the plane of the sky, PKS 1322110 lies very near the bright star Spica. Could this be coincidence, or might this bright foreground star have something to do with the extreme scattering observed?Diagram explaining the source of the intra-day radio source variability as intervening filaments surrounding a hot star. [M. Walker/CSIRO/Manly Astrophysics]Swarms of ClumpsWalker and collaborators put forward a hypothesis: perhaps the ultraviolet photons of nearby hot stars ionize plasma around them, which in turn causes the extreme scattering of the distant background sources.As a model, the authors consider the Helix Nebula, in which a hot, evolved star is surrounded by cool globules of molecular hydrogen gas. The radiation from the star hits these molecular clumps, dragging them into long radial streamers and ionizing their outer skins.Though the molecular clumps in the Helix Nebula were thought to have formed only as the star evolved late into its lifetime, Walker and collaborators are now suggesting that all stars regardless of spectral type or evolutionary stage may be surrounded by swarms of tiny molecular clumps. Aroundstars that are hot enough, these clumps become the ionized plasma streamers that can cause interference with the light traveling to us from distant sources.Significant MassTo test this theory, Walker and collaborators explore observations of two distant radio quasars that have both exhibited intra-day variability over many years of observations. The team identified a hot A-type star near each of these two sources: J1819+3845 has Vega nearby, and PKS 1257326 has Alhakim.Locations of stars along the line of site to two distant quasars, J1819+3845 (top panel) and PKS 1257326 (bottom panel). Both have a nearby, hot star (blue markers) radially within 2 pc: Vega (z = 7.7 pc) and Alhakim (z = 18 pc), respectively. [Walker et al. 2017]By modeling the systems of the sources and stars, the authors show that the size, location, orientation, and numbers of plasma concentrations necessary to explain observations are all consistent with an environment similar to that of the Helix Nebula. Walker and collaborators find that the total mass in the molecular clumps surrounding the two stars would need to be comparable to the mass of the stars themselves.If this picture is correct, and if all stars are indeed surrounded by molecular clumps like these, then a substantial fraction of the mass of ourgalaxy could be contained in these clumps. Besides explaining distant quasar scintillation, this idea would therefore have a significant impact on our overall understanding of how mass in galaxies is distributed. More observations of twinkling quasars are the next step toward confirming this picture.CitationMark A. Walker et al 2017 ApJ 843 15. doi:10.3847/1538-4357/aa705c

Batch versus column modes for the adsorption of radioactive metal onto rice husk waste: conditions optimization through response surface methodology.

PubMed

Kausar, Abida; Bhatti, Haq Nawaz; Iqbal, Munawar; Ashraf, Aisha

2017-09-01

Batch and column adsorption modes were compared for the adsorption of U(VI) ions using rice husk waste biomass (RHWB). Response surface methodology was employed for the optimization of process variables, i.e., (pH (A), adsorbent dose (B), initial ion concentration (C)) in batch mode. The B, C and C 2 affected the U(VI) adsorption significantly in batch mode. The developed quadratic model was found to be validated on the basis of regression coefficient as well as analysis of variance. The predicted and actual values were found to be correlated well, with negligible residual value, and B, C and C 2 were significant terms. The column study was performed considering bed height, flow rate and initial metal ion concentration, and adsorption efficiency was evaluated through breakthrough curves and bed depth service time and Thomas models. Adsorption was found to be dependent on bed height and initial U(VI) ion concentration, and flow rate decreased the adsorption capacity. Thomas models fitted well to the U(VI) adsorption onto RHWB. Results revealed that RHWB has potential to remove U(VI) ions and batch adsorption was found to be efficient versus column mode.

Ultratrace Determination of Cr(VI) and Pb(II) by Microsample Injection System Flame Atomic Spectroscopy in Drinking Water and Treated and Untreated Industrial Effluents

PubMed Central

Baig, Jameel Ahmed; Kazi, Tasneem Gul; Elci, Latif; Afridi, Hassan Imran; Khan, Muhammad Irfan; Naseer, Hafiz Muhammad

2013-01-01

Simple and robust analytical procedures were developed for hexavalent chromium (Cr(VI)) and lead (Pb(II)) by dispersive liquid-liquid microextraction (DLLME) using microsample injection system coupled with flame atomic absorption spectrophotometry (MIS-FAAS). For the current study, ammonium pyrrolidine dithiocarbamate (APDC), carbon tetrachloride, and ethanol were used as chelating agent, extraction solvent, and disperser solvent, respectively. The effective variables of developed method have been optimized and studied in detail. The limit of detection of Cr(VI) and Pb(II) were 0.037 and 0.054 µg/L, respectively. The enrichment factors in both cases were 400 with 40 mL of initial volumes. The relative standard deviations (RSDs, n = 6) were <4%. The applicability and the accuracy of DLLME were estimated by the analysis of Cr(VI) and Pb(II) in industrial effluent wastewater by standard addition method (recoveries >96%). The proposed method was successfully applied to the determination of Cr(VI) and Pb(II) at ultratrace levels in natural drinking water and industrial effluents wastewater of Denizli. Moreover, the proposed method was compared with the literature reported method. PMID:24163779

Observations of V420 Aur (HD 34921) needed to support spectroscopy

NASA Astrophysics Data System (ADS)

Waagen, Elizabeth O.

2016-10-01

Marcella Wijngaarden and Kelly Gourdji (graduate students at the University of Amsterdam/Anton Pannekoek Institute for Astronomy) have requested AAVSO observers' assistance in providing optical photometry of V420 Aur in support of their high-resolution spectroscopy with the Mercator telescope + Hermes spectrograph in La Palma 2016 October 7 through 17. They write: "[V420 Aur (HD 34921) is] the optical Be star that is part of a peculiar High Mass X-ray Binary...[that exhibits highly] complex and variable spectra...it is difficult to construct a physical model of this HMXB system, though based on these observations, the system is thought to contain a B[e] star with a dense plasma region, an accretion disk around a neutron star, a shell and circumstellar regions of cold dust. It has been over a decade since the last spectra were taken, and, given the highly variable nature of this star, we expect new observations to yield new information that will contribute to a better understanding of this system." Observations in BVRI (preferred over other bands) are requested beginning immediately and continuing through October 24. In all cases, timeseries in a few bands (i.e. BVRI) are preferred over single/a few observations in the other bands as it is the variability on relatively short timescales that is most important. "The target is bright so exposures should be long enough to reach good signal to noise in order to see the small variability amplitude but without saturating the target/comparison stars. We will study the variability on several timescales, so observations starting from a few per night to high cadence timeseries are useful." 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.

Future of Ultraviolet Astronomy Based on Six Years of IUE Research

NASA Technical Reports Server (NTRS)

Mead, J. M. (Editor); Chapman, R. D. (Editor); Kondo, Y. (Editor)

1984-01-01

Physical insights into the various astronomical objects which were studied using the International Ultraviolet Explorer (IUE) satellite. Topics covered included galaxies, cool stars, hot stars, close binaries, variable stars, the interstellar medium, the solar system, and IUE follow-on missions.

Stellar Laboratories: 3. New Ba 5, Ba 6, and Ba 7 Oscillator Strengths and the Barium Abundance in the Hot White Dwarfs G191-B2B and RE 0503-289

NASA Technical Reports Server (NTRS)

Rauch, T.; Werner, K.; Quinet, P.; Kruk, Jeffrey Walter

2014-01-01

Context. For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Aims. Reliable Ba 5-7 oscillator strengths are used to identify Ba lines in the spectra of the DA-type white dwarf G191-B2B and the DO-type white dwarf RE 0503-289 and to determine their photospheric Ba abundances. Methods. We newly calculated Ba v-vii oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Ba lines exhibited in high-resolution and high-S/N UV observations of G191-B2B and RE 0503-289. Results. For the first time, we identified highly ionized Ba in the spectra of hot white dwarfs. We detected Ba vi and Ba vii lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE 0503-289. The Ba vi/Ba vii ionization equilibrium is well reproduced with the previously determined effective temperature of 70 000 K and surface gravity of log g=7.5. The Ba abundance is 3.5 +/- 0.5 × 10(exp-4) (mass fraction, about 23 000 times the solar value). In the FUSE spectrum of G191-B2B, we identified the strongest Ba vii line (at 993.41 Å) only, and determined a Ba abundance of 4.0 +/- 0.5 × 10(exp-6) (about 265 times solar). Conclusions. Reliable measurements and calculations of atomic data are a pre-requisite for stellar-atmosphere modeling. Observed Ba vi-vii line profiles in two white dwarfs' (G191-B2B and RE 0503-289) far-ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. This allowed to determine the photospheric Ba abundance of these two stars precisely.

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.

Models of symbiotic stars

NASA Technical Reports Server (NTRS)

Friedjung, Michael

1993-01-01

One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical approach with existing models and discuss unresolved problems requiring new observational and theoretical work.

More Rapidly Rotating PMS M Dwarfs with Light Curves Suggestive of Orbiting Clouds of Material

NASA Astrophysics Data System (ADS)

Stauffer, John; Rebull, Luisa; David, Trevor J.; Jardine, Moira; Collier Cameron, Andrew; Cody, Ann Marie; Hillenbrand, Lynne A.; Barrado, David; van Eyken, Julian; Melis, Carl; Briceno, Cesar

2018-02-01

In a previous paper, using data from K2 Campaign 2, we identified 11 very low mass members of the ρ Oph and Upper Scorpius star-forming region as having periodic photometric variability and phased light curves showing multiple scallops or undulations. All of the stars with the “scallop-shell” light curve morphology are mid-to-late M dwarfs without evidence of active accretion and with photometric periods generally <1 day. Their phased light curves have too much structure to be attributed to non-axisymmetrically distributed photospheric spots and rotational modulation. We have now identified an additional eight probable members of the same star-forming region plus three stars in the Taurus star-forming region with this same light curve morphology and sharing the same period and spectral type range as the previous group. We describe the light curves of these new stars in detail and present their general physical characteristics. We also examine the properties of the overall set of stars in order to identify common features that might help elucidate the causes of their photometric variability.

Asymmetric Planetary Nebulae VI: the conference summary

NASA Astrophysics Data System (ADS)

De Marco, O.

2014-04-01

The Asymmetric Planetary Nebulae conference series, now in its sixth edition, aims to resolve the shaping mechanism of PN. Eighty percent of PN have non spherical shapes and during this conference the last nails in the coffin of single stars models for non spherical PN have been put. Binary theories abound but observational tests are lagging. The highlight of APN6 has been the arrival of ALMA which allowed us to measure magnetic fields on AGB stars systematically. AGB star halos, with their spiral patterns are now connected to PPN and PN halos. New models give us hope that binary parameters may be decoded from these images. In the post-AGB and pre-PN evolutionary phase the naked post-AGB stars present us with an increasingly curious puzzle as complexity is added to the phenomenologies of objects in transition between the AGB and the central star regimes. Binary central stars continue to be detected, including the first detection of longer period binaries, however a binary fraction is still at large. Hydro models of binary interactions still fail to give us results, if we make an exception for the wider types of binary interactions. More promise is shown by analytical considerations and models driven by simpler, 1D simulations such as those carried out with the code MESA. Large community efforts have given us more homogeneous datasets which will yield results for years to come. Examples are the ChanPlaN and HerPlaNe collaborations that have been working with the Chandra and Herschel space telescopes, respectively. Finally, the new kid in town is the intermediate-luminosity optical transient, a new class of events that may have contributed to forming several peculiar PN and pre-PN.

Mechanisms of hexavalent chromium resistance and removal by microorganisms.

PubMed

Joutey, Nezha Tahri; Sayel, Hanane; Bahafid, Wifak; El Ghachtouli, Naïma

2015-01-01

Chromium has been and is extensively used worldwide in multiple industrial processes and is routinely discharged to the environment from such processes. Therefore, this heavy metal is a potential threat to the environment and to public health, primarily because it is non-biodegradable and environmentally persistent. Chromium exists in several oxidation states, the most stable of which are trivalent Cr(Ill) and hexavalent Cr(VI) species. Each species possesses its own individual chemical characteristics and produces its own biological effects. For example, Cr (Ill) is an essential oligoelement for humans, whereas Cr(VI) is carcinogenic and mutagenic. Several chemical methods are used to remove Cr(VI) from contaminated sites. Each of these methods has advantages and disadvantages. Currently, bioremediation is often the preferred method to deal with Cr contaminated sites, because it is eco-friendly, cost-effective and is a "natural" technology. Many yeast, bacterial and fungal species have been assessed for their suitability to reduce or remove Cr(VI) contamination. The mechanisms by which these microorganisms resist and reduce Cr(VI) are variable and are species dependent. There are several Cr-resistance mechanisms that are displayed by microorganisms. These include active efflux of Cr compounds, metabolic reduction of Cr(VI) to Cr (ill), and either intercellular or extracellular prec1p1tation. Microbial Cr (VI) removal typically involves three stages: binding of chromium to the cell surface, translocation of chromium into the cell, and reduction of Cr(VI) to Cr (ill). Cr(VI) reduction by microorganisms may proceed on the cell surface, outside the cell, or intracellularly, either directly via chromate reductase enzymes, or indirectly via metabolite reduction of Cr(VI). The uptake of chromium ions is a biphasic process. The primary step is known as biosorption, a metabolic energyindependent process. Thereafter, bioaccumulation occurs, but is much slower, and is dependent on cell metabolic activity. Choosing an appropriate bioremediation strategy for Cr is extremely important and must involve investigating and understanding the key mechanisms that are involved in microbial resistance to and removal of Cr(VI).

Reduction of hexavalent chromium by fasted and fed human gastric fluid. II. Ex vivo gastric reduction modeling

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

Kirman, Christopher R., E-mail: ckirman@summittoxi

To extend previous models of hexavalent chromium [Cr(VI)] reduction by gastric fluid (GF), ex vivo experiments were conducted to address data gaps and limitations identified with respect to (1) GF dilution in the model; (2) reduction of Cr(VI) in fed human GF samples; (3) the number of Cr(VI) reduction pools present in human GF under fed, fasted, and proton pump inhibitor (PPI)-use conditions; and (4) an appropriate form for the pH-dependence of Cr(VI) reduction rate constants. Rates and capacities of Cr(VI) reduction were characterized in gastric contents from fed and fasted volunteers, and from fasted pre-operative patients treated with PPIs.more » Reduction capacities were first estimated over a 4-h reduction period. Once reduction capacity was established, a dual-spike approach was used in speciated isotope dilution mass spectrometry analyses to characterize the concentration-dependence of the 2nd order reduction rate constants. These data, when combined with previously collected data, were well described by a three-pool model (pool 1 = fast reaction with low capacity; pool 2 = slow reaction with higher capacity; pool 3 = very slow reaction with higher capacity) using pH-dependent rate constants characterized by a piecewise, log-linear relationship. These data indicate that human gastric samples, like those collected from rats and mice, contain multiple pools of reducing agents, and low concentrations of Cr(VI) (< 0.7 mg/L) are reduced more rapidly than high concentrations. The data and revised modeling results herein provide improved characterization of Cr(VI) gastric reduction kinetics, critical for Cr(VI) pharmacokinetic modeling and human health risk assessment. - Highlights: • SIDMS allows for measurement of Cr(VI) reduction rate in gastric fluid ex vivo • Human gastric fluid has three reducing pools • Cr(VI) in drinking water at < 0.7 mg/L is rapidly reduced in human gastric fluid • Reduction rate is concentration- and pH-dependent • A refined PK model is used to characterize inter-individual variability in Cr(VI) gastric reduction capacity.« less

SX Phoenecis Stars in the Extremely Metal-Poor Globular Clusters NGC 5053

NASA Astrophysics Data System (ADS)

Nemec, James M.; Mateo, Mario; Burke, Morgan; Olszewski, Edward W.

1995-09-01

The results of a major search for photometrically variable blue straggler stars (BSs) in the extremely metal-poor globular cluster NGC 5053 are presented. The survey is based on photometry of over 200 CCD frames (BVI passbands) taken on 18 nights between 1985 and 1994. Five of the 16 BSs monitored for variability are identified as SX Phe stars and their photometric characteristics derived. These five stars are among the shortest-period (49

On the structure of the outer layers of cool carbon stars

NASA Technical Reports Server (NTRS)

Querci, F.; Querci, M.; Wing, R. F.; Cassatella, A.; Heck, A.

1982-01-01

Exposures on the spectra of four late C-type stars have been made with the IUE satellite in the wavelength range of the LWR camera (1900-3200 A). Two Mira variables near maximum light and two semiregular variables were observed. Although the exposure times used, which range up to 240 min in the low-resolution mode, were more than sufficient to record the continuum and emission lines of Mg II, Fe II, and Al II in normal M stars of similar magnitude and temperature, no light was recorded. It is concluded that the far-ultraviolet continuum is strongly depressed in these cool carbon stars. The absence of UV emission lines implies either that the chromospheric lines observed in M stars require an ultraviolet flux for their excitation, or that cool carbon stars have no chromosphere at all or that the opacity source is located above even the emission-line-forming region. This opacity source, which is probably some carbon condensate since it is weak or absent in M stars while absorbing strongly in C stars, is discussed both in terms of the chromospheric interpretation of the emission lines and in terms of their shock-wave interpretation.

Using Photometric Variability to Detect Binarity in the Central Stars of Four Planetary Nebulae, A 43, A 74, NGC 6720, and NGC 6853

NASA Astrophysics Data System (ADS)

Smith, Alexander; De Marco, O.

2007-12-01

Recent observational evidence and theoretical models are challenging the classical paradigm of single star planetary nebula (PN) evolution, suggesting instead that binary stars play a significant role in the process of PN formation. In order to shape the 90% of PN that are non-spherical, the central star must be rotating and have a magnetic field; the most-likely source of the angular momentum needed to sustain magnetic fields is a binary companion. More observational evidence is needed to confirm that the fraction of PN with close binary central stars is indeed higher than the currently known value of 10-15%. As part of an international effort to detect binary central stars (PLAN-B - Panetary Nebula Binaries), we are carrying out a new photometric survey to look for close binary central stars of PN. Here we present the findings for 4 objects: A 43, A 74, NGC 6720, and NGC 6853. NGC 6720 and NGC 6853 show evidence of periodic variability, the former of which might even show one eclipse. Once completed, the survey will assess the binarity of about 100 central stars of PN.