Rapidly Rotating, X-Ray Bright Stars in the Kepler Field

NASA Technical Reports Server (NTRS)

Howell, Steve B.; Mason, Elena; Boyd, Patricia; Smith, Krista Lynne; Gelino, Dawn M.

2016-01-01

We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type F-K, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, which are evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a process believed to produce the FK Com class of variable and their descendants. The FK Com stage, including the presence of an excretion disk, is short lived but leads to longer-lived stages consisting of single, rapidly rotating evolved (sub)giants with high levels of stellar activity.

The distribution of star formation and metals in the low surface brightness galaxy UGC 628

NASA Astrophysics Data System (ADS)

Young, J. E.; Kuzio de Naray, Rachel; Wang, Sharon X.

2015-09-01

We introduce the MUSCEL Programme (MUltiwavelength observations of the Structure, Chemistry and Evolution of LSB galaxies), a project aimed at determining the star-formation histories of low surface brightness galaxies. MUSCEL utilizes ground-based optical spectra and space-based UV and IR photometry to fully constrain the star-formation histories of our targets with the aim of shedding light on the processes that led low surface brightness galaxies down a different evolutionary path from that followed by high surface brightness galaxies, such as our Milky Way. Here we present the spatially resolved optical spectra of UGC 628, observed with the VIRUS-P IFU at the 2.7-m Harlen J. Smith Telescope at the McDonald Observatory, and utilize emission-line diagnostics to determine the rate and distribution of star formation as well as the gas-phase metallicity and metallicity gradient. We find highly clustered star formation throughout UGC 628, excluding the core regions, and a log(O/H) metallicity around -4.2, with more metal-rich regions near the edges of the galactic disc. Based on the emission-line diagnostics alone, the current mode of star formation, slow and concentrated in the outer disc, appears to have dominated for quite some time, although there are clear signs of a much older stellar population formed in a more standard inside-out fashion.

RAPIDLY ROTATING, X-RAY BRIGHT STARS IN THE KEPLER FIELD

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

Howell, Steve B.; Mason, Elena; Boyd, Patricia

We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type F-K, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, which are evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a processmore » believed to produce the FK Com class of variable and their descendants. The FK Com stage, including the presence of an excretion disk, is short lived but leads to longer-lived stages consisting of single, rapidly rotating evolved (sub)giants with high levels of stellar activity.« less

Flattening and surface-brightness of the fast-rotating star δ Persei with the visible VEGA/CHARA interferometer

NASA Astrophysics Data System (ADS)

Challouf, M.; Nardetto, N.; Domiciano de Souza, A.; Mourard, D.; Tallon-Bosc, I.; Aroui, H.; Farrington, C.; Ligi, R.; Meilland, A.; Mouelhi, M.

2017-08-01

Context. Rapid rotation is a common feature for massive stars, with important consequences on their physical structure, flux distribution and evolution. Fast-rotating stars are flattened and show gravity darkening (non-uniform surface intensity distribution). Another important and less studied impact of fast-rotation in early-type stars is its influence on the surface brightness colour relation (hereafter SBCR), which could be used to derive the distance of eclipsing binaries. Aims: The purpose of this paper is to determine the flattening of the fast-rotating B-type star δ Per using visible long-baseline interferometry. A second goal is to evaluate the impact of rotation and gravity darkening on the V - K colour and surface brightness of the star. Methods: The B-type star δ Per was observed with the VEGA/CHARA interferometer, which can measure spatial resolutions down to 0.3 mas and spectral resolving power of 5000 in the visible. We first used a toy model to derive the position angle of the rotation axis of the star in the plane of the sky. Then we used a code of stellar rotation, CHARRON, in order to derive the physical parameters of the star. Finally, by considering two cases, a static reference star and our best model of δ Per, we can quantify the impact of fast rotation on the surface brightness colour relation (SBCR). Results: We find a position angle of 23 ± 6 degrees. The polar axis angular diameter of δ Per is θp = 0.544 ± 0.007 mas, and the derived flatness is r = 1.121 ± 0.013. We derive an inclination angle for the star of I = 85+ 5-20 degrees and a projected rotation velocity Vsini = 175+ 8-11 km s-1 (or 57% of the critical velocity). We find also that the rotation and inclination angle of δ Per keeps the V - K colour unchanged while it decreasing its surface-brightness by about 0.05 mag. Conclusions: Correcting the impact of rotation on the SBCR of early-type stars appears feasible using visible interferometry and dedicated models.

Search for Hot and Bright Stars for H_3^+ Spectroscopy Near the Galactic Center

NASA Astrophysics Data System (ADS)

Oka, Takeshi; Geballe, T. R.

2009-06-01

It is becoming increasingly clear that H_3^+ is abnormally abundant near the Galactic center and that it is a powerful probe for studying the gas in that region. To date we have observed a dozen sightlines toward bright and hot stars close to the Galactic plane (within 3 pc) and located in the region from the center to 30 pc east of the center. They are mostly stars belonging to the super-massive Quintuplet Cluster and the Central Cluster, but also include few lying between the two clusters. All sightlines showed H_3^+ with column densities on the order of 4 × 10^{15} cm^{-2} demonstrating the ubiquity of H_3^+, its high volume filling factor, and high ionization rate of H_{2} in the region. We plan to expand the region in which we have probed for H_3^+ by two orders of magnitude in solid angle by covering the whole of the Central Molecular Zone (CMZ), the region with a radius of ˜ 200 pc from the center. For this purpose, the first requirement is to find bright and hot stars suitable for the H_3^+ spectroscopy in this more extended region, in which few if any such stars are known outside of the clusters. We are using the recent GLIMPSE Point Source Catalogue provided by the Spitzer Space Telescope together with 2MASS photometry to identify such stars. Out of the over one million stars in GLIMPSE that are in the sightline to the CMZ, we have selected those few thousand stars with L < 7.5 mag. We then use results of J, K, L photometry to eliminate likely late-type stars, whose complex photospheric spectra would make it difficult to isolate the weak interstellar lines of H_3^+. For the few hundred stars thus chosen, we are obtaining medium resolution (R ˜ 2000) spectroscopy from 1.6 to 2.4 μm. The presence or absence of CO overtone bands (2-0, 3-1, 4-2, ...) near 2.3 microns allow us clearly discriminate the hot stars from late-type stars. So far we have observed 84 candidate hot stars and found a dozen that are usable for H_3^+ spectroscopy. Some of them are

Luminous Infrared Sources in the Local Group: Identifying the Missing Links in Massive Star Evolution

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Bonanos, A. Z.; Mehner, A.

2015-01-01

We present the first systematic survey of dusty massive stars (RSGs, LBVs, sgB[e]) in nearby galaxies, with the goal of understanding their importance in massive star evolution. Using the fact that these stars are bright in mid-infrared colors due to dust, we provide a technique for selecting and identifying dusty evolved stars based on the results of Bonanos et al. (2009, 2010), Britavskiy et al. (2014), and archival Spitzer/IRAC photometry. We present the results of our spectroscopic follow-up of luminous infrared sources in the Local Group dwarf irregular galaxies: Pegasus, Phoenix, Sextans A and WLM. The survey aims to complete the census of dusty massive stars in the Local Group.

Improving sodium laser guide star brightness by polarization switching

PubMed Central

Fan, Tingwei; Zhou, Tianhua; Feng, Yan

2016-01-01

Optical pumping with circularly polarized light has been used to enhance the brightness of sodium laser guide star. But the benefit is reduced substantially due to the precession of sodium atoms in geomagnetic field. Switching the laser between left and right circular polarization at the Larmor frequency is proposed to improve the return. With ESO’s laser guide star system at Paranal as example, numerical simulation shows that the return flux is increased when the angle between geomagnetic field and laser beam is larger than 60°, as much as 50% at 90°. The proposal is significant since most astronomical observation is at angle between 60° and 90° and it only requires a minor addition to the delivery optics of present laser system. PMID:26797503

Chandra's Darkest Bright Star: not so Dark after All?

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.

2008-11-01

The Chandra High Resolution camera (HRC) has obtained numerous short exposures of the ultraviolet (UV)-bright star Vega (α Lyrae; HD 172167: A0 V), to calibrate the response of the detector to out-of-band (non-X-ray) radiation. A new analysis uncovered a stronger "blue leak" in the imaging section (HRC-I) than reported in an earlier study of Vega based on a subset of the pointings. The higher count rate—a factor of nearly 2 above prelaunch estimates—raised the possibility that genuine coronal X-rays might lurk among the out-of-band events. Exploiting the broader point-spread function of the UV leak compared with soft X-rays identified an excess of counts centered on the target, technically at 3σ significance. A number of uncertainties, however, prevent a clear declaration of a Vegan corona. A more secure result would be within reach of a deep uninterrupted HRC-I pointing.

Determination of Li abundance in Solar type stars of intermediate brightness

NASA Astrophysics Data System (ADS)

Amazo-Gómez, E. M.; Hernandez-Águila, B.; Dagostino, M. C.; Bertone, E.; de la Luz, V.

2014-10-01

The determination of the lithium abundance in stellar atmospheres is of fundamental importance in multiple contexts of contemporary astrophysics. On the one hand, the lithium present in stars with global sub-solar metal abundances provides a strong restriction on the abundance of this element as a result of primordial nucleo-synthesis. On the other hand, Li can be an age indicator for stars with convective envelopes. Additionally, Li abundance appears to be correlated with the presence of sub-stellar companions. We present preliminary results of a project aimed at determining the Li abundance in an extended sample of solar-like stars (spectral type G and luminosity class V) of intermediate brightness. High resolution spectroscopic data (R=65000) were obtained with the CanHiS echelle spectrograph on the 2.11m telescope of the Guillermo Haro Observatory in Cananea, Sonora, Mexico. We report the equivalent widths of a first sub-sample of 33 stars.

Giant Low Surface Brightness Galaxies

NASA Astrophysics Data System (ADS)

Mishra, Alka; Kantharia, Nimisha G.; Das, Mousumi

2018-04-01

In this paper, we present radio observations of the giant low surface brightness (LSB) galaxies made using the Giant Metrewave Radio Telescope (GMRT). LSB galaxies are generally large, dark matter dominated spirals that have low star formation efficiencies and large HI gas disks. Their properties suggest that they are less evolved compared to high surface brightness galaxies. We present GMRT emission maps of LSB galaxies with an optically-identified active nucleus. Using our radio data and archival near-infrared (2MASS) and near-ultraviolet (GALEX) data, we studied morphology and star formation efficiencies in these galaxies. All the galaxies show radio continuum emission mostly associated with the centre of the galaxy.

Using RSpec in an introductory bright star spectroscopy lab activity

NASA Astrophysics Data System (ADS)

Howe, James; Sitar, David J.

2018-01-01

After presenting at the North Carolina Section of the American Association of Physics Teachers during the fall 2016 meeting, we were encouraged to turn our poster into a paper. This article describes the strengthening of a bright star spectroscopy lab activity for introductory astronomy lab students (AST1002) at Appalachian State University. Explanations of the tools and methods used in the activity are included, particularly the preparation of additional materials using RSpec and calibrated instrument response curves.

Documentation for the machine-readable version of the Bright Star Catalogue

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1982-01-01

The machine-readable version of The Bright Star Catalogue, 4th edition, is described. In addition to the large number of newly determined fundamental data, such as photoelectric magnitudes, MK spectral types, parallaxes, and radial velocities, the new version contains data and information not included in the third edition such as the identification of IR sources, U-B and R-I colors, radial velocity comments (indication and identification of spectroscopic and occultation binaries), and projected rotational velocities. The equatorial coordinates for equinoxes 1900 and 2000 are recorded to greater precision details concerning variability, spectral characteristics, duplicity, and group membership are included. Data compiled through 1979, some information and variable-star designations found through 1981 are considered.

The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico

2017-12-01

We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence ({SFR}-{M}* ) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 ± 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around {M}* ≈ {10}10 {M}⊙ , and can also be seen in the gas mass—stellar mass plane. The global Kennicutt-Schmidt law ({SFR}-{M}g) has a slope of 1.47 ± 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only ˜ 3 % of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with {M}* < {10}10 {M}⊙ ), while massive spirals (with {M}* > {10}10 {M}⊙ ) are weary giants that constitute more of a turn-off population.

Documentation for the machine-readable version of the thirteen color photometry of 1380 bright stars

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.; Roman, N. G.

1981-01-01

The magnetic tape version of the catalogue of thirteen-color photometry of 1380 bright stars, containing data on the 13 color medium narrow band photometric system is described. Observations of essentially all stars brighter than fifth visual magnitude north of delta = -20 deg and brighter than fourth visual magnitude south of delta = -20 deg are included. It is intended to enable users to read and process the tape without the common difficulties and uncertainties.

Keck Observations of the UV-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)

NASA Astrophysics Data System (ADS)

Dixon, William Van Dyke; Chayer, Pierre; Reid, Iain N.

2016-06-01

In color-magnitude diagrams of globular clusters, stars brighter than the horizontal branch and bluer than the red-giant branch are known as UV-bright stars. Most are evolving from the asymptotic giant branch (AGB) to the tip of the white-dwarf cooling curve. To better understand this important phase of stellar evolution, we have analyzed a Keck HIRES echelle spectrum of the UV-bright star Barnard 29 in M13. We begin by fitting the star's H I (Hα, Hβ, and Hγ) and He I lines with a grid of synthetic spectra generated from non-LTE H-He models computed using the TLUSTY code. We find that the shape of the star's Hα profile is not well reproduced with these models. Upgrading from version 200 to version 204M of TLUSTY solves this problem: the Hα profile is now well reproduced. TLUSTY version 204 includes improved calculations for the Stark broadening of hydrogen line profiles. Using these models, we derive stellar parameters of Teff = 21,100 K, log g = 3.05, and log (He/H) = -0.87, values consistent with those of previous authors. The star's Keck spectrum shows photospheric absorption from N II, O II, Mg II, Al III, Si II, Si III, S II, Ar II, and Fe III. The abundances of these species are consistent with published values for the red-giant stars in M13, suggesting that the star's chemistry has changed little since it left the AGB.

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

Models of bright nickel-free supernovae from stripped massive stars with circumstellar shells

NASA Astrophysics Data System (ADS)

Kleiser, Io K. W.; Kasen, Daniel; Duffell, Paul C.

2018-04-01

The nature of an emerging class of rapidly fading supernovae (RFSNe) - characterized by their short-lived light-curve duration, but varying widely in peak brightness - remains puzzling. Whether the RFSNe arise from low-mass thermonuclear eruptions on white dwarfs or from the core collapse of massive stars is still a matter of dispute. We explore the possibility that the explosion of hydrogen-free massive stars could produce bright but rapidly fading transients if the effective pre-supernova radii are large and if little or no radioactive nickel is ejected. The source of radiation is then purely due to shock cooling. We study this model of RFSNe using spherically symmetric hydrodynamics and radiation transport calculations of the explosion of stripped stars embedded in helium-dominated winds or shells of various masses and extent. We present a parameter study showing how the properties of the circumstellar envelopes affect the dynamics of the explosion and can lead to a diversity of light curves. We also explore the dynamics of the fallback of the innermost stellar layers, which might be able to remove radioactive nickel from the ejecta, making the rapid decline in the late-time light curve possible. We provide scaling relations that describe how the duration and luminosity of these events depend on the supernova kinetic energy and the mass and radius of the circumstellar material.

Identifying Young, Nearby Stars

NASA Technical Reports Server (NTRS)

Webb, Rich; Song, Inseok; Zuckerman, Ben; Bessell, Mike

2001-01-01

Young stars have certain characteristics, e.g., high atmospheric abundance of lithium and chromospheric activity, fast rotation, distinctive space motion and strong X-ray flux compared to that of older main sequence stars. We have selected a list of candidate young (<100Myr) and nearby (<60pc) stars based on their space motion and/or strong X-ray flux. To determine space motion of a star, one needs to know its coordinates (RA, DEC), proper motion, distance, and radial velocity. The Hipparcos and Tycho catalogues provide all this information except radial velocities. We anticipate eventually searching approx. 1000 nearby stars for signs of extreme youth. Future studies of the young stars so identified will help clarify the formation of planetary systems for times between 10 and 100 million years. Certainly, the final output of this study will be a very useful resource, especially for adaptive optics and space based searches for Jupiter-mass planets and dusty proto-planetary disks. We have begun spectroscopic observations in January, 2001 with the 2.3 m telescope at Siding Spring Observatory (SSO) in New South Wales, Australia. These spectra will be used to determine radial velocities and other youth indicators such as Li 6708A absorption strength and Hydrogen Balmer line intensity. Additional observations of southern hemisphere stars from SSO are scheduled in April and northern hemisphere observations will take place in May and July at the Lick Observatory of the University of California. AT SSO, to date, we have observed about 100 stars with a high resolution spectrometer (echelle) and about 50 stars with a medium spectral resolution spectrometer (the "DBS"). About 20% of these stars turn out to be young stars. Among these, two especially noteworthy stars appear to be the closest T-Tauri stars ever identified. Interestingly, these stars share the same space motions as that of a very famous star with a dusty circumstellar disk--beta Pictoris. This new finding better

IDENTIFYING NEARBY, YOUNG, LATE-TYPE STARS BY MEANS OF THEIR CIRCUMSTELLAR DISKS

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

Schneider, Adam; Song, Inseok; Melis, Carl

2012-10-01

It has recently been shown that a significant fraction of late-type members of nearby, very young associations (age {approx}<10 Myr) display excess emission at mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that the detection of mid-IR excess emission can be utilized to identify new nearby, young, late-type stars including two definite new members ('TWA 33' and 'TWA 34') of the TW Hydrae Association (TWA). Both new TWA members display mid-IR excess emission in the Wide-field Infrared Survey Explorer catalog and they show proper motion and youthful spectroscopic characteristics-namely, H{alpha} emission, strong lithium absorption, and low surface gravity featuresmore » consistent with known TWA members. We also detect mid-IR excess-the first unambiguous evidence of a dusty circumstellar disk-around a previously identified UV-bright, young, accreting star (2M1337) that is a likely member of the Lower-Centaurus Crux region of the Scorpius-Centaurus Complex.« less

Bright Young Star Clusters in NGC5253 with LEGUS

NASA Astrophysics Data System (ADS)

Calzetti, Daniela; Johnson, Kelsey E.; Adamo, Angela; Gallagher, John S.; Andrews, Jennifer E.; Smith, Linda J.; Clayton, Geoffrey C.; Lee, Janice C.; Sabbi, Elena; Ubeda, Leonardo; Kim, Hwihyun; Ryon, Jenna E.; Thilker, David A.; Bright, Stacey N.; Zackrisson, Erik; Kennicutt, Robert; de Mink, Selma E.; Whitmore, Bradley C.; Aloisi, Alessandra; Chandar, Rupali; Cignoni, Michele; Cook, David; Dale, Daniel A.; Elmegreen, Bruce; Elmegreen, Debra M.; Evans, Aaron S.; Fumagalli, Michele; Gouliermis, Dimitrios; Grasha, Kathryn; Grebel, Eva; Krumholz, Mark R.; Walterbos, Rene A. M.; Wofford, Aida; Brown, Thomas M.; Christian, Carol A.; Dobbs, Claire; Herrero-Davo`, Artemio; Kahre, Lauren; Messa, Matteo; Nair, Preethi; Nota, Antonella; Östlin, Göran; Pellerin, Anne; Sacchi, Elena; Schaerer, Daniel; Tosi, Monica

2016-01-01

Using UV-to-H broad and narrow-band HST imaging, we derive the ages and masses of the 11 brightest star clusters in the dwarf galaxy NGC5253. This galaxy, located at ~3 Mpc, hosts an intense starburst, which includes a centrally-concentrated dusty region with strong thermal radio emission (the `radio nebula'). The HST imaging includes data from the Cycle 21 Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), in addition to narrow--band H-alpha (6563 A), P-beta (12820 A), and P-alpha (18756 A). The bright clusters have ages ~1-15 Myr and masses ~1E4 - 2.5E5 Msun. Two of the 11 star clusters are located within the radio nebula, and suffer from significant dust attenuation. Both are extremely young, with a best-fit age around 1 Myr, and masses ~7.5E4 and ~2.5E5 Msun, respectively. The most massive of the two `radio nebula' clusters is 2-4 times less massive than previously estimated and is embedded within a cloud of dust with A_V~50 mag. The two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.

High Precision Photometry of Bright Transiting Exoplanet Hosts

NASA Astrophysics Data System (ADS)

Wilson, Maurice; Eastman, Jason; Johnson, John A.

2016-01-01

Within the past two decades, the successful search for exoplanets and the characterization of their physical properties have shown the immense progress that has been made towards finding planets with characteristics similar to Earth. For most exoplanets with a radius about the size of Earth, evaluating their physical properties, such as the mass, radius and equilibrium temperature, cannot be determined with satisfactory precision. The MINiature Exoplanet Radial Velocity Array (MINERVA) was recently built to obtain spectroscopic and photometric measurements to find, confirm, and characterize Earth-like exoplanets. MINERVA's spectroscopic survey targets the brightest, nearby stars which are well-suited to the array's capabilities, while its primary photometric goal is to search for transits around these bright targets. Typically, it is difficult to find satisfactory comparison stars within a telescope's field of view when the primary target is very bright. This issue is resolved by using one of MINERVA's telescopes to observe the primary bright star while the other telescopes observe a distinct field of view that contains satisfactory bright comparison stars. We describe the code used to identify nearby comparison stars, schedule the four telescopes, produce differential photometry from multiple telescopes, and show the first results from this effort.This work has been funded by the Ronald E. McNair Post-Baccalaureate Achievement Program, the ERAU Honors Program, the ERAU Undergraduate Research Spark Fund, and the Banneker Institute at the Harvard-Smithsonian Center for Astrophysics.

The origin of extended interstellar shells around Wolf-Rayet stars having bright optical ring nebulae

NASA Technical Reports Server (NTRS)

Nichols, J. S.; Fesen, R. A.

1994-01-01

Investigations of the interstellar environment around Wolf-Rayet (WR) stars have lead to the discovery of extended shells of gas and dust 50-100 pc in diameter in the lines of sight toward three WR stars. In this paper, several origins for these extended shells are discussed. While positional coincidences cannot be excluded, the locations of the WR stars near the projected centers of the shells, the detection of only shortward-shifted, high-velocity UV absorption line components in their IUE spectra, plus commonality of some WR star properties which are rare in the general WR star population suggest some casual connections between the WR stars and formation of interstellar shells. To access whether the high-velocity UV interstellar absorption lines are a frequent phenomenon related to WR stellar winds, we present a survey of such features in all WR stars observed with IUE through 1991. Of 35 stars studied, only four are found to have components with velocity displacements greater than 45 km/s which are not attributable to previously identified OB association superbubbles. The means a surprising 82% of non-OB association WR stars show no evidence of high-velocity gas in their lines of sight at IUE's spectral resolution, suggesting that high-velocity interstellar absorption lines are not a common consequence of Wolf-Rayet star stellar winds alone. We review the properties of three WR stars (HD 50896, HD 96548, and HD 192163) which may reside inside extended interstellar shells and find that they are similar in terms of spectral class (WN5-8), presence of an optical ring nebula, and reported photometric variability. Evaluation of possible origins of the extended shells suggests these three stars are in a post X-ray binary stage of high-mass binary star evolution. If this is correct, then the large interstellar shells detected might be evidence of either supernova remnant shells generated by the explosion of the binary's primary star, or non-conservative mass transfer

Update on the KELT Transit Survey: Hot Planets around Hot, Bright Stars

NASA Astrophysics Data System (ADS)

Gaudi, B. Scott; KELT Collaboration

2017-01-01

The KELT Transit Survey consists of a pair of small-aperture, wide-angle automated telescope located at Winer Observatory in Sonoita, Arizona and the South African Astronomical Observatory (SAAO) in Sutherland, South Africa. Together, they are surveying roughly 60% of the sky for transiting planets. By virtue of their small apertures (42 mm) and large fields-of-view (26 degrees x 26 degrees), KELT is most sensitive to hot Jupiters transiting relatively bright (V~8-11), and thus relatively hot stars. Roughly half of the dwarf stars targeted by KELT are hotter than 6250K; such stars pose novel challenges, but also provide unique opportunities. I will provide an update on the most recent companions discovered by KELT, focusing in detail on a few particularly interesting systems. KELT is a joint collaboration between the Ohio State University, Vanderbilt University, and Lehigh University. This work was partially supported by NSF CAREER grant AST-1056524.

Graviton mass bounds from an analysis of bright star trajectories at the Galactic Center

NASA Astrophysics Data System (ADS)

Zakharov, Alexander; Jovanović, Predrag; Borka, Dusko; Jovanović, Vesna Borka

2017-03-01

In February 2016 the LIGO & VIRGO collaboration reported the discovery of gravitational waves in merging black holes, therefore, the team confirmed GR predictions about an existence of black holes and gravitational waves in the strong gravitational field limit. Moreover, in their papers the joint LIGO & VIRGO team presented an upper limit on graviton mass such as mg < 1.2 × 10-22 eV (Abbott et al. 2016). So, the authors concluded that their observational data do not show any violation of classical general relativity. We show that an analysis of bright star trajectories could constrain graviton mass with a comparable accuracy with accuracies reached with gravitational wave interferometers and the estimate is consistent with the one obtained by the LIGO & VIRGO collaboration. This analysis gives an opportunity to treat observations of bright stars near the Galactic Center as a useful tool to obtain constraints on the fundamental gravity law such as modifications of the Newton gravity law in a weak field approximation. In that way, based on a potential reconstruction at the Galactic Center we obtain bounds on a graviton mass.

Socket stars: UBVRJIK radial profiles

NASA Astrophysics Data System (ADS)

Schaefer, Bradley E.

1995-05-01

Visual inspectin of stars embedded in H II nebulae has shown a significant fraction to be surrounded by nearly symmetric extended regions within which the nebular brightness is apparently significantly fainter than is typical for the surrounding area. These 'socket stars' might be caused by a bubble in the nebula blown out by a stellar wind or they might be caused by a circumstellar envelope of dust hiding the emission behind the star. As such, the sockets could be the first manifestation of a previously unknown component of pre-main-sequence stars. Unfortunately, no quantitative proof of the existence of sockets has been presented. To fill this need, I have imaged 10 socket stars and six background stars with CCD cameras and infrared array cameras. From these images, I have constructed radial plots which should reveal dips in brightness immediately outside the seeing disk. The radial plots do not show any evidence for the existence of sockets. A detailed examination of the photographs orginally used to identify the sockets show that the causes of these reports are (1) artifacts resulting from the photographic process of dodging and (2) random coincidence of stars with local minima in nebular brightness. Thus, I conclude that 'socket stars' do not exist.

First ultraviolet observations of the transition regions of X-ray bright solar-type stars in the Pleiades

NASA Technical Reports Server (NTRS)

Caillault, J.-P.; Vilhu, O.; Linsky, J. L.

1990-01-01

Results are reported from A UV study of the transition regions of two X-ray-bright solar-type stars from the Pleiades, in an attempt to extend the main sequence age baseline for the transition-region activity-age relation over more than two orders of magnitude. However, no emission lines were detected from either star; the upper limits to the fluxes are consistent with previously determined saturation levels, but do not help to further constrain evolutionary models.

To Be or not to Be: Simultaneous Spectroscopy and Photometry of Be Stars

NASA Astrophysics Data System (ADS)

Martin, John C.; O'Brien, J.; Cranford, K.; Gorski, L.; Hubbell-Thomas, J.; Lord, J.; McLain, D.; McLain, J.; Schlaf, E.; Schweighauser, C.

2008-05-01

After decades of study, aspects of the Be phenomenon still defy explanation. It is not clear how some stars are able to change from Be to Be-shell stars when the differences in the models of each type rely on differences in disk inclination with respect to the observer. It is also unclear what mechanism causes some Be stars to periodically cease showing emission in their spectra: thereby, entering a "normal" B star phase. The Barber Observatory at University of Illinois Springfield has embarked on a project to monitor simultaneously the photometry and spectra of selected bright Be and Be-shell stars and identify patterns in the variability of their brightness and line profiles that could provide insight into the Be mechanism. Our pilot study of Be-shell star Psi Per has identified sudden changes in the spectral line profiles that correlate with equally fast changes in V band brightness.

Where to Find Young Bright Stars in Geosciences: GGD, NSU

NASA Astrophysics Data System (ADS)

Rakhmenkoulova, I. F.; Sharapov, V. N.

2004-12-01

Geology and Geophysics Department (GGD) of Novosibirsk State University (NSU) can be regarded as infant, because it was founded in 1962. On the other hand, if to judge by what have been done - it is not only full-fledged, but well-known department. The unique location and specific educational and scientific traditions make GGD a famous school not only in Siberia, but in Russia, and all over the world. What are the tips to prepare bright stars in geosciences? 1.NSU is located in Academgorodok (Novosibirsk scientific center), unique place in Siberia, where more than 20 scientific institutions are located. This makes the University different from other schools in Russia. Famous Russian scientists, including members of RAS, together with foreign professors give lectures and seminars for NSU students. 2.The bright star hunting starts far below the NSU level. Each year in April there is a special event in Academgorodok -`Geologic Olympiad', where children of all Russian regions, as well as ex-Soviet republics are gathered together to submit their papers, to discuss most interesting geoscience problems and to win prizes for their knowledge. The youngest stars happen to be only 6-7 years old. The event is sponsored by NSU, UIGGM, and the Ministry of Natural Resources. The brightest geostars are grown from `Geologic Olympiad' participants. 3.There is special physics-mathematical high school in Academgorodok. Each summer this school gathers young stars from farthest Siberian and Far East regions and gives classes and seminars in mathematics, physics, chemistry and geology. As the result the most talented children become the students of this school (for two years). The school in turn supplies GGD with the students. 4.NSU has the study curriculum different from other universities in Russia. That is why the entrance examinations are much more difficult as compared to other schools and are taken in July (a month earlier then at other universities). However the entrance

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

Triggered star-formation in the bright rimmed globule IC1396A

NASA Astrophysics Data System (ADS)

Patel, Nimesh A.; Sicilia-Aguilar, Aurora; Goldsmith, Paul

2015-01-01

IC1396 is a well known HII region and molecular cloud complex surrounding the Trumpler 37 cluster of OB stars in the Cepheus OB2 association. The dense, elephant trunk shaped globules in this region typically show bright rims facing the central exciting O6 star HD~206267. This region, at a distance of 870 pc, is an excellent astrophysical laboratory for studying the feedback effects of massive stars on neighboring molecular clouds. Triggered star formation occurs when dense cores (which would otherwise remain stable) are compressed and made unstable by the sustained energy input from the OB association. Observationally it remains challenging to prove whether the onset of star-formation in such globules is triggered or spontaneous.Using the Submillimeter Array (SMA), we observed IC1396 globule A (Pottasch 1958 nomenclature), targeting four newly discovered protostars from recent Herschel PACS observations. Here we present 230 GHz molecular line (CO, 13CO, C18O, N2D+ and H2CO) and continuum results for the source IC1396A-PACS-1 (Sicilia-Aguilar et al. 2014). This is a Class 0 source very close to the edge of the ionization front and Herschel observations show this to be a most promisingcase of triggered star-formation. The SMA 230 GHz continuum source has a flux density of 280 mJy. We estimate a dust mass of about 0.1 Msun in this source which appears very compact in our 5" beam. CO, 13CO and C18O emission is largely resolved out by the interferometer and will require combined imaging with single-dish observations. (We have a parallel ongoing study being carried out with the IRAM 30m telescope). SMA N2D+ emission peaks on the continuum sourceand is partially resolved. H2CO emission appears to avoid the peak of continuum and N2D+, suggesting depletion. Both the morphology and kinematics in H2CO emission are indicative of internal disturbance, away from the PDR region into the globule.

Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies

NASA Astrophysics Data System (ADS)

Malko, Bradley Ann; Hunter, Deidre Ann

2018-06-01

Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.

Long-term Spectroscopic and Photometric Monitoring of Bright Interacting Algol-type Binary Stars

NASA Astrophysics Data System (ADS)

Reed, Phillip A.

2018-01-01

Binary stars have long been used as natural laboratories for studying such fundamental stellar properties as mass. Interacting binaries allow us to examine more complicated aspects such as mass flow between stars, accretion processes, magnetic fields, and stellar mergers. Algol-type interacting binary stars -- consisting of a cool giant or sub-giant donating mass to a much hotter, less evolved, and more massive main-sequence companion -- undergo steady mass transfer and have been used to measure mass transfer rates and to test stellar evolution theories. The method of back-projection Doppler tomography has also been applied to interacting Algols and has produced indirect velocity-space images of the accretion structures (gas streams, accretion disks, etc.) derived from spectroscopic observations of hydrogen and helium emission lines. The accretion structures in several Algol systems have actually been observed to change between disk-like states and stream-like states on timescales as short as several orbital cycles (Richards et al., 2014). Presented here are the first results from a project aimed at studying bright interacting Algol systems with simultaneous mid-resolution (11,000identify the various accretion phenomena, and to extract their physical properties.

The RAVE Survey: Rich in Very Metal-poor Stars

NASA Astrophysics Data System (ADS)

Fulbright, Jon P.; Wyse, Rosemary F. G.; Ruchti, Gregory R.; Gilmore, G. F.; Grebel, Eva; Bienaymé, O.; Binney, J.; Bland-Hawthorn, J.; Campbell, R.; Freeman, K. C.; Gibson, B. K.; Helmi, A.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G. M.; Siebert, A.; Siviero, A.; Steinmetz, M.; Watson, F. G.; Williams, M.; Zwitter, T.

2010-11-01

Very metal-poor stars are of obvious importance for many problems in chemical evolution, star formation, and galaxy evolution. Finding complete samples of such stars which are also bright enough to allow high-precision individual analyses is of considerable interest. We demonstrate here that stars with iron abundances [Fe/H] <-2 dex, and down to below -4 dex, can be efficiently identified within the Radial Velocity Experiment (RAVE) survey of bright stars, without requiring additional confirmatory observations. We determine a calibration of the equivalent width of the calcium triplet lines measured from the RAVE spectra onto true [Fe/H], using high spectral resolution data for a subset of the stars. These RAVE iron abundances are accurate enough to obviate the need for confirmatory higher-resolution spectroscopy. Our initial study has identified 631 stars with [Fe/H] <=-2, from a RAVE database containing approximately 200,000 stars. This RAVE-based sample is complete for stars with [Fe/H] lsim-2.5, allowing statistical sample analysis. We identify three stars with [Fe/H] lsim-4. Of these, one was already known to be "ultra metal-poor," one is a known carbon-enhanced metal-poor star, but we obtain [Fe/H] = -4.0, rather than the published [Fe/H] = -3.3, and derive [C/Fe] = +0.9, and [N/Fe] = +3.2, and the third is at the limit of our signal-to-noise ratio. RAVE observations are ongoing and should prove to be a rich source of bright, easily studied, very metal-poor stars. Based in part on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile, in the framework of proposals 081.B-0900 and 080.B-0927.

Trajectories of bright stars at the Galactic Center as a tool to evaluate a graviton mass

NASA Astrophysics Data System (ADS)

Zakharov, Alexander; Jovanović, Predrag; Borka, Dusko; Jovanović, Vesna Borka

2016-10-01

Scientists worked in Saint-Petersburg (Petrograd, Leningrad) played the extremely important role in creation of scientific school and development of general relativity in Russia. Very recently LIGO collaboration discovered gravitational waves [1] predicted 100 years ago by A. Einstein. In the papers reporting about this discovery, the joint LIGO & VIRGO team presented an upper limit on graviton mass such as mg < 1.2 × 10-22eV [1, 2]. The authors concluded that their observational data do not show violations of classical general relativity because the graviton mass limit is very small. We show that an analysis of bright star trajectories could bound graviton mass with a comparable accuracy with accuracies reached with gravitational wave interferometers and expected with forthcoming pulsar timing observations for gravitational wave detection. This analysis gives an opportunity to treat observations of bright stars near the Galactic Center as a tool for an evaluation specific parameters of the black hole and also to obtain constraints on the fundamental gravity law such as a modifications of Newton gravity law in a weak field approximation. In that way, based on a potential reconstruction at the Galactic Center we give a bounds on a graviton mass.

Studying the Variability of Bright Stars with the CONCAM Sky Monitoring Network

NASA Astrophysics Data System (ADS)

Pereira, W. E.; Nemiroff, R. J.; Rafert, J. B.; Perez-Ramirez, D.

2001-12-01

CONCAMs have now been deployed at some of the world's major observatories including KPNO in Arizona, Mauna Kea in Hawaii, and Wise Observatory in Israel. Data from these mobile, inexpensive and continuous sky cameras, consisting of a fish-eye lens mated to a CCD camera and run by a laptop, has been ever-increasing. Initial efforts to carry out photometric analysis of CONCAM fits images have now been fortified by a more automated technique of analyzing this data. Results of such analyses - variability of several bright stars, in particular, are presented, as well as the use of these cameras as cloud monitors to remote observers.

Three Small Planets Transiting the Bright Young Field Star K2-233

NASA Astrophysics Data System (ADS)

David, Trevor J.; Crossfield, Ian J. M.; Benneke, Björn; Petigura, Erik A.; Gonzales, Erica J.; Schlieder, Joshua E.; Yu, Liang; Isaacson, Howard T.; Howard, Andrew W.; Ciardi, David R.; Mamajek, Eric E.; Hillenbrand, Lynne A.; Cody, Ann Marie; Riedel, Adric; Schwengeler, Hans Martin; Tanner, Christopher; Ende, Martin

2018-05-01

We report the detection of three small transiting planets around the young K3 dwarf K2-233 (2MASS J15215519‑2013539) from observations during Campaign 15 of the K2 mission. The star is relatively nearby (d = 69 pc) and bright (V = 10.7 mag, K s = 8.4 mag), making the planetary system an attractive target for radial velocity follow-up and atmospheric characterization with the James Webb Space Telescope. The inner two planets are hot super-Earths (R b = 1.40 ± 0.06 {R}\\oplus , R c = 1.34 ± 0.08 {R}\\oplus ), while the outer planet is a warm sub-Neptune (R d = 2.6 ± 0.1 {R}\\oplus ). We estimate the stellar age to be {360}-140+490 Myr based on rotation, activity, and kinematic indicators. The K2-233 system is particularly interesting given recent evidence for inflated radii in planets around similarly aged stars, a trend potentially related to photo-evaporation, core cooling, or both mechanisms.

Temporal intensity interferometry: photon bunching in three bright stars

NASA Astrophysics Data System (ADS)

Guerin, W.; Dussaux, A.; Fouché, M.; Labeyrie, G.; Rivet, J.-P.; Vernet, D.; Vakili, F.; Kaiser, R.

2017-12-01

We report the first intensity correlation measured with starlight since the historical experiments of Hanbury Brown and Twiss. The photon bunching g(2)(τ, r = 0), obtained in the photon-counting regime, was measured for three bright stars: α Boo, α CMi and β Gem. The light was collected at the focal plane of a 1-m optical telescope, transported by a multi-mode optical fibre, split into two avalanche photodiodes and correlated digitally in real time. For total exposure times of a few hours, we obtained contrast values around 2 × 10-3, in agreement with the expectation for chaotic sources, given the optical and electronic bandwidths of our set-up. Comparing our results with the measurement of Hanbury Brown et al. for α CMi, we argue for the timely opportunity to extend our experiments to measuring the spatial correlation function over existing and/or foreseen arrays of optical telescopes diluted over several kilometres. This would enable microarcsec long-baseline interferometry in the optical, especially in the visible wavelengths, with a limiting magnitude of 10.

Can You See the Stars? Citizen-Science Programs to Measure Night Sky Brightness

NASA Astrophysics Data System (ADS)

Walker, Constance E.

2009-05-01

For the IYA2009 Dark Skies Awareness Cornerstone Project, partners in dark-sky, astronomy and environmental education are promoting three citizen-scientist programs that measure light pollution at local levels worldwide. These programs take the form of "star hunts", providing people with fun and direct ways to acquire heightened awareness about light pollution through first-hand observations of the night sky. Together the programs are spanning the entire IYA, namely: GLOBE at Night in March, Great World Wide Star Count in October, and How Many Stars during the rest of the year. Citizen-scientists - students, educators, amateur astronomers and the general public - measure the darkness of their local skies and contribute observations online to a world map. Anyone anywhere anytime can look within particular constellations for the faintest stars and match them to one of seven star maps. For more precise measurements, digital sky-brightness meters can be used. Measurements, along with the measurement location, time, and date, are submitted online, and within a few days to weeks a world map showing results is available. These measurements can be compared with data from previous years, as well as with satellite data, population densities, and electrical power-usage maps. Measurements are available online via Google Earth or other tools and as downloadable datasets. Data from multiple locations in one city or region are especially interesting, and can be used as the basis of a class project or science fair experiment, or even to inform the development of public policy. In the last few years these programs successfully conducted campaigns in which more than 35,000 observations were submitted from over 100 countries. The presentation will provide an update, describe how people can become involved and take a look ahead at the program's sustainability. For further information about these and other Dark Skies Awareness programs, please visit www.darkskiesawareness.org.

Spectral and Temporal Characteristics of X-Ray-Bright Stars in the Pleiades

NASA Technical Reports Server (NTRS)

Gagne, Marc; Caillault, Jean-Pierre; Stauffer, John R.

1995-01-01

We follow up our deep ROSAT imaging survey of the Pleiades (Stauffer et al. 1994) with an analysis of the spectral and temporal characteristics of the X-ray-bright stars in the Pleiades. Raymond & Smith (1977) one and two-temperature models have been used to fit the position-sensitive proportional counter (PSPC) pulse-height spectra of the dozen or so brightest sources associated with late-type Pleiades members. The best-fit temperatures suggest hot coronal temperatures for K, M, and rapidly rotating G stars, and cooler temperatures for F and slowly rotating G stars. In order to probe the many less X-ray-luminous stars, we have generated composite spectra by combining net counts from all Pleiades members according to spectral type and rotational velocity. Model fits to the composite spectra confirm the trend seen in the individual spectral fits. Particularly interesting is the apparent dependence of coronal temperature on L(sub x)/L(sub bol). A hardness-ratio analysis also confirms some of these trends. The PSPC data have also revealed a dozen or so strong X-ray flares with peak X-ray luminosities in excess of approx. 10(exp 30) ergs/sec. We have modeled the brightest of these flares with a simple quasi-static cooling loop model. The peak temperature and emission measure and the inferred electron density and plasma volume suggest a very large scale flaring event. The PSPC data were collected over a period of approx. 18 months, allowing us to search for source variability on timescales ranging from less than a day (in the case of flares) to more than a year between individual exposures. On approximately year-long timescales, roughly 25% of the late-type stars are variable. Since the Pleiades was also intensively monitored by the imaging instruments on the Einstein Observatory, we have examined X-ray luminosity variations on the 10 yr timescale between Einstein and ROSAT and find that up to 40% of the late-type stars are X-ray variable. Since there is only marginal

Interferometric Constraints on Surface Brightness Asymmetries in Long-Period Variable Stars: A Threat to Accurate Gaia Parallaxes

NASA Astrophysics Data System (ADS)

Sacuto, S.; Jorissen, A.; Cruzalèbes, P.; Pasquato, E.; Chiavassa, A.; Spang, A.; Rabbia, Y.; Chesneau, O.

2011-09-01

A monitoring of surface brightness asymmetries in evolved giants and supergiants is necessary to estimate the threat that they represent to accurate Gaia parallaxes. Closure-phase measurements obtained with AMBER/VISA in a 3-telescope configuration are fitted by a simple model to constrain the photocenter displacement. The results for the C-type star TX Psc show a large deviation of the photocenter displacement that could bias the Gaia parallax.

MASCARA-1 b. A hot Jupiter transiting a bright mV = 8.3 A-star in a misaligned orbit

NASA Astrophysics Data System (ADS)

Talens, G. J. J.; Albrecht, S.; Spronck, J. F. P.; Lesage, A.-L.; Otten, G. P. P. L.; Stuik, R.; Van Eylen, V.; Van Winckel, H.; Pollacco, D.; McCormac, J.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Snellen, I. A. G.

2017-10-01

We report the discovery of MASCARA-1 b, which is the first exoplanet discovered with the Multi-site All-Sky CAmeRA (MASCARA). This exoplanet is a hot Jupiter orbiting a bright mV = 8.3, rapidly rotating (vsini⋆ > 100 km s-1) A8 star with a period of 2.148780 ± 8 × 10-6 days. The planet has a mass and radius of 3.7 ± 0.9 MJup and 1.5 ± 0.3 RJup, respectively. As with most hot Jupiters transiting early-type stars, we find a misalignment between the planet orbital axis and the stellar spin axis, which may be a signature of the formation and migration histories of this family of planets. MASCARA-1 b has a mean density of 1.5 ± 0.9 g cm-3 and an equilibrium temperature of 2570+50-30K, that is one of the highest temperatures known for a hot Jupiter to date. The system is reminiscent of WASP-33, but the host star lacks apparent delta-scuti variations, making the planet an ideal target for atmospheric characterization. We expect this to be the first of a series of hot Jupiters transiting bright early-type stars that will be discovered by MASCARA. Tables of the photometry and the reduced spectra as FITS files 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/606/A73

Prior Knowledge Base of Constellations and Bright Stars among Non-Science Majoring Undergraduates and 14-15 Year Old Students

ERIC Educational Resources Information Center

Hintz, Eric G.; Hintz, Maureen L.; Lawler, M. Jeannette

2015-01-01

As part of an effort to improve students' knowledge of constellations and bright stars in an introductory level descriptive astronomy survey course, we measured the baseline knowledge that students bring to the class and how their score evolve over the course of the semester. This baseline is needed by the broader astronomy education research…

Guide star probabilities

NASA Technical Reports Server (NTRS)

Soneira, R. M.; Bahcall, J. N.

1981-01-01

Probabilities are calculated for acquiring suitable guide stars (GS) with the fine guidance system (FGS) of the space telescope. A number of the considerations and techniques described are also relevant for other space astronomy missions. The constraints of the FGS are reviewed. The available data on bright star densities are summarized and a previous error in the literature is corrected. Separate analytic and Monte Carlo calculations of the probabilities are described. A simulation of space telescope pointing is carried out using the Weistrop north galactic pole catalog of bright stars. Sufficient information is presented so that the probabilities of acquisition can be estimated as a function of position in the sky. The probability of acquiring suitable guide stars is greatly increased if the FGS can allow an appreciable difference between the (bright) primary GS limiting magnitude and the (fainter) secondary GS limiting magnitude.

Dead Star Warps Light of Red Star Artist Animation

NASA Image and Video Library

2013-04-04

This artist concept depicts an ultra-dense dead star, called a white dwarf, passing in front of a small red star. NASA planet-hunting Kepler was able to detect gravitational lensing by measuring a strangely subtle dip in the star brightness.

Bright Lights, Green City

NASA Image and Video Library

2010-07-28

Two extremely bright stars illuminate a greenish mist in this image from the new GLIMPSE360 survey from NASA Spitzer Space Telescope. The fog is comprised of hydrogen and carbon compounds called polycyclic aromatic hydrocarbons.

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.

Spectroscopic monitoring of bright A-F type candidate hybrid stars discovered by the Kepler mission

NASA Astrophysics Data System (ADS)

Lampens, Patricia; Frémat, Y.; Vermeylen, Lore; De Cat, Peter; Dumortier, Louis; Sódor, Ádám; Sharka, Marek; Bognár, Zsófia

2018-04-01

We report on a study of 250 optical spectra for 50 bright A/F-type candidate hybrid pulsating stars from the Kepler field. Most of the spectra have been collected with the high-resolution spectrograph HERMES attached to the Mercator telescope, La Palma. We determined the radial velocities (RVs), projected rotational velocities, fundamental atmospheric parameters and provide a classification based on the appearance of the cross-correlation profiles and the behaviour of the RVs with time in order to find true hybrid pulsators. Additionally, we also detected new spectroscopic binary and multiple systems in our sample and determined the fraction of spectroscopic systems. In order to be able to extend this investigation to the fainter A-F type candidate hybrid stars, various high-quality spectra collected with 3-4 m sized telescopes suitably equipped with a high-resolution spectrograph and furthermore located in the Northern hemisphere would be ideal. This programme could be done using the new instruments installed at the Devasthal Observatory.

HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2

NASA Astrophysics Data System (ADS)

Van Eylen, V.; Dai, F.; Mathur, S.; Gandolfi, D.; Albrecht, S.; Fridlund, M.; García, R. A.; Guenther, E.; Hjorth, M.; Justesen, A. B.; Livingston, J.; Lund, M. N.; Pérez Hernández, F.; Prieto-Arranz, J.; Regulo, C.; Bugnet, L.; Everett, M. E.; Hirano, T.; Nespral, D.; Nowak, G.; Palle, E.; Silva Aguirre, V.; Trifonov, T.; Winn, J. N.; Barragán, O.; Beck, P. G.; Chaplin, W. J.; Cochran, W. D.; Csizmadia, S.; Deeg, H.; Endl, M.; Heeren, P.; Grziwa, S.; Hatzes, A. P.; Hidalgo, D.; Korth, J.; Mathis, S.; Montañes Rodriguez, P.; Narita, N.; Patzold, M.; Persson, C. M.; Rodler, F.; Smith, A. M. S.

2018-05-01

We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star (V = 9.3 mag) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be 1.12^{+0.04}_{-0.01} M_⊙ and 1.657^{+0.020}_{-0.004} R_⊙, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4^{+0.4}_{-1.3} Gyr, and the non-detection of mixed modes. The star hosts a "warm Saturn" (P = 11.8 days, Rp = 6.86 ± 0.14 R⊕). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7 ± 3.3 M⊕. The data also show that the planet's orbit is eccentric (e ≈ 0.2). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.

Age-Defying Star

NASA Image and Video Library

2016-08-29

An age-defying star called IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA's Spitzer Space Telescope. IRAS 19312+1950 is the bright red star in the center of this image. A NASA-led team of scientists thinks the star -- which is about 10 times as massive as our sun and emits about 20,000 times as much energy -- is a newly forming protostar. That was a big surprise, because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. http://photojournal.jpl.nasa.gov/catalog/PIA20914

Stunningly bright optical emission

NASA Astrophysics Data System (ADS)

Heinke, Craig O.

2017-12-01

The detection of bright, rapid optical pulsations from pulsar PSR J1023+0038 have provided a surprise for researchers working on neutron stars. This discovery poses more questions than it answers and will spur on future work and instrumentation.

Brightness Variations of Sun-like Stars: The Mystery Deepens - Astronomers facing Socratic "ignorance"

NASA Astrophysics Data System (ADS)

2009-12-01

An extensive study made with ESO's Very Large Telescope deepens a long-standing mystery in the study of stars similar to the Sun. Unusual year-long variations in the brightness of about one third of all Sun-like stars during the latter stages of their lives still remain unexplained. Over the past few decades, astronomers have offered many possible explanations, but the new, painstaking observations contradict them all and only deepen the mystery. The search for a suitable interpretation is on. "Astronomers are left in the dark, and for once, we do not enjoy it," says Christine Nicholls from Mount Stromlo Observatory, Australia, lead author of a paper reporting the study. "We have obtained the most comprehensive set of observations to date for this class of Sun-like stars, and they clearly show that all the possible explanations for their unusual behaviour just fail." The mystery investigated by the team dates back to the 1930s and affects about a third of Sun-like stars in our Milky Way and other galaxies. All stars with masses similar to our Sun become, towards the end of their lives, red, cool and extremely large, just before retiring as white dwarfs. Also known as red giants, these elderly stars exhibit very strong periodic variations in their luminosity over timescales up to a couple of years. "Such variations are thought to be caused by what we call 'stellar pulsations'," says Nicholls. "Roughly speaking, the giant star swells and shrinks, becoming brighter and dimmer in a regular pattern. However, one third of these stars show an unexplained additional periodic variation, on even longer timescales - up to five years." In order to find out the origin of this secondary feature, the astronomers monitored 58 stars in our galactic neighbour, the Large Magellanic Cloud, over two and a half years. They acquired spectra using the high resolution FLAMES/GIRAFFE spectrograph on ESO's Very Large Telescope and combined them with images from other telescopes [1

All-sky brightness monitoring of light pollution with astronomical methods.

PubMed

Rabaza, O; Galadí-Enríquez, D; Estrella, A Espín; Dols, F Aznar

2010-06-01

This paper describes a mobile prototype and a protocol to measure light pollution based on astronomical methods. The prototype takes three all-sky images using BVR filters of the Johnson-Cousins astronomical photometric system. The stars are then identified in the images of the Hipparcos and General Catalogue of Photometric Data II astronomical catalogues, and are used as calibration sources. This method permits the measurement of night-sky brightness and facilitates an estimate of which fraction is due to the light up-scattered in the atmosphere by a wide variety of man-made sources. This is achieved by our software, which compares the sky background flux to that of many stars of known brightness. The reduced weight and dimensions of the prototype allow the user to make measurements from virtually any location. This prototype is capable of measuring the sky distribution of light pollution, and also provides an accurate estimate of the background flux at each photometric band. (c) 2010 Elsevier Ltd. All rights reserved.

The best and brightest metal-poor stars

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

Schlaufman, Kevin C.; Casey, Andrew R., E-mail: kschlauf@mit.edu, E-mail: arc@ast.cam.ac.uk

2014-12-10

The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. The acquisition of high signal-to-noise spectra for faint EMP stars requires a major telescope time commitment, making the construction of large samples of EMP star abundances prohibitively expensive. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared,more » and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns. We have used our selection to identify 11,916 metal-poor star candidates with V < 14, increasing the number of publicly available candidates by more than a factor of five in this magnitude range. Their bright apparent magnitudes have greatly eased high-resolution follow-up observations that have identified seven previously unknown stars with [Fe/H] ≲ –3.0. Our follow-up campaign has revealed that 3.8{sub −1.1}{sup +1.3}% of our candidates have [Fe/H] ≲ –3.0 and 32.5{sub −2.9}{sup +3.0}% have –3.0 ≲ [Fe/H] ≲ –2.0. The bulge is the most likely location of any existing Galactic Population III stars, and an infrared-only variant of our selection is well suited to the identification of metal-poor stars in the bulge. Indeed, two of our confirmed metal-poor stars with [Fe/H] ≲ –2.7 are within about 2 kpc of the Galactic center. They are among the most metal-poor stars known in the bulge.« less

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.

Coronal Properties of X-ray bright stars in young associations: abundances, temperatures and variability

NASA Astrophysics Data System (ADS)

Argiroffi, Costanza

2006-03-01

In this work I have investigated open issues related to the X-ray radiation from young stars, including heating mechanisms of the emitting plasma, its chemical composition, and possible effects due to circumstellar accretion disks. To this aim, I have analyzed observations of young nearby stars taken with the X-ray observatories XMM-Newton and Chandra. For a detailed study of the characteristics of the X-ray emitting plasma, I have selected two X-ray bright young stars, TWA 5 and PZ Tel, for which high-resolution X-ray spectroscopy was achievable, and two regions of the young stellar association Upper Scorpius (USco), for which X-ray images and medium-resolution spectra of individual sources were obtained. TWA 5 is a 10 Myr old star in the TW Hydrae association, which is still accreting material from its circumstellar envelope, while PZ Tel is a ? 12 Myr star in the beta Pictoris moving group, which already dissipated its circumstellar disk. The different evolutionary stages of these two stars allow to probe whether X-ray emission is produced, or affected, by accretion processes. High-resolution X-ray spectra of TWA 5 and PZ Tel were gathered with the grating spectrometers on board XMM-Newton and Chandra, respectively. From the measurements of individual emission line fluxes in their X-ray spectra, I have derived emission measure distributions vs. temperature, abundances, and electron densities of the X-ray emitting plasma. I have found that, in spite of their different evolutionary status, hot (T ? 10 MK) plasma is the main responsible for the observed X-ray emission of both stars. The hot plasma on TWA 5 displays peculiar element abundances with respect to the solar photospheric composition with Ne/Fe ? 10(Ne/Fe), while the coronal plasma on PZ Tel shows Ne/Fe ? 3(Ne/Fe). To explain the strong Fe underabundance (? 0.1 Fe) and the extremely high Ne/Fe ratio of TWA 5 I have considered three different scenarios: (1) coronal plasma may be affected by selective

Evaluation of parameters of Black Hole, stellar cluster and dark matter distribution from bright star orbits in the Galactic Center

NASA Astrophysics Data System (ADS)

Zakharov, Alexander

It is well-known that one can evaluate black hole (BH) parameters (including spin) analyz-ing trajectories of stars around BH. A bulk distribution of matter (dark matter (DM)+stellar cluster) inside stellar orbits modifies trajectories of stars, namely, generally there is a apoas-tron shift in direction which opposite to GR one, even now one could put constraints on DM distribution and BH parameters and constraints will more stringent in the future. Therefore, an analyze of bright star trajectories provides a relativistic test in a weak gravitational field approximation, but in the future one can test a strong gravitational field near the BH at the Galactic Center with the same technique due to a rapid progress in observational facilities. References A. Zakharov et al., Phys. Rev. D76, 062001 (2007). A.F. Zakharov et al., Space Sci. Rev. 148, 301313(2009).

Investigating a population of infrared-bright gamma-ray burst host galaxies

NASA Astrophysics Data System (ADS)

Chrimes, Ashley A.; Stanway, Elizabeth R.; Levan, Andrew J.; Davies, Luke J. M.; Angus, Charlotte R.; Greis, Stephanie M. L.

2018-07-01

We identify and explore the properties of an infrared-bright gamma-ray burst (GRB) host population. Candidate hosts are selected by coincidence with sources in WISE, with matching to random coordinates and a false alarm probability analysis showing that the contamination fraction is ˜0.5. This methodology has already identified the host galaxy of GRB 080517. We combine survey photometry from Pan-STARRS, SDSS, APASS, 2MASS, GALEX, and WISE with our own WHT/ACAM and VLT/X-shooter observations to classify the candidates and identify interlopers. Galaxy SED fitting is performed using MAGPHYS, in addition to stellar template fitting, yielding 13 possible IR-bright hosts. A further seven candidates are identified from the previously published work. We report a candidate host for GRB 061002, previously unidentified as such. The remainder of the galaxies have already been noted as potential hosts. Comparing the IR-bright population properties including redshift z, stellar mass M⋆, star formation rate SFR, and V-band attenuation AV to GRB host catalogues in the literature, we find that the infrared-bright population is biased towards low z, high M⋆, and high AV. This naturally arises from their initial selection - local and dusty galaxies are more likely to have the required IR flux to be detected in WISE. We conclude that while IR-bright GRB hosts are not a physically distinct class, they are useful for constraining existing GRB host populations, particularly for long GRBs.

Investigating a population of infrared-bright gamma-ray burst host galaxies

NASA Astrophysics Data System (ADS)

Chrimes, Ashley A.; Stanway, Elizabeth R.; Levan, Andrew J.; Davies, Luke J. M.; Angus, Charlotte R.; Greis, Stephanie M. L.

2018-04-01

We identify and explore the properties of an infrared-bright gamma-ray burst (GRB) host population. Candidate hosts are selected by coincidence with sources in WISE, with matching to random coordinates and a false alarm probability analysis showing that the contamination fraction is ˜ 0.5. This methodology has already identified the host galaxy of GRB 080517. We combine survey photometry from Pan-STARRS, SDSS, APASS, 2MASS, GALEX and WISE with our own WHT/ACAM and VLT/X-shooter observations to classify the candidates and identify interlopers. Galaxy SED fitting is performed using MAGPHYS, in addition to stellar template fitting, yielding 13 possible IR-bright hosts. A further 7 candidates are identified from previously published work. We report a candidate host for GRB 061002, previously unidentified as such. The remainder of the galaxies have already been noted as potential hosts. Comparing the IR-bright population properties including redshift z, stellar mass M⋆, star formation rate SFR and V-band attenuation AV to GRB host catalogues in the literature, we find that the infrared-bright population is biased toward low z, high M⋆ and high AV. This naturally arises from their initial selection - local and dusty galaxies are more likely to have the required IR flux to be detected in WISE. We conclude that while IR-bright GRB hosts are not a physically distinct class, they are useful for constraining existing GRB host populations, particularly for long GRBs.

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 mysterious age invariance of the planetary nebula luminosity function bright cut-off

NASA Astrophysics Data System (ADS)

Gesicki, K.; Zijlstra, A. A.; Miller Bertolami, M. M.

2018-05-01

Planetary nebulae mark the end of the active life of 90% of all stars. They trace the transition from a red giant to a degenerate white dwarf. Stellar models1,2 predicted that only stars above approximately twice the solar mass could form a bright nebula. But the ubiquitous presence of bright planetary nebulae in old stellar populations, such as elliptical galaxies, contradicts this: such high-mass stars are not present in old systems. The planetary nebula luminosity function, and especially its bright cut-off, is almost invariant between young spiral galaxies, with high-mass stars, and old elliptical galaxies, with only low-mass stars. Here, we show that new evolutionary tracks of low-mass stars are capable of explaining in a simple manner this decades-old mystery. The agreement between the observed luminosity function and computed stellar evolution validates the latest theoretical modelling. With these models, the planetary nebula luminosity function provides a powerful diagnostic to derive star formation histories of intermediate-age stars. The new models predict that the Sun at the end of its life will also form a planetary nebula, but it will be faint.

GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. I. SURFACE BRIGHTNESS PROFILE

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

Gilbert, Karoline M.; Guhathakurta, Puragra; Beaton, Rachael L.

2012-11-20

We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 {+-} 0.2 and extends to amore » projected distance of at least {approx}175 kpc ({approx}2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects.« less

EM Cep: The Be Star

NASA Astrophysics Data System (ADS)

Kochiashvili, N.; Kochiashvili, I.; Natsvlishvili, R.; Vardosanidze, M.; Beradze, S.

2017-07-01

On the basis of UBVR photometric data, obtained in the Abastumani Observatory during 1991-1999, very interesting and unusual flare of EM Cep has been revealed. Duration of the flare was over two hours. We estimated the percentage of brightness increase during the flare and brightness decrease of the corresponding anti- flare and the minimum amount of the lost mass during this event. We have solved the light curves of the star using the Wilson-Devinney code. But the resulting fraction of calculated brightness of the companion star was not in accordance with spectral data. Then we decided to check the idea of a pulsating single star using new spectral data. Together with our Buyrakan colleagues we obtained and analyzed spectra of the star. We could not find spectral lines of a companion star or any traces of the radial velocities using this data. Hence, we concluded that we need the higher resolution spectra for final resolution of the matter. On the basis of the latest spectral data of Bulgarian astronomers they concluded that EM Cep is a single star. This makes it possible to suggest, that the question of stellar pulsation could be solved using additional photometric observations.

Central-engine-powered Bright X-Ray Flares in Short Gamma-Ray Bursts: A Hint of a Black Hole–Neutron Star Merger?

NASA Astrophysics Data System (ADS)

Mu, Hui-Jun; Gu, Wei-Min; Mao, Jirong; Hou, Shu-Jin; Lin, Da-Bin; Liu, Tong

2018-05-01

Short gamma-ray bursts may originate from the merger of a double neutron star (NS) or the merger of a black hole (BH) and an NS. We propose that the bright X-ray flare related to the central engine reactivity may indicate a BH–NS merger, since such a merger can provide more fallback materials and therefore a more massive accretion disk than the NS–NS merger. Based on the 49 observed short bursts with the Swift/X-ray Telescope follow-up observations, we find that three bursts have bright X-ray flares, among which three flares from two bursts are probably related to the central engine reactivity. We argue that these two bursts may originate from the BH–NS merger rather than the NS–NS merger. Our suggested link between the central-engine-powered bright X-ray flare and the BH–NS merger event can be checked by future gravitational wave detections from advanced LIGO and Virgo.

Following the Cosmic Evolution of Pristine Gas. II. The Search for Pop III–bright Galaxies

NASA Astrophysics Data System (ADS)

Sarmento, Richard; Scannapieco, Evan; Cohen, Seth

2018-02-01

Direct observational searches for Population III (Pop III) stars at high redshift are faced with the question of how to select the most promising targets for spectroscopic follow-up. To help answer this, we use a large-scale cosmological simulation, augmented with a new subgrid model that tracks the fraction of pristine gas, to follow the evolution of high-redshift galaxies and the Pop III stars they contain. We generate rest-frame ultraviolet (UV) luminosity functions for our galaxies and find that they are consistent with current z≥slant 7 observations. Throughout the redshift range 7≤slant z≤slant 15, we identify “Pop III–bright” galaxies as those with at least 75% of their flux coming from Pop III stars. While less than 1% of galaxies brighter than {m}UV,{AB}}=31.4 mag are Pop III–bright in the range 7≤slant z≤slant 8, roughly 17% of such galaxies are Pop III–bright at z = 9, immediately before reionization occurs in our simulation. Moving to z = 10, {m}UV,{AB}}=31.4 mag corresponds to larger, more luminous galaxies, and the Pop III–bright fraction falls off to 5%. Finally, at the highest redshifts, a large fraction (29% at z = 14 and 41% at z = 15) of all galaxies are Pop III–bright regardless of magnitude. While {m}UV,{AB}}=31.4 mag galaxies are extremely rare during this epoch, we find that 13% of galaxies at z = 14 are Pop III–bright with {m}UV,{AB}}≤slant 33 mag, a intrinsic magnitude within reach of the James Webb Space Telescope using lensing. Thus, we predict that the best redshift to search for luminous Pop III–bright galaxies is just before reionization, while lensing surveys for fainter galaxies should push to the highest redshifts possible.

IRAS far-infrared colours of normal stars

NASA Technical Reports Server (NTRS)

Waters, L. B. F. M.; Cote, J.; Aumann, H. H.

1987-01-01

The analysis of IRAS observations at 12, 25, 60 and 100 microns of bright stars of spectral type O to M is presented. The objective is to identify the 'normal' stellar population and to characterize it in terms of the relationships between (B-V) and (V-/12/), between (R-I) and (V-/12/), and as a function of spectral type and luminosity class. A well-defined relation is found between the color of normal stars in the visual (B-V), (R-I) and in the IR, which does not depend on luminosity class. Using the (B-V), (V-/12/) relation for normal stars, it is found that B and M type stars show a large fraction of deviating stars, mostly with IR excess that is probably caused by circumstellar material. A comparison of IRAS colors with the Johnson colors as a function of spectral type shows good agreement except for the K0 to M5 type stars. The results will be useful in identifying the deviating stars detected with IRAS.

NO TIME FOR DEAD TIME: TIMING ANALYSIS OF BRIGHT BLACK HOLE BINARIES WITH NuSTAR

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

Bachetti, Matteo; Barret, Didier; Harrison, Fiona A.

Timing of high-count-rate sources with the NuSTAR Small Explorer Mission requires specialized analysis techniques. NuSTAR was primarily designed for spectroscopic observations of sources with relatively low count rates rather than for timing analysis of bright objects. The instrumental dead time per event is relatively long (∼2.5 msec) and varies event-to-event by a few percent. The most obvious effect is a distortion of the white noise level in the power density spectrum (PDS) that cannot be easily modeled with standard techniques due to the variable nature of the dead time. In this paper, we show that it is possible to exploitmore » the presence of two completely independent focal planes and use the cospectrum, the real part of the cross PDS, to obtain a good proxy of the white-noise-subtracted PDS. Thereafter, one can use a Monte Carlo approach to estimate the remaining effects of dead time, namely, a frequency-dependent modulation of the variance and a frequency-independent drop of the sensitivity to variability. In this way, most of the standard timing analysis can be performed, albeit with a sacrifice in signal-to-noise ratio relative to what would be achieved using more standard techniques. We apply this technique to NuSTAR observations of the black hole binaries GX 339–4, Cyg X-1, and GRS 1915+105.« less

Young Star and Its Infant Planet (Artist animation)

NASA Image and Video Library

2016-06-20

When a planet such as K2-33b passes in front of its host star, it blocks some of the star's light. Observing this periodic dimming, called a transit, from continual monitoring of a star's brightness, allows astronomers to detect planets outside our solar system with a high degree of certainty. This Neptune-sized planet orbits a star that is between 5 and 10 million years old. In addition to the planet, the star hosts a disk of planetary debris, seen as a bright ring encircling the star. An animation is available at: http://photojournal.jpl.nasa.gov/catalog/PIA20692

Observing the First Stars in Luminous, Red Galaxies

NASA Technical Reports Server (NTRS)

Heap, Sally; Lindler, Don

2010-01-01

Modern cosmological simulations predict that the first stars are to be found today in luminous, red galaxies. Although observing such stars individually against a background of younger, metal-rich stars is impossible, the first stars should make their presence known by their strong, line-free ultraviolet flux. We have found evidence for a UV-bright stellar population in Sloan spectra of LRG's at z=0.4-0.5. We present arguments for interpreting this UV-bright stellar population as the oldest stars, rather than other types of stellar populations (e.g. young stars or blue straggler stars in the dominant, metal-rich stellar population

Spectroscopic Observations of Nearby Low Mass Stars

NASA Astrophysics Data System (ADS)

Vican, Laura; Zuckerman, B. M.; Rodriguez, D.

2014-01-01

Young low-mass stars are known to be bright in X-ray and UV due to a high level of magnetic activity. By cross-correlating the GALEX Catalog with the WISE and 2MASS Point Source Catalogs, we have identified more than 2,000 stars whose UV excesses suggest ages in the 10-100 Myr range. We used the Shane 3-m telescope at Lick Observatory on Mount Hamilton, California to observe some of these 2,000 stars spectroscopically. We measured the equivalent width of lithium at 6708 A absorption and H-alpha emission lines. Out of a total of 122 stars observed with the Kast grating spectrometer, we find that roughly 10% have strong lithium absorption features. The high percentage of stars with lithium present is further evidence of the importance of UV emission as a youth indicator for low-mass stars. In addition, we used high-resolution spectra obtained with the Hamilton echelle spectrograph to determine radial velocities for several UV-bright stars. These radial velocities will be useful for the calculation of Galactic UVW space velocities for determination of possible moving group membership. This work is supported by NASA Astrophysics Data Analysis Program award NNX12AH37G to RIT and UCLA and Chilean FONDECYT grant 3130520 to Universidad de Chile. This submission presents work for the GALNYSS project and should be linked to abstracts submitted by David Rodriguez, Laura Vican, and Joel Kastner.

The Multi-site All-Sky CAmeRA (MASCARA). Finding transiting exoplanets around bright (mV < 8) stars

NASA Astrophysics Data System (ADS)

Talens, G. J. J.; Spronck, J. F. P.; Lesage, A.-L.; Otten, G. P. P. L.; Stuik, R.; Pollacco, D.; Snellen, I. A. G.

2017-05-01

This paper describes the design, operations, and performance of the Multi-site All-Sky CAmeRA (MASCARA). Its primary goal is to find new exoplanets transiting bright stars, 4 < mV < 8, by monitoring the full sky. MASCARA consists of one northern station on La Palma, Canary Islands (fully operational since February 2015), one southern station at La Silla Observatory, Chile (operational from early 2017), and a data centre at Leiden Observatory in the Netherlands. Both MASCARA stations are equipped with five interline CCD cameras using wide field lenses (24 mm focal length) with fixed pointings, which together provide coverage down to airmass 3 of the local sky. The interline CCD cameras allow for back-to-back exposures, taken at fixed sidereal times with exposure times of 6.4 sidereal seconds. The exposures are short enough that the motion of stars across the CCD does not exceed one pixel during an integration. Astrometry and photometry are performed on-site, after which the resulting light curves are transferred to Leiden for further analysis. The final MASCARA archive will contain light curves for 70 000 stars down to mV = 8.4, with a precision of 1.5% per 5 minutes at mV = 8.

Wish Upon a Star

NASA Image and Video Library

2015-01-05

What's that bright point of light in the outer A ring? It's a star, bright enough to be visible through the ring! Quick, make a wish! This star -- seen in the lower right quadrant of the image -- was not captured by coincidence, it was part of a stellar occultation. By monitoring the brightness of stars as they pass behind the rings, scientists using this powerful observation technique can inspect detailed structures within the rings and how they vary with location. This view looks toward the sunlit side of the rings from about 44 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 8, 2013. The view was acquired at a distance of approximately 1.1 million miles (1.8 million kilometers) from the rings and at a Sun-Rings-Spacecraft, or phase, angle of 96 degrees. Image scale is 6.8 miles (11 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18297

Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile

NASA Astrophysics Data System (ADS)

Gilbert, Karoline M.; Guhathakurta, Puragra; Beaton, Rachael L.; Bullock, James; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J.; Tollerud, Erik J.; Tanaka, Mikito; Chiba, Masashi

2012-11-01

We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 ± 0.2 and extends to a projected distance of at least ~175 kpc (~2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California

Have We Finally Found Pop III Stars?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

Elusive Population: Population III stars — the theoretical generation of extremely metal-poor stars that should have been formed in the early universe before metals existed — have been conspicuously absent in observations. But a team led by David Sobral (Institute of Astrophysics and Space Sciences, University of Lisbon, and Leiden Observatory) may have changed this paradigm with their recent detection of an extremely bright galaxy in the early universe. The team's broad survey of distant galaxies using ESO's Very Large Telescope provides a glimpse of the universe as it was only 800 million years after the Big Bang. The survey uncovered several unusually bright galaxies — including the brightest galaxy ever seen at this distance, an important discovery by itself. But further scrutiny of this galaxy, named CR7, produced an even more exciting find: a bright pocket of the galaxy contained no sign of any metals. Follow-up with other telescopes confirmed this initial detection. Formation Waves: Sobral and his team postulate that we are observing this galaxy at just the right time to have caught a cluster of Population III stars — the bright, metal-free region of the galaxy — at the end of a wave of early star formation. The observations of CR7 also suggest the presence of regular stars in clumps around the metal-free pocket. These older, surrounding clusters may have formed stars first, helping to ionize a local bubble in the galaxy and allowing us to now observe the light from CR7. It was previously thought that Population III stars might only be found in small, dim galaxies, making them impossible for us to detect. But CR7 provides an interesting alternative: this galaxy is bright, and the candidate Population III stars are surrounded by clusters of normal stars. This suggests that these first-generation stars might in fact be easier to detect than was originally thought. Additional follow-up observations with other telescopes will help to confirm the

B- and A-Type Stars in the Taurus-Auriga Star-Forming Region

NASA Technical Reports Server (NTRS)

Mooley, Kunal; Hillenbrand, Lynne; Rebull, Luisa; Padgett, Deborah; Knapp, Gillian

2013-01-01

We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B, and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral-type B. The second group consists of early-type stars compiled from (1) literature listings in SIMBAD, (2) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud, (3) magnitude- and color-selected point sources from the Two Micron All Sky Survey, and (4) spectroscopically identified early-type stars from the Sloan Digital Sky Survey coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emission indicative of stellar youth. For selected objects, we also model the scattered and emitted radiation from reflection nebulosity and compare the results with the observed spectral energy distributions to further test the plausibility of physical association of the B stars with the Taurus cloud. This investigation newly identifies as probable Taurus members three B-type stars: HR 1445 (HD 28929), t Tau (HD 29763), 72 Tau (HD 28149), and two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5 or earlier associated with the Taurus clouds. Several additional early-type sources including HD 29659 and HD 283815 meet some, but not all, of the membership criteria and therefore are plausible, though not secure, members.

Pulsating Stars

NASA Astrophysics Data System (ADS)

Catelan, M.; Smith, H. A.

2015-03-01

This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

Discovery of a New Wolf-Rayet Star Using SAGE-LMC

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Chené, A.-N.; Kniazev, A. Y.; Schnurr, O.

2012-12-01

We report the first-ever discovery of an extragalactic Wolf-Rayet (WR) star with Spitzer. A new WR star in the Large Magellanic Cloud (LMC) was revealed via detection of its circumstellar shell using 24 μm images obtained in the framework of the Spitzer Survey of the Large Magellanic Cloud (SAGE-LMC). Subsequent spectroscopic observations with the Gemini South resolved the central star in two components, one of which is a WN3b+abs star, while the second one is a B0 V star. We consider the lopsided brightness distribution over the circumstellar shell as an indication that the WR star is a runaway and use this interpretation to identify a possible parent cluster of the star.

Detection of a late B star companion of the bright cluster giant C PUP equals HD 63032

NASA Astrophysics Data System (ADS)

Groote, D.; Reimers, D.

1983-03-01

IUE observations show that c Pup, the central bright K giant in the open cluster NGC 2451, has a blue companion. A fit of theoretical line blanketed model atmosphere fluxes to the observed energy distribution yields reddening E(B-V) = 0.15 (from λ2200 Å feature), an effective temperature Te = 10,200K, and an angular diameter θ = 0.060. If the companion is a main-sequence star, c Pup and its companion are located at a distance of 310 ± 50 pc which lends additional support to membership of c Pup in NGC 2451. The evolutionary status of c Pup is briefly discussed.

SWIRLING GALAXY PARENTS GENERATIONS OF STARS IN ITS CENTER

NASA Technical Reports Server (NTRS)

2002-01-01

The NASA/ESA Hubble Space Telescope has snapped a view of several star generations in the central region of the Whirlpool Galaxy (M51), a spiral region 23 million light-years from Earth in the constellation Canes Venatici (the Hunting Dogs). The galaxy's massive center, the bright ball of light in the center of the photograph, is about 80 light-years across and has a brightness of about 100 million suns. Astronomers estimate that it is about 400 million years old and has a mass 40 million times larger than our Sun. The concentration of stars is about 5,000 times higher than in our solar neighborhood, the Milky Way Galaxy. We would see a continuously bright sky if we lived near the bright center. The dark 'y' across the center is a sign of dust absorption. The bright dot in the middle of the 'y' has a brightness of about one million suns, but a size of less than five light-years. Its power and its tiny size suggest that we have located the elusive central black hole that produces powerful radio jets. Surrounding the center is a much older stellar population that covers a region of about 1,500 light-years in diameter and is at least 8 billion years old, and may be as old as the Universe itself, about 13 billion years. Further away, there is a 'necklace' of very young star-forming regions, clusters of infant stars, younger than 10 million years, which are about 700 light-years away from the center. Normally, young stars are found thousands of light-years away. Astronomers believe that stars in the central region were formed when a dwarf companion galaxy - which is not in the photograph - passed close to it, about 400 million years ago, stirring up dust and material for new star birth. The close encounter has been felt for a long time and is believed to be responsible also for the unusually high star formation activity in the bright necklace of young stars. The color image was assembled from four exposures taken Jan. 15, 1995 with Wide Field Planetary Camera-2 in blue

Surface brightness and color distributions in blue compact dwarf galaxies. I - Haro 2, an extreme example of a star-forming young elliptical galaxy

NASA Technical Reports Server (NTRS)

Loose, Hans-Hermann; Thuan, Trinh X.

1986-01-01

The first results of a large-scale program to study the morphology and structure of blue compact dwarf galaxies from CCD observations are presented. The observations and reduction procedures are described, and surface brightness and color profiles are shown. The results are used to discuss the morphological type of Haro 2 and its stellar populations. It is found that Haro 2 appears to be an extreme example of an elliptical galaxy undergoing intense star formation in its central regions, and that the oldest stars it contains were made only about four million yr ago. The 'missing' mass problem of Haro 2 is also discussed.

How Bright Can Supernovae Get?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-04-01

Supernovae enormous explosions associated with the end of a stars life come in a variety of types with different origins. A new study has examined how the brightest supernovae in the Universe are produced, and what limits might be set on their brightness.Ultra-Luminous ObservationsRecent observations have revealed many ultra-luminous supernovae, which haveenergies that challenge our abilities to explain them usingcurrent supernova models. An especially extreme example is the 2015 discovery of the supernova ASASSN-15lh, which shone with a peak luminosity of ~2*1045 erg/s, nearly a trillion times brighter than the Sun. ASASSN-15lh radiated a whopping ~2*1052 erg in the first four months after its detection.How could a supernova that bright be produced? To explore the answer to that question, Tuguldur Sukhbold and Stan Woosley at University of California, Santa Cruz, have examined the different sources that could produce supernovae and calculated upper limits on the potential luminosities ofeach of these supernova varieties.Explosive ModelsSukhbold and Woosley explore multiple different models for core-collapse supernova explosions, including:Prompt explosionA stars core collapses and immediately explodes.Pair instabilityElectron/positron pair production at a massive stars center leads to core collapse. For high masses, radioactivity can contribute to delayed energy output.Colliding shellsPreviously expelled shells of material around a star collide after the initial explosion, providing additional energy release.MagnetarThe collapsing star forms a magnetar a rapidly rotating neutron star with an incredibly strong magnetic field at its core, which then dumps energy into the supernova ejecta, further brightening the explosion.They then apply these models to different types of stars.Setting the LimitThe authors show that the light curve of ASASSN-15lh (plotted in orange) can be described by a model (black curve) in which a magnetar with an initial spin period of 0.7 ms

Star Formation in NGC 4631

NASA Astrophysics Data System (ADS)

Smith, A. M.; Collins, N. R.; Bohlin, R.; Fanelli, M. N.; Neff, S. G.; O'Connell, R. W.; Roberts, M. S.; Stecher, T. P.; Waller, W. H.

1997-12-01

The group of galaxies including NGC 4631 provides an outstanding example of a galaxy interaction accompanied by intensive star formation. FUV imagery, recorded by the Ultraviolet Imaging Telescope (UIT), exhibits very bright far- ultraviolet (FUV) emission corresponding to the H II regions cataloged by Crillon and Monet (1969). This data is, in our experience, extraordinary in that NCG 4631 is observed nearly edge-on and strong attenuation of FUV light could be anticipated. Analysis of the ultraviolet imagery together with ground-based data leads to the following conclusions. The average extinction internal to the bright FUV regions is low [E(B--V) = 0.31], which combined with the optical morphology implies that the FUV bright regions are close to the edge of the galactic disk. The FUV luminosity of that part of the galaxy which can be observed is 8.2 x 10(40) ergs/s and is about a factor 6 less than the FUV luminosities of M101 and M83. FUV colors, M152-U, M152-B and M152-V, when compared to the predicted colors from cluster formation models utilizing a Salpeter IMF imply an internal extinction like that of a non-30Dor LMC extinction curve (Fitzpatrick 1985). Instantaneous burst models indicate an average age of the FUV bright regions of about 6 Myr and a total created stellar mass of 2.8 x 10(7) Msun . If the measured colors are compared to continuous star formation models, star formation beginning about 100 Myr in the past and continuing to the present with a total star formation rate in the FUV bright regions of 0.026 Msun /yr is implied. The total number of OB stars in the H II regions comprising the large ring in the eastern part of the galaxy (Rand's Shell #1, 1993) is inferred to be 20,000. This number can be compared to Rand's estimate of 10,000 to 35,000 supernova-producing OB stars which are required to impart momentum to an expanding shell of hydrogen gas.

Non-identical neutron star twins

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

Glendenning, Norman K.; Kettner, Christiane

1998-07-01

The work of J. A. Wheeler in the mid 1960's showed that forsmooth equations of state no stable stellar configurations with centraldensities above that corresponding to the limiting mass of 'neutronstars' (in the generic sense) were stable against acoustical vibrationalmodes. A perturbation would cause any such star to collapse to a blackhole or explode. Accordingly, there has been no reason to expect that astable degenerate family of stars with higher density than the knownwhite dwarfs and neutron stars might exist. We have found a class ofexceptions corresponding to certain equations of state that describe afirst order phase transition. We discussmore » how such a higher density familyof stars could be formed in nature, and how the promising new explorationof oscillations in the X-ray brightness of accreting neutron stars mightprovide a means of identifying them. Our proof of the possible existenceof a third family of degenerate stars is one of principle and rests ongeneral principles like causality, microstability of matter and GeneralRelativity.« less

The nature of solar brightness variations

NASA Astrophysics Data System (ADS)

Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Yeo, K. L.; Schmutz, W. K.

2017-09-01

Determining the sources of solar brightness variations1,2, often referred to as solar noise3, is important because solar noise limits the detection of solar oscillations3, is one of the drivers of the Earth's climate system4,5 and is a prototype of stellar variability6,7—an important limiting factor for the detection of extrasolar planets. Here, we model the magnetic contribution to solar brightness variability using high-cadence8,9 observations from the Solar Dynamics Observatory (SDO) and the Spectral And Total Irradiance REconstruction (SATIRE)10,11 model. The brightness variations caused by the constantly evolving cellular granulation pattern on the solar surface were computed with the Max Planck Institute for Solar System Research (MPS)/University of Chicago Radiative Magnetohydrodynamics (MURaM)12 code. We found that the surface magnetic field and granulation can together precisely explain solar noise (that is, solar variability excluding oscillations) on timescales from minutes to decades, accounting for all timescales that have so far been resolved or covered by irradiance measurements. We demonstrate that no other sources of variability are required to explain the data. Recent measurements of Sun-like stars by the COnvection ROtation and planetary Transits (CoRoT)13 and Kepler14 missions uncovered brightness variations similar to that of the Sun, but with a much wider variety of patterns15. Our finding that solar brightness variations can be replicated in detail with just two well-known sources will greatly simplify future modelling of existing CoRoT and Kepler as well as anticipated Transiting Exoplanet Survey Satellite16 and PLAnetary Transits and Oscillations of stars (PLATO)17 data.

Multifrequency observations of symbiotic stars

NASA Technical Reports Server (NTRS)

Kenyon, Scott J.

1988-01-01

The discovery of symbiotic stars is described, and the results of multifrequency observations made during the past two decades are presented. Observational data identify symbiotic stars as long-period binary systems that can be divided into two basic physical classes: detached symbiotics containing a red giant (or a Mira variable), and semidetached symbiotics containing a lobe-filling red giant and a solar-type main sequence star. Three components are typically observed: (1) the cool giant component with an effective temperature of 2500-4000 K, which can be divided by the IR spectral classification into normal M giants (S-types) and heavily reddened Mira variables (D-types); (2) the hot companion displaying a bright blue continuum at UV wavelengths, which is sometimes also an X-ray source; and (3) a gaseous nebula enveloping the binary.

Speed-Demon Star Creates a Shock

NASA Image and Video Library

2011-03-10

NASA Wide-field Infrared Survey Explorer captured this image of the star Alpha Camelopardalis, or Alpha Cam speeding through the sky like a motorcyclist zipping through rush-hour traffic. The supergiant star Alpha Cam is the bright star in the middle.

Extended Bright Bodies - Flight and Ground Software Challenges on the Cassini Mission at Saturn

NASA Technical Reports Server (NTRS)

Sung, Tina S.; Burk, Thomas A.

2016-01-01

Extended bright bodies in the Saturn environment such as Saturn's rings, the planet itself, and Saturn's satellites near the Cassini spacecraft may interfere with the star tracker's ability to find stars. These interferences can create faulty spacecraft attitude knowledge, which would decrease the pointing accuracy or even trip a fault protection response on board the spacecraft. The effects of the extended bright body interference were observed in December of 2000 when Cassini flew by Jupiter. Based on this flight experience and expected star tracker behavior at Saturn, the Cassini AACS operations team defined flight rules to suspend the star tracker during predicted interference windows. The flight rules are also implemented in the existing ground software called Kinematic Predictor Tool to create star identification suspend commands to be uplinked to the spacecraft for future predicted interferences. This paper discusses the details of how extended bright bodies impact Cassini's acquisition of attitude knowledge, how the observed data helped the ground engineers in developing flight rules, and how automated methods are used in the flight and ground software to ensure the spacecraft is continuously operated within these flight rules. This paper also discusses how these established procedures will continue to be used to overcome new bright body challenges that Cassini will encounter during its dips inside the rings of Saturn for its final orbits of a remarkable 20-year mission at Saturn.

Carbon Stars Identified from LAMOST DR4 Using Machine Learning

NASA Astrophysics Data System (ADS)

Li, Yin-Bi; Luo, A.-Li; Du, Chang-De; Zuo, Fang; Wang, Meng-Xin; Zhao, Gang; Jiang, Bi-Wei; Zhang, Hua-Wei; Liu, Chao; Qin, Li; Wang, Rui; Du, Bing; Guo, Yan-Xin; Wang, Bo; Han, Zhan-Wen; Xiang, Mao-Sheng; Huang, Yang; Chen, Bing-Qiu; Chen, Jian-Jun; Kong, Xiao; Hou, Wen; Song, Yi-Han; Wang, You-Fen; Wu, Ke-Fei; Zhang, Jian-Nan; Zhang, Yong; Wang, Yue-Fei; Cao, Zi-Huang; Hou, Yong-Hui; Zhao, Yong-Heng

2018-02-01

In this work, we present a catalog of 2651 carbon stars from the fourth Data Release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST). Using an efficient machine-learning algorithm, we find these stars from more than 7 million spectra. As a by-product, 17 carbon-enhanced metal-poor turnoff star candidates are also reported in this paper, and they are preliminarily identified by their atmospheric parameters. Except for 176 stars that could not be given spectral types, we classify the other 2475 carbon stars into five subtypes: 864 C-H, 226 C-R, 400 C-J, 266 C-N, and 719 barium stars based on a series of spectral features. Furthermore, we divide the C-J stars into three subtypes, C-J(H), C-J(R), and C-J(N), and about 90% of them are cool N-type stars as expected from previous literature. Besides spectroscopic classification, we also match these carbon stars to multiple broadband photometries. Using ultraviolet photometry data, we find that 25 carbon stars have FUV detections and that they are likely to be in binary systems with compact white dwarf companions.

VizieR Online Data Catalog: A Finding List of Faint UV-Bright Stars (Lanning+, 1998)

NASA Astrophysics Data System (ADS)

Lanning, H. H.

1997-02-01

The Sandage two-color photographic survey was originally made in support of the UHURU x-ray satellite in order to identify those optical counterparts of the detected x-ray sources found in the galactic plane. During inspection of the plates, however, many UV-bright objects fainter than 10th magnitude were seen in the general field. A larger image in the U filter suggested the possibility of a bluer object as in the case of low-luminosity stars, white dwarfs, novae, CVs, normal early B stars, etc. As these are interesting in themselves, it was decided to publish a catalog for the use of other observers. This multi-color photographic technique has been described, for example, by Haro and Herbig (1955). The survey was concentrated on objects with m(B)~10 or fainter. It employed the Palomar 48-in (Oschin) Schmidt telescope and was centered on the galactic plane with overlapping regions covering the galactic latitudes +- 9 degrees, and extending throughout most of the northern plane (l = 0 deg - 227 deg). Plates were taken by J. Kristian, A.R. Sandage, R.J. Brucato, and Lanning, primarily. The data presented here were found following a careful examination of the plates but it should not be assumed these data represent a complete survey of the fields examined. The categories were roughly calibrated against photoelectric (U-B) measures, but a full scale calibration program, including magnitude effects, etc. was not done. The numerical (U-B) limits of the tables should not therefore be taken precisely. The blue magnitude of the sources in the finding list has been estimated using these photoelectric values as a guide but should be considered accurate to only +- 0.5 mag. due to the difficulty of adjusting to the various plate characteristics. Positions were measured from images retrieved from the Space Telescope Science Institute collection of Guide Star digital plate scans. The accuracy of positions from the Guide Star Catalog images has been estimated to be on the order

Ground-based detection of G star superflares with NGTS

NASA Astrophysics Data System (ADS)

Jackman, James A. G.; Wheatley, Peter J.; Pugh, Chloe E.; Gänsicke, Boris T.; Gillen, Edward; Broomhall, Anne-Marie; Armstrong, David J.; Burleigh, Matthew R.; Chaushev, Alexander; Eigmüller, Philipp; Erikson, Anders; Goad, Michael R.; Grange, Andrew; Günther, Maximilian N.; Jenkins, James S.; McCormac, James; Raynard, Liam; Thompson, Andrew P. G.; Udry, Stéphane; Walker, Simon; Watson, Christopher A.; West, Richard G.

2018-07-01

We present high cadence detections of two superflares from a bright G8 star (V = 11.56) with the Next Generation Transit Survey (NGTS). We improve upon previous superflare detections by resolving the flare rise and peak, allowing us to fit a solar flare inspired model without the need for arbitrary break points between rise and decay. Our data also enables us to identify substructure in the flares. From changing star-spot modulation in the NGTS data, we detect a stellar rotation period of 59 h, along with evidence for differential rotation. We combine this rotation period with the observed ROSAT X-ray flux to determine that the star's X-ray activity is saturated. We calculate the flare bolometric energies as 5.4^{+0.8}_{-0.7}× 10^{34} and 2.6^{+0.4}_{-0.3}× 10^{34} erg and compare our detections with G star superflares detected in the Kepler survey. We find our main flare to be one of the largest amplitude superflares detected from a bright G star. With energies more than 100 times greater than the Carrington event, our flare detections demonstrate the role that ground-based instruments such as NGTS can have in assessing the habitability of Earth-like exoplanets, particularly in the era of PLATO.

Massive Young Star and its Cradle

NASA Image and Video Library

2010-07-14

This star-forming region, captured by NASA Spitzer Space Telescope, is dominated by the bright, young star IRAS 13481-6124; it is the first massive baby star for which astronomers could obtain a detailed look at the dusty disk closely encircling it.

Is there a relationship between AGN and star formation in IR-bright AGNs?

NASA Astrophysics Data System (ADS)

Dai, Y. Sophia; Wilkes, Belinda J.; Bergeron, Jacqueline; Kuraszkiewicz, Joanna; Omont, Alain; Atanas, Adam; Teplitz, Harry I.

2018-05-01

We report the relationship between the luminosities of active galactic nuclei (AGNs) and the rates of star formation (SF) for a sample of 323 far-infrared (FIR)-detected AGNs. This sample has a redshift range of 0.2 star formation rate (SFR) estimator. We also conclude that monochromatic luminosities at 60 and 100 μ m are also good SFR indicators with negligible AGN contributions, and are less sensitive than integrated infrared luminosities to the shape of the AGN SED, which is uncertain at λ >100 μm. Significant bivariate LX-LIR correlations are found, which remain significant in the combined sample when using residual partial correlation analysis to account for the inherent redshift dependence. No redshift or mass dependence is found for the ratio between SFR and black hole accretion rate (BHAR), which has a mean and scatter of log (SFR/BHAR) =3.1 ± 0.5, agreeing with the local mass ratio between supermassive black hole and host galaxies. The large scatter in this ratio and the strong AGN-SF correlation found in these IR-bright AGNs are consistent with the scenario of an AGN-SF dependence on a common gas supply, regardless of the evolutionary model.

Star from the Lizard Constellation Photobombs Hubble Observation

NASA Image and Video Library

2017-12-08

In space, being outshone is an occupational hazard. This NASA/ESA Hubble Space Telescope image captures a galaxy named NGC 7250. Despite being remarkable in its own right — it has bright bursts of star formation and recorded supernova explosions— it blends into the background somewhat thanks to the gloriously bright star hogging the limelight next to it. The bright object seen in this Hubble image is a single and little-studied star named TYC 3203-450-1, located in the constellation of Lacerta (The Lizard). The star is much closer than the much more distant galaxy. Only this way can a normal star outshine an entire galaxy, consisting of billions of stars. Astronomers studying distant objects call these stars “foreground stars” and they are often not very happy about them, as their bright light is contaminating the faint light from the more distant and interesting objects they actually want to study. In this case, TYC 3203-450-1 is million times closer than NGC 7250, which lies more than 45 million light-years away from us. If the star were the same distance from us as NGC 7250, it would hardly be visible in this image. Credit: ESA/Hubble & NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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.

VizieR Online Data Catalog: FIR data of IR-bright dust-obscured galaxies (DOGs) (Toba+, 2017)

NASA Astrophysics Data System (ADS)

Toba, Y.; Nagao, T.; Wang, W.-H.; Matsuhara, H.; Akiyama, M.; Goto, T.; Koyama, Y.; Ohyama, Y.; Yamamura, I.

2017-11-01

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, (i-[22])AB>7.0. Combining an IR-bright DOG sample with the flux at 22μm>3.8mJy discovered by Toba & Nagao (2016ApJ...820...46T) with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts (0.07star formation rate (SFR), and stellar mass based on the spectral energy distribution fitting. We found that (1) the WISE 22μm luminosity at the observed frame is a good indicator of IR luminosity for IR-bright DOGs and (2) the contribution of the active galactic nucleus to IR luminosity increases with IR luminosity. By comparing the stellar mass and SFR relation for our DOG sample and the literature, we found that most of the IR-bright DOGs lie significantly above the main sequence of star-forming galaxies at similar redshift, indicating that the majority of IRAS- or AKARI-detected IR-bright DOGs are starburst galaxies. (1 data file).

An Ultraviolet/Optical Atlas of Bright Galaxies

NASA Astrophysics Data System (ADS)

Marcum, Pamela M.; O'Connell, Robert W.; Fanelli, Michael N.; Cornett, Robert H.; Waller, William H.; Bohlin, Ralph C.; Neff, Susan G.; Roberts, Morton S.; Smith, Andrew M.; Cheng, K.-P.; Collins, Nicholas R.; Hennessy, Gregory S.; Hill, Jesse K.; Hill, Robert S.; Hintzen, Paul; Landsman, Wayne B.; Ohl, Raymond G.; Parise, Ronald A.; Smith, Eric P.; Freedman, Wendy L.; Kuchinski, Leslie E.; Madore, Barry; Angione, Ronald; Palma, Christopher; Talbert, Freddie; Stecher, Theodore P.

2001-02-01

We present wide-field imagery and photometry of 43 selected nearby galaxies of all morphological types at ultraviolet and optical wavelengths. The ultraviolet (UV) images, in two broad bands at 1500 and 2500 Å, were obtained using the Ultraviolet Imaging Telescope (UIT) during the Astro-1 Spacelab mission. The UV images have ~3" resolution, and the comparison sets of ground-based CCD images (in one or more of B, V, R, and Hα) have pixel scales and fields of view closely matching the UV frames. The atlas consists of multiband images and plots of UV/optical surface brightness and color profiles. Other associated parameters, such as integrated photometry and half-light radii, are tabulated. In an appendix, we discuss the sensitivity of different wavebands to a galaxy's star formation history in the form of ``history weighting functions'' and emphasize the importance of UV observations as probes of evolution during the past 10-1000 Myr. We find that UV galaxy morphologies are usually significantly different from visible band morphologies as a consequence of spatially inhomogeneous stellar populations. Differences are quite pronounced for systems in the middle range of Hubble types, Sa through Sc, but less so for ellipticals or late-type disks. Normal ellipticals and large spiral bulges are fainter and more compact in the UV. However, they typically exhibit smooth UV profiles with far-UV/optical color gradients which are larger than any at optical/IR wavelengths. The far-UV light in these cases is probably produced by extreme horizontal branch stars and their descendants in the dominant, low-mass, metal-rich population. The cool stars in the large bulges of Sa and Sb spirals fade in the UV while hot OB stars in their disks brighten, such that their Hubble classifications become significantly later. In the far-UV, early-type spirals often appear as peculiar, ringlike systems. In some spiral disks, UV-bright structures closely outline the spiral pattern; in others, the

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

Structural analysis of star-forming blue early-type galaxies. Merger-driven star formation in elliptical galaxies

NASA Astrophysics Data System (ADS)

George, Koshy

2017-02-01

Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L⋆ elliptical galaxies in the local Universe. Aims: We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods: We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results: We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio >0.5 and surface brightness profiles fitted by Sérsic profiles with index (n) mostly >2. Twenty-three galaxies are found to have n< 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions: The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.

Chemical Composition of Two Bright, Extremely Metal-poor Stars from the SDSS MARVELS Pre-survey

NASA Astrophysics Data System (ADS)

Bandyopadhyay, Avrajit; Sivarani, Thirupathi; Susmitha, Antony; Beers, Timothy C.; Giridhar, Sunetra; Surya, Arun; Masseron, Thomas

2018-06-01

SDSS J082625.70+612515.10 (V = 11.4 [Fe/H] = ‑3.1) and SDSS J134144.60+474128.90 (V = 12.4 [Fe/H] = ‑3.2) were observed with the SDSS 2.5m telescope as part of the SDSS MARVELS spectroscopic pre-survey and identified as extremely metal-poor (EMP; [Fe/H] < ‑3.0) stars during the high-resolution follow-up using the Hanle Echelle Spectrograph (HESP) on the 2.0-m Himalayan Chandra Telescope. In this paper, the first science results using HESP, we present a detailed analysis of their chemical abundances. Both stars exhibit under-abundances in their neutron capture elements, while one of them (SDSS J134144.60+474128.90) is clearly enhanced in carbon. Lithium was also detected in this star at a level of about A(Li) = 1.95. The spectra were obtained over a span of 6–24 months, and indicate that both stars could be members of binary systems. We compare the elemental abundances derived for these two stars along with other carbon-enhanced metal-poor (CEMP) and EMP stars, in order to understand the nature of their parent supernovae. We find that CEMP-no stars and EMP-dwarfs show a very similar trend in their lithium abundances at various metallicities. We also find indications of CEMP-no stars having larger abundances of Cr and Co at given metallicities compared to EMP stars.

Ground-based detection of G star superflares with NGTS

NASA Astrophysics Data System (ADS)

Jackman, James A. G.; Wheatley, Peter J.; Pugh, Chloe E.; Gänsicke, Boris T.; Gillen, Edward; Broomhall, Anne-Marie; Armstrong, David J.; Burleigh, Matthew R.; Chaushev, Alexander; Eigmüller, Philipp; Erikson, Anders; Goad, Michael R.; Grange, Andrew; Günther, Maximilian N.; Jenkins, James S.; McCormac, James; Raynard, Liam; Thompson, Andrew P. G.; Udry, Stéphane; Walker, Simon; Watson, Christopher A.; West, Richard G.

2018-04-01

We present high cadence detections of two superflares from a bright G8 star (V = 11.56) with the Next Generation Transit Survey (NGTS). We improve upon previous superflare detections by resolving the flare rise and peak, allowing us to fit a solar flare inspired model without the need for arbitrary break points between rise and decay. Our data also enables us to identify substructure in the flares. From changing starspot modulation in the NGTS data we detect a stellar rotation period of 59 hours, along with evidence for differential rotation. We combine this rotation period with the observed ROSAT X-ray flux to determine that the star's X-ray activity is saturated. We calculate the flare bolometric energies as 5.4^{+0.8}_{-0.7}× 10^{34}and 2.6^{+0.4}_{-0.3}× 10^{34}erg and compare our detections with G star superflares detected in the Kepler survey. We find our main flare to be one of the largest amplitude superflares detected from a bright G star. With energies more than 100 times greater than the Carrington event, our flare detections demonstrate the role that ground-based instruments such as NGTS can have in assessing the habitability of Earth-like exoplanets, particularly in the era of PLATO.

ACTIVITY-BRIGHTNESS CORRELATIONS FOR THE SUN AND SUN-LIKE STARS

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

Preminger, D. G.; Chapman, G. A.; Cookson, A. M.

2011-10-01

We analyze the effect of solar features on the variability of the solar irradiance in three different spectral ranges. Our study is based on two solar-cycles' worth of full-disk photometric images from the San Fernando Observatory, obtained with red, blue, and Ca II K-line filters. For each image we measure the photometric sum, {Sigma}, which is the relative contribution of solar features to the disk-integrated intensity of the image. The photometric sums in the red and blue continuum, {Sigma}{sub r} and {Sigma}{sub b}, exhibit similar temporal patterns: they are negatively correlated with solar activity, with strong short-term variability, and weakmore » solar-cycle variability. However, the Ca II K-line photometric sum, {Sigma}{sub K}, is positively correlated with solar activity and has strong variations on solar-cycle timescales. We show that we can model the variability of the Sun's bolometric flux as a linear combination of {Sigma}{sub r} and {Sigma}{sub K}. We infer that, over solar-cycle timescales, the variability of the Sun's bolometric irradiance is directly correlated with spectral line variability, but inversely correlated with continuum variability. Our blue and red continuum filters are quite similar to the Stroemgren b and y filters used to measure stellar photometric variability. We conclude that active stars whose visible continuum brightness varies inversely with activity, as measured by the Ca HK index, are displaying a pattern that is similar to that of the Sun, i.e., radiative variability in the visible continuum that is spot-dominated.« less

A BRIGHT RING OF STAR BIRTH AROUND A GALAXY'S CORE

NASA Technical Reports Server (NTRS)

2002-01-01

n image from NASA's Hubble Space Telescope reveals clusters of infant stars that formed in a ring around the core of the barred-spiral galaxy NGC 4314. This stellar nursery, whose inhabitants were created within the past 5 million years, is the only place in the entire galaxy where new stars are being born. The Hubble image is being presented today (June 11) at the American Astronomical Society meeting in San Diego, Calif. This close-up view by Hubble also shows other interesting details in the galaxy's core: dust lanes, a smaller bar of stars, dust and gas embedded in the stellar ring, and an extra pair of spiral arms packed with young stars. These details make the center resemble a miniature version of a spiral galaxy. While it is not unusual to have dust lanes and rings of gas in the centers of galaxies, it is uncommon to have spiral arms full of young stars in the cores. NGC 4314 is one of the nearest (only 40 million light-years away in the constellation Coma Berenices) examples of a galaxy with a ring of infant stars close to the core. This stellar ring - whose radius is 1,000 light-years - is a great laboratory to study star formation in galaxies. The left-hand image, taken in February 1996 by the 30-inch telescope Prime Focus Camera at the McDonald Observatory in Texas, shows the entire galaxy, including the bar of stars bisecting the core and the outer spiral arms, which begin near the ends of this bar. The box around the galaxy's core pinpoints the focus of the Hubble image. The right-hand image shows Hubble's close-up view of the galaxy's core, taken in December 1995 by the Wide Field and Planetary Camera 2. The bluish-purple clumps that form the ring are the clusters of infant stars. Two dark, wispy lanes of dust and a pair of blue spiral arms are just outside the star-forming ring. The lanes of dust are being shepherded into the ring by the longer, primary stellar bar seen in the ground-based (left-hand) image. The gas is trapped inside the ring

Spectrophotometry of Symbiotic Stars

NASA Astrophysics Data System (ADS)

Boyd, David

2017-06-01

Symbiotic stars are fascinating objects - complex binary systems comprising a cool red giant star and a small hot object, often a white dwarf, both embedded in a nebula formed by a wind from the giant star. UV radiation from the hot star ionises the nebula producing a range of emission lines. These objects have composite spectra with contributions from both stars plus the nebula and these spectra can change on many timescales. Being moderately bright, they lend themselves well to amateur spectroscopy. This paper describes the symbiotic star phenomenon, shows how spectrophotometry can be used to extract astrophysically useful information about the nature of these systems, and gives results for three symbiotic stars based on the author's observations.

Homogeneous spectroscopic parameters for bright planet host stars from the northern hemisphere . The impact on stellar and planetary mass

NASA Astrophysics Data System (ADS)

Sousa, S. G.; Santos, N. C.; Mortier, A.; Tsantaki, M.; Adibekyan, V.; Delgado Mena, E.; Israelian, G.; Rojas-Ayala, B.; Neves, V.

2015-04-01

Aims: In this work we derive new precise and homogeneous parameters for 37 stars with planets. For this purpose, we analyze high resolution spectra obtained by the NARVAL spectrograph for a sample composed of bright planet host stars in the northern hemisphere. The new parameters are included in the SWEET-Cat online catalogue. Methods: To ensure that the catalogue is homogeneous, we use our standard spectroscopic analysis procedure, ARES+MOOG, to derive effective temperatures, surface gravities, and metallicities. These spectroscopic stellar parameters are then used as input to compute the stellar mass and radius, which are fundamental for the derivation of the planetary mass and radius. Results: We show that the spectroscopic parameters, masses, and radii are generally in good agreement with the values available in online databases of exoplanets. There are some exceptions, especially for the evolved stars. These are analyzed in detail focusing on the effect of the stellar mass on the derived planetary mass. Conclusions: We conclude that the stellar mass estimations for giant stars should be managed with extreme caution when using them to compute the planetary masses. We report examples within this sample where the differences in planetary mass can be as high as 100% in the most extreme cases. Based on observations obtained at the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées and the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France (Run ID L131N11 - OPTICON_2013A_027).

Resonances in the Photoionization Cross Sections of Atomic Nitrogen Shape the Far-ultraviolet Spectrum of the Bright Star in 47 Tucanae

NASA Astrophysics Data System (ADS)

Dixon, William V.; Chayer, Pierre

2013-08-01

The far-ultraviolet spectrum of the Bright Star (B8 III) in 47 Tuc (NGC 104) shows a remarkable pattern: it is well fit by local thermodynamic equilibrium models at wavelengths longer than Lyβ, but at shorter wavelengths it is fainter than the models by a factor of two. A spectrum of this star obtained with the Far Ultraviolet Spectroscopic Explorer shows broad absorption troughs with sharp edges at 995 and 1010 Å and a deep absorption feature at 1072 Å none of which are predicted by the models. We find that these features are caused by resonances in the photoionization cross sections of the first and second excited states of atomic nitrogen (2s 2 2p 3 2 D 0 and 2 P 0). Using cross sections from the Opacity Project, we can reproduce these features, but only if we use the cross sections at their full resolution, rather than the resonance-averaged cross sections usually employed to model stellar atmospheres. These resonances are strongest in stellar atmospheres with enhanced nitrogen and depleted carbon abundances, a pattern typical of post-asymptotic giant branch stars.

A RE-EVALUATION OF THE EVOLVED STARS IN THE GLOBULAR CLUSTER M13

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

Sandquist, Eric L.; Gordon, Mark; Levine, Daniel

We have analyzed photometry from space- and ground-based cameras to identify all bright red giant branch (RGB), horizontal branch (HB), and asymptotic giant branch (AGB) stars within 10' of the center of the globular cluster M13. We identify a modest (7%) population of HB stars redder than the primary peak (including RR Lyrae variables at the blue end of the instability strip) that is somewhat more concentrated to the cluster core than the rest of the evolved stars. We find support for the idea that they are noticeably evolved and in the late stages of depleting helium in their cores.more » This resolves a disagreement between distance moduli derived from the tip of the RGB and from stars in or near the RR Lyrae instability strip. We identified disagreements between HB model sets on whether stars with T{sub eff} {approx}< 10, 000 K (near the 'knee' of the HB in optical CMDs) should evolve redward or blueward, and the differences may depend on the inclusion of diffusion in the stellar interior. The sharp cut at the red end of M13's HB provides strong evidence that stars from the dominant HB group still must be undergoing blue loops, which implies that diffusion is being inhibited. We argue that M13's HB is a somewhat pathological case-the dominant HB population occurs very near the 'knee' in optical CMDs, and evolved stars exclusively appear redward of that peak, leading to the incorrect appearance of a continuation of the unevolved HB. We identify two stars as 'blue hook' star candidates-the faintest stars in optical bands that remain significantly subluminous in the shortest ultraviolet wavelength photometry available. M13 also has a distinct group of stars previously identified with the 'second U jump'. Based on far-UV photometry, we find that these stars have genuinely high temperatures (probably 26,000 K {approx}brightness at lower temperature (T{sub eff} {approx} 22, 000 K) as previously

Identifying the stars on Johann Bayer's Chart of the South Polar Sky

NASA Astrophysics Data System (ADS)

Ridpath, I.

2014-04-01

The first chart of the stars in the region around the south celestial pole was published in 1603 by Johann Bayer (1572-1625) as part of his monumental star atlas called Uranometria. This south polar chart depicted 12 entirely new constellations that had been created only a few years earlier from stars observed during the first Dutch expedition to the East Indies in 1595-97. Bayer's chart plotted 121 stars in the 12 newly invented constellations. Five more stars formed a southern extension of the existing constellation Eridanus, while another twelve stars were left 'unformed', i.e. unattached to any constellation. Whereas Bayer famously applied Greek or Roman letters to the stars in the 48 Ptolemaic constellations, he left the stars in the newly invented constellations unlabelled. This paper attempts to identify the stars plotted on Bayer's chart. It also discusses the source of Bayer's data and the origin of the 12 new southern constellations.

RCW 108: Massive Young Stars Trigger Stellar Birth

NASA Technical Reports Server (NTRS)

2008-01-01

RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars.

This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image.

The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193.

Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas

VizieR Online Data Catalog: Calibrator stars catalog for interferometers (Swihart+, 2017)

NASA Astrophysics Data System (ADS)

Swihart, S. J.; Garcia, E. V.; Stassun, K. G.; van Belle, G.; Mutterspaugh, M. W.; Elias, N.

2017-04-01

In order to obtain accurate stellar angular sizes, each star was fit with a model SED using the fitting routine sedFit, written by A. Boden (van Belle & von Braun, 2009, Cat. J/ApJ/694/1085; van Belle et al. 2016, Cat. J/AJ/152/16). We compiled a list of positions, spectral types and visual magnitudes for ~3000 bright (Vmag<6) stars in the northern hemisphere with declinations -15°<δ<82° using the SIMBAD database (Wenger et al., 2000A&AS..143....9W). We chose a brightness limit (Vmag<6) given that most visible light interferometers can obtain scientifically useful data on bright stars. We also removed any stars which appear in the JMMC bad calibrator list. (4 data files).

The r-process Pattern of a Bright, Highly r-process-enhanced Metal-poor Halo Star at [Fe/H] ∼ ‑2

NASA Astrophysics Data System (ADS)

Sakari, Charli M.; Placco, Vinicius M.; Hansen, Terese; Holmbeck, Erika M.; Beers, Timothy C.; Frebel, Anna; Roederer, Ian U.; Venn, Kim A.; Wallerstein, George; Davis, Christopher Evan; Farrell, Elizabeth M.; Yong, David

2018-02-01

A high-resolution spectroscopic analysis is presented for a new highly r-process-enhanced ([Eu/Fe] = 1.27, [Ba/Eu] = ‑0.65), very metal-poor ([Fe/H] = ‑2.09), retrograde halo star, RAVE J153830.9–180424, discovered as part of the R-Process Alliance survey. At V = 10.86, this is the brightest and most metal-rich r-II star known in the Milky Way halo. Its brightness enables high-S/N detections of a wide variety of chemical species that are mostly created by the r-process, including some infrequently detected lines from elements like Ru, Pd, Ag, Tm, Yb, Lu, Hf, and Th, with upper limits on Pb and U. This is the most complete r-process census in a very metal-poor r-II star. J1538–1804 shows no signs of s-process contamination, based on its low [Ba/Eu] and [Pb/Fe]. As with many other r-process-enhanced stars, J1538–1804's r-process pattern matches that of the Sun for elements between the first, second, and third peaks, and does not exhibit an actinide boost. Cosmo-chronometric age-dating reveals the r-process material to be quite old. This robust main r-process pattern is a necessary constraint for r-process formation scenarios (of particular interest in light of the recent neutron star merger, GW170817), and has important consequences for the origins of r-II stars. Additional r-I and r-II stars will be reported by the R-Process Alliance in the near future.

Demonstrating the Likely Neutron Star Nature of Five M31 Globular Cluster Sources with Swift-NuSTAR Spectroscopy

NASA Technical Reports Server (NTRS)

Maccarone, Thomas J.; Yukita, Mihoko; Hornschemeier, Ann; Lehmer, Bret D.; Antoniou, Vallia; Ptak, Andrew; Wik, Daniel R.; Zezas, Andreas; Boyd, Padi; Kennea, Jamie;

Demonstrating the likely neutron star nature of five M31 globular cluster sources with Swift-NuSTAR spectroscopy

NASA Astrophysics Data System (ADS)

Maccarone, Thomas J.; Yukita, Mihoko; Hornschemeier, Ann; Lehmer, Bret D.; Antoniou, Vallia; Ptak, Andrew; Wik, Daniel R.; Zezas, Andreas; Boyd, Padi; Kennea, Jamie; Page, Kim L.; Eracleous, Mike; Williams, Benjamin F.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Stern, Daniel; Zhang, William W.

2016-06-01

We present the results of a joint Swift-NuSTAR spectroscopy campaign on M31. We focus on the five brightest globular cluster X-ray sources in our fields. Two of these had previously been argued to be black hole candidates on the basis of apparent hard-state spectra at luminosities above those for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (I.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis of simultaneous Swift and NuSTAR spectra which cover a broader range of energies. These new observations reveal spectral curvature above 6-8 keV that would be hard to detect without the broader energy coverage the NuSTAR data provide relative to Chandra and XMM-Newton. We show that the other three sources are also likely to be bright neutron star X-ray binaries, rather than black hole X-ray binaries. We discuss why it should already have been realized that it was unlikely that these objects were black holes on the basis of their being persistent sources, and we re-examine past work which suggested that tidal capture products would be persistently bright X-ray emitters. We discuss how this problem is likely due to neglecting disc winds in older work that predict which systems will be persistent and which will be transient.

AGB stars as tracers to IC 1613 evolution.

NASA Astrophysics Data System (ADS)

Hashemi, S. A.; Javadi, A.; van Loon, J. Th.

We are going to apply AGB stars to find star formation history for IC 1613 galaxy; this a new and simple method that works well for nearby galaxies. IC 1613 is a Local Group dwarf irregular galaxy that is located at distance of 750 kpc, a gas rich and isolated dwarf galaxy that has a low foreground extinction. We use the long period variable stars (LPVs) that represent the very final stage of evolution of stars with low and intermediate mass at the AGB phase and are very luminous and cool so that they emit maximum brightness in near-infrared bands. Thus near-infrared photometry with using stellar evolutionary models help us to convert brightness to birth mass and age and from this drive star formation history of the galaxy. We will use the luminosity distribution of the LPVs to reconstruct the star formation history-a method we have successfully applied in other Local Group galaxies. Our analysis shows that the IC 1613 has had a nearly constant star formation rate, without any dominant star formation episode.

An UXor among FUors: Extinction-related Brightness Variations of the Young Eruptive Star V582 Aur

NASA Astrophysics Data System (ADS)

Ábrahám, P.; Kóspál, Á.; Kun, M.; Fehér, O.; Zsidi, G.; Acosta-Pulido, J. A.; Carnerero, M. I.; García-Álvarez, D.; Moór, A.; Cseh, B.; Hajdu, G.; Hanyecz, O.; Kelemen, J.; Kriskovics, L.; Marton, G.; Mező, Gy.; Molnár, L.; Ordasi, A.; Rodríguez-Coira, G.; Sárneczky, K.; Sódor, Á.; Szakáts, R.; Szegedi-Elek, E.; Szing, A.; Farkas-Takács, A.; Vida, K.; Vinkó, J.

2018-01-01

V582 Aur is an FU Ori-type young eruptive star in outburst since ∼1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04 M ⊙. The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Hα profile. The color variations strongly indicate that both the ∼1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A V = 4.5 to 12.5 mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses.

The Optical Gravitational Lensing Experiment: Red Clump Stars as a Distance Indicator.

PubMed

Udalski

2000-03-01

We present relation of the mean I-band brightness of red clump stars on metallicity. Red clump stars were proposed to be a very attractive standard candle for distance determination. The calibration is based on 284 nearby red giant stars whose high-quality spectra made it possible to determine accurate individual metal abundances. High-quality parallaxes (sigmapi&solm0;pi<10%) and photometry of these very bright stars come from Hipparcos measurements. Metallicity of the sample covers a large range: -0.6 dex<&sqbl0;Fe&solm0;H&sqbr0;<+0.2 dex. We find a weak dependence of the mean I-band brightness on metallicity ( approximately 0.13 mag dex-1). What is more important, the range of metallicity of the Hipparcos sample partially overlaps with metallicity of field giants in the LMC, thus making it possible to determine the distance to the LMC by almost direct comparison of brightness of the local Hipparcos red clump giants with that of LMC stars. Photometry of field red clump giants in nine low-extinction fields of the LMC halo collected during the OGLE II microlensing survey compared with the Hipparcos red clump stars data yields the distance modulus to the LMC: &parl0;m-M&parr0;LMC=18.24+/-0.08 mag.

HAT-P-34b-HAT-P-37b: FOUR TRANSITING PLANETS MORE MASSIVE THAN JUPITER ORBITING MODERATELY BRIGHT STARS

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

Bakos, G. A.; Hartman, J. D.; Csubry, Z.

2012-07-15

We report the discovery of four transiting extrasolar planets (HAT-P-34b-HAT-P-37b) with masses ranging from 1.05 to 3.33 M{sub J} and periods from 1.33 to 5.45 days. These planets orbit relatively bright F and G dwarf stars (from V = 10.16 to V = 13.2). Of particular interest is HAT-P-34b which is moderately massive (3.33 M{sub J}), has a high eccentricity of e = 0.441 {+-} 0.032 at a period of P = 5.452654 {+-} 0.000016 days, and shows hints of an outer component. The other three planets have properties that are typical of hot Jupiters.

Characterizing Spiral Arm and Interarm Star Formation

NASA Astrophysics Data System (ADS)

Kreckel, K.; Blanc, G. A.; Schinnerer, E.; Groves, B.; Adamo, A.; Hughes, A.; Meidt, S.

2016-08-01

Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct Hα maps including detailed corrections for dust extinction and stellar absorption to identify 391 H II regions at 35 pc resolution over 12 kpc2. Using tracers sensitive to the underlying gravitational potential, we associate H II regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical properties (luminosity, size, metallicity, ionization parameter) of H II regions are independent of environment. We calculate the fraction of Hα luminosity due to the background of diffuse ionized gas (DIG) contaminating each H II region, and find the DIG surface brightness to be higher within H II regions than in the surroundings, and slightly higher within arm H II regions. Use of the temperature-sensitive [S II]/Hα line ratio instead of the Hα surface brightness to identify the boundaries of H II regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 109 yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H II regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.

CHARACTERIZING SPIRAL ARM AND INTERARM STAR FORMATION

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

Kreckel, K.; Schinnerer, E.; Meidt, S.

2016-08-20

Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct H α maps including detailed corrections for dust extinction and stellar absorption to identify 391 H ii regions at 35 pc resolution over 12 kpc{sup 2}. Using tracers sensitive to the underlying gravitational potential, we associate H ii regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical propertiesmore » (luminosity, size, metallicity, ionization parameter) of H ii regions are independent of environment. We calculate the fraction of H α luminosity due to the background of diffuse ionized gas (DIG) contaminating each H ii region, and find the DIG surface brightness to be higher within H ii regions than in the surroundings, and slightly higher within arm H ii regions. Use of the temperature-sensitive [S ii]/H α line ratio instead of the H α surface brightness to identify the boundaries of H ii regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 10{sup 9} yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H ii regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.« less

A bright-rimmed cloud sculpted by the H ii region Sh2-48

NASA Astrophysics Data System (ADS)

Ortega, M. E.; Paron, S.; Giacani, E.; Rubio, M.; Dubner, G.

2013-08-01

Aims: We characterize a bright-rimmed cloud embedded in the H ii region Sh2-48 while searching for evidence of triggered star formation. Methods: We carried out observations towards a region of 2' × 2' centered at RA = 18h22m11.39s, Dec = -14°35'24.81''(J2000) using the Atacama Submillimeter Telescope Experiment (ASTE; Chile) in the 12CO J = 3-2, 13CO J = 3-2, HCO+J = 4-3, and CS J = 7-6 lines with an angular resolution of about 22''. We also present radio continuum observations at 5 GHz carried out with the Jansky Very Large Array (JVLA; EEUU) interferometer with a synthetized beam of 7'' × 5''. The molecular transitions were used to study the distribution and kinematics of the molecular gas of the bright-rimmed cloud. The radio continuum data was used to characterize the ionized gas located on the illuminated border of this molecular condensation. Combining these observations with infrared public data allowed us to build up a comprehensive picture of the current state of star formation within this cloud. Results: The analysis of our molecular observations reveals a relatively dense clump with n(H2) ~ 3 × 103cm-3, located in projection onto the interior of the H ii region Sh2-48. The emission distribution of the four observed molecular transitions has, at VLSR ~ 38 km s-1, morphological anticorrelation with the bright-rimmed cloud as seen in the optical emission. From the new radio continuum observations, we identify a thin layer of ionized gas located on the border of the clump that is facing the ionizing star. The ionized gas has an electron density of about 73 cm-3, which is a factor three higher than the typical critical density (nc ~ 25 cm-3), above which an ionized boundary layer can be formed and maintained. This supports the hypothesis that the clump is being photoionized by the nearby O9.5V star, BD-14 5014. From the evaluation of the pressure balance between the ionized and molecular gas, we conclude that the clump would be in a prepressure balance

Identifying New Members of Nearby Moving Groups

NASA Astrophysics Data System (ADS)

Holmbeck, Erika; Vican, Laura

2014-06-01

Our group has assembled a sample of 14,000 stars of spectral types B9-M9 with measured UVW Galactic space velocities and lying within 125 pc of Earth. We have identified candidate members of three nearby young (less than 100 Myr) moving groups. For stars of spectral types G5 and later, we have used the Kast spectrometer on the Shane 3m telescope at Lick Observatory to measure lithium abundance in order to determine stellar ages. With the data we have obtained from this run, we will be able to establish whether our candidates are bona fide members of the moving groups in question. I will be presenting the preliminary results from this survey, including spectra of the ~50 stars observed thus far. These nearby young stars will make excellent targets for direct imaging followup surveys, since any giant planets around young stars will still be warm, and will therefore be bright enough to detect with instruments like GPI.

Polarization due to rotational distortion in the bright star Regulus

NASA Astrophysics Data System (ADS)

Cotton, Daniel V.; Bailey, Jeremy; Howarth, Ian D.; Bott, Kimberly; Kedziora-Chudczer, Lucyna; Lucas, P. W.; Hough, J. H.

2017-10-01

Polarization in stars was first predicted by Chandrasekhar1, who calculated a substantial linear polarization at the stellar limb for a pure electron-scattering atmosphere. This polarization will average to zero when integrated over a spherical star but could be detected if the symmetry was broken, for example, by the eclipse of a binary companion. Nearly 50 years ago, Harrington and Collins2 modelled another way of breaking the symmetry and producing net polarization—the distortion of a rapidly rotating hot star. Here we report the first detection of this effect. Observations of the linear polarization of Regulus, with two different high-precision polarimeters, range from +42 ppm at a wavelength of 741 nm to -22 ppm at 395 nm. The reversal from red to blue is a distinctive feature of rotation-induced polarization. Using a new set of models for the polarization of rapidly rotating stars, we find that Regulus is rotating at 96.5-0.8+0.6% of its critical angular velocity for break-up, and has an inclination greater than 76.5°. The rotation axis of the star is at a position angle of 79.5 ± 0.7°. The conclusions are independent of, but in good agreement with, the results of previously published interferometric observations of Regulus3. The accurate measurement of rotation in early-type stars is important for understanding their stellar environments4 and the course of their evolution5.

The Potential of Multicolor Photometry for Pulsating Subdwarf B Stars

NASA Astrophysics Data System (ADS)

Randall, S. K.; Fontaine, G.; Brassard, P.; Bergeron, P.

2005-12-01

We investigate the potential of multicolor photometry for partial mode identification in both long- and short-period variable subdwarf B stars. The technique presented is based on the fact that the frequency dependence of an oscillation's amplitude and phase bears the signature of the mode's degree index l, among other things. Unknown contributing factors can be eliminated through the evaluation of the amplitude ratios and phase differences arising from the brightness variation in different wavebands, theoretically enabling the inference of the degree index from observations in two or more bandpasses. Employing a designated model atmosphere code, we calculate the brightness variation expected across the visible disk during a pulsation cycle in terms of temperature, radius, and surface gravity perturbations to the emergent flux for representative EC 14026 and PG 1716 star models. Nonadiabatic effects are considered in detail and found to be significant from nonadiabatic pulsation calculations applied to our state-of-the-art models of subdwarf B stars. Our results indicate that the brightness variations observed in subdwarf B stars are caused primarily by changes in temperature and radius, with surface gravity perturbations playing a small role. For PG 1716 stars, temperature effects dominate in the limit of long periods with the result that the oscillatory amplitudes and phases lose their period dependence and nonadiabatic effects become unimportant. Outside this regime, however, their values are strongly influenced by both factors. We find that the phase shifts between brightness variations in different wavebands are generally small but may lie above the experimental detection threshold in certain cases. The prospect of mode discrimination seems much more promising on the basis of the corresponding amplitude ratios. While in EC 14026 stars the amplitude ratios predicted are very similar for modes with l=0, 1, or 2, they are well separated from those of modes with l

STELLAR POPULATIONS AND THE STAR FORMATION HISTORIES OF LSB GALAXIES. V. WFC3 COLOR–MAGNITUDE DIAGRAMS

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

Schombert, James; McGaugh, Stacy, E-mail: jschombe@uoregon.edu, E-mail: stacy.mcgaugh@case.edu

2015-09-15

We present WFC3 observations of three low surface brightness (LSB) galaxies from the Schombert et al. LSB catalog that are within 11 Mpc of the Milky Way. Deep imaging at F336W, F555W, and F814W allow the construction of the V − I color–magnitude diagrams (CMD) to M{sub I} = −2. Overall 1869, 465, and 501 stellar sources are identified in the three LSB galaxies F415-3, F608-1, and F750-V1, respectively. The spatial distribution of young blue stars matches the Hα maps from ground-based imaging, indicating that star formation in LSB galaxies follows the same style as in other irregular galaxies. Severalmore » star complexes are identified, matching regions of higher surface brightness as seen from ground-based imaging. The CMD for each LSB galaxy has a similar morphology to Local Volume (LV) dwarf galaxies (i.e., a blue main sequence, blue and red He burning branches, and asymptotic giant branch (AGB) stars). The LSB CMD’s distinguish themselves from nearby dwarf CMD’s by having a higher proportion of blue main sequence stars and fewer AGB stars than expected from their mean metallicities. Current [Fe/H] values below −0.6 are deduced from the position of the red helium-burning branch (rHeB) stars in the V − I diagram. The distribution of stars on the blue helium-burning branch (bHeB) and rHeB from the U − V and V − I CMD indicate a history of constant star formation for the last 100 Myr.« less

Far-infrared Properties of Infrared-bright Dust-obscured Galaxies Selected with IRAS and AKARI Far-infrared All-sky Survey

NASA Astrophysics Data System (ADS)

Toba, Yoshiki; Nagao, Tohru; Wang, Wei-Hao; Matsuhara, Hideo; Akiyama, Masayuki; Goto, Tomotsugu; Koyama, Yusei; Ohyama, Youich; Yamamura, Issei

2017-05-01

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, {(I-[22])}{AB}> 7.0. Combining an IR-bright DOG sample with the flux at 22 μm > 3.8 mJy discovered by Toba & Nagao with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts (0.07< z< 1.0) that were obtained from the literature, we estimated their IR luminosity, star formation rate (SFR), and stellar mass based on the spectral energy distribution fitting. We found that (1) the WISE 22 μm luminosity at the observed frame is a good indicator of IR luminosity for IR-bright DOGs and (2) the contribution of the active galactic nucleus to IR luminosity increases with IR luminosity. By comparing the stellar mass and SFR relation for our DOG sample and the literature, we found that most of the IR-bright DOGs lie significantly above the main sequence of star-forming galaxies at similar redshift, indicating that the majority of IRAS- or AKARI-detected IR-bright DOGs are starburst galaxies.

Star formation in infrared bright and infrared faint starburst interacting galaxies

NASA Technical Reports Server (NTRS)

Lamb, Susan A.; Bushouse, Howard A.; Towns, John W.

1990-01-01

Short wavelength IUE spectra of Arp 248b and UGC 8315N are combined with optical spectra and interpreted using a combination of spectrum synthesis and spectral diagnostics to place constraints on the massive star populations of the central regions of these galaxies and to deduce information about the star formation histories in the last 10(exp 8) years. The authors find that both galaxies have substantial fractions of their optical light coming from massive stars and that Arp 248b may be dominated in the UV by WR stars. The UV spectra are dominated by radiation from evolved massive stars and the authors place and age on the burst in Arp 248b of a few tens of millions of years.

'Peony Nebula' Star Settles for Silver Medal

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] [figure removed for brevity, see original site] Poster Version Movie

If our galaxy, the Milky Way, were to host its own version of the Olympics, the title for the brightest known star would go to a massive star called Eta Carina. However, a new runner-up now the second-brightest star in our galaxy has been discovered in the galaxy's dusty and frenzied interior. This image from NASA's Spitzer Space Telescope shows the new silver medalist, circled in the inset above, in the central region of our Milky Way.

Dubbed the 'Peony nebula' star, this blazing ball of gas shines with the equivalent light of 3.2 million suns. The reigning champ, Eta Carina, produces the equivalent of 4.7 million suns worth of light though astronomers say these estimates are uncertain, and it's possible that the Peony nebula star could be even brighter than Eta Carina.

If the Peony star is so bright, why doesn't it stand out more in this view? The answer is dust. This star is located in a very dusty region jam packed with stars. In fact, there could be other super bright stars still hidden deep in the stellar crowd. Spitzer's infrared eyes allowed it to pierce the dust and assess the Peony nebula star's true brightness. Likewise, infrared data from the European Southern Observatory's New Technology Telescope in Chile were integral in calculating the Peony nebula star's luminosity.

The Peony nebula, which surrounds the Peony nebular star, is the reddish cloud of dust in and around the white circle.

The movie begins by showing a stretch of the dusty and frenzied central region of our Milky Way galaxy. It then zooms in to reveal the 'Peony nebula' star the new second-brightest star in the Milky Way, discovered in part by NASA's Spitzer Space Telescope.

This is a three-color composite showing infrared observations from two Spitzer instruments. Blue represents 3.6-micron light and green shows light of 8 microns, both

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.

MOST detects corotating bright spots on the mid-O-type giant ξ Persei

NASA Astrophysics Data System (ADS)

Ramiaramanantsoa, Tahina; Moffat, Anthony F. J.; Chené, André-Nicolas; Richardson, Noel D.; Henrichs, Huib F.; Desforges, Sébastien; Antoci, Victoria; Rowe, Jason F.; Matthews, Jaymie M.; Kuschnig, Rainer; Weiss, Werner W.; Sasselov, Dimitar; Rucinski, Slavek M.; Guenther, David B.

2014-06-01

We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broad-band visual photometry of the O7.5III(n)((f)) star ξ Persei in 2011 November. This star is well known from previous work to show prominent DACs (discrete absorption components) on time-scales of about 2 d from UV spectroscopy and non-radial pulsation with one (l = 3) p-mode oscillation with a period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails to reveal any periodic light variations above the 0.1 mmag 3σ noise level for periods of a few hours, while several prominent Fourier peaks emerge at the 1 mmag level in the two-day period range. These longer period variations are unlikely due to pulsations, including gravity modes. From our simulations based upon a simple spot model, we deduce that we are seeing the photometric modulation of several corotating bright spots on the stellar surface. In our model, the starting times (random) and lifetimes (up to several rotations) vary from one spot to another yet all spots rotate at the same period of 4.18 d, the best-estimated rotation period of the star. This is the first convincing reported case of corotating bright spots on an O star, with important implications for drivers of the DACs (resulting from corotating interaction regions) with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.

ALMA constraints on star-forming gas in a prototypical z = 1.5 clumpy galaxy: the dearth of CO(5-4) emission from UV-bright clumps

NASA Astrophysics Data System (ADS)

Cibinel, A.; Daddi, E.; Bournaud, F.; Sargent, M. T.; le Floc'h, E.; Magdis, G. E.; Pannella, M.; Rujopakarn, W.; Juneau, S.; Zanella, A.; Duc, P.-A.; Oesch, P. A.; Elbaz, D.; Jagannathan, P.; Nyland, K.; Wang, T.

2017-08-01

We present deep ALMA CO(5-4) observations of a main-sequence, clumpy galaxy at z = 1.5 in the HUDF. Thanks to the ˜0{^''.}5 resolution of the ALMA data, we can link stellar population properties to the CO(5-4) emission on scales of a few kiloparsec. We detect strong CO(5-4) emission from the nuclear region of the galaxy, consistent with the observed LIR-L^' }_CO(5-4) correlation and indicating ongoing nuclear star formation. The CO(5-4) gas component appears more concentrated than other star formation tracers or the dust distribution in this galaxy. We discuss possible implications of this difference in terms of star formation efficiency and mass build-up at the galaxy centre. Conversely, we do not detect any CO(5-4) emission from the UV-bright clumps. This might imply that clumps have a high star formation efficiency (although they do not display unusually high specific star formation rates) and are not entirely gas dominated, with gas fractions no larger than that of their host galaxy (˜50 per cent). Stellar feedback and disc instability torques funnelling gas towards the galaxy centre could contribute to the relatively low gas content. Alternatively, clumps could fall in a more standard star formation efficiency regime if their actual star formation rates are lower than generally assumed. We find that clump star formation rates derived with several different, plausible methods can vary by up to an order of magnitude. The lowest estimates would be compatible with a CO(5-4) non-detection even for main-sequence like values of star formation efficiency and gas content.

Brightness variations of the FUor-type eruptive star V346 Normae

NASA Astrophysics Data System (ADS)

Kóspál, Á.; Ábrahám, P.; Westhues, Ch.; Haas, M.

2017-01-01

Decades after the beginning of its FU Orionis-type outburst, V346 Nor unexpectedly underwent a fading event of ΔK = 4.6 mag around 2010. We obtained near-infrared observations and re-analyzed data from the VISTA/VVV survey to outline the brightness evolution. In our VLT/NaCO images, we discovered a halo of scattered light around V346 Nor with a size of about 0".04 (30 au). The VISTA data outlined a well-defined minimum in the light curve in late 2010/early 2011, and tentatively revealed a small-amplitude periodic modulation of 58 days. Our latest data points from 2016 demonstrate that the source is still brightening but has not yet reached the 2008 level. We used a simple accretion disk model with varying accretion rate and line-of-sight extinction to reproduce the observed near-infrared magnitudes and colors. We found that the flux changes of V346 Nor before 2008 were caused by a correlated change of extinction and accretion rate, while the minimum around 2010 was mostly due to decreasing accretion. The source reached a highest accretion rate of ≈ 10-4M⊙ yr-1 in 1992. A combination of accretion and extinction changes has been invoked in the literature to interpret the flux variations of certain embedded young eruptive stars. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 71.C-0526(A), 179.B-2002, and 381.C-0241(A).

NuSTAR spectral analysis of two bright Seyfert 1 galaxies: MCG +8-11-11 and NGC 6814

NASA Astrophysics Data System (ADS)

Tortosa, A.; Bianchi, S.; Marinucci, A.; Matt, G.; Middei, R.; Piconcelli, E.; Brenneman, L. W.; Cappi, M.; Dadina, M.; De Rosa, A.; Petrucci, P. O.; Ursini, F.; Walton, D. J.

2018-01-01

We report on the NuSTAR observations of two bright Seyfert 1 galaxies, namely MCG +8-11-11 (100 ks) and NGC 6814 (150 ks). The main goal of these observations was to investigate the Comptonization mechanisms acting in the innermost regions of an active galactic nucleus (AGN) which are believed to be responsible for the UV/X-ray emission. The spectroscopic analysis of the NuSTAR spectra of these two sources revealed that although they had different properties overall (black hole masses, luminosity and Eddington ratios), they had very similar coronal properties. Both presented a power-law spectrum with a high-energy cut-off at ∼150-200 keV, a relativistically broadened Fe K α line and the associated disc reflection component, plus a narrow iron line likely emitted in Compton thin and distant matter. The intrinsic continuum was well described by Comptonization models that show for MCG +8-11-11 a temperature of the coronal plasma of kTe ∼ 60 keV and an extrapolated optical depth τ = 1.8; for NGC 6814, the coronal temperature was kTe ∼ 45 keV with an extrapolated optical depth of τ = 2.5. We compare and discuss these values to some most common Comptonization models that aim at explaining the energy production and stability of coronae in AGNs.

Tracers of Stellar Mass-loss. II. Mid-IR Colors and Surface Brightness Fluctuations

NASA Astrophysics Data System (ADS)

González-Lópezlira, Rosa A.

2018-04-01

I present integrated colors and surface brightness fluctuation magnitudes in the mid-infrared (IR), derived from stellar population synthesis models that include the effects of the dusty envelopes around thermally pulsing asymptotic giant branch (TP-AGB) stars. The models are based on the Bruzual & Charlot CB* isochrones; they are single-burst, range in age from a few Myr to 14 Gyr, and comprise metallicities between Z = 0.0001 and Z = 0.04. I compare these models to mid-IR data of AGB stars and star clusters in the Magellanic Clouds, and study the effects of varying self-consistently the mass-loss rate, the stellar parameters, and the output spectra of the stars plus their dusty envelopes. I find that models with a higher than fiducial mass-loss rate are needed to fit the mid-IR colors of “extreme” single AGB stars in the Large Magellanic Cloud. Surface brightness fluctuation magnitudes are quite sensitive to metallicity for 4.5 μm and longer wavelengths at all stellar population ages, and powerful diagnostics of mass-loss rate in the TP-AGB for intermediate-age populations, between 100 Myr and 2–3 Gyr.

High contrast observations of bright stars with a starshade

NASA Astrophysics Data System (ADS)

Harness, Anthony; Cash, Webster; Warwick, Steve

2017-11-01

Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. In an effort to advance starshade technology through system level demonstrations, the McMath-Pierce Solar Telescope was adapted to enable the suppression of astronomical sources with a starshade. The long baselines achievable with the heliostat provide measurements of starshade performance at a flight-like Fresnel number and resolution, aspects critical to the validation of optical models. The heliostat has provided the opportunity to perform the first astronomical observations with a starshade and has made science accessible in a unique parameter space, high contrast at moderate inner working angles. On-sky images are valuable for developing the experience and tools needed to extract science results from future starshade observations. We report on high contrast observations of nearby stars provided by a starshade. We achieve 5.6 × 10- 7 contrast at 30 arcseconds inner working angle on the star Vega and provide new photometric constraints on background stars near Vega.

Modelling Solar and Stellar Brightness Variabilities

NASA Astrophysics Data System (ADS)

Yeo, K. L.; Shapiro, A. I.; Krivova, N. A.; Solanki, S. K.

2016-04-01

Total and spectral solar irradiance, TSI and SSI, have been measured from space since 1978. This is accompanied by the development of models aimed at replicating the observed variability by relating it to solar surface magnetism. Despite significant progress, there remains persisting controversy over the secular change and the wavelength-dependence of the variation with impact on our understanding of the Sun's influence on the Earth's climate. We highlight the recent progress in TSI and SSI modelling with SATIRE. Brightness variations have also been observed for Sun-like stars. Their analysis can profit from knowledge of the solar case and provide additional constraints for solar modelling. We discuss the recent effort to extend SATIRE to Sun-like stars.

New visual companions of solar-type stars within 25 pc

NASA Astrophysics Data System (ADS)

Chini, R.; Fuhrmann, K.; Barr, A.; Pozo, F.; Westhues, C.; Hodapp, K.

2014-01-01

We report the discovery of faint common-proper-motion companions to the nearby southern solar-type stars HD 43162, HD 67199, HD 114837, HD 114853, HD 129502, HD 165185, HD 197214 and HD 212330 from near-infrared imaging and astrometry. We also confirm the previously identified tertiary components around HD 165401 and HD 188088. Since the majority of these stars were already known as binaries, they ascend now to higher level systems. A particularly interesting case is the G6.5 V BY Dra-type variable HD 43162, which harbours two common-proper-motion companions at distances of 410 and 2740 au. Our limited study shows that the inventory of common-proper-motion companions around nearby bright stars is still not completely known.

Dark Skies, Bright Kids Year 7

NASA Astrophysics Data System (ADS)

Bittle, Lauren E.; Johnson, Kelsey E.; Borish, H. Jacob; Burkhardt, Andrew; Firebaugh, Ariel; Hancock, Danielle; Rochford Hayes, Christian; Linden, Sean; Liss, Sandra; Matthews, Allison; Prager, Brian; Pryal, Matthew; Sokal, Kimberly R.; Troup, Nicholas William; Wenger, Trey

2016-01-01

We present updates from our seventh year of operation including new club content, continued assessments, and our fifth annual Star Party. Dark Skies, Bright Kids (DSBK) is an entirely volunteer-run outreach organization based out of the Department of Astronomy at the University of Virginia. Our core mission is to enhance elementary science education and literacy in Central Virginia through fun, hands-on activities that introduce basic Astronomy concepts. Our primary focus is hosting an 8-10 week after-school astronomy club at underserved elementary and middle schools. Each week, DSBK volunteers take the role of coaches to introduce astronomy-related concepts ranging from the Solar System to galaxies to astrobiology, and to lead students in interactive learning activities. Another hallmark of DSBK is hosting our Annual Central Virginia Star Party, a free event open to the community featuring star-gazing and planetarium shows.

Undercover Stars Among Exoplanet Candidates

NASA Astrophysics Data System (ADS)

2005-03-01

events by monitoring the brightness of a very large number of stars over extended time intervals. During the past years, it has also included a search for periodic, very shallow "dips" in the brightness of stars, caused by the regular transit of small orbiting objects (small stars, brown dwarfs [2] or Jupiter-size planets). The OGLE team has since announced 177 "planetary transit candidates" from their survey of several hundred thousand stars in three southern sky fields, one in the direction of the Galactic Centre, another within the Carina constellation and the third within the Centaurus/Musca constellations. The nature of the transiting object can however only be established by subsequent radial-velocity observations of the parent star. The size of the velocity variations (the amplitude) is directly related to the mass of the companion object and therefore allows discrimination between stars and planets as the cause of the observed brightness "dip". A Bonanza of Low-Mass Stars An international team of astronomers [3] has made use of the 8.2-m VLT Kueyen telescope for this work. Profiting from the multiplex capacity of the FLAMES/UVES facility that permits to obtain high-resolution spectra of up to 8 objects simultaneously, they have looked at 60 OGLE transit candidate stars, measuring their radial velocities with an accuracy of about 50 m/s [4]. This ambitious programme has so far resulted in the discovery of five new transiting exoplanets (see, e.g., ESO PR 11/04 for the announcement of two of those). Most of the other transit candidates identified by OGLE have turned out to be eclipsing binaries, that is, in most cases common, small and low-mass stars passing in front of a solar-like star. This additional wealth of data on small and light stars is a real bonanza for the astronomers. Constraining the Relation Between Mass and Radius Low-mass stars are exceptionally interesting objects, also because the physical conditions in their interiors have much in common with

Spectrophotometry of Symbiotic Stars (Abstract)

NASA Astrophysics Data System (ADS)

Boyd, D.

2017-12-01

(Abstract only) Symbiotic stars are fascinating objects - complex binary systems comprising a cool red giant star and a small hot object, often a white dwarf, both embedded in a nebula formed by a wind from the giant star. UV radiation from the hot star ionizes the nebula, producing a range of emission lines. These objects have composite spectra with contributions from both stars plus the nebula and these spectra can change on many timescales. Being moderately bright, they lend themselves well to amateur spectroscopy. This paper describes the symbiotic star phenomenon, shows how spectrophotometry can be used to extract astrophysically useful information about the nature of these systems, and gives results for three symbiotic stars based on the author's observations.

Hotel Clinic-Based Diarrheal and Respiratory Disease Surveillance in U.S. Service Members Participating in Operation Bright Star in Egypt, 2009

PubMed Central

Sebeny, Peter J.; Nakhla, Isabelle; Moustafa, Manal; Bruton, Jody A.; Cline, Joanne; Hawk, Douglas; El-Mohammady, Hanan; Nada, Rania A.; Ahmed, Salwa F.; Pimentel, Guillermo; Young, Sylvia Y. N.

2012-01-01

We conducted clinic-based, influenza-like illness and diarrheal disease surveillance among U.S. service members participating in Operation Bright Star 2009. Epidemiologic data and samples were collected. Nasopharyngeal swab specimens were tested for viruses, and feces was tested for microbiologic, immunologic, and molecular diagnostics. A survey was used to collect self-reported data. From 1,529 surveys, 41% reported diarrheal disease and 25% reported respiratory illness (incidence rate = 62 of 100 versus 37 of 100 person-months; incidence rate ratio = 1.7, 95% confidence interval = 1.5–1.9). Enterotoxigenic Escherichia coli was identified in 74% (69 of 93) of fecal samples. In the influenza-like illness case series, 17% (9 of 52) were positive for influenza A; all were positive for pandemic (pH1N1) 2009 virus. Rates of decreased work performance reported by patients with diarrhea and influenza-like illness were similar (46% versus 48%; P = 0.8). Diarrheal diseases and respiratory illness remain common among deployed military personnel, with important operational impact. Despite an ongoing influenza pandemic, diarrheal disease incidence was higher than that of respiratory illness. PMID:22855764

Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes

NASA Astrophysics Data System (ADS)

Thilker, David

-driven galaxy evolution using both existing NASA databases and operating instruments, in addition to upcoming space telescopes. While a legacy of our project will be the hierarchical photometric database (disseminated via MAST and NED) which supports extragalactic community science, our own goals from the proposed comprehensive measurements address some vital issues: (i) Currently there is controversy regarding the power-law slope of the empirical star formation law (SFL). Is there constant star formation efficiency above the HI-to-H_2 transition gas surface density (implying ~unity slope, see papers by Bigiel et al. and Leroy et al.), or is the SFL relation a stronger function of gas density with a super-linear form (as observed by Kennicutt et al. 2007)? Liu et al. (2011) have shown that the answer may depend critically on whether or not diffuse emission underlying star-forming substructures is removed. Our analysis will allow firm resolution of this issue, as we will also apply our photometry algorithm to Spitzer imaging for a subset of our sample galaxies, thus providing background-subtracted L(UV) and L(IR) measurements for substructures which can then be compared to existing and forthcoming (ALMA) CO imaging. (ii) We will also verify/calibrate our SED-fit based determination of age, extinction, and mass for UV-bright structures via direct comparison to the ground-truth stemming from resolved stellar populations (e.g. in ANGST galaxies) and also high-resolution HST UV-optical star cluster surveys (further out in the Local Volume). (iii) Finally, we will measure the diffuse UV fraction in a few hundred of the nearest galaxies (accounting for variation tied only to spatial resolution), trying to ascertain the characteristic fraction in galaxies of different Hubble type and dust-to-gas ratio. Systematic local variations in diffuse fraction and color will also be quantified as a function of environment.

Deepest Image of Exploded Star Uncovers Bipolar Jets

NASA Technical Reports Server (NTRS)

2004-01-01

This spectacular Chandra X-Ray Observatory (CXO) image of the supernova remnant Cassiopeia A is the most detailed image ever made of the remains of an exploded star. The one-million-second image shows a bright outer ring (green) 10 light years in diameter that marks the location of a shock wave generated by the supernova explosion. In the upper left corner is a large jet-like structure that protrudes beyond the shock wave, and a counter-jet can be seen on the lower right. The x-ray spectra show that the jets are rich in silicon atoms, and relatively poor in iron atoms. This indicates that the jets formed soon after the initial explosion of the star, otherwise, the jets should have contained large quantities of iron from the star's central regions. The bright blue areas are composed almost purely of iron gas, which was produced in the central, hottest regions of the star and somehow ejected in a direction almost perpendicular to the jets. The bright source at the center of the image is presumed to be a neutron star created during the supernova. Unlike most others, this neutron star is quiet, faint, and so far shows no evidence of pulsed radiation. A working hypothesis is that the explosion that created Cassiopeia A produced high speed jets similar to, but less energetic than, the hyper nova jets thought to produce gamma-ray bursts. During the explosion, the star may have developed an extremely strong magnetic filed that helped to accelerate the jets and later stifled any pulsar wind activity. CXO project management is the responsibility of NASA's Marshall Space Flight Center in Huntsville, Alabama.

ATLASGAL: Chemical evolution of star forming clumps

NASA Astrophysics Data System (ADS)

Figura, Charles C.; Urquhart, James S.; Wyrowski, Friedrich

2017-01-01

Although massive stars are few in number, they impact their host molecular clouds, clusters, and galaxies in profound ways, playing a vital role in regulating star formation in their host galaxy. Understanding the formation of these massive stars is critical to understanding this evolution, but their rapid early development causes them to reach the main sequence while still shrouded in their natal molecular cloud. Many studies have investigated these regions in a targeted manner, but a full understanding necessitates a broader view at all stages of formation across many star forming regions.We have used mid-infrared continuum surveys to guide selection of a statistically large sample of massive dust clumps from the 10,000 such clumps identified in the ATLASGAL Compact Source Catalogue (CSC), ensuring that all stages of the evolutionary process are included. A final sample of 600 fourth-quadrant sources within 1 degree of the Galactic plane were observed with the Mopra telescope with an 8 GHz bandwidth between 85.2 and 93.4 GHz.We present an overview of our results. We have identified over 30 molecular lines, seven of which with detected hyperfine structure, as well as several mm-radio recombination line transitions. Source velocities indicate that these regions trace the Crux-Scutum, Norma, and Carina Sagitarius arms. We have performed an analysis of linewidth and line intensity ratios, correlating these with star formation stages as identified by IR brightness at the 70 and 24 μm bands, and present several molecular pairs whose linewidth and intensity might serve as significant tracers of the evolutionary stage of star formation. We comment on the results of PCA analysis of the measured parameters for the overall population and the star formation stage subgroups with an eye toward characterising early stellar development through molecular line observations.

HUBBLE PROBES THE VIOLENT BIRTH OF STARS IN GALAXY NGC 253 [Left

NASA Technical Reports Server (NTRS)

2002-01-01

An image of the spiral galaxy NGC 253, taken with a ground-based telescope. The galaxy is located about 8 million light-years away in the constellation Sculptor. Credit: Jay Gallagher (University of Wisconsin-Madison), Alan Watson (Lowell Observatory, Flagstaff, AZ), and NASA [Right] This NASA Hubble Space Telescope image of the core of the nearest starburst spiral galaxy, NGC 253, reveals violent star formation within a region 1,000 light-years across. A starburst galaxy has an exceptionally high rate of star birth, first identified by its excess of infrared radiation from warm dust. Hubble's high resolution allows astronomers to quantify complex structures in the starburst core of the galaxy for the first time, including luminous star clusters, dust lanes which trace regions of dense gas and filaments of glowing gas. Hubble identifies several regions of intense star formation, which include a bright, super-compact star cluster. These observations confirm that stars are often born in dense clusters within starbursts, and that dense gas coexists with and obscures the starburst core. This image was taken with Hubble's Wide Field Planetary Camera 2 (in PC mode). Credit: Carnegie Institution of Washington

The local metallicity-surface brightness relationship in galactic disks

NASA Technical Reports Server (NTRS)

Ryder, Stuart D.

1995-01-01

We present the results of a first attempt to employ multiaperture masks to obtain spectrophotometry of H II regions in nearby galaxies. A total of 97 H II regions in six southern spiral galaxies were observed using a combination of multiaperture masks and conventional long-slit spectrophotometry. The oxygen abundances derived from the multiaperture mask observations using the empirical abundance diagnostic R(sub 23) are shown to be consistent with those from long-slit spectra and generally show better reproducibility and object definition. Although the number of objects that can be observed simultaneously with this particular system is still quite limited compared with either imaging spectrophotometry or fiber-fed spectrographs, the spectral resolution offered and high throughput in the blue help make multiaperture spectrophotometry a competitive technique for increasing the sampling of H II regions in both radial distance and luminosity. There is still no clear trend of abundance gradient with either the galaxy's luminosity or its Hubble type, although the extrapolated central abundance does appear to correlate with galaxy luminosity/mass. In order to avoid difficulty in choosing an appropriate normalizing radius, we instead plot the oxygen abundance against the underlying I-band surface brightness at the radial distance of the H II region and confirm the existence of a local metallicity-surface brightness reltaionship within the disks of spiral galaxies. Although the simple closed-boc model of galaxy evolution predicts almost the right form of this relationship, a more realistic multizone model employing expnentially decreasing gas infall provides a more satisfactory fit to the observational data, provided the expected enriched gas return from dying low-mass stars shedding their envelopes at late epochs is properly taken into account. This same model, with a star formation law based upon self-regulating star formation in a three-dimensional disk (Dopita & Ryder

The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003.

PubMed

Price, P A; Fox, D W; Kulkarni, S R; Peterson, B A; Schmidt, B P; Soderberg, A M; Yost, S A; Berger, E; Djorgovski, S G; Frail, D A; Harrison, F A; Sari, R; Blain, A W; Chapman, S C

2003-06-19

Past studies of cosmological gamma-ray bursts (GRBs) have been hampered by their extreme distances, resulting in faint afterglows. A nearby GRB could potentially shed much light on the origin of these events, but GRBs with a redshift z bright optical afterglow emission from the burst of 29 March 2003 (GRB030329; ref. 2). The brightness of the afterglow and the prompt report of its position resulted in extensive follow-up observations at many wavelengths, along with the measurement of the redshift, z = 0.169 (ref. 4). The gamma-ray and afterglow properties of GRB030329 are similar to those of GRBs at cosmological redshifts. Observations have already identified the progenitor as a massive star that exploded as a supernova.

X-ray selected stars in HRC and BHRC catalogues

NASA Astrophysics Data System (ADS)

Mickaelian, A. M.; Paronyan, G. M.

2014-12-01

A joint HRC/BHRC Catalogue has been created based on merging of Hamburg ROSAT Catalogue (HRC) and Byurakan Hamburg ROSAT Catalogue (BHRC). Both have been made by optical identifications of X-ray sources based on low-dispersion spectra of the Hamburg Quasar Survey (HQS) using ROSAT Catalogues. As a result, the largest sample of 8132 (5341+2791) optically identified X-ray sources was created having count rate (CR) of photons ≤ 0.04 ct/s in the area with galactic latitudes |b|≤ 20° and declinations d≤ 0°.There are 4253 AGN, 492 galaxies, 1800 stars and 1587 unknown objects in the sample. All stars have been found in GSC 2.3.2, as well as most of them are in GALEX, USNO-B1.0, 2MASS and WISE catalogues. In addition, 1429 are in SDSS DR9 and 204 have SDSS spectra. For these stars we have carried out spectral classification and along with the bright stars, many new cataclysmic variables (CV), white dwarfs (WD) and late-type stars (K-M and C) have been revealed. For all stars, statistical studies of their multiwavelength properties have been made. An attempt to find a connection between the radiation fluxes in different bands for different types of sources, and identify their characteristics was made as well.

Zeta Ophiuchi -- Runaway Star Plowing through Space Dust

NASA Image and Video Library

2011-01-24

The blue star near the center of this image is Zeta Ophiuchi. Zeta Ophiuchi is actually a very massive, hot, bright blue star plowing its way through a large cloud of interstellar dust and gas in this image from NASA Wide-field Infrared Survey Explorer.

WISE Identified Young Stellar Objects In BRC 38

NASA Astrophysics Data System (ADS)

Gibbs, John; Rebull, L. M.; Laurence, W.; Marshall, R.; Murphy, M.; Orr, L.; Whitworth, C.; Burton, A.; Corris, T.; Goodey, S.; McGinnis, S.; Laurence, C.; Aschman, O.; Kikuchi, R.; Prather, J.; Whitley, L.; Billings, C.; Mader, C.

2014-01-01

Bright rimmed clouds (BRCs) are dense clumps of gas and dust within HII regions at the edges of molecular clouds; while the BRCs themselves are dark, their rims are optically bright from illumination by nearby O or B stars. Many BRCs show evidence of active star formation possibly triggered by the ionizing radiation from the nearby O or B stars. The large molecular cloud IC1396 is home to eleven BRCs thought to be driven by the O6.5V star HD206267. BRC 38 is located in the north of IC1396, at 21:40:42 +58:16:13. The immediate ~5'x5' region around BRC 38 has been extensively studied in many wavelengths from X-rays to infrared (IR), identifying ~100 young stellar objects (YSOs). We used data from the Wide-field Infrared Survey Explorer (WISE) to expand the search for YSOs to a 20 arcminute radius from the center of BRC 38. Starting with approximately 7000 sources identified in the WISE catalog, we used an updated version of the IR color selection scheme developed by Koenig et al. (2012) to identify ~40 objects having IR colors consistent with those of YSOs; some overlapping with the literature YSO candidates. Combining confirmed and candidate YSOs from literature with those we identified by color selection, we find 115 unique objects of interest. For each of these sources, we analyzed (a) the WISE, 2MASS, and Spitzer images to determine if they were point-like sources; (b) their IR colors to determine if they exhibited a clear IR excess; and (c) their spectral energy distributions (SEDs) to determine if they had an SED shape consistent with their identification as YSO candidates. Our work adds several new YSO candidates to the list of YSOs in and near BRC 38 and newly identifies IR excesses for many of the previously identified YSOs in the region. We looked for evidence of triggered star formation in BRC 38, but are limited in our conclusions by small-number statistics. Support is provided for this work by the NASA/IPAC Teacher Archive Research Program (NITARP

New far infrared images of bright, nearby, star-forming regions

NASA Technical Reports Server (NTRS)

Harper, D. AL, Jr.; Cole, David M.; Dowell, C. Darren; Lees, Joanna F.; Lowenstein, Robert F.

1995-01-01

Broadband imaging in the far infrared is a vital tool for understanding how young stars form, evolve, and interact with their environment. As the sensitivity and size of detector arrays has increased, a richer and more detailed picture has emerged of the nearest and brightest regions of active star formation. We present data on M 17, M 42, and S 106 taken recently on the Kuiper Airborne Observatory with the Yerkes Observatory 60-channel far infrared camera, which has pixel sizes of 17 in. at 60 microns, 27 in. at 100 microns, and 45 in. at 160 and 200 microns. In addition to providing a clearer view of the complex central cores of the regions, the images reveal new details of the structure and heating of ionization fronts and photodissociation zones where radiation form luminous stars interacts with adjacent molecular clouds.

IRAS surface brightness maps of reflection nebulae in the Pleiades

NASA Technical Reports Server (NTRS)

Castelaz, Michael W.; Werner, M. W.; Sellgren, K.

1987-01-01

Surface brightness maps at 12, 25, 60, and 100 microns were made of a 2.5 deg x 2.5 deg area of the reflection nebulae in the Pleiades by coadding IRAS scans of this region. Emission is seen surrounding 17 Tau, 20 Tau, 23 Tau, and 25 Tau in all four bands, coextensive with the visible reflection nebulosity, and extending as far as 30 arcminutes from the illuminating stars. The infrared energy distributions of the nebulae peak in the 100 micron band, but up to 40 percent of the total infrared power lies in the 12 and 25 micron bands. The brightness of the 12 and 25 micron emission and the absence of temperature gradients at these wavelengths are inconsistent with the predictions of equilibrium thermal emission models. The emission at these wavelengths appears to be the result of micron nonequilibrium emission from very small grains, or from molecules consisting of 10-100 carbon atoms, which have been excited by ultraviolet radiation from the illuminating stars.

Night Sky Brightness Measurement by the Public through a Mobile Phone App

NASA Astrophysics Data System (ADS)

Kamegai, Kazuhisa; Tsukada, Ken; Inoue, Hiroki

2015-08-01

The darkness of night sky is important naturally for astronomy researchers, and also for the public people. Particularly, it is meaningful for those who begin to have an interest in gazing stars. Some previous studies suggest that light pollution may affect human health and ecosystem in various ways. Furthermore, it causes a lot of waste of electric energy for lighting.In Japan, the night sky brightness had been measured by Ministry of Environment for a few decades. Recently some global efforts have been also conducted. However the number of measured position is limited because the measurement needs some apparatus and takes long time.Here we show a result of quick and easy measurements of night sky brightness by the public people through a mobile phone app. The measurements were conducted in cooperation between some members of the Tenpla project and a weather forecasting company. The app has been developed by the company and has been installed by over 6.5 million people, which allow us to get a large number of data. Our purposes are (1) making map of night sky brightness all over Japan and (2) providing an opportunity to enjoy gazing star for those who are not usually interested in astronomy.As an interactive function of the app, we put a questionnaire of four choices in which we ask users how many stars are visible in a part of the constellation of Orion. When users answer the question, we get the answer and the position where they are. Depending on the answer, we can roughly recognize the sky brightness of the position.We opened the measurements for several nights. As a result, we could get 4000 - 5000 data all over the country per night. The map of each night is a snapshot of sky brightness of the night including effect of the weather. For example we can recognize that the sky is getting darker as a function of distance from the metropolitan area of Tokyo. We will show the detail results in the presentation.

Tracing the stellar component of low surface brightness Milky Way dwarf galaxies to their outskirts. I. Sextans

NASA Astrophysics Data System (ADS)

Cicuéndez, L.; Battaglia, G.; Irwin, M.; Bermejo-Climent, J. R.; McMonigal, B.; Bate, N. F.; Lewis, G. F.; Conn, A. R.; de Boer, T. J. L.; Gallart, C.; Guglielmo, M.; Ibata, R.; McConnachie, A.; Tolstoy, E.; Fernando, N.

2018-01-01

Aims: We present results from deep and very spatially extended CTIO/DECam g and r photometry (reaching out to 2 mag below the oldest main-sequence turn-off and covering 20 deg2) around the Sextans dwarf spheroidal galaxy. We aim to use this dataset to study the structural properties of Sextans overall stellar population and its member stars in different evolutionary phases, as well as to search for possible signs of tidal disturbance from the Milky Way, which would indicate departure from dynamical equilibrium. Methods: We performed the most accurate and quantitative structural analysis to-date of Sextans' stellar components by applying Bayesian Monte Carlo Markov chain methods to the individual stars' positions. Surface density maps are built by statistically decontaminating the sample through a matched filter analysis of the colour-magnitude diagram, and then analysed for departures from axisymmetry. Results: Sextans is found to be significantly less spatially extended and more centrally concentrated than early studies suggested. No statistically significant distortions or signs of tidal disturbances were found down to a surface brightness limit of 31.8 mag/arcsec2 in V-band. We identify an overdensity in the central regions that may correspond to previously reported kinematic substructure(s). In agreement with previous findings, old and metal-poor stars such as Blue Horizontal Branch stars cover a much larger area than stars in other evolutionary phases, and bright Blue Stragglers (BSs) are less spatially extended than faint ones. However, the different spatial distribution of bright and faint BSs appears consistent with the general age and metallicity gradients found in Sextans' stellar component. This is compatible with Sextans BSs having formed by evolution of binaries and not necessarily due to the presence of a central disrupted globular cluster, as suggested in the literature. We provide structural parameters for the various populations analysed and make

The far-ultraviolet emission spectrum of the K2 III star, Arcturus.

NASA Technical Reports Server (NTRS)

Moos, H. W.; Rottman, G. J.

1972-01-01

A moderate-resolution far-ultraviolet spectrum of the K2 IIIp star Arcturus, obtained with a rocket-borne spectrometer, shows chromospheric emission features. Hydrogen L-alpha and O I (1303 A) are clearly identified. The O I (1304 A) stellar surface brightness is as great or greater than that of the sun. Other metal lines, including those of carbon, are weak compared to the O I line.

NuSTAR view of the central region of M31

NASA Astrophysics Data System (ADS)

Stiele, H.; Kong, A. K. H.

2018-04-01

Our neighbouring large spiral galaxy, the Andromeda galaxy (M31 or NGC 224), is an ideal target to study the X-ray source population of a nearby galaxy. NuSTAR observed the central region of M31 in 2015 and allows studying the population of X-ray point sources at energies higher than 10 keV. Based on the source catalogue of the large XMM-Newton survey of M31, we identified counterparts to the XMM-Newton sources in the NuSTAR data. The NuSTAR data only contain sources of a brightness comparable (or even brighter) than the selected sources that have been detected in XMM-Newton data. We investigate hardness ratios, spectra, and long-term light curves of individual sources obtained from NuSTAR data. Based on our spectral studies, we suggest four sources as possible X-ray binary candidates. The long-term light curves of seven sources that have been observed more than once show low (but significant) variability.

MALS–NOT: Identifying Radio-bright Quasars for the MeerKAT Absorption Line Survey

NASA Astrophysics Data System (ADS)

Krogager, J.-K.; Gupta, N.; Noterdaeme, P.; Ranjan, A.; Fynbo, J. P. U.; Srianand, R.; Petitjean, P.; Combes, F.; Mahabal, A.

2018-03-01

We present a preparatory spectroscopic survey to identify radio-bright, high-redshift quasars for the MeerKAT Absorption Line Survey. The candidates have been selected on the basis of a single flux density limit at 1.4 GHz (>200 mJy), together with mid-infrared color criteria from the Wide-field Infrared Survey Explorer. Through spectroscopic observations using the Nordic Optical Telescope, we identify 72 quasars out of 99 candidates targeted. We measure the spectroscopic redshifts based on characteristic, broad emission lines present in the spectra. Of these 72 quasars, 64 and 48 objects are at sufficiently high redshift (z > 0.6 and z > 1.4) to be used for the L-band and UHF-band spectroscopic follow-up with the Square Kilometre Array precursor in South Africa: the MeerKAT.

Near-infrared spectroscopy of candidate red supergiant stars in clusters

NASA Astrophysics Data System (ADS)

Messineo, Maria; Zhu, Qingfeng; Ivanov, Valentin D.; Figer, Donald F.; Davies, Ben; Menten, Karl M.; Kudritzki, Rolf P.; Chen, C.-H. Rosie

2014-11-01

Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims: We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods: We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks< 7 mag) in GLIMPSE and 2MASS images. Results: A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M⊙ to 15 M⊙. Two red supergiants are located at Galactic coordinates (l,b) = (16.°7, -0.°63) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b) = (49.°3, + 0.°72) and at a distance of ~7.0 kpc. Conclusions: Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. Based on observations collected at the European Southern Observatory (ESO Programme 60.A-9700(E), and 089.D-0876), and on observations collected at the UKIRT telescope (programme ID H243NS).MM is currently employed by the MPIfR. Part of this work was performed at RIT (2009), at ESA (2010), and at the MPIfR.Tables 3, 4, and 6 are available in electronic form at http://www.aanda.org

IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS

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

Peters, Thomas; Girichidis, Philipp; Gatto, Andrea

2015-11-10

The halo of the Milky Way contains a hot plasma with a surface brightness in soft X-rays of the order 10{sup −12} erg cm{sup −2} s{sup −1} deg{sup −2}. The origin of this gas is unclear, but so far numerical models of galactic star formation have failed to reproduce such a large surface brightness by several orders of magnitude. In this paper, we analyze simulations of the turbulent, magnetized, multi-phase interstellar medium including thermal feedback by supernova explosions as well as cosmic-ray feedback. We include a time-dependent chemical network, self-shielding by gas and dust, and self-gravity. Pure thermal feedback alonemore » is sufficient to produce the observed surface brightness, although it is very sensitive to the supernova rate. Cosmic rays suppress this sensitivity and reduce the surface brightness because they drive cooler outflows. Self-gravity has by far the largest effect because it accumulates the diffuse gas in the disk in dense clumps and filaments, so that supernovae exploding in voids can eject a large amount of hot gas into the halo. This can boost the surface brightness by several orders of magnitude. Although our simulations do not reach a steady state, all simulations produce surface brightness values of the same order of magnitude as the observations, with the exact value depending sensitively on the simulation parameters. We conclude that star formation feedback alone is sufficient to explain the origin of the hot halo gas, but measurements of the surface brightness alone do not provide useful diagnostics for the study of galactic star formation.« less

ROSAT survey of emission from Be stars

NASA Technical Reports Server (NTRS)

Grady, Carol

1993-01-01

ROSAT pointed observations of bright, classical Be stars have demonstrated that detection of soft x-rays at a level expected for normal B stars of comparable T(sub eff) and luminosity is anti-correlated with the presence of episodes of enhanced mass ejection and formation of a dense, moderately ionized equatorial circumstellar disk. At epochs of lower than average disk column density, x-ray flaring has been detected in 2 Be stars, lambda Eri and pi Aqr.

The critical density for star formation in HII galaxies

NASA Technical Reports Server (NTRS)

Taylor, Christopher L.; Brinks, Elias; Skillman, Evan D.

1993-01-01

The star formation rate (SFR) in galaxies is believed to obey a power law relation with local gas density, first proposed by Schmidt (1959). Kennicutt (1989) has shown that there is a threshold density above which star formation occurs, and for densities at or near the threshold density, the DFR is highly non-linear, leading to bursts of star formation. Skillman (1987) empirically determined this threshold for dwarf galaxies to be approximately 1 x 10(exp 21) cm(exp -2), at a linear resolution of 500pc. During the course of our survey for HI companion clouds to HII galaxies, we obtained high resolution HI observations of five nearby HII galaxies. HII galaxies are low surface brightness, rich in HI, and contain one or a few high surface brightness knots whose optical spectra resemble those of HII regions. These knots are currently experiencing a burst of star formation. After Kennicutt (1989) we determine the critical density for star formation in the galaxies, and compare the predictions with radio and optical data.

HUBBLE SEES A VAST 'CITY' OF STARS

NASA Technical Reports Server (NTRS)

2002-01-01

In these pictures, a 'city' of a million stars glitters like a New York City skyline. The images capture the globular cluster 47 Tucanae, located 15,000 light-years from Earth in the southern constellation Tucana. Using NASA's Hubble Space Telescope, astronomers went hunting in this large city for planetary companions: bloated gaseous planets that snuggle close to their parent stars, completing an orbit in a quick three to five days. To their surprise, they found none. This finding suggests that the cluster's environment is too hostile for breeding planets or that it lacks the necessary elements for making them. The picture at left, taken by a terrestrial telescope, shows most of the cluster, a tightly packed group of middle-aged stars held together by mutual gravitational attraction. The box near the center represents the Hubble telescope's view. The image at right shows the Hubble telescope's close-up look at a swarm of 35,000 stars near the cluster's central region. The stars are tightly packed together: They're much closer together than our Sun and its closest stars. The picture, taken by the Wide Field and Planetary Camera 2, depicts the stars' natural colors and tells scientists about their composition and age. For example, the red stars denote bright red giants nearing the end of their lives; the more common yellow stars are similar to our middle-aged Sun. Most of the stars in the cluster are believed to have formed about 10 billion years ago. The bright, blue stars -- thought to be remnants of stellar collisions and mergers -- provide a few rejuvenated, energetic stars in an otherwise old system. The Hubble picture was taken in July 1999. Credits for Hubble image: NASA and Ron Gilliland (Space Telescope Science Institute) Credits for ground-based image: David Malin, c Anglo-Australian Observatory

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

NASA Technical Reports Server (NTRS)

Shipman, H. L.

1980-01-01

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

CARBON STARS IN THE SATELLITES AND HALO OF M31

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

Hamren, Katherine; Guhathakurta, Puragra; Rockosi, Constance M.

2016-09-01

We spectroscopically identify a sample of carbon stars in the satellites and halo of M31 using moderate-resolution optical spectroscopy from the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo survey. We present the photometric properties of our sample of 41 stars, including their brightness with respect to the tip of the red giant branch (TRGB) and their distributions in various color–color spaces. This analysis reveals a bluer population of carbon stars fainter than the TRGB and a redder population of carbon stars brighter than the TRGB. We then apply principal component analysis to determine the sample’s eigenspectra and eigencoefficients. Correlatingmore » the eigencoefficients with various observable properties reveals the spectral features that trace effective temperature and metallicity. Putting the spectroscopic and photometric information together, we find the carbon stars in the satellites and halo of M31 to be minimally impacted by dust and internal dynamics. We also find that while there is evidence to suggest that the sub-TRGB stars are extrinsic in origin, it is also possible that they are are particularly faint members of the asymptotic giant branch.« less

A catalog of low surface brightness galaxies - List II

NASA Technical Reports Server (NTRS)

Schombert, James M.; Bothun, Gregory D.; Schneider, Stephen E.; Mcgaugh, Stacy S.

1992-01-01

A list of galaxies characterized by low surface brightness (LSB) is presented which facilitates the recognition of galaxies with brightnesses close to that of the sky. A total of 198 objects and 140 objects are listed in the primary and secondary catalogs respectively, and LSB galaxies are examined by means of H I redshift distributions. LSB disk galaxies are shown to have similar sizes and masses as the high-surface-brightness counterparts, and ellipticals and SOs are rarely encountered. Many LSB spirals have stellarlike nuclei, and most of the galaxies in the present catalog are late-type galaxies in the Sc, Sm, and Im classes. The LSB region of observational parameter space is shown to encompass a spectrum of types as full as that of the Hubble sequence. It is suggested that studies of LSB galaxies can provide important data regarding the formation and star-formation history of all galaxies.

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.

Hubble Observes One-of-a-Kind Star Nicknamed ‘Nasty’

NASA Image and Video Library

2015-03-21

Astronomers using NASA’s Hubble Space Telescope have uncovered surprising new clues about a hefty, rapidly aging star whose behavior has never been seen before in our Milky Way galaxy. In fact, the star is so weird that astronomers have nicknamed it “Nasty 1,” a play on its catalog name of NaSt1. The star may represent a brief transitory stage in the evolution of extremely massive stars. First discovered several decades ago, Nasty 1 was identified as a Wolf-Rayet star, a rapidly evolving star that is much more massive than our sun. The star loses its hydrogen-filled outer layers quickly, exposing its super-hot and extremely bright helium-burning core. But Nasty 1 doesn’t look like a typical Wolf-Rayet star. The astronomers using Hubble had expected to see twin lobes of gas flowing from opposite sides of the star, perhaps similar to those emanating from the massive star Eta Carinae, which is a Wolf-Rayet candidate. Instead, Hubble revealed a pancake-shaped disk of gas encircling the star. The vast disk is nearly 2 trillion miles wide, and may have formed from an unseen companion star that snacked on the outer envelope of the newly formed Wolf-Rayet. Based on current estimates, the nebula surrounding the stars is just a few thousand years old, and as close as 3,000 light-years from Earth. Credits: NASA/Hubble

The R-Process Alliance: 2MASS J09544277+5246414, the Most Actinide-enhanced R-II Star Known

NASA Astrophysics Data System (ADS)

Holmbeck, Erika M.; Beers, Timothy C.; Roederer, Ian U.; Placco, Vinicius M.; Hansen, Terese T.; Sakari, Charli M.; Sneden, Christopher; Liu, Chao; Lee, Young Sun; Cowan, John J.; Frebel, Anna

2018-06-01

We report the discovery of a new actinide-boost star, 2MASS J09544277+5246414, originally identified as a very bright (V = 10.1), extremely metal-poor ([Fe/H] = ‑2.99) K giant in the LAMOST survey, and found to be highly r-process-enhanced (r-II; [Eu/Fe] = +1.28]), during the snapshot phase of the R-Process Alliance (RPA). Based on a high signal-to-noise ratio (S/N), high-resolution spectrum obtained with the Harlan J. Smith 2.7 m telescope, this star is the first confirmed actinide-boost star found by RPA efforts. With an enhancement of [Th/Eu] = +0.37, 2MASS J09544277+5246414 is also the most actinide-enhanced r-II star yet discovered, and only the sixth metal-poor star with a measured uranium abundance ([U/Fe] = +1.40). Using the Th/U chronometer, we estimate an age of 13.0 ± 4.7 Gyr for this star. The unambiguous actinide-boost signature of this extremely metal-poor star, combined with additional r-process-enhanced and actinide-boost stars identified by the RPA, will provide strong constraints on the nature and origin of the r-process at early times.

Identification Of (Bright) Carbon-Enhanced Metal-Poor Stars With J-Plus Photometry

NASA Astrophysics Data System (ADS)

Placco, Vinicius

2017-10-01

The chemical composition of our bodies, the Earth, the Sun, and the Universe is complex, and the end result of the formation and evolution of numerous stellar generations that contributed all of the elements heavier than helium. One way to understand the possible pathways that led to such complexity is to determine the chemical abundance patterns of ancient low-metallicity stars in the Halo of our Galaxy. However, it is impossible to observe each of the 100 billion stars in the Milky Way in sufficient detail to assess its chemical composition. Hence, astronomers have developed efficient ways to pre-select the most interesting stars for further high-resolution follow-up, based on the understanding that the colors of stars in specific regions of the optical spectrum are affected in predictable ways by changes in their chemical composition. I will discuss the importance of the J-PLUS photometry in selecting low-metallicity and carbon-enhanced stars, using its 12 magnitudes, which will fully exploit this approach, in a manner superior to all previous such efforts.

A YOUNG ECLIPSING BINARY AND ITS LUMINOUS NEIGHBORS IN THE EMBEDDED STAR CLUSTER Sh 2-252E

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

Lester, Kathryn V.; Gies, Douglas R.; Guo, Zhao, E-mail: lester@chara.gsu.edu, E-mail: gies@chara.gsu.edu, E-mail: guo@chara.gsu.edu

We present a photometric and light curve analysis of an eccentric eclipsing binary in the K2 Campaign 0 field, which resides in Sh 2-252E, a young star cluster embedded in an H ii region. We describe a spectroscopic investigation of the three brightest stars in the crowded aperture to identify which is the binary system. We find that none of these stars are components of the eclipsing binary system, which must be one of the fainter nearby stars. These bright cluster members all have remarkable spectra: Sh 2-252a (EPIC 202062176) is a B0.5 V star with razor sharp absorption lines, Sh 2-252b is amore » Herbig A0 star with disk-like emission lines, and Sh 2-252c is a pre-main-sequence star with very red color.« less

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

A model for the origin of bursty star formation in galaxies

NASA Astrophysics Data System (ADS)

Faucher-Giguère, Claude-André

2018-01-01

We propose a simple analytic model to understand when star formation is time steady versus bursty in galaxies. Recent models explain the observed Kennicutt-Schmidt relation between star formation rate and gas surface densities in galaxies as resulting from a balance between stellar feedback and gravity. We argue that bursty star formation occurs when such an equilibrium cannot be stably sustained, and identify two regimes in which galaxy-scale star formation should be bursty: (i) at high redshift (z ≳ 1) for galaxies of all masses, and (ii) at low masses (depending on gas fraction) for galaxies at any redshift. At high redshift, characteristic galactic dynamical time-scales become too short for supernova feedback to effectively respond to gravitational collapse in galactic discs (an effect recently identified for galactic nuclei), whereas in dwarf galaxies star formation occurs in too few bright star-forming regions to effectively average out. Burstiness is also enhanced at high redshift owing to elevated gas fractions in the early Universe. Our model can thus explain the bursty star formation rates predicted in these regimes by recent high-resolution galaxy formation simulations, as well as the bursty star formation histories observationally inferred in both local dwarf and high-redshift galaxies. In our model, bursty star formation is associated with particularly strong spatiotemporal clustering of supernovae. Such clustering can promote the formation of galactic winds and our model may thus also explain the much higher wind mass loading factors inferred in high-redshift massive galaxies relative to their z ∼ 0 counterparts.

The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

NASA Astrophysics Data System (ADS)

Ertel, S.; Defrère, D.; Hinz, P.; Mennesson, B.; Kennedy, G. M.; Danchi, W. C.; Gelino, C.; Hill, J. M.; Hoffmann, W. F.; Rieke, G.; Shannon, A.; Spalding, E.; Stone, J. M.; Vaz, A.; Weinberger, A. J.; Willems, P.; Absil, O.; Arbo, P.; Bailey, V. P.; Beichman, C.; Bryden, G.; Downey, E. C.; Durney, O.; Esposito, S.; Gaspar, A.; Grenz, P.; Haniff, C. A.; Leisenring, J. M.; Marion, L.; McMahon, T. J.; Millan-Gabet, R.; Montoya, M.; Morzinski, K. M.; Pinna, E.; Power, J.; Puglisi, A.; Roberge, A.; Serabyn, E.; Skemer, A. J.; Stapelfeldt, K.; Su, K. Y. L.; Vaitheeswaran, V.; Wyatt, M. C.

2018-05-01

The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from {60}-21+16% for stars with previously detected cold dust to {8}-3+10% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.

Lost in space: Onboard star identification using CCD star tracker data without an a priori attitude

NASA Technical Reports Server (NTRS)

Ketchum, Eleanor A.; Tolson, Robert H.

1993-01-01

There are many algorithms in use today which determine spacecraft attitude by identifying stars in the field of view of a star tracker. Some methods, which date from the early 1960's, compare the angular separation between observed stars with a small catalog. In the last 10 years, several methods have been developed which speed up the process and reduce the amount of memory needed, a key element to onboard attitude determination. However, each of these methods require some a priori knowledge of the spacecraft attitude. Although the Sun and magnetic field generally provide the necessary coarse attitude information, there are occasions when a spacecraft could get lost when it is not prudent to wait for sunlight. Also, the possibility of efficient attitude determination using only the highly accurate CCD star tracker could lead to fully autonomous spacecraft attitude determination. The need for redundant coarse sensors could thus be eliminated at substantial cost reduction. Some groups have extended their algorithms to implement a computation intense full sky scan. Some require large data bases. Both storage and speed are concerns for autonomous onboard systems. Neural network technology is even being explored by some as a possible solution, but because of the limited number of patterns that can be stored and large overhead, nothing concrete has resulted from these efforts. This paper presents an algorithm which, by descretizing the sky and filtering by visual magnitude of the brightness observed star, speeds up the lost in space star identification process while reducing the amount of necessary onboard computer storage compared to existing techniques.

Dark Skies, Bright Kids Year 6

NASA Astrophysics Data System (ADS)

Liss, Sandra; Troup, Nicholas William; Johnson, Kelsey E.; Barcos-Munoz, Loreto D.; Beaton, Rachael; Bittle, Lauren; Borish, Henry J.; Burkhardt, Andrew; Corby, Joanna; Dean, Janice; Hancock, Danielle; King, Jennie; Prager, Brian; Romero, Charles; Sokal, Kimberly R.; Stierwalt, Sabrina; Wenger, Trey; Zucker, Catherine

2015-01-01

Now entering our sixth year of operation, Dark Skies, Bright Kids (DSBK) is an entirely volunteer-run outreach organization based out of the Department of Astronomy at the University of Virginia. Our core mission is to enhance elementary science education and literacy in central Virginia through fun, hands-on activities that introduce basic Astronomy concepts beyond Virginia's Standards of Learning. Our primary focus is hosting an 8-10 week after-school astronomy club at underserved elementary and middle schools. Each week, DSBK volunteers take the role of coaches to introduce astronomy-related concepts ranging from the Solar System to galaxies to astrobiology, and to lead students in interactive learning activities. Another hallmark of DSBK is hosting our Annual Central Virginia Star Party, a free event open to the community featuring star-gazing and planetarium shows.DSBK has amassed over 15,000 contact hours since 2009 and we continue to broaden our impact. One important step we have taken in the past year is to establish a graduate student led assessment program to identify and implement directed learning goals for DSBK outreach. The collection of student workbooks, observations, and volunteer surveys indicates broad scale success for the program both in terms of student learning and their perception of science. The data also reveal opportunities to improve our organizational and educational practices to maximize student achievement and overall volunteer satisfaction for DSBK's future clubs and outreach endeavors.

The emerging planetary nebula CRL 618 and its unsettled central star(s)

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

Balick, B.; Riera, A.; Raga, A.

We report deep long-slit emission-line spectra, the line flux ratios, and Doppler profile shapes of various bright optical lines. The low-ionization lines (primarily [N I], [O I], [S II], and [N II]) originate in shocked knots, as reported by many previous observers. Dust-scattered lines of higher ionization are seen throughout the lobes but do not peak in the knots. Our analysis of these line profiles and the readily discernible stellar continuum shows that (1) the central star is an active symbiotic (whose spectrum resembles the central stars of highly bipolar and young planetary nebulae such as M2-9 and Hen2-437) whosemore » compact companion shows a WC8-type spectrum, (2) extended nebular lines of [O III] and He I originate in the heavily obscured nuclear H II region, and (3) the Balmer lines observed throughout the lobes are dominated by reflected Hα emission from the symbiotic star. Comparing our line ratios with those observed historically shows that (1) the [O III]/Hβ and He I/Hβ ratios have been steadily rising by large amounts throughout the nebula, (2) the Hα/Hβ ratio is steadily decreasing while Hγ/Hβ remains nearly constant, and (3) the low-ionization line ratios formed in the shocked knots have been in decline in different ways at various locations. We show that the first two of these results might be expected if the symbiotic central star has been active and if its bright Hα line has faded significantly in the past 20 years.« less

Possible Bright Starspots on TRAPPIST-1

NASA Astrophysics Data System (ADS)

Morris, Brett M.; Agol, Eric; Davenport, James R. A.; Hawley, Suzanne L.

2018-04-01

The M8V star TRAPPIST-1 hosts seven roughly Earth-sized planets and is a promising target for exoplanet characterization. Kepler/K2 Campaign 12 observations of TRAPPIST-1 in the optical show an apparent rotational modulation with a 3.3-day period, though that rotational signal is not readily detected in the Spitzer light curve at 4.5 μm. If the rotational modulation is due to starspots, persistent dark spots can be excluded from the lack of photometric variability in the Spitzer light curve. We construct a photometric model for rotational modulation due to photospheric bright spots on TRAPPIST-1 that is consistent with both the Kepler and Spitzer light curves. The maximum-likelihood model with three spots has typical spot sizes of R spot/R ⋆ ≈ 0.004 at temperature T spot ≳ 5300 ± 200 K. We also find that large flares are observed more often when the brightest spot is facing the observer, suggesting a correlation between the position of the bright spots and flare events. In addition, these flares may occur preferentially when the spots are increasing in brightness, which suggests that the 3.3-day periodicity may not be a rotational signal, but rather a characteristic timescale of active regions.

The formation of submillimetre-bright galaxies from gas infall over a billion years.

PubMed

Narayanan, Desika; Turk, Matthew; Feldmann, Robert; Robitaille, Thomas; Hopkins, Philip; Thompson, Robert; Hayward, Christopher; Ball, David; Faucher-Giguère, Claude-André; Kereš, Dušan

2015-09-24

Submillimetre-bright galaxies at high redshift are the most luminous, heavily star-forming galaxies in the Universe and are characterized by prodigious emission in the far-infrared, with a flux of at least five millijanskys at a wavelength of 850 micrometres. They reside in haloes with masses about 10(13) times that of the Sun, have low gas fractions compared to main-sequence disks at a comparable redshift, trace complex environments and are not easily observable at optical wavelengths. Their physical origin remains unclear. Simulations have been able to form galaxies with the requisite luminosities, but have otherwise been unable to simultaneously match the stellar masses, star formation rates, gas fractions and environments. Here we report a cosmological hydrodynamic galaxy formation simulation that is able to form a submillimetre galaxy that simultaneously satisfies the broad range of observed physical constraints. We find that groups of galaxies residing in massive dark matter haloes have increasing rates of star formation that peak at collective rates of about 500-1,000 solar masses per year at redshifts of two to three, by which time the interstellar medium is sufficiently enriched with metals that the region may be observed as a submillimetre-selected system. The intense star formation rates are fuelled in part by the infall of a reservoir gas supply enabled by stellar feedback at earlier times, not through major mergers. With a lifetime of nearly a billion years, our simulations show that the submillimetre-bright phase of high-redshift galaxies is prolonged and associated with significant mass buildup in early-Universe proto-clusters, and that many submillimetre-bright galaxies are composed of numerous unresolved components (for which there is some observational evidence).

Harvard Observing Project monitoring of Boyajian's Star (KIC 8462852)

NASA Astrophysics Data System (ADS)

Schumer, Clea F.; Vanderburg, Andrew; Bieryla, Allyson; Carmichael, Theron; Garrison, Lehman H.; Huang, Jane; Lewis, John; Mayo, Andrew; Alam, Munazza; Gomez, Sebastian; Kamdar, Harshil; Yuan, Sihan; Cordova, Rodrigo

2017-01-01

Between 2009 and 2013, the Kepler spacecraft observed ~200,000 stars, repeatedly measuring their brightness to look for regular dimmings that could indicate the presence of a transiting planet (Borucki et al. 2010). This endeavor led to the discovery of thousands of planets. However, the data pertaining to one star, KIC 8462852, nicknamed “Tabby's Star” or “Boyajian's Star" indicated sporadic dimmings thought to be resulting from massive, evolving, and erratic shapes passing in front of the star (Boyajian et al. 2016, Wright and Sigurdsson 2016). Additional observations have indicated that KIC 8462852 has faded by approximately 20% over the past century (Wright and Sigurdsson 2016). Kepler is now observing other areas of space, and consequently, ground-based efforts have emerged in order to continue tracking the brightness of KIC 8462852. The Harvard Observing Project (HOP) is an observational astronomy initiative that engages undergraduate students and provides graduate students with the opportunity to lead sessions of data collection. During the fall 2016 semester, HOP will be observing KIC 8462852 in BVRI filters using Harvard's 16-inch DFM Clay telescope. We will present a light curve of the star spanning the course of three months.

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.

Star-Formation Histories of MUSCEL Galaxies

NASA Astrophysics Data System (ADS)

Young, Jason; Kuzio de Naray, Rachel; Xuesong Wang, Sharon

2018-01-01

The MUSCEL program (MUltiwavelength observations of the Structure, Chemistry and Evolution of LSB galaxies) uses combined ground-based/space-based data to determine the spatially resolved star-formation histories of low surface brightness (LSB) galaxies. LSB galaxies are paradoxical in that they are gas rich but have low star-formation rates. Here we present our observations and fitting technique, and the derived histories for select MUSCEL galaxies. It is our aim to use these histories in tandem with velocity fields and metallicity profiles to determine the physical mechanism(s) that give these faint galaxies low star-formation rates despite ample gas supplies.

Follow up observationes of extremely metal-poor stars identified from SDSS and LAMOST

NASA Astrophysics Data System (ADS)

Aguado, David; Allende Prieto, Carlos; González Hernández, Jonay I.; Rebolo, Rafael

2017-06-01

The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or very few supernovae. Here we present a program to search for and characterize new ultra metal-poor stars in the Galactic halo. These stars are extremely rare; despite significant efforts, only a handful of stars have been identified with a metallicity [Fe/H]< -5. We select candidates from SDSS and LAMOST. Dozens of them have already been observed with the ISIS spectrograph on the 4.2 m William Herschel Telescope. The most interesting objects have been confirmed with OSIRIS on the 10.4m-GTC and HRS on the 9.2 m HET. Our analysis is highly automated, and based on the FERRE code. We report the discovery of a new carbon-rich ultra metal-poor (CRUMP) dwarf star at [Fe/H]~ -5.8 with an extreme carbon over-abundance [C/Fe]~ +5.0.

Dusty Death of a Massive Star

NASA Image and Video Library

2006-06-06

NASA Spitzer Space Telescope shows the supernova remnant 1E0102.2-7219 sits next to the nebula N76 in a bright, star-forming region of the Small Magellanic Cloud, a satellite galaxy to our Milky Way galaxy.

Dark Skies, Bright Kids Year 8

NASA Astrophysics Data System (ADS)

Bittle, Lauren E.; Wenger, Trey; Johnson, Kelsey E.; Angell, Dylan; Burkhardt, Andrew; Davis, Blair; Firebaugh, Ariel; Hancock, Danielle; Richardson, Whitney; Rochford Hayes, Christian; Linden, Sean; Liss, Sandra; Matthews, Allison; McNair, Shunlante; Prager, Brian; Pryal, Matthew; Troup, Nicholas William

2017-01-01

We present activities from the eighth year of Dark Skies Bright Kids (DSBK), an entirely volunteer-run outreach organization based out of the Department of Astronomy at the University of Virginia. Our core mission is to enhance elementary science education and literacy in Central Virginia through fun, hands-on activities that introduce basic Astronomy concepts. Over the past seven years, our primary focus has been hosting an 8-10 week after-school astronomy club at underserved elementary and middle schools, and over the past several years, we have partnered with local businesses to host our Annual Central Virginia Star Party, a free event open to the community featuring star-gazing and planetarium shows. This past summer we expanded our reach through a new initiative to bring week-long summer day camps to south and southwest Virginia, home to some of the most underserved communities in the commonwealth.

Dwarf Star Erupts in Giant Flare

NASA Technical Reports Server (NTRS)

2005-01-01

This movie taken by NASA'S Galaxy Evolution Explorer shows one of the largest flares, or star eruptions, ever recorded at ultraviolet wavelengths. The star, called GJ 3685A, just happened to be in the Galaxy Evolution Explorer's field of view while the telescope was busy observing galaxies. As the movie demonstrates, the seemingly serene star suddenly exploded once, then even more intensely a second time, pouring out in total about one million times more energy than a typical flare from our Sun. The second blast of light constituted an increase in brightness by a factor of at least 10,000.

Flares are huge explosions of energy stemming from a single location on a star's surface. They are caused by the brief destruction of a star's magnetic fields. Many types of stars experience them, though old, small, rapidly rotating 'red dwarfs' like GJ 3685A tend to flare more frequently and dramatically. These stars, called flare stars, can experience powerful eruptions as often as every few hours. Younger stars, in general, also erupt more often. One of the reasons astronomers study flare stars is to gain a better picture and history of flare events taking place on the Sun.

A preliminary analysis of the GJ 3685A flare shows that the mechanisms underlying stellar eruptions may be more complex than previously believed. Evidence for the two most popular flare theories was found.

Though this movie has been sped up (the actual flare lasted about 20 minutes), time-resolved data exist for each one-hundredth of a second. These observations were taken at 2 p.m. Pacific time, April 24, 2004. In the still image, the time sequence starts in the upper left panel, continues in the upper right, then moves to the lower left and ends in the lower right.

The circular and linear features that appear below and to the right of GJ 3685A during the flare event are detector artifacts caused by the extreme brightness of the flare.

Quasiperiodic oscillations in bright galactic-bulge X-ray sources

NASA Technical Reports Server (NTRS)

Lamb, F. K.; Shibazaki, N.; Alpar, M. A.; Shaham, J.

1985-01-01

Quasiperiodic oscillations with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and Sco X-1. These sources are weakly magnetic neutron stars accreting from disks which the plasma is clumped. The interaction of the magnetosphere with clumps in the inner disk causes oscillations in the X-ray flux with many of the properties observed.

Identifying Massive Runaway Stars by Detecting Infrared Bowshock Nebula: Four OB Stars and a New Massive Early-B Binary System

NASA Astrophysics Data System (ADS)

Sorber, Rebecca L.; Rebecca L. Sorber, Henry A. Kobulnicky, Daniel A. Dale, Matthew S. Povich, William T. Chick, Heather N. Wernke, Julian E. Andrews, Stephan Munari, Grace M. Olivier, Danielle Schurhammer

2016-01-01

Though the main sequence evolution of OB type stars is relatively well known, the mass loss rates for these stars are still highly uncertain. Some OB stars are gravitationally ejected from their birth sites, traveling at speeds of 30 km/s or more which results in a prominent bowshock nebulae. We identified OB bowshock candidates at low Galactic latitudes by visual inspection of the Wide-field Infrared Survey Explorer (WISE) 22-micron images. Each candidate was observed using the Longslit Spectrograph at the Wyoming Infrared Observatory (WIRO) 2.3 meter telescope. We present here the results from observing four such candidates, and all four are confirmed as early type stars: GO92.3191+0.0591 (B1V) (aka ALS11826), GO86.551014-1.0873935 (B2V; a probable short-period binary), G076.6921-2.4071 (B5V), and G075.5711-0.2558 (B0V) (aka HD 194303). These results enlarge the sample of candidate runaway massive stars hosting bowshocks and provide a promising sample of such objects for studying stellar mass loss. This work is supported by the National Science Foundation Grants AST-1063146 (REU), AST-1411851 (RUI), and AST-1412845.

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.

Spectra from the IRS of Bright Oxygen-Rich Evolved Stars in the SMC

NASA Astrophysics Data System (ADS)

Kraemer, Kathleen E.; Sloan, Greg; Wood, Peter

2016-06-01

We have used Spitzer's Infrared Spectrograph (IRS) to obtain spectra of stars in the Small Magellanic Cloud (SMC). The targets were chosen from the Point Source Catalog of the Mid-Course Space Experiment (MSX), which detected the 243 brightest infrared sources in the SMC. Our SMC sample of oxygen-rich evolved stars shows more dust than found in previous samples, and the dust tends to be dominated by silicates, with little contribution from alumina. Both results may arise from the selection bias in the MSX sample and our sample toward more massive stars. Additionally, several sources show peculiar spectral features such as PAHs, crystalline silicates, or both carbon-rich and silicate features. The spectrum of one source, MSX SMC 145, is a combination of an ordinary AGB star and a background galaxy at z~0.16, rather than an OH/IR star as previously suggested.

Stars in Orion as Seen from Mars

NASA Image and Video Library

2004-03-11

Stars in the upper portion of the constellation Orion the Hunter, including the bright shoulder star Betelgeuse and Orion three-star belt, appear in this image taken from the surface of Mars by the panoramic camera on NASA rover Spirit. Spirit imaged stars on March 11, 2004, after it awoke during the martian night for a communication session with NASA's Mars Global Surveyor orbiter. This image is an eight-second exposure. Longer exposures were also taken. The images tested the capabilities of the rover for night-sky observations. Scientists will use the results to aid planning for possible future astronomical observations from Mars. http://photojournal.jpl.nasa.gov/catalog/PIA05546

Prevalence of Earth-size planets orbiting Sun-like stars.

PubMed

Petigura, Erik A; Howard, Andrew W; Marcy, Geoffrey W

2013-11-26

Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration's Kepler mission. We found 603 planets, including 10 that are Earth size ( ) and receive comparable levels of stellar energy to that of Earth (1 - 2 R[Symbol: see text] ). We account for Kepler's imperfect detectability of such planets by injecting synthetic planet-caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ~200 d. Extrapolating, one finds 5.7(-2.2)(+1.7)% of Sun-like stars harbor an Earth-size planet with orbital periods of 200-400 d.

Prevalence of Earth-size planets orbiting Sun-like stars

PubMed Central

Petigura, Erik A.; Howard, Andrew W.; Marcy, Geoffrey W.

2013-01-01

Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration’s Kepler mission. We found 603 planets, including 10 that are Earth size () and receive comparable levels of stellar energy to that of Earth (). We account for Kepler’s imperfect detectability of such planets by injecting synthetic planet–caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ∼200 d. Extrapolating, one finds % of Sun-like stars harbor an Earth-size planet with orbital periods of 200–400 d. PMID:24191033

The Evolution of Carbon Stars

NASA Astrophysics Data System (ADS)

Chan, S. Josephine

1993-04-01

This dissertation is concerned with the nature of the carbon stars, unusual late-type stars in which the abundance of carbon in the photosphere is greater than that of oxygen. Data from the Infrared Astronomical Satellite (IRAS) survey has shown that carbon stars which were identified from optical surveys and those identified from the SiC dust features in their IRAS Low Resolution Spectrometer LRS spectra have different IRAS colours. The former (which will be referred to as visual carbon stars) are visually bright and have large excesses at 6 microns, while the latter group (which will be referred to as infrared carbon stars) have blackbody energy distributions. The origin of visual carbon stars has been discussed by Chan and Kwok (1988) based on the hypothesis of Willems and de Jong (1988). A complete sample of visual carbon stars detected by IRAS with 12 microns flux densities greater than 5 Jy was selected, and 207 LRS spectra were extracted for those sources without previous \\lrs data. Of these, 152 sources had new LRS spectra with reasonably good signal-to-noise ratio and 575 sources had previously released LRS spectra. All these spectra have been classified with the scheme of Volk and Cohen (1989). When the LRS spectra of these 727 IRAS CCGCS sources were examined, 15 were found to show the 9.7 microns silicate emission feature which is expected to occur only in an oxygen-rich circumstellar shell. Eight of these are reported for the first time in this dissertation. This group of visual carbon stars (hereafter called silicate carbon stars) may represent transition objects between oxygen-rich and carbon stars on the asymptotic giant branch (AGB) because the photosphere is carbon-rich while the circumstellar material resembles that from a typical M-type star. A radiative transfer dust shell model for these silicate carbon stars is presented. The model spectra produce excellent fits to the observed energy distributions of these silicate carbon stars. The J

The Unusual Central Star of the Planetary Nebula Sh 2-71

NASA Astrophysics Data System (ADS)

Močnik, Teo

2013-08-01

This thesis presents new photometric and spectroscopic observational results for the unusual central star of bipolar planetary nebula Sh2-71. The combined lightcurve, composed from the photometric datasets of three different telescopes, was in agreement with the reported ephemeris of the sinusoidal brightness variations with a period of 68 days. The two sharp brightness dips, indicated by the preliminary automated data reduction process, were confirmed. The presence of three additional dips tentatively suggested that the dips, possibly eclipses, are occurring periodically with a period of 17.2 days. The comparison between U and V lightcurves revealed that the 68 day brightness variations are accompanied by a variable reddening effect. Spectroscopic observations revealed pronounced spectral variations, which were not correlated with the 68 days brightness phase. On the other hand, the high-cadence echelle spectra did not exhibit any variability on hourly timescales, which implied that the spectral variations must occur on timescales of a few days. Radial velocity measurements suggested an amplitude of ±40 km/s but were not correlated with the brightness phase. The measured average radial velocity of the observed star 26 km/s was in near agreement with the reported mean radial velocity of the planetary nebula. As some doubt has been raised recently that the central star could be another field star, this near agreement between the radial velocities provided supporting evidence that the observed star actually is the central star of the planetary nebula. The comparison between the measured and synthetic spectra yielded stellar atmospheric parameters T_eff 12000 K, log(g) 4.0 cm/s^2, vrot\\cdot sin(i) 200 km/s with an indicated high value of metallicity. Fitted stellar parameters and the comparison with standard spectra classified the star as B8V. The obtained spectrophotometric observations have been used to construct a model for the central star. A previously

Spectroscopic Validation of Low-metallicity Stars from RAVE

NASA Astrophysics Data System (ADS)

Placco, Vinicius M.; Beers, Timothy C.; Santucci, Rafael M.; Chanamé, Julio; Sepúlveda, María Paz; Coronado, Johanna; Points, Sean D.; Kaleida, Catherine C.; Rossi, Silvia; Kordopatis, Georges; Lee, Young Sun; Matijevič, Gal; Frebel, Anna; Hansen, Terese T.; Holmbeck, Erika M.; Rasmussen, Kaitlin C.; Roederer, Ian U.; Sakari, Charli M.; Whitten, Devin D.

2018-06-01

We present results from a medium-resolution (R ∼ 2000) spectroscopic follow-up campaign of 1694 bright (V < 13.5), very metal-poor star candidates from the RAdial Velocity Experiment (RAVE). Initial selection of the low-metallicity targets was based on the stellar parameters published in RAVE Data Releases 4 and 5. Follow up was accomplished with the Gemini-N and Gemini-S, the ESO/NTT, the KPNO/Mayall, and the SOAR telescopes. The wavelength coverage for most of the observed spectra allows for the determination of carbon and α-element abundances, which are crucial for considering the nature and frequency of the carbon-enhanced metal-poor (CEMP) stars in this sample. We find that 88% of the observed stars have [{Fe}/{{H}}] ≤ ‑1.0, 61% have [{Fe}/{{H}}] ≤ ‑2.0, and 3% have [{Fe}/{{H}}] ≤ ‑3.0 (with four stars at [{Fe}/{{H}}] ≤ ‑3.5). There are 306 CEMP star candidates in this sample, and we identify 169 CEMP Group I, 131 CEMP Group II, and 6 CEMP Group III stars from the A(C) versus [Fe/H] diagram. Inspection of the [α /{{C}}] abundance ratios reveals that five of the CEMP Group II stars can be classified as “mono-enriched second-generation” stars. Gaia DR1 matches were found for 734 stars, and we show that transverse velocities can be used as a confirmatory selection criteria for low-metallicity candidates. Selected stars from our validated list are being followed-up with high-resolution spectroscopy to reveal their full chemical-abundance patterns for further studies.

CD94 surface density identifies a functional intermediary between the CD56bright and CD56dim human NK-cell subsets

PubMed Central

Mao, Hsiaoyin C.; Wei, Min; Hughes, Tiffany; Zhang, Jianying; Park, Il-kyoo; Liu, Shujun; McClory, Susan; Marcucci, Guido; Trotta, Rossana

2010-01-01

Human CD56bright natural killer (NK) cells possess little or no killer immunoglobulin-like receptors (KIRs), high interferon-γ (IFN-γ) production, but little cytotoxicity. CD56dim NK cells have high KIR expression, produce little IFN-γ, yet display high cytotoxicity. We hypothesized that, if human NK maturation progresses from a CD56bright to a CD56dim phenotype, an intermediary NK cell must exist, which demonstrates more functional overlap than these 2 subsets, and we used CD94 expression to test our hypothesis. CD94highCD56dim NK cells express CD62L, CD2, and KIR at levels between CD56bright and CD94lowCD56dim NK cells. CD94highCD56dim NK cells produce less monokine-induced IFN-γ than CD56bright NK cells but much more than CD94lowCD56dim NK cells because of differential interleukin-12–mediated STAT4 phosphorylation. CD94highCD56dim NK cells possess a higher level of granzyme B and perforin expression and CD94-mediated redirected killing than CD56bright NK cells but lower than CD94lowCD56dim NK cells. Collectively, our data suggest that the density of CD94 surface expression on CD56dim NK cells identifies a functional and likely developmental intermediary between CD56bright and CD94lowCD56dim NK cells. This supports the notion that, in vivo, human CD56bright NK cells progress through a continuum of differentiation that ends with a CD94lowCD56dim phenotype. PMID:19897577

CD94 surface density identifies a functional intermediary between the CD56bright and CD56dim human NK-cell subsets.

PubMed

Yu, Jianhua; Mao, Hsiaoyin C; Wei, Min; Hughes, Tiffany; Zhang, Jianying; Park, Il-kyoo; Liu, Shujun; McClory, Susan; Marcucci, Guido; Trotta, Rossana; Caligiuri, Michael A

2010-01-14

Human CD56(bright) natural killer (NK) cells possess little or no killer immunoglobulin-like receptors (KIRs), high interferon-gamma (IFN-gamma) production, but little cytotoxicity. CD56(dim) NK cells have high KIR expression, produce little IFN-gamma, yet display high cytotoxicity. We hypothesized that, if human NK maturation progresses from a CD56(bright) to a CD56(dim) phenotype, an intermediary NK cell must exist, which demonstrates more functional overlap than these 2 subsets, and we used CD94 expression to test our hypothesis. CD94(high)CD56(dim) NK cells express CD62L, CD2, and KIR at levels between CD56(bright) and CD94(low)CD56(dim) NK cells. CD94(high)CD56(dim) NK cells produce less monokine-induced IFN-gamma than CD56(bright) NK cells but much more than CD94(low)CD56(dim) NK cells because of differential interleukin-12-mediated STAT4 phosphorylation. CD94(high)CD56(dim) NK cells possess a higher level of granzyme B and perforin expression and CD94-mediated redirected killing than CD56(bright) NK cells but lower than CD94(low)CD56(dim) NK cells. Collectively, our data suggest that the density of CD94 surface expression on CD56(dim) NK cells identifies a functional and likely developmental intermediary between CD56(bright) and CD94(low)CD56(dim) NK cells. This supports the notion that, in vivo, human CD56(bright) NK cells progress through a continuum of differentiation that ends with a CD94(low)CD56(dim) phenotype.

Faint warm debris disks around nearby bright stars explored by AKARI and IRSF

NASA Astrophysics Data System (ADS)

Ishihara, Daisuke; Takeuchi, Nami; Kobayashi, Hiroshi; Nagayama, Takahiro; Kaneda, Hidehiro; Inutsuka, Shu-ichiro; Fujiwara, Hideaki; Onaka, Takashi

2017-05-01

Context. Debris disks are important observational clues for understanding planetary-system formation process. In particular, faint warm debris disks may be related to late planet formation near 1 au. A systematic search of faint warm debris disks is necessary to reveal terrestrial planet formation. Aims: Faint warm debris disks show excess emission that peaks at mid-IR wavelengths. Thus we explore debris disks using the AKARI mid-IR all-sky point source catalog (PSC), a product of the second generation unbiased IR all-sky survey. Methods: We investigate IR excess emission for 678 isolated main-sequence stars for which there are 18 μm detections in the AKARI mid-IR all-sky catalog by comparing their fluxes with the predicted fluxes of the photospheres based on optical to near-IR fluxes and model spectra. The near-IR fluxes are first taken from the 2MASS PSC. However, 286 stars with Ks < 4.5 in our sample have large flux errors in the 2MASS photometry due to saturation. Thus we have measured accurate J, H, and Ks band fluxes, applying neutral density (ND) filters for Simultaneous InfraRed Imager for Unbiased Survey (SIRIUS) on IRSF, the φ1.4 m near-IR telescope in South Africa, and improved the flux accuracy from 14% to 1.8% on average. Results: We identified 53 debris-disk candidates including eight new detections from our sample of 678 main-sequence stars. The detection rate of debris disks for this work is 8%, which is comparable with those in previous works by Spitzer and Herschel. Conclusions: The importance of this study is the detection of faint warm debris disks around nearby field stars. At least nine objects have a large amount of dust for their ages, which cannot be explained by the conventional steady-state collisional cascade model. The full version of Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A72

The photosphere of red supergiant stars as seen by optical interferometry

NASA Astrophysics Data System (ADS)

Montargès, M.; Kervella, P.; Perrin, G.; Chiavassa, A.; Norris, R.; Ridgway, S. T.; Decin, L.

2017-12-01

During the end of their lives, massive stars become red supergiant (RSG) stars. At this stage, they are forging heavy elements in their cores that are transported up to the photosphere thanks to convection and expelled to the interstellar medium through the star's mass loss. Cooling in the outer atmosphere causes these elements to become molecules and dust that are the building blocks of future planetary systems and eventually life. One of the scenarios to explain the launch of material from the photosphere involves convection that leads to an increased scale height and facilitates mass ejection. We present here observations of several bright features on the surface of nearby RSG stars using near infrared (NIR) interferometry. They are interpreted as being the top of convective cells. We compare them with 3D convective simulation predictions. These inhomogeneities are bright and large enough to cause a photocenter displacement that might bias parallax measurements.

Mystery of the Fading Star Artist Concept

NASA Image and Video Library

2010-01-05

Every 27 years, a bright star called Epsilon Aurigae fades over period of two years, then brightens back up again. A companion is known to be surrounded by a dusty disk, as illustrated in this artist concept.

Are solar brightness variations faculae- or spot-dominated?

NASA Astrophysics Data System (ADS)

Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Yeo, K. L.; Schmutz, W. K.

2016-05-01

Context. Regular spaceborne measurements have revealed that solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims: To understand whether the broader pattern of stellar variations is consistent with the solar paradigm, we assess relative contributions of faculae and spots to solar magnetically-driven brightness variability. We investigate how the solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods: We performed calculations with the SATIRE model, which returns solar brightness with daily cadence from solar disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results: Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Strömgren (b + y)/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year solar variability in the Strömgren (b + y)/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions: The rotational solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for

Coordinated NuSTAR and Swift observations of SU Lyncis: a hard X-ray bright symbiotic star with weak optical signatures

NASA Astrophysics Data System (ADS)

Lopes de Oliveira, Raimundo; Mukai, Koji; Luna, Gerardo Juan Manuel; Sokoloski, Jennifer; Nelson, Thomas; Lucy, Adrian B.

2018-01-01

The variable M giant SU Lyncis was recently identified as the optical counterpart of a hard, thermal X-ray source. Also considering the fact that the star displays weak high-excitation emission, it was classified as a symbiotic system purely powered by accretion without accompanying nuclear fusion. This discovery revealed the existence of a subclass of symbiotics which is "invisible" to optical surveys and thus underestimated since these surveys favour the identification of systems with more intense emission lines that arise when shell-burning is present. At the same time, this discovery opens up a new window to investigate accretion and evolution of symbiotic systems. Here we report on the X-ray and UV properties of SU Lyncis derived from simultaneous NuSTAR and Swift observations. The investigation is focused on the strong photometric variability in UV and on the X-ray spectral characterization, which is associated with a hot thermal plasma with sub-solar abundance and suffering the effects of a relatively dense local absorber. The results are discussed in the context of the accretion geometry and mass of the white dwarf, and the imposed limits to the reflection fraction.

A star recognition method based on the Adaptive Ant Colony algorithm for star sensors.

PubMed

Quan, Wei; Fang, Jiancheng

2010-01-01

A new star recognition method based on the Adaptive Ant Colony (AAC) algorithm has been developed to increase the star recognition speed and success rate for star sensors. This method draws circles, with the center of each one being a bright star point and the radius being a special angular distance, and uses the parallel processing ability of the AAC algorithm to calculate the angular distance of any pair of star points in the circle. The angular distance of two star points in the circle is solved as the path of the AAC algorithm, and the path optimization feature of the AAC is employed to search for the optimal (shortest) path in the circle. This optimal path is used to recognize the stellar map and enhance the recognition success rate and speed. The experimental results show that when the position error is about 50″, the identification success rate of this method is 98% while the Delaunay identification method is only 94%. The identification time of this method is up to 50 ms.

SU Lyncis, a Hard X-Ray Bright M Giant: Clues Point to a Large Hidden Population of Symbiotic Stars

NASA Technical Reports Server (NTRS)

Mukai, K.; Luna, G. J. M.; Cusumano, G.; Segreto, A.; Munari, U.; Sokoloski, J. L.; Lucy, A. B.; Nelson, T.; Nunez, N. E.

2016-01-01

Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain amore reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favour of shell-burning systems. We conclude that the true population of symbiotic stars has been underestimated, potentially by a large factor.

Su Lyncis, a Hard X-Ray Bright M Giant: Clues Point to a Large Hidden Population of Symbiotic Stars

NASA Technical Reports Server (NTRS)

Mukai, K.; Luna, G. J. M.; Cusumano, G.; Segreto, A.; Munari, U.; Sokoloski, J. L.; Lucy, A. B.; Nelson, T.; Nunez, N. E.

2016-01-01

Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain a more reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favor of shell-burning systems. We conclude that the true population of symbiotic stars has been underestimated, potentially by a large factor.

A COMPREHENSIVE CENSUS OF NEARBY INFRARED EXCESS STARS

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

Cotten, Tara H.; Song, Inseok, E-mail: tara@physast.uga.edu, E-mail: song@physast.uga.edu

The conclusion of the Wide-Field Infrared Survey Explorer ( WISE ) mission presents an opportune time to summarize the history of using excess emission in the infrared as a tracer of circumstellar material and exploit all available data for future missions such as the James Webb Space Telescope . We have compiled a catalog of infrared excess stars from peer-reviewed articles and perform an extensive search for new infrared excess stars by cross-correlating the Tycho-2 and all-sky WISE (AllWISE) catalogs. We define a significance of excess in four spectral type divisions and select stars showing greater than either 3 σmore » or 5 σ significance of excess in the mid- and far-infrared. Through procedures including spectral energy distribution fitting and various image analyses, each potential excess source was rigorously vetted to eliminate false positives. The infrared excess stars from the literature and the new stars found through the Tycho-2 and AllWISE cross-correlation produced nearly 500 “Prime” infrared excess stars, of which 74 are new sources of excess, and >1200 are “Reserved” stars, of which 950 are new sources of excess. The main catalog of infrared excess stars are nearby, bright, and either demonstrate excess in more than one passband or have infrared spectroscopy confirming the infrared excess. This study identifies stars that display a spectral energy distribution suggestive of a secondary or post-protoplanetary generation of dust, and they are ideal targets for future optical and infrared imaging observations. The final catalogs of stars summarize the past work using infrared excess to detect dust disks, and with the most extensive compilation of infrared excess stars (∼1750) to date, we investigate various relationships among stellar and disk parameters.« less

Using Brigham Young University's Orson Pratt Observatory 16" telescope to identify possible transiting planets discovered by the Kilodegree Extremely Little Telescope

NASA Astrophysics Data System (ADS)

Matt, Kyle; Stephens, Denise C.; Gaillard, Clement; KELT-North

2016-01-01

We use a 16" telescope on the Brigham Young University (BYU) campus to follow-up on the Kilodegree Extremely Little Telescope (KELT) survey to identify possible transiting planets. KELT is an all sky survey that monitors the same areas of the sky throughout the year to identify stars that exhibit a change in brightness. Objects found to exhibit a variation in brightness similar to predicted models of transiting planets are sent to the ground-based follow-up team where we get high precision differential photometry to determine whether or not a transit is occurring and if the transiting object is a planet or companion star. If a planetary transit is found, the object is forwarded for radial velocity follow-up and could eventually be published as a KELT planet. In this poster we present light curves from possible planets we have identified as well as eclipsing binary systems and non-detections. We will highlight features of our telescope and camera and the basic steps for data reduction and analysis.

The Dearth of UV-bright Stars in M32: Implications for Stellar Evolution Theory

NASA Technical Reports Server (NTRS)

Sweigart, Allen V.; Kimble, Randy A.; Bowers, Charles W.

2008-01-01

Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained deep far ultraviolet images of the compact elliptical galaxy M32. When combined with earlier near-ultraviolet images of the same field, these data enable the construction of an ultraviolet color-magnitude diagram of the hot horizontal branch (HB) population and other hot stars in late phases of stellar evolution. We find few post-asymptotic giant branch (PAGB) stars in the galaxy, implying that these stars either cross the HR diagram more rapidly than expected, and/or that they spend a significant fraction of their time enshrouded in circumstellar material. The predicted luminosity gap between the hot HB and its AGB-Manque (AGBM) progeny is less pronounced than expected, especially when compared to evolutionary tracks with enhanced helium abundances, implying that the presence of hot HB stars in this metal-rich population is not due to (Delta)Y/(Delta)Z greater than or approx. 4. Only a small fraction (approx. 2%) of the HB population is hot enough to produce significant UV emission, yet most of the W emission in this galaxy comes from the hot HB and AGBM stars, implying that PAGB stars are not a significant source of W emission even in those elliptical galaxies with a weak W excess. Subject headings: galaxies: evolution - galaxies: stellar content - galaxies: individual (M32) - stars: evolution - stars: horizontal branch

Follow-up observations of extremely metal-poor stars identified from SDSS

NASA Astrophysics Data System (ADS)

Aguado, D. S.; Allende Prieto, C.; González Hernández, J. I.; Carrera, R.; Rebolo, R.; Shetrone, M.; Lambert, D. L.; Fernández-Alvar, E.

2016-08-01

Context. The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Aims: Only two dozen stars with ([Fe/H] < -4) are known, and they show a wide range of abundance patterns. It is therefore important to enlarge this sample. We present the first results of an effort to identify new extremely metal-poor stars in the Milky Way halo. Methods: Our targets have been selected from low-resolution spectra obtained as part of the Sloan Digital Sky Survey, and followed-up with medium resolution spectroscopy on the 4.2 m William Herschel Telescope and, in a few cases, at high resolution on the 9.2 m Hobby-Eberly Telescope. Stellar parameters and the abundances of magnesium, calcium, iron, and strontium have been inferred from the spectra using classical model atmospheres. We have also derived carbon abundances from the G band. Results: We find consistency between the metallicities estimated from SDSS and those from new data at the level of 0.3 dex. The analysis of medium resolution data obtained with ISIS on the WHT allows us to refine the metallicities and in some cases measure other elemental abundances. Our sample contains 11 new metal-poor stars with [Fe/H] < -3.0, one of them with an estimated metallicity of [Fe/H] ~ -4.0. We also discuss metallicity discrepancies of some stars in common with previous works in the literature. Only one of these stars is found to be C-enhanced at about [C/Fe] ~ + 1, whereas the other metal-poor stars show C abundances at the level of [C/Fe] ~ + 0.45. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.The reduced spectra as FITS files are only available at

VizieR Online Data Catalog: Abundances of bright metal-poor stars (Schlaufman+, 2014)

NASA Astrophysics Data System (ADS)

Schlaufman, K. C.; Casey, A. R.

2016-11-01

As input to our sample selection, we use the APASS DR6 Catalog, the 2MASS All-Sky Point Source Catalog, and the AllWISE Source Catalog (Henden+ 2012JAVSO..40..430H; Skrutskie+ 2006AJ....131.1163S; Wright+ 2010AJ....140.1868W; Mainzer+ 2011ApJ...731...53M). We followed up our metal-poor star candidates with the Mayall 4m/Echelle, Gemini South/GMOS-S, and Magellan/MIKE telescopes and spectrographs. We observed 98 stars with the Mayall 4m/Echelle on 2013 June 25-27. We observed 90 stars with Gemini South/GMOS-S in service mode from 2014 March to July (R~3700). We observed 416 stars with Magellan/MIKE on 2014 June 21-23 and July 8-10 (R~41000 in the blue and R~35000 in the red). (3 data files).

Method and apparatus for radiometer star sensing

NASA Technical Reports Server (NTRS)

Wilcox, Jack E. (Inventor)

1989-01-01

A method and apparatus for determining the orientation of the optical axis of radiometer instruments mounted on a satellite involves a star sensing technique. The technique makes use of a servo system to orient the scan mirror of the radiometer into the path of a sufficiently bright star such that motion of the satellite will cause the star's light to impinge on the scan mirror and then the visible light detectors of the radiometer. The light impinging on the detectors is converted to an electronic signal whereby, knowing the position of the star relative to appropriate earth coordinates and the time of transition of the star image through the detector array, the orientation of the optical axis of the instrument relative to earth coordinates can be accurately determined.

Anomalous Eclipses of the Young Star RW Aur A

NASA Astrophysics Data System (ADS)

Lamzin, S.; Cheryasov, D.; Chuntonov, G.; Dodin, A.; Grankin, K.; Malanchev, K.; Nadzhip, A.; Safonov, B.; Shakhovskoy, D.; Shenavrin, V.; Tatarnikov, A.; Vozyakova, O.

2017-06-01

Results of UBVRIJHKLM photometry, VRI polarimetry and optical spectroscopy of a young star RW Aur A obtained during 2010-11 and 2014-16 dimming events are presented. During the second dimming the star decreased its brightness to ΔV >4.5 mag, polarization of its light in I-band was up to 30 %, and color-magnitude diagramm was similar to that of UX Ori type stars. We conclude that the reason of both dimmings is an eclipses of the star by dust screen, but the size of the screen is much larger than in the case of UXORs.

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.

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.

A Sparkling Spray of Stars

NASA Astrophysics Data System (ADS)

2008-12-01

The festive season has arrived for astronomers at the European Southern Observatory (ESO) in the form of this dramatic new image. It shows the swirling gas around the region known as NGC 2264 -- an area of sky that includes the sparkling blue baubles of the Christmas Tree star cluster. Omega Centauri ESO PR Photo 48/08 NGC 2264 and the Christmas Tree cluster NGC 2264 lies about 2600 light-years from Earth in the obscure constellation of Monoceros, the Unicorn, not far from the more familiar figure of Orion, the Hunter. The image shows a region of space about 30 light-years across. William Herschel discovered this fascinating object during his great sky surveys in the late 18th century. He first noticed the bright cluster in January 1784 and the brightest part of the visually more elusive smudge of the glowing gas clouds at Christmas nearly two years later. The cluster is very bright and can easily be seen with binoculars. With a small telescope (whose lenses will turn the view upside down) the stars resemble the glittering lights on a Christmas tree. The dazzling star at the top is even bright enough to be seen with the unaided eye. It is a massive multiple star system that only emerged from the dust and gas a few million years ago. As well as the cluster there are many interesting and curious structures in the gas and dust. At the bottom of the frame, the dark triangular feature is the evocative Cone Nebula, a region of molecular gas flooded by the harsh light of the brightest cluster members. The region to the right of the brightest star has a curious, fur-like texture that has led to the name Fox Fur Nebula. Much of the image appears red because the huge gas clouds are glowing under the intense ultra-violet light coming from the energetic hot young stars. The stars themselves appear blue as they are hotter, younger and more massive than our own Sun. Some of this blue light is scattered by dust, as can be seen occurring in the upper part of the image. This

Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey

NASA Astrophysics Data System (ADS)

Susmitha Rani, A.; Sivarani, T.; Beers, T. C.; Fleming, S.; Mahadevan, S.; Ge, J.

2016-05-01

We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] <-3.0) star, SDSS J134338.67+484426.6, identified during the course of the Multi-object Apache Point Observatory Radial Velocity Exoplanet Large-area Survey spectroscopic pre-survey of some 20 000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ˜20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having `normal' carbon and no enhancement of neutron-capture abundances. Strontium is underabundant, [Sr/Fe] = -0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of α-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high-resolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible long-period binary. We also discuss the abundance trends in EMP stars for r-process elements, and compare with other magnesium-poor stars.

Update on the KELT Transit Survey: Hot Planets around Hot Stars

NASA Astrophysics Data System (ADS)

Gaudi, B. Scott; Stassun, Keivan G.; Pepper, Joshua; KELT Collaboration

2018-01-01

The KELT Transit Survey consists of a pair of small-aperture, wide-angle automated telescopes located at Winer Observatory in Sonoita, Arizona and the South African Astronomical Observatory (SAAO) in Sutherland, South Africa. Together, they are surveying roughly 70% of the sky for transiting planets. By virtue of their small apertures (42 mm) and large fields-of-view (26 degrees x 26 degrees), KELT is most sensitive to hot Jupiters transiting relatively bright (V~8-11), and thus relatively hot stars. I will provide an update on the planets discovered by KELT, focusing in detail on our recent discoveries of very hot planets transiting several bright A and early F stars.

Illuminating Low Surface Brightness Galaxies with the Hyper Suprime-Cam Survey

NASA Astrophysics Data System (ADS)

Greco, Johnny P.; Greene, Jenny E.; Strauss, Michael A.; Macarthur, Lauren A.; Flowers, Xzavier; Goulding, Andy D.; Huang, Song; Kim, Ji Hoon; Komiyama, Yutaka; Leauthaud, Alexie; Leisman, Lukas; Lupton, Robert H.; Sifón, Cristóbal; Wang, Shiang-Yu

2018-04-01

We present a catalog of extended low surface brightness galaxies (LSBGs) identified in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first ∼200 deg2 of the survey, we have uncovered 781 LSBGs, spanning red (g ‑ i ≥ 0.64) and blue (g ‑ i < 0.64) colors and a wide range of morphologies. Since we focus on extended galaxies (r eff = 2.″5–14″), our sample is likely dominated by low-redshift objects. We define LSBGs to have mean surface brightnesses {\\bar{μ }}eff}(g)> 24.3 mag arcsec‑2, which allows nucleated galaxies into our sample. As a result, the central surface brightness distribution spans a wide range of μ 0(g) = 18–27.4 mag arcsec‑2, with 50% and 95% of galaxies fainter than 24.3 and 22 mag arcsec‑2, respectively. Furthermore, the surface brightness distribution is a strong function of color, with the red distribution being much broader and generally fainter than that of the blue LSBGs, and this trend shows a clear correlation with galaxy morphology. Red LSBGs typically have smooth light profiles that are well characterized by single-component Sérsic functions. In contrast, blue LSBGs tend to have irregular morphologies and show evidence for ongoing star formation. We cross-match our sample with existing optical, H I, and ultraviolet catalogs to gain insight into the physical nature of the LSBGs. We find that our sample is diverse, ranging from dwarf spheroidals and ultradiffuse galaxies in nearby groups to gas-rich irregulars to giant LSB spirals, demonstrating the potential of the HSC-SSP to provide a truly unprecedented view of the LSBG population.

Quantitative Measurements of Daytime Near Infrared Sky Brightness at the AEOS 3.6 m Telescope

DTIC Science & Technology

2014-09-01

photometric filters. In the case of the 1250 nm filter, the quoted results reflect the brightness that would be seen through a standard 2MASS J filter [9...brightness per unit wavelength through the broader 2MASS filter with 162 nm bandpass. Given the known colors of the star, we estimate this error to be...Megeath, S. T. “Spectral irradiance calibration in the infrared. XIV. The absolute calibration of 2MASS ,” Astron. J., 126, 1090–1096 (2003) [10] Jim

Long-Term Starspot Activity of Some Chromospherically Active Rs CVn and BY Dra Stars

NASA Astrophysics Data System (ADS)

Kozhevnikova, Alla; Ilya, Alekseev

2016-10-01

We present results of our long-term photometric observations of a sample of 15 chromospherically active BY Dra and RS CVn-type stars. Observations were carried out at a 70-cm telescope and multichannel photometer of Kourovka Astronomical Observatory of Ural Federal University and at a 1.25-m telescope of Crimean Astrophysical Observatory from 2003 to 2015 in Johnson B, V, R, I bands. We also use the previously published photometric data for all these stars to find the meaning of historical star's brightness, that we assume as a brightness of unspotted photosphere. Using a renewed zonal spot model for spotted stellar photospheres we determined spot parameters for all observational seasons, as our as published ones, that were spanning almost over 45 years for some stars (e.g. CG Cyg, WY Cnc, EV Lac, V 1396 Cyg). It is shown that the spots were located at low and middle latitudes up to 58 deg., are cooler than the surrounding photosphere by 200 - 2000 K according to the spectral class. The spotted area varied from season to season, comprising 13%-47% of the surface area of the star. Almost half of the stars display drifts of their spots towards the equator and poles during certain time intervals; however, the speeds of the spots' latitude drifts are lower than the analogous speeds for sunspots, by factors of 1.5-4, on average. Activity cycles lasting from 5 to 40 years have been determined or confirmed for majority of the studied stars. As a rule, cycles are expressed in synchronous variations of spot areas, spot latitudes and average photometric star's brightness.

Star Formation in M 33 (HerM33es)

NASA Astrophysics Data System (ADS)

Kramer, C.; Boquien, M.; Braine, J.; Buchbender, C.; Calzetti, D.; Gratier, P.; Mookerjea, B.; Relaño, M.; Verley, S.

2011-11-01

Within the key project "Herschel M 33 extended survey" (HerM33es), we are studying the physical and chemical processes driving star formation and galactic evolution in the nearby galaxy M 33, combining the study of local conditions affecting individual star formation with properties only becoming apparent on global scales. Here, we present recent results obtained by the HerM33es team. Combining Spitzer and Herschel data ranging from 3.6 μm to 500μm, along with H i, Hα, and GALEX UV data, we have studied the dust at high spatial resolutions of 150 pc, providing estimators of the total infrared (TIR) brightness and of the star formation rate. While the temperature of the warm dust at high brightness is driven by young massive stars, evolved stellar populations appear to drive the temperature of the cold dust. Plane-parallel models of photon dominated regions (PDRs) fail to reproduce fully the [C ii], [O i], and CO maps obtained in a first spectroscopic study of one 2' × 2' subregion of M 33, located on the inner, northern spiral arm and encompassing the H ii region BCLMP 302.

A Vanishing Star Revisited

NASA Astrophysics Data System (ADS)

1999-07-01

VLT Observations of an Unusual Stellar System Reinhold Häfner of the Munich University Observatory (Germany) is a happy astronomer. In 1988, when he was working at a telescope at the ESO La Silla observatory, he came across a strange star that suddenly vanished off the computer screen. He had to wait for more than a decade to get the full explanation of this unusual event. On June 10-11, 1999, he observed the same star with the first VLT 8.2-m Unit Telescope (ANTU) and the FORS1 astronomical instrument at Paranal [1]. With the vast power of this new research facility, he was now able to determine the physical properties of a very strange stellar system in which two planet-size stars orbit each other. One is an exceedingly hot white dwarf star , weighing half as much as the Sun, but only twice as big as the Earth. The other is a much cooler and less massive red dwarf star , one-and-a-half times the size of planet Jupiter. Once every three hours, the hot star disappears behind the other, as seen from the Earth. For a few minutes, the brightness of the system drops by a factor of more than 250 and it "vanishes" from view in telescopes smaller than the VLT. A variable star named NN Serpentis ESO PR Photo 30a/99 ESO PR Photo 30a/99 [Preview - JPEG: 400 x 468 pix - 152k] [Normal - JPEG: 800 x 936 pix - 576k] [High-Res - JPEG: 2304 x 2695 pix - 4.4M] Caption to ESO PR Photo 30a/99 : The sky field around the 17-mag variable stellar system NN Serpentis , as seen in a 5 sec exposure through a V(isual) filter with VLT ANTU and FORS1. It was obtained just before the observation of an eclipse of this unsual object and served to centre the telescope on the corresponding sky position. The field shown here measures 4.5 x 4.5 armin 2 (1365 x 1365 pix 2 ; 0.20 arcsec/pix). The field is somewhat larger than that shown in Photo 30b/99 and has the same orientation to allow comparison: North is about 20° anticlockwise from the top and East is 90° clockwise from that direction. The

Star Formation in low mass galaxies

NASA Astrophysics Data System (ADS)

Mehta, Vihang

2018-01-01

Our current hierarchical view of the universe asserts that the large galaxies we see today grew via mergers of numerous smaller galaxies. As evidenced by recent literature, the collective impact of these low mass galaxies on the universe is more substantial than previously thought. Studying the growth and evolution of these low mass galaxies is critical to our understanding of the universe as a whole. Star formation is one of the most important ongoing processes in galaxies. Forming stars is fundamental to the growth of a galaxy. One of the main goals of my thesis is to analyze the star formation in these low mass galaxies at different redshifts.Using the Hubble UltraViolet Ultra Deep Field (UVUDF), I investigate the star formation in galaxies at the peak of the cosmic star formation history using the ultraviolet (UV) light as a star formation indicator. Particularly, I measure the UV luminosity function (LF) to probe the volume-averaged star formation properties of galaxies at these redshifts. The depth of the UVUDF is ideal for a direct measurement of the faint end slope of the UV LF. This redshift range also provides a unique opportunity to directly compare UV to the "gold standard" of star formation indicators, namely the Hα nebular emission line. A joint analysis of the UV and Hα LFs suggests that, on average, the star formation histories in low mass galaxies (~109 M⊙) are more bursty compared to their higher mass counterparts at these redshifts.Complementary to the analysis of the average star formation properties of the bulk galaxy population, I investigate the details of star formation in some very bursty galaxies at lower redshifts selected from Spitzer Large Area Survey with Hyper-Suprime Cam (SPLASH). Using a broadband color-excess selection technique, I identify a sample of low redshift galaxies with bright nebular emission lines in the Subaru-XMM Deep Field (SXDF) from the SPLASH-SXDF catalog. These galaxies are highly star forming and have

What asteroseismology can do for exoplanets: Kepler-410A b is a small Neptune around a bright star, in an eccentric orbit consistent with low obliquity

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

Van Eylen, V.; Lund, M. N.; Aguirre, V. Silva

2014-02-10

We confirm the Kepler planet candidate Kepler-410A b (KOI-42b) as a Neptune-sized exoplanet on a 17.8 day, eccentric orbit around the bright (K {sub p} = 9.4) star Kepler-410A (KOI-42A). This is the third brightest confirmed planet host star in the Kepler field and one of the brightest hosts of all currently known transiting exoplanets. Kepler-410 consists of a blend between the fast rotating planet host star (Kepler-410A) and a fainter star (Kepler-410B), which has complicated the confirmation of the planetary candidate. Employing asteroseismology, using constraints from the transit light curve, adaptive optics and speckle images, and Spitzer transit observations,more » we demonstrate that the candidate can only be an exoplanet orbiting Kepler-410A. We determine via asteroseismology the following stellar and planetary parameters with high precision; M {sub *} = 1.214 ± 0.033 M {sub ☉}, R {sub *} = 1.352 ± 0.010 R {sub ☉}, age =2.76 ± 0.54 Gyr, planetary radius (2.838 ± 0.054 R {sub ⊕}), and orbital eccentricity (0.17{sub −0.06}{sup +0.07}). In addition, rotational splitting of the pulsation modes allows for a measurement of Kepler-410A's inclination and rotation rate. Our measurement of an inclination of 82.5{sub −2.5}{sup +7.5} [°] indicates a low obliquity in this system. Transit timing variations indicate the presence of at least one additional (non-transiting) planet (Kepler-410A c) in the system.« less

Pulsar-irradiated stars in dense globular clusters

NASA Technical Reports Server (NTRS)

Tavani, Marco

1992-01-01

We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

Ongoing Massive Star Formation in NGC 604

NASA Astrophysics Data System (ADS)

Martínez-Galarza, J. R.; Hunter, D.; Groves, B.; Brandl, B.

2012-12-01

NGC 604 is the second most massive H II region in the Local Group, thus an important laboratory for massive star formation. Using a combination of observational and analytical tools that include Spitzer spectroscopy, Herschel photometry, Chandra imaging, and Bayesian spectral energy distribution fitting, we investigate the physical conditions in NGC 604 and quantify the amount of massive star formation currently taking place. We derive an average age of 4 ± 1 Myr and a total stellar mass of 1.6+1.6 - 1.0 × 105 M ⊙ for the entire region, in agreement with previous optical studies. Across the region, we find an effect of the X-ray field on both the abundance of aromatic molecules and the [Si II] emission. Within NGC 604, we identify several individual bright infrared sources with diameters of about 15 pc and luminosity-weighted masses between 103 M ⊙ and 104 M ⊙. Their spectral properties indicate that some of these sources are embedded clusters in process of formation, which together account for ~8% of the total stellar mass in the NGC 604 system. The variations of the radiation field strength across NGC 604 are consistent with a sequential star formation scenario, with at least two bursts in the last few million years. Our results indicate that massive star formation in NGC 604 is still ongoing, likely triggered by the earlier bursts.

Update On the Puzzling Boyajian's Star

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-09-01

original article, or check out Wrights own summary of the article here!Pulsations, polar spots, and other stellar variability: unlikelyThe authors show that the variety of timescales observed for dimming events make scenarios involving stellar variations unlikely.Circumstellar material: unlikelyMaterial orbiting the star (like comets) would explain some of the light-curve dips, but it cant explain the long-term dimming observed.Post-merger return to normal: unclearPerhaps Boyajians Star recently merged with a brown dwarf or other star? Now it could be gradually dimming as it returns to its normal brightness, and restructuring of the stars material could causethe short-term dips. Though this scenariois possible, the timescales for the brightness changes are shorter than we would expect.Artificial structures: unclearSpherical swarms of structures would intercept the stars light and re-radiate it in infrared. Since long-wavelength observations have found no evidence of such radiation, the authors declare spherical geometries to be unlikely. Other structure geometries cant yet be ruled out, though.Small-scale interstellar medium (ISM) structure: plausibleSmall-scale density variations in the ISM between us and Boyajians Star could cause the dimming we observe, but the fact that nearby stars dont show similar dimming sets tight limits on the size of such ISM clumps.Spectral energy distribution of Boyajians Star. The upper-limit arrows on the right-hand side indicate that big clouds of megastructures are unlikely, because we would detect their heat as they re-radiate the stars light in infrared. [Wright et al. 2016]Looking to the FutureOf the possible locations for the source of the dimming, Wright and Sigurdsson deem the interstellar space between us and Boyajians Star to be the most likely culprit. They identify several future lines of research that could help us further eliminate possibilities, however, including a study of the ISM toward Boyajians Star, a hunt for similar

Energy-exchange collisions of dark-bright-bright vector solitons.

PubMed

Radhakrishnan, R; Manikandan, N; Aravinthan, K

2015-12-01

We find a dark component guiding the practically interesting bright-bright vector one-soliton to two different parametric domains giving rise to different physical situations by constructing a more general form of three-component dark-bright-bright mixed vector one-soliton solution of the generalized Manakov model with nine free real parameters. Moreover our main investigation of the collision dynamics of such mixed vector solitons by constructing the multisoliton solution of the generalized Manakov model with the help of Hirota technique reveals that the dark-bright-bright vector two-soliton supports energy-exchange collision dynamics. In particular the dark component preserves its initial form and the energy-exchange collision property of the bright-bright vector two-soliton solution of the Manakov model during collision. In addition the interactions between bound state dark-bright-bright vector solitons reveal oscillations in their amplitudes. A similar kind of breathing effect was also experimentally observed in the Bose-Einstein condensates. Some possible ways are theoretically suggested not only to control this breathing effect but also to manage the beating, bouncing, jumping, and attraction effects in the collision dynamics of dark-bright-bright vector solitons. The role of multiple free parameters in our solution is examined to define polarization vector, envelope speed, envelope width, envelope amplitude, grayness, and complex modulation of our solution. It is interesting to note that the polarization vector of our mixed vector one-soliton evolves in sphere or hyperboloid depending upon the initial parametric choices.

VizieR Online Data Catalog: Uranometria Argentina catalog of bright southern stars (Gould, 1879)

NASA Astrophysics Data System (ADS)

Gould, B. G.

2010-07-01

In 1879 Benjamin Apthorp Gould published in Buenos Aires, Argentina, the Uranometria Argentina catalog of 7756 stars south of declination +10 degrees. This included all those stars he considered magnitude 7 or brighter and some fainter stars which are close companions to brighter stars or to each other and have combined magnitude 7 or brighter. Star positions are in 1875 coordinates, and constellation boundaries also in 1875 coordinates were defined within the aforementioned declination range. With only a few small changes these were incorporated into the boundaries adopted by the IAU in 1930 and subsequently universally accepted. In terms of accurate photoelectric magnitude measurements the Uranometria Argentina is nearly complete to magnitude 6.5 in its declination range. In each constellation the individual stars considered to be magnitude 7 and brighter were numbered in sequence of increasing right ascension in 1875 coordinates, except that in a few cases this sequence was somewhat adjusted so that stars close together could be listed on adjacent lines of text. The numbering system is analogous to that in the Flamsteed Catalogus Brittanicus and now widely used. Star numbers from the Uranometria Argentina rarely appear in the 21st century despite the potential utility of their use. They were included in the American Ephemeris and Nautical Almanac until 1978, and in the FK5 catalog until 1999, always with the letter G following the number in the Uranometria Argentina catalog. This serves to distinguish Flamsteed numbers with no following letters from Gould numbers, and is utilized in this presentation and recommended for general use. The file catalog.dat includes every star in the original Uranometria Argentina. In the original the constellations were presented in sequence of increasing distance from the south pole and numbered accordingly. For the convenience of 21st century astronomers the constellations are presented here by alphabetical sequence in

Hubble Observes One-of-a-Kind Star Nicknamed ‘Nasty’

NASA Image and Video Library

2015-05-21

Astronomers using NASA’s Hubble Space Telescope have uncovered surprising new clues about a hefty, rapidly aging star whose behavior has never been seen before in our Milky Way galaxy. In fact, the star is so weird that astronomers have nicknamed it “Nasty 1,” a play on its catalog name of NaSt1. The star may represent a brief transitory stage in the evolution of extremely massive stars. First discovered several decades ago, Nasty 1 was identified as a Wolf-Rayet star, a rapidly evolving star that is much more massive than our sun. The star loses its hydrogen-filled outer layers quickly, exposing its super-hot and extremely bright helium-burning core. But Nasty 1 doesn’t look like a typical Wolf-Rayet star. The astronomers using Hubble had expected to see twin lobes of gas flowing from opposite sides of the star, perhaps similar to those emanating from the massive star Eta Carinae, which is a Wolf-Rayet candidate. Instead, Hubble revealed a pancake-shaped disk of gas encircling the star. The vast disk is nearly 2 trillion miles wide, and may have formed from an unseen companion star that snacked on the outer envelope of the newly formed Wolf-Rayet. Based on current estimates, the nebula surrounding the stars is just a few thousand years old, and as close as 3,000 light-years from Earth. Read more: www.nasa.gov/feature/hubble-observes-one-of-a-kind-star-n... Credits: NASA/Hubble NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Rotation periods of open-cluster stars, 2

NASA Technical Reports Server (NTRS)

Prosser, Charles F.; Shetrone, Matthew D.; Marilli, Ettore; Catalano, Santo; Williams, Scott D.; Backman, Dana E.; Laaksonen, Bentley D.; Adige, Vikram; Marschall, Laurence A.; Stauffer, John R.

1993-01-01

We present the results from a photometric monitoring program of 21 stars observed during 1992 in the Pleiades and Alpha Persei open clusters. Period determinations for 16 stars are given, 13 of which are the first periods reported for these stars. Brightness variations for an additional five cluster stars are also given. One K dwarf member of the alpha Per cluster is observed to have a period of rotation of only 4.39 hr. perhaps the shortest period currently known among BY Draconis variables. The individual photometric measurements have been deposited with the NSSDC. Combining current X-ray flux determinations with known photometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.

The Galactic O-Star Catalog (GOSC) and the Galactic O-Star Spectroscopic Survey (GOSSS): current status

NASA Astrophysics Data System (ADS)

Maíz Apellániz, J.; Alonso Moragón, A.; Ortiz de Zárate Alcarazo, L.; The Gosss Team

2017-03-01

We present the updates of the Galactic O-Star Catalog (GOSC) that we have undertaken in the last two years: new spectral types, more objects, additional information, and coordination with CDS. We also present updates for the Galactic O-Star Spectroscopic Survey (GOSSS). A new paper (GOSSS-III) has been published and ˜ 1000 targets have been observed since 2014. Four new setups have been added to our lineup and for two of them we have already obtained over 100 spectra: with OSIRIS at the 10.4 m GTC we are observing northern dim stars and with FRODOspec at the 2.0 m Liverpool Telescope we are observing northern bright stars. Finally, we also make available new versions of MGB, the spectral classification tool associated with the project, and of the GOSSS grid of spectroscopic standards.

Spectroscopy of Dwarf Stars Around the North Celestial Pole

NASA Astrophysics Data System (ADS)

Mikolaitis, Šarūnas; Tautvaišienė, Gražina; Drazdauskas, Arnas; Minkevičiūtė, Renata; Klebonas, Lukas; Bagdonas, Vilius; Pakšienė, Erika; Janulis, Rimvydas

2018-07-01

New space missions (e.g., NASA-TESS and ESA-PLATO) will perform an in-depth analysis of bright stars in large fields of the celestial sphere searching for extraterrestrial planets and investigating their host-stars. Asteroseismic observations will search for exoplanet-hosting stars with solar-like oscillations. In order to achieve all the goals, a full characterization of the stellar objects is important. However, accurate atmospheric parameters are available for less than 30% of bright dwarf stars of the solar neighborhood. In this study we observed high-resolution (R = 60,000) spectra for all bright (V < 8 mag) and cooler than F5 spectral class dwarf stars in the northern-most field of the celestial sphere with radius of 20° from the α(2000) = 161.°03 and δ(2000) = 86.°60 that is a center of one of the preliminary ESO-PLATO fields. Spectroscopic atmospheric parameters were determined for 140 slowly rotating stars, for 73% of them for the first time. The majority (83%) of the investigated stars are in the TESS object lists and all of them are in the preliminary PLATO field. Our results have no systematic differences when compared with other recent studies. We have 119 stars in common with the Geneva–Copenhagen Survey, where stellar parameters were determined photometrically, and find a 14 ± 125 K difference in effective temperatures, 0.01 ± 0.16 in log g, and ‑0.02 ± 0.09 dex in metallicities. Comparing our results for 39 stars with previous high-resolution spectral determinations, we find only a 7 ± 73 K difference in effective temperatures, 0.02 ± 0.09 in log g, and ‑0.02 ± 0.09 dex in metallicities. We also determined basic kinematic and orbital parameters for this sample of stars. From the kinematical point of view, almost all our stars belong to the thin disk substructure of the Milky Way. The derived galactocentric metallicity gradient is ‑0.066 ± 0.024 dex kpc‑1 (2.5σ significance) and the vertical metallicity gradient is ‑0.102 �

Bright compact bulges at intermediate redshifts

NASA Astrophysics Data System (ADS)

Sachdeva, Sonali; Saha, Kanak

2018-07-01

Studying bright (MB < -20), intermediate-redshift (0.4 < z< 1.0), disc-dominated (nB < 2.5) galaxies from Hubble Space Telescope/Advanced Camera for Surveys and Wide Field Camera 3 in Chandra Deep Field-South, in rest-frame B and I band, we found a new class of bulges that is brighter and more compact than ellipticals. We refer to them as `bright, compact bulges' (BCBs) - they resemble neither classical nor pseudo-bulges and constitute ˜12 per cent of the total bulge population at these redshifts. Examining free-bulge + disc decomposition sample and elliptical galaxy sample from Simard et al., we find that only ˜0.2 per cent of the bulges can be classified as BCBs in the local Universe. Bulge to total light ratio of disc galaxies with BCBs is (at ˜0.4) a factor of ˜2 and ˜4 larger than for those with classical and pseudo-bulges. BCBs are ˜2.5 and ˜6 times more massive than classical and pseudo-bulges. Although disc galaxies with BCBs host the most massive and dominant bulge type, their specific star formation rate is 1.5-2 times higher than other disc galaxies. This is contrary to the expectations that a massive compact bulge would lead to lower star formation rates. We speculate that our BCB host disc galaxies are descendant of massive, compact, and passive elliptical galaxies observed at higher redshifts. Those high-redshift ellipticals lack local counterparts and possibly evolved by acquiring a compact disc around them. The overall properties of BCBs support a picture of galaxy assembly in which younger discs are being accreted around massive pre-existing spheroids.

Photometric and Polarimetric Activity of the Herbig Ae Star VX Cas

NASA Astrophysics Data System (ADS)

Shakhovskoi, D. N.; Rostopchina, A. N.; Grinin, V. P.; Minikulov, N. Kh.

2003-04-01

We present the results of our simultaneous photometric and polarimetric observations of the Herbig Ae/Be star VX Cas acquired in 1987 2001. The star belongs to the UX Ori subtype of young variable stars and exhibits a rather low level of photometric activity: only six Algol-like minima with amplitudes ΔV>1m were recorded in 15 years of observations. Two of these minima, in 1998 and 2001, were the deepest in the history of the star’s photometric studies, with V amplitudes of about 2m. In each case, the dimming was accompanied by an increase in the linear polarization in agreement with the law expected for variable circumstellar extinction. The highest V polarization was about 5%. Observations of VX Cas in the deep minima revealed a turnover of the color tracks, typical of stars of this type and due to an increased contribution from radiation scattered in the circumstellar disk. We separated the observed polarization of VX Cas into interstellar (P is) and intrinsic (P in) components. Their position angles differ by approximately 60°, with P is dominating in the bright state and P in dominating during the deep minima. The competition of these two polarization components leads to changes in both the degree and position angle of the polarization during the star’s brightness variations. Generally speaking, in terms of the behavior of the brightness, color indices, and linear polarization, VX Cas is similar to other UX Ori stars studied by us earlier. A number of episodes of photometric and polarimetric activity suggest that, in their motion along highly eccentric orbits, circumstellar gas and dust clouds can enter the close vicinity of the star (and be disrupted there).

Activity in X-ray-selected late-type stars

NASA Technical Reports Server (NTRS)

Takalo, Leo O.; Nousek, J. A.

1988-01-01

A spectroscopic study has been conducted of nine X-ray bright late-type stars selected from two Einstein X-ray surveys: the Columbia Astrophysical Laboratory Survey (five stars) and the CFA Medium Sensitivity Survey (MSS; four stars). Spectral classes were determined and radial and V sin(i) velocities were measured for the stars. Four of the Columbia Survey stars were found to be new RS CVn-type binaries. The fifth Columbia survey star was found to be an active G dwarf star without evidence for binarity. None of the four MSS stars were found to be either binaries or optically active stars. Activity in these stars was assessed by measuring the excess emission in H-alpha and the Ca II IRT (8498, 8542) lines in comparison with inactive stars of similar spectral types. A correlation was found between X-ray luminosity and V sin(i) and H-alpha line excess. The measured excess line emission in H-alpha was also correlated with V sin(i) but not with the IRT line excess.

Synergies in Astrometry: Predicting Navigational Error of Visual Binary Stars

NASA Astrophysics Data System (ADS)

Gessner Stewart, Susan

2015-08-01

Celestial navigation can employ a number of bright stars which are in binary systems. Often these are unresolved, appearing as a single, center-of-light object. A number of these systems are, however, in wide systems which could introduce a margin of error in the navigation solution if not handled properly. To illustrate the importance of good orbital solutions for binary systems - as well as good astrometry in general - the relationship between the center-of-light versus individual catalog position of celestial bodies and the error in terrestrial position derived via celestial navigation is demonstrated. From the list of navigational binary stars, fourteen such binary systems with at least 3.0 arcseconds apparent separation are explored. Maximum navigational error is estimated under the assumption that the bright star in the pair is observed at maximum separation, but the center-of-light is employed in the navigational solution. The relationships between navigational error and separation, orbital periods, and observers' latitude are discussed.

Bright ZTF transients

NASA Astrophysics Data System (ADS)

Fremling, C.; Kulkarni, S. R.; Taggart, K.; Perley, D.

2018-05-01

As a part of ongoing commissioning of the Zwicky Transient Facility (ZTF; ATel #11266) Alert Infrastructure, here we report bright probable supernovae identified in the raw alert stream resulting from the public ZTF Northern Sky Survey ("Celestial Cinematagrophy"; see Bellm & Kulkarni, Nature Astronomy 1, 71, 2017).

A distance-limited sample of massive star-forming cores from the RMS

NASA Astrophysics Data System (ADS)

Maud, L. T.; Lumsden, S. L.; Moore, T. J. T.; Mottram, J. C.; Urquhart, J. S.; Cicchini, A.

2015-09-01

We analyse C18O (J = 3-2) data from a sample of 99 infrared (IR)-bright massive young stellar objects (MYSOs) and compact H II regions that were identified as potential molecular-outflow sources in the Red MSX Source survey. We extract a distance-limited (D < 6 kpc) sample shown to be representative of star formation covering the transition between the source types. At the spatial resolution probed, Larson-like relationships are found for these cores, though the alternative explanation, that Larson's relations arise where surface-density-limited samples are considered, is also consistent with our data. There are no significant differences found between source properties for the MYSOs and H II regions, suggesting that the core properties are established prior to the formation of massive stars, which subsequently have little impact at the later evolutionary stages investigated. There is a strong correlation between dust-continuum and C18O-gas masses, supporting the interpretation that both trace the same material in these IR-bright sources. A clear linear relationship is seen between the independently established core masses and luminosities. The position of MYSOs and compact H II regions in the mass-luminosity plane is consistent with the luminosity expected from the most massive protostar in the cluster when using an ˜40 per cent star formation efficiency and indicates that they are at a similar evolutionary stage, near the end of the accretion phase.

Radial distribution of dust, stars, gas, and star-formation rate in DustPedia⋆ face-on galaxies

NASA Astrophysics Data System (ADS)

Casasola, V.; Cassarà, L. P.; Bianchi, S.; Verstocken, S.; Xilouris, E.; Magrini, L.; Smith, M. W. L.; De Looze, I.; Galametz, M.; Madden, S. C.; Baes, M.; Clark, C.; Davies, J.; De Vis, P.; Evans, R.; Fritz, J.; Galliano, F.; Jones, A. P.; Mosenkov, A. V.; Viaene, S.; Ysard, N.

2017-09-01

Aims: The purpose of this work is the characterization of the radial distribution of dust, stars, gas, and star-formation rate (SFR) in a sub-sample of 18 face-on spiral galaxies extracted from the DustPedia sample. Methods: This study is performed by exploiting the multi-wavelength DustPedia database, from ultraviolet (UV) to sub-millimeter bands, in addition to molecular (12CO) and atomic (Hi) gas maps and metallicity abundance information available in the literature. We fitted the surface-brightness profiles of the tracers of dust and stars, the mass surface-density profiles of dust, stars, molecular gas, and total gas, and the SFR surface-density profiles with an exponential curve and derived their scale-lengths. We also developed a method to solve for the CO-to-H2 conversion factor (αCO) per galaxy by using dust- and gas-mass profiles. Results: Although each galaxy has its own peculiar behavior, we identified a common trend of the exponential scale-lengths versus wavelength. On average, the scale-lengths normalized to the B-band 25 mag/arcsec2 radius decrease from UV to 70 μm, from 0.4 to 0.2, and then increase back up to 0.3 at 500 microns. The main result is that, on average, the dust-mass surface-density scale-length is about 1.8 times the stellar one derived from IRAC data and the 3.6 μm surface brightness, and close to that in the UV. We found a mild dependence of the scale-lengths on the Hubble stage T: the scale-lengths of the Herschel bands and the 3.6 μm scale-length tend to increase from earlier to later types, the scale-length at 70 μm tends to be smaller than that at longer sub-mm wavelength with ratios between longer sub-mm wavelengths and 70 μm that decrease with increasing T. The scale-length ratio of SFR and stars shows a weak increasing trend towards later types. Our αCO determinations are in the range (0.3-9) M⊙ pc-2 (K km s-1)-1, almost invariant by using a fixed dust-to-gas ratio mass (DGR) or a DGR depending on metallicity

DISCOVERY OF TWIN WOLF-RAYET STARS POWERING DOUBLE RING NEBULAE

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

Mauerhan, Jon C.; Wachter, Stefanie; Van Dyk, Schuyler D.

We have spectroscopically discovered a pair of twin, nitrogen-type, hydrogen-rich, Wolf-Rayet stars (WN8-9h) that are both surrounded by circular, mid-infrared-bright nebulae detected with the Spitzer Space Telescope and MIPS instrument. The emission is probably dominated by a thermal continuum from cool dust, but also may contain contributions from atomic line emission. There is no counterpart at shorter Spitzer/IRAC wavelengths, indicating a lack of emission from warm dust. The two nebulae are probably wind-swept stellar ejecta released by the central stars during a prior evolutionary phase. The nebulae partially overlap on the sky and we speculate on the possibility that theymore » are in the early stage of a collision. Two other evolved massive stars have also been identified within the area subtended by the nebulae, including a carbon-type Wolf-Rayet star (WC8) and an O7-8 III-I star, the latter of which appears to be embedded in one of the larger WN8-9h nebulae. The derived distances to these stars imply that they are coeval members of an association lying 4.9 {+-} 1.2 kpc from Earth, near the intersection of the Galaxy's Long Bar and the Scutum-Centaurus spiral arm. This new association represents an unprecedented display of complex interactions between multiple stellar winds, outflows, and the radiation fields of evolved massive stars.« less

The GALEX/S4G Surface Brightness and Color Profiles Catalog. I. Surface Photometry and Color Gradients of Galaxies

NASA Astrophysics Data System (ADS)

Bouquin, Alexandre Y. K.; Gil de Paz, Armando; Muñoz-Mateos, Juan Carlos; Boissier, Samuel; Sheth, Kartik; Zaritsky, Dennis; Peletier, Reynier F.; Knapen, Johan H.; Gallego, Jesús

2018-02-01

We present new spatially resolved surface photometry in the far-ultraviolet (FUV) and near-ultraviolet (NUV) from images obtained by the Galaxy Evolution Explorer (GALEX) and IRAC1 (3.6 μm) photometry from the Spitzer Survey of Stellar Structure in Galaxies (S4G). We analyze the radial surface brightness profiles μ FUV, μ NUV, and μ [3.6], as well as the radial profiles of (FUV ‑ NUV), (NUV ‑ [3.6]), and (FUV ‑ [3.6]) colors in 1931 nearby galaxies (z < 0.01). The analysis of the 3.6 μm surface brightness profiles also allows us to separate the bulge and disk components in a quasi-automatic way and to compare their light and color distribution with those predicted by the chemo-spectrophotometric models for the evolution of galaxy disks of Boissier & Prantzos. The exponential disk component is best isolated by setting an inner radial cutoff and an upper surface brightness limit in stellar mass surface density. The best-fitting models to the measured scale length and central surface brightness values yield distributions of spin and circular velocity within a factor of two of those obtained via direct kinematic measurements. We find that at a surface brightness fainter than μ [3.6] = 20.89 mag arcsec‑2, or below 3 × 108 M ⊙ kpc‑2 in stellar mass surface density, the average specific star formation rate (sSFR) for star-forming and quiescent galaxies remains relatively flat with radius. However, a large fraction of GALEX Green Valley galaxies show a radial decrease in sSFR. This behavior suggests that an outside-in damping mechanism, possibly related to environmental effects, could be testimony of an early evolution of galaxies from the blue sequence of star-forming galaxies toward the red sequence of quiescent galaxies.

Ultraviolet spectrophotometry from Gemini 11 of stars in Orion

NASA Technical Reports Server (NTRS)

Morgan, T. H.; Spear, G. G.; Kondo, Y.; Henize, K. G.

1975-01-01

Ultraviolet spectrophotometry in the wavelength region 2600-3600 A is reported for the bright early-type stars beta, eta, gamma, delta, iota, epsilon, sigma, zeta, and kappa Ori. The results are in good agreement with other observations, and, with the possible exception of the supergiants, are in good agreement with recent line-blanketed model atmospheres. There is evidence that the supergiants possess a small ultraviolet deficiency shortward of 3000 A relative to main-sequence stars of similar spectral type. The most extreme example of this phenomenon is the star kappa Ori.

Observing Double Stars

NASA Astrophysics Data System (ADS)

Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

2012-05-01

Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

NEARBY MASSIVE STAR CLUSTER YIELDS INSIGHTS INTO EARLY UNIVERSE

NASA Technical Reports Server (NTRS)

2002-01-01

A NASA Hubble Space Telescope 'family portrait' of young, ultra-bright stars nested in their embryonic cloud of glowing gases. The celestial maternity ward, called N81, is located 200,000 light-years away in the Small Magellanic Cloud (SMC), a small irregular satellite galaxy of our Milky Way. Hubble's exquisite resolution allows astronomers to pinpoint 50 separate stars tightly packed in the nebula's core within a 10 light-year diameter - slightly more than twice the distance between earth and the nearest star to our sun. The closest pair of stars is only 1/3 of a light-year apart (0.3 arcseconds in the sky). This furious rate of mass loss from these super-hot stars is evident in the Hubble picture that reveals dramatic shapes sculpted in the nebula's wall of glowing gases by violent stellar winds and shock waves. A pair of bright stars in the center of the nebula is pouring out most of the ultraviolet radiation to make the nebula glow. Just above them, a small dark knot is all that's left of the cold cloud of molecular hydrogen and dust the stars were born from. Dark absorption lanes of residual dust trisect the nebula. The nebula offers a unique opportunity for a close-up glimpse at the 'firestorm' accompanying the birth of extremely massive stars, each blazing with the brilliance of 300,000 of our suns. Such galactic fireworks were much more common billions of years ago in the early universe, when most star formation took place. The 'natural-color' view was assembled from separate images taken with the Wide Field and Planetary Camera 2, in ultraviolet light and two narrow emission lines of ionized Hydrogen (H-alpha, H-beta). The picture was taken on September 4, 1997. Credit: Mohammad Heydari-Malayeri (Paris Observatory, France), NASA/ESA

The SW Sextantis-type star 2MASS J01074282+4845188: an unusual bright accretion disk with non-steady emission and a hot white dwarf

NASA Astrophysics Data System (ADS)

Khruzina, T.; Dimitrov, D.; Kjurkchieva, D.

2013-03-01

Context. Cataclysmic variables (CVs) present a short evolutional stage of binary systems. The nova-like stars are rare objects, especially those with eclipses (only several tens). But precisely these allow to determine the global parameters of their configurations and to learn more about the late stage of stellar evolution. Aims: The light curve solution allows one to determine the global parameters of the newly discovered nova-like eclipsing star 2MASS J01074282+4845188 and to estimate the contribution of the different light sources. Methods: We present new photometric and spectral observations of 2MASS J01074282+4845188. To obtain a light curve solution we used a model of a nova-like star whose emission sources are a white dwarf surrounded by an accretion disk, a secondary star filling its Roche lobe, a hot spot and a hot line. The obtained global parameters are compared with those of the eclipsing nova-like UX UMa. Results: 2MASS J01074282+4845188 shows the deepest permanent eclipse among the known nova-like stars. It is reproduced by covering the very bright accretion disk by the secondary component. The luminosity of the disk is much bigger than that of the rest light sources. The determined high temperature of the disk is typical for that observed during the outbursts of CVs. The primary of 2MASS J01074282+4845188 is one of the hottest white dwarfs in CVs. The temperature of 5090 K of its secondary is also quite high and more appropriate for a long-period SW Sex star. It might be explained by the intense heating from the hot white dwarf and the hot accretion disk of the target. Conclusions: The high mass accretion rate Ṁ = 8 × 10-9 M⊙ yr-1, the broad and single-peaked Hα emission profile, and the presence of an S-wave are sure signs for the SW Sex classification of 2MASS J01074282+4845188. The obtained flat temperature distribution along the disk radius as well as the deviation of the energy distribution from the black-body law are evidence of the non

The ZTF Bright Transient Survey

NASA Astrophysics Data System (ADS)

Fremling, C.; Sharma, Y.; Kulkarni, S. R.; Miller, A. A.; Taggart, K.; Perley, D. A.; Gooba, A.

2018-06-01

As a supplement to the Zwicky Transient Facility (ZTF; ATel #11266) public alerts (ATel #11685) we plan to report (following ATel #11615) bright probable supernovae identified in the raw alert stream from the ZTF Northern Sky Survey ("Celestial Cinematography"; see Bellm & Kulkarni, 2017, Nature Astronomy 1, 71) to the Transient Name Server (https://wis-tns.weizmann.ac.il) on a daily basis; the ZTF Bright Transient Survey (BTS; see Kulkarni et al., 2018; arXiv:1710.04223).

VVV high proper motion stars - I. The catalogue of bright KS ≤ 13.5 stars

NASA Astrophysics Data System (ADS)

Kurtev, R.; Gromadzki, M.; Beamín, J. C.; Folkes, S. L.; Pena Ramirez, K.; Ivanov, V. D.; Borissova, J.; Villanueva, V.; Minniti, D.; Mendez, R.; Lucas, P. W.; Smith, L. C.; Pinfield, D. J.; Kuhn, M. A.; Jones, H. R. A.; Antonova, A.; Yip, A. K. P.

2017-01-01

Knowledge of the stellar content near the Sun is important for a broad range of topics ranging from the search for planets to the study of Milky Way (MW) structure. The most powerful method for identifying potentially nearby stars is proper motion (PM) surveys. All old optical surveys avoid, or are at least substantially incomplete, near the Galactic plane. The depth and breadth of the `VISTA Variables in Vía Láctea' (VVV) near-IR survey significantly improves this situation. Taking advantage of the VVV survey data base, we have measured PMs in the densest regions of the MW bulge and southern plane in order to complete the census of nearby objects. We have developed a custom PM pipeline based on VVV catalogues from the Cambridge Astronomy Survey Unit, by comparing the first epoch of JHKS with the multi-epoch KS bands acquired later. Taking advantage of the large time baseline between the Two Micron All Sky Survey (2MASS) and the VVV observations, we also obtained 2MASS-VVV PMs. We present a near-IR PM catalogue for the whole area of the VVV survey, which includes 3003 moving stellar sources. All of these have been visually inspected and are real PM objects. Our catalogue is in very good agreement with the PM data supplied in IR catalogues outside the densest zone of the MW. The majority of the PM objects in our catalogue are nearby M-dwarfs, as expected. This new data base allows us to identify 57 common PM binary candidates, among which are two new systems within 30 pc of the Sun.

VizieR Online Data Catalog: BCool survey of solar-type stars (Marsden+ 2014)

NASA Astrophysics Data System (ADS)

Marsden, S. C.; Petit, P.; Jeffers, S. V.; Morin, J.; Fares, R.; Reiners, A.; Do Nascimento, J.-D., Jr.; Auriere, M.; Bouvier, J.; Carter, B. D.; Catala, C.; Dintrans, B.; Donati, J.-F.; Gastine, T.; Jardine, M.; Konstantinova-Antova, R.; Lanoux, J.; Lignieres, F.; Morgenthaler, A.; Ramirez-Velez, J. C.; Theado, S.; Van Grootel, V.; BCool Collaboration

2015-04-01

The goal of the BCool spectropolarimetric survey is to observe as many of the bright (V<~9.0) solar-type stars as possible to further our understanding of the magnetic activity of cool stars. In this first paper, we present the spectropolarimetric snapshots of 170 solar-type stars that we have observed starting in 2006 until 2013 as part of the BCool survey. (5 data files).

Unveiling the nature of bright z ≃ 7 galaxies with the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Bowler, R. A. A.; Dunlop, J. S.; McLure, R. J.; McLeod, D. J.

2017-04-01

We present new Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) imaging of 25 extremely luminous (-23.2 ≤ MUV ≲ -21.2) Lyman-break galaxies (LBGs) at z ≃ 7. The sample was initially selected from 1.65 deg2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman α emitters, 'Himiko' and 'CR7'. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW0(Hβ + [O III]) > 600 Å). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (fmulti > 0.4) in bright z ≃ 7 galaxies, and ubiquitous at the very bright end (MUV < -22.5). The galaxies have half-light radii in the range r1/2 ˜ 0.5-3 kpc. The size measurements provide the first determination of the size-luminosity relation at z ≃ 7 that extends to MUV ˜ -23. We find the relation to be steep with r1/2 ∝ L1/2. Excluding clumpy, multicomponent galaxies however, we find a shallower relation that implies an increased star formation rate surface density in bright LBGs. Using the new, independent, HST/WFC3 data we confirm that the rest-frame UV luminosity function at z ≃ 7 favours a power-law decline at the bright end, compared to an exponential Schechter function drop-off. Finally, these results have important implications for the Euclid mission, which we predict will detect >1000 similarly bright galaxies at z ≃ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination.

Sonneberg Plate Photometry for Boyajian’s Star in Two Passbands

NASA Astrophysics Data System (ADS)

Hippke, Michael; Kroll, Peter; Matthai, Frank; Angerhausen, Daniel; Tuvikene, Taavi; Stassun, Keivan G.; Roshchina, Elena; Vasileva, Tatyana; Izmailov, Igor; Samus, Nikolay N.; Pastukhova, Elena N.; Bryukhanov, Ivan; Lund, Michael B.

2017-03-01

The F3 main-sequence star KIC 8462852 (Boyajian’s Star) showed deep (up to 20%) day-long brightness dips of unknown cause during the four years of the Kepler mission. A 0.164 mag (16%) dimming between 1890 and 1990 was claimed, based on the analysis of photographic plates from the Harvard Observatory. We have gathered an independent set of historic plates from Sonneberg Observatory, Germany, covering the years of 1934-1995. With 861 mag in B, and 397 mag in V, we find the star to be of constant brightness within 0.03 mag per century (3%). Consistent outcomes are found using by-eye estimates of the best 119 plates. Results are supported by data from Sternberg Observatory, Moscow, which show the star as constant between 1895 and 1995. The previously claimed century-long dimming is inconsistent with our results at the 5σ -level, however, the recently reported modest dimming of 3% in the Kepler data is not inconsistent with our data. We find no periodicities or shorter trends within our limits of 5% per five year bin, but note a possible dimming event on 1978 October 24.

A multi-wavelength study of pre-main sequence stars in the Taurus-Auriga star-forming region

NASA Astrophysics Data System (ADS)

Guenther, E. W.; Stelzer, B.; Neuhäuser, R.; Hillwig, T. C.; Durisen, R. H.; Menten, K. M.; Greimel, R.; Barwig, H.; Englhauser, J.; Robb, R. M.

2000-05-01

Although many lowmass pre-main sequence stars are strong X-ray sources, the origin of the X-ray emission is not well known. Since these objects are variable at all frequencies, simultaneous observations in X-rays and in other wavelengths are able to constrain the properties of the X-ray emitting regions. In this paper, we report quasi-simultaneous observations in X-rays, the optical, and the radio regime for classical and weak-line T Tauri stars from the Taurus-Auriga star-forming region. We find that all detected T Tauri stars show significant night-to-night variations of the X-ray emission. For three of the stars, FM Tau and CW Tau, both classical T Tauri stars, and V773 Tau, a weak-line T Tauri star, the variations are especially large. From observations taken simultaneously, we also find that there is some correspondence between the strength of Hα and the X-ray brightness in V773 Tau. The lack of a strong correlation leads us to conclude that the X-ray emission of V773 Tau is not a superposition of flares. However, we suggest that a weak correlation occurs because chromospherically active regions and regions of strong X-ray emission are generally related. V773 Tau was detected at 8.46 GHz as a weakly circularly polarised but highly variable source. We also find that the X-ray emission and the equivalent width of Hα remained unchanged, while large variations of the flux density in the radio regime were observed. This clearly indicates that the emitting regions are different. Using optical spectroscopy we detected a flare in Hα and event which showed a flare-like light-curve of the continuum brightness in FM Tau. However, ROSAT did not observe the field at the times of these flares. Nevertheless, an interesting X-ray event was observed in V773 Tau, during which the flux increased for about 8 hours and then decreased back to the same level in 5 hours. We interpret this as a long-duration event similar to those seen on the sun and other active stars. In the

Brilliant Star in a Colourful Neighbourhood

NASA Astrophysics Data System (ADS)

2010-07-01

A spectacular new image from ESO's Wide Field Imager at the La Silla Observatory in Chile shows the brilliant and unusual star WR 22 and its colourful surroundings. WR 22 is a very hot and bright star that is shedding its atmosphere into space at a rate many millions of times faster than the Sun. It lies in the outer part of the dramatic Carina Nebula from which it formed. Very massive stars live fast and die young. Some of these stellar beacons have such intense radiation passing through their thick atmospheres late in their lives that they shed material into space many millions of times more quickly than relatively sedate stars such as the Sun. These rare, very hot and massive objects are known as Wolf-Rayet stars [1], after the two French astronomers who first identified them in the mid-nineteenth century, and one of the most massive ones yet measured is known as WR 22. It appears at the centre of this picture, which was created from images taken through red, green and blue filters with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile. WR 22 is a member of a double star system and has been measured to have a mass at least 70 times that of the Sun. WR 22 lies in the southern constellation of Carina, the keel of Jason's ship Argo in Greek mythology. Although the star lies over 5000 light-years from the Earth it is so bright that it can just be faintly seen with the unaided eye under good conditions. WR 22 is one of many exceptionally brilliant stars associated with the beautiful Carina Nebula (also known as NGC 3372) and the outer part of this huge region of star formation in the southern Milky Way forms the colourful backdrop to this image. The subtle colours of the rich background tapestry are a result of the interactions between the intense ultraviolet radiation coming from hot massive stars, including WR 22, and the vast gas clouds, mostly hydrogen, from which they formed. The central part of this enormous complex

AL Pictoris and FR Piscium: Two Regular Blazhko RR Lyrae Stars

NASA Astrophysics Data System (ADS)

de Ponthière, P.; Hambsch, F.-J.; Menzies, K.; Sabo, R.

2014-12-01

The results presented are a continuation of observing campaigns conducted by a small group of amateur astronomers interested in the Blazhko effect of RR Lyrae stars. The goal of these observations is to confirm the RR Lyrae Blazhko effect and to detect any additional Blazhko modulation which cannot be identified from all sky survey data-mining. The Blazhko effect of the two observed stars is confirmed, but no additional Blazhko modulations have been detected. The observation of the RR Lyrae star AL Pictoris during 169 nights was conducted from San Pedro de Atacama (Chile). From the observed light curve, 49 pulsation maxima have been measured. Fourier analyses of (O-C), magnitude at maximum light (Mmax), and the complete light curve have provided a confirmation of published pulsation and Blazhko periods, 0.548622 and 34.07 days, respectively. The second multi-longitude observation campaign focused on the RR Lyrae star FR Piscium and was performed from Europe, the United States, and Chile. Fourier analyses of the light curve and of 59 measured brightness maxima have improved the accuracy of pulsation and Blazhko periods to 0.45568 and 51.31 days, respectively. For both stars, no additional Blazhko modulations have been detected.

[right] - DUST RING AROUND STAR OFFERS NEW CLUES INTO PLANET FORMATION

NASA Technical Reports Server (NTRS)

2002-01-01

A NASA Hubble Space Telescope false-color near infrared image of a novel type of structure seen in space - a dust ring around a star. Superficially resembling Saturn's rings -- but on a vastly larger scale -- the 'hula-hoop' around the star called HR 4796A offers new clues into the possible presence of young planets. The near-infrared light reflecting off the dust ring is about 1,000 times fainter than the illuminating central star. Astronomers used a coronagraphic camera on Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS), specifically designed to enable observations of very faint and low surface brightness objects in the close proximity to bright stars. Even with the coronagraph, the glare from HR 4796A overwhelms the much-fainter ring at distances less than about 4 billion miles (inside the blacked-out circle, centered on the star). Hubble's crisp view was able to resolve the ring, seen at lower resolution at longer wavelengths, in ground-based thermal infrared images, as a disk with some degree of central clearing. The ring has an angular radius of 1.05 arc seconds, equivalent to the apparent size of a dime seen more than 4 miles away. Unlike the extensive disks of dust seen around other young stars, the HR 4796A dust ring, 6.5 billion miles from the star, is tightly confined within a relatively narrow zone less than 17 Astronomical Units wide. An Astronomical Unit is the distance from the Earth to the Sun). For comparison, the ring width is approximately equal to the distance separating the orbits of Mars and Uranus in our own Solar System. All dust rings, whether around stars or planets, can only stay intact by some mechanism confining the dust, likely the gravitational tug of unseen planets. The image was taken on March 15, 1998, centered at a near infrared wavelength of 1.1 microns. The false-color corresponds to the ring's brightness (yellow is bright, purple is faint). The ring, which is undoubtedly circular, appears elliptical since

Symbiotic Stars in X-rays

NASA Technical Reports Server (NTRS)

Luna, G. J. M.; Sokoloski, J. L.; Mukai, K.; Nelson, T.

2014-01-01

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 9 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 9 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the alpha/beta/gamma classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new sigma classification for sources with

Space Shuttle Star Tracker Challenges

NASA Technical Reports Server (NTRS)

Herrera, Linda M.

2010-01-01

The space shuttle fleet of avionics was originally designed in the 1970's. Many of the subsystems have been upgraded and replaced, however some original hardware continues to fly. Not only fly, but has proven to be the best design available to perform its designated task. The shuttle star tracker system is currently flying as a mixture of old and new designs, each with a unique purpose to fill for the mission. Orbiter missions have tackled many varied missions in space over the years. As the orbiters began flying to the International Space Station (ISS), new challenges were discovered and overcome as new trusses and modules were added. For the star tracker subsystem, the growing ISS posed an unusual problem, bright light. With two star trackers on board, the 1970's vintage image dissector tube (IDT) star trackers track the ISS, while the new solid state design is used for dim star tracking. This presentation focuses on the challenges and solutions used to ensure star trackers can complete the shuttle missions successfully. Topics include KSC team and industry partner methods used to correct pressurized case failures and track system performance.

HD 38452 - J. R. Hind's star that changed colour

NASA Technical Reports Server (NTRS)

Warner, Brian; Sneden, Christopher

1988-01-01

In 1851, John Russell Hind announced that a star previously observed by him to be very red had become bluish white in color. It is shown that this star, HD 38451, is a ninth magnitude shell star which presumably was ejecting a shell when Hind first observed it. From high dispersion coude spectra, low dispersion IUE spectra, and ground-based photometry, HD 38451 is found to be a normal A21V shell star. Its current values of E(B-V) of about 0.14 is probably caused by interstellar rather than circumstellar reddening. There remains a problem to reconcile the large amount of reddening present when Hind first observed the star with its evidently small diminution in visual brightness at that time.

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.

Cool Stars May Have Different Prebiotic Chemical Mix

NASA Technical Reports Server (NTRS)

2009-01-01

NASA's Spitzer Space Telescope detected a prebiotic, or potentially life-forming, molecule called hydrogen cyanide (HCN) in the planet-forming disks around yellow stars like our sun, but not in the disks around cooler, reddish stars.

The observations are plotted in this graph, called a spectrum, in which light from the gas in the disks around the stars has been split up into its basic components, or wavelengths. Data from stars like our sun are yellow, and data from cool stars are orange. Light wavelengths are shown on the X-axis, and the relative brightness of disk emission is shown on the Y-axis. The signature of a baseline molecule, called acetylene (C₂H₂), was seen for both types of stars, but hydrogen cyanide was seen only around stars like our sun.

Hydrogen cyanide is an organic, nitrogen-containing molecule. Five hydrogen cyanide molecules can link up to form adenine, one of the four chemical bases of DNA.

Identifying the Young Low-mass Stars within 25 pc. II. Distances, Kinematics, and Group Membership

NASA Astrophysics Data System (ADS)

Shkolnik, Evgenya L.; Anglada-Escudé, Guillem; Liu, Michael C.; Bowler, Brendan P.; Weinberger, Alycia J.; Boss, Alan P.; Reid, I. Neill; Tamura, Motohide

2012-10-01

We have conducted a kinematic study of 165 young M dwarfs with ages of lsim300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of lsim25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (lsim3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and β Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages lsim150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event. Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope, the du Pont Telescope at Las Campanas Observatory, and the Subaru Telescope. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial

Design of a Day/Night Star Camera System

NASA Technical Reports Server (NTRS)

Alexander, Cheryl; Swift, Wesley; Ghosh, Kajal; Ramsey, Brian

1999-01-01

This paper describes the design of a camera system capable of acquiring stars during both the day and night cycles of a high altitude balloon flight (35-42 km). The camera system will be filtered to operate in the R band (590-810 nm). Simulations have been run using MODTRAN atmospheric code to determine the worse case sky brightness at 35 km. With a daytime sky brightness of 2(exp -05) W/sq cm/str/um in the R band, the sensitivity of the camera system will allow acquisition of at least 1-2 stars/sq degree at star magnitude limits of 8.25-9.00. The system will have an F2.8, 64.3 mm diameter lens and a 1340X1037 CCD array digitized to 12 bits. The CCD array is comprised of 6.8 X 6.8 micron pixels with a well depth of 45,000 electrons and a quantum efficiency of 0.525 at 700 nm. The camera's field of view will be 6.33 sq degree and provide attitude knowledge to 8 arcsec or better. A test flight of the system is scheduled for fall 1999.

Analysis of the Herschel DEBRIS Sun-like star sample

NASA Astrophysics Data System (ADS)

Sibthorpe, B.; Kennedy, G. M.; Wyatt, M. C.; Lestrade, J.-F.; Greaves, J. S.; Matthews, B. C.; Duchêne, G.

2018-04-01

This paper presents a study of circumstellar debris around Sun-like stars using data from the Herschel DEBRIS Key Programme. DEBRIS is an unbiased survey comprising the nearest ˜90 stars of each spectral type A-M. Analysis of the 275 F-K stars shows that excess emission from a debris disc was detected around 47 stars, giving a detection rate of 17.1^{+2.6}_{-2.3} per cent, with lower rates for later spectral types. For each target a blackbody spectrum was fitted to the dust emission to determine its fractional luminosity and temperature. The derived underlying distribution of fractional luminosity versus blackbody radius in the population showed that most detected discs are concentrated at f ˜ 10-5 and at temperatures corresponding to blackbody radii 7-40 au, which scales to ˜40 au for realistic dust properties (similar to the current Kuiper belt). Two outlying populations are also evident; five stars have exceptionally bright emission ( f > 5 × 10-5), and one has unusually hot dust <4 au. The excess emission distributions at all wavelengths were fitted with a steady-state evolution model, showing that these are compatible with all stars being born with a narrow belt that then undergoes collisional grinding. However, the model cannot explain the hot dust systems - likely originating in transient events - and bright emission systems - arising potentially from atypically massive discs or recent stirring. The emission from the present-day Kuiper belt is predicted to be close to the median of the population, suggesting that half of stars have either depleted their Kuiper belts (similar to the Solar system) or had a lower planetesimal formation efficiency.

HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED

NASA Technical Reports Server (NTRS)

2002-01-01

BY ANCIENT ENCOUNTER This stunningly beautiful image [right] taken with the NASA Hubble Space Telescope shows the heart of the prototypical starburst galaxy M82. The ongoing violent star formation due to an ancient encounter with its large galactic neighbor, M81, gives this galaxy its disturbed appearance. The smaller picture at upper left shows the entire galaxy. The image was taken in December 1994 by the Kitt Peak National Observatory's 0.9-meter telescope. Hubble's view is represented by the white outline in the center. In the Hubble image, taken by the Wide Field and Planetary Camera 2, the huge lanes of dust that crisscross M82's disk are another telltale sign of the flurry of star formation. Below the center and to the right, a strong galactic wind is spewing knotty filaments of hydrogen and nitrogen gas. More than 100 super star clusters -- very bright, compact groupings of about 100,000 stars -- are seen in this detailed Hubble picture as white dots sprinkled throughout M82's central region. The dark region just above the center of the picture is a huge dust cloud. A collaboration of European and American scientists used these clusters to date the ancient interaction between M82 and M81. About 600 million years ago, a region called 'M82 B' (the bright area just below and to the left of the central dust cloud) exploded with new stars. Scientists have discovered that this ancient starburst was triggered by the violent encounter with M81. M82 is a bright (eighth magnitude), nearby (12 million light-years from Earth) galaxy in the constellation Ursa Major (the Great Bear). The Hubble picture was taken Sept. 15, 1997. The natural-color composite was constructed from three Wide Field and Planetary Camera 2 exposures, which were combined in chromatic order: 4,250 seconds through a blue filter (428 nm); 2,800 seconds through a green filter (520 nm); and 2,200 seconds through a red (820 nm) filter. Credits for Hubble image: NASA, ESA, R. de Grijs (Institute of

An Ultraviolet and Near-Infrared View of NGC 4214: A Starbursting Core Embedded in a Low Surface Brightness Disk

NASA Astrophysics Data System (ADS)

Fanelli, Michael N.; Waller, William W.; Smith, Denise A.; Freedman, Wendy L.; Madore, Barry; Neff, Susan G.; O'Connell, Robert W.; Roberts, Morton S.; Bohlin, Ralph; Smith, Andrew M.; Stecher, Theodore P.

1997-05-01

During the Astro-2 Spacelab mission in 1995 March, the Ultraviolet Imaging Telescope (UIT) obtained far-UV (λ = 1500 Å) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial resolution of ~3" and a limiting surface brightness, μ1500 > 25 mag arcsec-2, permitting detailed investigation of the intensity and spatial distribution of the young, high-mass stellar component. These data provide the first far-UV imagery covering the full spatial extent of NGC 4214. Comparison with a corresponding I-band image reveals the presence of a starbursting core embedded in an extensive low surface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r <~ 2.5 kpc) with ~15 resolved sources embedded in bright, diffuse emission; and a population of fainter knots extending to the edge of the optically defined disk (r ~ 5 kpc). The FUV light, which traces recent massive star formation, is observed to be more centrally concentrated than the I-band light, which traces the global stellar population. The FUV radial light profile is remarkably well represented by an R1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the result of an interaction, possibly a tidal encounter, with a dwarf companion(s). The brightest FUV source produces ~8% of the global FUV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of the FUV light distribution, giving NGC 4214 an active galactic nucleus-like morphology. Another strong source is present in the I band, located 19" west, 10" north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucleus of NGC 4214 or an evolved star cluster with an age greater than ~200 Myr. The global star formation rate derived from the total FUV flux is consistent with rates derived using data at other

Shocks and star formation in Stephan's Quintet. I. Gemini spectroscopy of Hα-bright knots

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

Konstantopoulos, I. S.; Cluver, M. E.; Appleton, P. N.

2014-03-20

We present a Gemini-GMOS spectroscopic study of Hubble Space Telescope (HST)-selected Hα-emitting regions in Stephan's Quintet (HCG 92), a nearby compact galaxy group, with the aim of disentangling the processes of shock-induced heating and star formation in its intra-group medium. The ≈40 sources are distributed across the system, but most densely concentrated in the ∼kiloparsec-long shock region. Their spectra neatly divide them into narrow- and broad-line emitters, and we decompose the latter into three or more emission peaks corresponding to spatial elements discernible in HST imaging. The emission-line ratios of the two populations of Hα-emitters confirm their nature as Hmore » II regions (90% of the sample) or molecular gas heated by a shock front propagating at ≲300 km s{sup –1}. Their redshift distribution reveals interesting three-dimensional structure with respect to gas-phase baryons, with no H II regions associated with shocked gas, no shocked regions in the intruder galaxy NGC 7318B, and a sharp boundary between shocks and star formation. We conclude that star formation is inhibited substantially, if not entirely, in the shock region. Attributing those H II regions projected against the shock to the intruder, we find a lopsided distribution of star formation in this galaxy, reminiscent of pileup regions in models of interacting galaxies. The Hα luminosities imply mass outputs, star formation rates, and efficiencies similar to nearby star-forming regions. Two large knots are an exception to this, being comparable in stellar output to the prolific 30 Doradus region. We also examine Stephan's Quintet in the context of compact galaxy group evolution, as a paradigm for intermittent star formation histories in the presence of a rich, X-ray-emitting intra-group medium. All spectra are provided as supplemental materials.« less

Hubble Sweeps a Messy Star Factory

NASA Image and Video Library

2017-12-08

This sprinkle of cosmic glitter is a blue compact dwarf galaxy known as Markarian 209. Galaxies of this type are blue-hued, compact in size, gas-rich, and low in heavy elements. They are often used by astronomers to study star formation, as their conditions are similar to those thought to exist in the early Universe. Markarian 209 in particular has been studied extensively. It is filled with diffuse gas and peppered with star-forming regions towards its core. This image captures it undergoing a particularly dramatic burst of star formation, visible as the lighter blue cloudy region towards the top right of the galaxy. This clump is filled with very young and hot newborn stars. This galaxy was initially thought to be a young galaxy undergoing its very first episode of star formation, but later research showed that Markarian 209 is actually very old, with an almost continuous history of forming new stars. It is thought to have never had a dormant period — a period during which no stars were formed — lasting longer than 100 million years. The dominant population of stars in Markarian 209 is still quite young, in stellar terms, with ages of under 3 million years. For comparison, the sun is some 4.6 billion years old, and is roughly halfway through its expected lifespan. The observations used to make this image were taken using Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys, and span the ultraviolet, visible, and infrared parts of the spectrum. A scattering of other bright galaxies can be seen across the frame, including the bright golden oval that could, due to a trick of perspective, be mistaken as part of Markarian 209 but is in fact a background galaxy. Credit: ESA/Hubble & NASA Acknowledgement: Nick Rose NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments

Deep Stromvil Photometry for Star Formation in the Head of the Pelican Nebula

NASA Astrophysics Data System (ADS)

Boyle, Richard P.; J., S.; Stott, J.; J., S.; Janusz, R.; J., S.; Straizys, V.

2010-01-01

The North America and Pelican Nebulae, and specifically the dark cloud L935 contain regions of active star formation (Herbig, G. H. 1958, ApJ, 128,259). Previously we reported on Vatican telescope observations by Stromvil intermediate-band filters in a 12-arcmin field in the "Gulf of Mexico" region of L935. There we classify A, F, and G-type stars. However, the many faint K and M-type dwarf stars remain somewhat ambiguous in calibration and classification. But attaining reasonable progress, we turn to another part of L935 located near the Pelican head. This area includes the "bright rim" which is formed by dust and gas condensed by the light pressure of an unseen O-type star hidden behind the dense dark cloud. Straizys and Laugalys (2008 Baltic Astronomy, 17, 143 ) have identified this star to be one of the 2MASS objects with Av=23 mag. A few concentrations of faint stars, V 13 to 14 mag. are immersed in this dark region. Among these stars are a few known emission-line objects (T-Tauri or post T-Tauri stars). A half degree nearby are some photometric Vilnius standards we use to calibrate our new field. We call on 2MASS data for correlative information. Also the Stromvil photometry offers candidate stars for spectral observations. The aim of this study in the Vilnius and Stromvil photometric systems is to classify stars down to V = 18 mag., to confirm the existence of the young star clusters, and to determine the distance of the cloud covering the suspected hidden ionizing star.

The primary role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Gaensicke, Boris; Rodriguez-Gil, Pablo; Long, Knox; Marsh, Tom; Steeghs, Danny; Munoz-Darias, Teodoro; Shahbaz, Tariq; Schmidtobreick, Linda; Schreiber, Matthias

2009-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) which plays a fundamental role in our understanding of CV structure and evolution. 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 a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the binary parameters, white dwarf temperature, and distance to the system for a SW Sex star for the first time. The measured stellar masses and radii will especially be a precious input to the theory of compact binary evolution as a whole.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Steeghs, Danny; Gaensicke, Boris; Marsh, Tom; Rodriguez-Gil, Pablo; Schmidtobreick, Linda; Long, Knox; Schreiber, Matthias

2007-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) 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 a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel

2007-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) 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 a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

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.

Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

NASA Technical Reports Server (NTRS)

Nakajima, Tadashi; Golimowski, David A.

1995-01-01

We have obtained R- and I-band coronagraphic images of the vicinities of 11 pre-main sequence (PMS) stars to search for faint, small-scale reflection nebulae. The inner radius of the search and the field of view are 1.9 arcsec and 1x1 arcmin, respectively. Reflection nebulae were imaged around RY Tau, T Tau,DG Tau, SU Aur, AB Aur, FU Ori, and Z CMa. No nebulae were detected around HBC 347, GG Tau, V773 Tau, and V830 Tau. Categorically speaking, most of the classical T Tauri program stars and all the FU Orionis-type program stars are associated with the reflection nebulae, while none of the weak-line T Tauri program stars are associated with nebulae. The detected nebulae range in size from 250 to 37 000 AU. From the brightness ratios of the stars and nebulae, we obtain a lower limit to the visual extinction of PMS star light through the nebulae of (A(sub V))(sub neb) = 0.1. The lower limits of masses and volume densities of the nebulae associated with the classical T Tauri stars are 10(exp-6) Solar mass and N(sub H) = 10(exp 5)/cu cm, respectively. Lower limits for the nebulae around FU Orionis stars are 10(exp -5) Solar mass and n(sub H) = 10 (exp 5)/cu cm, respectively. Some reflection nebulae may trace the illuminated surfaces of the optically thick dust nebulae, so these mass estimates are not stringent. All the PMS stars with associated nebulae are strong far-infrared emitters. Both the far-infrared emission and the reflection nebulae appear to originate from the remnant envelopes of star formation. The 100 micrometers emitting regions of SU Aur and FU Ori are likely to be cospatial with the reflection nebulae. A spatial discontinuity between FU Ori and its reflection nebula may explain the dip in the far-infrared spectral energy distribution at 60 micrometers. The warped, disk-like nebulae around T Tau and Z CMa are aligned with and embrace the inner star/circumstellar disk systems. The arc-shaped nebula around DG Tau may be in contact with the coaligned inner

Wolf-Rayet Stars

NASA Astrophysics Data System (ADS)

Hamann, Wolf-Rainer; Sander, Andreas; Todt, Helge

Nearly 150 years ago, the French astronomers Charles Wolf and Georges Rayet described stars with very conspicuous spectra that are dominated by bright and broad emission lines. Meanwhile termed Wolf-Rayet Stars after their discoverers, those objects turned out to represent important stages in the life of massive stars. As the first conference in a long time that was specifically dedicated to Wolf-Rayet stars, an international workshop was held in Potsdam, Germany, from 1.-5. June 2015. About 100 participants, comprising most of the leading experts in the field as well as as many young scientists, gathered for one week of extensive scientific exchange and discussions. Considerable progress has been reported throughout, e.g. on finding such stars, modeling and analyzing their spectra, understanding their evolutionary context, and studying their circumstellar nebulae. While some major questions regarding Wolf-Rayet stars still remain open 150 years after their discovery, it is clear today that these objects are not just interesting stars as such, but also keystones in the evolution of galaxies. These proceedings summarize the talks and posters presented at the Potsdam Wolf-Rayet workshop. Moreover, they also include the questions, comments, and discussions emerging after each talk, thereby giving a rare overview not only about the research, but also about the current debates and unknowns in the field. The Scientific Organizing Committee (SOC) included Alceste Bonanos (Athens), Paul Crowther (Sheffield), John Eldridge (Auckland), Wolf-Rainer Hamann (Potsdam, Chair), John Hillier (Pittsburgh), Claus Leitherer (Baltimore), Philip Massey (Flagstaff), George Meynet (Geneva), Tony Moffat (Montreal), Nicole St-Louis (Montreal), and Dany Vanbeveren (Brussels).

A SPITZER VIEW OF STAR FORMATION IN THE CYGNUS X NORTH COMPLEX

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

Beerer, I. M.; Koenig, X. P.; Hora, J. L.

2010-09-01

We present new images and photometry of the massive star-forming complex Cygnus X obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIRT Deep Infrared Sky Survey, and Two Micron All Sky Survey data are used to identify and classify young stellar objects (YSOs). Of the 8231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as class I and 7249 are classified as class II. Using spectra from the FAST Spectrograph at the Fred L. Whipple Observatory and Hectospecmore » on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9). We present a minimal spanning tree analysis of clusters in two regions in Cygnus X North. The fraction of infrared excess sources that belong to clusters with {>=}10 members is found to be 50%-70%. Most class II objects lie in dense clusters within blown out H II regions, while class I sources tend to reside in more filamentary structures along the bright-rimmed clouds, indicating possible triggered star formation.« less

Wide cool and ultracool companions to nearby stars from Pan-STARRS 1

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

Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.

2014-09-10

We present the discovery of 57 wide (>5'') separation, low-mass (stellar and substellar) companions to stars in the solar neighborhood identified from Pan-STARRS 1 (PS1) data and the spectral classification of 31 previously known companions. Our companions represent a selective subsample of promising candidates and span a range in spectral type of K7-L9 with the addition of one DA white dwarf. These were identified primarily from a dedicated common proper motion search around nearby stars, along with a few as serendipitous discoveries from our Pan-STARRS 1 brown dwarf search. Our discoveries include 23 new L dwarf companions and one knownmore » L dwarf not previously identified as a companion. The primary stars around which we searched for companions come from a list of bright stars with well-measured parallaxes and large proper motions from the Hipparcos catalog (8583 stars, mostly A-K dwarfs) and fainter stars from other proper motion catalogs (79170 stars, mostly M dwarfs). We examine the likelihood that our companions are chance alignments between unrelated stars and conclude that this is unlikely for the majority of the objects that we have followed-up spectroscopically. We also examine the entire population of ultracool (>M7) dwarf companions and conclude that while some are loosely bound, most are unlikely to be disrupted over the course of ∼10 Gyr. Our search increases the number of ultracool M dwarf companions wider than 300 AU by 88% and increases the number of L dwarf companions in the same separation range by 82%. Finally, we resolve our new L dwarf companion to HIP 6407 into a tight (0.''13, 7.4 AU) L1+T3 binary, making the system a hierarchical triple. Our search for these key benchmarks against which brown dwarf and exoplanet atmosphere models are tested has yielded the largest number of discoveries to date.« less

Stellar parameters of Be stars observed with X-shooter

NASA Astrophysics Data System (ADS)

Shokry, A.; Rivinius, Th.; Mehner, A.; Martayan, C.; Hummel, W.; Townsend, R. H. D.; Mérand, A.; Mota, B.; Faes, D. M.; Hamdy, M. A.; Beheary, M. M.; Gadallah, K. A. K.; Abo-Elazm, M. S.

2018-01-01

Aims: The X-shooter archive of several thousand telluric standard star spectra was skimmed for Be and Be shell stars to derive the stellar fundamental parameters and statistical properties, in particular for the less investigated late-type Be stars and the extension of the Be phenomenon into early A stars. Methods: An adapted version of the BCD method is used, using the Balmer discontinuity parameters to determine effective temperature and surface gravity. This method is optimally suited for late B stars. The projected rotational velocity was obtained by profile fitting to the Mg ii lines of the targets, and the spectra were inspected visually for the presence of peculiar features such as the infrared Ca ii triplet or the presence of a double Balmer discontinuity. The Balmer line equivalent widths were measured, but they are only useful for determining the pure emission contribution in a subsample of Be stars owing to uncertainties in determining the photospheric contribution. Results: A total of 78, mostly late-type, Be stars, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. We confirm the general trend that late-type Be stars have more tenuous disks and are less variable than early-type Be stars. The relatively large number (48) of relatively bright (V> 8.5) additional Be stars casts some doubt on the statistics of late-type Be stars; they are more common than currently thought. The Be/B star fraction may not strongly depend on spectral subtype. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 60.A-9022, 60.A-9024, 077.D-0085, 085.A-0962, 185.D-0056, 091.B-0900, and 093.D-0415.Table 6 is 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/609/A108

A Catalog of 1022 Bright Contact Binary Stars

NASA Astrophysics Data System (ADS)

Gettel, S. J.; Geske, M. T.; McKay, T. A.

2006-01-01

In this work we describe a large new sample of contact binary stars extracted in a uniform manner from sky patrol data taken by the ROTSE-I telescope. Extensive ROTSE-I light-curve data are combined with J-, H-, and K-band near-infrared data taken from the Two Micron All Sky Survey to add color information. Contact binary candidates are selected using the observed period-color relation. Candidates are confirmed by visual examination of the light curves. To enhance the utility of this catalog, we derive a new J-H period-color-luminosity relation and use this to estimate distances for the entire catalog. From these distance estimates we derive an estimated contact binary space density of (1.7+/-0.6)×10-5 pc-3.

Empirical effective temperatures and bolometric corrections for early-type stars

NASA Technical Reports Server (NTRS)

Code, A. D.; Bless, R. C.; Davis, J.; Brown, R. H.

1976-01-01

An empirical effective temperature for a star can be found by measuring its apparent angular diameter and absolute flux distribution. The angular diameters of 32 bright stars in the spectral range O5f to F8 have recently been measured with the stellar interferometer at Narrabri Observatory, and their absolute flux distributions have been found by combining observations of ultraviolet flux from the Orbiting Astronomical Observatory (OAO-2) with ground-based photometry. In this paper, these data have been combined to derive empirical effective temperatures and bolometric corrections for these 32 stars.

Adaptive Optics For Imaging Bright Objects Next To Dim Ones

NASA Technical Reports Server (NTRS)

Shao, Michael; Yu, Jeffrey W.; Malbet, Fabien

1996-01-01

Adaptive optics used in imaging optical systems, according to proposal, to enhance high-dynamic-range images (images of bright objects next to dim objects). Designed to alter wavefronts to correct for effects of scattering of light from small bumps on imaging optics. Original intended application of concept in advanced camera installed on Hubble Space Telescope for imaging of such phenomena as large planets near stars other than Sun. Also applicable to other high-quality telescopes and cameras.

Characterizing K2 Planet Discoveries: A Super-Earth Transiting the Bright K Dwarf HIP 116454

NASA Astrophysics Data System (ADS)

Vanderburg, Andrew; Montet, Benjamin T.; Johnson, John Asher; Buchhave, Lars A.; Zeng, Li; Pepe, Francesco; Collier Cameron, Andrew; Latham, David W.; Molinari, Emilio; Udry, Stéphane; Lovis, Christophe; Matthews, Jaymie M.; Cameron, Chris; Law, Nicholas; Bowler, Brendan P.; Angus, Ruth; Baranec, Christoph; Bieryla, Allyson; Boschin, Walter; Charbonneau, David; Cosentino, Rosario; Dumusque, Xavier; Figueira, Pedro; Guenther, David B.; Harutyunyan, Avet; Hellier, Coel; Kuschnig, Rainer; Lopez-Morales, Mercedes; Mayor, Michel; Micela, Giusi; Moffat, Anthony F. J.; Pedani, Marco; Phillips, David F.; Piotto, Giampaolo; Pollacco, Don; Queloz, Didier; Rice, Ken; Riddle, Reed; Rowe, Jason F.; Rucinski, Slavek M.; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Szentgyorgyi, Andrew; Watson, Chris; Weiss, Werner W.

2015-02-01

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 ± 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H] =-0.16 ± 0.08 and has a radius R sstarf = 0.716 ± 0.024 R ⊙ and mass M sstarf = 0.775 ± 0.027 M ⊙. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of Rp = 2.53 ± 0.18 R ⊕. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 ± 1.33 M ⊕ planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.

Are sdAs helium core stars?

NASA Astrophysics Data System (ADS)

Pelisoli, Ingrid; Kepler, S. O.; Koester, Detlev

2017-12-01

Evolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

Microlensing optical depth towards the Galactic Bulge using bright sources from OGLE-II

NASA Astrophysics Data System (ADS)

Sumi, T.; Woźniak, P.; Udalski, A.; Szymański, M.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Zebruń, K.; Szewczyk, O.; Wyrzykowski, L.

2004-12-01

We present a measurement of the microlensing optical depth towards the Galactic Bulge by using bright stars as sources from the central 20 OGLE-II Galactic bulge fields covering a range of 0o stars in an Extended Red Clump Giant (RCG) Region in the Colour Magnitude Diagram, where an extinction corrected I-band magnitude is brighter than about 15.5 mag. We find that a half of their source stars which are actually lensed are fainter blended stars. By using the 32 candidates whose actually lensed source stars are still in Extended RCG Region, we estimate the preliminary optical depth τ ˜ 2± 0.4 × 10-6 at (l,b)=(1.16, -2.75) for events with timescales 1< tE <200 days. This value is smaller than previous results with all sources but consistent with previous results with RCG sources and recent theoretical predictions.

A home for old stars

NASA Image and Video Library

2015-12-14

This image, taken with the Wide Field Planetary Camera 2 on board the NASA/ESA Hubble Space Telescope, shows the globular cluster Terzan 1. Lying around 20 000 light-years from us in the constellation of Scorpius (The Scorpion), it is one of about 150 globular clusters belonging to our galaxy, the Milky Way. Typical globular clusters are collections of around a hundred thousand stars, held together by their mutual gravitational attraction in a spherical shape a few hundred light-years across. It is thought that every galaxy has a population of globular clusters. Some, like the Milky Way, have a few hundred, while giant elliptical galaxies can have several thousand. They contain some of the oldest stars in a galaxy, hence the reddish colours of the stars in this image — the bright blue ones are foreground stars, not part of the cluster. The ages of the stars in the globular cluster tell us that they were formed during the early stages of galaxy formation! Studying them can also help us to understand how galaxies formed. Terzan 1, like many globular clusters, is a source of X-rays. It is likely that these X-rays come from binary star systems that contain a dense neutron star and a normal star. The neutron star drags material from the companion star, causing a burst of X-ray emission. The system then enters a quiescent phase in which the neutron star cools, giving off X-ray emission with different characteristics, before enough material from the companion builds up to trigger another outburst.

Stellar Population and Star Formation History of the Distant Galactic H II Regions NGC 2282 and Sh2-149

NASA Astrophysics Data System (ADS)

Dutta, S.; Mondal, S.; Jose, J.; Das, R. K.

2017-06-01

We present here the recent results on two distant Galactic H II regions, namely NGC 2282 and Sh2-149, obtained with multiwavelength observations. Our optical spectroscopic analysis of the bright sources have been used to identify the massive members, and to derive the fundamental parameters such as age and distance of these regions. Using IR color-color criteria and Hα-emission properties, we have identified and classified the candidate young stellar objects (YSOs) in these regions. The 12CO(1-0) continuum maps along with the K-band extinction maps, and spatial distribution of YSOs are used to investigate the structure and morphology of the molecular cloud associated with these H II regions. Overall analysis of these regions suggests that the star formation occurs at the locations of the denser gas, and we also find possible evidences of the induced star formation due to the feedback from massive stars to its surrounding molecular medium.

Identifying Treatment Effect Modifiers in the STarT Back Trial: A Secondary Analysis.

PubMed

Beneciuk, Jason M; Hill, Jonathan C; Campbell, Paul; Afolabi, Ebenezer; George, Steven Z; Dunn, Kate M; Foster, Nadine E

2017-01-01

Identification of patient characteristics influencing treatment outcomes is a top low back pain (LBP) research priority. Results from the STarT Back trial support the effectiveness of prognostic stratified care for LBP compared with current best care, however, patient characteristics associated with treatment response have not yet been explored. The purpose of this secondary analysis was to identify treatment effect modifiers within the STarT Back trial at 4-month follow-up (n = 688). Treatment response was dichotomized using back-specific physical disability measured using the Roland-Morris Disability Questionnaire (≥7). Candidate modifiers were identified using previous literature and evaluated using logistic regression with statistical interaction terms to provide preliminary evidence of treatment effect modification. Socioeconomic status (SES) was identified as an effect modifier for disability outcomes (odds ratio [OR] = 1.71, P = .028). High SES patients receiving prognostic stratified care were 2.5 times less likely to have a poor outcome compared with low SES patients receiving best current care (OR = .40, P = .006). Education level (OR = 1.33, P = .109) and number of pain medications (OR = .64, P = .140) met our criteria for effect modification with weaker evidence (.20 > P ≥ .05). These findings provide preliminary evidence for SES, education, and number of pain medications as treatment effect modifiers of prognostic stratified care delivered in the STarT Back Trial. This analysis provides preliminary exploratory findings about the characteristics of patients who might least likely benefit from targeted treatment using prognostic stratified care for LBP. Copyright © 2016 American Pain Society. Published by Elsevier Inc. All rights reserved.

Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903

NASA Technical Reports Server (NTRS)

Alonso-Herrero, A.; Ryder, S. D.; Knapen, J. H.

1994-01-01

We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS and ground-based spectroscopy of the hot-spot galaxy NGC 2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright H II regions, as revealed by the HST/NICMOS Pace image. Overall, the circumnuclear star formation in NGC 2903 shows a ring-like morphology with an approximate diameter of 625 pc. The SF properties of the stellar clusters and H II regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4 to 7 x 10(exp 6) yr after the peak of star formation, or absolute ages 6.5 to 9.5 x 10(exp 6) yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7 - 12% of the total stellar mass in the central 625 pc of NGC 2903. The H II regions in the ring of star formation have luminosities close to that of the super-giant H II region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC 2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.

Bright Compact Bulges (BCBs) at intermediate redshifts

NASA Astrophysics Data System (ADS)

Sachdeva, Sonali; Saha, Kanak

2018-04-01

Studying bright (MB < -20), intermediate-redshift (0.4 < z < 1.0), disc dominated (nB < 2.5) galaxies from HST/ACS and WFC3 in Chandra Deep Field South, in rest-frame B and I-band, we found a new class of bulges which is brighter and more compact than ellipticals. We refer to them as "Bright, Compact Bulges" (BCBs) - they resemble neither classical nor pseudo-bulges and constitute ˜12% of the total bulge population at these redshifts. Examining free-bulge + disc decomposition sample and elliptical galaxy sample from Simard et al. (2011), we find that only ˜0.2% of the bulges can be classified as BCBs in the local Universe. Bulge to total ratio (B/T) of disc galaxies with BCBs is (at ˜0.4) a factor of ˜2 and ˜4 larger than for those with classical and pseudo bulges. BCBs are ˜2.5 and ˜6 times more massive than classical and pseudo bulges. Although disc galaxies with BCBs host the most massive and dominant bulge type, their specific star formation rate is 1.5-2 times higher than other disc galaxies. This is contrary to the expectations that a massive compact bulge would lead to lower star formation rates. We speculate that our BCB host disc galaxies are descendant of massive, compact and passive elliptical galaxies observed at higher redshifts. Those high redshift ellipticals lack local counterparts and possibly evolved by acquiring a compact disc around them. The overall properties of BCBs supports a picture of galaxy assembly in which younger discs are being accreted around massive pre-existing spheroids.

Chandra Observatory Uncovers Hot Stars In The Making

NASA Astrophysics Data System (ADS)

2000-11-01

Cambridge, Mass.--In resolving the hot core of one of the Earth's closest and most massive star-forming regions, the Chandra X-ray Observatory showed that almost all the young stars' temperatures are more extreme than expected. Orion Trapezium JPEG, TIFF, PS The Orion Trapezium as observed on October 31st UT 05:47:21 1999. The colors represent energy, where blue and white indicate very high energies and therefore exterme temperatures. The size of the X-ray source in the image also reflects its brightness, i.e. more bright sources appear larger in size. The is an artifact caused by the limiting blur of the telescope optics. The projected diameter of the field of view is about 80 light days. Credit: NASA/MIT Orion Trapezium JPEG, TIFF, PS The Orion Trapezium as observed on November 24th UT 05:37:54 1999. The colors represent energy, where blue and white indicate very high energies and therefore exterme temperatures. The size of the X-ray source in the image also reflects its brightness, i.e. more bright sources appear larger in size. The is an artifact caused by the limiting blur of the telescope optics. The projected diameter of the field of view is about 80 light days. Credit: NASA/MIT The Orion Trapezium Cluster, only a few hundred thousand years old, offers a prime view into a stellar nursery. Its X-ray sources detected by Chandra include several externally illuminated protoplanetary disks ("proplyds") and several very massive stars, which burn so fast that they will die before the low mass stars even fully mature. One of the major highlights of the Chandra observations are identification of proplyds as X-ray point source in the near vicinity of the most massive star in the Trapezium. Previous observations did not have the ability to separate the contributions of the different objects. "We've seen high temperatures in stars before, but what clearly surprised us was that nearly all the stars we see appear at rather extreme temperatures in X-rays, independent of

Mass loss from red giant stars. II - Carbon stars

NASA Technical Reports Server (NTRS)

Wannier, P. G.; Sahai, R.; Andersson, B.-G.; Johnson, H. R.

1990-01-01

A millimeter-wave survey has been made of bright relatively unobscured, carbon stars, chosen on the basis of their optical properties. Out of 26 program objects, (J = 2-1)CO emission is detected from 15. Most of these had not been previously detected. There are many differences among the observed objects, but one rather interesting trend emerges: a positive correlation, at moderate IR excesses, between the IR dust emission and the expansion velocity of the dense wind. A similar, positive correlation with the mass-loss rate implies that stars with larger mass fluxes also accelerate them to larger velocities. At high-IR excesses, both correlations break down, and the momentum rate may be limited by the momentum rate of the stellar radiation. All these effects could be ascribed to differences in the gas-to-dust ratio, assuming that radiation pressure initiates and accelerates the wind.

Hubble Sees Pinwheel of Star Birth

NASA Image and Video Library

2017-12-08

NASA image release October 19, 2010 Though the universe is chock full of spiral-shaped galaxies, no two look exactly the same. This face-on spiral galaxy, called NGC 3982, is striking for its rich tapestry of star birth, along with its winding arms. The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars. The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the center. NGC 3982 is located about 68 million light-years away in the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy. This color image is composed of exposures taken by the Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between March 2000 and August 2009. The rich color range comes from the fact that the galaxy was photographed invisible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc. in Washington, D.C. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) Acknowledgment: A. Riess (STScI) NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us

Time-resolved multicolour photometry of bright B-type variable stars in Scorpius

NASA Astrophysics Data System (ADS)

Handler, G.; Schwarzenberg-Czerny, A.

2013-09-01

Context. The first two of a total of six nano-satellites that will constitute the BRITE-Constellation space photometry mission have recently been launched successfully. Aims: In preparation for this project, we carried out time-resolved colour photometry in a field that is an excellent candidate for BRITE measurements from space. Methods: We acquired 117 h of Strömgren uvy data during 19 nights. Our targets comprised the β Cephei stars κ and λ Sco, the eclipsing binary μ1 Sco, and the variable super/hypergiant ζ1 Sco. Results: For κ Sco, a photometric mode identification in combination with results from the spectroscopic literature suggests a dominant (l,m) = (1, -1) β Cephei-type pulsation mode of the primary star. The longer period of the star may be a rotational variation or a g-mode pulsation. For λ Sco, we recover the known dominant β Cephei pulsation, a longer-period variation, and observed part of an eclipse. Lack of ultraviolet data precludes mode identification for this star. We noticed that the spectroscopic orbital ephemeris of the closer pair in this triple system is inconsistent with eclipse timings and propose a refined value for the orbital period of the closer pair of 5.95189 ± 0.00003 d. We also argue that the components of the λ Sco system are some 30% more massive than previously thought. The binary light curve solution of μ1 Sco requires inclusion of the irradiation effect to explain the u light curve, and the system could show additional low amplitude variations on top of the orbital light changes. ζ1 Sco shows long-term variability on a time scale of at least two weeks that we prefer to interpret in terms of a variable wind or strange mode pulsations. Based on observations carried out at the South African Astronomical ObservatoryReduced time series for all stars are 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/557/A1

Distances to White Dwarf Stars from HIPPARCOS

NASA Astrophysics Data System (ADS)

Provencal, J.; Shipman, H.; Hoeg, E.; Thejll, P.

1996-12-01

We will present the results of a HIPPARCOS campaign to determine the distances to a number of white dwarf stars and we will discuss their implications. For bright stars, HIPPARCOS parallaxes have uncertainties that approach 1 milliarcsecond and thus they are considerably more accurate than earlier, ground-based parallaxes. Our most important finding is that the positions of important white dwarf stars in the mass-radius diagram, used to test our understanding of stellar degeneracy, have not changed appreciably. As a result the well known puzzles associated with 40 Eri B are still with us. The HIPPARCOS results indicate that the important binary V 471 Tau is a member of the Hyades cluster. The calibration star G 191-B2B is only an optical companion to the star G 191-B2A; these two objects are at different distances. The analysis of HIPPARCOS data has been supported by a grant from NASA.

X-ray bright points and He I lambda 10830 dark points

NASA Technical Reports Server (NTRS)

Golub, L.; Harvey, K. L.; Herant, M.; Webb, D. F.

1989-01-01

Using near-simultaneous full disk Solar X-ray images and He I 10830 lambda, spectroheliograms from three recent rocket flights, dark points identified on the He I maps were compared with X-ray bright points identified on the X-ray images. It was found that for the largest and most obvious features there is a strong correlation: most He I dark points correspond to X-ray bright points. However, about 2/3 of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced He I absorption which, however, would not a priori have been selected as a dark point. Therefore, the He I dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. He I dark points do, however, identify the locations of the stronger X-ray bright points.

X-ray bright points and He I lambda 10830 dark points

NASA Technical Reports Server (NTRS)

Golub, L.; Harvey, K. L.; Herant, M.; Webb, D. F.

1989-01-01

Using near-simultaneous full disk Solar X-ray images and He I 10830 lambda, spectroheliograms from three recent rocket flights, dark points identified on the He I maps were compared with x-ray bright points identified on the X-ray images. It was found that for the largest and most obvious features there is a strong correlation: most He I dark points correspond to X-ray bright points. However, about 2/3 of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced He I absorption which, however, would not a priori have been selected as a dark point. Therefore, the He I dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. He I dark points do, however, identify the locations of the stronger X-ray bright points.

Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

NASA Technical Reports Server (NTRS)

Frogel, Jay (Technical Monitor); Smith, Howard A.

2004-01-01

In this program we proposed to perform a series of spectroscopic studies, including data analysis and modeling, of star formation regions using an ensemble of archival space-based data from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and to take advantage of other spectroscopic databases including the first results from SIRTF. Our empha- sis has been on star formation in external, bright IR galaxies, but other areas of research have in- cluded young, low or high mass pre-main sequence stars in star formation regions, and the galactic center. The OH lines in the far infrared were proposed as one key focus of this inquiry because the Principal Investigator (H. Smith) had a full set of OH IR lines from IS0 observations. It was planned that during the proposed 2-1/2 year timeframe of the proposal other data (including perhaps from SIRTF) would become available, and we intended to be responsive to these and other such spec- troscopic data sets. Three papers are included:The Infrared Lines of OH: Diagnostics of Molecular Cloud Conditions in Infrared Bright Galaxies; The Far-Infrared Spectrum of Arp 220; andThe Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068.

Characterizing Wolf-Rayet stars in the near- and mid-infrared

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

Faherty, Jacqueline K.; Shara, Michael M.; Zurek, David

We present refined color-color selection criteria for identifying Wolf-Rayet (WR) stars using available mid-infrared (MIR) photometry from WISE in combination with near-infrared (NIR) photometry from the Two Micron All Sky Survey. Using a sample of spectrally classified objects, we find that WR stars are well distinguished from the field stellar population in the (W1 – W2) versus (J – K{sub s} ) color-color diagram, and further distinguished from other emission line objects such as planetary nebulae, Be, and cataclysmic variable stars using a combination of NIR and MIR color constraints. As proof of concept we applied the color constraints tomore » a photometric sample in the Galactic plane, located WR star candidates, and present five new spectrally confirmed and classified WC (1) and WN (4) stars. Analysis of the 0.8-5.0 μm spectral data for a subset of known, bright WC and WN stars shows that emission lines (primarily He I) extend into the 3.0-5.0 μm spectral region, although their strength is greatly diminished compared to the 0.8-2.5 μm region. The WR population stands out relative to background field stars at NIR and MIR colors due to an excess continuum contribution, likely caused by free-free scattering in dense winds. Mean photometric properties of known WRs are presented and imply that reddened late-type WN and WC sources are easier to detect than earlier-type sources at larger Galactic radii. WISE W3 and W4 images of 10 WR stars show evidence of circumstellar shells linked to mass ejections from strong stellar winds.« less

A Star-Formation Laboratory

NASA Image and Video Library

2011-05-13

The dwarf galaxy NGC 4214 is ablaze with young stars and gas clouds. Located around 10 million light-years away in the constellation of Canes Venatici (The Hunting Dogs), the galaxy's close proximity, combined with the wide variety of evolutionary stages among the stars, make it an ideal laboratory to research the triggers of star formation and evolution. Intricate patterns of glowing hydrogen formed during the star-birthing process, cavities blown clear of gas by stellar winds, and bright stellar clusters of NGC 4214 can be seen in this optical and near-infrared image. Observations of this dwarf galaxy have also revealed clusters of much older red supergiant stars. Additional older stars can be seen dotted all across the galaxy. The variety of stars at different stages in their evolution indicates that the recent and ongoing starburst periods are not the first, and the galaxy's abundant supply of hydrogen means that star formation will continue into the future. This color image was taken using the Wide Field Camera 3 in December 2009. Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: R. O'Connell (University of Virginia) and the WFC3 Scientific Oversight Committee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

The bright-bright and bright-dark mode coupling-based planar metamaterial for plasmonic EIT-like effect

NASA Astrophysics Data System (ADS)

Yu, Wei; Meng, Hongyun; Chen, Zhangjie; Li, Xianping; Zhang, Xing; Wang, Faqiang; Wei, Zhongchao; Tan, Chunhua; Huang, Xuguang; Li, Shuti

2018-05-01

In this paper, we propose a novel planar metamaterial structure for the electromagnetically induced transparency (EIT)-like effect, which consists of a split-ring resonator (SRR) and a pair of metal strips. The simulated results indicate that a single transparency window can be realized in the symmetry situation, which originates from the bright-bright mode coupling. Further, a dual-band EIT-like effect can be achieved in the asymmetry situation, which is due to the bright-bright mode coupling and bright-dark mode coupling, respectively. Different EIT-like effect can be simultaneously achieved in the proposed structure with the different situations. It is of certain significance for the study of EIT-like effect.

Einstein Observations of X-ray emission from A stars

NASA Astrophysics Data System (ADS)

Golub, L.; Harnden, F. R., Jr.; Maxson, C. W.; Rosner, R.; Vaiana, G. S.; Cash, W., Jr.; Snow, T. P., Jr.

1983-08-01

Results are reported from the combined CfA Stellar Survey of selected bright A stars and an Einstein Guest Observer program for Ap and Am stars. In an initial report of results from the CfA Stellar Surveys by Vaiana et al. (1981) it was noted that the spread in observed X-ray luminosities among the few A stars observed was quite large. The reasons for this large spread was studied by Pallavicini et al. (1981). It was found that the X-ray emission from normal stars is related very strongly to bolometric luminosity for early-type stars and to rotation rate for late-type stars. However, an exception to this rule has been the apparently anomalous behavior of A star X-ray emission, for which the large spread in luminosity showed no apparent correlation with either bolometric luminosity or stellar rotation rate. In the present study, it is shown that the level of emission from normal A stars agrees with the correlation observed for O and B stars.

Light and Velocity Variability in Seven Bright Proto-Planetary Nebulae

NASA Astrophysics Data System (ADS)

McGuire, Ryan

2009-01-01

Light and Velocity Variability in Seven Bright Proto-Planetary Nebulae R.B. McGuire, C.M. Steele, B.J. Hrivnak, W. Lu, D. Bohlender, C.D. Scarfe We present new contemporaneous light and velocity observations of seven proto-planetary nebulae obtained over the past two years. Proto-planetary nebulae are objects evolving between the AGB and planetary nebula phases. In these seven objects, the central star is bright (V= 7-10), surrounded by a faint nebula. We knew from past monitoring that the light from each of these varied by a few tenths of a magnitude over intervals of 30-150 days and that the velocity varied by 10 km/s. These appear to be due to pulsation. With these new contemporaneous observations, we are able to measure the correlation between the brightness, color, and velocity, which will constrain the pulsation models. This is an ongoing project with the light monitoring being carried out with the Valparaiso University 0.4 m telescope and CCD camera and the radial velocity observations being carried out with the Dominion Astrophysical Observatory 1.8 m telescope and spectrograph. This research is partially supported by NSF grant 0407087 and the Indiana Space Grant Consortium.

The Outcome of Neutron Star Mergers

NASA Astrophysics Data System (ADS)

Foucart, Francois

2014-10-01

Black hole-neutron star and neutron star-neutron star mergers are among the main sources of gravitational waves which will be detected in the coming years by the Advanced LIGO/VIRGO/KAGRA observatories. In some cases, these mergers can also power bright electromagnetic emissions: they are the most likely progenitors of short gamma-ray bursts, and the radioactive decay of neutron-rich material ejected by the merger can power optical/infrared transients days after the merger. Finally, they may provide important constraints on the equation of state of cold dense matter, and on the source of heavy elements in the universe. I will discuss the general relativistic simulations which are required to properly model these events, and what they have told us so far about the outcome of neutron star mergers. I will also discuss efforts to improve the physical realism of the simulations by improving the treatment of the most important effects beyond general relativistic hydrodynamics: magnetic fields, neutrinos, and the properties of nuclear matter.

Photometric light curves for ten rapidly rotating stars in Alpha Persei, the Pleiades, and the field

NASA Technical Reports Server (NTRS)

Prosser, Charles F.; Schild, Rudolph E.; Stauffer, John R.; Jones, Burton F.

1993-01-01

We present the results from a photometric monitoring program of ten rapidly rotating stars observed during 1991 using the FLWO 48-in. telescope. Brightness variations for an additional six cluster stars observed with the Lick 40-in. telescope are also given. The periods and light curves for seven Alpha Persei members, two Pleiades members, and one naked T Tauri field star are reported.

Low-Surface-Brightness Galaxies: Hidden Galaxies Revealed

NASA Astrophysics Data System (ADS)

Bothun, G.; Impey, C.; McGaugh, S.

1997-07-01

In twenty years, low surface brightness (LSB) galaxies have evolved from being an idiosyncratic notion to being one of the major baryonic repositories in the Universe. The story of their discovery and the characterization of their properties is told here. Their recovery from the noise of the night sky background is a strong testament to the severity of surface brightness selection effects. LSB galaxies have a number of remarkable properties which distinguish them from the more familiar Hubble Sequence of spirals. The two most important are 1) they evolve at a significantly slower rate and may well experience star formation outside of the molecular cloud environment, 2) they are embedded in dark matter halos which are of lower density and more extended than the halos around high surface brightness (HSB) disk galaxies. Compared to HSB disks, LSB disks are strongly dark matter dominated at all radii and show a systematic increase in $M/L$ with decreasing central surface brightness. In addition, the recognition that large numbers of LSB galaxies actually exist has changed the form of the galaxy luminosity function and has clearly increased the space density of galaxies at z =0. Recent CCD surveys have uncovered a population of red LSB disks that may be related to the excess of faint blue galaxies detected at moderate redshifts. LSB galaxies offer us a new window into galaxy evolution and formation which is every bit as important as those processes which have produced easy to detect galaxies. Indeed, the apparent youth of some LSB galaxies suggest that galaxy formation is a greatly extended process. While the discovery of LSB galaxies have lead to new insights, it remains unwise to presume that we now have a representative sample which encompasses all galaxy types and forms. (SECTION: Invited Review Paper)

Evolved stars in the Local Group galaxies - II. AGB, RSG stars and dust production in IC10

NASA Astrophysics Data System (ADS)

Dell'Agli, F.; Di Criscienzo, M.; Ventura, P.; Limongi, M.; García-Hernández, D. A.; Marini, E.; Rossi, C.

2018-06-01

We study the evolved stellar population of the Local Group galaxy IC10, with the aim of characterizing the individual sources observed and to derive global information on the galaxy, primarily the star formation history and the dust production rate. To this aim, we use evolutionary sequences of low- and intermediate-mass (M < 8 M⊙) stars, evolved through the asymptotic giant branch phase, with the inclusion of the description of dust formation. We also use models of higher mass stars. From the analysis of the distribution of stars in the observational planes obtained with IR bands, we find that the reddening and distance of IC10 are E(B - V) = 1.85 mag and d = 0.77 Mpc, respectively. The evolved stellar population is dominated by carbon stars, that account for 40% of the sources brighter than the tip of the red giant branch. Most of these stars descend from ˜1.1 - 1.3 M⊙ progenitors, formed during the major epoch of star formation, which occurred ˜2.5 Gyr ago. The presence of a significant number of bright stars indicates that IC10 has been site of significant star formation in recent epochs and currently hosts a group of massive stars in the core helium-burning phase. Dust production in this galaxy is largely dominated by carbon stars; the overall dust production rate estimated is 7 × 10-6 M⊙/yr.

Identifying Young Kepler Planet Host Stars from Keck–HIRES Spectra of Lithium

NASA Astrophysics Data System (ADS)

Berger, Travis A.; Howard, Andrew W.; Boesgaard, Ann Merchant

2018-03-01

The lithium doublet at 6708 Å provides an age diagnostic for main sequence FGK dwarfs. We measured the abundance of lithium in 1305 stars with detected transiting planets from the Kepler mission using high-resolution spectroscopy. Our catalog of lithium measurements from this sample has a range of abundance from A(Li) = 3.11 ± 0.07 to an upper limit of ‑0.84 dex. For a magnitude-limited sample that comprises 960 of the 1305 stars, our Keck–HIRES spectra have a median signal-to-noise ratio of 45 per pixel at ∼6700 Å with spectral resolution \\tfrac{λ }{{{Δ }}λ } = R = 55,000. We identify 80 young stars that have A(Li) values greater than the Hyades at their respective effective temperatures; these stars are younger than ∼650 Myr, the approximate age of the Hyades. We then compare the distribution of A(Li) with planet size, multiplicity, orbital period, and insolation flux. We find larger planets preferentially in younger systems, with an A–D two-sided test p-value = 0.002, a > 3σ confidence that the older and younger planet samples do not come from the same parent distribution. This is consistent with planet inflation/photoevaporation at early ages. The other planet parameters (Kepler planet multiplicity, orbital period, and insolation flux) are uncorrelated with age. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. Keck time has been granted by the University of Hawaii, the University of California, and Caltech.

Unveiling the Low Surface Brightness Stellar Peripheries of Galaxies

NASA Astrophysics Data System (ADS)

Ferguson, Annette M. N.

2018-01-01

The low surface brightness peripheral regions of galaxies contain a gold mine of information about how minor mergers and accretions have influenced their evolution over cosmic time. Enormous stellar envelopes and copious amounts of faint tidal debris are natural outcomes of the hierarchical assembly process and the search for and study of these features, albeit highly challenging, offers the potential for unrivalled insight into the mechanisms of galaxy growth. Over the last two decades, there has been burgeoning interest in probing galaxy outskirts using resolved stellar populations. Wide-field surveys have uncovered vast tidal debris features and new populations of very remote globular clusters, while deep Hubble Space Telescope photometry has provided exquisite star formation histories back to the earliest epochs. I will highlight some recent results from studies within and beyond the Local Group and conclude by briefly discussing the great potential of future facilities, such as JWST, Euclid, LSST and WFIRST, for major breakthroughs in low surface brightness galaxy periphery science.

Where Is the Flux Going? The Long-term Photometric Variability of Boyajian’s Star

NASA Astrophysics Data System (ADS)

Simon, Joshua D.; Shappee, Benjamin J.; Pojmański, G.; Montet, Benjamin T.; Kochanek, C. S.; van Saders, Jennifer; Holoien, T. W.-S.; Henden, Arne A.

2018-01-01

We present ∼800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ∼4000 days of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star has steadily decreased at a rate of 6.3 ± 1.4 mmag yr‑1, such that the star is now 1.5% fainter than it was in 2015 February. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ∼1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at ≳99.4% confidence. The 2015–2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star’s behavior proposed to date.

VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS

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

Clayton, Geoffrey C.; Zhang Wanshu; Geballe, T. R., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: wzhan21@lsu.edu, E-mail: tgeballe@gemini.edu

2013-08-01

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I {lambda}10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities {approx}400 km s{sup -1} appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the declinemore » and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.« less

Bright Merger-nova Emission Powered by Magnetic Wind from a Newborn Black Hole

NASA Astrophysics Data System (ADS)

Ma, Shuai-Bing; Lei, Wei-Hua; Gao, He; Xie, Wei; Chen, Wei; Zhang, Bing; Wang, Ding-Xiong

2018-01-01

Mergers of neutron star–neutron star (NS–NS) or neutron star–black hole (NS–BH) binaries are candidate sources of gravitational waves (GWs). At least a fraction of the merger remnants should be a stellar mass BH with sub-relativistic ejecta. A collimated jet is launched via the Blandford–Znajek mechanism from the central BH to trigger a short gamma-ray burst (sGRB). At the same time, a near-isotropic wind may be driven by the Blandford–Payne mechanism (BP). In previous work, additional energy injection to the ejecta from the BP mechanism was ignored, and radioactive decay has long been thought to be the main source of the kilonova energy. In this Letter, we propose that the wind driven by the BP mechanism from the newborn BH’s disk can heat up and push the ejecta during the prompt emission phase or even at late times when there is fall-back accretion. Such a BP-powered merger-nova could be bright in the optical band even for a low-luminosity sGRB. The detection of a GW merger event with a BH clearly identified as a remnant, accompanied by a bright merger-nova, would provide robust confirmation of our model.

Accurate age determinations of several nearby open clusters containing magnetic Ap stars

NASA Astrophysics Data System (ADS)

Silaj, J.; Landstreet, J. D.

2014-06-01

Context. To study the time evolution of magnetic fields, chemical abundance peculiarities, and other characteristics of magnetic Ap and Bp stars during their main sequence lives, a sample of these stars in open clusters has been obtained, as such stars can be assumed to have the same ages as the clusters to which they belong. However, in exploring age determinations in the literature, we find a large dispersion among different age determinations, even for bright, nearby clusters. Aims: Our aim is to obtain ages that are as accurate as possible for the seven nearby open clusters α Per, Coma Ber, IC 2602, NGC 2232, NGC 2451A, NGC 2516, and NGC 6475, each of which contains at least one magnetic Ap or Bp star. Simultaneously, we test the current calibrations of Te and luminosity for the Ap/Bp star members, and identify clearly blue stragglers in the clusters studied. Methods: We explore the possibility that isochrone fitting in the theoretical Hertzsprung-Russell diagram (i.e. log (L/L⊙) vs. log Te), rather than in the conventional colour-magnitude diagram, can provide more precise and accurate cluster ages, with well-defined uncertainties. Results: Well-defined ages are found for all the clusters studied. For the nearby clusters studied, the derived ages are not very sensitive to the small uncertainties in distance, reddening, membership, metallicity, or choice of isochrones. Our age determinations are all within the range of previously determined values, but the associated uncertainties are considerably smaller than the spread in recent age determinations from the literature. Furthermore, examination of proper motions and HR diagrams confirms that the Ap stars identified in these clusters are members, and that the presently accepted temperature scale and bolometric corrections for Ap stars are approximately correct. We show that in these theoretical HR diagrams blue stragglers are particularly easy to identify. Conclusions: Constructing the theoretical HR diagram

Ring nebulae around Wolf-Rayet stars in M33

NASA Technical Reports Server (NTRS)

Drissen, Laurent; Shara, Michael M.; Moffat, Anthony F. J.

1991-01-01

Results of a systematic search for H II ring nebulae surrounding Wolf-Rayet (WR) stars in M33 are presented. Eleven objects are found to be good candidates, while eight others are classified as possible WR ring nebulae. The WR rings in M33 are larger on average than their Galactic counterparts, but the H-alpha luminosity of most of them is comparable to the bright Galactic wind-blown bubbles. The rings are associated with WC as well as with WN stars.

Multiband Lightcurve of Tabby’s Star: Observations and Modeling

NASA Astrophysics Data System (ADS)

Yin, Yao; Wilcox, Alejandro; Boyajian, Tabetha S.

2018-06-01

Since March 2017, The Thacher Observatory in California has been monitoring changes in brightness of KIC 8462852 (Tabby's Star), an F-type main sequence star whose irregular dimming behavior was first discovered by Tabetha Boyajian by examining Kepler data. We obtained over 20k observations over 135 nights in 2017 in 4 photometric bands, and detected 4 dip events greater than 1%. The relative magnitude of each dip compared across our 4 different photometric bands provides critical information regarding the nature of the obscuring material, and we present a preliminary analysis of these events. The Thacher Observatory is continuing its monitoring of Tabby’s Star in 2018.

Astronomers puzzle over a peculiar age-defying massive star

NASA Image and Video Library

2017-12-08

An age-defying star designated as IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA’s Spitzer Space Telescope. A NASA-led team of scientists thinks the star – which is about 10 times as massive as our sun and emits about 20,000 times as much energy – is a newly forming protostar. That was a big surprise because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. Read more: go.nasa.gov/2bMza9d Image Credit: NASA/JPL-Caltech

New Herbig-Haro objects in star-forming regions

NASA Technical Reports Server (NTRS)

Reipurth, BO; Graham, J. A.

1988-01-01

A list of 25 new Herbig-Haro objects, HH 58 to HH 82, in the Orion molecular clouds and in southern molecular cloud complexes has been compiled. CCD images in the S II 6717, 6731 forbidden lines are presented for the objects, together with a few spectra and some IR observations. The individual objects and, when identified, their energy sources are discussed. HH 65 is located in the red lobe of the bipolar outflow associated with the highly variable reflection nebula Re 50. HH 67 is a 22-arcsec long sinusoidal jet. HH 68/69 consists of a long, linear chain of four HH knots. HH 72 emerges from a 120-solar luminosity IRAS source embedded in a Bok globule. HH 79 is the first HH object discovered in the Ophiuchus clouds. HH 80/81 in Sagittarius are among the brightest HH objects known, have complex velocities, high excitation conditions and emerge from a 6000-solar luminosity young B-star. HH 82 is associated with the bright variable star S Coronae Australis.

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).

Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds

NASA Astrophysics Data System (ADS)

Zakharov, A. F.; Jovanović, P.; Borka, D.; Borka Jovanović, V.

2018-04-01

Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as mg < 1.2 × 10‑22 eV [1] (see also more details in a complimentary paper [2]). In our previous papers we considered constraints on Yukawa gravity parameters [3] and on graviton mass from analysis of the trajectory of S2 star near the Galactic Center [4]. In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center. Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity [5] and graviton mass [6] from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around 5 × 10‑23 eV or slightly better than current estimates obtained with LIGO observations.

Winter sky brightness & cloud cover over Dome A

NASA Astrophysics Data System (ADS)

Yang, Yi; Moore, A. M.; Fu, J.; Ashley, M.; Cui, X.; Feng, L.; Gong, X.; Hu, Z.; Laurence, J.; LuongVan, D.; Riddle, R. L.; Shang, Z.; Sims, G.; Storey, J.; Tothill, N.; Travouillon, T.; Wang, L.; Yang, H.; Yang, J.; Zhou, X.; Zhu, Z.; Burton, M. G.

2014-01-01

At the summit of the Antarctic plateau, Dome A offers an intriguing location for future large scale optical astronomical Observatories. The Gattini DomeA project was created to measure the optical sky brightness and large area cloud cover of the winter-time sky above this high altitude Antarctic site. The wide field camera and multi-filter system was installed on the PLATO instrument module as part of the Chinese-led traverse to Dome A in January 2008. This automated wide field camera consists of an Apogee U4000 interline CCD coupled to a Nikon fish-eye lens enclosed in a heated container with glass window. The system contains a filter mechanism providing a suite of standard astronomical photometric filters (Bessell B, V, R), however, the absence of tracking systems, together with the ultra large field of view 85 degrees) and strong distortion have driven us to seek a unique way to build our data reduction pipeline. We present here the first measurements of sky brightness in the photometric B, V, and R band, cloud cover statistics measured during the 2009 winter season and an estimate of the transparency. In addition, we present example light curves for bright targets to emphasize the unprecedented observational window function available from this ground-based location. A ~0.2 magnitude agreement of our simultaneous test at Palomar Observatory with NSBM(National Sky Brightness Monitor), as well as an 0.04 magnitude photometric accuracy for typical 6th magnitude stars limited by the instrument design, indicating we obtained reasonable results based on our ~7mm effective aperture fish-eye lens.

Anomalous microwave emission from spinning nanodiamonds around stars

NASA Astrophysics Data System (ADS)

Greaves, J. S.; Scaife, A. M. M.; Frayer, D. T.; Green, D. A.; Mason, B. S.; Smith, A. M. S.

2018-06-01

Several interstellar environments produce anomalous microwave emission (AME), with brightness peaks at tens-of-gigahertz frequencies1. The emission's origins are uncertain; rapidly spinning nanoparticles could emit electric-dipole radiation2, but the polycyclic aromatic hydrocarbons that have been proposed as the carrier are now found not to correlate with Galactic AME signals3,4. The difficulty is in identifying co-spatial sources over long lines of sight. Here, we identify AME in three protoplanetary disks. These are the only known systems that host hydrogenated nanodiamonds5, in contrast with the very common detection of polycyclic aromatic hydrocarbons6. Using spectroscopy, the nanodiamonds are located close to the host stars, at physically well-constrained temperatures7. Developing disk models8, we reproduce the emission with diamonds 0.75-1.1 nm in radius, holding ≤1-2% of the carbon budget. Ratios of microwave emission to stellar luminosity are approximately constant, allowing nanodiamonds to be ubiquitous, but emitting below the detection threshold in many star systems. This result is compatible with the findings of similar-sized diamonds within Solar System meteorites9. As nanodiamond spectral absorption is seen in interstellar sightlines10, these particles are also a candidate for generating galaxy-scale3 AME.

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

NASA Technical Reports Server (NTRS)

Sandage, A.; Carlson, G.

1982-01-01

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

HUBBLE UNCOVERS MYSTERY OBJECTS IN THE DENSE CORE OF A NEARBY STAR CLUSTER

NASA Technical Reports Server (NTRS)

2002-01-01

Piercing the heart of a glittering swarm of stars, NASA's sharp-eyed Hubble Space Telescope unveils the central region of the globular cluster M22, a 12- to 14-billion-year-old grouping of stars in the constellation Sagittarius. The telescope's view of the cluster's core measures 3.3 light-years across. The stars near the cluster's core are 100,000 times more numerous than those in the Sun's neighborhood. Buried in the glow of starlight are about six 'mystery objects,' which astronomers estimate are no larger than one quarter the mass of the giant planet Jupiter, the solar system's heftiest planet. The mystery objects are too far and dim for Hubble to see directly. Instead, the orbiting observatory detected these unseen celestial bodies by looking for their gravitational effects on the light from far distant stars. In this case, the stars are far beyond the cluster in the galactic bulge, about 30,000 light-years from Earth at the center of the Milky Way Galaxy. M22 is 8,500 light-years away. The invisible objects betrayed their presence by bending the starlight gravitationally and amplifying it, a phenomenon known as microlensing. From February 22 to June 15, 1999, Hubble's Wide Field and Planetary Camera 2 looked through this central region and monitored 83,000 stars. During that time the orbiting observatory recorded six unexpectedly brief microlensing events. In each case a background star jumped in brightness for less than 20 hours before dropping back to normal. These transitory spikes in brightness mean that the object passing in front of the star must have been much smaller than a normal star. Hubble also detected one clear microlensing event. In that observation a star appeared about 10 times brighter over an 18-day span before returning to normal. Astronomers traced the leap in brightness to a dwarf star in the cluster floating in front of the background star. The inset photo shows the entire globular cluster of about 10 million stars. M22 is about 60

Identification of stars in a J1744.0 star catalogue Yixiangkaocheng

NASA Astrophysics Data System (ADS)

Ahn, S.-H.

2012-05-01

The stars in the Chinese star catalogue, Yixiangkaocheng, which were edited by the Jesuit astronomer Kögler in AD 1744 and published in AD 1756, are identified with their counterparts in the Hipparcos catalogue. The equinox of the catalogue is confirmed to be J1744.0. By considering the precession of equinox, proper motions and nutation, the star closest to the location of each star in Yixiangkaocheng, having a proper magnitude, is selected as the corresponding identified star. I identified 2848 stars and 13 nebulosities out of 3083 objects in Yixiangkaocheng, and so the identification rate reached 92.80 per cent. I find that the magnitude classification system in Yixiangkaocheng agrees with the modern magnitude system. The catalogue includes dim stars, whose visual magnitudes are larger than 7, but most of these stars have Flamsteed designations. I find that the stars whose declination is lower than -30° have relatively larger offsets and different systematic behaviour from other stars. This indicates that there might be two different sources of stars in Yixiangkaocheng. In particular, I find that μ1 Sco and γ1 Sgr approximately mark the boundary between two different source catalogues. The observer's location, as estimated from these facts, agrees with the latitude of Greenwich where Flamsteed made his observations. The positional offsets between the Yixiangkaocheng stars and the Hipparcos stars are 0.6 arcmin, which implies that the source catalogue of stars with δ > -30° must have come from telescopic observations. Nebulosities in Yixiangkaocheng are identified with a few double stars, o Cet (the variable star, Mira), the Andromeda galaxy, ω Cen and NGC6231. These entities are associated with listings in Halley's Catalogue of the Southern Stars of AD 1679 as well as Flamsteed's catalogue of AD 1690.

Near infrared observations of S155. evidence of induced star formation?

NASA Astrophysics Data System (ADS)

Hunt, L. K.; Lisi, F.; Felli, M.; Tofani, G.

At the interface of the giant molecular cloud Cepheus OB3, S155 represents one of the most interesting examples of bright rim produced by the ionization of a nearby O-star. The interaction between the ionized HII region S155 and the hot molecular core Cepheus B may constitute the ideal site for new stars, according to the sequential star-formation theory. Past observations of molecular lines have shown the evidence of a hot spot in the cloud core, probably a compact region associated to a young stellar object. New J,H,K images recently obtained with the ARNICA array at the TIRGO telescope give evidence of stars with strong near-infrared excess, which must represent the newest generation of young stars.

Iron Kα line of Proca stars

NASA Astrophysics Data System (ADS)

Shen, Tianling; Zhou, Menglei; Bambi, Cosimo; Herdeiro, Carlos A. R.; Radu, Eugen

2017-08-01

X-ray reflection spectroscopy can be a powerful tool to test the nature of astrophysical black holes. Extending previous work on Kerr black holes with scalar hair [1] and on boson stars [2], here we study whether astrophysical black hole candidates may be horizonless, self-gravitating, vector Bose-Einstein condensates, known as Proca stars [3]. We find that observations with current X-ray missions can only provide weak constraints and rule out solely Proca stars with low compactness. There are two reasons. First, at the moment we do not know the geometry of the corona, and therefore the uncertainty in the emissivity profile limits the ability to constrain the background metric. Second, the photon number count is low even in the case of a bright black hole binary, and we cannot have a precise measurement of the spectrum.

Iron Kα line of Proca stars

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

Shen, Tianling; Zhou, Menglei; Bambi, Cosimo

X-ray reflection spectroscopy can be a powerful tool to test the nature of astrophysical black holes. Extending previous work on Kerr black holes with scalar hair [1] and on boson stars [2], here we study whether astrophysical black hole candidates may be horizonless, self-gravitating, vector Bose-Einstein condensates, known as Proca stars [3]. We find that observations with current X-ray missions can only provide weak constraints and rule out solely Proca stars with low compactness. There are two reasons. First, at the moment we do not know the geometry of the corona, and therefore the uncertainty in the emissivity profile limitsmore » the ability to constrain the background metric. Second, the photon number count is low even in the case of a bright black hole binary, and we cannot have a precise measurement of the spectrum.« less

L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system

NASA Astrophysics Data System (ADS)

Leggett, S. K.; Hawarden, T. G.; Currie, M. J.; Adamson, A. J.; Carroll, T. C.; Kerr, T. H.; Kuhn, O. P.; Seigar, M. S.; Varricatt, W. P.; Wold, T.

2003-10-01

We present L' and M' photometry, obtained at the United Kingdom Infrared Telescope (UKIRT) using the Mauna Kea Observatories Near-Infrared (MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L' standards include 25 from the in-house `UKIRT Bright Standards' with magnitudes deriving from Elias et al. and observations at the Infrared Telescope Facility in the early 1980s, and 21 fainter stars. The M' magnitudes derive from the results of Sinton and Tittemore. We estimate the average external error to be 0.015 mag for the bright L' standards and 0.025 mag for the fainter L' standards, and 0.026 mag for the M' standards. The new results provide a network of homogeneously observed standards, and establish reference stars for the MKO system, in these bands. They also extend the available standards to magnitudes which should be faint enough to be accessible for observations with modern detectors on large and very large telescopes.

ATLASGAL - towards a complete sample of massive star forming clumps

NASA Astrophysics Data System (ADS)

Urquhart, J. S.; Moore, T. J. T.; Csengeri, T.; Wyrowski, F.; Schuller, F.; Hoare, M. G.; Lumsden, S. L.; Mottram, J. C.; Thompson, M. A.; Menten, K. M.; Walmsley, C. M.; Bronfman, L.; Pfalzner, S.; König, C.; Wienen, M.

2014-09-01

By matching infrared-selected, massive young stellar objects (MYSOs) and compact H II regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ˜1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1.5°. Combined with an existing sample of radio-selected methanol masers and compact H II regions, the result is a catalogue of ˜1700 massive stars embedded within ˜1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H II-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H II-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

WASP-12b and HAT-P-8b are Members of Triple Star Systems

NASA Astrophysics Data System (ADS)

Bechter, Eric B.; Crepp, Justin R.; Ngo, Henry; Knutson, Heather A.; Batygin, Konstantin; Hinkley, Sasha; Muirhead, Philip S.; Johnson, John Asher; Howard, Andrew W.; Montet, Benjamin T.; Matthews, Christopher T.; Morton, Timothy D.

2014-06-01

We present high spatial resolution images that demonstrate that WASP-12b and HAT-P-8b orbit the primary stars of hierarchical triple star systems. In each case, two distant companions with colors and brightnesses consistent with M dwarfs co-orbit the hot Jupiter planet host as well as one another. Our adaptive optics images spatially resolve the secondary around WASP-12, previously identified by Bergfors et al. and Crossfield et al. into two distinct sources separated by 84.3 ± 0.6 mas (21 ± 3 AU). We find that the secondary to HAT-P-8, also identified by Bergfors et al., is in fact composed of two stars separated by 65.3 ± 0.5 mas (15 ± 1 AU). Our follow-up observations demonstrate physical association through common proper motion. HAT-P-8 C has a particularly low mass, which we estimate to be 0.18 ± 0.02 M ⊙ using photometry. Due to their hierarchy, WASP-12 BC and HAT-P-8 BC will enable the first dynamical mass determination for hot Jupiter stellar companions. These previously well studied planet hosts now represent higher-order multi-star systems with potentially complex dynamics, underscoring the importance of diffraction-limited imaging and providing additional context for understanding the migrant population of transiting hot Jupiters.

Accuracy of measurement of star images on a pixel array

NASA Technical Reports Server (NTRS)

King, I. R.

1983-01-01

Algorithms are developed for predicting the accuracy with which the brightness of a star can be determined from its image on a digital detector array, as a function of the brightness of the background. The assumption is made that a known profile is being fitted by least squares. The two profiles used correspond to ST images and to ground-based observations. The first result is an approximate rule of thumb for equivalent noise area. More rigorous results are then given in tabular form. The size of the pixels, relative to the image size, is taken into account. Astronometric accuracy is also discussed briefly; the error, relative to image size, is very similar to the photometric error relative to brightness.

MODEL ATMOSPHERES FOR X-RAY BURSTING NEUTRON STARS

DOE PAGES

Medin, Zachary James; Steinkirch, Marina von; Calder, Alan C.; ...

2016-11-21

The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Also, observations from X-raymore » telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Lastly, here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.« less

The nature of X-ray selected star candidates

NASA Astrophysics Data System (ADS)

Mickaelian, A. M.; Paronyan, G. M.; Abrahamyan, H. V.; Gigoyan, K. S.; Gyulzadyan, M. V.; Kostandyan, G. R.

2016-12-01

The joint HRC/BHRC catalogue of optical identifications of ROSAT BSC and FSC X-ray sources is based on merging the Hamburg-ROSAT Catalogue (HRC) and Byurakan-Hamburg-ROSAT Catalogue (BHRC). Both have been made by optical identifications of X-ray sources based on low-dispersion spectra of the Hamburg QuasarSurvey (HQS) using the ROSAT Catalogues. HRC/BHRC contains a sample of 8132 (5341+2791) optically identified X-ray sources with count rate (CR) of photons ≥ 0.04 ct/s in the area of the low-dispersion Hamburg Quasar Survey (HQS), |b| ≥ 20° and δ ≥ 0°. Based on low-dispersion spectral classification, there are 4253 AGN, 492 galaxies, 1800 stars and 1587 unknown objects in the sample. 1800 star candidates include 1429 objects listed in SDSS DR12 photometric catalogue and 433 given in SDSS spectroscopic catalogue. Using these spectra, we have carried out classification of these star candidates to reveal new interesting objects, as well as to define the true content of our sample. 34 cataclysmic variables (including 7 new ones), 19 white dwarfs, 19 late-type stars (K-M and C types), 16 early type stars (O-B), 40 hot coronal stars (A-F types), 2 composite spectrum objects, and 17 bright stars have been revealed, as well as 286 objects which turned out to be extragalactic ones; 75 emission-line galaxies (HII/SB and AGN, including QSOs, Seyferts, and LINERs) and 211 absorption line galaxies were revealed (wrong classifications in HRC/BHRC due to their faint images and low-quality spectra). We have retrieved multiwavelength data from recent catalogues and carried out statistical investigations of the multiwavelength properties for the whole sample of stars. All stars have been found in GSC 2.3.2, as well as most of them are in GALEX, USNO-B1.0, 2MASS and WISE catalogues. Relations between the radiation fluxes in different bands from X-ray to radio for different types of sources are studied and analysis of their characteristics is made. X-ray selected stars are an

Infrared-Bright Interacting Galaxies

NASA Astrophysics Data System (ADS)

Rojas Ruiz, Sofia; Murphy, Eric Joseph; Armus, Lee; Smith, John-David; Bradford, Charles Matt; Stierwalt, Sabrina

2018-01-01

We present the mid-infrared spectral mapping of eight LIRG-class interacting galaxies: NGC 6670, NGC 7592, IIZw 96, IIIZw 35, Arp 302, Arp 236, Arp 238, Arp 299. The properties of galaxy mergers, which are bright and can be studied at high resolutions at low-z, provide local analogs for sources that may be important contributors to the Far Infrared Background (FIRB.) In order to study star formation and the physical conditions in the gas and dust in our sample galaxies, we used the Spitzer InfraRed Spectrograph (IRS) to map the galaxies over the 5-35 μm window to trace the PAH, molecular hydrogen, and atomic fine structure line emission on scales of 1.4 – 5.3 kpc. Here we present the reduction for low and high-resolution data, and preliminary results in the analysis of fine structure line ratios and dust features in the two nuclei and interacting regions from one of our sample galaxies, NGC 6670.

Long-term Accretion Variations of the Magnetic Cataclysmic Variable Star QQ Vulpecula

NASA Astrophysics Data System (ADS)

Cooper Rose, Sanaea; Kafka, Stella; Jorgenson, Regina; Carr, Derrick; Childs, Francesca; Christenson, Holly; Karim, Md. Tanveer; Konchady, Tarini; Walker, Gary E.; Honeycutt, R. K.

2017-01-01

Magnetic cataclysmic variable stars have brightness variations that repeat with each revolution of the two stars about the center of mass of the system. However, in the case of QQ Vulpecula (QQ Vul), this brightness variation pattern changes in the long term. This study makes use of two decades worth of data from the Roboscope Telescope as well as data from the American Association of Variable Star Observers (AAVSO) database to examine the long-term evolution of QQ Vul’s phase curves. Nightly observations using the Maria Mitchell Association's Vestal and Loines Observatories supplemented this analysis by clarifying short-term brightness variation. The long-term data was divided into four commonly observed behavioral types ranging from a double peaked curve of ~15.5 magnitude to a ~15.0 magnitude curve that had a primary minimum and a slow, linear rise in brightness in place of the secondary minimum. The nightly data kept within the confines of these categories, though the secondary minimum in the nightly data never vanished. No periodicity was found in the long-term variations. The model often invoked to explain the double peaked curve consists of single pole accretion in which a partial self-eclipse causes the secondary minimum and cyclotron beaming causes the primary minimum. However, the long-term variation may indicate a changing accretion rate, which may manifest itself in changes to the shape, size, or location of the accretion spot on the white dwarf such that it lessens or removes the secondary minimum. This project was supported by the NSF REU grant AST-1358980, the Massachusetts Space Grant, and the Nantucket Maria Mitchell Association.

Change in the activity character of the coronae of low-mass stars of various spectral types

NASA Astrophysics Data System (ADS)

Nizamov, B. A.; Katsova, M. M.; Livshits, M. A.

2017-03-01

We study the dependence of the coronal activity index on the stellar rotation velocity. This question has been considered previously for 824 late-type stars on the basis of a consolidated catalogue of soft X-ray fluxes. We carry out a more refined analysis separately for G, K, and M dwarfs. Two modes of activity are clearly identified in them. The first is the saturation mode, is characteristic of young stars, and is virtually independent of their rotation. The second refers to the solar-type activity whose level strongly depends on the rotation period. We show that the transition from one mode to the other occurs at rotation periods of 1.1, 3.3, and 7.2 days for stars of spectral types G2, K4, and M3, respectively. In light of the discovery of superflares on G and K stars from the Kepler spacecraft, the question arises as to what distinguishes these objects from the remaining active late-type stars. We analyze the positions of superflare stars relative to the remaining stars observed by Kepler on the "amplitude of rotational brightness modulation (ARM)—rotation period" diagram. The ARM reflects the relative spots area on a star and characterizes the activity level in the entire atmosphere. G and K superflare stars are shown to be basically rapidly rotating young objects, but some of them belong to the stars with the solar type of activity.

The nature of the companion star in Circinus X-1

NASA Astrophysics Data System (ADS)

Johnston, Helen M.; Soria, Roberto; Gibson, Joel

2016-02-01

We present optical spectra and images of the X-ray binary Circinus X-1. The optical light curve of Cir X-1 is strongly variable, changing in brightness by 1.2 mag in the space of four days. The shape of the light curve is consistent with that seen in the 1980s, when the X-ray and radio counterparts of the source were at least ten times as bright as they are currently. We detect strong, variable H α emission lines, consisting of multiple components which vary with orbital phase. We estimate the extinction to the source from the strength of the diffuse interstellar bands and the Balmer decrement; the two methods give AV = 7.6 ± 0.6 mag and AV > 9.1 mag, respectively. The optical light curve can be modelled as arising from irradiation of the companion star by the central X-ray source, where a low-temperature star fills its Roche lobe in an orbit of moderate eccentricity (e ˜ 0.4). We suggest that the companion star is overluminous and underdense, due to the impact of the supernova which occurred less than 5000 yr ago.

NuSTAR Detection of High-Energy X-Ray Emission and Rapid Variability from Sagittarius A(star) Flares

NASA Technical Reports Server (NTRS)

Barriere, Nicolas M.; Tomsick, John A.; Baganoff, Frederick K.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Dexter, Jason; Grefenstette, Brian; Hailey, Charles J.; Zhang, William W.

2014-01-01

Sagittarius A(star) harbors the supermassive black hole that lies at the dynamical center of our Galaxy. Sagittarius A(star) spends most of its time in a low luminosity emission state but flares frequently in the infrared and X-ray, increasing up to a few hundred fold in brightness for up to a few hours at a time. The physical processes giving rise to the X-ray flares are uncertain. Here we report the detection with the NuSTAR observatory in Summer and Fall 2012 of four low to medium amplitude X-ray flares to energies up to 79 keV. For the first time, we clearly see that the power-law spectrum of Sagittarius A(star) X-ray flares extends to high energy, with no evidence for a cut off. Although the photon index of the absorbed power-law fits are in agreement with past observations, we find a difference between the photon index of two of the flares (significant at the 95% confidence level). The spectra of the two brightest flares (approx. 55 times quiescence in the 2- 10 keV band) are compared to simple physical models in an attempt to identify the main X-ray emission mechanism, but the data do not allow us to significantly discriminate between them. However, we confirm the previous finding that the parameters obtained with synchrotron models are, for the X-ray emission, physically more reasonable than those obtained with inverse-Compton models. One flare exhibits large and rapid (less than 100 s) variability, which, considering the total energy radiated, constrains the location of the flaring region to be within approx. 10 Schwarzschild radii of the black hole.

Characterizing the Population of Bright Infrared Sources in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Kraemer, K. E.; Sloan, G. C.; Wood, P. R.; Jones, O. C.; Egan, M. P.

2017-01-01

We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks more like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3 μm. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z = 0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer, and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope (JWST). Color-color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.

Investigation of ultraviolet fluxes of normal and peculiar stars

NASA Technical Reports Server (NTRS)

Deutschman, W. A.; Schild, R. E.

1974-01-01

Data from Project Celescope, a program that photographed the ultraviolet sky, in order to study several problems in current astrophysics are analyzed. Two star clusters, the Pleiades and the Hyades, reveal differences between the two that we are unable to explain simply from their differences in chemical abundance, rotation, or reddening. Data for Orion show large scatter, which appears to be in the sense that the Orion stars are too faint for their ground-based photometry. Similarly, many supergiants in the association Sco OB1 are too faint in the ultraviolet, but the ultraviolet brightness appears to be only poorly correlated with spectral type. Ultraviolet Celescope data for several groups of peculiar stars have also been analyzed. The strong He I stars are too faint in the ultraviolet, possibly owing to enhancement of O II continuous opacity due to oxygen overabundance. The Be stars appear to have ultraviolet colors normal for their MK spectral types. The P Cygni stars are considerably fainter than main-sequence stars of comparable spectral type, probably owing, at least in part, to line blocking by resonance lines of multiply ionized light metals. The Wolf-Rayet stars have ultraviolet color temperatures of O stars.

Documentation for the machine-readable version of the third Santiago-Pulkovo Fundamental Stars Catalogue (SPF-3)

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1982-01-01

The machine-readable version of a catalog of right ascensions of 671 bright stars is described. The observations were made in a series consisting of 70 stars observed along the meridian from +42 deg to the pole in upper culmination and from the pole to -70 deg in lower culmination.

Precise stellar surface gravities from the time scales of convectively driven brightness variations.

PubMed

Kallinger, Thomas; Hekker, Saskia; García, Rafael A; Huber, Daniel; Matthews, Jaymie M

2016-01-01

A significant part of the intrinsic brightness variations in cool stars of low and intermediate mass arises from surface convection (seen as granulation) and acoustic oscillations (p-mode pulsations). The characteristics of these phenomena are largely determined by the stars' surface gravity (g). Detailed photometric measurements of either signal can yield an accurate value of g. However, even with ultraprecise photometry from NASA's Kepler mission, many stars are too faint for current methods or only moderate accuracy can be achieved in a limited range of stellar evolutionary stages. This means that many of the stars in the Kepler sample, including exoplanet hosts, are not sufficiently characterized to fully describe the sample and exoplanet properties. We present a novel way to measure surface gravities with accuracies of about 4%. Our technique exploits the tight relation between g and the characteristic time scale of the combined granulation and p-mode oscillation signal. It is applicable to all stars with a convective envelope, including active stars. It can measure g in stars for which no other analysis is now possible. Because it depends on the time scale (and no other properties) of the signal, our technique is largely independent of the type of measurement (for example, photometry or radial velocity measurements) and the calibration of the instrumentation used. However, the oscillation signal must be temporally resolved; thus, it cannot be applied to dwarf stars observed by Kepler in its long-cadence mode.

Accreting Millisecond Pulsars: Neutron Star Masses and Radii

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2004-01-01

High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries. The recent discovery of X-ray burst oscillations from two accreting millisecond pulsars has confirmed this basic picture and provided a new route to measuring neutron star properties and constraining the dense matter equation of state. I will briefly summarize the current observational understanding of accreting millisecond pulsars, and describe recent attempts to determine the mass and radius of the neutron star in XTE J1814-338.

Plasmonic EIT-like switching in bright-dark-bright plasmon resonators.

PubMed

Chen, Junxue; Wang, Pei; Chen, Chuncong; Lu, Yonghua; Ming, Hai; Zhan, Qiwen

2011-03-28

In this paper we report the study of the electromagnetically induced transparency (EIT)-like transmission in the bright-dark-bright plasmon resonators. It is demonstrated that the interferences between the dark plasmons excited by two bright plasmon resonators can be controlled by the incident light polarization. The constructive interference strengthens the coupling between the bright and dark resonators, leading to a more prominent EIT-like transparency window of the metamaterial. In contrary, destructive interference suppresses the coupling between the bright and dark resonators, destroying the interference pathway that forms the EIT-like transmission. Based on this observation, the plasmonic EIT switching can be realized by changing the polarization of incident light. This phenomenon may find applications in optical switching and plasmon-based information processing.

Star formation history: Modeling of visual binaries

NASA Astrophysics Data System (ADS)

Gebrehiwot, Y. M.; Tessema, S. B.; Malkov, O. Yu.; Kovaleva, D. A.; Sytov, A. Yu.; Tutukov, A. V.

2018-05-01

Most stars form in binary or multiple systems. Their evolution is defined by masses of components, orbital separation and eccentricity. In order to understand star formation and evolutionary processes, it is vital to find distributions of physical parameters of binaries. We have carried out Monte Carlo simulations in which we simulate different pairing scenarios: random pairing, primary-constrained pairing, split-core pairing, and total and primary pairing in order to get distributions of binaries over physical parameters at birth. Next, for comparison with observations, we account for stellar evolution and selection effects. Brightness, radius, temperature, and other parameters of components are assigned or calculated according to approximate relations for stars in different evolutionary stages (main-sequence stars, red giants, white dwarfs, relativistic objects). Evolutionary stage is defined as a function of system age and component masses. We compare our results with the observed IMF, binarity rate, and binary mass-ratio distributions for field visual binaries to find initial distributions and pairing scenarios that produce observed distributions.

Hubble Space Telescope and Spitzer Imaging of Red and Blue Galaxies at z ~ 2.5: A Correlation between Size and Star Formation Activity from Compact Quiescent Galaxies to Extended Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Toft, S.; van Dokkum, P.; Franx, M.; Labbe, I.; Förster Schreiber, N. M.; Wuyts, S.; Webb, T.; Rudnick, G.; Zirm, A.; Kriek, M.; van der Werf, P.; Blakeslee, J. P.; Illingworth, G.; Rix, H.-W.; Papovich, C.; Moorwood, A.

2007-12-01

We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2star-forming galaxies from quiescent galaxies by modeling their rest-frame UV-NIR SEDs. The star-forming galaxies span the full range of sizes, while the quiescent galaxies all have re<2 kpc. In the redshift range where MIPS 24 μm imaging is a sensitive probe of reradiated dust emission (z<2.5), the 24 μm fluxes confirm that the light of the small quiescent galaxies is dominated by old stars, rather than dust-enshrouded star formation or AGN activity. The inferred surface mass densities and velocity dispersions for the quiescent galaxies are very high compared to those in local galaxies. The galaxies follow a Kormendy relation (between surface brightness and size) with approximately the same slope as locally, but shifted to brighter surface brightnesses, consistent with a mean stellar formation redshift of zf~5. This paper demonstrates a direct relation between star formation activity and size at z~2.5 and the existence of a significant population of massive, extremely dense, old stellar systems without readily identifiable counterparts in the local universe. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407; and observations collected at the European Southern Observatory, Paranal, Chile (ESO Program 164.O-0612).

Dark Skies, Bright Kids! Year 5

NASA Astrophysics Data System (ADS)

Prager, Brian; Johnson, K. E.; Barcos-Munoz, L. D.; Beaton, R.; Bittle, L.; Borish, H.; Burkhardt, A.; Corby, J.; Damke, G.; Dean, J.; Dorsey, G.; Graninger, D.; Lauck, T.; Liss, S.; Oza, A.; Peacock, S.; Romero, C.; Sokal, K. R.; Stierwalt, S.; Walker, L.; Wenger, T.; Zucker, C.

2014-01-01

Our public outreach group Dark Skies, Bright Kids! (DSBK) fosters science literacy in Virginia by bringing a hands-on approach to astronomy that engages children's natural excitement and curiosity. We are an entirely volunteer-run group based out of the Department of Astronomy at the University of Virginia and we enthusiastically utilize astronomy as a 'gateway science.' We create long-term relationships with students during an 8 to 10 week long, after-school astronomy club at under served elementary schools in neighboring counties, and we visited 3 different schools in 2013. Additionally, we organize and participate in science events throughout the community. The fifth year of DSBK was marked by surpassing 10,000 contact hours in Spring 2013 Semester and by ringing in the fall semester with our biggest, most successful star party to date. We hosted the Third Annual Central Virginia Star Party, free and open to the community to encourage families to enjoy astronomy together. Nearly four hundred people of all ages attended, double the number from previous years. Joining with local astronomical societies, we offered an enlightening and exciting night with resources rarely accessible to the public, such as an IR camera and a portable planetarium. With numerous telescopes pointed at the sky, and a beautifully clear night with views of the Milky Way, the International Space Station, and numerous meteors, the star party was a fantastic opportunity to introduce many of our guests to the natural wonders of our night sky and enjoy some of the darkest skies on the eastern seaboard.

Exponential Stellar Disks in Low Surface Brightness Galaxies: A Critical Test of Viscous Evolution

NASA Astrophysics Data System (ADS)

Bell, Eric F.

2002-12-01

Viscous redistribution of mass in Milky Way-type galactic disks is an appealing way of generating an exponential stellar profile over many scale lengths, almost independent of initial conditions, requiring only that the viscous timescale and star formation timescale are approximately equal. However, galaxies with solid-body rotation curves cannot undergo viscous evolution. Low surface brightness (LSB) galaxies have exponential surface brightness profiles, yet have slowly rising, nearly solid-body rotation curves. Because of this, viscous evolution may be inefficient in LSB galaxies: the exponential profiles, instead, would give important insight into initial conditions for galaxy disk formation. Using star formation laws from the literature and tuning the efficiency of viscous processes to reproduce an exponential stellar profile in Milky Way-type galaxies, I test the role of viscous evolution in LSB galaxies. Under the conservative and not unreasonable condition that LSB galaxies are gravitationally unstable for at least a part of their lives, I find that it is impossible to rule out a significant role for viscous evolution. This type of model still offers an attractive way of producing exponential disks, even in LSB galaxies with slowly rising rotation curves.

The Widest-separation Substellar Companion Candidate to a Binary T Tauri Star

NASA Astrophysics Data System (ADS)

Kuzuhara, M.; Tamura, M.; Ishii, M.; Kudo, T.; Nishiyama, S.; Kandori, R.

2011-04-01

The results of near-infrared imaging and spectroscopy of a substellar companion (SR12 C), with a possible planetary mass, of a binary T Tauri star (SR12 AB) in the ρ Ophiuchi star-forming region are presented. The object is separated by ~8farcs7, corresponding to ~1100 AU at 125 pc, and has an H-band brightness of 15.2 mag and infrared spectra suggesting a spectral type of M9.0 ± 0.5. It is confirmed that SR12 C is physically related to the ρ Ophiuchi star-forming region from its common proper motion with SR12 AB and its youth is confirmed by a gravity-sensitive spectral feature. Furthermore, based on the number of known members of the ρ Ophiuchi star-forming region in the area in which SR12 AB exists, the probability of a chance alignment is ~1% and it is therefore likely that SR12 C is physically associated with SR12 AB. The mass of SR12 C is estimated by comparing its estimated luminosity and assumed age with the theoretical age-luminosity relation. SR12 C is identified as an extremely low-mass (0.013 ± 0.007 M sun) object, but its separation from its parent star is the widest among planetary-mass companion (PMC) candidates imaged to date. In addition, SR12 C is the first PMC candidate directly imaged around a binary star. This discovery suggests that PMCs form via multiple star formation processes including disk gravitational instability and cloud core fragmentation.

MWC 297: a young high-mass star rotating at critical velocity

NASA Astrophysics Data System (ADS)

Acke, B.; Verhoelst, T.; van den Ancker, M. E.; Deroo, P.; Waelkens, C.; Chesneau, O.; Tatulli, E.; Benisty, M.; Puga, E.; Waters, L. B. F. M.; Verhoeff, A.; de Koter, A.

2008-07-01

Context: MWC 297 is a nearby young massive B[e] star. The central star is attenuated by 8 mag in the optical and has a high projected rotational velocity of 350 km s-1. Despite the wealth of published observations, the nature of this object and its circumstellar environment is not understood very well. Aims: With the present paper, we intend to shed light on the geometrical structure of the circumstellar matter that is responsible for the near- to mid-infrared flux excess. Methods: The H-band (1.6-2.0 μm), K-band (2.0-2.5 μm), and N-band (8-13 μm) brightness distribution of MWC 297 was probed with the ESO interferometric spectrographs AMBER and MIDI, mounted on the VLTI in Paranal, Chile. We obtained visibility measurements on 3 AMBER and 12 MIDI baselines, covering a wide range of spatial frequencies. Different models (parametrized circumstellar disks, a dusty halo) were invoked to fit the data, all of which fail to do so in a satisfying way. We approximated the brightness distribution in H, K, and N with a geometric model consisting of three Gaussian disks with different extents and brightness temperatures. This model can account for the entire near- to mid-IR emission of MWC 297. Results: The circumstellar matter around MWC 297 is resolved on all baselines. The near- and mid-IR emission, including the silicate emission at 10 micron, emanates from a very compact region (FWHM < 1.5 AU) around the central star. Conclusions: We argue that the extinction towards the MWC 297 star+disk system is interstellar and most likely due to remnants of the natal cloud from which MWC 297 was formed. Furthermore, we argue that the circumstellar matter in the MWC 297 system is organized in a circumstellar disk, seen under moderate (i < 40°) inclination. The disk displays no inner emission-free gap at the resolution of our interferometric observations. The low inclination of the disk implies that the already high projected rotational velocity of the star corresponds to an actual

On the dispersion in brightness of far-ultraviolet emission lines of cool giant stars

NASA Technical Reports Server (NTRS)

Simon, T.

1984-01-01

Low-resolution spectra have been obtained with the short-wavelength camera of IUE for late-type giant stars of spectral type F5 III-G8 III. These stars are believed to be in their first crossing of the H-R diagram, as inferred from their location along the blue edge of the Hertzsprung gap or their high abundance of lithium. From the earliest spectral type observed along the blue edge of the gap, the normalized C IV flux, which is indicative of 100,000 K plasma, increases to a maximum at G0 and then falls with advancing spectral type. The total range in emission measure of 100,000 K gas is an order of magnitude or more among stars making their first appearance as yellow giants and averages about 25 times higher in these stars than in other G8-K0 yellow giants, the majority of which are probably He-burning post-red giants. The observations tentatively show that transition region emission, and by inference coronal emission, increases in intensity with the growth of convection zones in late-type giants and then declines at lower surface temperatures, perhaps because of rotational spin-down and a weakening of dynamo action.

Cluster of Stars in Kepler Sight

NASA Image and Video Library

2009-04-16

This image zooms into a small portion of NASA Kepler full field of view, an expansive, 100-square-degree patch of sky in our Milky Way galaxy. An eight-billion-year-old cluster of stars 13,000 light-years from Earth, called NGC 6791, can be seen in the image. Clusters are families of stars that form together out of the same gas cloud. This particular cluster is called an open cluster, because the stars are loosely bound and have started to spread out from each other. The area pictured is 0.2 percent of Kepler's full field of view, and shows hundreds of stars in the constellation Lyra. The image has been color-coded so that brighter stars appear white, and fainter stars, red. It is a 60-second exposure, taken on April 8, 2009, one day after the spacecraft's dust cover was jettisoned. Kepler was designed to hunt for planets like Earth. The mission will spend the next three-and-a-half years staring at the same stars, looking for periodic dips in brightness. Such dips occur when planets cross in front of their stars from our point of view in the galaxy, partially blocking the starlight. To achieve the level of precision needed to spot planets as small as Earth, Kepler's images are intentionally blurred slightly. This minimizes the number of saturated stars. Saturation, or "blooming," occurs when the brightest stars overload the individual pixels in the detectors, causing the signal to spill out into nearby pixels. http://photojournal.jpl.nasa.gov/catalog/PIA11986

The Stars behind the Curtain

NASA Astrophysics Data System (ADS)

2010-02-01

ESO is releasing a magnificent VLT image of the giant stellar nursery surrounding NGC 3603, in which stars are continuously being born. Embedded in this scenic nebula is one of the most luminous and most compact clusters of young, massive stars in our Milky Way, which therefore serves as an excellent "local" analogue of very active star-forming regions in other galaxies. The cluster also hosts the most massive star to be "weighed" so far. NGC 3603 is a starburst region: a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust. Located 22 000 light-years away from the Sun, it is the closest region of this kind known in our galaxy, providing astronomers with a local test bed for studying intense star formation processes, very common in other galaxies, but hard to observe in detail because of their great distance from us. The nebula owes its shape to the intense light and winds coming from the young, massive stars which lift the curtains of gas and clouds revealing a multitude of glowing suns. The central cluster of stars inside NGC 3603 harbours thousands of stars of all sorts (eso9946): the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars - extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae. Using another recent set of observations performed with the SINFONI instrument on ESO's Very Large Telescope (VLT), astronomers have confirmed that one of these stars is about 120 times more massive than our Sun, standing out as the most massive star known so far in the Milky Way [1]. The clouds of NGC 3603 provide us with a family picture of stars in different stages of their life, with gaseous structures that are

A triangle voting algorithm based on double feature constraints for star sensors

NASA Astrophysics Data System (ADS)

Fan, Qiaoyun; Zhong, Xuyang

2018-02-01

A novel autonomous star identification algorithm is presented in this study. In the proposed algorithm, each sensor star constructs multi-triangle with its bright neighbor stars and obtains its candidates by triangle voting process, in which the triangle is considered as the basic voting element. In order to accelerate the speed of this algorithm and reduce the required memory for star database, feature extraction is carried out to reduce the dimension of triangles and each triangle is described by its base and height. During the identification period, the voting scheme based on double feature constraints is proposed to implement triangle voting. This scheme guarantees that only the catalog star satisfying two features can vote for the sensor star, which improves the robustness towards false stars. The simulation and real star image test demonstrate that compared with the other two algorithms, the proposed algorithm is more robust towards position noise, magnitude noise and false stars.

The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500

NASA Astrophysics Data System (ADS)

Sota, A.; Maíz Apellániz, J.; Walborn, N. R.; Alfaro, E. J.; Barbá, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I.

2011-04-01

We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R ~ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of Maíz Apellániz et al. and Sota et al. The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B = 8 and north of δ = -20° and includes all of the northern objects in Maíz Apellániz et al. that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics. In the future, we will publish the rest of the survey, beginning with a second paper that will include most of the southern stars in Maíz Apellániz et al. The spectroscopic data in this article were gathered with three facilities: the 1.5 m telescope at the Observatorio de Sierra Nevada (OSN), the 3.5 m telescope at Calar Alto Observatory (CAHA), and the du Pont 2.5 m telescope at Las Campanas Observatory (LCO). Some of the supporting imaging data were obtained with the 2.2 m telescope at CAHA and the NASA/ESA Hubble Space Telescope (HST). The rest were retrieved from the DSS2 and Two Micron All Sky Survey (2MASS) surveys. The HST data were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Pulsating Star Mystery Solved

NASA Astrophysics Data System (ADS)

2010-11-01

evolution of stars. This embarrassing discrepancy has been known since the 1960s. To resolve this mystery, astronomers needed to find a double star containing a Cepheid where the orbit happened to be seen edge-on from Earth. In these cases, known as eclipsing binaries, the brightness of the two stars dims as one component passes in front of the other, and again when it passes behind the other star. In such pairs astronomers can determine the masses of the stars to high accuracy [3]. Unfortunately neither Cepheids nor eclipsing binaries are common, so the chance of finding such an unusual pair seemed very low. None are known in the Milky Way. Wolfgang Gieren, another member of the team, takes up the story: "Very recently we actually found the double star system we had hoped for among the stars of the Large Magellanic Cloud. It contains a Cepheid variable star pulsating every 3.8 days. The other star is slightly bigger and cooler, and the two stars orbit each other in 310 days. The true binary nature of the object was immediately confirmed when we observed it with the HARPS spectrograph on La Silla." The observers carefully measured the brightness variations of this rare object, known as OGLE-LMC-CEP0227 [4], as the two stars orbited and passed in front of one another. They also used HARPS and other spectrographs to measure the motions of the stars towards and away from the Earth - both the orbital motion of both stars and the in-and-out motion of the surface of the Cepheid as it swelled and contracted. This very complete and detailed data allowed the observers to determine the orbital motion, sizes and masses of the two stars with very high accuracy - far surpassing what had been done before for a Cepheid. The mass of the Cepheid is now known to about 1% and agrees exactly with predictions from the theory of stellar pulsation. However, the larger mass predicted by stellar evolution theory was shown to be significantly in error. The much-improved mass estimate is only one

Erratum: Sloan Magnitudes for the Brightest Stars

NASA Astrophysics Data System (ADS)

Mallama, A.

2018-06-01

In the article "Sloan Magnitudes for the Brightest Stars" (JAAVSO, 2014, 42, 443), Equation 3 in section A.1. of the Appendix is incorrect; the coefficient of ((R-I) - C1) should be 0.935, rather than 0.953. The mean differences between the new and old results are 0.00 in all cases, and the standard deviations are all 0.00 or 0.01, which is less than the photometric uncertainties of the Johnson or Sloan values. A revised version of the catalog has been published at https://arxiv.org/abs/1805.09324. The revision is proposed as a bright star extension to the APASS database.

Observational aspects of Herbig Ae/Be stars and of candidate young A/B stars

NASA Astrophysics Data System (ADS)

de Winter, Dolf

1996-06-01

The thesis consists of several studies on candidate young stars of which most material is published or in press and which can be divided into three parts roughly. Part A is about Herbig Ae/Be stars. A complete review of the observational properties of HAeBes is given in Chapter A1 together with a renewed up-to-date catalogue of HAeBes and HAeBe candidates. As an example of the selection of HAeBes from candidate stars, the observational properties of three candidates is discussed in Chapter A2. They are in particular interesting as they are relatively bright with respect to other HAeBes candidates. An advantage of bright HAeBes is that high resolution spectroscopy can be obtained. For two well know HAeBe objects with a favourable oriented disk, UX and BF Ori, a high resolution spectroscopy monitoring programme is presented in Chapters A3 and A4. First results presented indicate that the disk material of UX Ori is accreting in the form of comet-like bodies. Such pioneering results are also found for BF Ori but more details of the cometaries are given. As discussed in Chapter A1, the IR-excess is one of the fundamental discriminators for the selection of HAeBe candidates. A good understanding of the origin of the IR-excess of HAeBe candidates is necessary to study the disk material that ultimately could produce (proto-)planetary systems. Chapter A5 discusses the amount of IR-excess of HAeBe candidates and ideas about the probable origin. In Part B objects are discussed which were originally selected as HAeBe candidates, but for which a more detailed analysis of the observational characteristics show that they are probably more evolved. This group contains very interesting objects as is shown in Chapters B1, B2 and B3, in which the discovery of a new galactic Luminous Blue Variable (LBV) is reported, WRA 751. A well known B[e] star is HD 45677. The B[e]-group was collected to consist of evolved objects with masses less than those of LBVs and comparable with B[e] stars

CHARACTERIZING K2 PLANET DISCOVERIES: A SUPER-EARTH TRANSITING THE BRIGHT K DWARF HIP 116454

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

Vanderburg, Andrew; Montet, Benjamin T.; Johnson, John Asher

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 ± 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H] =–0.16 ± 0.08 and has a radius R {sub *} = 0.716 ± 0.024 R {sub ☉} and mass M {sub *} = 0.775 ± 0.027 M {sub ☉}. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014more » February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of R{sub p} = 2.53 ± 0.18 R {sub ⊕}. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 ± 1.33 M {sub ⊕} planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.« less

Astronomers Discover Most Distant Galaxy Showing Key Evidence For Furious Star Formation

NASA Astrophysics Data System (ADS)

2003-12-01

associated with regions of active star formation. What is different about the Cloverleaf is the huge quantity of dense gas along with very powerful infrared radiation from the star formation. Ten billion times the mass of the Sun is contained in dense, star-forming gas clouds. "At the rate this galaxy is seen to be forming stars, that dense gas will be used up in only about 10 million years," Solomon said. In addition to giving astronomers a fascinating glimpse of a huge burst of star formation in the early Universe, the new information about the Cloverleaf helps answer a longstanding question about bright galaxies of that era. Many distant galaxies have supermassive black holes at their cores, and those black holes power "central engines" that produce bright emission. Astronomers have wondered specifically about those distant galaxies that emit large amounts of infrared light, galaxies like the Cloverleaf which has a black hole and central engine. "Is this bright infrared light caused by the black-hole-powered core of the galaxy or by a huge burst of star formation? That has been the question. Now we know that, in at least one case, much of the infrared light is produced by intense star formation," Carilli said. The rapid star formation, called a starburst, and the black hole are both generating the bright infrared light in the Cloverleaf. The starburst is a major event in the formation and evolution of this galaxy. "This detection of HCN gives us a unique new window through which we can study star formation in the early Universe," Carilli said. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Dark-bright soliton pairs: Bifurcations and collisions

NASA Astrophysics Data System (ADS)

Katsimiga, G. C.; Kevrekidis, P. G.; Prinari, B.; Biondini, G.; Schmelcher, P.

2018-04-01

The statics, stability, and dynamical properties of dark-bright soliton pairs are investigated here, motivated by applications in a homogeneous two-component repulsively interacting Bose-Einstein condensate. One of the intraspecies interaction coefficients is used as the relevant parameter controlling the deviation from the integrable Manakov limit. Two different families of stationary states are identified consisting of dark-bright solitons that are either antisymmetric (out-of-phase) or asymmetric (mass imbalanced) with respect to their bright soliton. Both of the above dark-bright configurations coexist at the integrable limit of equal intra and interspecies repulsions and are degenerate in that limit. However, they are found to bifurcate from it in a transcritical bifurcation. This bifurcation interchanges the stability properties of the bound dark-bright pairs rendering the antisymmetric states unstable and the asymmetric ones stable past the associated critical point (and vice versa before it). Finally, on the dynamical side, it is found that large kinetic energies and thus rapid soliton collisions are essentially unaffected by the intraspecies variation, while cases involving near equilibrium states or breathing dynamics are significantly modified under such a variation.

Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

NASA Astrophysics Data System (ADS)

Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

2016-03-01

Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

The central star candidate of the planetary nebula Sh2-71: photometric and spectroscopic variability

NASA Astrophysics Data System (ADS)

Močnik, T.; Lloyd, M.; Pollacco, D.; Street, R. A.

2015-07-01

We present the analysis of several newly obtained and archived photometric and spectroscopic data sets of the intriguing and yet poorly understood 13.5 mag central star candidate of the bipolar planetary nebula Sh2-71. Photometric observations confirmed the previously determined quasi-sinusoidal light curve with a period of 68 d and also indicated periodic sharp brightness dips, possibly eclipses, with a period of 17.2 d. In addition, the comparison between U and V light curves revealed that the 68 d brightness variations are accompanied by a variable reddening effect of ΔE(U - V) = 0.38. Spectroscopic data sets demonstrated pronounced variations in spectral profiles of Balmer, helium and singly ionized metal lines and indicated that these variations occur on a time-scale of a few days. The most accurate verification to date revealed that spectral variability is not correlated with the 68 d brightness variations. The mean radial velocity of the observed star was measured to be ˜26 km s-1 with an amplitude of ±40 km s-1. The spectral type was determined to be B8V through spectral comparison with synthetic and standard spectra. The newly proposed model for the central star candidate is a Be binary with a misaligned precessing disc.

OBSERVATIONAL SIGNATURES OF CONVECTIVELY DRIVEN WAVES IN MASSIVE STARS

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

Aerts, C.; Rogers, T. M.

We demonstrate observational evidence for the occurrence of convectively driven internal gravity waves (IGWs) in young massive O-type stars observed with high-precision CoRoT space photometry. This evidence results from a comparison between velocity spectra based on two-dimensional hydrodynamical simulations of IGWs in a differentially rotating massive star and the observed spectra. We also show that the velocity spectra caused by IGWs may lead to detectable line-profile variability and explain the occurrence of macroturbulence in the observed line profiles of OB stars. Our findings provide predictions that can readily be tested by including a sample of bright, slowly and rapidly rotatingmore » OB-type stars in the scientific program of the K2 mission accompanied by high-precision spectroscopy and their confrontation with multi-dimensional hydrodynamic simulations of IGWs for various masses and ages.« less

Hubble Hotbed of Vigorous Star Formation

NASA Image and Video Library

2017-12-08

This galaxy is currently a hotbed of vigorous star formation. NGC 1569 is a starburst galaxy, meaning that — as the name suggests — it is bursting at the seams with stars, and is currently producing them at a rate far higher than that observed in most other galaxies. For almost 100 million years, NGC 1569 has pumped out stars more than 100 times faster than the Milky Way! As a result, this glittering galaxy is home to super star clusters, three of which are visible in this image — one of the two bright clusters is actually the superposition of two massive clusters. Each containing more than a million stars, these brilliant blue clusters reside within a large cavity of gas carved out by multiple supernovae, the energetic remnants of massive stars. In 2008, Hubble observed the galaxy's cluttered core and sparsely populated outer fringes. By pinpointing individual red giant stars, Hubble’s Advanced Camera for Surveys enabled astronomers to calculate a new — and much more precise — estimate for NGC 1569’s distance. This revealed that the galaxy is actually one and a half times farther away than previously thought, and a member of the IC 342 galaxy group. Astronomers suspect that the IC 342 cosmic congregation is responsible for the star-forming frenzy observed in NGC 1569. Gravitational interactions between this galactic group are believed to be compressing the gas within NGC 1569. As it is compressed, the gas collapses, heats up and forms new stars. Image credit: ESA/Hubble & NASA, Aloisi, Ford; Acknowledgement: Judy Schmidt

A NEAR-INFRARED SURVEY OF THE INNER GALACTIC PLANE FOR WOLF-RAYET STARS. II. GOING FAINTER: 71 MORE NEW W-R STARS

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

Shara, Michael M.; Faherty, Jacqueline K.; Zurek, David

We are continuing a J, K and narrowband imaging survey of 300 deg{sup 2} of the plane of the Galaxy, searching for new Wolf-Rayet (W-R) stars. Our survey spans 150 Degree-Sign in Galactic longitude and reaches 1 Degree-Sign above and below the Galactic plane. The survey has a useful limiting magnitude of K = 15 over most of the observed Galactic plane, and K = 14 (due to severe crowding) within a few degrees of the Galactic center. Thousands of emission-line candidates have been detected. In spectrographic follow-ups of 146 relatively bright W-R star candidates, we have re-examined 11 previouslymore » known WC and WN stars and discovered 71 new W-R stars, 17 of type WN and 54 of type WC. Our latest image analysis pipeline now picks out W-R stars with a 57% success rate. Star subtype assignments have been confirmed with the K-band spectra and distances approximated using the method of spectroscopic parallax. Some of the new W-R stars are among the most distant known in our Galaxy. The distribution of these new W-R stars is beginning to trace the locations of massive stars along the distant spiral arms of the Milky Way.« less

A COMPARATIVE STUDY OF KNOTS OF STAR FORMATION IN INTERACTING VERSUS SPIRAL GALAXIES

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

Smith, Beverly J.; Olmsted, Susan; Jones, Keith

2016-03-15

Interacting galaxies are known to have higher global rates of star formation on average than normal galaxies, relative to their stellar masses. Using UV and IR photometry combined with new and published Hα images, we have compared the star formation rates (SFRs) of ∼700 star forming complexes in 46 nearby interacting galaxy pairs with those of regions in 39 normal spiral galaxies. The interacting galaxies have proportionally more regions with high SFRs than the spirals. The most extreme regions in the interacting systems lie at the intersections of spiral/tidal structures, where gas is expected to pile up and trigger starmore » formation. Published Hubble Space Telescope images show unusually large and luminous star clusters in the highest luminosity regions. The SFRs of the clumps correlate with measures of the dust attenuation, consistent with the idea that regions with more interstellar gas have more star formation. For the clumps with the highest SFRs, the apparent dust attenuation is consistent with the Calzetti starburst dust attenuation law. This suggests that the high luminosity regions are dominated by a central group of young stars surrounded by a shell of clumpy interstellar gas. In contrast, the lower luminosity clumps are bright in the UV relative to Hα, suggesting either a high differential attenuation between the ionized gas and the stars, or a post-starburst population bright in the UV but faded in Hα. The fraction of the global light of the galaxies in the clumps is higher on average for the interacting galaxies than for the spirals. Thus either star formation in interacting galaxies is “clumpier” on average, or the star forming regions in interacting galaxies are more luminous, dustier, or younger on average.« less

Accretion Disks around Young Stars: An Observational Perspective

NASA Astrophysics Data System (ADS)

Ménard, F.; Bertout, C.

Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today

Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

NASA Technical Reports Server (NTRS)

Smith, Howard A.; Hasan, Hashima (Technical Monitor)

2002-01-01

This report details work done in a project involving spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data including some from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and other spectroscopic databases. We will include four kinds of regions: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR (infrared) galaxies; and (4) the galactic center. During this period, work proceeded fully on track and on time. Details on workshops and conferences attended and research results are presented. A preprint article entitled 'The Far Infrared Lines of OH as Molecular Cloud Diagnostics' is included as an appendix.

Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4

NASA Astrophysics Data System (ADS)

Donati, J.-F.; Hébrard, E.; Hussain, G.; Moutou, C.; Grankin, K.; Boisse, I.; Morin, J.; Gregory, S. G.; Vidotto, A. A.; Bouvier, J.; Alencar, S. H. P.; Delfosse, X.; Doyon, R.; Takami, M.; Jardine, M. M.; Fares, R.; Cameron, A. C.; Ménard, F.; Dougados, C.; Herczeg, G.; Matysse Collaboration

2014-11-01

We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri star LkCa 4 within the Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets (MaTYSSE) programme, involving ESPaDOnS at the Canada-France-Hawaii Telescope. Despite an age of only 2 Myr and a similarity with prototypical classical T Tauri stars, LkCa 4 shows no evidence for accretion and probes an interesting transition stage for star and planet formation. Large profile distortions and Zeeman signatures are detected in the unpolarized and circularly polarized lines of LkCa 4 using Least-Squares Deconvolution (LSD), indicating the presence of brightness inhomogeneities and magnetic fields at the surface of LkCa 4. Using tomographic imaging, we reconstruct brightness and magnetic maps of LkCa 4 from sets of unpolarized and circularly polarized LSD profiles. The large-scale field is strong and mainly axisymmetric, featuring a ≃2 kG poloidal component and a ≃1 kG toroidal component encircling the star at equatorial latitudes - the latter making LkCa 4 markedly different from classical T Tauri stars of similar mass and age. The brightness map includes a dark spot overlapping the magnetic pole and a bright region at mid-latitudes - providing a good match to the contemporaneous photometry. We also find that differential rotation at the surface of LkCa 4 is small, typically ≃5.5 times weaker than that of the Sun, and compatible with solid-body rotation. Using our tomographic modelling, we are able to filter out the activity jitter in the radial velocity curve of LkCa 4 (of full amplitude 4.3 km s-1) down to an rms precision of 0.055 km s-1. Looking for hot Jupiters around young Sun-like stars thus appears feasible, even though we find no evidence for such planets around LkCa 4.

Precise stellar surface gravities from the time scales of convectively driven brightness variations

PubMed Central

Kallinger, Thomas; Hekker, Saskia; García, Rafael A.; Huber, Daniel; Matthews, Jaymie M.

2016-01-01

A significant part of the intrinsic brightness variations in cool stars of low and intermediate mass arises from surface convection (seen as granulation) and acoustic oscillations (p-mode pulsations). The characteristics of these phenomena are largely determined by the stars’ surface gravity (g). Detailed photometric measurements of either signal can yield an accurate value of g. However, even with ultraprecise photometry from NASA’s Kepler mission, many stars are too faint for current methods or only moderate accuracy can be achieved in a limited range of stellar evolutionary stages. This means that many of the stars in the Kepler sample, including exoplanet hosts, are not sufficiently characterized to fully describe the sample and exoplanet properties. We present a novel way to measure surface gravities with accuracies of about 4%. Our technique exploits the tight relation between g and the characteristic time scale of the combined granulation and p-mode oscillation signal. It is applicable to all stars with a convective envelope, including active stars. It can measure g in stars for which no other analysis is now possible. Because it depends on the time scale (and no other properties) of the signal, our technique is largely independent of the type of measurement (for example, photometry or radial velocity measurements) and the calibration of the instrumentation used. However, the oscillation signal must be temporally resolved; thus, it cannot be applied to dwarf stars observed by Kepler in its long-cadence mode. PMID:26767193

Star Formation at the Galactic Center

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

The Star Blended with the MOA-2008-BLG-310 Source Is Not the Exoplanet Host Star

NASA Astrophysics Data System (ADS)

Bhattacharya, A.; Bennett, D. P.; Anderson, J.; Bond, I. A.; Gould, A.; Batista, V.; Beaulieu, J. P.; Fouqué, P.; Marquette, J. B.; Pogge, R.

2017-08-01

High-resolution Hubble Space Telescope (HST) image analysis of the MOA-2008-BLG-310 microlens system indicates that the excess flux at the location of the source found in the discovery paper cannot primarily be due to the lens star because it does not match the lens-source relative proper motion, {μ }{rel}, predicted by the microlens models. This excess flux is most likely to be due to an unrelated star that happens to be located in close proximity to the source star. Two epochs of HST observations indicate proper motion for this blend star that is typical of a random bulge star but is not consistent with a companion to the source or lens stars if the flux is dominated by only one star, aside from the lens. We consider models in which the excess flux is due to a combination of an unrelated star and the lens star, and this yields a 95% confidence level upper limit on the lens star brightness of {I}L> 22.44 and {V}L> 23.62. A Bayesian analysis using a standard Galactic model and these magnitude limits yields a host star mass of {M}h={0.21}-0.09+0.21 {M}⊙ and a planet mass of {m}p={23.4}-9.9+23.9 {M}\\oplus at a projected separation of {a}\\perp ={1.12}-0.17+0.16 au. This result illustrates that excess flux in a high-resolution image of a microlens-source system need not be due to the lens. It is important to check that the lens-source relative proper motion is consistent with the microlensing prediction. The high-resolution image analysis techniques developed in this paper can be used to verify the WFIRST exoplanet microlensing survey mass measurements.

HST/COS Observations of the UV-Bright Star Y453 in the Globular Cluster M4 (NGC 6121)

NASA Astrophysics Data System (ADS)

Dixon, William V.; Chayer, Pierre; Benjamin, Robert A.

2016-01-01

Post-AGB stars represent a short-lived phase of stellar evolution during which stars cross the optical color-magnitude diagram from the cool, red tip of the assymptotic giant branch (AGB) to the hot, blue tip of the white-dwarf cooling curve. Their surface chemistry reflects the nuclear-shell burning, mixing, and mass-loss processes characteristic of AGB stars, and their high effective temperatures allow the detection of elements that are unobservable in cool giants. Post-AGB stars in globular clusters offer the additional advantages of known distance, age, and initial chemistry. To better understand the AGB evolution of low-mass stars, we have observed the post-AGB star Y453 in the globular cluster M4 (NGC 6121) with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope. The star, which has an effective temperature of at least 60,000 K, shows absorption from He, C, N, O, Ne, Si, S, Ti, Cr, Mn, Fe, Co, Ni, and Ga. While the star's C and O abundances are consistent with those measured in a sample of nitrogen-poor RGB stars in M4, its N abundance is considerably enhanced. The star's low C abundance suggests that it left the AGB before the onset of third dredge-up.This work was supported by NASA grant HST-GO-13721.001-A to the University of Wisconsin, Whitewater. P.C. is supported by the Canadian Space Agency under a contract with NRC Herzberg Astronomy and Astrophysics.

Variability of Young Stars: the Importance of Keeping an Eye on Children

NASA Astrophysics Data System (ADS)

Herbst, W.

2013-06-01

(Abstract only) I will review the state of our understanding of young stars with an emphasis on how and why they vary in brightness. The main causes of the variations will be reviewed, including the rotation of spotted weak-lined T Tauri stars, accretion onto classical T Tauri stars, the eruptive behavior of FUors, and the enigmatic variations of the UXors. The important role that amateurs have and will continue to play in these studies is highlighted. I will also discuss the latest results on two unusual young binaries, BM Orionis in the Trapezium asterism and KH 15D in NGC 2264.

Photometric and Spectroscopic Analysis for the Determination of Physical Parameters of an Eclipsing Binary Star System

NASA Astrophysics Data System (ADS)

Reid, Piper

2013-01-01

A binary star system is a pair of stars that are bound together by gravity. Most of the stars that we see in the night sky are members of multiple star systems. A system of stars where one star passes in front of the other (as observed from Earth) on a periodic basis is called an eclipsing binary. Eclipsing binaries can have very short rotational periods and in all cases these pairs of stars are so far away that they can only be resolved from Earth as a single point of light. The interaction of the two stars serves to produce physical phenomena that can be observed and used to study stellar properties. By careful data collection and analysis is it possible for an amateur astronomer using commercial, low cost equipment (including a home built spectroscope) to gather photometric (brightness versus time) and spectroscopic (brightness versus wavelength) data, analyze the data, and calculate the physical properties of a binary star system? Using a CCD camera, tracking mount and telescope photometric data of BB Pegasi was collected and a light curve produced. 57 Cygni was also studied using a spectroscope, tracking mount and telescope to prove that Doppler shift of Hydrogen Balmer absorption lines can be used to determine radial velocity. The orbital period, orbital velocity, radius of each star, separation of the two stars and mass of each star was calculated for the eclipsing binary BB Pegasi using photometric and spectroscopic data and Kepler’s 3rd Law. These data were then compared to published data. By careful use of consumer grade astronomical equipment it is possible for an amateur astronomer to determine an array of physical parameters of a distant binary star system from a suburban setting.

Investigating the Bright End of LSST Photometry

NASA Astrophysics Data System (ADS)

Ojala, Elle; Pepper, Joshua; LSST Collaboration

2018-01-01

The Large Synoptic Survey Telescope (LSST) will begin operations in 2022, conducting a wide-field, synoptic multiband survey of the southern sky. Some fraction of objects at the bright end of the magnitude regime observed by LSST will overlap with other wide-sky surveys, allowing for calibration and cross-checking between surveys. The LSST is optimized for observations of very faint objects, so much of this data overlap will be comprised of saturated images. This project provides the first in-depth analysis of saturation in LSST images. Using the PhoSim package to create simulated LSST images, we evaluate saturation properties of several types of stars to determine the brightness limitations of LSST. We also collect metadata from many wide-field photometric surveys to provide cross-survey accounting and comparison. Additionally, we evaluate the accuracy of the PhoSim modeling parameters to determine the reliability of the software. These efforts will allow us to determine the expected useable data overlap between bright-end LSST images and faint-end images in other wide-sky surveys. Our next steps are developing methods to extract photometry from saturated images.This material is based upon work supported in part by the National Science Foundation through Cooperative Agreement 1258333 managed by the Association of Universities for Research in Astronomy (AURA), and the Department of Energy under Contract No. DE-AC02-76SF00515 with the SLAC National Accelerator Laboratory. Additional LSST funding comes from private donations, grants to universities, and in-kind support from LSSTC Institutional Members.Thanks to NSF grant PHY-135195 and the 2017 LSSTC Grant Award #2017-UG06 for making this project possible.

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.

Stellar Rubella: Starspots on F, G and K Stars of Different Ages and Rotation Periods

NASA Astrophysics Data System (ADS)

Guinan, E. F.; Dewarf, L. E.; Messina, S.; McCook, G. P.

1995-05-01

We present high precision photoelectric photometry of a sample of bright, single F, G, and K- type main-sequence and subgiant stars. Several of the stars are members of clusters or moving groups and thus have well determined ages. The majority of the stars are main-sequence to subgiant G-types stars that range in age from 70 Myr to 10 Gyr with directly measured rotation periods from 2.7 days up to 40-50 days. The observations have been carried out with Automatic Photometric Telescopes (APTs) located on Mt Hopkins, Arizona beginning in 1988; standard UBVRI \\ or uvby \\ filters were used. As expected, the youngest, fastest rotating stars in the sample typically have the largest, rotationally modulated starspot light variations. Some of the stars show relatively rapid changes in their light curves that are explained by differential rotation of the starspot groups. In addition, some of the stars that have been observed over several years show long-term, seasonal trends in their mean brightness levels that most likely arise from starspot cycles. The starspot properties (areal coverage, distribution, and temperature) are determined from the modelling of the multiwavelength light curves. For certain stars, comparisons of these photospheric starspots properties to their corresponding chromospheric, transition region, and coronal activity indicators obtained in the UV, EUV \\ and X-ray are presented and discussed. Analogies are also made to the magnetic properties of the Sun. This research is supported by NSF AST 86-16362, NASA NAG5-2160, and NAG5-2494.

Hubble space telescope near-ultraviolet spectroscopy of the bright cemp-no star BD+44°493

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

Placco, Vinicius M.; Beers, Timothy C.; Smith, Verne V.

2014-07-20

We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44°493 a ninth magnitude subgiant with [Fe/H] =–3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for berylliummore » and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44°493, log ε (B) <–0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we obtain even lower upper limits on the abundances of beryllium, log ε (Be) <–2.3, and lead, log ε (Pb) <–0.23 ([Pb/Fe] <+1.90), than those reported by previous analyses in the optical range. Taken together with the previously measured low abundance of lithium, the very low upper limits on Be and B suggest that BD+44°493 was formed at a very early time, and that it could well be a bona-fide second-generation star. Finally, the Pb upper limit strengthens the argument for non-s-process production of the heavy-element abundance patterns in CEMP-no stars.« less

Simultaneous UV and optical study of O star winds and UV and optical covariability of O star winds

NASA Technical Reports Server (NTRS)

Nichols, Joy S.

1995-01-01

Simultaneous ultraviolet and optical observations of 10 bright O stars were organized in several observing campaigns lasting 3-6 days each. The observing campaigns included 12 observatories in the Northern hemisphere obtaining high resolution spectroscopy, photometry, and polarimetry, as well as 24-hour coverage with the IUE (International Ultraviolet Explorer) observatory. Over 600 high dispersion SWP spectra were acquired with IUE at both NASA and VILSPA for the completion of this work. The massive amount of data from these observing campaigns, both from IUE and the ground-based instruments, has been reduced and analyzed. The accompanying paper describes the data acquisition, analysis, and conclusions of the study performed. The most important results of this study are the strong confirmation of the ubiquitous variability of winds of O stars, and the critical correlation between rotation of the star and the wind variability as seen in the ultraviolet and optical spectral lines.

Hubble Watches Super Star Create Holiday Light Show

NASA Image and Video Library

2017-12-08

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

Disk Evaporation in Star Forming Regions

NASA Technical Reports Server (NTRS)

Hollenbach, David; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Young stars produce sufficient ultraviolet photon luminosity and mechanical luminosity in their winds to significantly affect the structure and evolution of the accretion disks surrounding them. The Lyman continuum photons create a nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk at small distances from the star. Further out, they create a photoevaporative flow which relatively rapidly destroys the disk. The resulting slow (10-50 km/s) ionized outflow, which persists for approx. greater than 10(exp 5) years for disk masses M(sub d) approx. 0.3M(sub *), may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We apply the results to Ae and Be stars in order to determine the lifetimes of disks around such stars. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1) C.

A FEROS Survey of Hot Subdwarf Stars

NASA Astrophysics Data System (ADS)

Vennes, Stéphane; Németh, Péter; Kawka, Adela

2018-02-01

We have completed a survey of twenty-two ultraviolet-selected hot subdwarfs using the Fiber-fed Extended Range Optical Spectrograph (FEROS) and the 2.2-m telescope at La Silla. The sample includes apparently single objects as well as hot subdwarfs paired with a bright, unresolved companion. The sample was extracted from our GALEX catalogue of hot subdwarf stars. We identified three new short-period systems (P = 3.5 hours to 5 days) and determined the orbital parameters of a long-period (P = 62d.66) sdO plus G III system. This particular system should evolve into a close double degenerate system following a second common envelope phase.We also conducted a chemical abundance study of the subdwarfs: Some objects show nitrogen and argon abundance excess with respect to oxygen. We present key results of this programme.

HAT-P-68b: A Transiting Hot Jupiter Around a K5 Dwarf Star

NASA Astrophysics Data System (ADS)

Lindor, Bethlee; Hartman, Joel D.

2018-01-01

One of the main goals of the astrophysical society has been to detect sources of life outside of Earth. To aid this search, astronomers have spent the last 2 decades focused on the discovery and characterization of exoplanets. The most effective method for doing so has been transit photometry, wherein we measure the brightness of stars over periods of time. These measurements, or light curves, are later analyzed for dips in brightness caused by objects passing in front of the star. However, variations in these time series can also occur due to non-planetary systems and a meticulous process is needed to distinguish the planets from the various false positives that are detected. HATNet is one of many surveys involved in this endeavor, and in this work I analyze HAT-P-68. First, I model the system as a single star with a transiting planet and derive estimates of the stellar and planetary physical parameters. I also model HAT-P-68 as a number of a false positives such as a pair of stars in an eclipsing binary blended with a background star, and a planet-sized star orbiting a Sun-like star. In order to rule out the possibility that HAT-P-68 is a blend, I carried out a statistical blend analysis of the photometric data and find that all blend models tested can be ruled out. Thus, I conclude that HAT-P-68 is a system with a transiting hot jupiter and consider what future observations would be most promising to further characterize the system.

HUBBLE DISCOVERS POWERFUL LASER BEAMED FROM CHAOTIC STAR

NASA Technical Reports Server (NTRS)