scholarly journals The population of hot subdwarf stars studied with Gaia

2020 ◽  
Vol 635 ◽  
pp. A193 ◽  
Author(s):  
S. Geier
Keyword(s):  
Proper Motion ◽  
White Dwarfs ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Radial Velocities ◽  
Horizontal Branch ◽  
Atmospheric Parameters ◽  
Main Sequence Stars ◽  
Data Release ◽  
Hot Subdwarfs

In light of substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of new all-sky data from ground-based photometric surveys and the Gaia mission Data Release 2, we compiled an updated catalogue of the known hot subdwarf stars. The catalogue contains 5874 unique sources including 528 previously unknown hot subdwarfs and provides multi-band photometry, astrometry from Gaia, and classifications based on spectroscopy and colours. This new catalogue provides atmospheric parameters of 2187 stars and radial velocities of 2790 stars from the literature. Using colour, absolute magnitude, and reduced proper motion criteria, we identified 268 previously misclassified objects, most of which are less luminous white dwarfs or more luminous blue horizontal branch and main-sequence stars.

scholarly journals White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14

2019 ◽  
Vol 486 (2) ◽  
pp. 2169-2183 ◽  
Author(s):  
S O Kepler ◽  
Ingrid Pelisoli ◽  
Detlev Koester ◽  
Nicole Reindl ◽  
Stephan Geier ◽  
...  
Keyword(s):  
Survey Data ◽  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Sky Survey ◽  
Data Release ◽  
Hot Subdwarfs

ABSTRACT White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs provide insight into the early ages of each population. Examining the spectra of all stars with 3σ proper motion in the Sloan Digital Sky Survey Data Release 14, we report the classification for 20 088 spectroscopically confirmed white dwarfs, plus 415 hot subdwarfs, and 311 cataclysmic variables. We obtain Teff, log  g, and mass for hydrogen atmosphere white dwarf stars (DAs), warm helium atmosphere white dwarfs (DBs), hot subdwarfs (sdBs and sdOs), and estimate photometric Teff for white dwarf stars with continuum spectra (DCs). We find 15 793 sdAs and 447 dCs between the white dwarf cooling sequence and the main sequence, especially below $T_\mathrm{eff}\simeq 10\, 000$ K; most are likely low-mass metal-poor main-sequence stars, but some could be the result of interacting binary evolution.

scholarly journals White dwarfs in the Gaia era

2017 ◽  
Vol 12 (S330) ◽  
pp. 317-320
Author(s):  
P.-E. Tremblay ◽  
N. Gentile-Fusillo ◽  
J. Cummings ◽  
S. Jordan ◽  
B. T. Gänsicke ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Main Sequence ◽  
Milky Way ◽  
Mass Function ◽  
Initial Mass Function ◽  
Sequence Evolution ◽  
Atmospheric Parameters ◽  
Stellar Formation ◽  
Formation History ◽  
Data Release

AbstractThe vast majority of stars will become white dwarfs at the end of the stellar life cycle. These remnants are precise cosmic clocks owing to their well constrained cooling rates. Gaia Data Release 2 is expected to discover hundreds of thousands of white dwarfs, which can then be observed spectroscopically with WEAVE and 4MOST. By employing spectroscopically derived atmospheric parameters combined with Gaia parallaxes, white dwarfs can constrain the stellar formation history in the early developing phases of the Milky Way, the initial mass function in the 1.5 to 8 M⊙ range, and the stellar mass loss as well as the state of planetary systems during the post main-sequence evolution.

scholarly journals Diffusion and He Overabundances: Hydrodynamical Implications

1985 ◽  
Vol 87 ◽  
pp. 453-469
Author(s):  
G. Michaud
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
White Dwarfs ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Horizontal Branch ◽  
Main Sequence Stars ◽  
Horizontal Branch Stars ◽  
Cno Abundances

AbstractIn the absence of mass loss, diffusion leads to underabundances of He in main sequence stars. Because of a very strong observational link with Ap and He weak stars, it has however been suggested that diffusion is the explanation for the He rich stars of the upper main sequence. This requires a mass loss rate of 10−12 Mo yr−1 or slightly lower. The mass loss rate must decrease as Teff increases. Magnetic fields must apparently be involved to reduce the mass loss rate. Since this model predicts that the CNO abundances should be normal in the cooler He rich stars, it leads to a clear observational test. Detailed calculations should be made to confirm the importance of this test. The effects of separation in the wind, the atmosphere and the envelope are discussed to conclude that separation in the atmosphere is likely to be most important. The importance of diffusion for He rich white dwarfs and horizontal branch stars are briefly discussed.

scholarly journals A Limit on the Space Density of Short-Period Binary White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 492-497
Author(s):  
Edward L. Robinson ◽  
Allen W. Shafter
Keyword(s):  
Orbital Period ◽  
Binary Stars ◽  
White Dwarfs ◽  
Main Sequence ◽  
Close Binaries ◽  
Main Sequence Stars ◽  
Space Density ◽  
Short Period ◽  
Hot Subdwarfs ◽  
Orbital Periods

We infer that detached binary white dwarfs with orbital periods of a few hours exist because we observe both their progenitors and their descendents. The binary LB 3459 has an orbital period of 6.3 hr and contains a pair of hot subdwarfs that will eventually cool to become white dwarfs (Kilkenny, Hill, and Penfold 1981). L870-2 is a pair of white dwarfs and, given enough time, its 1.55 d orbital period will decay to shorter periods (Saffer, Liebert, and Olszewski 1988). GP Com, AM CVn, V803 Cen, and PG1346+082 are interacting binary white dwarfs with orbital periods between 1051 s for AM CVn and 46.5 min for GP Com (Nather, Robinson, and Stover 1981; Solheim et al. 1984; Wood et al. 1987; O’Donoghue and Kilkenny 1988). These ultrashort period systems must be descendents of detached pairs of white dwarfs. We also expect short-period binary white dwarfs to exist for theoretical reasons. All calculations of the evolution of binary stars show that main-sequence binaries can evolve to binary white dwarfs (e.g., Iben and Tutukov 1984). Among Population I stars, 1/2 to 2/3 of all main-sequence stars are binaries and about 20% of these binaries should become double white dwarfs with short orbital periods (Abt 1983, Iben and Tutukov 1986). Thus, about 1/10 of all white dwarfs could be close binaries (Paczynski 1985). Nevertheless, no detached binary white dwarfs with extremely short periods have yet been found.

scholarly journals The empirical Gaia G-band extinction coefficient

2018 ◽  
Vol 614 ◽  
pp. A19 ◽  
Author(s):  
C. Danielski ◽  
C. Babusiaux ◽  
L. Ruiz-Dern ◽  
P. Sartoretti ◽  
F. Arenou
Keyword(s):  
Extinction Coefficient ◽  
Main Sequence ◽  
Spectral Energy Distribution ◽  
Empirical Method ◽  
Spectral Energy ◽  
Red Giants ◽  
Main Sequence Stars ◽  
Empirical Estimation ◽  
Two Samples ◽  
Data Release

Context. The first Gaia data release unlocked the access to photometric information for 1.1 billion sources in the G-band. Yet, given the high level of degeneracy between extinction and spectral energy distribution for large passbands such as the Gaia G-band, a correction for the interstellar reddening is needed in order to exploit Gaia data. Aims. The purpose of this manuscript is to provide the empirical estimation of the Gaia G-band extinction coefficient kG for both the red giants and main sequence stars in order to be able to exploit the first data release DR1. Methods. We selected two samples of single stars: one for the red giants and one for the main sequence. Both samples are the result of a cross-match between Gaia DR1 and 2MASS catalogues; they consist of high-quality photometry in the G-, J- and KS-bands. These samples were complemented by temperature and metallicity information retrieved from APOGEE DR13 and LAMOST DR2 surveys, respectively. We implemented a Markov chain Monte Carlo method where we used (G – KS)0 versus Teff and (J – KS)0 versus (G – KS)0, calibration relations to estimate the extinction coefficient kG and we quantify its corresponding confidence interval via bootstrap resampling. We tested our method on samples of red giants and main sequence stars, finding consistent solutions. Results. We present here the determination of the Gaia extinction coefficient through a completely empirical method. Furthermore we provide the scientific community with a formula for measuring the extinction coefficient as a function of stellar effective temperature, the intrinsic colour (G – KS)0, and absorption.

Luminosity and Intrinsic Color Calibration of Main-Sequence Stars With 2Mass Photometry: All Sky Local Extinction

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
Jens Knude ◽  
Claus Fabricius
Keyword(s):  
Color Index ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Interstellar Extinction ◽  
Local Extinction ◽  
Sequence Information ◽  
Main Sequence Stars ◽  
Color Calibration

AbstractWe present a new color index vs. absolute magnitude calibration of 2MASS JHK photometry. For the A0 to ~G5 and M segments of the main sequence information on the amount of interstellar extinction and its location in space may be obtained.

Spectroscopic Binaries in the Halo

1992 ◽  
Vol 135 ◽  
pp. 158-160 ◽  
Author(s):  
David W. Latham ◽  
Tsevi Mazeh ◽  
Robert P. Stefanik ◽  
Robert J. Davis ◽  
Bruce W. Carney ◽  
...  
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Radial Velocities ◽  
Spectroscopic Binaries ◽  
Variable Velocity ◽  
Short Period ◽  
The Galaxy ◽  
Elliptical Orbits

AbstractFor almost 1500 stars in the Carney-Latham survey of proper-motion stars we have accumulated about 20,000 precise radial velocities. Already we have orbital solutions for more than 150 spectroscopic binaries in this sample, and about 100 additional binary candidates with variable velocity. We find that among the metal-poor halo field stars in this sample the frequency of short-period spectroscopic binaries is indistinguishable from that of the disk. The distribution of eccentricity versus period shows evidence for tidal circularization on the main sequence. For the binaries more metal poor than [m/H] = −1.6 there is a clean transition from circular to elliptical orbits at a period of about 19 days. For longer periods the distribution of eccentricity is the same as for stars in the disk of the Galaxy.

scholarly journals Ongoing astrometric microlensing events of two nearby stars

2018 ◽  
Vol 615 ◽  
pp. L11 ◽  
Author(s):  
J. Klüter ◽  
U. Bastian ◽  
M. Demleitner ◽  
J. Wambsganss
Keyword(s):  
Prior Knowledge ◽  
Gravitational Lensing ◽  
Proper Motion ◽  
Absolute Magnitude ◽  
Stellar Objects ◽  
Lens Position ◽  
Data Release ◽  
Nearby Stars ◽  
Excellent Tool ◽  
Background Star

Context. Astrometric microlensing is an excellent tool to determine the mass of stellar objects. By measuring the astrometric shift of a background source star in combination with precise predictions of its unlensed position and of the lens position, gravitational lensing allows to one determine the mass of the lensing star with a precision of 1%, independently of any prior knowledge. Aims. Making use of the recently published Gaia Data Release 2 (Gaia DR2) we predict astrometric microlensing events by fore-ground stars of high proper motion passing by a background star in the coming years. Methods. We compile a list of approximately 148 000 high-proper-motion stars within Gaia DR2 with µtot > 150 mas yr−1. We then search for background stars close to their paths and calculate the dates and separations of the closest approaches. Using color and absolute magnitude, we determine approximate masses of the lenses. Finally, we calculate the expected astrometric shifts and magnifications of the predicted events. Results. We detect two ongoing microlensing events by the high-proper-motion stars Luyten 143-23 and Ross 322 and predict closest separations of (108.5 ± 1.4) mas in July 2018 and (125.3 ± 3.4) mas in August 2018, respectively. The respective expected astrometric shifts are (1.74 ± 0.12) mas and (0.76 ± 0.06) mas. Furthermore, Luyten 143-23 will pass by another star in March 2021 with a closest separation of (280.1 ± 1.1) mas, which results in an expected shift of (0.69 ± 0.05) mas.

scholarly journals 33. Commission de la Statistique Stellaire

1936 ◽  
Vol 5 ◽  
pp. 228-232
Author(s):  
M. Lindblad ◽  
MM. Bok ◽  
Eddington ◽  
Hertzsprung ◽  
S. Hirayama ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Main Sequence ◽  
Spectral Characteristics ◽  
Absolute Magnitude ◽  
Wide Field ◽  
Continuous Absorption ◽  
Trigonometric Parallaxes ◽  
The One ◽  
Almost All ◽  
Made In

In the wide field of research covered by the Commission considerable progress has been made in recent years, and it is only possible here to touch briefly on the results of a few lines of investigation, without any attempt to completeness.Stellar luminosities. On the basis of the new list of Mount Wilson spectroscopic parallaxes and a compilation of the long series of modern trigonometric parallaxes A. van Maanen finds 617 objects within a distance of 20 parsecs from the sun. It is very doubtful, however, if we know all the stars even in the region of 5 parsecs radius. Almost all the known stars within 20 parsecs belong to the main sequence, the faintest star being of absolute magnitude +16.6. The most interesting deviations from the main sequence are the three “white dwarfs”, Сотр. of Sirius, Comp. o2 Eridani, and van Maanen’s F type star. G. P. Kuiper lists 3 additional white dwarfs at larger distances which were estimated to be of types Bo, B7 and A2. For the first two stars, A.C. 70°8247 and Wolf 1346, a revision of the spectral types by Adams and Humason gives A2 and A5, respectively, although the spectra differ considerably from normal ones. The A2 star in Kuiper’s list is the one discovered by Oosterhoff in the region of the cluster h, X Persei; its spectral characteristics have been examined by Öhman and by Humason. The absence of the high-numbered members of the Bahner series and of the continuous absorption at the Balmer limit seems to be an important criterion of such stars. A white dwarf of quite peculiar spectrum (type probably about B8) is the companion of o Ceti discovered spectro-graphically by Joy in 1922. There appear several additional deviations towards faint magnitudes from the main sequence which may be classed more or less safely among the white dwarfs. A few such cases have been discussed at Lund by J. Tuominen.

scholarly journals A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes

1970 ◽  
Vol 38 ◽  
pp. 232-235
Author(s):  
W. Becker ◽  
R. Fenkart
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Gradients ◽  
The Sun ◽  
Main Sequence Stars

The Basel Observatory program of the determination of disc- and halo-density gradients for different intervals of absolute magnitude comprises in addition to Milky Way fields several directions, all pointing to Selected Areas near a plane perpendicular to the galactic equator and passing through the sun and the galactic centre. It was started with SA 51 (Becker, 1965) and continued with Sa 57, 54 and 141 (Fenkart, 1967, 1968, 1969).

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