Catalogues of hot white dwarfs in the Milky Way from GALEX's ultraviolet sky surveys: constraining stellar evolution

We present comprehensive catalogs of hot star candidates in the Milky Way, selected from GALEX far-UV (FUV, 1344-1786u and near-UV (NUV, 1771-2831u imaging. The FUV and NUV photometry allows us to extract the hottest stellar objects, in particular hot white dwarfs (WD), which are elusive at other wavelengths because of their high temperatures and faint optical luminosities. We generated catalogs of UV sources from two GALEX’s surveys: AIS (All-Sky Imaging Survey, depth ABmag�19.9/20.8 in FUV/NUV) and MIS (Medium-depth Imaging Survey, depth �22.6/22.7mag). The two catalogs (from GALEX fifth data release) contain 65.3/12.6 million (AIS/MIS) unique UV sources with errorNUV60.5mag, over 21,435/1,579 square degrees. We also constructed subcatalogs of the UV sources with matched optical photometry from SDSS (seventh data release): these contain 0.6/0.9million (AIS/MIS) sources with errors 60.3mag in both FUV and NUV, excluding sources with multiple optical counterparts, over an area of 7,325/1,103 square degrees. All catalogs are available online. We then selected 28,319 (AIS) / 9,028 (MIS) matched sources with FUV-NUV 0.1 isolates binaries with largely differing Teff ’s, and some intruding QSOs (more numerous at faint magnitudes). Available spectroscopy for a subsample indicates that hot-star candidates with NUV-r<0.1 (mostly “single” hot stars) have negligible contamination by non-stellar objects. We discuss the distribution of sources in the catalogs, and the effects of error and color cuts on the samples. The density of hot-star candidates increases from high to low Galactic latitudes, but drops on the MW plane due to dust extinction. Our hot-star counts at all latitudes are better matched by Milky Way models computed with an initial-final mass relation (IFMR) that favours lower final masses. The model analysis indicates that the brightest sample is likely composed of WDs located in the thin disk, at typical distances between 0.151kpc, while the fainter sample comprises also a fraction of thick disk and halo stars. Proper motion distributions, available only for the bright sample (NUV<18 mag), are consistent with the kinematics of a thin-disk population.

[1]  A. Karakas.  Updated stellar yields from asymptotic giant branch models , 2009, 0912.2142.

[2]  A. Rebassa-Mansergas,et al.  Post-common envelope binaries from SDSS - VII. A catalogue of white dwarf-main sequence binaries , 2009, 0910.4406.

[3]  M. Catelán,et al.  THE MASSES OF POPULATION II WHITE DWARFS , 2009, 0909.2253.

[4]  S. Kleinman,et al.  The next SDSS white dwarf catalog , 2009 .

[5]  J. Thorstensen,et al.  SDSS unveils a population of intrinsically faint cataclysmic variables at the minimum orbital period , 2009, 0905.3476.

[6]  L. Bianchi.  The Ultraviolet sky surveys: filling the gap in our view of the Universe , 2009 .

[7]  A. Bressan,et al.  ULTRAVIOLET QUASI-STELLAR OBJECTS , 2009 .

[8]  A. Szalay,et al.  GALEX–SDSS CATALOGS FOR STATISTICAL STUDIES , 2009, 0904.1392.

[9]  Roy Ostensen,et al.  Spectral analysis of 636 white dwarf-M star binaries from the sloan digital sky survey , 2009 .

[10]  S. Anderson,et al.  CATACLYSMIC VARIABLES FROM SDSS. VII. THE SEVENTH YEAR (2006) , 2009, 0901.3177.

[11]  G. Sonneborn,et al.  Future Directions in Ultraviolet Spectroscopy , 2009 .

[12]  M. SubbaRao,et al.  Additional Ultracool White Dwarfs Found in the Sloan Digital Sky Survey , 2008, 0804.3810.

[13]  K. Eriksson,et al.  Intense mass loss from C-rich AGB stars at low metallicity? , 2008, 0804.2482.

[14]  Terry D. Oswalt,et al.  A NEW LOOK AT THE LOCAL WHITE DWARF POPULATION , 2008 .

[15]  R. Michael Rich,et al.  The Initial-Final Mass Relation: Direct Constraints at the Low-Mass End , 2007, 0706.3894.

[16]  D. Thilker,et al.  GALEX ultraviolet photometry of NGC 2420: searching for WDs , 2007, 0712.0755.

[17]  A. Szalay,et al.  The Calibration and Data Products of GALEX , 2007 .

[18]  S. Hawley,et al.  New Close Binary Systems from the SDSS-I (Data Release Five) and the Search for Magnetic White Dwarfs in Cataclysmic Variable Progenitor Systems , 2007, 0704.0789.

[19]  C. Zahn.  Thermohaline mixing: a physical mechanism governing the photospheric composition of low-mass giants , 2007, astro-ph/0703302.

[20]  -INAF,et al.  Evolution of asymptotic giant branch stars. I. Updated synthetic TP-AGB models and their basic calibration , 2007, astro-ph/0703139.

[21]  Qiong-hua Hu,et al.  The mass and luminosity functions and the formation rate of DA white dwarfs in the Sloan Digital Sky Survey , 2007, astro-ph/0701197.

[22]  David Schiminovich,et al.  Statistical Properties of the GALEX-SDSS Matched Source Catalogs, and Classification of the UV Sources , 2006, astro-ph/0611926.

[23]  P. Bergeron,et al.  Infrared Photometric Analysis of White Dwarfs from the Two Micron All Sky Survey and the Spitzer Space Telescope , 2006, astro-ph/0611899.

[24]  B. Milliard,et al.  The GALEX Ultraviolet Atlas of Nearby Galaxies , 2006, astro-ph/0606440.

[25]  S. O. Kepler,et al.  White dwarf mass distribution in the SDSS , 2006, astro-ph/0612277.

[26]  M. Barstow,et al.  Joint Discussion 4 UV astronomy: stars from birth to death , 2006, Proceedings of the International Astronomical Union.

[27]  James Liebert,et al.  A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4 , 2006, astro-ph/0606700.

[28]  M. Livio,et al.  The Local Group as an astrophysical laboratory: The Local Group as an Astrophysical Laboratory , 2006 .

[29]  L. Althaus,et al.  Mass-radius relations for massive white dwarf stars , 2005, astro-ph/0507559.

[30]  J. Liebert,et al.  The open cluster initial-final mass relationship and the high-mass tail of the white dwarf distribution , 2005, astro-ph/0506317.

[31]  E. Hatziminaoglou,et al.  Star counts in the Galaxy - Simulating from very deep to very shallow photometric surveys with the TRILEGAL code , 2005, astro-ph/0504047.

[32]  A. Szalay,et al.  Classification and Characterization of Objects from the Galaxy Evolution Explorer Survey and the Sloan Digital Sky Survey , 2005 .

[33]  P. Bergeron,et al.  The Formation Rate and Mass and Luminosity Functions of DA White Dwarfs from the Palomar Green Survey , 2004, astro-ph/0406657.

[34]  R. Wyse.  in The Local Group as an Astrophysical Laboratory , 2005 .

[35]  E. H. Olsen,et al.  The Geneva-Copenhagen survey of the Solar neighbourhood - Ages, metallicities, and kinematic properties of ~14 000 F and G dwarfs , 2004, astro-ph/0405198.

[36]  David G. Monet,et al.  An Improved Proper-Motion Catalog Combining USNO-B and the Sloan Digital Sky Survey , 2004 .

[37]  L. Althaus,et al.  Mass distribution of DA white dwarfs in the first Data Release of the Sloan Digital Sky Survey , 2004, astro-ph/0404344.

[38]  Oxford,et al.  The 2dF QSO Redshift Survey – XII. The spectroscopic catalogue and luminosity function , 2004, astro-ph/0403040.

[39]  J. Liebert,et al.  COOL WHITE DWARFS , 2003 .

[40]  Italy.,et al.  Probing AGB nucleosynthesis via accurate Planetary Nebula abundances , 2003, astro-ph/0307252.

[41]  Stefanie Wachter,et al.  Cool Companions to White Dwarfs from the Two Micron All-Sky Survey Second Incremental Data Release , 2002, astro-ph/0212174.

[42]  J. Lattanzio,et al.  Parameterising the Third Dredge-up in Asymptotic Giant Branch Stars , 2002, Publications of the Astronomical Society of Australia.

[43]  L. Miller,et al.  White dwarfs in the 2dF QSO Redshift Survey – I. Hydrogen-rich (DA) stars , 2002 .

[44]  E. Sion,et al.  A Determination of the Local Density of White Dwarf Stars , 2001, astro-ph/0102120.

[45]  P. Girardi.  Coupling emitted light and chemical yields from stars: A basic constraint to population synthesis models of galaxies , 2001, astro-ph/0107563.

[46]  A. Serenelli,et al.  Diffusion and the occurrence of hydrogen‐shell flashes in helium white dwarf stars , 2000, astro-ph/0012545.

[47]  P. Marigo.  Chemical Yields from Low- and Intermediate-Mass Stars , 1999, astro-ph/0012181.

[48]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .

[49]  D. Schlegel,et al.  Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds , 1997, astro-ph/9710327.

[50]  J. Binney,et al.  Local stellar kinematics from Hipparcos data , 1997, astro-ph/9710077.

[51]  Maria Teresa Ruiz,et al.  The Chemical Evolution of Cool White Dwarfs and the Age of the Local Galactic Disk , 1997 .

[52]  A. R. Klemola,et al.  The Absolute Magnitude and Kinematics of RR Lyrae Stars via Statistical Parallax , 1996, astro-ph/9608108.

[53]  A. Boothroyd,et al.  The CNO Isotopes: Deep Circulation in Red Giants and First and Second Dredge-up , 1995, astro-ph/9512121.

[54]  A. Renzini,et al.  Temperatures, gravities, and masses for a sample of bright DA white dwarfs and the initial-to-final mass relation , 1995 .

[55]  P. Wood,et al.  Post-asymptotic giant branch evolution of low- to intermediate-mass stars , 1994 .

[56]  James Liebert,et al.  A spectroscopic determination of the mass distribution of DA white dwarfs , 1992 .

[57]  John N. Bahcall,et al.  Comparisons of a Standard Galaxy Model With Stellar Observations in Five Fields , 1984 .

[58]  J. Bahcall,et al.  Models for the Galaxy and the Predicted Star Counts , 1979 .

[59]  Edward M. Sion,et al.  A Catalog of Spectroscopically Identified White Dwarfs , 1987 .

[60]  E. Salpeter.  The Luminosity function and stellar evolution , 1955 .