Bianchi, Luciana and Efremova, Boryana and Herald, James and Girardi, Léo and Zabot, Alexandre and Marigo, Paola and Martin, Christopher (2011) Catalogues of hot white dwarfs in the Milky Way from GALEX's ultraviolet sky surveys: constraining stellar evolution. Monthly Notices of the Royal Astronomical Society, 411 (4). pp. 2770-2791. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20110322-091233732
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We present comprehensive catalogues of hot star candidates in the Milky Way (MW), selected from Galaxy Evolution Explorer (GALEX) far-UV (FUV; 1344–1786 Å) and near-UV (NUV; 1771–2831 Å) 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 catalogues of UV sources from two GALEX’s surveys: All-Sky Imaging Survey (AIS; depth AB magnitude ~19.9/20.8 in FUV/NUV) and Medium-depth Imaging Survey (MIS; depth~22.6/22.7mag). The two catalogues (from GALEX fifth data release) contain 65.3/12.6 million (AIS/MIS) unique UV sources with error _(NUV) ≤ 0.5mag, over 21 435/1579 deg^2. We also constructed subcatalogues of the UV sources with matched optical photometry from Sloan Digital Sky Survey (SDSS;seventh data release): these contain 0.6/0.9 million (AIS/MIS) sources with errors ≤0.3mag in both FUV and NUV, excluding sources with multiple optical counterparts, over an area of 7325/1103 deg^2. All catalogues are available online. We then selected 28 319 (AIS)/9028 (MIS) matched sources with FUV − NUV < −0.13; this colour cut corresponds to stellar T_(eff) hotter than ~18 000 K (the exact value varying with gravity). An additional colour cut of NUV−r > 0.1 isolates binaries with largely differing T_(eff) s, and some intruding quasistellar objects (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 catalogues, and the effects of error and colour 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 MW 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 disc, at typical distances between 0.15 and 1 kpc, while the fainter sample comprises also a fraction of thick disc and halo stars. Proper motion distributions, available only for the bright sample (NUV < 18 mag), are consistent with the kinematics of a thin-disc population.
|Additional Information:||© 2010 The Authors. Monthly Notices of the Royal Astronomical Society © 2010 RAS. Accepted 2010 October 16. Received 2010 August 3; in original form 2010 March 9. Article first published online: 15 Dec. 2010. Data presented in this paper were obtained from the Multimission Archive at the Space Telescope Science Institute (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. GALEX is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and science analysis of the GALEX mission, developed in cooperation with the Centre National d’Etudes Spatiales of France and the Korean Ministry of Science and Technology. LB and JH acknowledge partial support from FUSE GI grant H901 (NASA NNX08AG97G). AZ acknowledges financial support from CNPq-MCT/Brazil. LG acknowledges partial funding from contract ASIINAF I/016/07/0.We are very grateful to A. Thakar for discussions of many issues regarding the SDSS data base, and to L. G. Althaus, A. Kanaan, S. O. Kepler, and D. Koester for providing their WD models.|
|Subject Keywords:||catalogues; surveys; stars: evolution; white dwarfs; Galaxy: stellar content; ultraviolet: stars|
|Official Citation:||Catalogues of hot white dwarfs in the Milky Way from GALEX’s ultraviolet sky surveys: constraining stellar evolution (pages 2770–2791) Luciana Bianchi, Boryana Efremova, James Herald, Léo Girardi, Alexandre Zabot, Paola Marigo and Christopher Martin Article first published online: 15 DEC 2010 | DOI: 10.1111/j.1365-2966.2010.17890.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||22 Mar 2011 18:15|
|Last Modified:||22 Mar 2011 18:24|
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