AAS 205th Meeting, 9-13 January 2005
Session 21 Stars Throughout the Milky Way
Poster, Monday, January 10, 2005, 9:20am-6:30pm, Exhibit Hall

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[21.05] GALEX Survey for Subdwarf B Stars

J. Rhee (Yonsei U. & Caltech), M. Seibert (Caltech), R.H. {Ø}stensen (ING), S.K. Yi (Oxford U.), S.-C. Rey (Chungnam N.U., Yonsei U., & Caltech), R.M. Rich (UCLA), L. Bianchi (JHU), Y.-W. Lee (Yonsei U.)

We have recently initiated a systematic search for the UV bright, hot subdwarf B (sdB) stars in the Milky Way, as a Guest Investigator Program with NASA's Galaxy Evolution Explorer (GALEX) satelite mission. The sdB star candidates are first chosen from the GALEX Far- & Near-UV photometry in combination with currently available optical and near IR photometry (e.g., 2MASS & SDSS). Ground-based follow-up spectroscopy is carried out to verify spectral type and luminosity class, particularly for distinction from white dwarf (WD) stars. We have already performed spectroscopic pilot observations for 15 sdB star candidates with the McDonald 2.7-m and Lick 3.0-m telescopes, and revealed that the sample includes stars over a range of luminosities and spectral types, i.e., sdB, blue horizontal-branch, narrow-lined B (supergiant or post-AGB), and WD stars.

Although the current and post evolutionary status of sdB stars is relatively well understood (i.e., immediate progenitors of WDs), very little physics behind their formation/evolution is known. Our preliminary test with 649 All-sky Imaging Survey (AIS) fields in GALEX IR0.2 indicates roughly 0.35 sdB star candidates per circular field (r = 0.6\circ), thus we expect to collect about 950 sdB candidate stars as faint as NUV \approx 20 (B \approx 18) from 2,700 AIS fields in GALEX DR1. The huge data set of GALEX sdB stars, which reach the entire UV visible Milky Way, will eventually answer most of the remaining questions associated with the formation and evolution mechanism of the stars, and help expand our understanding about dynamical history and structure of the Milky Way. In this poster, preliminary results and survey plan with the on-going spectroscopic follow-up will be described.

We gratefully acknowledge support for this work from NASA grant GALEX GI 04-0000-0096.

The author(s) of this abstract have provided an email address for comments about the abstract: rhee@caltech.edu

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