NOAO >   Observing Info >   Approved Programs >   2005B-0428

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Proposal Information for 2005B-0428


PI: Jaehyon Rhee, California Institute of Technology, rhee@srl.caltech.edu
Address: Space Astrophysics Laboratory, MC 405-47, 1200 E. California Blvd., Pasadena, CA 91125, U.S.A.

CoI: Mark Seibert, California Institute of Technology
CoI: Roy H. Ostensen, Issac Newton Group of Telescopes, Spain
CoI: Sukyoung K. Yi, Oxford University, U.K.
CoI: Soo-Chang Rey, Chungnam National University, S. Korea
CoI: R. Michael Rich, University of California, Los Angeles
CoI: Luciana Bianchi, Johns Hopkins University
CoI: Young-Wook Lee, Yonsei University, S. Korea

Title: Spectroscopic Survey for the Field Subdwarf B Stars Newly Identified from the GALEX

Abstract: We propose to carry out medium-resolution spectroscopic follow-up for the subdwarf B (sdB) star candidates chosen from the GALEX (Galaxy Evolution Explorer) photometry in Data Release 1, in combination with other optical and near IR photometry. The UV bright, hot sdB stars are considered to be core helium-burning stars of 0.5 M_\odot with very thin hydrogen envelopes of M_\mathrmenv \le 0.02 M_\odot, and immediate progenitors of white dwarfs. Although their current and post evolutionary status is relatively well understood, very little physics behind their formation/evolution is known. For instance, it is not clear whether such stars are born as single stars or can form only in binary systems. The number ratio of sdB stars in each Galactic stellar population (i.e., thin disk, thick disk, and halo) can give a clue to answer whether major formation mechanism can be explained by binary scenario or RGB peel-off scheme. This approach was hampered by lack of identified sdB stars belonging to thin disk and halo. Thus, of primarily importance is new detection of sdB stars with faint magnitudes and at lower Galactic latitudes. 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 their formation and evolution mechanism, and Galactic structure.


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