A Spectroscopic Search for New Sdb Stars from the Galex Survey

Abstract

We have recently initiated a systematic search for the UV-bright, subdwarf B (sdB) stars in the Milky Way. The sdB stars are core He-burning stars with very thin H envelopes and are known to be immediate progenitors of white dwarfs, but their formation mechanism is still enigmatic. For instance, it is not clear whether such objects 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) may give a clue to which of the suggested formation mechanisms dominates: the binary scenario or the RGB-peel-off scheme. This approach was hampered by the lack of identified sdB stars belonging to the thin disk and halo. Thus, it is of primary importance to find new sdB stars that are faint (halo) and lie at lower Galactic latitudes (thin disk). In this contribution, we will describe the motivation and plan for our spectroscopic survey and preliminary results based on pilot observations for 34 sdB star candidates from the GALEX All-sky Imaging Survey.

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