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Astron. Astrophys. 364, 102-136 (2000)

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2. The selection of candidates: notes on the individual objects

Green & Morrison (1993) found 10 BHB stars among the 23 candidates that they studied and considered that their sample was incomplete for BHB stars with V [FORMULA] 8.5. Many nearby BHB stars have been identified among high proper motion stars and so any sample of them will have kinematic bias. Thus Stetson (1991) made 4-colour observations of high proper motion early-type stars taken from the SAO Catalogue. More bright BHB stars might well be discovered by using a more recent source of proper motions such as the PPM Star Catalogue (Röser & Bastian 1991) in which a larger fraction of the stars have spectral types. To do this, even for a part of the sky, would be a large undertaking and we have therefore chosen to limit our observations to previously identified BHB star candidates. Strömgren photometry can only be used to distinguish BHB stars that are redder than [FORMULA] [FORMULA]-0.01 mag, so that the hotter stars (belonging to the extended horizontal branch) are excluded. This paper enlarges the local sample of definite BHB stars, but does not affect our knowledge of the local BHB space density because this depends only on the number of the very brightest of these stars. Our sample is limited to stars that are brighter than V = 10.9; these stars are near enough to have significant proper motions and bright enough for their high-resolution spectra to be obtainable with the Kitt Peak coudé feed spectrograph and with the ESO-CAT spectrograph.

Thirty-one nearby BHB candidates were selected from the literature. BD +00 0145 was listed by Huenemoerder et al. (1984). Twelve candidates were described by Philip (1984) who gave finding charts and some references to their original identification. These same stars and a (FHB) numbering system are also given in a more recent compilation and discussion of BHB star candidates by Gray et al. (1996). The remaining eighteen candidates were identified as possible HB stars by Stetson (1991) as a result of his 4-colour photometry of high proper motion A stars; some of these had been identified earlier as BHB stars as noted below.

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© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000