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T.D. Kinman (NOAO/KPNO), L.R. Miller (Macalester College)
BHB stars are good tracers of the halo. Accurate Teff are needed to obtain [Fe/H] from their spectra. For fainter stars, Teff may be derived from (B-V) , but this index is sensistive to surface gravity (log g) and increasingly insensitive to temperature as Teff increases. Kinman and Castelli (in preparation) show how Teff can be derived from 2MASS J, H and Ks and independently derived V magnitudes using an updated Kurucz model. We show that the Teff found in this way compare satisfactorily with those recently obtained by Di Benedetto, Fulbright and Gray et al. for dwarf stars with 6,500 < Teff < 10,000 K. They also agree with the Teff recently found for nearby BHB stars by Kinman et al.
There are, however, systematic differences between our 2MASS-derived Teff and the Teff derived from UBV data for both main-sequence A stars and BHB stars by Wilhelm et al. 1999, AJ, 117, 2308 & 2329. This difference is small for stars with Teff near 7,000 K but increases for stars whose 2MASS-derived temperatures are near 10,000 K. For these high temperature stars, the 2MASS -derived temperatures are approxinmately 1,000 K hotter. This systematic difference correlates with the difference between the log g assumed by Wilhelm et al. and that which would be predicted from recent theoretical models and which has been derived for nearby BHB stars. The metallicity distribution found by Wilhelm et al. for their BHB stars is skewed towards lower metallicities when compared with other recent distributions of [Fe/H] for halo stars. This would be expected if their temperatures were systematically too low.