1998A&A...333..231B

Broad band colors and bolometric corrections in the Johnson-Cousins-Glass system (Bessell, 1990PASP..102.1181B; Bessell & Brett, 1988PASP..100.1134B) have been computed from synthetic spectra from new model atmospheres of Kurucz (1995a, priv. comm.), Castelli (1997, priv. comm.), Plez, Brett & Nordlund (1992A&A...256..551P), Plez (1995-97, priv. comm.), and Brett (1995A&A...295..736B, 1995A&AS..109..263B). These atmospheres are representative of larger grids that are currently being completed. We discuss differences between the different grids and compare theoretical color-temperature relations and the fundamental color temperature relations derived from: (a) the infrared-flux method (IRFM) for A-K stars (Blackwell & Lynas-Gray 1994A&A...282..899B; Alonso et al. 1996A&AS..117..227A) and M dwarfs (Tsuji et al. 1996A&A...305L...1T); (b) lunar occultations (Ridgway et al. 1980ApJ...235..126R) and (c) Michelson interferometry (Di Benedetto & Rabbia 1987A&A...188..114D; Dyck et al. 1996AJ....111.1705D; Perrin et al. 1998A&A...331..619P) for K-M giants, and (d) eclipsing binaries for M dwarfs. We also compare color-color relations and color-bolometric correction relations and find good agreement except for a few colors. The more realistic fluxes and spectra of the new model grids should enable accurate population synthesis models to be derived and permit the ready calibration of non-standard photometric passbands. As well, the theoretical bolometric corrections and temperature-color relations will permit reliable transformation from observed color magnitude diagrams to theoretical HR diagrams.