Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars

We present new grids of colors and bolometric corrections for F-K starshaving 4000 K < Teff < 6500 K, 0.0 < log g < 4.5 and -3.0 < [Fe/H] < 0.0. Acompanion paper extends these calculations into the M giant regime. Colors aretabulated for Johnson U-V and B-V; Cousins V-R and V-I; Johnson-Glass V-K, J-Kand H-K; and CIT/CTIO V-K, J-K, H-K and CO. We have developed thesecolor-temperature (CT) relations by convolving synthetic spectra withphotometric filter-transmission-profiles. The synthetic spectra have beencomputed with the SSG spectral synthesis code using MARCS stellar atmospheremodels as input. Both of these codes have been improved substantially,especially at low temperatures, through the incorporation of new opacity data.The resulting synthetic colors have been put onto the observational systems byapplying color calibrations derived from models and photometry of field starswhich have Teffs determined by the infrared-flux method. The color calibrationshave zero points and slopes which change most of the original synthetic colorsby less than 0.02 mag and 5%, respectively. The adopted Teff scale (Bell &Gustafsson 1989) is confirmed by the extraordinary agreement between thepredicted and observed angular diameters of the field stars. We have alsoderived empirical CT relations from the field-star photometry. Except for thecoolest dwarfs (Teff < 5000 K), our calibrated, solar-metallicity model colorsare found to match these and other empirical relations quite well. Ourcalibrated, 4 Gyr, solar-metallicity isochrone also provides a good match tocolor-magnitude diagrams of M67. We regard this as evidence that our calibratedcolors can be applied to many astrophysical problems, including modelling theintegrated light of galaxies. (abridged)Comment: To appear in the March 2000 issue of the Astronomical Journal. 72 pages including 16 embedded postscript figures (one page each) and 6 embedded postscript tables (18 pages total