Abstract
We present new grids of colors and bolometric corrections for F--K stars having
4000 K < Teff < 6500 K, 0.0 < log g < 4.5 and -3.0 < [Fe/H] < 0.0. A companion
paper extends these calculations into the M giant regime (3000-4000 K). Colors
are tabulated for Johnson U-V and B-V; Cousins V-R and V-I; Johnson-Glass V-K,
J-K and H-K; and CIT/CTIO V-K, J-K, H-K and CO. We have developed these
color-temperature relations by convolving synthetic spectra with the
best-determined, photometric filter-transmission-profiles. The synthetic
spectra have been computed with the SSG spectral synthesis code using MARCS
stellar atmosphere models 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 by applying color calibrations derived from models and
photometry of field stars which have effective temperatures determined by the
infrared-flux method. These color calibrations have zero points which change
most of the original synthetic colors by less than 0.02 mag, and the
corresponding slopes generally alter the colors by less than 5%. The adopted
temperature scale (Bell & Gustafsson 1989) is confirmed by the extraordinary
agreement between the predicted and observed angular diameters of these field
stars, indicating that the differences between the synthetic colors and the
photometry of the field stars are not due to errors in the effective
temperatures adopted for these stars. Thus, we have derived empirical
color-temperature relations from the field-star photometry, which we use as one
test of our calibrated, theoretical, solar-metallicity, color-temperature
relations. Except for the coolest dwarfs (Teff < 5000 K), our calibrated model
colors are found to match these relations, as well as the empirical relations of
others, quite well, and our calibrated, 4 Gyr, solar-metallicity isochrone also
provides a good match to color-magnitude diagrams of M67. We regard this as
evidence that our calibrated colors can be applied to many astrophysical
problems, including modelling the integrated light of galaxies. Because there
are indications that the dwarfs cooler than 5000 K may require different
optical color calibrations than the other stars, we present additional colors
for our coolest dwarf models which account for this possibility.
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