Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars

Abstract

We present new grids of colors and bolometric corrections for F-K stars having 4000 K ≤ T eff ≤ 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 K ≤ T eff ≤ 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%. 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 (T eff < 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.

Testing the Initial–Final Mass Relationship of White Dwarfs

“…Then, we consider the suitable color-temperature relations derived by Houdashelt et al (2000) to infer their effective temperatures. For giants we adopt: Whereas for dwarfs we use:…”

“…Regarding HD 26965 we used the relations of Houdashelt et al (2000) corresponding to dwarf stars, obtaining T eff = 5200 K and T eff = 5345 K, from (V − I) C and (V − R) C respectively. Besides the Eggen RI photometry, the J and K Johnson magnitudes (Johnson et al 1968) of HD 26965 are also available at the Lausanne Photometric Database (GCPD).…”

“…Then, we used the (V − K)-temperature calibration of Houdashelt et al (2000): for dwarfs, obtaining T eff = 5135 K. We can also use the (V − K)-temperature relation from Masana et al (2006):…”

Chromosphere of K giant stars

“…The bolometric fluxes of each star are given in Table 4 and were computed using the bolometric correction in K band from Houdashelt et al (2000) and the interstellar absorption A V from the work of Chen et al (1998). For all the program stars, it turns out that the absorption is very small because they are not in the direction of the Galactic plane and are closer than 100 pc.…”

“…The luminosity is obtained from the absolute bolometric magnitude computed with the apparent magnitude in V band (see Table 1), the corrected Hipparcos parallax, and the bolometric correction from Houdashelt et al (2000). Results for L/L and R/R are given in Table 4.…”