PRECISE DELTA-TEFF AND DELTA(R-I) FOR SOLAR-TYPE STARS

The uncertain physical origin of low-amplitude (30-300 m s-1) radial-velocity variations observed for solar-type stars in our precise radial-velocity program has led us to make substantial additions to the reduction software to obtain additional information as constraints on possible models. In this paper we demonstrate that differences in temperature and R-I color with internal errors of less than 10 K and 0.002 mag, respectively, can be estimated from differential equivalent widths of a large number of lines for each program star from our more than a decade of high-quality spectra. While actual values for each program star will be published elsewhere, we give two examples that demonstrate that the temperature and color variations of the supergiant epsilon Pegasi are much larger than the dwarf tau Ceti. We have also reclassified the luminosities of two of our program stars. Gamma2 Delphini and gamma Cephei both appear to be K0 III stars, rather than K0 III-IV.