2009PASP..121.1312T

The slope and zero point of the unevolved main sequence as a function of metallicity are investigated using a homogeneous catalog of nearby field stars with absolute magnitudes defined with revised Hipparcos parallaxes, Tycho-2 photometry, and precise metallicities from high-dispersion spectroscopy. -temperature relations are derived from 1746 stars between and and 372 stars within 0.05 dex of solar abundance; for, the solar color is (SEM). From over 500 cool dwarfs between and, at fixed, with a very weak dependenceupon the adopted main-sequence slope with at a given [Fe/H]. At Hyades metallicity, this translates into at fixed, midway between the range of values empirically derived from smaller and/or less homogenous samples and model isochrones. From field stars of similar metallicity, the Hyades with no reddening has and M67, with,, and, has (SEM), where the errors quoted refer to internal errors alone. At the extreme end of the age and metallicity scale, with and, comparison of the fiducial relation for NGC 6791 to 19 field stars with above 0.90 and or higher, adjusted to the metallicity of NGC 6791, leads to, internal and systematic errors included.