  Line depth ratios measured on high resolution (R=42000), high S/N echelle
spectra are used for the determination of precise effective temperatures of 181
F,G,K Main Sequence stars with about solar metallicity (-0.5 < [Fe/H] < +0.5).
A set of 105 relations is obtained which rely Teff on ratios of the strengths
of lines with high and low excitation potentials, calibrated against previously
published precise (1%) temperature estimates. The application range of the
calibrations is 4000--6150 K (F8V--K7V). The internal error of a single
calibration is less than 100 K, while the combination of all calibrations for a
spectrum of S/N=100 reduces uncertainty to only 5-10 K, and for S/N=200 or
higher, to better than 5 K. The zero point of the temperature scale is directly
defined from reflection spectra of the Sun with an uncertainty about 1 K. The
application of this method to investigation of the planet host stars properties
is discussed.
