Determining the effective temperatures of G- and K-type giants and supergiants based on observed photometric indices

摘要

A method for determining the effective temperature T (eff) of G- and K-type giants and supergiants is proposed. The method is based on the use of two photometric indices free from the interstellar absorption influence: the Q index in the UBV photometric system and the [c (1)] index in the uvby system. Empirical relations between the T (eff) values found for nearby and bright G- and K-type giants and supergiants with the use of the infrared fluxes method (IRFM), on the one hand, and the observed Q and [c (1)] indices for these stars, on the other hand, are plotted. A systematic discrepancy between the dependences of T (eff) on Q for the stars with standard and reduced metallicities is found. Approximating the plotted dependences with second-order polynomials, one can obtain a relatively simple and a rather accurate method for determining the T (eff) value in the range of 3800 a parts per thousand currency sign T a parts per thousand currency sign 5100 K (based on the Q index) or 4900 a parts per thousand currency sign T (eff) a parts per thousand currency sign 5500 K (based on the [c (1)] index).