Abstract
Abstract Calibration relations have been obtained for the intrinsic color index θ0 (θ = 5040/Te, Te being the observed color temperature of a star) and absolute magnitudes M(104) (at Λ = 1.04 μ, in Wing's narrow-band photometric system), MV and MK as functions of TiO and CN photometric indices for K5-M5 supergiant stars. The accuracy of the distance moduli obtained when using these calibrations is about 0m·2. The distance moduli have been calculated for red supergiants which are members of open clusters. The distance scale for red supergiants based upon the M(104) (TiO, CN) absolute magnitude calibration (the distance modulus of 11m·4 being assumed for the Per OB1 stellar association) agrees with the distance scale for young open clusters based upon uvbyβ-photometry and Crawford's (1978) ZAMS for B-type stars.
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