Chekhonadskykh F. Chemical composition, intrinsic color indexes and luminosities of FGK supergiants.

The thesis is devoted to photometric and spectroscopic characteristics of FGK supergiants. Results of the search for the dependence between normal colors and fundamental parameters of stellar atmospheres are presented. The overview of the search of calibration relations for obtaining absolute stellar magnitudes from spectroscopic data is given. Calculations of normal colors and color excesses using the found dependence were made. We specified these data for 74 supergiants and 164 cepheids. The error in determining of (B - V)0 and EB-V was less than 0.05m , which yielded us the possibility to obtain AV with an accuracy better than 0.2m. Thanks to 80 found calibration relations we developed a technique that allows us to calculate absolute stellar magnitudes for supergiants from spectroscopic data. We obtained improved values of absolute stellar magnitudes for 98 supergiants and 53 cepheids with accuracy 0.2m-0.3m. For the testing of the new method of determining MV on spectroscopic criterion depending on pulsation phase we proposed the research of classical cepheids and s-cepheids. We obtained the conclusion that the technique is applicable in the phase interval 0.2-0.5. Also we concluded that the proposed technique can be used as a spectroscopic method of the pulsation mode identification for cepheids. We determined atmospheric parameters and abundances of 19 chemical elements for 31 Magellanic Clouds' supergiants for the first time. Thanks to values of studied stars, the mean metallicity of LMC (-0.20 dex) and MMC (-0.54 dex) were obtained. The distance modulus for LMC as m - M = 18.4m ± 0.3m has been defined. The new method of MV determination for FGK supergiants has been tested comprehensively, based on this we defined the interval of applicability for the new technique: luminosity types I and II; spectral classes F2-G8; range of effective temperatures 4500-7000 K; interval of the absolute stellar magnitudes from -0.5m to -8m; supergiants must have non-anomalous chemical composition with near-solar metallicity, allowed a temperate deficit of metals.