Astronomy letters-a journal of astronomy and space astrophysics vol:24 issue:3 pages:372-376
The ratio of the depths (equivalent widths) of spectral lines is a good indicator of the effective temperature. We derive 23 analytical relations for determining the effective temperatures of F-G supergiants from the depth ratio of lines in the red spectral range. These calibrations are valid for a wide range of surface gravities, microturbulent velocities, and chemical abundances. The effective temperature can be determined with an accuracy higher than 50-80 K by using determinations from several relations. Based on high-resolution CCD spectra, we obtain high-accuracy effective temperatures for six well-studied supergiants. The calibrations are in good agreement with theoretical and empirical temperature scales for F-G supergiants.