Effective Temperature Calibration of Galactic BA-Type Supergiants

Abstract

This study aims to establish a homogeneous effective temperature scale for a large sample of Galactic blue supergiants by combining medium-resolution spectroscopy with multi-band spectral energy distribution analysis. The sample includes about 140 stars in the B7-A0 spectral range. As the main spectroscopic diagnostic, the equivalent-width ratio of the temperature-sensitive He I λ4471 and Mg II λ4481 lines was used. An empirical calibration was constructed from standard supergiants with reliably determined atmospheric parameters, and the resulting polynomial relation was applied to derive effective temperatures for the full sample. To verify the spectroscopic estimates, spectral energy distributions were compiled from ultraviolet, optical, near-infrared, and mid-infrared photometry and compared with theoretical stellar atmosphere models. The obtained results show that the adopted line-ratio index provides an efficient observational temperature indicator across the studied range and allows all program stars to be placed on a single internally consistent temperature scale. The spectral energy distribution analysis supports the spectroscopic results and serves as an independent consistency check of the derived parameters. The scientific novelty of the work lies in the development and application of a uniform calibration framework suitable for a large observational sample without requiring full detailed atmospheric modeling for each object. The results enlarge the empirical basis for the study of blue supergiants and provide a practical reference for future Galactic and extragalactic stellar investigations.