Empirical Bolometric Correction and Zero-point Constants of Visual Magnitudes from High-resolution Spectra

Abstract A method of obtaining bolometric corrections (BC V ) from observed high-resolution, high signal-to-noise spectra is described. The method is applied to the spectra of 128 stars collected from the literature with well-determined effective temperatures ( T eff ) with the S λ ( V ) transparency profiles of Bessell and Landolt. The computed BC V values are found to be accurate within several millimagnitudes, and the effect of different S λ ( V ) values is found to be no more than 0.015 mag. The measured visual-to-bolometric ratio ( L V / L ) from the sample spectra and classically determined BC V from bolometric ( M Bol ) and visual ( M V ) absolute magnitudes helped us to determine the zero-point constant ( C 2 ) of the BC V scale. The determined C 2 for each star for each S λ ( V ) profile revealed C 2 = 2.3653 ± 0.0067 mag if the S λ ( V ) profile of Bessell is used and C 2 = 2.3826 ± 0.0076 mag if the S λ ( V ) profile of Landolt is used. Expanding C Bol = 71.197425... mag and c Bol = − 18.997351... mag announced by IAU2015GARB2, and using the definition of C 2 = C Bol – C V = c Bol – c V , where capital C is the absolute magnitude and lowercase c is the apparent magnitude and subscripts indicate bolometric and visual, the zero-point constants— C V = 68.8321 ± 0.0067 mag and c V = −21.3627 ± 0.0067 mag, if L V and are in SI units—were determined corresponding to S λ ( V ) of Bessell. The zero-point constants corresponding to S λ ( V ) of Landolt are smaller, but the difference is not more than 0.02 mag. Typical and limiting accuracies for predicting a stellar luminosity from an apparent magnitude and a distance are analyzed.