Accurate luminosities from the oxygen 7771-4 A triplet and the fundamental parameters of F-G supergiants

TL;DR

This paper develops new luminosity calibrations for F-G supergiants using the oxygen 7771-4 A triplet, accounting for atmospheric parameters, reducing uncertainties in absolute magnitude estimates.

Contribution

It provides the first disentangled calibration of the oxygen triplet's luminosity indicator considering multiple atmospheric parameters.

Findings

Uncertainty in triplet-based absolute magnitudes reduced to 0.26 mag.

Calibrations applicable for spectral types F0-K0 and luminosity classes I-II.

Effective temperature, microturbulence, gravity, and abundance effects are now accounted for.

Abstract

The oxygen 7771-4 A triplet is a good indicator of luminosity in A-G supergiants. However, its strength also depends on other atmospheric parameters. In this study, we present the luminosity calibrations, where, for the first time, the effects of the effective temperature, microturbulent velocity, surface gravity, and the abundance have been disentangled. The calibrations are derived on the basis of a dataset of high-dispersion spectra of 60 yellow supergiants with highly reliable luminosities and accurate atmospheric parameters. This allowed to bring the uncertainty of the triplet-based absolute magnitudes down to 0.26 mag. The calibrations are suitable for spectral types F0-K0 and luminosity classes I-II, covering absolute magnitudes Mv from -1.0 to -10 mag.