A new calibration of stellar parameters of Galactic O stars

TL;DR

This paper provides new calibrations for the stellar parameters of Galactic O stars, incorporating advanced models and recent spectroscopic data, resulting in cooler temperature scales and revised luminosities and ionising fluxes.

Contribution

It introduces two new effective temperature scales for O stars, based on observational data and sophisticated models, improving previous calibrations.

Findings

Effective temperatures are 2000-8000 K cooler than previous calibrations.

Bolometric corrections are lower by 0.1 to 0.6 mag.

Luminosities and ionising fluxes are significantly reduced.

Abstract

We present new calibrations of stellar parameters of O stars at solar metallicity taking non-LTE, wind, and line-blanketing effects into account. Gravities and absolute visual magnitudes are derived from results of recent spectroscopic analyses. Two types of effective temperature scales are derived: one from a compilation based on recent spectroscopic studies of a sample of massive stars - the ``observational scale'' - and the other from direct interpolations on a grid of non-LTE spherically extended line-blanketed models computed with the code CMFGEN (Hillier & Miller 1998) - the ``theoretical scale''. These Teff scales are then further used together with the grid of models to calibrate other parameters (bolometric correction, luminosity, radius, spectroscopic mass and ionising fluxes) as a function of spectral type and luminosity class. Compared to the earlier calibrations of Vacca et al. (1996) the main results are: 1) the effective temperature scales are cooler by 2000 to 8000 K, the reduction being the largest for early supergiants; 2) bolometric corrections are lower by 0.1 mag for a given temperature, and are lower by 0.3 - 0.6 mag for a given spectral type; 3) luminosities are reduced by 0.20 to 0.35 dex; 4) Lyman ionising fluxes are lower by 0.20 to 0.80 dex. We provide calibration tables for each luminosity class and for both types of Teff scales.