Accurate Fundamental Parameters or A, F, and G-type Supergiants in the Solar Neighbourhood

TL;DR

This study accurately determines fundamental parameters of 63 Galactic supergiants, improving measurement precision using updated parallaxes, and provides new stellar classifications, masses, ages, and metallicity insights for stars in the solar neighborhood.

Contribution

It offers a refined methodology for measuring supergiant parameters, including a new Teff scale and improved accuracy in log g, enhancing understanding of stellar properties and evolution.

Findings

Most supergiants have masses between 4 and 15 solar masses.

The mean iron abundance is close to solar, indicating similar metallicity.

A new Teff scale for A5-G5 supergiants is presented.

Abstract

The following parameters are determined for 63 Galactic supergiants in the solar neighbourhood: effective temperature Teff, surface gravity log g, iron abundance log e(Fe), microturbulent parameter Vt, mass M/Msun, age t and distance d. A significant improvement in the accuracy of the determination of log g and, all parameters dependent on it, is obtained through application of van Leeuwens (2007) re-reduction of the Hipparcos parallaxes. The typical error in the log g values is now +-0.06 dex for supergiants with distances d < 300 pc and +-0.12 dex for supergiants with d between 300 and 700 pc; the mean error in Teff for these stars is +-120 K. For supergiants with d > 700 pc parallaxes are uncertain or unmeasurable, so typical errors in their log g values are 0.2-0.3 dex. A new Teff scale for A5-G5 stars of luminosity classes Ib-II is presented. Spectral subtypes and luminosity classes of several stars are corrected. Combining the Teff and log g with evolutionary tracks, stellar masses and ages are determined; a majority of the sample has masses between 4 Msun and 15 Msun and, hence, their progenitors were early to middle B-type main sequence stars. Using Fe ii lines, which are insensitive to departures from LTE, the microturbulent parameter Vt and the iron abundance log e(Fe) are determined from high-resolution spectra. The parameter Vt is correlated with gravity: Vt increases with decreasing log g. The mean iron abundance for the 48 supergiants with distances d < 700 pc is log e(Fe)=7.48+-0.09, a value close to the solar value of 7.45+-0.05, and thus the local supergiants and the Sun have the same metallicity.