Painting a Family Portrait of the Yellow Super- and Hypergiants in the Milky Way I. Constraining the Distances and Luminosities

TL;DR

This study refines distance and luminosity estimates for yellow supergiants and hypergiants in the Milky Way by using Gaia data and stellar associations, improving understanding of their evolutionary states.

Contribution

It introduces a method combining Gaia astrometry and stellar group membership to better constrain distances and luminosities of evolved massive stars.

Findings

Improved distances for 28 stars via stellar associations.

Most YHGs have luminosities above log L/L = 5.4.

YSGs show a wider luminosity range, with the most luminous similar to YHGs.

Abstract

Context. Distances to evolved massive stars in the Milky Way are not well constrained by Gaia parallaxes due to their brightness and variability. This makes it difficult to determine their fundamental stellar parameters, such as radius or luminosity, and infer their evolutionary states. Aims. We aim to improve the distance estimates of Yellow Hypergiants (YHGs) and Yellow Supergiants (YSGs) by identifying possible cluster and association memberships. Using these distances, we derived updated luminosities and revised their positions in the Hertzsprung-Russell diagram. Methods. We compiled from the literature a sample of 35 luminous yellow massive stars (YHGs and the most luminous YSGs). We used Gaia DR3 astrometry to identify possible membership in clusters and OB associations. We derived distances by combining the parallaxes of nearby co-moving stars. We independently validated these distances by comparing the stellar radial velocities to the Galactic H I kinematic map. We combined angular diameters and effective temperature values from the literature with the new distances to estimate luminosities. Results. We improved the distance estimates for 28 of the 35 stars through association with co-moving stellar groups. For an additional six stars, we provided distance estimates based on the H I kinematic map. For one star, the distance remains unclear. Most YSGs are members of young stellar populations, while the environments of the YHGs are more diverse, and for some of them, their origin populations remain unclear. We derived updated luminosities for a subset of 20 stars. Most YHGs have luminosities above log L/L = 5.4, while YSGs occupy a wider range of luminosities and the most luminous YSGs have luminosities similar to YHGs.