On the evolutionary nature of massive B-type supergiants: a modern empirical reappraisal using data from IACOB, Gaia and TESS

TL;DR

This study uses extensive spectroscopic, astrometric, and photometric data to empirically reassess the physical, chemical, and evolutionary properties of over 1000 Galactic B-type supergiants, addressing longstanding discrepancies in stellar evolution models.

Contribution

It presents the largest empirical analysis of B-type supergiants combining multi-source data, offering new insights into their evolutionary status and properties.

Findings

Reassessed the evolutionary status of BSGs using a large, volume-limited sample.

Identified the complex nature and multiple evolutionary channels of BSGs.

Provided updated empirical constraints on properties like rotation and mass-loss rates.

Abstract

Massive stars are key contributors to the chemodynamical evolution of galaxies and the Universe. Despite their significance, discrepancies between observational data and theoretical models of massive stars challenge our understanding of these objects. A major uncertainty is the overdensity of B-type supergiants (BSGs) in the Hertzsprung-Russell diagram, where models predict the end of the main sequence phase (or TAMS). Is uncertain whether the TAMS needs to be redefined or if the overdensity results from overlapping populations following different evolutionary paths. Conceived as direct descendants of O-type stars, BSGs may include stars not only evolving in the main sequence but also returning from a post-red supergiant phase. A representative fraction of massive stars are predicted to be products of binary interaction, creating additional evolutionary channels. In addition, some fundamental properties of BSGs such as the spin- and mass-loss rates are not as well constrained as in O-type stars, having a significant impact on massive star evolution. To overcome this situation, statistically significant spectroscopic samples offer a unique opportunity to study the physical and chemical properties of BSGs. Moreover, the advent of space astrometry and photometry missions such as Gaia and TESS has brought a new era for studying additional properties in detail. This thesis comprises the study of 1000 Galactic blue supergiants (O- and B-type) combining multi-epoch high-resolution spectroscopic data from the IACOB project and the ESO archive with Gaia distances and TESS photometry, becoming the largest holistic empirical study of the physical, chemical, and pulsational properties of these objects performed to date. All these properties gathered into a unique volume-limited sample allowed to provide an empirical reassessment of the main properties of BSGs and investigate their intricate nature.