Stability boundaries for massive stars in the sHR diagram

TL;DR

This study compares theoretical stability boundaries of radial pulsations in massive stars with observed positions of blue-supergiants in the sHR diagram, revealing general agreement but also discrepancies in surface gravity estimates.

Contribution

It provides a comparison between theoretical pulsation stability boundaries and observational data in the sHR diagram, highlighting areas of agreement and inconsistency.

Findings

Variables generally have higher L/M ratios than non-variables.

Many variable blue-supergiants have lower L/M than predicted by theory.

Surface gravities may be overestimated by 0.2-0.3 dex in observations.

Abstract

Stability boundaries of radial pulsations in massive stars are compared with positions of variable and non-variable blue-supergiants in the spectroscopic HR (sHR) diagram (Langer & Kudritzki 2014), whose vertical axis is $4\log T_{\rm eff}-\log g \,(= \log L/M)$. Observational data indicate that variables tend to have higher $L/M$ than non-variables in agreement with the theoretical prediction. However, many variable blue-supergiants are found to have values of $L/M$ below the theoretical stability boundary; i.e., surface gravities seem to be too high by around 0.2-0.3 dex.