Letter to the Editor

The IACOB project

XI. No increase in mass-loss rates over the bistability region

¹ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
e-mail: astroabelink@gmail.com
² Instituto de Astrofísica de Canarias, Avenida Vía Láctea, 38205 La Laguna, Tenerife, Spain
³ Center for Computational Astrophysics, Division of Science, National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
⁴ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25/8, 6020 Innsbruck, Austria

Received: 9 April 2024
Accepted: 17 May 2024

Abstract

The properties of blue supergiants are key for constraining the end of the main sequence (MS) of massive stars. Whether the observed drop in the relative number of fast-rotating stars below ≈21 kK is due to enhanced mass-loss rates at the location of the bistability jump, or the result of the end of the MS is still debated. Here, we combine newly derived estimates of photospheric and wind parameters with Gaia distances and wind terminal velocities from the literature to obtain upper limits on the mass-loss rates for a sample of 116 Galactic luminous blue supergiants. The parameter space covered by the sample ranges between 35–15 kK in T_eff and 4.8–5.8 dex in log(L/L_⊙). Our results show no increase in the mass-loss rates over the bistability jump. Therefore, we argue that the drop in rotational velocities cannot be explained by enhanced mass loss. Since a large jump in the mass-loss rates is commonly included in evolutionary models, we suggest an urgent revision of the default prescriptions currently in use.