The IACOB project XI. No increase of mass-loss rates over the bistability region

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 $\sim$21kK 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 35-15kK in $T_{\mathrm{eff}}$ and 4.8-5.8dex in log(L/L${}_{\odot }$). 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 currently used default prescriptions.

Accepted for publication in Astronomy and Astrophysics, 9 pages, 5 figures

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• The IACOB project XI. No increase of mass-loss rates over the bistability region

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• The IACOB project XI. No increase of mass-loss rates over the bistability region