The extreme scarcity of dust-enshrouded red supergiants: consequences for producing stripped stars via winds

TL;DR

This study challenges the idea that dust-enshrouded red supergiants are a significant source of mass loss needed for forming Wolf-Rayets and stripped-envelope supernovae, showing such objects are extremely rare.

Contribution

The paper provides a detailed analysis of RSGs in the LMC, demonstrating that dust-enshrouded RSGs with high mass-loss rates are exceedingly rare, impacting models of stellar evolution and supernova progenitors.

Findings

Only one RSG (WOH G64) shows high mass-loss and dust extinction.

Most RSGs are not dust-enshrouded or do not have high mass-loss rates.

Extreme dust-enshrouded RSG phase is very short, removing ≤2 solar masses.

Abstract

Quiescent mass-loss during the red supergiant (RSG) phase has been shown to be far lower than prescriptions typically employed in single-star evolutionary models. Importantly, RSG winds are too weak to drive the production of Wolf-Rayets (WRs) and stripped-envelope supernovae (SE-SNe) at initial masses of roughly 20--40$M_{\odot}$. If single-stars are to make WRs and SE-SNe, this shifts the burden of mass-loss to rare dust-enshrouded RSGs (DE-RSGs), objects claimed to represent a short-lived high mass-loss phase. Here, we take a fresh look at the purported DE-RSGs. By modeling the mid-IR excesses of the full sample of RSGs in the LMC, we find that only one RSG has both a high mass-loss rate (\mdot $\ge$ 10$^{-4}$ $M_{\odot}$ yr$^{-1}$) and a high optical circumstellar dust extinction (7.92 mag). This one RSG is WOH G64, and it is the only one of the 14 originally proposed DE-RSGs that is actually dust enshrouded. The rest appear to be either normal RSGs without strong infrared-excess, or lower-mass asymptotic giant branch (AGB) stars. Only one additional object in the full catalog of RSGs (not previously identified as a DE-RSG) shows strong mid-IR excess. We conclude that if DE-RSGs do represent a pre-SN phase of enhanced \mdot\ in single-stars, it is extremely short-lived, only capable of removing $\leq$2\msun\ of material. This rules out the single-star post-RSG pathway for the production of WRs, LBVs, and SE-SN. Single-star models should not employ \mdot-prescriptions based on these extreme objects for any significant fraction of the RSG phase.