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ALMA detection of CO rotational line emission in red supergiant stars of the massive young star cluster RSGC1 -- Determination of a new mass-loss rate prescription for red supergiants

Leen DecinAnita M.S. RichardsPablo MarchantHugues Sana
Mar 2023
[Abridged] Aim: We aim to derive a new mass-loss rate prescription for RSGsthat is not afflicted with some uncertainties inherent in preceding studies.Methods: We have observed CO rotational line emission towards a sample of RSGsin the open cluster RSGC1 that all are of similar initial mass. The ALMACO(2-1) line detections allow to retrieve the gas mass-loss rates (Mdot_CO). Incontrast to mass-loss rates derived from the analysis of dust spectral features(Mdot_SED), the data allow a direct determination of the wind velocity and nouncertain dust-to-gas correction factor is needed. Results: Five RSGs in RSGC1have been detected in CO(2-1). The retrieved Mdot_CO values are systematicallylower than Mdot_SED. Although only five RSGs in RSGC1 have been detected, thedata allow to propose a new mass-loss rate relation for M-type red supergiantsthat is dependent on luminosity and initial mass. The new mass-loss raterelation is based on the new Mdot_CO values for the RSGs in RSGC1 and on priorMdot_SED values for RSGs in 4 clusters, including RSGC1. The newMdot-prescription yields a good prediction for the mass-loss rate of somewell-known Galactic RSGs that are observed in multiple CO rotational lines,including alpha Ori, mu Cep and VX Sgr. However, there are indications that astronger, potentially eruptive, mass-loss process - different than captured byour new mass-loss rate prescription - is occurring during some fraction of theRSG lifetime. Implementing a lower mass-loss rate in evolution codes formassive stars has important consequences for the nature of their end-state. Areduction of the RSG mass-loss rate implies that quiescent RSG mass loss is notenough to strip a single star's hydrogen-rich envelope. Upon core-collapse suchsingle stars would explode as RSG.