Investigating the metallicity dependence of the mass-loss rate relation of red supergiants

¹ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
² National and Kapodistrian University of Athens, 15784 Athens, Greece
³ Institute of Astrophysics FORTH, 71110 Heraklion, Greece
⁴ Physics Department, University of Crete, 71003 Heraklion, Greece
⁵ Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ UK
⁶ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109 USA
⁷ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ UK
⁸ IPAC, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA, 91125 USA
⁹ Department of Physics, Maynooth University, Maynooth, Co. Kildare, Ireland

^⋆ Corresponding author: k.antoniadis@noa.gr

Received: 7 March 2025
Accepted: 1 August 2025

Abstract

Context. Red supergiants (RSGs) are cool and evolved massive stars exhibiting enhanced mass loss compared to their main sequence phase, affecting their evolution and fate. However, despite recent advances, the theory of the wind-driving mechanism is not well established and the metallicity dependence has not been determined.

Aims. We aim to uniformly measure the mass-loss rates of large samples of RSGs in different galaxies with −0.7 ≲ [Z]≲0 to investigate whether there is a potential correlation with metallicity.

Methods. We collected photometry from the ultraviolet to the mid-infrared for all our RSG candidates to construct their spectral energy distribution (SED). Our final sample includes 893 RSG candidates in the Small Magellanic Cloud (SMC), 396 in NGC 6822, 527 in the Milky Way, 1425 in M31, and 1854 in M33. Each SED was modelled using the radiative transfer code DUSTY under the same assumptions to derive the mass-loss rate.

Results. The mass-loss rates range from approximately 10⁻⁹ M_⊙ yr⁻¹ to 10⁻⁵ M_⊙ yr⁻¹, with an average value of 1.5 × 10⁻⁷ M_⊙ yr⁻¹. We provide a new mass-loss rate relation as a function of luminosity and effective temperature for both the SMC and Milky Way and compare our mass-loss rates with those derived in the Large Magellanic Cloud (LMC). The turning point in the mass-loss rate versus luminosity relation differs by around 0.2 dex between the LMC and SMC. The mass-loss rates of the Galactic RSGs at log(L/L_⊙) < 4.5 are systematically lower than those determined in the other galaxies, possibly due to uncertainties in the interstellar extinction. We find 60–70% of the RSGs to be dusty, while 14% of the LMC and 2% of the SMC RSGs are significantly dusty. The results for M31 and M33 are inconclusive because of significant blending of sources at distances above 0.5 Mpc, given the resolution of Spitzer, which compromises the mid-IR photometry.

Conclusions. Overall, we find similar mass-loss rates among the galaxies, indicating no strong correlation with metallicity other than the location of the turning point. More accurate mid-IR photometry is needed to determine the metallicity dependence.