Establishing a mass-loss rate relation for red supergiants in the Large Magellanic Cloud

Abstract

Context. The high mass-loss rates of red supergiants (RSGs) drastically affect their evolution and final fate, but their mass-loss mechanism remains poorly understood. Various empirical prescriptions scaled with luminosity have been derived in the literature, yielding results with a dispersion of two to three orders of magnitude. Aims. We determine an accurate mass-loss rate relation with luminosity and other parameters using a large, clean sample of RSGs. In this way, we shed light into the underlying physical mechanism and explain the discrepancy between previous works. Methods. We assembled a sample of 2219 RSG candidates in the Large Magellanic Cloud, with ultraviolet to mid-infrared photometry in up to 49 filters. We determined the luminosity of each RSG by integrating the spectral energy distribution and the mass-loss rate using the radiative transfer code DUSTY. Results. Our derived RSG mass-loss rates range from approximately 10−9 M⊙ yr−1 to 10−5 M⊙ yr−1, mainly depending on the luminosity. The average mass-loss rate is 9.3 × 10−7 M⊙ yr−1 for log(L/L⊙) > 4, corresponding to a dust-production rate of ∼3.6 × 10−9 M⊙ yr−1. We established a mass-loss rate relation as a function of luminosity and effective temperature. Furthermore, we found a turning point in the relation of mass-loss rate versus luminosity at approximately log(L/L⊙) = 4.4, indicating enhanced rates beyond this limit. We show that this enhancement correlates with photometric variability. We compared our results with prescriptions from the literature, finding an agreement with works assuming steady-state winds. Additionally, we examined the effect of different assumptions on our models and found that radiatively driven winds result in mass-loss rates higher by two to three orders of magnitude, which is unrealistically high for RSGs. For grain sizes < 0.1 μm, the predicted mass-loss rates are higher by a factor of 25−30 than larger grain sizes. Finally, we found that 21% of our sample constitute current binary candidates. This has a minor effect on our mass-loss relation.