de Wit et al. 2024: Investigating episodic mass loss in evolved massive stars: II. Physical properties of red supergiants at subsolar metallicity

S. de Wit, A.Z. Bonanos, K. Antoniadis, E. Zapartas, A. Ruiz, N. Britavskiy, E. Christodoulou, K. De, G. Maravelias, G. Munoz-Sanchez, A. Tsopela

Mass loss during the red supergiant (RSG) phase plays a crucial role in the evolution of an intermediate massive star, however, the underlying mechanism remains unknown. We aim to increase the sample of well-characterized RSGs at subsolar metallicity, by deriving the physical properties of 127 RSGs in nine nearby, southern galaxies presented by Bonanos et al. For each RSG, we provide spectral types and used MARCS atmospheric models to measure stellar properties from their optical spectra, such as the effective temperature, extinction, and radial velocity. By fitting the spectral energy distribution, we obtained the stellar luminosity and radius for 97 RSGs, finding ∼50% with log(L/L⊙)≥5.0 and 6 RSGs with R≳1400 R⊙. We also find a correlation between the stellar luminosity and mid-IR excess of 33 dusty, variable sources. Three of these dusty RSGs have luminosities exceeding the revised Humphreys-Davidson limit. We then derive a metallicity-dependent JKs color versus temperature relation from synthetic photometry and two new empirical JKs color versus temperature relations calibrated on literature TiO and J-band temperatures. To scale our derived, cool TiO temperatures to values in agreement with the evolutionary tracks, we derive two linear scaling relations calibrated on J-band and i-band temperatures. We find that the TiO temperatures are more discrepant as a function of the mass-loss rate and discuss future prospects of the TiO bands as a mass-loss probe. Finally, we speculate that 3 hot, dusty RSGs may have experienced a recent mass ejection (12% of the K-type sample) and indicate them as candidate Levesque-Massey variables.

Fig. 9: Comparison of our modeled Teff with the average Teff of literature studies of RSGs based on line-free (red triangles), SED methods (green inverted triangles), J-band spectral lines (yellow circles), TiO bands (magenta squares) the i-band spectral lines (cyan stars), at a range of metallicities. TiO results from this work are marked with a thick border; larger squares represent larger sample sizes. The black solid line is the mean Teff of a population of RSGs based on default Posydon single star tracks, with the grey shades indicating up to one standard deviation. NGC 300∗ includes NGC 300, NGC 247, and NGC 7793; NGC 55∗ includes NGC 55 and NGC 1313.

arXiv: 2402.12442

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