Properties of luminous red supergiant stars in the Magellanic Clouds

¹ IAASARS, National Observatory of Athens, 15326 Penteli, Greece
e-mail: sdewit@noa.gr
² National and Kapodistrian University of Athens, Department of Physics, Panepistimiopolis, Zografos 15784, Greece
³ Institute of Astronomy, KU Leuven, Celestijnlaan 200D, 3001 Leuven, Belgium
⁴ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
⁵ Institute of Astrophysics FORTH, 71110 Heraklion, Greece
⁶ Carnegie Observatories, Las Campanas Observatory, Colina El Pino, Casilla 601, La Serena, Chile
⁷ University of Liège, 19C Allée du Six-Août (B5C), 4000 Sart Tilman, Liège, Belgium
⁸ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland

Received: 22 February 2022
Accepted: 20 September 2022

Abstract

Context. There is evidence that some red supergiants (RSGs) experience short-lived phases of extreme mass loss, producing copious amounts of dust. These episodic outburst phases help strip the hydrogen envelope from evolved massive stars, drastically affecting their evolution. However, to date, the observational data of episodic mass loss is limited.

Aims. This paper aims to derive surface properties of a spectroscopic sample of 14 dusty sources in the Magellanic Clouds using the Baade telescope. These properties can be used for future spectral energy distribution fitting studies to measure the mass-loss rates from present circumstellar dust expelled from the star through outbursts.

Methods. We applied MARCS models to obtain the effective temperature (T_eff) and extinction (A_V) from the optical TiO bands. We used a χ² routine to determine the model that best fits the obtained spectra. We computed the T_eff using empirical photometric relations and compared this to our modelled T_eff.

Results. We have identified a new yellow supergiant and spectroscopically confirmed eight new RSGs and one bright giant in the Magellanic Clouds. Additionally, we observed a supergiant B[e] star and find that the spectral type has changed compared to previous classifications, confirming that the spectral type is variable over decades. For the RSGs, we obtained the surface and global properties, as well as the extinction (A_V).

Conclusions. Our method has picked up eight new, luminous RSGs. Despite selecting dusty RSGs, we find values for A_V that are not as high as expected given the circumstellar extinction of these evolved stars. The most remarkable object from the sample, LMC3, is an extremely massive and luminous evolved massive star and may be grouped amongst the largest and most luminous RSGs known in the Large Magellanic Cloud (log(L_*/L_⊙) ~ 5.5 and R = 1400 R_⊙).