Investigating episodic mass loss in evolved massive stars IV. Comprehensive analysis of dusty red supergiants in NGC 6822, IC 10, and WLM

TL;DR

This study analyzes dusty red supergiants in three low-metallicity galaxies, revealing episodic mass loss events through spectral, photometric, and variability analyses, advancing understanding of mass loss mechanisms in massive stars.

Contribution

It provides a comprehensive multi-method analysis of red supergiants in low-metallicity environments, identifying episodic mass loss and spectral variability for the first time in these galaxies.

Findings

Evidence of episodic mass loss in four red supergiants.

Detection of photometric variability between 1-2.5 mag.

Identification of a candidate-dimming event.

Abstract

Mass loss shapes the fate of massive stars; however, the physical mechanism causing it remains uncertain. We present a comprehensive analysis of seven red supergiants, for which we searched evidence of episodic mass loss, in three low-metallicity galaxies: NGC~6822, IC~10, and WLM. Initially, the spectral classification of their optical spectra was refined and compared to previous reported classifications, finding four sources that display spectral variability. We derived the physical properties of five of them using the \textsc{marcs} atmospheric models corrected for nonlocal thermal equilibrium effects to measure stellar properties from our new near-infrared spectra, such as the effective temperature, surface gravity, metallicity, and microturbulent velocity. Additional empirical and theoretical methods were employed to calculate effective temperatures, finding consistent results. We constructed optical and infrared light curves, discovering two targets in NGC~6822 with photometric variability between 1 and 2.5 mag in amplitude in r and ~ 0.5 mag in the mid-infrared. Furthermore, we discovered a candidate-dimming event in one of these sources. Periods for three red supergiants were determined using epoch photometry, which were consistent with the empirical estimations from literature period-luminosity relations. Our comprehensive analysis of all the available data for each target provides evidence for episodic mass loss in four red supergiants.