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arXiv · 1603.08003

Luminous and Variable Stars in M31 and M33. III. The Yellow and Red Supergiants and Post-Red Supergiant Evolution

Michael S. Gordon·Roberta M. Humphreys·Terry J. Jones
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Abstract

Recent supernova and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-supernova mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of yellow and red supergiant candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions. Since the position of intermediate and late-type supergiants on the color-magnitude diagram can be heavily contaminated by foreground dwarfs, we employ spectral classification and multi-band photometry from optical and near-infrared surveys to confirm membership. Based on spectroscopic evidence for mass loss and the presence of circumstellar dust in their SEDs, we find that $30-40\%$ of the yellow supergiants are likely in a post-red supergiant state. Comparison with evolutionary tracks shows that these mass-losing, post-RSGs have initial masses between $20-40\,M_{\odot}$. More than half of the observed red supergiants in M31 and M33 are producing dusty circumstellar ejecta. We also identify two new warm hypergiants in M31, J004621.05+421308.06 and J004051.59+403303.00, both of which are likely in a post-RSG state.

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Michael S. Gordon, Roberta M. Humphreys, Terry J. Jones. 2016-03-25. Luminous and Variable Stars in M31 and M33. III. The Yellow and Red Supergiants and Post-Red Supergiant Evolution. https://doi.org/10.3847/0004-637x/825/1/50

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