Recent supernova (SN) 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-SN 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 (RSG) candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions (SEDs). 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 (CS) dust in their SEDs, we find that 30%-40% of the yellow supergiants are likely in a post-RSG state. Comparison with evolutionary tracks shows that these mass-losing, post-RSGs have initial masses between 20 and 40M_{sun}_. More than half of the observed RSGs in M31 and M33 are producing dusty CS 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.

Cone search capability for table J/ApJ/825/50/table2 (Spectroscopically-confirmed yellow supergiants (YSGs))

Cone search capability for table J/ApJ/825/50/table5 (YSG and YSG candidates with evidence for stellar winds and circumstellar dust)

Cone search capability for table J/ApJ/825/50/table8 (RSG candidates with evidence for circumstellar dust)

Cone search capability for table J/ApJ/825/50/table9 (Foreground dwarfs)

Cone search capability for table J/ApJ/825/50/ysg (Photometry and Extinction and luminosities of YSGs and YSG candidates (tables 3 and 4))

Cone search capability for table J/ApJ/825/50/rsg (Photometry and Extinction and luminosities of candidate red supergiants (RSGs) (tables 6 and 7))