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Title: LUMINOUS AND VARIABLE STARS IN M31 AND M33. I. THE WARM HYPERGIANTS AND POST-RED SUPERGIANT EVOLUTION

The progenitors of Type IIP supernovae (SNe) have an apparent upper limit to their initial masses of about 20 M{sub Sun }, suggesting that the most massive red supergiants evolve to warmer temperatures before their terminal explosion. But very few post-red supergiants are known. We have identified a small group of luminous stars in M31 and M33 that are candidates for post-red supergiant evolution. These stars have A-F-type supergiant absorption line spectra and strong hydrogen emission. Their spectra are also distinguished by the Ca II triplet and [Ca II] doublet in emission formed in a low-density circumstellar environment. They all have significant near- and mid-infrared excess radiation due to free-free emission and thermal emission from dust. We estimate the amount of mass they have shed and discuss their wind parameters and mass loss rates, which range from a few Multiplication-Sign 10{sup -6} to 10{sup -4} M{sub Sun} yr{sup -1}. On an H-R diagram, these stars will overlap the region of the luminous blue variables (LBVs) at maximum light; however, the warm hypergiants are not LBVs. Their non-spherical winds are not optically thick, and they have not exhibited any significant variability. We suggest, however, that the warm hypergiants may be themore » progenitors of the ''less luminous'' LBVs such as R71 and even SN1987A.« less
Authors:
; ; ;  [1] ;  [2] ; ;  [3]
  1. Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States)
  2. University of Illinois, Springfield, IL (United States)
  3. Astronomical Institute, Ruhr-Universitaet Bochum (Germany)
Publication Date:
OSTI Identifier:
22140260
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 773; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; DENSITY; EMISSION; EXPLOSIONS; GALAXIES; MASS TRANSFER; SPECTRA; SPHERICAL CONFIGURATION; STELLAR WINDS; SUPERNOVAE; VISIBLE RADIATION