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N. Gorlova (University of Arizona), A. Lobel (Harvard-Smithsonian Center for Astrophysics), A. J. Burgasser (American Museum of Natural History), G. Rieke, N. Woolf (University of Arizona)
We report the discovery of variability in the CO 1st overtone ro-vibrational band at 2.3 micron in the yellow hypergiant Rho Cassiopeiae.
Rho Cas belongs to a rare class of peculiar post-red hypergiants believed to be SN II progenitors. We present the near-IR low- to high resolution spectra of this star obtained over 5 pulsation epochs. We discover that the CO band transforms from pure absorption during the outburst minimum in Oct 2000 to prominent emission during the phases of fast atmospheric expansion in Oct 1998 and Sept 2004.
Our preliminary modeling of the recent high-resolution emission spectrum rules out the photospheric nature of the CO band and indicates a structure in the the atmosphere where the gas temperature drops below 4000K and then increases outwards. The relation to the optical emission spectrum and the P Cyg profiles are also discussed - in search of clues for the mechanisms behind the severe mass loss and chromospheric heating in extreme supergiants.
We would like to thank the UKIRT and the VATT observer support teams for assistance with observations, reductions and retrieving archival data. Financial support has been partially provided by the NASA Spitzer and FUSE GI-E068 grants.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.