Near-Infrared Spectroscopic Monitoring Observations of Three Yellow Hypergiants and Time Variation of 2.3 μm CO Features of ρ Cassiopeia

Details Near-Infrared Spectroscopic Monitoring Observations of Three Yellow Hypergiants and Time Variation of 2.3 μm CO Features of ρ Cassiopeia Near-Infrared Spectroscopic Monitoring Observations of Three Yellow Hypergiants and Time Variation of 2.3 μm CO Features of ρ Cassiopeia

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007pasj...59..973y&link_type=abstract

Publications of the Astronomical Society of Japan, Vol.59, No.5, pp.973--982

Astronomy and Astrophysics

Astronomy

1

Stars: Evolution, Stars: Mass-Loss, Stars: Supergiants

Scientific paper

We made spectroscopic monitoring observations of the three yellow hypergiants (ρ Cassiopeia, HR8752, and IRC+10420) in the 0.9--2.4 μm wavelength range with a resolution of ˜ 2600 over a fifteen month period. The spectra of HR8752 and IRC+10420 showed no time variations. On the other hand, those of ρ Cas showed just a series of time variation in 2.3 μm CO features from nondetection to absorption through emission during 2002-2004. We interpret this variation as being a result of an expanding gas shell whose excitation temperature was being cooled down to ˜ 800K. The CO column densities were estimated from the CO absorption depths. Moreover, assuming spherical symmetry of the expanding shell with a constant expansion velocity of 35 km s-1, a stellar effective temperature of 7000K, a stellar radius of 400 R&sun;, solar abundance, and all carbon atoms forming CO molecules, we estimated the mass of the shell to be ˜ 2 × 10-3M&sun; for a model with a single shell expanding from the photosphere, or ˜ 5 × 10-4M&sun; for another model with an expanding shell and a static envelope. These estimates of the released mass strongly depend on assumptions of the expansion velocity, the abundance, and the dissociation of the CO molecules.

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