Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...384..965b&link_type=abstract
Astronomy and Astrophysics, v.384, p.965-981 (2002)
Astronomy and Astrophysics
Astrophysics
6
Stars: Agb And Post-Agb, Stars: Atmospheres, Stars: Supergiants, Infrared: Stars
Scientific paper
We present spectra covering the wavelength range 2.28 to 2.36 mu m at a resolution of Delta lambda = 0.0007 mu m (or R = 3500) for a sample of 24 cool evolved stars. The sample comprises 8 M supergiants, 5 M giants, 3 S stars, 6 carbon stars, and 2 RV Tauri variables. The wavelengths covered include the main parts of the 12C16O v = 2-0 and 3-1 overtone bands, as well as the v = 4-2 and 13CO v = 2-0 bandhead regions. CO lines dominate the spectrum for all the stars observed, and at this resolution most of the observed features can be identified with individual CO R- or P-branch lines or blends. The observed transitions arise from a wide range of energy levels extending from the ground state to E/k > 20 000 K. We looked for correlations between the intensities of various CO absorption line features and other stellar properties, including IR colors and mass loss rates. Two useful CO line features are the v = 2-0 R14 line, and the CO v = 2-0 bandhead. The intensity of the 2-0 bandhead shows a trend with K-[12] color such that the reddest stars (K-[12] > 3 mag) exhibit a wide range in 2-0 bandhead depth, while the least reddened have the deepest 2-0 bandheads, with a small range of variation from star to star. Gas mass loss rates for both the AGB stars and the red supergiants in our sample correlate with the K-[12] color, consistent with other studies. The data imply that stars with dot M_gas < 5x 10-7 Msun y-1 exhibit a much narrower range in the relative strengths of CO 2-0 band features than stars with higher mass loss rates. The range in observed spectral properties implies that there are significant differences in atmospheric structure among the stars in this sample. Figures 4-9, 11-14, 16, 17, 19-21, 23, 24 are only avalaible in electronic form at http://www.edpsciences.org
Bieging John H.
Rieke George H.
Rieke Marcia J.
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