Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21431406s&link_type=abstract
American Astronomical Society, AAS Meeting #214, #314.06; Bulletin of the American Astronomical Society, Vol. 41, p.759
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the results of a program to obtain low-resolution infrared spectra from the Spitzer Space Telescope of a sample of evolved stars in Galactic globular clusters. The sample consists of 39 evolved stars in the fields of 24 clusters covering a range of metallicities ([Fe/H]) from solar (0.0) to 1/40th solar (-1.62), and it includes four Cepheid variables and 35 stars on the asymptotic giant branch (AGB). Analysis of the near-infrared light curves reveals that five of the AGB sources are probably field stars in the foreground or background of the clusters to which they have been previously assigned. The infrared spectra reveal that all of the AGB stars in clusters are oxygen-rich, and that their rate of dust production decreases as metallicity of the cluster decreases. This result supports recently published comparisons of infrared spectra of oxygen-rich evolved stars in the Magellanic Clouds and Galaxy, and it suggests that the absence of dust in more metal-rich globular clusters must be due to stripping instead of a lack of intrinsic dust production within the cluster. Several sources identified as Mira variables show emission from amorphous alumina grains, sometimes with surprisingly high contrast. Some spectra have narrow emission features, which can appear at 9.5, 11, 13, and/or 14 um.
Bernard-Salas Jeronimo
Devost Daniel
Houck James R.
Kraemer Kathleen E.
Matsunaga Norihito
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