Light-element Abundance Variations at Low Metallicity: The Globular Cluster NGC 5466
Abstract
We present low-resolution (R sime850) spectra for 67 asymptotic giant branch (AGB), horizontal branch, and red giant branch (RGB) stars in the low-metallicity globular cluster NGC 5466, taken with the VIRUS-P integral-field spectrograph at the 2.7 m Harlan J. Smith telescope at McDonald Observatory. Sixty-six stars are confirmed, and one rejected, as cluster members based on radial velocity, which we measure to an accuracy of 16 km s-1 via template-matching techniques. CN and CH band strengths have been measured for 29 RGB and AGB stars in NGC 5466, and the band-strength indices measured from VIRUS-P data show close agreement with those measured from Keck/LRIS spectra previously taken for five of our target stars. We also determine carbon abundances from comparisons with synthetic spectra. The RGB stars in our data set cover a range in absolute V magnitude from +2 to -3, which permits us to study the rate of carbon depletion on the giant branch as well as the point of its onset. The data show a clear decline in carbon abundance with rising luminosity above the luminosity function "bump" on the giant branch, and also a subdued range in CN band strength, suggesting ongoing internal mixing in individual stars but minor or no primordial star-to-star variation in light-element abundances.
Based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.- Publication:
-
The Astronomical Journal
- Pub Date:
- October 2010
- DOI:
- 10.1088/0004-6256/140/4/1119
- arXiv:
- arXiv:1009.0649
- Bibcode:
- 2010AJ....140.1119S
- Keywords:
-
- globular clusters: general;
- globular clusters: individual: NGC 5466;
- stars: abundances;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 10 pages, emulateapj format, AJ accepted