Light-Element Abundance Variations At Low Metallicity: The Globular Cluster NGC 5466

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Date

2010-10

Authors

Shetrone, Matthew
Martell, Sarah L.
Wilkerson, Rachel
Adams, Joshua
Siegel, Michael H.
Smith, Graeme H.
Bond, Howard E.

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Abstract

We present low-resolution (R similar or equal to 850) 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.

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Shetrone, Matthew, Sarah L. Martell, Rachel Wilkerson, Joshua Adams, Michael H. Siegel, Graeme H. Smith, and Howard E. Bond. >Light-element Abundance Variations at Low Metallicity: The Globular Cluster NGC 5466.> The Astronomical Journal, Vol, 140, No. 4 (Oct., 2010): 1119.