2008/09/25 by Sarah L. Martell, Graeme H. Smith, Michael M. Briley
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Globular cluster #Horizontal branch #Metallicity #Mixing (physics) #Red-giant branch #Spectral line #Spectrograph #Stellar evolution #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1088/0004-6256/136/6/2522
10 pages including 11 figures, emulateapj format, accepted by AJ
arxiv created 2008/09/25 · openalex publication_date 2008/11/17 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present the results of an observational study of the efficiency of deep mixing in globular cluster red giants as a function of stellar metallicity. We determine [C/Fe] abundances based on low-resolution spectra taken with the Kast spectrograph on the 3 m Shane telescope at Lick Observatory. Spectra centered on the 4300 Å CH absorption band were taken for 42 bright red giants in 11 Galactic globular clusters ranging in metallicity from M92 ([Fe/H] = −2.29) to NGC 6712 ([Fe/H] = −1.01). Carbon abundances were derived by comparing values of the CH-band strength index S 2 (CH) measured from the data with values measured from a large grid of SSG synthetic spectra. Present-day abundances are combined with theoretical calculations of the time since the onset of mixing, which is also a function of stellar metallicity, to calculate the carbon depletion rate across our metallicity range. We find that the carbon depletion rate is twice as high at a metallicity of [Fe/H] = −2.3 than at [Fe/H] = −1.3, which is a result qualitatively predicted by some theoretical explanations of the deep mixing process.