CN and CH Bandstrengths in Bright Globular Cluster Red Giants

Details CN and CH Bandstrengths in Bright Globular Cluster Red Giants CN and CH Bandstrengths in Bright Globular Cluster Red Giants

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.2615m&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #26.15; Bulletin of the American Astronomical Society, V

Astronomy and Astrophysics

Astronomy

Scientific paper

We present preliminary results from a survey of CN and CH bandstrengths in bright red giant stars (MV -1.5) in Galactic globular clusters. Our cluster sample spans a wide metallicity range, from M92 ([Fe/H]=-2.28) to M71 ([Fe/H]=-0.73). The data were all taken using the Shane 120-inch telescope and the Kast spectrograph at Lick Observatory; the homogeneity of the sample makes it ideal for a comparative study of carbon depletion (and therefore deep mixing rate) as a function of stellar metallicity. Thus far we have measured molecular bandstrength indices for CH and CN, as well as indices for Ca and Mg lines; the task of converting the index measurements to carbon and nitrogen abundances will require comparisons with synthetic spectra. The molecular CN index behaves as expected from a study of the literature: within individual clusters, it varies significantly from star to star. The data also allow us to examine the dependence of the Ca and Mg indices on cluster metallicity at a given MV. The index MHK shows clear sensitivity to [Fe/H] across the full metallicity range of our sample. A similar study is also in progress involving analogous stars in the open clusters NGC 188, NGC 2158, NGC 6791, and NGC 7789 (-0.3 < [Fe/H] < +0.3).

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