CN AND CH BAND STRENGTHS OF BRIGHT GIANTS IN THE GLOBULAR CLUSTER M10

Abstract

ABSTRACT The pattern of spectroscopic CN and CH band strengths among red giants in M10 is found to be similar to that seen in other globular clusters. Two groups of stars, CN-strong and CN-weak, can be discerned on the upper giant branch. Spectra obtained at Lick observatory of 10 such giants show that the CH and CN band strengths are anticorrelated, with star-to-star differences being apparent in both the lambda 3883 and lambda 4215 CN bands. Combining the Lick data with the [O/Fe] abundances measured by Kraft et al. (1995, AJ, 109, 2586) shows that the CN band strength is anticorrelated with [O/Fe]. With respect to these abundance peculiarities, as well as the [Fe/H] metallicity, M10 is similar to the clusters M3 and M13. One distinction between these clusters is the fraction of giants that show CN enhancements; within M10 CN-strong giants are in the minority by a ratio of almost 1:2 (CN-strong :CN-weak), whereas in M13 strong CN bands are found among a much larger percentage of giants.