Magnesium and Carbon isotopes in Globular Cluster Giants. Test of Deep Mixing.II.

The first Mg isotope ratios measured in globular cluster giants have been reported. Mg and C isotope ratios are determined for a sub-set of the giants studied in Shetrone (1996). Seven M13 red giants and 10 halo field giants were observed at high resolution (R = 61,000) with S/N ranging between 60 to 166 per pixel near 5140 Å. One giant, M13 II-90, was found to have asymmetric line profiles, indicating that it may be a spectroscopic binary. The slightly metal-poor field giants are found to have 12C/13C ratios ranging from 10-14, whereas the more metal poor cluster giants have ratios ranging from 3-6. Among the M13 giants, the distribution of 12C/13C is consistent (χ2υ=1.47) with no trend with [Na/Fe], from which it is concluded that nearly all the outer envelope has been processed through regions which have undergone 12CH→13C processing without significant portions of the atmosphere being processed through regions that have undergone the NeNa cycle. Isotopic analysis of the 5135 Å MgH bands reveal four M13 stars with super-solar ratios of 25Mg + 26Mg compared with 24Mg and one M13 star with solar isotopic ratios. Only one cluster star, L598, has sub-solar isotope ratios consistent with the isotopic ratios found in our and previous investigators' studies of halo field stars. The isotopic abundances [24Mg/Fe] are found to be anti-correlated with the Al abundances and correlated with the total Mg (24Mg + 25Mg + 26Mg) abundances. No correlation (χ2υ=1.08) is found between [(25Mg+26Mg)/Fe] and any of the elements potentially alterable by deep mixing (Na, O, Al, and 24Mg). However, [(25Mg+ 26Mg)/Fe] has been found to scale with the iron abundance over the entire metallicity range. it is established that the star-to-star [Mg/Fe] abundance differences in M13 are caused by differences in 24Mg. If deep mixing is responsible for the Al enhancements found in Mi3 giants, deep mixing cycles the atmospheres of some giants into regions where Al is produced from proton capture on 24Mg at T9∼0.07. Using the observations found in the literature and presented in this work, we establish a mixing sequence to constrain future models of deep mixing.