Light Element Abundances and Multiple Populations in M10

Abstract

We present CN and CH band measurements for 137 RGB and AGB stars in the Galactic globular cluster M10. Our measurements come from low resolution spectroscopy taken with the Hydra spectrograph on the WIYN-3.5m telescope. We use these measurements to identify two populations of stars within the cluster, a CN-normal and CN-enhanced, and find that in our sample 60% of stars are CN-enhanced. Our large sample allows us to conduct a detailed analysis on the carbon and nitrogen abundances and the radial distribution of each population separately. Our analysis of the radial dependence shows that each population has the same radial distribution in the cluster, which is likely due to the cluster being dynamically evolved. We also compare our results to other methods of classifying multiple populations in globular clusters such as the Na-O anti-correlation and the HST pseudo-color magnitude diagrams. We find that these three methods of identifying multiple populations are in good agreement with each other for M10 and all lead to an estimate of the fraction of second generation stars approximately equal to 60%. Among AGB stars, when classified by the CN band, there appears to be a lack of second generation stars when compared to the RGB stars. However, when classified by [N/Fe], we find a similar 60% of AGB stars in the second generation. Finally, we use the measured carbon and nitrogen abundances in RGB stars to study the change of each element with magnitude as stars evolve up the RGB, comparing the results to globular clusters of similar metallicity, M3 and M13.

Carbon Isotope Ratios in M10 Giants

“…The full list of atmospheric parameters can be found in Table 2. A microturbulence (ξ) of 2.0 km s −1 was adopted as a reasonable approximation for stars on the red giant branch, which matches what was adopted by Gerber et al (2018). To compare, Carretta et al (2009b) measured an average microtur- Figure 2.…”

“…The abundance correction for CO lines at [Fe/H] = −2 is ∼ −0.5 dex while the correction at [M/H] = -1 is near zero for lines with excitation potentials between 0 and 1 eV at 1600 nm. The effects on other molecular lines are smaller than on CO. We empirically test our carbon abundances from CO lines by comparing them to [C/Fe] derivations from CN and CH lines from Gerber et al (2018) in section 4.1.…”

“…Synthetic spectra were generated using the initial C and N abundances of Gerber et al (2018) and oxygen abundances from Carretta et al (2009a,b) when available. Average oxygen abundances were adopted for stars without known oxygen abundances: [O/Fe] = 0.39 dex for CN-normal stars and [O/Fe] = 0.11 dex for CNenhanced stars as in Gerber et al (2018).…”

“…Fig. 1 from Gerber et al 2018). To better constrain the models, we computed average T eff and log(g) values in M v bins of size 0.2 mag with a range from 3.8 < M v < 5.2; examining only turn-off stars.…”

A nitrogen-enhanced metal-poor star discovered in the globular cluster ESO280−SC06

“…Moderately nitrogen-enhanced (0 < [N/Fe] < 2) stars are well-known in globular clusters and dwarf galaxies (e.g., Simpson et al 2012;Simpson & Cottrell 2013;Simpson et al 2017a;Marino et al 2012;Carretta et al 2014;Roederer & Thompson 2015;Lardo et al 2016;Gerber et al 2018). Nitrogen-enhanced stars are classified as belonging to the "second population" 2 of stars in a globular cluster.…”