Light Element Abundances and Multiple Populations in M53

TL;DR

This study analyzes 94 red giant stars in M53 to investigate multiple populations using spectral features, revealing a split in populations, their spatial distribution, and chemical evolution, with findings consistent across different methods.

Contribution

It provides a comprehensive analysis of multiple populations in M53 using low-resolution spectra and compares results with photometric and other spectroscopic methods.

Findings

CN-enhanced stars are more centrally concentrated.

Both populations show similar evolutionary changes in C and N.

CN-enhanced stars have slightly higher C+N+O abundances.

Abstract

We present results from a study of 94 red giant stars in the globular cluster M53. We use low-resolution spectra to measure the strength of CN and CH features at $\sim$3800 and 4300 \r{A}, respectively. The strengths of these features are used to classify stars into a CN-enhanced and CN-normal population and to measure C and N abundances in all 94 stars. We find the red giant branch stars to be evenly split between the two populations identified, and observe the presence of CN-enhanced stars on the asymptotic giant branch. In addition, we identify 5 CH star candidates based on the strength of their CN and CH band features, and the presence of a P-branch in their CH band. We compare our identification of multiple populations to those based on the Na-O anti-correlation and pseudo-color indices in HST UV photometry, and find general agreement between all three methods. Our large sample size also allows us to study the radial distribution of each population, and we find that the CN-enhanced population is more centrally concentrated. We use our C and N measurements to compare the evolutionary changes in these elements as a function of magnitude between the two populations, and show that both populations experience similar evolutionary changes to the surface abundances of C and N. Finally, we calculate C+N+O abundances for each population and compare them to similar measurements made in M10; we find that in both clusters CN-enhanced stars have a slightly enhanced C+N+O ($\Delta$(C+N+O) $\sim$ 0.2 dex).