Light Element Abundances and Multiple Populations in M53
  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).
