Kavli Affiliate: Alexander P. Ji
| First 5 Authors: Sam A. Usman, Alexander P. Ji, Jandrie Rodriguez, Jeffrey D. Simpson, Sarah L. Martell
| Summary:
We present the first high-resolution abundance study of ESO 280-SC06, one of
the least luminous and most metal-poor gravitationally bound Milky Way globular
clusters. Using Magellan/MIKE spectroscopy for ten stars, we confirm the
cluster’s low metallicity as [Fe/H] = $-2.54 pm 0.06$ and the presence of a
nitrogen-enhanced star enriched by binary mass transfer. We determine
abundances or abundance upper limits for 21 additional elements from the light,
alpha, odd-Z, iron peak, and neutron-capture groups for all ten stars. We find
no spread in neutron-capture elements, unlike previous trends identified in
some metal-poor globular clusters such as M15 and M92. Eight of the ten stars
have light-element abundance patterns consistent with second-population
globular cluster stars, which is a significantly larger second-population
fraction than would be expected from the low present-day mass of $10^{4.1}$
Msun. We estimate the initial mass of the cluster as $10^{5.4 – 5.7}$ Msun
based on its orbit in the Milky Way. A preferential loss of first-population
stars could explain the high fraction of second-population stars at the present
time. Our results emphasize the importance of considering mass loss when
studying globular clusters and their enrichment patterns.
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