Globular Cluster Abundances from High-Resolution, Integrated-Light Spectroscopy. IV. The Large Magellanic Cloud: $\alpha$, Fe-peak, Light, and Heavy Elements

The Astrophysical Journal (Impact Factor: 5.99). 11/2011; 746(1). DOI: 10.1088/0004-637X/746/1/29
Source: arXiv


We present detailed chemical abundances in 8 clusters in the Large Magellanic
Cloud (LMC). We measure abundances of 22 elements for clusters spanning a range
in age of 0.05 to 12 Gyr, providing a comprehensive picture of the chemical
enrichment and star formation history of the LMC. The abundances were obtained
from individual absorption lines using a new method for analysis of high
resolution ($R\sim$25,000) integrated light spectra of star clusters. This
method was developed and presented in Papers I, II, and III of this series. In
this paper, we develop an additional integrated light $\chi^2$-minimization
spectral synthesis technique to facilitate measurement of weak ($\sim$15 m\AA)
spectral lines and abundances in low signal-to-noise ratio data (S/N$\sim$30).
Additionally, we supplement the integrated light abundance measurements with
detailed abundances that we measure for individual stars in the youngest
clusters (Age$<$2 Gyr) in our sample. In both the integrated light and stellar
abundances we find evolution of [$\alpha$/Fe] with [Fe/H] and age. Fe-peak
abundance ratios are similar to those in the Milky Way, with the exception of
[Cu/Fe] and [Mn/Fe], which are sub-solar at high metallicities. The heavy
elements Ba, La, Nd, Sm, and Eu are significantly enhanced in the youngest
clusters. Also, the heavy to light s-process ratio is elevated relative to the
Milky Way ([Ba/Y]$>+0.5$) and increases with decreasing age, indicating a
strong contribution of low-metallicity AGB star ejecta to the interstellar
medium throughout the later history of the LMC. We also find a correlation of
integrated light Na and Al abundances with cluster mass, in the sense that more
massive, older clusters are enriched in the light elements Na and Al with
respect to Fe, which implies that these clusters harbor star-to-star abundance
variations as is common in the Milky Way.

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Available from: Janet Colucci, Aug 08, 2014
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    • "Gray points are from [12], and measured using Lick system line indexes. synthesis code [7] for the best possible accuracy in our final measurements for Ca, Si, Eu, Ba and Y. Abundances for Ba and Eu include corrections for hyperfine splitting, as described in [7]. The IL abundance analysis is described in detail in [3] [4] [5]. "
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