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

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

2011-11-25

arxiv.org/abs/1111.6068v1

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

38 pages, Accepted for publication in the Astrophysical Journal

Scientific paper

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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