Article

# 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: 6.73). 11/2011; 746(1). DOI:10.1088/0004-637X/746/1/29
Source: arXiv

ABSTRACT 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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##### Conference Proceeding: High Resolution Integrated Light Spectroscopy of Galactic Globular Clusters
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ABSTRACT: Detailed chemical abundances of globular clusters can provide valuable information about nucleosynthesis, stellar evolution, and galaxy and cluster formation. High spectral resolution analyses enable abundance measurements of a larger number of elements with increased precision to study the relative contributions of different types of supernovae and AGB stars. In the Galaxy and its closest satellites, high resolution spectroscopy of individual stars has enabled the determination of chemical abundances in massive and low mass galaxies, with great success. Outside the Local Group of galaxies, however, integrated light spectra (ILS) of entire clusters must be used, as the individual stars cannot be resolved. A high resolution ILS analysis method, ILABUNDS, has been developed and tested on Galactic globular clusters by McWilliam & Bernstein (2008). This poster presents the analysis of the ILS of five Galactic globular clusters (47 Tuc, M3, M13, NGC 7006, and M15) with ILABUNDS. The latter four clusters were observed with the Hobby-Eberly Telescope at McDonald Observatory, while 47 Tuc was observed with the Las Campanas du Pont telescope (from McWilliam & Bernstein). Analyses of these clusters help to clarify the limits of the application of ILABUNDS to different stellar populations. In particular, the effects of different modeling assumptions are examined here, e.g. the effects of different horizontal branch morphologies.
XII International Symposium on Nuclei in the Cosmos; 08/2012