Light-element Abundance Variations in the Milky Way Halo

TL;DR

This study provides evidence that a significant portion of the Milky Way's stellar halo originated from high-mass globular clusters, based on spectral analysis revealing chemical signatures of globular cluster dissolution.

Contribution

It is the first to identify CN-strong stars in the halo, linking globular cluster dissolution to halo star formation and estimating up to 50% of halo stars originated from globular clusters.

Findings

2.5% of halo giants are CN-strong.

Globular cluster dissolution may account for up to 50% of halo stars.

Chemical signatures support globular cluster contribution to the halo.

Abstract

We present evidence for the contribution of high-mass globular clusters to the stellar halo of the Galaxy. Using SDSS-II/SEGUE spectra of over 1900 G- and K-type halo giants, we identify for the first time a subset of stars with CN bandstrengths significantly larger, and CH bandstrengths lower, than the majority of halo field stars, at fixed temperature and metallicity. Since CN bandstrength inhomogeneity and the usual attendant abundance variations are presently understood as a result of star formation in globular clusters, we interpret this subset of halo giants as a result of globular cluster dissolution into the Galactic halo. We find that 2.5% of our sample is CN-strong, and can infer based on recent models of globular cluster evolution that the fraction of halo field stars initially formed within globular clusters may be as large as 50%.