Heavy Element Dispersion in the Metal-Poor Globular Cluster M92

TL;DR

This study detects star-to-star variations in heavy r-process elements in the metal-poor globular cluster M92, revealing inhomogeneities in nucleosynthesis that are independent of lighter element dispersions.

Contribution

First detection of r-process element dispersion in M92, showing inhomogeneities in heavy elements unrelated to light element variations.

Findings

Heavy elements La, Eu, Ho show 0.5-0.8 dex dispersion.

R-process elements are correlated, indicating common nucleosynthesis origin.

R-process dispersion is similar to that in M15, but origin remains unknown.

Abstract

Dispersion among the light elements is common in globular clusters (GCs), while dispersion among heavier elements is less common. We present detection of r-process dispersion relative to Fe in 19 red giants of the metal-poor GC M92. Using spectra obtained with the Hydra multi-object spectrograph on the WIYN Telescope at Kitt Peak National Observatory, we derive differential abundances for 21 species of 19 elements. The Fe-group elements, plus Y and Zr, are homogeneous at a level of 0.07-0.16 dex. The heavy elements La, Eu, and Ho exhibit clear star-to-star dispersion spanning 0.5-0.8 dex. The abundances of these elements are correlated with one another, and we demonstrate that they were produced by r-process nucleosynthesis. This r-process dispersion is not correlated with the dispersion in C, N, or Na in M92, indicating that r-process inhomogeneities were present in the gas throughout star formation. The r-process dispersion is similar to that previously observed in the metal-poor GC M15, but its origin in M15 or M92 is unknown at present.