Abundance analysis of the outer halo globular cluster Palomar 14

TL;DR

This study analyzes the elemental abundances of nine red giant stars in the distant outer halo globular cluster Palomar 14, revealing its chemical similarities to other outer halo GCs and potential extragalactic origins.

Contribution

First detailed high-resolution abundance analysis of Palomar 14, comparing its chemical pattern with other GCs and halo stars to infer its origin.

Findings

Pal 14 shows an r-process signature in neutron-capture elements.

Its abundance pattern is similar to Pal 3 and Pal 4, other outer halo GCs.

Pal 14's chemical properties suggest an extragalactic accretion origin.

Abstract

We determine the elemental abundances of nine red giant stars belonging to Palomar 14 (Pal 14). Pal 14 is an outer halo globular cluster (GC) at a distance of \sim 70 kpc. Our abundance analysis is based on high-resolution spectra and one-dimensional stellar model atmospheres.We derived the abundances for the iron peak elements Sc, V, Cr, Mn, Co, Ni, the {\alpha}-elements O, Mg, Si, Ca, Ti, the light odd element Na, and the neutron-capture elements Y, Zr, Ba, La, Ce, Nd, Eu, Dy, and Cu. Our data do not permit us to investigate light element (i.e., O to Mg) abundance variations. The neutron-capture elements show an r-process signature. We compare our measurements with the abundance ratios of inner and other outer halo GCs, halo field stars, GCs of recognized extragalactic origin, and stars in dwarf spheroidal galaxies (dSphs). The abundance pattern of Pal 14 is almost identical to those of Pal 3 and Pal 4, the next distant members of the outer halo GC population after Pal 14. The abundance pattern of Pal 14 is also similar to those of the inner halo GCs, halo field stars, and GCs of recognized extragalactic origin, but differs from what is customarily found in dSphs field stars. The abundance properties of Pal 14 as well as those of the other outer halo GCs are thus compatible with an accretion origin from dSphs. Whether or not GC accretion played a role, it seems that the formation conditions of outer halo GCs and GCs in dSphs were similar.