Chemical abundances of seven stars in the GD-1 stream

TL;DR

This study provides detailed chemical abundance measurements for seven stars in the GD-1 stream, revealing their origin from a single disrupted globular cluster through their extreme chemical homogeneity and r-process element patterns.

Contribution

First detailed chemical abundances for GD-1 stream stars, demonstrating their common origin and chemical homogeneity using high-resolution spectroscopy.

Findings

All stars have very similar metallicities ([Fe/H] ≈ -2.38) with minimal dispersion.

Six stars show enhanced [Eu/Fe] indicating r-process enrichment.

Chemical patterns support a globular cluster origin for the GD-1 stream.

Abstract

We present the first detailed chemical abundances for seven GD-1 stream stars from Subaru/HDS spectroscopy. Atmospheric parameters were derived via color calibrations ($T\rm_{eff}$) and iterative spectroscopic analysis. LTE abundances for 14 elements ($\alpha$, odd-Z, iron-peak, n-capture) were measured. Six stars trace the main orbit, one resides in a `blob'. All exhibit tightly clustered metallicities ([Fe/H] = -2.38, {\bf intrinsic dispersion smaller than 0.05 dex, average uncertainty is about 0.13 dex}). While one star shows binary mass transfer signatures, the other six display consistent abundance patterns (dispersions $<$ uncertainties). Their iron-peak elements (Sc, Cr, Mn, Ni) match Milky Way halo stars. In contrast, Y and Sr are systematically lower than halo stars of similar [Fe/H]. Significantly, six stars show consistently enhanced [Eu/Fe] $\sim$ 0.60 ($\sigma$ = 0.08). A tight Ba-Eu correlation (r = 0.83, p=0.04) exists, with [Ba/Fe] = -0.03 $\pm$ 0.05, indicating a common r-process origin. This extreme chemical homogeneity strongly supports an origin from a single disrupted globular cluster. The lack of light-element anti-correlations may stem from our sample size or the progenitor's low mass.