The nature of the KFR08 stellar stream

TL;DR

This study analyzes the chemical composition, ages, and kinematics of the KFR08 stellar stream, suggesting it originated from the thick disk perturbed by an ancient merger, with no clear evidence of a common cluster origin.

Contribution

It provides detailed elemental abundances and ages for KFR08 stream stars, using chemical tagging to investigate their origins and linking the stream to the thick disk.

Findings

Stars are alpha-enhanced and match thick disk patterns.

Large metallicity dispersion suggests no common cluster origin.

Stream stars are older than 11 Gyr and have hot kinematics.

Abstract

The origin of a new kinematically identified metal-poor stellar stream, the KFR08 stream, has not been established. We present stellar parameters, stellar ages, and detailed elemental abundances for Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Ni, Zn, Sr, Y, Zr, Ba, La, and Eu for 16 KFR08 stream members based on analysis of high resolution spectra. Based on the abundance ratios of 14 elements, we use the chemical tagging method to identify the stars which have the same chemical composition, and thus, might have a common birthplace, such as a cluster. Although three stars were tagged with similar elemental abundances ratios, we find that, statistically, it is not certain that they originate from a dissolved star cluster. This conclusion is consistent with the large dispersion of [Fe/H] ($\sigma_{\rm{[Fe/H]}} = 0.29$) among the 16 stream members. We find that our stars are $\alpha$ enhanced and that the abundance patterns of the stream members are well matched to the thick disk. In addition, most of the stream stars have estimated stellar ages larger than 11 Gyr. These results, together with the hot kinematics of the stream stars, suggest that the KFR08 stream is originated from the thick disk population which was perturbed by a massive merger in the early universe.