The nature of the KFR08 stellar stream

A chemical tagging experiment^⋆

Lund ObservatoryDepartment of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
e-mail: cheng@astro.lu.se; sofia@astro.lu.se; greg@astro.lu.se

Received: 23 December 2014
Accepted: 24 June 2015

Abstract

The origin of the new kinematically identified metal-poor stellar stream, the KFR08 stream, has not been established to date. 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 an analysis of high-resolution spectra. Based on the abundance ratios of 14 elements, we use the chemical tagging method to identify the stars with the same chemical composition that therefore 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] (σ_{[ Fe / H ]} = 0.29) among the 16 stream members. We find that our stars are α enhanced and that the abundance patterns of the stream members match the thick-disc population well. In addition, most of the stream stars have estimated stellar ages greater than 11 Gyr. These results, together with the hot kinematics of the stream stars, suggest that the KFR08 stream originated from the thick-disc population, which was perturbed by a massive merger in the early Universe.