Detailed Chemical Abundance Analysis of the Brightest Stars in the Turranburra and Willka Yaku Stellar Streams

TL;DR

This study investigates the chemical signatures of two MW halo stellar streams, Turranburra and Willka Yaku, to infer their progenitors and enrichment histories. Using high-resolution Magellan/MIKE spectroscopy, the authors derive abundances for 27 elements and measure overall metallicities, including $[Fe/H]$, for the three brightest members in each stream. They find $[Fe/H] = -2.45 \pm 0.07$ with small scatter for Turranburra, and $[Fe/H] = -2.35 \pm 0.03$ with small scatter for Willka Yaku, consistent with a dwarf-galaxy progenitor for the former and a globular-cluster progenitor for the latter, respectively. Both streams show mild neutron-capture enhancements with $[Eu II/Fe] = 0.47 \pm 0.09$ (Turranburra) and $0.44 \pm 0.05$ (Willka Yaku), indicative of enrichment from an $r$-process event, a signature also observed in other streams and discussed in the context of their enrichment histories.

Abstract

We present a detailed chemical abundance analysis of the three brightest known stars from each of the Turranburra and Willka Yaku stellar streams using high-resolution Magellan/MIKE spectra. Abundances for 27 elements, ranging from carbon to dysprosium, were derived. Our results support the original classification that Turranburra, with a low average metallicity of $\mathrm{[Fe/H]=-2.45} \pm 0.07$, likely originates from a dwarf-galaxy progenitor. Willka Yaku has a low average metallicity of $\mathrm{[Fe/H]=-2.35 \pm 0.03}$ with a small scatter in the abundances, consistent with a globular cluster progenitor as suggested by previous studies. Both streams exhibit mild enhancements in neutron-capture elements, with averages of $\mathrm{[Eu II/Fe]}=$ $0.47 \pm{0.09}$ for Turranburra and $0.44 \pm{0.05}$ for Willka Yaku, consistent with enrichment from an $r$-process event. A similar enrichment is observed in other stellar streams, and we further discuss this signature as it relates to the potential enrichment histories of these two streams.

Figures (1)

• Figure 1: The left panels show the color-magnitude diagrams for the Turranburra and Willka Yaku fields. The right panels show the Declination vs. Right Ascension (Top) and Radial Velocity vs Right Ascension (Bottom) for the stream stars. Both streams were first reported in shipp2019 and further characterized by li2022; we refer the interested reader to those papers for further details on the membership selection. The pink squares and diamond are the Turranburra stars presented in this paper, and the diamond represents Tur-3, an RRL. The green squares are the Willka Yaku stars presented in this paper. For both streams, the black circles are other member stars from li2022. MIST isochrones dotter2016 shown as black lines were produced using the DECam photometric system, using an age of 12.5 Gyr for both streams, with metallicities taken from shipp2019, of Z= 0.0006 and 0.0003, respectively, and shifted to the distances of Turranburra and Willka Yaku (27.5 kpc and 34.7kpc, respectively). The blue lines represent the horizontal branch isochrone from M92.