Signature of a massive rotating metal-poor star imprinted in the Phoenix stellar stream*

Andrew R. Casey*, Alexander P. Ji, Terese T. Hansen, Ting S. Li, Sergey E. Koposov, Gary S. Da Costa, Joss Bland-Hawthorn, Lara Cullinane, Denis Erkal, Geraint F. Lewis, Kyler Kuehn, Dougal Mackey, Sarah L. Martell, Andrew B. Pace, Jeffrey D. Simpson, Daniel B. Zucker

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

The Phoenix stellar stream has a low intrinsic dispersion in velocity and metallicity that implies the progenitor was probably a low-mass globular cluster. In this work we use Magellan/Magellan Inamori Kyocera Echelle (MIKE) high-dispersion spectroscopy of eight Phoenix stream red giants to confirm this scenario. In particular, we find negligible intrinsic scatter in metallicity (σ([Fe II/H]) = 0.04-0.03+0.11) and a large peak-to-peak range in [Na/Fe] and [Al/Fe] abundance ratios, consistent with the light element abundance patterns seen in the most metal-poor globular clusters. However, unlike any other globular cluster, we also find an intrinsic spread in [Sr II/Fe] spanning ∼1 dex, while [Ba II/Fe] shows nearly no intrinsic spread (σ([Ba II/H ]) =  0.03-0.02+0.10). This abundance signature is best interpreted as slow-neutron-capture element production from a massive fast-rotating metal-poor star (15-20M, vini/vcrit = 0.4, [Fe/H] = -3.8). The low inferred cluster mass suggests the system would have been unable to retain supernovae ejecta, implying that any massive fast-rotating metal-poor star that enriched the interstellar medium must have formed and evolved before the globular cluster formed. Neutron-capture element production from asymptotic giant branch stars or magneto-rotational instabilities in core-collapse supernovae provide poor fits to the observations. We also report one Phoenix stream star to be a lithium-rich giant (A(Li) = 3.1 ± 0.1). At [Fe/H ] = -2.93; it is among the most metal-poor lithium-rich giants known.

Original languageEnglish
Article number67
Pages (from-to)1-14
Number of pages14
JournalAstrophysical Journal
Volume921
Issue number1
DOIs
Publication statusPublished - 1 Nov 2021

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