Chemical Analysis of the Ultra-Faint Dwarf Galaxy Grus~II. Signature of high-mass stellar nucleosynthesis
Creators: name: Hansen, T. T.
name: Marshall, J. L.
name: Simon, J. D.
name: Li, T. S.
name: Bernstein, R. A.
name: Pace, A. B.
name: Ferguson, P.
name: Nagasawa, D. Q.
name: Kuehn, K.
name: Carollo, D.
name: Geha, M.
name: James, D.
name: Walker, A.
name: Diehl, H. T.
name: Aguena, M.
name: Allam, S.
name: Avila, S.
name: Bertin, E.
name: Brooks, D.
name: Buckley-Geer, E.
name: Burke, D. L.
name: Rosell, A. Carnero
name: Kind, M. Carrasco
name: Carretero, J.
name: Costanzi, M.
name: da Costa, L. N.
name: Desai, S.
name: De Vicente, J.
name: Doel, P.
name: Eckert, K.
name: Eifler, T. F.
name: Everett, S.
name: Ferrero, I.
name: Frieman, J.
name: García-Bellido, J.
name: Gaztanaga, E.
name: Gerdes, D. W.
name: Gruen, D.
name: Gruendl, R. A.
name: Gschwend, J.
name: Gutierrez, G.
name: Hinton, S. R.
name: Hollowood, D. L.
name: Honscheid, K.
name: Kuropatkin, N.
name: Maia, M. A. G.
name: March, M.
name: Miquel, R.
name: Palmese, A.
name: Paz-Chinchón, F.
name: Plazas, A. A.
name: Sanchez, E.
name: Santiago, B.
name: Scarpine, V.
name: Serrano, S.
name: Smith, M.
name: Soares-Santos, M.
name: Suchyta, E.
name: Swanson, M. E. C.
name: Tarle, G.
name: Varga, T. N.
name: Wilkinson, R.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultra-faint dwarf galaxy Grus~II. All stars exhibit a higher than expected $\mathrm{[Mg/Ca]}$ ratio compared to metal-poor stars in other ultra-faint dwarf galaxies and in the Milky Way halo. Nucleosynthesis in high mass ($\geqslant 20$M$_\odot$) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (3) stars suggest the chemical enrichment of Grus~II could have occurred through substantial high-mass stellar evolution and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it can not be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture ($r$-process) elements. The abundance pattern of the $r$-process elements in this star matches the scaled $r$-process pattern of the solar system and $r$-process enhanced stars in other dwarf galaxies and in the Milky Way halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of $r$-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus~II would increase the likelihood of any of these events occurring. The time delay between the $α$ and $r$-process element enrichment of the galaxy favors a neutron star merger as the origin of the $r$-process elements in Grus~II.
description: 17 pages, 6 figures, accepted for publication in ApJ