Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis

T. T. Hansen, J. L. Marshall, J. D. Simon, T. S. Li, R. A. Bernstein, A. B. Pace, P. Ferguson, D. Q. Nagasawa, K. Kuehn, D. Carollo, M. Geha, D. James, A. Walker, H. T. Diehl, M. Aguena, S. Allam, S. Avila, E. Bertin, D. Brooks, E. Buckley-GeerD. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, M. Costanzi, L. N. Da Costa, S. Desai, J. De Vicente, P. Doel, K. Eckert, T. F. Eifler, S. Everett, I. Ferrero, J. Frieman, J. Garciá-Bellido, E. Gaztanaga, D. W. Gerdes, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, S. R. Hinton, D. L. Hollowood, K. Honscheid, N. Kuropatkin, M. A.G. Maia, M. March, R. Miquel, A. Palmese, F. Paz-Chinchón, A. A. Plazas, E. Sanchez, B. Santiago, V. Scarpine, S. Serrano, M. Smith, M. Soares-Santos, E. Suchyta, M. E.C. Swanson, G. Tarle, T. N. Varga, R. Wilkinson

Research output: Contribution to journalArticlepeer-review


We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass (20 M o) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests 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 cannot 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 MW 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 and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II.

Original languageEnglish (US)
Article number183
JournalAstrophysical Journal
Issue number2
StatePublished - Jul 10 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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