An $r$-process enhanced star in the dwarf galaxy Tucana III

T.T. Hansen , J.D. Simon , J.L. Marshall , T.S. Li , D. Carollo , D.L. Depoy , D.Q. Nagasawa , R.A. Bernstein , A. Drlica-Wagner , F.B. Abdalla , S. Allam , J. Annis , K. Bechtol , A. Benoit-Lévy (1) , D. Brooks , E. Buckley-Geer , A. Carnero Rosell , M. Carrasco Kind , J. Carretero , C.E. Cunha , L.N. da Costa , S. Desai , T.F. Eifler , A. Fausti Neto , B. Flaugher , J. Frieman , J. García-Bellido , E. Gaztanaga , D.W. Gerdes , D. Gruen , R.A. Gruendl , J. Gschwend , G. Gutierrez , D.J. James , E. Krause , K. Kuehn , N. Kuropatkin , O. Lahav , R. Miquel , A.A. Plazas , A.K. Romer , E. Sanchez , B. Santiago , V. Scarpine , R.C. Smith , M. Soares-Santos , F. Sobreira , E. Suchyta , M.E.C. Swanson , G. Tarle , A.R. Walker

1 IAP - Institut d'Astrophysique de Paris

Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate Tucana III. Because it is particularly bright for a star in an ultra-faint Milky Way satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. This star, DES J235532.66$-$593114.9 (DES J235532), shows a mild enhancement in neutron-capture elements associated with the $r$-process and can be classified as an $r$-I star. DES J235532 is the first $r$-I star to be discovered in an ultra-faint satellite, and Tuc III is the second extremely low-luminosity system found to contain $r$-process enriched material, after Reticulum II. Comparison of the abundance pattern of DES J235532 with $r$-I and $r$-II stars found in other dwarf galaxies and in the Milky Way halo suggests a common astrophysical origin for the neutron-capture elements seen in all $r$-process enhanced stars. We explore both internal and external scenarios for the $r$-process enrichment of Tuc III and show that with abundance patterns for additional stars it should be possible to distinguish between them.

Domaines: Astrophysique [astro-ph]

T.T. Hansen, J.D. Simon, J.L. Marshall, T.S. Li, D. Carollo, et al.. An $r$-process enhanced star in the dwarf galaxy Tucana III. Astrophys.J., 2017, 838 (1), pp.44. ⟨10.3847/1538-4357/aa634a⟩. ⟨hal-01554892⟩