2019/07/08 by Ian U. Roederer, Oleg Y. Gnedin
Physics and Astronomy · #Astronomy and Astrophysical Research #Blue straggler #Dwarf galaxy #Galactic halo #Galaxies: Formation, Evolution, Phenomena #Galaxy #Globular cluster #K-type main-sequence star #Star cluster #Stars #Stellar collision #Stellar evolution #Stellar, planetary, and galactic studies #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/ab365c
Accepted for publication in the Astrophysical Journal (17 pages, 4 figures, 3 tables)
arxiv created 2019/07/08 · openalex created_date 2019/07/23 · openalex publication_date 2019/09/20 · arxiv updated 2019/10/02 · openalex updated_date 2026/08/06
Abstract We observe two metal-poor main-sequence stars that are members of the recently discovered Sylgr stellar stream. We present radial velocities, stellar parameters, and abundances for 13 elements derived from high-resolution optical spectra collected using the Magellan Inamori Kyocera Echelle spectrograph. The two stars have identical compositions (within 0.13 dex or 1.2 σ ) among all elements detected. Both stars are very metal-poor ([Fe/H] = −2.92 ± 0.06). Neither star is highly enhanced in C ([C/Fe] < +1.0). Both stars are enhanced in the α elements Mg, Si, and Ca ([ α /Fe] = +0.32 ± 0.06), and the ratios among Na, Al, and all Fe-group elements are typical for other stars in the halo and ultra-faint and dwarf spheroidal galaxies at this metallicity. Sr is mildly enhanced ([Sr/Fe] = +0.22 ± 0.11), but Ba is not enhanced ([Ba/Fe] < −0.4), indicating that these stars do not contain high levels of neutron-capture elements. The Li abundances match those found in metal-poor unevolved field stars and globular clusters (GCs) (log ϵ (Li) = 2.05 ± 0.07), which implies that environment is not a dominant factor in determining the Li content of metal-poor stars. The chemical compositions of these two stars cannot distinguish whether the progenitor of the Sylgr stream was a dwarf galaxy or a GC. If the progenitor was a dwarf galaxy, the stream may originate from a dense region such as a nuclear star cluster. If the progenitor was a GC, it would be the most metal-poor GC known.