TY - JOUR
T1 - Abundance Analysis of Stars at Large Radius in the Sextans Dwarf Spheroidal Galaxy
AU - Roederer, Ian U.
AU - Pace, Andrew B.
AU - Placco, Vinicius M.
AU - Caldwell, Nelson
AU - Koposov, Sergey E.
AU - Mateo, Mario
AU - Olszewski, Edward W.
AU - Walker, Matthew G.
N1 - Funding Information:
We thank the referee for their helpful comments that have improved this manuscript. We thank the dedicated staff at Las Campanas Observatory for their efforts to develop remote observing capabilities during the COVID-19 travel restrictions. E.O. wishes to remember Jill Bechtold here. We acknowledge generous support from the U.S. National Science Foundation (NSF), provided by grant Nos. AST-1815403 and AST-2205847 (I.U.R., M.M.); AST-1813881, AST-1909584, and AST-2206046 (A.B.P., S.K., M.G.W.); AST-1812461 (N.C.); AST-1815767 (E.W.O.); and PHYS-1430152 (Physics Frontier Center/JINA-CEE; I.U.R.). The work of V.M.P. is supported by NOIRLab, which is managed by AURA under a cooperative agreement with the NSF. This research has made use of NASA’s Astrophysics Data System Bibliographic Services; the arXiv preprint server operated by Cornell University; the SIMBAD and VizieR databases hosted by the Strasbourg Astronomical Data Center; the ASD hosted by NIST; and the IRAF software package, which was distributed by the National Optical Astronomy Observatory, which was managed by AURA under a cooperative agreement with the NSF.
Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/8/22
Y1 - 2023/8/22
N2 - We present stellar parameters and chemical abundances of 30 elements for five stars located at large radii (3.5–10.7 times the half-light radius) in the Sextans dwarf spheroidal galaxy. We selected these stars using proper motions, radial velocities, and metallicities, and we confirm them as metal-poor members of Sextans with −3.34 ≤ [Fe/H] ≤ −2.64 using high-resolution optical spectra collected with the Magellan Inamori Kyocera Echelle spectrograph. Four of the five stars exhibit normal abundances of C (−0.34 ≤ [C/Fe] ≤ +0.36), mild enhancement of the α elements Mg, Si, Ca, and Ti ([α/Fe] = +0.12 ± 0.03), and unremarkable abundances of Na, Al, K, Sc, V, Cr, Mn, Co, Ni, and Zn. We identify three chemical signatures previously unknown among stars in Sextans. One star exhibits large overabundances ([X/Fe] > +1.2) of C, N, O, Na, Mg, Si, and K, and large deficiencies of heavy elements ([Sr/Fe] = −2.37 ± 0.25, [Ba/Fe] = −1.45 ± 0.20, [Eu/Fe] < +0.05), establishing it as a member of the class of carbon-enhanced metal-poor stars with no enhancement of neutron-capture elements. Three stars exhibit moderate enhancements of Eu (+0.17 ≤ [Eu/Fe] ≤ +0.70), and the abundance ratios among 12 neutron-capture elements are indicative of r-process nucleosynthesis. Another star is highly enhanced in Sr relative to heavier elements ([Sr/Ba] = +1.21 ± 0.25). These chemical signatures canall be attributed to massive, low-metallicity stars or their end states. Our results, the first for stars at large radius in Sextans, demonstrate that these stars were formed in chemically inhomogeneous regions, such as those found in ultra-faint dwarf galaxies.
AB - We present stellar parameters and chemical abundances of 30 elements for five stars located at large radii (3.5–10.7 times the half-light radius) in the Sextans dwarf spheroidal galaxy. We selected these stars using proper motions, radial velocities, and metallicities, and we confirm them as metal-poor members of Sextans with −3.34 ≤ [Fe/H] ≤ −2.64 using high-resolution optical spectra collected with the Magellan Inamori Kyocera Echelle spectrograph. Four of the five stars exhibit normal abundances of C (−0.34 ≤ [C/Fe] ≤ +0.36), mild enhancement of the α elements Mg, Si, Ca, and Ti ([α/Fe] = +0.12 ± 0.03), and unremarkable abundances of Na, Al, K, Sc, V, Cr, Mn, Co, Ni, and Zn. We identify three chemical signatures previously unknown among stars in Sextans. One star exhibits large overabundances ([X/Fe] > +1.2) of C, N, O, Na, Mg, Si, and K, and large deficiencies of heavy elements ([Sr/Fe] = −2.37 ± 0.25, [Ba/Fe] = −1.45 ± 0.20, [Eu/Fe] < +0.05), establishing it as a member of the class of carbon-enhanced metal-poor stars with no enhancement of neutron-capture elements. Three stars exhibit moderate enhancements of Eu (+0.17 ≤ [Eu/Fe] ≤ +0.70), and the abundance ratios among 12 neutron-capture elements are indicative of r-process nucleosynthesis. Another star is highly enhanced in Sr relative to heavier elements ([Sr/Ba] = +1.21 ± 0.25). These chemical signatures canall be attributed to massive, low-metallicity stars or their end states. Our results, the first for stars at large radius in Sextans, demonstrate that these stars were formed in chemically inhomogeneous regions, such as those found in ultra-faint dwarf galaxies.
U2 - 10.3847/1538-4357/ace3c1
DO - 10.3847/1538-4357/ace3c1
M3 - Article
SN - 0004-637X
VL - 954
SP - 1
EP - 16
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 55
ER -