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Title: Hunting the parent of the Orphan stream. II. The first high-resolution spectroscopic study

We present the first high-resolution spectroscopic study on the Orphan stream for five stream candidates, observed with the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Clay telescope. The targets were selected from the low-resolution catalog of Casey et al.: three high-probability members, one medium, and one low-probability stream candidate were observed. Our analysis indicates that the low- and medium-probability targets are metal-rich field stars. The remaining three high-probability targets range over ∼1 dex in metallicity, and are chemically distinct compared to the other two targets and all standard stars: low [α/Fe] abundance ratios are observed, and lower limits are ascertained for [Ba/Y], which sit well above the Milky Way trend. These chemical signatures demonstrate that the undiscovered parent system is unequivocally a dwarf spheroidal galaxy, consistent with dynamical constraints inferred from the stream width and arc. As such, we firmly exclude the proposed association between NGC 2419 and the Orphan stream. A wide range in metallicities adds to the similarities between the Orphan stream and Segue 1, although the low [α/Fe] abundance ratios in the Orphan stream are in tension with the high [α/Fe] values observed in Segue 1. Open questions remain before Segue 1 could possibly be claimedmore » as the 'parent' of the Orphan stream. The parent system could well remain undiscovered in the southern sky.« less
Authors:
; ; ;  [1] ;  [2]
  1. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)
  2. Department of Physics, Massachusetts Institute of Technology and Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States)
Publication Date:
OSTI Identifier:
22351522
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 784; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CATALOGS; COMPARATIVE EVALUATIONS; DATA; LIMITING VALUES; METALLICITY; METALS; MILKY WAY; PROBABILITY; RESOLUTION; STARS; STREAMS; TELESCOPES