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The Nature and Orbit of the Ophiuchus Stream

Sesar, Branimir and Bovy, Jo and Bernard, Edouard J. and Caldwell, Nelson and Cohen, Judith G. and Fouesneau, Morgan and Johnson, Christian I. and Ness, Melissa and Ferguson, Annette M. N. and Martin, Nicolas F. and Price-Whelan, Adrian M. and Rix, Hans-Walter and Schlafly, Edward F. and Burgett, William S. and Chambers, Kenneth C. and Flewelling, Heather and Hodapp, Klaus W. and Kaiser, Nick and Magnier, Eugene A. and Platais, Imants and Tonry, John L. and Waters, Christopher and Wyse, Rosemary F. G. (2015) The Nature and Orbit of the Ophiuchus Stream. Astrophysical Journal, 809 (1). Art. No. 59. ISSN 0004-637X.

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The Ophiuchus stream is a recently discovered stellar tidal stream in the Milky Way. We present high-quality spectroscopic data for 14 stream member stars obtained using the Keck and MMT telescopes. We confirm the stream as a fast moving (v_(los) ~ 290 km s^(−1)), kinematically cold group (σ _(v_(los)) ≾ 1 km s^(−1)) of α-enhanced and metal-poor stars ([α/Fe] ~ 0.4 dex, [Fe/H] ~ −2.0 dex). Using a probabilistic technique, we model the stream simultaneously in line-of-sight velocity, color–magnitude, coordinate, and proper motion space, and so determine its distribution in 6D phase-space. We find that the stream extends in distance from 7.5 to 9 kpc from the Sun; it is 50 times longer than wide, merely appearing highly foreshortened in projection. The analysis of the stellar population contained in the stream suggests that it is ~12 Gyr old, and that its initial stellar mass was ~2 × 10^4 M⊙ (or at least ≳7 × 10^3 M⊙). Assuming a fiducial Milky Way potential, we fit an orbit to the stream that matches the observed phase-space distribution, except for some tension in the proper motions: the stream has an orbital period of ~350 Myr, and is on a fairly eccentric orbit (e ~ 0.66) with a pericenter of ~3.5 kpc and an apocenter of ~17 kpc. The phase-space structure and stellar population of the stream show that its progenitor must have been a globular cluster that was disrupted only ~240 Myr ago. We do not detect any significant overdensity of stars along the stream that would indicate the presence of a progenitor, and conclude that the stream is all that is left of the progenitor.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Sesar, Branimir0000-0002-0834-3978
Cohen, Judith G.0000-0002-8039-4673
Ness, Melissa0000-0001-5082-6693
Martin, Nicolas F.0000-0002-1349-202X
Price-Whelan, Adrian M.0000-0003-0872-7098
Rix, Hans-Walter0000-0003-4996-9069
Schlafly, Edward F.0000-0002-3569-7421
Chambers, Kenneth C.0000-0001-6965-7789
Flewelling, Heather0000-0002-1050-4056
Hodapp, Klaus W.0000-0003-0786-2140
Kaiser, Nick0000-0001-6511-4306
Magnier, Eugene A.0000-0002-7965-2815
Tonry, John L.0000-0003-2858-9657
Waters, Christopher0000-0003-1989-4879
Additional Information:© 2015 The American Astronomical Society. Received 2015 January 3; accepted 2015 June 25; published 2015 August 10. B.S. acknowledges funding from the European Research Council under the European Union's Seventh Framework Programme (FP 7) ERC Grant Agreement n. [321035]. C.I.J. gratefully acknowledges support from the Clay Fellowship, administered by the Smithsonian Astrophysical Observatory. A.P.W. is supported by a National Science Foundation Graduate Research Fellowship under Grant No. 11-44155. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, and the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. Facilities: PS1 - Panoramic Survey Telescope and Rapid Response System Telescope #1 (Pan-STARRS), Keck:I (DEIMOS) -, MMT (Hectochelle) - MMT at Fred Lawrence Whipple Observatory.
Funding AgencyGrant Number
European Research Council (ERC)321035
Smithsonian Astrophysical ObservatoryUNSPECIFIED
NSF Graduate Research Fellowship11-44155
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Galaxy: halo – Galaxy: kinematics and dynamics – Galaxy: structure – globular clusters: general
Issue or Number:1
Record Number:CaltechAUTHORS:20151020-095138179
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:61313
Deposited By: Tony Diaz
Deposited On:20 Oct 2015 17:10
Last Modified:09 Mar 2020 13:19

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