Characterizing the high-velocity stars of RAVE: the discovery of a metal-rich halo star born in the Galactic disc

Journal
Date Issued
2015
Author(s)
Hawkins, K.
•
Kordopatis, G.
•
Gilmore, G.
•
Masseron, T.
•
Wyse, R. F. G.
•
Ruchti, G.
•
Bienaymé, O.
•
Bland-Hawthorn, J.
•
•
Freeman, K.
•
Gibson, B. K.
•
Grebel, E. K.
•
Helmi, A.
•
Kunder, A.
•
•
Navarro, J. F.
•
Parker, Q. A.
•
Reid, W. A.
•
Scholz, R. D.
•
Seabroke, G.
•
Siebert, A.
•
Steinmetz, M.
•
Watson, F.
•
Zwitter, T.
DOI
Description
We would like to thank the anonymous referee whose comments improved this manuscript. We also would like to thank P. Jofré, A. Casey, and V. Belokurov for discussions that greatly improved this work. KH is funded by the British Marshall Scholarship program and the King's College, Cambridge Studentship. RFGW acknowledges funding from the NSF grant OIA-1124403. This work is based on observations obtained with the APO 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium. Funding for RAVE has been provided by the Australian Astronomical Observatory; the Leibniz-Institut fuer Astrophysik Potsdam (AIP); the Australian National University; the Australian Research Council; the French National Research Agency; the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency; the Swiss National Science Foundation; the Science Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Groningen, Heidelberg, and Sydney. The RAVE website is at http://www.rave-survey.org
Abstract
We aim to characterize high-velocity (HiVel) stars in the solar vicinity both chemically and kinematically using the fourth data release of the RAdial Velocity Experiment (RAVE). We used a sample of 57 HiVel stars with Galactic rest-frame velocities larger than 275 km s-1. With 6D position and velocity information, we integrated the orbits of the HiVel stars and found that, on average, they reach out to 13 kpc from the Galactic plane and have relatively eccentric orbits consistent with the Galactic halo. Using the stellar parameters and [α/Fe] estimates from RAVE, we found the metallicity distribution of the HiVel stars peak at [M/H] = -1.2 dex and is chemically consistent with the inner halo. There are a few notable exceptions that include a hypervelocity star candidate, an extremely HiVel bound halo star, and one star that is kinematically consistent with the halo but chemically consistent with the disc. High-resolution spectra were obtained for the metal-rich HiVel star candidate and the second highest velocity star in the sample. Using these high-resolution data, we report the discovery of a metal-rich halo star that has likely been dynamically ejected into the halo from the Galactic thick disc. This discovery could aid in explaining the assembly of the most metal-rich component of the Galactic halo.
Volume
447
Issue
2
Start page
2046
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.447.2046H
Rights
open.access
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