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

Hawkins, K.; Kordopatis, G.; Gilmore, G.; Masseron, T.; Wyse, R. F. G.; Ruchti, G.; Bienaymé, O.; Bland-Hawthorn, J.; Boeche, C.; Freeman, K.; Gibson, B. K.; Grebel, E. K.; Helmi, A.; Kunder, A.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W. A.; Scholz, R. D.; Seabroke, G.; Siebert, A.; Steinmetz, M.; Watson, F.; Zwitter, T.

Abstract

© 2015 The Authors. 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 57HiVel starswith 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.

Citation

Hawkins, K., Kordopatis, G., Gilmore, G., Masseron, T., Wyse, R. F. G., Ruchti, G., Bienaymé, O., Bland-Hawthorn, J., Boeche, C., Freeman, K., Gibson, B. K., Grebel, E. K., Helmi, A., Kunder, A., Munari, U., Navarro, J. F., Parker, Q. A., Reid, W. A., Scholz, R. D., Seabroke, G., …Zwitter, T. (2015). Characterizing the high-velocity stars of RAVE: the discovery of a metal-rich halo star born in the Galactic disc. Monthly notices of the Royal Astronomical Society, 447(2), 2046-2058. https://doi.org/10.1093/mnras/stu2574

• Journal Article Type: Article
• Acceptance Date: Dec 2, 2014
• Online Publication Date: Jan 3, 2015
• Publication Date: Feb 21, 2015
• Deposit Date: Jun 29, 2018
• Publicly Available Date: Jul 11, 2018
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 447
• Issue: 2
• Pages: 2046-2058
• DOI: https://doi.org/10.1093/mnras/stu2574
• Keywords: Galaxy : abundances; Galaxy : halo; Galaxy : kinematics and dynamics
• Public URL: https://hull-repository.worktribe.com/output/543728
• Publisher URL: https://academic.oup.com/mnras/article/447/2/2046/2593778
• Contract Date: Jun 29, 2018