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The Nature of Hypervelocity Stars and the Time between Their Formation and Ejection

Brown, Warren R. and Cohen, Judith G. and Geller, Margaret J. and Kenyon, Scott J. (2012) The Nature of Hypervelocity Stars and the Time between Their Formation and Ejection. Astrophysical Journal Letters, 754 (1). Art. No. L2. ISSN 2041-8205. https://resolver.caltech.edu/CaltechAUTHORS:20120813-075720952

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Abstract

We obtain Keck HIRES spectroscopy of HVS5, one of the fastest unbound stars in the Milky Way halo. We show that HVS5 is a 3.62 ± 0.11 M_☉ main-sequence B star at a distance of 50 ± 5 kpc. The difference between its age and its flight time from the Galactic center is 105 ± 18 (stat) ±30 (sys) Myr; flight times from locations elsewhere in the Galactic disk are similar. This 10^8 yr "arrival time" between formation and ejection is difficult to reconcile with any ejection scenario involving massive stars that live for only 10^7 yr. For comparison, we derive arrival times of 10^7 yr for two unbound runaway B stars, consistent with their disk origin where ejection results from a supernova in a binary system or dynamical interactions between massive stars in a dense star cluster. For HVS5, ejection during the first 10^7 yr of its lifetime is ruled out at the 3σ level. Together with the 10^8 yr arrival times inferred for three other well-studied hypervelocity stars (HVSs), these results are consistent with a Galactic center origin for the HVSs. If the HVSs were indeed ejected by the central black hole, then the Galactic center was forming stars ≃200 Myr ago, and the progenitors of the HVSs took ≃100 Myr to enter the black hole's loss cone.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1088/2041-8205/754/1/L2DOIArticle
https://arxiv.org/abs/1206.4057arXivDiscussion Paper
ORCID:
AuthorORCID
Cohen, Judith G.0000-0002-8039-4673
Additional Information:© 2012 American Astronomical Society. Received 2012 March 27; accepted 2012 June 7; published 2012 June 27. This work was supported in part by the Smithsonian Institution. J. Cohen acknowledges partial support from NSF grant AST-0908139. This research makes use of NASA’s Astrophysics Data System Bibliographic Services. We are grateful to the many people who have worked to make the Keck Telescopes and their instruments a reality, and who operate and maintain these observatories. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible.
Funders:
Funding AgencyGrant Number
Smithsonian InstitutionUNSPECIFIED
NSFAST-0908139
Subject Keywords:Galaxy: center; Galaxy: halo; Galaxy: kinematics and dynamics; stars: early-type; stars: individual (SDSS J091759.47+672238.35)
Issue or Number:1
Record Number:CaltechAUTHORS:20120813-075720952
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20120813-075720952
Official Citation:The Nature of Hypervelocity Stars and the Time between Their Formation and Ejection Warren R. Brown et al. 2012 ApJ 754 L2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33110
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:13 Aug 2012 15:14
Last Modified:03 Oct 2019 04:07

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