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Investigating the Binarity of S0-2: Implications for Its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole

Chu, Devin S. and Do, Tuan and Hees, Aurelien and Ghez, Andrea and Naoz, Smadar and Witzel, Gunther and Sakai, Shoko and Chappell, Samantha and Gautam, Abhimat K. and Lu, Jessica R. and Matthews, Keith (2018) Investigating the Binarity of S0-2: Implications for Its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole. Astrophysical Journal, 854 (1). Art. No. 12. ISSN 1538-4357.

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The star S0-2, which orbits the supermassive black hole (SMBH) in our Galaxy with a period of 16 years, provides the strongest constraint on both the mass of the SMBH and the distance to the Galactic center. S0-2 will soon provide the first measurement of relativistic effects near a SMBH. We report the first limits on the binarity of S0-2 from radial velocity (RV) monitoring, which has implications for both understanding its origin and robustness as a probe of the central gravitational field. With 87 RV measurements, which include 12 new observations that we present, we have the requisite data set to look for RV variations from S0-2's orbital model. Using a Lomb–Scargle analysis and orbit-fitting for potential binaries, we detect no RV variation beyond S0-2's orbital motion and do not find any significant periodic signal. The lack of a binary companion does not currently distinguish different formation scenarios for S0-2. The upper limit on the mass of a companion star (M_(comp)) still allowed by our results has a median upper limit of M_(comp) sin i ≤ 1.6 M_⊙ for periods between 1 and 150 days, the longest period to avoid tidal break-up of the binary. We also investigate the impact of the remaining allowed binary system on the measurement of the relativistic redshift at S0-2's closest approach in 2018. While binary star systems are important to consider for this experiment, we find that plausible binaries for S0-2 will not alter a 5σ detection of the relativistic redshift.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Chu, Devin S.0000-0003-3765-8001
Do, Tuan0000-0001-9554-6062
Hees, Aurelien0000-0002-2186-644X
Ghez, Andrea0000-0003-3230-5055
Naoz, Smadar0000-0002-9802-9279
Witzel, Gunther0000-0003-2618-797X
Sakai, Shoko0000-0001-5972-663X
Gautam, Abhimat K.0000-0002-2836-117X
Lu, Jessica R.0000-0001-9611-0009
Additional Information:© 2018 American Astronomical Society. Received 2017 September 14. Accepted 2017 December 18. Published 2018 February 6. We are grateful for the helpful and constructive comments from the referee. We thank M. R. Morris and E. E. Becklin for their comments and long-term efforts on the Galactic Center Orbits Initiative. We also thank the staff of the Keck Observatory, especially Jim Lyke, Randy Campbell, Gary Puniwai, Heather Hershey, Hien Tran, Scott Dahm, Jason McIlroy, Joel Hicock, and Terry Stickel, for all their help in obtaining the new observations. Support for this work at UCLA was provided by NSF grant AST-1412615, the W. M. Keck Foundation for support of the NStarsOrbits Project, the Levine-Leichtman Family Foundation, Ken and Eileen Kaplan Student Support Fund, the Preston Family Graduate Fellowship (held by D.C. and A.G.), the Galactic Center Board of Advisors, and the Janet Marott Student Travel Awards. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The authors wish to recognize that the summit of Maunakea has always held a very significant cultural role for the indigenous Hawaiian community. We are most fortunate to have the opportunity to observe from this mountain. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Levine-Leichtman Family FoundationUNSPECIFIED
Ken and Eileen Kaplan Student Support FundUNSPECIFIED
Preston Family Graduate FellowshipUNSPECIFIED
Galactic Center Board of AdvisorsUNSPECIFIED
Janet Marott Student Travel AwardsUNSPECIFIED
Subject Keywords:Galaxy: center; gravitation; stars: early-type; techniques: high angular resolution
Issue or Number:1
Record Number:CaltechAUTHORS:20180206-084607328
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Official Citation:Devin S. Chu et al 2018 ApJ 854 12
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84682
Deposited By: Ruth Sustaita
Deposited On:06 Feb 2018 18:54
Last Modified:09 Mar 2020 13:18

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