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Galactic Center: An Improved Astrometric Reference Frame for Stellar Orbits around the Supermassive Black Hole

Sakai, Shoko and Lu, Jessica R. and Ghez, Andrea and Jia, Siyao and Do, Tuan and Witzel, Gunther and Gautam, Abhimat K. and Hees, Aurelien and Becklin, E. and Matthews, K. and Hosek, M. W., Jr. (2019) Galactic Center: An Improved Astrometric Reference Frame for Stellar Orbits around the Supermassive Black Hole. Astrophysical Journal, 873 (1). Art. No. 65. ISSN 1538-4357. doi:10.3847/1538-4357/ab0361.

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Precision measurements of the stars in short-period orbits around the supermassive black hole at the Galactic Center are now being used to constrain general relativistic effects, such as the gravitational redshift and periapse precession. One of the largest systematic uncertainties in the measured orbits has been errors in the astrometric reference frame, which is derived from seven infrared-bright stars associated with SiO masers that have extremely accurate radio positions, measured in the Sgr A*-rest frame. We have improved the astrometric reference frame within 14'' of the Galactic Center by a factor of 2.5 in position and a factor of 5 in proper motion. In the new reference frame, Sgr A* is localized to within a position of 0.645 mas and proper motion of 0.03 mas yr^(−1). We have removed a substantial rotation (2fdg25 per decade), that was present in the previous less-accurate reference frame used to measure stellar orbits in the field. With our improved methods and continued monitoring of the masers, we predict that orbital precession predicted by general relativity will become detectable in the next ~5 yr.

Item Type:Article
Related URLs:
URLURL TypeDescription
Sakai, Shoko0000-0001-5972-663X
Lu, Jessica R.0000-0001-9611-0009
Ghez, Andrea0000-0003-3230-5055
Jia, Siyao0000-0001-5341-0765
Do, Tuan0000-0001-9554-6062
Witzel, Gunther0000-0003-2618-797X
Gautam, Abhimat K.0000-0002-2836-117X
Hees, Aurelien0000-0002-2186-644X
Hosek, M. W., Jr.0000-0003-2874-1196
Additional Information:© 2019. The American Astronomical Society. Received 2018 October 13; revised 2019 January 14; accepted 2019 January 17; published 2019 March 5. We thank the staff of the Keck Observatory, especially Randy Campbell, Jason Chin, Scott Dahm, Heather Hershey, Carolyn Jordan, Marc Kassis, Jim Lyke, Gary Puniwai, Julie Renaud-Kim, Luca Rizzi, Terry Stickel, Hien Tran, Peter Wizinowich, Carlos Alvarez, Greg Doppman and current and former directors, Hilton Lewis and Taft Armandroff, for all their help in obtaining observations. We would also like to thank the anonymous referee for very useful comments and suggestions. Support for this work at UCLA was provided by Heising Simons Foundation (2017-282) and National Science Foundation (AST-1412615). Also, matching funds to The W. M. Keck Foundation (20170668) were provided to UCLA and UC Berkeley. Furthermore, S.J., J.R.L., and M.W.H. acknowledge support from NSF AAG (AST-1518273). 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 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 Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facility: Keck Observatory - . Software: astropy (Astropy Collaboration et al. 2013), KS2 (Anderson et al. 2008), Matplotlib (Hunter 2007), SciPy (Jones et al. 2001).
Funding AgencyGrant Number
Heising Simons Foundation2017-282
W. M. Keck Foundation20170668
Subject Keywords:instrumentation: adaptive optics; astrometry; black hole physics; Galaxy: center
Issue or Number:1
Record Number:CaltechAUTHORS:20190305-101624692
Persistent URL:
Official Citation:Shoko Sakai et al 2019 ApJ 873 65
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93521
Deposited By: George Porter
Deposited On:05 Mar 2019 18:26
Last Modified:16 Nov 2021 16:58

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