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An Improved Distance and Mass Estimate for Sgr A^* from a Multistar Orbit Analysis

Boehle, A. and Ghez, A. M. and Schödel, R. and Meyer, L. and Yelda, S. and Albers, S. and Martinez, G. D. and Becklin, E. E. and Do, T. and Lu, J. R. and Matthews, K. and Morris, M. R. and Sitarski, B. N. and Witzel, G. (2016) An Improved Distance and Mass Estimate for Sgr A^* from a Multistar Orbit Analysis. Astrophysical Journal, 830 (1). Art. No. 17. ISSN 0004-637X.

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We present new, more precise measurements of the mass and distance of our Galaxy's central supermassive black hole, Sgr A^*. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A^*, combining 2 decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star's orbit from the deep adaptive optics data (2005–2013) to inform the search for the star in the speckle years (1995–2005). When this new analysis technique is combined with the first complete re-reduction of Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 (K-band magnitude = 17, orbital period = 19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass (M_(bh)) and distance (R_o) of Sgr A^*: M_(bh) = (4.02 ± 0.16 ± 0.04) × 10^6 M_⊙ and 7.86 ± 0.14 ± 0.04 kpc. The uncertainties in M_(bh) and R_o as determined by the combined orbital fit of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of S0-2 alone and a factor of ~2.5 compared to previous results from stellar orbits. This analysis also limits the extended dark mass within 0.01 pc to less than 0.13 × 10^6 M_⊙ at 99.7% confidence, a factor of 3 lower compared to prior work.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Boehle, A.0000-0003-0439-7634
Ghez, A. M.0000-0003-3230-5055
Yelda, S.0000-0001-5036-4329
Albers, S.0000-0001-5496-2668
Martinez, G. D.0000-0002-7476-2521
Do, T.0000-0001-9554-6062
Lu, J. R.0000-0001-9611-0009
Morris, M. R.0000-0002-6753-2066
Witzel, G.0000-0003-2618-797X
Additional Information:© 2016 American Astronomical Society. Received 2015 November 17; revised 2016 May 27; accepted 2016 June 1; published 2016 October 3. 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, and former director Taft Armandroff, for all their help in obtaining the new observations. Support for this work at UCLA was provided by NSF grants AST-0909218 and AST-1412615, the Levine-Leichtman Family Foundation, the Preston Family Graduate Fellowship (held by A.B. and B.N.S.), the Galactic Center Board of Advisors, the Janet Marott Student Travel Awards, the UCLA Graduate Division Dissertation Year Fellowship (held by B.N.S.), and Janet Marott through her support of research on S0-38 through the Galactic Center Group's Stellar Patron Program. The research by R.S. leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 614922. 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
Levine-Leichtman Family FoundationUNSPECIFIED
Preston Family Graduate FellowshipUNSPECIFIED
Galactic Center Board of AdvisorsUNSPECIFIED
Janet Marott Student Travel AwardsUNSPECIFIED
European Research Council (ERC)614922
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:astrometry; Galaxy: center; Galaxy: fundamental parameters; infrared: stars; quasars: supermassive black holes; techniques: high angular resolution
Issue or Number:1
Record Number:CaltechAUTHORS:20161004-150325816
Persistent URL:
Official Citation:A. Boehle et al 2016 ApJ 830 17
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70841
Deposited By: Ruth Sustaita
Deposited On:04 Oct 2016 23:20
Last Modified:09 Mar 2020 13:18

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