K. Phifer, T. Do, L. Meyer, A. M. Ghez, G. Witzel, S. Yelda, A. Boehle, J. R. Lu, M. R. Morris, E. E. Becklin, K. Matthews
We present new observations and analysis of G2 - the intriguing red emission-line object which is quickly approaching the Galaxy's central black hole. The observations were obtained with the laser guide star adaptive optics systems on the W. M. Keck I and II telescopes and include spectroscopy (R ~ 3600) centered on the Hydrogen Br-gamma line as well as K' (2.1 micrometer) and L' (3.8 micrometer) imaging. Analysis of these observations shows the Br-gamma line emission has a positional offset from the L' continuum. This offset is likely due to background source confusion at L'. We therefore present the first orbital solution derived from Br-gamma line astrometry, which when coupled with radial velocity measurements, results in a later time of closest approach (2014.21 +/- 0.14), closer periastron (130 AU, 1900Rs), and higher eccentricity (0.9814 +/- 0.0060) compared to a solution using L' astrometry. The new orbit casts doubt on previous associations of G2 and a low surface brightness "tail". It is shown that G2 has no K' counterpart down to K' ~ 20 mag. G2's L' continuum and the Br-gamma line-emission is unresolved in almost all epochs; however it is marginally extended in our highest quality Br-gamma data set from 2006 and exhibits a clear velocity gradient at that time. While the observations altogether suggest that G2 has a gaseous component which is tidally interacting with the central black hole, there is likely a central star providing the self-gravity necessary to sustain the compact nature of this object.
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http://arxiv.org/abs/1304.5280
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