The Sgr A* stellar cluster: New NIR imaging and spectroscopy

ANDREAS ECKART, THOMAS OTT, REINHARD GENZEL

Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany

ASTRONOMY AND ASTROPHYSICS, 352:L22-L25


ABSTRACT

We report preliminary results based on new near-infrared observations of the central stellar cluster of our Galaxy conducted with the infrared spectrometer ISAAC at the ESO VLT UT1 and the MPE speckle camera SHARP at the ESO NTT. We obtained lambda /Delta lambda >= 3000 K-band spectroscopy of the 2.058 mu m He I, 2.165 mu m Brgamma emission lines, and 2.29 mu m CO bandhead absorption line. These data demonstrate clearly that there is no strong CO bandhead absorption originating in the northern part (S1/S2 area) of the central stellar cluster at the position of Sgr A*. This makes it likely that these K ~ 14.5 stars are O9 - B0.5 stars with masses of 15 to 20 Msun. Weaker CO bandhead absorption in the southern part of the cluster (S10/S11 area) could be due to contributions from neighbouring stars. We also report the detection of Brgamma line emission at the position of the central stellar cluster which could be associated with the `mini-spiral' rather than with the Sgr A* cluster itself. At the NTT we obtained another epoch epoch of proper motion measurments. The changes of source positions are consistent with the proper motion velocities derived from earlier epochs.

A&A Keywords:Galaxy:Center, Galaxies:Nuclei, Infrared:Galaxies, Infrared:Stars


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