Diffraction-limited Imaging Spectroscopy of the Sagittarius A* Region Using OSIRIS, a New Keck Instrument

We present diffraction-limited spectroscopic observations of an infrared flare associated with the radio source Sgr A*. These are the first results obtained with OSIRIS, the new facility infrared imaging spectrograph for the Keck Observatory operated with the laser guide star (LGS) adaptive optics (AO) system. After subtracting the spectrum of precursor emission at the location of Sgr A*, we find that the flare has a spectral index [F(ν) ∝ να] of α = -2.6 ± 0.9. If we do not subtract the precursor light, then our spectral index is consistent with earlier observations by Ghez et al. All observations published so far suggest that the spectral index is a function of the flare's K-band flux.