Adaptive optics near-infrared spectroscopy of the Sagittarius A* cluster.
GEZARI S., GHEZ A.M., BECKLIN E.E., LARKIN J., McLEAN I.S. and MORRIS M.
Abstract (from CDS):
We present K-band λ/Δλ∼2600 spectroscopy of five stars (K∼14-16 mag) within 0".5 of Sgr A*, the radio source associated with the compact massive object suspected to be a 2.6x106M☉black hole at the center of our Galaxy. High spatial resolution of ∼0".09 and good Strehl ratios of ∼0.2 achieved with adaptive optics on the 10 m Keck telescope make it possible to measure moderate-resolution spectra of these stars individually for the first time. Two stars (S0-17 and S0-18) are identified as late-type stars by the detection of CO band head absorption in their spectra. Their absolute K magnitudes and CO band head absorption strengths are consistent with early K giants. Three stars (S0-1, S0-2, and S0-16) with rproj<0.0075 pc (∼0".2) from Sgr A* lack CO band head absorption, confirming the results of earlier lower spectral and lower spatial resolution observations that the majority of the stars in the Sgr A* cluster are early-type stars. The absolute K magnitudes of the early-type stars suggest that they are late O, early B main-sequence stars of ages less than 20 Myr. The presence of young stars in the Sgr A* cluster so close to the central supermassive black hole poses the intriguing problem of how these stars could have formed or could have been brought within its strong tidal field.
Black Hole Physics - Galaxy: Center - Galaxy: Nucleus - open clusters and associations: individual (Sagittarius A*) - Techniques: High Anular Resolution