A Cluster of He i Emission-Line Stars in the Galactic Center

The present study reports 1.9 arcsec/300 km s resolution imaging spectroscopy of He I n = 2 1P - n = 1 1S 2.06-micron line emission in the Galactic center. There is a group of about a dozen compact broad-line 'He I emission-line stars', most of which are positionally coincident with compact 2-micron continuum sources. It is argued that IRS 16 and its 'broad-line region' is a central concentration of this 1-pc diameter He I star cluster. The He I stars may be blue supergiants with heavy mass loss. The high He I/H I (Br-alpha, Br-gamma) ratios suggest an overabundance of helium in their atmospheres indicative of a postmain-sequence phase. Mass-loss rates range between a few 10 exp -5 and 10 exp -4 solar mass/yr, and outflow velocities are between 500 and 1000 km/s. The present data show that massive star formation has taken place in the Galactic center within the last few million years.