High Spatial Resolution Spectroscopy of W51 IRS2E and IRS2W: Two Very   Massive Young Stars in Early Formation Stages
  We present $K$-band spectra of the near infrared counterparts to IRS2E and IRS2W which is associated with the ultracompact HII region W51d, both of them embedded sources in the Galactic compact HII region W51 IRS2. The high spatial resolution observations were obtained with the laser guide star facility and Near infrared Integral Field Spectrograph (NIFS) mounted at the Gemini North observatory. The spectrum of the ionizing source of W51d shows the photospheric features NIII (21155 \AA) in emission and HeII (21897 \AA) in absorption which lead us to classify it as an young O3 type star. We detected CO overtone in emission at 23000 \AA in the spectrum of IRS2E, suggesting that it is a massive young object still surrounded by an accretion disc, probably transitioning from the hot core phase to an ultracompact HII region. 
C. L. Barbosa (1), R. D. Blum (2), P. S. Conti (3), A. Damineli (4)   and E. Figueredo (5) ((1) IP&D-UNIVAP, (2) NOAO GSC, (...