Detections of Massive Stars in the Cluster MCM2005b77, in the Star-forming Regions GRS G331.34-00.36 (S62) and GRS G337.92-00.48 (S36)

Abstract

Large infrared and millimeter wavelength surveys of the Galactic plane have unveiled more than 600 new bubble H II regions and more than 3000 candidate star clusters. We present a study of the candidate clusters MCM2005b72, DBS2003-157, DBS2003-172, and MCM2005b77 based on near-infrared spectroscopy taken with SofI on the NTT and infrared photometry from the 2MASS, VVV, and GLIMPSE surveys. We find that (1) MCM2005b72 and DBS2003-157 are subregions of the same star-forming region, H II GRS G331.34-00.36 (bubble S62). MCM2005b72 coincides with the central part of this H II region, while DBS2003-157 is a bright mid-infrared knot of the S62 shell. We detected two O-type stars at extinction {A}_{K{{s}}} = 1.0-1.3 mag. Their spectrophotometric properties are consistent with the near-kinematic distance to GRS G331.34-00.36 of 3.9 ± 0.3 kpc. (2) DBS2003-172 coincides with a bright mid-infrared knot in the S36 shell (GRS G337.92-00.48), where we detected a pair of candidate He I stars embedded in a small cometary nebula. (3) The stellar cluster MCM2005b77 is rich in B-type stars, has an average {A}_{K{{s}}} of 0.91 mag, and is adjacent to the H II region IRAS 16137-5025. The average spectrophotometric distance of ∼5.0 kpc matches the near-kinematic distance to IRAS 16137-5025 of 5.2 ± 0.1 kpc.