We present high angular resolution near–infrared images of the obscured Galactic Giant HII ( GHII ) region G333.1–0.4 in which we detect an OB star cluster .
For G333.1–0.4 , we find OB stars and other massive objects in very early evolutionary stages , possibly still accreting .
We obtained K –band spectra of three stars ; two show O type photospheric features , while the third has no photospheric features but does show CO 2.3 \mu m band–head emission .
This object is at least as hot as an early B type star based on its intrinsic luminosity and is surrounded by a circumstellar disc/envelope which produces near infrared excess emission .
A number of other relatively bright cluster members also display excess emission in the K –band , indicative of disks/envelopes around young massive stars .
Based upon the O star photometry and spectroscopy , the distance to the cluster is 2.6 \pm 0.4 kpc , similar to a recently derived kinematic ( near side ) value .
The slope of the K –band luminosity function is similar to those found in other young clusters .
The mass function slope is more uncertain , and we find -1.3 \pm 0.2 < \Gamma < -1.1 \pm 0.2 - for stars with M > 5 M _ { \odot } where the upper an lower limits are calculated independently for different assumptions regarding the excess emission of the individual massive stars .
The number of Lyman continuum photons derived from the contribution of all massive stars in the cluster is 0.2 \times 10 ^ { 50 } s ^ { -1 } < NLyc < 1.9 \times 10 ^ { 50 } s ^ { -1 } .
The integrated cluster mass is 1.0 \times 10 ^ { 3 } M _ { \odot } < M _ { cluster } < 1.3 \times 10 ^ { 3 } M _ { \odot } .