The stellar content of obscured Galactic giant HII regions. II. W42

We present near-infrared J, H, and K images and K-band spectroscopy in the giant H II region W42. A massive star cluster is revealed; the color-color plot and K-band spectroscopic emission features of two of the brighter objects suggest the presence of young stellar objects. The spectrum of the bright central star is similar to unobscured stars with MK spectral types of O5-O6.5. If this star is on the zero-age main sequence, then the derived spectrophotometric distance is considerably smaller than previous estimates. The Lyman continuum luminosity of the cluster is a few times that of the Trapezium. The slope of the K-band luminosity function is similar to that for the Trapezium cluster and significantly steeper than that for the massive star cluster in M17 or in the Arches cluster near the Galactic center.