The Stellar Content of Two OB Associations in the LMC: LH 117 (NGC 2122) and LH 118

Using CCD photometry and digital spectroscopy, we have investigated the stellar content of these two adjacent OB associations in the LMC. We discuss in some depth the details of our CCD photometry since we will be using the same methods to study other Magellanic Cloud associations. We find that these associations contain about 50 stars more massive than 10M_sun_. We have spectra for nearly all the members more massive than 15M_sun_, allowing placement on a theoretical H-R diagram. Most of the association members lie near the ZAMS, but our spectroscopy has tentatively confirmed two red supergiants. These, and the previously known LH 117 B2 I supergiant, must be of lower mass than several of the unevolved massive members of these associations, implying that these supergiants formed earlier than the majority of the association members by about 6 to 10 million years. We derive an IMF for the associations, finding a slope similar to what is known for massive stars within a few kiloparsecs of the Sun. The Hα luminosity of the associated DEM 323 H II region reported by Kennicutt and Hodge is about a factor of 2 lower than should be produced by the stellar Lyman-continuum flux from stars, suggesting that either the nebulosity is density bounded and/or that the Lyman photons are lost to dust absorption.