In order to determine the physical properties of the hottest and most luminous stars and understand how these properties change as a function of metallicity, we have analyzed HST/UV and high-S/ N optical spectra of an additional 20 Magellanic Cloud stars, doubling the sample presented in the first paper in this series. Our analysis uses non-LTE line-blanketed models that include spherical extension and the hydrodynamics of the stellar wind. In addition, our data set includes FUSE observations of O vi and HST near-UV He i and He ii lines to test for consistency of our derived stellar properties for a few stars. The results from the complete sample are as follows:(1) We present an effective temperature scale for O stars as a function of metallicity. We find that the SMC O3-7 dwarfs are 4000 K hotter than Galactic stars of the same spectral type. The difference is in the sense expected due to the decreased significance of line blanketing and wind blanketing at the lower metallicities that characterize the SMC. The temperature difference between the SMC and Milky Way O dwarfs decreases with decreasing temperature, becoming negligible by spectral type B0, in accord with the decreased effects of stellar winds at lower temperatures and luminosities. The temperatures of the LMC stars appear to be intermediate between that of the Milky Way and SMC, as expected based on their metallicities. Supergiants show a similar effect but are roughly 3000-4000 K cooler than dwarfs for early O stars, also with a negligible difference by B0. The giants appear to have the same effective temperature scale as dwarfs, consistent with there being little difference in the surface gravities. When we compare our scale to other recent modeling efforts, we find good agreement with some CMFGEN results, while other CMFGEN studies are discordant, although there are few individual stars in common. WM-BASIC modeling by others has resulted in significantly cooler effective temperatures than what we find, as does the recent TLUSTY/CMFGEN study of stars in the NGC 346 cluster, but our results lead to a far more coeval placement of stars in the H-R diagram for this cluster. (2) We find that the wind momentum of these stars scales with luminosity and metallicity in the ways predicted by radiatively driven wind theory, supporting the use of photospheric analyses of hot luminous stars as a distance indicator for galaxies with resolved massive star populations. (3) A comparison of the spectroscopic masses with those derived from stellar evolutionary theory shows relatively good agreement for stars with effective temperatures below 45,000 K; however, stars with higher temperatures all show a significant mass discrepancy, with the spectroscopic masses a factor of 2 or more smaller than the evolutionary masses. This problem may in part be due to unrecognized binaries in our sample, but the result suggests a possible systematic problem with the surface gravities or stellar radii derived from our models. (4) Our sample contains a large number of stars of the earl...

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The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K-band and M-band spectroscopy of 14 intermediate mass young stars. In sources that have optically thick inner disks, i.e. E(K-L)>1, our detection rate of the rovibrational CO transitions is 100% and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the ro-vibrational CO transitions from HD 141569. In this case, we show that the gas is excited by UV fluorescence and that the inner disk is devoid of gas and dust. We discuss the plausibility of the various scenarios for forming this inner hole. Our modeling of the UV fluoresced gas suggests an additional method by which to search for and/or place stringent limits on gas in dust depleted regions in disks around Herbig Ae/Be stars.Subject headings: accretion, accretion disks ---circumstellar matter---line: profiles---molecular processes---planetary systems: protoplanetary disks---stars: pre-main sequence 1 Michelson Postdoctoral Fellow A complementary diagnostic of gas in the inner disk are the ro-vibrational transitions of CO. Previous work has shown that the ro-vibrational lines of CO are sensitive probes of circumstellar gas and are well suited to exploring conditions within the inner, planet-forming regions of disks These lines can be excited thermally or by UV fluorescence. Infrared observations can detect an amount of CO much smaller than an Earth mass, well below the threshold necessary to circularize the orbits of terrestrial planets. Although CO is not a useful probe of the total mass of circumstellar gas at large column densities, its presence can be used to trace the "skin" of the gas disk.An observational clarification of how the gas evolves in the inner disks of young stars is central to an understanding of early planet formation. If planets form by a two-step process where grains first agglomerate into a large rocky core followed by the accretion of a gaseous envelope (e.g. Lissauer 1993), then the disk should go through a gas-rich/dust-poor stage. Alternatively, if planets form by a gravitational instability (e.g. Boss 1998), then the gas and dust ObservationsWe have observed a heterogeneous sample of 14 young intermediate mass stars (2-10 M  ) to measure the emission from H I (Br γ) and CO (Δv=1) ( Table 1). The targets include two intermediate mass T Tauri stars (IMTTS), seven Herbig AeBe (HAeBe) stars, four transitional

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