We study the IR-through-UV wavelength dependence of 328 Galactic interstellar extinction curves affecting normal, near-main-sequence B and late O stars. We derive the curves using a new technique that employs stellar atmosphere models in lieu of unreddened ''standard'' stars. Under ideal conditions, this technique is capable of virtually eliminating spectral mismatch errors in the curves. In general, it lends itself to a quantitative assessment of the errors and enables a rigorous testing of the significance of relationships between various curve parameters, regardless of whether their uncertainties are correlated. Analysis of the curves gives the following results:1. In accord with our previous findings, the central position of the 2175 8 extinction bump is mildly variable, its width is highly variable, and the two variations are unrelated.2. Strong correlations are found among some extinction properties within the UV region, and within the IR region.3. With the exception of a few curves with extreme (i.e., large) values of R(V ), the UVand IR portions of Galactic extinction curves are not correlated with each other.4. The large sight lineYtoYsight line variation seen in our sample implies that any average Galactic extinction curve will always reflect the biases of its parent sample.5. The use of an average curve to deredden a spectral energy distribution (SED) will result in significant errors, and a realistic error budget for the dereddened SED must include the observed variance of Galactic curves.While the observed large sight lineYtoYsight line variations, and the lack of correlation among the various features of the curves, make it difficult to meaningfully characterize average extinction properties, they demonstrate that extinction curves respond sensitively to local conditions. Thus, each curve contains potentially unique information about the grains along its sight line.

We have determined accurate values of the product of the mass-loss rate and the ion fraction of P 4+ ,Ṁ q(P 4+ ), for a sample of 40 Galactic O-type stars by fitting stellar-wind profiles to observations of the P v resonance doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P 4+ is the dominant ion in the wind (i.e., 0.5 q(P 4+ ) ≤ 1),Ṁ q(P 4+ ) approximates the mass-loss rate to within a factor of 2. Theory predicts that P 4+ is the dominant ion in the winds of O7-O9.7 stars, though an empirical estimator suggests that the range from O4-O7 may be more appropriate. However, we find that the mass-loss rates obtained from P v wind profiles are systematically smaller than those obtained from fits to Hα emission profiles or radio free-free emission by median factors of ∼130 (if P 4+ is dominant between O7 and O9.7) or ∼20 (if P 4+ is dominant between O4 and O7). These discordant measurements can be reconciled if the winds of O stars in the relevant temperature range are strongly clumped on small spatial scales. We use a simplified two-component model to investigate the volume filling factors of the denser regions. This clumping implies that mass-loss rates determined from "ρ 2 " diagnostics have been systematically over-estimated by factors of 10 or more, at least for a subset of O stars. Reductions in the mass-loss rates of this size have important implications for the evolution of massive stars and quantitative estimates of the feedback that hot-star winds provide to their interstellar environments.

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We present a catalog of 1750 massive stars in the Large Magellanic Cloud, with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 − 24 µm in the UBV IJHK s +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant and luminous blue variable (LBV) stars are among the brightest infrared point sources in the Large Magellanic Cloud, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to freefree emission among ∼ 900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to 1 Giacconi Fellow.the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L ⊙ ≥ 4) and the rare, dusty progenitors of the new class of optical transients (e.g. SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.