Comparisons between optical and ultraviolet interstellar lines formed in the Carina Nebula (NGC 3372)

Discovery of complex Ca II H and K interstellar line profiles towards stars embedded in the giant H II region surrounding Eta Carinae led to a reconnaissance of the richer ultraviolet (UV) interstellar line spectrum. Single International Ultraviolet Explorer (IUE) spectra were secured for those stars exhibiting the greatest variety of structure in the optical interstellar lines, namely, HD 93130, 93160, 93162, 93204, 93205, 93206 and HDE 303308. Appraisal of the spectra suggests that: (1) longwards of Lyman Alpha many of the interstellar lines, including an unidentified one, in the spectrum of Zeta Oph seem to be present in the Carina Nebula spectra; (2) interstellar line structure varies widely in both velocity and intensity throughout the region, as well as along a given line of sight as the species change; (3) new high velocity components of UV lines appear to extend the total range of velocities in the nebular interstellar lines to about 400 m/s; and (4) lines of the high excitation species Si IV and C IV are strong and also structured in velocity space

Very Massive Stars and the Eddington Limit

We use contemporary evolutionary models for Very Massive Stars (VMS) to assess whether the Eddington limit constrains the upper stellar mass limit. We also consider the interplay between mass and age for the wind properties and spectral morphology of VMS, with reference to the recently modified classification scheme for O2-3.5If*/WN stars. Finally, the death of VMS in the local universe is considered in the context of pair instability supernovae.Comment: 6 pages, 4 figures, from "Four Decades of Massive Star Research" (Quebec, Jul 2011), ASP Conf Ser, in press (L. Drissen, C. Robert, N. St-Louis, A.F.J. Moffat, eds.

International Ultraviolet Explorer Atlas of O-typespectra from 1200 to 1900 Angstrom

The IUE archives provide an unprecedented sample of uniform, high-quality ultraviolet stellar spectra. In particular, they contain high-resolution SWP data for nearly 200 different O stars. We have undertaken a survey of the 1200-1900 A region in about 120 of them having homogeneous optical spectral classifications to investigate systematically the behavior of the ultraviolet features, incuding the prominent stellar wind profiles and the degree to which they correlate with the optical types. The standard extracted spectrograms have been rebinned to a constant wavelength resolution of 0.25A and uniformly normalized (not dereddened) at the GSFC RDAF. They are then plotted at 10A/cm, with reseau, photometric quality and echelle order junction flags available. This atlas contains such plots for about 100 stars, arranged in spectral-type, luminosity and peculiar object sequences. The results show a high degree of correlation between the ultraviolet features, both photospheric and stellar-wind, and the optical classifications for the majority of the O-type stars

Compact star clusters of the LMC HII region N11C

Based on imaging and spectroscopy obtained at the ESO NTT telescope and using an efficient image analysis algorithm, we study the core of the LMC OB association LH13, particularly the two compact stellar clusters Sk-6641 and HNT in the HII, region N11C. We resolve Sk-6641 into 15 components and for the first time the HNT cluster into 70 stars, and derive photometry for the members. Moreover, from medium resolution spectroscopy we determine the spectral types for sixteen stars in N11C. We compare the color-magnitude diagrams of the clusters with that of the field stars and discuss the cluster ages. With an age of ~100 Myr, the HNT cluster appears significantly older than the very young (< 5 Myr) Sk-6641 starburst. We suggest that most of the `field' O-stars in the core of N11C have actually been ejected from Sk-6641 through dynamical interactions in the compact cluster. The properties of the Sk-6641 and HNT clusters suggest that we are viewing different star formation regions lying at different distances along the same line of sight.Comment: 12 pages, 8 figure

New findings on the prototypical Of?p stars

In recent years several in-depth investigations of the three Galactic Of?p stars were undertaken. These multiwavelength studies revealed the peculiar properties of these objects (in the X-rays as well as in the optical): magnetic fields, periodic line profile variations, recurrent photometric changes. However, many questions remain unsolved. To clarify some of the properties of the Of?p stars, we have continued their monitoring. A new XMM observation and two new optical datasets were obtained. Additional information for the prototypical Of?p trio has been found. HD108 has now reached its quiescent, minimum-emission state, for the first time in 50--60yrs. The echelle spectra of HD148937 confirm the presence of the 7d variations in the Balmer lines and reveal similar periodic variations (though of lower amplitudes) in the HeI5876 and HeII4686 lines, underlining its similarities with the other two prototypical Of?p stars. The new XMM observation of HD191612 was taken at the same phase in the line modulation cycle but at a different orbital phase as previous data. It clearly shows that the X-ray emission of HD191612 is modulated by the 538d period and not the orbital period of 1542d - it is thus not of colliding-wind origin and the phenomenon responsible for the optical changes appears also at work in the high-energy domain. There are however problems: our MHD simulations of the wind magnetic confinement predict both a harder X-ray flux of a much larger strength than what is observed (the modeled DEM peaks at 30-40MK, whereas the observed one peaks at 2MK) and narrow lines (hot gas moving with velocities of 100--200km/s, whereras the observed FWHM is ~2000km/s).Comment: 10 pages, 8 figures (2 in jpg), accepted for publication by A&

The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)

Aims. We present the first orbital solution for the O-type supergiant star HD 74194, which is the optical counterpart of the supergiant fast X-ray transient IGR J08408-4503. Methods. We measured the radial velocities in the optical spectrum of HD 74194, and we determined the orbital solution for the first time. We also analysed the complex H{\alpha} profile. Results. HD 74194 is a binary system composed of an O-type supergiant and a compact object in a short-period ($P=9.5436\pm0.0002$ d) and high-eccentricity ($e=0.63\pm0.03$) orbit. The equivalent width of the H{\alpha} line is not modulated entirely with the orbital period, but seems to vary in a superorbital period ($P=285\pm10$ d) nearly 30 times longer than the orbital one.Comment: 4 pages, 6 figures, accepted for publication in A&

The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars

We present the second installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ~ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog (GOSC). In this paper we include bright stars and other objects drawn mostly from the first version of GOSC, all of them south of delta = -20 degrees, for a total number of 258 O stars. We also revise the northern sample of paper I to provide the full list of spectroscopically classified Galactic O stars complete to B = 8, bringing the total number of published GOSSS stars to 448. Extensive sequences of exceptional objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is also discussed. The magnitude and spatial distributions of the observed sample are analyzed. We also present new results from OWN, a multi-epoch high-resolution spectroscopic survey coordinated with GOSSS that is assembling the largest sample of Galactic spectroscopic massive binaries ever attained. The OWN data combined with additional information on spectroscopic and visual binaries from the literature indicate that only a very small fraction (if any) of the stars with masses above 15-20 M_Sol are born as single systems. In the future we will publish the rest of the GOSSS survey, which is expected to include over 1000 Galactic O stars.Comment: 110 pages, 16 figures, accepted for publication in ApJS. Some figures have low quality due to arXiv file size limitations, alternative version available at http://jmaiz.iaa.es/files/Sotaetal14.pd