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Observations of the WC9+OB system WR 65 in the infrared show variations of its dust emission consistent with a period near 4.8~yr, suggesting formation in a colliding-wind binary (CWB) having an elliptical orbit. If we adopt the IR maximum as zero phase, the times of X-ray maximum count and minimum extinction to the hard component measured by Oskinova & Hamann fall at phases 0.4--0.5, when the separation of the WC9 and OB stars is greatest. We consider WR 65 in the context of other WC8-9+OB stars showing dust emission., Comment: International Workshop on Wolf-Rayet Stars, Potsdam, Germany, 1 - 5 June 2015

We present infrared photometry of the episodic dust-making Wolf-Rayet system WR19 (LS3), tracking its fading from a third observed dust-formation episode in 2007 and strengthening the view that these episodes are periodic (P = 10.1+/-0.1 y). Radial velocities of the O9 component observed between 2001 and 2008 show RV variations consistent with WC19 being a spectroscopic binary of high eccentricity (e=0.8), having periastron passage in 2007.14, shortly before the phase of dust formation. In this respect, WR19 resembles the archetypical episodic dust-making colliding-wind binary system WR140., Comment: 5 pages and 4 figures, accepted for publication in MNRAS

We present XMM-Newton observations of the O supergiant Zeta Orionis (O9.7 Ib). The spectra are rich in emission lines over a wide range of ionization stages. The RGS-spectra show for the first time lines of low ion stages such as C VI, N VI, N VII, and O VII. The line profiles are symmetric and rather broad (FWHM approximately 1500 km/s) and show only a slight blue shift. With the XMM-epic spectrometer several high ions are detected in this star for the first time including Ar XVII and S XV. Simultaneous multi-temperature fits and DEM-modeling were applied to the RGS and EPIC spectra to obtain emission measures, elemental abundances and plasma temperatures. The calculations show temperatures in the range of about 0.07-0.6 keV. According to the derived models the intrinsic source X-ray luminosity at a distance of 251 pc Lx=1.37(.03) times 10^{32} ergs/s, in the energy range 0.3-10 keV. In the best multi-temperature model fit, the abundances of C, N, O, and Fe are near their solar values, while the abundances of Ne, Mg, and Si appear somewhat enhanced. The sensitivity of the He-like forbidden and intercombination lines to Zeta Ori's strong radiation field is used to derive the radial distances at which lines are formed. Values of 34 R-star for N VI, 12.5 R-star for O VII, 4.8 R-star for Ne IX, and 3.9 R-star for Mg XI are obtained., Comment: content: 11 pages, 4 figures

We present results from an optical spectroscopic investigation of the massive binary system [L72] LH~54-425 in the LH 54 OB association in the Large Magellanic Cloud. We revise the ephemeris of [L72] LH 54-425 and find an orbital period of 2.247409 +/- 0.000010 days. We find spectral types of O3 V for the primary and O5 V for the secondary. We made a combined solution of the radial velocities and previously published V-band photometry to determine the inclination for two system configurations, i = 52 degrees for the configuration of the secondary star being more tidally distorted and i = 55 degrees for the primary as the more tidally distorted star. We argue that the latter case is more probable, and this solution yields masses and radii of M_1 = 47 +/- 2 M_Sun and R_1 = 11.4 +/- 0.1 R_Sun for the primary, and M_2 = 28 +/- 1 M_Sun and R_2 = 8.1 +/- 0.1 R_Sun for the secondary. Our analysis places LH 54-425 amongst the most massive stars known. Based on the position of the two stars plotted on a theoretical HR diagram, we find the age of the system to be about 1.5 Myr., Comment: 21 pages, 6 figures. Accepted in ApJ. To appear vol. 683, Aug. 10th

X-ray properties of the stellar population in the Carina OB1 association are examined with special emphasis on early-type stars. Their spectral characteristics provide some clues to understanding the nature of X-ray formation mechanisms in the winds of single and binary early-type stars. A timing and spectral analysis of five observations with XMM-Newton is performed using various statistical tests and thermal spectral models. 235 point sources have been detected within the field of view. Several of these sources are probably pre-main sequence stars with characteristic short-term variability. Seven sources are possible background AGNs. Spectral analysis of twenty three sources of type OB and WR 25 was performed. We derived spectral parameters of the sources and their fluxes in three energy bands. Estimating the interstellar absorption for every source and the distance to the nebula, we derived X-ray luminosities of these stars and compared them to their bolometric luminosities. We discuss possible reasons for the fact that, on average, the observed X-ray properties of binary and single early type stars are not very different, and give several possible explanations., Comment: 20 pages, 16 figures

We present results from a spectroscopic search for massive companions to dust-making Galactic WC9 stars as a step to testing the paradigm that dust formation in these systems requires colliding winds to produce over densities. We find evidence for OB companions to the WC9 stars WR 59 and WR 65, but not WR 121 or WR 117. We identify lines of N III-V and possibly N II in the spectrum of WR 88, one of the few Galactic WC9 stars which do not make circumstellar dust, and suggest that WR 88 is a transitional WN-WC9 object and less evolved than the other WC9 stars. On the other hand, the possible identification of a strong emission line at 4176A in the spectrum of WR 117 with Ne I suggests that this star is more evolved than other WC9 stars studied., Comment: 4 pages, 3 figures, contribution to "Massive Stars and High-Energy Emission in OB Associations"; JENAM 2005, held in Liege (Belgium)

We present XMM-Newton observations of gamma^2 Velorum (WR 11, WC8+O7.5III, P = 78.53 d), a nearby Wolf-Ray binary system, at its X-ray high and low states. At high state, emission from a hot collisional plasma dominates from about 1 to 8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma is identified with the shock zone between the winds of the primary Wolf-Rayet star and the secondary O giant. The absorption at low state is interpreted as photoelectric absorption in the Wolf-Rayet wind. This absorption allows us to measure the absorbing column density and to derive a mass loss rate 8x10^{-6} M_sun/yr for the WC8 star. This mass loss rate, in conjunction with a previous Wolf-Rayet wind model, provides evidence for a clumped WR wind. A clumping factor of 16 is required. The X-ray spectra below 1 keV (12 Ang) show no absorption and are essentially similar in both states. There is a rather clear separation in that emission from a plasma hotter than 5 MK is heavily absorbed in low state while the cooler plasma is not. This cool plasma must come from a much more extended region than the hot material. The Neon abundance in the X-ray emitting material is 2.5 times the solar value. The unexpected detection of CV (25.3 Ang) and CVI (31.6 Ang) radiative recombination continua at both phases indicates the presence of a cool (~40,000 K) recombination region located far out in the binary system., Comment: 16 pages

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of \sim 3.675 days. Our spectra indicate that both components are most likely of WN6ha or O3If^*/WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of 70.7 \pm 4.0 and 68.8 \pm 3.8 M_{\odot} for the two stars. These properties make WR20a a cornerstone system for the study of massive star evolution., Comment: 5 pages, 3 figures, accepted by A&A Letters

We report the results of a survey of radio continuum emission of Galactic Wolf-Rayet stars north of declination -46 degrees. The observations were obtained at 8.46 GHz (3.6cm) using the Very Large Array (VLA), with an angular resolution of about 6 x 9 arcsec and typical rms noise of 0.04 mJy/beam. Our survey of 34 WR stars resulted in 15 definite and 5 probable detections, 13 of these for the first time at radio wavelengths. All detections are unresolved. Time variations in flux are confirmed in the cases of WR98a, WR104, WR105 and WR125. WR79a and WR89 are also variable in flux and we suspect they are also non-thermal emitters. Thus, of our sample 20-30% of the detected stars are non-thermal emiters. Average mass loss rates determinations obtained excluding definite and suspected non-thermal cases give similar values for WN (all subtypes) and WC5-7 stars, while a lower value was obtained for WC8-9 stars. Uncertainties in stellar distances largely contribute to the observed scatter in mass loss rates. Upper limits to the mass loss rates were obtained in cases of undetected sources or for sources which probably show additional non-thermal emission., Comment: 21 pages, Latex, 21 postscript figures, to be published in The Astronomical Journal, May 2004

The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibilty, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering long-slit capability over the same band with R~1,000. In addition, a number of UV and optical imagers view adjacent fields to that sampled by the spectrometers. Their performance compares well with that of HST/ACS and the spectral capabilities of WSO rival those of HST/COS., Comment: 11 pages, including 7 figures and 5 tables To be published in Proc SPIE, vol 4854

We report FUSE observations in 2006 of three O-type, double-lined spectroscopic binaries in the Magellanic Clouds. Their binary nature was discovered only in the past several years. The systems have very short periods (1.4 - 2.25 days), represent rare, young evolutionary stages of massive stars and binaries, and provide a unique glimpse at some of the most massive systems that form in dense clusters of massive stars. The systems are: LH54-425 in the LMC (O3IIIf + O6V, P=2.25 days, approx. 100+50 Mo), J053441-693139 in the LMC (O2-31f + O6V, P=1.4 days, 41+27 Mo), and Hodge 53-47 in the SMC (O6V + O4-5IIIf, P=2.2 days, 24+14 Mo, where the O4 star appears to be less massive than the O6 star). These represent some of the most massive binaries known. Their short periods indicates that wind interaction and mass transfer are likely important factors in their evolution. The spectra provide quantitative and systematic studies of phase-dependent stellar wind properties, wind collision effects in O+O binaries at lower metallicities, improved radial velocity curves, and FUV spectrophotometric changes as a function of orbital phase.

The star, Altair (A7 IV-V), is clearly shown to have Lyman-alpha emission of chromospheric origin, while no evidence is found for the Mg II emission reported in previous investigations. We present non-Local Thermodymanic Equilibrium (non-LTE) semiempirical models incorporating partial redistribution of the chromosphere of Altair that reproduce the observed Lyman-alpha emission and the Mg II resonance absorption at 2800 A. We unambiguously establihed that chromospheres exist at spectral types as early as A7 on the main sequence, and we also demonstrate that it very unlikely that the observed emission originates in a corotating expanding wind. This result represents a new challenge for chromospheric heating theories. It may indicate that both differential rotation and convection layers, at least near the equator, exist in this fast rotating (v sin i = 220 km/s) star.