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Aims. To better understand the phenomenon of colliding winds in massive binary stars, we study the X-ray lightcurve of a WR+O system of the Carina region, a system well known for the high mass of its primary.

Aims. We present the results obtained from a long-term spectroscopic campaign to study the multiplicity of O-type stars in both the young open cluster NGC 2244 and the Mon OB2 association.

Context. The properties of the early-type binary Cyg OB2 #5have been debated for many years and spectroscopic and photometric investigations yielded conflicting results.

Aims. The line profile variability and photometric variability of the O9.5 Vp star HD 93521are examined in order to establish the properties of the non-radial pulsations in this star.

Context. Westerlund 2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82 + 83 $M_{\odot}$), a dozen very early O-type stars (O3–7), and a wealth of PMS stars. Although of clear significance, this star cluster has not been well-studied.

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably Cyg OB2 #9.

Context.If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and γ-rays are expected through inverse Compton emission, but to date these have never been unambiguously detected.

Aims.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.

Aims.We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the Struve-Sahade effect (defined as the apparent strengthening of the secondary spectrum of the binary when the star is approaching, and the corresponding weakening of the lines when it is receding).

Aims.We analyze INTEGRAL-ISGRI data in order to probe the hard X-ray emission (above 20 keV) from point sources in the Cyg OB2 region and to investigate the putative non-thermal high-energy emission from early-type stars (Wolf-Rayet and O-type stars). Among the targets located in the field of view, we focus on the still unidentified EGRET source 3EG 2033+4118 that may be related to massive stars known to produce non-thermal emission in the radio domain, and on the wide colliding-wind binary WR 140.

Aims.The properties of the early-type stars in the core of the Westerlund 2cluster are examined in order to establish a link between the cluster and the very massive Wolf-Rayet binary WR 20aas well as the H iicomplex RCW 49.

Context.Since the discovery, with the EINSTEIN satellite, of strong X-ray emission associated with HD 93162 (≡WR 25), this object has been predicted to be a colliding-wind binary system. However, radial-velocity variations that would prove the suspected binary nature have yet to be found.

Aims.We address the issue of the multiplicity of the three brightest early-type stars of the young open cluster IC 1805, namely HD 15570, HD 15629 and HD 15558.

This paper is the first of a series dedicated to the X-ray properties of the young open cluster NGC 6231. Our data set relies on an XMM-Newtoncampaign of a nominal duration of 180 ks and reveals that NGC 6231  is very rich in the X-ray domain too. Indeed, 610 X-ray sources are detected in the present field of view, centered on the cluster core. The limiting sensitivity of our survey is approximately 6 $\times$10-15erg cm-2s-1but clearly depends on the location in the field of view and on the source spectrum. Using different existing catalogues, over 85% of the X-ray sources could be associated with at least one optical and/or infrared counterpart within a limited cross-correlation radius of 3´´ at maximum. The surface density distribution of the X-ray sources presents a slight N-S elongation. Once corrected for the spatial sensitivity variation of the EPIC instruments, the radial profile of the source surface density is well described by a King profile with a central density of about 8 sources per arcmin2and a core radius close to 3.1 arcmin. The distribution of the X-ray sources seems closely related to the optical source distribution. The expected number of foreground and background sources should represent about 9% of the detected sources, thus strongly suggesting that most of the observed X-ray emitters are physically belonging to NGC 6231. Finally, beside a few bright but soft objects – corresponding to the early-type stars of the cluster – most of the sources are relatively faint (~5 $\times$10-15erg cm-2s-1) with an energy distribution peaked around 1.0–2.0 keV.

Aims.We report the detection of hard X-ray emission from the field of the star-forming region NGC 6334  with the International Gamma-Ray Astrophysics Laboratory INTEGRAL.Methods.The JEM-Xmonitor and ISGRIimager aboard INTEGRALand ChandraACISimager were used to construct 3-80 keV images and spectra of NGC 6334.Results.The 3-10 keV and 10-35 keV images made with JEM-Xshow a complex structure of extended emission from NGC 6334. The ISGRIsource detected in the energy ranges 20-40 keV, 40-80 keV, and 20-60 keV coincides with the NGC 6334 ridge. The 20-60 keV flux from the source is ($1.8\pm0.37)\times10^{-11}~\rm ~erg~cm^{-2}~s^{-1}$. Spectral analysis of the source revealed a hard power-law component with a photon index about 1. The observed X-ray fluxes are in agreement with extrapolations of X-ray imaging observations of NGC 6334  by ChandraACISand ASCAGIS.Conclusions.The X-ray data are consistent with two very different physical models. A probable scenario is emission from a heavily absorbed, compact and hard Chandrasource that is associated with the AGN candidate radio source NGC 6334B. Another possible model is the extended Chandrasource of nonthermal emission from NGC 6334 that can also account for the hard X-ray emission observed by INTEGRAL. The origin of the emission in this scenario is due to electron acceleration in energetic outflows from massive early type stars. The possibility of emission from a young supernova remnant, as suggested by earlier infrared observations of NGC 6334, is constrained by the non-detection of 44Ti lines.

In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD - 41° 7742, deriving for the first time an orbital solution for both components of the system. In this second paper, we focus on the analysis of the optical light curve and on recent XMM-NewtonX-ray observations. In the optical, the system presents two eclipses, yielding an inclination $i\sim77\degr$. Combining the constraints from the photometry with the results of our previous work, we derive the absolute parameters of the system. We confirm that the two components of CPD - 41° 7742are main sequence stars (O9 V + B1–1.5 V) with masses ($M_1\sim18$$M_{\odot}$and $M_2\sim10$$M_{\odot}$) and respective radii ($R_1\sim7.5$$R_{\odot}$and $R_2\sim5.4$$R_{\odot}$) close to the typical values expected for such stars.
We also report an unprecedented set of X-ray observations that almost uniformly cover the 2.44-day orbital cycle. The X-ray emission from CPD - 41° 7742is well described by a two-temperature thermal plasma model with energies close to 0.6 and 1.0 keV, thus slightly harder than typical early-type emission. The X-ray light curve shows clear signs of variability. The emission level is higher when the primary is in front of the secondary. During the high emission state, the system shows a drop of its X-ray emission that almost exactly matches the optical eclipse. We interpret the main features of the X-ray light curve as the signature of a wind-photosphere interaction, in which the overwhelming primary O9 star wind crashes into the secondary surface. Alternatively the light curve could result from a wind-wind interaction zone located near the secondary star surface. As a support to our interpretation, we provide a phenomenological geometric model that qualitatively reproduces the observed modulations of the X-ray emission.

We discuss the results of two XMM-Newtonobservations of the open cluster NGC 6604 obtained in April and September 2002. We concentrate mainly on the multiple system HD 167971 (O5-8V + O5-8V + (O8I)). The soft part of the EPIC spectrum of this system is thermal with typical temperatures of about 2 $\times$106to 9 $\times$106K. The nature (thermal vs. non-thermal) of the hard part of the spectrum is not unambiguously revealed by our data. If the emission is thermal, the high temperature of the plasma (~2.3 $\times$107to 4.6 $\times$107K) would be typical of what should be expected from a wind-wind interaction zone within a long period binary system. This emission could arise from an interaction between the combined winds of the O5-8V + O5-8V close binary system and that of the more distant O8I companion. Assuming instead that the hard part of the spectrum is non-thermal, the photon index would be rather steep (~3). Moreover, a marginal variability between our two XMM-Newtonpointings could be attributed to an eclipse of the O5-8V + O5-8V system. The overall X-ray luminosity points to a significant X-ray luminosity excess of about a factor 4 possibly due to colliding winds. Considering HD 167971 along with several recent X-ray and radio observations, we propose that the simultaneous observation of non-thermal radiation in the X-ray (below 10.0 keV) and radio domains appears rather unlikely. Our investigation of our XMM-Newtondata of NGC 6604 reveals a rather sparse distribution of X-ray emitters. Including the two bright non-thermal radio emitters HD 168112 and HD 167971, we present a list of 31 X-ray sources along with the results of the cross-correlation with optical and infrared catalogues. A more complete spectral analysis is presented for the brightest X-ray sources. Some of the members of NGC 6604 present some characteristics suggesting they may be pre-main sequence star candidates.

We present a radio lightcurve of the O5.5 III(f+) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable variability and a negative spectral index, thereby confirming that HD 168112 is a non-thermal radio emitter. The non-thermal radio emission is believed to be due to synchrotron radiation from relativistic electrons that have been Fermi accelerated in shocks. For HD 168112, it is not known whether these shocks are due to a wind-wind collision in a binary system or to the intrinsic instability of the stellar wind driving mechanism. Assuming HD 168112 to be a single star, our synchrotron model shows that the velocity jump of the shocks should be very high, or there should be a very large number of shocks in the wind. Neither of these is compatible with time-dependent hydrodynamical calculations of O star winds. If, on the other hand, we assume that HD 168112 is a binary, the high velocity jump is easily explained by ascribing it to the wind-wind collision. By further assuming the star to be an eccentric binary, we can explain the observed radio variability by the colliding-wind region moving in and out of the region where free-free absorption is important. The radio data presented here show that the binary has a period of between one and two years. By combining the radio data with X-ray data, we find that the most likely period is ~1.4 yr.

We analyse the optical spectrum of the very massive binary system WR 20a (WN6ha + WN6ha). The most prominent emission lines, Hαand He iiλ4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR 20a indicates a reddening of $A_{\rm V} \simeq 6.0$mag and a distance of ~$ 7.9$kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at ∼1.1 pc from the cluster core could indicate that WR 20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: $T_{\rm eff} = 43\,000 \pm 2000$K, $\log{L_{\rm bol}/{L_{\odot}}} \simeq 6.0$, ${\dot{M}} = 8.5 \times 10^{-6}$$M_{\odot}$yr-1(assuming a clumped wind with a volume filling factor $f = 0.1$). Nitrogen is enhanced in the atmospheres of the components of WR 20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age.

We present the results of an XMM-Newtonobservation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources.

We present the very first analysis of the spectroscopic variability of the three rapidly rotating Oef stars HD 192281 (O5(ef)), HD 14442 (O5.5ef) and HD 14434 (O6.5(ef)). Radial velocities of the $\ion{He}{ii}$λ4541 line reveal no evidence of binarity on time scales of a few days, or from one year to the next, for any of the targets. The $\ion{He}{ii}$λ4686 double-peaked emission and, to some extent, the Hβabsorption line display significant profile variability in the spectra of all three stars. Data gathered during different observing runs spread over six years reveal a rather stable time scale for HD 192281 and HD 14442, whereas the variability pattern changes significantly from one year to the other. The case of HD 14434 is less clear as no obvious time scale emerges from our analysis. In a tentative way to interpret this variability, stellar rotation remains a possible clock for HD 192281 and HD 14442. However, currently available models addressing stellar rotation fail to explain some crucial aspects of the observed variability behaviour, which appear to be even more complex in the case of HD 14434.

Spatially resolved images of the galactic supernova remnant G78.2+2.1 (γ-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRIimager aboard the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The images are dominated by localized clumps of about ten arcmin in size. The flux of the most prominent North–Western (NW) clump is ($1.7\pm0.4)\times10^{-11} \rm ~erg~cm^{-2}~s^{-1}$in the 25–40 keV band. The observed X-ray fluxes are in agreement with extrapolations of soft X-ray imaging observations of γ-Cyg by ASCA GISand spatially unresolved RXTE PCAdata. The positions of the hard X-ray clumps correlate with bright patches of optical line emission, possibly indicating the presence of radiative shock waves in a shocked cloud. The observed spatial structure and spectra are consistent with model predictions of hard X-ray emission from nonthermal electrons accelerated by a radiative shock in a supernova interacting with an interstellar cloud, but the powerful stellar wind of the O9V star HD 193322 is a plausible candidate for the NW source as well.

We present the results of a spectroscopic campaign revealing that the non-thermal radio emitter Cyg OB2 #8A is an O6 + O5.5 binary system. We propose the very first orbital solution indicating a period of about 21.9 days. The system appears to be eccentric (0.24 ±0.04) and is likely seen under a rather low inclination angle. The mass ratio of the components is close to unity. The impact of the binarity of this star in the framework of our understanding of non-thermal radio emission from early-type stars is briefly discussed.

We analyse spectroscopic observations of WR 20a revealing that this star is a massive early-type binary system with a most probable orbital period of ~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 WR 20a a cornerstone system for the study of massive star evolution.

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newtonand VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decreaseof the X-ray flux of ~30%. The radio emission on the other hand increasesby a factor 5–7 between the two observations obtained roughly simultaneously with the XMM-Newtonpointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT~ 2–3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD 168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD 168112 is indeed a binary, it must be seen under a fairly low inclination.

Using the sensitive XMM-Newtonobservatory, we have observed the giant H iiregion N 11 in the LMC for ~30 ks. We have detected several large areas of soft diffuse X-ray emission along with 37 point sources. One of the most interesting results is the possible association of a faint X-ray source with BSDL 188, a small extended object of uncertain nature. 
The OB associations in the field-of-view (LH9, LH10 and LH13) are all detected with XMM-Newton, but they appear very different from one another. The diffuse soft X-ray emission associated with LH9 peaks near HD 32228, a dense cluster of massive stars. The combined emission of all individual massive stars of LH9 and of the superbubble they have created is not sufficient to explain the high level of emission observed: hidden SNRs, colliding-wind binaries and the numerous pre-main sequence stars of the cluster are most likely the cause of this discrepancy. The superbubble may also be leaking some hot gas in the ISM since faint, soft emission can be observed to the south of the cluster. The X-ray emission from LH10 consists of three pointlike sources and a soft extended emission of low intensity. The two brightest point sources are clearly associated with the fastest expanding bubbles blown by hot stars in the SW part of the cluster. The total X-ray emission from LH10 is rather soft, although it presents a higher temperature than the other soft emissions of the field. The discrepancy between the combined emission of the stars and the observed luminosity is here less severe than for LH9 and could be explained in terms of hot gas filling the wind-blown bubbles. On the other hand, the case of LH13 is different: it does not harbour any extended emission and its X-ray emission could most probably be explained by the Sk $-66^{\circ}$41 cluster alone. 
Finally, our XMM-Newtonobservation included simultaneous observations with the OM camera that provide us with unique UV photometry of more than 6000 sources and enable the discovery of the UV emission from the SNR N11L.

In 2001, using a large spectroscopic dataset from an extensive monitoring campaign, we discovered that the peculiar Of star HD 108 displayed extreme line variations. This strange behaviour could be attributed to a variety of models, and an investigation of the high energy properties of HD 108  was needed to test the predictions from these models. Our dedicated XMM-Newtonobservation of HD 108 shows that its spectrum is well represented by a two temperature thermal plasma model with $kT_1\sim0.2$keV and $kT_2\sim1.4$keV. In addition, we find that the star does not display any significant short-term changes during the XMM-Newtonexposure. Compared to previous Einsteinand ROSATdetections, it also appears that HD 108  does not present long-term flux variations either. While the line variations continue to modify HD 108's spectrum in the optical domain, the X-ray emission of the star appears thus surprisingly stable: no simple model is for the moment able to explain such an unexpected behaviour. Thanks to its high sensitivity, the XMM-Newtonobservatory has also enabled the serendipitous discovery of 57 new X-ray sources in the field of HD 108. Their properties are also discussed in this paper.

We report the analysis of an XMM-Newtonobservation of the close binary HD 159176 (O7 V + O7 V). The observed $L_\mathrm{X}$/$L_\mathrm{bol}$ratio reveals an X-ray luminosity exceeding by a factor ~7 the expected value for X-ray emission from single O-stars, therefore suggesting a wind-wind interaction scenario. EPIC and RGS spectra are fitted consistently with a two temperature mekaloptically thin thermal plasma model, with temperatures ranging from ~2 to $6\times10$6K. At first sight, these rather low temperatures are consistent with the expectations for a close binary system where the winds collide well before reaching their terminal velocities. We also investigate the variability of the X-ray light curve of HD 159176 on various short time scales. No significant variability is found and we conclude that if hydrodynamical instabilities exist in the wind interaction region of HD 159176, they are not sufficient to produce an observable signature in the X-ray emission. Hydrodynamic simulations using wind parameters from the literature reveal some puzzling discrepancies. The most striking one concerns the predicted X-ray luminosity which is one or more orders of magnitude larger than the observed one. A significant reduction of the mass loss rate of the components compared to the values quoted in the literature alleviates the discrepancy but is not sufficient to fully account for the observed luminosity. Because hydrodynamical models are best for the adiabatic case whereas the colliding winds in HD 159176 are most likely highly radiative, a totally new approach has been envisaged, using a geometrical steady-state colliding wind model suitable for the case of radiative winds. This model successfully reproduces the spectral shape of the EPIC spectrum, but further developments are still needed to alleviate the disagreement between theoretical and observed X-ray luminosities.

We present the very first high quality images of the He iiλ4686 emission in three high excitation nebulae of the Magellanic Clouds. A fourth high excitation nebula, situated around the WR star BAT99-2, was analysed in a previous letter. Using VLT FORS data, we investigate the morphology of the ring nebulae around the early-type WN stars BAT99-49 & AB7. We derive the total He iifluxes for each object and compare them with the most recent theoretical WR models. Whilst the ionization of the nebula around BAT99-49 can be explained by a WN star of temperature 90–100 kK, we find that the He iiemission measure of the nebula associated with AB7 requires an He+ionizing flux larger than predicted for the hottest WN model available. Using Hα, [O iii] and He iλ5876 images along with long-slit spectroscopy, we investigate the physical properties of these ring nebulae and find only moderate chemical enrichment. 
We also surveyed seven other LMC WR stars but we failed to detect any He iiemission. This holds also true for BAT99-9 which had been proposed to excite an He iinebula. Four of these surveyed stars are surrounded by a ring nebula, and we use the FORS data to derive their chemical composition: the nebula around BAT99-11 shows a N/O ratio and an oxygen abundance slightly lower than the LMC values, while the nebula around BAT99-134 presents moderate chemical enrichment similar to the one seen near BAT99-2, 49 and AB7. Comparing the WR stars of the LMC, BAT99-2 and 49 appear unique since similar stars do not reveal high excitation features.
The third high excitation nebula presented in this paper, N44C, does not harbor stars hotter than mid-O main sequence stars. It was suggested to be a fossil X-ray nebula ionized by the transient LMC X-5. Our observations of N44C reveal no substantial changes in the excitation compared to previous results reported in the literature. Therefore, we conclude that either the recombination timescale of the X-ray nebula has been underestimated or that the excitation of the nebula is produced by another, yet unknown, mechanism.

We report the detection of a number of X-ray sources associated with the very young open cluster NGC 6383. About two thirds of these objects are correlated with a rather faint optical source and all but one have at least one infrared counterpart within a correlation radius of 8 arcsec. Although NGC 6383 is not associated with a prominent star forming region, the overall properties of many of the X-ray sources suggest that they may be candidates for low-mass pre-main sequence stars. The number of X-ray sources increases towards the cluster center suggesting that there exists a close relation between the massive O-star binary system HD 159 176 in the cluster core and the population of X-ray bright low-mass objects in NGC 6383.

We present the results of a spectroscopic campaign on the early-type binary CPD?-?41°?7742. For the first time, we unambiguously detect the secondary's spectral signature and derive an accurate orbital solution for both components of the system. We confirm that the orbit displays a slight but definite eccentricity ($e=0.027\pm0.006$) despite the short period ($P=2.44070\pm0.00043$days). Previous radial velocity measurements available in the literature constitute together with our new observations a data set that spans more than 30 years. The combined primary orbital solution inferred is in excellent agreement with our solution and gives a period $P=2.44062\pm0.00005$?days. Based on spectroscopic criteria, we derive a spectral and luminosity classification of O9?III?+?B1?III. However, the luminosities and radii inferred from the membership of NGC?6231 rather indicate lower luminosity classes. We show that the equivalent widths of well isolated primary lines display variations that suggest that CPD?-?41°?7742 is an eclipsing binary. This makes CPD?-?41°?7742 the second known SB2 eclipsing early-type binary of the NGC?6231 cluster. We approximately constrain the inclination of the system $i_\mathrm{min}\approx60\degr$. This may indicate that the system does not offer enough room for two stars with radii typical of giant stars and lends further support to a less evolved luminosity classification for at least one of the objects.

We report the analysis of the first high-resolution X-ray spectra of the Wolf-Rayet (WR) object WR 25(HD 93162, WN6ha+O4f) obtained with the reflection grating spectrometers (rgs) and the european photon imaging cameras (epic-mosand pn) ccdspectrometers on board the XMM-Newtonsatellite. The spectrum exhibits bright emission lines of the H- and He-like ions of Ne, Mg, Si and S, as well as Fe xviiito Fe xxand Fe xxvlines. Line fluxes have been measured. The rgsand epicspectra have been simultaneously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Strong absorption by the dense WR stellar wind and the interstellar medium (ISM) is observed equivalent to $N_{\rm H} = 7 \times 10^{21}$cm-2. Multi-temperature (dem)fitting yields two dominant components around temperatures of 7.0 and 32 MK, respectively. The XMMintrinsic (i.e. unabsorbed, corrected for the stellar wind absorption and the absorption of ISM) X-ray luminosity of WR 25is Lx(0.5–10 keV) = $1.3 \times 10^{34}$erg s-1, and Lx(0.5–10 keV) = $0.85 \times 10^{34}$erg s-1, (when correcting for the ISM only) assuming $d=3.24$kpc. The obtained chemical abundances are subsolar, except for S. This may be real, but could equally well be due to a weak coupling to the continuum, which is strongly influenced by the absorption column density and the subtracted background. The expected high N-abundance, as observed in the optical wavelength region, could not be confirmed due to the strong wind absorption, blocking out its spectral signature. The presence of the Fe xxvemission-line complex at ~ 6.7 keV is argued as being indicative for colliding winds inside a WR+O binary system.

We present the first high resolution He iiλ4686 images of the high excitation nebula around the WR star Brey2 in the LMC. This nebula presents a striking morphology: a small arc-like feature some 3.6 pc in radius is particularly prominent in the He iiλ4686 line. We further discover a previously unknown faint He iiemission that extends over an area of $22\times 17$pc2. An even fainter He iiemission is apparently associated with the interstellar bubble blown by the progenitor of Brey2. The total He iiflux corresponds to an ionizing flux of $4\times 10^{47}$photons s-1. Hα, [O iii], and He iλ5876 images and long-slit spectra are also examined in this letter, enabling us to investigate the detailed physical properties at various locations of the nebula.

We report the results of an XMM-Newtonobservation of the Lagoon Nebula (M 8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC 6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M 8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of $kT \sim$a few keV. Only a few of the X-ray selected PMS candidates are known to display Hαemission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC 6530 are weak-line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD 164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC 6530 (LkHα115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect (probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region.

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD 164794). Our data include observations in the X-ray domain with XMM-Newton, in the radio domain with the VLA as well as optical spectroscopy. 9 Sgr is one of a few presumably single OB stars that display non-thermal radio emission. This phenomenon is attributed to synchrotron emission by relativistic electrons accelerated in strong hydrodynamic shocks in the stellar wind. Given the enormous supply of photospheric UV photons in the wind of 9 Sgr, inverse Compton scattering by these relativistic electrons is a priori expected to generate a non-thermal power law tail in the X-ray spectrum. Our EPIC and RGS spectra of 9 Sgr reveal a more complex situation than expected from this simple theoretical picture. While the bulk of the thermal X-ray emission from 9 Sgr arises most probably in a plasma at temperature ~$3 \times 10^6$K distributed throughout the wind, the nature of the hard emission in the X-ray spectrum is less clear. Assuming a non-thermal origin, our best fitting model yields a photon index of ≥2.9 for the power law component which would imply a low compression ratio of ≤1.79 for the shocks responsible for the electron acceleration. However, the hard emission can also be explained by a thermal plasma at a temperature ≥$2 \times 10^7$K. Our VLA data indicate that the radio emission of 9 Sgr was clearly non-thermal at the time of the XMM-Newtonobservation. Again, we derive a low compression ratio (1.7) for the shocks that accelerate the electrons responsible for the synchrotron radio emission. Finally, our optical spectra reveal long-term radial velocity variations suggesting that 9 Sgr could be a long-period spectroscopic binary.

We use an extensive set of spectroscopic observations to reinvestigate the properties of the massive binary HDE 228766. Conventional classification criteria suggest that HDE 228766 consists of an O7 primary and an Of+secondary. However, several spectral features of the secondary, such as the simultaneous presence of N iii, N ivand N vemissions, make it a rather unusual object. We find that the orbital motion of the secondary is probably best described by the radial velocities of the narrow N iiiemission lines. Our orbital solution yields $m_1\,\sin^3{i} = 31.7$and $m_2\,\sin^3{i} = 25.5~M_{\odot}$for the primary and secondary respectively. The He iiλ4542 absorption in the secondary's spectrum appears considerably blue-shifted with respect to the narrow emission lines, indicating that the absorption is probably formed in the accelerating part of the secondary's wind. We use a tomographic technique to investigate the profile variability of the broader emission lines. In addition to a strong emission from the secondary, the Hαline displays a weak emission feature that is probably associated with a wind interaction region located near the surface of the primary star. Finally, our analysis of the spectrum with a non-LTE code indicates that the secondary is an evolved object that exhibits some CNO processed material in its atmosphere and has a large mass loss rate. Assuming a distance of 3.5 kpc (which follows from adopting $M_{V, {\rm s}} = -6$for the secondary) we infer $\dot{M} \simeq 10^{-5}~M_{\odot}$yr-1for the secondary. Our results suggest that HDE 228766 could be in a post-Roche lobe overflow stage. The secondary may be classified as WN8ha and is currently in a transition stage between a “normal” Of star and a WNL-type Wolf-Rayet star.

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newtonobservatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD 93403 reveals a clear orbital modulation of the X-ray luminosity as a function of the orbital phase. Below 1.0 keV, the observed X-ray flux is modulated by the opacity of the primary wind. Above 1.0 keV, the observed variation of the X-ray flux is roughly consistent with a $1/r$dependence expected for an adiabatic colliding wind interaction. HD 93403 appears less overluminuous in X-rays than previously thought and a significant fraction of the total X-ray emission arises probably within the winds of the individual components of the binary. Optical monitoring of the system reveals strong variability of the He iiλ4686 and Hαline profiles. The He iiλ4686 line displays a broad asymmetrical emission component which is found to be significantly stronger between phases 0.80 and 0.15 than around apastron. This suggests that part of the emission arises in the interaction region and most probably in the trailing arm of a shock cone wrapped around the secondary. Some absorption lines of the secondary's spectrum display equivalent width variations reminiscent of the so-called Struve-Sahade effect. The differences in behaviour between individual lines suggest that the temperature may not be the only relevant parameter that controls this effect.

Since the beginning of the past century, the nature of HD 108 has been a subject of intense debate. One after another, astronomers explored its variability and attributed it either to binarity, or to changes in the stellar wind of a single star. In this article, we analyse a 30 year campaign of spectroscopic observations of this star with special emphasis on the last 15 years during which photographic plates have been replaced by CCD detectors. Our investigation of the radial velocities of HD 108 yields no significant short- or long-term period and does not confirm the published periodicities either. Though the radial velocity of HD 108 appears clearly variable, the variations cannot be explained by the orbital motion in a spectroscopic binary. However, our data reveal spectacular changes in the H iBalmer lines and some He iprofiles over the years. These lines continuously evolved from P Cygni profiles to "pure"absorption lines. A similar behaviour has already been observed in the past, suggesting that these changes are recurrent. HD 108 seems to share several characteristics of Oe stars and we discuss different hypotheses for the origin of the observed long-term variations. As we are now in a transition period, a continuous monitoring of HD 108 should be considered for the next few years.

We present the results of a four year spectroscopic campaign on the early-type binary system HD152248. Our analysis yields a new classification as O7.5III(f) + O7III(f), in contradiction with previous classifications of the components as supergiants. We derive improved orbital elements and the corresponding masses ($M_1=29.6 M_{\odot}$and $M_2=29.9 M_{\odot}$) are somewhat larger than previously reported in the literature, although they are still significantly lower than the ones expected from evolutionary tracks. Both components of the system are close to filling their Roche lobe at periastron passage. We also investigate the equivalent width variations of the lines of the two components and we discuss their relation to the Struve-Sahadeeffect. Finally, we show that the line profile variability of the Heiił4686 and Hαlines is consistent with a strong wind interaction between the two stars, quite as predicted by current colliding wind models.

We report the analysis of an extensive set of high-resolution spectroscopic observations of the massive binary system HD 149404. We compare different techniques to measure the radial velocities of the heavily blended absorption lines and we derive a new orbital solution. The absorption lines display strong variability that slightly affects the orbital solution and the determination of the spectral types of the components of the binary. We find that the primary is probably of spectral type O7.5 I(f), while the secondary is most likely an ON9.7 I supergiant. The secondary seems to be the most evolved component of the system and its current evolutionary status could best be explained if the system has undergone a Roche lobe overflow episode during the past. The secondary could actually still be rather close to filling its critical volume and this could lead to an enhanced mass loss of the secondary. The spectrum of HD 149404 displays many emission lines some of which show phase-locked line profile variations. In particular, the Hαline displays a double-peaked morphology at orbital phases near conjunction. We investigate the radial velocity behaviour of the emission lines and we find that some of them must be formed in an interaction region. We propose a simple model where some of the optical emission lines arise in a heavily bended shock region.

We report the analysis of an extensive set of spectroscopic data of the O(f) supergiant HD 192639. A Fourier analysis of our time-series reveals a recurrent variability with a "period"of roughly 4.8 days which is most prominent in the absorption components of the He iiλ4686 and HαP-Cygni profiles. The same periodicity is also detected in the blue wing of several absorption lines (e.g. Hβ). The variations of the absorption components correspond most probably to a cyclical modulation of the amount of stellar wind material along the line of sight towards the star. The 4.8-day period affects also the morphology of the double-peaked He iiλ4686 and Hαemission components, although these emission components display also variations on other (mainly longer) time scales. The most likely explanation for the 4.8-day modulation is that this cycle reflects the stellar rotational period (or half this period). We find that the most important observational properties can be explained -at least qualitatively -by a corotating interaction region or a tilted confined corotating wind.

We present the first high resolution X-ray spectrum of the bright O4Ief supergiant star ζPuppis, obtained with the Reflection Grating Spectrometer on-board XMM-Newton. The spectrum exhibits bright emission lines of hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon, as well as neon-like ions of iron. The lines are all significantly resolved, with characteristic velocity widths of order 1000-1500 km s-1. The nitrogen lines are especially strong, and indicate that the shocked gas in the wind is mixed with CNO-burned material, as has been previously inferred for the atmosphere of this star from ultraviolet spectra. We find that the forbidden to intercombination line ratios within the helium-like triplets are anomalously low for N VI, O VII, and Ne IX. While this is sometimes indicative of high electron density, we show that in this case, it is instead caused by the intense ultraviolet radiation field of the star. We use this interpretation to derive constraints on the location of the X-ray emitting shocks within the wind that are consistent with current theoretical models for this system.

Aims. To better understand the phenomenon of colliding winds in massive binary stars, we study the X-ray lightcurve of a WR+O?system of the Carina region, a system well known for the high mass of its primary.Methods. Phase-resolved X-ray observations of the massive WR+O binary system WR?22 were performed with the XMM-Newton facility. We observed the object at seven different phases from near apastron to near periastron.Results. The X-ray spectrum can be represented by a two-component, optically thin, thermal plasma model with a first one at a typical temperature of 0.6?keV and a second hotter one in the range 2.0?4.5?keV. The hot component is indicative of a colliding wind phenomenon, but its flux is remarkably constant with time despite the high eccentricity of the orbit. Although surprising at first, this actually does not contradict the results of the hydrodynamical simulations of the wind collision that we performed. When the system goes from apastron to periastron, the soft part of the X-ray flux is progressively lowered by an increasing intervening absorbing column. This behaviour can be interpreted in terms of an X-ray emitting plasma located near the O?star, but not fully intrinsic to it, and accompanying the star when it dives into the wind of the WR?component. A model is presented that interprets most of the observational constraints. This model suggests that the mass-loss rate of MWR~ 1.6 ? 10-5? M??yr-1assumed for the WR could still be slightly too high, whereas it is already lower than other published values. From the comparison of the observed and the expected absorptions at phases near periastron, we deduce that the hard X-ray emitting collision zone should at least have a typical size of 50?60?R?, but that the size for the soft X-ray emitting region could reach 244?R?if the assumed mass-loss rate is correct. We also present an upper limit to the X-ray luminosity of the WR?component that further questions the existence of intrinsic X-ray emission from single WN?stars.

Aims. We present a technique to determine the orbital and physical parameters of eclipsing eccentric Wolf-Rayet + O-star binaries, where one eclipse is produced by the absorption of the O-star light by the stellar wind of the W-R?star.Methods. Our method is based on the use of the empirical moments of the light curve that are integral transforms evaluated from the observed light curves. The optical depth along the line of sight and the limb darkening of the W-R?star are modelled by simple mathematical functions, and we derive analytical expressions for the moments of the light curve as a function of the orbital parameters and the key parameters of the transparency and limb-darkening functions. These analytical expressions are then inverted in order to derive the values of the orbital inclination, the stellar radii, the fractional luminosities, and the parameters of the wind transparency and limb-darkening laws.Results. The method is applied to the SMC W-R eclipsing binary HD?5980, a remarkable object that underwent an LBV-like event in August?1994. The analysis refers to the pre-outburst observational data. A synthetic light curve based on the elements derived for the system allows a quality assessment of the results obtained.