References of "Rauw, Grégor"
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See detailAn XMM-Newton view of the M 17 nebula
Mernier, François ULg; Rauw, Grégor ULg

in New Astronomy (2013), 20

We present the analysis of an XMM-Newton observation of the M 17 nebula. The X-ray point source population consists of massive O-type stars and a population of probable low-mass pre-main sequence stars ... [more ▼]

We present the analysis of an XMM-Newton observation of the M 17 nebula. The X-ray point source population consists of massive O-type stars and a population of probable low-mass pre-main sequence stars. CEN 1a,b and OI 352, the X-ray brightest O-type stars in M 17, display hard spectra (kT of 3.8 and 2.6 keV) consistent with a colliding wind origin in binary/multiple systems. We show that the strong interstellar reddening towards the O-type stars of M 17 yields huge uncertainties on their L[SUB]X[/SUB]/L[SUB]bol[/SUB] values. The low-mass pre-main sequence stars exhibit hard spectra resulting from a combination of high plasma temperatures and very large interstellar absorption. We find evidence for considerable long term (months to years) variability of these sources. M 17 is one of the few star formation complexes in our Galaxy producing diffuse X-ray emission. We analyze the spectrum of this emission and compare it with previous studies. Finally, we discuss the Optical Monitor UV data obtained simultaneously with the X-ray images. We find very little correspondence between the UV and X-ray sources, indicating that the majority of the UV sources are foreground stars, whilst the bulk of the X-ray sources are deeply embedded in the M 17 complex. [less ▲]

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See detailSpectral modelling of massive binary systems
Palate, Matthieu ULg; Rauw, Grégor ULg; Koenigsberger, Gloria et al

in Astronomy and Astrophysics (2013), 552

Context. The spectra of massive binaries may be affected by interactions between the stars in the system. These are believed to produce observational phenomena such as the Struve-Sahade effect. Aims: We ... [more ▼]

Context. The spectra of massive binaries may be affected by interactions between the stars in the system. These are believed to produce observational phenomena such as the Struve-Sahade effect. Aims: We simulate the spectra of massive binaries at different phases of the orbital cycle, accounting for the gravitational influence of the companion star on the shape and physical properties of the stellar surface. Methods: We used the Roche potential modified to account for radiation pressure to compute the stellar surface of close circular systems. We furthermore used the tidal interactions with dissipation of energy through shear code for surface computations of eccentric systems. In both cases, we accounted for gravity darkening and mutual heating generated by irradiation to compute the surface temperature. We then interpolated non-local thermodynamic equilibrium (NLTE) plane-parallel atmosphere model spectra in a grid to obtain the local spectrum at each surface point. We finally summed all contributions, accounting for the Doppler shift, limb-darkening, and visibility to obtain the total synthetic spectrum. We computed different orbital phases and different sets of physical and orbital parameters. Results: Our models predict line strength variations through the orbital cycle, but fail to completely reproduce the Struve-Sahade effect. Including radiation pressure allows us to reproduce a surface temperature distribution that is consistent with observations of semi-detached binary systems. Conclusions: Radiation pressure effects on the stellar surface are weak in (over)contact binaries and well-detached systems but can become very significant in semi-detached systems. The classical von Zeipel theorem is sufficient for the spectral computation. Broad-band light curves derived from the spectral computation are different from those computed with a model in which the stellar surfaces are equipotentials of the Roche potential scaled by the instantaneous orbital separation. In many cases, the fit of two Gaussian/Lorentzian profiles fails to properly measure the equivalent width of the lines and leads to apparent variations that could explain some of the effects reported in the literature. [less ▲]

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See detailA detailed X-ray investigation of ζ Puppis. III. Spectral analysis of the whole RGS spectrum
Hervé, Anthony ULg; Rauw, Grégor ULg; Nazé, Yaël ULg

in Astronomy and Astrophysics (2013), 551

Context. ζ Pup is the X-ray brightest O-type star of the sky. This object was regularly observed with the RGS instrument onboard XMM-Newton for calibration purposes, which led to an unprecedented set of ... [more ▼]

Context. ζ Pup is the X-ray brightest O-type star of the sky. This object was regularly observed with the RGS instrument onboard XMM-Newton for calibration purposes, which led to an unprecedented set of high-quality spectra. <BR /> Aims: We have previously reduced and extracted this data set and integrated it into the most detailed high-resolution X-ray spectrum of any early-type star so far. Here we present the analysis of this spectrum, taking into account for the presence of structures in the stellar wind. <BR /> Methods: For this purpose, we used our new modeling tool that allows fitting the entire spectrum with a multi-temperature plasma. We illustrate the impact of a proper treatment of the radial dependence of the X-ray opacity of the cool wind on the best-fit radial distribution of the temperature of the X-ray plasma. <BR /> Results: The best-fit of the RGS spectrum of ζ Pup is obtained assuming no porosity. Four plasma components at temperatures between 0.10 and 0.69 keV are needed to adequately represent the observed spectrum. Whilst the hardest emission is concentrated between ~3 and 4 R[SUB]∗[/SUB], the softer emission starts already at 1.5 R[SUB]∗[/SUB] and extends to the outer regions of the wind. <BR /> Conclusions: The inferred radial distribution of the plasma temperatures agrees rather well with theoretical expectations. The mass-loss rate and CNO abundances corresponding to our best-fit model also agree quite well with the results of recent studies of ζ Pup in the UV and optical domain. Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). [less ▲]

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See detailInteracting winds in massive binaries
Rauw, Grégor ULg

in Pavlovski, Kresimir; Tkachenko, Andrew; Torres, Guillermo (Eds.) EAS Publications Series (2013, February 01)

Massive stars feature highly energetic stellar winds that interact whenever two such stars are bound in a binary system. The signatures of these interactions are nowadays found over a wide range of ... [more ▼]

Massive stars feature highly energetic stellar winds that interact whenever two such stars are bound in a binary system. The signatures of these interactions are nowadays found over a wide range of wavelengths, including the radio domain, the optical band, as well as X-rays and even γ-rays. A proper understanding of these effects is thus important to derive the fundamental parameters of the components of massive binaries from spectroscopic and photometric observations. [less ▲]

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See detailX-ray emission of interacting wind binaries in Cyg OB2
Nazé, Yaël ULg; Cazorla, Constantin ULg; Rauw, Grégor ULg

in EAS Publications Series (2013, February 01)

Cyg OB2 #5, #8A, and #9 are binary or multiple massive stars in the Cyg OB2 association displaying several peculiarities, such as bright X-ray emission and non-thermal radio emission. Our X-ray monitoring ... [more ▼]

Cyg OB2 #5, #8A, and #9 are binary or multiple massive stars in the Cyg OB2 association displaying several peculiarities, such as bright X-ray emission and non-thermal radio emission. Our X-ray monitoring of these stars reveals the details of their behaviours at high energies, which can be directly linked to wind-wind collisions (WWCs). In addition, the X-ray emission of Cyg OB2 #12, an evolved massive star, shows a long-term decrease, which could hint at the presence of a companion (with associated colliding winds) or indicate the return to quiescence of the star following a recent eruption. [less ▲]

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See detailX-Ray Plasma Temperature Distribution in the Wind of ζ Puppis
Hervé, Anthony ULg; Rauw, Grégor ULg; Nazé, Yaël ULg

in Astronomical Society of the Pacific Conference Series (2013, January 01)

Different scenarios try to explain the X-ray production in the O-type star wind (magnetic confinement, embedded shocks…) and their plasma temperature distribution. In this context, we have developed a new ... [more ▼]

Different scenarios try to explain the X-ray production in the O-type star wind (magnetic confinement, embedded shocks…) and their plasma temperature distribution. In this context, we have developed a new modeling code which computes synthetic spectra as a function of plasma temperature, abundances, and localization of the X-ray emitting shell in the wind. Then we combine several synthetic spectra in order to fit the observed high-resolution spectra. Our preliminary results on ζ Puppis reveal a non-porous wind as well as non-solar abundances for the CNO elements. More important, an extended region with a low temperature plasma begins to emit close to the star surface while small shells with hotter temperature plasmas emit farther in the wind. [less ▲]

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See detailCoRoT Observations of O Stars: Diverse Origins of Variability
Blomme, R.; Briquet, Maryline ULg; Degroote, P. et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these ... [more ▼]

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these stars (HD 46202 and the binaries HD 46149 and Plaskett's star). These cover both opacity-driven modes and solar-like stochastic oscillations, both of importance to the asteroseismological modeling of O stars. Additional effects can be seen in the CoRoT light curves, such as binarity and rotational modulation. Some of the hottest O-type stars (HD 46223, HD 46150 and HD 46966) are dominated by the presence of red-noise: we speculate that this is related to a sub-surface convection zone. [less ▲]

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See detail2009: A Colliding-Wind Odyssey
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

We present the results from two optical spectroscopic campaigns on colliding-wind binaries (CWB) which both occurred in 2009. The first one was on WR 140 (WC7pd + O5.5fc), the archetype of CWB, which ... [more ▼]

We present the results from two optical spectroscopic campaigns on colliding-wind binaries (CWB) which both occurred in 2009. The first one was on WR 140 (WC7pd + O5.5fc), the archetype of CWB, which experienced periastron passage of its highly elliptical 8-year orbit in January. The WR 140 campaign consisted of a unique and constructive collaboration between amateur and professional astronomers and took place at half a dozen locations, including Teide Observatory, Observatoire de Haute Provence, Dominion Astrophysical Observatory, Observatoire du Mont-Mégantic and at several small private observatories. The second campaign was on a selection of 5 short-period WR + O binaries not yet studied for colliding-wind effects: WR 12 (WN8h), WR 21 (WN5o + O7 V), WR 30 (WC6 + O7.5 V), WR 31 (WN4o + O8), and WR 47 (WN6o + O5). The campaign took place at Leoncito Observatory, Argentina, during 1 month. We provide updated values of most of these systems for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates and colliding wind geometry. [less ▲]

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See detailNew INTEGRAL Observations of η Carinae Close to Periastron
Leyder, J.-C.; Walter, R.; Rauw, Grégor ULg

in Astronomical Society of the Pacific Conference Series (2013, January 01)

The soft X-ray thermal emission of η Carinae varies strongly around the periastron, following the orbital period of 5.5 yr. We studied the hard X-ray non-thermal emission of η Car using new INTEGRAL ... [more ▼]

The soft X-ray thermal emission of η Carinae varies strongly around the periastron, following the orbital period of 5.5 yr. We studied the hard X-ray non-thermal emission of η Car using new INTEGRAL observations taken close to periastron. We showed that the hard X-ray emission is very likely to be associated with η Car, and not with any other source found within the INTEGRAL error circle. We also showed that the 3-σ detection during the soft X-ray minimum is consistent with a hydrogen column density that does not exceed 6×10[SUP]23[/SUP] cm[SUP]-2[/SUP]. [less ▲]

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See detailDiscovery of a magnetic field in the rapidly rotating O-type secondary of the colliding-wind binary HD 47129 (Plaskett's star)
Grunhut, J. H.; Wade, G. A.; Leutenegger, M. et al

in Monthly Notices of the Royal Astronomical Society (2013), 428

We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context ... [more ▼]

We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Télescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 ± 150 and +680 ± 190 G, implying a minimum surface dipole polar strength of 2850 ± 500 G. In contrast, we derive an upper limit (3σ) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study. [less ▲]

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See detailSpectral Modelling of Massive Binary Systems: The Example of LZ Cep
Palate, Matthieu ULg; Rauw, Grégor ULg; Mahy, Laurent ULg

in Central European astrophysical bulletin (2013)

Despite their importance for many astrophysical processes, massive stars are still not fully understood. Massive binaries offer an attractive way to improve our knowledge of the fundamental properties of ... [more ▼]

Despite their importance for many astrophysical processes, massive stars are still not fully understood. Massive binaries offer an attractive way to improve our knowledge of the fundamental properties of these objects. However, some secondary effects are known to generate variations in the spectra of massive binaries, rendering their analyses more difficult. We present here a new approach to the computation of synthetic spectra of massive binaries at different phases of their orbital cycle. Our model starts with the Roche potential modified by radiation pressure and accounts for the influence of the companion star on the shape and physical properties of the stellar surface. We further account for gravity darkening and reflection effects to compute the surface temperature. Once the local gravity and temperature are determined, we interpolate in a grid of NLTE plan-parallel atmosphere model spectra to obtain the local contribution to the spectrum at each surface points. Then we sum all the contributions, accounting for the Doppler shift, and limb-darkening to obtain the total spectrum. The computation is repeated for different orbital phases and can be compared to the observations to determine the best parameters. We illustrate our method through the example of the LZ Cep system (O9III + ON9.7V). [less ▲]

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See detailA spectroscopic investigation of the O-type star population in four Cygnus OB associations. I. Determination of the binary fraction
Mahy, L.; Rauw, Grégor ULg; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2013), 550

Establishing the multiplicity of O-type stars is the first step towards accurately determining their stellar parameters. Moreover, the distribution of the orbital parameters provides observational clues ... [more ▼]

Establishing the multiplicity of O-type stars is the first step towards accurately determining their stellar parameters. Moreover, the distribution of the orbital parameters provides observational clues to the way that O-type stars form and to the interactions during their evolution. Our objective is to constrain the multiplicity of a sample of O-type stars belonging to poorly investigated OB associations in the Cygnus complex and for the first time to provide orbital parameters for binaries identified in our sample. Such information is relevant to addressing the issue of the binarity in the context of O-type star formation scenarios. We performed a long-term pectroscopic survey of nineteen O-type stars. We searched for radial velocity variations to unveil binaries on timescales from a few days up to a few years, on the basis of a large set of optical spectra. We confirm the binarity for four objects: HD193443, HD228989, HD229234 and HD194649. We derive for the first time the orbital solutions of three systems, and we confirm the values of the fourth, showing that these four systems all have orbital periods shorter than 10 days. Besides these results, we also detect several objects that show non-periodic line profile variations in some of their spectral lines. These variations mainly occur in the spectral lines, that are generally affected by the stellar wind and are not likely to be related to binarity. The minimal binary fraction in our sample is estimated to be 21%, but it varies from one OB association to the next. Indeed, 3 O stars of our sample out of 9 (33%) belonging to CygOB1 are binary systems, 0% (0 out of 4) in CygOB3, 0% (0 out of 3) in CygOB8, and 33% (1 out of 3) in CygOB9. Our spectroscopic investigation also stresses the absence of long-period systems among the stars in our sample. This result contrasts with the case of the O-type stellar population in NGC 2244 among which no object showed radial velocity variations on short timescales. However, we show that it is probably an effect of the sample and that this difference does not a priori suggest a somewhat different star forming process in these two environments. [less ▲]

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See detailORIGIN: metal creation and evolution from the cosmic dawn
den Herder, Jan-Willem; Piro, Luigi; Ohashi, Takaya et al

in Experimental Astronomy (2012), 34

ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to ... [more ▼]

ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z = 10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts ( z ˜0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/cm[SUP]2[/SUP]/s in 10 s in the 5-150 keV band) to identify and localize 2000 GRBs over a five year mission, of which ˜65 GRBs have a redshift >7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5 eV, a field of view of 30 arcmin and large effective area below 1 keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit. [less ▲]

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See detailThe nature of the high Galactic latitude O-star HD 93521: new results from X-ray and optical spectroscopy
Rauw, Grégor ULg; Morel, Thierry ULg; Palate, Matthieu ULg

in Astronomy and Astrophysics (2012), 546

Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. <BR /> Aims: We have collected X-ray and optical observations ... [more ▼]

Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. <BR /> Aims: We have collected X-ray and optical observations to characterize the star and its surroundings. <BR /> Methods: X-ray images and spectra are analysed to search for traces of a recent star formation event around HD 93521 and to search for the signature of a possible compact companion. Optical echelle spectra are analysed with plane-parallel model atmosphere codes, assuming either a spherical star or a gravity darkened rotationally flattened star, to infer the effective temperature and surface gravity, and to derive the He, C, N and O abundances of HD 93521. <BR /> Results: The X-ray images reveal no traces of a population of young low-mass stars coeval with HD 93521. The X-ray spectrum of HD 93521 is consistent with a normal late O-type star although with subsolar metallicity. No trace of a compact companion is found in the X-ray data. In the optical spectrum, He and N are found to be overabundant, in line with the effect of rotational mixing in this very fast rotator, whilst C and O are subsolar. A critical comparison with the properties of subdwarf OB stars, indicates that, despite some apparent similarities, HD 93521 does not belong to this category. <BR /> Conclusions: Despite some ambiguities on the runaway status of the star, the most likely explanation is that HD 93521 is a Population I massive O-type star that was ejected from the Galactic plane either through dynamical interactions or a result of a supernova event in a binary system. Based on observations collected at the Observatoire de Haute Provence (France) and with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA).Hα images are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A77">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A77</A> [less ▲]

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See detailThe x-ray microcalorimeter spectrometer onboard Athena
den Herder, J. W.; Bagnali, D.; Bandler, S. et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2012, September 01)

One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter ... [more ▼]

One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena. In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given. [less ▲]

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See detailMagnetometry of a sample of massive stars in Carina
Nazé, Yaël ULg; Bagnulo, Stefano; Petit, Véronique et al

in Monthly Notices of the Royal Astronomical Society (2012), 423

X-ray surveys of the Carina nebula have revealed a few hard and luminous sources associated with early-type stars. Such unusual characteristics for the high-energy emission may be related to magnetically ... [more ▼]

X-ray surveys of the Carina nebula have revealed a few hard and luminous sources associated with early-type stars. Such unusual characteristics for the high-energy emission may be related to magnetically confined winds. To search for the presence of magnetic fields in these objects, we performed a limited spectropolarimetric survey using the Focal reducer and low dispersion spectrograph (FORS) instrument. The multi-object mode was used, so that a total of 21 OB stars could be investigated during a one-night-long run. A magnetic field was detected in two objects of the sample, with a 6σ significance: Tr16-22 and 13. Such a detection was expected for Tr16-22, as its X-ray emission is too bright, variable and hard, compared to other late-type O or O+OB systems. It is more surprising for Tr16-13, a poorly known star which so far has never shown any peculiar characteristics. Subsequent monitoring is now needed to ascertain the physical properties of these objects and enable a full modelling of their magnetic atmospheres and winds. Based on data collected at ESO under Program ID 386.D-0624A. [less ▲]

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See detail9 Sagittarii: uncovering an O-type spectroscopic binary with an 8.6 year period
Rauw, Grégor ULg; Sana, H.; Spano, M. et al

in Astronomy and Astrophysics (2012), 542

Context. The O-type object 9 Sgr is a well-known synchrotron radio emitter. This feature is usually attributed to colliding-wind binary systems, but 9 Sgr was long considered a single star. <BR /> Aims ... [more ▼]

Context. The O-type object 9 Sgr is a well-known synchrotron radio emitter. This feature is usually attributed to colliding-wind binary systems, but 9 Sgr was long considered a single star. <BR /> Aims: We have conducted a long-term spectroscopic monitoring of this star to investigate its multiplicity and search for evidence for wind-wind interactions. <BR /> Methods: Radial velocities are determined and analysed using various period search methods. Spectral disentangling is applied to separate the spectra of the components of the binary system. <BR /> Results: We derive the first ever orbital solution of 9 Sgr. The system is found to consist of an O3.5 V((f[SUP]+[/SUP])) primary and an O5-5.5 V((f)) secondary moving around each other on a highly eccentric (e = 0.7), 8.6 year orbit. The spectra reveal no variable emission lines that could be formed in the wind interaction zone in agreement with the expected properties of the interaction in such a wide system. <BR /> Conclusions: Our results provide further support to the paradigm of synchrotron radio emission from early-type stars being a manifestation of interacting winds in a binary system. Based on observations collected at the European Southern Observatory (La Silla, Chile and Cerro Paranal, Chile) and the San Pedro Mártir observatory (Mexico).Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>The reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A95">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A95</A> [less ▲]

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See detailThe Struve-Sahade effect in the optical spectra of O-type binaries. I. Main-sequence systems (Corrigendum)
Linder, N.; Rauw, Grégor ULg; Sana, H. et al

in Astronomy and Astrophysics (2012), 541

Not Available.

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See detailGlobal Modeling of X-Ray Spectra Produced in O-type Star Winds
Hervé, Anthony ULg; Rauw, Grégor ULg; Nazé, Yaël ULg et al

in Astrophysical Journal (2012), 748

High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds ... [more ▼]

High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds, optically thick clumps, or an overall reduction of the mass-loss rates. The latter has a strong impact on the evolution of the star. Our final goal is to analyze high-resolution X-ray spectra of O-type stars with a multi-temperature plasma model in order to determine crucial stellar and wind parameters such as the mass-loss rate, the CNO abundances, and the X-ray temperature plasma distribution in the wind. In this context we are developing a modeling tool to calculate synthetic X-ray spectra. We present here the main ingredients and physics necessary for such a work. Our code uses the most recent version of the AtomDB emissivities to compute the intrinsic emissivity of the hot plasma as well as the CMFGEN model atmosphere code to evaluate the opacity of the cool wind. Following the comparison between two formalisms of stellar wind fragmentation, we introduce, for the first time in X-rays, the effects of a tenuous inter-clump medium. We then explore the quantitative impact of different model parameters on the X-ray spectra such as the position in the wind of the X-ray emitting plasma. For the first time, we also show that the two formalisms of stellar wind fragmentation yield different results, although the differences for individual lines are small and can probably not be tested with the current generation of X-ray telescopes. As an illustration of our method, we compare various synthetic line profiles to the observed O VIII λ18.97 line in the spectrum of ζ Puppis. We illustrate how different combinations of parameters can actually lead to the same morphology of a single line, underlining the need to analyze the whole spectrum in a consistent way when attempting to constrain the parameters of the wind. [less ▲]

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See detailDivision IV / Working Group on Massive Stars
Puls, Joachim; Leitherer, Claus; Owocki, Stan et al

in Transactions of the International Astronomical Union, Series B (2012), 28

Our Working Group (WG) studies massive, luminous stars, both individually and in resolved and unresolved populations, with historical focus on early-type (OB) stars, A-supergiants, and Wolf-Rayet stars ... [more ▼]

Our Working Group (WG) studies massive, luminous stars, both individually and in resolved and unresolved populations, with historical focus on early-type (OB) stars, A-supergiants, and Wolf-Rayet stars. Our group also studies lower mass stars (e.g., central stars of planetary nebulae and their winds) which display features similar or related to those present in massive stars, and thus may improve our understanding of the physical processes occurring in massive stars. In recent years, massive red supergiants that evolve from hot stars have been included into our activities as well. We emphasize the role of massive stars in other branches of astrophysics, particularly regarding the First Stars, long duration Gamma-Ray bursts, formation of massive stars and their feedback on star formation in general, pulsations of massive stars, and starburst galaxies. [less ▲]

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