References of "Rauw, Grégor"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailOptical spectroscopy of X-Mega targets - IV. CPD-59 degrees 2636: a new O-type multiple system in the Carina Nebula
Albacete Colombo, J. F.; Morrell, N. I.; Rauw, Grégor ULg et al

in Monthly Notices of the Royal Astronomical Society (2002), 336(4), 1099-1108

High-resolution optical spectroscopy of CPD -59degrees2636, one of the O-type stars in the open cluster Trumpler 16 in the Carina Nebula, reveals this object to be a multiple system displaying triple ... [more ▼]

High-resolution optical spectroscopy of CPD -59degrees2636, one of the O-type stars in the open cluster Trumpler 16 in the Carina Nebula, reveals this object to be a multiple system displaying triple lines which we label as components A, B and C of spectral types O7 V, O8 V and O9 V, respectively. From our radial velocity measurements we find that the components A and B form a close binary with a period of 3.6284 d, and we obtain the first circular radial velocity orbit for this system with semi-amplitudes of 184 and 192 km s(-1), leading to minimum masses of 10.1 and 9.7 M-.. We find that the component C is a single lined binary with a period of 5.034 d and semi-amplitude of 48 km s(-1). We also analyse the X-ray radiation from CPD -59degrees2636, finding neither appreciable overluminosity nor phase-related X-ray flux variations. [less ▲]

Detailed reference viewed: 8 (1 ULg)
Full Text
Peer Reviewed
See detailAn XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC 6530
Rauw, Grégor ULg; Nazé, Yaël ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2002), 395(2), 499-513

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very ... [more ▼]

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC6530. 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 M8 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 similar to a few keV. Only a few of the X-ray selected PMS candidates are known to display Halpha emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC6530 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 NGC6530 ( LkHalpha 115) 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. [less ▲]

Detailed reference viewed: 37 (9 ULg)
Full Text
Peer Reviewed
See detailA multi-wavelength investigation of the non-thermal radio emitting O-star 9 Sgr
Rauw, Grégor ULg; Blomme, R.; Waldron, W. L. et al

in Astronomy and Astrophysics (2002), 394(3), 993-1008

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD164794). Our data include observations in the X-ray domain with XMM-Newton, in the radio domain with the VLA as well ... [more ▼]

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD164794). 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 similar to3 x 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 greater than or equal to2.9 for the power law component which would imply a low compression ratio of less than or equal to1.79 for the shocks responsible for the electron acceleration. However, the hard emission can also be explained by a thermal plasma at a temperature greater than or equal to2 x 10(7) K. Our VLA data indicate that the radio emission of 9 Sgr was clearly non-thermal at the time of the XMM-Newton observation. 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. [less ▲]

Detailed reference viewed: 13 (0 ULg)
Full Text
Peer Reviewed
See detailThe evolved early-type binary HDE 228766 revisited
Rauw, Grégor ULg; Crowther, P. A.; Eenens, P. R. J. et al

in Astronomy and Astrophysics (2002), 392(2), 563-574

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 ... [more ▼]

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 IV and N V emissions, 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 III emission lines. Our orbital solution yields m(1) sin(3) i = 31:7 and m(2) sin(3) i = 25:5 M. for the primary and secondary respectively. The He II lambda 4542 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 Halpha line 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,M-s = -6 for the secondary) we infer (M) over dot similar or equal to 10(5) M. yr(-1) for 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 staranda WNL-type Wolf-Rayet star. [less ▲]

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailPhase-resolved X-ray and optical spectroscopy of the massive binary HD 93403
Rauw, Grégor ULg; Vreux, Jean-Marie ULg; Stevens, I. R. et al

in Astronomy and Astrophysics (2002), 388(2), 552-562

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 reveals a clear ... [more ▼]

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 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. HD93403 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 II lambda 4686 and Halpha line profiles. The He II lambda 4686 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. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
See detailOptical Spectroscopy of Colliding-Wind Systems to be Observed with XMM
Sana, H.; Rauw, Grégor ULg; Gosset, Eric ULg et al

in Interacting Winds from Massive Stars (2002)

Not Available

Detailed reference viewed: 6 (0 ULg)
Full Text
See detailSearching for Colliding-Wind Signatures in a Sample of O-Star Binaries
Rauw, Grégor ULg; Sana, H.; Vreux, Jean-Marie ULg et al

in Interacting Winds from Massive Stars (2002)

Not Available

Detailed reference viewed: 2 (0 ULg)
Full Text
See detailLine-Profile Variability in the Massive Binary System HD 149404
Nazé, Yaël ULg; Carrier, Fabien; Rauw, Grégor ULg

in Interacting Winds from Massive Stars (2002)

Not Available

Detailed reference viewed: 8 (0 ULg)
Full Text
Peer Reviewed
See detailA first detailed study of the colliding wind WR+O binary WR 30a
Gosset, Eric ULg; Royer, P.; Rauw, Grégor ULg et al

in Monthly Notices of the Royal Astronomical Society (2001), 327

We present a detailed, extensive investigation of the photometric and spectroscopic behaviour of WR 30a. This star is definitely a binary system with a period around 4.6d. We propose the value P=4.619d ... [more ▼]

We present a detailed, extensive investigation of the photometric and spectroscopic behaviour of WR 30a. This star is definitely a binary system with a period around 4.6d. We propose the value P=4.619d (sigma=0.002d). The identification of the components as WO4+O5((f)) indicates a massive evolved binary system; the O5 component is a main-sequence or, more likely, a giant star. The radial velocities of the O star yield a circular orbit with an amplitude K[SUB]O[/SUB]=29.9 (sigma=2.1)kms[SUP]-1[/SUP] and a mass function of 0.013 (sigma=0.003)M[SUB]solar[/SUB]. The spectrum of WR 30a exhibits strong profile variations of the broad emission lines that are phase-locked with the orbital period. We report the detection of the orbital motion of the WO component with K[SUB]WO[/SUB]=189kms[SUP]-1[/SUP], but this should be confirmed by further observations. If correct, it implies a mass ratio M[SUB]WO[/SUB] /M[SUB]O[/SUB]=0.16. The star exhibits sinusoidal light variations of amplitude 0.024mag peak-to-peak with the minimum of light occurring slightly after the conjunction with the O star in front. On the basis of the phase-locked profile variations of the Civ lambda4658 blend in the spectrum of the WO, we conclude that a wind-wind collision phenomenon is present in the system. We discuss some possibilities for the geometry of the interaction region. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
Peer Reviewed
See detailOptical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205
Morrell, N. I.; Barbá, R. H.; Niemela, V. S. et al

in Monthly Notices of the Royal Astronomical Society (2001), 326

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii ... [more ▼]

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii lambda4686Å (primary component) and Hei lambda4471Å (secondary component) absorption lines yield semi-amplitudes of 133+/-2 and 314+/-2kms[SUP]-1[/SUP] for each binary component, resulting in minimum masses of 31 and 13M[SUB]solar[/SUB] (q=0.42). We also confirm for the binary components the spectral classification of O3V+O8V previously assigned. Assuming for the O8V component a `normal' mass of 22-25M[SUB]solar[/SUB] we would derive for the primary O3V a mass of `only' 52-60M[SUB]solar[/SUB] and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185+/-16yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed. [less ▲]

Detailed reference viewed: 22 (3 ULg)
Full Text
Peer Reviewed
See detailOptical spectroscopy of XMEGA targets in the Carina Nebula - III. The multiple system Tr 16-104 (â ¡CPD -59° 2603)
Rauw, Grégor ULg; Sana, H.; Antokhin, I. I. et al

in Monthly Notices of the Royal Astronomical Society (2001), 326

We discuss the orbital elements of the multiple system Tr 16-104 which is usually believed to be a member of the open cluster Trumpler 16 in the Carina complex. We show that Tr 16-104 could be a ... [more ▼]

We discuss the orbital elements of the multiple system Tr 16-104 which is usually believed to be a member of the open cluster Trumpler 16 in the Carina complex. We show that Tr 16-104 could be a hierarchical triple system consisting of a short-period (2.15d) eclipsing O7V+O9.5V binary bound to a B0.2 IV star. Our preliminary orbital solution of the third body indicates that the B star most probably describes an eccentric orbit with a period of ~285 or ~1341d around the close binary. Folding photometric data from the literature with our new ephemerides, we find that the light curve of the close binary exhibits rather narrow eclipses indicating that the two O stars must be well inside their Roche lobes. Our analysis of the photometric data yields a lower limit on the inclination of the orbit of the close binary of i>=77°. The stellar radii and luminosities of the O7 V and O9.5 V stars are significantly smaller than expected for stars of this spectral type. Our results suggest that Tr 16-104 lies at a distance of the order of 2.5kpc and support a fainter absolute magnitude for zero-age main-sequence O stars than usually adopted. We find that the dynamical configuration of Tr 16-104 corresponds to a hierarchical system that should remain stable provided that it suffers no strong perturbation. Finally, we also report long-term temporal variations of high-velocity interstellar Caii absorptions in the line of sight towards Tr 16-104. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
Peer Reviewed
See detailWhat is the real nature of HD 108?
Nazé, Yaël ULg; Vreux, Jean-Marie ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2001), 372

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 ... [more ▼]

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 I Balmer lines and some He I profiles 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. Based on observations collected at the Observatoire de Haute-Provence (France). [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
Peer Reviewed
See detailHD 152248: Evidence for a colliding wind interaction
Sana, H.; Rauw, Grégor ULg; Gosset, Eric ULg

in Astronomy and Astrophysics (2001), 370

We present the results of a four year spectroscopic campaign on the early-type binary system HD 152248. Our analysis yields a new classification as O7.5III(f) + O7III(f), in contradiction with previous ... [more ▼]

We present the results of a four year spectroscopic campaign on the early-type binary system HD 152248. 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[SUB]sun[/SUB] and M_2=29.9 M[SUB]sun[/SUB]) 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-Sahade effect. Finally, we show that the line profile variability of the He Iil4686 and Halpha lines is consistent with a strong wind interaction between the two stars, quite as predicted by current colliding wind models. Based on data collected at the European Southern Observatory (La Silla, Chile) and at the Cerro Tololo Inter-American Observatory (Cerro Tololo, Chile). [less ▲]

Detailed reference viewed: 3 (0 ULg)
Full Text
Peer Reviewed
See detailThe strange case of the massive binary HD 149404
Rauw, Grégor ULg; Nazé, Yaël ULg; Carrier, F. et al

in Astronomy and Astrophysics (2001), 368

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 ... [more ▼]

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 Halpha line 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. Based on observations collected at the European Southern Observatory (La Silla, Chile) and at the Cerro Tololo Inter-American Observatory (CTIO). [less ▲]

Detailed reference viewed: 35 (5 ULg)
Full Text
Peer Reviewed
See detailThe spectral variability of HD 192639 and its implications for the star's wind structure
Rauw, Grégor ULg; Morrison, N. D.; Vreux, Jean-Marie ULg et al

in Astronomy and Astrophysics (2001), 366

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 ... [more ▼]

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 {ii}\ lambda 4686 and Halpha P-Cygni profiles. The same periodicity is also detected in the blue wing of several absorption lines (e.g. Hbeta ). 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 {ii}\ lambda 4686 and Halpha emission 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. Based on observations collected at the Observatoire de Haute Provence, France and the Ritter Observatory, Toledo, USA. [less ▲]

Detailed reference viewed: 7 (0 ULg)
Full Text
Peer Reviewed
See detailHigh resolution X-ray spectroscopy of zeta Puppis with the XMM-Newton reflection grating spectrometer
Kahn, S. M.; Leutenegger, M. A.; Cottam, J. et al

in Astronomy and Astrophysics (2001), 365

We present the first high resolution X-ray spectrum of the bright O4Ief supergiant star zeta Puppis, obtained with the Reflection Grating Spectrometer on-board XMM-Newton. The spectrum exhibits bright ... [more ▼]

We present the first high resolution X-ray spectrum of the bright O4Ief supergiant star zeta Puppis, 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[SUP]-1[/SUP]. 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. [less ▲]

Detailed reference viewed: 29 (3 ULg)
Full Text
See detailCorrection of Systematic Errors in Differential Photometry
Manfroid, Jean ULg; Royer, P.; Rauw, Grégor ULg et al

in Astronomical Data Analysis Software and Systems X (2001)

A common cause of errors in CCD differential photometry is an improper calibration of the array. The importance of these errors is evaluated for different cameras with fields between 3 and 30 arcminutes ... [more ▼]

A common cause of errors in CCD differential photometry is an improper calibration of the array. The importance of these errors is evaluated for different cameras with fields between 3 and 30 arcminutes. The usual superflat illumination corrections based on night sky exposures are often found to be unsatisfactory. ``Photometric superflats'' based on stellar measurements are more reliable and should be used instead. [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
Peer Reviewed
See detailCoordinated monitoring of the eccentric O-star binary Iota Orionis: the X-ray analysis
Pittard, Julian M; Stevens, Ian R; Corcoran, Michael F et al

in Monthly Notices of the Royal Astronomical Society (2000), 319

We analyse two ASCA observations of the highly eccentric O9 III+B1 III binary Iota Orionis obtained at periastron and apastron. Based on the assumption of a strong colliding-wind shock between the stellar ... [more ▼]

We analyse two ASCA observations of the highly eccentric O9 III+B1 III binary Iota Orionis obtained at periastron and apastron. Based on the assumption of a strong colliding-wind shock between the stellar components, we expected to see significant variation in the X-ray emission between these phases. The observations proved otherwise: the X-ray luminosities and spectral distributions were remarkably similar. The only noteworthy feature in the X-ray data was the hint of a proximity effect during periastron passage. Although this `flare' is of relatively low significance, it is supported by the notable proximity effects seen in the optical, and the phasing of the X-ray and optical events is in very good agreement. However, other interpretations are also possible. In view of the degradation of the SIS instrument and source contamination in the GIS data we discuss the accuracy of these results, and also analyse archival ROSAT observations. We investigate why we do not see a clear colliding-wind signature. A simple model shows that the wind attenuation to the expected position of the shock apex is negligible throughout the orbit, which poses the puzzling question of why the expected 1/D variation (i.e. a factor of 7.5) in the intrinsic luminosity is not seen in the data. Two scenarios are proposed: either the colliding-wind emission is unexpectedly weak such that intrinsic shocks in the winds dominate the emission, or, alternatively, the emission observed is colliding-wind emission but in a more complex form than we would naively expect. Complex hydrodynamical models are then analysed. Despite strongly phase-variable emission from the models, both are consistent with the observations. We find that if the mass-loss rates of the stars are low then intrinsic wind shocks could dominate the emission. However, when we assume higher mass-loss rates of the stars, we find that the observed emission could also be consistent with a purely colliding-wind origin. A summary of the strengths and weaknesses of each interpretation is presented. To distinguish between the different models X-ray observations with improved phase coverage will be necessary. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
Peer Reviewed
See detailCompact star clusters of the LMC H ii region N11 C
Heydari-Malayeri, Mohammad; Royer, Pierre; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2000), 361

Based on imaging and spectroscopy obtained at the ESO NTT telescope and using an efficient image analysis algorithm, we study the core of the LMC OB association LH 13, particularly the two compact stellar ... [more ▼]

Based on imaging and spectroscopy obtained at the ESO NTT telescope and using an efficient image analysis algorithm, we study the core of the LMC OB association LH 13, particularly the two compact stellar clusters Sk-66[SUP]deg[/SUP]41, and HNT in the H ii, region N 11C. We resolve Sk-66[SUP]deg[/SUP]41, into 15 components and for the first time the HNT cluster into 70 stars, and derive photometry for the members. Moreover, from medium resolution spectroscopy we determine the spectral types for sixteen stars in N 11C. We compare the color-magnitude diagrams of the clusters with that of the field stars and discuss the cluster ages. With an age of ~ ,100 Myr, the HNT cluster appears significantly older than the very young (<= 5 Myr) Sk-66[SUP]deg[/SUP]41, starburst. We suggest that most of the `field' O-stars in the core of N 11C have actually been ejected from Sk-66[SUP]deg[/SUP]41, through dynamical interactions in the compact cluster. The properties of the Sk-66[SUP]deg[/SUP]41, and HNT clusters suggest that we are viewing different star formation regions lying at different distances along the same line of sight. Based on observations obtained at the European Southern Observatory, La Silla, Chile [less ▲]

Detailed reference viewed: 17 (0 ULg)
Full Text
Peer Reviewed
See detailCoordinated monitoring of the eccentric O-star binary Iota Orionis: optical spectroscopy and photometry
Marchenko, Sergey V; Rauw, Grégor ULg; Antokhina, Eleonora A et al

in Monthly Notices of the Royal Astronomical Society (2000), 317

With the objective of investigating the wind-wind collision phenomenon and supporting contemporaneous X-ray observations, we have organized a large-scale, coordinated optical monitoring campaign of the ... [more ▼]

With the objective of investigating the wind-wind collision phenomenon and supporting contemporaneous X-ray observations, we have organized a large-scale, coordinated optical monitoring campaign of the massive, highly eccentric O9III+B1III binary Iota Orionis. Successfully separating the spectra of the components, we refine the orbital elements and confirm the rapid apsidal motion in the system. We also see strong interaction between the components during periastron passage and detect phase-locked variability in the spectrum of the secondary star. However, we find no unambiguous signs of the bow shock crashing on the surface of the secondary, despite the predictions of hydrodynamic simulations. Combining all available photometric data, we find rapid, phase-locked variations and model them numerically, thus restricting the orbital inclination to 50°<~i<~70°. [less ▲]

Detailed reference viewed: 16 (0 ULg)