References of "Rauw, Grégor"
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See detailTime series of high-resolution spectra of SN 2014J observed with the TIGRE telescope
Jack, D.; Mittag, M.; Schröder, K.-P. et al

in Monthly Notices of the Royal Astronomical Society (2015), 451

We present a time series of high-resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS échelle spectrograph installed at the ... [more ▼]

We present a time series of high-resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS échelle spectrograph installed at the 1.2-m TIGRE telescope. We present a series of 33 spectra with a resolution of R ≈ 20 000, which covers the important bright phases in the evolution of SN 2014J during the period from 2014 January 24 to April 1. The spectral evolution of SN 2014J is derived empirically. The expansion velocities of the Si II P-Cygni features were measured and show the expected decreasing behaviour, beginning with a high velocity of 14 000 km s[SUP]-1[/SUP] on January 24. The Ca II infrared triplet feature shows a high-velocity component with expansion velocities of >20 000 km s[SUP]-1[/SUP] during the early evolution apart from the normal component showing similar velocities as Si II. Further broad P-Cygni profiles are exhibited by the principal lines of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very sharp Na I D doublet absorption components. Our analysis suggests interesting substructures in the interstellar medium of the host galaxy M82, as well as in our Milky Way, confirming other work on this SN. We were able to identify the interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 Å as well as K I at 7664 and 7698 Å. Furthermore, we confirm several diffuse interstellar bands, at wavelengths of 6196, 6283, 6376, 6379and 6613 Å and give their measured equivalent widths. [less ▲]

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See detailThe Herschel view of the nebula around the luminous blue variable star AG Carinae
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

in Astronomy and Astrophysics (2015), 578

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter ... [more ▼]

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter. In the infrared light, the nebula appears as a clumpy ring shell that extends up to 1.2 pc with an inner radius of 0.4 pc. It coincides with the Halpha nebula, but extends further out. Dust modeling of the nebula was performed and indicates the presence of large grains. The dust mass is estimated to be ~ 0.2 Msun. The infrared spectrum of the nebula consists of forbidden emission lines over a dust continuum. Apart from ionized gas, these lines also indicate the existence of neutral gas in a photodissociation region that surrounds the ionized region. The abundance ratios point towards enrichment by processed material. The total mass of the nebula ejected from the central star amounts to ~ 15 Msun, assuming a dust-to-gas ratio typical of LBVs. The abundances and the mass-loss rate were used to constrain the evolutionary path of the central star and the epoch at which the nebula was ejected, with the help of available evolutionary models. This suggests an ejection during a cool LBV phase for a star of ~ 55 Msun with little rotation. [less ▲]

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See detailA spectroscopic investigation of the O-type star population in four Cygnus OB associations. II. Determination of the fundamental parameters
Mahy, Laurent ULg; Rauw, Grégor ULg; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2015), 577

Aims: Having established the binary status of nineteen O-type stars located in four Cygnus OB associations, we now determine their fundamental parameters to constrain their properties and their ... [more ▼]

Aims: Having established the binary status of nineteen O-type stars located in four Cygnus OB associations, we now determine their fundamental parameters to constrain their properties and their evolutionary status. We also investigate their surface nitrogen abundances, which we compare with other results from the literature obtained for galactic O-type stars. Methods: Using optical spectra collected for each object in our sample and some UV data from the archives, we apply the CMFGEN atmosphere code to determine their main properties. For the binary systems, we have disentangled the components to obtain their individual spectra and investigate them as if they were single stars. Results: We find that the distances of several presumably single O-type stars seem poorly constrained because their luminosities are not in agreement with the "standard" luminosities of stars with similar spectral types. The ages of these O-type stars are all less than 7 Myr. Therefore, the ages of these stars agree with those, quoted in the literature, of the four associations, except for Cyg OB8 for which the stars seem older than the association itself. However, we point out that the distance of certain stars is debatable relative to values found in the literature. The N content of these stars put in perspective with N contents of several other galactic O-type stars seems to draw the same five groups as found in the "Hunter" diagram for the O and B-type stars in the LMC even though their locations are obviously different. We determine mass-loss rates for several objects from the Halpha line and UV spectra. Finally, we confirm the "mass discrepancy" especially for O stars with masses smaller than 30 Msun;. [less ▲]

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See detailSpectroscopic variability of two Oe stars
Rauw, Grégor ULg; Morel, Thierry ULg; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2015), 575

Context. The two Oe stars HD 45 314 and HD 60 848 have recently been found to exhibit very different X-ray properties: whilst HD 60 848 has an X-ray spectrum and the emission level typical of most OB ... [more ▼]

Context. The two Oe stars HD 45 314 and HD 60 848 have recently been found to exhibit very different X-ray properties: whilst HD 60 848 has an X-ray spectrum and the emission level typical of most OB stars, HD 45 314 features a much harder and brighter X-ray emission, making it a so-called γ Cas analogue. Aims: Monitoring the optical spectra could provide hints towards the origin of these very different behaviours. Methods: We analyse a large set of spectroscopic observations of HD 45 314 and HD 60 848, extending over 20 years. We further attempt to fit the Hα line profiles of both stars with a simple model of emission line formation in a Keplerian disk. Results: Strong variations in the strengths of the Hα, Hβ, and He i λ 5876 emission lines are observed for both stars. In the case of HD 60 848, we find a time lag between the variations in the equivalent widths of these lines, which is currently not understood. The emission lines are double peaked with nearly identical strengths of the violet and red peaks. The Hα profile of this star can be successfully reproduced by our model of a disk seen under an inclination of 30°. In the case of HD 45 314, the emission lines are highly asymmetric and display strong line profile variations. We find a major change in behaviour between the 2002 outburst and the one observed in 2013. This concerns both the relationship between the equivalent widths of the various lines and their morphologies at maximum strength (double-peaked in 2002 versus single-peaked in 2013). Our simple disk model fails to reproduce the observed Hα line profiles of HD 45 314. Conclusions: Our results further support the interpretation that Oe stars do have decretion disks similar to those of Be stars. Whilst the emission lines of HD 60 848 are explained well by a disk with a Keplerian velocity field, the disk of HD 45 314 seems to have a significantly more complex velocity field that could be another signature of the phenomenon that produces its peculiar X-ray emission. [less ▲]

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See detailSearch for magnetic fields in particle-accelerating colliding-wind binaries
Neiner, C.; Grunhut, J.; Leroy, B. et al

in Astronomy and Astrophysics (2015), 575

Some colliding-wind massive binaries, called particle-accelerating colliding-wind binaries (PACWB), exhibit synchrotron radio emission, which is assumed to be generated by a stellar magnetic field ... [more ▼]

Some colliding-wind massive binaries, called particle-accelerating colliding-wind binaries (PACWB), exhibit synchrotron radio emission, which is assumed to be generated by a stellar magnetic field. However, no measurement of magnetic fields in these stars has ever been performed. We aim at quantifying the possible stellar magnetic fields present in PACWB to provide constraints for models. We gathered 21 high-resolution spectropolarimetric observations of 9 PACWB available in the ESPaDOnS, Narval and HarpsPol archives. We analysed these observations with the least squares deconvolution method. We separated the binary spectral components when possible. No magnetic signature is detected in any of the 9 PACWB stars and all longitudinal field measurements are compatible with 0 G. We derived the upper field strength of a possible field that could have remained hidden in the noise of the data. While the data are not very constraining for some stars, for several stars we could derive an upper limit of the polar field strength of the order of 200 G. We can therefore exclude the presence of strong or moderate stellar magnetic fields in PACWB, typical of the ones present in magnetic massive stars. Weak magnetic fields could however be present in these objects. These observational results provide the first quantitative constraints for future models of PACWB. [less ▲]

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See detailIs λ Cep a pulsating star?
Uuh-Sonda, J. M.; Eenens, P.; Rauw, Grégor ULg

in Meynet, Georges; Georgy, Cyril; Groh, José (Eds.) et al IAU Symposium (2015, January 01)

It has been proposed that the variability seen in absorption lines of the O6Ief star λ Cep is periodical and due to non-radial pulsations (NRP). We have obtained new spectra during six campaigns lasting ... [more ▼]

It has been proposed that the variability seen in absorption lines of the O6Ief star λ Cep is periodical and due to non-radial pulsations (NRP). We have obtained new spectra during six campaigns lasting between five and nine nights. In some datasets we find recurrent spectral variations which move redward in the absorption line profile, consistent with perturbations on the stellar surface of a rotating star. However the periods found are not stable between datasets, at odds with the NRP hypothesis. Moreover, even when no redward trend is found in a full dataset of an observing campaign, it can be present in a subset, suggesting that the phenomenon is short-lived, of the order of a few days, and possibly linked to transient magnetic loops. [less ▲]

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See detailShort-term spectroscopic variability of Plaskett's star
Palate, Matthieu ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2014), 572

Context. Plaskett's star (HD 47129) is a very massive O-star binary in a post Roche-lobe overflow stage. CoRoT observations of this system revealed photometric variability with a number of frequencies ... [more ▼]

Context. Plaskett's star (HD 47129) is a very massive O-star binary in a post Roche-lobe overflow stage. CoRoT observations of this system revealed photometric variability with a number of frequencies. <BR /> Aims: The aim of this paper is to characterize the variations in spectroscopy and investigate their origin. <BR /> Methods: To sample its short-term variability, HD 47129 was intensively monitored during two spectroscopic campaigns of six nights each. The spectra were disentangled and Fourier analyses were performed to determine possible periodicities and to investigate the wavelength dependence of the phase constant and the amplitude of the periodicities. <BR /> Results: Complex line profile variations are observed. Frequencies near 1.65, 0.82, and 0.37 d[SUP]-1[/SUP] are detected consistently in the He i λ 4471, He ii λ 4542, and N iii λ 4510-4518 lines. These frequencies are consistent with those of the strongest signals detected in photometry. The possibilities that these variations stem from pulsations, a recently detected magnetic field or tidal interactions are discussed. <BR /> Conclusions: Whilst all three scenarios have their strengths, none of them can currently account for all the observed properties of the line profile variations. Based on observations collected at the Observatoire de Haute Provence (OHP, France). [less ▲]

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See detailBuilding galaxies, stars, planets and the ingredients for life between the stars. The science behind the European Ultraviolet-Visible Observatory
Gómez de Castro, Ana I.; Appourchaux, Thierry; Barstow, Martin A. et al

in Astrophysics and Space Science (2014), 354

This contribution gathers the contents of the white paper submitted by the UV community to the Call issued by the European Space Agency in March 2013, for the definition of the L2 and L3 missions in the ... [more ▼]

This contribution gathers the contents of the white paper submitted by the UV community to the Call issued by the European Space Agency in March 2013, for the definition of the L2 and L3 missions in the ESA science program. We outlined the key science that a large UV facility would make possible and the instrumentation to be implemented. The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well-understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950 Å-3000 Å) spectral range that is unobservable from the ground. A versatile space observatory with UV sensitivity a factor of 50-100 greater than existing facilities will revolutionize our understanding of the Universe. Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the star-disk interaction that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by this UV field, providing unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Earth's atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. A 50-100 times improvement in sensitivity would enable the observation of the key atmospheric ingredients of Earth-like exoplanets (carbon, oxygen, ozone), provide crucial input for models of biologically active worlds outside the solar system, and provide the phenomenological baseline to understand the Earth atmosphere in context. [less ▲]

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See detailTIGRE: A new robotic spectroscopy telescope at Guanajuato, Mexico
Schmitt, J. H. M. M.; Schröder, K.-P.; Rauw, Grégor ULg et al

in Astronomische Nachrichten (2014), 335

TIGRE is a new robotic spectroscopy telescope located in central Mexico at the La Luz Observatory of the University of Guanajuato. The 1.2 m telescope is fiber-coupled to an échelle spectrograph with a ... [more ▼]

TIGRE is a new robotic spectroscopy telescope located in central Mexico at the La Luz Observatory of the University of Guanajuato. The 1.2 m telescope is fiber-coupled to an échelle spectrograph with a spectral resolving power exceeding 20 000 over most of the covered spectral range between 3800 Å and 8800 Å, with a small gap of 130 Å around 5800 Å. TIGRE operates robotically, i.e. it (normally) carries out all observations without any human intervention, including, in particular, the target selection in any given observing night. In this paper we describe the properties of the TIGRE instrumentation and its technical realization, as well as our first operational experience with the performance and efficiency of the overall system. Finally, we present some examples of recent TIGRE observations. [less ▲]

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See detailObservational signatures of past mass-exchange episodes in massive binaries
Raucq, Françoise ULg; Rauw, Grégor ULg; Gosset, Eric ULg et al

Poster (2014, September 05)

Mass and momentum exchanges in massive binaries can produce several observational signatures, such as asynchronous rotation and altered chemical compositions, which remain once the stars detach again. We ... [more ▼]

Mass and momentum exchanges in massive binaries can produce several observational signatures, such as asynchronous rotation and altered chemical compositions, which remain once the stars detach again. We have started to investigate these effects for a sample of detached massive O-star binaries that are thought to have previously experienced a Case A Roche lobe overflow. Using phase-resolved spectroscopy, we perform the disentangling of the spectra of the two stars. The reconstructed primary and secondary spectra are then analyzed to determine a range of stellar effective temperatures and gravity, as well as rotational velocities. Using model atmosphere codes we also constrain the chemical composition of the components. In this contribution, we present the first results of our analyses of HD149404 (O7.5If + ON9.5I, P = 9.81 days). [less ▲]

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See detailPhase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star (Corrigendum)
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 569

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), and on data collected at the San Pedro ... [more ▼]

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), and on data collected at the San Pedro Mártir observatory (Mexico). Corrigendum [less ▲]

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See detailX-raying the winds of the evolved massive binary HDE228766
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

Poster (2014, August)

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See detailThe X-ray Integral Field Unit (X-IFU) for Athena
Ravera, Laurent; Barret, Didier; den Herder, Jan Willem et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2014, July 01)

Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload ... [more ▼]

Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload consists of a large aperture high angular resolution X-ray optics (2 m2 at 1 keV) and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), offering 2:5 eV spectral resolution, with ~5" pixels, over a field of view of 50 in diameter. In this paper, we present the X-IFU detector and readout electronics principles, some elements of the current design for the focal plane assembly and the cooling chain. We describe the current performance estimates, in terms of spectral resolution, effective area, particle background rejection and count rate capability. Finally, we emphasize on the technology developments necessary to meet the demanding requirements of the X-IFU, both for the sensor, readout electronics and cooling chain. [less ▲]

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See detailX-ray emission from magnetic massive stars
Nazé, Yaël ULg; Petit, V.; Rindbrand, M. et al

Poster (2014, July 01)

Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. In an attempt to clarify the systematics of the observed X-ray properties, we have analyzed a large ... [more ▼]

Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. In an attempt to clarify the systematics of the observed X-ray properties, we have analyzed a large series of Chandra and XMM observations, corresponding to over 100 exposures of 60% of the known magnetic massive stars listed recently by Petit et al. (2013). We notably show that the X-ray luminosity is strongly correlated with mass-loss rate, in agreement with predictions of magnetically confined wind models. We also investigated the behavior of other X-ray properties (plasma temperature, absorption, variability), yielding additional constraints on models. This work not only advances our knowledge of the X-ray emission of massive stars, but also suggests new observational and theoretical avenues to further explore magnetically confined winds. [less ▲]

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See detailThe X-ray bright massive stars in Cyg OB2
Nazé, Yaël ULg; Cazorla, Constantin ULg; Rauw, Grégor ULg

Poster (2014, July 01)

As a complement to the results from the Cyg OB2 Chandra Legacy program, we present in this contribution the detailed analysis of the four X-ray bright massive stars dominating the cluster. Cyg OB2 #5, #8A ... [more ▼]

As a complement to the results from the Cyg OB2 Chandra Legacy program, we present in this contribution the detailed analysis of the four X-ray bright massive stars dominating the cluster. 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 behavior 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 system following a recent eruption. [less ▲]

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See detailInvestigation of the stellar content in the western part of the Carina nebula
Kumar, Brajesh; Sharma, Saurabh; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2014), 567

Context. The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. <BR ... [more ▼]

Context. The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. <BR /> Aims: To investigate this process, we generated a new catalog of the pre-main-sequence stars in the Carina west (CrW) region and studied their nature and spatial distribution. We also determined various parameters (reddening, reddening law, age, mass), which are used further to estimate the initial mass function and K-band luminosity function for the region under study. <BR /> Methods: We obtained deep UBVRI Hα photometric data of the field situated to the west of the main Carina nebula and centered on WR 22. Medium-resolution optical spectroscopy of a subsample of X-ray selected objects along with archival data sets from Chandra, XMM-Newton and 2MASS surveys were used for the present study. Different sets of color-color and color-magnitude diagrams are used to determine reddening for the region and to identify young stellar objects (YSOs) and estimate their age and mass. <BR /> Results: Our spectroscopic results indicate that the majority of the X-ray sources are late spectral type stars. The region shows a large amount of differential reddening with minimum and maximum values of E(B - V) as 0.25 and 1.1 mag, respectively. Our analysis reveals that the total-to-selective absorption ratio R[SUB]V[/SUB] is ~3.7 ± 0.1, suggesting an abnormal grain size in the observed region. We identified 467 YSOs and studied their characteristics. The ages and masses of the 241 optically identified YSOs range from ~0.1 to 10 Myr and ~0.3 to 4.8 M[SUB]⊙[/SUB], respectively. However, the majority of them are younger than 1 Myr and have masses below 2 M[SUB]⊙[/SUB]. The high mass star WR 22 does not seem to have contributed to the formation of YSOs in the CrW region. The initial mass function slope, Γ, in this region is found to be -1.13 ± 0.20 in the mass range of 0.5 < M/M[SUB]⊙[/SUB] < 4.8. The K-band luminosity function slope (α) is also estimated as 0.31 ± 0.01. We also performed minimum spanning tree analysis of the YSOs in this region, which reveals that there are at least ten YSO cores associated with the molecular cloud, and that leads to an average core radius of 0.43 pc and a median branch length of 0.28 pc. Full Table 3 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A109">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A109</A> [less ▲]

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See detailChemical abundances of fast-rotating OB stars
Cazorla, Constantin ULg; Morel, Thierry ULg; Nazé, Yaël ULg et al

Poster (2014, June 23)

Fast rotation in massive stars is predicted to induce mixing in their interior, but recent observations have challenged this concept by revealing a population of fast-rotating stars with normal nitrogen ... [more ▼]

Fast rotation in massive stars is predicted to induce mixing in their interior, but recent observations have challenged this concept by revealing a population of fast-rotating stars with normal nitrogen abundances at their surface (Hunter et al. 2009, A&A, 496, 841; Brott et al. 2011, A&A, 530, A116, but see Maeder et al. 2014, A&A, 565, A39). However, as the binary fraction of these stars is unknown, the importance of mass-transfer processes cannot be quantified. As a result, no definitive statements about the ability of single-star evolutionary models including rotation to reproduce these observations can be made. Our work combines for the first time a detailed surface abundance analysis with a radial-velocity monitoring for a sample of bright, fast-rotating Galactic OB stars to put strong constraints on stellar evolutionary and interior models. [less ▲]

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See detailPhase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 566

Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star ... [more ▼]

Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. <BR /> Aims: Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. <BR /> Methods: X-ray spectra have been collected at three key orbital phases to probe the winds of both stars. Optical photometry has been gathered to set constraints on the orbital inclination of the system. <BR /> Results: The X-ray spectra reveal prominent variations of the intervening column density toward the X-ray emission zone, which are in line with the expectations for a wind-wind collision. We use a toy model to set constraints on the stellar wind parameters by attempting to reproduce the observed variations of the relative fluxes and wind optical depths at 1 keV. <BR /> Conclusions: The lack of strong optical eclipses sets an upper limit of ~ 68° on the orbital inclination. The analysis of the variations of the X-ray spectra suggests an inclination in the range 54-61° and indicates that the secondary wind momentum ratio exceeds that of the primary by at least a factor 5. Our models further suggest that the bulk of the X-ray emission arises from the innermost region of the wind interaction zone, which is from a region whose outer radius, as measured from the secondary star, lies between 0.5 and 1.5 times the orbital separation. 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), and on data collected at the San Pedro Mártir observatory (Mexico). [less ▲]

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See detailThe X-ray properties of lambda Cep, a true twin of zeta Pup?
Rauw, Grégor ULg; Nazé, Yaël ULg; Gonzalez-Perez, Nicolas et al

Conference (2014, June)

Oef stars are O-stars that display a double-peaked He II λ 4686 line in their optical spectra, suggesting that the inner part of the stellar wind is co-rotating with the star. This hypothesis is also ... [more ▼]

Oef stars are O-stars that display a double-peaked He II λ 4686 line in their optical spectra, suggesting that the inner part of the stellar wind is co-rotating with the star. This hypothesis is also often used to explain their ubiquitous spectral variability in the optical domain. In this context, the fact that the high-resolution X-ray spectra of ζ Pup (O4Ief) meet the expectations of the wind-embedded shock model, assuming a spherically symmetric wind came as a surprise. To understand what is going on, we have obtained a 300 ksec observation of λ Cephei, the second brightest Oef star. This observation not only allows to collect the RGS high-resolution spectrum of the star, but further enables us to search for X-ray variability. To correlate the potential X-ray variability with that of the optical spectrum of λ Cep, we monitored the optical spectrum simultaneously with the TIGRE telescope. We present here the first results of this campaign, both in terms of the line profiles in the RGS spectrum and the search for X-ray variability in correlation with the optical variations. [less ▲]

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