References of "Sana, H"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailX-ray properties of the young open clusters HM1 and IC 2944/2948
Nazé, Yaël ULg; Rauw, Grégor ULg; Sana, H. et al

in Astronomy and Astrophysics (2013), 555

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC 2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or ... [more ▼]

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC 2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or foreground objects. Most massive stars in both clusters display the usual high-energy properties of that type of objects, though with log [L[SUB]X[/SUB]/L[SUB]BOL[/SUB]] apparently lower in HM1 than in IC 2944/2948. Compared with studies of other clusters, it seems that a low signal-to-noise ratio at soft energies, due to the high extinction, may be the main cause of this difference. In HM1, the two Wolf-Rayet stars show contrasting behaviors: WR89 is extremely bright, but much softer than WR87. It remains to be seen whether wind-wind collisions or magnetically confined winds can explain these emissions. In IC 2944/2948, the X-ray sources concentrate around HD 101205; a group of massive stars to the north of this object is isolated, suggesting that there exist two subclusters in the field-of-view. Tables 2, 5, and Figs. 5, 9 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>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).Tables 1, 3 and 4 are 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/555/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A83</A> [less ▲]

Detailed reference viewed: 3 (1 ULg)
Full Text
See detailRecent results on the hierarchical triple system HD 150136
Gosset, Eric ULg; Berger, J. P.; Absil, Olivier ULg et al

in Bonanos, Alceste (Ed.) Massive Stars: From alpha to Omega (2013, June 01)

HD 150136 is a hierarchical triple system, non-thermal radio emitter, made of three O stars totalling some 130 solar masses. The 2.67-day inner orbit is rather well-known. Recent works derived a good ... [more ▼]

HD 150136 is a hierarchical triple system, non-thermal radio emitter, made of three O stars totalling some 130 solar masses. The 2.67-day inner orbit is rather well-known. Recent works derived a good approximation for the outer orbit with a period of 3000 days. We report here on interferometric observations that allow us to angularly resolve the outer orbit. First evidences for an astrometric displacement are given. The determination of the outer system orbit gives access to the inclinations of the systems and to the masses, including the one of the O3-O3.5 primary star. [less ▲]

Detailed reference viewed: 17 (7 ULg)
Full Text
Peer Reviewed
See detailThree-dimensional orbits of the triple-O stellar system HD 150136
Sana, H.; Le Bouquin, J.-B.; Mahy, Laurent et al

in Astronomy and Astrophysics (2013), 553

Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital ... [more ▼]

Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital properties have been reliably constrained. Aims. To quantitatively understand the non-thermal emission process, accurate knowledge of the physical and orbital properties of the object is crucial. Here, we aim to investigate the orbital properties of the wide system and to constrain the inclinations of the inner and outer binaries, and with these the absolute masses of the system components. Methods. We used the PIONIER combiner at the Very Large Telescope Interferometer to obtain the very first interferometric measurements of HD 150136. We combined the interferometric observations with new and existing high resolution spectroscopic data to derive the orbital solution of the outer companion in the three-dimensional space. Results. The wide system is clearly resolved by PIONIER, with a projected separation on the plane of the sky of about 9 milli-arcsec. The best-fit orbital period, eccentricity, and inclination are 8.2 yr, 0.73 and 108 degr. We constrain the masses of the three stars of the system to 63 +/- 10, 40 +/- 6, and 33 +/- 12 Msun for the O3-3.5 V, O5.5-6 V and O6.5-7 V components. Conclusions. The dynamical masses agree within errors with the evolutionary masses of the components. Future interferometric and spectroscopic monitoring of HD 150136 should allow one to reduce the uncertainties to a few per cent only and to accurately constrain the distance to the system. This makes HD 150136 an ideal system to quantitatively test evolutionary models of high-mass stars as well as the physics of non-thermal processes occurring in O-type systems. [less ▲]

Detailed reference viewed: 7 (3 ULg)
See detailQuantitative NIR Spectroscopy of Massive Stars
Sana, H.; Stap, F. A.; de Koter, A. et al

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

Interest for near-infrared (NIR) spectroscopy of massive stars has been dramatically increasing over the last decade. Because it allows one to observe objects inaccessible at optical wavelengths due to ... [more ▼]

Interest for near-infrared (NIR) spectroscopy of massive stars has been dramatically increasing over the last decade. Because it allows one to observe objects inaccessible at optical wavelengths due to absorption, the infrared domain offers a privileged window to study highly extinguished objects. Yet, a detailed calibration of the massive star properties at NIR wavelength is still missing. Following the lines of the work of Repolust et al. (2005), we have acquired high resolution spectroscopy of several nearby massive stars using VLT/CRIRES, focusing on spectral lines of interest in the J, H, K, and L bands. In this work, we present the earliest results of our quantitative spectroscopic analysis of the main sequence stars in our sample. Using the unique combination of a genetic algorithm approach with the state-of-the-art non-LTE atmosphere model FASTWIND, we compare the stellar and wind properties as derived from the optical and the NIR regime. [less ▲]

Detailed reference viewed: 13 (4 ULg)
Full Text
Peer Reviewed
See detailBinary Interaction Dominates the Evolution of Massive Stars
Sana, H.; de Mink, S. E.; de Koter, A. et al

in Science (2012), 337(6093), 444-446

The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on ... [more ▼]

The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae. [less ▲]

Detailed reference viewed: 25 (17 ULg)
Full Text
Peer Reviewed
See detailThe long period eccentric orbit of the particle accelerator HD 167971 revealed by long baseline interferometry
De Becker, Michaël ULg; Sana, H; Absil, Olivier ULg et al

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

Using optical long baseline interferometry, we resolved for the first time the two wide components of HD167971, a candidate hierarchical triple system known to efficiently accelerate particles. Our multi ... [more ▼]

Using optical long baseline interferometry, we resolved for the first time the two wide components of HD167971, a candidate hierarchical triple system known to efficiently accelerate particles. Our multi-epoch VLTI observations provide direct evidence for a gravitational link between the O8 supergiant and the close eclipsing O + O binary. The separation varies from 8 to 15 mas over the three-year baseline of our observations, suggesting that the components evolve on a wide and very eccentric orbit (most probably e>0.5). These results provide evidence that the wide orbit revealed by our study is not coplanar with the orbit of the inner eclipsing binary. From our measurements of the near-infrared luminosity ratio, we constrain the spectral classification of the components in the close binary to be O6-O7, and confirm that these stars are likely main-sequence objects. Our results are discussed in the context of the bright non-thermal radio emission already reported for this system, and we provide arguments in favour of a maximum radio emission coincident with periastron passage. HD167971 turns out to be an efficient O-type particle accelerator that constitutes a valuable target for future high angular resolution radio imaging using VLBI facilities. [less ▲]

Detailed reference viewed: 21 (7 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 14 (1 ULg)
Full Text
Peer Reviewed
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.

Detailed reference viewed: 12 (0 ULg)
Full Text
Peer Reviewed
See detailEvidence for a physically bound third component in HD 150136
Mahy, Laurent ULg; Gosset, Eric ULg; Sana, H et al

in Astronomy and Astrophysics (2012), 540

Context. HD 150136 is one of the nearest systems harbouring an O3 star. Although this system was considered for a long time as a binary, more recent investigations have suggested the possible existence of ... [more ▼]

Context. HD 150136 is one of the nearest systems harbouring an O3 star. Although this system was considered for a long time as a binary, more recent investigations have suggested the possible existence of a third component. <BR /> Aims: We present a detailed analysis of HD 150136 to test its triple nature. In addition, we investigate the physical properties of the individual components of this system. <BR /> Methods: We analysed high-resolution, high signal-to-noise data collected through multi-epoch runs spread over ten years. We applied a disentangling program to refine the radial velocities and to obtain the individual spectra of each star. With the radial velocities, we computed the orbital solution of the inner system, and we describe the main properties of the orbit of the outer star such as the preliminary mass ratio, the eccentricity, and the orbital-period range. With the individual spectra, we determined the stellar parameters of each star by means of the CMFGEN atmosphere code. <BR /> Results: We offer clear evidence that HD 150136 is a triple system composed of an O3V((f[SUP]∗[/SUP]))-3.5V((f[SUP]+[/SUP])), an O5.5-6V((f)), and an O6.5-7V((f)) star. The three stars are between 0-3 Myr old. We derive dynamical masses of about 64, 40, and 35 M[SUB]&sun;[/SUB] for the primary, the secondary and the third components by assuming an inclination of 49° (sin[SUP]3[/SUP]i = 0.43). It currently corresponds to one of the most massive systems in our galaxy. The third star moves with a period in the range of 2950 to 5500 d on an outer orbit with an eccentricity of at least 0.3. However, because of the long orbital period, our dataset is not sufficient to constrain the orbital solution of the tertiary component with high accuracy. <BR /> Conclusions: We confirm there is a tertiary star in the spectrum of HD 150136 and show that it is physically bound to the inner binary system. This discovery makes HD 150136 the first confirmed triple system with an O3 primary star. Table 1 is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
See detailA spectroscopic investigation of early-type stars in the young open cluster Westerlund 2
Rauw, Grégor ULg; Sana, H.; Nazé, Yaël ULg

in Astronomy and Astrophysics (2011), 535

Context. The distance of the very young open cluster <ASTROBJ>Westerlund 2</ASTROBJ>, which contains the very massive binary system <ASTROBJ>WR 20a</ASTROBJ> and is likely associated with a TeV source ... [more ▼]

Context. The distance of the very young open cluster <ASTROBJ>Westerlund 2</ASTROBJ>, which contains the very massive binary system <ASTROBJ>WR 20a</ASTROBJ> and is likely associated with a TeV source, has been the subject of much debate. <BR /> Aims: We attempt a joint analysis of spectroscopic and photometric data of eclipsing binaries in the cluster to constrain its distance. <BR /> Methods: A sample of 15 stars, including three eclipsing binaries (<ASTROBJ>MSP 44</ASTROBJ>, <ASTROBJ>MSP 96</ASTROBJ>, and <ASTROBJ>MSP 223</ASTROBJ>) was monitored with the FLAMES multi-object spectrograph. The spectroscopic data are analysed together with existing B V photometry. <BR /> Results: The analysis of the three eclipsing binaries clearly supports the larger values of the distance, around 8 kpc, and rules out values of about 2.4 - 2.8 kpc that have been suggested in the literature. Furthermore, our spectroscopic monitoring reveals no clear signature of binarity with periods shorter than 50 days in either the WN6ha star <ASTROBJ>WR 20b</ASTROBJ>, the early O-type stars <ASTROBJ>MSP 18</ASTROBJ>, <ASTROBJ>MSP 171</ASTROBJ>, <ASTROBJ>MSP 182</ASTROBJ>, <ASTROBJ>MSP 183</ASTROBJ>, <ASTROBJ>MSP 199</ASTROBJ>, and <ASTROBJ>MSP 203</ASTROBJ>, or three previously unknown mid O-type stars. The only newly identified candidate binary system is <ASTROBJ>MSP 167</ASTROBJ>. The absence of a binary signature is especially surprising for WR 20b and MSP 18, which were previously found to be bright X-ray sources. <BR /> Conclusions: The distance of Westerlund 2 is confirmed to be around 8 kpc as previously suggested based on the spectrophotometry of its population of O-type stars and the analysis of the light curve of WR 20a. Our results suggest that short-period binary systems are not likely to be common, at least not among the population of O-type stars in the cluster. Based on observations collected at the European Southern Observatory (Cerro Paranal, Chile).Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
Peer Reviewed
See detailThe Non-thermal Radio Emitter HD 93250 Resolved by Long Baseline Interferometry
Sana, H.; Le Bouquin, J.-B.; De Becker, Michaël ULg et al

in Astrophysical Journal Letters (2011), 740

As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been ... [more ▼]

As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been invoked to explain its X-ray properties: wind-wind interaction and magnetic wind confinement. Yet, HD 93250 shows absolutely constant radial velocities over timescales of years suggesting either a single star, a binary system seen pole-on view or a very long period, and/or highly eccentric system. Using the ESO Very Large Telescope Interferometer, we resolved HD 93250 as a close pair with similar components. We measured a near-infrared flux ratio of 0.8 ± 0.1 and a separation of (1.5 ± 0.2) × 10-3 arcsec. At the distance of Carina, this corresponds to a projected physical distance of 3.5 AU. While a quantitative investigation would require a full characterization of the orbit, the binary nature of HD 93250 allows us to qualitatively explain both its X-ray flux and hardness and its non-thermal radio emission in the framework of a colliding wind scenario. We also discuss various observational biases. We show that, due to line blending of two similar spectral components, HD 93250 could have a period as short as 1 to several years despite the lack of measurable radial velocity variations. [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
Peer Reviewed
See detailThe massive star binary fraction in young open clusters - III. IC 2944 and the Cen OB2 association
Sana, H.; James, G.; Gosset, Eric ULg

in Monthly Notices of the Royal Astronomical Society (2011), 416

Using an extended set of multi-epoch high-resolution high signal-to-noise ratio optical spectra, we readdress the multiplicity properties of the O-type stars in IC 2944 and in the Cen OB2 association. We ... [more ▼]

Using an extended set of multi-epoch high-resolution high signal-to-noise ratio optical spectra, we readdress the multiplicity properties of the O-type stars in IC 2944 and in the Cen OB2 association. We present new evidence of binarity for five objects and we confirm the multiple nature of another two. We derive the first orbital solutions for HD 100099, HD 101436 and HD 101190 and we provide additional support for HD 101205 being a quadruple system. The minimal spectroscopic binary fraction in our sample is f[SUB]min[/SUB]= 0.57. Using numerical simulations, we show that the detection rate of our observational campaign is close to 90 per cent, leaving thus little room for undetected spectroscopic binary systems. The statistical properties of the O-star population in IC 2944 are similar, within the uncertainties, to the results obtained in the earlier papers in this series despite the fact that sample size effects limit the significance of the comparison. Using newly derived spectroscopic parallaxes, we reassess the distance to IC 2944 and obtained 2.3 ± 0.3 kpc, in agreement with previous studies. We also confirm that, as far as the O stars are concerned, the IC 2944 cluster is most likely a single entity. [less ▲]

Detailed reference viewed: 10 (1 ULg)
Full Text
Peer Reviewed
See detailThe multiplicity of O-type stars in NGC 2244
Mahy, Laurent ULg; Rauw, Grégor ULg; Martins, F. et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will ... [more ▼]

The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will present the main results from our long-term spectroscopic survey devoted to the young open cluster NGC 2244. We discuss the spectral classification, the projected rotational velocity (v sin{i}) and the multiplicity of O-stars. The stellar and wind parameters of each star, obtained using the CMFGEN atmosphere code, help us to better constrain the individual properties of these objects. Several of these stars were observed by the CoRoT satellite (SRa02) in the Asteroseismology channel. This intensive monitoring and the unprecedented quality of the light curves allow us to shed a new light on these objects. [less ▲]

Detailed reference viewed: 17 (2 ULg)
Full Text
Peer Reviewed
See detailA New Investigation of the Binary HD 48099
Mahy, Laurent ULg; Rauw, Grégor ULg; Martins, F. et al

in Astrophysical Journal (2010), 708

With an orbital period of about 3.078 days, the double-lined spectroscopic binary HD 48099 is, until now, the only short-period O+O system known in the Mon OB2 association. Even though an orbital solution ... [more ▼]

With an orbital period of about 3.078 days, the double-lined spectroscopic binary HD 48099 is, until now, the only short-period O+O system known in the Mon OB2 association. Even though an orbital solution has already been derived for this system, few information are available about the individual stars. We present, in this paper, the results of a long-term spectroscopic campaign. We derive a new orbital solution and apply a disentangling method to recover the mean spectrum of each star. To improve our knowledge concerning both components, we determine their spectral classifications and their projected rotational velocities. We also constrain the main stellar parameters of both stars by using the CMFGEN atmosphere code and provide the wind properties for the primary star through the study of International Ultraviolet Explorer spectra. This investigation reveals that HD 48099 is an O5.5 V ((f)) + O9 V binary with M [SUB]1[/SUB]sin[SUP]3[/SUP] i = 0.70 M [SUB]sun[/SUB] and M [SUB]2[/SUB]sin[SUP]3[/SUP] i = 0.39 M [SUB]sun[/SUB], implying a rather low orbital inclination. This result, combined with both a large effective temperature and log g, suggests that the primary star (vsin i sime 91 km s[SUP]â 1[/SUP]) is actually a fast rotator with a strongly clumped wind and a nitrogen abundance of about 8 times the solar value. [less ▲]

Detailed reference viewed: 26 (4 ULg)
Full Text
Peer Reviewed
See detailHigh-dispersion infrared spectroscopic observations of comet 8P/Tuttle with VLT/CRIRES
Kobayashi, H.; Bockelée-Morvan, D.; Kawakita, H. et al

in Astronomy and Astrophysics (2010), 509

We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT (Very ... [more ▼]

We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT (Very Large Telescope) with the CRIRES instrument as part of a multi-wavelength observation campaign of 8P/Tuttle performed in late January and early February 2008. Radar observations suggested that 8P/Tuttle is a contact binary, and it was proposed that these components might be heterogeneous in chemistry. We determined mixing ratios of organic volatiles with respect to H[SUB]2[/SUB]O and found that mixing ratios were consistent with previous near infrared spectroscopic observations obtained in late December 2007 and in late January 2008. It has been suggested that because 8P/Tuttle is a contact binary, it might be chemically heterogeneous. However, we find no evidence for chemical heterogeneity within the nucleus of 8P/Tuttle. We also compared the mixing ratios of organic molecules in 8P/Tuttle with those of both other HFCs and long period comets (LPCs) and found that HCN, C[SUB]2[/SUB]H[SUB]2[/SUB], and C[SUB]2[/SUB]H[SUB]6[/SUB] are depleted whereas CH[SUB]4[/SUB] and CH[SUB]3[/SUB]OH have normal abundances. This may indicate that 8P/Tuttle was formed in a different region of the early solar nebula than other HFCs and LPCs. We estimated the conversion efficiency from C[SUB]2[/SUB]H[SUB]2[/SUB] to C[SUB]2[/SUB]H[SUB]6[/SUB] by hydrogen addition reactions on cold grains by employing the C[SUB]2[/SUB]H[SUB]6[/SUB]/(C[SUB]2[/SUB]H[SUB]6[/SUB]+C[SUB]2[/SUB]H[SUB]2[/SUB]) ratio. The C[SUB]2[/SUB]H[SUB]6[/SUB]/(C[SUB]2[/SUB]H[SUB]6[/SUB]+C[SUB]2[/SUB]H[SUB]2[/SUB]) ratio in 8P/Tuttle is consistent with the ratios found in other HFCs and LPCs within the error bars. We also discuss the source of C[SUB]2[/SUB] and CN based on our observations and conclude that the abundances of C[SUB]2[/SUB]H[SUB]2[/SUB] and C[SUB]2[/SUB]H[SUB]6[/SUB] are insufficient to explain the C[SUB]2[/SUB] abundances in comet 8P/Tuttle and that the abundance of HCN is insufficient to explain the CN abundances in the comet, so at least one additional parent is needed for each species, as pointed out in previous study. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO Prog. 080.C-0615 and 280.C-5053).We regret to note the death of Dr. J. -M. Zucconi in 2009 May. [less ▲]

Detailed reference viewed: 51 (15 ULg)
Full Text
Peer Reviewed
See detailThe massive star binary fraction in young open clusters - II. NGC6611 (Eagle Nebula)
Sana, H.; Gosset, Eric ULg; Evans, C. J.

in Monthly Notices of the Royal Astronomical Society (2009), 400

Based on a set of over 100 medium- to high-resolution optical spectra collected from 2003 to 2009, we investigate the properties of the O-type star population in NGC6611 in the core of the Eagle Nebula ... [more ▼]

Based on a set of over 100 medium- to high-resolution optical spectra collected from 2003 to 2009, we investigate the properties of the O-type star population in NGC6611 in the core of the Eagle Nebula (M16). Using a much more extended data set than previously available, we revise the spectral classification and multiplicity status of the nine O-type stars in our sample. We confirm two suspected binaries and derive the first SB2 orbital solutions for two systems. We further report that two other objects are displaying a composite spectrum, suggesting possible long-period binaries. Our analysis is supported by a set of Monte Carlo simulations, allowing us to estimate the detection biases of our campaign and showing that the latter do not affect our conclusions. The absolute minimal binary fraction in our sample is f[SUB]min[/SUB] = 0.44 but could be as high as 0.67 if all the binary candidates are confirmed. As in NGC6231 (see Paper I), up to 75 per cent of the O star population in NGC6611 are found in an O+OB system, thus implicitly excluding random pairing from a classical IMF as a process to describe the companion association in massive binaries. No statistical difference could be further identified in the binary fraction, mass-ratio and period distributions between NGC6231 and NGC 6611, despite the difference in age and environment of the two clusters. [less ▲]

Detailed reference viewed: 2 (0 ULg)
Full Text
Peer Reviewed
See detailPhase-resolved XMM-Newton observations of the massive WR+O binary WR 22
Gosset, Eric ULg; Nazé, Yaël ULg; Sana, H. et al

in Astronomy and Astrophysics (2009), 508

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

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

Detailed reference viewed: 12 (5 ULg)
Full Text
Peer Reviewed
See detailOptical spectroscopy of X-Mega targets in the Carina nebula - VII. On the multiplicity of Tr16-112, HD93343 and HD93250
Rauw, Grégor ULg; Nazé, Yaël ULg; Fernández Lajús, E. et al

in Monthly Notices of the Royal Astronomical Society (2009), 398

We present the results of a spectroscopic monitoring campaign devoted to three O-type stars in the Carina nebula. We derive the full SB2 orbital solution of the binary system Tr16-112, an exceptional ... [more ▼]

We present the results of a spectroscopic monitoring campaign devoted to three O-type stars in the Carina nebula. We derive the full SB2 orbital solution of the binary system Tr16-112, an exceptional dissymmetrical system consisting of an O5.5-6V((f[SUP]+[/SUP]?p)) primary and a B2V-III secondary. We also report on low-amplitude brightness variations in Tr16-112 that are likely due to the ellipsoidal shape of the O5.5-6 primary revolving in an eccentric orbit around the system's centre of mass. We detect for the first time a clear SB2 binary signature in the spectrum of HD93343 (O8 + O8), although our data are not sufficient to establish an orbital solution. This system also displays low-amplitude photometric modulations. On the other hand, no indication of multiplicity is found in the optical spectra of HD93250. Finally, we discuss the general properties of multiple massive stars in the Carina OB1 association. Based on observations collected at the European Southern Observatory (La Silla, Chile), at Complejo Astronómico El Leoncito (Argentina), at the Cerro Tololo Inter-American Observatory (CTIO) and with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). E-mail: rauw@astro.ulg.ac.be â ¡ Research Associate FRS/FNRS (Belgium). § Postdoctoral Researcher FRS/FNRS (Belgium). ¶ Senior Research Associate FRS/FNRS (Belgium). [less ▲]

Detailed reference viewed: 35 (9 ULg)
Full Text
Peer Reviewed
See detailEarly-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association. I. The multiplicity of O-type stars
Mahy, Laurent ULg; Nazé, Yaël ULg; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2009), 502

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

Aims. We present the results obtained from a long-term spectroscopic campaign to study the multiplicity of O-type stars in both the young open cluster NGC 2244 and the Mon OB2 association. Methods: Our spectroscopic monitoring was performed over several years, allowing us to investigate different timescales. For each star, several spectral diagnostic tools were applied to search for line shifts and profile variations. We also measured the projected rotational velocity and revisited the spectral classification. Results: Several stars in our sample have been previously considered to be spectroscopic binaries, although only a few scattered observations were available. Our results now have identified a more complex situation for two new spectroscopic binaries (HD 46 149 in NGC 2244 and HD 46 573 in Mon OB2). The first object is a long-period double-lined spectroscopic binary, although the exact value of its period remains uncertain and the second object is classified as an SB1 system with a period of about 10.67 days but the time series of our observations do not enable us to derive a unique orbital solution for this system. We also find another star to be variable in radial velocity (HD 46 150) and detect line profile variations in two rapid rotators (HD 46 056 and HD 46 485). Conclusions: This spectroscopic investigation places a firm lower limit (17%) on the binary fraction of O-stars in NGC 2244 and reveals the lack of short-period O+OB systems in this cluster. In addition, a comparison of these new results with two other well-studied clusters (NGC 6231 and IC 1805) puts forward possible hints of a relation between stellar density and binarity, which could provide constraints on the theories of the formation and early evolution of hot stars. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/502/937 Based on observations collected at Observatoire de Haute-Provence (France), San Pedro Màrtir Observatory (Mexico), La Silla Observatory (European Southern Observatory), and Asiago Observatory (Italy). [less ▲]

Detailed reference viewed: 43 (8 ULg)
Full Text
Peer Reviewed
See detailLine profile variability in the massive binary HD 152219
Sana, H.; Gosset, Eric ULg

in Communication in Asteroseismology (2009, July 01), 158

HD 152219 is a massive binary system with O9.5 III and B1-2 III/V components and a short orbital period of 4.2 d. In a previous work, we showed that the primary star (M_{prim}˜21 M_&sun;) was presenting ... [more ▼]

HD 152219 is a massive binary system with O9.5 III and B1-2 III/V components and a short orbital period of 4.2 d. In a previous work, we showed that the primary star (M_{prim}˜21 M_&sun;) was presenting clear line profile variabilities (LPVs) that might be caused by nonradial pulsations (NRPs). In the present work, we report on an intensive spectroscopic monitoring, that aimed at unveiling the nature of the detected LPVs. Based on this new data set, we discard the NRPs and point out the Rossiter-McLaughlin effect as % being the cause of the observed LPVs. The upper limit derived on the amplitude of undetected NRPs, if any, is set at a couple of part per thousands of the continuum level. [less ▲]

Detailed reference viewed: 2 (0 ULg)