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See detailHot and cool: two emission-line stars with constrasting behaviours in the same XMM-Newton field
Nazé, Yaël ULg; Rauw, Grégor ULg; Ud-Doula, A.

in Astronomy and Astrophysics (2010), 510

High-energy emissions are good indicators of peculiar behaviours in stars. We have therefore obtained an XMM-Newton observation of HD 155806 and 1RXS J171502.4-333344, and derived their spectral ... [more ▼]

High-energy emissions are good indicators of peculiar behaviours in stars. We have therefore obtained an XMM-Newton observation of HD 155806 and 1RXS J171502.4-333344, and derived their spectral properties for the first time. The X-ray spectrum of HD 155806 appears soft, even slightly softer than usual for O-type stars (as shown by a comparison with the O9 star HD 155889 in the same XMM-Newton field). It is well-fitted with a two-component thermal model with low temperatures (0.2 and 0.6 keV), and it shows no overluminosity (log[L_X/L_BOL] = -6.75). The high-resolution spectrum, though noisy, reveals a few broad, symmetric X-ray lines (FWHMË 2500 km s[SUP]-1[/SUP]). The X-ray emission is compatible with the wind-shock model and therefore appears unaffected by the putative dense equatorial regions at the origin of the Oe classification. 1RXS J171502.4-333344 is a nearby flaring source of moderate X-ray luminosity (log[L_X/L_BOL] = -3), with a soft thermal spectrum composed of narrow lines and presenting a larger abundance of elements (e.g. Ne) with a high first ionization potential (FIP) compared to lower-FIP elements. All the evidence indicates a coronal origin for the X-ray emission, in agreement with the dMe classification of this source. 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).Research Associate FNRS. [less ▲]

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See detailThe Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission
Nandra, Kirpal; Barret, Didier; Barcons, Xavier et al

Report (2013)

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in ... [more ▼]

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics. [less ▲]

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See detailThe Hot and Energetic Universe: Star formation and evolution
Sciortino, S.; Rauw, Grégor ULg; Audard, M. et al

Report (2013)

Stars over a wide range of masses and evolutionary stages are nowadays known to emit X-rays. This X-ray emission is a unique probe of the most energetic phenomena occurring in the circumstellar ... [more ▼]

Stars over a wide range of masses and evolutionary stages are nowadays known to emit X-rays. This X-ray emission is a unique probe of the most energetic phenomena occurring in the circumstellar environment of these stars, and provides precious insight on magnetic phenomena or hydrodynamic shocks. Owing to its large collecting area, Athena+ will open up an entirely new window on these phenomena. Indeed, Athena+ will not only allow us to study many more objects with an unprecedented spectral resolution, but will also pioneer the study of the dynamics of these objects via time-resolved high-resolution spectroscopy. In this way, Athena+ will be a unique tool to study accretion processes in TTauri stars, flaring activity in young stars, dynamos in ultra-cool dwarfs, small and large-scale structures in the winds of single massive stars, wind interactions in massive binary systems, hot bubbles in planetary nebula... All these studies will lead to a deeper understanding of yet poorly understood processes which have profound impact in star and planetary system formation as well as in feedback processes on Galactic scale. [less ▲]

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See detailThe Hot and Energetic Universe: The X-ray Integral Field Unit (X-IFU) for Athena+
Barret, D.; den Herder, J. W.; Piro, L. et al

Report (2013)

The Athena+ mission concept is designed to implement the Hot and Energetic Universe science theme submitted to the European Space Agency in response to the call for White Papers for the definition of the ... [more ▼]

The Athena+ mission concept is designed to implement the Hot and Energetic Universe science theme submitted to the European Space Agency in response to the call for White Papers for the definition of the L2 and L3 missions of its science program. The Athena+ science payload consists of a large aperture high angular resolution X-ray optics and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager (WFI). 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 5 arc minutes in diameter. In this paper, we briefly describe the Athena+ mission concept and the X-IFU performance requirements. We then present the X-IFU detector and readout electronics principles, the current design of the focal plane assembly, the cooling chain and review the global architecture design. Finally, we describe the current performance estimates, in terms of effective area, particle background rejection, count rate capability and velocity measurements. Finally, we emphasize on the latest technology developments concerning TES array fabrication, spectral resolution and readout performance achieved to show that significant progresses are being accomplished towards the demanding X-IFU requirements. [less ▲]

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See detailHot carbon stars - More about V348 SGR
Houziaux, Léo ULg; Bouchet, P.; Heck, A. et al

in Quarterly Journal of the Royal Astronomical Society (1987), 28

New observational techniques (sensitive receivers, access to ultraviolet and infrared spectroscopy), as well as recent theoretical investigations on advanced stages of stellar evolution focus attention ... [more ▼]

New observational techniques (sensitive receivers, access to ultraviolet and infrared spectroscopy), as well as recent theoretical investigations on advanced stages of stellar evolution focus attention again on hydrogen-poor and helium-rich objects known as "carbon stars". The case of the hot peculiar variable V348 Sgr is discussed. New visible and infrared observations are presented, but the exact nature of the star remains much of an enigma. [less ▲]

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See detailHot Circumstellar Material around Vega
Absil, Olivier ULg; Di Folco, Emmanuel; Mérand, Antoine et al

in Coudé du Foresto, Vincent; Rouan, Daniel; Rousset, Gérard (Eds.) Visions for Infrared Astronomy (2006, March)

Using the FLUOR beam-combiner at the CHARA Array, we have obtained highprecision visibility measurements of Vega, a prototypic debris-disk star. The combination of long and short baselines has allowed us ... [more ▼]

Using the FLUOR beam-combiner at the CHARA Array, we have obtained highprecision visibility measurements of Vega, a prototypic debris-disk star. The combination of long and short baselines has allowed us to separately resolve the stellar photosphere and the close environment of the star (< 8 AU). Our observations show a significant deficit in square visibility at short baselines with respect to the expected visibility of a simple uniform disk stellar model, suggesting the presence of an extended source around Vega. We propose that the excess emission is most likely due to the presence of hot circumstellar dust in the inner part of Vega's debris disk, with a flux ratio of 1.29 ± 0.19% between the integrated dust emission and the stellar photosphere. Using this information together with archival photometric measurements in the nearand mid-infrared, we derive the expected physical properties of the circumstellar dust by modelling its infrared Spectral Energy Distribution. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations. [less ▲]

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See detailHot circumstellar material in Vega’s inner planetary system
Absil, Olivier ULg

Scientific conference (2006, March 21)

Using the FLUOR beam-combiner installed at the CHARA Array (Mt Wilson, CA), we have obtained high-precision visibility measurements of Vega, one of the prototypic debris-disk stars, known to be surrounded ... [more ▼]

Using the FLUOR beam-combiner installed at the CHARA Array (Mt Wilson, CA), we have obtained high-precision visibility measurements of Vega, one of the prototypic debris-disk stars, known to be surrounded by large amounts of cold dust in a ring-like structure at 80-100 AU. The combination of short and long baselines has allowed us to separately resolve the stellar photosphere and the close environment of the star (< 8 AU). Our observations show a significant deficit in square visibility at short baselines with respect to the expected visibility of a simple uniform disk stellar model (DV2 ~ 2%), suggesting the presence of an extended source of emission around Vega. The sparse (u, v) plane coverage does not allow for discriminating between a point source and an extended circumstellar emission as the origin of the extended emission. However, we show that the presence of a point-like source within the FLUOR field-ofview (1 arcsec in radius = 7.7 AU at the distance of Vega) is highly unlikely, and propose that the excess emission is most likely due to the presence of hot circumstellar dust in the inner part of Vega’s debris disk, with a flux ratio of 1.29±0.19% between the integrated dust emission and the stellar photosphere. Using this information together with archival photometric measurements in the near- and mid-infrared, we derive the expected physical properties of the circumstellar dust by modelling its infrared Spectral Energy Distribution. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations. [less ▲]

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See detailHot circumstellar material resolved around β Pic with VLTI/PIONIER
Defrère, D.; Lebreton, J.; Le Bouquin, J.-B. et al

in Astronomy and Astrophysics (2012), 546

Aims: We aim at resolving the circumstellar environment around β Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods: Precise interferometric fringe ... [more ▼]

Aims: We aim at resolving the circumstellar environment around β Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods: Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. Results: We detected near-infrared circumstellar emission around β Pic that accounts for 1.37% ± 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (≳1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of β Pic with an unprecedented accuracy (θLD= 0.736 ± 0.019 mas). Conclusions: The presence of a small H-band excess originating in the vicinity of β Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded. [less ▲]

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See detailHot dust in the inner parts of circumstellar debris discs
Absil, Olivier ULg

Scientific conference (2009, April 01)

Studying the warm inner part of debris discs—the extrasolar counterparts of the zodiacal dust cloud—is of prime importance to characterize the global architecture of planetary systems. Because of the high ... [more ▼]

Studying the warm inner part of debris discs—the extrasolar counterparts of the zodiacal dust cloud—is of prime importance to characterize the global architecture of planetary systems. Because of the high contrast and small angular separation between the star and the exozodiacal light, high-precision infrared interferometry is the best-suited tool to carry out such observations. In this paper, we review the first direct detection of an exozodiacal disc recently reported around Vega by Absil et al. (2006), and discuss the currently on-going observing efforts in this domain. We show how interferometric data can constrain the composition and the dynamics of extrasolar planetary systems, and thereby put useful constraints on the presence of small bodies and/or giant planets. First statistical trends for high-density exozodiacal discs towards a small sample of nearby main sequence stars are presented. Finally, we briefly discuss how next generation interferometric instruments could change our view of debris discs, pushing the detection limit towards meaningful density levels in the context of future life-finding missions such as Darwin/TPF. [less ▲]

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See detailHot electron production and diffuse excited states in C70, C82, and Sc3N@C80 characterized by angular-resolved photoelectron spectroscopy
Johansson, J. Olof; Bohl, Elvira; Henderson, Gordon G. et al

in Journal of Chemical Physics (2013), 139

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See detailHot exozodiacal dust resolved around Vega with IOTA/IONIC
Defrère, D.; Absil, Olivier ULg; Augereau, J.-C. et al

in Astronomy and Astrophysics (2011), 534

Context. Although debris discs have been detected around a significant number of main-sequence stars, only a few of them are known to harbour hot dust in their inner part where terrestrial planets may ... [more ▼]

Context. Although debris discs have been detected around a significant number of main-sequence stars, only a few of them are known to harbour hot dust in their inner part where terrestrial planets may have formed. Thanks to infrared interferometric observations, it is possible to obtain a direct measurement of these regions, which are of prime importance for preparing future exo-Earth characterisation missions. <BR /> Aims: We resolve the exozodiacal dust disc around Vega with the help of infrared stellar interferometry and estimate the integrated H-band flux originating from the first few AUs of the debris disc. <BR /> Methods: Precise H-band interferometric measurements were obtained on Vega with the 3-telescope IOTA/IONIC interferometer (Mount Hopkins, Arizona). Thorough modelling of both interferometric data (squared visibility and closure phase) and spectral energy distribution was performed to constrain the nature of the near-infrared excess emission. <BR /> Results: Resolved circumstellar emission within ~6 AU from Vega is identified at the 3-σ level. The most straightforward scenario consists in a compact dust disc producing a thermal emission that is largely dominated by small grains located between 0.1 and 0.3 AU from Vega and accounting for 1.23 ± 0.45% of the near-infrared stellar flux for our best-fit model. This flux ratio is shown to vary slightly with the geometry of the model used to fit our interferometric data (variations within ± 0.19%). <BR /> Conclusions: The presence of hot exozodiacal dust in the vicinity of Vega, initially revealed by K-band CHARA/FLUOR observations, is confirmed by our H-band IOTA/IONIC measurements. Whereas the origin of the dust is still uncertain, its presence and the possible connection with the outer disc suggest that the Vega system is currently undergoing major dynamical perturbations. [less ▲]

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See detailHot gas distribution in the wind of ζ Pup and ζ Ori
Herve, A.; Rauw, Grégor ULg; Nazé, Yaël ULg

Poster (2013, June 01)

We have developped a new X-ray modelling code based on embedded shocks which computes synthetic spectra as a function of plasma temperature, abundances and localization of the X-ray emitting shell in the ... [more ▼]

We have developped a new X-ray modelling code based on embedded shocks which computes synthetic spectra as a function of plasma temperature, abundances and localization of the X-ray emitting shell in the wind. We have also included a proper treatment of the radial dependence of the X-ray opacity of the cool matter as well as a treatment forthe Forbiden Inter combination Resonance (FIR) lines of He-like ions. Our code combines several synthetic spectra in order to fit all the lines of an X-ray spectrum simultaneously and coherently. Our results on two O-type stars ζ Pup and ζ Ori reveal non-porous winds with a mass loss rate consistent with studies in the optical domain as well as non-solar abundances for the CNO elements as expected for evolved stars. More important, the X-ray plasma starts emitting close to the stellarsurface. An improved version of our code allowing an analysis of the radial dependence of the hot gas filling factor reveals for ζ Ori a non continuity of the X-ray emission regions associated to high values of the hot gas filling factor. [less ▲]

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See detailThe hot Jupiter WASP-­121 b: A planet heading towards its doom
Delrez, Laetitia ULg

Conference (2015, May 28)

We present here the discovery by the WASP-South survey, in close collaboration with the Euler and TRAPPIST telescopes, of WASP-121 b, a new remarkable short-period transiting hot Jupiter. WASP-121 b is a ... [more ▼]

We present here the discovery by the WASP-South survey, in close collaboration with the Euler and TRAPPIST telescopes, of WASP-121 b, a new remarkable short-period transiting hot Jupiter. WASP-121 b is a very inflated (1.86 Rjup) Jupiter-mass (1.18 Mjup) planet that transits every 1.27 days a bright active F6V star. A notable property of WASP-121b is that its orbital semi-major axis is only 15% larger than its Roche limit, which suggests that the planet might be close to tidal disruption. Furthermore, its large size and extreme irradiation (7.1 10^9 erg s^-1 cm^-2) make it an excellent target for atmospheric studies via secondary eclipse observations. Using the TRAPPIST robotic telescope, we indeed detect its thermal emission in the z’-band at better than ~4sigma, the measured occultation depth being 603+-130 ppm. This measurement is a first for a ground-based 60cm telescope. Finally, from a measurement of the Rossiter-McLaughlin effect with the CORALIE spectrograph, we infer a sky-projected spin-orbit angle of 257.8+-6 deg. This result indicates a significant misalignment between the spin axis of the host star and the orbital plane of the planet, the planet being in a nearly polar orbit. [less ▲]

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See detailHot Jupiters with relatives: discovery of additional planets in orbit around WASP-41 and WASP-47
Neveu-VanMalle, M.; Queloz, D.; Anderson, D. R. et al

E-print/Working paper (2015)

We report the discovery of two additional planetary companions to WASP-41 and WASP-47. WASP-41 c is a planet of minimum mass 3.18 $\pm$ 0.20 M$_{\rm Jup}$ and eccentricity 0.29 $\pm$ 0.02, and it orbits ... [more ▼]

We report the discovery of two additional planetary companions to WASP-41 and WASP-47. WASP-41 c is a planet of minimum mass 3.18 $\pm$ 0.20 M$_{\rm Jup}$ and eccentricity 0.29 $\pm$ 0.02, and it orbits in 421 $\pm$ 2 days. WASP-47 c is a planet of minimum mass 1.24 $\pm$ 0.22 M$_{\rm Jup}$ and eccentricity 0.13 $\pm$ 0.10, and it orbits in 572 $\pm$ 7 days. Unlike most of the planetary systems that include a hot Jupiter, these two systems with a hot Jupiter have a long-period planet located at only $\sim$1 au from their host star. WASP-41 is a rather young star known to be chromospherically active. To differentiate its magnetic cycle from the radial velocity effect induced by the second planet, we used the emission in the H$\alpha$ line and find this indicator well suited to detecting the stellar activity pattern and the magnetic cycle. The analysis of the Rossiter-McLaughlin effect induced by WASP-41 b suggests that the planet could be misaligned, though an aligned orbit cannot be excluded. WASP-47 has recently been found to host two additional transiting super Earths. With such an unprecedented architecture, the WASP-47 system will be very important for understanding planetary migration. [less ▲]

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See detailThe Hot Oxygen Corona of Mars: Observations by MAVEN IUVS
Deighan; IUVS team; Stiepen, Arnaud ULg

Poster (2015, December)

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See detailHot shortness and scaling of Copper containing steels
Habraken, Louis; Lecomte-Beckers, Jacqueline ULg

in Le May, I.; Mc. Schetky, L. (Eds.) Copper in Iron and Steel (1982)

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See detailHot stars in the whole CoRoT mission
Briquet, Maryline ULg

Conference (2013, March 20)

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See detailHot stars observed by XMM-Newton. I. The catalog and the properties of OB stars
Nazé, Yaël ULg

in Astronomy and Astrophysics (2009), 506

Aims: Following the advent of increasingly sensitive X-ray observatories, deep observations of early-type stars became possible. However, the results for only a few objects or clusters have until now been ... [more ▼]

Aims: Following the advent of increasingly sensitive X-ray observatories, deep observations of early-type stars became possible. However, the results for only a few objects or clusters have until now been reported and there has been no large survey comparable to that based upon the ROSAT All-Sky Survey (RASS). <BR />Methods: A limited survey of X-ray sources, consisting of all public XMM-Newton observations (2XMMi) and slew survey data (XMMSL1), is now available. The X-ray counterparts to hot, massive stars have been searched for in these catalogs. <BR />Results: About 300 OB stars were detected with XMM-Newton. Half of them were bright enough for a spectral analysis to be possible, and we make available the detailed spectral properties that were derived. The X-ray spectra of O stars are represented well by low (<1 keV) temperature components and seem to indicate that an absorption column is present in addition to the interstellar contribution. The X-ray fluxes are well correlated with the bolometric fluxes, with a scatter comparable to that of the RASS studies and thus larger than found previously with XMM-Newton for some individual clusters. These results contrast with those of B stars that exhibit a large scatter in the L[SUB]X[/SUB] - L[SUB]BOL[/SUB] relation, no additional absorption being found, and the fits indicate a plasma at higher temperatures. Variability (either within one exposure or between multiple exposures) was also investigated whenever possible: short-term variations are far more rare than long-term ones (the former affects a few percent of the sample, while the latter concerns between one third and two thirds of the sources). <BR />Conclusions: This paper presents the results of the first high-sensitivity investigation of the overall high-energy properties of a sizable sample of hot stars. 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 accessed via the 2XMMi and XMM slew survey catalogs. Tables 1 and 5 are 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/506/1055 Postdoctoral Researcher FNRS. Visiting astronomer, UNAM-Morelos (Mexico). [less ▲]

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See detailHot stars survey with the GAIA space mission
Lobel, A.; Liu, C.; Frémat, Y. et al

Poster (2009)

Detailed reference viewed: 30 (11 ULg)
See detailHot Topic : Clinical and genetics features of familial isolated pituitary adenomas
Beckers, Albert ULg

Scientific conference (2006, October)

Detailed reference viewed: 10 (1 ULg)