References of "Absil, Olivier"
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See detailOn the sensitivity of closure phases to faint companions in optical long baseline interferometry
Le Bouquin, Jean-Baptiste; Absil, Olivier ULg

in Astronomy and Astrophysics (2012), 541

We explore the sensitivity and completeness of long baseline interferometric observations for detecting unknown, faint companions around bright unresolved stars. We derive a linear expression for the ... [more ▼]

We explore the sensitivity and completeness of long baseline interferometric observations for detecting unknown, faint companions around bright unresolved stars. We derive a linear expression for the closure phase signature of a faint companion in the high contrast regime (<0.1), and provide a quantitative estimation of the detection efficiency for the currently offered four-telescope configurations at the Very Large Telescope Interferometer. The results are compared to the performances provided by linear and Y-shaped interferometric configurations in order to identify the ideal array. We find that all configurations have a similar efficiency in discovering companions wider than 10mas. Assuming a closure phase accuracy of 0.25deg, that is typical of state-of-the-art instruments, we predict a median dynamic range of up to six magnitudes when stacking observations obtained at five different hour angles. Surveying bright stars to search for faint companions can be considered as an ideal filler programme for modern interferometric facilities because that places few constraints on the choice of the interferometric configuration. [less ▲]

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See detailDevelopment of diamond AGPM coronagraphs for VISIR and NACO
Delacroix, Christian ULg; Habraken, Serge ULg; Karlsson, Mikael et al

Conference (2012, March 22)

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See detailThe connection between inner and outer debris disks probed by infrared interferometry
Absil, Olivier ULg

Conference (2012, March 22)

The far-infrared surveys of nearby main sequence stars performed since the launch of IRAS have shown that a significant fraction of main sequence stars are surrounded by cold dust populations. These ... [more ▼]

The far-infrared surveys of nearby main sequence stars performed since the launch of IRAS have shown that a significant fraction of main sequence stars are surrounded by cold dust populations. These surveys are now culminating with the the DUNES and DEBRIS key projects of the Herschel Space Observatory, which is more sensitive than ever and is able to detect cold dust populations with densities similar to that of the solar system Kuiper belt. However, little is known about the occurence of warm dust populations, the equivalent of our zodiacal cloud. Since 2005, high-precision infrared interferometers have opened a new way to directly resolve these exozodiacal dust populations. Interferometric observations enable to reach dynamic ranges (larger than 100:1) that are generally not achievable with classical spectro-photometric observations. We are currently carrying out a survey to characterise the hot dust populations around main sequence stars. The first results of this survey, performed on the CHARA array with the FLUOR instrument, will be presented in this talk. The results are based on a magnitude-limited sample of stars surrounded by cold dust and on an equivalent sample of stars showing no cold dust emission. The statistics for the occurence of bright exozodiacal disks will be presented, and compared with the Spitzer and Herschel results. The possible (dynamical) connections between the two populations will be discussed. We will also review the results obtained by other interferometers and discuss the on-going projects. [less ▲]

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See detailModelling the huge, Herschel-resolved debris ring around HD 207129
Löhne, T.; Augereau, J.-C.; Ertel, S. et al

in Astronomy and Astrophysics (2012), 537

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation ... [more ▼]

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation and evolution are linked to those of planetary bodies, they provide valuable information. The few well-resolved debris disks are even more valuable because they can serve as modelling benchmarks and help resolve degeneracies in modelling aspects such as typical grain sizes and distances. Here, we present an analysis of the HD 207129 debris disk, based on its well-covered spectral energy distribution and Herschel/PACS images obtained in the framework of the DUNES (DUst around NEarby Stars) programme. We use an empirical power-law approach to the distribution of dust and we then model the production and removal of dust by means of collisions, direct radiation pressure, and drag forces. The resulting best-fit model contains a total of nearly 10[SUP]-2[/SUP] Earth masses in dust, with typical grain sizes in the planetesimal belt ranging from 4 to 7 μm. We constrain the dynamical excitation to be low, which results in very long collisional lifetimes and a drag that notably fills the inner gap, especially at 70 μm. The radial distribution stretches from well within 100 AU in an unusual, outward-rising slope towards a rather sharp outer edge at about 170-190 AU. The inner edge is therefore smoother than that reported for Fomalhaut, but the contribution from the extended halo of barely bound grains is similarly small. Both slowly self-stirring and planetary perturbations could potentially have formed and shaped this disk. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailDes franges à 4 télescopes au VLTI: premiers résultats de PIONIER
Absil, Olivier ULg

Scientific conference (2011, December 05)

Le 17 mars 2011, dix ans jour pour jour après les premières franges à deux télescopes au VLTI, les quatre grands télescopes de 8m ont été mis en phase en recombinés pour la première fois par ... [more ▼]

Le 17 mars 2011, dix ans jour pour jour après les premières franges à deux télescopes au VLTI, les quatre grands télescopes de 8m ont été mis en phase en recombinés pour la première fois par interférométrie. Cette prouesse technique a été rendue possible par l'installation d'un nouvel instrument à quatre faisceaux, PIONIER. Cet instrument visiteur, développé par l'IPAG (Grenoble), a été installé il y a un peu plus d'un an à Paranal, et utilise principalement les télescopes auxiliaires de 1.8m de diamètre pour ses programmes scientifiques. Dans ce séminaire, je décrirai brièvement le projet PIONIER et les caractéristiques techniques uniques de cet instrument. Je présenterai ensuite les objectifs scientifiques principaux et les premiers résultats obtenus, qui vont de la caractérisation des disques protoplanétaires à l'imagerie des surfaces stellaires, en passant par l'observation de binaires massives ou en interaction. Je m'attarderai davantage sur les deux programmes d'imagerie à haut contraste dans lesquels je suis plus particulièrement impliqué. Ils concernent la détection de disques exozodiacaux et de compagnons faibles autour d'étoiles de la séquence principale. [less ▲]

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See detailHerschel discovery of a new class of cold, faint debris discs
Eiroa, C.; Marshall, J. P.; Mora, A. et al

in Astronomy and Astrophysics (2011), 536

We present Herschel PACS 100 and 160 μm observations of the solar-type stars α Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel open time key programme (OTKP) DUNES ... [more ▼]

We present Herschel PACS 100 and 160 μm observations of the solar-type stars α Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel open time key programme (OTKP) DUNES (DUst around NEarby Stars). Our observations show small infrared excesses at 160 μm for all three stars. HD 210277 also shows a small excess at 100 μm, while the 100 μm fluxes of α Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. Both α Men and HD 88230 are spatially resolved in the PACS 160 μm images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from ~115 to ≤ 250 AU. The estimated black body temperatures from the 100 and 160 μm fluxes are ≲22 K, and the fractional luminosity of the cold dust is L[SUB]dust[/SUB]/L[SUB] ⋆ [/SUB] ~ 10[SUP]-6[/SUP], close to the luminosity of the solar-system's Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars, so they cannot be explained easily invoking "classical" debris disc models. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailPIONIER: a 4-telescope visitor instrument at VLTI
Le Bouquin, J.-B.; Berger, J.-P.; Lazareff, B. et al

in Astronomy and Astrophysics (2011), 535

Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer ... [more ▼]

Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer (ESO, Chile) using an integrated optics combiner. The instrument was integrated at IPAG in December 2009 and commissioned at the Paranal Observatory in October 2010. It has provided scientific observations since November 2010. <BR /> Aims: In this paper, we explain the instrumental concept and describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. <BR /> Methods: This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries δ Sco and HIP11231. <BR /> Results: PIONIER provides six visibilities and three independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R = 40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag = 7 in dispersed mode under median atmospheric conditions (seeing < 1, τ[SUB]0[/SUB] > 3ms) with the 1.8m Auxiliary Telescopes. We demonstrate a precision of 0.5deg on the closure phases. The precision on the calibrated visibilities ranges from 3% to 15% depending on the atmospheric conditions. <BR /> Conclusions: PIONIER was installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8m Unit Telescopes in March 2011 demonstrates that VLTI is ready for four-telescope operation. Based on observations collected at the European Southern Observatory, Paranal, Chile (commissioning data and 087.C-0709). [less ▲]

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See detailSearching for faint companions with VLTI/PIONIER. I. Method and first results
Absil, Olivier ULg; Le Bouquin, J.-B.; Berger, J.-P. et al

in Astronomy and Astrophysics (2011), 535

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. <BR /> Aims: We search ... [more ▼]

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. <BR /> Aims: We search for low-mass companions around a few bright stars using different strategies, and determine the dynamic range currently reachable with PIONIER. <BR /> Methods: Our method is based on the closure phase, which is the most robust interferometric quantity when searching for faint companions. We computed the χ[SUP]2[/SUP] goodness of fit for a series of binary star models at different positions and with various flux ratios. The resulting χ[SUP]2[/SUP] cube was used to identify the best-fit binary model and evaluate its significance, or to determine upper limits on the companion flux in case of non-detections. <BR /> Results: No companion is found around <ASTROBJ>Fomalhaut</ASTROBJ>, <ASTROBJ>tau Cet</ASTROBJ> and <ASTROBJ>Regulus</ASTROBJ>. The median upper limits at 3σ on the companion flux ratio are respectively of 2.3 × 10[SUP]-3[/SUP] (in 4 h), 3.5 × 10[SUP]-3[/SUP] (in 3 h) and 5.4 × 10[SUP]-3[/SUP] (in 1.5 h) on the search region extending from 5 to 100 mas. Our observations confirm that the previously detected near-infrared excess emissions around Fomalhaut and tau Cet are not related to a low-mass companion, and instead come from an extended source such as an exozodiacal disk. In the case of <ASTROBJ>del Aqr</ASTROBJ>, in 30 min of observation, we obtain the first direct detection of a previously known companion, at an angular distance of about 40 mas and with a flux ratio of 2.05 × 10[SUP]-2[/SUP] ± 0.16 × 10[SUP]-2[/SUP]. Due to the limited u,v plane coverage, its position can, however, not be unambiguously determined. <BR /> Conclusions: After only a few months of operation, PIONIER has already achieved one of the best dynamic ranges world-wide for multi-aperture interferometers. A dynamic range up to about 1:500 is demonstrated on unresolved targets, but significant improvements are still required to reach the ultimate goal of directly detecting hot giant extrasolar planets. Based on observations obtained at the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI), Paranal, Chile. [less ▲]

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See detailDetecting faint companions with PIONIER
Absil, Olivier ULg

Conference (2011, October 25)

One of the main goals of the PIONIER visitor instrument at VLTI is to search for faint companions around relatively bright stars. In this talk, we present a general method to search for companions in ... [more ▼]

One of the main goals of the PIONIER visitor instrument at VLTI is to search for faint companions around relatively bright stars. In this talk, we present a general method to search for companions in PIONIER data, with a particular emphasis on the exploitation of closure phases. Our search method is illustrated on a few exemples, including the detection of companions at the ~1% contrast level, and non-detections showing upper limits of a few 0.1% on the contrast of any companion within the interferometric field-of-view. In particular, we demonstrate that the small near-infrared excesses previously reported around several main-sequence stars with precision near-infrared interferometry is not related to the presence of low-mass companions around the target stars. The current limitations of PIONIER are shortly discussed, and we derive some general guidelines on how to best use an interferometric array for faint companion detection. Finally, we discuss how the dynamic range and angular resolution provided by of PIONIER can serve various scientific goals, ranging from low-mass companions around main sequence stars to massive binaries. We show that PIONIER could detect objects at the brown dwarf / planet boundary for young low-mass stars residing in nearby associations. [less ▲]

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See detailImaging the inner regions of debris disks with near-infrared interferometry
Defrère, D.; Absil, Olivier ULg; Augereau, J. C. et al

in EPSC-DPS Joint Meeting 2011 (2011, October 01)

Most debris disks resolved so far show extended structures located at tens to hundreds AU from the host star, and are more analogous to our solar system's dusty Kuiper belt than to the AU-scale zodiacal ... [more ▼]

Most debris disks resolved so far show extended structures located at tens to hundreds AU from the host star, and are more analogous to our solar system's dusty Kuiper belt than to the AU-scale zodiacal disk inside our solar system's asteroid belt. Over the last few years however, a few hot debris disks have been detected around a handful of main sequence stars thanks to the advance of infrared interferometry. The grain populations derived from these observations are quite intriguing, as they point towards very high dust replenishment rates, high cometary activity or major collisional events. In this talk, we review the ongoing efforts to detect bright exozodiacal disks with precision near-infrared interferometry in both hemispheres with CHARA/FLUOR and VLTI/PIONIER. We discuss preliminary statistical trends on the occurrence of bright exozodi around nearby main sequence stars and show how this information could be used to constrain the global architecture and evolution of debris disks. [less ▲]

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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 detailThe spin-orbit alignment of the Fomalhaut debris disk
Absil, Olivier ULg

Scientific conference (2011, September 30)

The measurement of the Rossiter-MacLaughlin effect in transiting planetary systems has revealed a significant population of hot giant planets orbiting outside the equatorial plane of their parent star. In ... [more ▼]

The measurement of the Rossiter-MacLaughlin effect in transiting planetary systems has revealed a significant population of hot giant planets orbiting outside the equatorial plane of their parent star. In an attempt to improve our understanding of these spin-orbit misalignements, and discriminate between various scenarios, we propose to determine whether debris disks are located within the equatorial plane of their star using infrared spectro-interferometry. To validate our approch, we have chosen the bright star Fomalhaut and measured the orientation of its rotationnally-distorted stellar photosphere using micro-arcsecond precision VLTI/AMBER spectro-astrometry within the Br-gamma line. The derived poition angle is in perfect agreement with the position angle of the cold debris disk imaged in the visible and sub-millimeter domains. We discuss the implications of this result on our understanding of the dust grain properties in the Fomalhaut disk, and how this study can be extended to other debris disk systems. [less ▲]

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See detailTaking the vector vortex coronagraph to the next level for ground- and space-based exoplanet imaging instruments: review of technology developments in the USA, Japan, and Europe
Mawet, Dimitri; Murakami, Naoshi; Delacroix, Christian ULg et al

in Shaklan, Stuart (Ed.) Techniques and Instrumentation for Detection of Exoplanets V. (2011, September 01)

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at ... [more ▼]

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris- Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive optics, extremely large ground-based telescopes, and space-based internal coronagraphs. [less ▲]

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See detailA Dim Candidate Companion to epsilon Cephei
Mawet, D.; Mennesson, B.; Serabyn, E. et al

in Astrophysical Journal Letters (2011), 738

Using a vector vortex coronagraph behind the 1.5 m well-corrected subaperture (WCS) at Palomar, we detected a second object very close to epsilon Cephei, a δ Scuti F0 IV star. The candidate companion, ~50 ... [more ▼]

Using a vector vortex coronagraph behind the 1.5 m well-corrected subaperture (WCS) at Palomar, we detected a second object very close to epsilon Cephei, a δ Scuti F0 IV star. The candidate companion, ~50 times fainter than epsilon Cephei, if physically associated, is a late-type K or early M star, and lies at an angular separation of 330 mas, or 1.1 λ/D for the WCS, making it the smallest angle detection ever realized with a coronagraph in terms of λ/D units. The projected separation of the putative companion is ~8.6 AU, most likely on a highly eccentric orbit. The recently detected near-infrared excess is thus likely not due to hot dust. Moreover, we also show that the previously reported IRAS 60 μm excess was due to source confusion on the galactic plane. [less ▲]

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See detailStudying the Fomalhaut debris disk with infrared interferometry
Absil, Olivier ULg

Scientific conference (2011, July 15)

In this talk, I will describe two recent studies carried out with infrared interferometry to characterise the planetary system around Fomalhaut, and its debris disk in particular. In the first study, we ... [more ▼]

In this talk, I will describe two recent studies carried out with infrared interferometry to characterise the planetary system around Fomalhaut, and its debris disk in particular. In the first study, we aimed to determine whether the debris disk is located within the equatorial plane of the stellar photosphere, in an attempt to improve our understanding of spin-orbit misalignements in planetary systems in general. We measured the orientation of the rotationnally-distorted stellar photosphere using micro-arcsecond precision VLTI/AMBER spectro-astrometry within the Br-gamma line. The derived poition angle is in perfect agreement with the position angle of the cold debris disk measured in visible and sub-millimeter images. We discuss the implications of this result on our understanding of the dust grain properties in the Fomalhaut disk. In the second study, we aimed at characterising the dust content of the innermost part of the debris disk. We used archival high-precision K-band visibility measurements with VLTI/VINCI and obtained N-band nulling observations with the Keck Interferometer Nuller. We report a significant excess emission at K band, and a marginal excess emission at N band, that we attempt to reproduce with a 2D debris disk model. A comprehensive Bayesian analysis of the main disk parameters is performed to derive most-probable values. Our analysis points towards a very compact ring of hot dust close to the sublimation radius as the origin of the reported excess emission. [less ▲]

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See detailOptimized fringe sensors for the VLTI next generation instruments
Blind, N.; Absil, Olivier ULg; Le Bouquin, J.-B. et al

in Astronomy and Astrophysics (2011), 530

Context. With the arrival of the next generation of ground-based imaging interferometers combining from four to possibly six telescopes simultaneously, there is also a strong need for a new generation of ... [more ▼]

Context. With the arrival of the next generation of ground-based imaging interferometers combining from four to possibly six telescopes simultaneously, there is also a strong need for a new generation of fringe trackers able to cophase these arrays. These instruments have to be very sensitive and to provide robust operations in quickly varying observational conditions. <BR /> Aims: We aim at defining the optimal characteristics of fringe sensor concepts operating with four or six telescopes. The current detector limitations lead us to consider solutions based on co-axial pairwise combination schemes. <BR /> Methods: We independently study several aspects of the fringe sensing process: 1) how to measure the phase and the group delay, and 2) how to combine the telescopes to ensure a precise and robust fringe tracking in real conditions. Thanks to analytical developments and numerical simulations, we define the optimal fringe-sensor concepts and compute the expected performance of the four-telescope one with our dedicated end-to-end simulation tool sim2GFT. <BR /> Results: We first show that measuring the phase and the group delay by obtaining the data in several steps (i.e. by temporally modulating the optical path difference) is extremely sensitive to atmospheric turbulence and therefore conclude that it is better to obtain the fringe position with a set of data obtained simultaneously. Subsequently, we show that among all co-axial pairwise schemes, moderately redundant concepts increase the sensitivity as well as the robustness in various atmospheric or observing conditions. Merging all these results, end-to-end simulations show that our four-telescope fringe sensor concept is able to track fringes at least 90% of the time up to limiting magnitudes of 7.5 and 9.5 for the 1.8- and 8.2-meter VLTI telescopes respectively. [less ▲]

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See detailSpin-orbit alignment in planetary systems: what can we learn from resolved debris disks?
Absil, Olivier ULg

Scientific conference (2011, May 17)

Since the first detection of the spectroscopic transit of a hot Jupiter by Queloz et al. (2000), the Rossiter-McLaughlin effect, which allows the measurement of the sky-projected angle between the stellar ... [more ▼]

Since the first detection of the spectroscopic transit of a hot Jupiter by Queloz et al. (2000), the Rossiter-McLaughlin effect, which allows the measurement of the sky-projected angle between the stellar rotation axis and a planet's orbit axis, has been investigated for a large number of planetary systems. These observations have lead to the detection of spin-orbit misalignments for many hot Jupiters, and even of retrograde orbits in some cases (e.g., Triaud et al. 2010). Such misalignments are generally interpreted as the signature of either Kozai migration, or of planet-planet scattering followed by inward migration of the planet (e.g., Morton & Johnson 2011). However, it has recently been proposed that circumstellar disks themselves might not be aligned with the stellar spin axis due to either to early stellar encounters (Bate et al. 2010) or to magnetosphere-disk interactions (Lai et al. 2011). In this talk, I discuss how resolved debris disks may be used to settle this question, in particular by measuring the position angle of oblate stellar photospheres deformed by rapid rotation using spectro-interferometric measurements within the Brackett-gamma line. The method is illustrated by our recent study of Fomalhaut with VLTI/AMBER (Le Bouquin et al. 2009), which confirms the spin-orbit alignment with a high accuracy for the first time in a debris disk system. Possible implications on the nature of the dust grains composing the Fomalhaut debris disk will also be discussed. [less ▲]

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See detailA Herschel resolved far-infrared dust ring around HD 207129
Marshall, J. P.; Löhne, T.; Montesinos, B. et al

in Astronomy and Astrophysics (2011), 529

Context. Dusty debris discs around main sequence stars are thought to be the result of continuous collisional grinding of planetesimals in the system. The majority of these systems are unresolved and ... [more ▼]

Context. Dusty debris discs around main sequence stars are thought to be the result of continuous collisional grinding of planetesimals in the system. The majority of these systems are unresolved and analysis of the dust properties is limited by the lack of information regarding the dust location. <BR /> Aims: The Herschel DUNES key program is observing 133 nearby, Sun-like stars (<20 pc, FGK spectral type) in a volume limited survey to constrain the absolute incidence of cold dust around these stars by detection of far infrared excess emission at flux levels comparable to the Edgeworth-Kuiper belt (EKB). <BR /> Methods: We have observed the Sun-like star HD 207129 with Herschel PACS and SPIRE. In all three PACS bands we resolve a ring-like structure consistent with scattered light observations. Using α Boötis as a reference point spread function (PSF), we deconvolved the images, clearly resolving the inner gap in the disc at both 70 and 100 μm. <BR /> Results: We have resolved the dust-producing planetesimal belt of a debris disc at 100 μm for the first time. We measure the radial profile and fractional luminosity of the disc, and compare the values to those of discs around stars of similar age and/or spectral type, placing this disc in context of other resolved discs observed by Herschel/DUNES. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailStudying debris disks with near‐infrared interferometry
Absil, Olivier ULg; Augereau, J.-C.; Le Bouquin, J.-B. et al

Conference (2011, April 13)

In this talk, I will describe and illustrate two different ways in which near-infrared stellar interferometry can be used to constrain the nature and physics of debris disks, and help understand the ... [more ▼]

In this talk, I will describe and illustrate two different ways in which near-infrared stellar interferometry can be used to constrain the nature and physics of debris disks, and help understand the global architecture of planetary systems in general. In the first part of the talk, I will review the on-going efforts to detect bright exozodiacal disks with precision near-infrared interferometry. I will describe the results of the exozodi survey that we are currently carrying out at the CHARA array, and briefly discuss our first results and perspectives with the new PIONIER instrument at the VLTI (including the identification of previously unknown low-mass companions). Preliminary statistical trends on the occurrence of bright exozodi around nearby main sequence stars will be presented, and I will discuss how this information could be used to constrain the global architecture and evolution of debris disks. In the second part of the talk, I will focus on our on-going project to characterize the “spin-orbit” alignment of resolved debris disks with the rotation axis of their (rapidly rotating) host star. Our first result obtained with the VLTI/AMBER spectro-interferometer on Fomalhaut will be presented, as well as its possible consequences on the dynamics of the planetary system and on the physics of the grains composing the Fomalhaut dust ring. I will then briefly describe the status and perspectives of this project. [less ▲]

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See detailImproving Interferometric null depth measurements using statistical distributions: theory and first results with the Palomar Fiber Nuller
Hanot, Charles ULg; Mennesson, Bertrand; Martin, Stefan et al

in Astrophysical Journal (2011), 729(2), 110

A new "self-calibrated" statistical analysis method has been developed for the reduction of nulling interferometry data. The idea is to use the statistical distributions of the fluctuating null depth and ... [more ▼]

A new "self-calibrated" statistical analysis method has been developed for the reduction of nulling interferometry data. The idea is to use the statistical distributions of the fluctuating null depth and beam intensities to retrieve the astrophysical null depth (or equivalently the object's visibility) in the presence of fast atmospheric fluctuations. The approach yields an accuracy much better (about an order of magnitude) than is presently possible with standard data reduction methods, because the astrophysical null depth accuracy is no longer limited by the magnitude of the instrumental phase and intensity errors but by uncertainties on their probability distributions. This approach was tested on the sky with the two-aperture fiber nulling instrument mounted on the Palomar Hale telescope. Using our new data analysis approach alone—and no observations of calibrators—we find that error bars on the astrophysical null depth as low as a few 10–4 can be obtained in the near-infrared, which means that null depths lower than 10–3 can be reliably measured. This statistical analysis is not specific to our instrument and may be applicable to other interferometers. [less ▲]

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