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See detailSystem overview of the VLTI Spectro-Imager
Jocou, L.; Berger, J.-P.; Malbet, F. et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope ... [more ▼]

The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility. The concept of VSI consists on 6 sub-systems: a common path distributing the light between the fringe tracker and the scientific instrument, the fringe tracker ensuring the co-phasing of the array, the scientific instrument delivering the interferometric observables and a calibration tool providing sources for internal alignment and interferometric calibrations. The two remaining sub-systems are the control system and the observation support software dedicated to the reduction of the interferometric data. This paper presents the global concept of VSI science path including the common path, the scientific instrument and the calibration tool. The scientific combination using a set of integrated optics multi-way beam combiners to provide high-stability visibility and closure phase measurements are also described. Finally we will address the performance budget of the global VSI instrument. The fringe tracker and scientific spectrograph will be shortly described. [less ▲]

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See detailPolar-interferometry: what can be learnt from the IOTA/IONIC experiment
Le Bouquin, Jean-Baptiste; Rousselet-Perraut, Karine; Berger, Jean-Philippe et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

We report the first near-IR polar-interferometric observations, performed at the IOTA array using its integrated optics combiner IONIC. Fringes have been obtained on calibration stars and resolved late ... [more ▼]

We report the first near-IR polar-interferometric observations, performed at the IOTA array using its integrated optics combiner IONIC. Fringes have been obtained on calibration stars and resolved late-type giants. Optical modeling of the array and dedicated laboratory measures allowed us to confirm the good accuracy obtained on the calibrated polarized visibilities and closure phases. However, no evidences for polarimetric features at high angular resolution have been detected. The simulations and the results presented here open several perspectives for polar-interferometry, especially in the context of fibered, single-mode combiners. [less ▲]

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See detailProspects for near-infrared characterisation of hot Jupiters with the VLTI Spectro-Imager (VSI)
Renard, Stéphanie; Absil, Olivier ULg; Berger, J.-P. et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

In this paper, we study the feasibility of obtaining near-infrared spectra of bright extrasolar planets with the 2nd generation VLTI Spectro-Imager instrument (VSI), which has the required angular ... [more ▼]

In this paper, we study the feasibility of obtaining near-infrared spectra of bright extrasolar planets with the 2nd generation VLTI Spectro-Imager instrument (VSI), which has the required angular resolution to resolve nearby hot Extrasolar Giant Planets (EGPs) from their host stars. Taking into account fundamental noises, we simulate closure phase measurements of several extrasolar systems using four 8-m telescopes at the VLT and a low spectral resolution (R = 100). Synthetic planetary spectra from T. Barman are used as an input. Standard chi[SUP]2[/SUP]-fitting methods are then used to reconstruct planetary spectra from the simulated data. These simulations show that low-resolution spectra in the H and K bands can be retrieved with a good fidelity for half a dozen targets in a reasonable observing time (about 10 hours, spread over a few nights). Such observations would strongly constrain the planetary temperature and albedo, the energy redistribution mechanisms, as well as the chemical composition of their atmospheres. Systematic errors, not included in our simulations, could be a serious limitation to these performance estimations. The use of integrated optics is however expected to provide the required instrumental stability (around 10[SUP]-4[/SUP] on the closure phase) to enable the first thorough characterisation of extrasolar planetary emission spectra in the near-infrared. [less ▲]

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See detailHigh dynamic range interferometric observations of exozodiacal discs: performance comparison between ground, space, and Antarctica
Absil, Olivier ULg; Defrere, Denis; Coudé du Foresto, Vincent et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

The possible presence of large amounts of exozodiacal dust around nearby main sequence stars represents a threat to the detection and characterisation of Earth-like extrasolar planets with future infrared ... [more ▼]

The possible presence of large amounts of exozodiacal dust around nearby main sequence stars represents a threat to the detection and characterisation of Earth-like extrasolar planets with future infrared space interferometers such as DARWIN or TPF. In this paper, we first review the current detection capabilities of ground-based infrared interferometers such as CHARA/FLUOR and the detections of hot dust that have been obtained so far around a few main sequence stars. With the help of realistic instrumental simulations, we then discuss the relative merits of various ground-based sites (temperate and Antarctic) versus space-based observatories for the detection of exozodiacal discs down to a few zodi by interferometric nulling as a preparation to future life-finding missions. In particular, we discuss the performance of four proposed nulling interferometers: GENIE, ALADDIN, PEGASE and FKSI. An optimised strategy for the characterisation of candidate DARWIN/TPF targets is finally proposed. [less ▲]

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See detailEarth-like planets: science performance predictions for future nulling interferometry missions
Defrere, Denis ULg; Lay, O.; den Hartog, R. et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

With the launch of planet-transit missions such as CoRoT and Kepler, it is expected that Earth-sized planets orbiting distant stars will be detected soon. This milestone will open the path towards the ... [more ▼]

With the launch of planet-transit missions such as CoRoT and Kepler, it is expected that Earth-sized planets orbiting distant stars will be detected soon. This milestone will open the path towards the definition of missions able to study the atmosphere of Earth-sized extrasolar planets, with the identification of bio-signatures as one of the main objectives. In that respect, both the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) have identified nulling interferometry as one of the most promising techniques. Trying to minimize the cost and the technological risks while maximizing the scientific return, ESA and NASA recently converged towards a single mission architecture, the Emma X-array. In this paper, we present the expected science performance of this concept computed with two independent mission simulators. The impact of different observational parameters such as planet radius and exozodiacal cloud density is specifically addressed. [less ▲]

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See detailOn the observability of resonant structures in planetesimal disks due to planetary migration
Reche, R.; Beust, H.; Augereau, J.-C. et al

in Astronomy and Astrophysics (2008), 480

Context: The observed clumpy structures in debris disks are commonly interpreted as particles trapped in mean-motion resonances with an unseen exo-planet. Populating the resonances requires a migrating ... [more ▼]

Context: The observed clumpy structures in debris disks are commonly interpreted as particles trapped in mean-motion resonances with an unseen exo-planet. Populating the resonances requires a migrating process of either the particles (spiraling inward due to drag forces) or the planet (moving outward). Because the drag time-scale in resolved debris disks is generally long compared to the collisional time-scale, the planet migration scenario might be more likely, but this model has so far only been investigated for planets on circular orbits. Aims: We present a thorough study of the impact of a migrating planet on a planetesimal disk, by exploring a broad range of masses and eccentricities for the planet. We discuss the sensitivity of the structures generated in debris disks to the basic planet parameters. Methods: We perform many N-body numerical simulations, using the symplectic integrator SWIFT, taking into account the gravitational influence of the star and the planet on massless test particles. A constant migration rate is assumed for the planet. Results: The effect of planetary migration on the trapping of particles in mean motion resonances is found to be very sensitive to the initial eccentricity of the planet and of the planetesimals. A planetary eccentricity as low as 0.05 is enough to smear out all the resonant structures, except for the most massive planets. The planetesimals also initially have to be on orbits with a mean eccentricity of less than than 0.1 in order to keep the resonant clumps visible. Conclusions: This numerical work extends previous analytical studies and provides a collection of disk images that may help in interpreting the observations of structures in debris disks. Overall, it shows that stringent conditions must be fulfilled to obtain observable resonant structures in debris disks. Theoretical models of the origin of planetary migration will therefore have to explain how planetary systems remain in a suitable configuration to reproduce the observed structures. [less ▲]

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See detailGENIE: a Ground-Based European Nulling Instrument at ESO Very Large Telescope Interferometer
Gondoin, P.; den Hartog, R.; Fridlund, M. et al

in Richichi, A.; Delplancke, F.; Paresce, F. (Eds.) et al The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation Instrumentation (2008)

Darwin is one of the most challenging space projects ever considered by the European Space Agency (ESA). Its principal objectives are to detect Earth-like planets around nearby stars, to analyze the ... [more ▼]

Darwin is one of the most challenging space projects ever considered by the European Space Agency (ESA). Its principal objectives are to detect Earth-like planets around nearby stars, to analyze the composition of their atmospheres and to assess their ability to sustain life as we know it. Darwin is conceived as a space ``nulling interferometer'' which makes use of on-axis destructive interferences to extinguish the stellar light while keeping the off-axis signal of the orbiting planet. Within the frame of the Darwin program, definition studies of a Ground based European Nulling Interferometry Experiment, called GENIE, were completed in 2005. This instrument built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. GENIE will operate in the L' band around 3.8 microns as a single Bracewell nulling interferometer using either two Auxiliary Telescopes (ATs) or two 8m Unit Telescopes (UTs). Its science objectives include the detection and characterization of dust disks and low-mass companions around nearby stars. [less ▲]

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See detailA Numerical Simulator for VITRUV
Lebouquin, J.-B.; Herwats, Emilie ULg; Carvalho, M.-I. et al

in Richichi, A.; Delplancke, F.; Paresce, F. (Eds.) et al The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation Instrumentation (2008)

VITRUVsim is a numerical tool with as much as possible physics included. Inputs are the source parameters (flux, morphology, position...) and outputs are sequences of observed fringes and/or reduced ... [more ▼]

VITRUVsim is a numerical tool with as much as possible physics included. Inputs are the source parameters (flux, morphology, position...) and outputs are sequences of observed fringes and/or reduced visibilities. VITRUVsim is written in a portable and free language. [less ▲]

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See detailGENIE: High-Resolution Study of Debris Disks
Absil, Olivier ULg; Augereau, Jean-Charles; Den Hartog, Roland et al

in Richichi, A.; Delplancke, F.; Paresce, F. (Eds.) et al The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation Instrumentation (2008)

GENIE, the Ground-based European Nulling Interferometer Experiment, will combine the lights collected in the L’ band by two VLT telescopes in a destructive way, thereby revealing the thermal and/or ... [more ▼]

GENIE, the Ground-based European Nulling Interferometer Experiment, will combine the lights collected in the L’ band by two VLT telescopes in a destructive way, thereby revealing the thermal and/or scattered emission of faint objects in the close neighbourhood of the target star. A prime scientific goal for GENIE thus consists in the detection and characterization of debris disks around nearby Vega-type stars. Thanks to its high angular resolution and operating wavelength (3.8 µm), GENIE will be particularly sensitive to the thermal emission from the warm dust standing within a few AU from the star, a part of the disks which is not accessible with current detection methods (IR photometric excesses, sub-millimeter imaging, …). In this paper, we investigate the capabilities of GENIE to detect and characterize the physical parameters of the debris disk around zeta Leporis, a prototypical Vega-type star suspected to harbour a warm dust component in its debris disk (Fajardo-Acosta et al., AJ 115, 2101). This study is then extended to the detection of faint exozodiacal disks around typical Darwin/TPF targets, thereby demonstrating the very high potential of GENIE in the field of high-contrast imaging. [less ▲]

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See detailDarwin: required performance (invited)
Absil, Olivier ULg

Scientific conference (2007, December 06)

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See detailNulling interferometry: performance comparison between Antarctica and other ground-based sites
Absil, Olivier ULg; Coudé Du Foresto, V.; Barillot, M. et al

in Astronomy and Astrophysics (2007), 475

Context: Detecting the presence of circumstellar dust around nearby solar-type main sequence stars is an important pre-requisite for the design of future life-finding space missions such as ESA's Darwin ... [more ▼]

Context: Detecting the presence of circumstellar dust around nearby solar-type main sequence stars is an important pre-requisite for the design of future life-finding space missions such as ESA's Darwin or NASA's Terrestrial Planet Finder (TPF). The high Antarctic plateau may provide appropriate conditions to perform such a survey from the ground. Aims: We investigate the performance of a nulling interferometer optimised for the detection of exozodiacal discs at Dome C, on the high Antarctic plateau, and compare it to the expected performance of similar instruments at temperate sites. Methods: Based on the currently available measurements of the atmospheric turbulence characteristics at Dome C, we adapt the GENIEsim software (Absil et al. 2006, A&A, 448, 787) to simulate the performance of a nulling interferometer on the high Antarctic plateau. To feed a realistic instrumental configuration into the simulator, we propose a conceptual design for ALADDIN, the Antarctic L-band Astrophysics Discovery Demonstrator for Interferometric Nulling. We assume that this instrument can be placed above the 30-m thick boundary layer, where most of the atmospheric turbulence originates. Results: We show that an optimised nulling interferometer operating on a pair of 1-m class telescopes located 30 m above the ground could achieve a better sensitivity than a similar instrument working with two 8-m class telescopes at a temperate site such as Cerro Paranal. The detection of circumstellar discs about 20 times as dense as our local zodiacal cloud seems within reach for typical Darwin/TPF targets in an integration time of a few hours. Moreover, the exceptional turbulence conditions significantly relax the requirements on real-time control loops, which has favourable consequences on the feasibility of the nulling instrument. Conclusions: The perspectives for high dynamic range, high angular resolution infrared astronomy on the high Antarctic plateau look very promising. [less ▲]

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See detailA near-infrared interferometric survey of debris disk stars. I. Probing the hot dust content around eps Eridani and tau Ceti with CHARA/FLUOR
Di Folco, Emmanuel; Absil, Olivier ULg; Augereau, J.-C. et al

in Astronomy and Astrophysics (2007), 475

Context: The quest for hot dust in the central region of debris disks requires high resolution and high dynamic range imaging. Near-infrared interferometry is a powerful means to directly detect faint ... [more ▼]

Context: The quest for hot dust in the central region of debris disks requires high resolution and high dynamic range imaging. Near-infrared interferometry is a powerful means to directly detect faint emission from hot grains. Aims: We probed the first 3 AU around tau Ceti and eps Eridani with the CHARA array (Mt Wilson, USA) in order to gauge the 2 mum excess flux emanating from possible hot dust grains in the debris disks and to also resolve the stellar photospheres. Methods: High precision visibility amplitude measurements were performed with the FLUOR single mode fiber instrument and telescope pairs on baselines ranging from 22 to 241 m of projected length. The short baseline observations allow us to disentangle the contribution of an extended structure from the photospheric emission, while the long baselines constrain the stellar diameter. Results: We have detected a resolved emission around tau Cet, corresponding to a spatially integrated, fractional excess flux of 0.98±0.21 × 10[SUP]-2[/SUP] with respect to the photospheric flux in the K'-band. Around eps Eri, our measurements can exclude a fractional excess of greater than 0.6× 10[SUP]-2[/SUP] (3sigma). We interpret the photometric excess around tau Cet as a possible signature of hot grains in the inner debris disk and demonstrate that a faint, physical or background, companion can be safely excluded. In addition, we measured both stellar angular diameters with an unprecedented accuracy: Theta_LD(tau Cet)= 2.015 ± 0.011 mas and Theta_LD(eps Eri)=2.126 ± 0.014 mas. [less ▲]

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See detailPotential of space-based infrared Bracewell interferometers for planet detection
Defrere, Denis ULg; Absil, Olivier ULg; Hanot, Charles ULg et al

in Coulter, D. (Ed.) Techniques and Instrumentation for Detection of Exoplanets III (2007, September 12)

The Darwin and TPF-I space missions will be able to study the atmosphere of distant worlds similar to the Earth. Flying these space-based interferometers will however be an extraordinary technological ... [more ▼]

The Darwin and TPF-I space missions will be able to study the atmosphere of distant worlds similar to the Earth. Flying these space-based interferometers will however be an extraordinary technological challenge and a first step could be taken by a smaller mission. Several proposals have already been made in this context, using the simplest nulling scheme composed of two collectors, i.e., the original Bracewell interferometer. Two of these projects, viz. Pegase and the Fourier-Kelvin Space Interferometer, show very good perspectives for the characterisation of hot extra-solar giant planets (i.e., Jupiter-size planets orbiting close to their parent star). In this paper, we build on these concepts and try to optimise a Bracewell interferometer for the detection of Earth-like planets. The major challenge is to efficiently subtract the emission of the exo-zodiacal cloud which cannot be suppressed by classical phase chopping techniques as in the case of multi-telescopes nulling interferometers. We investigate the potential performance of split-pupil configurations with phase chopping and of OPD modulation techniques, which are good candidates for such a mitigation. Finally, we give a general overview of the performance to be expected from space-based Bracewell interferometers for the detection of extra-solar planets. In particular, the prospects for known extra-solar planets are presented. [less ▲]

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See detailInterferometric Constraints on Gravity Darkening with Application to the Modeling of Spica A & B
Aufdenberg, J. P.; Ireland, M. J.; Mérand, A. et al

in Hartkopf, W. I.; Guinan, E. F.; Harmanec, P. (Eds.) Binary Stars as Critical Tools & Tests in Contemporary Astrophysics (2007, August 01)

In 2005 we obtained very precise interferometric measurements of the pole-on rapid rotator Vega (A0 V) with the longest baselines of the Center for High Angular Angular Resolution (CHARA) Array and the ... [more ▼]

In 2005 we obtained very precise interferometric measurements of the pole-on rapid rotator Vega (A0 V) with the longest baselines of the Center for High Angular Angular Resolution (CHARA) Array and the Fiber Linked Unit for Optical Recombination (FLUOR). For the analysis of these data, we developed a code for mapping sophisticated PHOENIX model atmospheres on to the surface of rotationally distorted stars described by a Roche-von Zeipel formalism. Given a setof input parameters for a star or binary pair, this code predicts the interferometric visibility, spectral energy distribution and high-resolution line spectrum expected for the system. For the gravity-darkened Vega, our model provides a very good match to the K-band interferometric data, a good match to the spectral energy distribution -- except below 160 nm -- and a rather poor match to weak lines in the high dispersion spectrum where the model appears overly gravity darkened. In 2006, we used the CHARA Array and FLUOR to obtain high precision measurements of the massive, non-eclipsing, double-line spectroscopic binary Spica, a 4-day period system where both components are gravity darkened rapid rotators. These data supplement recent data obtained with the Sydney University Stellar Interferometer. Our study follows the classic 1971 study by Herbison-Evans et al. who resolved Spica as a binary with the Narrabri Intensity Interferometer. We will report on our progress modelling the new interferometric and archival spectroscopic data, with the goal towards better constraining the apsidal constant. [less ▲]

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See detailThe Darwin mission within ESA’s Cosmic Vision
Absil, Olivier ULg

Scientific conference (2007, July 03)

Durant cet exposé, je présenterai la mission Darwin telle que proposée à l'ESA par un groupe de scientifiques européens et internationaux. Darwin s'inscrit parfaitement dans le Thème 1 du programme Cosmic ... [more ▼]

Durant cet exposé, je présenterai la mission Darwin telle que proposée à l'ESA par un groupe de scientifiques européens et internationaux. Darwin s'inscrit parfaitement dans le Thème 1 du programme Cosmic Vision: "What are the Conditions for Planet Formation and the Emergence of Life?". Je présenterai le cas scientifique de Darwin, qui a pour but principal de détecter et caractériser des planètes habitables semblables à la Terre autour d'étoiles du voisinage solaire. En complément à ce volet axé sur la planétologie comparée et l'astrobiologie, le cas scientifique de Darwin comprend aussi un volet consacré à l'imagerie à haute résolution angulaire d'objets astrophysiques et extragalactiques de types variés. Je m'attarderai finalement sur les avancées obtenues récemment tant sur le design de la mission que sur les technologies associées, qui devraient permettre d'atteindre ces objectifs dans le cadre de la première mission "Large" du programme Cosmic Vision et dans une enveloppe budgétaire raisonnable. [less ▲]

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See detailProspects for Nulling Interferometry from Antarctica
Coudé Du Foresto, V.; Absil, Olivier ULg; Barillot, M. et al

Poster (2007, June 01)

The high Antarctic plateau is a very unique environment whose main characteristics make it a premier site for high angular resolution, high dynamic range observations at infrared wavelengths. This is due ... [more ▼]

The high Antarctic plateau is a very unique environment whose main characteristics make it a premier site for high angular resolution, high dynamic range observations at infrared wavelengths. This is due to a combination of cold temperatures (low emissivity), dry air (infrared transparency), and a night time atmospheric turbulence which is concentrated in the first ~30m near the ground (which results in a large isoplanatic angle). Above that turbulent layer (a location that can be reached either by support structures or tethered balloons), the free air seeing is both exceptionally benign and slow. There, simulations show that a small dedicated interferometer (two 1m-class telescopes) equipped with a nuller instrument performs better than the same instrument behind 8m-class telescopes on a temperate site. It can characterize the distribution of dust emission around nearby main sequence stars, a necessary precursor science for Darwin and TPF-I. The nature of the site, intermediate between ground and space both in potential and technical challenge, adds particular relevance to the demonstration of nulling for a space mission. [less ▲]

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See detailThe Faint Hot Component of Debris Disks Revealed by Infrared Interferometry
di Folco, E.; Absil, Olivier ULg; Augereau, J.-C. et al

Conference (2007, June 01)

Very few main-sequence stars exhibit warm dust in their 5-10AU close environment, where terrestrial planets are expected to have formed. Near-infrared interferometry is a powerful means, combining high ... [more ▼]

Very few main-sequence stars exhibit warm dust in their 5-10AU close environment, where terrestrial planets are expected to have formed. Near-infrared interferometry is a powerful means, combining high dynamic range and high spatial resolution, to directly detect faint emission from hot grains in exozodiacal clouds. We will review the results of our search for 2 micron excesses around Vega-like stars, including the nearby Sun-like stars Tau Ceti and Epsilon Eridani, with the FLUOR interferometric instrument and the CHARA Array of telescopes. Our recent detections, combined with Spitzer observations around 10 micron, put strong constrains on the properties and distribution of hot grains in these inner planetary systems. We will present the conclusions of our preliminary modeling for the detected hot grains as well as their implication for the selection of targets for future planet finding missions like DARWIN or TPF. [less ▲]

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See detailObserving extrasolar planetary systems with infrared interferometry
Absil, Olivier ULg

Scientific conference (2007, May 02)

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See detailExozodiacal discs with infrared interferometry
Absil, Olivier ULg

Scientific conference (2007, March 05)

The detection of the warm inner part of debris discs---the extrasolar counterparts of the zodiacal cloud---is of prime importance to characterise the global architecture of planetary systems. Because of ... [more ▼]

The detection of the warm inner part of debris discs---the extrasolar counterparts of the zodiacal cloud---is of prime importance to characterise 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 detection of an exozodiacal disc by this method 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 give access to the composition and the dynamics (including LHB-like events) of extrasolar planetary systems, and thereby put useful constraints on the presence of small bodies and/or giant planets. This statement is illustrated with new data obtained on various bright Vega-type stars, including Vega itself. Finally, we show how the new generation of interferometric instruments will change our view of debris discs: with their increased sensitivity and imaging capabilities, they will constrain the morphology of bright exozodiacal discs and push 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 detailCoronagraphic imaging of three weak-line T Tauri stars: evidence of planetary formation around PDS 70
Riaud, Pierre ULg; Mawet, Dimitri ULg; Absil, Olivier ULg et al

in Astronomy and Astrophysics (2006), 458

Context: High angular resolution imaging of nearby pre-main sequence stars with ages between 1 and 30 Myr can give valuable information on planet formation mechanisms. This range of ages is thought to ... [more ▼]

Context: High angular resolution imaging of nearby pre-main sequence stars with ages between 1 and 30 Myr can give valuable information on planet formation mechanisms. This range of ages is thought to correspond to the dissipation of the optically thick dust disks surrounding young stars and to the end of the planet formation. Aims: This paper presents new observations of three weak-line T Tauri Stars (WTTS) of intermediate ages ranging from 7 to 16 Myr. It aims at increasing the knowledge and sample of circumstellar disks around "old" WTTS. Methods: We observed three stars with the VLT's NAOS-CONICA adaptive optics system in coronagraphic mode. The four-quadrant phase mask coronagraph was used to improve the dynamic range (by a factor of 100) while preserving the high angular resolution (inner working angle of 0farcs 15). Results: One object of our sample (PDS 70), a K5 star, exhibits a brown dwarf companion and a disk in scattered light with a surface brightness power law of r[SUP]-2.8[/SUP], extending from a distance of 14 to 140 AU (assuming a stellar distance of 140 pc) and an integrated luminosity of 16.7 mJy in the K_s-band. The mass of the companion can be estimated to be within a range between 27 and 50 Jupiter masses with an effective temperature of 2750 ± 100 K. This object also shows a resolved outflow stretching up to 550 AU. Conclusions: This newly detected circumstellar disk shows strong similarities with the disk around TW Hya, and adds to the observed population of "old" TTS surrounded by circumstellar material. Moreover, three clues of planetary formation are brought to light by this study. [less ▲]

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