References of "Augereau, Jean-Charles"
     in
Bookmark and Share    
Full Text
See detailFirst High-Angular Resolution L' Images of the β Pictoris Debris Disc with the VLT / NaCo
Milli, Julien; Mawet, Dimitri; Absil, Olivier ULg et al

in Booth, Mark; Matthews, Brenda; Graham, James (Eds.) Exploring the Formation and Evolution of Planetary Systems (2014, January 01)

Imaging debris discs in the L'-band (3.8 μm) is a difficult task. Quasi-static speckles from imperfect optics prevail below 1'' whereas background emission is the dominant noise source beyond that ... [more ▼]

Imaging debris discs in the L'-band (3.8 μm) is a difficult task. Quasi-static speckles from imperfect optics prevail below 1'' whereas background emission is the dominant noise source beyond that separation and is much larger than at shorter wavelengths. We demonstrate here the potential of the newly commissioned AGPM coronograph on VLT/NaCo combined with advanced star and sky subtraction technique based on Principal Component Analysis, and we analyze the morphology of the β Pictoris disc. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
See detailA near-infrared interferometric survey of debris disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR
Absil, Olivier ULg; Defrère, Denis; Coudé du Foresto, Vincent et al

in Astronomy and Astrophysics (2013), 555

Context. Dust is expected to be ubiquitous in extrasolar planetary systems due to the dynamical activity of minor bodies. Inner dust populations are, however, still poorly known due to the high contrast ... [more ▼]

Context. Dust is expected to be ubiquitous in extrasolar planetary systems due to the dynamical activity of minor bodies. Inner dust populations are, however, still poorly known due to the high contrast and small angular separation with respect to their host star. Yet, a proper characterisation of exozodiacal dust is mandatory for the design of future Earth-like planet imaging missions. Aims. We aim to determine the level of near-infrared exozodiacal dust emission around a sample of 42 nearby main sequence stars with spectral types ranging from A to K, and to investigate its correlation with various stellar parameters and with the presence of cold dust belts. Methods. We use high-precision K-band visibilities obtained with the FLUOR interferometer on the shortest baseline of the CHARA array. The calibrated visibilities are compared with the expected visibility of the stellar photosphere to assess the presence of an additional, fully resolved circumstellar emission source. Results. Near-infrared circumstellar emission amounting to about 1% of the stellar flux is detected around 13 of our 42 target stars. Follow-up observations showed that one of them (eps Cep) is associated with a stellar companion, while another one was detected around what turned out to be a giant star (kap CrB). The remaining 11 excesses found around single main sequence stars are most probably due to the presence of hot circumstellar dust, yielding an overall occurrence rate of 28+8-6% for our (biased) sample. We show that the occurrence rate of bright exozodiacal discs correlates with spectral type, K-band excesses being more frequent around A-type stars. It also correlates with the presence of detectable far-infrared excess emission in the case of solar-type stars. Conclusions. This study provides new insights regarding the phenomenon of bright exozodiacal disc, showing that hot dust populations are probably linked to outer dust reservoirs in the case of solar-type stars. In the case of A-type stars, no clear conclusion can be made regarding the origin of the detected near-infrared excesses. [less ▲]

Detailed reference viewed: 51 (13 ULg)
Full Text
Peer Reviewed
See detailThe twofold debris disk around HD 113766 A. Warm and cold dust as seen with VLTI/MIDI and Herschel/PACS
Olofsson, Johan; Henning, Thomas; Nielbock, Markus et al

in Astronomy and Astrophysics (2013), 551

Context. Warm debris disks are a sub-sample of the large population of debris disks, and display excess emission in the mid-IR. Around solar-type stars, very few objects show emission features in mid-IR ... [more ▼]

Context. Warm debris disks are a sub-sample of the large population of debris disks, and display excess emission in the mid-IR. Around solar-type stars, very few objects show emission features in mid-IR spectroscopic observations, that are attributed to small, warm silicate dust grains. The origin of this warm dust can possibly be explained either by a collision between several bodies or by transport from an outer belt. Aims. We present and analyse new far-IR Herschel/Pacs observations, supplemented by ground-based data in the mid-IR (VLTI/Midi and VLT/Visir), for one of these rare systems: the 10-16 Myr old debris disk around HD 113766 A. Methods. We improve an existing model to account for these new observations, and better constrain the spatial distribution of the dust and its composition. Results. We underline the limitations of SED modelling and the need for spatially resolved observations. We find that the system is best described by an inner disk located within the first AU, well constrained by the Midi data, and an outer disk located between 9-13 AU. In the inner dust belt, our previous finding of Fe-rich crystalline olivine grains still holds. We do not observe time variability of the emission features over at least a 8 years time span, in a environment subjected to strong radiation pressure. Conclusions. The time stability of the emission features indicates that µm-sized dust grains are constantly replenished from the same reservoir, with a possible depletion of sub-µm-sized grains. We suggest that the emission features may arise from multi-composition aggregates. We discuss possible scenarios concerning the origin of the warm dust. The compactness of the innermost regions as probed by Midi, as well as the dust composition, suggest that we are witnessing the outcomes of (at least) one collision between partially differentiated bodies, in an environment possibly rendered unstable by terrestrial planetary formation. [less ▲]

Detailed reference viewed: 27 (3 ULg)
Full Text
Peer Reviewed
See detailDirect imaging of extra-solar planets in star forming regions. Lessons learned from a false positive around IM Lup.
Mawet, Dimitri; Absil, Olivier ULg; Riaud, Pierre et al

in Astronomy and Astrophysics (2012), 544

Context. Most planet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the ... [more ▼]

Context. Most planet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the near-infrared window (1 - 5 µm). Because of these practical limitations, our current observational aim at detecting and characterizing planets puts heavy constraints on target selection, observing strategies, data reduction, and follow-up. Most surveys so far have thus targeted very young systems (1 - 100Myr) to catch the putative remnant thermal radiation of giant planets, which peaks in the near-infrared. They also favor systems in the solar neighborhood (d < 80 pc), which eases angular resolution requirements but also ensures a good knowledge of the distance and proper motion, which are critical to secure the planet status, and enable any subsequent characterization. Aims. Because of their youth, it is very tempting to target the nearby star forming regions, which are typically twice as far as the bulk of objects usually combed for planets by direct imaging. Probing these very interesting reservoirs in practice sets additional constraints that we review in this paper by presenting the planet search that we initiated in 2008 around the disk-bearing T Tauri star IM Lup, which is part of the Lupus star forming region (140-190 pc). Methods. We show and discuss why age determination, the choice of evolutionary model for both the central star and the planet, precise knowledge of the host star proper motion, relative or absolute (between different instruments) astrometric accuracy (including plate scale calibration), and patience are the key ingredients for exoplanet searches around more distant young stars. Results. Unfortunately, most of the time, precision and perseverance are not paying off: we discovered a candidate companion around IM Lup in 2008, which we report here to be a false positive event. We nevertheless review in details the lessons learned from our endeavor, and additionally present the best detection limits ever calculated for IM Lup. We also accessorily report on the successful use of innovative data reduction techniques, such as the damped-LOCI and iterative roll subtraction. [less ▲]

Detailed reference viewed: 56 (4 ULg)
Full Text
Peer Reviewed
See detailDeep near-infrared interferometric search for low-mass companions around β Pictoris
Absil, Olivier ULg; Le Bouquin, Jean-Baptiste; Lebreton, Jérémy et al

in Astronomy and Astrophysics (2010), 520

Aims. We search for low-mass companions in the innermost region (<300 mas, i.e., 6 AU) of the β Pic planetary system. Methods. We obtained interferometric closure phase measurements in the K-band with the ... [more ▼]

Aims. We search for low-mass companions in the innermost region (<300 mas, i.e., 6 AU) of the β Pic planetary system. Methods. We obtained interferometric closure phase measurements in the K-band with the VLTI/AMBER instrument used in its medium spectral resolution mode. Fringe stabilization was provided by the FINITO fringe tracker. Results. In a search region of between 2 and 60 mas in radius, our observations exclude at 3σ significance the presence of companions with K-band contrasts greater than 5×10^-3 for 90% of the possible positions in the search zone (i.e., 90% completeness). The median 1σ error bar in the contrast of potential companions within our search region is 1.2×10^-3. The best fit to our data set using a binary model is found for a faint companion located at about 14.4 mas from β Pic, which has a contrast of 1.8×10^-3 ± 1.1×10^-3 (a result consistent with the absence of companions). For angular separations larger than 60 mas, both time smearing and field-of-view limitations reduce the sensitivity. Conclusions. We can exclude the presence of brown dwarfs with masses higher than 29 MJup (resp. 47 MJup) at a 50% (resp. 90%) completeness level within the first few AUs around β Pic. Interferometric closure phases offer a promising way to directly image low-mass companions in the close environment of nearby young stars. [less ▲]

Detailed reference viewed: 73 (6 ULg)
Full Text
Peer Reviewed
See detailAn Interferometric Study of the Fomalhaut Inner Debris Disk. I. Near-Infrared Detection of Hot Dust with VLTI/VINCI
Absil, Olivier ULg; Mennesson, Bertrand; Le Bouquin, Jean-Baptiste et al

in Astrophysical Journal (2009), 704

The innermost parts of dusty debris disks around main-sequence stars are currently poorly known due to the high contrast and small angular separation with their parent stars. Using near-infrared ... [more ▼]

The innermost parts of dusty debris disks around main-sequence stars are currently poorly known due to the high contrast and small angular separation with their parent stars. Using near-infrared interferometry, we aim to detect the signature of hot dust around the nearby A4 V star Fomalhaut, which has already been suggested to harbor a warm dust population in addition to a cold dust ring located at about 140 AU. Archival data obtained with the VINCI instrument at the VLTI are used to study the fringe visibility of the Fomalhaut system at projected baseline lengths ranging from 4 m to 140 m in the K band. A significant visibility deficit is observed at short baselines with respect to the expected visibility of the sole stellar photosphere. This is interpreted as the signature of resolved circumstellar emission, producing a relative flux of 0.88% ± 0.12% with respect to the stellar photosphere. While our interferometric data cannot directly constrain the morphology of the excess emission source, complementary data from the literature allow us to discard an off-axis point-like object as the source of circumstellar emission. We argue that the thermal emission from hot dusty grains located within 6 AU from Fomalhaut is the most plausible explanation for the detected excess. Our study also provides a revised limb-darkened diameter for Fomalhaut (theta_LD = 2.223 ± 0.022 mas), taking into account the effect of the resolved circumstellar emission. Based on observations made with ESO Telescopes at the Paranal Observatory (public VINCI commissioning data). [less ▲]

Detailed reference viewed: 55 (7 ULg)
Full Text
See detailScience case for 1 mas spectro-imagining in the near-infrared
Garcia, Paulo J V; Berger, Jean-Phillipe; Marconi, Alessandro et al

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

We present the work developed within the science team of the Very Large Telescope Interferometer Spectro-Imager (VSI) during the Phase A studies. VSI aims at delivering ~ 1 milliarcsecond resolution data ... [more ▼]

We present the work developed within the science team of the Very Large Telescope Interferometer Spectro-Imager (VSI) during the Phase A studies. VSI aims at delivering ~ 1 milliarcsecond resolution data cubes in the near-infrared, with several spectral resolutions up to 12 000, by combining up to 8 VLTI telescopes. In the design of an instrument, the science case plays a central role by supporting the instrument construction decision, defining the top-level requirements and balancing design options. The overall science philosophy of VSI was that of a general user instrument serving a broad community. The science team addressed themes which included several areas of astrophysics and illustrated specific modes of operation of the instrument: a) YSO disks and winds; b) Multiplicity of young stars; c) Exoplanets; d) Debris disks; e) Stellar surface imaging; f) The environments of evolved stars; g) AGN tori; h) AGN's Broad Line Region; i) Supermassive black-holes; and j) Microlensing. The main conclusions can be summarized as follows: a) The accessible targets and related science are extremely sensitive to the instrument limiting magnitude; the instrument should be optimized for sensitivity and have its own fringe tracker. b) Most of the science cases are readily achievable with on-axis fringe tracking, off-axis fringe tracking enabling extra science. c) In most targets (YSOs, evolved stars and AGNs), the interpretation and analysis of circumstellar/nuclear dust morphology requires direct access to the gas via spectral resolved studies of emission lines, requiring at least a spectral resolution of 2 500. d) To routinely deliver images at the required sensitivity, the number of telescopes in determinant, with 6 telescopes being favored. e) The factorial increase in the number of closure phases and visibilities, gained in a single observation, makes massive surveys of parameters and related science for the first time possible. f) High dynamic range imaging and very high dynamic range differential closure phase are possible allowing the study of debris disks and characterization of pegasides. g) Spectro-imaging in the near-infrared is highly complementary to ALMA, adaptive optics and interferometric imaging in the thermal infrared. [less ▲]

Detailed reference viewed: 108 (13 ULg)
Full Text
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 ▲]

Detailed reference viewed: 10 (0 ULg)
Full Text
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 ▲]

Detailed reference viewed: 9 (0 ULg)
Full Text
See detailDetection of the inner-debris disk of Vega with CHARA/FLUOR
Absil, Olivier ULg; Di Folco, Emmanuel; Mérand, Antoine et al

in Monnier, John; Schöller, Markus; Danchi, Willian (Eds.) Advances in Stellar Interferometry (2006, July 01)

Using the FLUOR beam-combiner installed at the CHARA Array (Mt. Wilson, CA), we have obtained highprecision 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 highprecision visibility measurements of Vega, one of the prototypic debris-disk stars, known to be surrounded by a large amount 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 (less than 8 AU). Our observations show a significant deficit in square visibility at short baselines with respect to the expected visibility of a simple UD stellar model (DeltaV2 equal or equivalent to 2%), suggesting the presence of an extended source of emission around Vega. The sparse (u, v) plane coverage does not allow the discrimination between a point source and an extended circumstellar emission as the source of the extended emission. However, we show that the presence of a point-like source within the FLUOR field-of-view (1" in radius, i.e., 7.8 AU at the distance of Vega) is highly unlikely. 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 plus or minus 0.19% between the integrated dust emission and the stellar photosphere. Complementing this result with archival photometric data in the near- and mid-infrared and taking into account a realistic photospheric model for the rapidly rotating Vega, we derive the expected physical properties of the circumstellar dust by modelling its Spectral Energy Distribution. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations. [less ▲]

Detailed reference viewed: 15 (1 ULg)
Full Text
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 ▲]

Detailed reference viewed: 11 (0 ULg)