References of "Absil, Olivier"
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See detailPEGASE - A space interferometer for the spectro-photometry of Pegasides
Absil, Olivier ULg

Scientific conference (2004, August 25)

Pegase is an answer to the CNES call for ideas for a scientific payload on its Formation Flying technological mission. It proposes a Bracewell interferometer operating in the infrared (1.5 – 6 microns ... [more ▼]

Pegase is an answer to the CNES call for ideas for a scientific payload on its Formation Flying technological mission. It proposes a Bracewell interferometer operating in the infrared (1.5 – 6 microns) and visible regimes. It has small telescopes (40 cm) but a substantial baseline (25 to 500 m). Its angular resolution reaches 1 mas at 4 microns and 100 micro-as at 0.4 microns. Its main scientific objectives are the spectroscopic study of weak companions including pegasides and brown dwarfs bounded to other stars. The goal is to determine the composition of the atmospheres of these objects as well as their cloud structure. [less ▲]

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See detailEffects of atmospheric turbulence on the GENIE nulling interferometer
Absil, Olivier ULg

in Aime, Claude; Soummer, Rémi (Eds.) Astronomy with High Contrast Imaging II (2004)

Two competitive design studies for the Ground-based European Nulling Interferometer Experiment (GENIE) have recently been initiated by the European Space Agency and the European Southern Observatory. A ... [more ▼]

Two competitive design studies for the Ground-based European Nulling Interferometer Experiment (GENIE) have recently been initiated by the European Space Agency and the European Southern Observatory. A major issue in these studies is the influence of atmospheric turbulence on the performance of the instrument, and how atmospheric effects can be compensated in order to reach the goal performance (detection of faint exozodiacal clouds). In this paper, we review the main atmospheric processes affecting a nulling interferometer and discuss possible ways to reduce them by means of real-time control systems. Preliminary performance estimates of GENIE are then presented. The effects of the thermal background and its fluctuations (Absil & Bakker 2004) are not considered here. [less ▲]

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See detailGENIE: a ground-based precursor for Darwin
Absil, Olivier ULg

Scientific conference (2003, November 21)

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See detailGENIE: un précurseur pour Darwin
Absil, Olivier ULg

Scientific conference (2003, October 09)

L'instrument GENIE, un projet commun de l'ESA (Agence Spatiale Européenne) et de l'ESO (Observatoire Européen Austral), sera installé en 2007 sur le site du VLTI (Paranal, Chili). Cet instrument ... [more ▼]

L'instrument GENIE, un projet commun de l'ESA (Agence Spatiale Européenne) et de l'ESO (Observatoire Européen Austral), sera installé en 2007 sur le site du VLTI (Paranal, Chili). Cet instrument interférométrique recombinera de façon destructive la lumière infrarouge collectée par deux ou plusieurs Very Large Telescopes, permettant ainsi d'étudier l'environnement d'objets brillants avec une haute résolution angulaire. Son objectif principal est de valider le concept du "nulling interferometer", de gagner de l'expérience dans le design et l'opération d'un tel instrument, et de tester certaines des nouvelles technologies nécessaires pour Darwin. GENIE préparera aussi le programme scientifique de Darwin en détectant et caractérisant d'éventuels disques de poussière autour des étoiles cibles de Darwin. Cette étude permettra d'écarter les cibles inappropriées pour la recherche de planètes habitables. GENIE obtiendra également des spectres basse résolution pour le rayonnement thermique de quelques exoplanètes géantes. [less ▲]

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See detailOverview of the DARWIN mission
Kaltenegger, L.; Karlsson, A.; Fridlund, M. et al

in Fridlund, Malcolm; Henning, Thomas (Eds.) Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

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See detailCharacterisation of disks around YSOs with GENIE
Kaltenegger, Lisa; Absil, Olivier ULg; Eiroa, Carlos et al

in Fridlund, Malcolm; Henning, Thomas (Eds.) Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

Recent interferometric observations show that the interfered near-IR size of the circumstellar material around Young Stellar Object (YSO) are larger than those expected from accretion disk models. There ... [more ▼]

Recent interferometric observations show that the interfered near-IR size of the circumstellar material around Young Stellar Object (YSO) are larger than those expected from accretion disk models. There are currently different models that account for the excess IR emission of Young Stellar Objects (YSO). At the same time, the answers to many questions on the evolutionary status and the origin of the activity and variability depend critically on the relative importance of circumstellar distribution of material in disks or envelopes at different spatial scales. Operating at mid-infrared wavelengths, the Ground-based European Nulling Interferometer Experiment (GENIE) will be particularly sensitive to warm circumstellar dust and will thus provide the opportunity to characterize dust disks around YSOs. Observations with GENIE will enable us to investigate the properties of the circumstellar dust, which are responsible for the excess near-infrared fluxes. The nulling of the central star will bring out the disk in much more detail and hence put stronger constraints on these models. [less ▲]

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See detailCould GENIE detect hot Jupiters?
den Hartog, Roland; Absil, Olivier ULg; Kaltenegger, L. et al

in Fridlund, Malcolm; Henning, Thomas (Eds.) Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

The prime objective of GENIE (Ground-based European Nulling Interferometry Experiment) is to obtain experience with the design, construction and operation of an IR nulling interferometer, as a preparation ... [more ▼]

The prime objective of GENIE (Ground-based European Nulling Interferometry Experiment) is to obtain experience with the design, construction and operation of an IR nulling interferometer, as a preparation for the DARWIN/TPF mission. In this context, the detection of a planet orbiting another star would provide an excellent demonstration of nulling interferometry. Doing this through the atmosphere, however, is a formidable task. In this paper we assess the prospects of detecting, with nulling interferometry on ESO's VLT, a Hot Jupiter, a giant planet in a close orbit around its parent star. First we discuss the definition of the optimal target. Then we present a simulated observation of the Tau Bootis system, which suggests that GENIE, in a L'-band single Bracewell configuration, could detect the hot Jupiter in a few hours time with a signal-to-noise ratio of up to ~80. Although there are strong requirements on the control-loop performance, background subtraction and accuracy of the photometry calibration, we conclude that at present there do not seem to be fundamental problems that would prevent GENIE from detecting hot Jupiters. Hence the answer to the question in the title is yes. [less ▲]

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See detailThe Ground-based European Nulling Interferometry Experiment (DARWIN-GENIE)
Gondoin, P.; Absil, Olivier ULg; den Hartog, R. et al

in Fridlund, Malcolm; Henning, Thomas (Eds.) Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

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 and to characterise ... [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 and to characterise their atmospheres. 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, the European Space Agency (ESA) and the European Southern Observatory (ESO) intend to build a ground-based technology demonstrator called GENIE (Ground based European Nulling Interferometry Experiment). Such a ground-based demonstrator built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. It will demonstrate that nulling interferometry can be achieved in a broad mid-IR band as a precursor to the next phase of the Darwin program. [less ▲]

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See detailGENIEsim: the GENIE simulation software
Absil, Olivier ULg; den Hartog, R.; Erd, C. et al

in Fridlund, Malcolm; Henning, Thomas (Eds.) Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

GENIEsim, the GENIE simulation software, is an IDL-based code to simulate future observations with the Ground-based European Nulling Interferometer Experiment, which should be commissioned on the Very ... [more ▼]

GENIEsim, the GENIE simulation software, is an IDL-based code to simulate future observations with the Ground-based European Nulling Interferometer Experiment, which should be commissioned on the Very Large Telescope Interferometer (VLTI) in 2007. The code simulates operation in the mid-infrared (L' and N bands) and includes all major noise sources. The atmospheric turbulence is described by a Kolmogorov power spectrum, from which random time series are computed for perturbations to the optical paths. The effect of turbulence is reduced by means of control loops, which are either included in the VLTI facility (MACAO, PRIMA) or specific to the GENIE instrument. The output of GENIEsim is a time series of fluxes computed by integration of a source field multiplied by the GENIE transmission map, projected onto the plane of the sky. Simulations have already allowed to identify critical points in the design of the instrument, such as OPD and dispersion control, calibration of stellar leakage and background subtraction. [less ▲]

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See detailCan GENIE characterize debris disks around nearby stars?
Absil, Olivier ULg; Kaltenegger, L.; Eiroa, C. et al

in Fridlund, Malcolm; Henning, Thomas (Eds.) Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

The Ground-based European Nulling Interferometer Experiment will combine the light collected by two or more VLT telescopes and make them interfere in a destructive way, thereby revealing the close ... [more ▼]

The Ground-based European Nulling Interferometer Experiment will combine the light collected by two or more VLT telescopes and make them interfere in a destructive way, thereby revealing the close neighborhood of nearby stars. Operating at mid-infrared wavelengths, GENIE will be particularly sensible to warm circumstellar dust. This paper presents simulated observations of the debris disk around the nearby A2V star zeta Leporis obtained with the GENIE simulation software. Parameters such as inclination, density power-law exponent and inner radius can be retrieved with a relative precision of 1% or better using only six observations of 15 minutes. In the context of the DARWIN/TPF mission, warm circumstellar dust could be a serious limitation to the detection of Earth-like exoplanets. This paper shows that GENIE will detect disks as faint as 23 times our local zodiacal cloud around Sun-like stars at 10 pc, and will thus allow to discard unsuitable targets for DARWIN/TPF. [less ▲]

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See detailGENIEsim: the GENIE Science Simulator
Absil, Olivier ULg

Master of advanced studies dissertation (2003)

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See detailThe Darwin Ground-based European Nulling Interferometry Experiment
Gondoin, P.; Absil, Olivier ULg; Fridlund, M. et al

in Lacoste, H. (Ed.) GENIE - DARWIN Workshop - Hunting for Planets (2003, March 01)

Darwin is one of the most challenging space pro jects ever considered by the European Space Agency (ESA). Its principal ob jectives are to detect Earth-like planets around nearby stars and to characterise ... [more ▼]

Darwin is one of the most challenging space pro jects ever considered by the European Space Agency (ESA). Its principal ob jectives are to detect Earth-like planets around nearby stars and to characterise their atmospheres. Darwin is conceived as a space nulling interferometer" which makes use of on-axis destructive interferences to extinguish the stellar light while keeping the o -axis signal of the orbiting planet. Within the frame of the Darwin program, the European Space Agency (ESA) and the European Southern Observatory (ESO) intend to build a ground-based technology demonstrator called GENIE (Ground based European Nulling Interferometry Experiment). Such a ground-based demonstrator built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. It will demonstrate that nulling interferometry can be achieved in a broad mid-IR band as a precursor to the next phase of the Darwin program. The present paper will describe the ob jectives and the status of the project. [less ▲]

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See detailConfigurations and Modulation Schemes Trade-off
Absil, Olivier ULg

in Lacoste, H. (Ed.) GENIE - DARWIN Workshop - Hunting for Planets (2003, March)

During the preliminary phase A of the Ground-based European Nulling Interferometer Experiment (GENIE), a number of interferometric configurations have been studied, in the cases of exozodiacal cloud and ... [more ▼]

During the preliminary phase A of the Ground-based European Nulling Interferometer Experiment (GENIE), a number of interferometric configurations have been studied, in the cases of exozodiacal cloud and hot Jupiter detection. Their expected performances have been computed in light of the measured or expected performances of the VLTI subsystems. A simple Bracewell nulling interferometer, formed of two Unit Telescopes and working in the L’ or N bands, has been identified as a good candidate configuration for exozodiacal cloud detection. External or internal chopping, fringe tracking and intensity matching will be critical issues for this configuration. In the case of hot Jupiter detection, a double Bracewell with internal modulation in the L’ band seems well appropriate, and should allow to carry out low resolution spectroscopy on a few bright exoplanets. The basic assumptions and computations which have lead to these candidate configurations are described in this paper. [less ▲]

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See detailInherent modulation: a fast chopping method for nulling interferometry
Absil, Olivier ULg; Karlsson, Anders; Kaltenegger, Lisa

in Shao, Michael (Ed.) Interferometry in Space (2003, February 01)

The reduction of the thermal background emission from the local and exozodiacal dust clouds is a critical element for the success of ESA's space mission, DARWIN. Internal modulation, a technique using ... [more ▼]

The reduction of the thermal background emission from the local and exozodiacal dust clouds is a critical element for the success of ESA's space mission, DARWIN. Internal modulation, a technique using fast signal chopping, isolating the planetary signal from these noise sources, was proposed by Mennesson and Léger. In this paper, a short review of internal modulation is given, and new configurations with internal modulation are proposed to reduce the complexity of the beam-combining optics. A modification to the implementation of internal modulation is then investigated. It provides similar performance with a single detector and a greatly simplified optical layout: the number of beam-combiners is reduced by a factor of about two. The principle of inherent modulation is different from internal modulation in that no sub-interferometers are used: different phase shifts are applied to the input beams before recombination such that an asymmetric transmission map is obtained directly, without plus or minuspi/2 modulation as used in internal modulation. By combining the phase shifts and the input beams differently a transposed transmission map is obtained, allowing the signal to be chopped. During operations, multiplexing between the two interferometers is performed, such that at any time only one interferometer is being used. [less ▲]

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See detailDarwin ground-based European nulling interferometer experiment (GENIE)
Gondoin, Philippe; Absil, Olivier ULg; Fridlund, C V Malcolm et al

in Traub, Wesley (Ed.) Interferometry for Optical Astronomy II (2003, February 01)

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 and to characterize ... [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 and to characterize their atmospheres. 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, the European Space Agency (ESA) and the European Southern Observatory (ESO) intend to build a ground-based technology demonstrator called GENIE (Ground based European Nulling Interferometry Experiment). Such a ground-based demonstrator built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. It will demonstrate that nulling interferometry can be achieved in a broad mid-IR band as a precursor to the next phase of the Darwin program. The present paper will describe the objectives and the status of the project. [less ▲]

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See detailInfluence of optical path delay control on a ground-based nulling interferometer
Absil, Olivier ULg; Coude du Foresto, Vincent

in Traub, Wesley (Ed.) Interferometry for Optical Astronomy II (2003, February 01)

Atmospheric turbulence is a major source of noise in any fiber-linked interferometer through the piston effect between the two arms of the interferometer which induces an erratic movement of the fringes ... [more ▼]

Atmospheric turbulence is a major source of noise in any fiber-linked interferometer through the piston effect between the two arms of the interferometer which induces an erratic movement of the fringes. Because the stellar light has to be permanently cancelled by the central dark fringe, a ground-based nulling interferometer is not possible without stringent optical path delay (OPD) control. In this paper, we investigate the influence of the residual OPD error of a fringe tracking unit on the performances of a nulling interferometer. The accuracy required for this control system strongly depends on the observation wavelength. If we want to detect exozodiacal clouds ten times as dense as our zodiacal dust cloud in the near-infrared (L' band), the performances of the fringe tracker are crucial: the residual OPD should be about 20 nanometers RMS. This specification can only be reached if the fringe sensor is optimized for bright sources. In the mid-infrared (N band), the requirements are strongly relaxed: OPD control with an accuracy of 400 nm RMS is sufficient to be background-limited, but a lower residual OPD (about 50 nm RMS) is strongly recommended to reduce the stellar leakage. [less ▲]

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See detailThe Darwin-GENIE Experiment: An ESA-ESO Partnership
Gondoin, Ph; Absil, Olivier ULg; Erd, C. et al

in Sembach, K. R.; Blades, J. C.; Illingworth, G. D. (Eds.) et al Hubble's Science Legacy: Future Optical/Ultraviolet Astronomy from Space (2003)

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See detailDetails on DARWIN and the Search for Extrasolar Planets
Kaltenegger, L.; Fridlund, M.; Absil, Olivier ULg

in Deming, Drake; Seager, Sara (Eds.) Scientific Frontiers in Research on Extrasolar Planets (2003)

The direct detection of an earth-like planet close to its parent star is challenging because the signal detected from the parent star is between 10[SUB]9[/SUB] and 10[SUB]6[/SUB] times brighter than the ... [more ▼]

The direct detection of an earth-like planet close to its parent star is challenging because the signal detected from the parent star is between 10[SUB]9[/SUB] and 10[SUB]6[/SUB] times brighter than the signal of a planet in the visual and infrared (IR), respectively. Future space based missions like DARWIN and TPF concentrate on the region between 6 and 18 microns, a region that contains the carbon dioxide, water, and ozone spectral features of the atmosphere. Using several small collecting telescopes and a beam combiner allows us to build an instrument with an angular resolution normally associated with monolithic telescopes of much larger diameters. The relative positions of the telescopes, forming the interferometer, are selected such that when the optical signals, collected by the individual telescopes, are coherently combined, the small angular distance between the planet and the star can be resolved. Different configurations of the free flying interferometer array influence the performance of the nulling array. The concepts for space nulling interferometers and the influence of different schemes of beam combination on the detected signal are investigated. The contribution of background noise to the detected signal is examined. [less ▲]

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See detailCandidate VLTI Configurations for the GENIE Nulling Experiment
Absil, Olivier ULg; Gondoin, P.; Erd, C. et al

in Deming, Drake; Seager, Sara (Eds.) Scientific Frontiers in Research on Extrasolar Planets (2003)

The European Space Agency (ESA) and the European Southern Observatory (ESO) initiate a definition study for a Ground-based European Nulling Interferometer Experiment (Darwin-GENIE). The experiment will ... [more ▼]

The European Space Agency (ESA) and the European Southern Observatory (ESO) initiate a definition study for a Ground-based European Nulling Interferometer Experiment (Darwin-GENIE). The experiment will use the Very Large Telescope Interferometer (VLTI) operating on Mount Paranal (Chile). The objective of GENIE is to gain experience in the manufacture and operation of a nulling interferometer using a design concept and technology representative of the ESA IRSI-Darwin space mission. GENIE will prepare the IRSI-Darwin science program through a systematic search for exozodiacal dust clouds around IRSI-Darwin candidate targets. GENIE also aims to perform IRSI-Darwin related science achievable from ground including the detection of low-mass companions (if possible, hot jupiters) around nearby stars. Among the variety of telescope sizes and positions on the VLTI site, candidate interferometric configurations have been identified for GENIE, taking into account the limitation imposed by the Earth's atmosphere. They include a Bracewell interferometer for exozodiacal clouds detection in the N band and a double Bracewell configuration with internal modulation for extrasolar jupiter detection in the L' band. The present paper presents the prospective performance of these configurations in light of current specifications of major VLTI subsystems. [less ▲]

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See detailGENIE: a ground-based precursor for the IRSI-Darwin mission
Absil, Olivier ULg

in Aime, Claude; Soummer, Rémi (Eds.) Astronomy with High Contrast Imaging (2003)

During the preliminary phase A of the Ground-based European Nulling Interferometer Experiment (GENIE), a number of interferometric configurations have been studied, in the cases of exozodiacal cloud and ... [more ▼]

During the preliminary phase A of the Ground-based European Nulling Interferometer Experiment (GENIE), a number of interferometric configurations have been studied, in the cases of exozodiacal cloud and hot Jupiter detection. Their expected performances have been computed in light of the measured or expected performances of the VLTI sub-systems. A simple Bracewell nulling interferometer, formed of two Unit Telescopes and working in the L' or N bands, has been identified as a good candidate configuration for exozodiacal cloud detection. External or internal chopping, fringe tracking and intensity matching will be critical issues for this configuration. In the case of hot Jupiter detection, a double Bracewell with internal modulation in the L' band seems well appropriate, and should allow to carry out low resolution spectroscopy on a few bright exoplanets. The basic assumptions and computations which have lead to these candidate configurations are described in this paper. [less ▲]

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