Publications (29)15.19 Total impact
-
Article: Independent confirmation of {\beta} Pictoris b imaging with NICI
[show abstract] [hide abstract]
ABSTRACT: Context. {\beta} Pictoris b is one of the most studied objects nowadays since it was identified with VLT/NaCo as a bona-fide exoplanet with a mass of about 9 times that of Jupiter at an orbital separation of 8-9 AU. The link between the planet and the dusty disk is unambiguously attested and this system provides an opportunity to study the disk/planet interactions and to constrain formation and evolutionary models of gas giant planets. Still, {\beta} Pictoris b had never been confirmed with other telescopes so far. Aims. We aimed at an independent confirmation using a different instrument. Methods. We retrieved archive images from Gemini South obtained with the instrument NICI, which is designed for high contrast imaging. The observations combine coronagraphy and angular differential imaging and were obtained at three epochs in Nov. 2008, Dec. 2009 and Dec. 2010. Results. We report the detection with NICI of the planet {\beta} Pictoris b in Dec. 2010 images at a separation of 404 \pm 10 mas and P A = 212.1 \pm 0.7{\deg} . It is the first time this planet is observed with a telescope different than the VLT.02/2013; -
Article: Review of small-angle coronagraphic techniques in the wake of ground-based second-generation adaptive optics systems
[show abstract] [hide abstract]
ABSTRACT: Small-angle coronagraphy is technically and scientifically appealing because it enables the use of smaller telescopes, allows covering wider wavelength ranges, and potentially increases the yield and completeness of circumstellar environment - exoplanets and disks - detection and characterization campaigns. However, opening up this new parameter space is challenging. Here we will review the four posts of high contrast imaging and their intricate interactions at very small angles (within the first 4 resolution elements from the star). The four posts are: choice of coronagraph, optimized wavefront control, observing strategy, and post-processing methods. After detailing each of the four foundations, we will present the lessons learned from the 10+ years of operations of zeroth and first-generation adaptive optics systems. We will then tentatively show how informative the current integration of second-generation adaptive optics system is, and which lessons can already be drawn from this fresh experience. Then, we will review the current state of the art, by presenting world record contrasts obtained in the framework of technological demonstrations for space-based exoplanet imaging and characterization mission concepts. Finally, we will conclude by emphasizing the importance of the cross-breeding between techniques developed for both ground-based and space-based projects, which is relevant for future high contrast imaging instruments and facilities in space or on the ground.07/2012; -
Article: Morphology of the very inclined debris disk around HD 32297
[show abstract] [hide abstract]
ABSTRACT: Direct imaging of circumstellar disks at high angular resolution is mandatory to provide morphological information that bring constraints on their properties, in particular the spatial distribution of dust. New techniques combining observing strategy and data processing now allow very high contrast imaging with 8-m class ground-based telescopes (10^-4 to 10^-5 at ~1") and complement space telescopes while improving angular resolution at near infrared wavelengths. We carried out a program at the VLT with NACO to image known debris disks with higher angular resolution in the near IR than ever before in order to study morphological properties and ultimately to detect signpost of planets. The observing method makes use of advanced techniques: Adaptive Optics, Coronagraphy and Differential Imaging, a combination designed to directly image exoplanets with the upcoming generation of "planet finders" like GPI (Gemini Planet Imager) and SPHERE (Spectro-Polarimetric High contrast Exoplanet REsearch). Applied to extended objects like circumstellar disks, the method is still successful but produces significant biases in terms of photometry and morphology. We developed a new model-matching procedure to correct for these biases and hence to bring constraints on the morphology of debris disks. From our program, we present new images of the disk around the star HD 32297 obtained in the H (1.6mic) and Ks (2.2mic) bands with an unprecedented angular resolution (~65 mas). The images show an inclined thin disk detected at separations larger than 0.5-0.6". The modeling stage confirms a very high inclination (i=88{\deg}) and the presence of an inner cavity inside r_0~110AU. We also found that the spine (line of maximum intensity along the midplane) of the disk is curved and we attributed this feature to a large anisotropic scattering factor (g~0.5, valid for an non-edge on disk). Abridged ...06/2012; -
Article: Apodized Lyot coronagraph for SPHERE/VLT: II. Laboratory tests and performance
[show abstract] [hide abstract]
ABSTRACT: SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets whose first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The principal aim of this paper is to report the first laboratory experiment of the ALC designed for the SPHERE instrument. The performance and sensitivity of the optical configuration was first numerically studied with an end-to-end approach (see the results in paper I subtitled “Detailed numerical study”). Made confident by the results, we then tested a prototype on an infrared coronagraphic bench. We measured the transmission profiles of the apodizer prototype and the coronagraphic performance of the apodized Lyot coronagraph in Y, J, and H bands. The coronagraph sensitivity to lateral and longitudinal misalignments of its three main components (apodizer, coronagraphic mask and Lyot stop) was finally studied in H band. We can conclude that the prototype meets the SPHERE technical requirements for coronagraphy. KeywordsStellar coronagraphy–Apodized Lyot coronagraph–SPHERE–Laboratory testsExperimental Astronomy 04/2012; 30(1):59-81. · 1.82 Impact Factor -
Article: Apodized Lyot coronagraph for SPHERE/VLT
[show abstract] [hide abstract]
ABSTRACT: SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets which first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The present paper reports on the most interesting aspects and results of the whole numerical study made during the design of the ALC for SPHERE/VLT. The method followed for this study is purely numerical, but with an end-to-end approach which is largely fed by a number of instrumental feedbacks. The results obtained and presented in this paper firstly permit to finalize the optical design before laboratory performance testing of the ALC being built for SPHERE/VLT (see paper II “Laboratory tests and performances”), but will also hopefully help conceiving future other instruments alike, for example within the very promising extremely large telescope perspective. KeywordsStellar coronagraphy–Apodized Lyot coronagraph–SPHERE–Numerical simulationsExperimental Astronomy 04/2012; 30(1):39-58. · 1.82 Impact Factor -
Article: SPICES: Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems
[show abstract] [hide abstract]
ABSTRACT: SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450 - 900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/22, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars ($<$25 pc) with masses ranging from a few Jupiter masses to Super Earths ($\sim$2 Earth radii, $\sim$10 M$_{\oplus}$) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.03/2012; -
Article: Dissecting the Moth: Discovery of an off-centered ring in the HD 61005 debris disk with high-resolution imaging
[show abstract] [hide abstract]
ABSTRACT: The debris disk known as "The Moth" is named after its unusually asymmetric surface brightness distribution. It is located around the ~90 Myr old G8V star HD 61005 at 34.5 pc and has previously been imaged by the HST at 1.1 and 0.6 microns. Polarimetric observations suggested that the circumstellar material consists of two distinct components, a nearly edge-on disk or ring, and a swept-back feature, the result of interaction with the interstellar medium. We resolve both components at unprecedented resolution with VLT/NACO H-band imaging. Using optimized angular differential imaging techniques to remove the light of the star, we reveal the disk component as a distinct narrow ring at inclination i=84.3 \pm 1.0{\deg}. We determine a semi-major axis of a=61.25 \pm 0.85 AU and an eccentricity of e=0.045 \pm 0.015, assuming that periastron is located along the apparent disk major axis. Therefore, the ring center is offset from the star by at least 2.75 \pm 0.85 AU. The offset, together with a relatively steep inner rim, could indicate a planetary companion that perturbs the remnant planetesimal belt. From our imaging data we set upper mass limits for companions that exclude any object above the deuterium-burning limit for separations down to 0.3". The ring shows a strong brightness asymmetry along both the major and minor axis. A brighter front side could indicate forward-scattering grains, while the brightness difference between the NE and SW components can be only partly explained by the ring center offset, suggesting additional density enhancements on one side of the ring. The swept-back component appears as two streamers originating near the NE and SW edges of the debris ring. Comment: 6 pages, 6 figures. Accepted to Astronomy and Astrophysics letters11/2010; -
Article: First Results from Very Large Telescope NACO Apodizing Phase Plate: 4 μm Images of The Exoplanet β Pictoris b
[show abstract] [hide abstract]
ABSTRACT: Direct imaging of exoplanets requires both high contrast and high spatial resolution. Here, we present the first scientific results obtained with the newly commissioned apodizing phase plate coronagraph (APP) on VLT/NACO. We detected the exoplanet β Pictoris b in the narrowband filter centered at 4.05 μm (NB4.05). The position angle (20913 ± 212) and the projected separation to its host star (0354 ± 0012, i.e., 6.8 ± 0.2 AU at a distance of 19.3 pc) are in good agreement with the recently presented data from Lagrange et al. Comparing the observed NB4.05 magnitude of 11.20 ± 0.23 mag to theoretical atmospheric models, we find a best fit with a 7-10 M Jupiter object for an age of 12 Myr, again in agreement with previous estimates. Combining our results with published L' photometry, we can compare the planet's [L' – NB4.05] color to that of cool field dwarfs of higher surface gravity suggesting an effective temperature of ~1700 K. The best-fit theoretical model predicts an effective temperature of ~1470 K, but this difference is not significant given our photometric uncertainties. Our results demonstrate the potential of NACO/APP for future planet searches and provide independent confirmation as well as complementary data for β Pic b.The Astrophysical Journal Letters 09/2010; 722(1):L49. · 5.53 Impact Factor -
Article: First Results From VLT NACO Apodizing Phase Plate: 4-micron Images of the Exoplanet beta Pictoris b
[show abstract] [hide abstract]
ABSTRACT: Direct imaging of exoplanets requires both high contrast and high spatial resolution. Here, we present the first scientific results obtained with the newly commissioned Apodizing Phase Plate coronagraph (APP) on VLT/NACO. We detected the exoplanet beta Pictoris b in the narrow band filter centered at 4.05 micron (NB4.05). The position angle (209.13 +- 2.12 deg) and the projected separation to its host star (0."354 +- 0".012, i.e., 6.8 +- 0.2 AU at a distance of 19.3 pc) are in good agreement with the recently presented data from Lagrange et al. (2010). Comparing the observed NB4.05 magnitude of 11.20 +- 0.23 mag to theoretical atmospheric models we find a best fit with a 7-10 M_Jupiter object for an age of 12 Myr, again in agreement with previous estimates. Combining our results with published L' photometry we can compare the planet's [L' - NB4.05] color to that of cool field dwarfs of higher surface gravity suggesting an effective temperature of ~1700 K. The best fit theoretical model predicts an effective temperature of ~1470 K, but this difference is not significant given our photometric uncertainties. Our results demonstrate the potential of NACO/APP for future planet searches and provides independent confirmation as well as complementary data for beta Pictoris b. Comment: Accepted for publication by ApJL09/2010; -
Article: SPIE Astronomical Telescopes and Instrumentation: Observational Frontiers of Astronomy for the New Decade
[show abstract] [hide abstract]
ABSTRACT: To characterize orbits and atmospheres of exoplanets with large orbits (≥ a few AU), direct imaging is nowadays the sole way. From space, this involves high contrast imaging techniques as coronagraphy, differential imaging or wavefront control. Several methods exist or are under development and several small (~1.5m) space telescope missions are proposed. One of them is See-coast (super-Earth explorer coronagraphic off-axis space telescope) which will be proposed to the next ESA Cosmic Vision call. It will provide polarimetric and spectral characterization of giant gazeous planets and possibly Super-Earths in visible light. In this paper, we first detail science cases of this mission. We then describe the foreseen telescope design and its instrumentation. We finally derive performance for a particular instrumental configuration from numerical simulation and we show how See-coast can retrieve planet spectra.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.07/2010; -
Article: Photometric characterization of exoplanets using angular and spectral differential imaging
[show abstract] [hide abstract]
ABSTRACT: The direct detection of exoplanets has been the subject of intensive research in the recent years. Data obtained with future high-contrast imaging instruments optimized for giant planets direct detection are strongly limited by the speckle noise. Specific observing strategies and data analysis methods, such as angular and spectral differential imaging, are required to attenuate the noise level and possibly detect the faint planet flux. Even though these methods are very efficient at suppressing the speckles, the photometry of the faint planets is dominated by the speckle residuals. The determination of the effective temperature and surface gravity of the detected planets from photometric measurements in different bands is then limited by the photometric error on the planet flux. In this work we investigate this photometric error and the consequences on the determination of the physical parameters of the detected planets. We perform detailed end-to-end simulation with the CAOS-based Software Package for SPHERE to obtain realistic data representing typical observing sequences in Y, J, H and Ks bands with a high contrast imager. The simulated data are used to measure the photometric accuracy as a function of contrast for planets detected with angular and spectral+angular differential methods. We apply this empirical accuracy to study the characterization capabilities of a high-contrast differential imager. We show that the expected photometric performances will allow the detection and characterization of exoplanets down to the Jupiter mass at angular separations of 1.0" and 0.2" respectively around high mass and low mass stars with 2 observations in different filter pairs. We also show that the determination of the planets physical parameters from photometric measurements in different filter pairs is essentialy limited by the error on the determination of the surface gravity. Comment: 13 pages, 7 figures, 4 tables. Accepted for publication in MNRAS04/2010; -
Article: Constraining the orbit of the possible companion to Beta Pictoris: New deep imaging observations
[show abstract] [hide abstract]
ABSTRACT: We recently reported on the detection of a possible planetary-mass companion to Beta Pictoris at a projected separation of 8 AU from the star, using data taken in November 2003 with NaCo, the adaptive-optics system installed on the Very Large Telescope UT4. Eventhough no second epoch detection was available, there are strong arguments to favor a gravitationally bound companion rather than a background object. If confirmed and located at a physical separation of 8 AU, this young, hot (~1500 K), massive Jovian companion (~8 Mjup) would be the closest planet to its star ever imaged, could be formed via core-accretion, and could explain the main morphological and dynamical properties of the dust disk. Our goal was to return to Beta Pic five years later to obtain a second-epoch observation of the companion or, in case of a non-detection, constrain its orbit. Deep adaptive-optics L'-band direct images of Beta Pic and Ks-band Four-Quadrant-Phase-Mask (4QPM) coronagraphic images were recorded with NaCo in January and February 2009. We also use 4QPM data taken in November 2004. No point-like signal with the brightness of the companion candidate (apparent magnitudes L'=11.2 or Ks ~ 12.5) is detected at projected distances down to 6.5 AU from the star in the 2009 data. As expected, the non-detection does not allow to rule out a background object; however, we show that it is consistent with the orbital motion of a bound companion that got closer to the star since first observed in 2003 and that is just emerging from behind the star at the present epoch. We place strong constraints on the possible orbits of the companion and discuss future observing prospects. Comment: 8 pages, 8 figures, 1 table, accepted for publication in Astronomy and Astrophysics06/2009; -
Article: BIGRE: a low cross-talk integral field unit tailored for extrasolar planets imaging spectroscopy
[show abstract] [hide abstract]
ABSTRACT: Integral field spectroscopy (IFS) represents a powerful technique for the detection and characterization of extrasolar planets through high contrast imaging, since it allows to obtain simultaneously a large number of monochromatic images. These can be used to calibrate and then to reduce the impact of speckles, once their chromatic dependence is taken into account. The main concern in designing integral field spectrographs for high contrast imaging is the impact of the diffraction effects and the non-common path aberrations together with an efficient use of the detector pixels. We focus our attention on integral field spectrographs based on lenslet-arrays, discussing the main features of these designs: the conditions of appropriate spatial and spectral sampling of the resulting spectrograph's slit functions and their related cross-talk terms when the system works at the diffraction limit. We present a new scheme for the integral field unit (IFU) based on a dual-lenslet device (BIGRE), that solves some of the problems related to the classical TIGER design when used for such applications. We show that BIGRE provides much lower cross-talk signals than TIGER, allowing a more efficient use of the detector pixels and a considerable saving of the overall cost of a lenslet-based integral field spectrograph. Comment: 17 pages, 18 figures, accepted for publication in ApJThe Astrophysical Journal 01/2009; · 6.02 Impact Factor -
Article: Prototyping coronagraphs for exoplanet characterization with SPHERE
[show abstract] [hide abstract]
ABSTRACT: The detection and characterization of extrasolar planets with SPHERE (Spectro Polarimetric High contrast Exoplanet REsearch) is challenging and in particular relies on the ability of a coronagraph to attenuate the diffracted starlight. SPHERE includes 3 instruments, 2 of which can be operated simultaneously in the near IR from 0.95 to 1.8 microns. This requirements is extremely critical for coronagraphy. This paper briefly introduces the concepts of 2 coronagraphs, the Half-Wave Plate Four Quadrant Phase Masks and the Apodized Pupil Lyot Coronagraph, prototyped within the SPHERE consortium by LESIA (Observatory of Paris) and FIZEAU (University of Nice) respectively. Then, we present the measurements of contrast and sensitivity analysis. The comparison with technical specifications allows to validate the technology for manufacturing these coronagraphs. Comment: 10 pages, will be published in the proceeding of the SPIE conference Volume 7015 "Adaptive Optics", held in Marseille from 23 to 28 june 200807/2008; -
Article: End to End Simulation of AO-assisted coronagraphic differential imaging: estimation of performance for SPHERE
[show abstract] [hide abstract]
ABSTRACT: SPHERE (Spectro Polarimetric High contrast Exoplanet REsearch), the planet finder instrument for the VLT is designed to study relatively bright extrasolar giant planets around young or nearby stars. SPHERE is a set of three instruments fed by the same AO-system, two of them share the same coronagraph. This complex system has been modeled with Fourier Optics to investigate the performance of the whole instrument. In turns, this end-to-end model was useful to analyze the sensitivity to various parameters (WFE, alignment of the coronagraph, differential aberrations) and to put some specifications on the sub-systems. This paper presents some example of sensitivity analysis and some contrast performance of the instruments as a function of the flux for the main observing mode of SPHERE: the Dual Band Imaging (DBI), equivalent to the Spectral Differential Imaging technique. Comment: 11 pages, will be published in the proceeding of the SPIE conference Volume 7015 "Adaptive Optics", held in Marseille from 23 to 28 june 200807/2008; -
Chapter: Lyot Coronagraphy at the Palomar and Phase-Mask Coronagraphy at the VLT
[show abstract] [hide abstract]
ABSTRACT: In this paper, we report on observations of faint companions and circumstellar disks at the Palomar 200-inch telescope. As a result, we present successful detection of the low-mass companion to HR 7672 and of the dusty disk around HD 141569 using ground-based coronagraphy. Finally, we will present the first promising images obtained with a Four-Quadrant Phase-Mask coronagraph on NACO at the VLT.12/2005: pages 25-30; -
Article: Fundamental limitations on Earth-like planet detection with ELTs
[show abstract] [hide abstract]
ABSTRACT: A forthcoming step in the study of extrasolar planetary systems is the direct detection and characterization of Earth-like planets. An asset of the ELTs in that context is their very high angular resolution and their collecting area. The luminosity ratio between a terrestrial planet and its star ($10^{-10}$) is such an ambitious goal that a thorough study needs to be carried out. We started with a simple analysis of the fundamental limitations for the detection of extraterrestrial planets with ELTs. Here, we considered an extreme adaptive optics device upstream of a perfect coronagraph. Even with high Strehl ratios, the coronagraphic halo level is only $10^{-6}$ to $10^{-7}$ at typical exo-Earth angular distances. A calibration device is therefore mandatory to reach the contrast between a terrestrial planet and its star in the near infra-red. We considered a simple but realistic model taking into account dynamic aberrations left uncorrected by the adaptive optics system, static aberrations of optical system and differential static aberrations due to the calibration channel itself. Numerical simulations prove that, after the calibration, the limitations are set by the static aberrations which cannot be neglected anymore.Proceedings of the International Astronomical Union 10/2005; 1:334 - 338. -
Article: Astronomical Telescopes and Instrumentation
[show abstract] [hide abstract]
ABSTRACT: Numerical simulations have been carried out to assess the opportunity to detect extrasolar planets with MIRI: the mid-IR instrument of NGST. Several coronagraphs and telescope designs have been investigated. As a result, we found that very young planets (50Myr) as well as old planets (5Gyr) can be imaged in the thermal-IR (5μm to 20μm) down to a few Jupiter masses if an appropriate high-contrast coronagraph is in used. Promising results of numerical simulations are presented.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.03/2003; -
Article: Astronomical Telescopes and Instrumentation
[show abstract] [hide abstract]
ABSTRACT: The concept we recently introduced of a coronagraph using a four-quadrant phase mask has been the subject of detailed model calculations and of laboratory validation proving its great potential in planet finding. A nulling factor of 12500 is already demonstrated in the laboratory (Riaud et al., this conference). We first remind the principle of the 4QC: a destructive interference between the two equal fractions of the amplitude with opposite signs produces a very efficient nulling of the_star light. We propose to install such a device on several ground-based and space instruments, including present (NAOS/CONICA) or future (Planet Finder) VLT instruments and MIRI, the mid-IR camera of the NGST. The present paper focus on the question of direct imaging of exoplanets using this type of device. Indeed, one advantage of the four-quadrant coronagraph is to permit probing the vicinity of a star down to smaller angular distances than a classical Lyot mask. We examine the sources of uncertainties in different cases of optimized ground-based and space experiments and different situations of planet/star couples, using as far as possible realistic models of planetary evolution. On the VLT, even with an extremely powerful adaptive optics system, the speckle noise will be the main limitation: contrast in magnitude as large as Dm = 15 are however possible in the K band. The combination of a 4QC and differential imaging at two wavelength is likely the most promising concept for direct planet Detection from the ground. On the other hand, we show that with a 4QC on MIRI, a classical Jupiter is indeed detectable from space and at 20 μm for a star closer than 10 pc, while the more favorable cases of a young (hot) giant planet allows detection at 6 μm for a star belonging to the closest star forming region at 50 pc.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.02/2003; -
Article: First tests of the coronagraphic device of MIRI/JWST
[show abstract] [hide abstract]
ABSTRACT: One of the main objectives of the instrument MIRI, the Mid-InfraRed Instrument, of the JWST is the direct detection and characterization of extrasolar giant planets. For that purpose, a coronagraphic device including three Four-Quadrant Phase Masks and a Lyot coronagraph working in mid-infrared, has been developed. We present here the results of the first test campaign of the coronagraphic system in the mid-infrared in the facility developed at the CEA. The performances are compared to the expected ones from the coronagraphic simulations. The accuracy of the centering procedures is also evaluated to validate the choice of the on-board centering algorithm.
Top co-authors
Top Journals
Institutions
-
2010–2012
-
French National Centre for Scientific Research
Lyon, Rhone-Alpes, France -
Université Paris Diderot - Paris 7
Paris, Ile-de-France, France
-
-
2003–2010
-
Observatoire de Paris
Paris, Ile-de-France, France
-
-
2009
-
Université Pierre et Marie Curie Paris 6
- Laboratoire d'Etude Spatiales et Instrumentation en Astrophysique (LESIA)
Paris, Ile-de-France, France
-
