References of "Hanot, Charles"
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See detailHigh-contrast Stellar Observations within the Diffraction Limit at the Palomar Hale Telescope
Mennesson, B.; Hanot, Charles ULg; Serabyn, Eugene et al

in Astrophysical Journal (2011), 743

We report on high-accuracy high-resolution (<20 mas) stellar observations obtained with the Palomar Fiber Nuller (PFN), a near-infrared (sime2.2 μm) interferometric coronagraph installed at the Palomar ... [more ▼]

We report on high-accuracy high-resolution (<20 mas) stellar observations obtained with the Palomar Fiber Nuller (PFN), a near-infrared (sime2.2 μm) interferometric coronagraph installed at the Palomar Hale telescope. The PFN uses destructive interference between two elliptical (3 m × 1.5 m) sub-apertures of the primary to reach high dynamic range inside the diffraction limit of the full telescope. In order to validate the PFN's instrumental approach and its data reduction strategy, based on the newly developed "Null Self-Calibration" (NSC) method, we observed a sample of eight well-characterized bright giants and supergiants. The quantity measured is the source astrophysical null depth, or equivalently the object's visibility at the PFN 3.2 m interferometric baseline. For the bare stars α Boo, α Her, β And, and α Aur, PFN measurements are in excellent agreement with previous stellar photosphere measurements from long baseline interferometry. For the mass-losing stars β Peg, α Ori, ρ Per, and χ Cyg, circumstellar emission and/or asymmetries are detected. Overall, these early observations demonstrate the PFN's ability to measure astrophysical null depths below 10[SUP]-2[/SUP] (limited by stellar diameters), with 1 σ uncertainties as low as a few 10[SUP]-4[/SUP]. Such visibility accuracy is unmatched at this spatial resolution in the near-infrared and translates into a contrast better than 10[SUP]-3[/SUP] within the diffraction limit. With further improvements anticipated in 2011/2012, a state-of-the-art infrared science camera and a new extreme adaptive optics system, the PFN should provide a unique tool for the detection of hot debris disks and young self-luminous sub-stellar companions in the immediate vicinity of nearby stars. [less ▲]

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

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

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

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

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See detailNew Constraints on Companions and Dust within a Few AU of Vega
Mennesson, B.; Serabyn, E.; Hanot, Charles ULg et al

in Astrophysical Journal (2011), 736

We report on high contrast near-infrared (~2.2 μm) observations of Vega obtained with the Palomar Fiber Nuller, a dual sub-aperture rotating coronagraph installed at the Palomar Hale telescope. The data ... [more ▼]

We report on high contrast near-infrared (~2.2 μm) observations of Vega obtained with the Palomar Fiber Nuller, a dual sub-aperture rotating coronagraph installed at the Palomar Hale telescope. The data show consistent astrophysical null depth measurements at the ~= 10[SUP]–3[/SUP] level or below for three different baseline orientations spanning 60 deg in azimuth, with individual 1σ uncertainties <=7 × 10[SUP]–4[/SUP]. These high cancellation and accuracy levels translate into a dynamic range greater than 1000:1 inside the diffraction limit of the 5 m telescope beam. Such high contrast performance is unprecedented in the near-infrared and provides improved constraints on Vega's immediate (sime20 to 250 mas, or sime0.15 to 2 AU) environment. In particular, our measurements rule out any potential companion in the [0.25-1 AU] region contributing more than 1% of the overall near-infrared stellar flux, with limits as low as 0.2% near 0.6 AU. These are the best upper limits established so far by direct detection for a companion to Vega in this inner region. We also conclude that any dust population contributing a significant (>=1%) near-infrared thermal excess can arise only within 0.2 AU of the star, and that it must consist of much smaller grains than in the solar zodiacal cloud. Dust emission from farther than sime2 AU is also not ruled out by our observations, but would have to originate in strong scattering, pointing again to very small grains. Based on observations obtained at the Hale Telescope, Palomar Observatory as part of a continuing collaboration between the California Institute of Technology, NASA/JPL, and Cornell University. [less ▲]

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

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

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

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

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See detailExtra-solar planet imaging: ground vs space based coronagraphs
Hanot, Charles ULg; Absil, Olivier ULg; Boccaletti, A. et al

Conference (2010, October 28)

In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect methods. Today, progress in the field of high contrast and angular resolution imaging has ... [more ▼]

In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect methods. Today, progress in the field of high contrast and angular resolution imaging has allowed direct images of several exoplanetary systems to be taken (cf. HR 8799, Fomalhaut and β Pic). In the near future, several new instruments are going to dramatically improve our sensitivity to exoplanet detection. Among these, SPHERE (Spectro Polarimetric High contrast Exoplanet REsearch) at the VLT, MIRI (Mid Infra-Red Instrument) onboard JWST and EPICS at the ELT will be equipped with coronagraphs to reveal faint objects in the vicinity of nearby stars. We made use of the Lyon group (COND) evolutionary models of young (sub-)stellar objects and exoplanets to compare the sensitivities of these different instruments using their estimated coronagraphic profiles. From this comparison, we present a catalogue of targets which are particularly well suited for the different instruments. [less ▲]

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See detailFirst manufactured diamond AGPM vector vortex for the L- and N-bands: metrology and expected performances
Delacroix, Christian ULg; Forsberg, Pontus; Karlsson, Mikael et al

Conference (2010, October 28)

The AGPM (Annular Groove Phase Mask, Mawet et al. 2005) is an optical vectorial vortex coronagraph (or vector vortex) synthesized by a circular subwavelength grating, that is a grating with a period ... [more ▼]

The AGPM (Annular Groove Phase Mask, Mawet et al. 2005) is an optical vectorial vortex coronagraph (or vector vortex) synthesized by a circular subwavelength grating, that is a grating with a period smaller than λ/n (λ being the observed wavelength and n the refractive index of the grating substrate). Since it is a phase mask, it allows to reach a high contrast with a small working angle. Moreover, its subwavelength structure provides a good achromatization over wide spectral bands. Recently, we have manufactured and measured our first N-band prototypes that allowed us to validate the reproducibility of the microfabrication process. Here, we present newly produced mid-IR diamond AGPMs in the N-band (~10 µm), and in the most wanted L-band (~3.5 µm). We first give an extrapolation of the expected coronagraph performances. We then present the manufacturing and measurement results, using diamond-optimized microfabrication techniques such as nano-imprint lithography (NIL) and reactive ion etching (RIE). Finally, the subwavelength grating profile metrology combines surface metrology (scanning electron microscopy, atomic force microscopy, white light interferometry) with diffractometry on an optical polarimetric bench and cross correlation with theoretical simulations using rigorous coupled wave analysis (RCWA). [less ▲]

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See detailExtra-solar planet imaging: ground vs. space based coronagraphs
Hanot, Charles ULg

Conference (2010, October 28)

In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect methods. Today, progress in the field of high contrast and angular resolution imaging has ... [more ▼]

In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect methods. Today, progress in the field of high contrast and angular resolution imaging has allowed direct images of several exoplanetary systems to be taken (cf. HR 8799, Fomalhaut and β Pic). In the near future, several new instruments are going to dramatically improve our sensitivity to exoplanet detection. Among these, SPHERE (Spectro Polarimetric High contrast Exoplanet REsearch) at the VLT, MIRI (Mid Infra-Red Instrument) onboard JWST and EPICS at the ELT will be equipped with coronagraphs to reveal faint objects in the vicinity of nearby stars. We made use of the Lyon group (COND) evolutionary models of young (sub-)stellar objects and exoplanets to compare the sensitivities of these different instruments using their estimated coronagraphic profiles. From this comparison, we present a catalogue of targets which are particularly well suited for the different instruments. [less ▲]

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See detailA VLTI/AMBER closure-phase search for low-mass companions around nearby young stars: first results on beta Pictoris
Absil, Olivier ULg; Le Bouquin, J.-B.; Chauvin, G. et al

Conference (2010, October 25)

Young stars in nearby moving groups and associations are well suited to search for low-mass companions. In addition to their brightness, their proximity gives access to small linear separations and their ... [more ▼]

Young stars in nearby moving groups and associations are well suited to search for low-mass companions. In addition to their brightness, their proximity gives access to small linear separations and their youth makes potential low-mass companion brighter than around older main sequence stars. We have recently started a survey of such young nearby stars with the AMBER near-infrared interferometer at the VLTI. The closure phase measurements provided by AMBER on a triplet of baselines are particularly sensitive to nearby off-axis point-like sources. In this talk, we describe the first results of this survey obtained on beta Pictoris. Thanks to a closure phase accuracy of a few 0.1 degree, we show that a 3-sigma sensitivity of about 4e-3 can be reached on the contrast of potential companions for angular separations between 0.01 and 0.2 arcsec. This translates into a companion mass of about 35 Mjup from 0.2 to 4 AU in the case of beta Pictoris. We extrapolate this result on other stars of our survey and discuss the discovery space of AMBER. [less ▲]

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See detailInfluence of Exozodiacal Dust Clouds on Mid-IR Earth-like Planet Detection
Defrère, D.; Absil, Olivier ULg; den Hartog, R. et al

in Coudé du Foresto, Vincent; Gelino, Dawn; Ribas, Ignasi (Eds.) Pathways Towards Habitable Planets (2010, October 01)

The characterization of Earth-like extrasolar planets in the mid-infrared is a significant observational challenge that could be tackled by future space-based interferometers. A large effort has been ... [more ▼]

The characterization of Earth-like extrasolar planets in the mid-infrared is a significant observational challenge that could be tackled by future space-based interferometers. A large effort has been carried out the past two decades to define a design that provides the necessary scientific performance while minimizing cost and technical risks. These efforts have resulted in a consensus on a single mission architecture consisting of a non-coplanar X-array (the so-called Emma configuration), using four collector spacecraft and a single beam combiner spacecraft. The ability to study distant planets with an X-array interferometer will however depend on exozodiacal dust clouds, the counterparts of the solar zodiacal disk. In this paper, we briefly discuss the impact of exozodiacal clouds on the performance of an Emma X-array interferometer dedicated to Earth-like planet characterization. [less ▲]

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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 ▲]

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See detailCombining Coronagraphy with Interferometry as a Tool for Measuring Stellar Diameters
Riaud, P.; Hanot, Charles ULg

in Astrophysical Journal (2010)

The classical approach for determining stellar angular diameters is to use interferometry and to measure fringe visibilities. Indeed, in the case of a source having a diameter larger than typically λ/6B ... [more ▼]

The classical approach for determining stellar angular diameters is to use interferometry and to measure fringe visibilities. Indeed, in the case of a source having a diameter larger than typically λ/6B, B being the interferometer's baseline and λ the wavelength of observation, the fringe contrast decreases. Similarly, it is possible to perform angular diameter determinations by measuring the stellar leakage from a coronagraphic device or a nulling interferometer. However, all coronagraphic devices (including those using nulling interferometry) are very sensitive to pointing errors and to the size of the source, two factors with significant impact on the rejection efficiency. In this work, we present an innovative idea for measuring stellar diameter variations, combining coronagraphy together with interferometry. We demonstrate that, using coronagraphic nulling statistics, it is possible to measure such variations for angular diameters down to ≈λ/40B with 1σ error-bars as low as ≈λ/1500B. For that purpose, we use a coronagraphic implementation on a two-aperture interferometer, a configuration that significantly increases the precision of stellar diameter measurements. Such a design offers large possibilities regarding the stellar diameter measurement of Cepheids or Mira stars, at a 60-80 μas level. We report on a simulation of a measurement applied to a typical Cepheid case, using the VLTI-UT interferometer on Paranal. [less ▲]

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See detailHigh contrast stellar observations within the diffraction limit at the Palomar Hale telescope
Mennesson, B.; Hanot, Charles ULg; Serabyn, E. et al

in McLean, I.; Ramsay, S.; Takami, H. (Eds.) Ground-based and Airborne Instrumentation for Astronomy III (2010, July 01)

We report on high-accuracy, high-resolution (< 20mas) stellar measurements obtained in the near infrared ( 2.2 microns) at the Palomar 200 inch telescope using two elliptical (3m x 1.5m) sub-apertures ... [more ▼]

We report on high-accuracy, high-resolution (< 20mas) stellar measurements obtained in the near infrared ( 2.2 microns) at the Palomar 200 inch telescope using two elliptical (3m x 1.5m) sub-apertures located 3.4m apart. Our interferometric coronagraph, known as the "Palomar Fiber Nuller" (PFN), is located downstream of the Palomar adaptive optics (AO) system and recombines the two separate beams into a common singlemode fiber. The AO system acts as a "fringe tracker", maintaining the optical path difference (OPD) between the beams around an adjustable value, which is set to the central dark interference fringe. AO correction ensures high efficiency and stable injection of the beams into the single-mode fiber. A chopper wheel and a fast photometer are used to record short (< 50ms per beam) interleaved sequences of background, individual beam and interferometric signals. In order to analyze these chopped null data sequences, we developed a new statistical method, baptized "Null Self-Calibration" (NSC), which provides astrophysical null measurements at the 0.001 level, with 1 σ uncertainties as low as 0.0003. Such accuracy translates into a dynamic range greater than 1000:1 within the diffraction limit, demonstrating that the approach effectively bridges the traditional gap between regular coronagraphs, limited in angular resolution, and long baseline visibility interferometers, whose dynamic range is restricted to 100:1. As our measurements are extremely sensitive to the brightness distribution very close to the optical axis, we were able to constrain the stellar diameters and amounts of circumstellar emission for a sample of very bright stars. With the improvement expected when the PALM-3000 extreme AO system comes on-line at Palomar, the same instrument now equipped with a state of the art low noise fast read-out near IR camera, will yield 10[SUP]-4[/SUP] to 10[SUP]-3[/SUP] contrast as close as 30 mas for stars with K magnitude brighter than 6. Such a system will provide a unique and ideal tool for the detection of young (<100 Myr) self-luminous planets and hot debris disks in the immediate vicinity (0.1 to a few AUs) of nearby (< 50pc) stars. [less ▲]

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See detailAnnular groove phase mask coronagraph in diamond for mid-IR wavelengths: manufacturing assessment and performance analysis
Delacroix, Christian ULg; Forsberg, P.; Karlsson, M. et al

in Oschmann, J.; Clampin, M.; MacEwen, H. (Eds.) Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave (2010, July 01)

Phase-mask coronagraphs are known to provide high contrast imaging capabilities while preserving a small inner working angle, which allows searching for exoplanets or circumstellar disks with smaller ... [more ▼]

Phase-mask coronagraphs are known to provide high contrast imaging capabilities while preserving a small inner working angle, which allows searching for exoplanets or circumstellar disks with smaller telescopes or at longer wavelengths. The AGPM (Annular Groove Phase Mask, Mawet et al. 2005[SUP]1[/SUP]) is an optical vectorial vortex coronagraph (or vector vortex) induced by a rotationally symmetric subwavelength grating (i.e. with a period smaller than λ/n, λ being the observed wavelength and n the refractive index of the grating substrate). In this paper, we present our first midinfrared AGPM prototypes imprinted on a diamond substrate. We firstly give an extrapolation of the expected coronagraph performances in the N-band (~10 μm), and prospects for down-scaling the technology to the most wanted L-band (~3.5 μm). We then present the manufacturing and measurement results, using diamond-optimized microfabrication techniques such as nano-imprint lithography (NIL) and reactive ion etching (RIE). Finally, the subwavelength grating profile metrology combines surface metrology (scanning electron microscopy, atomic force microscopy, white light interferometry) with diffractometry on an optical polarimetric bench and cross correlation with theoretical simulations using rigorous coupled wave analysis (RCWA). [less ▲]

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See detailThe potential of rotating-baseline nulling interferometers operating within large single-telescope apertures
Serabyn, E.; Mennesson, B.; Martin, Stefan et al

in Danchi, W. C.; Delplancke, F.; Rajagopal, J. K. (Eds.) Optical and Infrared Interferometry II (2010, July 01)

The use of a rotating-baseline nulling interferometer for exoplanet detection was proposed several decades ago, but the technique has not yet been fully demonstrated in practice. Here we consider the ... [more ▼]

The use of a rotating-baseline nulling interferometer for exoplanet detection was proposed several decades ago, but the technique has not yet been fully demonstrated in practice. Here we consider the faint companion and exozodiacal disk detection capabilities of rotating-baseline nulling interferometers, such as are envisioned for space-based infrared nullers, but operating instead within the aperture of large single telescopes. In particular, a nulling interferometer on a large aperture corrected by a next-generation extreme adaptive optics system can provide deep interferometric contrasts, and also reach smaller angles (sub λ/D) than classical coronagraphs. Such rotating nullers also provide validation for an eventual space-based rotating-baseline nulling interferometer. As practical examples, we describe ongoing experiments with rotating nullers at Palomar and Keck, and consider briefly the case of the Thirty Meter Telescope. [less ▲]

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See detailDirect imaging of Earth-like planets: why we care about exozodis
Absil, Olivier ULg; Defrère, D.; Roberge, A. et al

in Danchi, W. C.; Delplancke, F.; Rajagopal, J. K. (Eds.) Optical and Infrared Interferometry II (2010, July)

The presence of large amounts of exozodiacal dust around nearby main sequence stars is considered as a potential threat for the direct detection of Earth-like exoplanets (exoEarths) with future space ... [more ▼]

The presence of large amounts of exozodiacal dust around nearby main sequence stars is considered as a potential threat for the direct detection of Earth-like exoplanets (exoEarths) with future space-based coronagraphic and interferometric missions. In this paper, we estimate the amount of exozodiacal light that can be tolerated around various stellar types without jeopardizing the detection of exoEarths with a space-based visible coronagraph or a free-flying mid-infrared interferometer. We also address the possible effects of resonant structures in exozodiacal disks. We then review the sensitivity of current ground-based interferometric instruments to exozodiacal disks, based on classical visibility measurements and on the nulling technique. We show that the current instrumental performances are not sufficient to help prepare future exoEarth imaging missions, and discuss how new groundor space-based instruments could improve the current sensitivity to exozodiacal disks down to a suitable level. [less ▲]

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See detailDevelopment of a statistical reduction method for the Palomar Fiber Nuller
Hanot, Charles ULg; Mennesson, Bertrand; Serabyn, Eugene et al

in Danchi, W. C.; Delplancke, F.; Rajagopal, J. K. (Eds.) Optical and Infrared Interferometry II (2010, July)

A unique statistical data analysis method has been developed for reducing nulling interferometry data. The idea is to make use of the statistical distributions of the fluctuating null depths and beam ... [more ▼]

A unique statistical data analysis method has been developed for reducing nulling interferometry data. The idea is to make use of the statistical distributions of the fluctuating null depths and beam intensities to retrieve the astrophysical null depth in the presence of fluctuations. The approach yields an accuracy much better than is possible with standard data reduction methods, because the accuracy of the null depth is not limited by the sizes of the phase and intensity errors but by the uncertainties on their statistical distributions. The result is an improvement in the instrumental null depth measurement limit of roughly an order of magnitude. We show in this paper that broadband null depths of 10[SUP]-4[/SUP] can be measured in the lab with our infrared Fiber Nuller without achromatic phase shifters. On sky results are also dramatically improved, with measured contrasts up to a couple of 10[SUP]-4[/SUP] with our instrument mounted on the Hale telescope at the Palomar Observatory. This statistical analysis is not specific to our instrument and may be applicable to other interferometers. [less ▲]

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See detailDevelopment of a CELestial Infrared Nuller Experiment (CELINE) for broadband nulling and new single-mode fiber testing
Hanot, Charles ULg; Riaud, Pierre; Mawet, Dimitri et al

in Danchi, W. C.; Delpancke, F.; Rajagopal, J. K. (Eds.) Optical and Infrared Interferometry II (2010, July)

he small angular distance (<100 mas) and the huge flux ratio (107) between an Earth-like exoplanet in the socalled habitable zone and its host star makes it very difficult to direct image such systems ... [more ▼]

he small angular distance (<100 mas) and the huge flux ratio (107) between an Earth-like exoplanet in the socalled habitable zone and its host star makes it very difficult to direct image such systems. Nulling interferometry consists of a very powerful technique that combines destructively the light from two or more collectors to dim the starlight and to reveal faint companions in its vicinity. We have developed a new nulling experiment based on the fiber nuller principle. This fully symmetric reflective nulling bench aims at testing broadband nulling in both H and K bands as well as characterizing photonic fibers for modal filtering. We present in this paper the design, the development as well as preliminary results of the experiment. [less ▲]

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See detailCompared sensitivities of VLT, JWST and ELT for direct exoplanet detection in nearby stellar moving groups
Hanot, Charles ULg; Absil, Olivier ULg; Surdej, Jean ULg et al

in Oschmann, J.; Clampin, M.; MacEwen, H. (Eds.) Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave (2010, July)

In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect methods. Today, progress in the field of high contrast and angular resolution imaging has ... [more ▼]

In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect methods. Today, progress in the field of high contrast and angular resolution imaging has allowed direct images of several exoplanetary systems to be taken (cf. HR 8799, Fomalhaut and β Pic).[SUP]1-4[/SUP] In the near future, several new instruments are going to dramatically improve our sensitivity to exoplanet detection. Among these, SPHERE (Spectro Polarimetric High contrast Exoplanet REsearch) at the VLT, MIRI (Mid Infra-Red Instrument) onboard JWST and EPICS at the ELT will be equipped with coronagraphs to reveal faint objects in the vicinity of nearby stars. We made use of the Lyon group (COND) evolutionary models of young (sub-)stellar objects and exoplanets to compare the sensitivities of these different instruments using their estimated coronagraphic profiles. From this comparison, we present a catalogue of targets which are particularly well suited for the different instruments. [less ▲]

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See detailImproving Interferometric Null Depth Measurement with statistics : theory and first results with the Palomar Fiber Nuller
Hanot, Charles ULg

Scientific conference (2010, June)

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

A new "self-calibrated" statistical analysis method has been developed for reducing nulling interferometry data. The idea is to use the statistical distributions of the fluctuating null depths and beam intensities to retrieve the astrophysical null depth (or equivalently the object's visibility) in the presence of fast instrumental fluctuations. The approach yields an accuracy much better (at least ten times) than is presently possible with standard data reduction methods, because the null depth accuracy is no longer limited by the magnitude of the phase and intensity errors but by uncertainties on their probability distributions. This approach was tested on the sky with the two-aperture fiber nulling instrument mounted on the Palomar Hale telescope. Using our new data analysis approach alone - and no observations of calibrators - , we find that astrophysical null depths lower than 0.001 can be reliably measured in the near infrared, with error bars as low as a few 10^-4. This statistical analysis is not specific to our instrument and may be applicable to other interferometers. Therefore I'll also present the application of this method to the measurement of Cepheids angular diameters at the VLTI with a sensitivities down to ~60µas. [less ▲]

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See detailThe Optimal Gravitational Lens Telescope
Surdej, Jean ULg; Delacroix, Christian ULg; Coleman, P. et al

in Astronomical Journal (The) (2010), 139

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster, . . . ), it is possible via numerical lens inversion to retrieve the real source image, taking ... [more ▼]

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster, . . . ), it is possible via numerical lens inversion to retrieve the real source image, taking full advantage of the magnifying power of the cosmic lens. This has been achieved in the past for several remarkable gravitational lens systems. Instead, we propose here to invert an observed multiply imaged source directly at the telescope using an ad-hoc optical instrument which is described in the present paper. Compared to the previous method, this should allow one to detect fainter source features as well as to use such an optimal gravitational lens telescope to explore even fainter objects located behind and near the lens. Laboratory and numerical experiments illustrate this new approach. [less ▲]

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