R. Waters

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (38)3.69 Total impact

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    ABSTRACT: Forsterite is one of the crystalline dust species that is often observed in protoplanetary disks and solar system comets. Being absent in the interstellar medium, it must be produced during the disk lifetime, though its connection with disk evolution and planet formation remains unclear. One reason for this is that mid infrared spectroscopy can only give a hint of crystal location and abundance. Additional information -- such as the shape of the temperature dependent 69 micron feature of forsterite -- is necessary to pin down its exact location. The DIGIT key program targets a sample of 24 Herbig stars with Herschel PACS at sufficient resolution to spectrally resolve the shape of the 69 micron feature. Combined with spatially resolved imaging and radiative transfer calculations, these data allow us to constrain the crystal location with great precision. We report on detailed studies of the spatial distribution and abundance of forsterite in three transitional disks. In HD100546 and HD169142, we find that forsterite is concentrated at the outer edge of the disk gap, with a local abundance that is much higher than the overall crystallinity. This suggests that the origin of forsterite in these objects is closely linked to the disk gap, carved by protoplanets. IRS 48 shows a different pattern: although similar in disk morphology, its forsterite is much colder and located further out in the disk, suggesting a different formation channel. These objects demonstrate the diagnostic power of the 69 micron forsterite feature observed as part of DIGIT, and show that the standard scenario of radial mixing of crystals from the inner disk does not suffice. A different formation mechanism, perhaps tied to the transitional nature of these disks, is necessary to explain the observed location of dust crystals.
    03/2012;
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    ABSTRACT: Direct imaging of extrasolar planets is one of the most exciting but also challenging topics in modern astrophysics. Up to now, more than 300 extrasolar planets have been detected by indirect methods, mostly by radial velocity measurements. A step further is the direct imaging of extrasolar planets, which is extremely demanding due to the huge contrast and the tiny separation between star and planet. There are different approaches to reach the goal. One amongst is imaging polarimetry. We will report on the polarimetric mode of SPHERE, an ESO VLT second generation instrument. We will emphasize the special technique used to reduce the noise to reach the extremely high polarimetric precision.
    11/2011;
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    ABSTRACT: SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. The instrument will search for direct light from old planets with orbital periods of several months to several years as we know them from our solar system. These are planets which are in or close to the habitable zone. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from extrasolar planets. The search for reflected light from extra-solar planets is very demanding because the signal decreases rapidly with the orbital separation. For a Jupiter-sized object and a separation of 1 AU the planet/star contrast to be achieved is on the order of 10-8 for a successful detection. This is much more demanding than the direct imaging of young self-luminous planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of 2012. ZIMPOL is currently in the subsystem testing phase. We describe the results of verification and performance testing done at the NOVA-ASTRON lab. We will give an overview of the system noise performance, the polarimetric accuracy and the high contrast testing. For the high contrast testing we will describe the impact of crucial system parameters on the contrast performance. SPHERE is an instrument designed and built by a consortium consisting of IPAG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève, ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
    Proc SPIE 09/2011;
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    ABSTRACT: The future SPHERE VLT planet finder instrument includes a high precision polarimeter (ZIMPOL) for the search and characterization of reflected and therefore polarized light from extra-solar planetary systems. We discuss first the expected polarization properties of extra-solar planets and circumstellar disks and the diagnostic potential of polarimetric observations. Then we describe what can be achieved by combining in SPHERE / VLT an 8m telescope, an extreme AO system, coronagraphy, and high precision polarimetry. Performance simulations show that a contrast of 10e-8 should be reachable with this instrument. With this sensitivity giant planets around the nearest stars could be detected in reflected light and the structure from many circumstellar disk can be mapped with a spatial resolution of up to 15 milli-arcsec.
    10/2010;
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    ABSTRACT: Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design of a “Planet Finder” instrument is therefore optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design, and expected performance of the SPHERE instrument.
    Coudé du Foresto, Vincent; Gelino, Dawn M.; Ribas, Ignasi: Pathways Towards Habitable Planets, ASP, 231-238 (2010). 01/2010;
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    ABSTRACT: ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of 2011. ZIMPOL is currently in the manufacturing, integration and testing phase. We describe the optical, polarimetric, mechanical, thermal and electronic design as well as the design trade offs. Specifically emphasized is the optical quality of the key performance component: the Ferro-electric Liquid Crystal polarization modulator (FLC). Furthermore, we describe the ZIMPOL test setup and the first test results on the achieved polarimetric sensitivity and accuracy. These results will give first indications for the expected overall high contrast system performance. SPHERE is an instrument designed and built by a consortium consisting of LAOG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève, ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
    01/2010;
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    ABSTRACT: SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second generation instrument for the VLT optimized for the very high-contrast imaging around bright stars [J.-L. Beuzit, M. Feldt, K. Dohlen et al. in Messenger 125, 29 (2006)]. The primary goal is the detection and characterization of new giant planets around a variety of nearby stars. Together with the observation of early planetary systems and disks, and in association with the results of other planet search techniques, SPHERE will be a primary contributor to get a complete picture of the variety of planetary systems and to better understand their mechanisms of formation and evolution. Such results will be obtained before even more ambitious projects for the direct imaging of planets either from the ground with ELTs or from space.
    Moorwood, Alan: Science with the VLT in the ELT Era, Springer Netherlands, 337-341 (2009). 01/2009;
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    ABSTRACT: SPHERE, the ESO extra-solar planet imager for the VLT is aimed at the direct detection and spectral characterization of extra-solar planets. Its whole design is optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star. SPHERE has passed its Final Design Review (FDR) in December 2008 and it is in the manufacturing and integration phase. We review the most challenging specifications and expected performance of this instrument; then we present the latest stage of the design chosen to meet the specifications, the progress in the manufacturing as well as the integration and test strategy to insure gradual verification of performances at all levels.
    Shaklan, Stuart B.: Techniques and Instrumentation for Detection of Exoplanets IV, SPIE, 74400P-74400P-11 (2009). 01/2009;
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    ABSTRACT: ABSTRACT High contrast imaging will be the new frontier of exoplanets search providing the opportunity to have at once a deep glance in the neighborhood of the target star. In addition, coupling integral field spectrographs to extreme adaptive optics module at the focus of 8m telescope class and in future to ELTs, gives also the possibility to have a first order characterization of the exoplanets itself. SPHERE, second generation instrument for VLT, is an exo-solar planet imager, which goal is to detect giant exo-solar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made of an extreme-Adaptive Optics (AO) turbulence correction, pupil tracker and interferential coronagraphs. At its back end, a differential dual imaging camera (IRDIS) and an integral field spectrograph (IFS) work in the Near Infrared (NIR) Y, J, H and Ks bands (0.95-2.32 μm) and a high resolution polarization camera (ZIMPOL) covers the visible (0.6 - 0.9 μm). The three instruments could work simultaneously. As matter of fact, as the instrument has been thought and designed, It should be considered more like an experiment than a typical ancillary instrumentation. The prime objective of SPHERE is the discovery and study of new planets orbiting stars by direct imaging of the circumstellar environment. The challenge consists in the very large contrast of luminosity between the star and the planet (larger than " 12.5 magnitudes or " 105 flux ratio), at very small angular separations, typically inside the seeing halo. The whole design of SPHERE is therefore optimized towards high contrast performance in a limited field of view and at short distances from the central star. Both evolved and young planetary systems will be detected, respectively through their reflected light (mostly by ZIMPOL) and through the intrinsic planet emission (IRDIS+IFS modes). Both components of the near-infrared arm of SPHERE will provide complementary detection capacities and characterization potential, in terms of field of view, contrast, and spectral domain. The number of planets expected to be detected is a very strong function of the (assumed) distribution of planet separation. Extending the semi-major axis distribution up to P=250 yr (about 40 AU) yield a number of planet detections about 3.5 larger than for the same distribution truncated at P=70 yr (about 17 AU). Several tens of planet detection (details depend on target number and selection criteria) are then expected between 20 and 40 AU if planets are there. SPHERE has clearly the potential for an accurate determination of the frequency of planets in wide orbits. Note that while giant planets are not expected to be found in large number at very wide separation (a >50-100 AU), brown dwarfs might instead be present. In this paper a brief description of the whole instrument is given. Furthermore, an analysis of the performances of the instrument with its foreseen ability in discovering and characterize warm planets is also given. Last, but not least, SPHERE and its USA counter part: GPI, open the path towards new high contrast istrumentation for ELT like EPICS.
    08/2008; -1:875.
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    ABSTRACT: The ESO planet finder instrument SPHERE will search for the polarimetric signature of the reflected light from extrasolar planets, using a VLT telescope, an extreme AO system (SAXO), a stellar coronagraph, and an imaging polarimeter (ZIMPOL). We present the design concept of the ZIMPOL instrument, a single-beam polarimeter that achieves very high polarimetric accuracy using fast polarization modulation and demodulating CCD detectors. Furthermore, we describe comprehensive performance simulations made with the CAOS problem-solving environment. We conclude that direct detection of Jupiter-sized planets in close orbit around the brightest nearby stars is achievable with imaging polarimetry, signal-switching calibration, and angular differential imaging.
    Proc SPIE 08/2008;
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    ABSTRACT: Not Available
    X Electromagnetic and Light Scattering Conference, International Center for Heat and Mass Transfer, Bodrum, Turkey; 06/2007
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    ABSTRACT: We are currently investigating the possibilities for a high-contrast, adaptive optics assisted instrument to be placed as a 2nd-generation instrument on ESO's VLT. This instrument will consist of an "extreme-ao" system capable of producing very high Strehl ratios, a contrast-enhancing device and an integral-field spectroscopic detection system. It will be designed directly take images of sub-stellar companions of nearby (< 100 pc) stars. We will present our current design study for such an instrument and discuss the various ways to tell stellar from companion photons. Results of our latest simulations regarding the instrument will be presented and the expected performance discussed. Derived from the simulated performance we will also give details about the expected science impact of the planet finder. This will comprise the chances of finding different types of exo-planets, the scientific return of such detections and follow-up examinations, as well as other topics like star-formation, debris disks, and planetary nebulae.
    Exploring the Cosmic Frontier, 261-264 (2007). 02/2007;
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    ABSTRACT: We present three scattering matrix elements as functions of the scattering angle, namely F_{11}(θ), -F_{12}(θ)/F_{11}(θ), and F_{22}(θ)/F_{11}(θ), at a wavelength of 632.8 nm for a number of fluffy aggregate samples with variable bulk porosity measured in random orientations. The aggregates are composed of coagulated magnesiosilica grains, ferrosilica grains, and alumina grains. The individual grains have diameters of the order of a few tens of nanometers. Most striking about the measured results is the extremely high degree of linear polarization for incident unpolarized light -F_{12}(θ)/F_{11}(θ) with maxima between about 60% to almost 100%.
    05/2006; -1:267-270.
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    ABSTRACT: This paper presents the scientific case for a next generation adaptive optics instrument at the VLT, temporarily named "Planet Finder", that is aimed at detecting and characterizing extrasolar planets through the direct analysis of their emitted photons in the visible and at near-IR wavelengths. We discuss the observational niche of such an instrument to have first light in 2010, in complement to other planet search methods. To improve the efficiency (and consistency) of the search for planets with the PF, the observations will need to be organized in the form of an extensive survey of hundreds of nearby stars, predicted outputs of which are also described here. This summarizes the study phase of the instrument, conducted by two competitive teams and the recent merging of both studies, regarding the scientific impact of Planet Finder.
    Proceedings of the International Astronomical Union 01/2006;
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    ABSTRACT: In the framework of the 2nd generation VLT instruments we have developed the design of an instrument, called CHEOPS, to detect and characterize faint objects (Jupiter-like planets) very close to a bright star. It consists of a high order adaptive optics system, at least an order of magnitude more sensitive in terms of giant planet detection with respect to the present VLT Adaptive Optics facility NACO plus Simultaneous Differential Imager. The adaptive optics system provides the necessary Strehl Ratio for the differential polarimetric imager (ZIMPOL) and an Integral Field Spectrograph (IFS).
    Memorie della Societa Astronomica Italiana Supplementi. 01/2006; 9:439.
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    ABSTRACT: Observations of extrasolar planets using integral field spectroscopy (IFS), if coupled with an extreme adaptive optics system and analyzed with a simultaneous differential imaging technique (SDI), serve as a powerful tool for directly detecting and characterizing extrasolar planets; they enhance the signal of the planet and at the same time reduce the impact of stellar light and, consequently, important noise sources, such as speckles. In order to verify the efficiency of such a technique, we have developed a simulation code that is able to test the capabilities of this IFS-SDI technique for different kinds of planets and telescopes by modeling the atmospheric and instrumental noise sources. The first results obtained with the simulations show that many significant extrasolar planet detections are indeed possible using the present 8 m class telescopes within a few hours of exposure time. The procedure that is adopted to simulate IFS observations is presented here in detail, where we explain in particular how we obtain estimates of the speckle noise, adaptive optics corrections, specific instrumental features, and how we test the efficiency of the SDI technique in order to increase the signal-to-noise ratio of the planet detection. The most important results achieved from simulations of various objects, from 1MJ objects to 30MJ brown dwarfs, and for observations with an 8 m telescope, are then presented and discussed.
    Publications of the Astronomical Society of the Pacific 01/2006; · 3.69 Impact Factor
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    ABSTRACT: Direct detection and spectral characterization of extrasolar planets is one of the most exciting but also one of the most challenging area in modern astronomy. For its second generation instrumentation on the VLT, ESO has supported two phase A studies for a so-called dedicated instrument. Based on the results of these two studies, a unique instrument is now considered for first light in early 2010, including a powerful extreme adaptive optics system, various coronagraphs, an infrared differential imaging camera, an infrared integral field spectrograph and a visible differential polarimeter. We will briefly summarize the science objectives and requirements, describe the proposed conceptual design and discuss the main limitations and corresponding instrumental issues of such a system. We will also derive the expected performance of the proposed Planet Finder and present the project organization.
    Proceedings of the International Astronomical Union 10/2005;
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    ABSTRACT: Light reflected from planets is polarized. This basic property of planets provides the possibility for detecting and characterizing extra-solar planets using polarimetry. The expected polarization properties of extra-solar planets are discussed that can be inferred from polarimetry of solar system planets. They show a large variety of characteristics depending on the atmospheric and/or surface properties. Best candidates for a polarimetric detection are extra-solar planets with an optically thick Rayleigh scattering layer.
    Proceedings of the International Astronomical Union 10/2005;
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    ABSTRACT: Light reflected from planets is polarized. This basic property of planets provides the possibility for detecting and characterizing extra-solar planets using polarimetry. The expected polarization properties of extra-solar planets are discussed that can be inferred from polarimetry of “our” solar system planets. They show a large variety of characteristics depending on the atmospheric and/or surface properties. Best candidates for a polarimetric detection are extra-solar planets with an optically thick Rayleigh scattering layer.
    Proceedings of the International Astronomical Union 09/2005; 1:165 - 170.
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    ABSTRACT: We present measurements of the complete scattering matrix as a function of the scattering angle of three different samples of forsterite particles at a wavelength of 632.8 nm. The three samples were prepared so that three different size distributions were obtained. The results indicate that the differences in sizes in the various sizes ranges affect the elements of the scattering matrix as a function of the scattering angle in a different way.
    05/2005;

Publication Stats

162 Citations
3.69 Total Impact Points

Institutions

  • 2010
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2003–2006
    • University of Amsterdam
      • Astronomical Institute Anton Pannekoek
      Amsterdam, North Holland, Netherlands
  • 2004
    • Leiden University
      Leyden, South Holland, Netherlands