Publications (26)0 Total impact
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Article: Exoplanet Characterization and the Search for Life
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ABSTRACT: Over 300 extrasolar planets (exoplanets) have been detected orbiting nearby stars. We now hope to conduct a census of all planets around nearby stars and to characterize their atmospheres and surfaces with spectroscopy. Rocky planets within their star's habitable zones have the highest priority, as these have the potential to harbor life. Our science goal is to find and characterize all nearby exoplanets; this requires that we measure the mass, orbit, and spectroscopic signature of each one at visible and infrared wavelengths. The techniques for doing this are at hand today. Within the decade we could answer long-standing questions about the evolution and nature of other planetary systems, and we could search for clues as to whether life exists elsewhere in our galactic neighborhood. Comment: 7 pages, 2 figures, submitted to Astro2010 Decadal Review11/2009; -
Article: Mid-infrared interferometry of massive young stellar objects. I. VLTI and Subaru observations of the enigmatic object M8E-IR
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ABSTRACT: [abridged] Our knowledge of the inner structure of embedded massive young stellar objects is still quite limited. We attempt here to overcome the spatial resolution limitations of conventional thermal infrared imaging. We employed mid-infrared interferometry using the MIDI instrument on the ESO/VLTI facility to investigate M8E-IR, a well-known massive young stellar object suspected of containing a circumstellar disk. Spectrally dispersed visibilities in the 8-13 micron range were obtained at seven interferometric baselines. We resolve the mid-infrared emission of M8E-IR and find typical sizes of the emission regions of the order of 30 milli-arcseconds (~45 AU). Radiative transfer simulations have been performed to interpret the data. The fitting of the spectral energy distribution, in combination with the measured visibilities, does not provide evidence for an extended circumstellar disk with sizes > 100 AU but requires the presence of an extended envelope. The data are not able to constrain the presence of a small-scale disk in addition to an envelope. In either case, the interferometry measurements indicate the existence of a strongly bloated, relatively cool central object, possibly tracing the recent accretion history of M8E-IR. In addition, we present 24.5 micron images that clearly distinguish between M8E-IR and the neighbouring ultracompact HII region and which show the cometary-shaped infrared morphology of the latter source. Our results show that IR interferometry, combined with radiative transfer modelling, can be a viable tool to reveal crucial structure information on embedded massive young stellar objects and to resolve ambiguities arising from fitting the SED. Comment: 7 pages, 5 figures, accepted for publication in A&A, new version after language editing, one important reference added, conclusions unchanged07/2009; -
Conference Proceeding: Exoplanet Characterization and the Search for Life
astro2010: The Astronomy and Astrophysics Decadal Survey; 01/2009 -
Chapter: SPHERE: A ‘Planet Finder’ Instrument for the VLT
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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.12/2008: pages 337-341; -
Article: SPHERE: exo-planets science with the new frontier of high contrast imaging
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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. -
Chapter: GENIE: a Ground-Based European Nulling Instrument at ESO Very Large Telescope Interferometer
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ABSTRACT: 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, to analyze the composition of their atmospheres and to assess their ability to sustain life as we know it. 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, definition studies of a Ground based European Nulling Interferometry Experiment, called GENIE, were completed in 2005. This instrument built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. GENIE will operate in the L’ band around 3.8 microns as a single Bracewell nulling interferometer using either two Auxiliary Telescopes (ATs) or two 8m Unit Telescopes (UTs). Its science objectives include the detection and characterization of dust disks and low-mass companions around nearby stars.12/2007: pages 445-456; -
Chapter: The CHEOPS Project: Characterizing Exoplanets by Opto-infrared Polarimetry and Spectroscopy
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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.02/2007: pages 261-264; -
Article: IR and SiO Maser Observations of Miras
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ABSTRACT: Preliminary results of a coordinated program of near IR and SiO maser interferometric observations of Mira variables are reported. The 2.2 and 3.6 micron results are from the FLUOR/TISIS beam combiners on the IOTA interferometer and the SiO maser observations from the VLBA. The ratio of the SiO ring diameter to the apparent diameter at 2.2 microns for stars in our sample cluster around 2, whereas the 3.6 micron diameters range from slightly larger than the 2.2 micron diameter to approximately the SiO ring diameter. This may be due to differences in the opacity of the molecular envelope at 3.6 microns.11/2005; 340:380. -
Article: Search and investigation of extra-solar planets with polarimetry
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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. -
Article: A new start for the VLTI.
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ABSTRACT: The complexity and ambitious scope of VLTI mean that its astrophysical repercussions are difficult to define fully, even for many of its most vocal supporters. However, the primary scientic issues that it seeks to address are well defined, although there remains a need to present these coherently to the wider community in order to justify the significant resources which the project requires. Another pressing need is to develop an implementation plan that will optimally exploit the various technological stages of the project and ensure their compatibility with a vigorous, yet realistic and timely, astrophysical programme.The Messenger. 02/1996; 83:14-21. -
Article: Polarization of Extrasolar Planets: Sample Simulations
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ABSTRACT: Polarization observations appear to be a valuable tool for detecting and studying extrasolar planetary atmospheres. Here, we present numerical simulations of the degree of linear polarization P of starlight reflected by an orbiting planet across the wavelength interval from 0.3 to 3.2 microns, for three types of model atmospheres. The simulations show that P varies with the wavelength and that the variation depends strongly on the atmospheric constituents.294:535-538. -
Article: A planet finder for VLT .
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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. 9:439. -
Article: VLBA observations of SiO masers towards Mira variable stars
Astronomy and Astrophysics, 414, 275 - 288 (2004). -
Article: CHEOPS: A second generation VLT instrument for the direct detection of exo-planets
Favata, F.; Aigrain, S.; Wilson, A.;: Stellar Structure and Habitable Planet Finding, ESA Publications Division, 301-304 (2004). -
Article: Search and investigation of extra-solar planets with polarimetry
Aime, C. ; Vakili, F.: Direct Imaging of Exoplanets: Science & Techniques, Cambridge Univ. Pr., 165-170 (2006). -
Article: Science case for VLT-Planet Finder
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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.Aime, C. ; Vakili, F.: Direct Imaging of Exoplanets: Science & Techniques, Cambridge Univ. Pr., 159-164 (2006). -
Article: The planet finder: Proposal for a 2nd generation VLT instrument
Deming, Drake; Seager, Sara: Scientific frontiers in research on extrasolar planets, ASP, 569-572 (2003). -
Article: VLBA observations of SiO masers towards Mira variable stars
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ABSTRACT: We present new total intensity and linear polarization VLBA observations of the $\nu=2$ and $\nu=1$ $J=1{-}0$ maser transitions of SiO at 42.8 and 43.1 GHz in a number of Mira variable stars over a substantial fraction of their pulsation periods. These observations were part of an observing program that also includes interferometric measurements at 2.2 and 3.6 micron [CITE]; comparison of the results from different wavelengths allows studying the envelope independently of the poorly known distances to these stars. Nine stars were observed at from one to four epochs during 2001. The SiO emission is largely confined to rings which are smaller than the inner radius of the dust shells reported by [CITE]. Two stars (U Orionis, R Aquarii) have maser rings with diameters corresponding to the size of the hot molecular layer as measured at 3.6 micron; in the other cases, the SiO rings are substantially larger. Variations of ring diameter for most, but not all stars, had an rms amplitude in agreement with the models of [CITE] although the expected relationship between the diameter and pulsation phase was not seen. The ring diameter in U Orionis shows remarkably small variation. A correlation between the 2.2/3.6 $\mu$m diameter ratio with that of the SiO/3.6 $\mu$m diameter ratio is likely due to differences in the opacities at 2.2 and 3.6 $\mu$m in a molecular layer. A further correlation with the inner size of the dust shell reported by [CITE] suggest some differences in the temperature structure. Clear evidence is seen in R Aquarii for an equatorial disk similar to that reported by [CITE]; rotation is possibly also detected in S Coronae Boralis.http://dx.doi.org/10.1051/0004-6361:20031597. -
Article: GENIE: a Ground-Based European Nulling Instrument at ESO Very Large Telescope Interferometer
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ABSTRACT: 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, to analyze the composition of their atmospheres and to assess their ability to sustain life as we know it. 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, definition studies of a Ground based European Nulling Interferometry Experiment, called GENIE, were completed in 2005. This instrument built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. GENIE will operate in the L’ band around 3.8 microns as a single Bracewell nulling interferometer using either two Auxiliary Telescopes (ATs) or two 8m Unit Telescopes (UTs). Its science objectives include the detection and characterization of dust disks and low-mass companions around nearby stars. -
Article: A "planet finder" instrument for the ESO VLT
Fridlund, M.; Henning, Th.: Towards other Earths: DARWIN/TPF and the search for extrasolar terrestrial planets, ESA, 99-107 (2003).
Top co-authors
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Institutions
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2005–2007
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Universiteit van Amsterdam
- Astronomical Institute Anton Pannekoek
Amsterdam, North Holland, Netherlands
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