Author
F. Joos
Bio: F. Joos is an academic researcher from ETH Zurich. The author has contributed to research in topics: Planet & Uranus. The author has an hindex of 12, co-authored 17 publications receiving 1250 citations.
Topics: Planet, Uranus, Exoplanet, Polarization (waves), Coronagraph
Papers
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TL;DR: The SPHERE instrument as discussed by the authors was designed for direct detection and spectral characterization of extra-solar planets, where the main challenge consists in the very large contrast between the host star and the planet, typically inside the seeing halo.
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.
672 citations
TL;DR: In this paper, a radial limb polarization on the order of 1% was detected with a position angle perpendicular to the limb in all observations of Uranus and Neptune in the R, i,a ndz bands.
Abstract: Imaging polarimetry of Uranus and Neptune in the R, i ,a ndz bands are presented. In all observations a radial limb polarization on the order of 1% was detected with a position angle perpendicular to the limb. The polarization is higher in both planets for the shorter wavelength bands. As a first approximation, the polarization seems to be equally strong along the entire limb. This is unlike Jupiter and Saturn, where significant limb polarization is only observed at the poles. We determined flux-weighted averages of the limb polarization and radial limb polarization profiles, and investigated the degradation and cancellation effects in the polarization signal due to the seeing-limited spatial resolution of our observations. Taking this into account we derived corrected values for the limb polarization in Uranus and Neptune. The results are compared with analytic models for Rayleigh scattering atmospheres for the semi-infinite case and finite layers with ground albedo. The comparison shows that the detected polarization is compatible with expectations. This indicates that limb-polarization measurements offer a powerful diagnostic tool for investigating the properties of scattering particles in the upper atmospheres of Uranus and Neptune, in particular if more sophisticated numerical modeling of the limb polarization becomes available. It is also concluded from the overall strength of the limb polarization that the disk-integrated polarization of Uranus and Neptune for large phase angles is high (p > 20%). This is of interest for future polarimetric detections of extra-solar planets with atmospheric properties similar to Uranus and Neptune.
163 citations
TL;DR: The ZIMPOL instrument as mentioned in this paper is a single-beam polarimeter that achieves very high polarimetric accuracy using fast polarization modulation and demodulating CCD detectors, which can detect Jupiter-sized planets in close orbit around the brightest nearby stars.
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.
94 citations
01 Jun 2007
TL;DR: The SPHERE instrument as mentioned in this paper was designed to reach the highest contrast in a limited field of view and at short distances from the central star, typically inside the seeing halo.
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.
72 citations
ETH Zurich1, European Southern Observatory2, ASTRON3, Centre national de la recherche scientifique4, University of Grenoble5, INAF6, University of Padua7, Aix-Marseille University8, University of Amsterdam9, Leiden University10, Paris Diderot University11, Max Planck Society12, Kiepenheuer Institut für Sonnenphysik13, University of Lyon14, University of Geneva15
TL;DR: In this article, the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region <2 ǫ' (< 400 AU) of R Aqr were determined from high-resolution images taken in H alpha and other filters.
Abstract: Context. R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. Because of its proximity to the Sun, this object has been studied in much detail with many types of high resolution imaging and interferometric techniques. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). Aims. We describe SPHERE /ZIMPOL test observations of the R Aqr system taken in H alpha and other filters in order to demonstrate the exceptional performance of this high resolution instrument. We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We use our data for a detailed characterization of the inner jet region of R Aqr. Methods. We analyze the high resolution approximate to 25 mas images from SPHERE /ZIMPOL and determine from the H alpha emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region <2 `' (< 400 AU) of R Aqr. The data are compared to simultaneous HST line filter observations. The H alpha fluxes and the measured sizes of the clouds yield H alpha emissivities for many clouds from which one can derive the mean density, mass, recombination time scale, and other cloud parameters. Results. Our H alpha data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 45 mas West (position angle ‐89.5 degrees) of the mira. The central jet source is the strongest H alpha component with a flux of about 2.5 x 10(‐12) erg cm(‐2) s(‐1). North east and south west from the central source there are many clouds with very diverse structures. Within 0.5 `' (100 AU) we see in the SW a string of bright clouds arranged in a zig‐zag pattern and, further out, at 1 `'‐2 `', fainter and more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure between 0.2 `'‐0.7 `' and faint perpendicular `` wisps'' further out. Some jet clouds are also detected in the ZIMPOL [O I] and He I filters, as well as in the HST‐WFC3 line filters for H alpha, [O III], [N II], and [O I]. We determine jet cloud parameters and find a very well defined correlation N‐e proportional to r(‐1.3) between cloud density and distance to the central binary. Densities are very high with typical values of N‐e approximate to 3 x 10(5) cm(‐3) for the ``outer'' clouds around 300 AU, N‐e approximate to 3 x 10(6) cm(‐3) for the ``inner'' clouds around 50 AU, and even higher for the central jet source. The high Ne of the clouds implies short recombination or variability timescales of a year or shorter. Conclusions. H alpha high resolution data provide a lot of diagnostic information for the ionized jet gas in R Aqr. Future H alpha observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion.
55 citations
Cited by
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TL;DR: A review of the current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multi-planet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems can be found in this paper.
Abstract: The basic geometry of the Solar System—the shapes, spacings, and orientations of the planetary orbits—has long been a subject of fascination as well as inspiration for planet-formation theories. For exoplanetary systems, those same properties have only recently come into focus. Here we review our current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multiplanet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems.
824 citations
TL;DR: In this paper, a new method to achieve point-spread function (PSF) subtractions for high-contrast imaging using principal component analysis that is applicable to both point sources or extended objects (disks) is described.
Abstract: We describe a new method to achieve point-spread function (PSF) subtractions for high-contrast imaging using principal component analysis that is applicable to both point sources or extended objects (disks). Assuming a library of reference PSFs, a Karhunen–Lo` eve transform of these references is used to create an orthogonal basis of eigenimages on which the science target is projected. For detection this approach provides comparable suppression to the Locally Optimized Combination of Images (LOCI) algorithm, albeit with increased robustness to the algorithm parameters and speed enhancement. For characterization of detected sources, the method enables forward modeling of astrophysical sources. This alleviates the biases in the astrometry and photometry of discovered faint sources, which are usually associated with LOCI-based PSF subtractions schemes. We illustrate the algorithm performance using archival Hubble Space Telescope images, but the approach may also be considered for ground-based data acquired with angular differential imaging or integral-field spectrographs.
677 citations
Book•
01 May 2011TL;DR: In this paper, the authors present an overview of the solar system and its evolution, including the formation and evolution of stars, asteroids, and free-floating planets, as well as their internal and external structures.
Abstract: 1. Introduction 2. Radial velocities 3. Astrometry 4. Timing 5. Microlensing 6. Transits 7. Imaging 8. Host stars 9. Brown dwarfs and free-floating planets 10. Formation and evolution 11. Interiors and atmospheres 12. The Solar System Appendixes References Index.
527 citations
TL;DR: In this article, a new method to achieve point spread function (PSF) subtractions for high contrast imaging using principal component analysis (PCA) that is applicable to both point sources or extended objects (disks) is described.
Abstract: We describe a new method to achieve point spread function (PSF) subtractions for high- contrast imaging using Principal Component Analysis (PCA) that is applicable to both point sources or extended objects (disks). Assuming a library of reference PSFs, a Karhunen-Lo`eve transform of theses references is used to create an orthogonal basis of eigenimages, on which the science target is projected. For detection this approach provides comparable suppression to the Locally Optimized Combination of Images (LOCI) algorithm, albeit with increased robustness to the algorithm parameters and speed enhancement. For characterization of detected sources the method enables forward modeling of astrophysical sources. This alleviates the biases in the astrometry and photometry of discovered faint sources, which are usually associated with LOCI- based PSF subtractions schemes. We illustrate the algorithm performance using archival Hubble Space Telescope (HST) images, but the approach may also be considered for ground-based data acquired with Angular Differential Imaging (ADI) or integral-field spectrographs (IFS).
515 citations
Max Planck Society1, University of Grenoble2, University of Chile3, European Southern Observatory4, Leiden University5, University of Oxford6, Paris Diderot University7, INAF8, Aix-Marseille University9, École normale supérieure de Lyon10, University of Tübingen11, University of Bern12, Hungarian Academy of Sciences13, ETH Zurich14, Diego Portales University15, Ludwig Maximilian University of Munich16, Kavli Institute for Theoretical Physics17, California Institute of Technology18, Rice University19, Stockholm University20, University of Cambridge21, Centre national de la recherche scientifique22, Valparaiso University23, University of Arizona24, Monash University, Clayton campus25, University of Geneva26, University of Hawaii at Manoa27, University of Atacama28, Heidelberg University29, University of Michigan30
TL;DR: In this article, the authors detect a point source within the gap of the transition disk at about 195 mas (~22 au) projected separation and detect a signal from an inner disk component.
Abstract: Context. Young circumstellar disks are the birthplaces of planets. Their study is of prime interest to understand the physical and chemical conditions under which planet formation takes place. Only very few detections of planet candidates within these disks exist, and most of them are currently suspected to be disk features.Aims. In this context, the transition disk around the young star PDS 70 is of particular interest, due to its large gap identified in previous observations, indicative of ongoing planet formation. We aim to search for the presence of an embedded young planet and search for disk structures that may be the result of disk–planet interactions and other evolutionary processes.Methods. We analyse new and archival near-infrared images of the transition disk PDS 70 obtained with the VLT/SPHERE, VLT/NaCo, and Gemini/NICI instruments in polarimetric differential imaging and angular differential imaging modes.Results. We detect a point source within the gap of the disk at about 195 mas (~22 au) projected separation. The detection is confirmed at five different epochs, in three filter bands and using different instruments. The astrometry results in an object of bound nature, with high significance. The comparison of the measured magnitudes and colours to evolutionary tracks suggests that the detection is a companion of planetary mass. The luminosity of the detected object is consistent with that of an L-type dwarf, but its IR colours are redder, possibly indicating the presence of warm surrounding material. Further, we confirm the detection of a large gap of ~54 au in size within the disk in our scattered light images, and detect a signal from an inner disk component. We find that its spatial extent is very likely smaller than ~17 au in radius, and its position angle is consistent with that of the outer disk. The images of the outer disk show evidence of a complex azimuthal brightness distribution which is different at different wavelengths and may in part be explained by Rayleigh scattering from very small grains.Conclusions. The detection of a young protoplanet within the gap of the transition disk around PDS 70 opens the door to a so far observationally unexplored parameter space of planetary formation and evolution. Future observations of this system at different wavelengths and continuing astrometry will allow us to test theoretical predictions regarding planet–disk interactions, planetary atmospheres, and evolutionary models.
497 citations