SPHERE: A ‘Planet Finder’ Instrument for the VLT
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.
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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
References
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TL;DR: Speckles dominate shot noise within the halo of adaptively corrected bright star images and, consequently, impose severe limits on ground-based attempts to directly detect planets around nearby stars as discussed by the authors.
Abstract: Speckles dominate shot noise within the halo of adaptively corrected bright star images and, consequently, impose severe limits on ground‐based attempts to directly detect planets around nearby stars. The effect is orders of magnitude greater than conventional photon noise. It depends on the dwell time of the speckle pattern, the brightness of the star, and the fraction \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc}
ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2}
ormalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $( 1-S) $ \end{document} of residual light in the halo (S being the Strehl ratio of the image). These pre...
478 citations
TL;DR: Two-dimensional power spectral density functions were calculated from the digitized measurement data, and roughnesses were obtained by integrating areas under the PSD curves between fixed upper and lower band limits.
Abstract: Surface topography and light scattering were measured on 15 samples ranging from those having smooth surfaces to others with ground surfaces. The measurement techniques included an atomic force microscope, mechanical and optical profilers, confocal laser scanning microscope, angle-resolved scattering, and total scattering. The samples included polished and ground fused silica, silicon carbide, sapphire, electroplated gold, and diamond-turned brass. The measurement instruments and techniques had different surface spatial wavelength band limits, so the measured roughnesses were not directly comparable. Two-dimensional power spectral density (PSD) functions were calculated from the digitized measurement data, and we obtained rms roughnesses by integrating areas under the PSD curves between fixed upper and lower band limits. In this way, roughnesses measured with different instruments and techniques could be directly compared. Although smaller differences between measurement techniques remained in the calculated roughnesses, these could be explained mostly by surface topographical features such as isolated particles that affected the instruments in different ways.
377 citations
TL;DR: In this paper, a four-quadrant binary phase mask (0, n) covering the full field of view at the focal plane is proposed to reduce the total amount of light from the bright source by a factor of 108.
Abstract: We describe a new type of coronagraph, based on the principle of a phase mask as proposed by Roddier and Roddier a few years ago but using an original mask design found by one of us (D. R.), a four-quadrant binary phase mask (0, n) covering the full Ðeld of view at the focal plane. The mutually destructive interferences of the coherent light from the main source produce a very efficient nulling. The computed rejection rate of this coronagraph appears to be very high since, when perfectly aligned and phase-error free, it could in principle reduce the total amount of light from the bright source by a factor of 108, corresponding to a gain of 20 mag in brightness at the location of the Ðrst Airy ring, relative to the Airy peak. In the real world the gain is of course reduced by a strong factor, but nulling is still performing quite well, provided that the perturbation of the phase, for instance, due to the EarthIs atmosphere, is efficiently corrected by adaptive optics. We show from simulations that a detection at a contrast of 10 mag between a star and a faint companion is achievable in excellent conditions, while 8 mag appears routinely feasible. This coronagraph appears less sensitive to atmospheric turbulence and has a larger dynamic range than other recently proposed nulling techniques : the phase-mask coronagraph (by Roddier and Roddier) or the Achro- matic Interfero-Coronagraph (by Gay and Rabbia). We present the principle of the four-quadrant corona- graph and results of a Ðrst series of simulations. We compare those results with theoretical performances of other devices. We brieNy analyze the di†erent limitations in space or ground-based observations, as well as the issue of manufacturing the device. We also discuss several ways to improve the detection of a faint companion around a bright object. We conclude that, with respect to previous techniques, an instrument equipped with this coronagraph should have better performance and even enable the imaging of extrasolar giant planets at a young stage, when coupled with additional cleaning techniques.
373 citations
TL;DR: In this article, an integral-field spectrograph coupled with a coronagraph was used to produce a data cube of two space dimensions and one wavelength for the detection of a Jovian planet at 2 pc with a 2 m coronagraphic space telescope.
Abstract: We propose that coronagraphic imaging in combination with moderate to high spectral resolution from the outset may prove more effective in both detecting extrasolar planets and characterizing them than a standard coronagraphic imaging approach. We envisage an integral-field spectrograph coupled to a coronagraph to produce a data cube of two space dimensions and one wavelength. For the idealized case where the spectrum of the star is well known and unchanging across the field, we discuss the utility of cross-correlation to seek the extrasolar planet signal and describe a mathematical approach to completely eliminate stray light from the host star (although not its Poisson noise). For the case where the point-spread function (PSF) is dominated by diffraction and scattering effects and comprises a multitude of speckles within an Airy pattern, typical of a space-based observation, we turn the wavelength dependence of the PSF to advantage and present a general way to eliminate the contribution from the star while preserving both the flux and spectrum of the extrasolar planet. We call this method spectral deconvolution. We illustrate the dramatic gains by showing an idealized simulation that results in a 20 ? detection of a Jovian planet at 2 pc with a 2 m coronagraphic space telescope, even though the planet's peak flux is only 1% that of the PSF wings of the host star. This scales to detection of a terrestrial extrasolar planet at 2 pc with an 8 m coronagraphic Terrestrial Planet Finder in ~7 hr (or less with appropriate spatial filtering). Data on the spectral characteristics of the extrasolar planet and hence on its atmospheric constituents and possible biomarkers are naturally obtained as part of this process.
366 citations
TL;DR: The SPHERE project as mentioned in this paper is an exo-solar planet imager, which aims to detect giant exosolar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations.
Abstract: The SPHERE 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) wavefront correction, a pupil tracker and diffraction suppression through a variety
of coronagraphs. At its back end, a differential dual imaging camera and an integral field spectrograph (IFS) work in the
Near Infrared (NIR) Y, J, H and Ks bands (0.95 - 2.32μm), and a high resolution polarization camera covers the optical
range (0.6 - 0.9 μm). The IFS is a low resolution spectrograph (R~50) working in the near IR (0.95-1.65 microns), an
ideal wavelength range for the detection of giant planet features. In our baseline design the IFU is a new philosophy
microlens array of about 145x145 elements designed to reduce as much as possible the cross talk when working at
diffraction limit. The IFU will cover a field of view of about 1.7 x 1.7 square arcsecs reaching a contrast of 10 -7 ,
providing a high contrast and high spatial resolution "imager" able to search for planet well inside the star PSF.
163 citations