SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. SPHERE commissioning is foreseen in 2013 on the VLT. 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 (600-900 nm) from extrasolar planets. It is located behind an extreme AO system (SAXO) and a stellar coronagraph. We present the first high contrast polarimetric results obtained for the fully integrated SPHERE-ZIMPOL system. We have measured the polarimetric high contrast performance of several coronagraphs: a Classical Lyot on substrate, a suspended Classical Lyot and two 4 Quadrant Phase Mask coronagraphs. We describe the impact of crucial system parameters – Adaptive Optics, Coronagraphy and Polarimetry - on the contrast performance.
Direct imaging of exoplanet is one of the most exciting field of planetology today. The light coming from exoplanet orbiting their host star witnesses for the chemical composition of the atmosphere, and the potential biomarkers for life. However, the faint flux to be imaged, very close to the huge flux of the parent star, makes this kind of observation extremely difficult to perform from the ground. The direct imaging instruments (SPHERE [1], GPI [2]) are nowaday reaching lab maturity. Such instrument imply the coordination of XAO for atmospherical turbulence real-time correction, coronagraphy for star light extinction, IR Dual band camera, IFS, and visible polarimetry. The imaging modes include single and double difference (spectral and angular). The SPHERE project is now at the end of AIT phase. This paper presents the very last results obtained in laboratory, with realistic working conditions. These AIT results allows one to predict on-sky performance, that should come within the next weeks after re-installation at Very Large Telescope at Paranal.
IRDIS is one of the science sub-systems of VLT/SPHERE dedicated to the detection and characterization of giant exoplanets at large orbital radii with high-contrast direct imaging. It offers a unique set of observational modes including dual-band imaging (DBI) with very low differential aberrations, and long slit spectroscopy (LSS) coupled with a classical Lyot coronograph that will be used to obtain spectra at low (R = ~50) and medium (R = ~500) resolution. During the past year, IRDIS has been integrated and tested in laboratory in a standalone configuration, and it has recently been integrated on the full SPHERE bench including the calibration unit, the common path optics and the extreme AO system. We present the first analysis of data obtained during laboratory tests of IRDIS in the DBI mode, both in standalone and with the full SPHERE bench, but without simulated seeing and AO correction. We show the first performance estimates of spectral differential imaging with IRDIS in H-band, which is used to attenuate the speckle noise induced by the instrumental aberrations. Similarly, for the LSS mode we present the first application of the spectral deconvolution data analysis method to attenuate the speckle noise on IRDIS data. Finally we compare these results to simulations that were performed during the development phase of the instrument.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second generation
instrument for the VLT optimized for very high-contrast imaging around bright stars. Its primary
science goal is the detection and characterization of giant planets, together with observation of
circumstellar environment. The infrared differential imager and spectrograph (IRDIS), one of the
three science instruments for SPHERE, provides simultaneous differential imaging in the near
infrared, among with long slit spectroscopy, classical imaging and infrared polarimetry. IRDIS is
designed to achieve very high contrast with the help of extreme-AO (Strehl < 90%), coronography,
exceptional image quality (including non-common-path aberrations compensation), very accurate
calibration strategies and very advanced data processing for speckle suppression. In this paper, we
report on the latest experimental characterizations of IRDIS performed with SPHERE/SAXO before
the preliminary acceptance in Europe.
SPHERE, the extra-solar planet imager for the Very Large Telescope is a program that has been running since 2006. The
instrument is now nearing completion and it is in the final integration stage. The 3 science instruments of SPHERE are
now complete and have passed the internal acceptance review while the complex common path with the extreme
Adaptive optics system, the coronographs and the calibration module is aggressively progressing. This paper reviews the
performance of the Common Path (CP) and three science instruments of SPHERE: IRDIS, the dual band imager; IFS, the
integral field spectrograph and ZIMPOL, the imaging polarimeter. We also present an outlook at the final system
integration.
ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets
direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas
giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The
segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the
detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the
overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and
post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the
concepts for common path and diffraction suppression system is presented. The performance of the instrument is
predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through
the various optical elements.
Extreme adaptive optics systems (XAO) dedicated to the search for extrasolar planets are currently being developed for
8-10 meter telescopes. The High-Order Test bench (HOT) is a
high-contrast imaging adaptive optics bench developed at
the European Southern Observatory to test and optimize different techniques and technologies (e.g. wavefront sensors,
coronagraphs, speckle calibration methods, image post-processing). It reproduces realistic conditions at a telescope (e.g.
Very Large Telescope, VLT), including a turbulence generator, a
high-order adaptive optics system, a near-IR
coronagraph, and sequential differential imaging modes (spectral and polarimetric). We discuss the results of XAO
coronagraphy obtained in the laboratory in the context of imminent planet-finder instruments (e.g. SPHERE1, GPI2, and
HiCIAO3). In particular, results obtained with HOT will be discussed and compared with contrast goals of the near-IR
camera of SPHERE.
EPOL is the imaging polarimeter part of EPICS (Exoplanet Imaging Camera and Spectrograph) for the 42-m E-ELT. It
is based on sensitive imaging polarimetry to differentiate between linearly polarized light from exoplanets and
unpolarized, scattered starlight and to characterize properties of exoplanet atmospheres and surfaces that cannot be
determined from intensity observations alone. EPOL consists of a coronagraph and a dual-beam polarimeter with a
liquid-crystal retarder to exchange the polarization of the two beams. The polarimetry thereby increases the contrast
between star and exoplanet by 3 to 5 orders of magnitude over what the extreme adaptive optics and the EPOL
coronagraph alone can achieve. EPOL operates between 600 and 900 nm, can select more specific wavelength bands
with filters and aims at having an integral field unit to obtain linearly polarized spectra of known exoplanets. We present
the conceptual design of EPOL along with an analysis of its performance.
Controlling the amplitude of light is crucial for many scientific applications, such as imaging systems, astronomical
instruments, optical testing, or laser physics. We provide an overview of the halftoning technique - the process of
displaying a continuous image with binary dots - for application to coronagraphy. Customized filters with spatially
varying transmission are produced using a binary array of metal pixels (namely microdot masks) that offers excellent
control of the local transmission, with intrinsic achromaticity. Applications, design guidelines, and tests of near-IR
prototypes for both pupil and focal plane coronagraphic devices are presented in the context of the VLT-SPHERE and EELT
EPICS instruments.
Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and
explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based
telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the discovery space
towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. EPICS is a
proposed instrument for the European ELT, dedicated to the detection and characterization of Exoplanets by direct
imaging, spectroscopy and polarimetry. ESO completed a phase-A study for EPICS with a large European consortium
which - by simulations and demonstration experiments - investigated state-of-the-art diffraction and speckle suppression
techniques to deliver highest contrasts. The paper presents the instrument concept and analysis as well as its main
innovations and science capabilities. EPICS is capable of discovering hundreds of giant planets, and dozens of lower
mass planets down to the rocky planets domain.
We report laboratory development of coronagraphic devices to be implemented on the High Order Testbench (HOT) to
assess intensity reduction between them at a high Strehl ratio regime. The high order test bench implements extreme
adaptive optics with realistic telescope conditions reproduced by star and turbulence generators. A 32×32 actuator micro
deformable mirror, one pyramid wave front sensor, one Shack-Hartmann wave front sensor and the ESO SPARTA real-time
computer. This will enable characterization and comparative study of different types of coronagraphs in realistic
conditions. We have developed several prototypes of promising coronagraphs concepts: Four Quadrants Phase Mask1
(FQPM), Lyot2 coronagraphs and Apodized Pupil Lyot Coronagraph3 (APLC). We will describe the design of the IR
coronagraphic path on HOT, prototyping processes used for each coronagraph and discuss quality control and first
results obtained on a IR coronagraphic testbench (Strehl ratio ~ 94%). Finally, we will present our experiment plan and
future coronagraph developments.
High-contrast imagers dedicated to the search for extrasolar planets are currently being developed for the VLT
(SPHERE) and Gemini (GPI) observatories. A vital part of such a high-contrast imager is the extreme adaptive optics
(XAO) system that very efficiently removes effects of atmospheric turbulence and instrument aberrations. The high
order test bench (HOT) implements an XAO system under realistic telescope conditions reproduced by star and
turbulence generators. New technological developments (32x32 actuator micro deformable mirror, read-noise free
electron multiplying CCD60, SPARTA real time computer) are used to study and compare two potential XAO wave
front sensors: The Pyramid- and the Shack-Hartmann wave front sensors. We will describe the overall design of HOT
including the sub-systems. We will present the closed loop study results of the behavior of the Shack-Hartmann wave
front sensor in terms of linearity, sensitivity to calibration errors, performance and other specific issues.
The Exo-Planets Imaging Camera and Spectrograph (EPICS), is the Planet Finder Instrument concept for the European
Extremely Large Telescope (ELT). The study made in the frame of the OWL 100-m telescope concept is being up-dated
in direct relation with the re-baselining activities of the European Extremely Large Telescope.
Extremely Large Telescopes are very promising to detect and characterize Earth-like planets because of their high angular resolution and the increased number of collected photons. We study the impact of aberrations on this detection and the limitations they impose. We consider an extreme adaptive optic device upstream of a perfect coronagraph. Even with the high Strehl ratio provided, the coronagraphic image is not sufficient to detect Earth-like planet. Indeed the contrast between this kind of planet and its star is about 10-10 in the near infra-red. As a consequence, a calibration device downstream of the coronagraph must be used to reach this contrast. We modelize a realistic system taking into account dynamic aberrations left uncorrected by the adaptive optics, static aberrations of optical system and differential static aberrations due to the calibration channel. Numerical simulations compare the respective assets of a 30 meter telescope in a median site to these of a 15 meter telescope in the dome C. In both cases, we must control common static aberrations at 8 nm and differential aberrations at 0.1 nm. Beyond this limitation due to the speckle noise and despite the great collecting area, another limitation is set by the photon noise. We also compare these results to simulations made with real coronagraphs and with an obstructed pupil.
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