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.
The Oxford SWIFT spectrograph, an I & z band (6500-10500 A) integral field spectrograph, is designed to operate as a
facility instrument at the 200 inch Hale Telescope on Palomar Mountain, in conjunction with the Palomar laser guide star
adaptive optics system PALAO (and its upgrade to PALM3000). SWIFT provides spectra at R(≡λ/▵λ)~4000 of a
contiguous two-dimensional field, 44 x 89 spatial pixels (spaxels) in size, at spatial scales of 0.235";, 0.16", and 0.08" per
spaxel. It employs two 250μm thick, fully depleted, extremely red sensitive 4k X 2k CCD detector arrays (manufactured
by LBNL) that provide excellent quantum efficiency out to 1000 nm.
We describe the commissioning observations and present the measured values of a number of instrument parameters. We
also present some first science results that give a taste of the range of science programs where SWIFT can have a
substantial impact.
HARMONI is a proposed visible and near-infrared integral field spectrograph for the European Extremely Large
Telescope. We are exploring the merits of adding a coronagraphic capability to HARMONI, specifically targeted at
enabling observations of faint, nearby companions (primarily extra-solar planets) that require high contrast. Although
HARMONI is not fed by extreme adaptive optics, we show that substantial contrasts can be achieved by post-processing
of the hyperspectral data cube using spectral deconvolution. We make predictions of achievable contrast as a function of
coronagraph design, based on realistic models of the telescope's aberrations.
We present the results of a design study for an integral field spectrograph as the "back-end" instrument for spectroscopy
of exoplanets carried out in the context of the EPICS Phase A study. EPICS is the planet finder imager and spectrograph
for the E-ELT. In our study we investigated the feasibility of an image slicer based integral field spectrograph and
developed an optical design for the image slicer and the necessary pre-optics, as well as the spectrograph optics. We
present a detailed analysis of the optical performance of the design.
As part of the Phase A study for the EPICS instrument, we investigate if there are any contrast limitations imposed by
the choice of the integral field spectrograph (IFS) technology, and if so, to determine the contrast limits applicable to
each technology. In this document we investigate (through production of a prototype and actual laboratory tests) the
contrast limitations inherent in a slicer based IFS.
Using an experimental set-up that generates speckles at the input to a slicer based integral field spectrograph, we have
conclusively demonstrated that a slicer based IFS (that has not been specifically designed for high contrast observations)
does NOT limit the contrast achieved by a planet finding instrument at the level of at least one part in 250 per spectral
channel at R~800. This limit is imposed by the limited source intensity available for the measurements made with the
test bed's current setup and is to be improved upon in the near future. This level of speckle noise rejection already
satisfies the top level requirements of the EPICS instrument.
As part of the Phase A study for the EPICS instrument, we investigate if there are any contrast limitations imposed by
the choice of the integral field spectrograph (IFS) technology, and if so, to determine the contrast limits applicable to
each technology. In this document we investigate (through simulations) the contrast limitations inherent in a slicer based
IFS.
Current results show the achievable contrast with the slicer to be promising when taking into consideration the fact that
the central region of the apodized PSF has not been masked. Limiting the maximum intensity by a factor of 100-1000
using an obscuring focal plane mask should also reduce the intensity of the secondary speckles by an equivalent factor.
Furthermore, the secondary speckles created in the slicer spectrograph only influence the few slices where the bright
central core is imaged. By orienting these slices to lie along the spider arms of the E-ELT secondary, the fraction of the
field of view affected can be minimized.
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.
Current simulation and experimental investigatory work is going on into the performance of slicer and lenslet IFS designs. The aim of this work is to determine which technology holds the best promise for achieving the highest contrasts with EPICS on the E-ELT.
Results from Spectral Deconvolution methods for high contrast detections are presented, both on sky images from AB Dor C observations using SINFONI on the VLT and improvements to the algorithms made through use of EPICS simulation data. Using these simulations, only containing photon and speckle noise, we have been able to detect simulated planets down to a contrast of 1010 located less than 1" from the parent star.
The effects of spectral resolution and wavelength range on high contrast observations are discussed. Shortening the wavelength range increases the inner working angle. It is seen that an outer working angle is also reached that decreases with spectral resolution. The limit on the inner working angle can be overcome partly by increasing the wavelength range of the instrument although another inner working angle limit will be reached if a coronagraph is used. The limit of the outer working angle can also be overcome by increasing the spectral resolution of the instrument or possibly by making an IFS that produces an output with a constant spectral resolution, R, instead of constant &Dgr;&lgr;. This is still a work in progress.
One of the main science objectives of the European ELT is the direct imaging of extrasolar planets. The large aperture of
the telescope has the potential to significantly enlarge the discovery space towards older gas giant exo-planets seen in
reflected light. In this paper, we give an overview of the EPICS system design strategy during the phase A study. In
order to tackle the critical limitations to high contrast, extensive end-to-end simulations will be developed since the start
to test different scenarios and guide the overall design.
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