KEYWORDS: Optical spheres, Sensors, Planets, Spectrographs, Iterated function systems, Stars, Spectral resolution, Coronagraphy, Adaptive optics, Signal to noise ratio
MedRes is a proposed MEDium RESolution integral field spectrograph for upgrading SPHERE, the high contrast instrument for the ESO VLT telescope. MedRes is actually thought of as a potential Visitor Instrument with the scope to provide high contrast diffraction limited medium-high resolution spectra (R ≥ 1000) over a reasonably large field of view (a square with a side of at least 0.4) and across the spectral region 1.2-1.65 microns. Two main science objectives are driving the proposition for such an instrument on SPHERE. First of all, MedRes shall improve the detection of previously unknown giant planets (contrast 10−5 , goal 10−6 ), in particular accreting planets, at small separation from the star (< 0.2”, goal, 0.1”). And second, MedRes will boost the characterisation of known (faint) planets at a spectral resolution substantially higher than currently possible with SPHERE IFS (R ~ 35 − 50) and for contrasts much better than achievable with IRDIS Long Slit Spectroscopy (LSS) at small separations. The design will be optimised for SPHERE, fully exploiting the capabilities offered by a second stage Adaptive Optics (SAXO+) and complementing the niches of IRDIS, IFS and HiRise in the near IR channel. A preliminary optomechanical design and simulations of performance will be presented.
SPHERE+ is a proposed upgrade of the SPHERE instrument at the VLT, which is intended to boost the current performances of detection and characterization for exoplanets and disks. SPHERE+ will also serve as a demonstrator for the future planet finder (PCS) of the European ELT. The main science drivers for SPHERE+ are 1/ to access the bulk of the young giant planet population down to the snow line (3 − 10 au), to bridge the gap with complementary techniques (radial velocity, astrometry); 2/ to observe fainter and redder targets in the youngest (1 − 10 Myr) associations compared to those observed with SPHERE to directly study the formation of giant planets in their birth environment; 3/ to improve the level of characterization of exoplanetary atmospheres by increasing the spectral resolution in order to break degeneracies in giant planet atmosphere models. Achieving these objectives requires to increase the bandwidth of the xAO system (from ~1 to 3 kHz) as well as the sensitivity in the infrared (2 to 3 mag). These features will be brought by a second stage AO system optimized in the infrared with a pyramid wavefront sensor. As a new science instrument, a medium resolution integral field spectrograph will provide a spectral resolution from 1000 to 5000 in the J and H bands. This paper gives an overview of the science drivers, requirements and key instrumental tradeoff that were done for SPHERE+ to reach the final selected baseline concept.
The VLT second generation instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanets Research) was commissioned in the Summer of 2014, and offered to the community in the Spring of 2015. SPHERE is a high contrast imager that exploits its three scientific channels in order to observe and discover young warm exoplanets in the glare of their host stars. The three scientific instrument are: ZIMPOL, a polarization analyzer and imager that works in the visible range of wavelength, IRDIS a dual band imager and spectro polarimetric Camera that works in the NIR range up to K band, and IFS, an integral field spectrograph working in the YJH band. Very important is the complementarity between IRDIS and IFS. The former has a larger Field of view (about 12 arcseconds) while the IFS push its examination very close to the central star (FoV ~ 1.7 arcsec). In one year of operational time a lot of very interesting scientific cases were investigated and very nice results were gathered. In this paper we would like to focus the attention on the high quality results and performances obtained with the IFS.
We present the current results of the astrometric characterization of the VLT planet finder SPHERE over 2 years of on-sky operations. We first describe the criteria for the selection of the astrometric fields used for calibrating the science data: binaries, multiple systems, and stellar clusters. The analysis includes measurements of the pixel scale and the position angle with respect to the North for both near-infrared subsystems, the camera IRDIS and the integral field spectrometer IFS, as well as the distortion for the IRDIS camera. The IRDIS distortion is shown to be dominated by an anamorphism of 0.60±0.02% between the horizontal and vertical directions of the detector, i.e. 6 mas at 1 arcsec. The anamorphism is produced by the cylindrical mirrors in the common path structure hence common to all three SPHERE science subsystems (IRDIS, IFS, and ZIMPOL), except for the relative orientation of their field of view. The current estimates of the pixel scale and North angle for IRDIS are 12.255±0.009 milliarcseconds/pixel for H2 coronagraphic images and -1.70±0.08°. Analyses of the IFS data indicate a pixel scale of 7.46±0.02 milliarcseconds/pixel and a North angle of -102.18±0.13°. We finally discuss plans for providing astrometric calibration to the SPHERE users outside the instrument consortium.
This article presents a proposal aimed at investigating the technical feasibility and the scientific capabilities of high
contrast cameras to be implemented at LBT. Such an instrument will fully exploit the unique LBT capabilities in
Adaptive Optics (AO) as demonstrated by the First Light Adaptive Optics (FLAO) system, which is obtaining excellent
results in terms of performance and reliability. The aim of this proposal is to show the scientific interest of such a
project, together with a conceptual opto-mechanical study which shows its technical feasibility, taking advantage of the
already existing AO systems, which are delivering the highest Strehl experienced in nowadays existing telescopes.
Two channels are foreseen for SHARK, a near infrared channel (2.5-0.9 um) and a visible one (0.9 – 0.6 um), both
providing imaging and coronagraphic modes. The visible channel is equipped with a very fast and low noise detector
running at 1.0 kfps and an IFU spectroscopic port to provide low and medium resolution spectra of 1.5 x 1.5 arcsec
fields.
The search of extra solar giant planets is the main science case and the driver for the technical choices of SHARK, but
leaving room for several other interesting scientific topics, which will be briefly depicted here.
SPHERE is an instrument aimed to the search for low mass companions around young stars in the solar neighborhood. To achieve this goal light from the host star (and in particular the speckle pattern due to the telescope aberrations) should be strongly attenuated while avoiding to cancel out the light from the faint companion. Different techniques can be used to fulfill this aim exploiting the multi-wavelength datacube produced by the Integral Field Spectrograph that is one of the scientific modules that composes SPHERE. In particular we have tested the application of the Spectral Deconvolution and of the Principal Components Analysis techniques. Both of them allow us to obtained a contrast better than 10−5 with respect to the central star at separations of the order of 0.4 arcsec. A further improvement of one order of magnitude can be obtained by combining one of these techniques to the Angular Differential Imaging. To investigate the expected performance of IFS in characterizing detected objects we injected in laboratory data synthetics planets with different intrinsic fluxes and projected separations from the host star. We performed a complete astrometric and photometric analysis of these images to evaluate the expected errors on these measurements, the spectral fidelity and the differences between the reduction methods. The main issue is to avoid the strong self-cancellation that is inherent to all the reduction methods. We have in particular tested two possible solutions: the use of a mask during the reduction on the positions of the companions or, alternatively, using a KLIP procedure for the IFS. This latter seems to give better results in respect o the classical PCA, allowing us to obtain a good spectral reconstruction for simulated objects down to a contrast of ~10-5.
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its ~130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope’s overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L’ (3.8 μm), as opposed to the shorter wavelength near-infrared bands (1-2.4 μm) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent (~0.1-1 Gyr) stars. LEECH’s contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5μm in preparation for JWST.
SPHERE is an extrasolar planet imager whose goal is to detect giant extrasolar 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, a pupil tracker and NIR and Visible coronagraph devices. At its
back end, a differential dual imaging camera and an integral field spectrograph (IFS) work in the Near Infrared (NIR)
(0.95 ≤λ≤2.32 μm) and a high resolution polarization camera covers the visible (0.6 ≤λ≤0.9 μm). The IFS is a low resolution spectrograph (R~50) operates in the near IR (0.95≤λ≤1.6 μm), an ideal wavelength range for the detection of planetary features, over a field of view of about 1.7 x 1.7 square arcsecs. Form spectra it is possible to reconstruct monochromatic images with high contrast (10-7) and high spatial resolution, well inside the star PSF. In this paper we describe the IFS, its calibration and the results of several performance which IFS underwent. Furthermore, using the IFS characteristics we give a forecast on the planetary detection rate.
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.
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) turbulence correction, pupil tracker and NIR and Visible coronagraph devices. 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≤λ≤2.32 μm) and a high resolution polarization camera covers the visible (0.6≤λ≤0.9 μm). The
IFS is a low resolution spectrograph (R~50) which works in the near IR (0.95≤λ≤1.6 μm), an ideal wavelength range for
the detection of planetary features. The IFS is based on a new conception microlens array (BIGRE) of 145X145 lenslets
designed to reduce as low as possible the contrast. The IFU will cover a field of view of about 1.7 x 1.7 square arcsecs
reaching a contrast of 10-7, giving an high contrast and high spatial resolution "imager" able to search for planet well
inside the star PSF. In the last year it has been integrated onto the huge optical bench of SPHERE and fully tested.
During the last months IFS, is the Integral Field Spectrograph for SPHERE, devoted to the search of exoplanets has been
integrated in the clean room of Padova Observatory. The design of IFS is based on a new concept of double microlens
array sampling the focal plane. This device named BIGRE consists of a system made of two microlens arrays with
different focal lengths and thickness equal to the sum of them and precisely aligned each other. Moreover a mask has
been deposited on the first array to produce a field stop for each lenslet, and a second mask is located on the intermediate
pupil of the IFS to provide an aperture stop. After characterization of a previous prototype of BIGRE in the visible range,
now the first measurements of the performances of the device in the IR range have been obtained on the instrument that
will be mounted at the VLT telescope. These tests confirmed that specifications and properties of the prototype are met
by state of the art on optics microlens manufacturing.
Currently in the phase of the assembly, the Integral Field Spectrograph (IFS) is part of Sphere, which will see the first
light at ESO Paranal as a VLT second generation instruments in the 2011. In this paper we will describe the main aspects
in the Assembly, Integration and Testing phase (AIT) of the instrument at INAF-Osservatorio Astronomico di Padova
(OAPD) laboratory at the current stage. As result of the AIT, a full set of tests and qualifications of IFS subcomponents
will be discussed. These tests have been designed and realized with the purpose to obtain an accurate comparison
between design goals and effective performances of the instrument.
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.
One of the main challenges to obtain the contrast of >15mag targeted by an extra-solar planet imager like SPHERE lies
in the calibration of all the different elements participating in the final performance. Starting with the calibration of the
AO system and its three embedded loops, the calibration of the non-common path aberrations, the calibration of the NIR
dual band imager, the NIR integral field spectrograph, the NIR spectrograph, the visible high accuracy polarimeter and
the visible imager all require sophisticated calibration procedures. The calibration process requires a specific extensive
calibration unit that provides the different sources across the spectrum (500-2320nm) with the stabilities and precisions
required. This article addresses the challenges met by the hardware and the instrument software used for the calibration
of SPHERE.
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) turbulence correction, pupil tracker and interferential 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 visible (0.6 - 0.9 μm). The IFS is a low
resolution spectrograph (R~50 and R~30) which works in the near IR (0.95-1.7 microns), an ideal wavelength range for
the detection of planetary features. In our baseline design the IFU is a new philosophy microlens array of about 145x145
elements designed to reduce as low as possible the contrast. The IFU will cover a field of view of about 1.8 x 1.8 square
arcsecs reaching a contrast of 10-7, giving an high contrast and high spatial resolution "imager" able to search for planet
well inside the star PSF.
Integral field spectroscopy coupled with an extreme adaptive optics system and coronagraphy allows a marked
improvement of the standard spectroscopic simultaneous differential imaging calibration technique. Hence, with an
integral field spectrograph (IFS) direct imaging of extrasolar giant planets becomes potentially feasible over a wide
range of ages, masses, and separations from the hosting stars. This aim represents the prime goal of the planet finder
instrument for the VLT (SPHERE). Inside SPHERE, the IFS channel exploits various spectral features of the candidate
planets in the near infrared, in order to reduce the speckles noise at the level of the stellar background noise, over a field
of view comprised between the coronagraphic inner working angle and the outer working angle provided by the
SPHERE extreme adaptive optic system (SAXO). The IFS allows then to realize an extensive spectroscopic
simultaneous differential imaging calibration technique, and at least in few cases, to get the spectrum of the candidate
extrasolar giant planets. Here we present the IFS baseline design, which is based upon a new optical concept we
developed for its integral field unit (BIGRE). When applied to the technical specifications of SPHERE IFS, a BIGRE
integral field unit is able to take into account all the effects appearing when integral field spectroscopy is used in
diffraction limited conditions and for high-contrast imaging purposes. Finally a BIGRE-oriented IFS optical design is
shown here to reach the requested high optical quality by standard lenses-based optical devices.
IFS is the Integral Field Spectrograph for SPHERE, a 2nd generation instrument for VLT devoted to the search of
exoplanets.
To achieve the performances required for the IFS a new device sampling the focal plane has been designed, prototyped
and tested in laboratory. This device named BIGRE consists of a system made of two microlens arrays with different
focal lengths and thickness equal to the sum of them and precisely aligned each other. Moreover a mask has been
deposited on the first array to produce a field stop for each lenslet. Laboratory tests confirmed that specifications and
properties of the prototype are met by state of the art on optics microlens manufacturing.
To characterize the device, a simulator of IFS has been built in laboratory and the BIGRE properties have been tested in
real working conditions, showing that the design of the double array fulfills IFS requirements.
The 2nd generation VLT instrument SPHERE will include an integral field spectrograph to enhance the capabilities
of detection of planetary companions close to bright stars. SPHERE-IFS is foreseen to work in near
IR (0.95-1.65 micron) at low spectral resolution. This paper describes the observing strategies, the adopted
hardware solutions for calibrating the instrument, and the data reduction procedures that are mandatory for the
achievement of the extreme contrast performances for which the instrument is designed.
Direct detection and spectral characterization of Extrasolar Planets is one of the most exciting but also one of the most
challenging areas in modern astronomy.
For the second-generation instrumentation on the VLT, ESO has supported the study and the design of instrument, called
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research). SPHERE includes a powerful extreme adaptive
optics system, various coronagraphs, an infrared differential imaging camera (IRDIS), an infrared Integral Field
Spectrograph (IFS) and a visible differential polarimeter (ZIMPOL).
IFS is a very low resolution spectrograph (R~50) which works in the near IR (0.95-1.7 microns), an ideal wavelength
range for the ground based detection of planetary features. The IFS requirements have been met via an innovative
integrated design merging passive stiffness and active control to obtain a light, accessible and functional assembly. This
paper gives a description of its cryogenic and mechatronic integrated design.
We summarize here an experimental frame combination pipeline we developed for ultra high-contrast imaging with
systems like the upcoming VLT SPHERE instrument. The pipeline combines strategies from the Drizzle technique, the
Spitzer IRACproc package, and homegrown codes, to combine image sets that may include a rotating field of view and
arbitrary shifts between frames. The pipeline is meant to be robust at dealing with data that may contain non-ideal
effects like sub-pixel pointing errors, missing data points, non-symmetrical noise sources, arbitrary geometric distortions,
and rapidly changing point spread functions. We summarize in this document individual steps and strategies, as well as
results from preliminary tests and simulations.
SPHERE is an instrument designed and built by a consortium of French, German, Italian, Swiss and Dutch institutes in collaboration with ESO. The project is currently in its Phase B. The main goal of SPHERE is to gain at least one order of magnitude with respect to the present VLT AO facility (NACO) in the direct detection of faint objects very close to a bright star, especially giant extrasolar planets. Apart from a high Strehl ratio, the instrument will be designed to reduce the scattered light of the central bright star and subtract the residual speckle halo. Sophisticated post-AO capabilities are needed to provide maximum detectivity and possibly physical data on the putative planets.
The Integral Field Spectrograph (IFS), one of the three scientific channels foreseen in the SPHERE design, is a very low resolution spectrograph (R~20) which works in the near IR (0.95-1.35 μm), an ideal wavelength range for the ground based detection of planetary features. Its goal is to suppress speckle to a contrast of 107, with a goal of 108, and at the same time provide spectral information in a field of view of about 1.5 × 1.5 arcsecs2 in proximity of the target star.
In this paper we describe the overall IFS design concept.
Observations of extrasolar planets using Integral Field Spectroscopy (IFS), if coupled with an extreme Adaptive
Optics system and analyzed with a Simultaneous Differential Imaging technique (SDI), are a powerful tool to
detect and characterize extrasolar planets directly; they enhance the signal of the planet and, at the same
time, reduces the impact of stellar light and consequently important noise sources like speckles. We developed a
simulation code able to test the capabilities of this IFS-SDI technique for different kinds of planets and telescopes,
modeling the atmospheric and instrumental noise sources, and the main results of this code have been presented
in Ref.1. This code, although it takes into account many parameters and sources of noise, can still be improved,
and in order to do it we studied in detail two aspects that have been neglected in the first version of the code:
the not uniform illumination of the microlenses and the speckle undersampling. The results of these studies are
presented here.
A new IDL code for simulations of observation made with an Integral Field Spectrograph attached to an adaptive optics system is here presented in detail. It is conceived to support CHEOPS, a high contrast imaging instrument for exo-planets detection. The aim of this sofware is to achieve simulated images and spectra considering realistic values of speckle noise, Adaptive Optics corrections and the specific instrumental features. This code can help us in particular to simulate close binary systems or exo-planetary system, in order to find the limit of detectability of faint objects using simultaneous differential imaging.
The Integral Field Spectrograph (IFS) of CHEOPS, the 2nd generation VLT instrument for planet finding, will attain a very low resolution (R=15) in order to search for cold (and warm) planets in stellar neighbourhood. This will allow to exploit wide band integral field spectroscopy to perform differential photometry. The complete description of CHEOPS IFS is given as a separate contribution to this conference; in this paper the analysis and the project of the very low disperser are outlined.
CHEOPS is a 2nd generation VLT instrument for the direct detection of extrasolar planets. The project is currently in its Phase A. It consists of an high order adaptive optics system which provides the necessary Strehl ratio for the differential polarimetric imager (ZIMPOL) and an Integral Field Spectrograph (IFS). The IFS is a very low resolution spectrograph (R~15) which works in the near IR (0.95-1.7 μm), an ideal wavelength range for the ground based detection of planetary features. In our baseline design, the Integral Field Unit (IFU) is a microlens array of about 250x250 elements which will cover a field of view of about 3.5x3.5 arcsecs2 in proximity of the target star. In this paper we describe the instrument, its preliminary optical design and the basic requirements about detectors. In a separate contribution to this conference, we present the very low resolution disperser.
The CHEOPS Planet Finder is one of the proposed second generation instruments for the VLT. Its purpose is to image and characterize giant extrasolar planets in different phases of their evolution: young, warm planets as well as old, cold ones. Imaging the last ones is the most challenging task because of the very large (>108) flux contrast with their star. Detection of such faint sources close to the stars from the ground requires a very high Strehl ratio and efficient suppression of the speckle noise. Two complementary strategies, based on imaging polarimetry using fast modulation and on integral field spectroscopy, are included as scientific channels of CHEOPS, after the high order adaptive optics module. The outputs of the two channels will allow a close insight into the main properties of detected extrasolar planets. In
addition, the CHEOPS instrument is well suited for a number of astrophysical projects, which are briefly described.
We present results of laboratory test of the high resolution spectrograph, that will be soon in operation at TNG telescope, La Palma. These first result shows that the instruments performs according to specifications, providing the expected very high resolution; and that can be operated remotely according to the TNG standards.
The high resolution spectrograph of the TNG (SARG) was projected to cover a spectral range from (lambda) equals 0.37 up to 0.9 micrometer, with resolution ranging from R equals 19,000 up to R equals 144,000. The dispersing element of the spectrograph is an R4 echelle grating in Quasi-Littrow mode; the beam size is 100 mm giving an RS product of RS equals 46,000 at order center. Both single object and long slit (up to 30 arcsec) observing modes are possible: in the first case cross-dispersion is provided by means of a selection of four grisms; interference filters are used for the long slit mode. A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048 X 4096 EEV CCDs (pixel size: 13.5 micrometer) allowing complete spectral coverage at all resolving power for (lambda) less than 0.8 micrometer. Confocal image slicers are foreseen for observations at R greater than or equal to 76,000; an absorbing cell for accurate radial velocities is also considered. SARG will be rigidly fixed to one of the arms of the TNG fork by means of an optical table and a special thermally insulating enclosure (temperature of all spectrograph components will be kept constant at a preset value by a distributed active thermal control system). All functions are motorized in order to allow very stable performances and full remote control. The architecture of SARG controls will be constructed around a VME crate linked to the TNG LAN and the instrument Workstation B by a fiber optic link.
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