CHEOPS is the first small class mission adopted by ESA in the framework of the Cosmic Vision 2015-2025. Its launch is foreseen in early 2019. CHEOPS aims to get transits follow-up measurements of already known exo-planets, hosted by near bright stars (V<12). Thanks to its ultra-high precision photometry, CHEOPS science goal is accurately measure the radii of planets in the super-Earth to Neptune mass range (1<Mplanet/MEarth<20). The knowledge of the radius by transit measurements, combined with the determination of planet mass through radial velocity techniques, will allow the determination/refinement of the bulk density for a large number of small planets during the scheduled 3.5 years life mission. The instrument is mainly composed of a 320 mm aperture diameter Ritchey-Chretien telescope and a Back End Optics, delivering a de-focused star image onto the focal plane. In this paper we describe the opto-thermo-mechanical model of the instrument and the measurements obtained during the opto-mechanical integration and alignment phase at Leonardo company premises, highlighting the level of congruence between the predictions and measurements.
PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery, adopted in the framework of the Cosmic Vision program. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars, constraining with unprecedented precision their radii by mean of transits technique and the age of the stars through by asteroseismology. By coupling the radius information with the mass knowledge, provided by a dedicated ground-based spectroscopy radial velocity measurements campaign, it would be possible to determine the planet density. Ultimately, PLATO will deliver the largest samples ever of well characterized exo-planets, discriminating among their ‘zoology’. The large amount of required bright stars can be achieved by a relatively small aperture telescope (about 1 meter class) with a wide Field of View (about 1000 square degrees). The PLATO strategy is to split the collecting area into 24 identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about 2232 square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit, is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet.
PLATO (Planetary Transits and Oscillations of stars) is a new space telescope selected by ESA to detect terrestrial exoplanets in nearby solar-type stars. The telescope is composed by 26 small telescopes to achieve a large instantaneous field of view. INAF-OAPD is directly involved in the optical design and in the definition and testing of the alignment strategy. A prototype of the Telescope Optical Unis (TOU) was assembled and integrated in warm condition (room temperature) and then the performance is tested in warm and cold temperature (-80C). The mechanical structure of the TOU is representative in terms of thermal expansion coefficient and Young's modulus with respect to the actual one. A dedicated GSE (Ground Support Equipment) is used to manipulate the lenses. By co-align an interferometer and a laser with respect to the center of the third CaF2 lens, a several observables references are used to define the position and tilt of the chief ray. The total procedure tolerances for every lens is 30'' in tilt, between 15-40 μm for focus and 22 μm for decentering and the total error budget of the optical setup bench is below this requirement. In this paper, we describe the AIV procedure and test performed on the prototype of the TOU in the INAF laboratory.
PLATO stands for PLAnetary Transits and Oscillation of stars and is a Medium sized mission selected as M3 by the
European Space Agency as part of the Cosmic Vision program. The strategy behind is to scrutinize a large fraction of the
sky collecting lightcurves of a large number of stars and detecting transits of exo-planets whose apparent orbit allow for
the transit to be visible from the Earth. Furthermore, as the transit is basically able to provide the ratio of the size of the
transiting planet to the host star, the latter is being characterized by asteroseismology, allowing to provide accurate
masses, radii and hence density of a large sample of extra solar bodies. In order to be able to then follow up from the
ground via spectroscopy radial velocity measurements these candidates the search must be confined to rather bright stars.
To comply with the statistical rate of the occurrence of such transits around these kind of stars one needs a telescope with
a moderate aperture of the order of one meter but with a Field of View that is of the order of 50 degrees in diameter. This
is achieved by splitting the optical aperture into a few dozens identical telescopes with partially overlapping Field of
View to build up a mixed ensemble of differently covered area of the sky to comply with various classes of magnitude
stars. The single telescopes are refractive optical systems with an internally located pupil defined by a CaF2 lens, and
comprising an aspheric front lens and a strong field flattener optical element close to the detectors mosaic. In order to
continuously monitor for a few years with the aim to detect planetary transits similar to an hypothetical twin of the Earth,
with the same revolution period, the spacecraft is going to be operated while orbiting around the L2 Lagrangian point of
the Earth-Sun system so that the Earth disk is no longer a constraints potentially interfering with such a wide field
continuous uninterrupted survey.
The CHaracterizing ExOPlanet Satellite (CHEOPS) is an ESA Small Mission whose launch is planned for the end of 2017. It is a Ritchey-Chretien telescope with a 320 mm aperture providing a FoV of 0.32 degrees, which will target nearby bright stars already known to host planets, and measure, through ultrahigh precision photometry, the radius of exo-planets, allowing to determine their composition. This paper will present the details of the AIV plan for a demonstration model of the CHEOPS Telescope with equivalent structure but different CTEs. Alignment procedures, needed GSEs and devised verification tests will be described and a path for the AIV of the flight model, which will take place at industries premises, will be sketched.
Spreading the PSF over a quite large amount of pixels is an increasingly used observing technique in order to reach
extremely precise photometry, such as in the case of exoplanets searching and characterization via transits observations.
A PSF top-hat profile helps to minimize the errors contribution due to the uncertainty on the knowledge of the detector
flat field. This work has been carried out during the recent design study in the framework of the ESA small mission
CHEOPS. Because of lack of perfect flat-fielding information, in the CHEOPS optics it is required to spread the light of
a source into a well defined angular area, in a manner as uniform as possible. Furthermore this should be accomplished
still retaining the features of a true focal plane onto the detector. In this way, for instance, the angular displacement on
the focal plane is fully retained and in case of several stars in a field these look as separated as their distance is larger
than the spreading size. An obvious way is to apply a defocus, while the presence of an intermediate pupil plane in the
Back End Optics makes attractive to introduce here an optical device that is able to spread the light in a well defined
manner, still retaining the direction of the chief ray hitting it. This can be accomplished through an holographic diffuser
or through a lenslet array. Both techniques implement the concept of segmenting the pupil into several sub-zones where
light is spread to a well defined angle. We present experimental results on how to deliver such PSF profile by mean of
holographic diffuser and lenslet array. Both the devices are located in an intermediate pupil plane of a properly scaled
laboratory setup mimicking the CHEOPS optical design configuration.
The Telescopio Nazionale Galileo (TNG) hosts, starting in April 2012, the visible spectrograph HARPS-N. It is based
on the design of its predecessor working at ESO's 3.6m telescope, achieving unprecedented results on radial velocity
measurements of extrasolar planetary systems. The spectrograph's ultra-stable environment, in a temperature-controlled
vacuum chamber, will allow measurements under 1 m/s which will enable the characterization of rocky, Earth-like
planets. Enhancements from the original HARPS include better scrambling using octagonal section fibers with a shorter
length, as well as a native tip-tilt system to increase image sharpness, and an integrated pipeline providing a complete set
Observations in the Kepler field will be the main goal of HARPS-N, and a substantial fraction of TNG observing time
will be devoted to this follow-up. The operation process of the observatory has been updated, from scheduling
constraints to telescope control system. Here we describe the entire instrument, along with the results from the first
Because of its nicely chromatic behavior, Calcium Fluoride (CaF2) is a nice choice for an optical designer as it can easily
solve a number of issues, giving the right extra degree of freedom in the optical design tuning. However, switching from
tablet screens to real life, the scarcity of information -and sometimes the bad reputation in term of fragility- about this
material makes an overall test much more than a "display determination" experiment. We describe the extensive tests
performed in ambient temperature and in thermo-vacuum of a prototype, consistent with flight CTEs, of a 200mm class
camera envisaged for the PLATO (PLAnetary Transit and Oscillations of Stars) mission. We show how the CaF2 lens
uneventfully succeeded to all the tests and handling procedures, and discuss the main results of the very intensive test
campaign of the PLATO Telescope Optical Unit prototype.
In MCAO the correction of the wavefront for an extended Field of View is obtained at the expense of a stretching of the
actual instantaneous meta-pupils over the high altitude layers, just to compensate their average curvature. While this
effect does average out in long term exposures and is of secondary interest in compensated imaging, it gives the input for
the idea of using MCAO-like information, collectable over a certain Field of View, to assess in a time resolved mode
(not necessarily in real time) the actual geometrical light throughput in a given direction. In principle this would allow,
with proper time tagging, to achieve high precision photometry, as part of the scintillation could be measured on line
during the observation. Simple averaging of neighbor stars to flat field starlight, for example, represents the equivalent of
this concept for the ground-layer correction only. It can be seen that, once a direction is defined, it is relevant only the
derivative of the wavefront around or in the proximity of that edges, but the range at which this happen is a crucial
parameter. However, the strong interest in high precision measurements of exoplanetary transits or asteroseismology
could make this approach not as lunatic as it could sound. view
PLATO is the acronym of PLAnetary Transits and Oscillations of stars, and it is a mission proposed for the ESA Cosmic
Vision program in the Medium size program, with the target to detect and characterize exoplanets by the means of their
transit on a bright star. The instrumental overall layout proposed by the Plato Payload Consortium consists in a multitelescope
concept instrument, composed by several tens of telescope units, for which we are developing an all refractive
optical solution. These devices are characterized by a very large Field of View (more than 20 degrees on one side) with
an optical quality that fits most of the energy into a single CCD pixel. Such a goal can be achieved in a variety of
solutions, some including aspheric elements as well. A complete prototype of one telescope unit is foreseen to be built
initially (during phase B1) to show the alignment feasibility and, only in a second moment (Phase B2), to perform full
environmental and functional test. The aim of this article is to describe the alignment, integration and verification
strategy of the opto-mechanics of the prototype. Both the approaches of testing the telescope at the target working
temperature or to test it at ambient temperature around a displaced zero point, taking into account the effects of thermal
deformations, are considered and briefly sketched in this work.
The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the three medium class (M class) missions
selected in 2010 for definition study in the framework of the ESA Cosmic Vision 2015-2025 program. The main
scientific goals of PLATO are the i) discovery and study of extra-solar planetary systems, (including those hosting Earth-like
planets in their habitable zone) by means of planetary transits detection from space and radial velocity follow-up
from ground, and ii) the characterization of the hosting stars through seismic analysis, in order to determine with high
accuracy planetary masses and ages. According to the study made by the PLATO Payload Consortium (PPLC) during
the PLATO assessment phase, the scientific payload consists of 34 all refractive telescopes having small aperture (120
mm) and wide field of view (greater than 1000 degree2) observing over 0.5-1 micron wavelength band. The telescopes
are mounted on a common optical bench and are divided in four families with an overlapping line-of-sight in order to
maximize the science return. In this paper, we will describe the detailed design of the Telescope Optical Units (TOUs)
focusing on the selected optical configuration and the expected performances.
MICADO is the adaptive optics imaging camera for the E-ELT. It has been designed and optimised to be mounted
to the LGS-MCAO system MAORY, and will provide diffraction limited imaging over a wide (~1 arcmin) field
of view. For initial operations, it can also be used with its own simpler AO module that provides on-axis
diffraction limited performance using natural guide stars. We discuss the instrument's key capabilities and
expected performance, and show how the science drivers have shaped its design. We outline the technical
concept, from the opto-mechanical design to operations and data processing. We describe the AO module,
summarise the instrument performance, and indicate some possible future developments.
The Multi-conjugate Adaptive optics Demonstrator, MAD, successfully demonstrated on sky the MCAO technique
both in Layer Oriented and Star Oriented modes. As results of the Guaranteed Time Observations in
Layer Oriented mode quality astronomy papers have been published. In this paper we concentrate on the
instrumentation issues and technical aspects which stay behind this success.
The Layer Oriented Wavefront Sensor for MAD has been used in the sky to achieve science. The preliminary results
from a six night run and the perspectives in terms of achieved performances and projections of sky coverage for slightly
more sophisticated system like the Multiple Field of View one are shown indicating that the sensor is keeping its
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.
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.