Antoine Crouzier

NEAT: ultra-precise differential astrometry to characterize planetary systems with Earth-mass exoplanets in the vicinity of our Sun

The nearest solar-type stars are of prime interest for the science of exoplanets because they are the objects most suitable for direct detection and future spectroscopic investigations. Astrometry combined with radial velocity is the technique that can reveal planets with mass as small as the Earth mass in the 1 AU domain. We present in this contribution the result of a 3-year study on a mission capable to perform ultra-precise differential astrometry called NEAT (Nearby Earth Astrometric Telescope) and characterize planetary systems with Earth- mass exoplanets in the vicinity of our Sun. This mission requires exquisite calibration of the focal plane together with innovative approaches to obtain a very stable long focal telescope. This mission will be submitted in 2014 to the ESA M4 Call for Mission.

NEAT: a spaceborne astrometric mission for the detection and characterization of nearby habitable planetary systems

The NEAT (Nearby Earth Astrometric Telescope) mission is a proposal submitted to ESA for its 2010 call for M-size mission within the Cosmic Vision 2015-2025 plan. The main scientific goal of the NEAT mission is to detect and characterize planetary systems in an exhaustive way down to 1 Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to that mass limit. NEAT will continue the work performed by Hipparcos and Gaia by reaching a precision that is improved by two orders of magnitude on pointed targets.

An experimental testbed for NEAT to demonstrate micro-pixel accuracy

NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. In NEAT, one fundamental aspect is the capability to measure stellar centroids at the precision of 5 x 10-6 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 4 x 10-5 pixel at Nyquist sampling. Simulations showed that a precision of 2 μ-pixels can be reached, if intra and inter pixel quantum efficiency variations are calibrated and corrected for by a metrology system. The European part of the NEAT consortium is designing and building a testbed in vacuum in order to achieve 5 x 10-6 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. In this paper we give the basic relations and trade-offs that come into play for the design of a centroid testbed and its metrology system. We detail the different conditions necessary to reach the targeted precision, present the characteristics of our current design and describe the present status of the demonstration.

NEAT: an astrometric mission to detect nearby planetary systems down to the Earth mass

The NEAT (Nearby Earth Astrometric Telescope) mission is a proposition for an ESA space M-size mission within the Cosmic Vision 2015-2025 plan. The main scientific goal of the NEAT mission is to detect and characterize planetary systems in an exhaustive way down to one Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to that mass limit. NEAT will continue the work performed by Hipparcos and Gaia by reaching a precision that is improved by two orders of magnitude on pointed targets. We report in this paper the status of the work being carried out to technically validate NEAT.

Metrology calibration and very high accuracy centroiding with the NEAT testbed

NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. NEAT requires the capability to measure stellar centroids at the precision of 5 x 10-6 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 2 x 10-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment. A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors. The European part of the NEAT consortium is building a testbed in vacuum in order to achieve 5 x 10-6 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. The testbed consists of two main sub-systems. The first one produces pseudo stars: a blackbody source is fed into a large core fiber and lights-up a pinhole mask in the object plane, which is imaged by a mirror on the CCD. The second sub-system is the metrology, it projects young fringes on the CCD. The fringes are created by two single mode fibers facing the CCD and fixed on the mirror. In this paper we present the experiments conducted and the results obtained since July 2013 when we had the first light on both the metrology and pseudo stars. We explain the data reduction procedures we used.

First experimental results of very high accuracy centroiding measurements for the neat astrometric mission

NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. In NEAT, one fundamental aspect is the capability to measure stellar centroids at the precision of 5 × 10-6 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 2 × 10-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment.1 A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors. The European part of the NEAT consortium is building a testbed in vacuum in order to achieve 5 × 10-6 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. In this paper we present the metrology and the pseudo stellar sources sub-systems, we present a performance model and an error budget of the experiment and finally we describe the present status of the demonstration.

NEAT breadboard system analysis and performance models

NEAT (Nearby Earth Astrometric Telescope) is an astrometric space mission aiming at detecting Earth-like exoplanets located in the habitable zone of nearby solar-type stars. For that purpose, NEAT should be able to measure stellar centroids within an accuracy of 5 10-6 pixels. In order to fulfil such stringent requirement, NEAT incorporates an interferometric metrology system measuring pixel gains and location errors. To validate this technology and assess the whole performance of the instrument, a dedicated test bench has been built at IPAG, in Grenoble (France). In this paper are summarized the main system engineering considerations allowing to define sub-systems specifications. Then we describe the general architecture of the performance models (including photometric, interferometric, and final astrometric budgets) and confront their predictions with the experimental results obtained on the test bench. It is concluded that most of error items are well understood, although some of them deserve further investigations.

Formation flying for very high precision astrometry: NEAT and micro-NEAT mission concepts

The nearest solar-type stars are of prime interest for the science of exoplanets because they are the objects most suitable for direct detection and future spectroscopic study of telluric planets. In addition, the habitable zone is a region of special interest for astrobiology and for comparison with our own Earth. These two features point to astrometry as a unique tool for a systematic study of the architectures of planetary systems in that domain because the astrometric signal is larger the nearer the stars and the wider the planetary orbits whereas the other techniques favour smaller orbits. The astrometric technique is highly complementary and better suited for planets in the habitable zone (HZ). Recently, we have proposed two astrometric missions to ESA with different scales, but both of them use flying formation capability for the platform: Nearby Earth Astrometric Telescope (NEAT) as an M-class mission with a 1 m telescope and μNEAT as an S-class mission with a 0.3 m telescope. μNEAT can search and characterise giant planets, i.e., Neptune’s mass and heavier, in the HZ around these stars, whereas NEAT can detect even smaller planets down to an Earth mass. The scientific impact of NEAT/μNEAT would be tremendous because they would provide the first exhaustive census of terrestrial/giant planet architecture in the HZ and beyond, around the nearest solar-type stars.

The exoplanet program of the microarcsecond astrometric observatory Theia (Conference Presentation)

The Theia mission, as a natural successor to Gaia, will be the first extremely-high-precision astrometric surveyor that may emerge from the last ESA M5 call in October 2016. A major objective of Theia in the context of this conference is the detection by astrometry of Earths and Super-Earths exoplanets in the habitable zone of nearby A to M stars. This can be done by astrometry from space if a motion of <1-microarcesec can be recorded (0.3 microarcsec for an Earth/Sun system at 10 pc). Such an accuracy can be reached by Theia in the form of an 0.8-m telescope with 0.5° FOV in orbit at L2 for 3,5 years and providing repeated differential astrometric measurements between the science target and background reference stars. The exoplanet program will use circa 10% of the mission lifetime and will be able to survey 63 nearby stars with a ~0.6 microarssec astrometric floor to eventually detect planets down to 0.2 M_earth over circa 50 visits. In order to measure a centroid position on the CCD with an accuracy of 1e-5 pixels, Theia’s high-precision measurement relies on an on-board interferometric laser metrology unit to calibrate out the pixel’s offset to the nominal position, as well as the inter- and intra-pixel quantum efficiency. The preliminary Theia mission assessment allowed us to identify a safe and robust mission architecture that demonstrates the mission feasibility within the Soyuz ST launch envelope and a small M-class mission cost cap. We present here these features and the corresponding exoplanet program.

The latest results from DICE (Detector Interferometric Calibration Experiment)

Theia is an astrometric mission proposed to ESA in 2014 for which one of the scientific objectives is detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. This objective requires the capability to measure stellar centroids at the precision of 1x10-5 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 3x10-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment. A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors. The Theia consortium is operating a testbed in vacuum in order to achieve 1x10-5 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the Theia spacecraft. The testbed consists of two main sub-systems. The first one produces pseudo stars: a blackbody source is fed into a large core fiber and lights-up a pinhole mask in the object plane, which is imaged by a mirror on the CCD. The second sub-system is the metrology, it projects young fringes on the CCD. The fringes are created by two single mode fibers facing the CCD and fixed on the mirror. In this paper we present the latest experiments conducted and the results obtained after a series of upgrades on the testbed was completed. The calibration system yielded the pixel positions to an accuracy estimated at 4x10-4 pixel. After including the pixel position information, an astrometric accuracy of 6 x 10-5 pixel was obtained, for a PSF motion over more than 5 pixels. In the static mode (small jitter motion of less than 1 x 10-3 pixel), a photon noise limited precision of 3x10-5 pixel was reached.