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  • 1
    In: Monthly Notices of the Royal Astronomical Society, 2012, Vol. 419(3), pp.2356-2368
    Description: Point spread function (PSF) modelling is a central part of any astronomy data analysis relying on measuring the shapes of objects. It is especially crucial for weak gravitational lensing, in order to beat down systematics and allow one to reach the full potential of weak lensing in measuring dark energy. A PSF modelling pipeline is made of two main steps: the first one is to assess its shape on stars, and the second is to interpolate it at any desired position (usually galaxies). We focus on the second part, and compare different interpolation schemes, including polynomial interpolation, radial basis functions, Delaunay triangulation and Kriging. For that purpose, we develop simulations of PSF fields, in which stars are built from a set of basis functions defined from a principal components analysis of a real ground-based image. We find that Kriging gives the most reliable interpolation, significantly better than the traditionally used polynomial interpolation. We also note that although a Kriging interpolation on individual images is enough to control systematics at the level necessary for current weak lensing surveys, more elaborate techniques will have to be developed to reach future ambitious surveys’ requirements.
    Keywords: Gravitational Lensing: Weak ; Methods: Data Analysis ; Methods: Statistical
    ISSN: 0035-8711
    E-ISSN: 1365-2966
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  • 2
    Language: English
    In: Physical review letters, 06 April 2018, Vol.120(14), pp.141101
    Description: The existence of a light or massive scalar field with a coupling to matter weaker than gravitational strength is a possible source of violation of the weak equivalence principle. We use the first results on the Eötvös parameter by the MICROSCOPE experiment to set new constraints on such scalar fields. For a massive scalar field of mass smaller than 10^{-12}  eV (i.e., range larger than a few 10^{5}  m), we improve existing constraints by one order of magnitude to |α|〈10^{-11} if the scalar field couples to the baryon number and to |α|〈10^{-12} if the scalar field couples to the difference between the baryon and the lepton numbers. We also consider a model describing the coupling of a generic dilaton to the standard matter fields with five parameters, for a light field: We find that, for masses smaller than 10^{-12}  eV, the constraints on the dilaton coupling parameters are improved by one order of magnitude compared to previous equivalence principle tests.
    Keywords: General Relativity And Quantum Cosmology ; Astrophysics - Cosmology And Nongalactic Astrophysics ; High Energy Physics - Experiment;
    ISSN: 00319007
    E-ISSN: 1079-7114
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  • 3
    Description: The ISLAND (Inverse Square Law And Newtonian Dynamics) Space Explorer is a new concept to test the gravitational Inverse Square Law at: (1) submillimeter scale and (2) at the largest Solar System scales (dozens of Astronomical Units --AU). The main idea is to embark a torsion pendulum at the center of gravity of a dedicated, possibly drag-free and attitude-controlled, interplanetary probe whose gravitational environment is accurately probed by, and corrected for thanks to six ultrasensitive accelerometers arranged as a cross around the torsion pendulum. Comment: Moriond Gravitation session 2017 proceeding + COSPAR meeting 2018
    Keywords: General Relativity And Quantum Cosmology
    Source: Cornell University
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  • 4
    Language: English
    In: Astronomy and Computing, 2013, Vol.1, p.23(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ascom.2013.01.001 Byline: Joel Berge, Lukas Gamper, Alexandre Refregier, Adam Amara Abstract: Simulated wide-field images are becoming an important part of observational astronomy, either to prepare for new surveys or to test measurement methods. In order to efficiently explore vast parameter spaces, the computational speed of simulation codes is a central requirement to their implementation. We introduce the Ultra Fast Image Generator (UFig) which aims to bring wide-field imaging simulations to the current limits of computational capabilities. We achieve this goal through: (1) models of galaxies, stars and observational conditions, which, while simple, capture the key features necessary for realistic simulations, and (2) state-of-the-art computational and implementation optimizations. We present the performances of UFig and show that it is faster than existing public simulation codes by several orders of magnitude. It allows us to produce images more quickly than SExtractor needs to analyze them. For instance, it can simulate a typical 0.25deg.sup.2 Subaru SuprimeCam image (10kx8k pixels) with a 5-[sigma] limiting magnitude of R=26 in 30 s on a laptop, yielding an average simulation time for a galaxy of 30 [mu]s. This code is complementary to end-to-end simulation codes and can be used as a fast, central component of observational methods relying on simulations. For instance, it can be used to efficiently calibrate high-precision measurements, as recently suggested for cosmic shear. Article History: Received 5 September 2012; Accepted 22 January 2013
    ISSN: 2213-1337
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Physical review letters, 08 December 2017, Vol.119(23), pp.231101
    Description: According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10^{-15} precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[-1±9(stat)±9(syst)]×10^{-15} (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.
    Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Cosmology And Nongalactic Astrophysics ; General Relativity And Quantum Cosmology;
    ISSN: 00319007
    E-ISSN: 1079-7114
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  • 6
    In: Proceedings of the International Astronomical Union, 2014, Vol.10(S306), pp.382-384
    Description: Abstract Theories beyond the Standard Model and General Relativity predict a violation of the Weak Equivalence Principle (WEP) just below the current best experimental upper limits. MICROSCOPE (Micro-Satellite à traînée Compensée pour l'Observation du Principe d'Equivalence) will allow us to lower them by two orders of magnitude, and maybe to detect a WEP violation. However, analyzing the MICROSCOPE data will be challenging, mostly because of missing data and a colored noise burrying the signal of interest. In this communication, we apply an inpainting technique to simulated MICROSCOPE data and show that inpainting will help detect a WEP violation signal.
    Keywords: Contributed Papers; Gravitation; Methods: Data Analysis; Methods: Statistical
    ISSN: 1743-9213
    E-ISSN: 1743-9221
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  • 7
    Language: English
    In: 52nd Rencontres de Moriond on Gravitation, 2017, pp.191-198
    Description: The ISLAND (Inverse Square Law And Newtonian Dynamics) Space Explorer is a new concept to test the gravitational Inverse Square Law at: (1) submillimeter scale and (2) at the largest Solar System scales (dozens of Astronomical Units {AU). The main idea is to embark a torsion pendulum at...
    Keywords: Physics ; Physics ; General Physics ; Physics
    Source: Hyper Article en Ligne (CCSd)
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  • 8
    Language: English
    In: Journal of Physics: Conference Series, 2015, Vol.610(1), p.012009 (6pp)
    Description: MICROSCOPE is a French Space Agency mission that aims to test the Weak Equivalence Principle in space down to an accuracy of 10 -15 . This is two orders of magnitude better than the current constraints, which will allow us to test General Relativity as well as theories beyond General Relativity which predict a possible Weak Equivalence Principle violation below 10 -13 . In this communication, we describe the MICROSCOPE mission, its measurement principle and instrument, and we give an update on its status. After a successful instrument's commissioning, MICROSCOPE is on track for on-schedule launch, expected in 2016.
    Keywords: General Relativity And Quantum Cosmology ; Astrophysics - Instrumentation And Methods For Astrophysics;
    ISSN: 1742-6588
    E-ISSN: 1742-6596
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  • 9
    Language: English
    In: Astronomy and Computing, February 2013, Vol.1, pp.23-32
    Description: Simulated wide-field images are becoming an important part of observational astronomy, either to prepare for new surveys or to test measurement methods. In order to efficiently explore vast parameter spaces, the computational speed of simulation codes is a central requirement to their implementation. We introduce the Ultra Fast Image Generator ( ) which aims to bring wide-field imaging simulations to the current limits of computational capabilities. We achieve this goal through: (1) models of galaxies, stars and observational conditions, which, while simple, capture the key features necessary for realistic simulations, and (2) state-of-the-art computational and implementation optimizations. We present the performances of and show that it is faster than existing public simulation codes by several orders of magnitude. It allows us to produce images more quickly than needs to analyze them. For instance, it can simulate a typical Subaru SuprimeCam image (10k×8k pixels) with a 5- limiting magnitude of in 30 s on a laptop, yielding an average simulation time for a galaxy of 30 μs. This code is complementary to end-to-end simulation codes and can be used as a fast, central component of observational methods relying on simulations. For instance, it can be used to efficiently calibrate high-precision measurements, as recently suggested for cosmic shear. ► We introduce the Ultra Fast Image Generator (UFig), a new fast image simulation code. ► We present its implementation and performance. ► We show that it is faster than existing public simulation codes. ► It is complementary to end-to-end simulation codes.
    Keywords: Simulations ; Wide-Field Imaging ; Computational Speed ; Astronomy & Astrophysics
    ISSN: 2213-1337
    E-ISSN: 2213-1345
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  • 10
    Language: English
    In: Nat Astron, 2018, Vol.2(2), pp.174-174
    Keywords: Physics ; Physics ; Space Physics ; Accelerometrie Spatiale ; Microscope ; Principe Equivalence ; Compensation Trainee ; Physics;
    ISSN: 2397-3366
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