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SAIt 2008M. Gai - INAF-OATo1 GAME: Gamma Astrometric Measurement Experiment Space-time curvature parameter  Light deflection close to the Sun Apparent.

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Presentation on theme: "SAIt 2008M. Gai - INAF-OATo1 GAME: Gamma Astrometric Measurement Experiment Space-time curvature parameter  Light deflection close to the Sun Apparent."— Presentation transcript:

1 SAIt 2008M. Gai - INAF-OATo1 GAME: Gamma Astrometric Measurement Experiment Space-time curvature parameter  Light deflection close to the Sun Apparent star position variation Small mission class M. Gai INAF-Osservatorio Astronomico di Torino

2 SAIt 2008M. Gai - INAF-OATo2 Scientific rationale The GAME concept Implementation highlights Status and next steps Outline of talk:

3 SAIt 2008M. Gai - INAF-OATo3 Goals: Fundamental physics and cosmology Scientific rationale of GAME Review of basic framework: The classical tests on General Relativity Spacetime curvature in General Relativity   in Parametrised Post-Newtonian (PPN) formulation Current experimental findings on  Potential cosmological implications of  Science bonus

4 SAIt 2008M. Gai - INAF-OATo4 A space mission in the visible range to achieve long permanent artificial eclipses no atmospheric disturbances, low noise Method: repeated measurement of star angular separation The GAME concept

5 SAIt 2008M. Gai - INAF-OATo5 Observation sequence Fully differential measurement Precision on image location Systematic error control: beam combiner Fizeau-like interferometer solution PSF of the phased array Elementary astrometric performance Photon limited mission performance Key GAME concepts

6 SAIt 2008M. Gai - INAF-OATo6 Implementation highlights Payload layout Telescope configuration Detector Baffling Metrology Mission profile

7 SAIt 2008M. Gai - INAF-OATo7 Status and next steps Proposal submitted to FP7 IDEAS call (Feb. 2008) Next presentations: SPIE, COSPAR Preparation of proposals for next calls: ASI, MIUR, … Realistic simulations of observations and baffling Lab tests on telescope + BC feasibility / criticalities Lab test on metrology and baffling performance System level tests on sky of representative GAME mock-up Dissemination among scientific community to build support to the GAME concept

8 SAIt 2008M. Gai - INAF-OATo8 The current GAME team INAF-OATo: M. Gai, M.G. Lattanzi,S. Ligori, L. Corcione, M.T. Crosta, A. Vecchiato, G. Massone, D. Loreggia, D. Gardiol, A. Sozzetti, D. Bonino, D. Busonero INRIM: M. Bisi, F. Bertinetto, F. Alasia, P. Cordiale Industry: Thales Alenia Space; Altec Collaborations: A. Tartaglia (PoliTo); S. Capozziello (Univ. NA)

9 SAIt 2008M. Gai - INAF-OATo9 GAME OVER [PRESENTATION]

10 SAIt 2008M. Gai - INAF-OATo10 1. Perihelion precession of planetary orbit  Mercury 2. Light deflection by massive objects  Sun Eddington’s parameter  3. Gravitational redshift / blueshift of light “Modern” tests: Gravitational lensing; Equivalence principle; Time delay of electromagnetic waves (Shapiro effect); Frame dragging tests (Lense-Thirring effect); Gravitational waves; Cosmological tests (cosmic background) Classical tests of general relativity [Einstein, 1916]

11 SAIt 2008M. Gai - INAF-OATo11 Light deflection around massive objects 1".74 at Solar limb  8.4  rad Apparent variation of star position depending on light bending due to the gravitational field of the Sun  spacetime curvature

12 SAIt 2008M. Gai - INAF-OATo12 Repeated through XX century Precision achieved: ~10% Limiting factors: Need for natural eclipses Atmospheric turbulence ValueYearAuthors 1.66 ± 0.19 1973TMET 1.98 ± 0.46 1961Schmeidler 2.17 ± 0.34 1959Schmeidler 1.70 ± 0.10 1952van Biesbroeck 2.01 ± 0.27 1947van Biesbroeck 2.73 ± 0.31 1936Mikhailov 2.24 ± 0.10 1929Freundlich & al. 1.77 ± 0.40 1922Dodwell & al. 1.98 ± 0.16 1920Dyson & al. Dyson - Eddington - Davidson experiment (1919): First test of General Relativity by light deflection nearby the Sun Short exposures, high background Large astrometric noise [A. Vecchiato et al., MGM 11 2006]

13 SAIt 2008M. Gai - INAF-OATo13 Cassini Radio link delay timing,  / ~1e-14 (similarly for Viking, VLBI: Shapiro delay effect, i.e. “temporal” component) Alternative experiment results Hipparcos Different observing conditions: global astrometry, estimate of full-sky level deflection on survey sample Precision achieved: 1e-4 ~ 2e-5 Earth Sun Cassini [B. Bertotti et al. Nature 2003]

14 SAIt 2008M. Gai - INAF-OATo14 Cosmology: Dark Matter, Dark Energy

15 SAIt 2008M. Gai - INAF-OATo15 [Capozziello & Francaviglia Gen. Relativ Gravit 40, 2008 and references therein]

16 SAIt 2008M. Gai - INAF-OATo16 f(R) gravitation fits experimental data

17 SAIt 2008M. Gai - INAF-OATo17 f(R) gravitation within Solar System Local measurements  cosmological constraints

18 SAIt 2008M. Gai - INAF-OATo18 Additional science topics Light deflection effects due to oblate and moving planets Monopole and quadrupole terms of asymmetric mass distribution Close encounters between Jupiter and selected quasars and stars Speed of gravity; link between dynamical reference system and ICRF Upper limits on masses of massive planets and brown dwarfs Nearby (d < 30-50 pc), bright (4 < V < 9) stars, orbital radii 3-7 AU Time resolved photometry on transiting exo-planet systems Constraints on additional companions: mass, period, eccentricity Observation in / through inner part of Solar System NEO orbits and asteroid dynamics (a few close encounters) Circumsolar environment transient phenomena Mercury’s orbit  perihelion precession determination

19 SAIt 2008M. Gai - INAF-OATo19 Observation sequence Measurements epochs: E1, E2 to modulate deflection on fields F1, F2 (Sun action on/off) Deflection  measurement Calibration fields,   0

20 SAIt 2008M. Gai - INAF-OATo20 Star separation variation: deflection + instrument [base angle] Calibration fields affected mainly by instrument variations Fully differential measurement Basic equations referred to stars in Fields 1, 2, 3, 4; Epochs 1, 2 Base Angle: hardware separation between observing directions

21 SAIt 2008M. Gai - INAF-OATo21 Precision on image location  : Standard deviation of image location : Effective wavelength of observation Signal to Noise Ratio  photons, RON, background N: Number of photons collected  : Instrumental factor of degradation (geometry, sampling, …) X: Root Mean Square size of the aperture  can be a small fraction of pixel/image size Diffraction Statistics [MG et al., PASP 110, 1998]

22 SAIt 2008M. Gai - INAF-OATo22 Image displacement  BC mirror tilt only: 1  as x 1 m = 5 pm Base angle materialised in one component / degree of freedom Systematic error control: beam combiner [MG et al., Meas. Sci. Tech 10, 1999] HIPPARCOS-like split mirror

23 SAIt 2008M. Gai - INAF-OATo23 Basic technical requirements Sufficient angular resolution and photometric SNR  increase telescope size [collect more photons and concentrate them more effectively] Sufficient rejection of high Solar (background + diffracted) flux  reduce telescope size; increase baffling [shield line of sight from sources at narrow angle] Conflicting requirements!

24 SAIt 2008M. Gai - INAF-OATo24 A solution: Fizeau-like interferometer Pupil masking: set of elementary apertures cut on telescope pupil F1 F2 Top / bottom: pointed to different lines of sight, separated by Base Angle BA 7-aperture Phased Array Elementary aperture: 4  12 cm Aperture spacing: 4 cm External diameter: 0.57 m Internal diameter: 0.30 m Geometry to be optimised vs. astrometry / background

25 SAIt 2008M. Gai - INAF-OATo25 PSF of the phased array Monochromatic, = 650 nm Image size: ~4 arcsec Central peak: ~200 mas FWHM [MG & Cancelliere, MNRAS 377, 2007]

26 SAIt 2008M. Gai - INAF-OATo26 Bright case: 100 s exposures, close to Sun Background: 15.5 mag per square arcsec Faint case: 500 s exposures, away from Sun Background: 19.5 mag per square arcsec Elementary astrometric performance Band: _0 = 650 nm,  = 120 nm

27 SAIt 2008M. Gai - INAF-OATo27 Photon limited mission performance Precision on one 15 mag star: < 1 mas 1 million stars required to achieve 1  as cumulative  1e-6 equivalent precision on  Observing time required: 20 + 20 days [on average Galactic plane stellar density from GSCII] Observation in Galactic center direction: higher density 1e-7 equivalent precision on  (3 + 3 month) [Vecchiato et al., IAUS 248, 2007]

28 SAIt 2008M. Gai - INAF-OATo28 PM: Pupil Mask FM1: Folding Mirror 1 FM2: Folding mirror 2 (Beam Combiner) TM1: Telescope Primary TM2: Telescope Secondary CCD: Detector Camera Volume of payload: ~1.5  1.5  1 m Mass budget: 120 kg + baffling structure Payload layout

29 SAIt 2008M. Gai - INAF-OATo29 Telescope configuration Ritchey-Chrétien, 5 mirrors, EFL = 20.6 m, visibility > 95% over 7  7 arcmin field; distortion < 1e-4 [Loreggia et al., IAUS 248, 2007]

30 SAIt 2008M. Gai - INAF-OATo30 [MG et al., A&A 367, 2001] E2V CCD42-80 Back illuminated, high performance CCD sensor Format: 2k  4k, 13.5  m pixels Two devices required for 7  7 arcmin field, sampling ~5 pixels/peak A possible CCD detector

31 SAIt 2008M. Gai - INAF-OATo31 Baffling Pupil masking on subsequent folding mirrors Observed field (solid) transmitted by facing surfaces, forbidden directions (dashed) shielded by pupil masks AND side baffles

32 SAIt 2008M. Gai - INAF-OATo32 Base Angle Metrology Metrology: considered to complement on-sky calibration

33 SAIt 2008M. Gai - INAF-OATo33 Stowed in launcher fairing Operating configuration – Side view Operating configuration – Top view Telemetry requirements OK with Kiruna and Fucino ground stations Mission profile Polar orbit, 1500 km elevation  no eclipse Spacecraft: ~Simbol-X Lifetime: 2(+2) years

34 SAIt 2008M. Gai - INAF-OATo34 GSCII star counts along ecliptic plane Astrometric performance depends on actual number, brightness and spectral type of observed targets

35 SAIt 2008M. Gai - INAF-OATo35 and GAIA (1-10 mas) Measurement range of GAME (0.1 – 1 arcsec) Observations are set in region of high amplitude deflection

36 SAIt 2008M. Gai - INAF-OATo36 GAME concept validation on-sky Observations close to full Moon: realistic performance on diffused background; set-up of pointing strategy

37 SAIt 2008M. Gai - INAF-OATo37 Baffling concept validation in lab Validation of rejection performance predictions

38 SAIt 2008M. Gai - INAF-OATo38 E2V CCD42-80 Quantum Efficiency Spectral band optimised on detector response AND sunlight rejection performance

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