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Gravitation Astrometric Measurement Experiment

Gravitation Astrometric Measurement Experiment . M. Gai - INAF-Osservatorio Astronomico di Torino. On some Fundamental Physics results achievable through astronomical techniques… . Goal of GAME:  to 10 -7 -10 -8 ;  to 10 -5 -10 -6. GAME: Gamma Astrometric Measurement

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Gravitation Astrometric Measurement Experiment

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  1. Gravitation Astrometric Measurement Experiment M. Gai - INAF-Osservatorio Astronomico di Torino On some Fundamental Physics results achievable through astronomical techniques… Goal of GAME:  to 10-7-10-8;  to 10-5-10-6 La Thuile, Rencontres de Moriond XLVI, 2011

  2. GAME: Gamma Astrometric Measurement Experiment [previous] Space-time curvature parameter  Apparent star position variation Light deflection close to the Sun Space mission Approach: build on flight inheritance from past missions [SOHO, STEREO, Hipparcos, Gaia] La Thuile, Rencontres de Moriond XLVI, 2011

  3. Outline of talk: • Scientific rationale • The GAME implementation concept Quick review of historical / scientific framework Goal of GAME:  to 10-7-10-8;  to 10-5-10-6 La Thuile, Rencontres de Moriond XLVI, 2011

  4. Scientific rationale of GAME Goals: Fundamental physics; cosmology; astrophysics • The classical tests on General Relativity • Light deflection from spacetime curvature • The Dyson - Eddington - Davidson experiment (1919) • Current experimental findings on  • Cosmological implications of  • Science bonus: additional topics La Thuile, Rencontres de Moriond XLVI, 2011

  5. Classical tests of general relativity [Einstein, 1900+] 1. Perihelion precession of planetary orbit [Mercury]  Eddington’s parameter  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); … La Thuile, Rencontres de Moriond XLVI, 2011

  6. Scientific rationale of GAME Goals: Fundamental physics; cosmology; astrophysics • The classical tests on General Relativity • Light deflection from spacetime curvature • The Dyson - Eddington - Davidson experiment (1919) • Current experimental findings on  • Cosmological implications of  • Science bonus: additional topics La Thuile, Rencontres de Moriond XLVI, 2011

  7. Spacetime curvature around massive objects G: Newton’s gravitational constant d: distance Sun-observer M: solar mass c: speed of light : angular distance of the source to the Sun 1".74 at Solar limb  8.4 rad Light deflectionApparent variation of star position, related to the gravitational field of the Sun   in Parametrised Post-Newtonian (PPN) formulation La Thuile, Rencontres de Moriond XLVI, 2011

  8. Scientific rationale of GAME Goals: Fundamental physics; cosmology; astrophysics • The classical tests on General Relativity • Light deflection from spacetime curvature • The Dyson - Eddington - Davidson experiment (1919) • Current experimental findings on  • Cosmological implications of  • Science bonus: additional topics La Thuile, Rencontres de Moriond XLVI, 2011

  9. Dyson-Eddington-Davidson experiment (1919) - I Moon Real (curved) photon trajectories Negative sample from Eddington's photographs, presented in 1920 paper First test of General Relativity by light deflection nearby the Sun Epoch (a): unperturbed direction of stars S1, S2 (dashed lines) Epoch (b): apparent direction as seen by observer (dotted line) La Thuile, Rencontres de Moriond XLVI, 2011

  10. Authors Year Deflection ["] Dyson & al. 1920 1.98 ± 0.16 Dodwell & al. 1922 1.77 ± 0.40 Freundlich & al. 1929 2.24 ± 0.10 Mikhailov 1936 2.73 ± 0.31 van Biesbroeck 1947 2.01 ± 0.27 van Biesbroeck 1952 1.70 ± 0.10 Schmeidler 1959 2.17 ± 0.34 Schmeidler 1961 1.98 ± 0.46 TMET 1973 1.66 ± 0.19 Dyson-Eddington-Davidson experiment (1919) - II Repeated throughout XX century Precision achieved: ~10% [A. Vecchiato et al., MGM 11 2006] Limiting factors: • Need for natural eclipses • Atmospheric turbulence • Portable instruments Short exposures, high background Large astrometric noise Limited resolution, collecting area La Thuile, Rencontres de Moriond XLVI, 2011

  11. Why is space better than ground? Atmospheric imaging limit without adaptive optics: ~1" [seeing ]  10 degradation of individual location performance Atmospheric coherence length in the visible: ~10"  small differential deflection 100 degradation Astrometric decorrelation noise ~0".1  degraded statistics on stars  10 degradation Atmospheric diffusion of Sun light  increased background  10100 degradation Measurement performance loss vs. space: 10^5 10^6 La Thuile, Rencontres de Moriond XLVI, 2011

  12. Improvements achievable with adaptive optics AO recovers at most 1-2 orders of magnitude  GAME needs space! Future multi-conjugate AO system Large, state-of-the-art solar telescope equipped with high performance Adaptive Optics La Thuile, Rencontres de Moriond XLVI, 2011

  13. Scientific rationale of GAME Goals: Fundamental physics; cosmology; astrophysics • The classical tests on General Relativity • Light deflection from spacetime curvature • The Dyson - Eddington - Davidson experiment (1919) • Current experimental findings on  • Cosmological implications of  • Science bonus: additional topics La Thuile, Rencontres de Moriond XLVI, 2011

  14. Current experimental results on … Hipparcos Different observing conditions: global astrometry, estimate of full sky deflection on survey sample Earth Sun Precision achieved: 3e-3 Cassini Radio link delay timing, /~1e-14 (similarly for Viking, VLBI: Shapiro delay effect, “temporal” component) Cassini [B. Bertotti et al., Nature 2003] Precision achieved: 2e-5 La Thuile, Rencontres de Moriond XLVI, 2011

  15. Scientific rationale of GAME Goals: Fundamental physics; cosmology; astrophysics • The classical tests on General Relativity • Light deflection from spacetime curvature • The Dyson - Eddington - Davidson experiment (1919) • Current experimental findings on  • Cosmological implications of  • Science bonus: additional topics La Thuile, Rencontres de Moriond XLVI, 2011

  16. Cosmological implications • Dark Matter and Dark Energy: explain experimental data • Alternative explanations: modified gravity theories – e.g. f(R) • Possible check: fit of gravitation theories with observations • Check of modified gravitation theories within Solar System Rationale: replacement in Einsten’s field equations of source terms [new particles] on one side with geometry terms [curvature] on the other side La Thuile, Rencontres de Moriond XLVI, 2011

  17. La Thuile, Rencontres de Moriond XLVI, 2011

  18. Check of gravitation theories within Solar System Taking advantage of PPN limit, e.g. for f(R) theories… [Capozziello & Troisi 2005] Alternative formulation: [Capone & Ruggiero 2010] Local measurements  cosmological constraints La Thuile, Rencontres de Moriond XLVI, 2011

  19. Scientific rationale of GAME Goals: Fundamental physics; cosmology; astrophysics • The classical tests on General Relativity • Light deflection from spacetime curvature • The Dyson - Eddington - Davidson experiment (1919) • Current experimental findings on  • Cosmological implications of  • Science bonus: additional topics La Thuile, Rencontres de Moriond XLVI, 2011

  20. Additional science topics - I Fundamental physics experiments in the Solar System  planetary physics • Light deflection effects due to oblate and moving giant planets: Jupiter and Saturn • 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 • Mercury’s orbit monitoring • Perihelion precession determination  PPN  parameter La Thuile, Rencontres de Moriond XLVI, 2011

  21. Additional science topics - II Astrophysics of planet-star transition region • 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 • [Sample not conveniently observable by Gaia or Corot] La Thuile, Rencontres de Moriond XLVI, 2011

  22. Additional science topics - III Monitoring of Solar corona and asteroids • Observation in / through inner part of Solar System • NEO orbits and asteroid dynamics (a few close encounters) • Circumsolar environment transient phenomena (high resolution corona observations) La Thuile, Rencontres de Moriond XLVI, 2011

  23. Additional science topics - IV Complementary GR tests: measurement of  from Mercury orbit Same instrument  cross-calibration La Thuile, Rencontres de Moriond XLVI, 2011

  24. Mercury observability ~6 periods in 2 year period (dotted line) Orbit region accessible to GAME: <30° to Sun Magnitude / pixel fits GAME dynamic range (scaling exposure time) Performance assessment in progress La Thuile, Rencontres de Moriond XLVI, 2011

  25. Outline of talk: • Scientific rationale • The GAME implementation concept Description focus on  measurement Goal of GAME:  to 10-7-10-8;  to 10-5-10-6 La Thuile, Rencontres de Moriond XLVI, 2011

  26. The GAME concept (I) Observer in space with CCD technology A space mission in the visible range to achieve • long permanent artificial eclipses • no atmospheric disturbances, low noise La Thuile, Rencontres de Moriond XLVI, 2011

  27. The GAME concept (II) Base Angle of ~4° between Lines of Sight (LOS) N and S Experimental approach: Repeated observation of fields close to the Ecliptic Measurement of angular separation of starsbetween fields Track separation with epoch  distance to Sun La Thuile, Rencontres de Moriond XLVI, 2011

  28. Mission profile Sun-synchronous orbit, 1500 km elevation  no eclipse 100% nominal observing time Stable solar power supply and thermal environment  instrument structural stability La Thuile, Rencontres de Moriond XLVI, 2011

  29. GSCII star counts along ecliptic plane Astrometric performance depends on actual number, brightness and spectral type of observed targets (7’ field) “Gaps” due to - extinction / reddening - removal of “blended” stars Average values La Thuile, Rencontres de Moriond XLVI, 2011

  30. Observing calendar Convenient observing periods: ~June + December La Thuile, Rencontres de Moriond XLVI, 2011

  31. Field superposition at high stellar density Field crowding manageable due to > high angular resolution: ~0.1 arcsec > magnitude limit to ~16 mag [visible, wide band] La Thuile, Rencontres de Moriond XLVI, 2011

  32. Astrometric signature at 2° ecliptic latitude South North Peak displacement between stars @ 2°: 466 mas Largest signature over 10° along the ecliptic, i.e. about 10 days La Thuile, Rencontres de Moriond XLVI, 2011

  33. Key issues of GAME • Observation sequence • Fully differential measurement • Precision on image location • Systematic error control: beam combiner • The Fizeau interferometer/coronagraph • Elementary astrometric performance • Photon limited mission performance La Thuile, Rencontres de Moriond XLVI, 2011

  34. Two-epoch observation sequence (I) Deflection  measurement Calibration fields,  0 Two measurements epochs to modulate deflection on fields F1, F2 (Sun“switched”on/off) La Thuile, Rencontres de Moriond XLVI, 2011

  35. Two-epoch observation sequence (II) Field superposition to ease differential measurement La Thuile, Rencontres de Moriond XLVI, 2011

  36. Key issues of GAME • Observation sequence • Fully differential measurement • Precision on image location • Systematic error control: beam combiner • The Fizeau interferometer/coronagraph • Elementary astrometric performance • Photon limited mission performance La Thuile, Rencontres de Moriond XLVI, 2011

  37. Fully differential measurement (I) Epoch 1 Epoch 12: deflection modulation switched between field pairs Epoch 2 La Thuile, Rencontres de Moriond XLVI, 2011

  38. Fully differential measurement (II) Basic equations referred to stars in Fields 1, 2, 3, 4; Epochs 1, 2 Star separation variation: deflection  + instrument [base angle] ADDITIVE variations of Base Angle COMPENSATED Base Angle : hardware separation between observing directions La Thuile, Rencontres de Moriond XLVI, 2011

  39. Fully differential measurement (III) Optical scale variation (in each field) Deflection between fields • Different collective effects on field images from • instrument evolution (focal length, distortion) • deflection (field displacement)  simple calibration of MULTIPLICATIVE terms La Thuile, Rencontres de Moriond XLVI, 2011

  40. Key issues of GAME • Observation sequence • Fully differential measurement • Precision on image location • Systematic error control: beam combiner • The Fizeau interferometer/coronagraph • Elementary astrometric performance • Photon limited mission performance La Thuile, Rencontres de Moriond XLVI, 2011

  41. Precisionon image location s: Standard deviation of image location l: Effective wavelength of observation Statistics Diffraction X: Root Mean Square size of the aperture Signal to Noise Ratio photons, RON, background N: Number of photons collected a>1: Instrumental factor of degradation (geometry, sampling, …)  can be a small fraction of pixel/image size [Gai et al., PASP 110, 1998] La Thuile, Rencontres de Moriond XLVI, 2011

  42. Precisionon image separation Arc length defined by composition of individual locations x1 x2 • Precision related to • Instrument resolution  Pupil size • Source magnitude  Exposure time • Average on # arcs  Field of view } Observing strategy La Thuile, Rencontres de Moriond XLVI, 2011

  43. Key issues of GAME • Observation sequence • Fully differential measurement • Precision on image location • Systematic error control: beam combiner • The Fizeau interferometer/coronagraph • Elementary astrometric performance • Photon limited mission performance La Thuile, Rencontres de Moriond XLVI, 2011

  44. Solution: Fizeau-like interferometer + coronagraph Goal: achieve higher resolution through small apertures Fizeau interferometer implemented by Pupil Masking: set of elementary apertures cut on pupil of underlying monolithic telescope  cophasing by alignment Coronagraphic techniques applied to each aperture  replication of individual coronagraphs in phased array Geometry optimised vs. astrometry and background La Thuile, Rencontres de Moriond XLVI, 2011

  45. Beam distribution (front) N and S stellar beams retained, separated by geometric optics Sun photons rejected either at first or second surface Apodisation La Thuile, Rencontres de Moriond XLVI, 2011

  46. Beam distribution (rear) Secondary mirror + light screen Larger beams from opposite-to-Sun (Out-ward) directions /2injected into the telescope with acceptable vignetting Simultaneous observation: multiplex + systematics rejection La Thuile, Rencontres de Moriond XLVI, 2011

  47. Imaging performance Monochromatic PSF ( = 600 nm) Polychromatic PSF (T = 6000 K) La Thuile, Rencontres de Moriond XLVI, 2011

  48. Beam Combination (I) N and S stellar beams folded onto telescope optical axis by beam combiner: Two flat, pierced mirrors set at fixed angle La Thuile, Rencontres de Moriond XLVI, 2011

  49. Beam Combination (II) Proposed solution: Pierced prism hosting one optical surface and supporting flat mirror e.g. by silicon bonding (LISA) Near-monolithic assembly High dimensional stability over mission lifetime 90115 mm2 Zerodur prototype La Thuile, Rencontres de Moriond XLVI, 2011

  50. Key issues of GAME • Observation sequence • Fully differential measurement • Precision on image location • Systematic error control: beam combiner • The Fizeau interferometer/coronagraph • Elementary astrometric performance • Photon limited mission performance La Thuile, Rencontres de Moriond XLVI, 2011

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