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Gravitation Astrometric Measurement Experiment M. Gai - INAF-Osservatorio Astronomico di Torino On some Fundamental Physics results achievable through astronomical techniques… Goal of GAME: M. Gai - GAME to 10-7-10-8; to 10-5-10-6 La Thuile, Rencontres de Moriond XLVI, 2011 1 [previous] GAME: Gamma Astrometric Measurement Experiment 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] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 2 Outline of talk: • Scientific rationale • The GAME implementation concept Quick review of historical / scientific framework Goal of GAME: M. Gai - GAME to 10-7-10-8; to 10-5-10-6 La Thuile, Rencontres de Moriond XLVI, 2011 3 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 4 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); … M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 5 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 6 Spacetime curvature around massive objects Deflection angle [arcsec] 1.5 G: Newton’s gravitational constant 1".74 at Solar limb 8.4 rad GM 1 2 c d 1 d: distance Sunobserver 1 cos 1 cos M: solar mass 0.5 0 0 c: speed of light : angular distance of the source to the Sun 1 2 3 4 5 Distance from Sun centre [degs] 6 Light deflection Apparent variation of star position, related to the gravitational field of the Sun in Parametrised Post-Newtonian (PPN) formulation M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 7 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 8 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) M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 9 Dyson-Eddington-Davidson experiment (1919) - II Authors Dyson & al. Repeated throughout Dodwell & al. XX century Freundlich & al. Precision achieved: Mikhailov ~10% van Biesbroeck van Biesbroeck [A. Vecchiato et al., MGM 11 2006] Schmeidler Schmeidler TMET Limiting factors: Year 1920 1922 1929 1936 1947 1952 1959 1961 1973 Deflection ["] 1.98 ± 0.16 1.77 ± 0.40 2.24 ± 0.10 2.73 ± 0.31 2.01 ± 0.27 1.70 ± 0.10 2.17 ± 0.34 1.98 ± 0.46 1.66 ± 0.19 • Need for natural eclipses Short exposures, high background • Atmospheric turbulence Large astrometric noise • Portable instruments Limited resolution, collecting area M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 10 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 10100 degradation Measurement performance loss vs. space: 10^5 10^6 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 11 Improvements achievable with adaptive optics 10 Deflection [arcsec] 10 10 AO recovers at most 1-2 orders of magnitude 0 Full deflection Differential over 10" Differential over 100" -1 -2 GAME needs space! Future multi-conjugate AO system 10 10 -3 -4 2 M. Gai - GAME 4 6 Angle to Sun centre [deg] 8 10 Large, state-of-theart solar telescope equipped with high performance Adaptive Optics La Thuile, Rencontres de Moriond XLVI, 2011 12 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 13 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 14 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 15 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 16 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 17 Check of gravitation theories within Solar System Taking advantage of PPN limit, e.g. for f(R) theories… RPPN 2 PPN d f " R 1 f ' R f " R PPN R 1 , R 1 2 2 4 2 f ' R 3 f " R d f ' R 2 f " R [Capozziello & Troisi 2005] Alternative formulation: dR dR f " f ' f " d 1 d dR d PPN 1 , 1 R 2 2 4 dR dR dR d 2 Zf '3 f " Zf '2 f " d d 2 RPPN [Capone & Ruggiero 2010] Local measurements cosmological constraints M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 18 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 19 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 20 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] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 21 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) M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 22 Additional science topics - IV Complementary GR tests: measurement of from Mercury orbit 2 2 Same instrument cross-calibration M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 23 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 24 Outline of talk: • Scientific rationale • The GAME implementation concept Description focus on measurement Goal of GAME: M. Gai - GAME to 10-7-10-8; to 10-5-10-6 La Thuile, Rencontres de Moriond XLVI, 2011 25 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 26 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 stars between fields Track separation with epoch distance to Sun M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 27 Mission profile Sun-synchronous orbit, 1500 km elevation no eclipse 100% nominal observing time Stable solar power supply and thermal environment instrument structural stability M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 28 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 29 Observing calendar Convenient observing periods: ~June + December M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 30 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] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 31 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 32 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 33 Two-epoch observation sequence (I) Deflection measurement Calibration fields, 0 Two measurements epochs to modulate deflection on fields F1, F2 (Sun“switched”on/off) M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 34 Two-epoch observation sequence (II) Field superposition to ease differential measurement M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 35 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 36 Fully differential measurement (I) Epoch 1 Epoch 12: deflection modulation switched between field pairs Epoch 2 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 37 Fully differential measurement (II) Basic equations referred to stars in Fields 1, 2, 3, 4; Epochs 1, 2 F1; E1 F 2; E1 F1; E2 F 2; E2 F1, F 2 E1; E2 Star separation variation: deflection + instrument [base angle] F 3; E2 F 4; E2 F 3; E1 F 4; E1 F 3, F 4 E1; E2 ADDITIVE variations of Base Angle COMPENSATED Base Angle : hardware separation between observing directions M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 38 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 39 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 40 Precision on image location 1 4 X SNR : Standard deviation of image location : 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 SNR N >1: Instrumental factor of degradation (geometry, sampling, …) can be a small fraction of pixel/image size [Gai et al., PASP 110, 1998] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 41 Precision on image separation Arc length defined by composition of individual locations x1 x2 2 x1 x2 2 x1 2 x2 Precision related to Instrument resolution Pupil size Source magnitude Exposure time Average on # arcs Field of view } Observing strategy M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 42 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 43 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 44 Beam distribution (front) N and S stellar beams retained, separated by geometric optics Sun photons rejected either at first or second surface Apodisation M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 45 Beam distribution (rear) Secondary mirror + light screen Larger beams from opposite-to-Sun (Out-ward) directions /2 injected into the telescope with acceptable vignetting Simultaneous observation: multiplex + systematics rejection M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 46 Imaging performance Monochromatic PSF ( = 600 nm) M. Gai - GAME Polychromatic PSF (T = 6000 K) La Thuile, Rencontres de Moriond XLVI, 2011 47 Beam Combination (I) N and S stellar beams folded onto telescope optical axis by beam combiner: Two flat, pierced mirrors set at fixed angle M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 48 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 90115 mm2 Zerodur prototype M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 49 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 M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 50 Elementary astrometric performance Bright case: 100 s exposures, close to Sun Precision on a 15 mag star: < 1 mas [Gai et al., PASP 110, 1998] Band: _0 = 650 nm, = 120 nm M. Gai - GAME Background: 15.5 mag per square arcsec Faint case: 500 s exposures, away from Sun Background: 19.5 mag per square arcsec La Thuile, Rencontres de Moriond XLVI, 2011 51 Key issues of GAME • Observation sequence • Fully differential measurement • Precision on image location • Systematic error control: beam combiner • The Fizeau interferometer/coronagraph • PSF of the phased array • Photon limited mission performance M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 52 Scaling and tuning GAME geometry Basic concept can be modified to fit Experiment “scale”: goal budget Engineering / technological constraints Additional science case requirements Example: small mission / medium mission class Performance factors: ~diameter^2, (field of view)^{3/2} M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 53 Small mission version Pupil map N S Entrance slit (solid) Output slit (dotted) Optics size: ~0.50.7 m Front mask size: ~0.70.8 m M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 54 Overall layout (small mission version) Korsch, 4 mirrors, EFL = 19.50 m, visibility > 95% over 2020 arcmin field; distortion < 1e-4 [Loreggia et al., SPIE 2010] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 55 Photon limited small mission performance ~1 million 15 mag stars required to achieve 1 as cumulative 2e-6 equivalent precision on Observing time required: 20 + 20 days [Gai et al., SPIE 2009] [on average Galactic plane stellar density from GSCII] Observation focused on Galactic centre / anti-centre region: 3e-7 precision on 2 + 2 months over 2 years [Gai et al., COSPAR 2010; Vecchiato et al., COSPAR 2010] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 56 Medium mission version Pupil map Overall diameter: ~1.5 m Individual diameter: 7 cm Simultaneous observation of 4 Sunward + 4 outward fields M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 57 Optical configuration Beam Combiner 10:35:08 Hole on M1 = 0.7 m FP Hole on M3 = 0.4 m 2.7 m M1 M2 SF1_SCHOTT BSM24_OHARA M3 2.0 m M4 M. Gailens - GAME La Thuile, Rencontres de Moriond XLVI,0.05 2011 New from CVMACRO:cvnewlens.seq Scale: 471.70 MM 58 08-Oct-10 Photon limited medium mission performance Error budget: photon limit + 30% systematics 10-7 level reached in one year observation 5 years mission: 4e-8 precision on 5e-6 precision on ESA M3 proposal: Cosmic Visions 2015-2025 3.9 10 8 [not approved! ] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 59 Concluding remarks GAME as modern rendition of Dyson, Eddington & Davidson experiment Simple geometry / differential measurement concept Robust rejection of instrumental disturbances Scalable to 10^-7 – 10^-8 precision range Instrument suitable to additional science applications Future steps: strengthen science case and consortium; optimise design AND get consensus to implementation M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 60 GAME OVER READY TO PLAY AGAIN? [Y/N] M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 61 GAME vs. Gaia Commonality: • Use of natural sources (stars) in two (or >2) fields of view • Position measurement on CCD images • Resolution (image size) ~200 mas GAME peculiarity: • Observing instrument in low orbit • Payload optimised for and measurement • Fully differential M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 62 1 GAME: ~ 0.5 arcsec 0.5 GAIA: ~ 2-20 mas 0 0 1 2 3 Distance from Sun centre [degs] GAME observes sky regions with deflection larger (by 10-100) than that seen by Gaia Minimum correlation among variables 4 Deflection angle [arcsec] Deflection angle [arcsec] Deflection range 1.5 10 10 -1 -2 0 M. Gai - GAME 50 100 150 Distance from Sun centre [degs] La Thuile, Rencontres de Moriond XLVI, 2011 63 Sensitivity: amplitude of deflection / angular precision Location precision @ V = 15 mag S Gaia: () ~ 300 as S = 7 ~ 70 GAME: () ~ 400 as S = 1250 More than one order of magnitude of improvement Lower number of measurements (stars) required by GAME Lower sensitivity to systematic errors (deflection signal ~0".5, ~ PSF size) M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 64 Beam footprint superposition on M1 Sun-ward fields Out-ward fields Vignetting of out-ward beams on both M1 and M2 Vignetting on M2 M. Gai - GAME Vignetting on M1 La Thuile, Rencontres de Moriond XLVI, 2011 65 Coronagraphic + baffling section M. Gai - GAME La Thuile, Rencontres de Moriond XLVI, 2011 66