Transcript transparencies - Rencontres de Moriond

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
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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
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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
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Spacetime curvature around massive objects
Deflection angle [arcsec]
1.5
G: Newton’s
gravitational constant
1".74 at Solar limb  8.4 rad
d: distance Sunobserver
GM 1  cos
  1    2
c d 1  cos
1
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
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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
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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
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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
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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
M. Gai - GAME
La Thuile, Rencontres de Moriond XLVI, 2011
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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
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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
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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
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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
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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
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M. Gai - GAME
La Thuile, Rencontres de Moriond XLVI, 2011
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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 
 2Zf '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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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La Thuile, Rencontres de Moriond XLVI, 2011
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Observing
calendar
Convenient
observing
periods:
~June +
December
M. Gai - GAME
La Thuile, Rencontres de Moriond XLVI, 2011
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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
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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
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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
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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
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Two-epoch observation sequence (II)
Field superposition
to ease differential
measurement
M. Gai - GAME
La Thuile, Rencontres de Moriond XLVI, 2011
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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
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Fully differential measurement (I)
Epoch 1
Epoch 12: deflection modulation switched between field pairs
Epoch 2
M. Gai - GAME
La Thuile, Rencontres de Moriond XLVI, 2011
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Fully differential measurement (II)
Basic equations referred to stars in Fields 1, 2, 3, 4; Epochs 1, 2
 F1; E1   F 2; E1   F1; E 2   F 2; E 2   F1, F 2   E1; E 2
Star separation variation: deflection  + instrument [base angle]
 F 3; E 2   F 4; E 2   F 3; E1   F 4; E1   F 3, F 4   E1; E 2
ADDITIVE variations of Base Angle COMPENSATED
Base Angle :
hardware separation
between observing
directions
M. Gai - GAME
La Thuile, Rencontres de Moriond XLVI, 2011
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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
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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
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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
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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
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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
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La Thuile, Rencontres de Moriond XLVI, 2011
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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
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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
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Imaging performance
Monochromatic PSF
( = 600 nm)
M. Gai - GAME
Polychromatic PSF
(T = 6000 K)
La Thuile, Rencontres de Moriond XLVI, 2011
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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
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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
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
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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
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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
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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}
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Small mission version
Pupil map
N
S
Entrance slit (solid)
Output slit (dotted)
Optics size: ~0.50.7 m
Front mask size: ~0.70.8 m
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Overall layout
(small mission version)
Korsch, 4 mirrors,
EFL = 19.50 m,
visibility > 95% over
2020 arcmin field;
distortion < 1e-4
[Loreggia et al., SPIE 2010]
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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]
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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
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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! ]
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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
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GAME
OVER
READY TO PLAY
AGAIN? [Y/N]
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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
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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