Download 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
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  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
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
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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 
 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
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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
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
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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
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
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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
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 12: 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
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
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: ~0.50.7 m
Front mask size: ~0.70.8 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
2020 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