Fundamental Physics with Gaia

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Fundamental Physics with Gaia

• Sergei A.Klioner

Lohrmann-Observatorium, Technische Universität
Dresden International workshop Advances in
Precision Tests and Experimental Gravitation in
Space Galileo Galilei Institute, Florence, 30
September 2006
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Accuracy of astrometric observations
4.5 orders of magnitude in 2000 years
1 ?as is the thickness of a sheet of paper seen
from the other side of the Earth
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Accuracy of astrometric observations
1 ?as is the thickness of a sheet of paper seen
from the other side of the Earth
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Gaia
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Gaia in brief quantitative impact
109 stars ? 4 µas V lt 12, 10 µas V
15, 150 µas V 20 106 V lt 12, 30 x
10 6 V lt 15 200 x 106 radial velocities 5 x
105 minor bodies of the solar system 5 x 105
QSOs ( z photometry) Stellar classification
for all object Variability analysis over 108
stars 10 000 stellar masses ? lt 1 Extra solar
planets to 200 pc
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Gaia in brief telescope
Aperture1.45 m ? 0.5 m Focal length 35 m FOV
1.6 ? 0.7
106 CCDs, 1Gpixel, TDI
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Gaia in brief photometry and spectroscopy

• Low-resolution spectra
• 330-1000 nm
• 4-32 nm/pixel
• Radial velocities from
• Doppler shifts of spectral
• lines
• 847-874 nm,
• 0.036 nm/pixel

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Gaia in brief scanning satellite
spin/Sun angle 45 scan rate 60
"/s period 6.0 h precession 63.12 d basic
angle 106.5
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Gaia in brief components of the scanning motion
animation Lennart Lindegren, 2004
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Gaia in brief observation distribution
ecliptic coordinates
J. de Bruijne, 2003
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Gaia in brief principles of data processing
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Gaia in brief data processing

• Parameters
• At least 5 parameters for each star 5 ? 109
• 4 parameters of orientation each 15 seconds
  108
• 2000 calibrartion parameters per day 4 ? 106
• global parameters (e.g., PPN ?) 102
• Observations
• about 1000 raw images for each star 1012
• Data volume 1 PB (iterative data processing)
• Computational efforts 1019 to 1021

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Gaia in brief timetable
2000
2004
2008
2012
2016
2020
Concept Technology Study ESA SCI 2000(4)
Acceptance
Re-Assessment Ariane ? Soyuz
Technology Development
Design, Build, Test
Launch
To L2
Observations
Phase B2
Analysis
Catalogue
Early Data
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Gaia in brief goals
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Gaia in brief goals

• Mapping of the Milky Way
• Stellar physics (classification, L, log g,
  Teff, Fe/H)
• Galactic kinematics and dynamics
• Distance scale (geometric, HR diagrams,
  cepheids, RR Lyr)
• Age of the Universe (globular clusters,
  distance and luminosity)
• Dark matter (potential tracers)
• Reference frames (quasars)
• Extra-solar planets (astrometry, photometric
  transits)
• Solar system objects (survey, taxonomy, masses)
• Fundamental physics (relativity experiments)

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Relativity as a driving force for Gaia
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Gaias main goals for testing relativity
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Fundamental physics with Gaia
Improved ephemeris
Consistency checks
Global tests
Local tests
Local Positional Invariance
Differential solutions
Pattern matching
Local Lorentz Invariance
Monopole
Light deflection
SS acceleration
Quadrupole
Primordial GW
One single ?
Gravimagnetic
Unknown deflector in the SS
Four different ?s
Asteroids
Stability checks for ?
Perihelion precession
Special objects
Higher-order deflection
Non-Schwarzschild effects
SEP with the Trojans
Compact binaries
Alternative angular dependence
J_2 of the Sun
Non-radial deflection
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Necessary condition consistency of the whole
data processing chain

• Any kind of inconsistency is very dangerous for
  the quality and reliability of
• the estimates
• The whole data processing and all the auxiliary
  information should be
• assured to be compatible with the PPN formalism
  (or at least GR)
• planetary ephemeris coordinates, scaling,
  constants
• Gaia orbit coordinates, scaling, constants
• astronomical constants
• ???
• Monitoring of the consistency during the whole
  project
• First task is to ensure the consistency of
  fundamental astronomical algorithms
• Commission 52 of the IAU on Relativity in
  Fundamental Astronomy, 2006-

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LPI gravitational red shift

• The mean rate of the proper time on the Gaia
  orbit is different
• from Terrestrial Time (or TAI) by about 6.9 10
  10
• Periodic terms of order 0.2 0.4 ms
• The gravity term itself is about 8 10 10 (20
  times larger than for the ISS)

Gaia-TAI as a function of TAI
linear trend removed 6.9 10 10
sec
days
The accuracy is still unclear since not all
technical details are fixed by now
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LLI aberration

• Robertson (1949) and Mansouri Sexl (1977)
  a test theory against which one can test
  special relativity
• Lorentz transformations with additional
  numerical parameters
• Many experiments can be interpreted in terms of
  constraints
• on those parameters e.g. Michelson-Morley and
  similar
• The idea is to use Gaia data to check
• if the special-relativistic formula
  for aberration is correct

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LLI aberration

• For a general linear transformation

• The aberrational formula takes the form

• Accuracy of the Mansouri-Sexl parameters
  expected from Gaia is relatively low about
  10-4
• but this is still a different experiment

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PPN ? from light deflection

• Most precise test possible with Gaia

• Advantages of the Gaia experiment
• optical,
• deflection (not Shapiro),
• wide range of angular distances,
• full-scale simulations of the experiments
• Problems with some of the current best
  estimates of ?
• 1. special fits of the post-fit residuals
  of a standard solution
• (e.g., missed correlations leads to
  wrong estimates of the uncertainty)
• 2. no special simulations with faked data
  to check what kind
• of effects we are really sensitive to

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Monopole gravitational light deflection

• Monopole light deflection distribution over the
  sky on 25.01.2006 at 1645
• equatorial coordinates

?as
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Monopole gravitational light deflection

• Monopole light deflection distribution over the
  sky on 25.01.2006 at 1645
• equatorial coordinates

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Gaia sensitivity to the gravitational light
deflection due to the Sun
66.2
along scan
S/N
across scan
angular distance to the Sun (degrees)
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Gaia sensitivity to the gravitational light
deflection due to the Sun
64.1
full
S/N
angular distance to the Sun (degrees)
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Mapping the light deflection

• The PPN ? is just the amplitude of one
  particular deflection pattern
• Several additional tests are planned
• (this could be also considered as stability
  tests)
• data subsets
• splitting in time
• splitting in angular distance
• splitting in brightness, etc
• additional degrees of freedom
• higher-order deflection
• separate ?s for Sun, Jupiter, Saturn,
• purely empirical deflection pattern
  representations

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Light deflection from the planets
For other planets the results are worse
0.1-0.007 for the monopole Problem rings, dust,
gas, etc. in the vicinity of the giant planets
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Relativistic effects with asteroids
I. Schwarzschild effects due to the Sun
perihelion precession Historically the first
test of general relativity
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Perihelion precession (the first 20001 asteroids)
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Perihelion precession (12.09.05 253113)
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Relativistic effects with asteroids
I. Schwarzschild effects due to the Sun
perihelion precession Hestroffer,
Berthier, Mouret, 2004- Preliminary results
with limited number of sources and
with perihelion only
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Relativistic effects with asteroids

• II. Non-Schwarzschild effects
• Orbital consequences of the EIH equations for
  asteroids are still poorly known.
• Especially interesting for resonant asteroids for
  which the relativistic effects of e.g. Jupiter
  can be enhanced

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Maximal post-Sun perturbations in meters
20000 Integrations over 200 days
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Relativistic effects in asteroids

• III. Nordtvedt effect with Trojan asteroids (and
  some other resonant ones)
• Historically the first example of an observable
  effect due to a violation of the Strong
  Equivalence Principle (Nordtvedt, 1968)
• shift of L4 and L5 by 1 for ?1
• Orellana, Vucetich, 1993 ?-0.540.48
• 12 Trojans,
• 100-200 observations for each,
• accuracy 1
• Gaia 103-10 4 better

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Pattern matching in positions/proper motions

• Acceleration of the Solar system relative to
  remote sources leads to
• a time dependency of secular aberration ?5
  ?as/yr
• constraint for the galactic potential model
• important for the binary pulsar test of
  relativity (at 1 level)
• Mathematics
• expansion of the proper motion field into
  vector spherical harmonics
• the coefficients for n1 give - rotations
  
• 
  - the solar system acceleration
• 1993- Ongoing unsuccessful attempts with
  geodetic VLBI
• Gaia will measure the acceleration with
  at least 10 accuracy

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Pattern matching in positions/proper motions

• Constraint on very low frequency gravitational
  waves
• - constraint of stochastic GW flux with ? lt
  310-9 Hz (similar study done for VLBI
  Pyne et al. 1996, 1997)
• - attempts to fit a pattern of proper motions
  induced by an individual GW with ? lt 310-8
  Hz

Example a GW of strain h and frequency ?
propagating in the direction ?90
The coefficients for ngt1 give the GW-flux
constraints From Gaia for ? lt 310-9 Hz
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Ephemeris improvement with Gaia

• A short-arc (5 years) ephemeris with highest
  possible accuracy is necessary
• Observations relevant for the solar system
  ephemeris
• direct observations of the giant planets
• indirect from differential light deflection
• indirect from their natural satellites
• masses of hundreds of asteroids
• (marginally important for the giant planets)
• 1. Improve the ephemeris and redo the data
  processing
• 2. This Improves also the accuracy of normal
  tests

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Individual relativistically interesting objects
can Gaia provide the ultimate test for the
existence of black holes?

• Fuchs, Bastian, 2004 Weighing stellar-mass
  black holes in binaries
• Astrometric wobble of the companions (just from
  binary motion)

• Already known objects
• Unknown objects, e.g.
• binaries with
• failed supernovae
• (Gould, Salim, 2002)
• Gaia advantage
• we record all what we see!

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Search for the optimal strategy for Gaia

• The mission would survive without fundamental
  physics tests
• the tests cannot be too heavy so that
  they disturb the main goals
• But the tests are more than welcome and they are
  for free ?

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REMAT Gaia collaboration forRElativistic Models
And Tests
About 15 members Barcelona, Dresden, Nice,
Padova, Paris, Turin
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