10 ⎧as = 10% distances at 10 kpc
equiv 1AU at 100 kpc
N A Walton: GAIA Data
Science
@ NGSS
@ GSD2008
Kickoff: -17
NESC
Mar, :2008
6 July, 2009
p1
10 ⎧as/yr = 1 km/sec at 20 kpc
Printed:
p1 05/07/09
Printed: 05/07/09
Gaia
Summary and Data
Nicholas Walton
Institute of Astronomy
University of Cambridge
What's driving Gaia?
z
Towards a more precise understanding of the
current structure and history of our galaxy:
−
Distributions of mass, energy and angular momentum
z
−
Signatures of mergers
z
−
z
Missing mass, dark matter?
Dwarf galaxies within the local group
History of star formation and enrichment of the interstellar dust and gas
In a nutshell – map the Galaxy and Local Universe
−
−
a billion stars, µ arcsec astrometry, to V=20 mag
one µarcsec : 'resolve a finger nail on the moon!'
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p3
Printed: 05/07/09
What's required for this mapping?
• Accurate positions and velocities of stars over a large
volume of space
−
z
Complete survey down to a limiting magnitude
−
z
size of the galaxy implies a Radius ~10 to 20 kpc (dist.mod: 15.0
to 16.5)
Approximately 20th magnitude, 109 objects
Complementary data required to 'sort' the objects
−
−
−
−
effective temperature
surface gravity
metallicity
luminosity
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p4
Printed: 05/07/09
Gaia: Design Considerations
• Astrometry (V < 20):
– completeness to 20th mag (with on-board detection) : 109 stars
– accuracy: 10–25 µarcsec at 15th mag
• (c.f. Hipparcos: 1 milliarcsec at 9th mag)
– scanning satellite, two viewing directions
global accuracy, with optimal use of observing time
– principles: global astrometric reduction (as for Hipparcos)
• Spectro-Photometry (330nm-1000nm, all V < 20):
– astrophysical diagnostics (low-dispersion photometry)/ chromaticity
• Teff ~ 200 K, log g, [Fe/H] to 0.2 dex, extinction
• Radial velocity (V < 16–17):
– application:
• third component of space motion, perspective acceleration
• dynamics, population studies, binaries
• spectra: chemistry, rotation
– principles: slitless spectroscopy using Ca triplet (847–874 nm)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p5
Printed: 05/07/09
Gaia: Complete, Faint, Accurate
Hipparcos
Gaia
Magnitude limit
Completeness
Bright limit
Number of objects
12
7.3 – 9.0
0
120 000
Effective distance limit
Quasars
Galaxies
Accuracy
1 kpc
None
None
1 milliarcsec
Photometry photometry
Radial velocity
Observing programme
2-colour (B and V)
None
Pre-selected
20 mag
20 mag
6 mag
26 million to V = 15
250 million to V = 18
1000 million to V = 20
1 Mpc
5 x 105
106 – 107
7 µarcsec at V = 10
10-25 µarcsec at V = 15
300 µarcsec at V = 20
Low-res. spectra to V = 20
15 km/s to V = 16-17
Complete and unbiased
source: ESA
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p6
Printed: 05/07/09
Figure courtesy Alex Short
Focal Plane: a large array
104.26cm
42.35cm
Red Photometer
CCDs
Wave Front
Sensor
Blue Photometer
CCDs
Wave Front
Sensor
Radial-Velocity Spectrometer
CCDs
Basic Angle
Monitor
Basic Angle
Monitor
Sky Mapper
CCDs
Astrometric Field
CCDs
Total field:
- active area: 0.75 deg2
- CCDs: 14 + 62 + 14 + 12
- 4500 x 1966 pixels (TDI)
- pixel size = 10 µm x 30 µm
= 59 mas x 177 mas
Star motion in 10
s
Sky mapper:
Photometry:
- detects all objects to 20
mag
- rejects cosmic-ray events
- FoV discrimination
- two-channel
photometer
- blue and red CCDs
Astrometry:
- total detection noise: 6 ep7-
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
Spectroscopy:
- high-resolution spectra
- red CCDs
Printed: 05/07/09
On-Board Object Detection
• Requirements:
– unbiased sky sampling (mag, colour, resolution)
– no all-sky catalogue at Gaia resolution (0.1 arcsec) to V~20
• Solution: on-board detection:
– no input catalogue or observing programme
– good detection efficiency to V~21 mag
– low false-detection rate, even at high star densities
• Will therefore detect:
–
–
–
–
variable stars (eclipsing binaries, Cepheids, etc.)
supernovae: 20,000
microlensing events: ~1000 photometric; ~100 astrometric
Solar System objects, including NEOs and KBOs
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p8
Printed: 05/07/09
Photometry Measurement Concept (2/2)
700
40
1050
18
650
35
1000
16
30
950
Blue photometer
600
550
25
500
20
450
15
400
10
wavelength (nm)
900
12
850
10
800
8
750
wavelength
(nm)
350
spe
5
0
300
0
14
Red photometer
5
10
15
20
25
30
6
700
4
650
2
600
35
spe
0
0
5
10
AL pixels
15
20
25
30
35
AL pixels
RP spectrum of M dwarf (V=17.3)
Red box: data sent to ground
White contour: sky-background level
Colour coding: signal intensity
Figures courtesy Anthony Brown
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p9
Printed: 05/07/09
Spectral sensitivity of astrometric G band
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
SIM-Gaia Meeting,
p10
Printed: 05/07/09
Astrometric performance of 10
Skymappers and astrometric field
RVS3
RVS2
RVS1
RP
BP
radial velocity
(dispersed
images)
BAM-N BAM-R WFS1
WFS2
AF9
photometry
(dispersed
images)
AF8
AF7
AF6
AF5
AF3
AF2
AF1
SM2
SM1
AF4
astrometric
measurements
detection
and FOV
discrimination
both FOVs are superposed
in the astrometric field
SM2 sees only the following FOV
SM1 sees only the preceding FOV
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
SIM-Gaia Meeting,
p11
Printed: 05/07/09
Astrometric performance of
11
Samples and windows
On-chip
binning
window of 18*12
pixels centred on the star
18 samples
transmitted to ground
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
SIM-Gaia Meeting,
p12
Printed: 05/07/09
Astrometric performance of 12
Sampling/windowing (read and transmit)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
SIM-Gaia Meeting,
p13
Printed: 05/07/09
Astrometric performance of 13
Charge injection (2/2)
Many traps are
empty prior to
charge injection
TDI motion




Most traps are full
following charge
injection





 










“Self injection” by stars and
background is statistically negligible
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
SIM-Gaia Meeting,
p14
Printed: 05/07/09
Astrometric performance of 14
Gaia: mapping Dark Matter, forming a Galaxy
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
10 µas = 10% distances at 10 kpc
10 µas/yr = 1 km/sec at 20 kpc
p15
Printed: 05/07/09
GAIA is the ideal Nemesis survey
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p16
Printed: 05/07/09
Galaxies, Quasars, and the Reference Frame
Parallax distances, orbits, and internal dynamics of nearby galaxies
Galaxy survey, including large-scale structure
~500,000 quasars: kinematic and photometric detection
~20,000 supernovae [10/day Î real-time alerts]
ΩM, ΩΛ from multiple quasar images (3500 to 21 mag)
Galactocentric acceleration: 0.2 nm/s2 ⇒ ∆(aberration) = 4 µas/yr
Globally accurate reference frame to ~0.4 µas/yr
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p17
Printed: 05/07/09
Will Gaia contribute to cosmology and fundamental physics?
•Gaia will detect?/constrain very low frequency gravitational waves, from
coherence/stability of reference frame. a la VLBI
•Gravitational wave energy: 10-12 < f < 10-9 Hz
•This range – well below LISA – is a sensitive test of inflation models, and
later neutrino effects eg PRD 75 104009 2007
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p18
Printed: 05/07/09
Summary: General Relativity/Metric
From positional displacements:
γ to 5×10-7 (cf. 10 -5 presently) ⇒ scalar-tensor theories
effect of Sun: 4 mas at 90o; Jovian limb: 17 mas; Earth: ~40 µas
From perihelion precession of minor planets:
β to 3×10-4 - 3×10-5 (×10-100 better than lunar laser ranging)
Solar J2 to 10-7 - 10-8 (cf. lunar libration and planetary motion)
From white dwarf cooling curves:
dG/dT to 10-12 - 10-13 per year (cf. PSR 1913+16 and solar structure)
Gravitational wave energy: 10-12 < f < 10-9 Hz
Microlensing: photometric (~1000) and astrometric (few) events
Cosmological shear and rotation (cf. VLBI)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p19
Printed: 05/07/09
Gaia data products will be staged releases.
what will be able to do to get full value?
Assumption 1: Gaia data will revolutionise most of astrophysics
– in a few years every proposal will be based on Gaia data.
And all Gaia data go public with no priority access.
Assumption 2: nothing will happen unless someone plans
it*.
*first law of planning – make sure all your text fits on a single line
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p20
Printed: 05/07/09
Gaia data products will be staged releases.
what will be able to do to get full value?
Assumption 1: Gaia data will revolutionise most of astrophysics
– in a few years every proposal will be based on Gaia data.
And all Gaia data go public with no priority access.
Assumption 2: nothing will happen unless someone plans
it.
Assumption 3: telescopes and research funding are already
heavily oversubscribed: to get a lot of Gaia exploitation, we
need to get organised: scientifically, financially, politically.
Context one: Gaia data products will be staged releases. We
need to match plans appropriately
Context two: Europe’s mid-sized telescopes are being
restructured right now, with Gaia science as a primary driver
for their continued operation and development.
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p21
Printed: 05/07/09
Gaia-related data
Since Gaia affects almost all astrophysics, almost
everything is Gaia-related – there is nothing `special’
about being Gaia-relevant
Exclude here pure `calibration`
All science advances advance Gaia science*
And vice versa**
So here just consider sources detected by Gaia, and
being studied because of a Gaia detection
* people complain scientific euro-english has a vocabulary of only 100 words –
actually, even fewer are apparently adequate...
** Latin doesn’t count
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p22
Printed: 05/07/09
Gaia data products (tbc)
this is only a planning hypothesis, prior to CU9!!!
Alerts: quasi real-time flux alerts from mid 2012
then:
2014
Billion sources, HST spatial resolution, all-sky
Limited precision astrometry (cut at mas-level?)
2016 and 2018
BP/RP spectrophotometry 330nm-1000nm
Brighter-star spectroscopy R=11500, CaT
Alerts from mid-2012
All-sky data to be bundled in stages 2014-2018(tbc)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p23
Printed: 05/07/09
Gaia data products
first– alerts
Alerts: quasi real-time flux alerts, starting early
How will/can we prepare for these?
Leave aside alert verification process, which is CU
internal
Wide range of public sources, but which is which?:
It needs a lot of observing time, much to identify sources
of interest only to others... Î teams are needed?;
It can be pre-planned – like SNae factory – so needs
special arrangements with observatories
It really needs all-sky coverage
Do we just tell the world, and leave them to it?
Or organise?
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p24
Printed: 05/07/09
SNae are the basic Dark Energy calibration, through Gaia Cepheids Î critical science
should we have a cosmology/Dark Energy WG, for distance indicators...?
Science case: map the true SN luminosity DF, from Cepheid distances
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p25
Printed: 05/07/09
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p26
Printed: 05/07/09
Present precision
depends
on an
empirical
relation
Systematic
changecosmology
of SNIa L_max
with
decline
rate:[phillips]
empirical
Whoseamplitude
amplitude ~10x
is an order
of magnitude
thaneffect…
dark energy
cosmological
darklarger
energy
Gaia will provide not only the absolute Cepheid distances, but the true
SNIa luminosity DF vs whatever parameters
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p27
Printed: 05/07/09
Current supernova calibration set (Prieto etal ApJ 647 501 2006)
The Gaia supernova discoveries require good follow-up
light curves for cosmology
Gaia SNIa detection limit
G=19 Gaia SNIa alerts limit
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p28
Printed: 05/07/09
Faint as possible matters Î early, before CCD decay
cf KAIT finds ~80 SNae/year to 19mag: Gaia is an order of magnitude gain
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p29
Printed: 05/07/09
Should we prepare ``follow-up’’ surveys along the high cadence areas?
The Nominal Scanning Law
N A Walton: GAIA Data
Berry Holl,
AGISLab
@ NGSS Kickoff - NESC : 6 July, 2009
p30
Printed: 05/07/09
Main Performances and Capabilities
Accuracies:
20 µas at V = 15 0.2 mas at V = 20
radial velocities to <10 km/s complete to V ~ 17.5
sky survey at ~0.2 arcsec spatial resolution to V = 20
multi-colour multi-epoch spectrophotometry to V = 20
dense quasar link to inertial reference frame
Capabilities:
10 µas ≡ 10% at 10 kpc ≡ 1 AU at 100 kpc
[~1cm on the Moon]
10 µas/yr at 20 kpc ≡ 1 km/s
⇒ every star in the Galaxy and Local Group will be seen to move
⇒ GAIA will quantify 6-D phase space for over 300 million stars,
and 5-D phase-space for over 109 stars
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p31
Printed: 05/07/09
How will Gaia behave in crowded regions? We have no prior data!
much of the sky is complex.. But LMC and M31 interestingly seen
M
31
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
L
M
C
p32
Printed: 05/07/09
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
20
18
20
19
20
20
Gaia Timelines: not so far away ...
now
Proposal
Concept & Technology Study
Mission Selection
Re-Assessment Study
Phase B1
Definition
Selection of Prime Contractor (EADS Astrium)
Phase B2
Phase C/D
Implementation
Launch 2012-Mar-03
Scientific operation
Operation
Studies
Software Development
Data Processing
Mission Products
6 July 2009: N A Walton
Mission Data Processing
Intermediate
Final
Gaia Scientific Organisation
• Gaia Science Team (GST):
– 7 members + DPAC Executive Chair + ESA Project Scientist
• Direct scientific community participation:
– organised in Data Processing and Analysis Consortium (DPAC)
– ~350 scientists active at some level
• Community is active and productive:
– regular science team/DPAC meetings
– growing archive of scientific reports
– advance of simulations, algorithms, accuracy models, etc.
• Data distribution policy:
– Intermediate data releases
– final catalogue ~2019–20
– no proprietary data rights
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p34
Printed: 05/07/09
Gaia Data Processing and Analysis
Consortium: http://www.rssd.esa.int/gaia/dpac
To prepare, test, implement and execute all the
software required to process all the science and
auxiliary data produced by the Gaia satellite, to such
level that the reduced data is ready for further
astrophysical exploration
ESA Critical Design Review passed in June 2009
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p35
Printed: 05/07/09
GAIA DPAC in the UK
z
z
Gaia Data Flow System project – UK DPAC
Multi institute consortium
−
−
−
−
−
−
z
z
IoA, Cambridge
MSSL
Leicester
Edinburgh
RAL
OU
Provides leadership of CU5 (photometry) and
major partner on CU6 (spectroscopy)
DPC at IoA during operation/ exploitation phase
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p36
Printed: 05/07/09
Large Computers ... at least for AGIS
Data are compressed encoded and requires a lot of processing
(~10^21 FLOP)
As a courtesy of Barcelona Supercomputing Center
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p37
Printed: 05/07/09
Relevance for other large surveys
z
Implementation of Analysis System
−
−
z
Organisation
−
−
z
Use of standard development processes
Guidelines and clear procedures
Structure of DPAC
Multi-site development
Community
−
−
Assure best data products – via DPAC
Build end user community – via GREAT
z
z
http://www.ast.cam.ac.uk/GREAT
Planning
−
End to end plan – development/ operations/ science use
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p38
Printed: 05/07/09
summary
Gaia is on-schedule for launch in 3/2012
- will be the first precision survey of the Universe
- will revolutionise galactic formation and evolution
- will quantify dark matter
- will map the solar system – and find any earth-killers
- will find 10000 giant planets – with masses
- will be the primary precision map of dark energy
- will quantify stellar evolution, formation to death
- 500000 qso, 10000SNae, 200000WDs, ...
- and much, much, more
Î Gaia is Europe’s top science priority mid-term
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p39
Printed: 05/07/09
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p40
Printed: 05/07/09
Gaia by the numbers
z
z
z
z
z
z
z
z
z
Primary mirrors: 1.45 m x 0.5 m
Focal length: 35 m
Pixel: 59 x 177 mas (10 µas
~1/6000 pixel)
1 µas: rotation M1 < 10
picometers at the edge
Focal plane: 420 x 850 mm
106 CCDs, ~1 Gpixel
Star on CCD: mean: 150, peak:
36000 (magnitude 20)
Stellar flux: 20 000 e-/s @ V=15,
200 e-/s @ V=20
Sample datation accuracy: 50 ns
z
z
z
z
z
z
z
z
z
Tore (3 m diameter) thermal
stability required ~some tens of
µK
Rate measurement error < 0.9
mas/s
Rate pointing error < 5 mas
Attitude High Frequency
Disturbance < 3.4 µas
S/C launch mass 2.1 tons
Solar Array capability 1.9 kW
Mass memory capability 1 Tb
S/C Height 3 m
Deployed Sunshield ø = 10 m
source: Moisson – EADS Astrium
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p41
Printed: 05/07/09
10 ⎧as = 10% distances at 10 kpc
equiv 1AU at 100 kpc
N A Walton: GAIA Data
Science
@ NGSS
@ GSD2008
Kickoff: -17
NESC
Mar, :2008
6 July, 2009
p42
10 ⎧as/yr = 1 km/sec at 20 kpc
Printed:
p42 05/07/09
Printed: 05/07/09
DPAC coordination units
•
•
•
•
•
•
•
•
•
CU1: System Architecture
CU2: Data Simulations
CU3: Core Processing
CU4: Object Processing
CU5: Photometric Processing
CU6: Spectroscopic Processing
CU7: Variability Processing
CU8: Astrophysical Parameters
CU9: Catalogue Access
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p43
ESA areas of
Contribution
Printed: 05/07/09
DPAC: Data Processing Centres
DPCs underpin and support CUs
−
−
z
z
z
z
z
z
Software support and production
Operation of processing system(s)
ESAC
BPC
CNES
ISDC
IoA
OATO
(CU1,3)
(CU2,3)
(CU4,6,8)
(CU7)
(CU5)
(CU3)
Madrid
Barcelona
Toulouse
Geneva
Cambridge
Torino
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p44
Printed: 05/07/09
Gaia: Timescales & Data
z
Final astrometry – dependent on global iterative
solution of entire mission data
−
z
Intermediate data releases
−
−
z
final catalogues to be released ~ 2020
one or more during the course of the mission
Science alerts
Synergies with new and existing instruments
−
−
e.g. Star-formation: Herschel/ ALMA
most GAIA sources can be followed up with existing 24-8m class ground based telescopes
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p45
Printed: 05/07/09
Data Reduction Principles
Scan width: 0.7°
Figure courtesy Michael Perryman
Sky scans
(highest accuracy
along scan)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
1. Object matching in successive scans
2. Attitude and calibrations are updated
3. Objects positions etc. are solved
4. Higher terms are solved
5. More scans are added
6. System
p46 is iterated
Printed: 05/07/09
slide: wil o'mullane
Astrometric GIS – What ?
Calculate parameters describing
• observed (proper) directions to a subset of "well-behaved"
(primary) sources
• attitude of the instrument as function of time
• transformation from field angles to pixel coordinates
This will directly give:
•
•
•
•
astrometric parameters for the primary sources
attitude parameters (for the relevant time intervals)
geometric calibration parameters (for the relevant detectors)
if desired, any other parameter entering the calculation of
proper directions (e.g. paramaterised post newtonian (PPN) )
and indirectly:
• approximate astrometric parameters for all other (secondary)
sources (except solar system sources)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p47
Printed: 05/07/09
Downlink
z
Using Cebreros (35M)
−
3-8Mb/s downlink
z
z
−
−
z
~ 30GB/day -> ~100TB
so download 'windows' around objects
occasionally New Norcia
−
−
z
depends on encoding
which depends on weather
during Galactic plane scans
data accumulated onboard downlinked later
Data are compressed encoded and requires a lot of
processing (~10^21 FLOP)
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p48
Printed: 05/07/09
The Participating Institutes
Graphic : Francois Mignard - DPAC
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p49
Printed: 05/07/09
Photometry Measurement Concept (1/2)
Blue
photometer:
330–680 nm
Red photometer:
640–1000 nm
Figures courtesy EADS-Astrium
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p50
Printed: 05/07/09
http://www.rssd.esa.int/gaia
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p51
Printed: 05/07/09
Light-bending by Jupiter to test monopole (l)
quadrupole(r) and any motion-dependence
Figs from
Crosta & Mignard CQG 23 2006, cf Kopeikin
etal PRD 75 2007
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p52
Printed: 05/07/09
Light Deflection : γ
Hipparcos
σH / σ G
GAIA
• 105 stars V < 10
• 8 x 106 stars V < 13
• 2.5 x 106 abscissas
• 2.5 x 108 abscissas
10
• σ ~ 3 to 8 mas
• σ ~ 10 µas
400
• χ > 47 degrees
• χ > 35 degrees
⇓
• + fainter stars
3
⇓
−3
γ = 1± 3×10
σ γ ≈ 1× 10
(Froeschlé, Mignard & Arénou, 1997)
−6
to 3 × 10
Vecchiato etal 2003 A+A 399 337
N A Walton: GAIA Data @ NGSS Kickoff - NESC : 6 July, 2009
p53
Printed: 05/07/09
−7