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GAIA
Composition, Formation and Evolution
of our Galaxy
thanks to Michael Perryman, the GAIA Science
Team (present and past) and 200+ others
M83
M83 image (with Sun marked)
(AAO, D. Malin)
‘the Sun’
GAIA: Key science objectives
• Structure and kinematics of our Galaxy:
–
–
–
–
shape and rotation of bulge, disk and halo
internal motions of star forming regions, clusters, etc
nature of spiral arms and the stellar warp
space motions of all Galactic satellite systems
• Stellar populations:
– physical characteristics of all Galactic components
– initial mass function, binaries, chemical evolution
– star formation histories
• Tests of galaxy formation:
– dynamical determination of dark matter distribution
– reconstruction of merger and accretion history
 Origin, Formation and Evolution of the Galaxy
Overview
1.
2.
3.
4.
5.
6.
Measurement principles
The GAIA satellite and mission
Some science examples
Schedule, organisation of work
Current situation
Summary
Some history…
610 B.C.: Obliquity of the ecliptic (Anaximander)
125 B.C.: Precession of the equinoxes (Hipparchus)
1717:
First proper motions (Halley)
1725:
Stellar aberration (Bradley), confirming:
– Earth’s motion through space
– finite velocity of light
– immensity of stellar distances
1761/9:
Transits of Venus across the Sun (various)
– solar parallax
1783:
Sun’s motion through space (Herschel)
1838-9:
First parallaxes (Bessel/Henderson/Struve)
Principle of parallax measurement
parallax angle
Orbit about Sun
Star of interest
Background
stars
Measurement
Principle
Measurement principle: b
Global astrometry
basic angle
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
Broad band
photometry
Medium band
photometry
Radial
velocity
Observing programme
2-colour (B and V)
None
None
Pre-selected
20-21 mag
~20 mag
~3-7 mag
26 million to V = 15
250 million to V = 18
1000 million to V = 20
1 Mpc
~5 
106 - 107
4 arcsec at V = 10
10 arcsec at V = 15
200 arcsec at V = 20
4-colour to V = 20
11-colour to V = 20
1-10 km/s to V = 16-17
On-board and unbiased
Scientific design considerations
• Astrometry (V < 20):
– completeness  on-board detection
– accuracies: 10 as at 15 mag (science)
– continuously scanning satellite, two viewing directions
 global accuracy, optimal with respect to observing time
• Radial velocity (V < 17-18):
– third component of space motion
– account for perspective acceleration (nearby, fast stars)
• Photometry (V < 20):
– astrophysical diagnostics (4-band + 11-band) + chromatic correction
 extinction, Teff ~ 200 K, [Fe/H] to 0.2 dex
Satellite
• Deployable: solar array/sun-shield
• Size: 8.5m diameter (4.2m stowed)
2.9m height (2.1m for payload)
• Mass: 3100 kg (800 kg payload)
• Power: 2600 W
• Launch: dual Ariane 5
• Orbit: Sun-Earth L2 (Lissajous)
• Data rate (phased array):
1 Mbs-1 sustained
3 Mbs-1 downlink (1 ground station)
• Launch date: 2010-12
• Attitude control: FEEP thrusters
• Design lifetime: 5 years
• ESA only mission
Payload overview
• Two astrometric instruments:
• field of view = 0.6o  0.6o
• separation = 106o
• Monolithic mirrors: 1.7 m  0.7 m
• Non-deployable, 3-mirror, SiC optics
• Astrometric focal planes: TDI CCDs
• Radial velocity/photometry telescope
• Survey principles:
• revolving scanning
• onboard detection
• complete and unbiased sample
Astrometric instrument: Light path
1
2
3
4
Astrometric focal plane
Sky mapper:
- detects all objects to 20 mag
- rejects cosmic-ray hits
- mag + x,y to main field
Main field:
- area: 0.66 x 0.56 deg = 0.37 deg2
- size: 60  70 cm2
- number of CCDs: 17 x 8=136
- CCDs: 2780 x 2150 pixels
- 120´´/s  0.86s per CCD
Pixels:
- size: 9 x 27 m2 (37 x 111 mas)
- read in TDI mode
Broad-band photometry:
- 4 band (chromatic correction)
On-board source detection
Requirements and constraints:
–
–
–
unbiased sky sampling (mag, colour, resolution, etc.)
no all-sky catalogue at GAIA resolution (0.1 arcsec) to V~20
cannot transmit entire sky at 0.1 arcsec resolution (telemetry limitations)
Solution: on-board detection and sampling
–
–
–
–
no input catalogue or observing programme (big effort for Hipparcos)
good detection efficiency to V~21 mag
maximum star density: ~ 3 million stars/deg2 (Baade’s Window)
reduces data rate from several Gbps to a few Mbps
Will therefore also detect:
–
–
–
–
supernovae: 105 expected
microlensing events: ~1000 photometric
variable stars (eclipsing binaries, Cepheids, etc)
Solar System objects, including near-Earth asteroids and KBOs
Sky scanning principle
55o to Sun
120 ´´/s
(3 hours)
Precession rate: 0.20 ´´/s
(76 days)
Spin axis:
Scan rate:
Continuously observing
Full sky coverage
Each position observed
67 times (on average) per
astrometric instrument
Scanning law
Observations over 5 months
Ecliptic co-ordinates
Astrometric accuracies
G (~V mag)
10
11
12
13
14
15
16
17
18
19
20
21
Parallax
4
4
4
5
7
11
17
27
45
80
160
500
Position
3
3
3
4
6
9
15
23
39
70
140
440
Annual proper motion
3
3
3
4
5
8
13
20
34
60
120
380
5-year
accuracies
in as
Derived from detailed analysis:
• image formation (polychromatic PSF)
• evaluation vs. spectral type/reddening
• comprehensive detector signal model
• sky background and image saturation
• attitude rate errors and sky scanning
• on-board detection probability
• on-ground location estimation
(centroid to 0.001 pixel in hardest case)
• error margin of 20 per cent included
• results folded with Galaxy model
Fraction of stars with given relative parallax
error vs. magnitude (towards Galactic poles)
CCD centroiding tests
Astrium contract (Sep 2000)
‘GAIA-mode’ operation
EEV CCD 42-10
13m pixels
Illumination: 240,000 eFrequencies:
TDI: 2.43 kHz
Readout: 90 kHz
Differential centroid errors:
rms = 0.0038 pixels
(1.2 theoretical limit)
1 as is a very small angle ...
• Earth-Sun system seen from 1 Mpc (by definition)
• the Earth seen from the Pleiades (100 pc)
• Baden-Württemberg seen from  Centauri (1.3 pc)
• a grain of rice seen on the Moon (380 000 km)
• a human hair observed in Kabul from Heidelberg (5000 km)
Astrometric reduction
•
Approximate single epoch astrometry (<<1´´) from star
mapper and GAIA orbit/attitude
•
Great circle scans  1D positions in two fields separated by a
well-known basic angle (monitored)
Object matching in different scans (e.g. GSC II method)
Full sphere reduction to determine 5 astrometric parameters
per star by a global iterative method (>100 measures)
Binary models fitted to systems with large residuals
GAIA observations of quasars (known and new) put the
astrometry on a quasi-inertial reference system
•
•
•
•
GAIA spectrophotometry and radial velocities
• High resolution spectra for:
- 3rd component of space motion
- perspective acceleration
- stellar abundances, rotation velocities
• Medium band photometer for:
- classification of all objects
- physical parametrization of stars
Teff, log g, [Fe/H], [/H], A()
Radial Velocity Measurement Concept
F3 giant
S/N = 7 (single measurement)
S/N = 130 (summed over mission)
Radial Velocity and Photometric Instrument
• Mounted on same toroidal support
• Observes same scanning circles
• Independent star mappers
• Photometry for all stars (to 20 mag)
• Radial velocities to ~ 18 mag
1-10 km/s accuracy
• 0.5´´ spatial resolution
Spectral Sequences around Ca II
Effect of temperature: A to M stars
Effect of metal abundance in G stars
Photometric system and accuracies
• 11 medium band (in Spectro, 100 obs.)
F33
B45
B63
B82
• 4 broad band filters (in Astro, 2x67 obs.)
• SNR: 100-500 at V=15 (10-100 at V=20)
(end of mission)
GAIA and our Galaxy
10 as = 10% distances at 10 kpc
10 as/yr = 1 km/sec at 20 kpc
GAIA: Why a survey to 20 mag?
Population
Tracer
Mv
l
b
d
Av
V1
V2
T
1
1
1
mag
deg
deg
kpc
mag
mag
mag
km/s
as/yr
-
-
Bulge
gM
HB
MS
-1
+0.5
+4.5
Spiral arms
Cepheids
B-M supergiants
Perseus Arm (B)
Thin disk
0
0
1
<20
<20
-4
8
8
8
2-10
2-10
0-2
15
17
19
20
20
21
100
100
100
10
20
60
0.01
0.01
0.02
0.10
0.20
0.60
-4
-5
-2
All
All
140
<10
<10
<10
10
10
2
3-7
3-7
2-6
14
13
12
18
17
16
7
7
10
5
4
3
0.03
0.03
0.01
0.06
0.05
0.01
gK
GK
-1
-1
0
180
<15
<15
8
10
1-5
1-5
14
15
18
19
40
10
6
8
0.01
0.04
0.06
0.10
Disk warp
gM
-1
All
<20
10
1-5
15
19
10
8
0.04
0.10
Thick disk
Miras, gK
HB
Miras, gK
HB
-1
+0.5
-1
+0.5
0
0
180
180
<30
<30
<30
<30
8
8
20
20
2
2
2
2
15
15
15
15
19
19
21
19
50
50
30
30
10
20
25
60
0.01
0.02
0.08
0.20
0.10
0.20
0.65
1.50
Halo
gG
HB
-1
+0.5
All
All
<20
>20
8
30
2-3
0
13
13
21
21
100
100
10
35
0.01
0.05
0.10
1.40
Gravity, K-z
dK
dF8-dG2
+7-8
+5-6
All
All
All
All
2
2
0
0
12
12
20
20
20
20
60
20
0.01
0.01
0.16
0.05
Globular clusters
gK
+1
All
All
50
0
12
21
100
10
0.01
0.10
Satellite orbits
gM
-1
All
All
100
0
13
20
100
60
0.30
8.00
GAIA capabilities
Distances:
<0.1% for 700 000 stars
<1% for 21 million
Transverse motions:
<0.5% km/s for 44 million
<3 km/s for 210 million <10 km/s for 440 million
<10% for 220 million
Radial velocities to a few km/s complete to V=17-18
15-band photometry (250-950nm) at ~100 epochs over 4 years
Complete survey of the sky to V=20, observing 109 objects:
108 binary star systems (detected astrometrically; 105 orbits)
200 000 disk white dwarfs
50 000 brown dwarfs
50 000 planetary systems
106-107 resolved galaxies
105 quasars
105 extragalactic supernovae
105-106 Solar System objects (65 000 presently known)
Exosolar planets: Detection domains
No sin i ambiguity
in mass
determination
from astrometry
Expected astrometric planetary discoveries
• Monitoring of hundreds of thousands of stars to 200 pc for
1MJ planets with P < 10 years:
– complete census of all stellar types (P=2-9 years)
– actual masses, not just lower limits (m sin i)
– 20,000-30,000 planets expected to 150-200 pc
– e.g. 47 UMa: astrometric displacement 360 as
• Orbits for many (~ 5000) systems
• Masses down to 10 MEarth to 10 pc
General Relativity
Solar eclipse (image)
(light bending)
Light Bending at L2 by solar system bodies
Klioner (2002)
de Bruijne (2002)
Gravitational light deflection
de Bruijne (2002)
General Relativity
• Parametrized Post-Newtonian (PPN) formulation
–  = 1.0 for General Relativity (GR)
– alternative scalar-tensor theories deviate by 10-5- 10-7
• GAIA will measure  to 510-7 from positional displacement at large
angles from the Sun
–  currently known to 10-5
– GAIA tests GR at 10-100 times lower mass than presently
– effect of Sun: 4 mas at 90o; Jovian limb: 17 mas; Earth: 40 as
• Microlensing: photometric (~1000) and astrometric (few) events
Galaxies, quasars, and the reference frame
•
•
•
•
Parallax distances, orbits, and internal dynamics of nearby galaxies
Galaxy survey (106-107 resolved at 0.1´´ in four bands, 0.5´´ in 11 bands)
~500,000 quasars: kinematic and photometric detection
~100,000 supernovae
• Galactocentric acceleration: 0.2 nm/s2  (aberration) = 4 as/yr
• Globally accurate reference frame to ~0.4 as/yr
Schedule
2000
2004
2008
2012
2016
2020
Acceptance
Technology Development
Design, Build, Test
Launch
Observations
Analysis
Catalogue
Organisation of scientific work
GAIA Science Team
(12 people)
Satellite/Payload
Specific Objects
Data Processing
Error Budget
Multiple Stars
Data Base
Focal Plane/Detection
Planetary Systems
Simulations
Photometry
Variable Stars
Imaging
Radial Velocity
Solar System Objects
Classification
Calibration
Relativistic Model
Sampling/Telemetry
Science Alerts
Working groups: about 150 European ‘core’ and ‘associate’ members
GAIA Science Team (GST)
Frederic Arenou (Meudon)
Coryn Bailer-Jones (MPIA, Heidelberg)
Ulrich Bastian (ARI, Heidelberg)
Erik Hoeg (Copenhagen)
Andrew Holland (Leicester)
Carme Jordi (Barcelona)
David Katz (Meudon)
Maria Lattanzi (Torino)
Lennart Lindegren (Lund)
Xavier Luri (Barcelona)
Francois Mignard (Nice)
Michael Perryman (Project Scientist, ESA)
Current GAIA activities
ESA/industrial:
•
•
•
•
•
•
Phased array antenna (Alcatel)
High stability optical bench (Astrium)
Telemetry budget and compression algorithms (ESA)
FEEPs: will be based on SMART-2 activities (ESA + industry)
Proof of concept data reduction system (Barcelona + GMV)
New important industrial study contracts (CCD and focal plane study,
mirrors) are on hold due to internal ESA SPC/IPC conflict
Scientific community (working groups):
•
•
•
•
•
On-board detection algorithms
Detailed specification of radial velocity instrument
Definition of optimal photometric system
Simulations of data stream
Development of object classification and physical parametrization methods
Data processing demonstration (GDAAS)
•
•
•
•
•
•
under development since mid-2000 (GMV/UB/CESCA)
sky divided into hierarchical triangular mesh (level 6)
presently: 8 nodes, 4 processors per node, 0.5 Tbyte disk
telemetry ingestion, object matching, sphere iteration
iterative processing for 1 million stars (final results April 2002)
platform for further development/experimentation
Database
Processing
1
1
Database
Processing
Master
N
N
Special
Processing
Object classification/physical parametrization
• classification as star, galaxy, quasar, supernovae, solar system objects etc.
• determination of physical parameters:
- Teff, logg, [Fe/H], [/H], A(), Vrot, Vrad, activity etc.
• combination with parallax to determine stellar:
- luminosity, radius, (mass, age)
• use all available data (photometric, spectroscopic, astrometric)
• must be able to cope with:
- unresolved binaries (help from astrometry)
- photometric variability (can exploit, e.g. Cepheids, RR Lyrae)
- missing and censored data (unbiased: not a ‘pre-cleaned’ data set)
• multidimensional iterative methods:
- cluster analysis, k-nn, neural networks, interpolation methods
• required for astrometric reduction (identification of quasars, variables etc.)
 produce detailed classification catalogue of all 109 objects
Recent developments
Oct. 2000:
GAIA approved by SPC for launch by 2012
Nov. 2001:
Ministerial meeting reduces science budget
by 435 MEuro over 2002-2006 (20% reduction)
Nov. 2001:
ESA+Astrium start to identify cost savings
Dec. 2001:
SPC requests review of whole ESA science program
April 2002:
AWG subgroup (Rix, Aerts, Ward) reports on GAIA
to AWG; (AWG to SSAC to SPC)
April 2002:
Astrium presents revised GAIA design to GST
May 2002:
ESA/Astrium deliver final report to SPC
June 2002:
SPC decide on future science program
GAIA cost saving measures (ongoing)
Substantial savings possible if released from ESA constraints:
1.
2.
3.
re-use of satellite subsystem designs from other missions
cheaper contract competition mechanism
Soyuz-Fregat launch instead of Ariane 5 (110  40 MEuro)
- smaller mirrors in along-scan direction, accommodated
by increased across-scan dimension, field-of-view size...
Other possible cost savings from:
•
•
•
•
•
smaller solar array/sunshield by reducing solar aspect angle
(accommodate for lost astrometric precision in optics)
C-SiC optical bench
unification of pixel scales
field superposition (as in Hipparcos)
smaller ESA project team
Cost reduction from 570 to 400-450 MEuro possible
without any reduction in accuracies or scientific goals
Main performances and capabilities
Accuracies:
–
–
–
–
4 as at V=10
10 as at V=15 200 as at V=20
radial velocities to few km/s complete to V=17-18
10 as  distances to 1% at 1 kpc or 10% at 10 kpc (V=15)
10 as/yr at 20 kpc  1 km/s
Capabilities:
– sky survey in four bands at ~0.1 arcsec spatial resolution to V=20
– 15 band multi-epoch photometry to V=20
– dense quasar link to inertial reference frame
 every star observed in the Galaxy and Local Group will be seen to
move
 GAIA will quantify a 6-D phase space for over 300 million stars
and a 5-D phase-space for over 109 stars
GAIA and our Galaxy
10 as = 10% distances at 10 kpc
10 as/yr = 1 km/sec at 20 kpc
Perryman et al. (1997)
Hyades
60,000 years
Hyades (animation)
core radius  3 pc
Aldebaran
(non-member)
direction
of motion
Gravitational light deflection
de Bruijne (2002)
GAIA stands for ...
Global Astrometric Interferometer for Astrophysics
Galactic Astrophysics through Imaging and Astrometry
General Astrometric Instrument for Astronomy
Great Accuracy In Astrometry
Great Advances In Astrophysics