GAIA Composition, Formation and Evolution

of our Galaxy

thanks to Michael Perryman, the GAIA ScienceTeam (present and past) and 200+ others

M83 image (with Sun marked)M83 (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. Measurement principles2. The GAIA satellite and mission3. Some science examples4. Schedule, organisation of work5. Current situation6. Summary

Some history…

1725: Stellar aberration (Bradley), confirming:– Earth’s motion through space– finite velocity of light– immensity of stellar distances

125 B.C.: Precession of the equinoxes (Hipparchus)

1717: First proper motions (Halley)

1783: Sun’s motion through space (Herschel)

1838-9: First parallaxes (Bessel/Henderson/Struve)

610 B.C.: Obliquity of the ecliptic (Anaximander)

1761/9: Transits of Venus across the Sun (various)– solar parallax

Principle of parallax measurement

Orbit about Sun Backgroundstars

Star of interest

parallax angle

Measurement Principle

Measurement principle: b

Global astrometry

basic angle

GAIA: complete, faint, accurate

Hipparcos GAIA

Magnitude limit 12 20-21 magCompleteness 7.3 – 9.0 ~20 magBright limit ~0 ~3-7 magNumber of objects 120 000 26 million to V = 15

250 million to V = 181000 million to V = 20

Effective distance limit 1 kpc 1 MpcQuasars None ~5

Galaxies None 106 - 107

Accuracy ~1 milliarcsec 4 arcsec at V = 10 10 arcsec at V = 15200 arcsec at V = 20

Broad bandphotometry

2-colour (B and V) 4-colour to V = 20Medium bandphotometry

None 11-colour to V = 20Radial velocity None 1-10 km/s to V = 16-17Observing programme Pre-selected 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 path1 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

Spin axis: 55o to SunScan rate: 120 ´´/s

(3 hours)Precession rate: 0.20 ´´/s (76 days)

Continuously observing

Full sky coverage

Each position observed67 times (on average) per astrometric instrument

Scanning law

Observations over 5 months Ecliptic co-ordinates

Astrometric accuracies

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)

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-yearaccuracies

in as

CCD centroiding tests

Astrium contract (Sep 2000)

‘GAIA-mode’ operationEEV CCD 42-1013m pixels

Illumination: 240,000 e-

Frequencies: 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 ...

• the Earth seen from the Pleiades (100 pc)

• Baden-Württemberg seen from Centauri (1.3 pc)

• a human hair observed in Kabul from Heidelberg (5000 km)

• Earth-Sun system seen from 1 Mpc (by definition)

• a grain of rice seen on the Moon (380 000 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 giantS/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.)

• 4 broad band filters (in Astro, 2x67 obs.)

• SNR: 100-500 at V=15 (10-100 at V=20)

(end of mission)

F33 B45

B63 B82

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

T1

11

mag deg deg kpc mag mag mag km/s as/yr - -

Bulge gM -1 0 <20 8 2-10 15 20 100 10 0.01 0.10

HB +0.5 0 <20 8 2-10 17 20 100 20 0.01 0.20

MS +4.5 1 -4 8 0-2 19 21 100 60 0.02 0.60

Spiral arms Cepheids -4 All <10 10 3-7 14 18 7 5 0.03 0.06

B-M supergiants -5 All <10 10 3-7 13 17 7 4 0.03 0.05

Perseus Arm (B) -2 140 <10 2 2-6 12 16 10 3 0.01 0.01

Thin disk gK -1 0 <15 8 1-5 14 18 40 6 0.01 0.06

GK -1 180 <15 10 1-5 15 19 10 8 0.04 0.10

Disk warp gM -1 All <20 10 1-5 15 19 10 8 0.04 0.10

Thick disk Miras, gK -1 0 <30 8 2 15 19 50 10 0.01 0.10

HB +0.5 0 <30 8 2 15 19 50 20 0.02 0.20

Miras, gK -1 180 <30 20 2 15 21 30 25 0.08 0.65

HB +0.5 180 <30 20 2 15 19 30 60 0.20 1.50

Halo gG -1 All <20 8 2-3 13 21 100 10 0.01 0.10

HB +0.5 All >20 30 0 13 21 100 35 0.05 1.40

Gravity, K-z dK +7-8 All All 2 0 12 20 20 60 0.01 0.16

dF8-dG2 +5-6 All All 2 0 12 20 20 20 0.01 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 <10% for 220 million

Transverse motions:

<0.5% km/s for 44 million <3 km/s for 210 million <10 km/s for 440 million

Radial velocities to a few km/s complete to V=17-1815-band photometry (250-950nm) at ~100 epochs over 4 yearsComplete 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 ambiguityin massdeterminationfrom 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

Solar eclipse (image)General Relativity

(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 510-7 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

Sam pling/Telem etry

Calibration

Radial Velocity

Photom etry

Focal P lane/Detection

Error Budget

Satellite/Payload

Solar System Objects

Variable Stars

Planetary System s

Multiple Stars

Specific Objects

Science Alerts

Relativistic Model

Classification

Im aging

Sim ulations

Data Base

Data Processing

GAIA Science Team(12 people)

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

Processing 1 Processing NSpecial

Processing

Master

Database 1 Database N

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

Nov. 2001: Ministerial meeting reduces science budget by 435 MEuro over 2002-2006 (20% reduction)

Nov. 2001: ESA+Astrium start to identify cost savings

Oct. 2000: GAIA approved by SPC for launch by 2012

Dec. 2001: SPC requests review of whole ESA science program

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

April 2002: AWG subgroup (Rix, Aerts, Ward) reports on GAIAto AWG; (AWG to SSAC to SPC)

GAIA cost saving measures (ongoing)

Substantial savings possible if released from ESA constraints:1. re-use of satellite subsystem designs from other missions2. cheaper contract competition mechanism3. Soyuz-Fregat launch instead of Ariane 5 (110 40 MEuro)

- smaller mirrors in along-scan direction, accommodatedby 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 starsand 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

Hyades (animation)Hyades

60,000 years

Aldebaran(non-member)

core radius 3 pc

directionof motion

Perryman et al. (1997)

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 Advances In Astrophysics

Great Accuracy In Astrometry