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GaiaUnravelling the chemical and dynamical history

of our galaxy

C. Cacciari - SAIt 2008, Teramo

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GAIA = all-sky astrometric survey follow up of Hipparcos (+ photometry + radial velocities)

A brief history of astrometric accuracy

Comparable astrometric accuracy will be obtained from other future space-based & ground-based facilities (e.g. EELT etc.), but on pencil-beam areas of the sky

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Satellite and System

• ESA-only mission• Launch date: end 2011• Lifetime: 5 years (+2?) • Launcher: Soyuz–Fregat, from Kourou• Orbit: L2 (1.5 million km opposite the Sun)• Ground station: Cebreros (& New Norcia)• Downlink rate: 4–8 Mbps

• Mass: 2030 kg (payload 690 kg)

• Power: 1720 W (payload 830 W)• Cost: about 500 MEu

Figures courtesy EADS-Astrium

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Payload and Telescope

Two SiC primary mirrors1.45 0.50 m2 at 106.5°

SiC toroidalstructure

(optical bench)

Basic anglemonitoring system

Combinedfocal plane

(CCDs)

Rotation axis (6 h)

Figure courtesy EADS-Astrium

Superposition of two Fields of View

(FoV)

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Sky Scanning Principle

Spin axis 45o to SunScan rate: 60 arcsec/sSpin period: 6 hours

less transits per FoV than Hipparcos (2.13 hr spin period) higher spatial resolution in focal plane

45o

Figure courtesy Karen O’Flaherty

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Sky Scanning Principle

Figure courtesy Karen O’Flaherty

Ecliptic coordinates Ecliptic coordinates Galactic coordinates

End-of mission End of mission (5 yr) average (maximum) number of transits: about 80 (240)

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Focal Plane

Star motion in 10 s

Total field: - active area: 0.75 deg2

- CCDs: 14 + 62 + 14 + 12 - each CCD: 4500x1966 px (TDI) - pixel size = 10 µm x 30 µm

= 59 mas x 177 mas

Astrometric Field CCDs

Blu

e Ph

oto

meter C

CD

s

Sky Mapper CCDs

104.26cm

Red

Ph

oto

meter C

CD

s Radial-Velocity Spectrometer

CCDs

Basic Angle

Monitor

Wave Front

Sensor

Basic Angle

Monitor

Wave Front

Sensor

Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events - FoV discriminationAstrometry: - total detection noise: 6 e-

Photometry: - spectro-photometer - blue and red CCDsSpectroscopy: - high-resolution spectra - red CCDs

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.35

cmFigure courtesy Alex Short

along-scan

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Data Reduction Principles

Sky scans(highest accuracy

along scan)

Scan width: 0.7°

1. Object matching in successive scans2. Attitude and calibrations are updated3. Objects positions etc. are solved4. Higher terms are solved5. More scans are added6. System is iterated (Global Iterative Solution)Figure courtesy Michael Perryman

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On-board object detection

Requirements: unbiased sky sampling (mag, colour, resolution) no observing programme all-sky catalogue at Gaia resolution (0.1 arcsec) to V~20

On-board detection: initial Gaia Source List GSC-II (first ~ 6 months) subsequent self-calibration (Global Iterative Solution) good detection efficiency to V~21 mag low false-detection rate, even at high star densities

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Gaia characteristics

Astrometry (V < 20): completeness to 20 mag (on-board detection) 109 stars accuracy: 7 μas at V < 12, 20 μas at V=15, 300 μas at V=20 cf. Hipparcos: 1 mas at 9 mag scanning satellite, two viewing directions

global accuracy, with optimal use of observing time principles: global astrometric reduction (as for Hipparcos)

Photometry (V < 20): integrated (G-band) and BP(330-680 nm)-RP(640-1050 nm) colours dispersed BP/RP images (low-dispersion photometry, R ~ 20-300) astrophysical diagnostics (see Vallenari’s talk) Teff ~ 200 K, log g & [Fe/H] to ~ 0.2 dex, extinction

Radial velocity (V < 16–17):

slitless spectroscopy on Ca triplet (847–874 nm), R ~ 10,000

third component of space motion, perspective acceleration

dynamics, population studies, binaries

spectra: chemistry, rotation

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Comments on astrometric accuracy

Massive leap from Hipparcos to Gaia: accuracy: 2 orders of magnitude (1 mas to 7 μas) limiting sensitivity: > 3 orders of magnitude (~12 mag to 20 mag) number of stars: 4 orders of magnitude (105 to 109)

Measurement principles identical: two viewing directions (absolute parallaxes) sky scanning over 5 (+2?) years parallaxes and proper motions

Instrument improvement: larger (x8) primary mirror: 0.3 0.3 m2 1.45 0.50 m2, D-(3/2)

improved detector (IDT CCD): QE, bandpass, multiplexing improved spatial resolution better treatment of crowding

Control of all associated error sources: aberrations, chromaticity, solar system ephemerides attitude control (basic angle stability) homogeneous distribution (the two FoV) of stars contributing to GIS use of QSOs for attitude recontruction and absolute reference frame

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Astrometric accuracy: the Pleiades

π = 7.69 mas (Kharchenko et al. 2005 ) various methods π = 7.59 ± 0.14 mas (Pinsonneault et al. 1998) MS fitting π = 8.18 ± 0.13 mas (Van Leeuwen 2007) (mod=5.44 ±0.03, 122pc) new red. Hipparcos dataπ = 7.49 ± 0.07 mas (Soderblom et al. 2005) from 3 HST parallaxes in inner halo

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Distances as a function of Mv (V) σπ/π N(Hip) N(Gaia) Mv V d(pc)

< 0.1 % 0 0.7 106 0 7 270 5 12 270 10 15 100

15 17 25

< 1 % 188 21 106 -5 7 2 700 0 12 2 700 5 15 1 000 10 17 270

15 20 100 < 10 % ~ 22 103 ~ 22 107 -5 12 27 000 0 15 10 000 5 17 2 700 10 20 1 000

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One billion stars in 3-d will provide …

in our Galaxy … the distance and velocity distributions of all stellar populations the spatial and dynamical structure of the disk and halo its formation and chemical history (accretion/interaction events) a rigorous framework for stellar structure and evolution theories a large-scale survey of extra-solar planets (up to ~20,000) a large-scale survey of Solar System bodies (~100,000) rare stellar types and rapid evolutionary phases in large numbers support to developments such as JWST, etc.

… and beyond definitive and robust definition of the cosmic distance scale rapid reaction alerts for supernovae and burst sources (~20,000) QSO detection (~ 500,000 in 20,000 deg2 of the sky) redshifts gravitational lensing events: ~1000 photometric; ~100 astrometric microlensing structure fundamental quantities to unprecedented accuracy: to 10-7 (10-5 present)

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Stellar Astrophysics Comprehensive luminosity calibration, for example:

distances to 1% for ~20 million stars to 2.5 kpc

distances to 10% for ~200 million stars to 25 kpc

parallax calibration of all primary distance indicators

e.g. Cepheids and RR Lyrae to LMC/SMC

Physical properties, for example: clean Hertzsprung–Russell diagrams throughout the Galaxy

solar neighbourhood mass function and luminosity function

e.g. white dwarfs (~200,000) and brown dwarfs (~50,000)

initial mass and luminosity functions in star forming regions

luminosity function for pre main-sequence stars

detection and dating of all spectral types and Galactic populations

detection and characterisation of variability for all spectral types

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The distance scale: local calibrators

Hipparcos

RR Lyrae stars in the field - RR Lyr

<V> = 7.75 ± 0.05 – only RRL variable star with ``decent’’ π (d~260-290 pc)

π = 3.46 ± 0.64 mas mod=7.30 mag(new Hipparcos data, Van Leeuwen 2007)

π = 3.82 ± 0.20 mas mod = 7.09 mag (HST, Benedict et al. 2002)

ΔMv = 0.2 mag?

Metal-poor Sub Dwarfs fit with GC mainsequences Only ~ 30 Sub Dwarfs available with MV = 5.0 – 7.5 between ~ 6 and 80 pc Vlim ~ 10

Gaia

RR Lyrae stars in the field – no RR Lyr

126 RR Lyraes with < V > = 10 to 12.5 (750-2500 pc) (Fernley et al. 1998) from Hipparcos data ΔMv = ± 0.02-0.05 mag

all individual RR Lyrae stars within 3 kpc will have σ(π)/π < 1%

RR Lyraes in globular clusters

mean distance to better than 1% for 110 globular clusters (up to ≥ 30 kpc) accurate MV (ZAHB) Mv = α + β[Fe/H]

Metal-poor Sub Dwarfs as far as Vlim~15

a factor 10 (1000) in distance (volume) several thousand expected

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The distance scale: Cepheids in the MW & LMC/SMC

The MW

• Hipparcos: about 250 Cepheids with parallax & photometry (9 with HST parallax)

PLC(met) calibration mod (LMC) = 18.48 ± 0.03 mag (no metallicity correction)

• Gaia: distances to all Galactic Cepheids to < 4% (most to < 1%)

The Magellanic Clouds • no Hipparcos• Gaia: Cepheids in the Magellanic Clouds with distances to 10-30%

Along with MW data PLC(met) relation

■ metallicity dependence ■ zero-point ■ universality of the relation

application to galaxies H0

Cepheids: main PopI bridge between the MW & LMC to spiral & irregular galaxies first direct calibration of the cosmological distance scale with Hipparcos in the MW, with Gaia in the LMC/SMC

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Age determination: e.g. M3

• Mod ~ 15.0 d ~ 10 kpc π ~ 0.10 mas • RGB & HB stars: V ~ 12.5 – 15 σ(π) ~ ± 0.01 mas individually• with only 1000 such stars the distance would be known to about 0.3% … ... unprecedented accuracy - no need of calibrators

• Error budget on absolute age determination via the TO: Logt9 ~ -0.41 + 0.37 MV(TO) – 0.43Y – 0.13[Fe/H] (Renzini 1993)

Input quantiy (IQ) σ(t)/t σ(IQ) σ(t)/t %

VTO 0.85σVTO ± 0.10

± 0.01

8.5

0.9

mod 0.85σ(mod) ± 0.15

± 0.007

12.8

0.6

AV (AK ?) 2.64σ(AV) ± 0.03 7.9

Helium (Y) 0.99σ(Y) ± 0.02 2.0

[M/H] 0.30σ[M/H] ± 0.10 3.0

Max error comes from distance modulus & V(TO): from table values ~ 18% i.e. 2.2 Gyr

If distance were known to ±0.3% and V(TO) to ±0.01 mag age could be known to ~ 9% i.e. 1.1 Gyr

Further improvement on reddening & chemical abundance e.g. from gb surveys or Gaia APs age could be known to ≤ 5% or better (errors on theoretical models not included)

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Photometry Measurement Concept (1/2)

Figures courtesy EADS-Astrium

Blue photometer:330–680 nm

Red photometer:640–1050 nm

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Photometry Measurement Concept (2/2)

Figures courtesy Anthony Brown

Blue photometer

300

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700

0 5 10 15 20 25 30 35

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wav

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) . Red photometer

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) .

RP spectrum of M dwarf (V=17.3)Red box: data sent to ground

White contour: sky-background levelColour coding: signal intensity

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Photometric accuracy

• External calibration From about 1 to a few %,

depending on accuracy of SPSS SEDs magnitude specific spectral range for BP/RP spectra

• Astrophysical parameters From BP/RP dispersed images

(low res SEDs) one can derive Teff ~ 200 K log g & [Fe/H] to 0.2 dex extinction

► complete characterisation of all stellar populations

► detailed reddening map

(see Vallenari’s talk)

G σ(mmag)

G

σ(mmag)

GBP

σ(mmag)

GRP

13.0 2.5 2.5 2.4

14.0 3.0 4.1 4.0

15.0 4.8 7.1 6.7

16.0 7.6 12.9 12.3

17.0 12.3 26.3 24.7

18.0 20.3 58.6 54.7

19.0 35.1 139.0 129.4

20.0 66.2 340.6 316.8

Internal calibration(Jordi et al 2007, GAIA-C5-TN-UB-CJ-042)

22Figures courtesy EADS-Astrium

Spectroscopy:847–874 nm

(resolution 11,500)

Radial Velocity Measurement Concept (1/2)

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Radial Velocity Measurement Concept (2/2) to all sources up to V < 16–17

RVS spectra of F3 giant (V=16)S/N = 7 (single measurement)S/N = 130 over mission (~350 transits)

NOTE: average (max) expected transits over mission ~ 80 (260) S/N ~ 60 (110)

Field of view RVS spectrograph CCD detectors

Figures courtesy David Katz

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Scientific Organisation

• Gaia Science Team (GST): – 8 members + ESA Project Scientist (Timo Prusti)

• Scientific community:– organised in Data Processing and Analysis Consortium (DPAC)– ~270 scientists active at some level

• Community is active and productive:– regular science team/DPAC meetings– growing archive of scientific reports (Livelink)– advance of simulations, algorithms, accuracy models, pipeline, etc.

• Data distribution policy:– final catalogue ~2019–20– intermediate catalogues as appropriate– science alerts data released immediately– no proprietary data rights

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Ingestion, preprocessing,data base + versions,

astrometric iterative solutionESAC (+ Barcelona + OATo)

Object processing+ Classification

CNES, Toulouse

PhotometryCambridge (IOA-C)

+ VariabilityGeneva (ISDC)

Spectroscopicprocessing

CNES, Toulouse

Overall system architecture

ESACData simulations

Barcelona

From ground station

Community access

Data Processing Concept (simplified)

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DPAC structure

CU5:Photometric Processingvan Leeuwen

(Brown, Cacciari, De Angeli, Richards

CU6:Spectroscopic ProcessingKatz/Cropper

(+ steering committee)

CU7:Variability ProcessingEyer/Evans/Dubath

CU8:Astrophysical ParametersBailer-Jones/Thevenin

CU9:Catalogue AccessTo be activated

CU1: System Architecture O’Mullane

(Lammers/Levoir)

CU2:Data SimulationsLuri

(Babusiaux/Mignard)

CU4:Object ProcessingPourbaix/Tanga

(Arenou, Cellino, Ducourant Frezouls)

CU3: Core ProcessingBastian

(Lattanzi/Torra)

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The Italian contribution - I (from the response to the ASI Gaia RfQ)

Torino (OA, Uni, Poli) + Trieste: ~ 20 people, CU2/3/4 - simulations, astrometry (core & object)

Padova (OA, Uni): ~ 10 people CU8/5 – astrophysical parameters, photometric calibration

Bologna (OA): ~ 12 people CU5/7 – absolute photometric calibration, variability

Roma+Teramo (OA, Uni): ~ 12 people CU5/7 – flux extraction in crowded fields, variability

Napoli (OA): ~ 9 people CU7/8 - variability, astrophysical parameters

Catania (OA, Uni): ~ 9 people CU2/7/8 - simulations, variability, astrophysical parameters

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The Italian contribution – main activities DPC (TO) astrometric verification for a subset of bright stars V ≤ 15 ( ~30 million stars) bright star treatment for astrometric accuracy monitoring of Basic Angle (astrometric accuracy) simulations astrometric and spectro-photometric payload national facility with final end-of-mission database

Astrophysical parameters (PD, NA) stellar libraries for complete characterisation, special objects

Spectro- Photometry flux extraxtion in crowded conditions (RM-TE see Posters 11, 12) absolute flux calibration model (BO/PD) observing campaign for SPSS (BO)

Variability analysis (BO/RM/TE/NA/CT) impact on astrometric accuracy variability characterisation, special objects

General Relativity model (TO/PD)

Others (interstellar reddening model, Solar System objects, extra-solar planets, etc.)

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More information on

http://www.rssd.esa.int/Gaia

http://www.to.astro.it

http://www.bo.astro.it

Thank you !

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Status and Schedule

• Prime contractor: EADS-Astrium– implementation phase started early 2006

• Main activities and challenges:– CCDs and FPA (including PEM electronics)– SiC primary mirror– high-stability optical bench– payload data handling electronics– phased-array antenna– micro-propulsion– scientific calibration of CCD radiation-damage effects

• Schedule:– no major identified uncertainties to affect cost or launch schedule– launch in 2011– technology/science ‘window’: 2010–12

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Schedule

Catalogue

2000 2004 2008 2012 2016 2020

ESA acceptance

Technology Development

Design, Build, Test

Launch

Observations

Data Analysis

Early Data

Concept & Technology Study (ESA)

Re-assessment:Ariane-5 Soyuz

Cruise to L2

320

0.2

0.4

0.6

0.8

1

1.2

cos (")

1/01/00

1/01/01

1/01/02

1/01/03

1/07/00

1/07/01

1/07/02(")

0 0.2 0.4 0.6 0.8 1.0

Planète : = 100 mas P = 18 mois

Exo-Planets: Expected Discoveries

• Astrometric survey:– monitoring of hundreds of thousands of FGK stars to ~200 pc

– detection limits: ~1MJ and P < 10 years

– complete census of all stellar types, P = 2–9 years

– masses, rather than lower limits (m sin i)

– multiple systems measurable, giving relative inclinations

• Results expected:– 10–20,000 exo-planets (~10 per day)

– displacement for 47 UMa = 360 μas

– orbits for ~5000 systems

– masses down to 10 MEarth to 10 pc

• Photometric transits: ~5000?

Figure courtesy François Mignard

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• Asteroids etc.:– deep and uniform (20 mag) detection of all moving objects

– 105–106 new objects expected (340,000 presently)

– taxonomy/mineralogical composition versus heliocentric distance

– diameters for ~1000, masses for ~100

– orbits: 30 times better than present, even after 100 years

– Trojan companions of Mars, Earth and Venus

– Kuiper Belt objects: ~300 to 20 mag (binarity, Plutinos)

• Near-Earth Objects: – Amors, Apollos and Atens (1775, 2020, 336 known today) – ~1600 Earth-crossers >1 km predicted (100 currently known)– detection limit: 260–590 m at 1 AU, depending on albedo

Studies of the Solar System

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Light Bending in Solar System

Movie courtesy Jos de Bruijne

Light bending in microarcsec, after subtraction of the much larger effect by the Sun

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Gaia: complete, faint, accurate Hipparcos Gaia

Magnitude limit 12 20 mag Completeness 7.3 – 9.0 20 mag Bright limit 0 6 mag

Number of objects 120 000 26 million to V = 15 250 million to V = 18 1000 million to V = 20 Effective distance limit

1 kpc 50 kpc Quasars None 5 x 105

Galaxies None 106 – 107 Parallax Accuracy 1 milliarcsec 7 µarcsec at V = 10 10-25 µarcsec at V = 15 300 µarcsec at V = 20 Photometry photometry

2-colour (B and V) Low-res. spectra to V = 20 Abs. Accuracy ~ 0.10 mag 1-3% at V < 16

Rel. Accuracy ~ 0.01 – 0.10 mag 1-10 mmag Radial velocity None 15 km/s to V = 16-17 Observing programme

Pre-selected Complete and unbiased