GaiaUnravelling the chemical and dynamical history of our galaxy

C. Cacciari - SAIt 2008, Teramo

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

Satellite and System ESA-only mission Launch date: end 2011 Lifetime: 5 years (+2?) Launcher: SoyuzFregat, from Kourou Orbit: L2 (1.5 million km opposite the Sun) Ground station: Cebreros (& New Norcia) Downlink rate: 48 Mbps Mass: 2030 kg (payload 690 kg) Power: 1720 W (payload 830 W) Cost: about 500 MEuFigures courtesy EADS-Astrium

Payload and TelescopeTwo SiC primary mirrors1.45 0.50 m2 at 106.5SiC toroidalstructure(optical bench)Basic anglemonitoring systemCombinedfocal plane(CCDs)Rotation axis (6 h)Figure courtesy EADS-AstriumSuperposition of two Fields of View (FoV)

Sky Scanning PrincipleSpin 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 45oFigure courtesy Karen OFlaherty

Sky Scanning PrincipleFigure courtesy Karen OFlahertyEcliptic coordinates Ecliptic coordinates Galactic coordinates End-of mission End of mission (5 yr) average (maximum) number of transits: about 80 (240)

Focal PlaneStar motion in 10 sTotal field: - active area: 0.75 deg2 - CCDs: 14 + 62 + 14 + 12 - each CCD: 4500x1966 px (TDI) - pixel size = 10 m x 30 m = 59 mas x 177 masAstrometric Field CCDsBlue Photometer CCDsSky Mapper CCDs104.26cmRed Photometer CCDsRadial-Velocity Spectrometer CCDsBasic Angle MonitorWave Front SensorBasic Angle MonitorWave Front SensorSky 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 CCDs42.35cmFigure courtesy Alex Shortalong-scan

Data Reduction Principles1. 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

On-board object detectionRequirements: unbiased sky sampling (mag, colour, resolution)no observing programmeall-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 maglow false-detection rate, even at high star densities

Gaia characteristics Astrometry (V < 20):completeness to 20 mag (on-board detection) 109 starsaccuracy: 7 as at V < 12, 20 as at V=15, 300 as at V=20 cf. Hipparcos: 1 mas at 9 magscanning satellite, two viewing directions global accuracy, with optimal use of observing timeprinciples: 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 Vallenaris talk) Teff ~ 200 K, log g & [Fe/H] to ~ 0.2 dex, extinction

Radial velocity (V < 1617):slitless spectroscopy on Ca triplet (847874 nm), R ~ 10,000 third component of space motion, perspective acceleration dynamics, population studies, binaries spectra: chemistry, rotation

Comments on astrometric accuracyMassive leap from Hipparcos to Gaia:accuracy: 2 orders of magnitude (1 mas to 7 as)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, multiplexingimproved 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

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

Distances as a function of Mv (V)

/

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

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 theoriesa 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 numberssupport to developments such as JWST, etc.

and beyonddefinitive 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 astrometricmicrolensing structure fundamental quantities to unprecedented accuracy: to 10-7 (10-5 present)

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/SMCPhysical properties, for example: clean HertzsprungRussell diagrams throughout the Galaxy solar neighbourhood mass function and luminosity functione.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

The distance scale: local calibrators Hipparcos

RR Lyrae stars in the field - RR Lyr

= 7.75 0.05 only RRL variable star with ``decent (d~260-290 pc)

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

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

Mv = 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 Mv = 0.02-0.05 mag

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

RR Lyraes in globular clusters

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

Metal-poor Sub Dwarfs as far as Vlim~15

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

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

Age determination: e.g. M3 Mod ~ 15.0 d ~ 10 kpc ~ 0.10 mas RGB & HB stars: V ~ 12.5 15 () ~ 0.01 mas individuallywith 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)

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)

Photometry Measurement Concept (1/2)Figures courtesy EADS-AstriumBlue photometer:330680 nm

Red photometer:6401050 nm

Photometry Measurement Concept (2/2)Figures courtesy Anthony BrownRP spectrum of M dwarf (V=17.3)Red box: data sent to groundWhite contour: sky-background levelColour coding: signal intensity

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

Radial Velocity Measurement Concept (1/2)Figures courtesy EADS-AstriumSpectroscopy:847874 nm(resolution 11,500)

Radial Velocity Measurement Concept (2/2) to all sources up to V < 1617RVS 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 viewRVS spectrographCCD detectorsFigures courtesy David Katz

Scientific OrganisationGaia 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 meetingsgrowing archive of scientific reports (Livelink)advance of simulations, algorithms, accuracy models, pipeline, etc.

Data distribution policy:final catalogue ~201920intermediate catalogues as appropriatescience alerts data released immediatelyno proprietary data rights

Ingestion, preprocessing,data base + versions, astrometric iterative solutionESAC (+ Barcelona + OATo)Object processing+ ClassificationCNES, ToulousePhotometryCambridge (IOA-C)+ VariabilityGeneva (ISDC)SpectroscopicprocessingCNES, ToulouseOverall system architectureESACData simulationsBarcelonaFrom ground stationCommunity accessData Processing Concept (simplified)

DPAC structureCU9:Catalogue AccessTo be activated

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

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.)

More information on

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

http://www.to.astro.ithttp://www.bo.astro.it

Thank you !

Status and SchedulePrime contractor: EADS-Astriumimplementation phase started early 2006

Main activities and challenges:CCDs and FPA (including PEM electronics)SiC primary mirrorhigh-stability optical benchpayload data handling electronicsphased-array antennamicro-propulsionscientific calibration of CCD radiation-damage effects

Schedule:no major identified uncertainties to affect cost or launch schedulelaunch in 2011technology/science window: 201012

ScheduleCatalogue200020042008201220162020ESA acceptanceTechnology DevelopmentDesign, Build, TestLaunchObservationsData AnalysisEarly DataConcept & Technology Study (ESA)Re-assessment:Ariane-5 SoyuzCruise to L2

Exo-Planets: Expected DiscoveriesAstrometric survey:monitoring of hundreds of thousands of FGK stars to ~200 pcdetection limits: ~1MJ and P < 10 yearscomplete census of all stellar types, P = 29 yearsmasses, rather than lower limits (m sin i)multiple systems measurable, giving relative inclinations

Results expected:1020,000 exo-planets (~10 per day)displacement for 47 UMa = 360 asorbits for ~5000 systemsmasses down to 10 MEarth to 10 pc

Photometric transits: ~5000? Figure courtesy Franois Mignard

Studies of the Solar SystemAsteroids etc.:deep and uniform (20 mag) detection of all moving objects105106 new objects expected (340,000 presently)taxonomy/mineralogical composition versus heliocentric distancediameters for ~1000, masses for ~100orbits: 30 times better than present, even after 100 yearsTrojan companions of Mars, Earth and VenusKuiper 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: 260590 m at 1 AU, depending on albedo

Light Bending in Solar SystemMovie courtesy Jos de BruijneLight bending in microarcsec, after subtraction of the much larger effect by the Sun

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 arcsec at V = 10

10-25 arcsec at V = 15

300 arcsec 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

Numbers quoting today refer to MPC statistics from 10 September 2006