1. 1 Gaia Unravelling the chemical and dynamical history of our galaxy C. Cacciari - SAIt 2008, Teramo

2. 2 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

3. 3 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

4. 4 Payload and Telescope Two SiC primary mirrors 1.45  0.50 m 2 at 106.5° SiC toroidal structure (optical bench) Basic angle monitoring system Combined focal plane (CCDs) Rotation axis (6 h) Figure courtesy EADS-Astrium Superposition of two Fields of View (FoV)

5. 5 Sky Scanning Principle Spin axis 45 o to Sun Scan rate: 60 arcsec/s Spin period: 6 hours  less transits per FoV than Hipparcos (2.13 hr spin period)  higher spatial resolution in focal plane 45 o Figure courtesy Karen O’Flaherty

6. 6 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)

7. 7 Focal Plane Star motion in 10 s Total field: - active area: 0.75 deg 2 - 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 Blue Photometer CCDs Sky Mapper CCDs 104.26cm Red Photometer CCDs 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 discrimination Astrometry: - total detection noise: 6 e - Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs 42.35cm Figure courtesy Alex Short along-scan

8. 8 Data Reduction Principles Sky scans (highest accuracy along scan) Scan width: 0.7° 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 is iterated (Global Iterative Solution) Figure courtesy Michael Perryman

9. 9 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

10. 10 Gaia characteristics Astrometry (V < 20): completeness to 20 mag (on-board detection)  10 9 stars accuracy: 7 μ as at V < 12, 20 μ as at V=15, 300 μ as 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)   T eff ~ 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

11. 11 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 (10 5 to 10 9 ) 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 m 2  1.45  0.50 m 2,   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

12. 12 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 data π = 7.49 ± 0.07 mas (Soderblom et al. 2005) from 3 HST parallaxes in inner halo

13. 13 Distances as a function of Mv (V)

14. 14 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 deg 2 of the sky)  redshifts  gravitational lensing events: ~1000 photometric; ~100 astrometric  microlensing structure  fundamental quantities to unprecedented accuracy:  to 10 -7 (10 -5 present)

15. 15 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

16. 16 The distance scale: local calibrators Hipparcos RR Lyrae stars in the field - RR Lyr = 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 main sequences Only ~ 30 Sub Dwarfs available with M V = 5.0 – 7.5 between ~ 6 and 80 pc V lim ~ 10 Gaia RR Lyrae stars in the field – no RR Lyr 126 RR Lyraes with = 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 M V (ZAHB)  Mv = α + β[Fe/H] Metal-poor Sub Dwarfs as far as V lim ~15  a factor 10 (1000) in distance (volume)  several thousand expected

17. 17 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  H 0 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

18. 18 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: Logt 9 ~ -0.41 + 0.37 M V (TO) – 0.43Y – 0.13[Fe/H] (Renzini 1993) Input quantiy (IQ) σ(t)/t σ(IQ)σ(t)/t % V TO 0.85σV TO ± 0.10 ± 0.01 8.5 0.9 mod0.85σ(mod)± 0.15 ± 0.007 12.8 0.6 A V (AK ?)2.64σ(A V )± 0.037.9 Helium (Y)0.99σ(Y)± 0.022.0 [M/H]0.30σ[M/H]± 0.103.0 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)

19. 19 Photometry Measurement Concept (1/2) Figures courtesy EADS-Astrium Blue photometer: 330–680 nm Red photometer: 640–1050 nm

20. 20 Photometry Measurement Concept (2/2) Figures courtesy Anthony Brown RP spectrum of M dwarf (V=17.3) Red box: data sent to ground White contour: sky-background level Colour coding: signal intensity

21. 21 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   T eff ~ 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) G BP σ(mmag) G RP 13.02.5 2.4 14.03.04.14.0 15.04.87.16.7 16.07.612.912.3 17.012.326.324.7 18.020.358.654.7 19.035.1139.0129.4 20.066.2340.6316.8 Internal calibration (Jordi et al 2007, GAIA-C5-TN-UB-CJ-042)

22. 22 Figures courtesy EADS-Astrium Spectroscopy: 847–874 nm (resolution 11,500) Radial Velocity Measurement Concept (1/2)

23. 23 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

24. 24 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

25. 25 Ingestion, preprocessing, data base + versions, astrometric iterative solution ESAC (+ Barcelona + OATo) Object processing + Classification CNES, Toulouse Photometry Cambridge (IOA-C) + Variability Geneva (ISDC) Spectroscopic processing CNES, Toulouse Overall system architecture ESAC Data simulations Barcelona From ground station Community access Data Processing Concept (simplified)

26. 26 DPAC structure CU5:Photometric Processing van Leeuwen (Brown, Cacciari, De Angeli, Richards CU6:Spectroscopic Processing Katz/Cropper (+ steering committee) CU7:Variability Processing Eyer/Evans/Dubath CU8:Astrophysical Parameters Bailer-Jones/Thevenin CU9:Catalogue Access To be activated CU1: System Architecture O’Mullane (Lammers/Levoir) CU2:Data Simulations Luri (Babusiaux/Mignard) CU4:Object Processing Pourbaix/Tanga (Arenou, Cellino, Ducourant Frezouls) CU3: Core Processing Bastian (Lattanzi/Torra)

27. 27 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

28. 28 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.)

29. 29 More information on http://www.rssd.esa.int/Gaia http://www.to.astro.it http://www.bo.astro.it Thank you ! http://www.to.astro.it

30. 30 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

31. 31 Schedule Catalogue 2000 20042008 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

32. 32 Exo-Planets: Expected Discoveries Astrometric survey: –monitoring of hundreds of thousands of FGK stars to ~200 pc –detection limits: ~1M J 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 μ as –orbits for ~5000 systems –masses down to 10 M Earth to 10 pc Photometric transits: ~5000? Figure courtesy François Mignard

33. 33 Asteroids etc.: –deep and uniform (20 mag) detection of all moving objects –10 5 –10 6 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

34. 34 Light Bending in Solar System Movie courtesy Jos de Bruijne Light bending in microarcsec, after subtraction of the much larger effect by the Sun

35. 35 Gaia: complete, faint, accurate