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Gaia Unravelling the chemical and dynamical history of our galaxy

Gaia Unravelling 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.

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Gaia Unravelling the chemical and dynamical history of our galaxy

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

  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. 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. Payload and Telescope Basic angle monitoring system Rotation axis (6 h) Two SiC primary mirrors 1.45  0.50 m2 at 106.5° SiC toroidal structure (optical bench) Combined focal plane (CCDs) Superposition of two Fields of View (FoV) Figure courtesy EADS-Astrium

  5. Sky Scanning Principle 45o Spin axis 45o 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 Figure courtesy Karen O’Flaherty

  6. Sky Scanning Principle Ecliptic coordinatesGalactic coordinates Ecliptic coordinates End of mission (5 yr) average (maximum) number of transits: about 80 (240) End-of mission Figure courtesy Karen O’Flaherty

  7. Figure courtesy Alex Short Focal Plane 104.26cm Wave Front Sensor Red Photometer CCDs Blue Photometer CCDs 42.35cm Wave Front Sensor Radial-Velocity Spectrometer CCDs Basic Angle Monitor Basic Angle Monitor Star motion in 10 s Sky Mapper CCDs Astrometric Field CCDs along-scan Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events - FoV discrimination Astrometry: - total detection noise: 6e- 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 Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs

  8. Scan width: 0.7° Sky scans (highest accuracy along scan) Data Reduction Principles 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. 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. Gaiacharacteristics • 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

  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 (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

  12. Astrometric accuracy: the Pleiades π = 7.69 mas (Kharchenko et al. 2005 )various methods π = 7.59 ± 0.14mas (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. Distances as a function of Mv (V)

  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 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)

  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. The distance scale: local calibrators Gaia RR Lyrae stars in the field – no RR Lyr 126 RR Lyraeswith < 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 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, VanLeeuwen 2007) π = 3.82 ± 0.20 mas  mod =7.09mag (HST, Benedict et al.2002)  ΔMv= 0.2 mag? Metal-poor Sub Dwarfs fit with GC main sequences Only ~30 Sub Dwarfsavailable with MV = 5.0 – 7.5 between ~ 6 and 80 pc Vlim ~ 10

  17. The distance scale: Cepheids in the MW & LMC/SMC Cepheids: main PopI bridge between the MW & LMC to spiral & irregular galaxies  first direct calibration of the cosmological distance scalewith Hipparcos in the MW, with Gaiain the 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

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

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

  21. Photometric accuracy Internal calibration (Jordi et al 2007, GAIA-C5-TN-UB-CJ-042) • 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)

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

  23. Radial Velocity Measurement Concept (2/2)to all sources up to V < 16–17 RVS spectrograph CCD detectors Field of view 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) Figures courtesy David Katz

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

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

  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 calibrationBologna (OA): ~ 12 people  CU5/7 – absolute photometric calibration, variabilityRoma+Teramo (OA, Uni): ~ 12 people  CU5/7 – flux extraction in crowded fields, variabilityNapoli (OA): ~ 9 people CU7/8 - variability, astrophysical parameters Catania (OA, Uni): ~ 9 people CU2/7/8 - simulations, variability, astrophysical parameters

  28. The Italian contribution– main activitiesDPC(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 databaseAstrophysical 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. More information on http://www.rssd.esa.int/Gaiahttp://www.to.astro.ithttp://www.bo.astro.itThank you !

  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. Schedule 2020 2004 2008 2016 2000 2012 Concept & Technology Study (ESA) ESA acceptance Re-assessment: Ariane-5 Soyuz Technology Development Design, Build, Test Launch Cruise to L2 Observations Data Analysis Catalogue Early Data

  32. 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

  33. Studies of the Solar System • 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

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

  35. Gaia:complete, faint, accurate

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