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Gaia Unravelling the chemical and dynamical history of our galaxy C. Cacciari - SAIt 2008, Teramo 1 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 spacebased & ground-based facilities (e.g. EELT etc.), but on pencil-beam areas of the sky 2 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 3 Figures courtesy EADS-Astrium Payload and Telescope Two SiC primary mirrors 1.45 0.50 m2 at 106.5° Rotation axis (6 h) Basic angle monitoring system SiC toroidal structure (optical bench) Superposition of two Fields of View (FoV) Combined focal plane (CCDs) 4 Figure courtesy EADS-Astrium Sky Scanning Principle 45o Spin axis Scan rate: Spin period: 45o to Sun 60 arcsec/s 6 hours less transits per FoV than Hipparcos (2.13 hr spin period) higher spatial resolution in focal plane 5 Figure courtesy Karen O’Flaherty Sky Scanning Principle Ecliptic coordinates Galactic coordinates Ecliptic coordinates End of mission (5 yr) average (maximum) number of transits: about 80 (240) End-of mission 6 Figure courtesy Karen O’Flaherty Figure courtesy Alex Short Focal Plane 104.26cm 42.35cm Basic Angle Monitor Basic Angle Monitor Red Photometer CCDs Wave Front Sensor Blue Photometer CCDs Wave Front Sensor Radial-Velocity Spectrometer CCDs Star motion in 10 s Sky Mapper CCDs Astrometric Field CCDs along-scan 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 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: 7 - high-resolution spectra - red CCDs Data Reduction Principles Scan width: 0.7° Sky scans (highest accuracy along scan) Figure courtesy Michael Perryman 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 8 6. System is iterated (Global Iterative Solution) 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 9 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 10 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 11 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 12 Distances as a function of Mv (V) σπ/π N(Hip) N(Gaia) Mv V d(pc) < 0.1 % 0 0.7 106 0 5 10 15 7 12 15 17 270 270 100 25 <1% 188 21 106 -5 0 5 10 15 7 12 15 17 20 2 700 2 700 1 000 270 100 < 10 % ~ 22 103 ~ 22 107 -5 0 5 10 12 15 17 20 27 000 10 000 2 700 1 000 13 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) 14 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 15 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 main sequences 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 (7502500 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 16 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 scale with Hipparcos in the MW, with Gaia in the LMC/SMC The Magellanic Clouds 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%) • 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 17 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) 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) 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 18 Photometry Measurement Concept (1/2) Blue photometer: 330–680 nm Red photometer: 640–1050 nm 19 Figures courtesy EADS-Astrium 1050 18 650 35 1000 16 30 950 Blue photometer wavelength (nm) 600 550 25 500 20 450 15 400 10 350 5 300 0 0 5 10 15 20 AL pixels 25 30 35 wavelength (nm) 40 spectral dispersion per pixel (nm) . 700 14 Red photometer 900 12 850 10 800 8 750 6 700 4 650 2 600 0 0 5 10 15 20 25 30 35 AL pixels RP spectrum of M dwarf (V=17.3) Red box: data sent to ground White contour: sky-background level Colour coding: signal intensity 20 Figures courtesy Anthony Brown spectral dispersion per pixel (nm) . Photometry Measurement Concept (2/2) 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 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 (see Vallenari’s talk) 21 Radial Velocity Measurement Concept (1/2) Spectroscopy: 847–874 nm (resolution 11,500) 22 Figures courtesy EADS-Astrium Radial Velocity Measurement Concept (2/2) to all sources up to V < 16–17 Field of view RVS spectrograph CCD detectors 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) 23 Figures courtesy David Katz 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 24 Data Processing Concept (simplified) From ground station Community access Overall system architecture ESAC Object processing + Classification CNES, Toulouse Ingestion, preprocessing, data base + versions, astrometric iterative solution ESAC (+ Barcelona + OATo) Photometry Cambridge (IOA-C) + Variability Geneva (ISDC) Data simulations Barcelona Spectroscopic processing CNES, Toulouse 25 DPAC structure CU1: System Architecture O’Mullane (Lammers/Levoir) (Brown, Cacciari, De Angeli, Richards CU2:Data Simulations Luri (Babusiaux/Mignard) CU6:Spectroscopic Processing Katz/Cropper (+ steering committee) CU3: Core Processing Bastian (Lattanzi/Torra) CU4:Object Processing Pourbaix/Tanga (Arenou, Cellino, Ducourant Frezouls) CU5:Photometric Processing van Leeuwen CU7:Variability Processing Eyer/Evans/Dubath CU8:Astrophysical Parameters Bailer-Jones/Thevenin CU9:Catalogue Access To be activated 26 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 27 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.) 28 More information on http://www.rssd.esa.int/Gaia http://www.to.astro.it http://www.bo.astro.it Thank you ! 29 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 30 Schedule 2000 2004 2008 2016 2012 2020 Concept & Technology Study (ESA) ESA acceptance Re-assessment: Ariane-5 Technology Soyuz Development Design, Build, Test Launch Cruise to L2 Observations Data Analysis Early Data Catalogue 31 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: – – – – 1.2 d(") Planète : r = 100 mas P = 18 mois 1/07/02 10–20,000 exo-planets (~10 per day) 1 displacement for 47 UMa = 360 μas0.8 orbits for ~5000 systems 0.6 masses down to 10 MEarth to 10 pc 0.4 1/01/03 1/07/01 1/01/02 1/01/01 1/07/00 • Photometric transits: ~5000? 0.2 0 Figure courtesy François Mignard 1/01/00 0 0.2 0.6 0.4 acos d (") 0.832 1.0 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 33 Light Bending in Solar System Light bending in microarcsec, after subtraction of the much larger effect by the Sun 34 Movie courtesy Jos de Bruijne Gaia: complete, faint, accurate Hipparcos Gaia Magnitude limit Completeness Bright limit Number of objects 12 7.3 – 9.0 0 120 000 Effective distance limit Quasars Galaxies Parallax Accuracy 1 kpc None None 1 milliarcsec Photometry photometry Abs. Accuracy Rel. Accuracy Radial velocity Observing programme 2-colour (B and V) ~ 0.10 mag ~ 0.01 – 0.10 mag None Pre-selected 20 mag 20 mag 6 mag 26 million to V = 15 250 million to V = 18 1000 million to V = 20 50 kpc 5 x 105 106 – 107 7 µarcsec at V = 10 10-25 µarcsec at V = 15 300 µarcsec at V = 20 Low-res. spectra to V = 20 1-3% at V < 16 1-10 mmag 15 km/s to V = 16-17 Complete and unbiased 35