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Gaia A Stereoscopic Census of our Galaxy http://www.rssd.esa.int/Gaia May 2008 Gaia: Design Considerations • Astrometry (V < 20): – completeness to 20 mag (on-board detection) 109 stars – accuracy: 10–25 μarcsec at 15 mag (Hipparcos: 1 milliarcsec 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): – astrophysical diagnostics (low-dispersion photometry) + chromaticity Teff ~ 200 K, log g, [Fe/H] to 0.2 dex, extinction • Radial velocity (V < 16–17): – application: • third component of space motion, perspective acceleration • dynamics, population studies, binaries • spectra: chemistry, rotation – principles: slitless spectroscopy using Ca triplet (847–874 nm) 2 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 Accuracy 1 kpc None None 1 milliarcsec Photometry photometry Radial velocity Observing programme 2-colour (B and V) 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 15 km/s to V = 16-17 Complete and unbiased 3 Stellar Astrophysics • Comprehensive luminosity calibration, for example: – – – – distances to 1% for ~10 million stars to 2.5 kpc distances to 10% for ~100 million stars to 25 kpc rare stellar types and rapid evolutionary phases in large numbers parallax calibration of all 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 4 One Billion Stars in 3-d will Provide … • in our Galaxy … – – – – – – – the distance and velocity distributions of all stellar populations the spatial and dynamic structure of the disk and halo its formation history a rigorous framework for stellar structure and evolution theories a large-scale survey of extra-solar planets (~20,000) a large-scale survey of Solar System bodies (~ few 100,000) support to developments such as VLT, JWST, etc. • … and beyond – – – – definitive distance standards out to the LMC/SMC rapid reaction alerts for supernovae and burst sources (~20,000) QSO detection, redshifts, microlensing structure (~500,000) fundamental quantities to unprecedented accuracy: to 10-7 (10-5 present) 5 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 ~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 (") 0.8 6 1.0 Studies of the Solar System • Asteroids etc.: – – – – – – – deep and uniform (20 mag) detection of all moving objects ~ few 100,000 new objects expected (357,614 with orbits 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 (2249, 2643, 406 known today) – ~1600 Earth-crossers >1 km predicted (937 currently known) – detection limit: 260–590 m at 1 AU, depending on albedo 7 Light Bending in Solar System Light bending in microarcsec, after subtraction of the much larger effect by the Sun 8 Movie courtesy Jos de Bruijne Satellite and System • ESA-only mission • Launch date: 2011 • Lifetime: 5 years • Launcher: Soyuz–Fregat from CSG • Orbit: L2 • Ground station: New Norcia and Cebreros • Downlink rate: 4–8 Mbps • Mass: 2120 kg (payload 700 kg) • Power: 1720 W (payload 735 W) 9 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) 10 Figure courtesy EADS-Astrium 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 Total field: Astrometric Field CCDs Sky mapper: - detects all objects to 20 mag - active area: 0.75 deg2 - rejects cosmic-ray events - CCDs: 14 + 62 + 14 + 12 - FoV discrimination - 4500 x 1966 pixels (TDI) - pixel size = 10 µm x 30 µm Astrometry: = 59 mas x 177 mas - total detection noise: ~6 e- Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: 11 - high-resolution spectra - red CCDs On-Board Object Detection • Requirements: – unbiased sky sampling (mag, colour, resolution) – all-sky catalogue at Gaia resolution (0.1 arcsec) to V~20 • Solution: on-board detection: – no input catalogue or observing programme – good detection efficiency to V~21 mag – low false-detection rate, even at high star densities • Will therefore detect: – – – – variable stars (eclipsing binaries, Cepheids, etc.) supernovae: ~20,000 gravitational lensing events: ~1000 photometric; ~100 astrometric Solar System objects, including near-Earth asteroids and KBOs 12 Sky Scanning Principle 45o Spin axis Scan rate: Spin period: 45o to Sun 60 arcsec/s 6 hours 13 Figure courtesy Karen O’Flaherty Comments on Astrometric Accuracy • Massive leap from Hipparcos to Gaia: – accuracy: 2 orders of magnitude (1 milliarcsec to 7 microarcsec) – limiting sensitivity: 4 orders of magnitude (~10 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 years parallaxes and proper motions • Instrument improvement: – larger primary mirror: 0.3 0.3 m2 1.45 0.50 m2, D-(3/2) – improved detector (IDT CCD): QE, bandpass, multiplexing • Control of all associated error sources: – aberrations, chromaticity, solar system ephemerides, attitude control … 14 Photometry Measurement Concept (1/2) Blue photometer: 330–680 nm Red photometer: 640–1000 nm 15 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 16 Figures courtesy Anthony Brown spectral dispersion per pixel (nm) . Photometry Measurement Concept (2/2) Radial Velocity Measurement Concept (1/2) Spectroscopy: 847–874 nm (resolution 11,500) 17 Figures courtesy EADS-Astrium Radial Velocity Measurement Concept (2/2) Field of view RVS spectrograph CCD detectors RVS spectra of F3 giant (V=16) S/N = 7 (single measurement) S/N = 130 (summed over mission) 18 Figures courtesy David Katz 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 19 6. System is iterated Scientific Organisation • Gaia Science Team (GST): – 7 members + ESA Project Scientist + DPAC Executive Chair • Scientific community: – organised in Data Processing and Analysis Consortium (DPAC) – ~375 scientists in 16 countries active at some level • Community is active and productive: – regular science team/DPAC meetings – growing archive of scientific reports – advance of simulations, algorithms, accuracy models, etc. • Data distribution policy: – – – – final catalogue ~2019–20 intermediate catalogues as appropriate science alerts data released immediately no proprietary data rights 20 Data Processing Concept (simplified) From ground station Community access Overall system architecture ESAC Object processing + Classification CNES, Toulouse Ingestion, pre-processing, data base + versions, astrometric iterative solution ESAC + Barcelona + OATo Photometry Cambridge (IoA) + Variability Geneva (ISDC) Data simulations Barcelona Spectroscopic processing CNES, Toulouse 21 Status and Schedule • Prime contractor: EADS-Astrium – implementation phase started early 2006 – preliminary design review completed June 2007 • Main activities and challenges: – CCDs and FPA (including proximity electronics) – SiC primary mirrors – 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 22 Schedule 2004 2000 2008 2016 2012 2020 Concept & Technology Study (ESA) ESA Acceptance Re-assessment: Ariane-5 Soyuz Technology Development Design, Build, Test Launch Cruise to L2 Observations Data Analysis Early Data Catalogue 23 Gaia Unraveling the chemical and dynamical history of our Galaxy 24