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GAIA Composition, Formation and Evolution of our Galaxy

GAIA Composition, Formation and Evolution of our Galaxy. thanks to Michael Perryman, the GAIA Science Team (present and past) and 200+ others. M83 image (with Sun marked). ‘the Sun’. M83 (AAO, D. Malin). GAIA: Key science objectives. Structure and kinematics of our Galaxy:

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GAIA Composition, Formation and Evolution of our Galaxy

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  1. GAIA Composition, Formation and Evolution of our Galaxy thanks to Michael Perryman, the GAIA Science Team (present and past) and 200+ others

  2. M83 image (with Sun marked) ‘the Sun’ M83 (AAO, D. Malin)

  3. GAIA: Key science objectives • Structure and kinematics of our Galaxy: • shape and rotation of bulge, disk and halo • internal motions of star forming regions, clusters, etc • nature of spiral arms and the stellar warp • space motions of all Galactic satellite systems • Stellar populations: • physical characteristics of all Galactic components • initial mass function, binaries, chemical evolution • star formation histories • Tests of galaxy formation: • dynamical determination of dark matter distribution • reconstruction of merger and accretion history  Origin, Formation and Evolution of the Galaxy

  4. Overview • Measurement principles • The GAIA satellite and mission • Some science examples • Schedule, organisation of work • Current situation • Summary

  5. Some history… 610 B.C.: Obliquity of the ecliptic (Anaximander) 125 B.C.: Precession of the equinoxes (Hipparchus) 1725: Stellar aberration (Bradley), confirming: • Earth’s motion through space • finite velocity of light • immensity of stellar distances 1717: First proper motions (Halley) • 1761/9: Transits of Venus across the Sun (various) • solar parallax 1783: Sun’s motion through space (Herschel) 1838-9: First parallaxes (Bessel/Henderson/Struve)

  6. Principle of parallax measurement

  7. Measurement Principle

  8. Measurement principle: b

  9. Global astrometry basic angle

  10. GAIA: complete, faint, accurate

  11. Scientific design considerations • Astrometry (V < 20): • completeness  on-board detection • accuracies: 10 as at 15 mag (science) • continuously scanning satellite, two viewing directions  global accuracy, optimal with respect to observing time • Radial velocity (V < 17-18): • third component of space motion • account for perspective acceleration (nearby, fast stars) • Photometry (V < 20): • astrophysical diagnostics (4-band + 11-band) + chromatic correction  extinction, Teff~ 200 K, [Fe/H] to 0.2 dex

  12. Satellite • Deployable: solar array/sun-shield • Size: 8.5m diameter (4.2m stowed) • 2.9m height (2.1m for payload) • Mass: 3100 kg (800 kg payload) • Power: 2600 W • Launch: dual Ariane 5 • Orbit: Sun-Earth L2 (Lissajous) • Data rate (phased array): • 1 Mbs-1 sustained • 3 Mbs-1 downlink (1 ground station) • Launch date: 2010-12 • Attitude control: FEEP thrusters • Design lifetime: 5 years • ESA only mission

  13. Payload overview • Two astrometric instruments: • field of view = 0.6o 0.6o • separation = 106o • Monolithic mirrors: 1.7 m 0.7 m • Non-deployable, 3-mirror, SiC optics • Astrometric focal planes: TDI CCDs • Radial velocity/photometry telescope • Survey principles: • revolving scanning • onboard detection • complete and unbiased sample

  14. Astrometric instrument: Light path 1 2 4 3

  15. Astrometric focal plane Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray hits - mag + x,y to main field Main field: - area: 0.66 x 0.56 deg = 0.37 deg2 - size: 60  70 cm2 - number of CCDs: 17 x 8=136 - CCDs: 2780 x 2150 pixels - 120´´/s  0.86s per CCD Pixels: - size: 9 x 27 m2 (37 x 111 mas) - read in TDI mode Broad-band photometry: - 4 band (chromatic correction)

  16. On-board source detection Requirements and constraints: • unbiased sky sampling (mag, colour, resolution, etc.) • no all-sky catalogue at GAIA resolution (0.1 arcsec) to V~20 • cannot transmit entire sky at 0.1 arcsec resolution (telemetry limitations) Solution: on-board detection and sampling • no input catalogue or observing programme (big effort for Hipparcos) • good detection efficiency to V~21 mag • maximum star density: ~ 3 million stars/deg2 (Baade’s Window) • reduces data rate from several Gbps to a few Mbps Will therefore also detect: • supernovae: 105 expected • microlensing events: ~1000 photometric • variable stars (eclipsing binaries, Cepheids, etc) • Solar System objects, including near-Earth asteroids and KBOs

  17. Sky scanning principle Spin axis: 55o to Sun Scan rate: 120 ´´/s (3 hours) Precession rate: 0.20 ´´/s (76 days) Continuously observing Full sky coverage Each position observed 67 times (on average) per astrometric instrument

  18. Scanning law Observations over 5 months Ecliptic co-ordinates

  19. Astrometric accuracies 5-year accuracies in as • Derived from detailed analysis: • image formation (polychromatic PSF) • evaluation vs. spectral type/reddening • comprehensive detector signal model • sky background and image saturation • attitude rate errors and sky scanning • on-board detection probability • on-ground location estimation • (centroid to 0.001 pixel in hardest case) • error margin of 20 per cent included • results folded with Galaxy model Fraction of stars with given relative parallax error vs. magnitude (towards Galactic poles)

  20. CCD centroiding tests Astrium contract (Sep 2000) ‘GAIA-mode’ operation EEV CCD 42-10 13m pixels Illumination: 240,000 e- Frequencies: TDI: 2.43 kHz Readout: 90 kHz Differential centroid errors: rms = 0.0038 pixels (1.2 theoretical limit)

  21. 1 as is a very small angle ... • Earth-Sun system seen from 1 Mpc (by definition) • the Earth seen from the Pleiades (100 pc) • Baden-Württemberg seen from  Centauri (1.3 pc) • a grain of rice seen on the Moon (380 000 km) • a human hair observed in Kabul from Heidelberg (5000 km)

  22. Astrometric reduction • Approximate single epoch astrometry (<<1´´) from star mapper and GAIA orbit/attitude • Great circle scans  1D positions in two fields separated by a well-known basic angle (monitored) • Object matching in different scans (e.g. GSC II method) • Full sphere reduction to determine 5 astrometric parameters per star by a global iterative method (>100 measures) • Binary models fitted to systems with large residuals • GAIA observations of quasars (known and new) put the astrometry on a quasi-inertial reference system

  23. GAIA spectrophotometry and radial velocities • High resolution spectra for: • - 3rd component of space motion • - perspective acceleration • - stellar abundances, rotation velocities • Medium band photometer for: • - classification of all objects • - physical parametrization of stars • Teff, log g, [Fe/H], [/H], A()

  24. Radial Velocity Measurement Concept F3 giant S/N = 7 (single measurement) S/N = 130 (summed over mission)

  25. Radial Velocity and Photometric Instrument • Mounted on same toroidal support • Observes same scanning circles • Independent star mappers • Photometry for all stars (to 20 mag) • Radial velocities to ~ 18 mag • 1-10 km/s accuracy • 0.5´´ spatial resolution

  26. Spectral Sequences around Ca II Effect of temperature: A to M stars Effect of metal abundance in G stars

  27. Photometric system and accuracies • 11 medium band (in Spectro, 100 obs.) • 4 broad band filters (in Astro, 2x67 obs.) • SNR: 100-500 at V=15 (10-100 at V=20) • (end of mission) F33 B45 B63 B82

  28. GAIA and our Galaxy 10 as/yr = 1 km/sec at 20 kpc 10 as = 10% distances at 10 kpc

  29. GAIA: Why a survey to 20 mag?

  30. GAIA capabilities • Distances: • <0.1% for 700 000 stars <1% for 21 million <10% for 220 million • Transverse motions: • <0.5% km/s for 44 million <3 km/s for 210 million <10 km/s for 440 million • Radial velocities to a few km/s complete to V=17-18 • 15-band photometry (250-950nm) at ~100 epochs over 4 years • Complete survey of the sky to V=20, observing 109 objects: • 108 binary star systems (detected astrometrically; 105 orbits) • 200 000 disk white dwarfs • 50 000 brown dwarfs • 50 000 planetary systems • 106-107 resolved galaxies • 105 quasars • 105 extragalactic supernovae • 105-106 Solar System objects (65 000 presently known)

  31. Exosolar planets: Detection domains No sin i ambiguity in mass determination from astrometry

  32. Expected astrometric planetary discoveries • Monitoring of hundreds of thousands of stars to 200 pc for 1MJ planets with P < 10 years: • complete census of all stellar types (P=2-9 years) • actual masses, not just lower limits (m sin i) • 20,000-30,000 planets expected to 150-200 pc • e.g. 47 UMa: astrometric displacement 360 as • Orbits for many (~5000) systems • Masses down to 10 MEarth to 10 pc

  33. Solar eclipse (image) General Relativity (light bending)

  34. Light Bending at L2 by solar system bodies Klioner (2002) de Bruijne (2002)

  35. Gravitational light deflection de Bruijne (2002)

  36. General Relativity • Parametrized Post-Newtonian (PPN) formulation •  = 1.0 for General Relativity (GR) • alternative scalar-tensor theories deviate by 10-5- 10-7 • GAIA will measure  to 510-7 from positional displacement at large angles from the Sun •  currently known to 10-5 • GAIA tests GR at 10-100 times lower mass than presently • effect of Sun: 4 mas at 90o; Jovian limb: 17 mas; Earth: 40 as • Microlensing: photometric (~1000) and astrometric (few) events

  37. Galaxies, quasars, and the reference frame • Parallax distances, orbits, and internal dynamics of nearby galaxies • Galaxy survey (106-107 resolved at 0.1´´ in four bands, 0.5´´ in 11 bands) • ~500,000 quasars: kinematic and photometric detection • ~100,000 supernovae • Galactocentric acceleration: 0.2 nm/s2  (aberration) = 4 as/yr • Globally accurate reference frame to ~0.4 as/yr

  38. Schedule 2020 2004 2008 2016 2000 2012 Acceptance Technology Development Design, Build, Test Launch Observations Analysis Catalogue

  39. Organisation of scientific work Working groups: about 150 European ‘core’ and ‘associate’ members

  40. GAIA Science Team (GST) Frederic Arenou (Meudon) Coryn Bailer-Jones (MPIA, Heidelberg) Ulrich Bastian (ARI, Heidelberg) Erik Hoeg (Copenhagen) Andrew Holland (Leicester) Carme Jordi (Barcelona) David Katz (Meudon) Maria Lattanzi (Torino) Lennart Lindegren (Lund) Xavier Luri (Barcelona) Francois Mignard (Nice) Michael Perryman (Project Scientist, ESA)

  41. Current GAIA activities ESA/industrial: • Phased array antenna (Alcatel) • High stability optical bench (Astrium) • Telemetry budget and compression algorithms (ESA) • FEEPs: will be based on SMART-2 activities (ESA + industry) • Proof of concept data reduction system (Barcelona + GMV) • New important industrial study contracts (CCD and focal plane study, mirrors) are on hold due to internal ESA SPC/IPC conflict Scientific community (working groups): • On-board detection algorithms • Detailed specification of radial velocity instrument • Definition of optimal photometric system • Simulations of data stream • Development of object classification and physical parametrization methods

  42. Database N Database 1 Special Processing N Processing 1 Processing Master Data processing demonstration (GDAAS) • under development since mid-2000 (GMV/UB/CESCA) • sky divided into hierarchical triangular mesh (level 6) • presently: 8 nodes, 4 processors per node, 0.5 Tbyte disk • telemetry ingestion, object matching, sphere iteration • iterative processing for 1 million stars (final results April 2002) • platform for further development/experimentation

  43. Object classification/physical parametrization • classification as star, galaxy, quasar, supernovae, solar system objects etc. • determination of physical parameters: • - Teff, logg, [Fe/H], [/H], A(), Vrot, Vrad, activity etc. • combination with parallax to determine stellar: • - luminosity, radius, (mass, age) • use all available data (photometric, spectroscopic, astrometric) • must be able to cope with: • - unresolved binaries (help from astrometry) • - photometric variability (can exploit, e.g. Cepheids, RR Lyrae) • - missing and censored data (unbiased: not a ‘pre-cleaned’ data set) • multidimensional iterative methods: • - cluster analysis, k-nn, neural networks, interpolation methods • required for astrometric reduction (identification of quasars, variables etc.)  produce detailed classification catalogue of all 109 objects

  44. Recent developments Oct. 2000: GAIA approved by SPC for launch by 2012 Nov. 2001: Ministerial meeting reduces science budget by 435 MEuro over 2002-2006 (20% reduction) Nov. 2001: ESA+Astrium start to identify cost savings Dec. 2001: SPC requests review of whole ESA science program April 2002: AWG subgroup (Rix, Aerts, Ward) reports on GAIA to AWG; (AWG to SSAC to SPC) April 2002: Astrium presents revised GAIA design to GST May 2002: ESA/Astrium deliver final report to SPC June 2002: SPC decide on future science program

  45. GAIA cost saving measures (ongoing) • Substantial savings possible if released from ESA constraints: • re-use of satellite subsystem designs from other missions • cheaper contract competition mechanism • Soyuz-Fregat launch instead of Ariane 5 (110  40 MEuro) • smaller mirrors in along-scan direction, accommodated • by increased across-scan dimension, field-of-view size... • Other possible cost savings from: • smaller solar array/sunshield by reducing solar aspect angle • (accommodate for lost astrometric precision in optics) • C-SiC optical bench • unification of pixel scales • field superposition (as in Hipparcos) • smaller ESA project team • Cost reduction from 570 to 400-450 MEuro possible • without any reduction in accuracies or scientific goals

  46. Main performances and capabilities Accuracies: • 4 as at V=10 10 as at V=15 200 as at V=20 • radial velocities to few km/s complete to V=17-18 • 10 as  distances to 1% at 1 kpc or 10% at 10 kpc (V=15) • 10 as/yr at 20 kpc  1 km/s Capabilities: • sky survey in four bands at ~0.1 arcsec spatial resolution to V=20 • 15 band multi-epoch photometry to V=20 • dense quasar link to inertial reference frame  every star observed in the Galaxy and Local Group will be seen to move  GAIA will quantify a 6-D phase space for over 300 million stars and a 5-D phase-space for over 109 stars

  47. GAIA and our Galaxy 10 as/yr = 1 km/sec at 20 kpc 10 as = 10% distances at 10 kpc

  48. core radius  3 pc Aldebaran (non-member) direction of motion Hyades 60,000 years Perryman et al. (1997) Hyades (animation)

  49. Gravitational light deflection de Bruijne (2002)

  50. GAIA stands for ... Global Astrometric Interferometer for Astrophysics Galactic Astrophysics through Imaging and Astrometry General Astrometric Instrument for Astronomy Great Accuracy In Astrometry Great Advances In Astrophysics

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