GAIA Science and Mission

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1 GAIA Science and Mission Nicholas Walton Institute of Astronomy The University of Cambridge p1

2 Outline Gaia high level science drivers Example science objectives Gaia mission overview Gaia data analysis and processing Gaia Science Team Gaia and the UK dimension Thanks to Gerry Gilmore and Floor van Leeuwen at the IoA for input to these slides. p2

3 What's driving Gaia? Towards a more precise understanding of the current structure and history of our galaxy: Distributions of mass, energy and angular momentum Signatures of mergers Missing mass, dark matter? Dwarf galaxies within the local group History of star formation and enrichment of the interstellar dust and gas In a nutshell map the Galaxy and Local Universe a billion stars, μ arcsec astrometry, to V= mag one μarcsec : 'resolve a finger nail on the moon!' p3

4 What's required for this mapping? Accurate positions and velocities of stars over a large volume of space Complete survey down to a limiting magnitude size of the galaxy implies a Radius ~10 to kpc (dist.mod: 15.0 to 16.5) Approximately th magnitude, 109 objects Complementary data required to 'sort' the objects effective temperature surface gravity metallicity luminosity p4

5 Gaia: Design Considerations Astrometry (V < ): completeness to th mag (with on-board detection) : 109 stars accuracy: 1025 μarcsec at 15th mag (c.f. Hipparcos: 1 milliarcsec at 9th mag) scanning satellite, two viewing directions global accuracy, with optimal use of observing time principles: global astrometric reduction (as for Hipparcos) Photometry (V < ): astrophysical diagnostics (low-dispersion photometry)/ chromaticity Teff ~ 0 K, log g, [Fe/H] to 0.2 dex, extinction Radial velocity (V < 1617): application: third component of space motion, perspective acceleration dynamics, population studies, binaries spectra: chemistry, rotation principles: slitless spectroscopy using Ca triplet ( nm) p5

6 Gaia: Complete, Faint, Accurate Hipparcos Gaia Magnitude limit Completeness Bright limit Number of objects 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 mag mag 6 mag 26 million to V = million to V = million to V = 1 Mpc 5 x µarcsec at V = µarcsec at V = µarcsec at V = Low-res. spectra to V = 15 km/s to V = Complete and unbiased source: ESA p6

7 Main Performances and Capabilities Two orders of magnitude improvement over current best precision First large-area high-spatial resolution survey Unbiased sample of 1% of Galactic stars Every one of these stars in the Galaxy and LG will have its movement observed A major resource for astronomy p7

8 GAIA: Some Science Objectives Structure and kinematics of our Galaxy: Stellar populations: 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 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 p8

9 10 as = 10% distances at 10 kpc equiv 1AU at 100 kpc N A Walton: GAIA Science GSD08 17 KIAA Mar,: 08 2 Dec, 08 p9 10 as/yr = 1 km/sec at kpc Printed: p9 02/12/08

10 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 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: 0.3x0.3 m2 1.45x0.50 m2, D-(3/2) improved detector (IDT, CCD): QE, bandpass, multiplexing Control of all associated error sources: aberrations, chromaticity, solar system ephemerides, attitude control p10

11 Astrometric Accuracy Numbers due to Jos de Bruijne p11

12 % Parallax horizon for K5III stars 10 AV = 5 mag 10 kpc AV = LAMOST: R=00 to 17.5 kpc (V=16) 2 p12 5 Figure courtesy of Lennart Lindegren %

13 GAIA: Science Objectives... cont.. Solar System studies Extra Solar Planets masses (down to 10Mearth at 10pc) for nearby sample great for more detailed followup Stellar AstroPhysics distances to 1% for ~2x10^7 stars at 2.5Kpc and to 10% for ~2x10^8 stars to 25kpc calibration of distance indicators (Cepheids/ RRLyrae/ MCs) light deflection, PPN asteroids, kuiper belt objects, trojans orbits, masses and near earth objects Fundamental Physics... and lots more... p13

14 Exo-Planets: Expected Discoveries Astrometric survey: monitoring hundreds of thousands of FGK stars to ~0 pc detection limits: ~1MJ and P < 10 years complete census of all stellar types, P = 29 years masses, rather than lower limits (m sin i) multiple systems measurable, giving relative inclinations Results expected: 10,000 exo-planets (~10 per day) displacement for 47 UMa = 360 μas orbits for ~5000 systems masses down to 10 MEarth to 10 pc Planet: ρ=100 mas, P=18 mths Δδ('') Photometric transits: ~5000? Δαcos δ('') Figure courtesy François Mignard p14

15 Field of Streams: Insights on Assembly p15

16 The Local Group & Gaia Large scale kinematic/ chemical surveys from e.g. Gaia allow for better characterisation of Local Group features e.g. further detail on the dwarf galaxies recently discovered from SDSS star counts e.g. Leo T (Irwin et al, 07, ApJ, 656, L13) identification of disrupted satellites LG orbits [Sawa+Fujimoto 05] Orbits of the dwarf spheroidal galaxies (Dsph) Draco and Sagittarius projected onto the LGG plane. They started from the formation site in similar directions, spiraled along the orbit of the Galaxy and reached their present positions, respectively. p16

17 Chemistry of the Galaxy / LG [Renzini+Fusi Pecci (1988)] For our galaxy insights on the formation of the bulge the thick/ thin disk formation and the halo Gaia allows for a better selection of volume complete samples p17

18 GAIA and complementary missions Gaia is a unique mission but can benefit from: radial velocity programmes for faint stars VISTA / IR surveys (dust models) LSST and Pan Starrs will complement Gaia SDSS and extensions radial velocities for stars with V > 17 Impact of LAMOST for wide field spectroscopic pre or followup observations of Gaia objects Time to define and prepare focused programmes in preparation for the 'age of Gaia' p18

19 Schedule: not so far away now! now Proposal source: ESA Concept & Technology Study Mission Selection Re-Assessment Study Phase B1 Definition Selection of Prime Contractor (EADS Astrium) Phase B2 Phase C/D Implementation Launch 11-Dec-01 Scientific operation Operation Studies Software Development Data Processing Mission Data Processing Intermediate Mission Products p19 Final

20 Gaia by the numbers Primary mirrors: 1.45 m x 0.5 m Focal length: 35 m Pixel: 59 x 177 mas (10 µas ~1/6000 pixel) 1 µas: rotation M1 < 10 picometers at the edge Focal plane: 4 x 850 mm 106 CCDs, ~1 Gpixel Star on CCD: mean: 150, peak: (magnitude ) Stellar flux: 000 V=15, 0 V= Sample datation accuracy: 50 ns Tore (3 m diameter) thermal stability required ~some tens of µk Rate measurement error < 0.9 mas/s Rate pointing error < 5 mas Attitude High Frequency Disturbance < 3.4 µas S/C launch mass 2.1 tons Solar Array capability 1.9 kw Mass memory capability 1 Tb S/C Height 3 m Deployed Sunshield ø = 10 m source: Moisson EADS Astrium p

21 Satellite and System ESA-only mission Launch date: late 11 Lifetime: 5 years (+ possible 1 year) Launcher: SoyuzFregat from CSG Orbit: L2 Ground station: New Norcia and/or Cebreros Downlink rate: 48 Mbps Mass: 30 kg (payload 690 kg) Power: 17 W (payload 830 W) Figures courtesy EADS-Astrium p21

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23 Payload and Telescope Two SiC primary mirrors 1.45 ξ 0.50 m2 at Basic angle monitoring system Rotation axis (6 h) SiC toroidal structure (optical bench) Superposition of two Fields of View (FoV) Figure courtesy EADS-Astrium p23 Combined focal plane (CCDs)

24 Figure courtesy Alex Short Focal Plane cm 42.35cm Wave Front Sensor Red Photometer CCDs Blue Photometer CCDs Wave Front Sensor Radial-Velocity Spectrometer CCDs Basic Angle Monitor Basic Angle Monitor Star motion in 10 s Sky Mapper CCDs Astrometric Field CCDs Total field: - active area: 0.75 deg2 - CCDs: x 1966 pixels (TDI) - pixel size = 10 µm x 30 µm = 59 mas x 177 mas Photometry: Sky mapper: - detects all objects to mag - rejects cosmic-ray events - FoV discrimination Astrometry: - total detection noise: 6 e- p24 - two-channel photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs

25 Downlink Using Cebreros (35M) 3-8Mb/s downlink ~ 30GB/day -> ~100TB so download 'windows' around objects occasionally New Norcia depends on encoding which depends on weather! during Galactic plane scans data accumulated onboard downlinked later Data is compressed encoded and requires a lot of processing (~10^21 FLOP) p25

26 On-Board Object Detection Requirements: unbiased sky sampling (mag, colour, resolution) no all-sky catalogue at Gaia resolution (0.1 arcsec) to V~ 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:,000 microlensing events: ~1000 photometric; ~100 astrometric Solar System objects, including NEOs and KBOs p26

27 Sky Scanning Principle 45o Spin axis Scan rate: Spin period: Figure courtesy Karen O Flaherty p27 45o to Sun 60 arcsec/s 6 hours

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30 Photometry Measurement Concept (1/2) Blue photometer: nm Red photometer: nm Figures courtesy EADS-Astrium p30

31 Photometry Measurement Concept (2/2) Blue photometer wavelength (nm) wavelength (nm) spectral dispersion per pixel (nm) Red photometer AL pixels spectral dispe 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 Figures courtesy Anthony Brown p31

32 Radial Velocity Measurement Concept Spectroscopy: nm (resolution 11,500) Figures courtesy EADS-Astrium p32

33 Radial Velocity Measurement Concept 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) Figures courtesy David Katz p33

34 Data Reduction Principles Scan width: 0.7 Figure courtesy Michael Perryman Sky scans (highest accuracy along scan) 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 p34

35 slide: wil o'mullane Astrometric GIS What? Calculate parameters describing observed (proper) directions to a subset of "well-behaved" (primary) sources attitude of the instrument as function of time transformation from field angles to pixel coordinates This will directly give: astrometric parameters for the primary sources attitude parameters (for the relevant time intervals) geometric calibration parameters (for the relevant detectors) if desired, any other parameter entering the calculation of proper directions (e.g. paramaterised post newtonian (PPN) ) and indirectly: approximate astrometric parameters for all other (secondary) sources (except solar system sources) p35

36 Large Computers... at least for AGIS As a courtesy of Barcelona Supercomputing Center p36

37 Gaia Scientific Organisation Gaia Science Team (GST): 7 members + DPAC Executive Chair + ESA Project Scientist Direct scientific community participation: organised in Data Processing and Analysis Consortium (DPAC) ~350 scientists 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: Intermediate data releases final catalogue ~19 no proprietary data rights p37

38 Gaia Data Processing and Analysis Consortium: To prepare, test, implement and execute all the software required to process all the science and auxiliary data produced by the Gaia satellite, to such level that the reduced data is ready for further astrophysical exploration p38

39 DPAC coordination units CU1: System Architecture CU2: Data Simulations CU3: Core Processing CU4: Object Processing CU5: Photometric Processing CU6: Spectroscopic Processing CU7: Variability Processing CU8: Astrophysical Parameters CU9: Catalogue Access p39 ESA areas of Contribution

40 The Participating Institutes Graphic : Francois Mignard - DPAC p40

41 DPAC: Data Processing Centres DPCs underpin and support CUs Software support and production Operation of processing system(s) ESAC BPC CNES ISDC IoA OATO (CU1,3) (CU2,3) (CU4,6,8) (CU7) (CU5) (CU3) Madrid Barcelona Toulouse Geneva Cambridge Torino p41

42 GAIA DPAC in the UK Gaia Data Flow System project UK DPAC Multi institute consortium IoA, Cambridge MSSL Leicester Edinburgh RAL OU Provides leadership of CU5 (photometry) and major partner on CU6 (spectroscopy) DPC at IoA during operation/ exploitation phase p42

43 Gaia: Timescales & Data Final astrometry dependent on global iterative solution of entire mission data Intermediate data releases final catalogues to be released ~ one or more during the course of the mission Science alerts Synergies with new and existing instruments e.g. Star-formation: Herschel/ ALMA most GAIA sources can be followed up with existing 24-8m class ground based telescopes p43

44 Gaia and the Virtual Observatory ESA/ DPAC create the required software infrastructure to process and generate intermediate and final data products Scientific & Cost effective delivery of these projects will be facilitated by use of the Euro-VO/AstroGrid Virtual Observatory infrastructure reduces cost of development: no bespoke interfaces p44

45 Hipparcos via AstroGrid in 4 clicks p45

46 GREAT: Gaia Research for European Astronomy Training ESA Project/ Science Team/ DPACE sponsored initiative to build community awareness of science opportunities from Gaia Funding proposal to ESF Research Network Prog Involved 70+ groups from ~ countries representing ~600 European researchers To fund 'science of Gaia' activities over Workshops, training events, exchanges, conferences, information First co-i meeting ~Easter 09 Options for Chinese involvement p46

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