Gaia A Stereoscopic Census of our Galaxy http://www.rssd.esa.int/Gaia November 2003 - PowerPoint PPT Presentation

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Gaia A Stereoscopic Census of our Galaxy http://www.rssd.esa.int/Gaia November 2003

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global accuracy, with optimal use of observing time ... Early Data. Concept & Technology Study ESA SCI 2000(4) Re-Assessment: Ariane Soyuz ... – PowerPoint PPT presentation

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Title: Gaia A Stereoscopic Census of our Galaxy http://www.rssd.esa.int/Gaia November 2003


1
Gaia A Stereoscopic Census of our
Galaxy http//www.rssd.esa.int/Gaia November 2003
2
Gaia Design Considerations
  • Astrometry (V lt 20)
  • completeness to 20 mag (on-board detection) ? 109
    stars
  • accuracy 10-20 ?arcsec 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)
  • Radial velocity (V lt 16-17)
  • application
  • third component of space motion, perspective
    acceleration
  • dynamics, population studies, binaries
  • spectra chemistry, rotation
  • principles slitless spectroscopy using Ca
    triplet (848-874 nm)
  • Photometry (V lt 20)
  • astrophysical diagnostics (5 broad 11
    narrow-band) chromaticity
  • ? ?Teff 200 K, log g, Fe/H to 0.2 dex,
    extinction

3
Gaia Complete, Faint, Accurate
4
Stellar Astrophysics
  • Comprehensive luminosity calibration, for
    example
  • distances to 1 for 20 million stars to 2.5 kpc
  • distances to 10 for 150 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 sequences 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

5
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
    (1020,000)
  • a large-scale survey of Solar System bodies
    (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 (10-3 present)

6
Planets Expected Discoveries
  • Astrometric survey
  • monitoring of hundreds of thousands of FGK stars
    to 200 pc
  • detection limits 1MJ and P lt 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
  • 1020,000 planets (10 per day)
  • displacement for 47 UMa 360 ?as
  • orbits for 5000 systems
  • masses down to 10 MEarth to 10 pc
  • Photometric transits 5000?

7
Gaia Studies of the Solar System
  • Asteroids etc
  • deep and uniform (20 mag) detection of all moving
    objects
  • 105106 new objects expected (65,000 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 (442, 455, 75 known
    today)
  • 1600 Earth-crossers gt1 km predicted (100
    currently known)
  • detection limit 260590 m at 1 AU, depending on
    albedo

8
Light Bending in Solar System
9
Satellite and System
  • ESA only mission
  • Launch date 2010 targetted
  • Lifetime 5 years
  • Launcher Soyuz
  • Orbit L2
  • Ground station Perth or Madrid
  • Data rate 1 Mbps
  • Mass 1700 kg (payload 800 kg)
  • Power 2000 W (payload 1200 W)

10
Payload and Telescope
Rotation axis
SiC primary mirrors 1.4 ? 0.5 m2 at 106
Superposition of fields of view
SiC toroidal structure
Combined focal plane (CCDs)
Basic angle monitoring system
11
Astrometric Focal Plane
Total field - area 0.6 deg2 - size 75 ?
60 cm2 - number of CCD chips 11070 - CCDs
4500 x 1966 pixels Sky mapper - detects all
objects to 20 mag - rejects cosmic-ray
events Astrometric field - pixel size 10 ? 30
?m2 - window area 6 ? 12 pixels - flush
frequency 15 MHz - readout frequency 30 kHz
- total read noise 6e- Broad-band photometry
- 5 colour
Star motion
12
On-Board Object Detection
  • Requirements
  • unbiased sky sampling (mag, colour, resolution)
  • no all-sky catalogue at Gaia resolution (0.1
    arcsec) to V20
  • Solution on-board detection
  • no input catalogue or observing programme
  • good detection efficiency to V21 mag
  • low false detection rate, even at very high star
    densities
  • Will therefore detect
  • variable stars (eclipsing binaries, Cepheids,
    etc)
  • supernovae 20,000
  • microlensing events 1000 photometric 100
    astrometric
  • Solar System objects, including near-Earth
    asteroids and KBOs

13
Sky Scanning Principle
Spin axis 50o to Sun Scan rate 60
arcsec/s Spin period 6 hours
14
Radial Velocity Measurement Concept
F3 giant S/N 7 (single measurement) S/N 130
(summed over mission)
15
Comments on Astrometric Accuracy
  • massive leap from Hipparcos to Gaia
  • accuracy 2-3 orders of magnitude (1 milliarcsec
    to 4 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 ? 0.3m2 ? 1.4 ? 0.5m2,
    ? ? D-(3/2)
  • improved detector (IDT ? CCD) QE, bandpass,
    multiplexing
  • control of all associated error sources
  • aberrations, chromaticity, solar system
    ephemerides, attitude control

16
Technical Studies (2002-04) and Schedule
  • Main activities
  • two parallel system studies Astrium
    Alenia/Alcatel
  • CCD/focal plane development Astrium e2v
    first CCDs produced
  • SiC primary mirror Boostec mirror prototype
    under production
  • high-stability optical bench Astrium TPD Delft
    testing underway
  • payload data handling electronics Astrium-D
    breadboard starting
  • radial velocity instrument optimisation
    MSSL/Paris
  • mission analysis ESOC
  • also studied FEEPs transmitter solar array
    deployment refocus mechanism ground
    verification/calibration active optics (backup)
  • Schedule
  • implementation phase start May 2005 launch
    mid-2010
  • overall system design advanced and stable since
    2000
  • no major identified uncertainties to affect cost
    or launch schedule
  • technology/science window 2010-12

17
Scientific Organisation
  • Gaia Science Team
  • 12 members
  • Scientific working groups
  • 16 groups focused on payload, specific objects,
    and data analysis
  • 220 scientists active in the working groups at
    some level
  • Community is active and productive
  • regular science team/working group meetings 20
    in both 2002 2003
  • active archive of scientific working group
    reports 150 since 1 Jan 2003
  • advance of simulations, algorithms, accuracy
    models, etc
  • Data distribution policy
  • final catalogue 2018
  • intermediate catalogues as appropriate
  • science alerts data released immediately
  • no proprietary data rights

18
Data Reduction Principles
1. Objects are matched 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
19
Schedule
2000
2004
2008
2012
2016
2020
Concept Technology Study ESA SCI 2000(4)
Acceptance
Re-Assessment Ariane ? Soyuz
Technology Development
Design, Build, Test
Launch
To L2
Observations
Assumed start of Phase B2
Analysis
Catalogue
Early Data
20
Huge and timely scientific impact
Well-defined payload and spacecraft
Technology, cost and schedule maturity
Substantial and active ESA-based community
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