Gaia: Design Considerations Astrometry (V < 20)



Yüklə 523 b.
tarix02.01.2018
ölçüsü523 b.
#19065


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


Gaia: Design Considerations

  • Astrometry (V < 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 < 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 < 20):

    • astrophysical diagnostics (5 broad + 11 narrow-band) + chromaticity
      •  Teff ~ 200 K, log g, [Fe/H] to 0.2 dex, extinction


Gaia: Complete, Faint, Accurate



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


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 (~10–20,000)
    • 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)


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:

    • 10–20,000 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?



Gaia: Studies of the Solar System

  • Asteroids etc:

    • deep and uniform (20 mag) detection of all moving objects
    • 105–106 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 >1 km predicted (100 currently known)
    • detection limit: 260–590 m at 1 AU, depending on albedo


Light Bending in Solar System



Satellite and System



Payload and Telescope



Astrometric Focal Plane



On-Board Object Detection

  • Requirements:

    • unbiased sky sampling (mag, colour, resolution)
    • no 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 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


Sky Scanning Principle



Radial Velocity Measurement Concept



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:



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


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




Schedule





Yüklə 523 b.

Dostları ilə paylaş:




Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©genderi.org 2024
rəhbərliyinə müraciət

    Ana səhifə