|
Gaia: Design Considerations Astrometry (V < 20)
|
tarix | 02.01.2018 | ölçüsü | 523 b. | | #19065 |
|
Gaia A Stereoscopic Census of our Galaxy http://www.rssd.esa.int/Gaia November 2003
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
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 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
Dostları ilə paylaş: |
|
|