Transcript GAIA A Stereoscopic Census of our Galaxy - RSSD

Gaia
A Stereoscopic Census of our Galaxy
http://www.rssd.esa.int/Gaia
May 2008
Gaia: Design Considerations
• Astrometry (V < 20):
– completeness to 20 mag (on-board detection)  109 stars
– accuracy: 10–25 μarcsec 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)
• Photometry (V < 20):
– astrophysical diagnostics (low-dispersion photometry) + chromaticity
Teff ~ 200 K, log g, [Fe/H] to 0.2 dex, extinction
• 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 (847–874 nm)
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Gaia: Complete, Faint, Accurate
Hipparcos
Gaia
Magnitude limit
Completeness
Bright limit
Number of objects
12
7.3 – 9.0
0
120 000
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
20 mag
20 mag
6 mag
26 million to V = 15
250 million to V = 18
1000 million to V = 20
50 kpc
5 x 105
106 – 107
7 µarcsec at V = 10
10-25 µarcsec at V = 15
300 µarcsec at V = 20
Low-res. spectra to V = 20
15 km/s to V = 16-17
Complete and unbiased
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Stellar Astrophysics
• Comprehensive luminosity calibration, for example:
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distances to 1% for ~10 million stars to 2.5 kpc
distances to 10% for ~100 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 diagrams 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
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One Billion Stars in 3-d will Provide …
• in our Galaxy …
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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 (~20,000)
a large-scale survey of Solar System bodies (~ few 100,000)
support to developments such as VLT, JWST, etc.
• … and beyond
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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 (10-5 present)
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Exo-Planets: Expected Discoveries
• Astrometric survey:
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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:
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1.2
d(")
Planète : r = 100 mas P = 18 mois
1/07/02
~20,000 exo-planets (~10 per day) 1
displacement for 47 UMa = 360 μas0.8
orbits for ~5000 systems
0.6
masses down to 10 MEarth to 10 pc
0.4
1/01/03
1/07/01
1/01/02
1/01/01
1/07/00
• Photometric transits: ~5000?
0.2
0
Figure courtesy François Mignard
1/01/00
0
0.2
0.6
0.4
acos d (")
0.8 6
1.0
Studies of the Solar System
• Asteroids etc.:
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deep and uniform (20 mag) detection of all moving objects
~ few 100,000 new objects expected (357,614 with orbits 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 (2249, 2643, 406 known today)
– ~1600 Earth-crossers >1 km predicted (937 currently known)
– detection limit: 260–590 m at 1 AU, depending on albedo
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Light Bending in Solar System
Light bending in microarcsec, after subtraction of the much larger effect by the Sun
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Movie courtesy Jos de Bruijne
Satellite and System
• ESA-only mission
• Launch date: 2011
• Lifetime: 5 years
• Launcher: Soyuz–Fregat from CSG
• Orbit: L2
• Ground station: New Norcia and Cebreros
• Downlink rate: 4–8 Mbps
• Mass: 2120 kg (payload 700 kg)
• Power: 1720 W (payload 735 W)
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Figures courtesy EADS-Astrium
Payload and Telescope
Two SiC primary mirrors
1.45  0.50 m2 at 106.5°
Rotation axis (6 h)
Basic angle
monitoring system
SiC toroidal
structure
(optical bench)
Superposition of
two Fields of View
(FoV)
Combined
focal plane
(CCDs)
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Figure courtesy EADS-Astrium
Figure courtesy Alex Short
Focal Plane
104.26cm
42.35cm
Basic
Angle
Monitor
Basic
Angle
Monitor
Red Photometer CCDs
Wave
Front
Sensor
Blue Photometer CCDs
Wave
Front
Sensor
Radial-Velocity
Spectrometer
CCDs
Star motion in 10 s
Sky Mapper
CCDs
Total field:
Astrometric Field CCDs
Sky mapper:
- detects all objects to 20 mag
- active area: 0.75 deg2
- rejects cosmic-ray events
- CCDs: 14 + 62 + 14 + 12
- FoV discrimination
- 4500 x 1966 pixels (TDI)
- pixel size = 10 µm x 30 µm
Astrometry:
= 59 mas x 177 mas - total detection noise: ~6 e-
Photometry:
- spectro-photometer
- blue and red CCDs
Spectroscopy:
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- high-resolution spectra
- red CCDs
On-Board Object Detection
• Requirements:
– unbiased sky sampling (mag, colour, resolution)
– 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 high star densities
• Will therefore detect:
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variable stars (eclipsing binaries, Cepheids, etc.)
supernovae: ~20,000
gravitational lensing events: ~1000 photometric; ~100 astrometric
Solar System objects, including near-Earth asteroids and KBOs
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Sky Scanning Principle
45o
Spin axis
Scan rate:
Spin period:
45o to Sun
60 arcsec/s
6 hours
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Figure courtesy Karen O’Flaherty
Comments on 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 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  0.3 m2  1.45  0.50 m2,   D-(3/2)
– improved detector (IDT  CCD): QE, bandpass, multiplexing
• Control of all associated error sources:
– aberrations, chromaticity, solar system ephemerides, attitude control …
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Photometry Measurement Concept (1/2)
Blue photometer:
330–680 nm
Red photometer:
640–1000 nm
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Figures courtesy EADS-Astrium
1050
18
650
35
1000
16
30
950
Blue photometer
wavelength (nm)
600
550
25
500
20
450
15
400
10
350
5
300
0
0
5
10
15
20
AL pixels
25
30
35
wavelength (nm)
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spectral dispersion per pixel (nm) .
700
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Red photometer
900
12
850
10
800
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750
6
700
4
650
2
600
0
0
5
10
15
20
25
30
35
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
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Figures courtesy Anthony Brown
spectral dispersion per pixel (nm) .
Photometry Measurement Concept (2/2)
Radial Velocity Measurement Concept (1/2)
Spectroscopy:
847–874 nm
(resolution 11,500)
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Figures courtesy EADS-Astrium
Radial Velocity Measurement Concept (2/2)
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)
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Figures courtesy David Katz
Data Reduction Principles
Scan width: 0.7°
Sky scans
(highest accuracy
along scan)
Figure courtesy Michael Perryman
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
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6. System is iterated
Scientific Organisation
• Gaia Science Team (GST):
– 7 members + ESA Project Scientist + DPAC Executive Chair
• Scientific community:
– organised in Data Processing and Analysis Consortium (DPAC)
– ~375 scientists in 16 countries 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:
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final catalogue ~2019–20
intermediate catalogues as appropriate
science alerts data released immediately
no proprietary data rights
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Data Processing Concept (simplified)
From ground station
Community access
Overall system
architecture
ESAC
Object processing
+ Classification
CNES, Toulouse
Ingestion, pre-processing,
data base + versions,
astrometric iterative solution
ESAC + Barcelona + OATo
Photometry
Cambridge (IoA)
+ Variability
Geneva (ISDC)
Data simulations
Barcelona
Spectroscopic
processing
CNES, Toulouse
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Status and Schedule
•
Prime contractor: EADS-Astrium
– implementation phase started early 2006
– preliminary design review completed June 2007
•
Main activities and challenges:
– CCDs and FPA (including proximity electronics)
– SiC primary mirrors
– high-stability optical bench
– payload data handling electronics
– phased-array antenna
– micro-propulsion
– scientific calibration of CCD radiation-damage effects
•
Schedule:
– no major identified uncertainties to affect cost or launch schedule
– launch in 2011
– technology/science ‘window’: 2010–12
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Schedule
2004
2000
2008
2016
2012
2020
Concept & Technology Study (ESA)
ESA Acceptance
Re-assessment:
Ariane-5  Soyuz
Technology
Development
Design, Build, Test
Launch
Cruise to L2
Observations
Data
Analysis
Early Data
Catalogue
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Gaia
Unraveling the chemical and dynamical
history of our Galaxy
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