Transcript GAIA A Stereoscopic Census of our Galaxy

Gaia
Unravelling the chemical and dynamical history
of our galaxy
C. Cacciari - SAIt 2008, Teramo
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GAIA = all-sky astrometric survey  follow up of Hipparcos
(+ photometry + radial velocities)
A brief history of astrometric accuracy
Comparable astrometric accuracy will be obtained from other future spacebased & ground-based facilities (e.g. EELT etc.), but on pencil-beam areas
of the sky
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Satellite and System
• ESA-only mission
• Launch date: end 2011
• Lifetime: 5 years (+2?)
• Launcher: Soyuz–Fregat, from Kourou
• Orbit: L2 (1.5 million km opposite the Sun)
• Ground station: Cebreros (& New Norcia)
• Downlink rate: 4–8 Mbps
• Mass: 2030 kg (payload 690 kg)
• Power: 1720 W (payload 830 W)
• Cost: about 500 MEu
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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
Sky Scanning Principle
45o
Spin axis
Scan rate:
Spin period:
45o to Sun
60 arcsec/s
6 hours
 less transits per FoV than
Hipparcos (2.13 hr spin
period)
 higher spatial resolution
in focal plane
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Figure courtesy Karen O’Flaherty
Sky Scanning Principle
Ecliptic coordinates
Galactic coordinates
Ecliptic coordinates
End of mission (5 yr) average
(maximum) number of transits: about 80 (240)
End-of mission
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Figure courtesy Karen O’Flaherty
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
Astrometric Field CCDs
along-scan
Total field:
- active area: 0.75 deg2
- CCDs: 14 + 62 + 14 + 12
- each CCD: 4500x1966 px (TDI)
- pixel size = 10 µm x 30 µm
= 59 mas x 177 mas
Sky mapper:
- detects all objects to 20 mag
- rejects cosmic-ray events
- FoV discrimination
Astrometry:
- total detection noise: 6 e-
Photometry:
- spectro-photometer
- blue and red CCDs
Spectroscopy:
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- high-resolution spectra
- red CCDs
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 (Global Iterative Solution)
On-board object detection
 Requirements:
 unbiased sky sampling (mag, colour, resolution)
 no observing programme
 all-sky catalogue at Gaia resolution (0.1 arcsec) to V~20
 On-board detection:
 initial Gaia Source List  GSC-II (first ~ 6 months)
 subsequent self-calibration (Global Iterative Solution)
 good detection efficiency to V~21 mag
 low false-detection rate, even at high star densities
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Gaia characteristics
 Astrometry (V < 20):
 completeness to 20 mag (on-board detection)  109 stars
 accuracy: 7 μas at V < 12, 20 μas at V=15, 300 μas at V=20
 cf. Hipparcos: 1 mas 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):
 integrated (G-band) and BP(330-680 nm)-RP(640-1050 nm) colours
 dispersed BP/RP images (low-dispersion photometry, R ~ 20-300)
 astrophysical diagnostics (see Vallenari’s talk)
 Teff ~ 200 K, log g & [Fe/H] to ~ 0.2 dex, extinction
 Radial velocity (V < 16–17):
 slitless spectroscopy on Ca triplet (847–874 nm), R ~ 10,000
 third component of space motion, perspective acceleration
 dynamics, population studies, binaries
 spectra: chemistry, rotation
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Comments on astrometric accuracy
 Massive leap from Hipparcos to Gaia:
 accuracy: 2 orders of magnitude (1 mas to 7 μas)
 limiting sensitivity: > 3 orders of magnitude (~12 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 (+2?) years  parallaxes and proper motions
 Instrument improvement:
 larger (x8) primary mirror: 0.3  0.3 m2  1.45  0.50 m2,   D-(3/2)
 improved detector (IDT  CCD): QE, bandpass, multiplexing
 improved spatial resolution  better treatment of crowding
 Control of all associated error sources:
 aberrations, chromaticity, solar system ephemerides
 attitude control (basic angle stability)
 homogeneous distribution (the two FoV) of stars contributing to GIS
 use of QSOs for attitude recontruction and absolute reference frame
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Astrometric accuracy: the Pleiades
π = 7.69 mas (Kharchenko et al. 2005 ) various methods
π = 7.59 ± 0.14 mas (Pinsonneault et al. 1998) MS fitting
π = 8.18 ± 0.13 mas (Van Leeuwen 2007) (mod=5.44 ±0.03, 122pc) new red. Hipparcos data
π = 7.49 ± 0.07 mas (Soderblom et al. 2005) from 3 HST parallaxes in inner halo
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Distances as a function of Mv (V)
σπ/π
N(Hip)
N(Gaia)
Mv
V
d(pc)
< 0.1 %
0
0.7 106
0
5
10
15
7
12
15
17
270
270
100
25
<1%
188
21 106
-5
0
5
10
15
7
12
15
17
20
2 700
2 700
1 000
270
100
< 10 %
~ 22 103
~ 22 107
-5
0
5
10
12
15
17
20
27 000
10 000
2 700
1 000
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One billion stars in 3-d will provide …
 in our Galaxy …
 the distance and velocity distributions of all stellar populations
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 the spatial and dynamical structure of the disk and halo
 its formation and chemical history (accretion/interaction events)
a rigorous framework for stellar structure and evolution theories
a large-scale survey of extra-solar planets (up to ~20,000)
a large-scale survey of Solar System bodies (~100,000)
rare stellar types and rapid evolutionary phases in large numbers
support to developments such as JWST, etc.
 … and beyond

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
definitive and robust definition of the cosmic distance scale
rapid reaction alerts for supernovae and burst sources (~20,000)
QSO detection (~ 500,000 in 20,000 deg2 of the sky)
redshifts
gravitational lensing events: ~1000 photometric; ~100 astrometric
microlensing structure
fundamental quantities to unprecedented accuracy:  to 10-7 (10-5 present)
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Stellar Astrophysics
 Comprehensive luminosity calibration, for example:



distances to 1% for ~20 million stars to 2.5 kpc
distances to 10% for ~200 million stars to 25 kpc
parallax calibration of all primary 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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The distance scale: local calibrators
Hipparcos
RR Lyrae stars in the field - RR Lyr
<V> = 7.75 ± 0.05 – only RRL variable star
with ``decent’’ π (d~260-290 pc)
π = 3.46 ± 0.64 mas mod=7.30 mag
(new Hipparcos data, Van Leeuwen 2007)
π = 3.82 ± 0.20 mas  mod = 7.09 mag (HST,
Benedict et al. 2002)
 ΔMv = 0.2 mag?
Metal-poor Sub Dwarfs fit with GC main
sequences
Only ~ 30 Sub Dwarfs available with
MV = 5.0 – 7.5 between ~ 6 and 80 pc
Vlim ~ 10
Gaia
RR Lyrae stars in the field – no RR Lyr
126 RR Lyraes with < V > = 10 to 12.5 (7502500 pc) (Fernley et al. 1998) from Hipparcos
data  ΔMv = ± 0.02-0.05 mag
 all individual RR Lyrae stars within 3 kpc
will have σ(π)/π < 1%
RR Lyraes in globular clusters
 mean distance to better than 1% for 110
globular clusters (up to ≥ 30 kpc)
 accurate MV (ZAHB)
 Mv = α + β[Fe/H]
Metal-poor Sub Dwarfs as far as Vlim~15
 a factor 10 (1000) in distance (volume)
 several thousand expected
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The distance scale: Cepheids
in the MW & LMC/SMC
Cepheids: main PopI bridge between the MW & LMC to spiral & irregular
galaxies  first direct calibration of the cosmological distance scale
with Hipparcos in the MW, with Gaia in the LMC/SMC
The Magellanic Clouds
The MW
•
Hipparcos: about 250 Cepheids
with parallax & photometry (9
with HST parallax)
 PLC(met) calibration
 mod (LMC) = 18.48 ± 0.03 mag
(no metallicity correction)
•
Gaia: distances to all Galactic
Cepheids to < 4% (most to < 1%)
• no Hipparcos
• Gaia: Cepheids in the Magellanic Clouds
with distances to 10-30%
Along with MW data  PLC(met) relation
■ metallicity dependence
■ zero-point
■ universality of the relation
 application to galaxies  H0
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Age determination: e.g. M3
•
•
•
Mod ~ 15.0  d ~ 10 kpc  π ~ 0.10 mas
RGB & HB stars: V ~ 12.5 – 15  σ(π) ~ ± 0.01 mas individually
with only 1000 such stars the distance would be known to about 0.3% …
... unprecedented accuracy - no need of calibrators
•
Error budget on absolute age determination via the TO:
Logt9 ~ -0.41 + 0.37 MV(TO) – 0.43Y – 0.13[Fe/H] (Renzini 1993)
Max error comes from distance
modulus & V(TO): from table values
 ~ 18% i.e. 2.2 Gyr
If distance were known to ±0.3% and
V(TO) to ±0.01 mag  age could be
known to ~ 9% i.e. 1.1 Gyr
Further improvement on reddening
& chemical abundance e.g. from gb
surveys or Gaia APs  age could
be known to ≤ 5% or better (errors
on theoretical models not included)
Input quantiy (IQ)
σ(t)/t
σ(IQ)
σ(t)/t
%
VTO
0.85σVTO
± 0.10
± 0.01
8.5
0.9
mod
0.85σ(mod)
± 0.15
± 0.007
12.8
0.6
AV (AK ?)
2.64σ(AV)
± 0.03
7.9
Helium (Y)
0.99σ(Y)
± 0.02
2.0
[M/H]
0.30σ[M/H]
± 0.10
3.0
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Photometry Measurement Concept (1/2)
Blue photometer:
330–680 nm
Red photometer:
640–1050 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
8
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)
Photometric accuracy
Internal calibration
(Jordi et al 2007, GAIA-C5-TN-UB-CJ-042)
• External calibration
From about 1 to a few %,
depending on
 accuracy of SPSS SEDs
 magnitude
 specific spectral range for
BP/RP spectra
• Astrophysical parameters
From BP/RP dispersed images
(low res SEDs) one can derive
 Teff ~ 200 K
 log g & [Fe/H] to 0.2 dex
 extinction
► complete characterisation of all
stellar populations
► detailed reddening map
G
σ(mmag)
G
σ(mmag)
GBP
σ(mmag)
GRP
13.0
2.5
2.5
2.4
14.0
3.0
4.1
4.0
15.0
4.8
7.1
6.7
16.0
7.6
12.9
12.3
17.0
12.3
26.3
24.7
18.0
20.3
58.6
54.7
19.0
35.1
139.0
129.4
20.0
66.2
340.6
316.8
(see Vallenari’s talk)
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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)
to all sources up to V < 16–17
Field of view
RVS spectrograph
CCD detectors
RVS spectra of F3 giant (V=16)
S/N = 7 (single measurement)
S/N = 130 over mission (~350 transits)
NOTE:
average (max) expected transits over
mission ~ 80 (260)  S/N ~ 60 (110)
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Figures courtesy David Katz
Scientific Organisation
• Gaia Science Team (GST):
– 8 members + ESA Project Scientist (Timo Prusti)
• Scientific community:
– organised in Data Processing and Analysis Consortium (DPAC)
– ~270 scientists active at some level
• Community is active and productive:
– regular science team/DPAC meetings
– growing archive of scientific reports (Livelink)
– advance of simulations, algorithms, accuracy models, pipeline, etc.
• Data distribution policy:
–
–
–
–
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, preprocessing,
data base + versions,
astrometric iterative solution
ESAC (+ Barcelona + OATo)
Photometry
Cambridge (IOA-C)
+ Variability
Geneva (ISDC)
Data simulations
Barcelona
Spectroscopic
processing
CNES, Toulouse
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DPAC structure
CU1: System Architecture
O’Mullane
(Lammers/Levoir)
(Brown, Cacciari, De Angeli, Richards
CU2:Data Simulations
Luri
(Babusiaux/Mignard)
CU6:Spectroscopic Processing
Katz/Cropper
(+ steering committee)
CU3: Core Processing
Bastian
(Lattanzi/Torra)
CU4:Object Processing
Pourbaix/Tanga
(Arenou, Cellino, Ducourant
Frezouls)
CU5:Photometric Processing
van Leeuwen
CU7:Variability Processing
Eyer/Evans/Dubath
CU8:Astrophysical Parameters
Bailer-Jones/Thevenin
CU9:Catalogue Access
To be activated
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The Italian contribution - I
(from the response to the ASI Gaia RfQ)
Torino (OA, Uni, Poli) + Trieste: ~ 20 people,
 CU2/3/4 - simulations, astrometry (core & object)
Padova (OA, Uni): ~ 10 people
 CU8/5 – astrophysical parameters, photometric calibration
Bologna (OA): ~ 12 people
 CU5/7 – absolute photometric calibration, variability
Roma+Teramo (OA, Uni): ~ 12 people
 CU5/7 – flux extraction in crowded fields, variability
Napoli (OA): ~ 9 people
 CU7/8 - variability, astrophysical parameters
Catania (OA, Uni): ~ 9 people
 CU2/7/8 - simulations, variability, astrophysical parameters
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The Italian contribution – main activities
DPC (TO)
 astrometric verification for a subset of bright
stars V ≤ 15 ( ~30 million stars)
 bright star treatment for astrometric accuracy
 monitoring of Basic Angle (astrometric accuracy)
 simulations astrometric and spectro-photometric payload
 national facility with final end-of-mission database
Astrophysical parameters (PD, NA)  stellar libraries for complete
characterisation, special objects
Spectro- Photometry  flux extraxtion in crowded conditions (RM-TE see Posters 11, 12)
 absolute flux calibration model (BO/PD)
 observing campaign for SPSS (BO)
Variability analysis (BO/RM/TE/NA/CT)
 impact on astrometric accuracy
variability characterisation, special objects
General Relativity model (TO/PD)
Others (interstellar reddening model, Solar System objects, extra-solar planets, etc.)
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More information on
http://www.rssd.esa.int/Gaia
http://www.to.astro.it
http://www.bo.astro.it
Thank you !
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Status and Schedule
• Prime contractor: EADS-Astrium
– implementation phase started early 2006
• Main activities and challenges:
–
–
–
–
–
–
–
CCDs and FPA (including PEM electronics)
SiC primary mirror
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
2000
2004
2008
2016
2012
2020
Concept & Technology Study
(ESA)
ESA acceptance
Re-assessment:
Ariane-5 
Technology
Soyuz
Development
Design, Build,
Test
Launch
Cruise to
L2
Observations
Data
Analysis
Early Data
Catalogue
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Exo-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:
–
–
–
–
1.2
d(")
Planète : r = 100 mas P = 18 mois
1/07/02
10–20,000 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 (")
0.832
1.0
Studies of the Solar System
• Asteroids etc.:
–
–
–
–
–
–
–
deep and uniform (20 mag) detection of all moving objects
105–106 new objects expected (340,000 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 (1775, 2020, 336 known today)
– ~1600 Earth-crossers >1 km predicted (100 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
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
Parallax Accuracy
1 kpc
None
None
1 milliarcsec
Photometry
photometry
Abs. Accuracy
Rel. Accuracy
Radial velocity
Observing
programme
2-colour (B and V)
~ 0.10 mag
~ 0.01 – 0.10 mag
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
1-3% at V < 16
1-10 mmag
15 km/s to V = 16-17
Complete and unbiased
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