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Content
Gaia and its science instruments w The satellite w The instruments
• Astrometry • Spectrophotometry • Spectroscopy
Gaia – ngCFHT synergies w The Galactic MIS in 3-D w Stellar astrophysics w Multiple stars and giant exoplanets w Milky Way formation and evolution
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Gaia: a unique experiment
The next cornerstone of the ESA Science Programme
Unique characteristics w Unprecedented astrometric accuracy (5-300 µas),
function of target magnitude and colour
w Systematic sky survey from V = 6 down to V = 20
w More than 109 objects observed all over the sky
w Simultaneous astrophysical characterisation of all observed objects + radial velocity for V < 17
w 70 observations (average) per object over 5 years
w Stars, Solar System objects, QSOs, galaxies
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© Astrium
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A few photos of the instruments
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© EADS Astrium SAS, France
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Protoflight Payload Module
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© Astrium SAS, 11 August 2012
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Focal plane
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Sky mappers
Astrometric field
Spectrophotometers
RVS
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© Astrium, 20 October 2011
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Astrometry (1)
Magnitude [mag] 6 – 12 15 20
Precision [μas] 5-14 9-26 100-330
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)
The precision depends on magnitude and spectral type: • The brightest and reddest stars are most precisely measured.
The standard-error includes all known instrumental effects w and a 20% margin for scientific calibration errors such as mismatch of the
model point spread function, sky-background estimation errors, etc.
End-of-mission parallax standard error, averaged over the sky:
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Astrometry (2) Trigonometric parallaxes to better than
w 0,1 % for ~ 100 000 stars (3 in Hipparcos) w 1 % for ~ 11 millions stars (719 in Hipparcos) w 10 % for ~ 100 millions stars (30 000 in Hipparcos)
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End of mission sky average standard errors u on positions = 0.7 x σπ u on proper motions = 0.5 x σπ
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Parallel astrometric, photometric, and spectroscopic observations
Broad-band photometry: the most accurate, 4 broad-bands: G (350-1000 nm), BP, RP, GRVS
Spectro-photometry (BP and RP) to G=20 • to account for chromatic aberrations in the astrometric focal
plane and achieve microarcsec accuracy level • to obtain the astrophysical parameters of the observed objects
Radial velocity spectometer (RVS) • to measure radial velocities, to V = 17 • to obtain rotational velocities, atmospheric parameters,
abundances and extinction to V = 12-13 all three instruments multi-epoch!
Difficulty for all three instruments: self-calibration.
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The red and blue spectrophotometers
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© Astrium"
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Spectro-photometric instrument
© EADS-Astrium
Blue: 330–680 nm, 3-27 nm/pixel Red: 640–1050 nm, 7-15 nm/pixel RP spectrum of
M dwarf V=17.3
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Well-defined and huge sample: u limiting magnitude as a function of stellar density
Stellar parameters u Teff to a few 10 K V ≤ 15
to < 200 K V ≤ 19 u Gravity to 0.1 – 0.2 dex V ≤ 19 u Metallicity to 0.1 – 0.35 dex V ≤ 19 u Extinction to 0.05-0.2 mag V ≤ 15
to < 1 mag V ≤ 19 Variability: single epoch accuracy of 5-15 mmag at V = 15 End-of-mission photometric errors: < 10 mmag for BP/RP and V ≤ 18 1-3 mmag for G up to G = 20
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Radial Velocity Spectrometer
Field of view Detectors
Over the mission: ~ 40 obs. = 120 spectra per object RVS spectra of G2V star V S/N S/N transit mission 6 150 1060 14 2 20
Integral field spectrograph λ range: 847 – 874 nm R = 11 500 to V=17 (end of mission)
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© Astrium"
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Gaia spectroscopy Systematic all-sky survey
w Well-defined and huge sample, limiting mag function of stellar density w Multi-epoch scan: ~ 40 observations over 5 years (average)
Stellar and interstellar parameters u Radial velocities (15 km/s) V ≤ 17 ~ 150 × 106 stars u Radial velocities (1 km/s) V ≤ 13 ~ 5 × 106 stars u Rotational velocities V ≤ 13-14 ~ 5-10 × 106 u Atmospheric parameters V ≤ 13-14 ~ 5-10 × 106 u Abundances (Mg, Ti, Si, N) V ≤ 12-13 ~ 2-5 × 106
u Interstellar reddening V ≤ 13-14 from 862 nm DIB Diagnostics
u Binarity/multiplicity, variability, … From astrometry + BP/RP: atmospheric parameters to V=18-20,
[Fe/H] ± 0.1 dex to V=15 (target 18), ± 0.4 dex to V=18.5 (target 20) ngCFHT Workshop, 27-29 March 2013 13
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Gaia huge discovery potentialities
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■ Deciphering the Galaxy (complete census of Solar neighbourhood, stellar populations: distances, kinematics, metallicity, astrophysical characteristics; thin-thick disc; 1st stars; luminosity function; 3-D ISM; etc)
■ Stellar physics (clean HR diagram, M, L, log g, Teff, [Fe/H], etc) ■ Distance scale (geometric to 10 kpc, Cepheids, RR Lyr, etc) ■ Galaxy and Local Group dynamics (hierarchical formation, streams, dark
matter distribution, etc) ■ Ages (cluster diagrams, distances, absolute luminosity) ■ Reference systems (1st optical; link to VLBI and dynamical systems) ■ Exo-planets (astrometry: systematic monitoring of hundreds of thousands
of stars within about 200 pc --> giant planets + identification of nearby targets for further detailed observation ; transits)
■ Fundamental physics ( γ ~ 5 x 10-7 , precession of asteroids perihelia to ~ 5 x 10-4)
■ Solar System (Taxonomy, Masses, Orbits) And serendipity !!!
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Gaia – ngCFHT synergies: 3D study of the Galactic MIS Gaia
w Very dense net of stars down to V ≈ 20 with very accurate distances w Individual extinction measurements for millions of stars w 8620 Å DIB from the RVS down to V = 13-14
ngCFHT w High multiplexing + wide field of view --> many stars in a large fraction of the sky w High R and S/N within adequate λ --> key ISM absorption features
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Ø Spectroscopic absorption towards huge number of individual stars of known distances from the different gas phases, tracers of dense molecular, diffuse atomic, diffuse ionized gas + DIBs
Ø Smaller distance between target stars --> much better identification of gas structures and distances, at higher spatial resolution.
3D distribution of Na I absorption + Hipparcos distances
--> structure of the Local Cavity --> min size of clouds = 20pc
300 x 300 pc
Welsh et al, (2010)
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Gaia – ngCFHT synergies: stellar astrophysics Gaia w Accurate luminosities, temperatures, chemical abundances, masses, rotation
+ extinction for all types of stars, covering the full range of the HR diagram w Systematic detection of variable stars + geometric calibration of stellar candles w Age determination: A-F stars, subdwarfs, etc., clean sequences of clusters w Size of convective cores, internal diffusion of elements, etc. w Selection of rare stellar types and stars in rapid evolutionary status ngCFHT w Unprecedented survey of temperatures, chemical abundances, luminosities,
mass, magnetic field, etc. for all Galactic components w Rare types of stars: first stars, very massive stars, solar
twins, bulge metal poor stars, white dwarfs, etc. Ø High-precision position in the HR diagram of a huge sample
of stars of known surface abundances Ø Test of models of stellar internal structure Ø Successive stages of stellar evolution (≠ masses) Ø Calibration of stellar candles as a function of metallicity, etc.
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Y. Lebreton-2009
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Gaia – ngCFHT synergies: multiple stars and giant planets
Gaia w Systematic detection of binaries + 3x106 (RV + astrometric) orbits + 3x106 non-
linear pm + 40x106 resolved binaries + x00 000 eclipsing binaries w Systematic detection of giant (and Jupiter-like) planets orbiting x00 000 bright
stars ≤ 200 pc, 7 orbital elements -> mass for x000 planets, P: 2-10 yrs + transits w Luminosities, atmospheric parameters and metallicity stars hosting planets w <1% distance estimates for all bright Corot-Kepler transiting planet hosts and radial
velocity detected systems. ngCFHT w Systematic detection of binaries: RV orbits w Detailed chemical abundances for stars hosting
gas giants / rocky planets Ø Complete census and characterization of low-mass
stellar and brown dwarfs companions Ø Planets - and multiple planet systems - frequency
as a function of the host star’s properties Ø Characterization of stars hosting planets versus planet mass
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Solar motion at 100 pc
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µas
µas
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2010
2020
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Mouvement du Soleil à 10 pc
µas
GAIA at V = 15 mag
© F. Mignard
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Gaia – ngCFHT synergies: Milky Way Gaia: 1 billion stars, all over the sky, over all Galaxy components w 3D-position + kinematics + metallicity for ~1% of the stars of the Galaxy w Detailed characterization of all Galaxy components: structure, kinematics, ages,
metallicity distribution, astrophysical characteristics, luminosity function w 3D-position + kinematical and chemical tagging of stars members of all galactic
clusters, globular clusters and stellar streams --> unbiased selection w Complete census of Solar neighbourhood down to giant planets ngCFHT: millions of stars, over ¼ of the sky, over all Galaxy components w Precise radial velocities and extensive chemical tagging down to g = 20 for Gaia
stars with precise astrometry but no spectra (stars fainter than 16-17) w Detailed and comprehensive chemical tagging for Gaia stars with the most
precise astrometry Ø Complementary, extensive and in-situ characterization of millions of stars --> the
most detailed dataset ever obtained on the Galaxy (and on any galaxy ...) Ø Major breakthrough in the detailed study and understanding of the composition,
structure, dynamics, star formation history and chemo-dynamical evolution of our Galaxy, especially the halo and thick disc
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Merci de votre attention
True 6D in 2020!
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