The Three Dimensional Universe, Meudon - October, 2004

Transcription

1 GAIA : The science machine Scientific objectives and impacts F. Mignard OCA/ Cassiopée 1

2 Summary Few figures about Gaia Gaia major assets What science with Gaia Few introductory highlights Conclusion 2

3 Gaia 9 Sources V = 15 mag 3 ESA Mission Launch : 2011 Mission : 5 years Photometry ( bands) Radial velocity Low resolution spectroscopy

4 Strength of Gaia A single mission with three instruments Astrometric, photometric and spectroscopic data Uniform coverage of the sky Quasi regular time sampling over 5 years Survey mission sensitivity limited Internal and autonomous detection system Global astrometry of staggering precision Internal metrology, thermal and mechanical stability Experimented community in Europe after Hipparcos scientific and industrial 4

5 Space astrometry Direct results Position, parallaxes, proper motions on a very large number of stars 1 mas for Hipparcos - 4µas to 0 µas for Gaia Photometry to the mmag, ~ 150 epochs, ~ 12 bands Radial velocity to few km/s Spectrophotometry in the visible and near IR to V ~17.5 Survey of stars to V = 20 Detection of visual, spectroscopic and astrometric binaries Solar system objects ~ 500,000 Extragalactic sources ~ 400,000 5

6 Overall science goals : very broad Mapping of the Milky-way Stellar physics (classification, M, L, Ln g, T eff, [Fe/H] ) Galactic kinematics and dynamics Distance scale (geometric to kpc, HR diagram, cepheids, RR Lyr) Age of the Universe (cluster diagramms, distances, luminosity) Dark matter (potential tracers) Reference frame (Quasars, astrometry) Planet detection ( ~ M J, astrometry and photometric transits) Fundamental physics ( γ ~ 5 x -7, β ~ 5 x -4 ) Solar Physics (J2 sun ~ 5x -7 ) Solar system science (Taxonomy, Masses, Orbits, 5x 5 bodies) 6

7 A versatile mission Stellar Astrophys. Stellar systems 3 Oral presentations Galactic Structure Exo-planets 1 Posters GC, Qsos and galaxies Solar system 4 4 Physics and modelling Methodology 7

8 Pieces of Science in brief 8

9 A versatile mission Stellar Astrophys. Stellar systems 3 Oral presentations Exo-planets Galactic Structure Posters GC, Qsos and galaxies Solar system 4 4 Physics and modelling Methodology 9

10 Extra-solar Planets: Expected Discoveries Astrometric survey: monitoring of hundreds of thousands of FGK stars to ~200 pc detection limits: ~1M J and P < 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: ) 1/07/02 20,000 planets (~ per day) displacement for 47 UMa = 360 µas orbits for ~5000 systems 1/07/01 1/01/02 1/01/03 masses down to M Earth to pc 1/07/00 1/01/01 Photometric transits: ~5000? 1/01/00

11 A versatile mission Stellar Astrophys. Stellar systems 3 Oral presentations Galactic Structure Exo-planets 1 Posters GC, Qsos and galaxies Solar system 4 4 Physics and modelling Methodology 11

12 Solar system science Observational material from Gaia GAIA will survey solar system objects to V = 20 Objects will be repeatedly observed over 5 years Single measurement astrometry (1 transit) : 0 V = 15 2 V= 20 Photometric data in ~ bands Results expected Detection of NEOs, specifically inside the Earth orbit taxonomic classification relation with orbital properties Light curves and rotation parameters Observed Fitted Cellino et al.,2003 Orbits drastically improved with 5 years of observation then use of the astrometric archives with the new catalogue ~ 0 masses expected from close approaches 12

13 Close approaches and masses Number of approaches < 0.05 AU between : - a large planet (ID < 0) -one of the first,

14 A versatile mission Stellar Astrophys. 3 Stellar systems Oral presentations Galactic Structure Exo-planets 1 Posters GC, Qsos and galaxies Solar system 4 4 Physics and modelling Methodology 14

15 Small stellar systems Power of Gaia Survey mode, sensitivity to non linear motion ~ regular time sampling over 5 yrs Large range of separations and dm Spectroscopic measurements Expected results Detection of Detection of various kind of binaries : ~ 6x 7 binaries 7 resolved within 250 pc 7 astrometric binaries 6-7 eclipsing, 6 spectro 50% Complete census to 250 pc Masses to 1% for 4 stars Severe constraints on evolutionary models 15 < V < 17.5 S. Söderhjelm 15

16 A versatile mission Stellar Astrophys. Stellar systems 3 Galactic Structure Oral presentations Exo-planets 1 Posters GC, Qsos and galaxies Solar system 4 4 Physics and modelling Methodology 16

17 σ = V=15 V=15 Meudon temperature metallicity reddening luminosity M V kpc K0 IV K0 III K0 II From U. Munari

18 Stellar and galactic Physics :: too much to say New astrophysical text books for the 2020s : What is the mass of the heaviest stars? What is the rate of formation of stars in the milky way? What are the cooling sequence and the LF of the white dwarfs? Are brown-dwarfs common in binary systems? Are all stars ultimately variable? Are M, T eff, log g, [Fe/H] enough to make a star? How often a planetary system is found in binary systems? Are massive stars still forming in the galactic halo? Where does the halo come from? Is there dark matter out there? - 18

19 Stellar distances GAIA at V = 15 : Percentage of stars with σ π /π < 0.02 Galactic coordinates

20 Luminosity Calibration σ(π)/π : < 1% 21x 6 < 5% 116x 6 < % 220x 6 Stars with σ π / π % M V Type V limit d limit [mag] [pc] -5 O V A0 V K3 III G5 V M2 V M7 V M8 V brown dwarfs 20

21 A versatile mission Stellar Astrophys. Stellar systems 3 Oral presentations Galactic Structure Exo-planets 1 Posters GC, Qsos and galaxies Solar system Physics 4 4 Methodology 21

22 Fundamental physics The relativity experiments Light deflection in mas min χ χ = 45 deg Sun 13 mas Jupiter 16 2 µas r χ With 2x 7 stars V < 14 Gaia should yield : σ γ 1 6 to orders of magnitude better than Cassini More with Jupiter : J2 deflection = 240 µas Gaia will test the GR prediction 22

23 A versatile mission Stellar Astrophys. Stellar systems 3 Oral presentations Galactic Structure Exo-planets 1 Posters GC, Qsos and galaxies Solar system 4 4 Physics and modelling Methodology 23

24 Quasars and reference frame The inertial frame Gaia will detect and measure the position of ~ 400,000 QSOs They will be identified with photometric filtering + astrometry This will improve the current survey by a factor ~ A clean subset (free of stars) can be constructed The Gaia sphere will be rigidly attached to the EG sources N qso = galactic coordinates 0.5 µas/yr 24

25 More on QSOs and reference frame Detection of tangential velocity Random and systematic motion of QSO optical photo-centers Correlation with optical variability Observation of multi-imaged lensed Quasars Any acceleration Γ wrt to QSOs systematic proper motion du Γ Γ = ( u) u dt c c u Precision of ~ 0.4 µas/an (2 prad/an) on Γ/c = 0.2x - m s -2 (Γ 0 Pionner/40) Galactic rotation ( µ ~ 4 µas/yr Acceleration of the local group CDM? 25

26 Key questions for the distance scale Two major indicators Cepheids with PL, SNe Ia LMC is the keystone for calibration Standard PL : M v = log P 1.46 M I = log P 1.87 (Madore & Freeman, 1991) M v = log P 1.79 M I = log P 2.12 (Udalski, from OGLE 1999) Slope and zero point from LMC with µ = But there are indications that : Galactic Cepheids behave differently the PL relation depends on the metallicity Not a single relation applies to all periods Gaia will bring much light there with. 26

27 Distance to the LMC Cepheid Subdwarf Miras RR Lyr C LPV Red clump Eclip. Bin. RGB Reid Whitelock Romaniello 57.5 Distance modulus Feast Gratton Madore Van Leeuwen Bergeat Luri Fernley Luri Luri Luri Udalski Udalski Stansk Cioni Nelson Girardi Groenwegen Distance in kpc Madore Girardi Kovacs with Gaia : π = 20 µas N* ~ 6 σ π /π ~ 1-2% 27

28 And more Cepheids σ π / π < 1% d < 3 kpc (55 d < 1 kpc) σ π / π < 4% all galactic cepheids RR Lyr σ π / π < 1% d < 3 kpc (26 d < 1 kpc) σ π / π < % most galactic RR Lyr Mirae σ π / π < 6% all galactic Mirae Glob. Clust. 20 with σ π / π < % per star ages of oldest stars mean distance < 1% for 1 clusters LMC-SMC ~ 6 stars observable <d> ~ 1 to 2 % Cepheids with σ π / π < 30% Local group Geometric distances to ~ 8 galaxies Rotational parallaxes for few others SNe Ia Gaia could detect ~ 20 per month ( GB follow up) 28

29 A versatile mission Stellar Astrophys. Stellar systems 3 Oral presentations Galactic Structure Exo-planets 1 Posters GC, Qsos and galaxies Solar system 4 4 Physics Methodology & Modelling 29

30 Modelling and Methodology : big incentive Development of sophisticated tools of general interest Big effort to model the astrometry at the µas level Relativistic framework from the start Improved concepts around PM, parallax, radial velocity Developments of several extinction models Orbit determination over short arcs The data processing is a real challenge Developpement of numerical tools for automatic classification Application of powerful statisticial methods to a wide range of problems Efficient algorithms are tested to search for periods in time series Set up of a data base of consistent astronomical and physical data 30

31 Therefore if everything goes well. 31

32 In stars 6 V = 12, 30 x 6 V = 15, 250 x 6 v = 18 σ 4 µas V < 12, µas V = 15, 150 µas V = / deg 2 ; max : 3 x 6 /deg x 6 radial velocities Stellar classification for all classes and types Variability analysis over ~ 8 stars 000 stellar masses σ < 1 % Extra solar planets to 200 pc 5 x 5 minor bodies of the solar system, 0 masses ~ 5 x 5 QSOs + z + photometry, ICRF in the visible γ to ~ 7 and this will really be 32

33 the golden age of astrometry as 0 1 mas 0 1 µas Hipparchus Ulugh Beg Wilhelm IV Tycho Brahe Hevelius Flamsteed 2000 yrs dex Naked eye telescopes Bradley-Bessel FK5 20 Hipparcos yrs GAIA SIM GC 4.5 dex ICRF as 0 1 mas 0 1 µas 33

34 34 USNO A2