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GAIA and a new Optical Reference Frame Alexandre H. Andrei * GPA - Observatorio Nacional / MCT

GAIA and a new Optical Reference Frame Alexandre H. Andrei * GPA - Observatorio Nacional / MCT * GEA - Observatorio do Valongo / UFRJ This presentation was prepared using material from the ESA’s GAIA scientific community web site. GAIA. G A I A.

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GAIA and a new Optical Reference Frame Alexandre H. Andrei * GPA - Observatorio Nacional / MCT

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  1. GAIA and a new Optical Reference Frame Alexandre H. Andrei *GPA - Observatorio Nacional / MCT *GEA - Observatorio do Valongo / UFRJ This presentation was prepared using material from the ESA’s GAIA scientific community web site

  2. GAIA G A I A • 109 sources (stars, galaxies, QSOs, planets) • 10 µas @ V = 15 mag • Photometry ( 5 + 11 bands) ESA Mission Launch : 2011 Mission : 5 years • Radial velocity • Low resolution spectroscopy

  3. GAIA Schedule 2020 2004 2008 2016 2000 2012 Acceptance Technology Development Design, Build, Test Launch Observations Analysis Catalogue

  4. Main Science Goals • Mapping of the Milky Way • Stellar physics (classification, M, L, Ln g, Teff, [Fe/H] ) • Kinematics and dynamics of the Galaxy • Distance scales (trig parallaxes to 10 kpc, cepheids, RR Lyr) • Age of the Universe (Cluster diagrams, distances, luminosity) • Dark matter (Potential tracers) • Reference systems(Quasars, astrometry) • Extra-solar planets ( ~ MJ, astrometric and photometric method) • Fundamental physics ( g ~ 5 x 10-7 , b ~ 5 x 10-4 ) • Solar system (Taxonomy, Masses, Orbits, 5x105 bodies)

  5. Payload and Telescope Rotation axis SiC primary mirrors 1.4  0.5 m2 at 106° Superposition of fields of view SiC toroidal structure Combined focal plane (CCDs) Basic angle monitoring system

  6. Astrometric Focal Plane Total field: - area: 0.6 deg2 - size: 75  60 cm2 - number of CCD chips: 110+70 - CCDs: 4500 x 1966 pixels Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events Astrometric field: - pixel size: 10  30 m2 - f 46.67m, 44.2  132.5 mas - integration 3.3s per CCD - 10 measurements per crossing - window area: 6  12 pixels Broad-band photometry: - 5 colour Star motion

  7. Number of observations Spin axis 50o to Sun Scan rate: 60 arcsec/s Spin period: 6 hours Astrometric Fields over 1500 days - 50 to 150 astro. obs. - 150 – 200 phot. obs

  8. Scan width: 0.7° Sky scans (highest accuracy along scan) Data Reduction Principles 1. Objects are matched 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 6. System is iterated

  9. Astrometric Accuracy

  10. Basic procedure with GAIA • Observe extragalactic sources in the visible • There are plenty brighter than V =20 • Look for the anomalous proper motions to clean the sample • The remaining set will display an overall spin • Find w and apply -w everywhere • The results will be referred to the best inertial frame • paradigm of the ICRS

  11. Results of a Simulation • Assumptions : • QSOs observed with the same accuracy as a normal star • Additional noise included for source jitter : 20 µas • - larger than spos for V < 16 • QSOs have no peculiar transverse motion • Observed PM reveal the global rotation of the GAIA sphere • Space and magnitude distribution from Veron- Cety Catalogue

  12. 1000 V < 16 2500 V < 18 4000 V < 20 400 V < 16 4000 V < 18 16000 V < 20 Precision of the spin rate Direct materialization of the ICRS in optical wavelengths

  13. Zero point of the reference frame • One must set the pole and the origin : 3 parameters • On the principle large freedom • In practice : one must ensure continuity with previous frames • - Same as ICRS to FK5 : origin and pole within the uncertainties of FK5 • Solution : best fit, in some sense, to the ICRF. • - Overall rotation ex, ey, ez • For the defining sources : spos ~ 0.4 mas > GAIA measurement error • s(e) ~ 2 spos/n1/2 ~ 50 µas with n = 200 sources with V < 20

  14. Transverse motion • So far no systematic transverse motion detected • QSOs have fixed comoving coordinates • If Vt ~ H0 D ===> µ ~ 10 µas/yr • VLBI in 20 yrs with spos ~ 1 mas ===> µ < 50 µas • but sub-mas structure instabilities • Other sources : • microlensing P = 10-6 (Belokurov) ==> only a handful • matter ejection, superluminous motion • Variable galactic aberration • Macrolensing • Accelerated motion in the local group ? • GAIA has the opportunity to test the ICRS paradigm • Small proper motion is not a good test to keep or reject • Large PM and/or distance is a good one to reject stars

  15. Galactic Aberration 250" Galactic aberration over 250x106 years • The solar system is in motion in the Galaxy, V ~ 220 km s-1 • constant aberration of ~ 250" for the QSO wrt to comoving frame • not detectable (principle of relativity) • du = v/c • But the solar motion is not uniform • ~ circular motion of radius R ~ 8.5 kpc and period 250x106 yrs • the aberration is then variable

  16. How many QSOs GAIA will observe on ~ half of the sky • B  16 200 • B  18 20 000 • B  20 400 000 Hartwick & Schade, 1990

  17. Current catalogue of QSOs • Catalogue of Véron-Cety & Véron (2003) • 48921 QSOs brighter than B = - 23 • 15069 AGNs fainter than B = - 23 • z, photometry, position • Not a systematic survey but a compilation • heterogeneous mix of observations • Lack of data in the galactic plane • small regions densely populated due to local surveys • -60° < a < 60° and d ~ 0° • 130° < a < 260° and d ~ 47° • More from the SDSS

  18. Space Distribution AGN QSO BL Lac

  19. Gaia Magnitude Distribution

  20. GAIA Redshifts Distribution

  21. Three possibilities • ICRF sources • needed for the zero point • excellent subset for validation • very small • Current compilation or survey of QSO's • gives ~ 40 000 well identified QSOs • the SDSS survey • local surveys give an idea of the number of sources • GAIA autonomous recognition scheme • very few QSOs compared to stars • the needle in a haystack problem

  22. The challenge for GAIA • GAIA will observe ~ 500 000 QSOs G< 20 • ~ 10 9 stars : so classification test much better than 2x10-3 • Consequences • A survey over 100 deg2 with a 1% error selection test will yield : • 2000 QSOs and • 30 000 stars at b = 0° ==> efficiency of 3% • 3000 stars at b = 60° ==> efficiency of 40%

  23. The challenge for GAIA • Three independant methods based on GAIA data : • variability • proper motions and parallaxes • photometry with ~ 15 passbands (baseline) • Two goals : • complete survey allowing contaminants :: classification • clean subsample with no contaminants • Major on-going work at the CU8 and CU3. • Requirements will be met for a clean subsample

  24. Exemple of parametrized SED Smette et al, 2003

  25. QSOs recognition • Material available • Data base of 7600 synthetic spectra (Kurucz atlas) • 81 WD synthetic spectral • parametrized SED for quasars (continuum, emission lines, z) • Correct identification of • 96.1% of QSOs, • 98.9% of stars • 90.1% of WDs. • Only 0.3% of stars and no WDs are classified as quasars • this by decreasing identified QSOs to 91% A. Smette, J.F. Claeskens, 2002

  26. Relevance of the ICRF sources for GAIA • Current status of the ICRF : • Built upon the ICRS principles on extragalactic sources • Materialized in radio wavelengths with VLBI observations • GAIA will materialize the primary celestial frame in the optics • In principle no links with previous frame required • But one must ensure the best continuity with existing frame • No overall rotation relatively ICRF sources • Zero point should be within the uncertainties of the ICRF • Hence ICRF sources should be looked at with particular care • Stable sources must be selected

  27. ICRF 1998 Defining sources (212) Candidate sources (294) Other sources (102)

  28. ICRF sources in the visible

  29. Effect of galactic latitude

  30. Summary • • 500, 000 quasars: `kinematic’ and photometric detection • The multicolor selection should be very efficient • Distribution at medium and high galactic latitude ( |b| > 20°) ~ 20 / deg2 • Redshift to better than ~ 5% with spectral energy distribution • • Globally accurate reference frame to ~ 0. 4 µas/ yr • Direct materialization of the ICRS in optical wavelengths

  31. (Drimmell et al., 2005, Proc. “The Three-Dimensional Universe with Gaia”)

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