The Gaia Mission. Coryn Bailer-Jones Max Planck Institute for Astronomy Heidelberg, Germany. ISYA 2016, Tehran

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1 The Gaia Mission Coryn Bailer-Jones Max Planck Institute for Astronomy Heidelberg, Germany ISYA 2016, Tehran

2 What Gaia should ultimately achieve high accuracy positions, parallaxes, proper motions e.g. ~20 μas at G=15 entire sky to G~20 ~10 9 sources astrophysical parameters of sources light curves optical spectrophotometry radial velocities to G<15 (1-15 km/s)

3 Main science goals What is the Galaxy made of? distribution and properties of stars distribution of dark matter How did the Galaxy form? substructure in disk and halo (mergers) star formation history

4 Astrometry Earth Sun a r! star distant background stars Earth six months later

5 Astrometry Earth Sun a r! star distant background stars Gaia orbits Sun to create parallax effect Earth six months later Six dimensions of phase space positions: right ascension, declination distance (from parallax) tangential velocities (from proper motions and parallax) radial velocity

6 Gaia observations star positions as a function of time

7 Solving the astrometry Source parameters position, parallax, PM, RV Astrometric Global Iterative Solution Satellite attitude CCD calibration

8 The satellite Graphics: ESA, Astrium

9 Gaia (minus sunshield) in Kourou cleanroom

10 Payload Graphics: ESA, Astrium

11 Instruments Graphics: ESA, Astrium

12 Launch (19 Dec. 2013)

13 Earth-Sun L2 orbit

14 Astrometric accuracy End-of-mission parallax standard error [µas] Hipparcos calibration noise floor photon noise non-uniformity over the sky B1V M6V V [mag] Graphic: Anthony Brown (2013) μas at V<12; μas at V=15; ~350 μas at V=20-22

15 Gaia parallaxes fpe = fractional parallax error 8kpc within 80pc, fpe <0.1% 10 million within 800pc, fpe <1% 150 million within 8kpc, fpe <10% Image: NGC4565 from panther-observatory.com

16 Parallaxes are noisy: distance 1/parallax PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 127: , 2015 October The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A. Estimating Distances from Parallaxes CORYN A. L. BAILER-JONES Max Planck Institute for Astronomy, Heidelberg, Germany; Received 2015 May 06; accepted 2015 July 08; published 2015 September 21 ABSTRACT. Astrometric surveys such as Gaia and LSST will measure parallaxes for hundreds of millions of stars. Yet they will not measure a single distance. Rather, a distance must be estimated from a parallax. In this didactic article, I show that doing this is not trivial once the fractional parallax error is larger than about 20%, which will be the case for about 80% of stars in the Gaia catalog. Estimating distances is an inference problem in which the use of prior assumptions is unavoidable. I investigate the properties and performance of various priors and examine their implications. A supposed uninformative uniform prior in distance is shown to give very poor distance estimates (large bias and variance). Any prior with a sharp cut-off at some distance has similar problems. The choice of prior depends on the information one has available and is willing to use concerning, e.g., the survey and the Galaxy. I demonstrate that a simple prior which decreases asymptotically to zero at infinite distance has good performance, accommodates nonpositive parallaxes, and does not require a bias correction.

17 Inferring distance from parallax $ parallax $ error in parallax r distance $/as = 1 r/pc likelihood P ($ r, $) = " 1 p exp 2 $ $ $ 1 # 2 r posterior P(r $, $) / P ($ r, $) P(r) r = 100 uniform prior $ =0.01 P(ϖ r, σ ϖ ) ϖ σ/ῶ = 0.1 σ/ῶ = 0.2 σ/ῶ = 0.5 P (r ϖ, σ ϖ ) r

18 Stellar clusters Hertzsprung-Russell Diagram Hyades Hipparcos stars (colour is dust extinction) (Bailer-Jones 2011) 70 clusters within 500pc distances of individual stars to <1% for G<15 individual transverse velocities to <1km/s cluster ages from luminosities, main sequence position/turn off cluster dispersion from kinematics search for new structures in 6D phase and astro. param. space

19 Spectrophotometry (BP/RP) T eff = 5000 K, A V = 0 mag photon counts per band wavelength / nm

20 Spectrophotometry (BP/RP) T eff = 5000 to K photon counts per band wavelength / nm

21 Spectrophotometry (BP/RP) galaxies quasars ultracool dwarfs emission line stars photon counts per band x constant stars Teff variation stars A0 variation stars [Fe/H] variation stars logg variation wavelength / nm

22 Radial velocity spectra (RVS) [Fe/H] variation logg variation photon counts + offset Teff variation emission line stars wavelength / nm

23 Science objectives Composition, origin, evolution of the Galaxy Stellar structure and evolution (fundamental parameters) Stellar clusters (formation, dispersion) Astrometric reference frame Cosmological distance scale Binary stars (masses, mass-luminosity relation) Exoplanets (especially Jupiter-mass) Solar system asteroids (including near-earth objects) General Relativity tests (light bending) 3D map of interstellar extinction Galaxies, quasars, supernovae

24 Summary of the Gaia mission Gaia is the only large-scale, high accuracy astrometric mission It is operating well and producing huge amounts of data Gaia will contribute to many areas of astrophysics For more information see First data release is on 14 September 2016

25 The first Gaia data release

26 GDR-1 release date: 14 Acknowledgements: September 2016 DPAC, ESA, Airbus 1000 D&S, days after subcontractors launch

27 What will be released? Results of global astrometric solution 2D positions of 1.1 billion sources down to G 20.7 with a positional accuracy of about 10 mas the secondary set 2D positions, 2D proper motions, and parallaxes of 2 million sources down to G 12 with accuracies of about 0.3 mas and 0.3 mas/yr the primary set or TGAS (Tycho-Gaia Astrometric Solution) Light curves of 3360 variables (RR Lyrae, Cepheids) around the south ecliptic pole over 28 days with around 200 epochs Caveat: this is a preliminary release based on incomplete processing

28 Photometry in broad G-band throughput wavelength / nm

29 TGAS principle Gaia data (~2015) Tycho-2 position (~1991.5)

30 Astrometric solution Data: 5 25 Gaia transits over 14 (11) months (all sources) Set prior on 5 astrometric parameters for 2 million primary sources Tycho-2/Hipparcos positions and uncertainties broad priors on parallaxes and PMs (Tycho-2/Hipparcos not used) Run iterative solution over primary set get useful 5-parametric solutions fix attitude and CCD parameters Apply solution to secondary set only positions meaningful (with larger errors due parallax/pm neglect)

31 Limitations of GDR-1 short time span and few observations (11/14 months) no solution for accelerations (e.g. binarity, perspective acceleration) simplified attitude modelling (data gaps, long knot sequence, clanks) use of nominal PSF; no chromaticity correction; CTI neglected no closed loop on photometric astrometric solution simplified fit to Basic Angle Monitor data bright star photometry/astrometry is the hardest to calibrate

32 These images have been redacted prior to the data release. See for details

33 Some other aspects of the data Bright limit: G ~ 6 mag Photometric precision: mmag for sources with 10 transits Maximum source density in secondary set is about 1 million/deg 2 minimum separation to detect equal G binary: 0.23" / 0.70 Some filtering of data sources with too few observations or long data gaps for TGAS: σ(parallax) > 1 mas or σ(pos) > 20 mas for secondaries: σ(pos) > 100 mas or excess noise > 20 mas or N<5

34 Verification Parallaxes (and positions) solved for known quasars assuming them to have negligible proper motions defining quasars used to align GDR-1 with ICRF check on parallax zero point: good to 0.1 mas globally Hipparcos parallaxes for overlap with TGAS independent check on zero point with LMC, Cepheids, clusters, etc. used to inflate formal errors to get parallax accuracy of ~0.3 mas

35 And after Gaia DR-1? Gaia DR-2 planned for end of parameter astrometry on most Gaia sources (~ 1 billion) 22 months of data Tycho-2/Hipparcos positions will no longer be used G, GBP, GRP (with Teff calibration) for most sources mean radial velocities to GRVS < 12 for stars with constant RV and possibly more

36 Summary of Gaia Data Release 1 huge amount of work by DPAC, ESA, and industry positions for 1.1 billion sources, G<20.7, accuracy ~10 mas positions, proper motions, parallaxes for 2 million sources, G<12, accuracy ~0.3 mas and 0.3 mas/yr averaging will not give you a 1/ N error reduction (local error correlations) data from ESAC and mirrors; query tools, file download