Gaia Stereoscopic Census of our Galaxy

http://www.cosmos.esa.int/web/gaia http://gaia.ac.uk

one billion pixels for one billion stars one percent of the visible Milky Way

Gerry Gilmore, UK Gaia PI, on behalf of DPAC

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Data flow: 50Gb/day for 5-8 years; total processed data and archives 1PByte Computational challenge : 1.5 x 10²¹ FLOP – and highly sophisticated algorithms

Gaia: the goddess who created the universe and knowledge Gaia is transformational – the first 3-D galaxy

precision distances and motions for 1 billion stars • Astrometry, photometry, spectroscopy, spectrophotometry, Teff, log g, Av, [Fe/H], binarity, planets, periods for variables,…

The heart of Gaia is a large camera array, 1 giga-pixel, sending us a video of the sky for 5-8 years. The imaging data is being processed in Cambridge. 4 billion transits processed so far

Launch: 12/2013 Work started: ~1993 Project approved: 2000 Operations start 7/2014 5-7.5 years data Project end: 2023+ Total cost: 960M€

2 telescopes, 1.45 x 0.5 m primary, monolithic SiC optical bench, 0.06arcsec pixels

GAIA: Key Science Objectives ⇒ Origin, Formation and Evolution of the Galaxy

Structure and kinematics of our Galaxy: – shape and rotation of bulge, disk and halo – internal motions of star forming regions, clusters, etc – nature of spiral arms and the stellar warp – space motions of all Galactic satellite systems

Stellar populations: – physical characteristics of all Galactic components – initial mass function, binaries, chemical evolution – star formation histories

Tests of galaxy formation: – dynamical determination of dark matter distribution – reconstruction of merger and accretion history Revolutionary science from solar system to cosmology planets, cosmology, fundamental physics, NEOs, ….. This broad range of topics allows a range of follow-up transients, detailed studies, rare objects, outreach,... but most of the science case requires statistics!

What will Gaia see as stars move?

Trend: stellar orbit Galactic dynamics, dark matter, assembly history, ... Cycloid: parallax = 1/distance Galactic structure, star formation history Loops: high frequency motion massive planetary systems

Gaia accuracy 10 to 100 times better

These are real Hipparcos observations

47 UMa

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What does micro-arcsecond mean?

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• Precision: 50pico-rad, human hair at 1000km, coin on the moon • Astrometry needs more than signal to noise and image processing • One must have a physical model and understanding of every

contribution to the error budget at an appropriate level • Einstein light bending at the Sun’s edge is 1,750,000 microarcsec • One mu-as is the limit to which we have tested GR… • For Gaia the spin rate is controlled to 15 ppm • The spacecraft distance is known to a few metre (at 1.5 Million km) • The spacecraft speed is known to a few mm/s • On-board interferometer measures mirror locations to picometre level

every few seconds – a helium atom is 30picometre • clocks, pixel substructure -- and very much more

• 400 people are busy with the data processing and analysis

Gaia – 5-year parallax standard error

complete to G=0, with poorer standard error

Calibration floor

How does Gaia work?: Sky Scanning Principle

Observe sky with two telescopes

Precision: 50pico-rad, human hair at 1000km, 2cm on the moon...

Gaia is a simple 2-telescope optical bench

Absolute astrometry One field gives only relative measures model dependancy Two fields break the degeneracy allows absolute measurements. Combining data at the limits of accuracy is not trivial!

9 Single field astrometry Two field astrometry

two-telescope scanning mission is optimal. Since across-scan data is much less important, can save mass and use rectangular mirrors

Why rectangular?

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Gaia science data flow: 5,000 stars/second on average

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The astrometric data reduction • 1013 individual position measurements

• 1010 unknowns – based on physical models • all connected - must be determined simultaneously • a vast modelling and parameter adjustment problem • Iterative, self-calibrating, needs GR metric • 5000 million star unknowns (for simple stars) • 150 million attitude unknowns • 50+ million calibration unknowns • a few dozen “global” unknowns • DPAC involves 400 people and 6 processing centres

Eg, photometric ubercalibration:

Another order of magnitude to improve, but we are on the way

05/06/2014 IoA Seminar 14

Higher L2 dust environs will gently sand-blast JWST’s mirror….

CCDs, electronics, clocks, communications, spacecraft control, … functioning nominally

Complete sky survey from 0 < G > 20 Mission extension from 5 years to 7.5 years under analysis

05/06/2014 IoA Seminar 15

Heating cleans the mirrors

Scattered Light (RVS): mean level 30x expected adds noise to faint sources – astrometry recovered by mission extension

6 hour period = Gaia’s spin period

Sunlight diffracted around sunshield

Astronomical sources

RVS is delivering 60million spectra, R=11,000, complete to V<15.3

Scattered Light (RVS): mean level 30x expected adds noise to faint sources – astrometry recovered by mission extension

6 hour period = Gaia’s spin period

Sunlight diffracted around sunshield

Astronomical sources

RVS is delivering 60million spectra, R=11,000, complete to V<15.3

Gaia Performance (at In Orbit Commissioning Review)

http://www.cosmos.esa.int/web/gaia/science-performance

Astrometric Performance

Photometric Performance: units=mmag

Spectroscopic Performance: 60 million RVs Plus Spectro-Photometry, T_e, log g, A_v, light curves, variability, [Fe/H]… for 1 billion sources

Complete sky survey 0 < G > 20

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What’s the science? Part 1

• Proper motions of 20 muas/a: (V=15)

• 20 muas/a = 10 m/s at 100 pc, i.e. planets can be found at half a million stars (Jupiter moves the sun by 15m/s) • 20 muas/a = 1 km/s at 10 kpc, i.e. even the lowest-velociy stellar populations can be kinematically studied throughout the entire galaxy • 20 muas/a = 5 km/s at 50 kpc, i.e. the internal kinematics of the Magellanic clouds can be studied in as much detail as the solar neighbourhood can be now (5 km/s = 2.5 mas/a at 400 pc!) • 20 muas/a = 100 km/s at 1 Mpc, i.e. a handful of very luminous stars in M31 will show the galaxy’s rotation

(MV=+10)

(MV=-10)

(MV=0)

(MV=-3.5)

• Parallaxes of 20 muas: (V=15)

• 20 muas = 1 percent at 0.5 kpc, i.e. 6-dimensional structure of the Orion complex at 2pc depth resolution • 20 muas = 10 percent at 5 kpc, i.e. direct high-precision distance determination of even very small stellar groups throughout most of the Galaxy • 20 muas = 100 percent at 50 kpc, i.e. a direct distance determination of the Magellanic clouds is at the edge

•Linear sizes of 20 muas: (V=15)

• 20 muas = 1 solar diameter at 0.5 kpc, i.e. normal sunspots do not disturb the measurements, but Jupiters do, structure on giants,

• 20 muas = 1 AU at 50 kpc, the limit of parallax measurements

NEO/Aten/Apollo (Chelyabinsk!)

Main belt asteroid

Best ground > mas accuracy

Gaia

Gaia is providing a survey of NEO-threat asteroids with orbits interior to Earth and improved orbits for many MB asteroids, with many masses, radii,…

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accu

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Planetary systems – Gaia will find some transiting systems, but the real value is definition of volume-complete stellar parent samples, plus direct astrometric discovery, and mass determinations, of nearby non-eclipsing jupiters. These will be ideal for follow-up direct coronographic imaging

Perryman etal 2014 arXiv:1411.1173

Astr

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gnat

ure

Period (yr)

RV Jupiters are easy astrometric detections

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Stellar evolution, young stars, rare objects, Galactic structure, SFR(t)

Omega Cen: 140K stars, 1min data

At LMC 20muas/yr=5km/s

Stellar populations Gaia manages most of the sky uncrowded ~HST spatial resolution

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Cosmological distance scale calibration at mmag level

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General Relativity/Metric

• From positional displacements: – γ to 5×10-7 (cf. 10 -5 presently) ⇒ scalar-tensor theories – effect of Sun: 4 mas at 90o; Jovian limb: 17 mas; Earth: ~40 µas

• From perihelion precession of minor planets: – β to 3×10-4 - 3×10-5 (×10-100 better than lunar laser ranging)

– Solar J2 to 10-7 - 10-8 (cf. lunar libration and planetary motion)

• From white dwarf cooling curves: – dG/dT to 10-12 - 10-13 per year (cf. PSR 1913+16 and solar structure)

• Gravitational wave energy: 10-12 < f < 10-9 Hz

• Microlensing: photometric (~1000) and astrometric (few) events

• Cosmological shear and rotation (cf. VLBI)

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Gaia will repeat the Eddington 1919 light-bending test 100 years later, with 100,000 times higher precision

Gaia will measure light bending by Jupiter to test GR

Gaia is a transient explorer

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High-resolution transient photometry and spectro-phot

Sky sampling for nominal 5-year mission

Some examples from 1-month ecliptic pole high sampling

SN Gaia14aaa: correct deduction of type, age, redshift

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Images from Liverpool Telescope Gaia discovery spectrophotometry

Gaia discovery photometry

Gaia science has started! This will support a big outreach & education programme w. Las Cumbres few 1000 local SNe

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The Gaia Data Release (GDR) Scenario http://www.cosmos.esa.int/web/gaia/release

● GDR1 ~7/16: positions, G-magnitudes (~all sky, single stars) proper motions for Hipparcos stars (~50 µarcsec/yr) – the Hundred

Thousand Proper Motions (HTPM) catalogue ● GDR2 ~2/17: + radial velocities for bright stars, two band

photometry and full astrometry (α, δ, ϖ, μα, μδ ) where available for intermediate brightness stars

● GDR3 ~1/18: + first all sky 5 parameter astrometric results (α, δ, ϖ, μα, μδ ) BP/RP data, RVS radial velocities and spectra, astrophysical parameters, orbital solutions short period binaries

● GDR4 ~1/19: + variability, solar system objects, updates on previous releases, source classifications, astrophysical parameters, variable star solutions, epoch photometry

● GDR-Final: final data release (thus in 2022/23 or 2025) Full dataset for more sophisticated modelling released at end of mission

We have Gaia! We want more…

• Gaia will provide 60 million spectra to V=15.2 • Many ambitious ground-based projects plan

to complement the Gaia astrometry • Weave, 4most …+ AAT, lamost, US… • eg MOONS contract signed 25/09 • One precursor is the Gaia-ESO Spectroscopic

Survey http://www.gaia-eso.eu

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Gaia-ESO Survey

300+ VLT-night survey of Galaxy stellar pops •Co-PIs Gerry Gilmore, Sofia Randich

•+400 Co-Is, 90+ Institutes across all ESO

•19 Working Groups •active wiki internal communications – 100-800 views/day

•~110 Co-I science projects listed in wiki

•DR1 data release through ESO completed •25+ refereed papers published or in late draft (+archive)

•Big ESO DR2 due in a few months

http://gaia-eso.eu (public survey pages) http://great.ast.cam.ac.uk/GESwiki/GESHome http://casu.ast.cam.ac.uk/gaiaeso/ http://ges.roe.ac.uk (public archive)

Gaia-ESO core philosophy

• Involve all spectroscopic analysis methods • Identify the dominant systematic variables,

and fix them – version control • Analyse spectra through all interested groups • In principle, this allows us to identify both

systematic method errors and random errors • parameter +/- random +/- systematic

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Gaia-ESO Giraffe spectra even with narrow target selection, a very

wide range of parameters is evident there is no single analysis aproach

summary

• Gaia is working. First science alerts are appearing now. Data will be good.

• Gaia-ESO is working. First science is good. • The sociology in astronomy is changing,

towards data free to everyone- you! • Realising the Gaia potential provides huge

opportunities to extend our community, as well as our knowledge

• Its worth the considerable effort.

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Is there a thin-thick difference in alpha/Fe DF? Furhmann was there first – careful, single method approach

Recent fuss from SDSS about (lack of) complexity in disk chemistry-kinematics Disagreed with available high-resolution studies: issue was biases, need survey

Fuhrmann MNRAS 414 2893 (2011)

Clear bimodality between thick and thin disks