GaiaStereoscopic Census of our Galaxy
https://www.cosmos.esa.int/web/gaia/home https://gaia.ac.uk
one billion pixels for one billion starsone percent of the visible Milky Way
Gerry Gilmore FRS, UK Gaia PI, on behalf of DPAC
1
Launch 12/2013Mission to 08/2019
Extend to 12/2023(end of gas)
Image Credit: A Moitinho, M. Barros, F. Mignard on behalf of DPAC
1.1 billion objects: calibrated brightness measurementsAccuracy better than predicted already Gaia GDR1 9/2016
The value of extra information:
This is the Hipparcos-basedHertzsprung-Russell diagram
Colour code is proper motion:Blue=small, red=large.
The Galactic age-velocity relationis immediately obvious.
Spectra add elementalabundances and precise radialvelocity
With 2-3-4 families of elements, (and sub-giant ages with Gaia)this increases dimensionalityand adds statistical weight.
V-I Colour
HIPPARCOS mission 2005
stellar distances tells us how bright stars really arethis provides the key to how stars evolve
the Hertzsprung-Russell diagram
Gaia GDR1: two millionstellar distances
Colour-magnitude relationaccurate distances define the way stars evolve
Science applications: stellar evolution, structure of the Milky Way, spiral arm dynamics,Dark Matter distribution, stellar mass function, planet host properties, history of thechemical elements, solar siblings, star cluster evolution and dissolution……
Quantify the history of the growth of structure, chemical and dynamical evolution in our local Universe.
76 103 to101 −− ××≈γσ
•in our Galaxy …–the distance and velocity distributions of all stellar populations–the spatial and dynamic structure of the disk and halo–its formation history–a detailed mapping of the Galactic dark-matter distribution–a rigorous framework for stellar-structure and evolution theories–a large-scale survey of extra-solar planets (~70,000 systems)–a large-scale survey of Solar-system bodies (~250,000)•… and beyond–definitive distance standards out to the LMC/SMC–rapid reaction alerts for supernovae and burst sources (~10,000)–quasar detection, redshifts, lensing structures (1,000,000)–fundamental quantities to unprecedented accuracy: e.g. relativistic light bending due to gravity: PPN σγ ~2×10-6 (~2×10-5 present)
7
Precision: 50pico-rad, human hair at 1000km, 2cm on the moon...
8
9
NEO/AtiraEarth-crossing?
Best ground > mas accuracy
Gaia
Gaia is providing a survey of NEO-threat asteroids with orbits interior to Earthand improved orbits for many MB asteroids, with many masses, radii,…
Orb
ital
accu
racy
Planetary systems – Gaia will find some transiting systems, but the real valueis definition of volume-complete stellar parent samples, plus direct astrometricdiscovery, 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
omet
ricsi
gnat
ure
Period (yr)
RV Jupiters are easy astrometric detections
Galaxies, Quasars, and the Reference Frame
• Parallax distances, orbits, and internal dynamics of nearby galaxies
• Galaxy survey, including large-scale structure
• 1,000,000+ quasars: kinematic and photometric detection
• ~10,000 supernovae [few/day real-time alerts]
• ΩM, ΩΛ from multiple quasar images (3500 to 21 mag)
• Galactocentric acceleration: 0.2 nm/s2 ⇒∆(aberration) = 4 µas/yr
• Globally accurate reference frame to ~0.4 µas/yr
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: 10-9 < f < 10-7 Hz
• Microlensing: photometric (~1000) and astrometric (few) events
• Cosmological shear and rotation (cf. VLBI)
13
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
The astrometric GW sky
14
Simulation by Mihailovic, Moore, Gilmore, Lasenby
A passing GW imposes a – low amplitude! – quadrupole distortion on the sky
Gaia is a useful Time-Domain system: not optimised, but no alert delaysimultaneous photometry, astrometry, spectrophotometry
Gaia spectrophotometry 350 – 1020nm
Data are NOT flux corrected forinstrumental response
Data flow: 50Gb/day for 5-8 years; total processed data and archives 1PByteComputational 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 galaxyprecision 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 largecamera array, 1 giga-pixel, sending us a video of the sky for 5-10 years.
The imaging data is being processed in Cambridge.130 billion transits processed so far
Launch: 12/2013
Work started: ~1993Project approved: 2000Operations start 7/20145-7.5 years dataProject end: 2023+
Total cost: 960M€
2 telescopes, 1.45 x 0.5 m primary, monolithic SiC optical bench, 0.06arcsec pixels
20
Gaia's L2 Orbit
Gaia in orbit
How does Gaia work?: Sky Scanning Principle
Observe sky with two telescopes
Precision: 50pico-rad, human hair at 1000km, 2cm on the moon...
Absolute astrometryOne field gives only relative measures model dependancyTwo fields break the degeneracy allows absolute measurements.
Combining data at the limits of accuracy is not trivial!
22Single field astrometry Two field astrometry
.
05/06/2014 24
Photometric processingat DPCI Cambridge
Flux calibration Evans etal1701.05873
Gaia is a micro-arcsec/pico-radian machine
• We measure pixel-flux at a measured time • Need spacecraft position, attitude, velocity, structure … to convert
time to sky coordinate• pico-radian = one part in 10^12, • Special, General Relativity are dominant terms• velocity to mm/sec [c= 3.10^11 mm/s]• position at L2 to ~km• instantaneous spin rate• Solar light bending at 90deg from Sun = 4 mas• Mirrors create colour terms• All this needs real physical models of everything – parametric fits
inadequate • Precision astrometry is MUCH HARDER than you think.
25
26
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
Gaia science data flow: 5,000 stars/second on averageNote: science-ready data don’t exist until all pipelines converge – we then release after minimal verification
Gaia is a superb instrumentwith some real-world complexity
• Scattered light – mitigated through optimising and mission extension
• Ice on mirrors: heaters
• Micro-clanks
• Basic-angle variations• Amplitude (1mas) =1/10 He atom
28
Heating cleans the mirrors
What will Gaia see as stars move?
Trend: stellar orbit Galactic dynamics, dark matter, assembly history, ...Cycloid: parallax = 1/distance Galactic structure, star formation historyLoops: high frequency motion massive planetary systems
Gaia accuracy 10 to 100 times better
These are real Hipparcos observations
47 UMa
29
Gaia DR1 Sept 2016GDR1 introduces the community to Gaia
data: its has limitations.
05/06/2014 IoA Seminar 30
GDR1:two million
stellar distancesPleiades cluster distance:progress and a puzzle
32
Testing stellar evolution
NGC2547
Pleiades
Galactic structure
33
Vrot = 220 km/s
Distance calibration
05/06/2014 36LMC Cepheids & RRLyrae
Cepheids
RR Lyrae
https://gsaweb.ast.cam.ac.uk/alerts
Time domain astronomy
Gaia science: learning how to learn Science results – new sources, supernovae directly to the public. For schools, amateurs, anyone….• https://gaia.ac.uk is a simple interface
to all Gaia science
We are working with global robotic telescopes [LCOGT, FAULKES…] and the Institute for Research in Schools to follow-up Gaia discoveries.
School classes can learn science by doing original science. “Adopt a Supernova”
follow Copernicus:learn from data, not preconceptions.
Mission status
• Launch Dec 2013• Operations start July 2014• Spacecraft healthy• Data quality on-track to meet ambitions• Nominal 5-year mission end mid 2019• Extension approval underway – up to 5-years • Gas supply end Nov 2023 (+/- 1Yr)
40
GDR1 - First release: 14 September 2016
GDR2 - Second release: Q4 2017 : changing to April 2018, with enlarged data setsPotentially, the catalogue will be consisting of:Five-parameter astrometric solutions of objects with single-star behaviourIntegrated BP/RP photometry, where basic astrophysical parameter estimation has been verified (these parameters will also be released for G<17).Mean radial velocities will be released for objects showing no radial-velocity variation
GDR3 - Third release: 2018 (TBC)Potentially, the catalogue will be consisting of:Orbital solutions, together with the system radial velocity and five-parameter astrometric solutions, for binaries having periods between 2 months and 75% of the observing time Object classification and astrophysical parameters, together with BP/RP spectra and/or RVS spectra they are based on, will be released for spectroscopically and (spectro)photometrically well-behaved objects.Mean radial velocities will be released for those stars not showing variability and with available atmospheric-parameter estimates.
+ Solar Sysytem Objectshttps://www.cosmos.esa.int/web/gaia/home
Gaia public Data Releases: no proprietary science
Gaia Statistics @ 02-Feb-2017 11:36TCB• Days of mission data 922• Science data volume (Tb) 32.826• Number of object transits 63,856,881,667• Astrometric CCD measures 629,446,405,002• Spectrophotometric measures 133,721,923,582• Spectra measured 12,443,401,236• Transits of spectra 3,911,614,378• Mag limits 2 to 20.7 [-1<G<3 stars special scan mode]
during this talk Gaia measured ~3,000,000 objects0.5M spectra, 6M photometric, 25M astrometric points
All this will soon be freely available to all for science analyses43
