Gaia Lecture
0 likes217 views
Gaia is a spacecraft that collects data to create a 3D map of the Milky Way galaxy. It was launched in 2013 and orbits the Sun-Earth L2 point. Gaia has two telescopes that collect images which are processed to provide astrometric and photometric data on over 1 billion sources. Gaia's data releases provide five-parameter astrometric solutions including positions, parallaxes, and motions for sources, as well as magnitudes, temperatures, and classifications for many variable sources. Future releases will provide improved measurements, classifications, astrophysical parameters, and potentially exoplanet detections.
![Main table
SOURCE ID [Gaia DRx] + ID (unique within DR).
RANDOM INDEX to extract representative subsets.
REF EPOCH ”at DR2 this reference epoch is always J2015.5”.
RA, DEC Barycentric α and δ of the source in ICRS at the
reference epoch, in degrees.
11/44](https://image.slidesharecdn.com/lecture-180913130831/85/Gaia-Lecture-11-320.jpg)
![Main table
SOURCE ID [Gaia DRx] + ID (unique within DR).
RANDOM INDEX to extract representative subsets.
REF EPOCH ”at DR2 this reference epoch is always J2015.5”.
RA, DEC Barycentric α and δ of the source in ICRS at the
reference epoch, in degrees.
RA ERROR, DEC ERROR
PARALLAX, PARALLAX ERROR in mas.
15/44](https://image.slidesharecdn.com/lecture-180913130831/85/Gaia-Lecture-15-320.jpg)
![Main table
SOURCE ID [Gaia DRx] + ID (unique within DR).
RANDOM INDEX to extract representative subsets.
REF EPOCH ”at DR2 this reference epoch is always J2015.5”.
RA, DEC Barycentric α and δ of the source in ICRS at the
reference epoch, in degrees.
RA ERROR, DEC ERROR
PARALLAX, PARALLAX ERROR in mas.
PARALLAX OVER ERROR
PMRA, PMDEC, PMRA ERROR, PMDEC ERROR in
mas/year.
* CORR - 10 correlation coefficients for RA, DEC,
PARALLAX, PMRA, PMDEC.
20/44](https://image.slidesharecdn.com/lecture-180913130831/85/Gaia-Lecture-20-320.jpg)
![Main table
ASTROMETRIC PARAMS SOLVED byte flag, =31 for
five-parametric fit and =3 for two-parametric one.
ASTROMETRIC PRIMARY FLAG ”contribute to the
estimation of attitude, calibration, and global
parameters”.
ASTROMETRIC WHEIGHT AL mas−2.
ASTROMERTIC PSEUDO COLOUR , ERROR - from
chromatic displacement
MEAN VARPHI FACTOR AL typically in the range
[−0.23, +0.32]
ASTROMETRIC MATCHED OBSERVATIONS observations
actually used to compute the astrometric solution.
26/44](https://image.slidesharecdn.com/lecture-180913130831/85/Gaia-Lecture-26-320.jpg)
Gaia Lecture
- 1. Gaia data SAGE lecture Alexey Mints Max-Planck Institute for Solar System Research (MPS), Goettingen, Germany September 13, 2018
- 3. Spacecraft Spacecraft parameters 4.6m × 2.3m, 1392 kg, 1910 watts. Launch Soyuz rocket, 19 December 2013 from Kourou in French Guiana. Orbit Large Lissajous orbit around L2, 1.5 million km from Earth 3/44
- 4. Spacecraft Two primary mirrors 1.45 × 0.5 m, 106.5 degree angle. 106 CCDs = 938 megapixels. 4/44
- 5. Scanning method Orientation 6 hour spin period 63 day spin axis precession 45 degree solar aspect angle 5/44
- 6. Data release history / plan First release: 14 September 2016 Second release: 25 April 2018 Third release: first half of 2021 Final release for the nominal mission: TBD 6/44
- 7. DR2 content The five-parameter astrometric solution - positions on the sky (α, δ), parallaxes, and proper motions - for more than 1.3 billion (109) sources Median radial velocities for more than 7.2 million stars An additional set of more than 361 million sources for which a two-parameter solution G magnitudes for more than 1.69 billion sources GBP and GRP magnitudes for more than 1.38 billion sources The effective temperatures Teff for more than 161 million sources Classifications for more than 550,000 variable sources 7/44
- 9. Access 1. Gaia archive: http://gea.esac.esa.int/archive/ 2. Vizier 3. TopCat / Aladin / Your favourite tool 9/44
- 10. Gaia Clestial Reference Frame (GaiaCRF2) 2820 sources from ICRF3 (Quasars with VLBI measurements). Gaia-CRF2 realisation: 556869 sources down to G = 19m. 10/44
- 11. Main table SOURCE ID [Gaia DRx] + ID (unique within DR). RANDOM INDEX to extract representative subsets. REF EPOCH ”at DR2 this reference epoch is always J2015.5”. RA, DEC Barycentric α and δ of the source in ICRS at the reference epoch, in degrees. 11/44
- 12. Positions 12/44
- 13. RA / DEC uncertainties 13/44
- 14. Astrometric uncertainties Dense (left) and sparse (right) field pairs. 14/44
- 15. Main table SOURCE ID [Gaia DRx] + ID (unique within DR). RANDOM INDEX to extract representative subsets. REF EPOCH ”at DR2 this reference epoch is always J2015.5”. RA, DEC Barycentric α and δ of the source in ICRS at the reference epoch, in degrees. RA ERROR, DEC ERROR PARALLAX, PARALLAX ERROR in mas. 15/44
- 20. Main table SOURCE ID [Gaia DRx] + ID (unique within DR). RANDOM INDEX to extract representative subsets. REF EPOCH ”at DR2 this reference epoch is always J2015.5”. RA, DEC Barycentric α and δ of the source in ICRS at the reference epoch, in degrees. RA ERROR, DEC ERROR PARALLAX, PARALLAX ERROR in mas. PARALLAX OVER ERROR PMRA, PMDEC, PMRA ERROR, PMDEC ERROR in mas/year. * CORR - 10 correlation coefficients for RA, DEC, PARALLAX, PMRA, PMDEC. 20/44
- 21. Systematics Hints of small and large scale correlations (up to a 20-degree scales). Parallax zero-point offset of −0.029mas (from quasars!). 60 stars with parallaxes larger than Proxima Cen. 21/44
- 25. Main table ASTROMETRIC N OBS AL/AC total number of observations (along/across scan). ASTROMETRIC N GOOD OBS AL number of good observations. ASTROMETRIC N BAD OBS AL number of bad observations. ASTROMETRIC GOF AL goodness-of-fit, ”for good fits should approximately follow a normal distribution with zero mean value and unit standard deviation”. ASTROMETRIC CHI2 AL without the excess noise. ASTROMETRIC EXCESS NOISE the excess noise, in mas. ASTROMETRIC EXCESS NOISE SIG the excess noise significance D. If D < 2 the excess noise is likely insignificant. 25/44
- 26. Main table ASTROMETRIC PARAMS SOLVED byte flag, =31 for five-parametric fit and =3 for two-parametric one. ASTROMETRIC PRIMARY FLAG ”contribute to the estimation of attitude, calibration, and global parameters”. ASTROMETRIC WHEIGHT AL mas−2. ASTROMERTIC PSEUDO COLOUR , ERROR - from chromatic displacement MEAN VARPHI FACTOR AL typically in the range [−0.23, +0.32] ASTROMETRIC MATCHED OBSERVATIONS observations actually used to compute the astrometric solution. 26/44
- 27. Main table VISIBILITY PERIODS USED ”A visibility period is a group of observations separated from other groups by a gap of at least 4 days” ASTROMETRIC SIGMA5D MAX The longest principal axis in the 5-dimensional error ellipsoid, in mas. FRAME ROTATOR OBJECT TYPE 0 / 2 / 3. MATCHED OBSERVATIONS The total number of FOV transits. DUPLICATED SOURCE 27/44
- 28. Main table: photometry PHOT (G/BP/RP) N OBS number of observations used for photometry PHOT G MEAN FLUX PHOT G MEAN FLUX ERROR PHOT G MEAN FLUX OVER ERROR PHOT G MEAN MAG in Vega scale. ”No error is provided for this quantity as the error distribution is only symmetric in flux space. This converts to an asymmetric error distribution in magnitude space which cannot be represented by a single error value.” PHOT BP RP EXCESS FACTOR ≈ FBP +FRP FG 28/44
- 31. Main table PHOT PROC MODE 0 - ”gold”; 1 - ”silver” (no reference photometry); 2 - ”bronze” no colour. BP RP, BP G, G RP colours. RADIAL VELOCITY median of all measurements in km/s RADIAL VELOCITY ERROR a calibration floor of 0.11 km/s added. RV NB TRANSITS RV TEMPLATE (TEFF/LOGG/FE H) PHOT VARIABLE FLAG ”Not available”, ”Constant” or ”Variable”. L, B, ECL LON, ECL LAT galactic and ecliptic coordinates. 31/44
- 34. Main table: astrophysical parameters PRIAM FLAGS TEFF (VAL,PERCENTILE (LOWER,UPPER)) value and 16 to 84 percentiles. A G (VAL,PERCENTILE (LOWER,UPPER)) value and 16 to 84 percentiles. E BP MIN RP (VAL,PERCENTILE (LOWER,UPPER)) value and 16 to 84 percentiles. FLAME FLAGS RADIUS (VAL,PERCENTILE (LOWER,UPPER)) value and 16 to 84 percentiles, extinction ignored. LUM (VAL,PERCENTILE (LOWER,UPPER)) value and 16 to 84 percentiles, extinction ignored. 34/44
- 36. Extinction 36/44
- 37. Warning on extinctions Forbes effect: magnitude change is a non-linear function of extinction: m ∝ −2.5 log (F(λ)−AλExt(λ))t(λ)dλ = −2.5 log F(λ)t(λ)dλ+Aλ 37/44
- 38. How to select good sources? χ2 ν < 1.2 × max(1, exp(−0.2(G − 19.5))) χ2 = astrometric chi2 al; ν = astrometric n good obs al - 5 38/44
- 39. How to select good sources? 1.0 + 0.015(GBP − GRP)2 < E < 1.3 + 0.06(GBP − GRP)2 E = astrometric excess noise 39/44
- 40. Other tables Solar System objects tables Variability tables External catalogues in Gaia archive: AllWISE, GSC23, Hipparcos, PanSTARRS, PPMXL, SDSS, 2MASS, Tycho2, URAT1 Cross-matches: same + APASS, RAVE Lists of quasars used to define the reference frame (GaiaCRF2). 40/44
- 41. Variables 41/44
- 42. DR3 content (early 2021) Improved astrometry and photometry 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. Variable-star classifications will be released together with the epoch photometry used for the stars. Solar-system results will be released with preliminary orbital solutions and individual epoch observations. Non-single star catalogues will be released. 42/44
- 43. DR4 content Full astrometric, photometric, and radial-velocity catalogues. All available variable-star and non-single-star solutions. Source classifications (probabilities) plus multiple astrophysical parameters (derived from BP/RP, RVS, and astrometry) for stars, unresolved binaries, galaxies, and quasars. Some parameters may not be available for faint(er) stars. An exo-planet list. All epoch and transit data for all sources (!!!). 43/44