I/350 Gaia EDR3 (Gaia Collaboration, 2020)
Gaia Early Data Release 3 (Gaia EDR3).
Gaia collaboration
<Astron. Astrophys., 649, A1 (2021)>
=2020yCat.1350....0G 2020yCat.1350....0G
=2021A&A...649A...1G 2021A&A...649A...1G
ADC_Keywords: Surveys ; Stars, standard ; Positional data ; Proper motions ;
Photometry, photographic ; Cross identifications ;
Radial velocities ; Stars, variable ; Minor planets;
Parallaxes, trigonometric
Mission_Name: Gaia
Keywords: catalogs - astrometry - parallaxes - proper motions -
techniques: photometric - techniques: radial velocities
Abstract:
Gaia DR3 data (both Gaia EDR3 and the full Gaia DR3) are based on data
collected between 25 July 2014 (10:30 UTC) and 28 May 2017 (08:44
UTC), spanning a period of 34 months. As a comparison, Gaia DR2 was
based on 22 months of data and Gaia DR1 was based on observations
collected during the first 14 months of Gaia's routine operational
phase.
Survey completeness:
The Gaia EDR3 catalogue is essentially complete between G=12 and G=17.
The source list for the release is incomplete at the bright end and
has an ill-defined faint magnitude limit, which depends on celestial
position.
The combination of the Gaia scan law coverage and the filtering on
data quality which will be done prior to the publication of Gaia EDR3,
does lead to some regions of the sky displaying source density
fluctuations that reflect the scan law pattern. In addition, small
gaps exist in the source distribution, for instance close to bright
stars.
Astrometry:
The parallax improvement is typically 20% with respect to Gaia DR2.
The proper motions are typically a factor two better than in Gaia DR2.
An overall reduction of systematics has been achieved. E.g., the
parallax zero point deduced from the extragalactic sources is about
-20µas. A tentative correction formula for the parallax zero point
will be provided.
Closer to the release date of Gaia Early Data Release 3, an update
will be given on the astrometry.
Photometry:
The G-band photometric uncertainties are ∼0.25mmag for G<13, 1mmag
at G=17, and 5mmag at G=20mag.
The GBP-band photometric uncertainties are ∼1mmag for G<13, 10mmag
at G=17, and 100mmag at G=20mag.
The GRP-band photometric uncertainties are ∼1mmag for G<13, 5mmag at
G=17, and 50mmag at G=20mag.
Closer to the release date of Gaia Early Data Release 3, an update
will be given on the photometry.
Gaia EDR3 does not contain new radial velocities. The radial
velocities of Gaia Data Release 2 have been added to Gaia EDR3 in
order to ease the combination of spectrosopic and astrometric data.
Radial velocities:
Gaia EDR3 hence contains Gaia DR2 median radial velocities for about
7.21 million stars with a mean G magnitude between ∼4 and ∼13 and an
effective temperature (Teff) in the range ∼3550 to 6900K. The overall
precision of the radial velocities at the bright end is of the order
of ∼200-300m/s while at the faint end, the overall precision is
∼1.2km/s for a Teff of 4750K and ∼3.5km/s for a Teff of 6500K.
Before publication in Gaia EDR3, an additional filtering has been
performed onto the Gaia DR2 radial velocities to remove some 4000
sources that had wrong radial velocities.
Please be aware that the Gaia DR2 values are assigned to the Gaia EDR3
sources through an internal cross-match operation. In total, ∼10000
Gaia DR2 radial velocities could not be associated to a Gaia EDR3
source.
Astrophysical parameters:
Gaia EDR3 does not contain new astrophysical parameters. Astrophysical
parameters have been published in Gaia DR2 and a new set is expected
to be released with the full Gaia DR3 release.
Variable stars:
Gaia EDR3 does not contain newly classified variable stars. For the
overview of the currently available variable stars from Gaia DR2, have
a look here. Classifications for a larger set of variable stars are
expected with the full Gaia DR3 release.
Solar system objects:
A large set of solar system objects with orbits will become available
with the full Gaia DR3 release. Information on the currently available
asteroids in Gaia DR2 can be found here.
Documentation:
Data release documentation is provided along with each data release in
the form of a downloadable PDF and a webpage. The various chapters of
the documentation have been indexed at ADS allowing them to be cited.
Please visit the Gaia Archive (https://gea.esac.esa.int/archive) to
access this documentation, and make sure to check out all relevant
information given through the documentation overview page
(https://www.cosmos.esa.int/web/gaia-users/archive).
Description:
Contents of Gaia EDR3:
The five-parameter astrometric solution - positions on the sky
(alpha,delta), parallaxes, and proper motions - for around 1.5 billion
(1.5x109) sources, with a limiting magnitude of about G~=21 and a
bright limit of about G~=3. The astrometric solution will be
accompanied with some new quality indicators, like RUWE, and source
image descriptors.
In addition, two-parameters solutions - positions on the sky
(alpha,delta) - for around 300 million additional sources.
G magnitudes for around 1.8 billion sources.
GBP and GRP magnitudes for around 1.5 billion sources.
Please be aware that the photometric system for the G, GBP, and GRP
bands in Gaia EDR3 is different from the photometric system as used in
Gaia DR2 and Gaia DR1.
Full passband definitions for G, GBP, and GRP. More information will
become available here.
About 1.5 million celestial reference frame (Gaia-CRF) sources.
Cross-matches between Gaia EDR3 sources on the one hand and
Hipparcos-2, Tycho-2 + TDSC merged, 2MASS PSC (merged with 2MASX),
SDSS DR13, Pan-STARRS1 DR1, SkyMapper DR1, GSC 2.3, APASS DR9, RAVE
DR5, allWISE, and URAT-1 data on the other hand.
Additionally, a Gaia EDR3 to Gaia DR2 match will be provided.
Simulated data from Gaia Object Generator (GOG) and Gaia Universe
Model Snapshot (GUMS) will be provided.
The commanded scan law covering the Gaia EDR3 data collection period
will be provided. Also the major periods where data was not sent to
the ground or could not be processed are identified.
Gaia DR3 data (both Gaia EDR3 and the full Gaia DR3) are based on data
collected between 25 July 2014 (10:30 UTC) and 28 May 2017 (08:44
UTC), spanning a period of 34 months. As a comparison, Gaia DR2 was
based on 22 months of data and Gaia DR1 was based on observations
collected during the first 14 months of Gaia's routine operational
phase.
The reference epoch for Gaia DR3 (both Gaia EDR3 and the full Gaia
DR3) is 2016.0. Remember that the reference epoch is different for
each Gaia data release (it was was J2015.5 for Gaia DR2 and J2015.0
for Gaia DR1).
Positions and proper motions are referred to the ICRS, to which the
optical reference frame defined by Gaia EDR3 is aligned. The time
coordinate for Gaia EDR3 is the barycentric coordinate time (TCB).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
gaiaedr3.sam 1035 1000 GaiaSource EDR3 data
agncrid.dat 88 1614173 AGN cross-identifications (AgnCrossId.csv)
tyc2tdsc.dat 348 2561887 Tycho-2 merged with the TDSC catalog and
TDSC supplement
comscanl.dat 198 8967691 *Representation of the Gaia scanning law over the
34 month time period covered by the Gaia Data
Release 3
framers.dat 42 429249 Sources used to compute the Gaia reference frame
(FrameRotatorSource.csv)
--------------------------------------------------------------------------------
Note on comscanl.dat: (from 2014-07-25 10:31:26 to 2017-05-28 08:46:29)
(CommandedScanLaw.csv)
--------------------------------------------------------------------------------
See also:
II/328 : AllWISE Data Release (Cutri+ 2013)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
I/329 : URAT1 Catalog (Zacharias+ 2015)
https://www.cosmos.esa.int/web/gaia/earlydr3 : Gaia EDR3 Home Page
Byte-by-byte Description of file: gaiaedr3.sam
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 29 A29 --- EDR3Name Unique source designation (unique
across all Data Releases)
(designation) (1)
31- 45 F15.11 deg RAdeg Barycentric right ascension of the
source (ICRS) at Ep=2016.0 (ra)
47- 61 F15.11 deg DEdeg Barycentric declination of the source
(ICRS) at Ep=2016.0 (dec)
63- 81 I19 --- Source Unique source identifier (unique
within a particular Data Release)
(source_id) (2)
83- 101 I19 --- SolID Solution Identifier (solution_id) (3)
103- 112 I10 --- RandomI Random index used to select subsets
(random_index) (4)
114- 119 F6.1 yr Epoch Reference epoch (ref_epoch) (5)
121- 127 F7.4 mas e_RAdeg Standard error eRA=eRA*cosDE of the
right ascension of the source in ICRS
at Ep=2016.0 (ra_error)
129- 135 F7.4 mas e_DEdeg Standard error of the declination of
the source in ICRS at at Ep=2016.0
(dec_error)
137- 146 F10.4 mas Plx ? Absolute stellar parallax of the
source at the Ep=2016.0 (parallax)
148- 153 F6.4 mas e_Plx ? Standard error of the stellar
parallax at Ep=2016.0 (parallax_error)
155- 164 F10.4 --- RPlx ? Parallax divided by its standard
error (parallaxovererror)
166- 174 F9.3 mas/yr PM ? Total proper motion (pm) (6)
176- 184 F9.3 mas/yr pmRA ? Proper motion in right ascension
pmRA*cosDE of the source in ICRS at
Ep=2016.0 (pmra) (7)
186- 190 F5.3 mas/yr e_pmRA ? Standard error of proper motion in
right ascension direction
(pmra_error) (8)
192- 200 F9.3 mas/yr pmDE ? Proper motion in declination
direction (pmdec) (9)
202- 206 F5.3 mas/yr e_pmDE ? Standard error of proper motion in
declination direction
(pmdec_error) (10)
208- 214 F7.4 --- RADEcor [-1/1] Correlation between right
ascension and declination
(radeccorr)
216- 222 F7.4 --- RAPlxcor [-1/1]? Correlation between right
ascension and parallax
(raparallaxcorr)
224- 230 F7.4 --- RApmRAcor [-1/1]? Correlation between right
ascension and proper motion in
right ascension (rapmracorr)
232- 238 F7.4 --- RApmDEcor [-1/1]? Correlation between right
ascension and proper motion in
declination (rapmdeccorr)
240- 246 F7.4 --- DEPlxcor [-1/1]? Correlation
between declination and parallax
(decparallaxcorr)
248- 254 F7.4 --- DEpmRAcor [-1/1]? Correlation between
declination and proper motion in
right ascension (decpmracorr)
256- 262 F7.4 --- DEpmDEcor [-1/1]? Correlation between
declination and proper motion in
declination (decpmdeccorr)
264- 270 F7.4 --- PlxpmRAcor [-1/1]? Correlation between parallax
and proper motion in right ascension
(parallaxpmracorr)
272- 278 F7.4 --- PlxpmDEcor [-1/1]? Correlation between parallax
and proper motion in declination
(parallaxpmdeccorr)
280- 286 F7.4 --- pmRApmDEcor [-1/1]? Correlation between proper
motion in right ascension and proper
motion in declination
(pmrapmdeccorr)
288- 291 I4 --- NAL Total number of observations AL
(astrometricnobs_al) (11)
293- 296 I4 --- NAC Total number of observations AC
(astrometricnobs_ac) (12)
298- 301 I4 --- NgAL Number of good observations AL
(astrometricngoodobsal) (13)
303- 305 I3 --- NbAL Number of bad observations AL
(astrometricnbadobsal) (14)
307- 315 F9.4 --- gofAL Goodness of fit statistic of model
wrt along-scan observations
(astrometricgofal)
317- 329 F13.2 --- chi2AL AL chi-square value
(astrometricchi2al) (15)
331- 338 F8.3 mas epsi Excess noise of the source
(astrometricexcessnoise) (16)
340- 349 E10.3 --- sepsi Significance of excess noise
(astrometricexcessnoise_sig) (17)
351- 352 I2 --- Solved Which parameters have been solved for?
(astrometricparamssolved) (18)
354 I1 --- APF Primary or secondary
(astrometricprimaryflag) (19)
356- 361 F6.3 um-1 nueff ? Effective wavenumber of the source
used in the astrometric solution
(nueffusedinastrometry) (20)
363- 369 F7.4 um pscol ? Astrometrically estimated
pseudocolour of the source
(pseudocolour) (21)
371- 377 F7.4 um e_pscol ? Standard error of the pseudocolour
of the source
(pseudocolour_error) (22)
379- 384 F6.3 --- RApscolCorr [-1/1]? Correlation between right
ascension and pseudocolour
(rapseudocolourcorr)
386- 391 F6.3 --- DEpscolCorr [-1/1]? Correlation between
declination and pseudocolour
(decpseudocolourcorr)
393- 398 F6.3 --- PlxpscolCorr [-1/1]? Correlation between parallax
and pseudocolour
(parallaxpseudocolourcorr)
400- 405 F6.3 --- pmRApscolCorr [-1/1]? Correlation between proper
motion in right ascension and
pseudocolour (pmrapseudocolourcorr)
407- 412 F6.3 --- pmDEpscolCorr [-1/1]? Correlation between proper
motion in declination and
pseudocolour
(pmdecpseudocolourcorr)
414- 416 I3 --- MatchObsA Matched FOV transits used in the AGIS
solution
(astrometricmatchedtransits) (23)
418- 419 I2 --- Nper Number of visibility periods used in
Astrometric solution
(visibilityperiodsused)
421- 432 E12.6 mas amax The longest semi-major axis of the
-5--10 error ellipsoid
(astrometricsigma5dmax) (24)
434- 436 I3 --- MatchObs The total number of field-of-view
transits matched to this source
(matched_transits)
438- 440 I3 --- NewMatchObs The number of transits newly
incorporated into an existing source
in the current cycle
(newmatchedtransits) (25)
442- 444 I3 --- MatchObsrm The number of transits removed from
an existing source in the current
cycle (matchedtransitsremoved) (26)
446- 454 E9.3 --- IPDgofha Amplitude of the IPD GoF versus
position angle of scan
(ipdgofharmonic_amplitude) (27)
456- 464 E9.3 deg IPDgofhp Phase of the IPD GoF versus position
angle of scan
(ipdgofharmonic_phase) (28)
466- 468 I3 --- IPDfmp Percent of successful-IPD windows with
more than one peak
(ipdfracmulti_peak) (29)
470- 472 I3 --- IPDfow Percent of transits with truncated
windows or multiple gate
(ipdfracodd_win) (30)
474- 481 F8.3 --- RUWE ? Renormalised unit weight error
(ruwe)
483- 491 E9.3 --- SDSk1 ? Degree of concentration of scan
directions across the source
(scandirectionstrength_k1) (31)
493- 501 E9.3 --- SDSk2 ? Degree of concentration of scan
directions across the source
(scandirectionstrength_k2) (31)
503- 511 E9.3 --- SDSk3 ? Degree of concentration of scan
directions across the source
(scandirectionstrength_k3) (31)
513- 521 E9.3 --- SDSk4 ? Degree of concentration of scan
directions across the source
(scandirectionstrength_k4) (31)
523- 530 F8.3 deg SDMk1 ? Mean position angle of scan
directions across the source
(scandirectionmean_k1) (32)
532- 539 F8.3 deg SDMk2 ? Mean position angle of scan
directions across the source
(scandirectionmean_k2) (32)
541- 548 F8.3 deg SDMk3 ? Mean position angle of scan
directions across the source
(scandirectionmean_k3) (32)
550- 557 F8.3 deg SDMk4 ? Mean position angle of scan
directions across the source
(scandirectionmean_k4) (32)
559 I1 --- Dup Source with multiple source
identifiers (duplicated_source) (33)
561- 564 I4 --- o_Gmag Number of observations (CCD transits)
that contributed to the G mean flux
and mean flux error (photgn_obs)
566- 576 E11.5 e-/s FG ? Mean flux in the G-band
(photgmean_flux)
578- 588 E11.5 e-/s e_FG ? Standard deviation of the G-band
fluxes divided by sqrt(photGNObs)
(photgmeanfluxerror)
590- 598 F9.3 --- RFG ? Mean flux in the G-band divided by
its error
(photgmeanfluxover_error)
600- 608 F9.6 mag Gmag ? G-band mean magnitude (Vega)
(photgmean_mag) (34)
610- 612 I3 --- o_BPmag ? Number of observations contributing
to BP photometry (photbpn_obs) (35)
614- 624 E11.5 e-/s FBP ? Mean flux in the integrated BP band
(photbpmean_flux)
626- 636 E11.5 e-/s e_FBP ? Error on the integrated BP mean flux
(photbpmeanfluxerror) (36)
638- 646 F9.3 --- RFBP ? Integrated BP mean flux divided by
its error
(photbpmeanfluxover_error) (37)
648- 656 F9.6 mag BPmag ? Integrated BP mean magnitude (Vega)
(photbpmean_mag) (38)
658- 660 I3 --- o_RPmag Number of observations (CCD transits)
that contributed to the integrated
RP mean flux and mean flux error
(photrpn_obs)
662- 672 E11.5 e-/s FRP ? Mean flux in the integrated RP band
(photrpmean_flux)
674- 684 E11.5 e-/s e_FRP ? Error on the integrated RP mean
flux (photrpmeanfluxerror) (39)
686- 694 F9.3 --- RFRP ? Integrated RP mean flux divided by
its error
(photrpmeanfluxover_error) (40)
696- 704 F9.6 mag RPmag ? Integrated RP mean magnitude (Vega)
(photrpmean_mag) (41)
706- 708 I3 --- NBPcont ? Number of BP contaminated transits
(photbpncontaminatedtransits) (42)
710- 712 I3 --- NBPblend ? Number of BP blended transits
(photbpnblendedtransits) (43)
714- 716 I3 --- NRPcont ? Number of RP contaminated transits
(photrpncontaminatedtransits) (44)
718- 720 I3 --- NRPblend ? Number of RP blended transits
(photrpnblendedtransits) (45)
722 I1 --- Mode Photometry processing mode
(photprocmode)
724- 729 F6.3 --- E(BP/RP) ? BP/RP excess factor
(photbprpexcessfactor)
731- 739 F9.6 mag BP-RP ? BP-RP colour
(photBpMeanMag - photRpMeanMag)
(bp_rp)
741- 749 F9.6 mag BP-G ? BP-G colour
(photBpMeanMag - photGMeanMag) (bp_g)
751- 759 F9.6 mag G-RP ? G-RP colour
(photGMeanMag - photRpMeanMag) (g_rp)
761- 767 F7.2 km/s RVDR2 ? Radial velocity from Gaia DR2
(dr2radialvelocity) (46)
769- 773 F5.2 km/s e_RVDR2 ? Radial velocity error from Gaia DR2
(dr2radialvelocity_error) (47)
775- 777 I3 --- o_RVDR2 Number of transits used to compute
radial velocity in Gaia DR2
(dr2rvnb_transits) (48)
779- 784 F6.1 K Tefftemp ? Teff of the template used to compute
radial velocity in Gaia DR2
(dr2rvtemplate_teff) (49)
786- 789 F4.1 [cm/s2] loggtemp ? logg of the template used to compute
radial velocity in Gaia DR2
(dr2rvtemplate_logg) (50)
791- 795 F5.2 [-] [Fe/H]temp ? [Fe/H] of the template used to
compute radial velocity in Gaia DR2
(dr2rvtemplatefeh) (51)
797- 810 F14.10 deg GLON Galactic longitude (l) (52)
812- 825 F14.10 deg GLAT Galactic latitude (b) (53)
827- 840 F14.10 deg ELON Ecliptic longitude (ecl_lon)
842- 855 F14.10 deg ELAT Ecliptic latitude (ecl_lat) (54)
857- 874 I18 --- PS1 ? Pan-STARRS1 cross-id name
(panstarrs1) (55)
876- 894 I19 --- SDSSDR13 ? SDSS DR13 cross-id name
(sdssdr13) (55)
896- 904 I9 --- SkyMapper2 ? SkyMapper2 cross-id name
(skymapper2) (55)
906- 914 I9 --- URAT1 ? URAT1 cross-id name (urat1) (55)
916- 923 F8.6 mag e_Gmag ? Standard error of G-band mean
magnitude (Vega) (added by CDS)
(photgmeanmagerror) (G1)
925- 932 F8.6 mag e_BPmag ? Standard error of BP mean magnitude
(Vega) (added by CDS)
(photbpmeanmagerror) (G1)
934- 941 F8.6 mag e_RPmag ? Standard error of RP mean magnitude
(Vega) (added by CDS)
(photrpmeanmagerror) (G1)
943- 951 F9.6 mag GmagCorr ? Calibration corrected G magnitude
(added by CDS)
(photgmeanmagcorrected) (G2)
953- 960 F8.6 mag e_GmagCorr ? Standard error of calibration
corrected G magnitude (added by CDS)
(photgmeanmagerror_corrected) (G2)
962- 972 E11.5 mag FGCorr ? Calibration corrected G-band mean
flux (added by CDS)
(photgmeanfluxcorrected) (G2)
974- 979 F6.3 --- E(BP/RP)Corr ? Calibration corrected BP/RP excess
factor (added by CDS)
(photbprpexcessfactor_corrected)
(G2)
981- 995 F15.11 deg RAJ2000 Barycentric right ascension (ICRS) at
Ep=2000.0 (added by CDS)
(ra_epoch2000)
997-1011 F15.11 deg DEJ2000 Barycentric declination (ICRS) at
Ep=2000.0 (added by CDS)
(dec_epoch2000)
1013-1019 F7.4 mas e_RAJ2000 Standard error of right ascension
(e_RA*cosDE) (added by CDS)
(raepoch2000error)
1021-1027 F7.4 mas e_DEJ2000 Standard error of declination
(added by CDS) (decepoch2000error)
1029-1035 F7.4 --- RADEcorJ2000 [-1/1] Correlation between right
ascension and declination at epoch
2000 (added by CDS)
(radecepoch2000_corr)
--------------------------------------------------------------------------------
Note (1): A source designation, unique across all Gaia Data Releases, that is
constructed from the prefix "Gaia DRx" followed by a string of digits
corresponding to source_id (3 space-separated words in total). Note that
the integer source identifier source_id is NOT guaranteed to be unique
across Data Releases; moreover it is not guaranteed that the same
astronomical source will always have the same source_id in different
Data Releases. Hence the only safe way to compare source records between
different Data Releases in general is to check the records of proximal
source(s) in the same small part of the sky.
Note (2): A unique numerical identifier of the source, encoding the approximate
position of the source (roughly to the nearest arcmin), the provenance
(data processing centre where it was created), a running number, and a
component number.
The approximate equatorial (ICRS) position is encoded using the nested
HEALPix scheme at level 12 (Nside = 4096), which divides the sky into
∼200 million pixels of about 0.7 arcmin2.
The source ID consists of a 64-bit integer, least significant bit = 1
and most significant bit = 64, comprising:
- a HEALPix index number (sky pixel) in bits 36 - 63; by definition
the smallest HEALPix index number is zero.
- a 3-bit Data Processing Centre code in bits 33 - 35; for example
MOD(sourceId / 4294967296, 8) can be used to distinguish between
sources initialised via the Initial Gaia Source List by the Torino
DPC (code = 0) and sources otherwise detected and assigned by Gaia
observations (code > 0)
- a 25-bit plus 7 bit sequence number within the HEALPix pixel in bits
1 - 32 split into:
- a 25 bit running number in bits 8 - 32; the running numbers are
defined to be positive, i.e. never zero
- a 7-bit component number in bits 1 - 7
This means that the HEALpix index at level 12 of a given source is
contained in the most significant bits. HEALpix index of level 12 and
lower can thus be retrieved as follows:
- HEALpix index at level 12 = source_id / 34359738368
- HEALpix index at level 11 = source_id / 137438953472
- HEALpix index level 10 = source_id / 549755813888
- HEALpix index at level n = source_id / (235x4(12-n)) = source_id/2(59-2n)
Additional details can be found in the Gaia DPAC public document _Source
Identifiers - Assignment and Usage throughout DPAC (document code
GAIA-C3-TN-ARI-BAS-020) available from
https://www.cosmos.esa.int/web/gaia/public-dpac-documents
Note (3): All Gaia data processed by the Data Processing and Analysis Consortium
comes tagged with a solution identifier. This is a numeric field attached to
each table row that can be used to unequivocally identify the version of all
the subsystems that where used in the generation of the data as well as the
input data used. It is mainly for internal DPAC use but is included in the
published data releases to enable end users to examine the provenance of
processed data products. To decode a given solution ID visit
Note (4): Random index which can be used to select smaller subsets of the data
that are still representative. The column contains a random permutation
of the numbers from 0 to N-1, where N is the number of sources in the table.
The random index can be useful for validation (testing on 10 different random
subsets), visualization (displaying 1% of the data), and statistical
exploration of the data, without the need to download all the data.
Note (5): Reference epoch to which the astrometric source parameters are
referred, expressed as a Julian Year in TCB.
Note (6): The total proper motion calculated as the magnitude of the resultant
vector of the proper motion component vectors pmra and pmdec, i.e.
pm2 = pmRA2 + pmDE2.
Note (7): This is the local tangent plane projection of the proper motion vector
in the direction of increasing right ascension.
Note (8): Standard error e_pmRA*cosDE of the local tangent plane projection of
the proper motion vector in the direction of increasing right ascension at
the reference epoch refEpoch
Note (9): Proper motion in declination of the source at the reference
epoch refEpoch. This is the projection of the proper motion vector in the
direction of increasing declination.
Note (10): Standard error of the proper motion component in declination at the
reference epoch refEpoch
Note (11): Total number of AL observations (= CCD transits) used in the
astrometric solution of the source, independent of their weight. Note that
some observations may be strongly downweighted (see astrometricNBadObsAl).
Note (12): Total number of AC observations (= CCD transits) used in the
astrometric solution of the source, independent of their weight (note that some
observations may be strongly downweighted). Nearly all sources having
G<13 will have AC observations from 2d windows, while fainter than that
limit only ∼1% of transit observations (the so-called 'calibration faint
stars') are assigned 2d windows resulting in AC observations.
Note (13): Number of AL observations (= CCD transits) that were not strongly
downweighted in the astrometric solution of the source. Strongly downweighted
observations (with downweighting factor w<0.2) are instead counted in
astrometricNBadObsAl. The sum of astrometricNGoodObsAl and
astrometricNBadObsAl equals astrometricNObsAl, the total number of AL
observations used in the astrometric solution of the source.
Note (14): Number of AL observations (= CCD transits) that were strongly
downweighted in the astrometric solution of the source, and therefore
contributed little to the determination of the astrometric parameters.
An observation is considered to be strongly downweighted if its
downweighting factor w<0.2, which means that the absolute value of the
astrometric residual exceeds 4.83 times the total uncertainty of the
observation, calculated as the quadratic sum of the centroiding
uncertainty, excess source noise, and excess attitude noise.
Note (15): Astrometric goodness-of-fit (chi2) in the AL direction.
chi2 values were computed for the 'good' AL observations of the source,
without taking into account the astrometricExcessNoise (if any) of the
source. They do however take into account the attitude excess noise (if
any) of each observation.
Note (16): This is the excess noise εi of the source. It measures the
disagreement, expressed as an angle, between the observations of a source and
the best-fitting standard astrometric model (using five astrometric
parameters). The assumed observational noise in each observation is
quadratically increased by εi in order to statistically match the
residuals in the astrometric solution. A value of 0 signifies that the
source is astrometrically well-behaved, i.e. that the residuals of the
fit statistically agree with the assumed observational noise. A positive
value signifies that the residuals are statistically larger than expected.
The significance of εi is given by astrometricExcessNoiseSig (D). If
D≤2 then εi is probably not significant, and the source may be
astrometrically well-behaved even if εi is large.
The excess noise εi may absorb all kinds of modelling errors that are
not accounted for by the observational noise (image centroiding error)
or the excess attitude noise. Such modelling errors include LSF and PSF
calibration errors, geometric instrument calibration errors, and part of
the high-frequency attitude noise. These modelling errors are
particularly important in the early data releases, but should decrease
as the astrometric modelling of the instrument and attitude improves
over the years.
Additionally, sources that deviate from the standard five-parameter astrometric
model (e.g. unresolved binaries, exoplanet systems, etc.) may have positive
εi. Given the many other possible contributions to the excess noise,
the user must study the empirical distributions of εi and D to make
sensible cutoffs before filtering out sources for their particular application.
The excess source noise is further explained in Sects. 3.6 and 5.1.2
Note (17): A dimensionless measure (D) of the significance of the calculated
astrometricExcessNoise (εi). A value D>2 indicates that the given i
is probably significant.
For good fits in the limit of a large number of observations, D should
be zero in half of the cases and approximately follow the positive half
of a normal distribution with zero mean and unit standard deviation for
the other half. Consequently, D is expected to be greater than 2 for
only a few percent of the sources with well-behaved astrometric solutions.
In the early data releases εi will however include instrument and
attitude modelling errors that are statistically significant and could
result in large values of εi and D. The user must study the empirical
distributions of these statistics and make sensible cutoffs before
filtering out sources for their particular application.
The excess noise significance is further explained in Sect. 5.1.2.
Note (18): The seven bits of astrometricParamsSolved indicate which parameters
have been estimated in AGIS for this source. A set bit means the parameter
was updated, an unset bit means the parameter was not updated. The
least-significant bit corresponds to ra. The table below shows the
values of astrometricParamsSolved for relevant combinations of the parameters.
The radial proper motion (µr) is formally considered to be one of the
astrometric parameters of a source, and the sixth bit is therefore
reserved for it. It is also in principle updatable in AGIS, but in
practice it will always be computed from a spectroscopic radial velocity
and the estimated parallax, in which case the bit is not set.
C is the pseudocolour of the source, i.e. the astrometrically estimated
effective wavenumber.
astrometricParamsSolved ra dec parallax pmra pmdec µr C
------------------------- ---- ----- ---------- ------ ------- ---- ---
0000011 = 3
0000111 = 7
0011011 = 27
0011111 = 31
0111111 = 63
1011111 = 95
In practice all the sources in DR3 have only values of 3, 31 or 95 for
the astrometricParamsSolved, corresponding to two-parameter (position),
five-parameter (position, parallax, and proper motion) and six-parameter
(position, parallax, proper motion and astrometrically estimated effective
wavenumber) solutions.
Note (19): Flag indicating if this source was used as a primary source (true) or
secondary source (false). Only primary sources contribute to the estimation of
attitude, calibration, and global parameters. The estimation of source
parameters is otherwise done in exactly the same way for primary and
secondary sources.
Note (20): Effective wavenumber of the source, νeff, in µm-1.
This νeff is the value used in the image parameter determination and in
the astrometric calibration if reliable mean BP and RP photometry were
available. It is the photon-flux weighted inverse wavelength, as estimated
from the BP and RP bands. The field is provided for astrometric solutions with
five parameters but is empty for those with two or six parameters.
Due to cyclic processing of the astrometry and the photometry, this
effective wavenumber might be different from the one computed using the
latest available photometry. Moreover, if no reliable photometry was
available at the time of the astrometric processing, this field is empty
and an astrometrically estimated value of the effective wavenumber may
instead be given in the pseudocolour field.
Note (21): The pseudocolour is the astrometrically estimated effective
wavenumber of the photon flux distribution in the astrometric (G) band,
measured in µm-1. The value in this field was estimated from the
chromatic displacements of image centroids, calibrated by means of the
photometrically determined effective wavenumbers (νeff) of primary sources.
The field is empty when chromaticity was instead taken into account using the
photometrically determined νeff given in the field nuEffUsedInAstrometry.
Note (22): Standard error σ_pseudocolour of the astrometrically determined
pseudocolour of the source.
Note (23): The number of field-of-view transits matched to this source, counting
only the transits containing CCD observations actually used to compute the
astrometric solution.
This number will always be equal to or smaller than matchedTransits, the
difference being the FOV transits that were not used in the astrometric
solution because of bad data or excluded time intervals.
Note (24): The longest principal axis in the 5-dimensional error ellipsoid.
This is a 5-dimensional equivalent to the semi-major axis of the
position error ellipse and is therefore useful for filtering out cases
where one of the five parameters, or some linear combination of several
parameters, is particularly ill-determined. It is measured in mas and
computed as the square root of the largest singular value of the scaled
5x5 covariance matrix of the astrometric parameters. The matrix is
scaled so as to put the five parameters on a comparable scale, taking
into account the maximum along-scan parallax factor for the parallax and
the time coverage of the observations for the proper motion components.
If C is the unscaled covariance matrix, the scaled matrix is SCS, where
S = diag(1, 1, sin ζ, T/2, T/2), ζ = 45° is the solar aspect
angle in the nominal scanning law, and T the time coverage of the data used in
the solution.
astrometricSigma5dMax is given for all the solutions, as its size is one
of the criteria for accepting or rejecting the 5 or 6-parameter
solution. In case of a 2- parameter solution (astrometricParamsSolved = 3)
it gives the value for the rejected 5 or 6-parameter solution, and
can then be arbitrarily large.
Note (25): Individual field-of-view transits are crossmatched into unique
sources at the start of each reprocessing cycle taking the source list from the
previous cycle as a starting point. During that process a combination of
appending, merging and splitting operations is performed to create a
more complete and reliable map of unique sources given the available
information. Existing individual sources may accrete further transits, may be
merged into fewer unique sources, or may split into two or more new, unique
sources as more measurements are accumulated. Field newMatchedTransits logs
the number of transits newly appended to an existing source during the most
recent cyclic reprocessing crossmatch. It refers exclusively to the sourceId.
Note (26): Individual field-of-view transits are crossmatched into unique
sources at the start of each reprocessing cycle taking the source list from the
previous cycle as a starting point. During that process a combination of
appending, merging and splitting operations is performed to create a
more complete and reliable map of unique sources given the available
information. Existing individual sources may accrete further transits,
may be merged into fewer unique sources, or may split into two or more
new, unique sources as more measurements are accumulated. Field
matchedTransitsRemoved logs the number of transits removed during the
most recent cyclic reprocessing crossmatch from those allocated to an
existing source during all previous cycles. It refers exclusively to the
sourceId.
Note (27): This statistic measures the amplitude of the variation of the IPD GoF
(reduced chi-square) as function of the position angle of the scan direction.
A large amplitude indicates that the source is double, in which case the phase
indicates the position angle of the pair modulo 180 degrees. The quantity was
computed using only transits used in the astrometric solution, for example
those without the EPSL and without outliers.
Let ψ be the position angle of the scan direction. The following
expression is fitted to the IPD GoF for all the AF observations of the
source:
ln(GoF) = c0 + c2cos(2ψ) + s2sin(2ψ)
The amplitude and phase of the variation are calculated as
ipdGofHarmonicAmplitude = sqrt{c22+s22}
ipdGofHarmonicPhase = 1/2atan2(s2,c2) (+180°)
where atan2 returns the angle in degrees, and 180 is added for negative values.
Note (28): This statistic measures the phase of the variation of the IPD GoF
(reduced chi-square) as function of the position angle of the scan direction.
The quantity was computed using only transits used in the astrometric solution,
for example those without the EPSL and without outliers. See the description
of parameter ipdGofHarmonicAmplitude for further details.
Note (29): This field provides information on the raw windows used for the
astrometric processing of this source coming from the Image Parameters
Determination (IPD) module in the core processing. It provides the fraction of
windows (having a successful IPD result), as percentage (from 0 to 100), for
which the IPD algorithm has identified a double peak, meaning that the
detection may be a visually resolved double star (either just visual double or
real binary). The quantity was computed using all transits where the IPD was
successful.
Note (30): This field is calculated during AGIS and provides information on
the raw windows used for the astrometric processing of this source. It provides
the fraction (as a percentage, from 0 to 100) of transits having either
truncation or multiple gates flagged in one or more windows. Such a
situation invariably means that the on-board VPU detected some nearby
source (which may be just a spurious detection, but typically could be
some real nearby source - having another distinct transit and most
probably assigned to a different source). So in general a non-zero
fraction indicates that this source may be contaminated by another
nearby source. The quantity was computed using all transits where the
IPD was successful.
Note (31): The scanDirectionStrengthK1...4 and scanDirectionMeanK1...4
quantify the distribution of AL scan directions across the source.
scanDirectionStrengthK1 (and similarly 2,3,4) are the absolute value of
the trigonometric moments mk = exp(ikθ) for k = 1, 2, 3, 4 where
θ is the position angle of the scan and the mean value is taken over the
astrometricNGoodObsAl observations contributing to the astrometric
parameters of the source. θ is defined in the usual astronomical sense:
θ = 0 when the FoV is moving towards local North, and θ = 90°
towards local East.
N.B. When astrometricNObsAc >0 the scan direction attributes are not provided
at Gaia EDR3. Hence for all sources brighter than G≃13, and for a tiny
fraction of fainter sources (∼1%), these 8 scan direction fields will be NULL.
The scanDirectionStrengthK1...4 are numbers between 0 and 1, where 0
means that the scan directions are well spread out in different
directions, while 1 means that they are concentrated in a single
direction (given by the corresponding scanDirectionMeanK1...4).
The different orders k are statistics of the scan directions modulo
360°/k. For example, at first order (k=1), θ=10° and
θ=190° count as different directions, but at second order (k=2)
they are the same.
Thus, scanDirectionStrengthK1 is the degree of concentration when the
sense of direction is taken into account, while scanDirectionStrengthK2
is the degree of concentration without regard to the sense of direction.
A large value of scanDirectionStrengthK4 indicates that the scans are
concentrated in two nearly orthogonal directions.
Note (32): The scanDirectionStrengthK1...4 and scanDirectionMeanK1...4
attributes quantify the distribution of AL scan directions across the source.
scanDirectionMeanK1 (and similarly for k = 2, 3, 4) is 1/k times the
argument of the trigonometric moments mk = exp(ikθ), where θ is the
position angle of the scan and the mean value is taken over the
astrometricNGoodObsAl observations contributing to the astrometric parameters
of the source. θ is defined in the usual astronomical sense:
θ=0 when the FoV is moving towards local North, and
θ=90° towards local East.
N.B. When astrometricNObsAc>0 the scan direction attributes are not
provided at Gaia EDR3. Hence for all sources brighter than G∼13, and
for a tiny fraction of fainter sources (∼1%), these 8 scan direction
fields will be NULL.
scanDirectionMeanK1 (and similarly for k = 2, 3, 4) is an angle between
-180°/k and +180°/k, giving the mean position angle of the scans at
order k.
The different orders k are statistics of the scan directions modulo
360°/k. For example, at first order (k=1), θ=10° and
θ=190° count as different directions, but at second order (k=2)
they are the same. Thus, scanDirectionMeanK1 is the mean direction when the
sense of direction is taken into account, while scanDirectionMeanK2 is the mean
direction without regard to the sense of the direction. For example,
scanDirectionMeanK1 = 0 means that the scans preferentially go towards
North, while scanDirectionMeanK2 = 0 means that they preferentially go
in the North-South direction, and scanDirectionMeanK4 = 0 that they
preferentially go either in the North-South or in the East-West
direction.
Note (33): During data processing, this source happened to be duplicated and
only one source identifier has been kept. Observations assigned to the
discarded source identifier(s) were not used. This may indicate
observational, cross-matching or processing problems, or stellar
multiplicity, and probable astrometric or photometric problems in all
cases. The duplicity criterion used for Gaia DR3 is an angular distance
of 0.18 arcsec, while a limit of 0.4 arcsec was used for Gaia DR2.
Note (34): Mean magnitude in the G band. This is computed from the G-band mean
flux applying the magnitude zero-point in the 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.
Note (35): Number of observations (CCD transits) that contributed to the
integrated BP mean flux and mean flux error.
Note (36): Error on the mean flux in the integrated BP band (errors are computed
from the dispersion about the weighted mean of input calibrated photometry).
A handful of sources have error equal to zero.
Note (37): Integrated BP mean flux divided by its error. A handful of sources
have error equal to zero, meaning that the ratio is NULL.
Note (38): Mean magnitude in the integrated BP band. This is computed from the
BP-band mean flux applying the magnitude zero-point in the 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.
Note (39): Error on the mean flux in the integrated RP band (errors are computed
from the dispersion about the weighted mean of input calibrated
photometry). A handful of sources have error equal to zero.
Note (40): Integrated RP mean flux divided by its error. A handful of sources
have error equal to zero, meaning that the ratio is NULL.
Note (41): Mean magnitude in the integrated RP band. This is computed from the
RP-band mean flux applying the magnitude zero-point in the 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.
Note (42): Number of BP transits that contributed to the mean photometry and
were considered to be contaminated by one or more nearby sources. The
contaminating sources may come from the other field of view.
Note (43): Number of BP transits that contributed to the mean photometry and
were flagged to be blends of more than one source (i.e. more than one source
is present in the observing window). The blended sources may come from
different fields of view.
Note (44): Number of RP transits that contributed to the mean photometry and
were considered to be contaminated by one or more nearby sources. The
contaminating sources may come from the other field of view.
Note (45): Number of RP transits that contributed to the mean photometry and
were flagged to be blends of more than one source (i.e. more than one source
is present in the observing window). The blended sources may come from
different fields of view.
Note (46): Spectroscopic radial velocity in the solar barycentric reference
frame. The radial velocity provided is the median value of the radial velocity
measurements at all epochs. At Gaia EDR3 this value is simply that
copied in from Gaia DR2. The Gaia DR2 values are assigned to the Gaia
EDR3 sources through an internal cross-match operation and about 11000
sources could not be matched. In addition about 4000 identified spurious
radial velocities are not copied. For further details see
Section [ssec:cu6spe_nonewdata] in the online documentation for the release.
Note (47): The dr2RadialVelocityError is the error on the median to which a
constant noise floor of 0.11km/s has been added in quadrature to take
into account the calibration contribution. At Gaia EDR3 this column is
simply that copied in from Gaia DR2. The Gaia DR2 radial velocities and
associated quantities are assigned to the Gaia EDR3 sources through an
internal cross-match operation and about 11000 sources could not be
matched. In addition about 4000 identified spurious radial velocities,
along with their associated values, are not copied. For further details
see Section [ssec:cu6spe_nonewdata] in the online documentation for the
release.
In detail, dr2RadialVelocityError = sqrt(sigma2Vrad + 0.112)
where sigmaVrad is the error on the median:
sigmaVrad = sqrt(pi/2).(sigma(Vradt)/sqrt(dr2RvNbTransits))
where sigma(Vradt) is the standard deviation of the
epoch radial velocities and dr2RvNbTransits the number of transits for
which a Vradt has been obtained.
Note (48): The number of transits (epochs) used to compute dr2RadialVelocity.
At Gaia EDR3 this value is simply that copied in from Gaia DR2. The Gaia
DR2 radial velocities and associated quantities are assigned to the Gaia
EDR3 sources through an internal cross-match operation and about 11000
sources could not be matched. In addition about 4000 identified spurious
radial velocities, along with their associated values, are not copied.
For further details see Section [ssec:cu6spe_nonewdata] in the online
documentation for the release.
Note (49): Effective temperature of the synthetic spectrum template used to
determine dr2RadialVelocity. N.B. the purpose of this parameter is to
provide information on the synthetic template spectrum used to determine
dr2RadialVelocity, and not to provide an estimate of the stellar
effective temperature of this source.
At Gaia EDR3 this value is simply that copied in from Gaia DR2. The Gaia
DR2 radial velocities and associated quantities are assigned to the Gaia
EDR3 sources through an internal cross-match operation and about 11000
sources could not be matched. In addition about 4000 identified spurious
radial velocities, along with their associated values, are not copied.
For further details see Section [ssec:cu6spe_nonewdata] in the online
documentation for the release.
Note (50): log of the synthetic spectrum template used to determine
dr2RadialVelocity. N.B. the purpose of this parameter is to provide
information on the synthetic template spectrum used to determine
dr2RadialVelocity, and not to provide an estimate of the logg of this source.
At Gaia EDR3 this value is simply that copied in from Gaia DR2. The Gaia
DR2 radial velocities and associated quantities are assigned to the Gaia
EDR3 sources through an internal cross-match operation and about 11000
sources could not be matched. In addition about 4000 identified spurious
radial velocities, along with their associated values, are not copied.
For further details see Section [ssec:cu6spe_nonewdata] in the online
documentation for the release.
Note (51): Fe/H of the synthetic spectrum template used to determine
dr2RadialVelocity. N.B. the purpose of this parameter is to provide
information on the synthetic template spectrum used to determine
dr2RadialVelocity, and not to provide an estimate of the stellar
atmospheric Fe/H of this source.
At Gaia EDR3 this value is simply that copied in from Gaia DR2. The Gaia
DR2 radial velocities and associated quantities are assigned to the Gaia
EDR3 sources through an internal cross-match operation and about 11000
sources could not be matched. In addition about 4000 identified spurious
radial velocities, along with their associated values, are not copied.
For further details see Section [ssec:cu6spe_nonewdata] in the online
documentation for the release.
Note (52): Galactic Longitude of the object at reference epoch refEpoch, see
Section [ssec:cu3astintrogalactic] of the release documentation for
conversion details.
Note (53): Galactic Latitude of the object at reference epoch refEpoch, see
Section [ssec:cu3astintrogalactic] of the release documentation for
conversion details.
Note (54): Ecliptic Latitude of the object at reference epoch refEpoch.
For further details see the description for attribute eclLon.
Note (55): Cross-identifications from Gaia EDR3 "best neighbour" tables,
panstarrs1bestneighbour, sdssr13bestneighbour,
skymapperdr2bestneighbour and urat1bestneighbour.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: agncrid.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 25 A25 --- Name Source name in the external catalog
(sourcenamein_catalogue)
27- 45 I19 --- Source Gaia source ID (source_id)
47- 88 A42 --- Cat Catalog name (catalogue_name) (1)
--------------------------------------------------------------------------------
Note (1): Catalog names as follows:
2WHSP (Changet al. 2017) = 2WHSP catalog,
Chang et al., 2017A&A...598A..17C 2017A&A...598A..17C, Cat. J/A+A/598/A17
ALMA calibrators (Bonato et al. 2019) = ALMA Calibrator Catalogue,
Bonato et al., 2019MNRAS.485.1188B 2019MNRAS.485.1188B, Cat. J/MNRAS/485/1188
AllWISE (Secrestet al. 2015) = AllWISE Data Release, Cat. II/328
Secrest et al., 2015ApJS..221...12S 2015ApJS..221...12S, Cat. J/ApJ/221/12
Gaia-unWISE (Shuet al. 2019) = Gaia-unWISE catalog of AGN,
Shu et al., 2019MNRAS.489.4741S 2019MNRAS.489.4741S
ICRF3K
ICRF3S/X
ICRF3X/Ka
LAMOST phase1 DR1-5 = LAMOST DR1-DR5
Luo et al., 2015RAA....15.1095L 2015RAA....15.1095L, DR5 Cat, V/164
LQAC5 (Souchay et al.2019) = Astrometric Catalogue 5, LQAC-5,
Souchay et al., 2019A&A...624A.145S 2019A&A...624A.145S, Cat. J/A+A/624/A145
LQRF(Andrei et al. 2009) = LQRF: Large Quasar Reference Frame,
Andrei et al., 2009A&A...505..385A 2009A&A...505..385A, Cat. I/313
Milliquas v6.5 update (Flesch 2019) = Million Quasars (Milliquas) catalog,
Flesch et al., 2015PASA...32...10F 2015PASA...32...10F, Cat. VII/283 (v6.3)
OCARS (Malkin 2018) = OCARS catalog, Malkin, 2016ARep...60..996M 2016ARep...60..996M,
http://www.gaoran.ru/english/as/ac_vlbi/ocars.txt
R90 (Assefet al. 2018) = WISE AGN catalog,
Assef et al;, 2018ApJS..234...23A 2018ApJS..234...23A, Cat. J/ApJS/234/23
Roma-BZCAT release 5 (Massaro et al.2015) = Roma BZCAT - 5th edition,
Massaro et al., 2015Ap&SS.357...75M 2015Ap&SS.357...75M, Cat. VII/274
SDSS DR14Q (Pariset al. 2018) = SDSS quasar catalog, fourteenth data
release, Paris et al., 2018A&A...613A..51P 2018A&A...613A..51P, Cat. VII/286
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tyc2tdsc.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- IDTyc2 Tycho-2 identifier (TYC1-TYC2-TYC3) (id)
16- 21 I6 --- HIP ? Hipparcos number (hip)
23- 28 I6 --- TYC1 TYC1 component from TYC or GSC (tyc1)
30- 36 I7 --- TYC2 TYC2 component from TYC or GSC (tyc2)
38- 40 I3 --- TYC3 TYC2 component from TYC or GSC (tyc3)
42- 51 I10 --- TYC Numeric Tycho-2 identifier
((tyc1*1000000)+(tyc2*10)+(tyc3)) (id_tycho)
53- 55 A3 --- IDTyc1 Tycho-1 star (tyc)
57- 68 E12.8 deg RATdeg Observed Tycho-2 Right Ascension (ICRS)
at epoch 1990+EpRA1990 (ra)
70- 81 E12.8 deg DETdeg Observed Tycho-2 Declination (ICRS)
at epoch 1990+EpDE1990 (dec)
83- 94 E12.8 --- --- ---
96-107 E12.8 --- --- ---
109-120 E12.8 deg RAmdeg ? Mean Right Ascension (ICRS) at Ep=J2000
(ra_mdeg)
122-133 E12.8 deg DEmdeg ? Mean Declination (ICRS) at Ep=J2000
(de_mdeg)
135-141 F7.1 mas/yr pmRA ? Proper motion in right ascension,
pmRA*cos(DE) (pm_ra)
143-149 F7.1 mas/yr pmDE ? Proper motion in Declination (pm_de)
151-154 F4.2 yr EpRA1990 Epoch-1990 of RAdeg (ep_ra1990)
156-159 F4.2 yr EpDE1990 Epoch-1990 of DEdeg (ep_de1990)
161-167 F7.2 yr EpRAmdeg ? Mean epoch of RAmdeg (epram)
169-175 F7.2 yr EpDEmdeg ? Mean epoch of DEmdeg (epdem)
177-178 I2 --- Num ? Number of positions used for forming mean
data (num)
180-184 F5.1 mas e_RATdeg Uncertainty RA*cos(dec), of observed
Tycho-2 RA (eradeg)
186-190 F5.1 mas e_DETdeg Uncertainty of observed Tycho-2 Dec (ededeg)
192-195 F4.1 --- Corr ? Correlation (RAdeg,DEdeg) (corr)
197-201 F5.1 mas e_RAmdeg ? Uncertainty RA*cos(dec),at mean epoch
(eramdeg)
203-207 F5.1 mas e_DEmdeg ? Uncertainty of Dec at mean epoch (edemdeg)
209-212 F4.1 mas/yr e_pmRA ? Uncertainty proper motion in RA*cos(dec)
(epmra)
214-217 F4.1 mas/yr e_pmDE ? Uncertainty of proper motion in Dec
(epmde)
219-221 F3.1 --- q_RAmdeg ? Goodness of fit for mean RA (qramdeg)
223-225 F3.1 --- q_DEmdeg ? Goodness of fit for mean DE (qdemdeg)
227-229 F3.1 --- q_pmDE ? Goodness of fit for pmDe (qpmde)
231-233 F3.1 --- q_pmRA ? Goodness of fit for pmRa (qpmra)
235-237 A3 --- pflag Mean position flag (pflag)
239-241 A3 --- posflg Type of Tycho-2 solution (posflg)
243-246 A4 --- CCDM CCDM component identifier for HIP stars
(ccdm)
248-250 I3 --- prox ? Proximity indicator (prox)
252-257 F6.3 mag BTmag ? Tycho-2 BT magnitude (bt_mag)
259-264 F6.3 mag VTmag ? Tycho-2 VT magnitude (vt_mag)
266-270 F5.3 mag e_BTmag ? Uncertainty of BTmag (ebtmag)
272-276 F5.3 mag e_VTmag ? Uncertainty of VTmag (evtmag)
278-282 I5 --- TDSC ? TDSC identifier for the system (sys_no)
284-287 A4 --- cmp Component designation (cmp)
289-290 I2 --- Nmain ? Number of components in TDSC main catalogue
(n_main)
292 I1 --- Nsup ? Number of components in the TDSC supplement
(n_sup)
294 A1 --- magflg TDSC photometry flag (magflg)
296-307 A12 --- WDS WDS identifier for the system (wds)
309 A1 --- Note TDSC notes (note)
311-316 I6 --- HD ? HD identifier for TDSC entries (hd)
318-321 A4 --- rcmp Reference component for position angle and
separation (rcmp)
323-327 F5.1 deg PA ? Position angle of the present component
(cmp) with respect to the reference component
(rcmp) (pa)
329-335 F7.2 arcsec Sep ? Separation of the present component (cmp)
with respect to the reference component
(rcmp) (sep)
337-340 F4.1 deg e_PA ? Uncertainty of the position angle (e_pa)
342-344 I3 --- e_PA.Sep ? Uncertainty of the position
angle * separation (epasep)
346-348 I3 mas e_Sep ? Uncertainty of the separation (e_sep)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: comscanl.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 F18.13 d JD [1666.42/2704.38] Julian date in TCB at Gaia
(JD-2455197.5) (jd_time) (1)
20- 37 F18.13 d BJD-FOV1 [1666.42/2704.38] Observation time for FOV1
Barycentric JD (in TCB)
(BJD-2455197.5) (bjd_fov1) (2)
39- 56 F18.13 d BJD-FOV2 [1666.42/2704.38] Observation time for FOV2
Barycentric JD (in TCB)
(BJD-2455197.5) (bjd_fov2) (3)
58- 75 I18 --- OBMT Observation time at Gaia converted to OBMT
using the HATT (High Accuracy Time
Transformation) (obmt_time)
77- 88 E12.10 deg RA1deg FOV1 barycentric right ascension in ICRS at
given time BJD-FOV1 (ra_fov1)
90-103 E14.10 deg DE1deg FOV1 barycentric declination in ICRS at
given time BJD-FOV1 (dec_fov1)
105-113 I9 --- HP1 [0/201326589] FOV1 HEALPix level 12
(healpixfov1) (4)
115-127 E13.10 --- SA1 [-180/180] FOV1 Scan position angle
(scananglefov1)
129-140 E12.10 deg RA2deg FOV2 barycentric right ascension in ICRS at
given time BJD-FOV2 (ra_fov2)
142-154 E13.10 deg DE2deg FOV1 barycentric declination in ICRS at
given time BJD-FOV2 (dec_fov2)
156-164 I9 --- HP2 [56/201326571] FOV2 HEALPix level 12
(healpixfov2) (4)
166-178 E13.10 --- SA2 [-180/180] FOV2 Scan position angle
(scananglefov2)
180-198 I19 --- SolID Solution ID (solution_id) (5)
--------------------------------------------------------------------------------
Note (1): The time at which the scan angles and FoV angles are evaluated in TCB
(Temps Coordonnee Barycentrique) with an offset of 2455197.5 days is applied
(corresponding to a reference time T0 at 2010-01-01T00:00:00) to have a
conveniently small numerical value.
Note (2): First the observation time is converted from On-board Mission Time
(OBMT) into Julian date in TCB (Temps Coordonnee Barycentrique). Next a
correction is applied for the light-travel time to the Solar system barycentre
corresponding to an infinitely distant source at (raFov1, decFov1), resulting
in Barycentric Julian Date (BJD). Finally, an offset of 2455197.5 days is
applied (corresponding to a reference time T0 at 2010-01-01T00:00:00) to have
a conveniently small numerical value.
Note (3): First the observation time is converted from On-board Mission Time
(OBMT) into Julian date in TCB (Temps Coordonnee Barycentrique). Next a
correction is applied for the light-travel time to the Solar system barycentre
corresponding to an infinitely distant source at (raFov2, decFov2), resulting
in Barycentric Julian Date (BJD). Finally, an offset of 2455197.5 days is
applied (corresponding to a reference time T0 at 2010-01-01T00:00:00) to have
a conveniently small numerical value.
Note (4): Level 12 nested scheme HEALPix containing the Field of View
(preceding) right ascension and declination.
This field can be used in conjunction with sourceId, whose most significant
bits contain HEALPix information.
Note (5): All Gaia data processed by the Data Processing and Analysis Consortium
comes tagged with a solution identifier. This is a numeric field attached to
each table row that can be used to unequivocally identify the version of all
the subsystems that where used in the generation of the data as well as the
input data used. It is mainly for internal DPAC use but is included in the
published data releases to enable end users to examine the provenance of
processed data products. To decode a given solution ID visit.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: framers.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- Source Gaia source ID (source_id)
21- 25 A5 --- CRFO [False/True ] True if the source was a
considered source for the reference frame
orientation, false otherwise
(consideredforreferenceframeorientation)
27- 31 A5 --- URFO [False/True ] True if the source was
effectively used for the reference frame
orientation, false otherwise
(usedforreferenceframeorientation)
33- 36 A4 --- CRFF [False/True ] True if the source was a
considered source for the reference frame
spin determination, false otherwise
(consideredforreferenceframespin)
38- 42 A5 --- URFF [False/True ] True if the source was
effectively used for the reference frame spin
determination, false otherwise
(usedforreferenceframespin)
--------------------------------------------------------------------------------
Global notes:
Note (G1): Note on magnitude errors:
They are obtained with a simple propagation of errors with the formulas
e_Gmag = sqrt((-2.5/ln(10)*e_FG/FG)**2 + sigmaG_0**2)
e_GBPmag = sqrt((-2.5/ln(10)*e_FGBP/FGBP)**2 + sigmaGBP_0**2))
e_GRPmag = sqrt((-2.5/ln(10)*e_FGRP/FGRP)**2 + sigmaGRP_0**2))
with the G, G_BP, G_RP zero point uncertainties
sigmaG_0 = 0.0027553202
sigmaGBP_0 = 0.0027901700
sigmaGRP_0 = 0.0037793818
See https://www.cosmos.esa.int/web/gaia/edr3-passbands for more details
Note (G2): Note on Calibration corrected values.
G-band magnitude correction for sources with 6-parameter astrometric solutions.
The paper Gaia Early Data Release 3: Photometric content and validation by
Riello et al. (2020) explains that for sources with 6-parameter astrometric
solutions the G-band magnitude should be corrected and a formula to do so is
provided. The corresponding Python code to do this is presented in Gaia Early
Data Release 3: Summary of the contents and survey properties
(Gaia Collaboration et al., 2020). The source code can be found as a Jupyter
notebook in this repository:
https://github.com/agabrown/gaiaedr3-6p-gband-correction
Corrected flux excess factor.
The paper Gaia Early Data Release 3: Photometric content and validation by
Riello et al. (2020) presents a corrected version of the photometric flux
excess factor as published in the Gaia EDR3 catalogue. The corrected version
acounts for the average variation of the flux excess for 'normal' sources.
A formula for calculating the corrected excess factor is provided. The
corresponding Python code to do this is presented in Gaia Early Data
Release 3: Summary of the contents and survey properties (Gaia Collaboration
et al., 2020). The source code can be found as a Jupyter notebook in this
repository:
https://github.com/agabrown/gaiaedr3-flux-excess-correction
See also:
https://www.cosmos.esa.int/web/gaia/edr3-code
--------------------------------------------------------------------------------
History:
From Gaia team
Acknowledgements:
Gaia team
References:
Gaia Early Data Release 3: Summary of the contents and survey properties
Brown, A.G.A., et al., 2021A&A...649A...1G 2021A&A...649A...1G
Gaia Early Data Release 3: The astrometric solution
Lindegren, L., et al., 2021A&A...649A...2L 2021A&A...649A...2L
Gaia Early Data Release 3: Photometric content and validation
Riello, M., et al., 2021A&A...649A...3R 2021A&A...649A...3R, Cat. J/A+A/649/A3
Gaia Early Data Release 3: Parallax bias versus magnitude, colour and position
Lindegren, L., et al., 2021A&A...649A...4L 2021A&A...649A...4L
Gaia Early Data Release 3: Catalogue Validation
Fabricius, C., et al., 2021A&A...649A...5F 2021A&A...649A...5F
Gaia Early Data Release 3: The Gaia catalogue of nearby stars
Gaia Collaboration, Smart, R.L., et al.,
2021A&A...649A...6G 2021A&A...649A...6G, Cat. J/A+A/649/A6
Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds
Gaia Collaboration, Luri et al, 2021A&A...649A...7G 2021A&A...649A...7G
Gaia Early Data Release 3: The Galactic anticentre
Gaia Collaboration, Antoja, T., et al., 2021A&A...649A...8G 2021A&A...649A...8G
Gaia Early Data Release 3: Acceleration of the solar system from
Gaia astrometry
Gaia Collaboration, Klioner, S.A., et al., 2021A&A...649A...9G 2021A&A...649A...9G
Gaia Early Data Release 3: Building the Gaia DR3 source list -
Cross-match of Gaia observations
Torra, F., et al., 2021A&A...649A..10T 2021A&A...649A..10T
Gaia Early Data Release 3: Modelling and calibration of Gaia's point and
line spread functions
Rowell, N., et al., 2021A&A...649A..11R 2021A&A...649A..11R
Gaia Early Data Release 3: The celestial reference frame (GAIA-CRF3)
Gaia Collaboration, et al.
Gaia Early Data Release 3: Updated radial velocities from Gaia DR2
Seabroke, G.M., et al., %R 2021A&A...653A.160S 2021A&A...653A.160S, Cat. J/A+A/653/A160
Gaia Early Data Release 3: Cross-match with external catalogues -
Algorithm and results
Marrese, P., et al.
(End) Giacomo Monari, Thomas Boch, Patricia Vannier [CDS] 03-Dec-2020