Gaia Data Release 1 (DR1)
This schema contains data re-published from the official
Gaia mirrors (such as ivo://uni-heidelberg.de/gaia/tap) either to
support combining its data with local tables (the various Xlite tables)
or to make the data more accessible to VO clients (e.g., epoch fluxes).
Other Gaia-related data is found in, among others, the gdr2dist, gdr3mock,
gdr3spec, gedr3auto, gedr3dist, gedr3mock, and gedr3spur schemas.
Gaia Collaboration
Catalog
Optical
2016-09-19T13:29:08Z
1000
stars
surveys
astrometry
proper-motions
2016A&A...595A...2G
2015-01-01 2015-01-01
0/0-11
1.986e-19 4.966e-19
If you use public Gaia DR1 data in your paper, please take note of
`ESAC's guide`_ on how to acknowledge and cite Gaia DR1.
.. _ESAC's guide: http://gaia.esac.esa.int/documentation/GDR1/Miscellaneous/sec_credit_and_citation_instructions.html
We do not publish Gaia DR1 data here any more. If you actually
need DR1 data, refer to the full Gaia mirrors, for instance
`the one at ARI`_. Otherwise, please use more recent data releases,
for instance `eDR3`_.
.. _the one at ARI: http://gaia.ari.uni-heidelberg.de
.. _eDR3: /browse/gaia/q3
Time TCB "ref_epoch"
Position ICRS BARYCENTER SPHER3 Epoch J2015.0 "ra" "dec" "parallax"
Velocity "pmra" "pmdec" 0
For the contents of Gaia DR1 (and hence TGAS), which does not include
Solar System objects, 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 2-bit Data Processing Centre code in bits 34 - 35; for example
MOD(source_id / 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
to 32 split into:
* a 25 bit running number in bits 8 x 32; the running numbers are
defined to be positive, i.e. never zero (except in the case of forced
empty windows)
* a 7-bit component number in bits 1 x 7 one spare bit in bit 33
This means that the HEALpix index level 12 of a given source is contained
in the most significant bits. HEALpix index of 12 and lower levels can
thus be retrieved as follows:
* HEALpix level 12 = source_id / 34359738368
* HEALpix level 11 = source_id / 137438953472
* HEALpix level 10 = source_id / 549755813888
* HEALpix level n = source_id / 2^35 * 4^(12 - level).
In the TGAS solution astrometric_delta_q (ΔQ)
indicates the discrepancy between the Hipparcos proper motion and the
TGAS proper motion. A large value of ΔQ could indicate non-linear motion
(e.g. in a binary).
For more details, see the paper referenced in the source metadata.
This is the excess noise ϵ\ :sub:`i` 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 ϵ\ :sub:`i`. 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 ϵ\ :sub:`i` is given by astrometric_excess_noise_sig.
If this is larger than 2, then ϵ\ :sub:`i` is probably not significant,
and the source may be astrometrically well-behaved even if ϵ\ :sub:`i`
is large.
The excess noise 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 excess noise. . Given the many other possible
contributions to the excess noise, the user must study the empirical
distributions of ϵ\ :sub:`i` and astrometric_excess_noise_sig.
to make sensible cutoffs before filtering out sources for their
particular application.
In Gaia DR1, the excess source noise has the same interpretation as
described above for both the primary (TGAS) and secondary data sets. It
measures the disagreement between the five-parameter model and the
observations, augmented by the different priors used. Thus, in TGAS the
excess noise may be increased if the proper motion seen during the 14
months of Gaia observations are not in agreement with the proper motion
inferred from the Tycho-2/Gaia comparison. In the secondary solution the
excess noise may be increased if the Gaia observations indicate a proper
motion or parallax several times larger than the prior uncertainty.
Number of AC or 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.
Number of AC/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 astrometric_n_bad_obs_ac/_al. The sum of
astrometric_n_good_obs_ac/_al and astrometric_n_bad_obs_ac/_al equals
astrometric_n_obs_ac/_al, the total number of AC/AL observations used in
the astrometric solution of the source.
Total number of AC/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
astrometric_n_bad_obs_ac/_al).
Nearly all sources having G<13 will have AC observations from
2d windows, while fainter than that limit only ∼ 1% of stars (the
so–called “calibration faint stars”) are assigned 2d windows
resulting in AC observations (this does not apply to AL).
Type of prior used in the astrometric solution:
0:
No prior used
1:
Galaxy Bayesian Prior for parallax and proper motion
2:
Galaxy Bayesian Prior for parallax and proper motion relaxed by factor
10
3:
Hipparcos prior for position
4:
Hipparcos prior for position and proper motion
5:
Tycho2 prior for position
6:
Quasar prior for proper motion
The Galaxy Bayesian Prior is defined in :bibcode:`2015A&A...583A..68M`,
where it is denoted σ\ :sub:`ϖ,F90` (for the parallax) and
σ\ :sub:`μ,F90` (for proper motion).
For Gaia DR1 the only types of priors used are 2 (for the secondary data
set), 3 (for the Hipparcos subset of the primary data set), or 5 (for the
non-Hipparcos subset of the primary data set). Type 6 was used for
internal calibration purposes and alignment of the reference frame, but
the corresponding astrometric results are in general not published.
Mean astrometric weight of the source in AC or AL direction.
The mean astrometric weight of the source is calculated as per Eq. (119)
in :bibcode:`2012A&A...538A..78L`\ .
All off-diagonal members entries of the covariance matrix
(ra_dec_corr, ra_pmra_corr, ra_pmdec_corr, dec_pmra_corr, dec_pmdec_corr,
pmra_pmdec_corr, ra_parallax_corr, dec_parallax_corr, parallax_pmra_corr,
parallax_pmdec_corr) are dimensionless values normalised to
between -1 and 1.
This may indicate observational, cross-matching or processing problems,
or stellar multiplicity, and probable astrometric or photometric problems
in all cases. In DR1, for close doubles with separations below some 2
arcsec, truncated windows have not been processed, neither in astrometry
and photometry. The transmitted window is centred on the brighter part of
the acquired window, so the brighter component has a better chance to be
selected, even when processing the fainter transit. If more than two
images are contained in a window, the result of the image parameter
determination is un-predictable in the sense that it might refer to
either (or neither) image, and no consistency is assured.
Flag indicating if variability was identified in the photometric G band:
* NULL: source not processed and/or exported to catalogue
* "CONSTANT": Source not identified as variable (not in this release)
* "VARIABLE": source identified and processed as variable;
see ivo://esavo/gaia/tap for more information on these objects.
Note that for this data release only a small subset of (variable) sources
was processed and/or exported, so for many (known) variable sources this
flag is set to NULL.
The scan_direction_strength and scan_direction_mean quantify
the distribution of AL scan directions across the source.
scan_direction_mean_kK (K=1..4) is 1/K times the argument of the
trigonometric moments m\ :sub:`k` = exp(ikθ), where
θ is the position angle of the scan and the mean value is taken over the
nObs[0] AL 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.
scan_direction_mean_kK 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, scan_direction_mean_k1 is the mean
direction when the sense of direction is taken into account, while
scan_direction_mean_k2 is the mean direction without regard to the sense
of the direction.
For example, scan_direction_mean_k1 = 0 means that the scans
preferentially go towards North, while scan_direction_mean_k2 = 0 means
that they preferentially go in the North-South direction, and
scan_direction_mean_k4 = 0 that they preferentially go either in the
North-South or in the East-West direction.
The scan_direction_strength is a number between 0 and 1, where 0 means
that the scan directions are well spread out in different directions,
while 1 mean sthat they are concentrated in a single direction (given by
scan_angle_mean).
Gaia Data Release 1 (DR1) gaia_source
This table, corresponding to gaia_source of the full DR1,
contains the 1.15 billion objects reliably detected in the first 14
months of Gaia observations. It essentially consists of high-precision positions and
magnitudes. The TGAS subset (about 2 million objects observed by both Gaia
and Hipparcos) has proper motions and parallaxes. Users are advised to
beware strong correlations between the astrometric parameters present for
some of the less densely observed objects and the inhomogeneous coverage in
this first data release (solution id: 1635378410781933568).
- psql gaia -c "COPY gaiadr1.gaia_source TO STDOUT WITH (FORMAT text)"
ssh msdemlei@mintaka.ari.uni-heidelberg.de
/browse/gaia/q
',
'href="/browse/gaia/q3">eDR3')
]]>