Information on Service 'Gaia DR2-light Cone Search'

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Further access options are discussed below

At the GAVO data Center, we hold several data collections part of or derived from Gaia data release 2:

For a list of all services and tables belonging to this service's resource, see Information on resource 'Selections from Gaia Data Release 2 (DR2)'

Overview

You can access this service using:

This service is published as follows:

local means it is listed on our front page, ivo_managed means it has a record in the VO registry.

Other services provided on the underlying data include:

Spatial Coverage

Input Fields

The following fields are available to provide input to the service (with some renderers, some of these fields may be unavailable):

NameTable Head DescriptionUnitUCD
DEC Delta (ICRS) Declination (ICRS decimal) deg pos.eq.dec
hscs_pos Position/Name Coordinates (as h m s, d m s or decimal degrees), or SIMBAD-resolvable object N/A N/A
hscs_sr Search radius Search radius in arcminutes N/A N/A
MAXREC Match limit Maximum number of records returned. Pass 0 to retrieve service parameters. N/A N/A
parallax Parallax Absolute barycentric stellar parallax of the source at the reference epoch ref_epoch. If looking for a distance, consider joining with gdr2dist.main and using the distances from there. mas pos.parallax
phot_bp_mean_mag Mag BP 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. For errors small compared to the flux (less than 10%, say), the magnitude error is well approximated by 1.09*flux/flux_err. mag phot.mag;em.opt.B
phot_g_mean_mag m_G Mean magnitude in the G band. This is computed from the G-band mean flux applying the magnitude zero-point in the Vega scale. mag phot.mag;em.opt;stat.mean
phot_rp_mean_mag Mag RP 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. For errors small compared to the flux (less than 10%, say), the magnitude error is well approximated by 1.09*flux/flux_err. mag phot.mag;em.opt.R
RA Alpha (ICRS) Right Ascension (ICRS decimal) deg pos.eq.ra
RESPONSEFORMAT Output Format File format requested for output. N/A meta.code.mime
SR Search Radius Search radius deg N/A
VERB Verbosity Exhaustiveness of column selection. VERB=1 only returns the most important columns, VERB=2 selects the columns deemed useful to the average user, VERB=3 returns a table with all available columns. N/A N/A

Default Output Fields

The following fields are contained in the output by default. More fields may be available for selection; these would be given below in the VOTable output fields.

NameTable Head DescriptionUnitUCD
_r Dist. Distance to cone center deg pos.distance
astrometric_gof_al GoF Goodness-of-fit statistic of the astrometric solution for the source in the along-scan direction (you probably want to use RUWE instead of this). Note gof N/A stat.fit.goodness
astrometric_params_solved PS This is a binary code indicating which astrometric parameters were estimated for the source. A set bit means the parameter was estimated. The least-significant bit represents α, the next bits δ, parallax, PM(RA) and PM(De). For Gaia DR2 the only relevant values are 31 (all five parameters solved) and 3 (only positions). N/A meta.code
dec Dec (ICRS) Barycentric Declination in ICRS at ref_epoch deg pos.eq.dec;meta.main
dec_error Err. Dec Standard error of dec mas stat.error;pos.eq.dec
parallax Parallax Absolute barycentric stellar parallax of the source at the reference epoch ref_epoch. If looking for a distance, consider joining with gdr2dist.main and using the distances from there. mas pos.parallax
parallax_error Parallax_error Standard error of parallax mas stat.error;pos.parallax
phot_bp_mean_flux Flux BP Mean flux in the integrated BP band. Note phot s**-1 phot.flux;em.opt.B
phot_bp_mean_flux_error Err. Fl. BP Error in the mean flux in the integrated BP band. Errors are computed from the dispersion about the weighted mean of the input calibrated photometry. s**-1 stat.error;phot.flux;em.opt.B
phot_bp_mean_mag Mag BP 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. For errors small compared to the flux (less than 10%, say), the magnitude error is well approximated by 1.09*flux/flux_err. Note phot mag phot.mag;em.opt.B
phot_bp_rp_excess_factor BP/RP excess BP/RP excess factor estimated from the comparison of the sum of integrated BP and RP fluxes with respect to the flux in the G band. This measures the excess of flux in the BP and RP integrated photometry with respect to the G band. This excess is believed to be caused by background and contamination issues affecting the BP and RP data. Therefore a large value of this factor for a given source indicates systematic errors in the BP and RP photometry. N/A stat.fit.goodness
phot_g_mean_flux Flux_G G-band mean flux as electrons per second. Note phot s**-1 phot.flux;em.opt;stat.mean
phot_g_mean_flux_error Err. Flux(G) Error on phot_g_mean_flux s**-1 stat.error;phot.flux;em.opt;stat.mean
phot_g_mean_mag m_G Mean magnitude in the G band. This is computed from the G-band mean flux applying the magnitude zero-point in the Vega scale. Note phot mag phot.mag;em.opt;stat.mean
phot_rp_mean_flux Flux RP Mean flux in the integrated RP band. Note phot s**-1 phot.flux;em.opt.R
phot_rp_mean_flux_error Err. Fl. RP Error in the mean flux in the integrated RP band. Errors are computed from the dispersion about the weighted mean of the input calibrated photometry. s**-1 stat.error;phot.flux;em.opt.R
phot_rp_mean_mag Mag RP 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. For errors small compared to the flux (less than 10%, say), the magnitude error is well approximated by 1.09*flux/flux_err. Note phot mag phot.mag;em.opt.R
pmdec µ(Dec) Proper motion in declination at ref_epoch. mas/yr pos.pm;pos.eq.dec
pmdec_error Err. PM(Dec) Standard error of pmdec mas/yr stat.error;pos.pm;pos.eq.dec
pmra µ(RA) Proper motion in right ascension of the source in ICRS at ref_epoch. This is the projection of the proper motion vector in the direction of increasing right ascension. mas/yr pos.pm;pos.eq.ra
pmra_error Err. PM(RA) Standard error of pmra mas/yr stat.error;pos.pm;pos.eq.ra
ra RA (ICRS) Barycentric Right Ascension in ICRS at ref_epoch deg pos.eq.ra;meta.main
ra_error Err. RA Standard error of ra (with cos δ applied). mas stat.error;pos.eq.ra
radial_velocity RV 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. Warning: in the vicinity of bright stars, DR2 RVs can be grossly wrong. See arXiv:1901.10460 for details. km/s spect.dopplerVeloc
radial_velocity_error Err. RV The radial velocity error is the error on the median to which a constant noise floor of 0.11 km/s has been added in quadrature to take into account the calibration contribution. km/s stat.error;spect.dopplerVeloc
random_index Random Random index that can be used to deterministically select subsets N/A meta.code
ruwe RUWE Renormalized Unit Weight Error; this is a revised measure for the overall consistency of the solution as defined by GAIA-C3-TN-LU-LL-124-01. A suggested cut on this is RUWE <1.40) See the note for details. Note ruwe N/A stat.weight
source_id Source Id Unique source identifier. Note that this *cannot* be matched against the DR1 source_id. Note id N/A meta.id;meta.main

VOTable Output Fields

The following fields are available in VOTable output. The verbosity level is a number intended to represent the relative importance of the field on a scale of 1 to 30. The services take a VERB argument. A field is included in the output if their verbosity level is less or equal VERB*10.

NameTable Head DescriptionUnitUCD Verb. Level
source_id Source Id Unique source identifier. Note that this *cannot* be matched against the DR1 source_id. Note id N/A meta.id;meta.main 1
ra RA (ICRS) Barycentric Right Ascension in ICRS at ref_epoch deg pos.eq.ra;meta.main 1
dec Dec (ICRS) Barycentric Declination in ICRS at ref_epoch deg pos.eq.dec;meta.main 1
pmra µ(RA) Proper motion in right ascension of the source in ICRS at ref_epoch. This is the projection of the proper motion vector in the direction of increasing right ascension. mas/yr pos.pm;pos.eq.ra 1
pmdec µ(Dec) Proper motion in declination at ref_epoch. mas/yr pos.pm;pos.eq.dec 1
parallax Parallax Absolute barycentric stellar parallax of the source at the reference epoch ref_epoch. If looking for a distance, consider joining with gdr2dist.main and using the distances from there. mas pos.parallax 1
phot_g_mean_mag m_G Mean magnitude in the G band. This is computed from the G-band mean flux applying the magnitude zero-point in the Vega scale. Note phot mag phot.mag;em.opt;stat.mean 1
phot_rp_mean_mag Mag RP 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. For errors small compared to the flux (less than 10%, say), the magnitude error is well approximated by 1.09*flux/flux_err. Note phot mag phot.mag;em.opt.R 1
phot_bp_mean_mag Mag BP 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. For errors small compared to the flux (less than 10%, say), the magnitude error is well approximated by 1.09*flux/flux_err. Note phot mag phot.mag;em.opt.B 1
radial_velocity RV 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. Warning: in the vicinity of bright stars, DR2 RVs can be grossly wrong. See arXiv:1901.10460 for details. km/s spect.dopplerVeloc 1
ruwe RUWE Renormalized Unit Weight Error; this is a revised measure for the overall consistency of the solution as defined by GAIA-C3-TN-LU-LL-124-01. A suggested cut on this is RUWE <1.40) See the note for details. Note ruwe N/A stat.weight 5
_r Dist. Distance to cone center deg pos.distance 10
ra_error Err. RA Standard error of ra (with cos δ applied). mas stat.error;pos.eq.ra 20
dec_error Err. Dec Standard error of dec mas stat.error;pos.eq.dec 20
pmra_error Err. PM(RA) Standard error of pmra mas/yr stat.error;pos.pm;pos.eq.ra 20
pmdec_error Err. PM(Dec) Standard error of pmdec mas/yr stat.error;pos.pm;pos.eq.dec 20
parallax_error Parallax_error Standard error of parallax mas stat.error;pos.parallax 20
phot_g_mean_flux Flux_G G-band mean flux as electrons per second. Note phot s**-1 phot.flux;em.opt;stat.mean 20
phot_g_mean_flux_error Err. Flux(G) Error on phot_g_mean_flux s**-1 stat.error;phot.flux;em.opt;stat.mean 20
phot_rp_mean_flux Flux RP Mean flux in the integrated RP band. Note phot s**-1 phot.flux;em.opt.R 20
phot_rp_mean_flux_error Err. Fl. RP Error in the mean flux in the integrated RP band. Errors are computed from the dispersion about the weighted mean of the input calibrated photometry. s**-1 stat.error;phot.flux;em.opt.R 20
phot_bp_mean_flux Flux BP Mean flux in the integrated BP band. Note phot s**-1 phot.flux;em.opt.B 20
phot_bp_mean_flux_error Err. Fl. BP Error in the mean flux in the integrated BP band. Errors are computed from the dispersion about the weighted mean of the input calibrated photometry. s**-1 stat.error;phot.flux;em.opt.B 20
phot_bp_rp_excess_factor BP/RP excess BP/RP excess factor estimated from the comparison of the sum of integrated BP and RP fluxes with respect to the flux in the G band. This measures the excess of flux in the BP and RP integrated photometry with respect to the G band. This excess is believed to be caused by background and contamination issues affecting the BP and RP data. Therefore a large value of this factor for a given source indicates systematic errors in the BP and RP photometry. N/A stat.fit.goodness 20
radial_velocity_error Err. RV The radial velocity error is the error on the median to which a constant noise floor of 0.11 km/s has been added in quadrature to take into account the calibration contribution. km/s stat.error;spect.dopplerVeloc 20
astrometric_gof_al GoF Goodness-of-fit statistic of the astrometric solution for the source in the along-scan direction (you probably want to use RUWE instead of this). Note gof N/A stat.fit.goodness 20
astrometric_params_solved PS This is a binary code indicating which astrometric parameters were estimated for the source. A set bit means the parameter was estimated. The least-significant bit represents α, the next bits δ, parallax, PM(RA) and PM(De). For Gaia DR2 the only relevant values are 31 (all five parameters solved) and 3 (only positions). N/A meta.code 20
random_index Random Random index that can be used to deterministically select subsets N/A meta.code 20

Copyright, License, Acknowledgements

If you use public Gaia DR2 data in a paper, please take note of ESAC's guide on how to acknowledge and cite it.

VOResource XML (that's something exclusively for VO nerds)

Note gof

This is the “gaussianized chi-square”, which for good fits should approximately follow a normal distribution with zero mean value and unit standard deviation. Values exceeding, say, +3 thus indicate a bad fit to the data.

This statistic is computed according to the formula

gof = sqrt(9ν/2) [(χ²/ν)^(1/3) + 2/(9ν) − 1],

where χ² (astrometric_chi2_al) is the AL chi-square statistic and ν = (astrometric_n_good_obs_al − 5) is the number of degrees of freedom for a source update. Here, 5 is the number of astrometric parameters. Note that only “good” (i.e. not strongly downweighted) observations are included in χ² and ν.

An alternative indicator of bad fits is the astrometric excess noise. In AGIS the source update deals with bad fits by adding astrometric excess noise to the formal observation noise. This reduces the weight of the observations and inflates the covariance of the estimated astrometric parameters correspondingly. However, the chi-square values used to calculate astrometric_gof_al do not take into account the astrometric excess noise, and astrometric_gof_al can therefore always be used as a goodness-of-fit indicator of the source solution in AGIS.

Note id

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).
Note phot

Note that several systematics have been found for both Gaia G and BP photometry on the level of 10s of mmags. See 2018A&A...616A..17A and 2018A&A...616A...4E for a description of the problem as well as some proposed empirical corrections. For sources brighter than 16.5, see also 2018MNRAS.479L.102C and 2018A&A...617A.138W, where the latter also discusses systematics in BP.

Note ruwe

The Renormalized Unit Weight Error (RUWE) is defined in L. Lindegren: Re-normalising the astrometric chi-square in Gaia DR2 (Gaia tech note GAIA-C3-TN-LU-LL-124-01). This is essentially the astrometric_chi2 from the DR2 release, but corrected for its strong dependency on magnitude and colour. For quality cuts, this is the recommended quantity to use. Lindegren suggests using RUWE<1.4 as a quality cut for “good” solutions based on the shape of the distribution.

The values given here were calculated independently of DPAC and do not use interpolation on the grids provided by Lindegren et al. Thus, minor differences from the “official” RUWE values are expected. As Lindegren et al point out, such differences should not matter in science applications, though.