Information on Service 'Estimated distances to 1.33 billion stars in Gaia DR2'

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This catalogue provides distances estimates (and uncertainties therein) for 1.33 billion stars over the whole sky brighter than about G=20.7. These have been estimated using the parallaxes (and their uncertainties) from Gaia DR2. A Bayesian procedure was used involving a prior with a single parameter L(l,b), which varies smoothly with Galactic longitude and latitude according to a Galaxy model. The posterior is summarized with a point estimate (usually the mode) and a confidence interval (usually the 68% highest density interval). The estimation procedure is described in detail in the accompanying paper, which also analyses the catalogue content.

For a list of all services and tables belonging to this service's resource, see Information on resource 'Estimated distances to 1.33 billion stars in Gaia DR2'

Overview

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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.

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
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
dec Dec (ICRS) Barycentric Declination in ICRS at ref_epoch deg pos.eq.dec;meta.main
r_est Dist Estimated distance pc pos.distance
r_hi Max. Dist. Upper bound on the 1 σ confidence interval pc stat.error;stat.max;pos.distance
r_len Prior scale Length scale used in the prior for the distance estimation. pc stat.fit.param;pos.distance
r_lo Min. Dist. Lower bound on the 1 σ confidence interval pc stat.error;stat.min;pos.distance
ra RA (ICRS) Barycentric Right Ascension in ICRS at ref_epoch deg pos.eq.ra;meta.main
result_flag Res. Code Type of result. Note rc N/A meta.code.qual
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
r_est Dist Estimated distance pc pos.distance 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
r_lo Min. Dist. Lower bound on the 1 σ confidence interval pc stat.error;stat.min;pos.distance 5
r_hi Max. Dist. Upper bound on the 1 σ confidence interval pc stat.error;stat.max;pos.distance 5
_r Dist. Distance to cone center deg pos.distance 10
r_len Prior scale Length scale used in the prior for the distance estimation. pc stat.fit.param;pos.distance 15
result_flag Res. Code Type of result. Note rc N/A meta.code.qual 15
modality_flag #modes Result regime flag: number of modes in the posterior (1 or 2). N/A meta.code 25

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

Note id

For the contents of Gaia DR2, 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 rc

result_flag has three possible values:

0:failed estimate (r_est, r_lo, r_hi are all NaN)
1:_est is the mode (highest if the posterior is bimodal); r_lo/r_hi define the lower/upper limits of the highest density interval (HDI) containing 68% of the posterior probability
2:r_est is the median; r_lo/r_hi define the lower/upper limits of the equal-tailed interval (ETI), containing 68% of the posterior probability."

99.9% of the rows have result_code=1.