Information on Service 'Gaia DR3 Lite Distances Subset Cone Search'

For a list of all services and tables belonging to this service's resource, see Information on resource 'Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3 (eDR3)'

Overview

You can access this service using:

• form -- an interface for web browsers through an HTML form
• scs.xml -- a standard SCS interface as defined by the IVOA to access catalog-type data; SCS clients use https://dc.zah.uni-heidelberg.de/gedr3dist/q/cone/scs.xml? to access the service
• static -- static (i.e. prepared) data or custom client-side code; probably used to access ancillary files here

Copyright, License, Acknowledgements

• The Gaia eDR3 (photo-) geometric distances catalogue. is licensed under the Creative Commons Attribution 4.0 License

  
• https://spdx.org/licenses/CC-BY-4.0.html

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

Note d

For each source we compute two posterior probability distributions over distance: a geometric one and a photogeometric one. “Geometric” means only parallax and the parallax uncertainty were used. “Photogeometric” means the G magnitude and the BP-RP colour were used as well. For each of these posterior distributions we estimate and provide three quantiles: 0.158655 (“Lo“), 0.5 (“Med”), and 0.841345 (“Hi”).

“Med” is the median of the distribution, and should be taken as the distance estimate itself. “Lo” and “Hi” define the lower and upper ends of the equal-tailed 68% (actually 68.269%) confidence interval on this estimate. If the posterior were Gaussian, then (r_hi_geo-r_lo_geo)/2 would be the 1-σ Gaussian uncertainty of the geometric distance (and similarly for the photogeometric distance). However, we stress that these confidence bounds are asymmetric, sometimes significantly so.

The distance estimates are predicated on the assumption that the source is a single star in our Galaxy. Estimates are provided whereever possible for sources that have the required input data, independent of any other knowledge on the nature of that source (e.g. being a binary star or quasar).

Note e

As long as the SNR is larger than 10 or so, 1.09*mag/snr is a reasonable approximation for an roughly symmetric magnitude error. For smaller SNR, the error distribution of the magnitude becomes very asymmetric and highly non-Gaussian.

Note f

The flag is normally a string with 5 decimal digits, ABBCC, the meaning of which is explained below. In some cases it can be "99", as also explained below.

This flag field is for information. It is not recommended to use this to filter out sources. Users may want to filter on the size of the distance confidence interval or on quality fields in the eDR3 gaia_source catalogue, such as ruwe, visibility_periods_used, or parallax_over_error. See the accompanying paper for more information.

A:	0: source does not have a G magnitude 1: source has G <= G_lim for that HEALpixel 2: source has G > G_lim for that HEALpixel
B:	The first (left-most) digit refers to the geometric posterior, the second to the photogeometric posterior. It indicates whether we have a low p-value (<1e-3) in the Hartigan Dip test (null hypothesis that posterior is unimodal, so small p suggests evidence against this). Two-digit integer. Each digit can be: 0: not set, so assume unimodal hypothesis okay (or if test is not done or gives no answer) 1: set, so possibly multimodal. For instance, 10 means geo possibly multimodal, photgeo probably unimodal Moreover, the computed confidence interval often spans any multimodality, so generally speaking sources do not need to be excluded just because of evidence of multimodality from this test. This flag refers to the posterior as sampled by the MCMC rather than the true posterior.
C:	QG models used to compute the photogeometric posterior. Two digit integer. Each digit can be: 0: NULL 1: one-component Gaussian model 2: two-component Gaussian model 3: smoothing spline The first (left-most) digit refers to the lower (bluer) model, the second to the upper (redder) model. E.g. 13 means the lower one was a one-component Gaussian and the upper one was was spline.

There is also a special setting of this flag:

99:	data (G or BP-RP) were missing (so no photogeo distance could be computed)

Note id

For the contents of Gaia DR3, 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(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 - 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 - 7

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 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.