This table contains the Renormalised Unit Weight Error (RUWE) associated to each source in gaia_source.
The RUWE is expected to be around 1.0 for sources where the single-star model provides a good fit to the astrometric observations. A value significantly greater than 1.0 (say, >1.4) could indicate that the source is non-single or otherwise problematic for the astrometric solution.
The desciption of how this parameter is calculated is described in the document ”Re-normalising the astrometric
chi-square in Gaia DR2”, which can be downloaded from:
source_id : Unique source identifier (unique within a particular Data Release) (long)
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 million pixels of about 0.7 arcmin.
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 )
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 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: