2.1.8 sso_observation

Solar System object observations. Each table line contains data obtained during the transit of the source on a single CCD, during a single transit. The corresponding epoch is provided. Data not varying within the transit are repeated identically for all single observations of that transit.

Columns description:

solution_id : Solution Identifier (long)

All Gaia data processed by the Data Processing and Analysis Consortium comes tagged with a solution identifier. This is a numeric field attached to each table row that can be used to unequivocally identify the version of all the subsystems that were used in the generation of the data as well as the input data used. It is mainly for internal DPAC use but is included in the published data releases to enable end users to examine the provenance of processed data products. To decode a given solution ID visit https://gaia.esac.esa.int/decoder/solnDecoder.jsp

source_id : Source identifier (long)

A unique single numerical identifier of the source obtained from the Gaia DR3 main source catalogue (for a detailed description see gaiadr3.gaia_source.source_id). Note in particular that these identifiers are by convention negative for SSOs.

denomination : standard MPC denomination of the asteroid (string)

Name of the object. It follows the Minor Planet Centre convention for the minor planets and natural satellites of the planets.

transit_id : Transit Identifier (long)

The transit_id is a unique identifier assigned to each detected (and confirmed) source as it transits the Gaia focal plane. Each time a given source is detected as Gaia scans and re-scans the sky a new transit_id will be created to badge that apparition. Hence the along–scan time and the across–scan position along with the telescope in which the source was detected are used to form a unique integer with which to label the transit.

The several features of a detection that are encoded in transit_id can be easily retrieved using bit masks (&) and shifts ($\mathit{>>}$) as follows:

• •

  On-Board Mission Time line [ns]
  = 204800 * ((transit_id $\mathit{>>}$ 17) & (0x000003FFFFFFFFFF))

• •

  Field-of-view = 1 + (transit_id $\mathit{>>}$ 15) & 0x03 [1 for ‘preceding’ and 2 for ‘following’ fields-of-view respectively]

• •

  CCD row = (transit_id $\mathit{>>}$ 12) & 0x07 [dimensionless, in the range 1 to 7]

• •

  Across-scan ‘reference acquisition pixel’ in strip AF1 = (transit_id) & 0x0FFF [pixels] (this is the across-scan centre of the AF1 window and is odd if immediately below the mid-point of the window and even if immediately above)

where the bit mask prefix ‘0x’ denotes hexadecimal.

For further details see Portell et al. (2020). For convenience a decoder for transit_id is available on-line at

https://gaia.esac.esa.int/decoder/transitidDecoder.jsp

observation_id : Observation Identifier (long)

Identifier at single CCD level of the observation of a Solar System object. It is unique, and obtained from a combination of transit_id and an integer number representing the CCD strip: observation_id = transit_id x 10 + AF CCD number.

number_mp : Minor Planet number (long)

Minor planet number attributed by the Minor Planet Centre (MPC). It is set to zero for the natural planetary satellites.

epoch : Gaia-Centric epoch TCB(Gaia) (double, Time[Gaia-Centric JD in TCB $-$ 2 455 197.5 (day)])

Gaia-Centric epoch TCB(Gaia) in JD corresponding to the time of crossing of the fiducial line of the CCD (mid exposure). This is the epoch to which the target coordinates and the position/velocity of Gaia are referred. To avoid loss of precision the reference time J2010.0 has been subtracted.

epoch_err : Error in Gaia-Centric epoch (double, Time[day])

The error in the Gaia-Centric epoch (for both epoch and epoch_utc).

epoch_utc : Gaia-Centric TCB epoch converted to UTC (double, Time[Gaia-Centric JD in UTC $-$ 2 455 197.5 (day)])

Gaia-Centric epoch in UTC in JD-J2010.0 corresponding to right ascension and declination obtained from the conversion of TCB(Gaia) to UTC.

ra : Right ascension of the source (double, Angle[deg])

ICRS right ascension of the source as observed by Gaia at epoch, corrected for full relativistic aberration but not for relativistic light deflection in the gravitational field of the Solar System.

dec : Declination of the source (double, Angle[deg])

ICRS declination of the source as observed by Gaia at epoch, corrected for full relativistic aberration but not for relativistic light deflection in the gravitational field of the Solar System.

ra_error_systematic : Standard error of right ascension, systematic (double, Angle[mas])

Uncertainty on right ascension, systematic component (assumed to be constant during a transit), multiplied by cos of declination.

dec_error_systematic : Standard error of declination, systematic (double, Angle[mas])

Standard error for declination, systematic component (assumed to be constant during a transit).

ra_dec_correlation_systematic : Correlation of ra and dec errors, systematic (double)

Correlation of ra_error_systematic and dec_error_systematic.

ra_error_random : Standard error of right ascension, random (double, Angle[mas])

Uncertainty on right ascension, random component, multiplied by cos of declination.

dec_error_random : Standard error of declination, random (double, Angle[mas])

Standard error for declination, random component.

ra_dec_correlation_random : Correlation of ra and dec errors, random (double)

Correlation of ra and dec uncertainty, random component.

x_gaia : Barycentric x position of Gaia (double, Length & Distance[AU] )

Barycentric equatorial J2000 (ICRS) x position of Gaia at the epoch of the observation.

y_gaia : Barycentric y position of Gaia (double, Length & Distance[AU] )

Barycentric equatorial J2000 y position (ICRS) of Gaia at the epoch of the observation.

z_gaia : Barycentric z position of Gaia (double, Length & Distance[AU] )

Barycentric equatorial J2000 z position (ICRS) of Gaia at the epoch of observation.

vx_gaia : Barycentric x velocity of Gaia (double, Velocity[AU day${}^{-1}$] )

Barycentric equatorial J2000 (ICRS) x velocity of Gaia at the epoch of the observation.

vy_gaia : Barycentric y velocity of Gaia (double, Velocity[AU day${}^{-1}$] )

Barycentric equatorial J2000 (ICRS) y velocity of Gaia at the epoch of observation.

vz_gaia : Barycentric z velocity of Gaia (double, Velocity[AU day${}^{-1}$] )

Barycentric equatorial J2000 (ICRS) z velocity of Gaia at the epoch of observation.

x_gaia_geocentric : Geocentric x position of Gaia (double, Length & Distance[AU])

Geocentric equatorial J2000 x position of Gaia at the epoch of observation, in a reference aligned to ICRS.

y_gaia_geocentric : Geocentric y position of Gaia (double, Length & Distance[AU])

Geocentric equatorial J2000 y position of Gaia at the epoch of observation in a reference aligned to ICRS.

z_gaia_geocentric : Geocentric z position of Gaia (double, Length & Distance[AU])

Geocentric equatorial J2000 z position of Gaia at the epoch of observation in a reference aligned to ICRS.

vx_gaia_geocentric : Geocentric x velocity of Gaia (double, Velocity[AU day${}^{-1}$])

Geocentric equatorial J2000 x velocity of Gaia at the epoch of observation in a reference aligned to ICRS.

vy_gaia_geocentric : Geocentric y velocity of Gaia (double, Velocity[AU day${}^{-1}$])

Geocentric equatorial J2000 y velocity of Gaia at the epoch of observation in a reference aligned to ICRS.

vz_gaia_geocentric : Geocentric z velocity of Gaia (double, Velocity[AU day${}^{-1}$])

Geocentric equatorial J2000 z velocity of Gaia at the epoch of observation in a reference aligned to ICRS.

position_angle_scan : Position angle of the scanning direction (double, Angle[deg])

Position angle of the scan direction at the epoch of observation in the equatorial reference frame. 0 = North direction, $\pi$/2 = increasing right ascension, pi = South, 3$\pi$/2 = decreasing right ascension. It is defined as the angle between the AL direction and the direction to the North Pole, at the SSO position, after applying the correction for aberration. As a consequence of this correction for aberration, the AC direction is not strictly perpendicular to the AL direction.

astrometric_outcome_ccd : Result of processing the CCDs (int)

Result of the astrometric processing of the individual CCDs in the transit. Values presently defined:

• 1

  Good position derived.

• 11

  No position derived, because no centroid could be determined.

• 12

  Position rejected a priori, because previous studies have shown that it is unreliable.

• 24

  Position rejected, because this CCD has some samples that have been eliminated.

• 25

  Position rejected, because this CCD is affected by an AOCS update.

• 26

  Position rejected, because this CCD is affected by a non-nominal gating.

• 29

  Position rejected, because of more than one reason, combination of codes 21–26.

• 32

  Position rejected as outlier, because this position does not fit on the regression line.

• 35

  Position rejected, because it does not fulfill the magnitude-uncertainty relation, see documentation.

• 39

  Position rejected, because the value of the distance to last charge injection event recorded for the relevant CCD is invalid.

• 40

  Position rejected, because the epoch corresponds to known bad attitude, see documentation.

• 41

  Position rejected, because no attitude or no calibration is available for the epoch of observation.

astrometric_outcome_transit : Result of processing the transit (int)

Result of the astrometric processing of the transit. Values defined at present are:

• 1

  The transit contains at least one good position.

• 2

  Positions derived, but less consistent than expected. This means that the criterion to reject outliers had to be relaxed to find an unambiguous set of consistent positions.

• 5

  Positions derived, but outlier rejection was not possible because of dramatic loss of precision.

• 6

  Positions derived, but no future field angles in RP/BP, because no attitude is available for the future epochs (reference epoch + 45, 50 and 55 seconds).

fov : Field of view (byte)

Field of view (0 = preceding, 1 = following)

is_rejected : Flag indicating if rejected by the orbital fit (boolean)

This flag indicates if the observation was considered as an outlier by the orbital fit. This happens if the post–fit residuals are above a given threshold (provided in the DR3 documentation), in which case the flag is set to true.