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gaia data release 3 documentation

6.2 Properties of the input data

6.2.1 Input data from the upstream processing

The input data to the spectroscopic pipeline were pre-processed by the upstream Initial Data Treatment (IDT) described in Section 3.4.2 where the telemetry information (Section 1.1.3) is reconstructed into several data types. The data used by the spectroscopic pipeline are: SpectroObservation (Section 3.4.3) containing the three CCD spectra acquired in the transit together with various information related to the observation (like the on-board magnitude, the window size, position and truncation); ObjectLogRvs and ObjectLogRvsRotSmear, containing the detection features including the information on the satellite solar rotation phase; AcShift; PreScan; SpectroObservationVo, containing the spectra of the Virtual Objects (empty windows acquired for calibration purposes).

In addition to the IDT data, some other input data are produced by the upstream astrometric processing described in Chapter 4. These data are: a preliminary version of the AGIS position of the sources (V 3.1), of the attitude model OGA3 and of the CorrectiveOga3 (Section 4.3.5), the IDU3 Crossmatch table Section 3.4.13 and the spurious detection transits (Section 3.4.13). The Gaia ephemeris (Section 4.2.3), and the solar-system ephemerides (Section 4.2.1) are also needed.

The stellar atmospheric parameters computed with a preliminary version of Apsis (V 3.1) (see Chapter 11 for a description of the Apsis pipeline) and the magnitude G and GRP from Gaia DR2 were also input via a DPAC internal data model called CompleteSource. The file ExtPhotSystem, produced by the photometric processing (Section 5.4.1), and containing the G and GRP zero-points is also input.

The quality of the CU6 products is impacted by the quality of the input data, in particular by the quality of AGIS and OGA3 and by the quality of the atmospheric parameters. The AGIS positions and OGA3 are used in the wavelength calibration and any significant systematic error impacts the epoch radial velocities (in general these errors affect few transits and do not affect significantly the radial_velocity). The atmospheric parameters are used to select the synthetic template spectrum to compare to the star spectrum to obtain radial and broadening velocities. Inappropriate atmospheric parameters result in template mismatch affecting all the transits of the star and potentially result in a spurious radial_velocity.

Trending epochs and bad-data intervals

The events producing a discontinuity in the wavelength calibration zero-point are defined as breakpoints. In the Gaia DR3 dataset, which includes the data acquired between 25 July 2014 (OBMT 1078.4; see Section 1.3.1 for the definition of OBMT) and 28 May 2017 (OBMT 5230.1), the breakpoints are the following: OBMT 1192.13 EPSL/NSL transition; OBMT 1317, 2330.6 and OBMT 4112.7 decontaminations (Section 1.3.3); OBMT 1443.9 and OBMT 2574.5 refocus. Then, in addition to these physical breakpoints, there are 3 additional breakpoints: OBMT 3904 and 5084 (related to a discontinuity in OGA3 due to a jump in the basic angles) and OBMT 4513.16, due to a discontinuity in OGA3 related to the change in the ELSF calibration in the Initial Data Update (IDU), which is expected to go away in DR4, when an improved AGIS version will be used. These 9 breakpoints are used to separate the dataset into the 10 trending epochs shown in Figure 6.2. The epochs separated by these last three breakpoints are named with suffix B and C.

The effective time covered by the trending epochs are reduced because of the time intervals where the data known to be of bad quality are removed. In particular, the duration of TE2, TE4 and TE6A are significantly reduced because of large BadDataIntervals, due to the cool-down time of the payload after the decontaminations (Figure 6.2).

The bad data intervals used by the RVS pipeline include the time during decontaminations, the refocusing, the commissioning of a new version of the on-board VPU (Section 1.3.3), the time intervals where the AGIS residuals are high, the gaps in the ObjectLogs, and are available for each CCD and FoV via the web page:

Figure 6.2: The Global-R3 timeline. The bad data intervals are marked in red (top timeline plot, obtained by Automated Verification). The total time covered by the BadDataInterval is about 7.8 % of the total observing time. The largest intervals are due to decontamination (D), and to the tests done for the new version of the on-board VPU (T). Most of the small intervals are due to the AGIS3.1 excluded intervals, and to gaps in the ObjectLogs. The bad data intervals are available on The Trending Epochs (TE) are indicated in the bottom part of the figure: the TEs starting after a decontamination (TE2, TE4, and TE6A) are coloured in dark red, in blue those starting after a re-focusing (TE3 and TE5A), in grey those starting after a ‘non-physical’ break-point: TE5B, TE6B, and TE6C. The EPSL TE0 is coloured in green. The decontamination events become rarer as the mission progresses. Shortly after the first and the second decontamination a refocusing was needed, and the trending epochs between these two events (TE2 and TE4) are short.

Filters applied

The filters applied to the input data and during Pre-processing are of two types: at source-level and at transit-level. The filters at source-level remove all the transits of the source, while the filters at transit-level remove only the relevant transits. The following filters are applied to the input data:

  • Poor or not existing AGIS coordinates (the good astrometric positions provided by AGIS are indispensable for wavelength calibration and thus for the radial velocity estimation): The sources are not treated by the pipeline if 1) the source coordinates are not from AGIS 3.1, or AGIS did not converge; 2) the source is flagged as duplicated by AGIS; 3) there are less than 5 observations used by AGIS; 4) the source has large astrometric excess noise astrometric_excess_noise >20 mas; 5) astrometric_sigma5d_max >100 mas. This filter is at source-level.

  • Bad field angles: the spectra for which the uncertainty of the field angle η are > 200 mas are filtered out. This filter is at transit-level.

  • Bad data intervals: The spectra acquired during the bad data intervals (Section 6.2.1) are excluded. This filter is at transit-level.

  • GRVSext (Section 6.1.2): The filters on GRVSext depend on the pipeline (see Figure 6.1). In the Scatter pipeline the border of the spectra of the faint sources are used, then the sources with GRVSext<15 are filtered out. In the Calibration pipeline, instead, only the bright sources are used, and the sources with GRVSext>10 are filtered out. In the FullExtraction pipeline, to make deblending possible, there is no filter for the input sources: however, after the deblending has been applied, the sources with GRVSext>14 are filtered out.

  • Truncated windows: The filters on the truncated windows depend on the pipeline. In the Scatter pipeline all the truncated windows and also the rectangular windows with AC size <10 are filtered out (to avoid blended spectra). In the Calibration pipeline the truncated windows are filtered out, but the rectangular-truncated windows are kept (in order to permit re-blending). In FullExtraction, where the spectra are deblended, there is no filter on the truncated windows.