2.3 The Gaia Object Generator

Author(s): Eduard Masana

The Gaia Object Generator (GOG) is a simulation tool to directly get Catalogue, Main Database (MDB) and final (in the sense of statistically equivalent to the final mission data) Gaia mission data.

GOG is based on the Universe model, described in the previous section, and spacecraft & payload models and uses error models to provide rapid simulations of large amounts of data. The realism of the simulations depends on the realism of the available error models. The implementation of the instrumental error models is a gradual process based on the real data. The simulation of processed data requires models of the calibration errors that are provided by the CUs in charge of the calibration algorithms development.

Among its features, GOG provides:

• •

  Main database Astrometric, Photometric and RVS derived parameters per source transit (EpochData) and for several transits (CombinedData)

• •

  Main database RP/BP/RVS spectra (epoch and combined).

For Gaia EDR3, GOG produced the Main database Combined Data gaia_source_simulation. It has been adapted to Gaia EDR3 by scaling the observation time to 34 months of observations.

Note that the relative positions of the sources with each other will not be used by GOG to add overlapping effects. GOG only works source by source. Only the density at the source position could be used to adjust the error models (if they are provided as a function of density).

In this document we will focus on the error model used by GOG. The current version of GOG is 20.0.3.