7.6.1 Overview

In order to fulfill the objectives of its mission, Gaia makes repeated observations of the sources it identifies. During the data acquisition interval covered by Gaia DR3, an average of $\sim 70$ photometric measurements were obtained for each identified source, varying between $\sim 30$ and $\sim 240$ measurements, depending on the position of the source as per the Gaia scanning law. These observations represent a treasure trove for stellar variability studies, and a significant part of the Gaia data reduction effort is dedicated to the characterisation and classification of the different types of variable stars. One outcome of this work for Gaia DR3 has been the identification of $\sim 2.2\times {10}^6$ eclipsing binary (EB) and ellipsoidal systems for which a number of parameters characterising their light curves (LCs) have been calculated. These include the photometric period, the times of mid-eclipse, as well as eclipse durations and depths, and were obtained by fitting the LCs with Gaussian or cosine functions in the variability processing stage (see Section 10.7.1 and Mowlavi et al. 2023).

Owing to the special value of eclipsing systems in astrophysical studies, NSS processing goes a step farther by extracting physical parameters from the LCs of the EBs identified in the preceding stage. This is accomplished by fitting the data with synthetic LCs generated by simulated binary stars of known physical parameters. For a small number of cases, photometric data were fitted simultaneously with radial velocity data to yield a combined solution; this is described in Section 7.7. The present section documents the solutions obtained using exclusively photometric data.

Sections 7.6.2, 7.6.3 and 7.6.4 below describe, respectively, the properties of the input data, the physical model used to fit the data, and the fitting process (“solver”) that was used to accomplish it. These three components are then put together in Section 7.6.5 which describes the processing steps and the output parameters. Section 7.6.6 discusses a series of known issues and concerns that should be taken into account by the user of these results. Finally, Section 7.6.7 concludes with a few words regarding the verification and validation process, which is described in detail in Siopis (2022).