The Gaia DR2 provides the first Gaia all-sky catalogue of Long Period Variable (LPV) candidates.
They are the result of the processing of a selection of sources classified as MIRA_SR with the nTransits:2+ classifier and the nTransits:20+ classifier.
Because of the time series properties inherent to the data published in Gaia DR2, i.e. the limited range of observation durations (22 months, to be compared to LPV periods that can be larger than a thousand days) and the small number of observations (a mean of 26 observations per source for all LPV candidates, knowing that the majority of these objects are multi-periodic), we restrict the search of Gaia LPV candidates in Gaia DR2 to sources that satisfy certain criteria.
In particular, we consider only large amplitude LPVs (variability amplitudes larger than 0.2 mag in ), and therefore exclude all small amplitude red giants such as OSARGs.
Moreover, we do not aim at completeness in Gaia DR2.
The selection procedure is described in Section 7.7.2, and the LPV parameters published in Gaia DR2 are described together with the processing steps in Section 7.7.3 and Section 7.7.4.
The quality assessment and validation procedures are then presented in Section 7.7.5.