# 6.4.8 Multi-transit analysis

Multi-transit analysis receives single-transit radial velocities and their uncertainties from STA (see Section 6.4.7). The STA Gaia-centric radial velocities are converted to barycentric by adding their barycentric radial velocity correction, which can range from $+30$ km s${}^{-1}$ to $-30$ km s${}^{-1}$ as a function of Gaia’s six hour revolution (Figure 6.6).

The radial velocities ${V}_{\mathrm{rad}}$ published in Gaia DR2 are obtained by taking the median of the STA barycentric single-transit radial velocities $({V}_{\mathrm{rad}}^{\mathrm{t}})$ (Equation 6.1). ${V}_{\mathrm{rad}}$ is computed only if the number of transits $N$ for which a valid ${V}_{\mathrm{rad}}^{\mathrm{t}}$ has been obtained is $N\ge 2$ (when $N=2$ the mean value is computed). Not all the transits entering the pipeline result in a ${V}_{\mathrm{rad}}^{\mathrm{t}}$. Some transits have been removed from the pipeline upstream STA before calculating ${V}_{\mathrm{rad}}^{\mathrm{t}}$ (see Section 6.4.4). The transits flagged as double-lined spectra are also excluded.

The ${V}_{\mathrm{rad}}$ uncertainty provided in Gaia DR2, is given by Equation 6.2, where $N$ is the number of transits used to obtain ${V}_{\mathrm{rad}}$. $N$ is also provided in Gaia DR2.