present. This offset is calculated by correlating the 1[$^{\textrm{\scriptsize st}}$ ]{}order spectral traces of both stars, and considering that the same shift applies to the 0[$^{\textrm{\scriptsize th}}$ ]{}orders. The best correlation is obtained by applying a constant shift of 118 pixels in the $x$ direction and 99 pixels in the $y$ direction for visit 1 and 2 for XO-2 N with respect to XO-2 S, and a shift of 118 pixels in the $x$ direction and $-99$ pixels in the $y$ direction for visit 3 for XO-2 S with respect to XO-2 N.

-   Angle and FWHM of the spectral trace.\
    The angle and FWHM of the 1[$^{\textrm{\scriptsize st}}$ ]{}order spectral trace are derived for each star. The spectral trace is divided into boxes of 5 pixels wide in $x$ and 40 pixels wide in $y$. Each box is averaged in $x$ by a median filter, and a 1-dimension Gaussian fit is computed in the $y$ direction. A linear fit of the center of all Gaussians yields the angle of the spectral trace. Each Gaussian also provides a FWHM in $y$, and the median of all values gives the FWHM of the spectral trace.

-   Detector temperature and state.\
    The 