1[$^{\textrm{\scriptsize st}}$ ]{}and 2[$^{\textrm{\scriptsize nd}}$ ]{}visits, and different in the 3[$^{\textrm{\scriptsize rd}}$ ]{}visit (Figure \[fig:images xo2\]). The images always show the 1[$^{\textrm{\scriptsize st}}$ ]{}order spectrum of both stars, as well as the 0[$^{\textrm{\scriptsize th}}$ ]{}order of XO-2 S for the 1[$^{\textrm{\scriptsize st}}$ ]{}and 2[$^{\textrm{\scriptsize nd}}$ ]{}visits and of XO-2 N for the 3[$^{\textrm{\scriptsize rd}}$ ]{}visit. A fainter 2[$^{\textrm{\scriptsize nd}}$ ]{}order spectrum is also visible.

![Position of the stars on the detector during the 1[$^{\textrm{\scriptsize st}}$ ]{}(left), 2[$^{\textrm{\scriptsize nd}}$ ]{}(middle), and 3[$^{\textrm{\scriptsize rd}}$ ]{}visit (right). XO-2 N is the upper star in the images. The images contain the 1[$^{\textrm{\scriptsize st}}$ ]{}order spectra of both stars, and the 0[$^{\textrm{\scriptsize th}}$ ]{}order of XO-2 S for the 1[$^{\textrm{\scriptsize st}}$ ]{}and 2[$^{\textrm{\scriptsize nd}}$ ]{}visits and of XO-2 N for the 3[$^{\textrm{\scriptsize rd}}$ ]{}visit, due to a different orientation of HST.[]{data-label="fig:images xo2"}](fig1.png "fig:"){width="2.8cm"} ![Position of the stars on the detector during the 1[$^{\textrm{\scriptsize st}}$ ]{}(left), 2[$^{\textrm{\scriptsize nd}}$ ]{}(middle), and 3[$^{\textrm{\scriptsize rd}}$ ]{}visit (right). XO-2 N is the upper star in the images. The images contain the 1[$^{\textrm{\scriptsize st}}$ ]{}order spectra of both stars, and the 0[$^{\textrm{\scriptsize th}}$ ]{}order of XO-2 S for the 1[$^{\textrm{\scriptsize st}}$ ]{}and 2[$^{\textrm{\scriptsize nd}}$ ]{}visits and of XO-2 N for the 