Simultaneous Hα, Na~{sc i} D₁, D₂, and He~{sc i} D₃ observations of a flare on the RS CVn system UX Ari

We present simultaneous H$\alpha$, Na~{\sc i} D$_{1}$, D$_{2}$, and He~{\sc i} D$_{3}$ spectroscopic observations on the RS CVn system UX Ari. We have found a dramatic increase in the excess H$\alpha$ emission equivalent width by a factor of 2 in an interval of 1 day that indicates the beginning of a strong flare in this system. The presence of the He~{\sc i} D$_{3}$ in emission in coincidence with the enhancement of the H$\alpha$ emission confirms the detection of a flare. The application of the spectral subtraction technique reveals that the core of the Na~{\sc i} D$_{1}$ and D$_{2}$ lines are also filled-in by chromospheric emission.