Simultaneous H α , Na i D 1 , D 2 , and He i D 3 observations of a flare on the RS CVn system UX Ari ⋆

We present simultaneous Hα, Na i D 1 , D 2 , and He i D 3 spectroscopic observations on the RS CVn system UX Ari. We have found a dramatic increase in the excess Hα 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 i D 3 in emission in coincidence with the enhancement of the Hα emission confirms the detection of a flare. The application of the spectral subtraction technique reveals that the core of the Na i D 1 and D 2 lines are also filled-in by chromospheric emission.