The role of non-thermal electrons in the hydrogen and calcium lines of stellar flares

There is observational evidence showing that stellar and solar flares occur with a similar circumstance, although the former are usually much more ene rgetic. It is expected that the bombardment by high-energy electrons is one of the chief heating processes of the flaring atmosphere. In this paper we study how a precipitating electron beam can influence the line profiles of Ly alpha, H alpha, Ca II K and lambda 8542. We use a model atmosphere of a dMe star and make non-LTE computations taking into account the non-thermal collisional rates owing to the electron beam. The results show that the fo ur lines can be enhanced to different extents. The relative enhancement inc reases with increasing formation height of the lines. Varying the energy fl ux of the electron beam has different effects on the four lines. The wings of Ly alpha and H alpha become increasingly broad with the beam flux; chang e of the Ca II K and lambda 8542 lines, however, is most significant in the line centre. Varying the electron energy (i.e. the low-energy cut-off for a power-law beam) has a great influence on the Ly alpha line, but little on the H alpha and Call lines. An electron beam of higher energy precipitates deeper, thus producing less enhancement of the Ly alpha line. The Ly alpha /H alpha flux ratio is thus sensitive to the electron energy.