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 in a similar circumstance, although the former are usually much more energetic. 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 Lyα, Hα, Ca ii K and λ8542. We use a model atmosphere of a dMe star and make non-LTE computations taking into account the non-thermal collisional rates due to the electron beam. The results show that the four lines can be enhanced to different extents. The relative enhancement increases with increasing formation height of the lines. Varying the energy flux of the electron beam has different effects on the four lines. The wings of Lyα and Hα become increasingly broad with the beam flux; change of the Ca ii K and λ8542 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 Lyα line, but little on the Hα and Ca ii lines. An electron beam of higher energy precipitates deeper, thus producing less enhancement of the Lyα line. The Lyα/Hα flux ratio is thus sensitive to the electron energy.