Predicted light variations of HD 64740 in Hp photometric filter calculated using abundance maps of one element only. The abundance of other elements was fixed. Upper plot: light variations due to helium only. Silicon abundance was fixed to ε_Si =  − 4.3. Lower plot: light variations due to silicon only. The helium abundance was fixed to ε_He =  − 1.0. Light curves were calculated using the solar iron abundance (ε_Fe =  − 4.6, solid lines) and without iron (dashed lines).