Statistical equilibrium and photospheric abundance of silicon in the Sun and in Vega

Based on detailed non-LTE calculations, an updated determination of the abundance of silicon in the Sun and Vega is presented. The model atom includes neutral and singly ionized stages of silicon with 115 energy levels and 84 line transitions. Non-LTE effects are found to be quite small in the Sun. The mean non-LTE abundance correction is -0.010 dex with respect to standard LTE calculations, leading to a solar abundance of log epsilon (NLTE) = 7.550 +/- 0.056. For the prototype A0 V star Vega the non-LTE effects are small, too. With a non-LTE abundance correction of Delta log epsilon = -0.054, a silicon abundance of log epsilon (NLTE) = 6.951 +/- 0.100 is derived, implying a deficiency of -0.599 dex with respect to the Sun. This confirms the classification of Vega as a mild lambda Boo star.