1997A&A...323..524K

The assumption of plane-parallel geometry is tested for the case of NLTE model atmospheres of central stars of planetary nebulae. As a test example, two hot hydrogen deficient central stars, namely LoTr4 and K1-27 were used. It was found that for atmospheric parameters of the star K1-27, namely T_eff=100000K, gravity logg=6.5, stellar mass 0.52M_☉, and abundance of hydrogen n_H/n_He=0.2, the sphericity effects are very small. On the other hand, atmospheric parameters of LoTr4, namely T_eff=120000K, gravity logg=5.5, stellar mass 0.65M_☉, and abundance of hydrogen n_H/n_He=0.5, yield much greater extension and remarkable sphericity effects.