Shemakha Astrophysical ObservatoryWith 12 figures (Received 1979 .\ugust I ) Ten-colour photoelectric observations are presented for twelve Ap-stars. Improved ephemeris for seven of them is given. Phase relations between the light curves and line intensity variations are discussed. The problem of thc electromagnetic flux conctancy of IOTA Cas is approached from a qualitative point of view.

Z e n t r a l i n s t i t u t ftir Astrophysik d e r Akademie d e r Wissenschaften der DDR Mit 15 Abbildungen. (Eingegangen 1975 Juli 11)Twelve Ap stars with known periods and fairly large amplitudes were photoelectrically investigated in a ten colour system (A 3400 A to A7600 A). The amplitude-wavelength relations following from the light curves cannot be explained by the influence of the backwarming effect. These relations point to complicated structures in the atmospheres of the peculiar regions of the magnetic stars. Zw6lf Ap-Sterne mit bekannter Periode und grbker Amplitude wurden in &em Zehnfarbensystem

A method has been developed to determine the geometrical parameters of surface distributions of chemical elements on a spotted rotator from observations of variable line strengths. On the basis of simple assumptions for spot geometry and limb darkening this problem has been traced back to the same inverse problem as the determination of surface brightness parameters from photometric observations. The method was applied to eight He-peculiar (CP4) stars (HR 1441, HR 1890, HR 1932, H D 37776, HR 2509 to derive the He surface distribution of these He-rich and He-weak stars from the line strength variation of the He1 R 4026 line. The result and a discussion of the analysis is given.