The behaviour of certain helium lines in the P Cygni spectrum

Sixty-two spectrograms of the supergiant P Cyg, obtained with the Coudé spectrograph of the 2 m RCC telescope at NAO (National Astronomical Observatory, Bulgaria) were used in order to study the behaviour (we mean the displacements of the absorption components only) of the Hei spectrum of this star. Twelve lines from four series (2³ P ⁰–n³S, 2³P⁰ –n ³ D, 2 ¹ P ⁰ –n ¹ D, and 2¹ S–n ¹ P ⁰) were examined. It was established that all observed cases can be reduced to a few (three or four) which are typical. These cases are stated in the form of the comparison between the hydrogen and helium lines. All profiles were rectified and their complex structure was taken into consideration. The fixed peculiarities were explained by an optical depth effect.