Pulsational properties of nuclei of planetary nebulae

The mechanism responsible for the excitation of pulsations in the envelopes of central stars of planetary nebulae is studied. It is found that with the increase of luminosity the dissipation in the deeper layers of the envelope decreases which results in a shift of the blue edge of the instability strip towards earlier spectral types. The location of the blue edge of the instability strip is found. With the increase of the luminosity from 10000 Lsun to 28000 Lsun the blue edge moves from 5200 K to 7300 K. 9 refs., 6 figs. (author)