The instability strip and pulsation features of post-AGB star models

Tohoku gakuin University, Sendai 981-3193, Japan e-mail: aikawa@cs.tohoku-gakuin.ac.jp

Received: 27 July 2009
Accepted: 15 January 2010

Abstract

Aims. The instability strip and characteristics of the nonlinear behavior of the radial pulsation are examined for the observed photometric variability of post-AGB stars.

Methods. A linear stability analysis for radial pulsation modes is performed in the domain 3.70 ≤ log T_eff ≤ 3.90, 0.0 ≤ log g ≤ 1.8 , assuming a total mass 0.6  and 0.8  for post-AGB stars. Radial modes up to the 5th overtone are considered, since we expect that there are some strange modes amongst high-order modes. Nonlinear simulations are tried for all the models, which have at least one pulsationally unstable mode.

Results. Pulsationally unstable modes are found in a large region of the domain, and these modes may be responsible for the observed variability. Nonlinear simulations on models that have unstable modes with higher overtones reveal the variability through small peak-to-peak variations. These variations are characteristics of the observed variations for some post-AGB stars located in the bluer region of the classical instability strip.