Atmospheric motions in classical cepheid stars. II. The pre-resonance cepheids : eta Aquilae, S Sagittae.
In this second paper of this series we study the effect of the well-known resonance of the fundamental and the second overtone pulsation mode on the turbulence. Thus, we observed high resolution spectra of the classical cepheid stars η Aquilae and S Sagittae at two different spectral domains, one including Hα and the other one including the sodium D lines. We find that for both stars the resonance delays the compression of the stellar atmosphere so that the increase of turbulence caused by this compression occurs nearly at the same time as the strong rise of turbulent velocity υturb due to the acceleration front propagating outward. This explains why no standstill can be seen in the ascending branch of the υrot curve as it is the case for & δ Cephei.
Astronomy and Astrophysics
- Pub Date:
- October 1993
- stars: variables: Cepheids - line: profiles - turbulence - shock waves - stars: individual: η Aquilae;
- S Sagittae