On the origin of the alternating deep and shallow light minima in RV Tauri stars : R Scuti and AC Herculis.
Abstract
Clean power spectra of the two well-known RV Tauri stars, R Scuti and AC Herculis, are presented. R Sct is one of the most irregular stars of this pulsating variable class, while AC Her is one of the most regular. Except the frequency peaks at nu0/2 and 3nu0/2, where the fundamental period P0 = 1/nu0 is assumed to be the interval between two successive shallow and deep light minima, none of the higher subharmonics or their multiples are detected. Moreover, for R Sct, each frequency peak shows a multicomponent structure which is not encountered within power spectra deduced from hydrodynamical stellar models. This means that the pulsation of R Sct is never strictly periodic. Thus, both the period-doubling bifurcation scenario suggested by Kovacs & Buchler (1988) and the type-I intermittency occurring just after a 4-cycle period-doubling bifurcation (Aikawa, 1990) are clearly not confirmed. The origin of the characteristic alternation of shallow and deep minima is qualitatively consistent with a radiative shock wave effect associated with the development of an extended pulsation running wave. This suggestion merits a realistic but difficult theoretical investigation.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 1992
- Bibcode:
- 1992A&A...259..215G
- Keywords:
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- Line Spectra;
- Power Spectra;
- Stellar Models;
- Stellar Oscillations;
- Variable Stars;
- Hydrodynamic Equations;
- Line Shape;
- Shock Wave Propagation;
- Astrophysics