Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........5k&link_type=abstract
Ph.D. Thesis, University of Leuven
Astronomy and Astrophysics
Astrophysics
13
Stars: Variables: Rr Lyrae, Stars: Oscillations, Stars: Blazhko Effect, Line: Profiles, Stars: Individual: Rr Lyr
Scientific paper
RR Lyrae stars play a very significant role in astrophysics, not only as standard candles for distance determination, but also because they are witnesses of the evolution of the universe at young age. At the same time, they are considered to be prototypes of pure radial pulsators, with periods ranging from some hours up to one day. Although these stars are well studied, major questions remain to be solved, like the origin of the so-called Blazhko effect, which is shown by some 20-30% of the RRab stars. It manifests itself as the long-term modulation of the lightcurve shape and its amplitude, on a time scale of typically tens of days.
This thesis is devoted to a spectroscopic study of the Blazhko effect in RR Lyrae, the prototype of this class of variable stars. The manuscript is subdivided in two complementary parts. In Part I, we discuss the temporal behavior of the line profile variations of RR Lyrae. In Part II, we concentrate on the identification of the nonradial modes in RR Lyrae. After giving a brief overview of the characteristics of RR Lyrae stars, we situate the unsolved question of the mechanism behind the Blazhko effect, and the viable models proposed to explain this phenomenon, which are all based upon the presence of non-radial pulsation components in the star. The results of a period analysis performed on a set of high-resolution line profiles of RR Lyrae imply a strong evidence for the presence of nonradial modes in RR Lyrae, of which the precise identification is the following step in our work. Basically, we have considered three different approaches to unravel the nonradial modes from our data, which are subsequently discussed in Part II of this work. We end with the conclusions in the framework of the studies on the Blazhko effect and the outlook for future projects.
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