Abstract:
The present thesis is an attempt to study some
aspects of trie pulsation theory of the variable stars.
Keeping in view the theoretical developments on the
structure and evolution of stars, a stellar model of
15.6 solar masses in the helium burning phase of its
evolution has been selected to see if it could be a
representative model of the pulsating cepheids.
After calculating the inner structure of the
model in detail, it has been studied for its pulsation
properties on the basis of the Eddington's hypothesis
of small radial oscillations. The periods of pulsation of
the model in the fundamental and the next three higher
modes of pulsation have be -n calculated. Skewness and
shape of the radial velocity curve of the model are det
ermined on the basis of the theory of anharmonic pulsations
The effect of the radiation pressure, which is quite
significant and a variable quantity in the model, on the
pulsation periods and the shape and skewness of the radial
velocity curve has been studied. An attempt has also been
made to study the effects of the inclusion of the different
number of higher modes, the inclusion of second and third
order terms, and the variation of the amplitude of pulsat
ion on the shape and skewness of the radial velocity curve.
-ii-
The capacity of the nuclear energy sources in the
interior of the star in sustaining the pulsations is
investigated. Inclusion of non-adiabatic effects of the
outer layers and the contribution of the region of second
helium ionization towards the pulsational stability of
the model and the observed phase lag of the model has also
been explored. An attempt has also been made to see which
mode out of the various modes of pulsation considered will
be most favoured for pulsations.
A detailed introduction to the present work and a
chapter-wise summary of the contents of the thesis is given
in section 1.7 of Chapter I.
