Summary:
The present doctoral thesis presents new astrophysical information concerning
absolute parameters and evolutionary status of 40 eclipsing binaries of EA, oEA
and EB type. The systems were selected due to the lack of literature
information concerning their complete light curves, absolute parameters and
evolutionary status of their components. In addition, the majority of the
systems were either candidate for including a pulsating component or they show
peculiar orbital period changes.
All the categories of variable stars are presented in brief, but we focused
mostly on the categories of the eclipsing binaries and δ Scuti type pulsators
which they were of prime interest. The fundamental dynamical equations and the
Roche geometry of eclipsing binaries as well as the physics (e.g. excitation
mechanisms) of stellar pulsations are also presented.
We briefly describe the fundamentals of CCD and the general use of the CCD
images in Astronomy. The main observing site for the data collection was the
Gerostathopouleion observatory of the University of Athens (~95% of the total
observations), while the Kryonerion observatory and the Skinakas observatory
were used as additional observing sites for either fainter objects or for
applying another observation technique.
Concerning our observational methods used, a detailed description is given for
the CCD data reduction techniques of differential aperture photometry and slit
spectroscopy for the eclipsing binaries and pulsating stars. In particular, we
discuss in detail the steps that should be made using modern photometry and
spectroscopy tools in order one to obtain a light curve of an eclipsing binary
or a pulsating star, calculate the respective times of minima/maxima, obtain
its radial velocity curve and classify the spectral type of the component(s).
The data analysis of the eclipsing binaries was based on the W-D code using the
PHOEBE software. For the cases of eclipsing binaries including a δ Scuti
component, their light curve residuals were furthermore analysed with the
Fourier method, using the software PERIOD04, in order to calculate the
pulsating frequencies and estimate the excitation modes. Given that the most of
the selected systems show orbital period changes, the influence of the most
possible physical mechanisms in the system’s orbital period (i.e. Light-Time
effect, mass exchange, mass loss, Applegate mechanism and apsidal motion) and
their respective mathematical background are presented in full detail. It is
shown that the results of the OC diagram analysis can be combined with the
results of the light and radial velocity curves solution in order to obtain a
more comprehensive view of the system. Particularly, it is shown that it is
feasible to find the best Roche geometry that describes the system (e.g.
detached or semidetached configuration), or to conclude about the existence of
a third body orbiting the system, if one compares qualitatively and/or
quantitatively the results of these two independent methods of analysis.
The light curves of ten detached and twelve semidetached systems were analysed,
while, since most of them have variable orbital period, an OC analysis was
also performed. The results of the light curve modelling were used to calculate
the absolute parameters and estimate the present evolutionary status of their
components. In the cases where orbital period modulation was detected, the
results of light curve and OC analyses were compared and the most possible
explanations were proposed. In order to check the accuracy of the methods used,
we compared our results with the sample of well studied detached and
semidetached systems of Ibanoglu et al. (2006). The comparison showed that,
except for a few members of some systems, all the components follow well the
distributions of Ibanoglu et al. (2006) in the M-R and CM diagrams. In
addition, since all systems have total mass less than 3 Μ, they can be
considered as very useful information for this range of masses in the sample of
Ibanoglu et al. (2006). Mass-Luminosity relations were calculated but they did
not differ significantly from those of Ibanoglu et al. (2006).
The most significant part of this thesis, which offers very valuable
astrophysical information, is the survey for the eclipsing systems with a
pulsating component. Given that this field of Astrophysics combines the
eclipsing binaries and the Asteroseismology and, in addition, that there only a
few known such systems, our new observations, discoveries and results can be
considered very important. We tested over a hundred candidate systems for
including a δ Scuti component and we discovered thirteen new cases for which we
performed systematic observations in order to cover the whole light curves and
obtain the most possible detailed frequency study. In addition, we observed for
the same reasons mentioned before eight already known such systems, which they
were generally neglected so far. The steps of the analysis of these systems
were the same with those described in the previous paragraph, but the Fourier
method was also applied in order to perform the frequency search. Using the
results of the 79 known so far such systems, new correlations between pulsation
frequency and fundamental stellar characteristics were found, while the basic
characteristics of the δ Scuti binary-members are now well distinguished from
those of the single δ Scuti stars. However, through this investigation some of
critical questions, such as e.g. how the mass transfer affects the pulsations
or which mechanism plays a significant role for an A-F Main Sequence star to
become a pulsator, remain still open.
Keywords:
Eclipsing binaries, Stellar evolution, Pulsating stars, Photometry, Spectroscopy
