| Περίληψη |
Context: The study of the optical counterparts in Be/X-ray binaries is essential for
understanding the nature and the variability of these high-energy systems. In
particular, optical spectroscopy gives insights into the structure and evolution of the
discretion disk, which represents the source of matter available for accretion.
Aims: The purpose of this thesis is to examine the optical variability of the X-ray
pulsar IGR J06074+2205 analyzing the spectra obtained through several years. This
work is focused on the Hα line as a diagnostic tool for the process of the disk
evolution and the interactions between the neutron star and the Be star.
Methods: The monitoring of the IGR J06074+2205 has been taking place since 2006.
I present the spectroscopic data obtained from Skinakas Observatory, Greece, fitting
the Hα line with Lorentzian profiles in order to obtain the line parameters and the
equivalent width.
Results: The equivalent width went through several maxima and minima revealing a
highly variable disk. Some of the minima coincided with an absorption line profile,
indicating that the disk was absent. I estimated a period of about 3 years between
maxima, which would represent the typical time scales for disk formation and
dissipation. I also found V/R variability that can be attributed to density perturbations
in the disk. I measured a full cycle of the V/R ratio of about ~ 2yr. The separation of
the two peaks in the split profile of the line is connected with the rotational velocity
law of the particles in the disk. I found a correlation between the peak separation and
the equivalent width ΔV.
Conclusions: The relatively rapid phases of formation and dissipation of the disk and
the short precision cycle of the density perturbation within the disk points to a system
with a short orbital period, where the neutron star affects the evolution of the disk.
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Study of the optical variability of the X-ray pulsar IGR J06074+2205
