  This thesis focuses on the statistical properties of wide binary (WB) star
systems in the Galactic field. For the present study we select a homogeneous
sample covering about 675 square degrees in the direction of the NGP. It
contains nearly 670,000 MS stars with apparent magnitudes between 15 and 20.5
mag and spectral classes later than G5. The data were taken from the SDSS. We
construct the two-point correlation function (2PCF) for angular separations
between 2 and 30 arcsecs. The resulting clustering signal is modeled by means
of the Wasserman-Weinberg technique. We show that the distribution of
semi-major axis is consistent with the canonical Oepik law and infer that about
10% of all stars in the solar neighbourhood belong to a WB system. To reduce
the noise from optical pairs and to increase the sensitivity of the analysis at
larger separations, we include distance information from photometric
parallaxes. Introducing a novel weighting procedure based on the binding
probability of a double star, we infer the distribution of colours and mass
ratios, which were carefully corrected for observational selection effects.
About 4,000 WBs were taken into account statistically, whose components have
masses between 0.2 and 0.85 solar masses. We find that the WB colour
distribution is in accord with the colour distribution of single field stars.
However, pairs with a mass difference exceeding 0.5 solar masses seem to be
systematically underrepresented as compared to a random pairing of field stars.
Our results are broadly in agreement with prior studies but a direct comparison
is difficult and often impossible. The novel procedure presented in this thesis
can be regarded as complementary to common proper motion studies, and
constitutes a viable approach to study the statistical properties of WBs in the
Galactic field.
