  Homogeneous observations and careful analysis of transit light curves can
lead to the identification of transit timing variations (TTVs). TrES-2 is one
of few exoplanets, which offer the matchless possibility to combine long-term
ground-based observations with continuous satellite data. Our research aimed at
the search for TTVs that would be indicative of perturbations from additional
bodies in the system. We also wanted to refine the system parameters and the
orbital elements. We obtained 44 ground-based light curves of 31 individual
transit events of TrES-2. Eight 0.2 - 2.2-m telescopes located at six
observatories in Germany, Poland and Spain were used. In addition, we analysed
18 quarters (Q0-Q17) of observational data from NASA's space telescope Kepler
including 435 individual transit events and 11 publicly available ground-based
light curves. Assuming different limb darkening (LD) laws we performed an
analysis for all light curves and redetermined the parameters of the system. We
also carried out a joint analysis of the ground- and space-based data. The long
observation period of seven years (2007-2013) allowed a very precise
redetermination of the transit ephemeris. For a total of 490 transit light
curves of TrES-2, the time of transit mid-point was determined. The transit
times support neither variations on long time-scale nor on short time-scales.
The nearly continuous observations of Kepler show no statistically significant
increase or decrease in the orbital inclination i and the transit duration D.
Only the transit depth shows a slight increase which could be an indication of
an increasing stellar activity. In general, system parameters obtained by us
were found to be in agreement with previous studies but are the most precise
values to date.
