  Locating planets in HabitableZones (HZs) around other stars is a growing
field in contemporary astronomy. Since a large percentage of all G-M stars in
the solar neighbourhood are expected to be part of binary or multiple stellar
systems, investigations of whether habitable planets are likely to be
discovered in such environments are of prime interest to the scientific
community. As current exoplanet statistics predicts that the chances are higher
to find new worlds in systems that are already known to have planets, we
examine four known extrasolar planetary systems in tight binaries in order to
determine their capacity to host additional habitable terrestrial planets.
Those systems are Gliese 86, gamma Cephei, HD 41004 and HD 196885. In the case
of gamma Cephei, our results suggest that only the M dwarf companion could host
additional potentially habitable worlds. Neither could we identify stable,
potentially habitable regions around HD 196885 A. HD 196885 B can be considered
a slightly more promising target in the search for Earth-twins. Gliese 86 A
turned out to be a very good candidate, assuming that the systems history has
not been excessively violent. For HD 41004, we have identified admissible
stable orbits for habitable planets, but those strongly depend on the
parameters of the system. A more detailed investigation shows that for some
initial conditions stable planetary motion is possible in the HZ of HD 41004 A.
In spite of the massive companion HD 41004 Bb, we found that HD 41004 B, too,
could host additional habitable worlds.
