  The finite temperature chiral and deconfinement phase transitions at zero
density for light and heavy quarks, respectively, have analytic continuations
to imaginary chemical potential. At some critical imaginary chemical potential,
they meet the Roberge-Weiss transition between adjacent $Z(3)$ sectors. For
light and heavy quarks, where the chiral and deconfinement transitions are
first order, the transition lines meet in a triple point. For intermediate
masses chiral or deconfinement transitions are crossover and the Roberge-Weiss
transition ends in a second order point. At the boundary between these regimes
the junction is a tricritical point, as shown in studies with $N_f=2,3$ flavors
of staggered and Wilson quarks on $N_\tau=4$ lattices. Employing finite size
scaling we investigate the nature of this point as a function of quark mass for
$N_f=2$ flavors of Wilson fermions with a temporal lattice extent of
$N_\tau=6$. In particular we are interested in the change of the location of
tricritical points compared to our ealier study on $N_\tau=4$.
