  We identify the ballistically and diffusively rescaled limit distribution of
the second class particle position in a wide range of asymmetric and symmetric
interacting particle systems with established hydrodynamic behavior,
respectively (including zero-range, misanthrope and many other models). The
initial condition is a step profile which, in some classical cases of
asymmetric models, gives rise to a rarefaction fan scenario. We also point out
a model with non-concave, non-convex hydrodynamics, where the rescaled second
class particle distribution has both continuous and discrete counterparts. The
results follow from a substantial generalization of P.A. Ferrari and C. Kipnis'
arguments ("Second class particles in the rarefaction fan", Ann. Inst. H.
Poincar\'e, 31, 1995) for the totally asymmetric simple exclusion process. The
main novelty is the introduction of a signed coupling measure as initial data,
which nevertheless results in a proper probability initial distribution for the
site of the second class particle and makes the extension possible. We also
reveal in full generality a very interesting invariance property of the
one-site marginal distribution of the process underneath the second class
particle which in particular proves the intrinsicality of our choice for the
initial distribution. Finally, we give a lower estimate on the probability of
survival of a second class particle-antiparticle pair.
