  We study the excitation of nonaxisymmetric modes in the post-merger phase of
binary compact object mergers and the associated gravitational wave emission.
Our analysis is based on general-relativistic simulations, in the spatial
conformal flatness approximation, using smoothed-particle-hydrodynamics for the
evolution of matter, and we use a set of equal and unequal mass models,
described by two nonzero-temperature hadronic equations of state and by one
strange star equation of state. Through Fourier transforms of the evolution of
matter variables, we can identify a number of oscillation modes, as well as
several nonlinear components (combination frequencies). We focus on the
dominant m=2 mode, which forms a triplet with two nonlinear components that are
the result of coupling to the quasiradial mode. A corresponding triplet of
frequencies is identified in the gravitational wave spectrum, when the
individual masses of the compact objects are in the most likely range of 1.2 to
1.35 $M_\odot$. We can thus associate, through direct analysis of the dynamics
of the fluid, a specific frequency peak in the gravitational wave spectrum with
the nonlinear component resulting from the difference between the m=2 mode and
the quasiradial mode. Once such observations become available, both the m=2 and
quasiradial mode frequencies could be extracted, allowing for the application
of gravitational-wave asteroseismology to the post-merger remnant and leading
to tight constraints on the equation of state of high-density matter.
