  The linearised time dependent coupled Gross-Pitaevskii equations describing
the long wavelength excitations of Bose-condensed binary mixtures are solved,
in the bulk and in harmonic traps for the case where only the binary phase is
present. In the former case we obtain two zero-sound branches.In the latter
case the dispersion law also contains two branches whose dependence on the
quantum numbers of the modes is the same as for a one-component condensate,but
with different prefactors, depending on the ratios of the three s-wave
scattering lengths of the two atomic species. In the general case where the
binary phase in the trap coexists with one or both one-component phases, the
mode spectrum depends on the geometry of the interphase boundaries due to the
boundary conditions there. Measurements of the oscillation frequencies as in
recent experiments with modulated traps would yield very detailed information
on this system.
