  In the broad subclass of Horndeski theories with a luminal speed of
gravitational waves, we derive gravitational waveforms emitted from a compact
binary by considering the wave propagation on a spatially flat cosmological
background. A scalar field nonminimally coupled to gravity gives rise to hairy
neutron star (NS) solutions with a nonvanishing scalar charge, whereas black
holes (BHs) do not have scalar hairs in such theories. A binary system
containing at least one hairy neutron star modifies the gravitational waveforms
in comparison to those of the BH-BH binary. Using the tensor gravitational
waveforms, we forecast the constraints on a parameter characterizing the
difference of scalar charges of NS-BH or NS-NS binaries for Advanced LIGO and
Einstein Telescope. We illustrate how these constraints depend on redshift and
signal-to-noise ratio, and on different possible priors. We show that in any
case it is possible to constrain the scalar charge precisely, so that some
scalarized NS solutions known in the literature can be excluded.
