  We study the equation of state of beta-stable dense matter and models of
neutron stars in the relativistic mean field theory with the isovector scalar
mean field corresponding to the delta-meson [a_0(980)]. A range of values of
the delta-meson coupling compatible with the Bonn potentials is explored.
Parameters of the model in the isovector sector are constrained to fit the
nuclear symmetry energy, E_s=30 MeV. We find that the quantity most sensitive
to the delta-meson coupling is the proton fraction of neutron star matter. It
increases significantly in the presence of the delta-field. The energy per
baryon also increases but the effect is smaller. The equation of state becomes
slightly stiffer and the maximum neutron star mass increases for stronger
delta-meson coupling.
