  Low-mass neutron stars are directly associated with the nuclear saturation
parameters because their central density is definitely low. We have already
found a suitable combination of nuclear saturation parameters for expressing
the neutron star mass and gravitational redshift, i.e., $\eta\equiv
(K_0L^2)^{1/3}$ with the incompressibility for symmetric nuclear matter, $K_0$,
and the density-dependent nuclear symmetry energy, $L$. In this study, we newly
find another suitable combination given by $\eta_\tau\equiv (-K_\tau
L^5)^{1/6}$ with the isospin dependence of incompressibility for asymmetric
nuclear matter, $K_\tau$, and derive the empirical relations for the neutron
star mass and gravitational redshift as a function of $\eta_\tau$ and the
normalized central number density. With these empirical relations, one can
evaluate the mass and gravitational redshift of the neutron star, whose central
number density is less than threefold the saturation density, within $\sim
10\%$ accuracy, and the radius within a few \% accuracies. In addition, we
discuss the neutron star mass and radius constraints from the terrestrial
experiments, using the empirical relations, together with those from the
astronomical observations. Furthermore, we find a tight correlation between
$\eta_\tau$ and $\eta$. With this correlation, we derive the constraint on
$K_\tau$ as $-348\le K_\tau\le -237$ MeV, assuming that $L=60\pm 20$ and
$K_0=240\pm 20$ MeV.
