  We present a model for determining the dimensionless spin parameter and mass
of the black hole remnant of black hole-neutron star mergers with parallel
orbital angular momentum and initial black hole spin. This approach is based on
the Buonanno, Kidder, and Lehner method for binary black holes, and it is
successfully tested against the results of numerical-relativity simulations:
the dimensionless spin parameter is predicted with absolute error $\lesssim
0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its
distribution in the tests being pronouncedly peaked at $1$%. Our approach and
the fit to the torus remnant mass reported in Foucart (2012) thus constitute an
easy-to-use analytical model that accurately describes the remnant of black
hole-neutron star mergers. The space of parameters consisting of the binary
mass ratio, the initial black hole spin, and the neutron star mass and equation
of state is investigated. We provide indirect support to the cosmic censorship
conjecture for black hole remnants of black hole-neutron star mergers. We show
that the presence of a neutron star affects the quasinormal mode frequency of
the black hole remnant, thus suggesting that the ringdown epoch of the
gravitational wave signal may virtually be used to (1) distinguish black
hole-black hole from black hole-neutron star mergers and to (2) constrain the
neutron star equation of state.
