Black hole-neutron star mergers from triples II: the role of metallicity
  and spin-orbit misalignment
  Observations of black hole-neutron star (BH-NS) mergers via gravitational
waves (GWs) are of great interest for their electromagnetic counterparts, such
as short gamma-ray bursts, and could provide crucial information on the nature
of BHs and the NS crust and magnetosphere. While no event has been confirmed, a
recent possible detection of a BH-NS merger event by the LIGO-Virgo
collaboration has attracted a lot of attention to these sources. In this second
paper of the series, we follow-up our study of the dynamical evolution of
triples comprised of an inner BH-NS binary. In particular, we examine how the
progenitor metallicity affects the characteristics of the BH-NS mergers in
triples. We determine the distributions of masses, orbital parameters and
merger times, as a function of the progenitor metallicity and initial triple
orbital distributions, and show that the typical eccentricity in the LIGO band
is $\sim 10^{-2}-10^{-1}$. We derive a merger rate range of
$\Gamma_\mathrm{BH-NS}=1.9\times 10^{-4}-22 \ \mathrm{Gpc}^{-3}\
\mathrm{yr}^{-1}$, consistent the LIGO-Virgo upper limit. Finally, we study the
expected spin-orbit misalignments of merging BH-NS binaries from this channel,
and find that typically the effective spin distribution is peaked at $\chi_{\rm
eff}\sim 0$ with significant tails.
