Parameter study of r-process lanthanide production and heating rates in kilonovae

\def\h{heating rate}\def\l{lanthanide}\def\u{luminosity}\def\t{the }Explosive r-process nucleosynthesis in material ejected during compact object mergers may lead to radioactively powered transients called kilonovae. The timescale and peak \u\ of these transients are sensitive to \t composition of \t material after nuclear burning ceases, as \t composition determines \t local \h\ from nuclear decays and \t opacity. The presence of \l{s} in \t ejecta can drastically increase \t opacity. We use \t new general-purpose nuclear reaction network SkyNet to run a parameter study of r-process nucleosynthesis for a range of initial electron fractions $Y_e$, initial entropies $s$, and density decay timescales $\tau$. We find that \t ejecta is \l-free for $Y_e\agt0.22-0.3$, depending on $s$ and $\tau$. The \h\ is insensitive to $s$ and $\tau$, but certain, larger values of $Y_e$ lead to reduced \h{s}, because single nuclides dominate \t heating. With a simple model we estimate \t\u, time, and effective temperature at \t peak of \t light curve. Since \t opacity is much lower in \t\l-free case, we find \t\u\ peaks much earlier at $\sim1$ day vs.\ $\sim15$ days in \t\l-rich cases. Although there is significant variation in \t\h\ with $Y_e$, changes in \t\h\ do not mitigate \t effect of \t\l{s}.