Nodal curves on surfaces of general type

Abstract

We study the family of irreducible curves with $δ$ nodes belonging to a free linear system $|C|$ with smooth general member on a surface $S$ such that $|K_S|$ is ample. Under the assumption that $C$ is numerically equivalent to $pK_S$, $p\ge 3$ rational, we give an upper bound on $δ$ ensuring that the family is smooth of codimension $δ$ in $|C|$ (plus another slightly different result of the same type). We give examples showing that the bound is sharp. Some related results concerning linear normality of nodal curves are proved.

15 pages, AMSTeX