The unirationality of the moduli spaces of 2-elementary K3 surfaces (with an Appendix by Ken-Ichi Yoshikawa)

We prove that the moduli spaces of K3 surfaces with non-symplectic involutions are unirational. As a by-product we describe configuration spaces of 4<d<9 points in the projective plane as arithmetic quotients of type IV.Comment: 32 pages, simplified exposition, to appear in Proc. London Math. So