2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/106334For certain complex projective manifolds (such as K3 surfaces and their higher dimensional analogues, the complex symplectic projective manifolds) the period map takes values in a locally symmetric variety of type IV. It is often an open embedding and in such cases it has been observed that the image is the complement of a locally symmetric (Heegner) divisor. We explain that phenomenon and get our hands on the complementary divisor in terms of geometric data.23 pAlgebraic Geometry14D07; 32N15text