Map of heterotic and type IIB moduli in eight dimensions

Explicit relations among moduli of the heterotic and Type IIB string theories in 8 dimensions are obtained. We identify the BPS states responsible for gauge enhancements in the type IIB theory and their dual partners in the Heterotic theory compactified with and without Wilson lines. The masses of BPS states in Type IIB string theory compactified on the base space of an elliptically fibred K3 are computed explicitly for the special cases in which the complex structure of the fibre is constant, i.e. for constant scalar fields backgrounds