2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53751We construct new four-dimensional superstring vacua with extended superconformal symmetries. A non-trivial dilaton background implies the existence of Abelian killing symmetries. These are used to construct dual equivalent backgrounds in a way preserving the N=2 superconformal invariance.(Talk given at the EPS 93 Conference at Marseilles, 7 pages, HUB-IEP-93/7High Energy Physics - Theorytext