"To obtain a (1,0) supersymmetric compactification of the heterotic string to six dimensions, one should choose an internal CFT with (0,4) supersymmetry and right-moving central charge c_R=6." e.g. NLSM with K3 target.
Maybe interesting: T. Eguchi, H. Ooguri, A. Taormina and S. -K. Yang, "Superconformal Algebras and String Compactification on Manifolds with SU(N) Holonomy," Nucl. Phys. B 315, 193 (1989).
"To obtain a (1,0) supersymmetric compactification of the heterotic string to six dimensions, one should choose an internal CFT with (0,4) supersymmetry and right-moving central charge c_R=6." e.g. NLSM with K3 target.
etc