New examples of Weierstrass semigroups associated with a double covering of a curve on a Hirzebruch surface of degree one

Let φ : Σ1 −→ P 2 be a blow up at a point on P2. Let C be the proper transform of a smooth plane curve of degree d ≥ 4 by φ, and let P be a point on C. Let π : C̃ −→ C be a double covering branched along the reduced divisor on C obtained as the intersection of C and a reduced divisor in | − 2KΣ1 | containing P . In this paper, we investigate the Weierstrass semigroup H(P̃ ) at the ramification point P̃ of π over P , in the case where the intersection multiplicity at φ(P ) of φ(C) and the tangent line at φ(P ) of φ(C) is d− 1.