Fibre de Milnor d'un cône sur une courbe plane singulière.
Let C be a smooth 5-gonal curve of genus 9. Assume all linear systems g15 on C are of type I (i.e. they can be counted with multiplicity 1) and let m be the numer of linear systems g15 on C. The only possibilities are m=1; m=2; m=3 and m=6. Each of those possibilities occur.
In this paper we study the 5 families of genus 3 compact Riemann surfaces which are normal coverings of the Riemann sphere branched over 4 points from very different aspects: their moduli spaces, the uniform Belyi functions that factorize through the quotient by the automorphism groups and the Weierstrass points of the non hyperelliptic families.
We consider the space Curv of complex affine lines t ↦ (x,y) = (ϕ(t),ψ(t)) with monic polynomials ϕ, ψ of fixed degrees and a map Expan from Curv to a complex affine space Puis with dim Curv = dim Puis, which is defined by initial Puiseux coefficients of the Puiseux expansion of the curve at infinity. We present some unexpected relations between geometrical properties of the curves (ϕ,ψ) and singularities of the map Expan. For example, the curve (ϕ,ψ) has a cuspidal singularity iff it is a critical...