Weierstrass points on X0(pM) and supersingular j-invariants

Research output: Contribution to journalArticle

3 Citations (Scopus)


Weierstrass points are special points on a Riemann surface that carry a lot of information. Ogg studied such points on X0(pM) (for M such that X0(M) has genus zero and p prime with p ł M), and he proved that if Q is a Q-rational Weierstrass point on X0(pM), then its reduction modulo p is supersingular. The paper shows that, for square-free M on the list, all supersingular j-invariants are obtained in this way. Furthermore, for most cases where M is prime, the explicit correspondence between Weierstrass points and supersingular j-invariants in characteristic p is described. Along the way, a useful formula of Rohrlich for computing a certain Wronskian of modular forms modulo p is generalized.

Original languageEnglish
Pages (from-to)1-22
Number of pages22
JournalJournal of the London Mathematical Society
Issue number1
Publication statusPublished - Aug 2004


ASJC Scopus subject areas

  • Mathematics(all)

Cite this