Last update: 07/24/02
Abstract
In this paper, we determine for all primes p the automorphism group Aut(X0*(p)) of the modular curve $X0*(p)$, which is the quotient of X0(p) by its Atkin-Lehner involution. The main tools used are complex multiplication theory and a study of how Aut(X0*(p)) acts on the special fibers of various minimal regular models of the curve. We also make some progress on the general square-free level case.