Covariants of binary sextics and vector-valued Siegel modular forms of   genus two
  We extend Igusa's description of the relation between invariants of binary sextics and Siegel modular forms of degree two to a relation between covariants and vector-valued Siegel modular forms of degree two. We show how this relation can be used to effectively calculate the Fourier expansions of Siegel modular forms of degree two. 
Fabien Cl\'ery, Carel Faber and Gerard van der Geer
math.AG math.NT