Invariant star-products on S^2 and the canonical trace
  In the literature there are two different ways of describing an invariant star product on $S^2$. We show that the products are actually the same. We also calculate the canonical trace and use the Fedosov-Nest-Tsygan index theorem to obtain the characteristic class of this product. 
Keizo Matsubara and M{\aa}rten Stenmark