Let $C$ be a smooth curve. I know that $Pic^0(C)$, i.e. the Picard group of degree 0 line bundles on $C$, is isomorphic to the jacobian $J(C)$, so it is an abelian variety. My question is, what about $Pic^d(C)$, $d>0$, i.e. the set of line bundles of degree $d$ which are a principal homogeneous space under $Pic^0(C)$? Are they projective? Are they normal? Can you give me a reference on the subject?
Thank you..