code: def _vmomentsurfaceIntegrand(vR,vT,R,az,df,n,m,sigmaR1,sigmaT1,t,initvmoment):
      
      o= Orbit([R,vR*sigmaR1,vT*sigmaT1,az])
      return vR**n*vT**m*df(o,t)/initvmoment
docs: Internal function that is the integrand for the velocity moment times
      surface mass integration