Abstract

Abstract. I report on a new method for measuring deviations from ax-isymmetry in the velocity elds of gas disks. The method is an extension of the method that Franx, van Gorkom and de Zeeuw developed for a single orbit gas ring. The measurement is based upon a higher order harmonic expansion of the full velocity eld. Epicyclic theory is used to calculate the eects of a perturbation in the potential on these harmonic terms. It is shown how the s 1 and s