def sigOmega(self,dangle):
        """
        NAME:

           sigmaOmega

        PURPOSE:

           calculate the 1D sigma in frequency as a function of angle, assuming a uniform time distribution up to a maximum time

        INPUT:

           dangle - angle offset

        OUTPUT:

           sigma Omega

        HISTORY:

           2013-12-05 - Written - Bovy (IAS)

        """
        dOmin= dangle/self._tdisrupt
        meandO= self._meandO
        sO1D2= ((numpy.sqrt(2./numpy.pi)*numpy.sqrt(self._sortedSigOEig[2])\
                     *(meandO+dOmin)\
                     *numpy.exp(-0.5*(meandO-dOmin)**2.\
                                   /self._sortedSigOEig[2])/
                (1.+special.erf((meandO-dOmin)\
                                    /numpy.sqrt(2.*self._sortedSigOEig[2]))))\
                   +meandO**2.+self._sortedSigOEig[2])
        mO= self.meanOmega(dangle,oned=True,use_physical=False)
        return numpy.sqrt(sO1D2-mO**2.)