Change in RV of star 1 for time separation dt (default=days)

        :param dt:
            Time separation for which to compute RV change.  If not a ``Quantity``,
            then assumed to be in days.
        :type dt:
            float, array-like, or ``Quantity``

        :param com: (``bool``, optional)
            If ``True``, then return dRV of star 1 in center-of-mass frame.

        :return dRV:
            Change in radial velocity over time ``dt``.

def dRV(self,dt,com=False):
        """Change in RV of star 1 for time separation dt (default=days)

        :param dt:
            Time separation for which to compute RV change.  If not a ``Quantity``,
            then assumed to be in days.
        :type dt:
            float, array-like, or ``Quantity``

        :param com: (``bool``, optional)
            If ``True``, then return dRV of star 1 in center-of-mass frame.

        :return dRV:
            Change in radial velocity over time ``dt``.

        """
        if type(dt) != Quantity:
            dt *= u.day

        mean_motions = np.sqrt(G*(self.mred)*MSUN/(self.semimajor*AU)**3)
        mean_motions = np.sqrt(const.G*(self.mred)/(self.semimajor)**3)

        newM = self.M + mean_motions * dt
        pos,vel = orbit_posvel(newM,self.ecc,self.semimajor.value,
                               self.mred.value,
                               self.obspos)

        if com:
            return (vel.z - self.RV) * (self.M2 / (self.M1 + self.M2))
        else:
            return vel.z-self.RV