def dRV(self,dt,com=False):
if type(dt) != Quantity:<EOL><INDENT>dt *= u.day<EOL><DEDENT>mean_motions = np.sqrt(G*(self.mred)*MSUN/(self.semimajor*AU)**<NUM_LIT:3>)<EOL>mean_motions = np.sqrt(const.G*(self.mred)/(self.semimajor)**<NUM_LIT:3>)<EOL>newM = self.M + mean_motions * dt<EOL>pos,vel = orbit_posvel(newM,self.ecc,self.semimajor.value,<EOL>self.mred.value,<EOL>self.obspos)<EOL>if com:<EOL><INDENT>return (vel.z - self.RV) * (self.M2 / (self.M1 + self.M2))<EOL><DEDENT>else:<EOL><INDENT>return vel.z-self.RV<EOL><DEDENT>
Change in RV of star 1 for time separation dt (default=days)

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

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

        Returns
        -------
        dRV : ``Quantity``
            Change in radial velocity over time dt.