Radial Velocity time series for star 1 at given times ts.

        :param ts:
            Times.  If not ``Quantity``, assumed to be in days.
        :type ts:
            array-like or ``Quantity``

        :param recalc: (optional)
            If ``False``, then if called with the exact same ``ts``
            as last call, it will return cached calculation.

def RV_timeseries(self,ts,recalc=False):
        """
        Radial Velocity time series for star 1 at given times ts.

        :param ts:
            Times.  If not ``Quantity``, assumed to be in days.
        :type ts:
            array-like or ``Quantity``

        :param recalc: (optional)
            If ``False``, then if called with the exact same ``ts``
            as last call, it will return cached calculation.

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

        if not recalc and hasattr(self,'RV_measurements'):
            if (ts == self.ts).all():
                return self._RV_measurements
            else:
                pass

        RVs = Quantity(np.zeros((len(ts),self.N)),unit='km/s')
        for i,t in enumerate(ts):
            RVs[i,:] = self.dRV(t,com=True)
        self._RV_measurements = RVs
        self.ts = ts
        return RVs