A Theory for the Maximum Magnitude versus Rate of Decline Relation of Classical Novae

We propose a theory for the maximum magnitude versus rate of decline (MMRD) relation of novae using free-free emission model light curves built on the optically thick wind theory. We calculated for various sets of , where is the peak absolute V magnitude, t3 is the 3 mag decay time from the peak, and is the mass accretion rate onto the white dwarf (WD) of mass MWD. The model light curves are uniquely characterized by , where Menv is the hydrogen-rich envelope mass and Msc is the scaling mass at which the wind has a certain wind mass-loss rate. For a given ignition mass Mig, we can specify the first point on the model light curve and calculate the corresponding peak brightness and t3 time from this first point. Our points cover well the distribution of existing novae. The lower the mass accretion rate, the brighter the peak. The maximum brightness is limited to by the lowest mass accretion rate of yr−1. A significant part of the observational MMRD trend corresponds to the yr−1 line with different WD masses. A scatter from the trend line indicates a variation in their mass accretion rates. Thus, the global trend of an MMRD relation does exist, but its scatter is too large for it to be a precision distance indicator of individual novae.