chemical composition. They called this method the time-stretching method. By directly fitting the theoretical light curves of $M_V$ with the observed $m_V$, we can also estimate the WD mass $M_{\rm WD}$ and distance modulus in the $V$ band of $\mu_V\equiv (m-M)_V$ for a target nova. @hac18kb confirmed that the time-stretching method is applicable to fast and very fast novae in our Galaxy, LMC, and M31.

There are also common properties in the color evolution in nova outbursts. @hac14k [hereafter Paper I] found that many novae in outburst evolve on a common path in the $(B-V)_0$-$(U-B)_0$ color-color diagram. Here, $(B-V)_0$ and $(U-B)_0$ are the intrinsic colors of $B-V$ and $U-B$, respectively. The evolution path starts from the nova-giant sequence and then moves to the free-free emission phase followed by the emission line dominant nebular phase. (See, e.g., their Figure 28.)

@hac16kb [Paper II] found that many novae follow similar evolution path in the $(B-V)_0$-$M_V$ color-magnitude diagram. Here, $M_V$ is the absolute $V$ magnitude in the $V$ band. They extensively examined the color-magnitude tracks of 40 novae in outburst and found several distinct “template tracks” in the $(B-V)_0$-$M_V$ diagram. They proposed six template tracks of novae and dubbed them the V1500 Cyg, 