  CN Cha is a slow symbiotic nova characterized by a three-years-long optical
flat peak followed by a rapid decline. We present theoretical light curves for
CN Cha, based on hydrostatic approximation, and estimate the white dwarf (WD)
mass to be $\sim 0.6 ~M_\odot$ for a low metal abundance of Z = 0.004. This
kind of flat peak novae are border objects between classical novae having a
sharp optical peak and extremely slow novae, the evolutions of which are too
slow to be recognized as a nova outburst in human timescale. Theoretically,
there are two types of nova envelope solutions, static and optically-thick
wind, in low mass WDs ($\lesssim 0.7 ~M_\odot$). Such a nova outburst begins
first in a hydrostatic manner, and later it could change to an optically-thick
wind evolution due to perturbation by the companion star in the nova envelope.
Multiple peaks are a reflection of the relaxation process of transition. CN Cha
supports our explanation on the difference between long-lasted flat peak novae
like CN Cha and multiple peak novae like V723 Cas, because the companion star
is located far outside, and does not perturb, the nova envelope in CN Cha.
