Theoretical light curve models of the symbiotic nova CN Cha -- Optical flat peak for three years

TL;DR

This paper presents theoretical light curve models for the symbiotic nova CN Cha, explaining its long flat peak and transition between static and wind solutions, highlighting the role of the companion star in its evolution.

Contribution

The study introduces hydrostatic approximation models for CN Cha, estimating its white dwarf mass and explaining the flat peak phenomenon through static and wind envelope solutions.

Findings

CN Cha's white dwarf mass is estimated at ~0.6 M_sun.

The flat peak results from a transition between static and wind envelope solutions.

The companion star's position influences the nova's evolution and peak characteristics.

Abstract

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.