Optical Spectroscopy and Temporal Evolution of the Nova V1405 Cas

This paper presents the findings from our study of nova V1405~Cas over the first 1051 days after the outburst. The study includes an analysis of the photometric light curve evolution, along with a detailed spectroscopic evolution. Photometric analysis shows that the nova is a very slow nova, with a decline timescale of $t_2 \approx 165$ days. The mass of the white dwarf is calculated as $M_{\rm WD} \sim 0.7\~M_{\odot}$. The secondary star is a low-mass main-sequence star, with a mass of $M_{\rm sec} \approx 0.43\~M_{\odot}$. Spectral observations show initial dominance by Balmer emission lines accompanied by prominent P Cygni profiles during the first +339 days. These features disappeared in later epochs, being replaced by high-ionization coronal lines, indicating that the nova had transitioned to the coronal phases by day +371. To investigate the physical conditions of the ejecta and the central source, we conducted photoionization modeling using \textsc{cloudy}. Our model reveals a gradual increase in the temperature and luminosity of the system, and suggests that the ejecta were primarily composed of He, N, Fe, Ne, and Ca, with noticeable temporal variations in their relative abundances. The estimated mean ejected mass is approximately $1.10~\times~10^{-4}\~M_{\odot}$, which is relatively high and suggests a low-mass white dwarf. Our optical spectroscopic and photometric analyses, combined with detailed photoionization modeling, indicate that the white dwarf in Nova V1405 Cas is unlikely to be of the ONeMg type.