2024MNRAS.527.1405H

We present the results of the investigation of the nova V1674 Her (2021), recognized as the swiftest classical nova, with t₂ ∼ 0.90 d. The distance to the nova is estimated to be 4.97 kpc. The mass and radius of the WD are calculated to be ∼1.36 M_⊙ and ∼0.15 R_⊕, respectively. Over the course of 1 month following the outburst, V1674 Her traversed distinct phases - pre-maxima, early decline, nebular, and coronal - displaying a remarkably swift transformation. The nebular lines emerged on day 10 making it the classical nova with the earliest observed commencement to date. We modelled the observed optical spectrum using the photoionization code CLOUDY. From the best-fitting model we deduced different physical and chemical parameters associated with the system. The temperature and luminosity of the central ionizing sources are found in the range of 1.99-2.34 × 10⁵ K and 1.26-3.16 × 10³⁸ erg s^–1, respectively. Elements such as He , O , N , and Ne are found to be overabundant compared to solar abundance in both the nebular and coronal phases. According to the model, Fe II abundance diminishes while Ne abundance increases, potentially elucidating the rare hybrid transition between Fe and He/N nova classes. The ejected mass across all epochs spanned from 3.42 to 7.04 × 10^–5 M_⊙. Morpho-kinematic modelling utilizing SHAPE revealed that the nova V1674 Her possesses a bipolar structure with an equatorial ring at the centre and an inclination angle of i = 67 ± 1.5°.