Year: 2026
Type: preprint
Abstract: Novae are spectroscopically classified as Fe II or He/N according to the dominance of Fe II, or He and N emission lines in their pre-nebular spectra, while spectra exhibiting both are classified as hybrid. Whereas the spectral class of a nova is known to correlate with its progenitor properties, a recent detailed spectroscopic follow-up of ten novae suggests instead a time evolution from "early He/N" to "Fe II" and to "late He/N". We investigate here this apparent contradiction using a spectroscopic dataset of 26 novae from the Astronomical Ring for Amateur Spectroscopy (ARAS) Database. For this purpose we introduce a quantitative coefficient, $κ$, defined as the ratio of the flux of the Fe II $λ$5169 line to the mean flux of five He and N emission lines, with $κ> 1$ indicating Fe II-dominated spectra and $κ< 1$ indicating He/N-dominated spectra. This coefficient is shown to provide a reliable quantitative tool for tracing nova spectral evolution while reducing biases from incomplete coverage. A significant fraction of the novae in our sample exhibit at least one transition between Fe II- and He/N-dominated phases. The time evolution of $κ$ closely follows their optical light-curves, repeatedly crossing unity in novae exhibiting jitters, which reveal non-monotonic spectral evolution. Since the light-curve shapes and their time-scales depend on intrinsic progenitor properties, particularly white dwarf mass, they also determine the duration of Fe II- and He/N-dominated phases, introducing a bias in spectral classification when it relies on early, sparse spectra.
Source: arXiv (Cornell University)
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G1105844351, G1175115578, G2262748287, G288263039, G2998051782, G300979063, G3383458737, G3480869486, G3715634343, G373897614, G4019291869, G425668148, G4526231891, G463062595, G4793013703, G5080475149, G5404395142, G5635532810, G5852091828, G5894067328, G617610489, G643559596, G7001747737, G7084143925, G717256432, G7805626310, G7863371703, G8497050386, G9000357636
OpenAlex ID: W7214056612