发表机构
Institute of Space Sciences (ICE, CSIC); Institut d’Estudis Espacials de Catalunya (IEEC); Instituto de Astrofísica de Andalucía–CSIC; Instituto de Radioastronomía y Astrofísica (IRyA), Universidad Nacional Autónoma de México (UNAM)（空间科学研究所; 加泰罗尼亚太空研究学院; 安达卢西亚天体物理研究所; 墨西哥国立自治大学无线电天文学与天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出定量系数κ衡量新星光谱中Fe II与He/N发射线相对强度，应用于26颗新星，发现多数新星光谱类别随时间演化，支持光谱类别为演化阶段而非固定类型。
AI 中文摘要
新星根据其前星云光谱中Fe II或He和N发射线的优势被光谱分类为Fe II型或He/N型，而同时表现出两者的光谱被分类为混合型。有证据表明这些光谱类别代表了光谱演化。我们利用一个大型光谱数据集研究这一情景，并引入一个定量系数$\kappa$来表征Fe II和He/N发射的相对强度。该系数定义为Fe II（$\lambda5169$）线的通量与五条He和N发射线平均通量的比值，其中$\kappa>1$表示Fe II主导的光谱，$\kappa<1$表示He/N主导的光谱。我们使用来自天文业余光谱环（ARAS）数据库的光谱将此方法应用于26颗新星，并将$\kappa$的演化与光学光变曲线进行比较。在24颗经典新星中的15颗和两颗再发新星中的一颗表现出至少一次Fe II主导和He/N主导阶段之间的转变，而时间趋势表明，在完整光谱覆盖下，这一比例可能接近90%。$\kappa$系数紧密跟踪光学光变曲线，并在表现出抖动的新星中反复跨越1，揭示了与亮度波动相关的非单调光谱演化。这些结果支持将Fe II、He/N和混合光谱解释为演化阶段而非不同类型的新星，并将$\kappa$确立为追踪新星光谱演化的定量工具，同时减少不完整光谱覆盖带来的偏差。
英文摘要
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. Evidence suggests that these spectral classes represent spectral evolution. We investigate this scenario using a large spectroscopic dataset and introduce a quantitative coefficient, $κ$, to characterise the relative strength of Fe II and He/N emission. The coefficient is defined as the ratio of the flux of the Fe II ($\lambda5169$) 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. We apply this method to 26 novae using spectra from the Astronomical Ring for Amateur Spectroscopy (ARAS) Database and compare the evolution of $κ$ with optical light curves. Fifteen of the 24 classical novae and one of the two recurrent novae exhibit at least one transition between Fe II- and He/N-dominated phases, while temporal trends suggest this fraction could approach 90% with complete spectroscopic coverage. The $κ$ coefficient closely tracks the optical light curves and repeatedly crosses unity in novae exhibiting jitters, revealing non-monotonic spectral evolution linked to brightness fluctuations. These results support the interpretation of Fe II, He/N, and hybrid spectra as evolutionary stages rather than distinct nova types and establish $κ$ as a quantitative tool for tracing nova spectral evolution while reducing biases from incomplete spectroscopic coverage.
