无钠I D线踪迹的尘埃：高衰减Ib型超新星2024vjc的案例
Dust Without Na I D Trace: The Case of Highly Attenuated Type Ib SN 2024vjc
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中文总结 AI 辅助
研究高衰减Ib型超新星SN 2024vjc，通过光学和近红外观测，发现常用的钠I D吸收等效宽度诊断失效。基于超新星的多种诊断方法及巴尔末递减表明有显著消光，揭示弱钠I D吸收或因光电离，强调多方法诊断的重要性。
中文摘要 AI 辅助
理解河外瞬变源的尘埃消光对于恢复其固有特性和探测遥远星系的局部环境至关重要。一种常用诊断方法是广泛应用于河外瞬变源的钠I D吸收等效宽度。本文展示了Ib型超新星SN 2024vjc爆炸后约130天的早期光学和近红外观测。SN 2024vjc仅显示微弱的钠I D吸收，表明宿主星系消光适中，$E (B-V)_{\rm host} \sim 0.18$ 星等。但基于超新星的诊断方法（固有颜色模板、颜色曲线演化和光谱消红化）以及巴尔末递减表明存在显著消光，$E(B-V) \sim 0.45$ - $0.8$ 星等。弱钠I D吸收可能是由于爆炸地点年轻H₂区域的强辐射场使中性钠发生光电离所致，后期光谱中窄Hα、[N₂]和Hβ发射线以及蓝色连续谱过剩直接支持了这一情景。SN 2024vjc是一个明显的反例，表明通常认为弱或无钠I D吸收意味着宿主星系消光可忽略不计的假设不成立，凸显了采用多种独立消光诊断方法的重要性。
英文摘要
Understanding dust attenuation toward extragalactic transients is critical for recovering their intrinsic properties and probing the local environments of distant galaxies. A popular diagnostic is the Na I D absorption equivalent width widely applied to extragalactic transients. In this paper, we present early-time optical and near-infrared observations of the Type Ib supernova (SN) SN 2024vjc, followed for $\sim$130 days post-explosion. SN~2024vjc exhibits only weak Na~I~D absorption, indicating only a modest host attenuation with $E (B-V)_{\rm host} \sim 0.18$ mag; if this argument were applied, SN~2024vjc would be a peculiar, faint, and red SN Ib while showing the light-curve shape and spectral evolution broadly consistent with those of canonical SNe Ib. We show that this is not the case; SN-based diagnostics (intrinsic color templates, color-curve evolution, and spectral dereddening) together with the Balmer decrement indicate substantial attenuation, $E(B-V) \sim 0.45$ $-$ $0.8$\,mag. The weak Na I D absorption may result from photoionization of neutral sodium by the intense radiation field of a young H$_{2}$ region at the explosion site; this scenario is directly supported by the detection of narrow H$_α$, [N$_{2}$], and H$_β$ emission lines and a blue continuum excess in late-time spectroscopy. SN~2024vjc represents a clear counterexample to the commonly assumption that weak or absent Na I D absorption implies negligible host-galaxy attenuation, and highlights the importance of employing multiple, independent attenuation diagnostics.
