作为激波驱动瞬变源的亮红新星 I：电子散射翼与对 B 情况的偏离
Luminous Red Novae as shock-powered transients I: Electron-scattering wings and deviations from Case B
AI总结：
研究亮红新星光谱行为，通过六个样本识别出激波过程光谱证据，如快速抛射物扫过上游物质等，发现激波光度可解释其总能量，平台期后光谱学有用，还从复合线比值得到上游介质密度限制。
AI中文摘要：
亮红新星（LRNe）是由双星合并或共包层事件产生的一类光学瞬变源。其光变曲线多样，光度平台期延长和/或有次峰，可能由氢复合或合并前后抛射物间的激波驱动。但很多光谱行为仍未得到解释。我们用六个 LRNe 样本，识别出整个 LRNe 光度范围（\(10^{38}\)-\(10^{41}\,\mathrm{erg/s}\)）内激波过程的光谱证据：快速抛射物扫过较慢的上游物质；有两个不同成分的复合阶段；极宽的谱线翼展至\(1000\)-\(10000\,\mathrm{km/s}\)。这种谱线轮廓揭示了光子在流出物（\(T_e\sim5000\)-\(10000 \,\mathrm{K}\)，\(v_{es}\!\sim\!300\)-\(500\, \mathrm{km/s}\)）中与热电子散射，在激波表面上下游都有复合现象。此外，从复合线比值得到上游介质密度的限制，更亮的 LRNe 显示出与 B 情况的偏离，与更密集的周围环境一致。考虑流出物速度和周围密度限制，激波光度足以解释 LRNe 的总能量，无需其他能量注入机制。在平台期，散射翼被隐藏，线比值受辐射传输效应影响，这突出了平台期后光谱学的效用。
英文摘要：
Luminous red novae (LRNe) are a class of optical transients resulting from the mergers of binary stars or common envelope events. The population displays heterogeneous light curves with extended luminosity plateaus and/or secondary peaks, suggested to be powered by hydrogen recombination or shocks between pre- and post-merger ejecta. However, much of their spectroscopic behaviour remains unexplained. Using a sample of six LRNe, we identify telltale spectral evidence for shock processes across the LRNe luminosity range ($10^{38}$-$10^{41}\,\mathrm{erg/s}$): (i) fast ejecta sweeping up slower upstream material; (ii) composite epochs with two distinct components, namely a cool stellar-like continuum underneath a hot nebular recombination region; and (iii) extremely broad line wings extending to $1000$-$10\,000\,\mathrm{km/s}$. Such line profiles reveal photons scattering off hot electrons in an outflow ($T_e\sim5000$-$10\,000 \,\mathrm{K},\,v_{es}\!\sim\!300$-$500\, \mathrm{km/s}$), with recombination seen from both the upstream and downstream of the shock surface. Additionally, constraints on the density of the upstream medium are obtained from recombination-line ratios, where brighter LRNe show deviations from Case B, consistent with denser surrounding environments. Given the outflow's velocity and surrounding density constraints, the shock luminosity is sufficient to account for the total energetics of LRNe without requiring other energy-injection mechanisms. During the plateau phase, the scattering wings are hidden and line ratios are affected by radiative transport effects, which highlights the utility of post-plateau phase spectroscopy.
