[论文解读] Optical spectroscopy of EX Lupi during quiescence and outburst: Infall, wind, and dynamics in the accretion flow

A. Sicilia‐Aguilar, Á. Kóspál+7 more|Discovery Research Portal (University of Dundee)|Jun 14, 2012

Astrophysics and Star Formation Studies参考文献 48被引用 32

一句话总结

本研究分析了EX Lupi在休眠期及其2008年爆发期间的高分辨率光学光谱，揭示宽发射线轮廓起源于一个高温、高密度、非轴对称的吸积柱，该吸积柱在24–72小时时间尺度内经历快速速度变化。数据证实，爆发期间吸积速率显著增加，伴随强烈的内盘风，且系统迅速恢复至爆发前状态，表明尽管吸积速率波动，吸积通道仍保持稳定。

ABSTRACT

We explore the accretion mechanisms in EX Lupi, prototype of EXor variables, during its quiescence and outburst phases. We analyse high-resolution optical spectra taken before, during, and after its 2008 outburst. In quiescence and outburst, the star presents many permitted emission lines, including typical CTTS lines and numerous neutral and ionized metallic lines. During the outburst, the number of emission lines increases to over a thousand, with narrow plus broad component structure (NC+BC). The BC profile is highly variable on short timescales (24-72h). An active chromosphere can explain the metallic lines in quiescence and the outburst NC. The dynamics of the BC line profiles suggest an origin in a hot, dense, non-axisymmetric, and non-uniform accretion column that suffers velocity variations along the line-of-sight on timescales of days. Assuming Keplerian rotation, the emitting region would be located at ~0.1-0.2 AU, consistent with the inner disk rim, but the velocity profiles of the lines reveal a combination of rotation and infall. Line ratios of ions and neutrals can be reproduced with a temperature of T~6500 K for electron densities of a few times 10$^{12}$cm$^{-3}$ in the line-emitting region. The data confirm that the 2008 outburst was an episode of increased accretion, albeit much stronger than previous EX Lupi and typical EXors outbursts. The line profiles are consistent with the infall/rotation of a non-axisymmetric structure that could be produced by clumpy accretion during the outburst phase. A strong inner disk wind appears in the epochs of higher accretion. The rapid recovery of the system after the outburst and the similarity between the pre-outburst and post-outburst states suggest that the accretion channels are similar during the whole period, and only the accretion rate varies, providing a superb environment for studying the accretion processes.

研究动机与目标

• 理解EX Lupi在休眠期、爆发期和爆发后阶段的吸积机制。
• 研究光学光谱中观测到的宽线和窄线成分的起源与动力学特性。
• 确定爆发是否由吸积速率增加驱动，以及内盘结构是否保持稳定。
• 检查高吸积状态期间是否存在与吸积相关的风及其特性。
• 比较爆发前与爆发后的状态，评估系统的恢复能力与结构稳定性。

提出的方法

• 获取并分析EX Lupi在爆发前、爆发期和爆发后阶段的10组高分辨率光学光谱。
• 利用多普勒位移分析，将发射线轮廓分解为窄线（NC）和宽线（BC）成分。
• 通过线比值建模（如Fe I/Fe II、Si I/Si II）推断发射区域的电子温度和密度（约6500 K和~10^12 cm⁻³）。
• 对宽线成分的速度变化进行时间监测，以推断24–72小时时间尺度内的动力学行为。
• 将H I巴尔末线与金属线进行比较，以区分来自色球层、吸积和风主导的发射区域。
• 使用开普勒旋转模型估算发射区域的径向位置（约0.1–0.2 AU）。

实验结果

研究问题

• RQ1 EX Lupi在2008年爆发期间，发射线强度和复杂性的显著增加是由什么引起的？
• RQ2 发射气体位于吸积流的何处？需要何种物理条件（T, n_e）才能重现观测到的线比值？
• RQ3 宽发射线的速度轮廓如何随时间演化？它们揭示了何种吸积动力学信息？
• RQ4 是否存在吸积驱动风的证据？其强度与吸积速率之间有何相关性？
• RQ5 内盘结构在爆发周期中保持稳定到何种程度？这能否从爆发前后光谱的相似性中得到证实？

主要发现

• 2008年爆发期间的宽发射线成分（BC）起源于位于约0.1–0.2 AU处的高温、高密度、非轴对称吸积柱，与内盘边缘位置一致。
• 在24–72小时时间尺度内，BC的速度变化表明存在独立运动的气体团块，支持成团吸积的场景。
• 中性与离子物种的线比值（如Fe I/Fe II等）的最佳拟合结果为温度约6500 K，电子密度为数倍10^12 cm⁻³。
• 在爆发期间检测到强烈的内盘风，速度范围为-50至-200 km/s，休眠期则未见此现象。
• 爆发前后光谱的相似性表明系统恢复迅速，暗示尽管吸积速率增加了三个数量级，吸积通道仍保持稳定。
• 禁线的缺失排除了外部物质碰撞激波的可能性，证实风和发射均源自吸积过程本身。