CSI 2264：用随机变化的光变曲线表征NGC 2264中的年轻恒星
CSI 2264: Characterizing Young Stars in NGC 2264 with Stochastically Varying Light Curves
摘要：
我们提供了NGC 2264中17个经典金牛座T的CoRoT和Spitzer光变曲线，以及宽带多波长光度学和高分辨率，多历元和单历元光谱学，其CoRoT光变曲线（LC）符合Cody等人（2014）定义的“随机”LC类。最有可能的物理机制来解释在这个LC类的光学变化是随时间变化的质量吸积到恒星光球，产生瞬态热点。作为支持这一假设的证据，这些恒星的一个子集的多历元高分辨率光谱显示，它们的面纱水平也随时间而变化，这种面纱的变化在振幅和时间尺度上与光学LC形态是一致的。此外，面纱的可变性与HeI 6678 A发射线的强度密切相关，这是模型预测的恒星光球层上或附近的吸积冲击中出现的一个特征。具有吸积爆发LC形态的恒星（Stauffer et al. 2014）也归因于变质量吸积。随机和吸积爆发LC可以解释由一个简单的模型随机发生的通量爆发，与随机LC类具有较高的频率较低的振幅事件。根据他们的紫外线过剩，面纱，和平均哈等效宽度，随机LC类的成员只有中等的时间平均质量吸积率。它们的Ha剖面最常见的特征是它们表现出蓝移吸收特征，最有可能起源于盘风。LC中缺乏周期性特征表明，几乎没有变化是由于长寿命的热点旋转进入或离开我们的视线;相反，观测到的光度变化的主要驱动因素可能是内部盘的不稳定性，导致可变质量吸积。
英文摘要：
We provide CoRoT and Spitzer light curves, as well as broad-band multi-wavelength photometry and high resolution, multi- and single-epoch spectroscopy for 17 classical T Tauris in NGC 2264 whose CoRoT light curves (LCs) exemplify the "stochastic" LC class as defined in Cody et al. (2014). The most probable physical mechanism to explain the optical variability in this LC class is time-dependent mass accretion onto the stellar photosphere, producing transient hot spots. As evidence in favor of this hypothesis, multi-epoch high resolution spectra for a subset of these stars shows that their veiling levels also vary in time and that this veiling variability is consistent in both amplitude and timescale with the optical LC morphology. Furthermore, the veiling variability is well-correlated with the strength of the HeI 6678A emission line, a feature predicted by models to arise in accretion shocks on or near the stellar photosphere. Stars with accretion burst LC morphology (Stauffer et al. 2014) are also attributed to variable mass accretion. Both the stochastic and accretion burst LCs can be explained by a simple model of randomly occurring flux bursts, with the stochastic LC class having a higher frequency of lower amplitude events. Based on their UV excesses, veiling, and mean Ha equivalent widths, members of the stochastic LC class have only moderate time-averaged mass accretion rates. The most common feature of their Ha profiles is for them to exhibit blue-shifted absorption features, most likely originating in a disk wind. The lack of periodic signatures in the LCs suggests that little of the variability is due to long-lived hot spots rotating into or out of our line of sight; instead, the primary driver of the observed photometric variability is likely to be instabilities in the inner disk that lead to variable mass accretion.
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