Spectropolarimetry and Modeling of the Eclipsing T Tauri Star KH 15D
Spectropolarimetry and Modeling of the Eclipsing T Tauri Star KH 15D
复制标题
食金牛座 T 星 KH 15D 的分光偏振测量和建模
DOI：
10.1086/379893
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
D. Charbonneau
中科院分区：
文献类型：
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作者：
E. Agol;A. Barth;S. Wolf;D. Charbonneau
KH 15 D是年轻的星星星团NGC 2264中的一颗强变金牛座星星，它的光通量减少了3.5等，持续了18天，每48天重复一次。食物质很可能是由于部分环或弯曲盘中的轨道尘埃或岩石体周期性地遮蔽星星。我们在凯克和帕洛玛天文台测量了日食前后的偏振光谱。在日食之外，这颗星星表现出与零一致的低偏振。在日食期间，整个光谱中的偏振急剧增加到约2%，而光谱具有与日食外部相同的连续形状，并显示出更大的等效宽度的发射线，如前所述。从这些数据中，我们得出结论：（1）散射区是无食的，（2）散射几乎是消色差的，（3）星星很可能完全被食，因此食时的通量完全是由于散射光，这一结论也被入口和出口的形状所证明。我们认为，散射不是由于电子，但可能是由于大尘埃颗粒的大小约10 μm，类似于行星际颗粒散射黄道光。我们构造了一个具有扩展尘埃大气的翘曲圆盘模型，它再现了光变曲线的主要特征，即（1）在进入大气之前由于大气中的消光而逐渐减小（类似于出口），（2）由于大气层的光学厚基，入口内的急剧下降，以及（3）日食期间的偏振通量为日食外部总通量的0.1%，这不需要对模型进行微调。假设经线位于开普勒半径，经线的倾角由进入和离开的持续时间设定，观察者的倾角则由日食的持续时间确定。
KH 15D is a strongly variable T Tauri star in the young star cluster NGC 2264 that shows a decrease in flux of 3.5 mag lasting for 18 days and repeating every 48 days. The eclipsing material is likely due to orbiting dust or rocky bodies in a partial ring or warped disk that periodically occults the star. We measured the polarized spectrum in and out of eclipse at the Keck and Palomar observatories. Outside of the eclipse, the star exhibited low polarization consistent with zero. During eclipse, the polarization increased dramatically to ~2% across the optical spectrum, while the spectrum had the same continuum shape as outside of eclipse and exhibited emission lines of much larger equivalent width, as previously seen. From the data, we conclude that (1) the scattering region is uneclipsed, (2) the scattering is nearly achromatic, and (3) the star is likely completely eclipsed so that the flux during eclipse is entirely due to scattered light, a conclusion also argued for by the shape of the ingress and egress. We argue that the scattering is not due to electrons but may be due to large dust grains of size ~10 μm, similar to the interplanetary grains that scatter the zodiacal light. We construct a warped-disk model with an extended dusty atmosphere that reproduces the main features of the light curve, namely, (1) a gradual decrease before ingress due to extinction in the atmosphere (similar for egress), (2) a sharper decrease within ingress due to the optically thick base of the atmosphere, and (3) a polarized flux during eclipse that is 0.1% of the total flux outside of eclipse, which requires no fine-tuning of the model. The inclination of the warp is set by the duration of ingress and egress assuming that the warp is located at the Keplerian radius, and the inclination of the observer is then determined by the duration of the eclipse.