The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is associated with a pair of reflection nebulae, Re50 and Re50N, which appeared sometime between 1955 and 1979. We have found that a dramatic brightening of Re50N has taken place sometime between 2006 and 2014. This could result if the embedded source is undergoing a FUor eruption. However, the near-infrared spectrum shows a featureless very red continuum, in contrast to the strong CO bandhead absorption displayed by FUors. Such heavy veiling, and the high luminosity of the protostar, is indicative of strong accretion but seemingly not in the manner of typical FUors. We favor the alternative explanation that the major brightening of Re50N and the simultaneous fading of Re50 is caused by curtains of obscuring material that cast patterns of illumination and shadows across the surface of the molecular cloud. This is likely occurring as an outflow cavity surrounding the embedded protostar breaks through to the surface of the molecular cloud. Several Herbig-Haro objects are found in the region.
Now you see me, now you don't: Deep, long-lived obscuration events of white dwarfs by dust and debris from disintegrating planetesimals
Institute of Science and Technology Austria（奥地利科学技术研究所）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安顿·潘内科克天文学研究所）；Cahill Center for Astrophysics, California Institute of Technology（加州理工学院凯斯天体物理中心）；Department of Astronomy & Institute for Astrophysical Research, Boston University（波士顿大学天文系与天体物理研究所）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Instituto de Astrofisica de Canarias（加那利天体物理学研究所）；Department of Physics, University of Warwick（华威大学物理系）；Columbia University（哥伦比亚大学）
Variability of Disk Emission in Pre-Main Sequence and related Stars. V. Occultation Events from the innermost disk region of the Herbig Ae Star HD 163296
HD 163296是一颗赫比格Ae型恒星，在2001年经历了V光度带亮度的戏剧性下降$\sim$ 0.8等，并在2002年经历了近红外亮度的增亮。由于这颗恒星拥有赫比格-哈罗天体，它们以流出的双极喷流的形式运动，因此有人认为亮度的下降是由于盘风中夹带的一团尘埃，阻挡了朝向恒星的视线。为了量化这一假设，我们研究了亮度下降，在可见光波长和亮度在近红外波长的HD 163296使用蒙特卡罗辐射转移代码，HOCHUNK 3D。我们创建了三个模型来理解这些事件。模型1描述了系统的静态。模型2描述了导致2001年亮度下降的结构变化。模型3描述了产生2002年观测到的近红外波长增亮所需的结构。模型2和模型3利用圆盘风和中心双极流的组合。通过在模型2和模型3中引入填充的双极腔，我们能够成功地模拟具有盘风的恒星的喷流状结构，并创造了系统亮度的下降和随后的增加。另一方面，当双极腔未填充时，模型1复制系统的静态。
