EPIC 204376071中的深长非对称掩星
Deep Long Asymmetric Occultation in EPIC 204376071
摘要：
我们发现了一颗质量为$0.16\,M_\odot$、半径为$0.63\,R_\odot$的年轻M星，可能位于上天球星协，它只出现了一次持续1天的$80\%$深掩。这颗恒星有频繁的耀斑和低振幅的旋转调制，但在K2活动C2和C15期间的160天累积观测中是安静的。我们讨论如何这样一个深的日食是不可能的一个恒星穿越另一个在任何二进制或更高阶的恒星系统，其中没有发生质量转移。我们剩下的两种可能的解释是（1）轨道尘埃或小颗粒（例如，一个圆盘被束缚在一个较小的轨道物体上，或者从这样的物体散发出来的未束缚的尘埃）;或者（2）在恒星的共转半径附近的尘埃物质的瞬时吸积事件。在任何一种情况下，这种掩星事件之间的时间必须长于$\sim$ 80天。我们将一个可能的轨道掩星建模为均匀的椭圆形表面（例如，倾斜的圆盘）和在其前缘后面具有光学深度梯度的“防尘片”。在这两种情况下，这种粉尘特征所需的质量分别为$\gtrsim 3 \times 10^{19}$ g和$\gtrsim 10^{19}$ g。
英文摘要：
We have discovered a young M star of mass $0.16\,M_\odot$ and radius $0.63\,R_\odot$, likely in the Upper Sco Association, that exhibits only a single $80\%$ deep occultation of 1-day duration. The star has frequent flares and a low-amplitude rotational modulation, but is otherwise quiet over 160 days of cumulative observation during K2 Campaigns C2 and C15. We discuss how such a deep eclipse is not possible by one star crossing another in any binary or higher-order stellar system in which no mass transfer has occurred. The two possible explanations we are left with are (1) orbiting dust or small particles (e.g., a disk bound to a smaller orbiting body, or unbound dust that emanates from such a body); or (2) a transient accretion event of dusty material near the corotation radius of the star. In either case, the time between such occultation events must be longer than $\sim$80 days. We model a possible orbiting occulter both as a uniform elliptically shaped surface (e.g., an inclined circular disk) and as a `dust sheet' with a gradient of optical depth behind its leading edge. The required masses in such dust features are then $\gtrsim 3 \times 10^{19}$ g and $\gtrsim 10^{19}$ g, for the two cases, respectively.
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