标题： 年轻“摇摆”星在上 Scorpius 和 Oph$ρ$中被 K2 观测到 显示英文标题

标题： Young "Dipper" Stars in Upper Sco and $ρ$ Oph Observed by K2

摘要： We present ten young ($\lesssim$10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show $\sim$10-20 dips in flux over the 80-day observing campaign with durations of $\sim$0.5-2 days and depths of up to $\sim$40%. These stars are all members of the $\rho$ Ophiuchus ($\sim$1 Myr) or Upper Scorpius ($\sim$10 Myr) star-forming regions. To investigate the nature of these "dippers" we obtained: optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. 光谱显示了与恒星年轻 (<50 Myr) 一致的锂 I 吸收和 H$\alpha$发射，但也显示出经典 T Tauri 星和弱线 T Tauri 星的吸积率范围。红外过量现象在大多数情况下与延伸至距离恒星中心约$\sim$10 个恒星半径内的原行星盘一致；然而，亚毫米观测表明盘质量比典型原行星盘低一个数量级。 我们发现掩食深度与 WISE-2 过量之间存在正相关关系，我们认为这是掩食现象与内盘遮挡结构有关的证据，尽管这很难与弱吸积的非周期性掩食现象相协调。 我们考虑了三种机制来解释掩食现象：与吸积相关的共旋转半径附近的内盘弯曲；由罗斯贝波不稳定性在内盘边缘产生的漩涡；以及与星子形成相关的星际物质团块。 显示英文摘要

摘要： We present ten young ($\lesssim$10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show $\sim$10-20 dips in flux over the 80-day observing campaign with durations of $\sim$0.5-2 days and depths of up to $\sim$40%. These stars are all members of the $\rho$ Ophiuchus ($\sim$1 Myr) or Upper Scorpius ($\sim$10 Myr) star-forming regions. To investigate the nature of these "dippers" we obtained: optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. The spectra reveal Li I absorption and H$\alpha$ emission consistent with stellar youth (<50 Myr), but also accretion rates spanning those of classical and weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary disks extending to within $\sim$10 stellar radii in most cases; however, the sub-mm observations imply disk masses that are an order of magnitude below those of typical protoplanetary disks. We find a positive correlation between dip depth and WISE-2 excess, which we interpret as evidence that the dipper phenomenon is related to occulting structures in the inner disk, although this is difficult to reconcile with the weakly accreting aperiodic dippers. We consider three mechanisms to explain the dipper phenomenon: inner disk warps near the co-rotation radius related to accretion; vortices at the inner disk edge produced by the Rossby Wave Instability; and clumps of circumstellar material related to planetesimal formation.