HD 142527圆盘中的涡旋状运动学信号、螺旋和光束拖尾效应
Vortex-like kinematic signal, spirals, and beam smearing effect in the HD 142527 disk
摘要：
涡旋是最有希望的机制之一，局部集中毫米尘埃颗粒，并允许通过引力坍缩形成星子。双星系统HD 142527周围的外盘以其巨大的马蹄形结构而闻名，气体表面密度的方位角对比度为3-5，尘埃的方位角对比度约为50。使用13 CO和C18 O J = 3-2过渡线，我们检测到的开普勒旋转，这是一致的存在下，一个大的漩涡周围的尘埃新月，以及一些螺旋在磁盘的外部区域的运动偏差。与涡流模型的比较表明，与背景开普勒旋转相比，在解投影后速度偏差高达350 m/s，以及在涡流两侧径向延伸约40 au，方位角延伸200度，产生方位角与径向纵横比为5。另一种用于解释涡旋状信号的替代方案意味着与由于环双星盘的内边缘和外边缘处的气体压力梯度引起的气体速度的变化相关联的由光束拖尾产生的人工速度偏差。这两种情况目前难以区分，为此，可能需要使用更高空间分辨率的多条线。由于观测的有限空间分辨率和线发射的梯度，光束拖尾效应在原行星盘的观测中应该是常见的，并可能导致对气体速度的误解，特别是在环状结构周围。
英文摘要：
Vortices are one of the most promising mechanisms to locally concentrate millimeter dust grains and allow the formation of planetesimals through gravitational collapse. The outer disk around the binary system HD 142527 is known for its large horseshoe structure with azimuthal contrasts of 3-5 in the gas surface density and of about 50 in the dust. Using 13CO and C18O J = 3-2 transition lines, we detect kinematic deviations to the Keplerian rotation, which are consistent with the presence of a large vortex around the dust crescent, as well as a few spirals in the outer regions of the disk. Comparisons with a vortex model suggest velocity deviations up to 350 m/s after deprojection compared to the background Keplerian rotation, as well as an extension of about 40 au radially on both sides of the vortex and 200 degrees azimuthally, yielding an azimuthal-to-radial aspect ratio of 5. Another alternative for explaining the vortex-like signal implies artificial velocity deviations generated by beam smearing in association with variations of the gas velocity due to gas pressure gradients at the inner and outer edges of the circumbinary disk. The two scenarios are currently difficult to differentiate and, for this purpose, would probably require the use of multiple lines at a higher spatial resolution. The beam smearing effect, due to the finite spatial resolution of the observations and gradients in the line emission, should be common in observations of protoplanetary disks and may lead to misinterpretations of the gas velocity, in particular around ring-like structures.
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