The young planetary system β Pictoris is surrounded by a circumstellar disk of dust and gas. Because both dust and gas have a lifetime shorter than the system age, they need to be replenished continuously. The gas composition is partly known, but its location and its origin are still a puzzle. The gas source could be the exocomets (or so-called falling and evaporating bodies, FEBs), which are observed as transient features in absorption lines of refractory elements (Mg, Ca, and Fe) when they transit in front of the star at several tens of stellar radii.
Nearly 1700 high-resolution spectra of β Pictoris have been obtained from 2003 to 2015 using the HARPS spectrograph. In these spectra, the circumstellar disk is always detected as a stable component among the numerous variable absorption signatures of transiting exocomets.
Summing all the 1700 spectra allowed us to reach a signal-to-noise ratio higher than 1000, which is an unprecedentedly high number for a β Pictoris spectrum. It revealed many weak Fe I absorption lines of the circumstellar gas in more than ten excited states. These weak lines bring new information on the physical properties of the neutral iron gas in the circumstellar disk. The population of the first excited levels follows a Boltzmann distribution with a slope consistent with a gas temperature of about 1300 K; this temperature corresponds to a distance to the star of ~ 38 RStar and implies a turbulence of ξ ~ 0.8 km/s.
VLTI/MATISSE observations of the hot dust around $β$ Pictoris: Observing faint objects with MATISSE
Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学）；Univ. Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台）；Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, HUN-REN（孔科利天文台，地球与天文学研究中心）；CSFK, MTA Centre of Excellence（匈牙利科学院天文学研究所，MTA卓越中心）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）
我们已经进行了搜索的光学拱星吸收线的光谱中的16个碎片盘的主机星。在我们的样本中，没有一颗恒星在H $_α$、Ca II或Na I中显示出发射谱线活动的迹象，这证实了它们更进化的性质。发现四颗恒星在光球Ca II和Na I D线的核心附近表现出窄吸收特征（当Na I D数据可用时）。我们分析这些光谱特征的特点，以确定它们是否是拱星或星际起源。最强有力的证据是在HD 110058的光谱中看到的拱星气体，这是已知的主机碎片盘观察到接近边缘。这是一致的，最近ALMA检测分子气体在这个碎片盘，这表明许多相似之处，$β$风景如画的系统。
An icy Kuiper-Belt around the young solar-type star HD 181327
HD 181327是一颗年轻的F5/F6 V恒星，属于美如画β移动星群（1200万年前）。它在90天文单位处有一条光学薄的星周物质带。我们的目标是详细研究粉尘的性质，并约束气尘比。我们获得了远红外观测与赫歇尔/PACS仪器，和3.2毫米的ATCA阵列的意见。带的几何形状的约束与新减少的HST/NICMOS图像，打破了磁盘的几何形状和尘埃属性之间的简并。我们使用辐射转移代码GRaTer来计算模型的大网格，并且我们通过贝叶斯分析来确定最佳再现光谱能量分布的晶粒模型。我们试图用PACS光谱检测[OI]和[CII]线，为我们的光化学代码ProDiMo提供可观的数据。HST的观测证实了尘埃被限制在一个狭窄的带中。用PACS在远红外中检测连续谱，并用PACS和ATCA两者解析盘。气体谱线的中等积分仅提供线通量的上限。我们发现，HD 181327尘埃盘由微米级颗粒的多孔无定形硅酸盐和碳质材料包围的一个重要的冰层，总尘埃质量为0.05 M \oplus（最多1毫米）。我们讨论的证据表明，颗粒是蓬松的聚集体。气体管线上的上限没有提供明确的约束：只有当PAH丰度高时，气体质量才必须低于17 M \oplus。尽管对气体盘的约束很弱，但HD 181327的年龄和尘埃盘的性质表明它已经通过了气态行星形成的阶段。尘埃揭示了一群冰冷的小行星，类似于原始的柯伊伯带，这可能是未来向形成中的类地行星输送水和挥发物的…
