Water Transport and Dispersal of Gas in Protoplanetary Disks

该奖项由2009年《美国复苏和再投资法案》(Public Law 111-5)资助。通过这一奖项，帕斯库奇博士将与学生和合作者一起完成一项正在进行的地面活动，将斯皮策太空望远镜探测到的明亮气体发射线光谱解析到许多原行星圆盘上。这些观测，结合基于空间的数据，将解决与巨型行星和类地行星形成有关的两个基本问题：(1)气盘何时分散，通过哪些机制？(2)水蒸气能否在气盘中保持较长时间，以影响类地行星的水丰度？具体地说，帕斯库奇博士和她的合作者将：(1)研究如何使用12.81微米电离霓虹灯的发射线来追踪正在消散的气体盘。圆盘模型预测，这种发射是陆地和巨行星形成圆盘区域中的小气团的灵敏示踪剂。斯皮策太空望远镜已经探测到许多年轻的圆盘在空间和光谱上没有分辨出的霓虹发射线。帕斯库奇博士和她的合作者将使用地面望远镜，从30个原行星圆盘上对明亮的霓虹线进行光谱解析。通过测量宽度、峰值速度和对谱线轮廓进行建模，他们将把源自圆盘的发射与喷射/外流中的发射分开，并测量对光谱通量有贡献的圆盘半径，并揭示X射线或紫外线光子是霓原子的主要电离源。这可以澄清光蒸发在分散气体盘中的作用，并指导使用大量光谱上未分辨的霓虹线来测量气体扩散的时间尺度。(2)绘制出原行星盘中水的分布和演化图。一个关键但尚未回答的问题是地球是如何获得水的。一种新出现的情景表明，这发生在地球完全形成之前的相对较早的时期，原因是水合硅酸盐从外部小行星带向内迁移。演化中的原行星盘中的水传输模型确定了水蒸气演化的强劲趋势。帕斯库奇博士和她的合作者将获得测试这些模型的数据集。特别是，他们将获得不同演化阶段的盘的高分辨率L波段光谱，这些盘具有斯皮策探测到的中红外水线。他们将使用不同的程序模拟谱线轮廓：a)估计L水线所追踪的气体的性质；b)调查水发射谱线是否与圆盘模型所提出的圆盘演化阶段相关。最后，他们将对L波段、中红外和远红外水线进行联合解释，这些水线将从他们批准的赫歇尔关键计划中获得，以绘制出原行星盘中水的分布和演化图。拟议的工作是对目前和即将进行的天基观测的必要补充，对于充分了解盘中气体的演化以及这种演化对巨型行星和类地行星形成的影响是必要的。这项研究计划将为约翰霍普金斯大学研究生的博士论文奠定基础，并为对行星形成研究感兴趣的本科生提供小规模和大型项目。这些活动将培训学生使用最先进的地面和天基设施，并解决行星形成研究中的一些最基本的问题。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Through this award, Dr. Pascucci, along with students and collaborators, will complete an on-going ground-based campaign to spectrally resolve bright gas emission lines detected with the Spitzer Space Telescope toward many protoplanetary disks. These observations, combined with the space-based data, will address two fundamental questions related to the formation of giant and terrestrial planets: (1) When and through which mechanisms do gas disks disperse? (2) Can water vapor remain long in the disk to affect the water abundance of terrestrial planets? Specifically, Dr. Pascucci and her collaborators will:(1) Investigate how to use the emission line from ionized neon at 12.81 microns to trace dissipating gas disks. Disk models predict that this emission is a sensitive tracer of small gas masses in the terrestrial and giant planet forming region of disks. The Spitzer Space Telescope has detected spatially and spectrally unresolved neon emission lines toward many young disks. Dr. Pascucci and her collaborators will use ground-based telescopes to spectrally resolve bright neon lines from 30 prototoplanetary disks. By measuring the widths, peak velocities, and modeling the line profiles, they will separate the emission originating in a disk from that in a jet/outflow and measure the disk radii contributing to the spectal flux, and reveal if X-rays or ultraviolet photons are the major ionization source for neon atoms. This can clarify the role of photoevaporation in dispersing gas disks and guide the use of the numerous spectrally unresolved neon lines in measuring the timescale over which gas disperses.(2) Map out the distribution and evolution of water in protoplanetary disks. A key yet unanswered question is how Earth acquired its water. A new emerging scenario suggests that this happened relatively early, before Earth was fully formed, by accretion of hydrated silicates migrating inward from the outer asteroid belt. Models of the transport of water in an evolving protoplanetary disk identify robust trends in the evolution of water vapor. Dr. Pascucci and her collaborators will acquire the datasets to test these models. In particular, they will obtain high-resolution L-band spectra of disks in different evolutionary stages that have mid-infrared water lines detected with Spitzer. They will model the line profiles using various codes to: a) estimate the properties of the gas traced by the L-band water lines; and b) investigate if water emission lines are correlated with the disk evolutionary stage as proposed by disk models. Finally, they will work on the combined interpretation of L-band, mid-infrared and far-infrared water lines that they will obtain from their approved Herschel Key program to map out the distribution and evolution of water in protoplanetary disks. The proposed work is an essential complement to current and upcoming space-based observations, necessary to fully understand the evolution of gas in disks and the implications of this evolution on the formation of giant and terrestrial planets. This research program will form the basis for a PhD thesis for a Johns Hopkins University graduate student and offer small- and large- scale projects for undergraduate students interested in planet formation studies. These activities will train students in using state-of-the-art ground- and space-based facilities and in addressing some of the most fundamental questions in planet formation studies.