Water Transport and Dispersal of Gas in Protoplanetary Disks

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。通过该奖项，Pascucci博士，沿着与学生和合作者，将完成一项正在进行的地面活动，以光谱解析斯皮策太空望远镜探测到的许多原行星盘的明亮气体发射线。这些观测与天基数据相结合，将解决与巨行星和类地行星形成有关的两个基本问题：（1）气体盘何时以及通过何种机制分散？(2)水蒸气能在盘中长时间停留以影响类地行星的水丰度吗？具体来说，Pascucci博士和她的合作者将：（1）研究如何使用12.81微米的电离氖的发射线来追踪耗散的气体盘。磁盘模型预测，这种排放是一个敏感的示踪剂的小气体质量在陆地和巨大的行星形成区域的磁盘。斯皮策太空望远镜已经探测到了许多年轻圆盘的空间和光谱上无法分辨的氖发射线。Pascucci博士和她的合作者将使用地面望远镜从光谱上解析来自30个原行星盘的明亮氖线。通过测量宽度，峰值速度和模拟线轮廓，他们将把来自盘的发射从喷流/流出中分离出来，并测量对光谱通量有贡献的盘半径，并揭示X射线或紫外光子是否是氖原子的主要电离源。 这可以澄清光蒸发在分散气体盘中的作用，并指导使用许多光谱未分辨的氖线测量气体分散的时间尺度。(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。一种新出现的情况表明，这发生在地球完全形成之前的相对较早的时间，是由从外小行星带向内迁移的水合硅酸盐的吸积造成的。在一个不断发展的原行星盘的水的运输模型确定水蒸气的演变强劲的趋势。Pascucci博士和她的合作者将获得数据集来测试这些模型。特别是，他们将获得高分辨率的L波段光谱的磁盘在不同的进化阶段，有中红外水线检测斯皮策。他们将使用各种代码对谱线轮廓进行建模，以：a）估计L波段水线追踪的气体性质;以及B）调查水发射谱线是否与圆盘模型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综合解释，这些水线将从他们批准的Herschel Key计划中获得，以绘制出水在原行星盘中的分布和演化。拟议的工作是对当前和即将进行的天基观测的重要补充，这是充分了解气盘中气体演变以及这种演变对巨型和类地行星形成的影响所必需的。这项研究计划将构成约翰霍普金斯大学研究生博士论文的基础，并为对行星形成研究感兴趣的本科生提供小型和大型项目。这些活动将培训学生使用最先进的地面和空间设施，并解决行星形成研究中的一些最基本问题。

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.