Observational Studies on the Euolution of Protoplanetary Disks

在这笔赠款的帮助下，在了解原行星盘的形成过程方面取得了进展。总而言之，在早期恒星演化的嵌入阶段，原行星盘通过从其大小为-10，000 Au的包层吸积气体而围绕原恒星生长。这颗星星是一颗金牛座T型星星，在它的包层因吸积而消散后，周围有一个原行星盘。详情概述如下。用东京大学野边山射电天文台60厘米望远镜在CO（J=2-1）谱线上对金牛座分子云进行的观测表明，整个分子云的J=2-1与J=1-0强度之比相对较低，为0.6，这表明整个分子云的密度和温度较低。这可能会影响在这种云中只产生低质量的启动。对<18>与金牛座分子云有关的32个IRAS源进行了C^ O（J=1-0）测量。较年轻的源，如由其较红的IRAS颜色所指示的，往往具有较大量的伴生气体，而较蓝的，即，老了，来源不。这意味着原恒星包层中的气体在从嵌入恒星到可见恒星的演化过程中会减少。首次在HL Tau周围的气体盘中发现了动力吸积现象，表明HL Tau正处于从嵌入的原星星向金牛T星星的过渡阶段。一个-40 Au的原行星盘正在HL Tau.4周围形成。在GG Tau和DM Tau周围的圆盘中检测到CO及其同位素排放。人们发现，重分子在磁盘中耗尽。

Progress was made on understanding the formation process of protoplanetary disks with the aid of this grant. In summary, a protoplanetary disk grows around a protostar in the embedded phase of early stellar evolution through accreting gas from its envelope with -10,000 AU in size. The star appears as a T Tauri star with a surrounding protoplanetary disk after the envelope is dissipated due to accretion. Details are summarized as follows.1. Observations of Taurus molecular cloud with the University of Tokyo-Nobeyama Radio Observatory 60 cm telesope in the CO (J=2-1) line revealed that the molecular cloud as a whole exhibits relatively low value of 0.6 for the ratio of the J=2-1 to J=1-0 intensities, suggesting that the entire molecular cloud is less dense and cold. This may affect to produce only low mass starts in this cloud.2. A C^<18>O (J=1-0) survey was made toward 32 IRAS sources associated with the Taurus molecular cloud. Younger sources as indicated by their redder IRAS colors tend to have larger amount of associated gas, while the bluer, i.e., older, sources do not. This means that the gas in the envelope of protostars decreases in the course of evolution from embedded to visible stars.3. Dynamical accretion was first detected from the gas disk aroud HL Tau, suggesting that HL Tau is in the transitional phase from an embedded protostar to a T Tauri star. A protoplanetary disk of -40 AU is forming around HL Tau.4. CO and its isotopic emissions have been detected from the disks around GG Tau and DM Tau. It was found that heavy molecules are depleted in disks.