Observational Studies on the Euolution of Protoplanetary Disks

在这笔赠款的帮助下，在理解原行星盘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，原行星盘围绕着原恒星生长，通过从其包层中吸积-10,000 AU大小的气体来实现。这颗恒星看起来像是一颗T-Tauri星，周围有一个原行星盘，包层由于吸积而消散。具体内容总结如下：1.在CO(J=2-1)线上用东京-野山大学射电天文台60厘米望远镜对金牛座分子云进行的观测表明，整个分子云在J=2-1和J=1-0强度之比上表现出相对较低的0.6值，这表明整个分子云密度较低，温度较低。这可能会影响在这片云中只产生低质量的开始。对与金牛座分子云有关的32个IRAS源进行了C^&lt；18&gt；O(J=1-0)调查。较年轻的来源，如其红色的IRAS颜色所指示的，往往具有更多的伴生气体，而较蓝色的来源，即较年长的来源，则没有。这意味着原恒星包层中的气体在从嵌入恒星向可见恒星演化的过程中减少。首先从HL-Tau周围的气盘中探测到动力学吸积，这表明HL-Tau处于从嵌入的原星到T-Tauri星的过渡阶段。一个-40AU的原行星盘正在HL Tau4周围形成。从GG Tau和DM Tau周围的圆盘中检测到了CO及其同位素发射。人们发现，重分子在圆盘中被耗尽。

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.