Observational Studies on the Euolution of Protoplanetary Disks

在这项拨款的帮助下，对原行星盘形成过程的理解取得了进展。总之，在早期恒星演化的嵌入阶段，原行星盘在原恒星周围生长，其大小为-10,000天文单位。这颗恒星看起来像一颗金牛座T星，周围有一个原行星盘，在包层因吸积而消散后。详细情况总结如下。利用东京大学野山射电天文台60cm望远镜对金牛座分子云的CO （J=2-1）线进行观测发现，整个分子云的J=2-1与J=1-0强度之比相对较低，仅为0.6，说明整个分子云密度较低，温度较低。这可能会影响在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^<18>O （J=1-0）调查。较红的IRAS颜色表明，较年轻的来源往往有较多的伴生气体，而较蓝的，即较老的来源则没有。这意味着原恒星包层中的气体在从嵌入恒星到可见恒星的演化过程中会减少。在HL Tau周围的气体盘中首次检测到动态吸积，这表明HL Tau正处于从嵌入的原恒星到金牛座T星的过渡阶段。一个- 40au的原行星盘正在HL ta4周围形成。从GG Tau和DM Tau周围的圆盘上检测到CO及其同位素排放。人们发现圆盘中的重分子被耗尽了。

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.