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Evolution of Molecular Abundances in Prohoplanetary Gaseous Disks

原行星气盘中分子丰度的演化

基本信息

批准号：
10640224
负责人：
UMEBAYASHI Toyoharu
金额：
$ 2.05万
依托单位：
YAMAGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

We investigate the chemical and physical evolution of protoplanetary gaseous disks and obtain the following results :1. We investigate the evolution of molecular abundances in a protoplanetary gaseous disk in which matter is accreting toward the central star by solving numerically the reaction equations of molecules as an initial value problem. We find that molecular abundances both in the gas phase and in ice mantles of dust grains depend crucially on the temperature and thus vary significantly with the distance from the central star. The timescale of molecular evolution, which is slightly smaller that the lifetime of the disk, is dependent on the physical conditions such as ionization rate and grain size in the disk. We also find that our results naturally explain the coexistence of oxidized (e.g. COィイD22ィエD2) ice and reduced (e.g. CHィイD24ィエD2, NHィイD23ィエD2) ice in the observed comets.2. We next investigate the regions of protoplanetary disks in which magnetorotational instability can operate the transport of angular momentum. We calculate the spatial distribution of various charges particles and compare the ohmic dissipation time of magnetic field with the Keplerian orbit period. We find that for a variety of disk models there exist inner regions where the gas is decoupled from the magnetic field and is magnetorotationally stable due to ohmic dissipation. This must made the accretion onto the central star non-steady. In the later evolutionary stages the stable region shrinks as the grain size increases and/or the sedimentation of grains toward the midplain of the disk proceeds.

我们研究了原行星气盘的化学和物理演化，得到以下结果：1。通过数值求解分子反应方程作为初值问题，研究了物质向中心星星吸积的原行星气盘中分子丰度的演化。我们发现，在气相和尘埃颗粒的冰地幔中的分子丰度取决于关键的温度，从而显着变化与距离中央星星。分子演化的时间尺度比圆盘的寿命略小，取决于圆盘中的电离率和晶粒尺寸等物理条件。我们还发现，我们的结果自然地解释了在观测彗星中氧化态（如CO冰D22）冰和还原态（如CH冰D24）冰D2，NH冰D23）冰的共存.接下来，我们调查的区域的原行星盘中的磁旋转不稳定性可以操作的角动量的运输。计算了各种带电粒子的空间分布，并将磁场的欧姆耗散时间与开普勒轨道周期进行了比较。我们发现，对于各种磁盘模型存在内部区域的气体是从磁场解耦，是磁旋转稳定的欧姆耗散。这必然使得中心星星上的吸积是不稳定的。在后期的演化阶段的稳定区域缩小的晶粒尺寸的增加和/或沉降的颗粒向中盘的进行。