Methanol along the path from envelope to protoplanetary disc
Methanol along the path from envelope to protoplanetary disc
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DOI：
10.1093/mnras/stu1789
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发表时间：
2014-11-21
影响因子：
4.8
通讯作者：
van Dishoeck, Ewine F.
中科院分区：
文献类型：
--
作者：
Drozdovskaya, Maria N.;Walsh, Catherine;van Dishoeck, Ewine F.
星际甲醇被认为是更大、更复杂的有机分子的母体。对低质量恒星形成系统进行了物理化学模拟，以追踪从云到盘的化学演化。一个轴对称的2D半解析模型产生的时间依赖的密度和速度分布，和完整的连续辐射传输进行计算的尘埃温度和紫外辐射场在每个位置作为时间的函数。采用一个综合的气粒化学网络来计算沿沿着下落轨迹的化学丰度。两个物理方案进行了研究，其中一个占主导地位的光盘增长机制是粘性传播，另一个是持续的物质流入盛行。结果表明，下落路径影响进入每种类型的光盘的甲醇的丰度，范围从甲醇的完全损失到相对于星前相的> 1倍的增强。确定了不同物理条件下甲醇化学的关键化学过程和参数。甲醇的精确丰度和分布对于圆盘中复杂有机分子的预算非常重要，这些分子将被纳入形成行星系统物体，如原行星和彗星。这些模拟结果表明，彗星形成区含有较少的甲醇比在前坍缩阶段，这是主要的星前起源，但也有额外的层建立在信封在下落。这种有趣的联系将很快被罗塞塔使命即将获得的数据所检验。
Interstellar methanol is considered to be a parent species of larger, more complex organic molecules. A physicochemical simulation of infalling parcels of matter is performed for a low-mass star-forming system to trace the chemical evolution from cloud to disc. An axisymmetric 2D semi-analytic model generates the time-dependent density and velocity distributions, and full continuum radiative transfer is performed to calculate the dust temperature and the UV radiation field at each position as a function of time. A comprehensive gas-grain chemical network is employed to compute the chemical abundances along infall trajectories. Two physical scenarios are studied, one in which the dominant disc growth mechanism is viscous spreading, and another in which continuous infall of matter prevails. The results show that the infall path influences the abundance of methanol entering each type of disc, ranging from complete loss of methanol to an enhancement by a factor of > 1 relative to the prestellar phase. Critical chemical processes and parameters for the methanol chemistry under different physical conditions are identified. The exact abundance and distribution of methanol is important for the budget of complex organic molecules in discs, which will be incorporated into forming planetary system objects such as protoplanets and comets. These simulations show that the comet-forming zone contains less methanol than in the precollapse phase, which is dominantly of prestellar origin, but also with additional layers built up in the envelope during infall. Such intriguing links will soon be tested by upcoming data from the Rosetta mission.