摘要
本文在非均匀条件下研究了和红外源成协的分子云的能量平衡问题,建立了包括CO分子和H_2O分子冷却(或加热)、尘埃-气体碰撞加热、引力坍缩加热及宇宙线加热等过程的中心有红外源的非均匀分子云热模型.通过对具有不同参量的这种模型的计算研究,得到如下主要结论:(1)对于红外光度为10~3L_☉,半径为spc的分子云,气体数密度n(H_2)∝r^(-1)、光学厚度τ_(0.63μm)=100的非均匀分子云热模型与现有观测结果符合得较好.(2)在非均匀分子云的不同区域中,起主要作用的加热、冷却机制是各不相同的.(3)在一个中心有红外源的非均匀分子云中,水分子总是起冷却作用.而且,在分子云内层,水分子还是最主要的冷却剂.(4)在一定的物理条件下,一氧化碳分子可能是加热剂.
The energy equilibrium of molecular clouds with an IR source at the center is studied allowing the nonuniformity in density distribution. The thermal model of this kind of clouds is set up, in which several cooling and heating processes are considered, such as radiative cooling (or heating) by CO and H_2O molecules, heating by dust-gas collisions, heatig due to gravitational contraction, and cosmic-ray heating. Six spherical models are constructed by varying two model parameters, i.e., the index of density-law, α=-d(log n)/d(log r), and the optical thickness at the center, τ_(0.63μm)(or, the gas column density through the center, N_(H_2)), and then, heat balance and radiative transfer processes are treated numerically to get heatig/cooling rates and gas kinetic temperature; the physical constraints common to these models are the total(IR) luminosity of 10~5L_⊙, the radius of 5pc, the velocity gradient of 1km sec^(-1)pc^(-1), and molecular abundaces of X(CO)=3×10^(-5) and X(H_2O)=3×10^(-6). The result of calculations leads to following conclusions: (1) In view of the radial distribution of gas kinetic temperature, the Model 5 shows the best agreement with the observational data by Evans et al. (1977—1981). (2) Relative importance of different heating/cooling mechanisms changes considerably from region to region. (3) The water molecule is always a coolant and the dominant one in the innermost region. (4) The CO molecule generally works as a coolant, but it may play a role of gas-heating agent under some physical conditions.
出处
《天文学报》
CSCD
北大核心
1989年第3期262-275,共14页
Acta Astronomica Sinica
基金
国家自然科学基金
