标题： 热脉动AGB上的冷底过程以及星际尘埃颗粒的同位素组成 显示英文标题

标题： Cool bottom processes on the thermally-pulsing AGB and the isotopic composition of circumstellar dust grains

摘要： （摘要）我们研究了在初始质量为1.5 M_sun、初始成分为太阳的恒星演化过程中，在热脉冲AGB阶段对流包层中冷却底部处理（CBP）对几个同位素比率的影响。我们使用了一个参数模型，通过引入对流包层和下方辐射区之间的质量流动来处理额外混合。该模型的参数是质量循环速率（Mdot）和循环物质经历的最大温度（T_P）。核反应在流动物质中的影响是通过一组从完整的恒星演化计算中选择的辐射区结构来计算的。获得了流动物质的组成，并确定了包层中的变化。对于log T_P > 7.65，CBP产生了丰富的^26Al。虽然^26Al/^27Al取决于T_P，但CNO元素的同位素比率主要取决于循环速率。显示了在恒星演化模型中用扩散公式参数化的CBP模型与这里使用的质量流动公式的模型之间的对应关系。同位素比率与围绕恒星的尘埃颗粒数据进行了比较。发现对于在C/O < 1时形成的氧化物颗粒观察到的比率^{18}O/^{16}O，^{17}O/^{16}O和^26Al/^27Al可以合理理解。然而，碳化物颗粒（C/O > 1）中的^15N/^14N，^12C/^13C和^26Al/^27Al需要许多恒星源，其^14N/^15N至少比太阳低4倍。具有^12C/^13C < 10的稀有颗粒无法由任何红巨星或AGB源产生。 显示英文摘要

摘要： (Abridged) We examine the effects of cool bottom processing (CBP) on several isotopic ratios in the convective envelope during the TP-AGB phase of evolution in a 1.5 M_sun initial-mass star of solar initial composition. We use a parametric model which treats extra mixing by introducing mass flow between the convective envelope and the underlying radiative zone. The parameters of this model are the mass circulation rate (Mdot) and the maximum temperature (T_P) experienced by the circulating material. The effects of nuclear reactions in the flowing matter were calculated using a set of structures of the radiative zone selected from a complete stellar evolution calculation. The compositions of the flowing material were obtained and the resulting changes in the envelope determined. Abundant ^26Al was produced by CBP for log T_P > 7.65. While ^26Al/^27Al depends on T_P, the isotopic ratios in CNO elements depend dominantly on the circulation rate. The correspondence is shown between models of CBP as parameterized by a diffusion formalism within the stellar evolution model and those using the mass-flow formalism employed here. The isotopic ratios are compared with the data on circumstellar dust grains. It is found that the ratios ^{18}O/^{16}O, ^{17}O/^{16}O, and ^26Al/^27Al observed for oxide grains formed at C/O < 1 are reasonably well-understood. However, the ^15N/^14N, ^12C/^13C, and ^26Al/^27Al in carbide grains (C/O > 1) require many stellar sources with ^14N/^15N at least a factor of 4 below solar. The rare grains with ^12C/^13C < 10 cannot be produced by any red-giant or AGB source.