大质量恒星的外壳对流和物质损失

Convection in massive stars has common characteristics as other stars and its own characteristics which is different from others. There is semi-convection in the core. And convective envelopes of massive stars are different from those in intermediate and small mass stars. The two convective shells, we found, develop in different forms with different turbulent diffusion parameters and evolution. But they are linked to a certain extent. The turbulent dynamic energy increases in the HeII convective shell but decreases in the HeIII convective shell with different turbulent diffusion parameters and as evolution proceeds. It seems that the turbulent dynamic energy is transmitted from the HeIII convective shell to the HeII convective shell. As the HeII convective shell is near to stellar surface, maybe the phenomenon is linked to mass loss of star. This research dedicates to study the two convective shells' characteristics, the link between them and the relationship of them with the mass loss of star. And hence to build the mass loss model, compare it with observation and calibrate it.

大质量恒星中的对流有着恒星对流的共性，以及自身的特性。大质量恒星中心对流区存在着半对流现象，外壳对流层也有着与中小质量星所不同的独特特征。针对这个外壳对流层，我们展开研究发现，随着所采取的湍流扩散参数的不同以及随着恒星的演化，两对流壳层各自有着不同的发展规律，并且相互之间有着特定方向的联系。随着湍流扩散系数的增大，以及随着恒星的演化，氦一次电离(HeII)对流壳层的湍动能在增加，氦二次电离(HeIII)对流壳层的湍动能在减少，而两对流壳层总的湍动能变动幅度不大。这似乎在说明HeIII壳层湍动能在向HeII壳层输运。由于HeII壳层离恒星表层很近，其与星风物质损失之间可能会有直接的关系。此项目的主要研究内容就是研究两对流壳层各自发展规律以及相互之间的关系及其与物质损失之间的关系，建立物质损失模型，与观测进行对比并校正。

对流是大质量恒星中一个重要的现象。对流对不同演化阶段都有影响。该项目利用TCM（湍对流模型）对30个太阳质量的恒星后主序时期的外壳进行湍流计算发现：氦二次电离对流层和氦一次电离对流层中间的超射区湍动能非零，这意味着该两对流层存在着湍动能输运的可能；随着湍流扩散系数增大，氦一次电离对流层的湍动能增加而氦二次电离对流层的湍动能减少，这意味着湍动能在向外输运，湍动能向外输运有可能引起外壳动力学不稳定性的增加从而引发物质损失；随着演化的进行，氦一次电离对流层的湍动能比氦二次电离对流层的增加的更多，同时意味着恒星外壳的动力学不稳定性增加，验证了随着恒星的演化物质损失率的增加。建立简单的物质损失模型计算表明，当有效温度对数为3.9左右时，物质损失率可达10的-7到-6次方量级。