We examine the stability and observational consequences of mixing induced by 3He burning in the envelopes of first ascent red giants. We demonstrate that there are two unstable modes: a rapid, nearly adiabatic mode that we cannot identify with an underlying physical mechanism, and a slow, nearly radiative mode that can be identified with thermohaline convection. We present observational constraints that make the operation of the rapid mode unlikely to occur in real stars. Thermohaline convection turns out to be fast enough only if fluid elements have finger-like structures with a length to diameter ratio l/d > 10. We identify some potentially serious obstacles for thermohaline convection as the predominant mixing mechanism for giants. We show that rotation-induced horizontal turbulent diffusion may suppress the 3He-driven thermohaline convection. Another potentially serious problem for it is to explain observational evidence of enhanced extra mixing. The 3He exhaustion in stars approaching the red giant branch (RGB) tip should make the 3He mixing inefficient on the asymptotic giant branch (AGB). In spite of this, there are observational data indicating the presence of extra mixing in low-mass AGB stars similar to that operating on the RGB. Overmixing may also occur in carbon-enhanced metal-poor stars.
用非定域含时对流理论计算了10个质量为1- 3 M $_\odot$的演化模型系列的线性非绝热振荡。结果表明，在Hertzsprung-Russel（HR）图的低温侧存在一条红巨星不稳定带，该不稳定带沿红巨星支（RGB）和渐近巨星支（AGB）的序列延伸。对于低光度的红巨星，在高阶泛音处存在脉动不稳定性，从基频到二阶泛音的低阶模是稳定的。随着光度的升高和有效温度的降低，不稳定性向低阶模移动，振荡的振幅增长率也增大。在光带的高亮度端，基频和一阶泛音变得不稳定，而所有四阶以上的模式变得稳定。详细研究了其激发机理。结果表明，湍流压力对红变量的激发起着关键作用。冻结对流近似对于具有扩展对流包层的低温星是不适用的。无论如何，这种近似既不能解释造父变星不稳定带的红边，也不能解释脉动红巨星不稳定带的蓝边。本文给出了脉动常数随恒星质量、光度和有效温度变化的解析表达式。
Spectroscopic Observations of Convective Patterns in the Atmospheres of Metal-Poor Stars
对流线的不对称性的光谱的两个贫金属的恒星，HD140283，进行了比较，观察到的太阳金属量的恒星。次巨星HD 140283是最缺乏金属的恒星，它的线平分线显示出比相同光谱类型和光度等级的太阳金属丰度恒星更大的速度跨度。增强的线不对称性被解释为较低的金属含量的签名，因此不透明，在对流光球图案。这些研究结果指出了三维对流速度场的重要性，在解释所观察到的线不对称性，在贫金属恒星，特别是，敦促谨慎推导同位素比时，从观察到的线的形状和变化，使用一维模型大气。光球原子线的平均线平分线进行了比较，与测得的强Mg I b1和b2功能。平分线的上部是相似的，假设它们重叠，在大气层中形成的较强线条的底端更接近红色。这与大气上层对流蓝移的预期减小相一致，并且与晚型恒星色球层、过渡区和日冕中观测到的高速红移相一致。
