The astrophysical context of diffusion in stars
The astrophysical context of diffusion in stars
复制标题
恒星扩散的天体物理学背景
DOI：
--
复制
发表时间：
1980
期刊：
影响因子：
--
通讯作者：
G. Michaud
中科院分区：
文献类型：
--
作者：
G. Michaud
元素的化学分离被证明可以解决许多令人困惑的天体物理学问题。扩散自然解释了低丰度的氦在Ap-Bp星和一些水平分支星，但它同时预测低丰度的氦在Am星，自然解释了附近的排斥Am和三角洲盾牌现象。类似地，太阳风中氦的低丰度也可以用扩散来解释。太阳粒子外流中的许多其他观测到的现象暗示着化学分离。考虑到在大气中观察到的高度湍流，太阳会导致化学差异的外流是令人惊讶的。那些在主序星上部的恒星是缓慢旋转的，有很强的磁场，大概比太阳更稳定。因此，它们的表面会出现化学差异也就不足为奇了。结果表明，在Ap星上观测到的丰度“点”要持续10/sup 2/-10/sup 3/ yr以上，对流区必须在这些星上消失。对于持续10/sup 8/ yr或更长时间的斑点，湍流扩散系数必须足够小，以允许元素通过扩散进行垂直分离。这可能排除了吸积和更多的其他模型作为丰度异常的主要来源。最后讨论了斑点的产生，或者说，扩散环，并表明敏感地依赖于一些鲜为人知的参数，可能从星星到星星。这解释了观测到的丰度模式的多样性。尽管出现的情况是一致的，但扩散模型仍然没有回答观察所提出的所有问题。可能缺少一个参数。这里提出了一个可能的。«少
Chemical separation of the elements is shown to solve a number of puzzling astrophysical problems. Diffusion naturally explains the low abundance of helium in the Ap-Bp stars and in some horizontal branch stars, but it simultaneously predicts a low helium abundance in Am stars which naturally explains the near exclusion of the Am and delta-Scuti phenomena. Similarly the low helium abundance in the solar wind is explained by diffusion. Many other observed phenomena in the solar particle outflux imply chemical separation. That the sun should lead to a chemically differentiated outflux is surprising, given the high turbulence observed in the atmosphere. Those stars of the upper main sequence that are slow rotators and have strong magnetic fields presumably are more stable than the sun. It is not too surprising, then, that chemical differentiation should appear on their surfaces. It is shown that for the observed abundance 'spots' to last on Ap stars for more than 10/sup 2/--10/sup 3/ yr the convection zones must disappear on those stars. For the spots to last 10/sup 8/ yr or more, the turbulent diffusion coefficient must be small enough to allow vertical separation of the elements by diffusion. This probably rules out accretion, andmore » many other models, as the main source of the abundance anomalies. The creation of spots or, rather, rings by diffusion is finally discussed and is shown to depend sensitively on a number of poorly known parameters that probably vary from star to star. This explains the variety of observed abundance patterns. Even though the emerging picture is consistent, the diffusion model still has not answered all the questions that observations suggest. There might be a missing parameter. A possible one is suggested here.« less