SMC中B型脉动之谜
The Enigma of B-type Pulsators in the SMC
摘要：
自90年代初以来，人们普遍认为B-型中子在主序上的激发机制是由于铁族元素在$T\approx 200,000$ K处的不透明度峰。Fe含量则在$β$ Cep和SPB脉动的激发中起主要作用。虽然理论上的非绝热计算预测没有$β$ Cep的候选者，只有少量的SPB的低金属丰度的环境，如麦哲伦云（MC），最近的变化调查的B星在SMC报告检测到大量的SPB和$β$ Cep的候选者。由于SMC是MCs中金属含量最少的（Z $\approx$ 0.001-0.004），它构成了研究理论和观测之间不一致的有趣对象。我们的做法的问题，通过质疑一些在以前的研究中提出的假设：鉴于不同的化学演化的SMC与我们当地的银河系环境相比，它是适当的描述SMC B星的化学成分，通过缩放太阳能混合物，以降低$Z$？这种结构在空间和时间上是均匀的吗？在本文中，我们提出了一个稳定性分析的结果，B型恒星模型计算与修订的化学成分和金属丰度特定的SMC。
英文摘要：
Since the early nineties it is accepted that the excitation mechanism of B-type pulsators on the main sequence is due to the opacity peak in the iron-group elements at $T\approx 200,000$ K. The Fe content plays then a major role in the excitation of $β$ Cep and SPB pulsations. While theoretical non-adiabatic computations predict no $β$ Cep pulsators and only a small number of SPBs for low metallicity environments such as that of the Magellanic Clouds (MCs), recent variability surveys of B stars in the SMC have reported the detection of a significant number of SPB and $β$ Cep candidates. Since the SMC is the metal poorest (Z$\approx$0.001-0.004) of the MCs, it constitutes an interesting object for investigating the disagreement between theory and observations. We approach the problem by calling into question some of the hypotheses made in previous studies: given the different chemical evolution of the SMC compared with our local galactic environment, is it appropriate to describe the chemical composition of SMC B stars by scaling the solar mixture to lower $Z$? Is that composition uniform in space and time? In this paper we present the results of a stability analysis of B-type stellar models computed with a revised chemical composition and metallicity specific to the SMC.
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