早型星磁场双峰分布的成因
The Origin of the Bimodal Distribution of Magnetic Fields in Early-type Stars
摘要：
在早期型恒星中，化石磁场可能是在恒星形成过程中产生的，也可能是恒星合并事件的结果。表面磁场被认为会被（亚）表面对流层消除，这通常会留下弱的无序场。然而，如果化石场足够强，它可以阻止（次）地表对流的发生，从而被保存在主层序上。我们计算的临界场强发生这种情况下，发现它对应的下限振幅观测到的领域在强磁化的Ap/Bp星（$\approx$ 300 G）。预测的临界场强略有增加，在主序星演化，这也可以解释观测到的磁星的分数下降。这支持了早期型恒星中观测到的磁场的双峰分布反映了两种不同的磁场起源故事的结论：强磁场是恒星形成或合并事件中继承的化石场，弱磁场是持续发电机作用的产物。
英文摘要：
In early-type stars a fossil magnetic field may be generated during the star formation process or be the result of a stellar merger event. Surface magnetic fields are thought to be erased by (sub)surface convection layers, which typically leave behind weak disordered fields. However, if the fossil field is strong enough it can prevent the onset of (sub)surface convection and so be preserved onto the main sequence. We calculate the critical field strength at which this occurs, and find that it corresponds well with the lower limit amplitude of observed fields in strongly magnetised Ap/Bp stars ($\approx$ 300 G). The critical field strength is predicted to increase slightly during the main sequence evolution, which could also explain the observed decline in the fraction of magnetic stars. This supports the conclusion that the bimodal distribution of observed magnetic fields in early-type stars reflects two different field origin stories: strongly magnetic fields are fossils fields inherited from star formation or a merger event, and weak fields are the product of on-going dynamo action.
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