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arXiv 0902.1314astro-ph.SR
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造父β星和慢脉动B星的新磁场测量

New magnetic field measurements of beta Cephei stars and Slowly Pulsating B stars

S. Hubrig, M. Briquet, P. De Cat, M. Schoeller, T. Morel, I. Ilyin

摘要:

我们目前的结果继续我们的磁调查与FORS 1在VLT的一个样本的B型星组成的确认或候选人的仙王座β星和慢脉动B(以下简称SPB)的明星,以及少量的正常B型星。在三颗仙王座β星和两颗疑似仙王座β星、五颗SPB星和八颗疑似SPB星中检测到了几百高斯量级的弱平均纵向磁场。此外,在两颗正常的B型恒星中,即富氮的早期B型恒星HD 52089和B5 IV型恒星HD 153716中,也发现了大于3 σ的纵向磁场。大约三分之一的仙王座β星已经探测到磁场:在FORS 1研究的13颗仙王座β星中,有4颗星拥有弱磁场,在6颗疑似仙王座β星的样本中,有2颗显示出弱磁场。发现磁性SPB和候选SPB的比例更高:34颗SPB恒星中大约有一半被发现是磁性的,16颗候选SPB恒星中有8颗拥有磁场。为了理解为什么只有一小部分脉动星具有磁场,我们研究了磁脉动星和非磁脉动星在H-R图中的位置。我们发现它们在H-R图上的区域有很大的重叠,并且没有清晰的图像显示出磁场在主序列上的可能演化。有可能在脉动频率较低和脉动幅度较小的恒星中发现更强的场。如果我们考虑磁场强度和v sin i值之间的相关性,也会发现类似的趋势,即更强的磁场往往出现在旋转更慢的恒星中。

英文摘要:

We present the results of the continuation of our magnetic survey with FORS1 at the VLT of a sample of B-type stars consisting of confirmed or candidate beta Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B-type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three beta Cephei stars and two stars suspected to be beta Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3sigma has been diagnosed in two normal B-type stars, the nitrogen-rich early B-type star HD52089 and in the B5 IV star HD153716. Roughly one third of beta Cephei stars have detected magnetic fields: Out of 13 beta Cephei stars studied to date with FORS1, four stars possess weak magnetic fields, and out of the sample of six suspected beta Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non-magnetic pulsating stars in the H-R diagram. We find that their domains in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i-values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars.

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