OB星（BOB）中的B场：两颗罕见的刚性旋转磁层星HD23478和HD345439的FORS2光谱偏振跟踪
B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD23478 and HD345439
摘要：
具有强磁场和快速旋转的大质量B型恒星非常罕见，为恒星形成和磁场演化理论提供了一个谜。只有两颗这样的恒星，称为sigma Ori E类似物，以前已知。最近，一个参与APOGEE的团队，斯隆数字巡天III计划之一，宣布发现了另外两颗刚性旋转的磁层恒星，HD 23478和HD 345439。在这些新发现的σ Ori E类似物中存在磁场在过去没有被研究过。在我们的ESO大型计划和一个正常的ESO计划的框架内，我们对HD 23478和HD 345439进行了低分辨率FORS 2光谱偏振观测。从氢谱线的测量中，我们发现HD 23478中存在一个相当强的纵向磁场，其量级可达1.5kG，而用整个谱线的测量则可达1.3kG。使用4次后续分光偏振亚曝光对HD 345439进行的分析未显示存在显著性水平为3 σ的磁场。另一方面，对单个子暴露的检查表明，HD 345439可能具有强磁场，在88分钟内迅速变化。HD345439快速旋转的暗示也是由几个金属和He I线在低分辨率FORS 2光谱中的行为给出的，显示了在如此短的时间尺度上已经存在的轮廓变化。
英文摘要：
Massive B-type stars with strong magnetic fields and fast rotation are very rare and provide a mystery for theories of both star formation and magnetic field evolution. Only two such stars, called sigma Ori E analogs, were previously known. Recently, a team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, announced the discovery of two additional rigidly rotating magnetosphere stars, HD23478 and HD345439. The presence of magnetic fields in these newly discovered sigma Ori E analogs was not investigated in the past. In the framework of our ESO Large Programme, and one normal ESO programme, we carried out low-resolution FORS2 spectropolarimetric observations of HD23478 and HD345439. From the measurements using hydrogen lines, we discover a rather strong longitudinal magnetic field of the order of up to 1.5kG in HD23478, and up to 1.3kG using the entire spectrum. The analysis of HD345439 using four subsequent spectropolarimetric subexposures does not reveal the presence of a magnetic field at a significance level of 3sigma. On the other hand, the inspection of individual subexposures indicates that HD345439 may host a strong magnetic field, rapidly varying over 88 minutes. A hint at the fast rotation of HD345439 is also given by the behaviour of several metallic and He I lines in the low-resolution FORS2 spectra, showing profile variations already on such a short time scale.
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