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arXiv 1003.3601astro-ph.SR
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B2Vn星HR 7355的磁场探测

Magnetic field detection in the B2Vn star HR 7355

Th. Rivinius, Th. Szeifert, L. Barrera, R. H. D. Townsend, S. Stefl, D. Baade

摘要:

B2 Vn星HR 7355是一颗富氦磁星。使用帕拉纳尔天文台UT 2的FORS 1获得了光谱偏振数据,以测量假定的0.52 d周期各个阶段的磁盘平均纵向磁场。发现了一个强度在B_z = -2200 ~+3200G之间的可变磁场,置信限为100 ~ 130 G。磁场拓扑结构是斜偶极子,而恒星本身在赤道附近。在强度谱中,HeI线显示了典型的He强恒星的等效宽度变化,通常归因于表面丰度点。与其他情况相比,HeI线的等效宽度变化的幅度非常强。这些结果不仅将HR 7355明确地归入早期型磁星之列,而且证实了它的杰出性质:当v sin i = 320 km/s时,已知存在He强恒星的参数空间在自转速度方面增加了一倍。

英文摘要:

The B2Vn star HR 7355 is found to be a He-rich magnetic star. Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory to measure the disk-averaged longitudinal magnetic field at various phases of the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z = -2200 and +3200G was found, with confidence limits of 100 to 130G. The field topology is that of an oblique dipole, while the star itself is seen about equator-on. In the intensity spectra the HeI-lines show the typical equivalent width variability of He-strong stars, usually attributed to surface abundance spots. The amplitudes of the equivalent width variability of the HeI lines are extraordinarily strong compared to other cases. These results not only put HR 7355 unambiguously among the early-type magnetic stars, but confirm its outstanding nature: With v sin i = 320 km/s the parameter space in which He-strong stars are known to exist has doubled in terms of rotational velocity.

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