用William Herschel望远镜的低分辨率分光偏振计测量恒星磁场
Measuring stellar magnetic fields with the low resolution spectropolarimeter of the William Herschel Telescope
摘要：
尽管磁场对恒星结构和演化的影响在很大程度上已从理论上得到证实，但在非简并恒星中的观测证据仍然相当缺乏，而且主要局限于明亮的天体（V<10）。恒星磁场通常是基于圆偏振光谱法在金属线轮廓上以高/中分辨率测量的。以目前望远镜和摄谱仪的灵敏度来看，这仍然是一种几乎令人望而却步的方法。原则上，恒星磁场也可以在低分辨率分光偏振法的基础上进行测量，在欧洲南方天文台8米望远镜上使用FORS 1获得了非常重要的结果。在测量恒星磁场的S/N和光谱分辨率之间的权衡证明了在4.5米威廉赫歇尔望远镜进行这些测量的尝试。用偏振分光光度计ISIS在3785-4480 A波段观测到了已知磁场最弱的恒星之一HD 3360和磁化学特殊星HD 10783、HD 74521和HD 201601。从S/N > 600的Stokes I和V光谱中测量的恒星磁场显示，选择整个间隔的内部误差<50 G，在巴耳末线内的内部误差<200 G。HD 3360的斯托克斯V谱中的波纹导致仪器正磁场肯定不大于80 G。
英文摘要：
Despite the influence of magnetic fields on the structure and evolution of stars is largely demonstrated from the theoretical point of view, their observational evidence in non-degenerated stars is still rather scanty and mainly circumscribed to bright objects (V<10). Stellar magnetic fields are commonly measured on the basis of circular spectropolarimetry at high/middle resolution across the profile of metal lines. The present sensitivity of telescopes and spectrographs makes this still an almost prohibitive method for faint stars. In principle, stellar magnetic fields can be also measured on the basis of low resolution spectropolarimetry, with very important results obtained at the 8 m ESO telescopes with FORS1. The trade off between S/N and spectral resolution in measuring stellar magnetic fields justify an attempt, here presented, to perform these measurements at the 4.5 m William Herschel Telescope. HD3360, one of the stars with the weakest known magnetic field, and the magnetic chemically peculiar stars HD10783, HD74521 and HD201601 have been observed with the spectropolarimeter ISIS in the 3785-4480 A range. Measured stellar magnetic fields, from Stokes I and V spectra with S/N > 600, show an internal error of <50 G selecting the whole interval and <200 G within a Balmer line. Ripples in the Stokes V spectra of HD3360 result in an instrumental positive magnetic field certainly not larger than 80 G.
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