arXiv 1502.007792015-02-03astro-ph.SR

FORS分光偏振观测的全面和关键的再分析：HD92207的情况

A comprehensive and critical re-analysis of FORS spectropolarimetric observations: the case of HD92207

L. Fossati, S. Bagnulo, J. D. Landstreet, O. Kochukhov

备注：: Proceedings of the International Conference "Physics and Evolution of Magnetic and Related Stars" held at the Special Astrophysical Observatory (Russia) in August 2014

摘要：

在过去的十年里，恒星偏振光谱测量变得非常流行，并导致我们对恒星磁场及其对恒星结构和演化的影响的理解取得了重大进展。许多重要的发现都归功于欧洲南方天文台甚大望远镜的FORS低分辨率分光偏振仪的观测。我们首先回顾和总结了所有单缝FORS 1分光偏振观测的均匀再还原和分析的主要结果。这项工作揭示了一个不可忽略的依赖于所采用的减少和分析程序的结果，以及不稳定性的存在，揭示了光子噪声不是唯一的不确定性来源。由于我们对不确定性进行了新的分析和评估，我们无法确认过去对各种恒星进行的大量磁场探测。我们进一步总结了A0超巨星HD 92207的FORS 2光谱偏振观测结果，这使我们能够进一步探索不稳定性的性质，大致限制其对导出的斯托克斯轮廓和磁场值的最大影响。最后，我们提出了新的结果与进一步的独立管道上的FORS2数据的HD92207，证实了我们以前的分析，并讨论了简单的质量检查控制，可以执行的数据，以区分真正的和虚假的信号。总之，我们的研究结果表明，FORS分光偏振仪确实是可靠的仪器，当他们的能力没有超过卡塞格伦安装的低分辨率光谱仪的限制。

英文摘要：

Stellar spectropolarimetry has become extremely popular during the last decade, and has led to major advances in our understanding of stellar magnetic fields and of their impact on stellar structure and evolution. Many important discoveries have been obtained thanks to observations performed with the FORS low-resolution spectropolarimeters of the ESO Very Large Telescope. We first review and summarise the major results of a homogeneous re-reduction and analysis of all single-slit FORS1 spectropolarimetric observations. This work revealed a non-negligible dependence of the results upon the adopted reduction and analysis procedure, as well as the presence of instabilities, revealing that photon noise is not the only source of uncertainty. As a consequence of our new analysis and assessment of the uncertainties, we are not able to confirm a large number of magnetic field detections presented in the past for a variety of stars. We further summarise the results of FORS2 spectropolarimetric observations of the A0 supergiant HD92207 which allowed us to explore further the nature of the instabilities, roughly constraining their maximum impact on the derived Stokes profiles and magnetic field values. We finally present new results obtained with a further independent pipeline on the FORS2 data of HD92207, confirming our previous analysis, and discuss simple quality-check controls which can be performed on the data in order to distinguish between genuine and spurious signals. All together, our results reveal that the FORS spectropolarimeters are indeed reliable instruments, when their capabilities are not pushed beyond the limits of a Cassegrain mounted low-resolution spectrograph.

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