arXiv 1102.44472011-02-22astro-ph.IM

CAFOS线性分光偏振计的特性

Characterisation of the CAFOS linear spectro-polarimeter

F. Patat, S. Taubenberger

备注：: 5 pages, 5 figures, Accepted for publication in A&A (Research Note)
DOI：: 10.1051/0004-6361/201116566

摘要：

目标。本研究报告对安装在卡拉阿尔托2.2米望远镜上的CAFOS偏振计进行了全面分析。它还为这种模式的未来用户提供了所有必要的信息，以正确校正使用该仪器获得的偏振数据中的仪器效应。方法. 2010年11月，利用CAFOS卫星16个半波片角对标准星BD+59 d389（偏振）和HD 14069（非偏振）进行了观测。用傅立叶分析法研究了CAFOS的线性偏振光谱特性。结果在4000和8600 A之间，CAFOS显示出约0.3%水平的大致恒定的仪器极化。低于4000 A时，寄生偏振增长到3600 A时达到~0.7%。这种仪器效应很可能是由望远镜的光学系统产生的，并且似乎是加性的。沃拉斯顿棱镜呈现出与理想行为的明显偏离。通过使用至少4个延迟板角度，该问题在很大程度上被消除。半波片的色差导致偏振角的~11度的峰-峰振荡。这可以有效地纠正使用本文中列出的值。傅立叶分析表明，k！在3800和7400 A之间，0.4谐波几乎可以忽略不计。结论.在对仪器偏振和延迟板色差进行校正后，采用4个半波片角，CAFOS可以达到0.1%的均方根线偏振精度。

英文摘要：

Aims. This research note presents a full analysis of the CAFOS polarimeter mounted at the Calar Alto 2.2m telescope. It also provides future users of this mode with all necessary information to properly correct for instrumental effects in polarization data obtained with this instrument. Methods. The standard stars BD+59d389 (polarized) and HD14069 (unpolarized) were observed with CAFOS in November, 2010, using 16 half-wave plate angles. The linear spectropolarimetric properties of CAFOS were studied using a Fourier Analysis of the resulting data. Results. CAFOS shows a roughly constant instrumental polarization at the level of ~0.3% between 4000 and 8600 A. Below 4000 A the spurious polarization grows to reach ~0.7% at 3600 A. This instrumental effect is most likely produced by the telescope optics, and appears to be additive. The Wollaston prism presents a clear deviation from the ideal behavior. The problem is largely removed by the usage of at least 4 retarder plate angles. The chromatism of the half-wave plate causes a peak-to-peak oscillation of ~11 degrees in the polarization angle. This can be effectively corrected using the tabulated values presented in this paper. The Fourier analysis shows that the k!=0,4 harmonics are practically negligible between 3800 and 7400 A. Conclusions. After correcting for instrumental polarization and retarder plate chromatism, with 4 half-wave plate angles CAFOS can reach an rms linear polarization accuracy of about 0.1%.

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