WIRC+Pol: A Low-resolution Near-infrared Spectropolarimeter
WIRC+Pol: A Low-resolution Near-infrared Spectropolarimeter
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DOI：
10.1088/1538-3873/aaef0f
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发表时间：
2018-07
影响因子：
3.5
通讯作者：
S. Tinyanont;M. Millar-Blanchaer;R. Nilsson;D. Mawet;H. Knutson;T. Kataria;G. Vasisht;C. Henderson;K. Matthews;E. Serabyn;J. Milburn;D. Hale;Roger M. Smith;S. Vissapragada;L. D. Santos;Jason Kekas;M. Escuti
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文献类型：
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作者：
S. Tinyanont;M. Millar-Blanchaer;R. Nilsson;D. Mawet;H. Knutson;T. Kataria;G. Vasisht;C. Henderson;K. Matthews;E. Serabyn;J. Milburn;D. Hale;Roger M. Smith;S. Vissapragada;L. D. Santos;Jason Kekas;M. Escuti
WIRC+Pol是帕洛玛天文台200英寸黑尔望远镜上的宽视场红外照相机（WIRC）的一种新的低分辨率（R 100）、近红外（J和H波段）分光偏振测量模式。该仪器采用了基于四分之一波片和偏振光栅（PG）的新型偏振计设计，可在一次曝光中提供完整的线性偏振测量（斯托克斯I，Q和U）。PG在J和H波段也有很高的透射率。该仪器位于赤道望远镜的主焦点处。结果，该系统在光路中仅具有一个反射，从而提供最小的望远镜诱导偏振。已经为WIRC+Pol开发了一个数据简化管道，以便从观测中产生线性偏振测量。WIRC+Pol自2017年2月以来一直在天空中。第一年的调试结果表明，该仪器具有偏振光栅所期望的高色散效率。我们证明了仪器的偏振稳定性与均方根变化在0.2%的水平超过30分钟的明亮的标准星星（J = 8.7）。虽然光谱提取是光子噪声限制的，但源之间的偏振校准仍然受到系统学的限制，可能与重力相关的指向效应有关。我们讨论我们在数据中发现的仪器系统学，它们的潜在原因，沿着消除它们所必需的校准。我们描述了一个调制器升级，将消除缓慢变化的系统，并提供极化精度优于0.1%。
WIRC+Pol is a newly commissioned low-resolution (R ∼ 100), near-infrared (J and H bands) spectropolarimetry mode of the Wide-field InfraRed Camera (WIRC) on the 200 inch Hale Telescope at Palomar Observatory. The instrument utilizes a novel polarimeter design based on a quarter-wave plate and a polarization grating (PG), which provides full linear polarization measurements (Stokes I, Q, and U) in one exposure. The PG also has high transmission across the J and H bands. The instrument is situated at the prime focus of an equatorially mounted telescope. As a result, the system only has one reflection in the light path providing minimal telescope induced polarization. A data reduction pipeline has been developed for WIRC+Pol to produce linear polarization measurements from observations. WIRC+Pol has been on-sky since 2017 February. Results from the first year commissioning data show that the instrument has a high dispersion efficiency as expected from the polarization grating. We demonstrate the polarimetric stability of the instrument with rms variation at 0.2% level over 30 minutes for a bright standard star (J = 8.7). While the spectral extraction is photon noise limited, polarization calibration between sources remain limited by systematics, likely related to gravity dependent pointing effects. We discuss instrumental systematics we have uncovered in the data, their potential causes, along with calibrations that are necessary to eliminate them. We describe a modulator upgrade that will eliminate the slowly varying systematics and provide polarimetric accuracy better than 0.1%.