POLICAN：2.1米OAGH望远镜上的近红外成像偏振计
POLICAN: A Near-infrared Imaging Polarimeter at the 2.1m OAGH Telescope
摘要：
POLICAN是一种近红外成像线性偏振仪，为位于墨西哥索诺拉州卡纳内阿的吉列尔莫·哈罗天体物理观测站（OAGH）的2.1米望远镜上的卡纳内阿近红外相机（CANICA）开发。POLICAN安装在CANICA之前，由一个旋转的超消色差1-2.7微米半波片（HWP）作为调制器和一个固定的线栅偏振器作为分析器组成。CANICA有一个1024 x 1024的碲镉汞探测器，板级为0.32弧秒/像素，视场为5.5 x 5.5弧分^[2]。偏振观测是通过半波片角度0、22.5、45、67.5度的不同步长调制入射光来进行的，以建立线性斯托克斯参数（I、Q和U）。图像缩减包括暗减法、偏振平场和天空减法。天体测量和测光校准是使用两微米全天巡天的公开数据进行的。偏振校准包括观测球状星团和偏振标准在文献中。对球状星团多次观测的分析得出仪器偏振度为0.51%。从最亮的7等星到最暗的16等星，偏振度的范围从0.1%到10%不等。对于H波段亮度大于13等的恒星，其偏振测量精度优于0.5%，位置角误差小于5 °。POLICAN主要用于研究星际介质中恒星形成区域及其周围的散射极化和磁场。
英文摘要：
POLICAN is a near-infrared imaging linear polarimeter developed for the Cananea Near-infrared Camera (CANICA) at the 2.1m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, Mexico. POLICAN is mounted ahead of CANICA and consist of a rotating super-achromatic 1-2.7 micron half-wave plate (HWP) as the modulator and a fixed wire-grid polarizer as the analyzer. CANICA has a 1024 x 1024 HgCdTe detector with a plate scale of 0.32 arcsec/pixel and provides a field of view of 5.5 x 5.5 arcmin^2. The polarimetric observations are carried out by modulating the incoming light through different steps of half-wave plate angles 0, 22.5, 45, 67.5 deg, to establish linear Stokes parameters (I, Q, and U). Image reduction consists of dark subtraction, polarimetric flat fielding, and sky subtraction. The astrometry and photometric calibrations are performed using the publicly available data from the Two Micron All Sky Survey. Polarimetric calibration includes observations of globular clusters and polarization standards available in the literature. Analysis of multiple observations of globular clusters yielded an instrumental polarization of 0.51%. Uncertainties in polarization range from 0.1% to 10% from the brightest 7 mag to faintest 16 mag stars. The polarimetric accuracy achieved is better than 0.5% and the position angle errors less than 5 deg for stars brighter than 13 mag in H-band. POLICAN is mainly being used to study the scattered polarization and magnetic fields in and around star-forming regions of the interstellar medium.
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