Polarimetric Differential Imaging with VLT/NACO. A comprehensive PDI pipeline for NACO data (PIPPIN)

This dataset consists of the reduced data products generated with PIPPIN (PDI pipeline for NACO data). PIPPIN employs the Polarimetric Differential Imaging (PDI) technique to distinguish the polarised scattered light from the (largely) un-polarised stellar light. As a result, circumstellar dust can be uncovered around young stellar objects. PIPPIN was specifically developed to reduce the archival polarimetric observations made by the VLT/NACO instrument. During its operation, NACO employed different instrument configurations (e.g. half-wave plate or de-rotator usage, Wollaston beam-splitter or wiregrid observations) which are appropriately handled by PIPPIN. As part of the PDI reduction, PIPPIN performs various levels of corrections for instrumental polarisation and crosstalk. Documentation for the PIPPIN pipeline can be found here. If you use PIPPIN or PIPPIN-reduced data products for your publication, we ask you to cite our paper. The dataset is sorted per (potential) young stellar object and sub-divided into the respective nights of observation (if applicable). Within the pipeline_output/ directories, the data are sorted by the utilised observing strategy (<OBS_ID>_<EXPTIME>_<FILTER>/). The _beams.fits files comprise the sky-subtracted, cropped images that are used to generate the PDI data products in the PDI/ directory. Depending on the observations, the PDI/ directory contains the following files: Total intensities: I.fits: Total intensity \(I = \frac{1}{2}(I_{Q}+I_{U})\).[CUBE_I, MEDIAN_I, CUBE_I_CTC, MEDIAN_I_CTC] I_Q.fits: Intensity as \(I_Q = \frac{1}{2}(I_{Q^+}+I_{Q^-})\).[CUBE_I_Q, MEDIAN_I_Q] I_Q+.fits: Intensity of \(Q^+\) measurements.[CUBE_I_Q+, MEDIAN_I_Q+] I_Q-.fits: Intensity of \(Q^-\) measurements.[CUBE_I_Q-, MEDIAN_I_Q-] I_U.fits: Intensity as \(I_U = \frac{1}{2}(I_{U^+}+I_{U^-})\).[CUBE_I_U, MEDIAN_I_U, CUBE_I_U_CTC, MEDIAN_I_U_CTC] I_U+.fits: Intensity of \(U^+\) measurements.[CUBE_I_U+, MEDIAN_I_U+, CUBE_I_U+_CTC, MEDIAN_I_U+_CTC] I_U-.fits: Intensity of \(U^-\) measurements.[CUBE_I_U-, MEDIAN_I_U-, CUBE_I_U+_CTC, MEDIAN_I_U-_CTC] Stokes parameters: Q.fits: Stokes \(Q = \frac{1}{2}(Q^+-Q^-)\). [CUBE_Q, MEDIAN_Q, MEDIAN_Q_IPS, MEDIAN_Q_CTC_IPS] Q+.fits: Stokes \(Q^+=I_\mathrm{ord}-I_\mathrm{ext}\).[CUBE_Q+, MEDIAN_Q+] Q-.fits: Stokes \(Q^-=I_\mathrm{ord}-I_\mathrm{ext}\). [CUBE_Q-, MEDIAN_Q-] U.fits: Stokes \(U = \frac{1}{2}(U^+-U^-)\).[CUBE_U, MEDIAN_U, MEDIAN_U_IPS, MEDIAN_U_CTC_IPS] U+.fits: Stokes \(U^+=I_\mathrm{ord}-I_\mathrm{ext}\).[CUBE_U+, MEDIAN_U+] U-.fits: Stokes \(U^-=I_\mathrm{ord}-I_\mathrm{ext}\). [CUBE_U-, MEDIAN_U-] Final polarised light products: PI.fits: Polarised intensity \(PI = \sqrt{Q^2+U^2}\).[PI, PI_R2, PI_IPS, PI_IPS_R2, PI_CTC_IPS, PI_CTC_IPS_R2] Q_phi.fits: Azimuthal Stokes parameter \(Q_\phi = -Q\cos 2\phi - U\sin 2\phi\).[Q_PHI, Q_PHI_R2, Q_PHI_IPS, Q_PHI_IPS_R2, Q_PHI_CTC_IPS, Q_PHI_CTC_IPS_R2, Q_PHI_UPC_CTC_IPS, Q_PHI_UPC_CTC_IPS_R2] U_phi.fits: Azimuthal Stokes parameter \(U_\phi = +Q\sin 2\phi - U\cos 2\phi\).[U_PHI, U_PHI_R2, U_PHI_IPS, U_PHI_IPS_R2, U_PHI_CTC_IPS, U_PHI_CTC_IPS_R2, U_PHI_UPC_CTC_IPS, U_PHI_UPC_CTC_IPS_R2] The values given in brackets [] are the fits extensions. CUBE_ extensions are given for each cycle, while MEDIAN_ indicates the median-combination of the CUBE_ images. The extension _IPS gives the instrumental-polarisation subtracted result, _CTC gives the crosstalk-corrected image, and _UPC gives the \(U_\phi\)-minimised result. _R2-products are scaled by the squared projected radius. _EXTENDED data products are generated if the position angle was rotated, rather than the half-wave plate, to obtain the linear Stokes parameters. The position-angle rotation permits a broader coverage of the sky, which results in images with the characteristic shape of an eight-pointed star.本数据集包含由PIPPIN（用于NACO数据的PDI处理管线）生成的精简数据产品。PIPPIN采用偏振差分成像（Polarimetric Differential Imaging, PDI）技术，将偏振散射光与（主要）非偏振恒星光区分开来，借此可探测年轻恒星天体周围的星周尘埃。PIPPIN是专门为处理VLT/NACO仪器获取的归档偏振观测数据而开发的。在运行过程中，NACO会采用不同的仪器配置（例如半波片或消旋器的使用、沃拉斯顿分束器或线栅观测模式），而PIPPIN可对这些配置进行恰当处理。作为PDI数据处理的一部分，PIPPIN会对仪器偏振和串扰进行多等级校正。 PIPPIN管线的相关文档可在此处查阅。若您的研究成果中使用了PIPPIN或经PIPPIN处理的数据产品，请引用我们的相关论文。 本数据集按（潜在）年轻恒星天体进行分组，并根据观测夜进一步细分（如适用）。在pipeline_output/目录下，数据按照所用观测策略进行分类，目录命名格式为<OBS_ID>_<EXPTIME>_<FILTER>/。其中的_beams.fits文件包含经天空减除、裁剪后的图像，这些图像用于在PDI/目录下生成PDI数据产品。 根据观测需求的不同，PDI/目录下包含以下几类文件： 总强度图像： I.fits：总强度 (I = frac{1}{2}(I_{Q}+I_{U}))，包含扩展名组[CUBE_I, MEDIAN_I, CUBE_I_CTC, MEDIAN_I_CTC] I_Q.fits：强度定义为 (I_Q = frac{1}{2}(I_{Q^+}+I_{Q^-}))，包含扩展名组[CUBE_I_Q, MEDIAN_I_Q] I_Q+.fits：(Q^+) 测量对应的强度图像，包含扩展名组[CUBE_I_Q+, MEDIAN_I_Q+] I_Q-.fits：(Q^-) 测量对应的强度图像，包含扩展名组[CUBE_I_Q-, MEDIAN_I_Q-] I_U.fits：强度定义为 (I_U = frac{1}{2}(I_{U^+}+I_{U^-}))，包含扩展名组[CUBE_I_U, MEDIAN_I_U, CUBE_I_U_CTC, MEDIAN_I_U_CTC] I_U+.fits：(U^+) 测量对应的强度图像，包含扩展名组[CUBE_I_U+, MEDIAN_I_U+, CUBE_I_U+_CTC, MEDIAN_I_U+_CTC] I_U-.fits：(U^-) 测量对应的强度图像，包含扩展名组[CUBE_I_U-, MEDIAN_I_U-, CUBE_I_U+_CTC, MEDIAN_I_U-_CTC] 斯托克斯参数图像： Q.fits：斯托克斯参数 (Q = frac{1}{2}(Q^+-Q^-))，包含扩展名组[CUBE_Q, MEDIAN_Q, MEDIAN_Q_IPS, MEDIAN_Q_CTC_IPS] Q+.fits：斯托克斯参数 (Q^+=I_mathrm{ord}-I_mathrm{ext})，包含扩展名组[CUBE_Q+, MEDIAN_Q+] Q-.fits：斯托克斯参数 (Q^-=I_mathrm{ord}-I_mathrm{ext})，包含扩展名组[CUBE_Q-, MEDIAN_Q-] U.fits：斯托克斯参数 (U = frac{1}{2}(U^+-U^-))，包含扩展名组[CUBE_U, MEDIAN_U, MEDIAN_U_IPS, MEDIAN_U_CTC_IPS] U+.fits：斯托克斯参数 (U^+=I_mathrm{ord}-I_mathrm{ext})，包含扩展名组[CUBE_U+, MEDIAN_U+] U-.fits：斯托克斯参数 (U^-=I_mathrm{ord}-I_mathrm{ext})，包含扩展名组[CUBE_U-, MEDIAN_U-] 最终偏振光产品： PI.fits：偏振强度 (PI = sqrt{Q^2+U^2})，包含扩展名组[PI, PI_R2, PI_IPS, PI_IPS_R2, PI_CTC_IPS, PI_CTC_IPS_R2] Q_phi.fits：方位角斯托克斯参数 (Q_phi = -Qcos 2phi - Usin 2phi)，包含扩展名组[Q_PHI, Q_PHI_R2, Q_PHI_IPS, Q_PHI_IPS_R2, Q_PHI_CTC_IPS, Q_PHI_CTC_IPS_R2, Q_PHI_UPC_CTC_IPS, Q_PHI_UPC_CTC_IPS_R2] U_phi.fits：方位角斯托克斯参数 (U_phi = +Qsin 2phi - Ucos 2phi)，包含扩展名组[U_PHI, U_PHI_R2, U_PHI_IPS, U_PHI_IPS_R2, U_PHI_CTC_IPS, U_PHI_CTC_IPS_R2, U_PHI_UPC_CTC_IPS, U_PHI_UPC_CTC_IPS_R2] 方括号[]内的数值为该fits文件的扩展名标识。其中CUBE_为对应每个观测循环的扩展名，MEDIAN_表示对CUBE_系列图像进行中值合并后的结果。后缀_IPS代表已扣除仪器偏振的处理结果，_CTC代表已完成串扰校正的图像，_UPC代表已实现(U_phi)最小化的结果。_R2系列产物已按投影半径的平方进行缩放。 若通过旋转位置角而非半波片来获取线性斯托克斯参数，则会生成_EXTENDED扩展数据产品。旋转位置角可实现更宽的天空覆盖范围，最终得到具有八角星特征形状的图像。