Precise photometric and astrometric measurements on astronomical images require an accurate knowledge of the Point Spread Function (PSF). When the PSF cannot be modelled directly from the image, PSF-reconstruction techniques become the only viable solution. So far, however, their performance on real observations has rarely been quantified. Aims. In this Letter, we test the performance of a novel hybrid technique, called PRIME, on Adaptive Optics-assisted SPHERE/ZIMPOL observations of the Galactic globular cluster NGC6121. Methods. PRIME couples PSF-reconstruction techniques, based on control-loop data and direct image fitting performed on the only bright point-like source available in the field of view of the ZIMPOL exposures, with the aim of building the PSF model. Results. By exploiting this model, the magnitudes and positions of the stars in the field can be measured with an unprecedented precision, which surpasses that obtained by more standard methods by at least a factor of four for on-axis stars and by up to a factor of two on fainter, off-axis stars. Conclusions. Our results demonstrate the power of PRIME in recovering precise magnitudes and positions when the information directly coming from astronomical images is limited to only a few point-like sources and, thus, paving the way for a proper analysis of future Extremely Large Telescope observations of sparse stellar fields or individual extragalactic objects.
Pushing Point spread function reconstruction to the next level. Application to SPHERE/ZIMPOL
点扩散函数（PSF）重建（PSF-R）是一种成熟的技术，用于从自适应光学（AO）控制回路数据可靠且准确地确定PSF。我们已经成功地应用这种技术，以提高精度的测光和天体测量的观测NGC 6121获得的SPHERE/ZIMPOL，因为它将在即将到来的信。首先，我们介绍了使用我们的PSF-R方法PRIME（Beltramo-Martin et al. 2019）结合光瞳平面和焦平面测量重建PSF的方法，与之前的论文相比，模型和最佳拟合步骤都进行了升级。其次，我们强调，PRIME允许保持PSF拟合残差低于0.2%，超过2小时的观察，仅使用30秒的AO遥测，这可能对未来30-40米级望远镜的PSF-R遥测存储的重要后果。最后，我们部署PRIME在一个更现实的制度，使用微弱的恒星，以确定所需的精度对初始猜测参数，以确保收敛到最优解。
Modelling the Point Spread Function of ILMT images
Aryabhatta Research Institute of Observational Sciences (ARIES)（阿里亚巴塔观测科学研究所）；Mahatma Jyotiba Phule Rohilkhand University（马哈特马·乔提巴·普尔罗希勒坎德大学）；Physical Research Laboratory（物理研究实验室）；National University of Uzbekistan（乌兹别克斯坦国立大学）；Ulugh Beg Astronomical Institute of the Uzbek Academy of Sciences（乌兹别克斯坦科学院乌鲁伯格天文研究所）；Institute of Astrophysics and Geophysics, Liège University（列日大学天体物理学与地球物理学研究所）；Department of Physics and Astronomy, The University of British Columbia（不列颠哥伦比亚大学物理与天文学系）；Outer Space Institute, The University of British Columbia（不列颠哥伦比亚大学外层空间研究所）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学柯夫利天体物理学研究所）；Department of Applied Optics and Photonics, University of Calcutta（加尔各答大学应用光学与光子学系）
Point Spread Function Estimation for Wide Field Small Aperture Telescopes with Deep Neural Networks and Calibration Data
Taiyuan University of Technology（太原理工大学）；Durham University（杜伦大学）；Nanjing Institute of Astronomical Optics and Technology CAS（中国科学院南京天文光学技术研究所）；Silesian University of Technology（西里西亚工业大学）
COCOA Code for Creating Mock Observations of Star Cluster Models
我们介绍和目前的结果从COCOA（集群simulatiOn比较与ObservAtions）代码，已开发出理想化的模拟光度观测星团演化的数值模拟结果。COCOA能够提供使用蒙特卡罗或\textit{N}体代码对星团进行的真实数值模拟的输出，这种方式有助于与光度观测进行直接比较。本文介绍了COCOA程序，并利用MOCCA程序模拟的球状星团（GC）模型演示了COCOA程序的不同应用。COCOA被用来用光学望远镜综合观测这些不同的GC模型，进行PSF测光，随后产生观测到的色星等图。我们还使用COCOA比较的结果，从一个集群模型，具有相同的年龄和金属丰度的银河系GC NGC 2808与同一集群的观测进行了2.2米的光学望远镜的合成观测。我们发现，COCOA可以有效地模拟现实的观测和恢复光度数据。COCOA有许多科学应用，可能对研究星团的理论家和观测者都有帮助。本文还讨论了进一步改进和发展该代码的计划。
The Panchromatic High-Resolution Spectroscopic Survey of Local Group Star Clusters - I. General Data Reduction Procedures for the VLT/X-shooter UVB and VIS arm
