The Impact of Bias Row Noise to Photometric Accuracy:Case Study Based on a Scientific CMOS Detector

We tested a new model of CMOS detector manufactured by the Gpixel Inc,for potential space astronomical application.In laboratory,we obtain some bias images under the typical application environment.In these bias images,clear random row noise pattern is observed.The row noise also contains some characteristic spatial frequencies.We quantitatively estimated the impact of this feature to photometric measurements,by making simulated images.We compared different bias noise types under strict parameter control.The result shows the row noise will significantly deteriorate the photometric accuracy.It effectively increases the readout noise by a factor of2-10.However,if it is properly removed,the image quality and photometric accuracy will be significantly improved.

Development and application of high-precision multifunction astronomical plate digitizers in China

Before charge-coupled device detectors became widely employed in observational astronomy,for more than a hundred years,the main detection method was photography on astronomical glass plates.Recently,in order to preserve these historical data and maintain their usability,the International Astronomical Union has appealed to all countries for global digitization of astronomical plates by developing or adopting advanced digitization technology.Specialized digitizers with high precision and high measuring speed represent key equipment for this task.The Shanghai Astronomical Observatory and the Nishimura Co.,Ltd in Japan cooperated between 2013 and 2016 to develop the first Chinese high-precision astronomical plate digitizer,which was then used for complete digitization of all nighttime-observation astronomical plates in China.Then,in 2019–2021,the Shanghai Astronomical Observatory independently developed new models of plate digitizers that enabled countries such as Uzbekistan and Italy to digitize their astronomical plates.Additionally,a new high-precision and multifunction digitizer was also used to digitize valuable microscope slides from the Shanghai Natural History Museum,providing a successful example of cross-domain application of high-precision digitization technology.

Nonlinear Variability Observed with Insight-HXMT in MAXI J1820+070 and MAXI J1535-571

We present the timing analysis of the nonlinear variability in two black hole low mass X-ray binaries MAXI J1820+070 and MAXI J1535-571 by using the bicoherence,a measure of phase coupling at different Fourier frequencies.We found different patterns,e.g.,“cross”and“hypotenuse,”for LFQPOs in different outburst states.When they can be clearly distinguished,bicoherence patterns are similar over a wide energy range of 1–100 keV.It is intriguing that in some type-C QPOs we found the patterns that are normally observed in type-B QPOs.On the contrary,the“hypotenuse”pattern,a characteristic of type-C QPOs,was detected in a type-B QPO.This suggests that different types of QPOs may originate from similar underlying mechanisms.In addition,we speculate that the nonlinear variability may be a promising approach to disentangle distinct QPO models which assume different interactions between the broadband noise and QPO components.

Preliminary Simulation and Manufacture of a 40-element PAF Prototype for FAST

This paper presents the preliminary simulation results of the prototype 40-element phased array feed(PAF)array for the Five-hundred-meter Aperture Spherical radio Telescope(FAST)and the measurement of a manufactured single Vivaldi element.The simulation results include the characteristic of a standalone Vivaldi element.The full-wave simulation of the explicit PAF array is carried out,from which the performance of the embedded elements and the mutual coupling among the elements could be accurately inferred.The performance of the combination of the PAF and the main reflector of FAST is calculated.The results imply that the PAF combined with the FAST antenna could operate over a much wider bandwidth from 650 to 1450 MHz compared with the standalone element.The antenna temperature remains almost the same for zenith angles from 0 to 40°.From the simulation results,the PAF shows good potential to improve the performance of FAST.A measurement of a manufactured Vivaldi element is also presented.

A method for aligning the plastic scintillator detector on DAMPE

The Plastic Scintillator Detector(PSD) onboard the DArk Matter Particle Explorer(DAMPE)is designed to measure cosmic ray charge(Z) and to act as a veto detector for gamma ray identification.To fully exploit the charge identification potential of PSD and to enhance its capability to identify gamma ray events, we develop an alignment method for the PSD. The path length of a given track in the volume of a PSD bar is derived taking into account the shift and rotation alignment corrections. By examining energy spectra of corner-passing events and fully contained events, position shifts and rotations of all PSD bars are obtained, and are found to be on average about 1 mm and 0.0015 radian respectively. To validate the alignment method, we introduce artificial shifts and rotations of PSD bars into the detector simulation.These shift and rotation parameters can be recovered successfully by the alignment procedure. As a result of the PSD alignment procedure, the charge resolution of the PSD is improved from 4% to 8%, depending on the nuclei.

Faint Space Debris Detection Algorithm Based on Small Aperture Telescope Detection System

Ground-based optical observation has unique advantages in space target observation.However,due to the weak light-gathering ability of small-aperture optoelectronic observation telescopes,the space debris in the image is weak and easily drowned in noise.In order to solve the above problems,we use digital image processing technology to extract faint space debris.We propose a high detection rate space debris automatic extraction algorithm,aiming to automatically detect space debris.We first establish a new space target description model.Our algorithm is mainly divided into two stages.The purpose of the first stage is to reduce the influence of a large number of stars.We perform wavelet transform and guided filtering for three consecutive frames,and the reconstructed wavelet that takes the median value can achieve the effect of eliminating stars.In the second stage,we adopt the method of robust principal component analysis and attribute the problem of target detection to the problem of separating the target and background of a single frame of image.After a large number of experimental results analysis,it is proved that the algorithm can effectively detect faint debris in the monitoring system of small aperture telescope,and has high precision and low computational complexity.

Correction and simulation of the intensity compensation algorithm used in curvature wavefront sensing

The wavefront measuring range and recovery precision of a curvature sensor can be improved by an intensity compensation algorithm. However, in a focal system with a fast f-number, especially a telescope with a large field of view, the accuracy of this algorithm cannot meet the requirements. A theoretical analysis of the corrected intensity compensation algorithm in a focal system with a fast f-number is first introduced and afterwards the mathematical equations used in this algorithm are expressed. The corrected result is then verified through simulation. The method used by such a simulation can be described as follows. First, the curvature signal from a focal system with a fast f-number is simulated by Monte Carlo ray tracing; then the wavefront result is calculated by the inner loop of the FFT wavefront recovery algorithm and the outer loop of the intensity compensation algorithm. Upon comparing the intensity compensation algorithm of an ideal system with the corrected intensity compensation algorithm, we reveal that the recovered precision of the curvature sensor can be greatly improved by the corrected intensity compensation algorithm.