Nanjing Institute of Astronomical Optics & Technology

Abstract The Shanghai Jiao Tong University Spectroscopic Telescope(JUST) holds significant importance for astronomy in China. It will assist scientists in achieving a series of influential research results in fields such as supernova explosions, identification of gravitational wave sources, and exoplanet detection with its outstanding sky survey capability and high-precision observation technology. The 4.4-meter primary mirror of JUST will adopt segmented mirror active optics technology,which could be divided into two cases: the segmented primary mirror will be in co-focus under the limit of seeing;it will be equipped with adaptive optics, and the segmented primary mirror will achieve co-phasing in the near-infrared waveband(such as 1.8 µm). This paper will focus on the research of errors of the hexagonal segments in the primary mirror under the two conditions. Additionally, separate and comprehensive error simulations were conducted, obtaining a large number of successful simulation results.

Abstract The primary reflector of the Leighton Chajnantor Telescope (LCT) is usually affected by various environmental loads and panel misalignments, both of which can significantly degrade its radiation pattern performances. To address these effects, this paper focuses on optimizing actuator adjustments and proposes a Mixed-Integer Nonlinear Programming (MINLP) model that takes key radiation pattern performance indicators as the optimization objective. Recognizing the limitations of traditional optimization methods, which are prone to falling into local optima due to high-dimensional and complex nonlinear constraints, and struggle to optimize both actuator positions and adjustment values simultaneously, we introduce an enhanced genetic algorithm combined with a heuristic actuator selection rule, which
efficiently solves the beam performance optimization problem by regulating part of the actuators. Notably, the approach demonstrates a significant reduction in the magnitude of the pointing deviation (PD), achieving approximately 80% of decrease when utilizing 20 actuators. Furthermore, with the application of 40 actuators, the method successfully reduces the RMS surface error induced by gravitational deformation to below 12 µm across all zenith angles. The proposed method is applied to typical deformation scenarios caused by environmental loads and panel misalignments, resulting in actuator adjustment schemes for varying numbers of actuators. A systematic evaluation of each scheme’s impact on beam performances is provided, and further analysis reveals the relationship between actuator position distribution, adjustment values, and surface error. Additionally, the influence of surface error distributions on the selection of key actuators is systematically revealed.

This paper focuses on the phase distortion problem caused by atmospheric turbulence and conducts research based on titanium alloy metal adaptive ultra-thin mirrors by using numerical simulation and modeling methods. Specifically, the Zernike polynomial method was adopted to simulate the distorted wavefront of atmospheric turbulence, and the simulation results were verified. Based on the finite element analysis results of the metal ultra-thin mirror, the influence function of a single actuator was fitted using the super-Gaussian function. The correlation coefficient for the matching degree of the obtained influence function exceeded 0.9. Then, the distorted wavefront was corrected by the fitted influence function. After correction, the root means square value (RMS) of the distorted wavefront decreased by 77.56%, which verified the feasibility of correcting wavefront distortion with titanium alloy metal mirrors.

Abstract We present the Mid-Infrared Instrument (MIRI) Extended Groth Strip (EGS) Galaxy and Active Galactic Nucleus (MEGA) survey, a four-band MIRI survey with 25 pointings in the EGS extragalactic field. Three pointings utilized only the three reddest bands (F1000W, F1500W, and F2100W), while the remainder also included a blue filter (F770W). MEGA builds upon the existing observations in the EGS field by providing MIRI imaging for 68.9% of CEERS NIRCam imaging, filling a crucial gap in order to understand galaxy evolution by observing the obscured Universe. Here, we present the technical design, data reduction, photometric catalog creation for our first data release, and science drivers of the MEGA survey. Our data reduction starts with the standard James Webb Space Telescope calibration pipeline but adds additional warm pixel masking and custom background subtraction steps to improve the quality of the final science image. We estimate the image depth of the reduced mosaics and present new galaxy number counts in four MIRI bands.

This paper presents an in-depth study of the application of Active Disturbance Rejection Control (ADRC) in the high-precision motion control system of the “WeHoST” 2.5-meter large-aperture telescope using a Programmable Multi-Axis Controller (PMAC). The goal is to enhance the telescope's tracking accuracy and stability under complex environmental conditions. In response to disturbances encountered during the telescope's observation process, an optimized solution based on ADRC was designed and implemented. At first, based on ADRC theory, a controller architecture was constructed, incorporating an Extended State Observer (ESO) and a Nonlinear State Error Feedback (NLSEF) control law. Subsequently, the key parameters of the controller were determined according to the specific parameters and performance requirements of the “WeHoST” telescope to ensure the controller's fast response and stability. The ADRC was then implemented in the PMAC control system, and the telescope's position was monitored in real-time using high-precision encoders. Experimental data show that the positioning accuracy of the “WeHoST” telescope was significantly improved after the introduction of ADRC. In dynamic tracking tests, the tracking error decreased from 0.01817” to 0.01261”, a reduction of approximately 30.59%. The PP(Peak to Peak) value decreased from 0.04585” to 0.03201”, a reduction of approximately 30.18%, significantly enhancing the telescope's tracking accuracy and stability. The study successfully applied ADRC to the main axes of the “WeHoST” telescope. demonstrating its effectiveness in improving the tracking accuracy and stability of the telescope. It provides valuable insights and references for instruments requiring high-precision motion control.

This work is devoted to the study of the effect of the oscillating Poiseuille flow on the diffraction of light passing through a nematic layer bounded by a submicron relief at one of the inner surfaces of the plane capillary. In experimental nematic liquid crystal (NLC) cells with a hybrid planar–homeotropic orientation, a photo-profiled PAZO polymer layer with a sinusoidal relief with a depth of 180 and 360 nm and a period of 2 μm was used as a diffraction grating. The experimentally obtained dependencies of the flow-induced changes in the intensity of polarized light at the main and the first diffraction maxima on the amplitude of the low-frequency oscillating pressure gradient applied to the NLC layer are presented. Processing of the obtained results indicates the possibility of modulating the intensity of diffracted polarized light transmitted through the NLC layer by up to 10% when applying an oscillating pressure difference of up to 700 Pa to the layer of corresponding experimental cells in the absence of an analyzer in the optical scheme. Possible mechanisms responsible for the modulation of optical radiation in the main and first diffraction maxima are discussed. The discussed principles of controlling diffracted electromagnetic radiation can be used to create optofluidic modulators operating in both the visible and THz ranges.

This paper introduces a novel dual-functional calibration source for astronomical spectrographs. The light source primarily consists of a supercontinuum light source, a dispersion system, and a digital micromirror device (DMD) spatial light modulator. The intensity of each dispersed spectral component of the supercontinuum can be precisely adjusted by accurately controlling the proportion of micromirrors in the “on” and “off” states, with each micromirror being individually addressable. Utilizing this programmable spectral functionality, we have designed two different calibration modes for astronomical spectrographs. The first mode is “flat spectrum” for flat-field calibration; the second mode is “narrow-band filter” for testing and calibrating the system's optical efficiency.

Aims. This work aims to investigate the coevolution of metals and dust for 173 galaxies at 4.0 < z ≤ 11.4 spectroscopically observed by the NIRSpec instrument onboard the James Webb Space Telescope (JWST) in the Cosmic Evolution Early Release Science Survey (CEERS) project. More specifically, we want to study and analyse the properties of a sample of galaxies that show an extremely low dust attenuation and try to understand the possible physical processes at play in these galaxies. Methods. We developed a new version of the CIGALE code that accepts spectroscopic and photometric data. From a statistical comparison of the observations with the modelled spectra, we derived a set of physical parameters that allowed us to constrain the above physical processes. Results. Our analysis reveals a population of 49 extremely low-dust-attenuation galaxies (GELDAs) consistent with AFUV = 0.0 within 2σA_FUV and Mstar<109 M⊙. After stacking the spectra of the 49 GELDAs to increase the signal-to-noise ratio, we measured a very blue UV slope of βFUV=−2.451±0.066 and a Balmer decrement of Hα/Hβ = 2.932±0.660 without underlying absorption and consistent with no dust attenuation; Case B assumes an underlying absorption of 2.5%. Furthermore, the proportion of GELDAs is much higher at z > 8.8 (83.3% of the total sample) than at z < 8.8 (26.3% of the total sample). This suggests that GELDAs became dominant in the early Universe. Assuming a prior far-infrared dust spectrum from the ALPINE sample, we performed an analysis of the properties of this galaxy population. The trends observed in the Mdust versus Mstar diagram feature an upper and a lower sequence linked by objects that can be transitional. A comparison with models suggests that we might observe a critical transition at Mstar≈108.5 M⊙, corresponding to a critical metallicity of Zcrit = 12+log10(O/H) ≈ 7.60 (i.e. Z/Z⊙≈0.1). At this point, galaxies transition from being dominated by stellar-dust production (mainly from supernovae) to grain growth through gas–dust accretion in the ISM. The observational critical metallicity Zcrit derived in this paper is in good agreement with predictions from theoretical models for the onset of efficient grain growth. Furthermore, the mean gas-mass fraction of our entire sample at 4.0 < z < 11.4 is very high: fgas≳0.9. All of our galaxies, including GELDAs at all redshifts, contain a large amount of gas that was not expelled from the galaxies. Finally, the small size of the galaxies combined with the mass of gas lead to very high surface-gas densities – which put our sample below high-redshift sub-millimeter galaxies – at relatively low star formation efficiency. The population of high-redshift GELDAs would provide us with a natural and inherent explanation for the origin of the apparent tension between observations and theoretical models in the number density of bright galaxies at z ≳ 9.

Abstract This study utilized Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) low-resolution spectra to identify M-type young stellar objects (YSOs) and characterize their accretion signatures. We measured characteristic features, including hydrogen Balmer, Li i, He i, Na i, and Ca ii lines, as well as molecular absorption bands such as CaH. These features were evaluated for their potential to distinguish between different classes of M-type stars. In addition to the commonly used Hα emission and Li i λ6708 absorption, other features such as He i, Na i, Ca ii HK and infrared triplet (IRT) lines, and CN, CaH, and VO bands also show potential for identifying YSOs from M-type dwarfs and giants. Based on key red-band features, we identified over 8500 M-type YSO candidates from the LAMOST DR8 archive using the random forest technique, with over 2300 of them likely being classical T Tauri stars (CTTSs). By incorporating Gaia astrometry, Two Micron All Sky Survey photometry, and extinction from 3D dust maps, we estimated the basic properties (such as age and mass) of the YSO candidates based on parsec models. We also estimated the mass accretion rates of the CTTS candidates using Hα emission. The derived accretion rates show a dependence on age and mass similar to that described in previous studies. Significant scatter in mass accretion rates exists even among stars with a similar age and mass, which may be partly attributed to variations in Hα emission and the veiling.