Astrometry.net与SCAMP在天测位置定标中的应用研究

为探究Astrometry.net和SCAMP两款软件在天测位置定标时的应用差异以及以不同方式运行软件所得定标效果的差异,分别介绍了两款软件位置定标的原理,以ZTF(Zwicky Transient Facility)的100张巡天图像为测试图像,以Gaia DR2为参考星表,分别以4种不同的定标流程对测试图像进行了位置定标。从计算总耗时、星表匹配情况和坐标均方根(Root Mean Square,RMS)偏差3个方面,比较了不同流程所得定标的结果,同时也与ZTF给出的定标结果进行了对比。结果表明,Astrometry.net能够快速给出粗略的线性定标结果,SCAMP可以快速在前者的基础上直接进行扭曲修正,两者相结合的定标流程平均耗时仅为1 s,所得定标结果的平均赤经赤纬均方根偏差均小于70毫角秒(小于0.1个像素),优于仅使用Astrometry.net所得定标结果。由此可见,搭配使用Astrometry.net和SCAMP可以实现更快速且更准确的天测位置定标,可推广应用到时域天文巡天项目的数据处理上。

The Possibility of Detecting our Solar System through Astrometry

Searching for exoplanets with different methods has always been the focus of astronomers over the past few years.Among multiple planet detection techniques,astrometry stands out for its capability to accurately determine the orbital parameters of exoplanets.In this study,we examine the likelihood of extraterrestrial intelligent civilizations detecting planets in our solar system using the astrometry method.By conducting injection-recovery simulations,we investigate the detectability of the four giant planets in our solar system under different observing baselines and observational errors.Our findings indicate that extraterrestrial intelligence could detect and characterize all four giant planets,provided they are observed for a minimum of 90 yr with signal-noise ratios exceeding 1.For individual planets such as Jupiter,Saturn,and Neptune,a baseline that surpasses half of their orbital periods is necessary for detection.However,Uranus requires longer observing baselines since its orbital period is roughly half of that of Neptune.If the astrometry precision is equal to or better than 10μas,all 8707 stars located within30 pc of our solar system possess the potential to detect the four giant planets within 100 yr.Additionally,our prediction suggests that over 300 stars positioned within 10 pc from our solar system could detect our Earth if they achieve an astrometry precision of 0.3μas.

Improved astrometry of space debris with image restoration

In order to implement an observing strategy, image degradation that occurs during optical observation of space debris is ineluctable and has distinct characteris- tics. Image restoration is presented as a way to remove the influence of degradation in CCD images of space debris, based on assumed PSF models with the same F-WHM as images of the object. In the process of image restoration, the maximum entropy method is adopted. The results of reduction using observed raw CCD images indi- cate that the precision in estimating positions of objects is improved and the effects of degradation are reduced. Improving the astrometry of space debris using image restoration is effective and feasible.

Astrometry of three near Earth asteroids with the Lijiang 2.4 m telescope

Under the framework of observational campaigns organized by the GAIA Follow Up Network for Solar System Objects, three near Earth asteroids, 367943 Duende, 99942 Apophis and 2013 TV135, were observed with the Lijiang 2.4m telescope administered by Yunnan Observatories. The software package PRISM was used to calibrate the CCD fields and measure the positions of 99942 Apophis and 2013 TV135, and our own software was used for 367943 Duende. A comparison of the results show that the ephemerides of INPOP10a and JPL are consistent for 99942 Apophis and 2013 TV135, however, they are quite inconsistent for 367943 Duende. Moreover, we have found that differences between the mean values in the ephemerides of INPOP10a and JPL are about 72＂ and -199＂ in right ascension and declination respectively for 367943 Duende. Moreover, the ephemeris published by JPL is reliable in terms of the mean observed-minus-calculated （O - C） residuals in right ascension and declination of about 2.72＂ and 1.49＂ respectively.

Leveraging the Empirical Wavelet Transform in Combination with Convolutional LSTM Neural Networks to Enhance the Accuracy of Polar Motion Prediction

High-precision polar motion prediction is of great significance for deep space exploration and satellite navigation.Polar motion is affected by a variety of excitation factors,and nonlinear prediction methods are more suitable for polar motion prediction.In order to explore the effect of deep learning in polar motion prediction.This paper proposes a combined model based on empirical wavelet transform(EWT),Convolutional Neural Networks(CNN)and Long Short Term Memory(LSTM).By training and forecasting EOP 20C04 data,the effectiveness of the algorithm is verified,and the performance of two forecasting strategies in deep learning for polar motion prediction is explored.The results indicate that recursive multi-step prediction performs better than direct multi-step prediction for short-term forecasts within 15 days,while direct multi-step prediction is more suitable for medium and long-term forecasts.In the 365 days forecast,the mean absolute error of EWT-CNN-LSTM in the X direction and Y direction is 18.25 mas and 15.78 mas,respectively,which is 23.5% and 16.2% higher than the accuracy of Bulletin A.The results show that the algorithm has a good effect in medium and long term polar motion prediction.

The Velocity Aberration Effect of the CSST Main Survey Camera

In this study,we conducted simulations to find the geometric aberrations expected for images taken by the Main Survey Camera of the Chinese Space Station Telescope(CSST)due to its motion.As anticipated by previous work,our findings indicate that the geometric distortion of light impacts the focal plane's apparent scale,with a more pronounced influence as the size of the focal plane increases.Our models suggest that the effect consistently influences the pixel scale in both the vertical and parallel directions.The apparent scale variation follows a sinusoidal distribution throughout one orbital period.Simulations reveal that the effect is particularly pronounced in the center of the Galaxy and gradually diminishes along the direction of ecliptic latitude.At low ecliptic latitudes,the total aberration leads to about a 0.94 pixel offset(a 20 minute exposure)and a 0.26 pixel offset(a 300 s exposure)at the edge of the field of view.Appropriate processings for the geometric effect during the CSST pre-and post-observation phases are presented.

A Preliminary Comparative Study on the Centering Algorithms for CassiniISS NAC Images

Obtaining high precision is an important consideration for astrometric studies using images from the Narrow Angle Camera(NAC)of the Cassini Imaging Science Subsystem(ISS).Selecting the best centering algorithm is key to enhancing astrometric accuracy.In this study,we compared the accuracy of five centering algorithms:Gaussian fitting,the modified moments method,and three point-spread function(PSF)fitting methods(effective PSF(ePSF),PSFEx,and extended PSF(x PSF)from the Cassini Imaging Central Laboratory for Operations(CICLOPS)).We assessed these algorithms using 70 ISS NAC star field images taken with CL1 and CL2 filters across different stellar magnitudes.The ePSF method consistently demonstrated the highest accuracy,achieving precision below 0.03 pixels for stars of magnitude 8-9.Compared to the previously considered best,the modified moments method,the e PSF method improved overall accuracy by about 10%and 21%in the sample and line directions,respectively.Surprisingly,the xPSF model provided by CICLOPS had lower precision than the ePSF.Conversely,the ePSF exhibits an improvement in measurement precision of 23%and 17%in the sample and line directions,respectively,over the xPSF.This discrepancy might be attributed to the xPSF focusing on photometry rather than astrometry.These findings highlight the necessity of constructing PSF models specifically tailored for astrometric purposes in NAC images and provide guidance for enhancing astrometric measurements using these ISS NAC images.

Fast Two-dimensional Positioning Method of Crab Pulsar Based on Multiple Optimization Algorithms

In the two-dimensional positioning method of pulsars, the grid method is used to provide non-sensitive direction and positional estimates. However, the grid method has a high computational load and low accuracy due to the interval of the grid. To improve estimation accuracy and reduce the computational load, we propose a fast twodimensional positioning method for the crab pulsar based on multiple optimization algorithms(FTPCO). The FTPCO uses the Levenberg–Marquardt(LM) algorithm, three-point orientation(TPO) method, particle swarm optimization(PSO) and Newton–Raphson-based optimizer(NRBO) to substitute the grid method. First, to avoid the influence of the non-sensitive direction on positioning, we take an orbital error and the distortion of the pulsar profile as optimization objectives and combine the grid method with the LM algorithm or PSO to search for the non-sensitive direction. Then, on the sensitive plane perpendicular to the non-sensitive direction, the TPO method is proposed to fast search the sensitive direction and sub-sensitive direction. Finally, the NRBO is employed on the sensitive and sub-sensitive directions to achieve two-dimensional positioning of the Crab pulsar. The simulation results show that the computational load of the FTPCO is reduced by 89.4% and the positioning accuracy of the FTPCO is improved by approximately 38% compared with the grid method. The FTPCO has the advantage of high real-time accuracy and does not fall into the local optimum.

Astrometric Observations of NEA 1998 HH49 Using the Daocheng 50 cm Telescope

This study details an astrometric observation campaign of the Near-Earth Asteroid 1998 HH49,conducted with the aim of refining our understanding of its physical characteristics.Utilizing the 50 cm telescope located at the Wumingshan Mountain in Daocheng,Sichuan,images were obtained over four nights,from 2023 October 19 to October 22.These observations were processed using Astrometrica software,facilitating the precise determination of the asteroid's position.The observational results were compared with the ephemerides from three distinct sources to verify accuracy:the Jet Propulsion Laboratory(JPL)Horizons System,the Institut de Mécanique Céleste et de Calcul deséphémérides(IMCCE)Miriade,and the Near-Earth Objects Dynamic Site(NEODyS-2).When compared with the JPL ephemeris,a mean observed-minus-calculated(O-C)result of 0.″07 in the R.A.direction and-0.″35 in the decl.direction was yielded.Furthermore,the comparison with the IMCCE ephemeris yielded mean O-C results of 0.″08 in the R.A.direction and-0.″06 in the decl.direction.The comparison with the NEODyS-2 ephemeris yielded the mean O-C results of 0.″06 in R.A.and-0.″49 in decl.direction.The study's findings demonstrate a general consistency between the observed data and the ephemeris predictions,with minor discrepancies observed across the data sets.Notably,both the JPL and NEODyS-2 ephemerides show that the residuals in the decl.direction exceed those in the R.A.direction.The disparities may result from atmospheric differential color refraction,ephemeris discrepancies,observational errors,and other factors.Additionally,it is worth noting that further investigation is required due to the potential influence of additional factors.Overall,the Daocheng 50 cm Telescope exhibits the ability to conduct high-precision positional measurements.

All-sky Guide Star Catalog for CSST

The China Space Station Telescope(CSST)is a two-meter space telescope with multiple back-end instruments.The Fine Guidance Sensor(FGS)is an essential subsystem of the CSST Precision Image Stability System to ensure the required absolute pointing accuracy and line-of-sight stabilization.In this study,we construct the Main Guide Star Catalog for FGS.To accomplish this,we utilize the information about the FGS and object information from the Gaia Data Release 3.We provide an FGS instrument magnitude and exclude variables,binaries,and high proper motion stars from the catalog to ensure uniform FGS guidance capabilities.Subsequently,we generate a HEALPix index,which provides a hierarchical tessellation of the celestial sphere,and employ the Voronoi algorithm to achieve a homogeneous distribution of stars across the catalog.This distribution ensures adequate coverage and sampling of the sky.The performance of the CSST guide star catalog was assessed by simulating the field of view of the FGS according to the CSST mock survey strategy catalog.The analysis of the results indicates that this catalog provides adequate coverage and accuracy.The catalog's performance meets the FGS requirements,ensuring the functioning of the FGS and its guidance capabilities.

PyMsOfa:A Python Package for the Standards of Fundamental Astronomy(SOFA)Service

The Standards of Fundamental Astronomy(SOFA)is a service provided by the International Astronomical Union that offers algorithms and software for astronomical calculations,which was released in two versions for FORTRAN77 and ANSI C,respectively.In this work,we implement the Python package PyMsOfa for SOFA service by three ways:(1)a Python wrapper package based on a foreign function library for Python(ctypes),(2)a Python wrapper package with the foreign function interface for Python calling C code(cffi)and(3)a Python package directly written in pure Python codes from SOFA subroutines.The package PyMsOfa has fully implemented 247 functions of the original SOFA routines released on 2023 October 11.In addition,PyMsOfa is also extensively examined,which is exactly consistent with those test examples given by the original SOFA.This Python package can be suitable to not only the astrometric detection of habitable planets from the Closeby Habitable Exoplanet Survey mission,but also for the frontier themes of black holes and dark matter related to astrometric calculations and other fields.The source codes are available via http://pypi.org/project/PyMsOfa/and https://github.com/CHES2023/PyMsOfa.

A Positioning System based on Communication Satellites and the Chinese Area Positioning System(CAPS)

The Chinese Area Positioning System （CAPS） is a positioning system based on satellite communication that is fundamentally different from the 3＂G＂ （GPS, GLONASS and GALILEO） systems. The latter use special-purpose navigation satellites to broadcast navigation information generated on-board to users, while the CAPS transfers ground-generated navigation information to users via the communication satellite. In order to achieve accurate Positioning, Velocity and Time （PVT）, the CAPS employs the following strategies to over- come the three main obstacles caused by using the communication satellite： （a） by real-time following-up frequency stabilization to achieve stable frequency; （b） by using a single carrier in the transponder with 36 MHz band-width to gain sufficient power; （c） by incorporating Decommissioned Geostationary Orbit communication satellite （DGEO）, barometric pressure and Inclined Geostationary Orbit communication satellite （IGSO） to achieve the 3-D posi- tioning. Furthermore, the abundant transponders available on DGEO can be used to realize the large capacity of communication as well as the integrated navigation and communication. With the communication functions incorporated, five new functions appear in the CAPS： （1） combination of navigation and communication; （2） combination of navigation and high accu- racy orbit measurement; （3） combination of navigation message and wide/local area differen- tial processing; （4） combination of the switching of satellites, frequencies and codes; and （5） combination of the navigation message and the barometric altimetry. The CAPS is thereby labelled a PVT5C system of high accuracy. In order to validate the working principle and the performance of the CAPS, a trial system was established in the course of two years at a cost of about 20 million dollars. The trial constellation consists of two GEO satellites located at E87.5° and E110.5°, two DGEOs located at E130° and E142°, as well as barometric altimetry as a virtual satellite. Static and dynamic performance tests were completed for the Eastern, the Western, the Northern, the Southern and the Middle regions of China. The evaluation results are as follows： （1） land static test, plane accuracy range： C/A code, 15-25 m; P code, 5-10 meters; altitude accuracy range, 1- m; （2） land dynamic test, plane accuracy range, C/A code, 15-25 m; P code, 8-10m; （3） velocity accuracy, C/A code, 0.13-0.3 m s-1, P code, 0.15-0.17 m s- 1; （4） timing accuracy, C/A code, 160 ns, P code, 13 ns; （5） timing compared accuracy of Two Way Satellite Time and Frequency Transfer （TWSTFT）, average accuracy, 0.068 ns; （6） random error of the satellite ranging, 10.7 mm; （7） orbit determination accuracy, better than 2 m. The above stated random error is 1σ error. At present, this system is used as a preliminary operational system and a complete system with 3 GEO, 3 DGEO and 3 IGSO is being established.

CHES: A Space-borne Astrometric Mission for the Detection of Habitable Planets of the Nearby Solar-type Stars

The Closeby Habitable Exoplanet Survey(CHES) mission is proposed to discover habitable-zone Earth-like planets of nearby solar-type stars(~10 pc away from our solar system) via microarcsecond relative astrometry.The major scientific objectives of CHES are:to search for Earth Twins or terrestrial planets in habitable zones orbiting100 FGK nearby stars;further to conduct a comprehensive survey and extensively characterize nearby planetary systems.The primary payload is a high-quality,low-distortion,high-stability telescope.The optical subsystem is a coaxial three-mirror anastigmat(TMA) with a 1.2 m-aperture,0°.44 × 0°.44 field of view and 500 nm-900 nm working wave band.The camera focal plane is composed of a mosaic of 81 scientific CMOS detectors each with4 k × 4 k pixels.The heterodyne laser interferometric calibration technology is employed to ensure microarcsecond level(1 μas) relative astrometry precision to meet the requirements for detection of Earth-like planets.The CHES satellite operates at the Sun-Earth L2 point and observes all the target stars for 5 yr.CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on microarcsecond astrometry from space.This will definitely enhance our understanding of the formation of diverse nearby planetary systems and the emergence of other worlds for solar-type stars,and finally provide insights to the evolution of our own solar system.

The principle of measuring unusual change of underground mass by optical astrometric instrument

Optical observations from a ground-based astrometric instrument provide a unique set of data sensi- tive to variations of local plumb line, which represent the change of local gravitational field on the ground. The local gravitational change could be caused by density variation or movement of underground mass in addition to tidal action. Earthquake was found to be related with gravitational change. A seismic zone could have abnor- mal underground material density, causing the variation of plume line on the ground. In this frame, the astro- metric telescope can measure the variation of local plumb line by observing the local astronomical longitudes and latitudes from stars in the Hipparcos catalog. In this study, we estimate the deflection angle of the plumb line on a ground site, and give a relation be- tween the angle, abnormal mass and site distance （depth and horizontal distance）. Then we derive the abnor- mality of underground material density using the plumb lines measured at different sites, and study the earth- quake gestation, development and occurrence. Using the deflection angles of plumb lines observed at two sites, we give a method to calculate the mass and the center of gravity of underground materials. We also esti- mate the abnormal masses of latent seismic zones with different energy, using thermodynamic relations, and in- troduce a new optical astrometric instrument we had developed.

Experiment on diffuse reflection laser ranging to space debris and data analysis

Space debris poses a serious threat to human space activities and needs to be measured and cataloged. As a new technology for space target surveillance, the measurement accuracy of diffuse reflection laser ranging （DRLR） is much higher than that of microwave radar and optoelectronic measurement. Based on the laser ranging data of space debris from the DRLR system at Shanghai Astronomical Observatory acquired in March-April, 2013, the characteristics and precision of the laser ranging data are analyzed and their applications in orbit determination of space debris are discussed, which is implemented for the first time in China. The experiment indicates that the precision of laser ranging data can reach 39 cm-228 cm. When the data are sufficient enough （four arcs measured over three days）, the orbital accuracy of space debris can be up to 50 m.

The spiral structure of the Milky Way

The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way.Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail.Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km s-1.We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.

The use of laser ranging to measure space debris

Space debris is a major problem for all the nations that are currently active in space. Adopting high-precision measuring techniques will help produce a reliable and accurate catalog for space debris and collision avoidance. Laser ranging is a kind of real-time measuring technology with high precision for space debris observation. The first space-debris laser-ranging experiment in China was performed at the Shanghai Observatory in July 2008 with a ranging precision of about 60-80 cm. The experi- mental results showed that the return signals from the targets with a range of 900 km were quite strong, with a power of 40W （2J at 20 Hz） using a 10ns pulse width laser at 532 nm wavelength. The performance of the preliminary laser ranging system and the observed results in 2008 and 2010 are also introduced.

Test area of the SAGE survey

Sky surveys represent one of the most important efforts to improve developments in astrophysics,especially when using new photometric bands. We are performing the Stellar Abundance and Galactic Evolution(SAGE) survey with a self-designed SAGE photometric system, which is composed of eight photometric bands. The project mainly aims to study the stellar atmospheric parameters of ～0.5 billion stars in ～12 000 deg2 of the northern sky, which mainly focuses on Galactic astronomy, as well as some aspects of extragalactic astronomy. This work introduces the detailed data reduction process of the test field NGC 6791, including the data reduction of single-exposure images and stacked multi-exposure images, and properties of the final catalog.

Searching for exoplanets with HEPS:I.detection probability of Earth-like planets in multiple systems

The astrometry method has great advantages in searching for exoplanets in the habitable zone around solar-like stars. However, the presence of multiple planets may cause a problem with degeneracy when trying to compute accurate planet parameters from observation data and reduce detectability. The degeneracy problem is extremely critical, especially in a space mission which has limited observation time and cadence. In this series of papers, we study the detectability of habitable Earth-mass planets in different types of multi-planet systems, aiming to find the most favorable targets for the potential space mission–Habitable ExoPlanet Survey(HEPS). In the first paper, we present an algorithm to find planets in the habitable zone around solar-like stars using astrometry. We find the detectability can be well described by planets' signal-to-noise ratio(SNR) and a defined parameter S = M2/(T1-T2)2, where M2 and T2are the mass and period of the second planet, respectively. T1 is the period of the planet in the habitable zone. The parameter S represents the influence of planetary architectures. We fit the detectability as a function of both the SNR of the planet in the habitable zone and the parameter S. An Earth-like planet in a habitable zone is harder to detect(with detectability PHP< 80%) in a system with a hot Jupiter or warm Jupiter(within2 AU), in which the parameter S is large. These results can be used in target selections and to determine the priority of target stars for HEPS, especially when we select and rank nearby planet hosts with a single planet.

The SAGE photometric survey: technical description

To investigate a huge sample of data related to the Stellar Abundance and Galactic Evolution(SAGE) survey in more detail, we are performing a northern sky photometric survey named SAGES with the SAGE photometric system.This system consists of eight filters: Str?mgren-u, SAGE-v, SDSS g, r, i, DDO-51, Hαwideand Hαnarrow, including three Sloan broadband filters, three intermediateband filters, two narrow-band filters and one newly-designed narrow-band filter.SAGES covers～12 000 square degrees of the northern sky with δ >-5°, excluding the Galactic disk(|b| < 10°) and the sky area 12 h <RA <18 h.The photometric detection limit depth at signal-to-noise ratio 5σ can be as deep as V～20 mag.SAGES will produce a photometric catalog with uniform depth for～500 million stars with atmospheric parameters including effective temperature Teff, surface gravity log g and metallicity[Fe/H], as well as interstellar extinction to each individual target.In this work, we will briefly introduce the SAGE photometric system, the SAGE survey and a preliminary test field of the open cluster NGC 6791 and its surroundings.