分类： 天文学 >> 天文学 提交时间： 2024-06-08
摘要： The Standards of Fundamental Astronomy (SOFA) is a service provided by the International Astronomical Union (IAU) that offers algorithms and software for astronomical calculations, which was released in two versions by FORTRAN 77 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. 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 of the Closeby Habitable Exoplanet Survey (CHES) mission (Ji et al. 2022), but also for the frontiers themes of black holes and dark matter related to astrometric calculations and other fields. The source codes are available via https://github.com/CHES2023/PyMsOfa.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jianghui Ji
Haitao Li
Junbo Zhang
Liang Fang
Dong Li
Su Wang
Yang Cao
Lei Deng
Baoquan Li
Hao Xian
Xiaodong Gao
Ang Zhang
Fei Li
Jiacheng Liu
Zhaoxiang Qi
Sheng Jin
Yaning Liu
Guo Chen
Mingtao Li
Yao Dong
摘要： The Closeby Habitable Exoplanet Survey (CHES) mission is proposed to discover habitable-zone Earth-like planets of the nearby solar-type stars ($\sim 10~\mathrm{pc}$ away from our solar system) via micro-arcsecond relative astrometry. The major scientific objectives of CHES are: to search for Earth Twins or terrestrial planets in habitable zones orbiting 100 FGK nearby stars; further to conduct a comprehensive survey and extensively characterize the 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 $1.2 \mathrm{~m}$-aperture, $0.44^{\circ} \times 0.44^{\circ}$ field of view and $500 \mathrm{~nm}-900 \mathrm{~nm}$ working waveband. The camera focal plane is composed of 81 MOSAIC scientific CMOS detectors each with $4 \mathrm{~K} \times 4 \mathrm{~K}$ pixels. The heterodyne laser interferometric calibration technology is employed to ensure micro-arcsecond level (1 $\mu$as) relative astrometry precision to meet the requirements for detection of Earth-like planets. CHES satellite operates at the Sun-Earth L2 point and observes the entire target stars for 5 years. CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on micro-arcsecond 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 to reflect the evolution of our own solar system.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Here we present an open source Python-based Bayesian orbit retrieval code (Nii) that implements an automatic parallel tempering Markov chain Monte Carlo (APT-MCMC) strategy. Nii provides a module to simulate the observations of a space-based astrometry mission in the search for exoplanets, a signal extraction process for differential astrometric measurements using multiple reference stars, and an orbital parameter retrieval framework using APT-MCMC. We further verify the orbit retrieval ability of the code through two examples corresponding to a single-planet system and a dual-planet system. In both cases, efficient convergence on the posterior probability distribution can be achieved. Although this code specifically focuses on the orbital parameter retrieval problem of differential astrometry, Nii can also be widely used in other Bayesian analysis applications.
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