Chinese Astronomy and Astrophysics最新文献

Fireball monitoring network is the main equipment for monitoring impact from small-size near-Earth objects (NEOs), and determining meteorite fall locations. In this paper, a monitoring system using a multi-station distributed all-sky video camera network is proposed, and a regional prototype system has been constructed in Jiangsu and surrounding areas. The main processes of fireball monitoring were implemented, including network control, video capture, data processing, trajectory determination, and orbit calculation. After running for 1 yr, the results show that the limiting apparent magnitude - 1.0 for meteors in the video, and the absolute magnitude exhaustive detection regime can reach around - 2.5. The flux of fireballs is found to be $2.68\times {10}^{-7}$ km${}^{-2}$ $·$ h${}^{-1}$. The percentages of streams and sporadic meteors are 46% and 54%, respectively, and the fraction of cometary orbits equals 72.9%, while for asteroidal-type it is 27.1%. The statistical results are close to those of the international meteor monitoring networks, which verified the monitoring capability of the network system in practical operation.

This paper proposes a new method of deriving the launch and landing locations based on the orbital motion characteristics of the missiles and elevation database. In this method, the DEM support is introduced to change the assumption of the earth from the reference ellipsoid to a more real shape. The method to improve the prediction accuracy of the position and time of the launch and landing points is discussed. The results with DEM (Digital Elevation Model) indicate the accuracy can be improved by adding a few elevation iterations on the original method. The higher the elevation of the starting and landing points, the better the result would be.

Affected by a large number of radio frequency interference signals, it has become an important task for astronomical data processing to quickly and accurately identify single pulse signals from massive observation data. Designing and extracting effective data features is the key issue for efficient identification of single pulse signals using machine learning. This paper proposes an ensemble feature selection method for single pulse signal classification. The method first mixed three types of features, including the parametric features, statistical features, and abstract features of single pulse signals, and then used five individual feature selection methods to select the corresponding optimal feature set, respectively. At last, the features selected by the five individual methods are mixed, and the greedy strategy was used to select the optimal ensemble feature set. The experimental results show that the ensemble feature set can improve F1-score by a value of 1.8% at most, and can obtain higher accuracy than the features selected by individual methods. Under the background of high-speed and large-scale sky survey, the ensemble feature selection method plays an important role in reducing the number of features, improving classification performance, and speeding up data processing.

The orbital eccentricity is one of the key parameters to describe the orbit of celestial bodies, which can provide important clues to reveal their dynamical evolution, and thus help to understand their formation and evolution processes along with the physical mechanisms behind them. The continuous improvement of observational technologies, enable us to explore the orbit of celestial bodies beyond the solar system, i.e., from stellar systems to planetary systems. Focusing on the orbital eccentricity of celestial bodies, this paper reviews the progress in stellar systems (including the main sequence stars, brown dwarfs, and compact stars) and planetary systems (including gas-giants, low-mass exoplanets such as “super-Earth” and “sub-Neptune”), and summarizes several similarities and issues among the investigations of orbital eccentricity under different scales. Finally, based on the ongoing and future astronomical facilities and missions, we discuss the future prospect on eccentricity studies of stellar systems, extra-solar planetary systems, and even extra-solar satellite systems.

Satellite constellations are widely used for communication, navigation, and Earth observation purposes. They provide good ground coverages and serve better for these needs. Of all the configurations, the Walker constellation is extensively applied in many navigation satellite systems and some low Earth orbit communication constellations, since it can be easily designed and has good coverage. Despite of these advantages, the satellites in Walker constellation generally have different ground tracks. When multiple Walker constellations are to be coordinated, in terms that the orbital planes precess synchronously with the same satellite mean motion ${\Omega }_1$, the semi-major axes $a$ of these Walker constellations would be significantly different even when the orbital inclinations differ by a small amount. The Space Exploration Corp (SpaceX) claimed a new constellation design in a patent for their multi-shell Starlink satellite constellation. Constellation shells with different inclinations have small altitude differences, which facilitates regulatory approval and deployment. Satellites in the same shell can also be easily designed to share the same ground track. Although they claimed these features in the patent, SpaceX shared little technical details regarding how to design these constellations. Here in this paper, we analyze the features of the Starlink constellation, and try to find a practical approach to design a Starlink-like constellation, as well as how to determine the rules for inter-satellite links within the constellation.

Magnetic reconnection is a crucial energy conversion process in plasmas, and it is important to study the forms of energy conversion and their distribution in this process. Previous research has focused mainly on the energy fluxes in symmetric reconnection, while the study of asymmetric reconnection at the Earth’s magnetopause, especially in terms of statistical analysis of multiple events, has not been reported before. Therefore, 10 magnetic reconnection events at the magnetopause observed by MMS (Magnetospheric Multiscale) satellite that passed through the electron diffusion region were used for analysis. Although the contribution of different energy flux varies case by case, our results show that in most events, the ion enthalpy flux is dominant, followed by the Poynting flux. The ion heat flux is slightly smaller than the Poynting flux, while the sum of ion kinetic energy flux, electron enthalpy flux and electron heat flux only accounts for less than 10% of the total energy flux. By projecting the normalized energy flux of all events into $B_L-V_{(i,L)}$ plane (in $LMN$ coordinate), we find that the energy flux in $M$ direction is comparable to the energy flux in $L$ direction and also there is an “anti-correlated” relationship between the ion velocity and ion heat flux around reconnection diffusion region, consistent with previous studies.

HE 1005-1439 is a carbon-enhanced metal-poor (CEMP) star with [Fe/H]$\sim -3.0$, which is largely enhanced in elements produced by slow neutron-capture process (s-process; e.g., [Ba/Fe]=1.16$\pm 0.31$, [Pb/Fe]=$1.98\pm 0.19$), and mildly enhanced in elements produced by rapid neutron-capture process (r-process; e.g., [Eu/Fe]=0.46$\pm 0.22$). The neutron-capture element patterns of the star can not be fitted by the s-process model or intermediate process (i-process) model. Studying the astrophysical origins of chemical elements in the star based on the method of abundance decomposition can help understanding the formation and evolution of the CEMP stars. Using the combination of s-process and r-process abundances, we fully fit the abundance patterns of the neutron-capture elements of this star. We find that the neutron-capture elements are mainly produced by the s-process of the AGB companion with low mass and low metallicity, and the r-process nucleosynthesis also contributes a little to this star.

The co-orbital motion occurs when a celestial body (e.g. an asteroid) shares the same semimajor axis with the perturbing object (e.g. a planet), and thus they are in a 1:1 mean motion resonance. Trojan asteroids in the tadpole orbits around planets in the Solar System are these co-orbital objects. The motion and origin of some Trojan asteroids, particularly those on high-inclination orbits, are still not fully understood. In this paper, a newly developed perturbation function expansion, which is applicable to the 1:1 resonance, is used to investigate the co-orbital motion in three-dimensional space. The position of the resonance center and the resonance width are calculated for different initial orbital elements, and the relationship between the orbital types and the initial orbital elements is analyzed. The results obtained by the analytical method are compared with and verified by the results from numerical simulations. A panorama of the co-orbital motion in the wide orbital elements space is obtained.

Fast Radio Bursts (FRBs) are extra-galactic origin milli-second duration bright radio bursts. Theoretically, FRBs may produce optical counterparts with durations from milliseconds to hours. The FRB optical counterparts may be detectable in future large field telescopes, including the China Space Station Telescope (CSST), the 2.5-meter Wide Field Survey Telescope (WFST) lead by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO), and the Earth 2.0 (ET). The fast radio burst optical counterparts are grouped into millisecond time-scale optical counterparts, hourly time-scale optical counterparts, and optical afterglow for our study. The first two can be generated by the high-energy extension of the radio radiation of fast radio bursts and the inverse Compton scattering of high-energy electrons. The event rates highly depend on the optical-to-radio flux ratio ${\eta }_{\nu }$. For millisecond duration optical counterparts, the detection rate of WFST, CSST, and ET can reach hundreds per year in an ideal case. If ${\eta }_{\nu }\sim {10}^{-3}$, the corresponding annual detection rates of WFST and CSST are in the order of 1, and the annual detection rate of ET is 19.5. For the hourly timescale optical counterparts, ideally, the age of the supernova remnant is 5 years, ${\eta }_{\nu }$ is about ${10}^{-6}$, and the annual detection rates are above 100. The X-ray counterpart of FRB 200428 indicates that FRBs may produce relativistic outflow, which will interact with the interstellar medium to produce optical afterglows. Combined with the standard afterglow model, the detectability of optical afterglow is explored with a simulation of fast radio bursts following the redshift and energy distribution from the literature. With a total energy-radio energy ratio similar to FRB 200428, ($\zeta ={10}^5$), the estimated annual detection rates of CSST, WFST, and ET are 1.3, 1.0, and 67, respectively.

The origin, acceleration, and propagation of high-energy cosmic rays is one of the most important questions in modern physics and astronomy. To fully uncover such a mystery, precise measurements of the energy spectra and anisotropies of cosmic rays, as well as multi-wavelength electromagnetic radiation from various types of energetic objects are required. The direct measurements of energy spectra of different species via particle detectors in space are an essential way to study cosmic ray physics. China launched the first space astronomical satellite, the Dark Matter Particle Explorer (DAMPE) in the end of 2015, which keeps operation in space for more than 7 years. The DAMPE has a relatively large acceptance and a high energy resolution, and has made important progresses in measuring the spectral structures of cosmic ray protons, helium nuclei, and boron-to-carbon and boron-to-oxygen ratios. These new measurements bring new insights in understanding the origin and propagation of cosmic rays. This paper reviews the instrumentation and operation of DAMPE, with an emphasis on its scientific results and physical implications in cosmic ray studies.