Chinese Astronomy and Astrophysics最新文献

Comets are the primitive planetesimals left in the solar system. Studying the evolution of comet nucleus is of great significance for understanding the formation and evolution history of other celestial bodies in the solar system. Under the action of solar radiation, the volatile components of comets sublimate and drive the dust movement, resulting in the loss of comet nucleus material. Therefore, the activity of comet nucleus affects the surface morphology and even the overall shape evolution. The orbit data were obtained from IAU (International Astronomical Union) MPC (Minor Planet Center), and the spin and precession of comet nucleus were taken into account. The shape evolution model of Mass loss-driven shape evolution model (MONET) was used to simulate the short period comet. The distribution of solar radiation energy and surface erosion depth of short-period comet 1P/Halley, 9P/Tempel 1, 19P/Borrelly, 67P/C-G (Churyumov-Gerasimenko), 81P/Wild 2, and 103P/Hartley 2 in one orbital period is calculated. Combined with its dynamic parameters, the effects of rotation, precession, and revolution on the sublimation distribution of surface water ice and the possibility of causing the difference in erosion between north and south are discussed.

The detection of exoplanets in the past three decades has revealed the fact that planets are ubiquitous in the universe. In order to deeply study the ubiquity of habitable planets, on one hand, we need to understand the characteristics of habitable planets; on the other hand, we can analyze the the distribution characteristics of exoplanets have been found, and to calculate the probability of occurrence of such planets around stars. Among the exoplanets that have been found so far, most of them are discovered by the transit method. For example, the number of the planets detected by the Kepler space telescope is 2344. Kepler telescope officially retired in 2018, and the Kepler team released the final version of Kepler Data Release (DR25), including a total of 198709 stars observed quarterly Q1–Q17. Here we analyze the Kepler data by using two different methods, Inverse Detection Efficiency Method (IDEM) and Maximum Likelihood Analysis (ML), to estimate planet occurrence rates in the space of the parameters of radius and orbital period. At the same time, the samples were classified according to the spectral types of stars, and the planet occurrence rates around F, G, and K Kepler stars as well as its overall formation rate were estimated respectively. We estimate the planetary occurrence rates for planets among radius range of 1–20 $R_{\oplus }$ ($R_{\oplus }$ is one radius of the Earth) and orbital period range of 0.4–400 days by IDEM and ML, for which around F stars are respectively $0.36\pm 0.02$ and $0.47\pm 0.02$. The rates around G stars by IDEM and ML are respectively $1.62\pm 0.05$ and $1.23\pm 0.04$. The rates around K stars by IDEM and ML are respectively $2.61\pm 0.12$ and $2.73\pm 0.13$. And the overall occurrence rate of such planets around F, G, K stars by IDEM and ML are respectively $1.16\pm 0.03$ and $0.90\pm 0.02$. According to our estimation, we further show the results for the planet occurrence rates around stars with different spectral types by different methods, and discuss the reliability of the results in comparison with the previous studies.

Atmospheric turbulence has been confirmed as the primary source affecting the quality of ground-based telescope image. To reduce the effect of atmosphere, a good site should be selected, and adaptive optics (AO) should be installed for the telescope. In general, the daytime atmospheric turbulence is more intense than that at night under the effect of solar radiation. Numerous solar telescopes have built AO systems worldwide. Conventional AO is only capable of improving the image quality in a small field of view, whereas it cannot satisfy the needs of a large field of view. The novel wide field adaptive optical system is capable of achieving a large field of view and high-resolution images, whereas the atmospheric turbulence profile should be accurately detected, which is the prerequisite and key parameter of the novel AO system. Moreover, the astronomical high-resolution technology in accordance with the turbulence imaging theory requires more detailed detection of turbulence. Accordingly, a brief review about the latest detection technology of the daytime optical turbulence profile is valuable for astronomical observations. Besides, the parameters of atmospheric turbulence are briefly introduced. Subsequently, SNODAR, SHABAR, MOSP, DIMM+, A-MASP, and other detection technologies of the stratified atmospheric turbulence for daytime are primarily presented, and the advantages and disadvantages of the different technologies are summarized.

Position prediction is the basis of guiding radar to seek, capture, and track space targets, although there’s a risk of insufficient accuracy for narrow beam radar due to the influence of orbit determination and propagation error. Since the along-track error is the main factor that affects the accuracy of position prediction, this paper proposed a Constant Elevation Search (CES) method for narrow beam radar, based on the idea of along-track error compensation, to seek and capture transit targets. With along-track error estimation, all possible positions on a specified elevation can be observed, thus the success rate of capturing transit targets will be improved. Simulation shows that when the position prediction method fails, the CES method still works.

Optically “changing-look” active galactic nuclei (AGNs) are a class of objects that exhibit appearance or disappearance of broad lines. Recent studies have shown that these “changing-look” activities very likely result from the accretion activities of the central supermassive black holes. Large variation of the accretion rate might cause jet ejection and fading events, thus lead to a certain variability of observational radio properties. From the published literature, 74 “changing-look” AGNs and 90 “changing-look” AGNs candidates identified in optical observations were collected. Based on this largest, complex, and incomplete sample to date, the radio properties of “changing-look” AGNs were investigated. The radio counterparts of 51 “changing-look” AGNs (including 21 candidates) were discovered from the all-sky surveys conducted by the Australian Square Kilometre Array Pathfinder (ASKAP) and Very Large Array (VLA) covering the frequency range of 0.9–3 GHz. This corresponds to a detection rate of about 41 percent, which is similar to general AGNs. The radio spectral indices between 0.9 and 1.4 GHz and between 1.4 and 3 GHz were calculated, which suggest that these “changing-look” AGNs tend to have flatter radio spectra than normal AGNs. This statistical result indicates that “changing-look” AGNs might host some young, compact, and faint radio jets.

According to Bamboo Annals, “The year Emperor Yao ascended the throne was the year of Bingzi” and “In the forty-second year of his reign, Jing star appeared on the Yi xiu (constellation)”. LunHeng says that “during the era of emperor Yao, Jing star was seen in the Zhen xiu (constellation)”. This star may be a supernova between Yi xiu and Zhen xiu. Calculated by already known years that was designated by Heavenly Stems and Earthly Branches, the 42nd year of Emperor Yao’s reign was B.C.2164. If we take a wide range (${180}^{\circ }\pm {23}^{\circ }$) as the transition area between ‘Yi’ and ‘Zhen’, we can find 20 supernovae in the Green Supernova Remnant Table. Among them, only the high silver latitude remnant PKS 1209-52 (G296.5+10.0) conforms to brightness and age limitations of Emperor Yao’s Jing star that appeared “like a half moon”. It is the only candidate of Emperor Yao’s Jing star (SN-B.C.2164). According to the relationship between the surface brightness of supernovae and the line diameter that SNR $\Sigma \propto D^{-\beta }$, as well as the adiabatic expansion theory, the adiabatic phase age ($t=4165$ yr) is calculated to be consistent with the era of Emperor Yao. In addition, according to the limitation that the Jing stars are as bright as “half moon”, the distance $d=$ 1–1.2 kpc can be figured out. Then according to the Sedov relation $D=0.94t^{2/5}$, the age of Emperor Yao’s Jing star was (4450 $\pm$ 900) years ago. It is also in accordance with the times of Emperor Yao. This is one of the earliest recorded supernovae in the history of astronomy, which advances the history recorded in Chinese literature and confirmed by science to more than 4100 years ago.

In the era of big science, the construction of large science projects is becoming more complex. Designers have to comprehensively consider factors such as instrument performance, technical reserves, funding, risks, and the environment to make a reasonable decision. On the basis of domestic and international astronomy, this paper sorts out the process of the formation of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) concept and the decisions made by the FAST team, including the Chinese concept of the large telescope, the proposal of the prototype, and the adoption of the active reflector, etc. We also discuss the process of decision-making. FAST was born in the process of interaction and integration between Chinese and international astronomy development, and realized the transformation from following up to taking the lead. It can provide a reference for constructing future large science projects with limited foundations in terms of technology and funding.

The United States provide Element Sets (ELSET) database in Two-Line Element (TLE) format for public use, which plays an important role in the inversion of atmospheric density in the thermosphere, ballistic coefficient estimation, early-warning and so on. Due to large uncertainties existing in the TLE generation process, space environment changes, and space events, ELSET database contains a large number of abnormal TLE data to be filtered, such as corrected TLE, orbital element outlier, and Bstar outlier. The existing methods to filter out the outliers lack general applicability and are very complicated, which are only applicable to a few space targets in certain orbit regions. To overcome the shortcomings of the existing methods, a filtering method is proposed based on Expectation Maximization (EM) algorithm employing a sliding window and polynomial fitting method, which can detect outliers for different orbital elements and space events. The research shows that the algorithm can effectively single out the outliers in TLE sequences and is suitable for all orbital debris.

The High Sensitivity Terahertz Detection Module (HSTDM) is one of the scientific payloads of the China Space Station Survey Telescope, which mainly conducts terahertz astronomical observations. The core of the HSTDM is the NbN superconducting tunnel junction (Superconductor - Insulator - Superconductor (SIS)) mixer, operating at the temperature $\le$ 10 K, cooled by a space-qualified two-stage pulse tube refrigerator. The cryostat, which can minimize the heat load of the refrigerator, is a key component to realize the 10 K refrigeration environment in space, and it needs to adapt to the mechanical vibration during launch. This paper mainly introduces the structural design, mechanical characteristics simulation analysis and actual measurement, and thermal characteristics simulation analysis of this special cryostat. The fundamental frequency of the cryostat is 189.36 Hz. The mechanical analysis results demonstrate that the maximum stress of the support structures is lower than the yield stress of the materials. The vibration test results show that the cryostat can adapt to mechanical environments. The cryostat has a heat leakage of 1800 mW to the first cold stage and 20.6 mW to the second cold stage, both of which are less than the cooling power of the refrigerator. The thermal analysis results show that the thermal design of the cryostat satisfies the thermal insulation requirements. The research results demonstrate that the cryostat design can meet the space application requirements of the HSTDM.

Being China’s first comprehensive space solar observatory, ASO-S (Advanced Space-based Solar Observatory) has been launched into orbit at 7:43 Beijing Time on October 9, 2022. A very brief introduction on ASO-S is presented here, including the background, scientific goals, payload deployments, mission assembly, and organizations. A short prospect is made for the operation of the mission and the future scientific output.