Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： The features of upper atmospheric midnight density maximum (MDM) around low geographic latitudes are studied based on neutral mass densities data at altitudes 360--480\;km, derived from the accelerometer measurements aboard on the three polar orbiting satellites CHAMP (CHAllenging Minisatellite Payload), GRACE-A (Gravity Recovery and Climate Experiment-A) and SWARM-C (The Earth's Magnetic Field and Environment Explorers-C). The MDM appears during the local times from 23:00 to 02:00\;LT, whose peak locates at the low latitudes within ${15}^\circ$ and two valleys locate at the middle latitudes between ${35}^\circ$ and ${45}^\circ$ on both hemispheres separately. The structure of MDM drifts toward the southern hemisphere overall. The MDM's amplitude decreases with increases in altitude and solar radiation level. The seasonal effect weakens the MDM's amplitudes around the summer and winter solstices, while the amplitudes around the spring and autumn equinoxes are extremely significant due to the slight seasonal difference between both hemispheres. Three atmospheric density models DTM2000 (Drag Temperature Model 2000), NRLMSISE00 (Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended atmosphere model) and JB2008 (Jacchia-Bowman 2008 model) are used to simulate the MDM along these three satellites' orbits, and compared with the observations. It is found that the JB2008 model is failed to describe the MDM, and the other two models underestimate the MDM's amplitudes at altitudes 360 km and 480 km: the simulated amplitudes by the DTM2000 model are 46\% and 53\% of the observed amplitudes respectively, and only 33\% and 26\% for the NRLMSISE00 model. These three models are also failed to depict the MDM's variation with altitude, solar radiation level and seasonal effects. In order to correct the model prediction, a 6th-order Legendre polynomial of geographic latitude, coupled with arguments of local time and altitude, is designed to fit the MDM signals from the three satellites' observations. In terms of amplitude and phase of the MDM, the fitting results agree with the observations very well, and the correlation coefficient is 0.923. It indicates that this empirical polynomial could be helpful to the density model correction and high accuracy prediction of spacecrafts in low Earth orbits.}
Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： We investigate the umbral oscillation at multi-height solar atmospheres above a sunspot in the active region National Oceanic and Atmospheric Administration (NOAA) 12680 on 2017 September 15. In this study, the extreme ultraviolet images were measured by the Atmospheric Imaging Assembly (AIA), while the ultraviolet spectral lines and images were observed by the Interface Region Imaging Spectrograph. At the sunspot umbra, the AIA~1700\;{\AA} intensity curve shows the primary oscillation with a long period of $\sim$(4.2$\pm$0.8)~minutes, while the intensity curves in AIA~1600\;{\AA}, 171\;{\AA} and 193\;{\AA} exhibit an apparent oscillation with a short period of $\sim$(2.8$\pm$0.3)~minutes. Meanwhile, a short period of $\sim$(3.1$\pm$0.5)~minutes is found in the Mg~II~h \& k lines and the slit-jaw image at 2796\;{\AA}, a short period of $\sim$(2.9$\pm$0.4)~minutes is detected in the Si~IV~1393.76\;{\AA} line. Our observations suggest that the oscillatory periods at the sunspot umbra decrease with the height of solar outer atmospheres. The short period is roughly equal to 3 minutes, which could be interpreted as the propagating slow magnetoacoustic wave above the sunspot umbra, and it might originate from the temperature minimum region and then propagate up to the corona. While the long period is close to 5 minutes oscillation in the photosphere, which might be regarded as the solar P-mode wave.
Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： CK (Karoonda-like) carbonaceous chondrites (CCs) are highly oxidized meteorites, with metal/magnetite ratio close to zero. Unlike other CCs (petrologic type: 1--3), most CK chondrites have suffered intense thermal process (550--1270 K) on their parent body with a petrologic type 4 or above. Lines of evidence indicate that CK chondrites could be genetically related to CV (Vigarano-like) chondrites which are mostly type 3 meteorites. However, there are still slight differences in petrographic texture and chemical composition between these two meteorites. Therefore, it is crucial to distinguish their geochemical characteristics for testing the CK-CV single parent body hypothesis. Northwest Africa (NWA) 13943, a newly found meteorite which has undergone intense thermal metamorphism, was classified using scanning electron microscopy and electron microprobe. The whole-rock oxygen and chromium isotope composition of NWA 13943 meteorite were also determined by mass spectrometer. Integrating petrology, mineralogy, oxygen isotope anomaly ($\Delta^{17}$O, where $\Delta$ represents isotopic fractionation value), and chromium isotope anomaly ($\varepsilon^{54}$Cr, where $\varepsilon$ expresses parts per ten thousand mass-independent isotope deviation) data, it is legitimated to infer that CK and CV chondrites may derive from two similar but distinct isotopic reservoirs within the protoplanetary disk.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： The data-fusion orbit determination software SPODFMD (Space debris Precise Orbit Determination fusing Multi-source Data) is developed with the purpose of cataloging space debris, characterized by integrating pure numerical integrators and given birth in the lab of SPOD (Satellite Precise Orbit Determination) at PMO (Purple Mountain Observatory). At the initial stage of the birth, developers fully investigated national space debris monitoring equipment, fully understood the orbit and physical complexity of numerous space debris, fully recognized the requirement for high efficiency when renewing orbits for lots of debris, and fully considered the robustness requirement in engineering. In addition, SPODFMD integrates several algorithms with indigenous intellectual property rights, including a rapid and non-singular algorithm for computing the Earth's gravitational potential and its derivatives, analytical and non-singular expressions for the DTM94 thermosphere model and its derivatives, an accurate and efficient method for calculating dense ephemeris of high-eccentricity orbit, and a robust adaptive weighting method. Integrating these advanced algorithms by applying software engineering theory, SPODFMD can freely fuse observation data from 14 kinds of equipment, achieving a second-level computation efficiency in a majority of typical orbit determination cases. Moreover, the software shows similar performance for GEO (Geosynchronous Equatorial Orbit), MEO (Medium Earth Orbit), LEO (Low Earth Orbit), and HEO (Highly Elliptical Orbit) objects without computation and pole singularity. It is tested and proved to be multi-source, efficient, general, and robust.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： 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 in China, including the China Space Station Survey Space Telescope (CSST), the 2.5-meter Large Field Survey Telescope (WFST) of the University of Science and Technology of China (USTC), and the Purple Mountain Observatory (PMO), and 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 FRBs or the radio radiation of fast radio bursts and the inverse Compton scattering of high-energy electrons. The event rates highly depend on the optical-radio flux ratio $\eta_{\rm \nu}$. For millisecond duration optical counterparts, the detection rate of WFST, CSST, and ET can reach hundreds per year in an ideal case. If $\eta_{\rm \nu} \sim 10^{-3}$, 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 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.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： 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.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： The High Sensitivity Terahertz Detection Module (HSTDM) is one of the scientific payloads of the China Space Survey Telescope. The core of the HSTDM is the NbN superconducting tunnel junction SIS (Superconductor Insulator Superconductor) mixer, operating at temperature 10 K. The installation structure of the superconducting SIS mixer needs to be specially designed to cope with the mechanical vibration during the launch phase and the thermal insulation requirements during the operation phase. Material thermal expansion characteristics investigation based on the low-temperature LVDT (Linear Variable Differential Transformer) measurement and marking scratch measurement were carried out to confirm the design validity of the thermal expansion locking mechanism. The two methods are cross-verified. The LVDT experimental measurement results show that the shrinkage rate of Teflon material changes with temperature and meets the theoretical model. At the same time, we verified the LVDT results with the marking scratch method. Consistently, the shrinkage rate of the material is 1.86\% at 80 K, so the Teflon front-end locking mechanism of the superconducting SIS mixer can achieve effective separation.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： Massive stars tend to form in clustered environments. The origin of the massive stars and binaries outside clusters is one key to understand the formation and evolution of massive stars. The authors selected two colliding wind candidates, MTT68 and MTT71, and probed their origin by analyzing the \emph{Chandra} X--ray observation and the proper motions queried from the \emph{Gaia} Data Release 2 (\emph{Gaia}~DR2) catalog. Those two targets are located on the margin of NGC 3603, the galactic massive cluster 7.6\;kpc away. MTT68 has been resolved as a visual binary of MTT68A/B, and MTT68A itself was proposed as a close massive binary. The authors compared the centroid of the X--ray emission and the coordinate queried from \emph{Gaia}~DR2 catalog, to those of MTT68A/B on the \emph{HST} image, and found that both of them are close to MTT68A but far away from MTT68B, which suggests the X--ray characteristic and the astrometry measurement both mainly describe MTT68A instead of MTT68B. They also carried out the X-ray spectral analysis of MTT68A and MTT71, and found (1) the existence of the Fe XXV line in their spectra, (2) a second component of temperature $kT\gtrsim2.0$\;keV is required when fitting their spectra with hot plasma models, and (3) their ratio of X-ray to bolometric luminosity, lg($L_{\rm X}/L_{\rm bol})\gtrsim-5.8$, is at least one order of magnitude higher than the value of isolated O-type stars. All above features further prove their colliding wind scenario. Besides that, they analyzed the astrometry measurements of MTT68A and MTT71 queried from the \emph{Gaia}~DR2 database. MTT71 has an absolute proper motion similar to the overall value of NGC 3603, which suggests it formed associated with NGC 3603 without ejection process. In contrast, MTT68A has a significant proper motion relative to NGC 3603: the relative proper motion in the right ascension direction $\Delta\mu_\alpha=(-2.5\pm1.1)$\;mas\,$\cdot$\,yr$^{-1}$ and declination direction $\Delta\mu_\delta=(3.3\pm0.9)$\;mas\,$\cdot$\,yr$^{-1}$, resulting a direction that opposites to the core region of NGC 3603. Hence the authors propose that MTT68A is a massive binary ejected 20\;kyr ago, and single-binary and binary--binary interactions are possible mechanisms. A search for the massive star with reverse relative proper motion at the opposite side of the cluster will be helpful to verify this hypothesis.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Collisionless magnetic reconnection, which converts the magnetic energy into the kinetic energy of plasma particles via the heating or acceleration, has been believed widely to be able to explain various eruptive phenomena such as solar flares and geomagnetic storms. However, the microphysical mechanism of anomalous resistivity in the collisionless magnetic reconnection is still an unsolved fundamental problem. Among the many physical mechanisms of anomalous resistivity formation, chaos-induced resistivity based on the chaos of the charged particle orbits near the magnetic neutral point is not the most popular formation mechanism, but its microscopic physical picture is the clearest. This paper first briefly reviews the early research and physical model of the chaos-induced resistivity in collisionless magnetic reconnection region, introduces the recent research progress of the chaos-induced resistivity, and expounds the future research direction of the chaos-induced resistivity.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Wave-particle interactions can naturally result in energy transfer between electromagnetic fields and particles in collisionless plasmas, and these interactions can therefore reshape the particle velocity distribution function. How to quantify wave-particle interaction is one fundamental problem in the heliosphere and astrophysical plasma communities. Recently, there are many important findings related to the wave-particle interaction. This paper will report recent theoretical developments in the study of the wave-particle interactions. In particular, this paper will introduce a newly-developed theoretical method in quantifying both resonant and nonresonant wave-particle interactions. This paper will also introduce applications of quantifying wave-particle interactions for the Alfv\'en-mode wave, the proton beam instability, and the electron heat flux instability in the inner heliosphere.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Compared to solar radio bursts, interplanetary (IP) radio bursts with lower radiation frequencies are generally believed to originate in the interplanetary space far from the low corona. The cutoff by Earth's ionosphere makes the ground-based observations for it impossible. Parker Solar Probe (PSP), launched by the National Aeronautics and Space Administration (NASA) to explore the Sun with the closer heliocentric distance than any previous spacecraft, provides an opportunity to study the low-frequency radio burst. The radio spectrometer it carries can observe radio radiation in the frequency range of 10 kHz--19.17 MHz. PSP can approach the radiation source region of the IP type III radio burst. Therefore, it has an unprecedented advantage to observe the interplanetary radio bursts. This paper reviews the studies about type III radio bursts observed by PSP so far. These studies include the occurrence rate, polarization, scattering, cutoff frequency, possible radiation mechanisms, and related radiation source regions of radio bursts and so on. Finally, future research prospects are discussed.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： The radio emission mechanisms, especially the coherent radio emission mechanisms of radio bursts, are one of the most complicated and controversial topics in astrophysics. Due to the complex influence of multiple physical factors, theoretical studies of coherent radio emission mechanisms are very difficult. There has been a constant controversy between the two types of coherent emission mechanisms, i.e., the plasma emission and the electron cyclotron maser emission, for a long time. In recent years, people have been trying to apply the fully-kinetic Particle-in-Cell (PIC) numerical simulations to the study of coherent radio emissions, and have made some positive progress. In addition to reviewing some existing problems and difficulties in this topic, this paper will focus on the research of PIC simulations for the coherent radio emissions from space plasmas and the main progress in recent years.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： The heliospheric radio emissions are the strongest radio emissions phenomenon in the solar system, with a radiation power of at least 10$^{13}$\;W, which can provide important physical information of high energy electron beam and magnetic plasma structure near the heliospheric boundary. Since the first detection by the Voyager spacecraft in 1983, those radio emissions have widely and continuously attracted much attention from researchers. There are generally two types of the heliospheric radio emissions: instantaneous or drifting emission with relatively high frequency, and continuous emission or non-drifting emission with relatively low frequency. Usually, both types of emissions start from about 2\;kHz. For the drifting emission, it has the characteristic of drifting to high frequency, the drifting rate is about 1--3\;kHz/yr, the frequency range is 1.8--3.6\;kHz, and the duration is about 100--300\;days. For the non-drifting emission, it has no obvious frequency drift, the frequency range is 1.8--2.6\;kHz, and the duration is about 3\;yr. It is generally believed that the heliospheric radio emissions are related to shock. In this paper, the possible source region of the radio emissions, the emission mechanisms, and the source of shock related to the emissions are introduced. Furthermore, the existing scientific problems and the future perspectives on the research of heliospheric radio emissions are discussed.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Ion cyclotron waves (ICWs) are one kind of plasma waves whose frequency is close to the ion cyclotron frequency. They exist widely in the upstream of Mars, and the frequency observed by satellites is generally near the proton cyclotron frequency. ICWs are byproducts in the production processes of pick-up ions. The occurrence of ICWs constitutes, in principle, an indirect signature of the presence of newborn planetary protons. ICWs upstream of Mars have received much attention since they were first reported in 1990. In this review, we summarize the research progress of ICWs in the upstream of Mars, including the observation of ICWs, the wave generation mechanism, their statistical properties and related future research trends.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： The evolution process of the solar wind is an important topic in space physics. High-frequency electrostatic waves have attracted wide attention because they are closely related to the distributions of the solar wind particles. The recently launched Parker Solar Probe (PSP) has observed a variety of high-frequency electrostatic waves in the near-Sun solar wind (solar distance $r<0.3$\;AU), which provides a new opportunity to study the wave-particle interactions therein. In this review, we introduce the research status of high-frequency electrostatic waves, summarize the observational features of each wave, including the well-known ion-acoustic waves, electron Bernstein waves and some unknown electrostatic waves. We also discuss the possible excitation mechanisms or free energy sources of each wave. Besides, we present our perspectives on the topic.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： The solar wind originates from the solar atmosphere. It undergoes heating when it propagates in the interplanetary space. It is unclear what heats the solar wind, a frontier problem in space physics. The solar wind is commonly in the state of turbulence, and the turbulence energy is believed to be an important source of the solar wind heating. However, two key questions remain, i.e., what is the specific medium heating the solar wind and what is the microscopic mechanism of the heating. This paper reviews the history of the studies on the solar wind heating problem, with the focus on domestic works about solar wind ion-scale turbulence and its heating. This paper also raises several questions to be solved and interesting topics on the solar wind heating in the future.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-06-28 Cooperative journals: 《天文研究与技术》
Abstract：现代天文学认为分子云核是恒星诞生的区域，对分子云核的检测和其性质的全方面研究有利于理解恒星的形成过程以及星系和宇宙的演化。随着银河画卷巡天项目 (Milky Way Imaging Scroll Painting, MWISP)的开展和实测数据的快速积累，开发分子云核智能仿真与检测系统成为必要。系统提供分子云核智能检测、仿真建模、参数还原、三维可视化、数据存储等功能。借助该系统，科研人员可以方便快捷的对MWISP实测数据开展分子云核的检测和三维可视化，更好地研究其物理性质。
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