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： 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 capturing, 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$^{-2}$\,$\cdot $\,h$^{-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.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： 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.
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： 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 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.
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