分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
Xiaoyu Luo, Sheng Zheng, Zhibo Jiang, Zhiwei Chen, Yao Huang, Shuguang Zeng, Xiangyun Zeng, Rui Zhang, Chen Long, Guangrong Zhou et al.
Sheng Zheng
Zhibo Jiang
Zhiwei Chen
Yao Huang
Shuguang Zeng
Xiangyun Zeng
Rui Zhang
Chen Long
Guangrong Zhou
Jinbo Hu
摘要： In this study, we present a catalog of molecular clumps extracted from 13CO (J = 1 − 0) emission data of the Milky Way Imaging Scroll Painting (MWISP) project. The data covers the inner Milky Way within the longitude range 10° ≤ l ≤ 20° and the latitude strip of . The workflow for the extraction of clumps, namely Facet-SS-3D-Clump, consists of two parts: the identification of clump candidates and their verification. First, Facet-SS-3D-Clump employs FacetClumps to identify clump candidates. Subsequently, high-confidence clumps are obtained by cross-matching with the clumps detected by other algorithms, such as dendrogram. Second, these high-confidence clumps are used as prior knowledge to train a semi-supervised deep clustering approach, SS-3D-Clump, which is applied to verify clump candidates detected by FacetClumps, providing confidence levels for the molecular clumps. Finally, the catalog comprising 18,757 molecular clumps was obtained using Facet-SS-3D-Clump, and the catalog is 90% complete above 37 K km s−1. We observe a significant deviation of the mean Galactic latitude for clumps within ∣b∣ ≤ 2° from the midplane, with . We found that 82.3% of the dust clumps correspond to 13CO clumps by matching with Herschel infrared dust clumps. In the future, Facet-SS-3D-Clump will be applied to detect 13CO clumps in the entire MWISP data.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Cassiopeia A (Cas A) is a well-known candidate for studying cosmic-ray acceleration, in which compact features of various scales have attracted much attention. Based on observations by the Very Large Array of Cas A at 6 cm and 21 cm, we measure the spectral index distribution of various scale components using the observation of the 1998 epoch. We decompose its total density image into nine scale components, and map the temperature spectral index distribution of each component, which ranges from −2.48 ± 0.01 to −2.91 ± 0.05. We find that the spectral indices increase from the small scale to large scale components. A damped post-shock magnetic field model with a strength larger than ∼200 μG and a damping length scale less than ∼10% of the remnant radius can account for the spectral index variation naturally.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Temporary capture efficiency is studied in the framework of the circular restricted three-body problem in two steps. First, a non-uniform distribution of test particles around the secondary’s orbit is obtained by fully accounting the secondary’s gravitational influence. Second, the capture efficiency is computed based on the non-uniform distribution. Several factors influencing the result are discussed. By studying the capture efficiency in the circular restricted three-body problem of different mass ratios, a power-law relation between the capture efficiency (p) and the mass ratio (μ) is established, which is given by p ≈ 0.27 × μ0.53, within the range of 3.0035 ×10−6 ≤ μ ≤ 3.0034 × 10−5. Taking the Sun–Earth system as an example, the influence from the orbit eccentricity of the secondary on the non-uniform distribution and the capture efficiency is studied. Our studies find that the secondary’s orbit eccentricity has a negative influence on the capture efficiency.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The distribution of the LSBGs is bimodal in the g − r color, indicating the two distinct populations of the blue (g − r 0.60) LSBGs. The blue LSBGs appear spiral, disk or irregular while the red LSBGs are spheroidal or elliptical and spatially clustered. This trend shows that the color has a strong correlation with galaxy morphology for LSBGs. In the spatial distribution, the blue LSBGs are more uniformly distributed while the red ones are highly clustered, indicating that red LSBGs preferentially populate a denser environment than the blue LSBGs. Besides, both populations have a consistent distribution of ellipticity (median ), half-light radius (median reff ∼ 4”) and Sérsic index (median n = 1), implying the dominance of the full sample by the round and disk galaxies. This sample has definitely extended the studies of LSBGs to a regime of lower surface brightness, fainter magnitude and broader other properties than the previously Sloan Digital Sky Survey-based samples.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Open clusters (OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each method has its limitations and therefore, different approaches to discovering OCs hold significant values. We develop a comprehensive approach method to automatically explore the data space and identify potential OC candidates with relatively reliable membership determination. This approach combines the techniques of Hierarchical Density-Based Spatial Clustering of Applications with Noise, Gaussian mixture model, and a novel cluster member identification technique, color excess constraint. The new method exhibits efficiency in detecting OCs while ensuring precise determination of cluster memberships. Because the main feature of this technique is to add an extra constraint (EC) for the members of cluster candidates using the homogeneity of color excess, compared to typical blind search codes, it is called Blind Search-Extra Constraint (BSEC) method. It is successfully applied to the Gaia Data Release 3, and 83 new OCs are found, whose color–magnitude diagrams (CMDs) are fitted well to the isochrones. In addition, this study reports 621 new OC candidates with discernible main sequence or red giant branch. It is shown that BSEC technique can discard some false negatives of previous works, which takes about three percentage of known clusters. It shows that as an EC, the color excess (or two-color) constraint is useful for removing fake cluster member stars from the clusters that are identified from the positions and proper motions of stars, and getting more precise CMDs, when differential reddening of member stars of a cluster is not large (e.g., ΔE(GBP − GRP) < 0.5 mag). It makes the CMDs of 15% clusters clearer (in particular for the region near turnoff) and therefore is helpful for CMD and stellar population studies. Our result suggests that the color excess constraint is more appropriate for clusters with small differential reddening, such as globular clusters or older OCs, and clusters that the distances of member stars cannot be determined accurately.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
Hao Li, Qing Zhao, Long Shao, Tao Liu, Chenzhou Cui and Yunfei Xu
Hao Li
Qing Zhao
Long Shao
Tao Liu
Chenzhou Cui
Yunfei Xu
摘要： Nowadays, astronomy has entered the era of Time-Domain Astronomy, and the study of the time-varying light curves of various types of objects is of great significance in revealing the physical properties and evolutionary history of celestial bodies. The Ground-based Wide Angle Cameras telescope, on which this paper is based, has observed more than 10 million light curves, and the detection of anomalies in the light curves can be used to rapidly detect transient rare phenomena such as microgravity lensing events from the massive data. However, the traditional statistically based anomaly detection methods cannot realize the fast processing of massive data. In this paper, we propose a Discrete Wavelet (DW)-Gate Recurrent Unit-Attention (GRU-Attention) light curve warning model. Wavelet transform has good effect on data noise reduction processing and feature extraction, which can provide richer and more stable input features for a neural network, and the neural network can provide more flexible and powerful output model for wavelet transform. Comparison experiments show an average improvement of 61% compared to the previous pure long-short-term memory unit (LSTM) model, and an average improvement of 53.5% compared to the previous GRU model. The efficiency and accuracy of anomaly detection in previous paper work are not good enough, the method proposed in this paper possesses higher efficiency and accuracy, which incorporates the Attention mechanism to find out the key parts of the light curve that determine the anomalies. These parts are assigned higher weights, and in the actual anomaly detection, the star is detected with 83.35% anomalies on average, and the DW-GRU-Attention model is compared with the DW-LSTM model, and the detection result f1 is improved by 5.75% on average, while having less training time, thus providing valuable information and guidance for astronomical observation and research.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： In this work, we consider a conventional test of gravitational wave (GW) propagation which is based on the phenomenological parameterized dispersion relation to describe potential departures from General Relativity (GR) along the propagation of GWs. But different from tests conventionally performed previously, we vary multiple deformation coefficients simultaneously and employ the principal component analysis (PCA) method to remedy the strong degeneracy among deformation coefficients and obtain informative posteriors. The dominant PCA components can be better measured and constrained, and thus are expected to be more sensitive to potential departures from the waveform model. Using this method we analyze ten selected events and get the result that the combined posteriors of the dominant PCA parameters are consistent with GR within 99.7% credible intervals. The standard deviation of the first dominant PCA parameter is three times smaller than that of the original dispersion parameter of the leading order. However, the multi-parameter test with PCA is more sensitive to not only potential deviations from GR but also systematic errors of waveform models. The difference in results obtained by using different waveform templates hints that the demands of waveform accuracy are higher to perform the multi-parameter test with PCA. Whereas, it cannot be strictly proven that the deviation is indeed and only induced by systematic errors. It requires more thorough research in the future to exclude other possible reasons in parameter estimation and data processing.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Based on the collected multiwavelength data, namely in the radio (NVSS, FIRST, RATAN-600), IR (WISE), optical (Pan-STARRS), UV (GALEX), and X-ray (ROSAT, Swift-XRT) ranges, we have performed a cluster analysis for the blazars of the Roma-BZCAT catalog. Using two machine learning methods, namely a combination of PCA with k-means clustering and Kohonen’s self-organizing maps (SOMs), we have constructed an independent classification of the blazars (five classes) and compared the classes with the known Roma-BZCAT classification (FSRQs, BL Lacs, galaxy-dominated BL Lacs, and blazars of an uncertain type) as well as with the high synchrotron peaked (HSP) blazars from the 3HSP catalog and blazars from the TeVCat catalog. The obtained groups demonstrate concordance with the BL Lac/FSRQ classification along with a continuous character of the change in the properties. The group of HSP blazars stands out against the overall distribution. We examine the characteristics of the five groups and demonstrate distinctions in their spectral energy distribution shapes. The effectiveness of the clustering technique for objective analysis of multiparametric arrays of experimental data is demonstrated.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： This work shows details of an evaluation of an observational system comprising a complementary metal-oxide-semiconductor detector, 60 cm telescope and filter complement. The system's photometric precision and differential photometric precision, and extinction coefficients were assessed through observations of Supersky flat fields, open clusters, standard stars and exoplanets. Photometry was precision achieved at the 0.02 mag level, with differential photometry of 0.004 mag precision. Extinction was found to agree with previous studies conducted at Xinglong Observatory. Ultimately, the results demonstrate this observing system is capable of precision scientific observations with a charge-coupled device across the optical wavelengths.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The near-infrared imaging channel constitutes a crucial component of the multichannel high-resolution imaging system of the New Vacuum Solar Telescope (NVST). We have successfully achieved high-resolution, narrowband imaging of the chromosphere using He i 10830 Å triplet within this channel, which significantly enhances the imaging observation capabilities of NVST. This paper provides a concise overview of the optical system associated with the near-infrared imaging channel, detailing data processing procedures and presenting several observed images. Leveraging a high-resolution image reconstruction algorithm, we were able to generate a narrowband image near the diffraction limit at 10830 Å with a temporal resolution of less than 10 s.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The occurrence of the first significant digits from real world sources is usually not equally distributed, but is consistent with a logarithmic distribution instead, known as Benford's law. In this work, we perform a comprehensive investigation on the first digit distributions of the duration, fluence, and energy flux of gamma-ray bursts (GRBs) for the first time. For a complete GRB sample detected by the Fermi satellite, we find that the first digits of the duration and fluence adhere to Benford's law. However, the energy flux shows a significant departure from this law, which may be due to the fact that a considerable part of the energy flux measurements is restricted by lack of spectral information. Based on the conventional duration classification scheme, we also check if the durations and fluences of long and short GRBs (with duration T90 > 2 s and T90 ≤ 2 s, respectively) obey Benford's law. We find that the fluences of both long and short GRBs still agree with the Benford distribution, but their durations do not follow Benford's law. Our results hint that the long–short GRB classification scheme does not directly represent the intrinsic physical classification scheme.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： We have chosen the Large Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code to calculate the coalescence of silicon carbide (SiC), silicon oxide dust (SiO) in the AGB stellar wind. LAMMPS is a classical molecular dynamics simulation code. At the same time, we consider the effect of temperature on the evolution of molecular dynamics. We also calculated the temperature change of non-spherical SiC, SiO dust coalescence. The condensation temperature range of SiC dust in the AGB stellar wind is 300–500 k and 900–1100 k for SiO. Finally, the infrared spectrum of SiC was calculated using Gaussian 16 software. The 77SiC, 70Si3C3, and 121Si3C3 models have clear characteristic peaks of infrared spectra responding at 5, 8.6, 11.3, 15, 19, and 37 μm.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The first photometric light curve investigation of the NSVS 8294044, V1023 Her, and V1397 Her binary systems is presented. We used ground-based observations for the NSVS 8294044 system and Transiting Exoplanet Survey Satellite data for V1023 Her and V1397 Her. The primary and secondary times of minima were extracted from all the data, and, by collecting the literature, a new ephemeris was computed for each system. Linear fits for the O − C diagrams were conducted using the Markov Chain Monte Carlo (MCMC) method. Light curve solutions were performed using the PHysics Of Eclipsing BinariEs Python code and the MCMC approach. The systems were found to be contact binary stars based on the fillout factor and mass ratio. V1023 Her showed the O’Connell effect, and a cold starspot on the secondary component was required for the light curve solution. The absolute parameters of the system were estimated based on an empirical relationship between orbital period and mass. We presented a new T–M equation based on a sample of 428 contact binary systems and found that our three target systems were in good agreement with the fit. The positions of the systems were also depicted on the M–L, M–R, q–Lratio, and Mtot–J0 diagrams in the logarithmic scales.
分类： 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类： 天文学 >> 天文学 提交时间： 2024-05-22
摘要： The electromagnetic fields of point sources with time varying charges moving in the vacuum are derived using the Liénard-Wiechert potentials. The properties of the propagation velocities and the Doppler effect are discussed based on their far fields. The results show that the velocity of the electromagnetic waves and the velocity of the sources cannot be added like vectors; the velocity of electromagnetic waves of moving sources are anisotropic in the vacuum; the transverse Doppler shift is intrinsically included in the fields of the moving sources and is not a pure relativity effect caused by time dilation. Since the fields are rigorous solutions of the Maxwell’s equations, the findings can help us to abort the long-standing misinterpretations concerning about the classic mechanics and the classic electromagnetic theory. Although it may violate the theory of the special relativity, we show mathematically that, when the sources move faster than the light in the vacuum, the electromagnetic barriers and the electromagnetic shock waves can be clearly predicted using the exact solutions. Since they cannot be detected by observers in the region outside their shock wave zones, an intuitive and reasonable hypothesis can be made that the superluminal sources may be considered as a kind of electromagnetic blackholes.
分类： 天文学 >> 天文学 提交时间： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Attitude is one of the crucial parameters for space objects and plays a vital role in collision prediction and debris removal. Analyzing light curves to determine attitude is the most commonly used method. In photometric observations, outliers may exist in the obtained light curves due to various reasons. Therefore, preprocessing is required to remove these outliers to obtain high quality light curves. Through statistical analysis, the reasons leading to outliers can be categorized into two main types: first, the brightness of the object significantly increases due to the passage of a star nearby, referred to as "stellar contamination," and second, the brightness markedly decreases due to cloudy cover, referred to as "cloudy contamination." The traditional approach of manually inspecting images for contamination is time-consuming and labor-intensive. However, we propose the utilization of machine learning methods as a substitute. Convolutional Neural Networks and SVMs are employed to identify cases of stellar contamination and cloudy contamination, achieving F1 scores of 1.00 and 0.98 on a test set, respectively. We also explore other machine learning methods such as ResNet-18 and Light Gradient Boosting Machine, then conduct comparative analyses of the results.
分类： 天文学 >> 天文学 提交时间： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive. This paper presents a new approach that combines a simplified Cellinoid shape model with the Parallel Differential Evolution (PDE) algorithm to accelerate inversion. The PDE algorithm is more efficient than the Differential Evolution algorithm, achieving an extraordinary speedup of 37.983 with 64 workers on multicore CPUs. The PDE algorithm accurately derives period and pole values from simulated data. The analysis of real asteroid lightcurves validates the method's reliability: in comparison with results published elsewhere, the PDE algorithm accurately recovers the rotational periods and, given adequate viewing geometries, closely matches the pole orientations. The PDE approach converges to solutions within 20,000 iterations and under one hour, demonstrating its potential for large-scale data analysis. This work provides a promising new tool for unveiling asteroid physical properties by overcoming key computational bottlenecks.
分类： 天文学 >> 天文学 提交时间： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Infrared dust bubbles play an important role in the study of star formation and the evolution of the interstellar medium. In this work, we study the infrared dust bubble N75 and the infrared dark cloud G38.93 mainly using the tracers C18O, HCO+, HNC and N2H+ observed by the 30 m IRAM telescope. We also study the targets using data from large-scale surveys: GLIMPSE, MIPSGAL, GRS, NRAO VLA Sky Survey and Bolocam Galactic Plane Survey. We found that the C18O emission is morphologically similar to the Spitzer IRAC 8.0 μm emission. The 1.1 mm cold dust emission of G38.93 shows an elongated structure from southwest to northeast. The ionized gas from G38.93 is surrounded by polycyclic aromatic hydrocarbon emission, which may be excited by radiation from G38.93. We found that the identified young stellar objects tend to cluster around G38.93 and are mostly in class II, with several class I cases distributed around N75, but no class II examples. We also found evidence of expanding feedback, which could have triggered star formation.
分类： 天文学 >> 天文学 提交时间： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： We have conducted a comprehensive investigation into the bright single pulse emission from PSR B1133+16 using the Giant Metrewave Radio Telescope. High time resolution data (61 μs) were obtained at a center frequency of 322 MHz with a bandwidth of 32 MHz over a continuous observation period of 7.45 hr. A total of 1082 bright pulses were sporadically detected with peak flux densities ranging from 10 to 23 times stronger than the average pulse profile. However, no giant pulse-like emission with a relative pulse energy larger than 10 and extremely short duration was detected, indicating that these bright pulses cannot be categorized as giant pulse emission. The majority of these bright pulses are concentrated in pulse phases at both the leading and trailing windows of the average pulse profile, with an occurrence ratio of approximately 2.74. The pulse energy distribution for all individual pulses can be described by a combination of two Gaussian components and a cutoff power-law with an index of α = − 3.2. An updated nulling fraction of 15.35% ± 0.45% was determined from the energy distribution. The emission of individual pulses follows a log-normal distribution in peak flux density ratio. It is imperative that regular phase drifting in bright pulse sequence is identified in both the leading and trailing components for the first time. Possible physical mechanisms are discussed in detail to provide insights into these observations.
分类： 天文学 >> 天文学 提交时间： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The initial condition of high-mass star formation is a complex area of study because of the high densities () and low temperatures (Tdust < 18 K) involved. Under such conditions, many molecules become depleted from the gas phase by freezing out onto dust grains. However, the N-bearing and deuterated species could remain gaseous under these extreme conditions, suggesting that they may serve as ideal tracers. In this paper, using the Plateau de Bure Interferometer and Very Large Array observations at 1.3 mm, 3.5 mm, and 1.3 cm, we investigate the possible habitats for NH3, NH2D, H13CN, HC15N, SO, and C18O in eight massive precluster and protocluster clumps G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71. We found that the NH3 cores are in good agreement with the 3.5 mm peak emission, but the NH3 is much more extended than the 3.5 mm emission structure. The SO distributions agree well with the 3.5 mm peaks for the evolved star formation stage, but we did not detect any SO emission in the four earliest star formation sources. C18O is a poor tracer in conditions of the cold (≲18 K) and dense (≳104 cm−3) cores, e.g., the prestellar cores. We also found that the NH2D cores are mainly located in the temperature range of 13.0–20.0 K, and the NH2D lines may be strongly depleted above 20 K.
分类： 天文学 >> 天文学 提交时间： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： This study introduces a novel convolutional neural network, the WISE Galaxy Classification Network (WGC), for classifying spiral and elliptical galaxies using Wide-field Infrared Survey Explorer (WISE) images. WGC attains an accuracy of 89.03%, surpassing the combined use of K-means or SVM with the Color–Color method in more accurately identifying galaxy morphologies. The enhanced variant, WGC_mag, integrates magnitude parameters with image features, further boosting the accuracy to 89.89%. The research also delves into the criteria for galaxy classification, discovering that WGC primarily categorizes dust-rich images as elliptical galaxies, corresponding to their lower star formation rates, and classifies less dusty images as spiral galaxies. The paper explores the consistency and complementarity of WISE infrared images with SDSS optical images in galaxy morphology classification. The SDSS Galaxy Classification Network (SGC), trained on SDSS images, achieved an accuracy of 94.64%. The accuracy reached 99.30% when predictions from SGC and WGC were consistent. Leveraging the complementarity of features in WISE and SDSS images, a novel variant of a classifier, namely the Multi-band Galaxy Morphology Integrated Classifier, has been developed. This classifier elevates the overall prediction accuracy to 95.39%. Lastly, the versatility of WGC was validated in other data sets. On the HyperLEDA data set, the distinction between elliptical galaxies and Sc, Scd and Sd spiral galaxies was most pronounced, achieving an accuracy of 90%, surpassing the classification results of the Galaxy Zoo 2 labeled WISE data set. This research not only demonstrates the effectiveness of WISE images in galaxy morphology classification but also represents an attempt to integrate multi-band astronomical data to enhance understanding of galaxy structures and evolution.
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