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.
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 Solar Polar-orbit Observatory (SPO), proposed by Chinese scientists, is designed to observe the solar polar regions in an unprecedented way with a spacecraft traveling in a large solar inclination angle and a small ellipticity. However, one of the most significant challenges lies in ultra-long-distance data transmission, particularly for the Magnetic and Helioseismic Imager (MHI), which is the most important payload and generates the largest volume of data in SPO. In this paper, we propose a tailored lossless data compression method based on the measurement mode and characteristics of MHI data. The background out of the solar disk is removed to decrease the pixel number of an image under compression. Multiple predictive coding methods are combined to eliminate the redundancy utilizing the correlation (space, spectrum, and polarization) in data set, improving the compression ratio. Experimental results demonstrate that our method achieves an average compression ratio of 3.67. The compression time is also less than the general observation period. The method exhibits strong feasibility and can be easily adapted to MHI.
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 light curve analyses and orbital period variations for two contact binary stars, LS Del and V997 Cyg, are presented in this work which was conducted in the frame of the Binary Systems of South and North project. Ground-based photometric observations were performed at two observatories in France. We used the Transiting Exoplanet Survey Satellite (TESS) data for extracting times of minima and light curve analysis of the target systems. The O − C diagram for both systems displays a parabolic trend. LS Del and V997 Cyg's orbital periods are increasing at rates of dP/dt = 7.20 × 10−08 days yr−1 and dP/dt = 2.54 × 10−08 days yr−1, respectively. Therefore, it can be concluded that mass is being transferred from the less massive star to the more massive component with a rate of dM/dt = –1.96 × 10−7M⊙ yr−1 for the LS Del system, and dM/dt =–3.83 × 10−7M⊙ yr−1 for V997 Cyg. The parameters of a third possible object in the system are also considered. The PHysics Of Eclipsing BinariEs Python code was used to analyze the light curves. The light curve solutions needed a cold starspot due to the asymmetry in the LS Del system's light curve maxima. The mass ratio, fill-out factor, and star temperature all indicate that both systems are contact binary types in this investigation. Two methods were applied to estimate the absolute parameters of the systems: one method relied on the parallax of Gaia DR3, and the other used a P − M relationship. The positions of the systems are also depicted on the M − L, M − R, q − Lratio, and diagrams. We recommend that further observations and investigations be done on the existence of a fourth body in this system.
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 Multi-channel Photometric Survey Telescope (Mephisto) is a real-time, three-color photometric system designed to capture the color evolution of stars and transients accurately. This telescope system can be crucial in cosmological distance measurements of low-redshift (low-z, z ≲0.1) Type Ia supernovae (SNe Ia). To optimize the capabilities of this instrument, we perform a comprehensive simulation study before its official operation is scheduled to start. By considering the impact of atmospheric extinction, weather conditions, and the lunar phase at the observing site involving the instrumental features, we simulate light curves of SNe Ia obtained by Mephisto. The best strategy in the case of SN Ia cosmology is to take the image at an exposure time of 130 s with a cadence of 3 days. In this condition, Mephisto can obtain hundreds of high-quality SNe Ia to achieve a distance measurement better than 4.5%. Given the on-time spectral classification and monitoring of the Lijiang 2.4 m Telescope at the same observatory, Mephisto, in the whole operation, can significantly enrich the well-calibrated sample of supernovae at low-z and improve the calibration accuracy of high-z SNe Ia.
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 study the structural and dynamical properties of A209 based on Chandra and XMM-Newton observations. We obtain detailed temperature, pressure, and entropy maps with the contour binning method, and find a hot region in the NW direction. The X-ray brightness residual map and corresponding temperature profiles reveal a possible shock front in the NW direction and a cold front feature in the SE direction. Combined with the galaxy luminosity density map we propose a weak merger scenario. A young sub-cluster passing from the SE to NW direction could explain the optical subpeak, the intracluster medium temperature map, the X-ray surface brightness excess, and the X-ray peak offset together.
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： Deriving atmospheric parameters of a large sample of stars is of vital importance to understand the formation and evolution of the Milky Way. Photometric surveys, especially those with near-ultraviolet filters, can offer accurate measurements of stellar parameters, with the precision comparable to that from low/medium resolution spectroscopy. In this study, we explore the capability of measuring stellar atmospheric parameters from Chinese Space Station Telescope (CSST) broad-band photometry (particularly in the near-ultraviolet bands), based on synthetic colors derived from model spectra. We find that colors from the optical and near-ultraviolet filter systems adopted by CSST show significant sensitivities to the stellar atmospheric parameters, especially the metallicity. According to our mock data tests, the precision of the photometric metallicity is quite high, with typical values of 0.17 and 0.20 dex for dwarf and giant stars, respectively. The precision of the effective temperature estimated from broad-band colors are within 50 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： Using the data on magnetic field maps and continuum intensity for Solar Cycles 23 and 24, we explored 100 active regions (ARs) that produced M5.0 or stronger flares. We focus on the presence/absence of the emergence of magnetic flux in these ARs 2–3 days before the strong flare onset. We found that 29 ARs in the sample emerged monotonically amidst quiet-Sun. A major emergence of a new magnetic flux within a pre-existing AR yielding the formation of a complex flare-productive configuration was observed in another 24 cases. For 30 ARs, an insignificant (in terms of the total magnetic flux of pre-existing AR) emergence of a new magnetic flux within the pre-existing magnetic configuration was observed; for some of them the emergence resulted in a formation of a configuration with a small δ-sunspot; 11 out of 100 ARs exhibited no signatures of magnetic flux emergence during the entire interval of observation. In six cases the emergence was in progress when the AR appeared on the Eastern limb, so that the classification and timing of emergence were not possible. We conclude that the recent flux emergence is not a necessary and/or sufficient condition for strong flaring of an AR. The flux emergence rate of flare-productive ARs analyzed here was compared with that of flare-quiet ARs analyzed in our previous studies. We revealed that the flare-productive ARs tend to display faster emergence than the flare-quiet ones do.
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 correlation between close-in super Earths and distant cold Jupiters in planetary systems has important implications for their formation and evolution. Contrary to some earlier findings, a recent study conducted by Bonomo et al. suggests that the occurrence of cold Jupiter companions is not excessive in super-Earth systems. Here we show that this discrepancy can be seen as a Simpson's paradox and is resolved once the metallicity dependence of the super-Earth–cold Jupiter relation is taken into account. A common feature is noticed that almost all the cold Jupiter detections with inner super-Earth companions are found around metal-rich stars. Focusing on the Sun-like hosts with super-solar metallicities, we show that the frequency of cold Jupiters conditioned on the presence of inner super Earths is , whereas the frequency of cold Jupiters in the same metallicity range is no more than 20%. Therefore, the occurrences of close-in super Earths and distant cold Jupiters appear correlated around metal-rich hosts. The relation between the two types of planets remains unclear for stars with metal-poor hosts due to the limited sample size and the much lower occurrence rate of cold Jupiters, but a correlation between the two cannot be ruled out.
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： A spatial template is important to study nearby supernova remnants (SNRs). For SNR G332.5-5.6, we report a Gaussian disk with a radius of about 106 to be a potential good spatial model in the γ-ray band. Employing this new Gaussian disk, its GeV lightcurve shows a significant variability of about seven sigma. The γ-ray observations of this SNR could be explained well either by a leptonic model or a hadronic model, in which a flat spectrum for the ejected electrons/protons is required.
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： AT2021lfa, also known as ZTF21aayokph, was detected by the Zwicky Transient Facility on 2021 May 4, at 05:34:48 UTC. Follow-up observations were conducted using a range of ground-based optical telescopes, as well as Swift/XRT and VLA instruments. AT2021lfa is classified as an "orphan afterglow" candidate due to its rapid flux decline and its reddened color (g − r = 0.17 ± 0.14 mag). For an optical transient source without prompt gamma-ray detection, one key point is to determine its burst time. Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3, at 22:09:50 UTC. Using afterglowpy, we model the multi-band afterglow of AT2021lfa and find that the standard model cannot reproduce the late radio observations well. Considering that the microphysical parameters (the energy fraction given to electrons and magnetic field), and ξN (the fraction of accelerated electrons) may vary with time, we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters , and ξN and find in this case the multi-wavelength observations can be reproduced well. The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow, which yields a value of about 18, suggesting that AT2021lfa should be classified as a "dirty fireball." From the upper limit for the prompt emission energy of AT2021lfa, we obtain that the radiation efficiency is less than 0.02%, which is much smaller than that of ordinary gamma-ray bursts (GRBs). It is also interesting that the fitted values of jet angle and viewing angle are very large, θc ∼ 0.66 rad, θv ∼ 0.53 rad, which may lead to the low Lorentz factor and radiation efficiency. When compared with GRB afterglow samples, it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples. Additionally, the luminosity of AT2021lfa falls within the range of observations for GRB samples; however, approximately 1 day after the burst, its luminosity exceeds that of the majority of GRB samples.
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： Rotating Radio Transients (RRATs) are a relatively new subclass of pulsars that emit detectable radio bursts sporadically. We analyzed 10 RRATs observed using the Parkes telescope, with eight of these observed via the ultra-wide-bandwidth low-frequency (UWL) receiver. We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs. We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs. All of their integrated pulses follow a simple power law, consistent with the known range of pulsar spectral indices. Their average spectral indices of single pulses are −0.9, −1.2, and −1.0 respectively, which are within the known range of pulsar spectral indices. Additionally, we find that the spreads of single-pulse spectral indices for these RRATs (ranging from −3.5 to +0.5) are narrower compared to what has been observed in other RRATs. Notably, the average spectral index and scatter of single pulses are both relatively small. For the remaining five RRATs observed at the UWL receiver, we also provide the upper limits on fluence and flux density. In addition, we obtain the timing solution of PSR J1709-43. Our analysis shows that PSRs J1919+1745, J1709-43, and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.
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 developed a novel method for co-adding multiple under-sampled images that combines the iteratively reweighted least squares and divide-and-conquer algorithms. Our approach not only allows for the anti-aliasing of the images but also enables Point-Spread Function (PSF) deconvolution, resulting in enhanced restoration of extended sources, the highest peak signal-to-noise ratio, and reduced ringing artefacts. To test our method, we conducted numerical simulations that replicated observation runs of the China Space Station Telescope/ the VLT Survey Telescope (VST) and compared our results to those obtained using previous algorithms. The simulation showed that our method outperforms previous approaches in several ways, such as restoring the profile of extended sources and minimizing ringing artefacts. Additionally, because our method relies on the inherent advantages of least squares fitting, it is more versatile and does not depend on the local uniformity hypothesis for the PSF. However, the new method consumes much more computation than the other approaches.
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 investigate the population and several properties of radio pulsars whose emission does not null (non-nulling) through simulation of a large pulsar sample. Emission from a pulsar is identified as non-nulling if (i) the emission does not cease across the whole pulse profile, and (ii) the emission is detectable. For (i), we adopt a model for switching in the plasma charge density, and emission persists if the charge density is non-zero. For (ii), we assume that detectable emission originates from source points where it is emitted tangentially to the magnetic field-line and parallel to the line-of-sight. We find that pulsars exhibiting non-nulling emission possess obliquity angles with an average of 425, and almost half the samples maintain a duty cycle between 0.05 and 0.2. Furthermore, the pulsar population is not fixed but dependent on the obliquity angle, with the population peaking at 20°. In addition, three evolutionary phases are identified in the pulsar population as the obliquity angle evolves, with the majority of samples having an obliquity angle between 20° and 65°. Our results also suggest that emission from a pulsar may evolve between nulling and non-nulling during its lifetime.
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 triggering mechanism for radio lobes from late-type galaxies is not fully understood. More samples are desired for a thorough investigation and statistics. By utilizing the optical data from the newly released Dark Energy Spectroscopic Instrument imaging surveys and the radio sources from the NRAO VLA Sky Survey and the Faint Images of the Radio Sky at Twenty-centimeter, we identify four Late-type Galaxies with double Radio Lobes (LaGRLs): J0217−3645, J0947+6220, J1412+3723 and J1736+5108. Including previously known LaGRLs, we confirm the correlation between radio power P1.4 GHz and stellar mass M* of host galaxies. Most (25/35) LaGRLs belong to the blue cloud galaxies, while the newly identified cases in this work are located within the region of the red sequence. We find a clear correlation between the differential radio power, i.e., the offset from the P1.4 GHz − M* relation, and the galaxy color, indicating that bluer galaxies at a fixed M* tend to host more powerful radio lobes. Furthermore, the majority (31/36) of LaGRLs are either located in a galaxy group or displaying a disturbed morphology. We suggest that all of the galaxy mass, color and surrounding environment could play important roles in triggering radio lobes in late-type galaxies.
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 receiver is a signal receiving device placed at the focus of the telescope. In order to improve the observation efficiency, the concept of phased array receiver has been proposed in recent years, which places a small phased array at the focal plane of the reflector, and flexible pattern and beam scanning functions can be achieved through a beamforming network. If combined with the element multiplexing, all beams within the entire field of view can be observed simultaneously to achieve continuous sky coverage. This article focuses on the front-end array of phased array receiver at 0.7–1.8 GHz for QiTai Telescope, and designs a Vivaldi antenna array of PCB structure with dual line polarization. Each polarization antenna is designed to arrange in a rectangle manner by 11 × 10. Based on the simulation results of the focal field, 32, 18, and eight elements were selected to form one beam at 0.7, 1.25, and 1.8 GHz. An analog beamforming network was constructed, and the measured gains of axial beam under uniform weighting were 19.32, 13.72, and 15.22 dBi. Combining the beam scanning method of reflector antenna, the pattern test of different position element sets required for PAF beam scanning was carried out under independent array. The pattern optimization at 1.25 GHz was carried out by weighting method of conjugate field matching. Compared with uniform weighting, the gain, sidelobe level, and main beam direction under conjugate field matching have been improved. Although the above test and simulation results are slightly different, which is related to the passive array and laboratory testing condition, the relevant work has accumulated experience in the development of the front-end array for the phased array receiver, and has good guiding significance for future performance verification after the array is installed on the telescope.
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