检索结果-南通市图书馆

Research in Astronomy and Astrophysics 2021年第9期21卷 207-216页

作者： Jibrin Adejoh Alhassan Ogbonnaya Okike Augustine Ejikeme Chukwude Department of Physics and Astronomy University of NigeriaNsukka 400001Nigeria Department of Industrial Physics Ebonyi State UniversityAbakaliki 840001Nigeria

Forbush decrease(FD),discovered by Scott *** about 80 years ago,is referred to as the non-repetitive short-term depression in Galactic cosmic ray(GCR)flux,presumed to be associated with large-scale perturbations in solar wind and interplanetary magnetic field(IMF).It is the most spectacular variability in the GCR intensity which appears to be the compass for investigators seeking solar-terrestrial *** method of selection and validation of FD events is very important to cosmic ray(CR)*** have deployed new computer software to determine the amplitude and timing of FDs from daily-averaged CR data at Oulu Neutron Monitor *** code selected 230 FDs between 1998 and *** an attempt to validate the new FD automated catalog,the relationship between the amplitude of FDs,and IMF,solar wind speed(SWS)and geomagnetic storm indices(Dst,kp,ap)is tested here.A two-dimensional regression analysis indicates significant linear relationship between large FDs(CR(%)≤-3)and solar wind data and geomagnetic storm indices in the present *** implications of the relationship among these parameters are discussed.

关键词： methods:data analysis methods:statistical Sun:coronal mass ejections(CMEs) (Sun:)solar-terrestrial relations (Sun:)solar wind (ISM:)cosmic rays

Analysis of the Distribution,Rotation and Scale Characteristics of Solar Wind Switchbacks:Comparison between the First and Second Encounters of Parker Solar Probe

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2022年第3期22卷 178-185页

作者： Ming-Ming Meng Ying D.Liu Chong Chen Rui Wang State Key Laboratory of Space Weather National Space Science CenterChinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China

The S-shaped magnetic structure in the solar wind formed by the twisting of magnetic field lines is called a switchback,whose main characteristics are the reversal of the magnetic field and the significant increase in the solar wind radial *** identify 242 switchbacks during the first two encounters of Parker Solar *** methods are applied to analyze the distribution and the rotation angle and direction of the magnetic field rotation of the *** diameter of switchbacks is estimated with a minimum variance analysis(MVA)method based on the assumption of a cylindrical magnetic *** also make a comparison between switchbacks from inside and the boundary of coronal *** main conclusions are as follows:(1)the rotation angles of switchbacks observed during the first encounter seem larger than those of the switchbacks observed during the second encounter in general;(2)the tangential component of the velocity inside the switchbacks tends to be more positive(westward)than in the ambient solar wind;(3)switchbacks are more likely to rotate clockwise than counterclockwise,and the number of switchbacks with clockwise rotation is 1.48 and 2.65 times those with counterclockwise rotation during the first and second encounters,respectively;(4)the diameter of switchbacks is about 10;km on average and across five orders of magnitude(10^(3)–10^(7)km).

关键词： ISM:magnetic fields methods:statistical (Sun:)solar wind

Photometric Redshift Estimates using Bayesian Neural Networks in the CSST Survey

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2022年第11期22卷 190-206页

作者： Xingchen Zhou Yan Gong Xian-Min Meng Xuelei Chen Zhu Chen Wei Du Liping Fu Zhijian Luo National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Science Center for China Space Station Telescope National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Key Laboratory of Computational Astrophysics National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Center for High Energy Physics Peking UniversityBeijing 100871China Shanghai Key Lab for Astrophysics Shanghai Normal UniversityShanghai 200234China

Galaxy photometric redshift(photoz)is crucial in cosmological studies,such as weak gravitational lensing and galaxy angular clustering *** this work,we try to extract photoz information and construct its probability distribution function(PDF)using the Bayesian neural networks from both galaxy flux and image data expected to be obtained by the China Space Station Telescope(CSST).The mock galaxy images are generated from the Hubble Space Telescope-Advanced Camera for Surveys(HST-ACS)and COSMOS catalogs,in which the CSST instrumental effects are carefully *** addition,the galaxy flux data are measured from galaxy images using aperture *** construct a Bayesian multilayer perceptron(B-MLP)and Bayesian convolutional neural network(B-CNN)to predict photoz along with the PDFs from fluxes and images,*** combine the B-MLP and B-CNN together,and construct a hybrid network and employ the transfer learning techniques to investigate the improvement of including both flux and image *** galaxy samples with signal-to-noise ratio(SNR)>10 in g or i band,we find the accuracy and outlier fraction of photoz can achieve σ_(NMAD)=0.022 and η=2.35% for the B-MLP using flux data only,and σ_(NMAD)=0.022 and η=1.32% for the B-CNN using image data *** Bayesian hybrid network can achieve σ_(NMAD)=0.021 and η=1.23%,and utilizing transfer learning technique can improve results to σ_(NMAD)=0.019 and η=1.17%,which can provide the most confident predictions with the lowest average uncertainty.

关键词： (cosmology:)large-scale structure of universe methods:statistical techniques:image processing

The Quasar Candidate Catalogs of DESI Legacy Imaging Survey Data Release 9

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2022年第9期22卷 267-277页

作者： Zizhao He Nan Li Key Laboratory of Space Astronomy and Technology National Astronomical ObservatoriesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China

Quasars can be used to measure baryon acoustic oscillations at high redshift, which are considered as direct tracers of the most distant large-scale structures in the universe. It is fundamental to select quasars from observations before implementing the above research. This work focuses on creating a catalog of quasar candidates based on photometric data to provide primary priors for further object classification with spectroscopic data in the future, such as the Dark Energy Spectroscopic Instrument(DESI) Survey. We adopt a machine learning algorithm(Random Forest, RF) for quasar identification. The training set includes 651,073 positives and 1,227,172 negatives, in which the photometric information are from DESI Legacy Imaging Surveys(DESI-LIS) and Wide-field Infrared Survey Explore(WISE), and the labels are from a database of spectroscopically confirmed quasars based on Sloan Digital Sky Survey and the Set of Identifications& Measurements and Bibliography for Astronomical Data. The trained RF model is applied to point-like sources in DESI-LIS Data Release 9. To quantify the classifier’s performance, we also inject a testing set into the to-be-applied ***, we obtained 1,953,932 Grade-A quasar candidates and 22,486,884 Grade-B quasar candidates out of425,540,269 sources(~5.7%). The catalog covers ~99% of quasars in the to-be-applied data by evaluating the completeness of the classification on the testing set. The statistical properties of the candidates agree with that given by the method of color-cut selection. Our catalog can intensely decrease the workload for confirming quasars with the upcoming DESI data by eliminating enormous non-quasars but remaining high completeness. All data in this paper are publicly available online.

关键词： galaxies:quasars:general catalogs methods:statistical

DmpIRFs and DmpST:DAMPE instrument response functions and science tools for gamma-ray data analysis

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2019年第9期19卷 109-118页

作者： Kai-Kai Duan Wei Jiang Yun-Feng Liang Zhao-Qiang Shen Zun-Lei Xu Yi-Zhong Fan Fabio Gargano Simone Garrappa Dong-Ya Guo Shi-Jun Lei Xiang Li Mario Nicola Mazziotta Maria Ferna Munoz Salinas Meng Su Valerio Vagelli Qiang Yuan Chuan Yue Stephan Zimmer Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing210033China University of Chinese Academy of Sciences Beijing100049China School of Astronomy and Space Science University of Science and Technology of ChinaHefei230026China Istituto Nazionale di Fisica Nucleare Sezione di Bari I-70125BariItaly Istituto Nazionale di Fisica Nucleare Sezione di Perugia I-06123PerugiaItaly Dipartimento di Fisica e Geologia Universita degli Studi di PerugiaI-06123PerugiaItaly Institute of High Energy Physics Chinese Academy of SciencesBeijing100049China Department of Nuclear and Particle Physics University of GenevaCH-1211Switzerland Department of Physics and Laboratory for Space Research University of Hong KongPok Fu LamHong KongChina

Observing GeV gamma-rays is an important goal of the DArk Matter Particle Explorer(DAMPE)for indirect dark matter searching and high energy astrophysics. In this work, we present a set of accurate instrument response functions for DAMPE(DmpIRFs) including the effective area, point-spread function and energy dispersion, which are crucial for gamma-ray data analysis based on statistics from simulation data. A dedicated software named DmpST is developed to facilitate the scientific analyses of DAMPE gamma-ray data. Considering the limited number of photons and angular resolution of DAMPE, the maximum likelihood method is adopted in DmpST to better disentangle different source components. The basic mathematics and framework regarding this software are also introduced in this paper.

关键词： gamma rays:general instrumentation:detectors methods:statistical

Low Surface Brightness Galaxies Selected by Different Model Fitting

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2024年第1期24卷 223-236页

作者： Bing-Qing Zhang Hong Wu Wei Du Pin-Song Zhao Min He Feng-Jie Lei Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China

We present a study of low surface brightness galaxies(LSBGs) selected by fitting the images for all the galaxies inα.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models(disk+bulge):single exponential,single sersic,exponential+deVaucular(exp+deV),and exponential+sérsic(exp+ser).Under the criteria of the B band disk central surface brightness μ_(0,disk)(B)≥22.5 mag arcsec^(-2) and the axis ratio b/a> 0.3,we selected four none-edge-on LSBG samples from each of the models which contain 1105,1038,207,and 75 galaxies,*** are 756 galaxies in common between LSBGs selected by exponential and sersic models,corresponding to 68.42% of LSBGs selected by the exponential model and 72.83% of LSBGs selected by the sersic model,the rest of the discrepancy is due to the difference in obtaining μ_(0) between the exponential and sersic *** on the fitting,in the range of 0.5≤n≤1.5,the relation of μ_(0) from two models can be written as μ_(0,sérsic)-μ_(0,exp)=-1.34(n-1).The LSBGs selected by disk+bulge models(LSBG_(2)comps) are more massive than LSBGs selected by single-component models(LSBG_1comp),and also show a larger disk *** the bulges in the majority of our LSBG_(2)comps are not prominent,more than 60% of our LSBG_(2)comps will not be selected if we adopt a single-component model *** also identified 31 giant low surface brightness galaxies(gLSBGs) from LSBG_(2)*** are located at the same region in the color-magnitude diagram as other *** we compared different criteria of gLSBGs selection,we find that for gas-rich LSBGs,M_(*)> 10^(10)M_⊙ is the best to distinguish between gLSBGs and normal LSBGs with bulge.

关键词： catalogs galaxies:spiral galaxies:bulges methods:data analysis methods:statistical

Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data ReleaseⅠ

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2023年第7期23卷 300-311页

作者： Heng Xu Siyuan Chen Yanjun Guo Jinchen Jiang Bojun Wang Jiangwei Xu Zihan Xue RNicolas Caballero Jianping Yuan Yonghua Xu Jingbo Wang Longfei Hao Jingtao Luo Kejia Lee Jinlin Han Peng Jiang Zhiqiang Shen Min Wang Na Wang Renxin Xu Xiangping Wu Richard Manchester Lei Qian Xin Guan Menglin Huang Chun Sun Yan Zhu National Astronomical Observatory Chinse Academy of SciencesBeijing 100101China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy School of PhysicsPeking UniversityBeijing 100871China Max-Planck institut fúr Radioastronomie Auf Dem HúgelBonnD-53121Germany Hellenic Open University School of Science and Technology26335 PatrasGreece Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China Yunnan Astronomical Observatories Chinese Academy of SciencesKunming 650216China Institute of Optoelectronic Technology Lishui UniversityLishui 323000China National Time Service Center Chinese Academy Of SciencesXi'an 710600China Key Laboratory of Radio Astronomy and Technology Chinese Academy of SciencesBeijing 100101China Beijing Laser Acceleration Innovation Center HuairouBeijing 101400China Shanghai Astronomical Observatory Chinese Academy of SciencesShanghai 200030China State Key Laboratory of Nuclear Physics and Technology School of PhysicsPeking UniversityBeijing 100871China Australia Telescope National Facility CSIRO Space and AstronomyP.O.Box 76Epping NSW 1710Australia

Observing and timing a group of millisecond pulsars with high rotational stability enables the direct detection of gravitational waves(GWs).The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced *** Chinese Pulsar Timing Array(CPTA)is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio *** short article serves as a“table of contents”for a forthcoming series of papers related to the CPTA Data Release 1(CPTA DR1)which uses observations from the Five-hundred-meter Aperture Spherical radio ***,after summarizing the time span and accuracy of CPTA DR1,we report the key results of our statistical inference finding a correlated signal with amplitude logA_(c)=-14.4_(-2.8)^(+1.0)for spectral index in the range ofα∈[-1.8,1.5]assuming a GW background(GWB)induced quadrupolar *** search for the Hellings–Downs(HD)correlation curve is also presented,where some evidence for the HD correlation has been found that a 4.6σstatistical significance is achieved using the discrete frequency method around the frequency of 14 n *** expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the n Hz GWB,which could verify the current results.

关键词： (stars:)pulsars:general gravitational waves methods:statistical methods:observational

Effects of Binaries on Open Cluster Age Determination in Bayesian Inference

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2022年第8期22卷 230-237页

作者： Zhong-Mu Li Su Zhang Jing Chen Wen-Chang Zhao Wu You Institute for Astronomy Dali UniversityDali 671003China

We investigate the effects of binaries on the cluster age determination for 561 open clusters in the Galactic disk via the Bayesian statistical *** properties of these star clusters,including age,metallicity,distance modulus,color excess,binary fraction,and rotating star fraction,are derived from color–magnitude-diagrams(CMDs)via isochrone fitting to high-precision Gaia EDR3 *** the simple stellar population of binary and single-star,age differences can be found with the same star cluster.A Bayesian applied regression modeling software,Stan,is employed to explore how much binaries affect the age determination of open *** results present less statistically significant difference between the binary-star simple populations(bs SSPs)and the singlestar simple populations(ss SSPs)for cluster age *** all clusters in our sample,the ages estimated using the bs SSPs models are younger than those estimated using the ss SSPs,with a mean value of~70 ***,it is found that for 52.5%clusters in our sample,ages are relatively sensitive to the presence of binaries,at least~25%*** suggests that in studies of open cluster age determinations,the effects of binary interactions on the whole sample are not prominent,but its effects on some clusters should still be included as an essential ingredient.

关键词： (stars:)Hertzsprung-Russell and CM diagrams (Galaxy:)open clusters and associations methods:statistical

Pulsar Glitch Activities:The Spin Parameters Approach

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2024年第6期24卷 334-357页

作者： Innocent Okwudili Eya Evaristus Uzochukwu Iyida Physics/Electronics Technique—Department of Science Laboratory Technology University of NigeriaNsukkaNigeria Department of Physics and Astronomy University of NigeriaNsukkaNigeria Astronomy and Astrophysics Research Lab University of NigeriaNsukkaNigeria

Glitch activity refers to the mean increase in pulsar spin frequency per year due to rotational *** is an important tool for studying super-nuclear matter using neutron star interiors as *** events are typically observed in the spin frequency(ν) and frequency derivative( ν) of *** rate of glitch recurrence decreases as the pulsar ages,and the activity parameter is usually measured by linear regression of cumulative glitches over a given *** method is effective for pulsars with multiple regular glitch ***,due to the scarcity of glitch events and the difficulty of monitoring all known pulsars,only a few have multiple records of glitch *** limits the use of the activity parameter in studying neutron star interiors with multiple *** this study,we examined the relationship between the activity parameters and pulsar spin parameters(spin frequency,frequency derivative,and pulsar characteristic age).We found that a quadratic function provides a better fit for the relationship between activity parameters and spin parameters than the commonly used linear *** this information,we were able to estimate the activity parameters of other pulsars that do not have records of *** analysis shows that the relationship between the estimated activity parameters and pulsar spin parameters is consistent with that of the observed activity parameters in the ensemble of pulsars.

关键词： stars:neutron (stars:)pulsars:general methods:statistical

A novel stellar spectrum denoising method based on deep Bayesian modeling

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2021年第7期21卷 127-142页

作者： Xin Kang Shi-Yuan He Yan-Xia Zhang Institute of Statistics and Big Data Renmin University of ChinaBeijing 100872China CAS Key Laboratory of Optical Astronomy National Astronomical ObservatoriesBeijing 100101China

Spectrum denoising is an important procedure for large-scale spectroscopical surveys. This work proposes a novel stellar spectrum denoising method based on deep Bayesian modeling. The construction of our model includes a prior distribution for each stellar subclass, a spectrum generator and a flow-based noise model. Our method takes into account the noise correlation structure, and it is not susceptible to strong sky emission lines and cosmic rays. Moreover, it is able to naturally handle spectra with missing flux values without ad-hoc imputation. The proposed method is evaluated on real stellar spectra from the Sloan Digital Sky Survey(SDSS) with a comprehensive list of common stellar subclasses and compared to the standard denoising auto-encoder. Our denoising method demonstrates a superior performance to the standard denoising auto-encoder, in respect of denoising quality and missing flux imputation. It may be potentially helpful in improving the accuracy of the classification and physical parameter measurement of stars when applying our method during data preprocessing.

关键词： methods:data analysis methods:numerical methods:statistical techniques:spectroscopic