查看更多>>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.
查看更多>>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.
查看更多>>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 waming 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.
查看更多>>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.,△E(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.
查看更多>>摘要：From～5000 deg2 of the combination of the Beijing-Arizona Sky Survey and Mayall z-band Legacy Survey which is also the northern sky region of the Dark Energy Spectroscopic Instrument(DESI)Legacy Imaging Surveys,we selected a sample of 31,825 candidates of low surface brightness galaxies(LSBGs)with the mean effective surface brightness 24.2＜(μ)eff,g＜28.8 mag arcsec-2 and the half-light radius 2″.5＜reff＜20″ based on the released photometric catalog and the machine learning model.The distribution of the LSBGs is bimodal in the g-r color,indicating the two distinct populations of the blue(g-r＜0.60)and red(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 ϵ～0.3),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.
查看更多>>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.
查看更多>>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.
查看更多>>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|b|≤ 5°.25.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 Kkms-1.We observe a significant deviation of the mean Galactic latitude for clumps within|b|≤ 2° from the midplane,with b=-0°.110.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.
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