Dust extinction law is crucial to recover the intrinsic energy distribution of celestial objects and infer the characteristics of interstellar dust.Based on the traditional pair method,an improved pair method is propo...Dust extinction law is crucial to recover the intrinsic energy distribution of celestial objects and infer the characteristics of interstellar dust.Based on the traditional pair method,an improved pair method is proposed to model the dust extinguished spectral energy distribution(SED)of an individual star.Instead of the mathematically parameterizing extinction curves,the extinction curves in this work are directly from the silicate-graphite dust model,so that the dust extinction law can be obtained and the dust properties can be analyzed simultaneously.The ATLAS9 stellar model atmosphere is adopted for the intrinsic SEDs in this work,while the silicate-graphite dust model with a dust size distribution of dn da~a^(-a)exp(-a a_(c)),0.005<a<5μmfor each component is adopted for the model extinction curves.One typical extinction tracer in the dense region(V410 Anon9)and one in the diffuse region(Cyg OB2#12)of the Milky Way are chosen to test the reliability and the practicability of the improved pair method in different stellar environments.The results are consistent with their interstellar environments and are in agreement with the previous observations and studies,which prove that the improved pair method is effective and applicable in different stellar environments.In addition to the reliable extinction results,the derived parameters in the dust model can be used to analyze the dust properties,which cannot be achieved by other methods with the mathematical extinction models.With the improved pair method,the stellar parameters can also be inferred and the extinction law beyond the wavelengths of observed data can be predicted based on the dust model as well.展开更多
This paper reports results from our long-term BV(RI)_(c) photometric CCD observations of eight pre-main sequence stars collected from 2008 June to 2022 October.These stars are located in the young open cluster Trumple...This paper reports results from our long-term BV(RI)_(c) photometric CCD observations of eight pre-main sequence stars collected from 2008 June to 2022 October.These stars are located in the young open cluster Trumpler 37,in the field of GM Cephei.The observational data indicate that all stars from our study exhibit variability in all-optical passbands,typical for young stars.In this paper,we describe and discuss the photometric behavior of the stars and the possible reasons for their variability.For two of the objects,we identified periodicity in their light variation.展开更多
The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.C...The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.Case studies have been extensively presented to analyze the effect of extremely large flares on the Martian upper atmosphere,but the general features of the Martian thermospheric response to flares are still poorly understood.In this work,we select 12 intense solar flares that occurred between 2015 and 2017 and investigate the densities and compositional variations of the dayside Martian thermosphere to these flares with the aid of the measurements made by the Mars Atmosphere and Volatile EvolutioN.The statistical studies indicate that the responses of the Martian thermosphere to flares are complicated that both the class of the flare and the wavelength of the enhanced radiation may have prominent influences on the thermal expansion of the atmosphere and the atmospheric photochemical reactions.展开更多
We present a method by using the phase characteristics of radio observation data for pulsar search and candidate identification.The phase characteristics are relations between the pulsar signal and the phase correctio...We present a method by using the phase characteristics of radio observation data for pulsar search and candidate identification.The phase characteristics are relations between the pulsar signal and the phase correction in the frequency-domain,and we regard it as a new search diagnostic characteristic.Based on the phase characteristics,a search method is presented:calculating dispersion measure(DM)—frequency data to select candidate frequencies,and then confirming of candidates by using the broadband characteristics of pulsar signals.Based on this method,we performed a search test on short observation data of M15 and M71,which were observed by Five-hundredmeter Aperture Spherical radio Telescope,and some of the Galactic Plane Pulsar Snapshot survey data.Results show that it can get similar search results to PRESTO(Pulsa R Exploration and Search TOolkit)while having a faster processing speed.展开更多
Element diffusion has small but significant effects on the structure of the stellar interior.It is interesting to investigate the effects of element diffusion using asteroseismology.We have constructed two grids of st...Element diffusion has small but significant effects on the structure of the stellar interior.It is interesting to investigate the effects of element diffusion using asteroseismology.We have constructed two grids of stellar models,one with diffusion and one without,for solar-like stars with masses between 0.9 and 1.4 solar masses,and varied initial helium abundance and metallicity.The oscillation frequencies of all stellar models have also been calculated.Piecewise Hermite cubic polynomials are adopted to interpolate stellar p-mode frequencies at an arbitrary age on a stellar evolutionary track.We have investigated 16 Kepler solar-like stars by comparing the model frequencies with observations.The suggested ranges of stellar parameters and some global variables are obtained.For all stars,the best model reproduces the observational frequencies with aχ^(2)of the order of unity.It has been found that element diffusion is important in modeling solar-like stars.Without diffusion,the best value of the initial helium abundance is below the primordial helium abundance from Big Bang nucleosynthesis.When diffusion is taken into account,the required initial helium abundance increases to be higher than the primordial abundance.Diffusion also generally improves the frequency fitting results by reducing the minimum ofχ^(2).Investigation of the second difference of the oscillation frequencies on KIC 8694723 and KIC 10454113 indicates that the current model of element diffusion may underestimate the strength of settling.展开更多
The acceleration of LMXB 4U 1820-30 derived from its orbital-period derivative P_(b)was supposed to be the evidence for an Intermediate-mass black hole(IMBH)in the Galactic globular cluster(GC)NGC 6624.However,we find...The acceleration of LMXB 4U 1820-30 derived from its orbital-period derivative P_(b)was supposed to be the evidence for an Intermediate-mass black hole(IMBH)in the Galactic globular cluster(GC)NGC 6624.However,we find that the anomalous P_(b)is mainly due to the gravitational wave emission,rather than the acceleration in cluster potential.Using the standard structure models of GCs,we simulate acceleration distributions for pulsars in the central region of the cluster.By fitting the acceleration of J1823-3021 A with the simulated distribution profiles(maximum values),it is suggested that an IMBH with mass M■950_(-350)^(+550)M_(⊙) may reside in the cluster center.We further show that the second period derivative P of J1823-3021 A is probably due to the gravitational perturbation of a nearby star.展开更多
Our analysis presents an explanation of the Sun–Earth coupling mechanism during declining phase of a solar cycle,and how the dominant 13.5 and 27 day periods play roles in the coupling mechanism which led to intense ...Our analysis presents an explanation of the Sun–Earth coupling mechanism during declining phase of a solar cycle,and how the dominant 13.5 and 27 day periods play roles in the coupling mechanism which led to intense terrestrial magnetic storms during this declining phase compared to the rising phase of a solar cycle.Moreover,it is observed that while the 27 day period gets strongly modulated in the rising phase,the 13.5 day period modulation is more prominent during the declining phase.It is suggested that out of the 27 and 13.5 day periods of Sun–Earth interaction,the preferred period of modulation happens to be the one which is more dominant for the less random or quieter system participating in the coupling.It is reported for the first time that the 13.5 day period is more prominent in the Sun–Earth interaction during the declining phase of a solar cycle,as it is the most dominant period of Earth's magnetic system,which happens to be more persistent as a dynamical system and hence quieter or more receptive than the Sun.展开更多
With a collecting area of 9400 m^(2),the Xinjiang QiTai 110 m radio Telescope(QTT) will allow for a significant advance in the search and observation of pulsars.We have updated the galactic electron density model,scat...With a collecting area of 9400 m^(2),the Xinjiang QiTai 110 m radio Telescope(QTT) will allow for a significant advance in the search and observation of pulsars.We have updated the galactic electron density model,scattering model,spectral distribution,and radial distribution of PSRPOPPY to generate the population of isolate radio pulsars in the Galaxy.The spiral arm,including the local spiral arm,is considered when generating pulsar locations.By simulation,we estimate the number of previously undetected radio pulsars that QTT will discover with its possible receivers for different strategies.Using the PAF receiver,2200 previously unknown pulsars could be discovered in43 days.The 96-beam PAF receiver can produce~10.56 GB of data per second.展开更多
This paper presents a new method to obtain the deformation distribution on the main reflector of an antenna only by measuring the electric intensity on a spherical surface with the focal point as the center of the sph...This paper presents a new method to obtain the deformation distribution on the main reflector of an antenna only by measuring the electric intensity on a spherical surface with the focal point as the center of the sphere,regardless of phase.Combining the differential geometry theory with geometric optics method,this paper has derived a deformation-intensity equation to relate the surface deformation to the intensity distribution of a spherical near-field directly.Based on the finite difference method(FDM)and GaussSeidel iteration,deformation has been calculated from intensity simulated by geometrical optics(GO)and physical optics(PO)methods,respectively,with relatively small errors,which prove the effectiveness of the equation proposed in this paper.By means of this method,it is possible to measure the deformation only by scanning the electric intensity of a single hemispherical near-field whose area is only about 1/15 of the aperture.The measurement only needs a plane wave at any frequency as the incident wave,which means that both the signals from the outer space satellite and the far-field artificial beacon could be used as the sources.The scanning can be realized no matter what attitude and elevation angle the antenna is in because the size and angle of the hemisphere are changeable.展开更多
In Cassini ISS(Imaging Science Subsystem)images,contour detection is often performed on disk-resolved objects to accurately locate their center.Thus,contour detection is a key problem.Traditional edge detection method...In Cassini ISS(Imaging Science Subsystem)images,contour detection is often performed on disk-resolved objects to accurately locate their center.Thus,contour detection is a key problem.Traditional edge detection methods,such as Canny and Roberts,often extract the contour with too much interior details and noise.Although the deep convolutional neural network has been applied successfully in many image tasks,such as classification and object detection,it needs more time and computer resources.In this paper,a contour detection algorithm based on H-ELM(Hierarchical Extreme Learning Machine)and Dense CRF(Dense Conditional Random Field)is proposed for Cassini ISS images.The experimental results show that this algorithm’s performance is better than both traditional machine learning methods,such as Support Vector Machine,Extreme Learning Machine and even deep Convolutional Neural Network.The extracted contour is closer to the actual contour.Moreover,it can be trained and tested quickly on the general configuration of PC,and thus can be applied to contour detection for Cassini ISS images.展开更多
We developed a pulsar search pipeline based on PulsaR Exploration and Search TOolkit(PRESTO).This pipeline simply runs dedispersion,Fast Fourier Transform(FFT)and acceleration search in process-level parallel to short...We developed a pulsar search pipeline based on PulsaR Exploration and Search TOolkit(PRESTO).This pipeline simply runs dedispersion,Fast Fourier Transform(FFT)and acceleration search in process-level parallel to shorten the processing time.With two parallel strategies,the pipeline can highly shorten the processing time in both normal searches and acceleration searches.This pipeline was first tested with Parkes Multibeam Pulsar Survery(PMPS)data and discovered two new faint pulsars.Then,it was successfully applied in processing the Five-hundred-meter Aperture Spherical radio Telescope(FAST)drift scan data with tens of new pulsar discoveries up to now.The pipeline is only CPU-based and can be easily and quickly deployed in computing nodes for testing purposes or data processing.展开更多
We investigate the relationship between cosmic curvature and model of dark energy(hereafter DE)with recent TypeⅠa supernovae(hereafter SNeⅠa)data,i.e.,the Pantheon sample including 1048 SNeⅠa with 0.01<z<2.3....We investigate the relationship between cosmic curvature and model of dark energy(hereafter DE)with recent TypeⅠa supernovae(hereafter SNeⅠa)data,i.e.,the Pantheon sample including 1048 SNeⅠa with 0.01<z<2.3.We obtain measurements of the dimensionless spatial curvature density today,i.e.,Ωk0=-0.062-0.169+0.189,-0.004-0.134+0.228,0.127-0.276+0.280 and 0.422-0.338+0.213 at 68%confidence level(CL),respectively,in the scenarios of ACDM,φCDM(i.e.,scalar field DE),ωCDM andω0ωaCDM models.In the scenario of ACDM model,a closed universe is preferred by the Pantheon sample,which is consistent with that from the Planck CMB spectra.However,the uncertainty of Qko from the Pantheon SNe sample is about 8 times larger than that from the Planck data,so the former one supports a closed universe at a much lower CL than that from the latter one.An open unverse is supported by the Pantheon sample at^32%and^78%CLs,respectively,in theωCDM andω0ωaCDM models.Among these models,theφCDM model is the one which supports the flat universe most strongly.It shows that Qk0 is significantly dependent on the adopted model of DE,and there is a negative correlation betweenΩk0 and the equation of state of DE.展开更多
We consider the coplanar planetary four-body problem,where three planets orbit a large star without the cross of their orbits.The system is stable if there is no exchange or cross of orbits.Starting from the Sundman i...We consider the coplanar planetary four-body problem,where three planets orbit a large star without the cross of their orbits.The system is stable if there is no exchange or cross of orbits.Starting from the Sundman inequality,the equation of the kinematical boundaries is derived.We discuss a reasonable situation,where two planets with known orbits are more massive than the third one.The boundaries of possible motions are controlled by the parameter c^2E.If the actual value of c^2E is less than or equal to a critical value(c^2 E)cr,then the regions of possible motions are bounded and therefore the system is stable.The criteria obtained in special cases are applied to the Solar System and the currently known extrasolar planetary systems.Our results are checked using N-body integrator.展开更多
The DArk Matter Particle Explorer(DAMPE)can measureγ-rays in the energy range from a few GeV to about 10 TeV.The direction of eachγ-ray photon is reconstructed in the DAMPE payload reference system.To convert this t...The DArk Matter Particle Explorer(DAMPE)can measureγ-rays in the energy range from a few GeV to about 10 TeV.The direction of eachγ-ray photon is reconstructed in the DAMPE payload reference system.To convert this to celestial coordinates,we require the celestial orientation of the payload system,which,however,may slightly deviate from that of the satellite system provided by the star-tracker.In this paper,we adopt a maximum likelihood method and use theγ-rays centered around several bright point-like sources to measure and correct the angular deviations between the DAMPE payload and satellite system,the so-called"boresight alignment".We also check our method of boresight alignment for some sets of simulation data with artificial orientations and obtain consistent results.The time-dependent boresight alignment analysis does not show evidence for significant variation of the parameters.展开更多
Defocusing spot size detection is especially essential for aberration analysis and correction of optical systems. In the case of far defocusing, the celestial forms a pupil image on the detector, and the size of the i...Defocusing spot size detection is especially essential for aberration analysis and correction of optical systems. In the case of far defocusing, the celestial forms a pupil image on the detector, and the size of the image is linearly changed with the defocusing distance, and can be used to correct the optical system and analyze the image quality. Based on the focal plane attitude detection of Large Sky Area MultiObject Fiber Spectroscopy Telescope(LAMOST), this paper uses a variety of methods to detect the size of the defocusing spot of LAMOST telescope. For the particularity of the spot, the average value spacing algorithm, the peak value spacing algorithm, the ellipse fitting algorithm, and the multi-peak Gaussian fitting algorithm are used to detect the spot size. This paper will introduce these four methods, in which the average value spacing algorithm is proposed by the author of this paper. The advantages and disadvantages of the four methods are compared. The experimental results show that the average value spacing algorithm can achieve better accuracy of spot size detection in the four algorithms.展开更多
The Nanshan One-meter Wide-field Telescope is a prime focus system that is located at Nanshan Station of Xinjiang Astronomical Observatories.The field of view was designed to 1.5°× 1.5°,and the Johnson-...The Nanshan One-meter Wide-field Telescope is a prime focus system that is located at Nanshan Station of Xinjiang Astronomical Observatories.The field of view was designed to 1.5°× 1.5°,and the Johnson-Cousins UBVRI system was chosen as the main filter set.The telescope has been providing observation services for astronomers since September 2013.Variable source searching and time-domain surveys are the main scientific goals.The system’s test results are reported including linearity,dark current,bias,readout noise and gain of the CCD camera.The accurate instrumental calibration coefficients in UBVRI bands were driven with Landolt standard stars during photometric nights.Finally,the limiting magnitudes are given with signal-to-noise ratios and various exposure times for observers.展开更多
Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope.Most of them are main-sequence stars,but some of them are post main-...Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope.Most of them are main-sequence stars,but some of them are post main-sequence systems.They are good astrophysical laboratories for studying several problems such as the merging of binary stars,evolution of the common envelope,the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems.A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic survey.Based on follow-up observations,the evolutionary states and geometrical structures of some systems were understood well.In this review,we will introduce and catalog new stellar atmospheric parameters(i.e.,the effective temperature(Teff),the gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(Vr))for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of LAMOST.Then we will focus on several groups of contact binary stars,i.e.,marginal contact binary systems,deep and low-mass ratio contact binary stars,binary systems below the short-period limit of contact binaries and evolved contact binaries.Marginal contact binaries are at the beginning of the contact stage,while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked binaries.Several statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are reviewed.The period-color relation of M-type binaries reveals that there are contact binaries below the short-period limit.Searching for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period limit is about 0.15 d.Some evolved contact binaries were detected by the LAMOST survey where both components are sub-giants or giants.They provide a good opportunity to investigate evolution of the common envelope and are the progenitors of luminous red novae like V1309 Sco.展开更多
With the increasing precision of the GRAIL gravity field models and topography from LOLA, it is possible to investigate the substructure beneath crater Clavius. An admittance between gravity and topography data is com...With the increasing precision of the GRAIL gravity field models and topography from LOLA, it is possible to investigate the substructure beneath crater Clavius. An admittance between gravity and topography data is commonly used to estimate selenophysical parameters, including load ratio, crustal thickness and density, and elastic thickness. Not only a surface load, but also a subsurface load is considered in estimation. The algorithm of particle swarm optimization(PSO) with a swarm size of 400 is employed as well.Results indicate that the observed admittance is best-fitted by the modeled admittance based on a spherical shell model, which was proved to be unsatisfactory in the previous study. The best-fitted load ratio f is around-0.194. Such a small load ratio conforms to the direct proportion between the nearly uncompensated topography and its corresponding negative gravity anomaly. It also indicates that a surface load dominates all the loads. Constrained within 2σSTD, a small crustal thickness(～30 km) and a crustal density of ～2587 kg m-3are found, quite close to the results from previous GRAIL research. Considering the well constrained crustal thickness and density, the best-fitted elastic thickness(～7 km) is rational. This result is slightly smaller than the previous study(～12 km). Such difference can be attributed to the difference in crustal density used and the precision of gravity and topography data. Considering that the small difference between the modeled gravity anomaly and observations is quite small, a parameter inversed here could be an indicator of the subsurface structure beneath Clavius.展开更多
Detecting supernova remnant(SNR) candidates in the interstellar medium is a challenging task because SNRs have weak radio signals and irregular shapes. The use of a convolutional neural network is a deep learning meth...Detecting supernova remnant(SNR) candidates in the interstellar medium is a challenging task because SNRs have weak radio signals and irregular shapes. The use of a convolutional neural network is a deep learning method that can help us extract various features from images. To extract SNRs from astronomical images and estimate the positions of SNR candidates, we design the SNR-Net model composed of a training component and a detection component. In addition, transfer learning is used to initialize the network parameters, which improves the speed and accuracy of network training. We apply a T-T plot(of the different brightness temperatures of map pixels at two different frequencies) to calculate the spectral index of SNR candidates. To accelerate the scientific computing process, we take advantage of innovative hardware architecture, such as deep learning optimized graphics processing units, which increases the speed of computation by a factor of 5. A case study suggests that SNR-Net may be applicable to detecting extended sources in the images automatically.展开更多
We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-b...We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-band). Our three systems are KIC 2715417, KIC 6050116 and KIC 6287172. The first system, KIC 2715417, is considered a semi-detached system with the secondary component filling its Roche lobe. The second system, KIC 6050116, is an overcontact system, while the third system, KIC 6287172, belongs to ellipsoidal variables as deduced from the Roche lobe geometry. For photometric analysis, we used the PHOEBE software package, which is based on the Wilson-Devinney code. Due to lack of spectroscopic data, the photometric mass ratios are determined from the analyses of light curves using the q-search method. The absolute parameters are determined using three different methods(Harmanec, Maceroni &Van'tVeer and Gazeas & Niarchos).展开更多
基金supported by the National Natural Science Foundation of China(NSFC)through grant Nos.12133002,U2031209 and 12203025Shandong Provincial Natural Science Foundation through project ZR2022QA064the CSST Milky Way and Nearby Galaxies Survey on Dust and Extinction Project CMS-CSST2021-A09。
文摘Dust extinction law is crucial to recover the intrinsic energy distribution of celestial objects and infer the characteristics of interstellar dust.Based on the traditional pair method,an improved pair method is proposed to model the dust extinguished spectral energy distribution(SED)of an individual star.Instead of the mathematically parameterizing extinction curves,the extinction curves in this work are directly from the silicate-graphite dust model,so that the dust extinction law can be obtained and the dust properties can be analyzed simultaneously.The ATLAS9 stellar model atmosphere is adopted for the intrinsic SEDs in this work,while the silicate-graphite dust model with a dust size distribution of dn da~a^(-a)exp(-a a_(c)),0.005<a<5μmfor each component is adopted for the model extinction curves.One typical extinction tracer in the dense region(V410 Anon9)and one in the diffuse region(Cyg OB2#12)of the Milky Way are chosen to test the reliability and the practicability of the improved pair method in different stellar environments.The results are consistent with their interstellar environments and are in agreement with the previous observations and studies,which prove that the improved pair method is effective and applicable in different stellar environments.In addition to the reliable extinction results,the derived parameters in the dust model can be used to analyze the dust properties,which cannot be achieved by other methods with the mathematical extinction models.With the improved pair method,the stellar parameters can also be inferred and the extinction law beyond the wavelengths of observed data can be predicted based on the dust model as well.
基金partly supported by the research fund of the University of Shumen,Bulgaria。
文摘This paper reports results from our long-term BV(RI)_(c) photometric CCD observations of eight pre-main sequence stars collected from 2008 June to 2022 October.These stars are located in the young open cluster Trumpler 37,in the field of GM Cephei.The observational data indicate that all stars from our study exhibit variability in all-optical passbands,typical for young stars.In this paper,we describe and discuss the photometric behavior of the stars and the possible reasons for their variability.For two of the objects,we identified periodicity in their light variation.
基金supported by the Guangdong Basic and Applied Research Foundation through Grant 2021A1515110271。
文摘The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.Case studies have been extensively presented to analyze the effect of extremely large flares on the Martian upper atmosphere,but the general features of the Martian thermospheric response to flares are still poorly understood.In this work,we select 12 intense solar flares that occurred between 2015 and 2017 and investigate the densities and compositional variations of the dayside Martian thermosphere to these flares with the aid of the measurements made by the Mars Atmosphere and Volatile EvolutioN.The statistical studies indicate that the responses of the Martian thermosphere to flares are complicated that both the class of the flare and the wavelength of the enhanced radiation may have prominent influences on the thermal expansion of the atmosphere and the atmospheric photochemical reactions.
基金supported by the National Natural Science Foundation of China(Nos.12203039 and 11873083)the National Natural Science Foundation of China(Nos.12173053 and 12041303)+4 种基金supported by the National SKA Program of China(No.2020SKA0120100)the Youth Innovation Promotion Association of CAS(id.2018075)the CAS“Light of West China”Programthe Specialized Research Fund for State Key Laboratoriesthe Science and Technology Program of Guizhou Province([2021]4001)。
文摘We present a method by using the phase characteristics of radio observation data for pulsar search and candidate identification.The phase characteristics are relations between the pulsar signal and the phase correction in the frequency-domain,and we regard it as a new search diagnostic characteristic.Based on the phase characteristics,a search method is presented:calculating dispersion measure(DM)—frequency data to select candidate frequencies,and then confirming of candidates by using the broadband characteristics of pulsar signals.Based on this method,we performed a search test on short observation data of M15 and M71,which were observed by Five-hundredmeter Aperture Spherical radio Telescope,and some of the Galactic Plane Pulsar Snapshot survey data.Results show that it can get similar search results to PRESTO(Pulsa R Exploration and Search TOolkit)while having a faster processing speed.
基金Funding for Yunnan Observatories is co-sponsored by the National Key R&D Program of China(Grant No.2021YFA1600400/2021YFA1600402)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB 41000000)+3 种基金the National Natural Science Foundation of China(Grant Nos.1177064 and 12133011)the Foundation of the Chinese Academy of Sciences(Light of West China Program and Youth Innovation Promotion Association)the Yunnan Ten Thousand Talents Plan Young and Elite Talents ProjectInternational Centre of Supernovae,Yunnan Key Laboratory(No.202302AN360001)。
文摘Element diffusion has small but significant effects on the structure of the stellar interior.It is interesting to investigate the effects of element diffusion using asteroseismology.We have constructed two grids of stellar models,one with diffusion and one without,for solar-like stars with masses between 0.9 and 1.4 solar masses,and varied initial helium abundance and metallicity.The oscillation frequencies of all stellar models have also been calculated.Piecewise Hermite cubic polynomials are adopted to interpolate stellar p-mode frequencies at an arbitrary age on a stellar evolutionary track.We have investigated 16 Kepler solar-like stars by comparing the model frequencies with observations.The suggested ranges of stellar parameters and some global variables are obtained.For all stars,the best model reproduces the observational frequencies with aχ^(2)of the order of unity.It has been found that element diffusion is important in modeling solar-like stars.Without diffusion,the best value of the initial helium abundance is below the primordial helium abundance from Big Bang nucleosynthesis.When diffusion is taken into account,the required initial helium abundance increases to be higher than the primordial abundance.Diffusion also generally improves the frequency fitting results by reducing the minimum ofχ^(2).Investigation of the second difference of the oscillation frequencies on KIC 8694723 and KIC 10454113 indicates that the current model of element diffusion may underestimate the strength of settling.
基金supported by the National Natural Science Foundation of China under Grant Nos.11803009 and 11603009the Natural Science Foundation of Fujian Province under Grant Nos.2018J05006,2018J01416 and 2016J05013。
文摘The acceleration of LMXB 4U 1820-30 derived from its orbital-period derivative P_(b)was supposed to be the evidence for an Intermediate-mass black hole(IMBH)in the Galactic globular cluster(GC)NGC 6624.However,we find that the anomalous P_(b)is mainly due to the gravitational wave emission,rather than the acceleration in cluster potential.Using the standard structure models of GCs,we simulate acceleration distributions for pulsars in the central region of the cluster.By fitting the acceleration of J1823-3021 A with the simulated distribution profiles(maximum values),it is suggested that an IMBH with mass M■950_(-350)^(+550)M_(⊙) may reside in the cluster center.We further show that the second period derivative P of J1823-3021 A is probably due to the gravitational perturbation of a nearby star.
基金MOTA for providing a fellowship under the NFST projectIISER,Kolkata for providing all necessary support。
文摘Our analysis presents an explanation of the Sun–Earth coupling mechanism during declining phase of a solar cycle,and how the dominant 13.5 and 27 day periods play roles in the coupling mechanism which led to intense terrestrial magnetic storms during this declining phase compared to the rising phase of a solar cycle.Moreover,it is observed that while the 27 day period gets strongly modulated in the rising phase,the 13.5 day period modulation is more prominent during the declining phase.It is suggested that out of the 27 and 13.5 day periods of Sun–Earth interaction,the preferred period of modulation happens to be the one which is more dominant for the less random or quieter system participating in the coupling.It is reported for the first time that the 13.5 day period is more prominent in the Sun–Earth interaction during the declining phase of a solar cycle,as it is the most dominant period of Earth's magnetic system,which happens to be more persistent as a dynamical system and hence quieter or more receptive than the Sun.
基金supported by the National SKA Program of China (No. 2020SKA0120100)the National Natural Science Foundation of China (No. 12041304)+2 种基金the National Key Research and Development Program of China (2017YFA0402600)the Youth Innovation Promotion Association of Chinese Academy of Sciencesthe 201* Project of Xinjiang Uygur Autonomous Region of China for Flexibly Fetching in Upscale Talents。
文摘With a collecting area of 9400 m^(2),the Xinjiang QiTai 110 m radio Telescope(QTT) will allow for a significant advance in the search and observation of pulsars.We have updated the galactic electron density model,scattering model,spectral distribution,and radial distribution of PSRPOPPY to generate the population of isolate radio pulsars in the Galaxy.The spiral arm,including the local spiral arm,is considered when generating pulsar locations.By simulation,we estimate the number of previously undetected radio pulsars that QTT will discover with its possible receivers for different strategies.Using the PAF receiver,2200 previously unknown pulsars could be discovered in43 days.The 96-beam PAF receiver can produce~10.56 GB of data per second.
基金supported by the National Key Research and Development Program of China of Research on Key Technologies of real-time shape control and ultra wideband pulsar signal processing for large aperture radio telescopesupported by the National Natural Science Foundation of China(Project U1931137)。
文摘This paper presents a new method to obtain the deformation distribution on the main reflector of an antenna only by measuring the electric intensity on a spherical surface with the focal point as the center of the sphere,regardless of phase.Combining the differential geometry theory with geometric optics method,this paper has derived a deformation-intensity equation to relate the surface deformation to the intensity distribution of a spherical near-field directly.Based on the finite difference method(FDM)and GaussSeidel iteration,deformation has been calculated from intensity simulated by geometrical optics(GO)and physical optics(PO)methods,respectively,with relatively small errors,which prove the effectiveness of the equation proposed in this paper.By means of this method,it is possible to measure the deformation only by scanning the electric intensity of a single hemispherical near-field whose area is only about 1/15 of the aperture.The measurement only needs a plane wave at any frequency as the incident wave,which means that both the signals from the outer space satellite and the far-field artificial beacon could be used as the sources.The scanning can be realized no matter what attitude and elevation angle the antenna is in because the size and angle of the hemisphere are changeable.
基金partly supported by the National Natural Science Foundation of China(Grant Nos.U1431227 and 11873026)Natural Science Foundation of Guangdong Province,China(Grant No.2016A030313092)the Fundamental Research Funds for the Central Universities(Grant No.21619413)
文摘In Cassini ISS(Imaging Science Subsystem)images,contour detection is often performed on disk-resolved objects to accurately locate their center.Thus,contour detection is a key problem.Traditional edge detection methods,such as Canny and Roberts,often extract the contour with too much interior details and noise.Although the deep convolutional neural network has been applied successfully in many image tasks,such as classification and object detection,it needs more time and computer resources.In this paper,a contour detection algorithm based on H-ELM(Hierarchical Extreme Learning Machine)and Dense CRF(Dense Conditional Random Field)is proposed for Cassini ISS images.The experimental results show that this algorithm’s performance is better than both traditional machine learning methods,such as Support Vector Machine,Extreme Learning Machine and even deep Convolutional Neural Network.The extracted contour is closer to the actual contour.Moreover,it can be trained and tested quickly on the general configuration of PC,and thus can be applied to contour detection for Cassini ISS images.
基金supported by the National Key R&D Program of China(2017YFA0402600)State Key DevelopmentProgram for Basic Research(2015CB857100)+4 种基金National Basic Research Program of China(973 program,No.2015CB857101)National Natural Science Foundation of China(Grant Nos.11703047,11773041,U1631132and U1831131)supported by the CAS“Light of West China”Programby the CAS Key Laboratory of FAST,National Astronomical Observatories,Chinese Academy of Sciencessupported in part by the Youth Innovation Promotion Association of CAS(id.2018075)。
文摘We developed a pulsar search pipeline based on PulsaR Exploration and Search TOolkit(PRESTO).This pipeline simply runs dedispersion,Fast Fourier Transform(FFT)and acceleration search in process-level parallel to shorten the processing time.With two parallel strategies,the pipeline can highly shorten the processing time in both normal searches and acceleration searches.This pipeline was first tested with Parkes Multibeam Pulsar Survery(PMPS)data and discovered two new faint pulsars.Then,it was successfully applied in processing the Five-hundred-meter Aperture Spherical radio Telescope(FAST)drift scan data with tens of new pulsar discoveries up to now.The pipeline is only CPU-based and can be easily and quickly deployed in computing nodes for testing purposes or data processing.
基金the National Natural Science Foundation of China(Nos.11633001,11920101003,11703034,11773032 and 11573031)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB23000000)+1 种基金the Interdiscipline Research Funds of Beijing Normal Universitythe NAOC Nebula Talents Program。
文摘We investigate the relationship between cosmic curvature and model of dark energy(hereafter DE)with recent TypeⅠa supernovae(hereafter SNeⅠa)data,i.e.,the Pantheon sample including 1048 SNeⅠa with 0.01<z<2.3.We obtain measurements of the dimensionless spatial curvature density today,i.e.,Ωk0=-0.062-0.169+0.189,-0.004-0.134+0.228,0.127-0.276+0.280 and 0.422-0.338+0.213 at 68%confidence level(CL),respectively,in the scenarios of ACDM,φCDM(i.e.,scalar field DE),ωCDM andω0ωaCDM models.In the scenario of ACDM model,a closed universe is preferred by the Pantheon sample,which is consistent with that from the Planck CMB spectra.However,the uncertainty of Qko from the Pantheon SNe sample is about 8 times larger than that from the Planck data,so the former one supports a closed universe at a much lower CL than that from the latter one.An open unverse is supported by the Pantheon sample at^32%and^78%CLs,respectively,in theωCDM andω0ωaCDM models.Among these models,theφCDM model is the one which supports the flat universe most strongly.It shows that Qk0 is significantly dependent on the adopted model of DE,and there is a negative correlation betweenΩk0 and the equation of state of DE.
基金the National Natural Science Foundation of China(Grant Nos.11772167 and 11822205)。
文摘We consider the coplanar planetary four-body problem,where three planets orbit a large star without the cross of their orbits.The system is stable if there is no exchange or cross of orbits.Starting from the Sundman inequality,the equation of the kinematical boundaries is derived.We discuss a reasonable situation,where two planets with known orbits are more massive than the third one.The boundaries of possible motions are controlled by the parameter c^2E.If the actual value of c^2E is less than or equal to a critical value(c^2 E)cr,then the regions of possible motions are bounded and therefore the system is stable.The criteria obtained in special cases are applied to the Solar System and the currently known extrasolar planetary systems.Our results are checked using N-body integrator.
基金founded by the strategic priority science and technology projects in space science of the Chinese Academy of Sciences(Nos.XDA04040000 and XDA04040400)supported in part by the National Key Program for Research and Development(No.2016YFA0400200)+5 种基金the National Basic Research Program(No.2013CB837000)the Strategic Priority Research Program of Chinese Academy of Sciences(CAS)"Multi-Waveband Gravitational Wave Universe”(No.XDB23040000)the Strategic Priority Research Program of CAS(No.XDB23040000)the Youth Innovation Promotion Association of CAS,the National Natural Science Foundation of China(Nos.U1738123 and U1631111)the 100 Talents program of Chinese Academy of Sciences and the Young Elite Scientists Sponsorship Programsupport by the Swiss National Science Foundation(SNSF),Switzerland and the National Institute for Nuclear Physics(INFN),Italy。
文摘The DArk Matter Particle Explorer(DAMPE)can measureγ-rays in the energy range from a few GeV to about 10 TeV.The direction of eachγ-ray photon is reconstructed in the DAMPE payload reference system.To convert this to celestial coordinates,we require the celestial orientation of the payload system,which,however,may slightly deviate from that of the satellite system provided by the star-tracker.In this paper,we adopt a maximum likelihood method and use theγ-rays centered around several bright point-like sources to measure and correct the angular deviations between the DAMPE payload and satellite system,the so-called"boresight alignment".We also check our method of boresight alignment for some sets of simulation data with artificial orientations and obtain consistent results.The time-dependent boresight alignment analysis does not show evidence for significant variation of the parameters.
基金Funding for the project has been provided by the National Development and Reform Commissionsupported by the National Key Basic Research Program of China(2015CB857100)the National Natural Science Foundation of China(Grant Nos.U1331204 and 14473050).
文摘Defocusing spot size detection is especially essential for aberration analysis and correction of optical systems. In the case of far defocusing, the celestial forms a pupil image on the detector, and the size of the image is linearly changed with the defocusing distance, and can be used to correct the optical system and analyze the image quality. Based on the focal plane attitude detection of Large Sky Area MultiObject Fiber Spectroscopy Telescope(LAMOST), this paper uses a variety of methods to detect the size of the defocusing spot of LAMOST telescope. For the particularity of the spot, the average value spacing algorithm, the peak value spacing algorithm, the ellipse fitting algorithm, and the multi-peak Gaussian fitting algorithm are used to detect the spot size. This paper will introduce these four methods, in which the average value spacing algorithm is proposed by the author of this paper. The advantages and disadvantages of the four methods are compared. The experimental results show that the average value spacing algorithm can achieve better accuracy of spot size detection in the four algorithms.
基金supported by the program of the light in China’s Western Region(LCWRGrant Nos.2015-XBQN-B-04,2015-XBQN-A02)+5 种基金the National Natural Science Foundation of China(Grant Nos.11803076,11873081,11661161016 and U1831209)the 13th Five-year Informatization Plan of Chinese Academy of Sciences(Grant No.XXH13503–03–107)the Youth Innovation Promotion Association CAS(Grant Nos.2014050,2018080)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB23040100)2017 Heaven Lake Hundred-Talent Program of Xinjiang Uygur Autonomous Region of Chinathe Open Project Program of the Key Laboratory of Optical Astronomy(NAOC)。
文摘The Nanshan One-meter Wide-field Telescope is a prime focus system that is located at Nanshan Station of Xinjiang Astronomical Observatories.The field of view was designed to 1.5°× 1.5°,and the Johnson-Cousins UBVRI system was chosen as the main filter set.The telescope has been providing observation services for astronomers since September 2013.Variable source searching and time-domain surveys are the main scientific goals.The system’s test results are reported including linearity,dark current,bias,readout noise and gain of the CCD camera.The accurate instrumental calibration coefficients in UBVRI bands were driven with Landolt standard stars during photometric nights.Finally,the limiting magnitudes are given with signal-to-noise ratios and various exposure times for observers.
基金supported by the National Natural Science Foundation of China(Nos.11933008,11922306,11773066 and 11903076)the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences。
文摘Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope.Most of them are main-sequence stars,but some of them are post main-sequence systems.They are good astrophysical laboratories for studying several problems such as the merging of binary stars,evolution of the common envelope,the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems.A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic survey.Based on follow-up observations,the evolutionary states and geometrical structures of some systems were understood well.In this review,we will introduce and catalog new stellar atmospheric parameters(i.e.,the effective temperature(Teff),the gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(Vr))for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of LAMOST.Then we will focus on several groups of contact binary stars,i.e.,marginal contact binary systems,deep and low-mass ratio contact binary stars,binary systems below the short-period limit of contact binaries and evolved contact binaries.Marginal contact binaries are at the beginning of the contact stage,while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked binaries.Several statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are reviewed.The period-color relation of M-type binaries reveals that there are contact binaries below the short-period limit.Searching for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period limit is about 0.15 d.Some evolved contact binaries were detected by the LAMOST survey where both components are sub-giants or giants.They provide a good opportunity to investigate evolution of the common envelope and are the progenitors of luminous red novae like V1309 Sco.
基金supported by a grants from the National Natural Science Foundation of China (Grant Nos. 41864001 and U1831132)Open Fund of State Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University (Grant No. 17P03)+3 种基金Guizhou Normal University Doctoral Research Fundsupported by grants from the Hubei Province Foundation innovation group project (2015CFA011, 2018CFA087)Open Project of Lunar and Planetary Science Laboratory, Macao University of Science and Technology (FDCT 119/2017/A3)Open Fund of Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing (KF201813)
文摘With the increasing precision of the GRAIL gravity field models and topography from LOLA, it is possible to investigate the substructure beneath crater Clavius. An admittance between gravity and topography data is commonly used to estimate selenophysical parameters, including load ratio, crustal thickness and density, and elastic thickness. Not only a surface load, but also a subsurface load is considered in estimation. The algorithm of particle swarm optimization(PSO) with a swarm size of 400 is employed as well.Results indicate that the observed admittance is best-fitted by the modeled admittance based on a spherical shell model, which was proved to be unsatisfactory in the previous study. The best-fitted load ratio f is around-0.194. Such a small load ratio conforms to the direct proportion between the nearly uncompensated topography and its corresponding negative gravity anomaly. It also indicates that a surface load dominates all the loads. Constrained within 2σSTD, a small crustal thickness(～30 km) and a crustal density of ～2587 kg m-3are found, quite close to the results from previous GRAIL research. Considering the well constrained crustal thickness and density, the best-fitted elastic thickness(～7 km) is rational. This result is slightly smaller than the previous study(～12 km). Such difference can be attributed to the difference in crustal density used and the precision of gravity and topography data. Considering that the small difference between the modeled gravity anomaly and observations is quite small, a parameter inversed here could be an indicator of the subsurface structure beneath Clavius.
基金supported bythe National Natural Science Foundation of China(No. 41272359)the Ministry of Land and Resourcesfor the Public Welfare Industry Research Projects(201511079-02)the Natural Science Foundation ofShandong (No. ZR2015FL006)
文摘Detecting supernova remnant(SNR) candidates in the interstellar medium is a challenging task because SNRs have weak radio signals and irregular shapes. The use of a convolutional neural network is a deep learning method that can help us extract various features from images. To extract SNRs from astronomical images and estimate the positions of SNR candidates, we design the SNR-Net model composed of a training component and a detection component. In addition, transfer learning is used to initialize the network parameters, which improves the speed and accuracy of network training. We apply a T-T plot(of the different brightness temperatures of map pixels at two different frequencies) to calculate the spectral index of SNR candidates. To accelerate the scientific computing process, we take advantage of innovative hardware architecture, such as deep learning optimized graphics processing units, which increases the speed of computation by a factor of 5. A case study suggests that SNR-Net may be applicable to detecting extended sources in the images automatically.
文摘We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-band). Our three systems are KIC 2715417, KIC 6050116 and KIC 6287172. The first system, KIC 2715417, is considered a semi-detached system with the secondary component filling its Roche lobe. The second system, KIC 6050116, is an overcontact system, while the third system, KIC 6287172, belongs to ellipsoidal variables as deduced from the Roche lobe geometry. For photometric analysis, we used the PHOEBE software package, which is based on the Wilson-Devinney code. Due to lack of spectroscopic data, the photometric mass ratios are determined from the analyses of light curves using the q-search method. The absolute parameters are determined using three different methods(Harmanec, Maceroni &Van'tVeer and Gazeas & Niarchos).
