We develop an x-ray Ti/Au transition-edge sensor(TES)with an Au absorber deposited on the center of TES and improved its energy resolution using the K-means clustering algorithm in combination with Wiener filter.We fi...We develop an x-ray Ti/Au transition-edge sensor(TES)with an Au absorber deposited on the center of TES and improved its energy resolution using the K-means clustering algorithm in combination with Wiener filter.We firstly extract the main parameters of each recorded pulse trace,which are adopted to classify these traces into several clusters in the K-means clustering algorithm.Then real traces are selected for energy resolution analysis.Following the baseline correction,the Wiener filter is used to improve the signal-to-noise ratio.Although the silicon underneath the TES has not been etched to reduce the thermal conductance,the energy resolution of the developed x-ray TES is improved from 94 eV to 44 eV at 5.9 keV.展开更多
Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation bet...Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation between average dispersion measure(■)and dispersion measure difference(ΔDM)of known pulsars in GCs is lgΔDM∝1.52lg■.The sensitivity could be the key to finding more pulsars.As a result,several years after the construction of a large radio telescope facility,the number of known GC pulsars will likely be increased accordingly.We suggest that currently GCs in the southern hemisphere could have higher possibilities for finding new pulsars.展开更多
In radio astronomy,radio frequency interference(RFI)becomes more and more serious for radio observational facilities.The RFI always influences the search and study of the interesting astronomical objects.Mitigating th...In radio astronomy,radio frequency interference(RFI)becomes more and more serious for radio observational facilities.The RFI always influences the search and study of the interesting astronomical objects.Mitigating the RFI becomes an essential procedure in any survey data processing.The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is an extremely sensitive radio telescope.It is necessary to find out an effective and precise RFI mitigation method for FAST data processing.In this work,we introduce a method to mitigate the RFI in FAST spectral observation and make a statistic for the RFI using~300 h FAST data.The details are as follows.First,according to the characteristics of FAST spectra,we propose to use the Asymmetrically Reweighted Penalized Least Squares algorithm for baseline fitting.Our test results show that it has a good performance.Second,we flag the RFI with four strategies,which are to flag extremely strong RFI,flag long-lasting RFI,flag polarized RFI,and flag beam-combined RFI,respectively.The test results show that all the RFI above a preset threshold could be flagged.Third,we make a statistic for the probabilities of polarized XX and YY RFI in FAST observations.The statistical results could tell us which frequencies are relatively quiescent.With such statistical data,we are able to avoid using such frequencies in our spectral observations.Finally,based on the~300 h FAST data,we obtained an RFI table,which is the most complete database currently for FAST.展开更多
We present the estimation of solar observation with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).For both the quiet Sun and the Sun with radio bursts,when pointing directly to the Sun,the total powe...We present the estimation of solar observation with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).For both the quiet Sun and the Sun with radio bursts,when pointing directly to the Sun,the total power received by FAST would be out of the safe operational range of the signal chain,even resulting in damage to the receiver.As a conclusion,the Sun should be kept at least~2°away from the main beam during observations at~1.25 GHz.The separation for lower frequency should be larger.For simplicity,the angular separation between the FAST beam and the Sun is suggested to be~5°for observations at 200 MHz or higher bands.展开更多
The ROSAT All-Sky Survey (RASS) represents one of the most complete and sensitive soft X- ray all-sky surveys to date. However, the deficient positional accuracy of the RASS Bright Source Catalog (BSC) and subsequ...The ROSAT All-Sky Survey (RASS) represents one of the most complete and sensitive soft X- ray all-sky surveys to date. However, the deficient positional accuracy of the RASS Bright Source Catalog (BSC) and subsequent lack of firm optical identifications affect multi-wavelength studies of X-ray sources. The widely used positional errors σpos based on the Tycho Reference Catalog (Tycho-1) have previously been applied for identifying objects in the optical band. The considerably sharper Chandra view covers a fraction of RASS sources, whose ~rpos could be improved by utilizing the sub-arcsec positional accuracy of Chandra observations. We cross-match X-ray objects between the BSC and Chandra sources extracted from the Advanced CCD Imaging Spectrometer (ACIS) archival observations. A combined list of counter- parts (BSCxACIS) with Chandra spatial positions weighted by the X-ray flux of multiple counterparts is employed to evaluate and improve the former identifications of BSC when used with other surveys. Based on these identification evaluations, we suggest that the point-source likeness of BSC sources and INS (iso- lated neutron star) candidates should be carefully reconsidered.展开更多
We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These pulsars are discovered in a pilot program of the C...We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These pulsars are discovered in a pilot program of the Commensal Radio Astronomy FAST Survey(CRAFTS)with the ultra-widebandwidth commissioning receiver.Five of them are normal pulsars and two are extreme nulling slow pulsars.PSR J2111+2132’s dispersion measure(DM:78.5 pc cm^(-3))is above the upper limits of the two Galactic free electron density models,NE2001 and YMW16,and PSR J2057+2133’s position is out of the Scutum-Crux Arm,making them uniquely useful for improving the Galactic free electron density model in their directions.We present a detailed single pulse analysis for the slow nulling pulsars.We show evidence that PSR J2323+1214’s main pulse component follows a non-Poisson distribution and marginal evidence for a sub-pulse-drift or recurrent period of 32.3±0.4 rotations from PSR J0539+0013.We discuss the implication of our finding to the pulsar radiation mechanism.展开更多
Nomenclatures for lunar features always accompany the progresses of human lunar exploration,which has an important dual meaning in culture and science. The naming of lunar features not only can commemorate the outstan...Nomenclatures for lunar features always accompany the progresses of human lunar exploration,which has an important dual meaning in culture and science. The naming of lunar features not only can commemorate the outstanding contributions of academics,masters in various fields, and popularize the traditional cultures of ethnic groups all over the world, but also have a critical function of providing accurate indicative information on features with special morphology, origin, nature and scientific value. However, nomenclature for features at the Chang'e-3 landing site, which has a more arbitrary form without many constrains posed by a uniformed system, is unlike the features for other morphological units.This paper originated from the actual needs for the description of scientific exploration activities, interpretation of scientific research and dissemination of scientific results. Some prominent morphological units with great scientific importance and identification purpose were chosen from the images taken by the terrain camera, panorama cameras and landing camera onboard the Chang'e lander and Yutu rover. A nomenclature system was established under the three enclosures, four quadrants and twenty-eight lunar lodges' system of the Chinese ancient sky division method. Finally, a standard feature names set waspublished after some necessary approval procedures by the International Astronomical Union.展开更多
Magnetic cataclysmic variables (CVs) contain a white dwarf (WD) with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV (CXOGSG J2155...Magnetic cataclysmic variables (CVs) contain a white dwarf (WD) with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV (CXOGSG J215544.4+380116) from the Chandra archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source is a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2-M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass (~ 0.4 34⊙) and radius (~0.4 R⊙) for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/radius. The estimated low X-ray luminosity and accretion rate may suggest the source is a low-accretion-rate polar. In addition, Very Large Array observations reveal a possible radio counterpart to the X-ray source, but with a low significance. Further radio observations with high quality are needed to confirm the radio counterpart and explore the properties of this binary system.展开更多
Machine learning has increasingly gained more popularity with its incredibly powerful ability to make predictions or calculate suggestions for large amounts of data. We apply machine learning clas-sification to 85 613...Machine learning has increasingly gained more popularity with its incredibly powerful ability to make predictions or calculate suggestions for large amounts of data. We apply machine learning clas-sification to 85 613 922 objects in the Gala Data Release 2, based on a combination of Pan-STARRS I and AI1WISE data. The classification results are cross-matched with the Simbad database, and the to-tal accuracy is 91.9%. Our sample is dominated by stars, ~98%, and galaxies make up 2%. For the objects with negative parallaxes, about 2.5% are galaxies and QSOs, while about 99.9% are stars if the relative parallax uncertainties are smaller than 0.2. Our result implies that using the threshold of 0 〈 σπ/π 〈 0.2 could yield a very clean stellar sample.展开更多
From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6...From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6 h)over 25 nights,yielding a total of about 767000 spectra,and the medium-resolution survey took 177 exposures(≈49.1 h)over 27 nights,collecting about 478000 spectra.More than 70%/50%of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10.We determine stellar parameters(e.g.,Teff,log g,[Fe/H])and radial velocity(RV)with different methods,including LASP,DD-Payne and SLAM.In general,these parameter estimations from different methods show good agreement,and the stellar parameter values are consistent with those of APOGEE.We use the Gaia DR2 RV values to calculate a median RV zero point(RVZP)for each spectrograph exposure by exposure,and the RVZP-corrected RVs agree well with the APOGEE data.The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters,multi-band magnitudes,distances and extinction values.Finally,we construct a binary catalog including about 2700 candidates by analyzing their light curves,fitting the RV data,calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3.The LAMOST TD survey is expected to represent a breakthrough in various scientific topics,such as binary systems,stellar activity,stellar pulsation,etc.展开更多
We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa (Porb≈0.48 d). In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no ev...We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa (Porb≈0.48 d). In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly (〈 0.125 Porb) after a primary eclipse, and the other two happening shortly (〈 0.05/9orb) before a primary eclipse. Two flares occurred within roughly one orbital period (△Ф≈ 1.024 Porb) of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.展开更多
We report the discovery of three new pulsars in the globular cluster(GC)NGC 6517,namely NGC 6517 E,F and G,made with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The spin periods of NGC 6517 E,F and...We report the discovery of three new pulsars in the globular cluster(GC)NGC 6517,namely NGC 6517 E,F and G,made with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The spin periods of NGC 6517 E,F and G are 7.60 ms,24.89 ms and 51.59 ms,respectively.Their dispersion measures are 183.29,183.713 and 185.3 pc cm^(-3),respectively,all slightly larger than those of the previously known pulsars in this cluster.The spin period derivatives are at the level of 1×10^(-18) s s^(-1),which suggests these are recycled pulsars.In addition to the discovery of these three new pulsars,we updated the timing solutions of the known isolated pulsars,NGC 6517 A,C and D.The solutions are consistent with those from Lynch et al.but with smaller timing residuals.From the timing solution,NGC6517 A,B(position from Lynch et al.),C,E and F are very close to each other on the sky and only a few arcseconds from the optical core of NGC 6517.With currently published and unpublished discoveries,nine pulsars have been discovered in NGC 651,ranking it 6 thfor GCs with the most known pulsars.The discoveries take advantage of the high sensitivity of FAST and a new algorithm used to check and filter possible candidate signals.展开更多
X-ray emission is an important indicator of stellar activity.In this paper,we study stellar Xray activity using the XMM-Newton and LAMOST data for different types of stars.We provide a sample including 1259 X-ray-emit...X-ray emission is an important indicator of stellar activity.In this paper,we study stellar Xray activity using the XMM-Newton and LAMOST data for different types of stars.We provide a sample including 1259 X-ray-emitting stars,of which 1090 have accurate stellar parameter estimations.Our sample size is much larger than those used in previous works.We find a bimodal distribution of the X-ray to optical flux ratio(log(fX/fV)) for G and K stars.We interpret that this bimodality is due to two subpopulations with different coronal heating rates.Furthermore,using the full widths at half maxima calculated from Hα and Hβ lines,we show that these stars in the inactive peaks have smaller rotational velocities.This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity.We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the Hα line,and find a tight relation between the coronal and chromospheric activity indicators.展开更多
The age of the Galactic halo is a critical parameter that can constrain the origin of the stellar halo. In general, the Galactic stellar halo is believed to be very old. However, different independent measurements and...The age of the Galactic halo is a critical parameter that can constrain the origin of the stellar halo. In general, the Galactic stellar halo is believed to be very old. However, different independent measurements and techniques based on various types of stars are required so that the age estimates of the Galactic halo are accurate, robust, and reliable. In this work, we provide a novel approach to determine the age of the halo with turn-off stars. We first carefully select 63 field halo turn-off stars from the literature. Then, we compare them with the GARSTEC model, which takes the process of atomic diffusion into account in the B - V vs. metallicity plane. Finally, we run Monte Carlo simulations to consider the uncertainty of the color index and obtain the age of 10.5 ± 1.5 Gyr. This result is in agreement with previous studies. Future works are needed to collect more turn-off samples with more accurate photometry to reduce the uncertainty of the age.展开更多
We take advantage of Gaia Data Release 2 to present 275 and 1774 ultraviolet luminous stars in the far ultraviolet(FUV) and near ultraviolet(NUV), respectively.These stars exceed their expected values by 5σ with resp...We take advantage of Gaia Data Release 2 to present 275 and 1774 ultraviolet luminous stars in the far ultraviolet(FUV) and near ultraviolet(NUV), respectively.These stars exceed their expected values by 5σ with respect to over one million ultraviolet stars in the log g vs.Teffdiagram.Galactic extinction is corrected with a 3 D dust map.In order to limit the Lutz-Kelker bias to an insignificant level, we select stars with relative uncertainties in luminosity less than 40% and trigonometric parallaxes less than 20%.We cross-identified our sample with the catalogs of RR Lyr stars and possible white dwarf main-sequence binaries, and find they compose ~62% and ~16% of our sample in the FUV and NUV, respectively.This catalog provides a unique sample to study stellar activity, spectrally unresolved compact main-sequence binaries and variable stars.展开更多
The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily i...The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily identified.It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes,the products of supernovae.However,neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/γ-ray emitters.Here we report the discovery of one of the nearest(127.7±0.3 pc)neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9(hereafter J2354).Utilizing the time-resolved ground-based spectroscopy and space photometry,we find that J2354 hosts an unseen compact object with M_(inv)being 1.4-1.6 M_(⊙).The follow-up Swift ultraviolet(UV)and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object.Hence,J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf.Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the 6σflux upper limit of 12.5μJy.Therefore,the neutron star candidate in J2354 can only be revealed via our time-resolved observations.Interestingly,the distance between J2354 and our Earth can be as close as~50 pc around 2.5 million years(Myrs)ago,as revealed by the Gaia kinematics.Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain,thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.展开更多
Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, car...Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Fivehundred-meter Aperture Spherical radio Telescope(FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.展开更多
In order to expand the coverage area of satellite navigation systems, a combined navigation constellation which is formed by a global navigation constellation and a Lagrangian navigation constellation was studied. Onl...In order to expand the coverage area of satellite navigation systems, a combined navigation constellation which is formed by a global navigation constellation and a Lagrangian navigation constellation was studied. Only the crosslink range measurement was used to achieve long-term precise autonomous orbit determination for the combined navigation constellation, and the measurement model was derived. Simulations of 180 days based on the international global navigation satellite system(GNSS) service(IGS) ephemeris showed that the mentioned autonomous orbit determination method worked well in the Earth–Moon system. Statistical results were used to analyze the accuracy of autonomous orbit determination under the influences of different Lagrangian satellite constellations.展开更多
With the largest dish Five-hundred-meter Aperture Spherical radio Telescope(FAST), both the mean and single pulses of PSR B2016+28, especially including the single-pulse structure, are investigated in detail in this s...With the largest dish Five-hundred-meter Aperture Spherical radio Telescope(FAST), both the mean and single pulses of PSR B2016+28, especially including the single-pulse structure, are investigated in detail in this study. The mean pulse profiles at different frequencies can be well fitted in a conal model, and the peak separation of intensity-dependent pulse profiles increases with intensity. The integrated pulses are obviously frequency dependent(pulse width decreases by ~20% as frequency increases from 300 to 750 MHz), but the structure of single pulses changes slightly(the corresponding correlation scale decreases by only~1%). This disparity between mean and single pulses provides independent evidence for the existence of the RS-type vacuum inner gap, indicating a strong bond between particles on the pulsar surface. Diffused drifting sub-pulses are analyzed. The results show that the modulation period along pulse series(P_3) is positively correlated to the separation between two adjacent sub-pulses(P_2). This correlation may hint a rough surface on the pulsar, eventually resulting in the irregular drift of sparks. All the observational results may have significant implications in the dynamics of pulsar magnetosphere and are discussed extensively in this paper.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12293032,120101002,12173097,and U1931123)the National Key Basic Research and Development Program of China(Grant Nos.2020YFC2201703 and 2018YFA0404701)Chinese Academy of Sciences(Grant No.GJJSTD20210002)。
文摘We develop an x-ray Ti/Au transition-edge sensor(TES)with an Au absorber deposited on the center of TES and improved its energy resolution using the K-means clustering algorithm in combination with Wiener filter.We firstly extract the main parameters of each recorded pulse trace,which are adopted to classify these traces into several clusters in the K-means clustering algorithm.Then real traces are selected for energy resolution analysis.Following the baseline correction,the Wiener filter is used to improve the signal-to-noise ratio.Although the silicon underneath the TES has not been etched to reduce the thermal conductance,the energy resolution of the developed x-ray TES is improved from 94 eV to 44 eV at 5.9 keV.
基金supported by the National SKA Program of China No.2020SKA0120100the National Natural Science Foundation of China(NSFC,Grant Nos.11963002,11703047,11773041,U2031119,12173052,12003047 and 12173053)+7 种基金the fostering project of Guizhou University with No.201911Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the Specialized Research Fund for State Key Laboratoriessupported by the CAS“Light of West China”Programthe Youth Innovation Promotion Association of CAS(id 2023064)supported by the Youth Innovation Promotion Association of CAS(id.2018075 and Y2022027)supported by Guizhou Provincial Basic Research Program(Natural Science)(ZK[2023]039)Key Technology R&D Program([2023]352)。
文摘Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation between average dispersion measure(■)and dispersion measure difference(ΔDM)of known pulsars in GCs is lgΔDM∝1.52lg■.The sensitivity could be the key to finding more pulsars.As a result,several years after the construction of a large radio telescope facility,the number of known GC pulsars will likely be increased accordingly.We suggest that currently GCs in the southern hemisphere could have higher possibilities for finding new pulsars.
基金supported by the National Key R&D Program of China(2018YFE0202900)support by the NAOC Nebula Talents Program and the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS。
文摘In radio astronomy,radio frequency interference(RFI)becomes more and more serious for radio observational facilities.The RFI always influences the search and study of the interesting astronomical objects.Mitigating the RFI becomes an essential procedure in any survey data processing.The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is an extremely sensitive radio telescope.It is necessary to find out an effective and precise RFI mitigation method for FAST data processing.In this work,we introduce a method to mitigate the RFI in FAST spectral observation and make a statistic for the RFI using~300 h FAST data.The details are as follows.First,according to the characteristics of FAST spectra,we propose to use the Asymmetrically Reweighted Penalized Least Squares algorithm for baseline fitting.Our test results show that it has a good performance.Second,we flag the RFI with four strategies,which are to flag extremely strong RFI,flag long-lasting RFI,flag polarized RFI,and flag beam-combined RFI,respectively.The test results show that all the RFI above a preset threshold could be flagged.Third,we make a statistic for the probabilities of polarized XX and YY RFI in FAST observations.The statistical results could tell us which frequencies are relatively quiescent.With such statistical data,we are able to avoid using such frequencies in our spectral observations.Finally,based on the~300 h FAST data,we obtained an RFI table,which is the most complete database currently for FAST.
基金supported by National Key R&D Program of China No. 2018YFE0202900 and National SKA Program of China No. 2020SKA0120100supported by the Specialized Research Fund for State Key Laboratories and National Natural Science Foundation of China (NSFC, Grant Nos. 11703047, 11773041, U2031119, 12041303, 12173052, 12003047 and 12173053)+2 种基金supported by the CAS “Light of West China” Programsupported by the Youth Innovation Promotion Association of CAS (id. 2018075)the CAS “Light of West China” Program and the Science and Technology Program of Guizhou Province ([2021] 4001)。
文摘We present the estimation of solar observation with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).For both the quiet Sun and the Sun with radio bursts,when pointing directly to the Sun,the total power received by FAST would be out of the safe operational range of the signal chain,even resulting in damage to the receiver.As a conclusion,the Sun should be kept at least~2°away from the main beam during observations at~1.25 GHz.The separation for lower frequency should be larger.For simplicity,the angular separation between the FAST beam and the Sun is suggested to be~5°for observations at 200 MHz or higher bands.
基金supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 11503002 and 11533002)the "Fundamental Research Funds for the Central Universities"
文摘The ROSAT All-Sky Survey (RASS) represents one of the most complete and sensitive soft X- ray all-sky surveys to date. However, the deficient positional accuracy of the RASS Bright Source Catalog (BSC) and subsequent lack of firm optical identifications affect multi-wavelength studies of X-ray sources. The widely used positional errors σpos based on the Tycho Reference Catalog (Tycho-1) have previously been applied for identifying objects in the optical band. The considerably sharper Chandra view covers a fraction of RASS sources, whose ~rpos could be improved by utilizing the sub-arcsec positional accuracy of Chandra observations. We cross-match X-ray objects between the BSC and Chandra sources extracted from the Advanced CCD Imaging Spectrometer (ACIS) archival observations. A combined list of counter- parts (BSCxACIS) with Chandra spatial positions weighted by the X-ray flux of multiple counterparts is employed to evaluate and improve the former identifications of BSC when used with other surveys. Based on these identification evaluations, we suggest that the point-source likeness of BSC sources and INS (iso- lated neutron star) candidates should be carefully reconsidered.
基金supported by the National Natural Science Foundation of China(Grant Nos.11988101,U2031117,11725313,12041303,11873067,U1831131 and U1631132)the China Scholarship Council(No.201704910686)+4 种基金the CASMPG LEGACY projectthe Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB23000000)the National SKA Program of China(No.2020SKA0120200)the Foundation of Guizhou Provincial Education Department(No.KY(2020)003)the Cultivation Project for FAST Scientific Payoff and the Research Achievement of CAMS-CAS。
文摘We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These pulsars are discovered in a pilot program of the Commensal Radio Astronomy FAST Survey(CRAFTS)with the ultra-widebandwidth commissioning receiver.Five of them are normal pulsars and two are extreme nulling slow pulsars.PSR J2111+2132’s dispersion measure(DM:78.5 pc cm^(-3))is above the upper limits of the two Galactic free electron density models,NE2001 and YMW16,and PSR J2057+2133’s position is out of the Scutum-Crux Arm,making them uniquely useful for improving the Galactic free electron density model in their directions.We present a detailed single pulse analysis for the slow nulling pulsars.We show evidence that PSR J2323+1214’s main pulse component follows a non-Poisson distribution and marginal evidence for a sub-pulse-drift or recurrent period of 32.3±0.4 rotations from PSR J0539+0013.We discuss the implication of our finding to the pulsar radiation mechanism.
基金provided by National Major Projects-GRAS Construction of China Lunar Exploration Project
文摘Nomenclatures for lunar features always accompany the progresses of human lunar exploration,which has an important dual meaning in culture and science. The naming of lunar features not only can commemorate the outstanding contributions of academics,masters in various fields, and popularize the traditional cultures of ethnic groups all over the world, but also have a critical function of providing accurate indicative information on features with special morphology, origin, nature and scientific value. However, nomenclature for features at the Chang'e-3 landing site, which has a more arbitrary form without many constrains posed by a uniformed system, is unlike the features for other morphological units.This paper originated from the actual needs for the description of scientific exploration activities, interpretation of scientific research and dissemination of scientific results. Some prominent morphological units with great scientific importance and identification purpose were chosen from the images taken by the terrain camera, panorama cameras and landing camera onboard the Chang'e lander and Yutu rover. A nomenclature system was established under the three enclosures, four quadrants and twenty-eight lunar lodges' system of the Chinese ancient sky division method. Finally, a standard feature names set waspublished after some necessary approval procedures by the International Astronomical Union.
基金the National Natural Science Foundation of China(Grant Nos.11273028 and 11333004)support from National Astronomical Observatories,Chinese Academy of Sciences under the Young Researcher Grant
文摘Magnetic cataclysmic variables (CVs) contain a white dwarf (WD) with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV (CXOGSG J215544.4+380116) from the Chandra archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source is a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2-M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass (~ 0.4 34⊙) and radius (~0.4 R⊙) for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/radius. The estimated low X-ray luminosity and accretion rate may suggest the source is a low-accretion-rate polar. In addition, Very Large Array observations reveal a possible radio counterpart to the X-ray source, but with a low significance. Further radio observations with high quality are needed to confirm the radio counterpart and explore the properties of this binary system.
基金supported by the National Program on Key Research and Development Project (Grant No.2016YFA0400804)the National Natural Science Foundation of China (Grant Nos.11603038,11333004,11425313 and 11403056)
文摘Machine learning has increasingly gained more popularity with its incredibly powerful ability to make predictions or calculate suggestions for large amounts of data. We apply machine learning clas-sification to 85 613 922 objects in the Gala Data Release 2, based on a combination of Pan-STARRS I and AI1WISE data. The classification results are cross-matched with the Simbad database, and the to-tal accuracy is 91.9%. Our sample is dominated by stars, ~98%, and galaxies make up 2%. For the objects with negative parallaxes, about 2.5% are galaxies and QSOs, while about 99.9% are stars if the relative parallax uncertainties are smaller than 0.2. Our result implies that using the threshold of 0 〈 σπ/π 〈 0.2 could yield a very clean stellar sample.
基金the National Natural Science Foundation of China(Grant Nos.11988101,11933004 and 12003050)supported by the National Key Research and Development Program of China(Grant Nos.2019YFA0405000,2019YFA0405504 and 2016YFA0400804)+2 种基金the B-type Strategic Priority Program of the Chinese Academy of Sciences(CAS)under grant number XDB41000000the Youth Innovation Promotion Association of CAS(id.2019057 and 2020060,respectively)the European Research Council(ERC)under the European Union Horizon 2020 research and innovation programme(Cartograph Y GA.804752)。
文摘From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6 h)over 25 nights,yielding a total of about 767000 spectra,and the medium-resolution survey took 177 exposures(≈49.1 h)over 27 nights,collecting about 478000 spectra.More than 70%/50%of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10.We determine stellar parameters(e.g.,Teff,log g,[Fe/H])and radial velocity(RV)with different methods,including LASP,DD-Payne and SLAM.In general,these parameter estimations from different methods show good agreement,and the stellar parameter values are consistent with those of APOGEE.We use the Gaia DR2 RV values to calculate a median RV zero point(RVZP)for each spectrograph exposure by exposure,and the RVZP-corrected RVs agree well with the APOGEE data.The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters,multi-band magnitudes,distances and extinction values.Finally,we construct a binary catalog including about 2700 candidates by analyzing their light curves,fitting the RV data,calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3.The LAMOST TD survey is expected to represent a breakthrough in various scientific topics,such as binary systems,stellar activity,stellar pulsation,etc.
文摘We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa (Porb≈0.48 d). In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly (〈 0.125 Porb) after a primary eclipse, and the other two happening shortly (〈 0.05/9orb) before a primary eclipse. Two flares occurred within roughly one orbital period (△Ф≈ 1.024 Porb) of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.
基金supported by the Basic Science Center Project of the National Natural Science Foundation of China(NSFC,Grant Nos.11703047,11773041 and U2031119)supported by the CAS“Light of West China”Program+1 种基金supported by the Youth Innovation Promotion Association of CAS(id.2018075)supported by the NSF Physics Frontiers Center award 1430284。
文摘We report the discovery of three new pulsars in the globular cluster(GC)NGC 6517,namely NGC 6517 E,F and G,made with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The spin periods of NGC 6517 E,F and G are 7.60 ms,24.89 ms and 51.59 ms,respectively.Their dispersion measures are 183.29,183.713 and 185.3 pc cm^(-3),respectively,all slightly larger than those of the previously known pulsars in this cluster.The spin period derivatives are at the level of 1×10^(-18) s s^(-1),which suggests these are recycled pulsars.In addition to the discovery of these three new pulsars,we updated the timing solutions of the known isolated pulsars,NGC 6517 A,C and D.The solutions are consistent with those from Lynch et al.but with smaller timing residuals.From the timing solution,NGC6517 A,B(position from Lynch et al.),C,E and F are very close to each other on the sky and only a few arcseconds from the optical core of NGC 6517.With currently published and unpublished discoveries,nine pulsars have been discovered in NGC 651,ranking it 6 thfor GCs with the most known pulsars.The discoveries take advantage of the high sensitivity of FAST and a new algorithm used to check and filter possible candidate signals.
基金Funding for the project has been provided by the National Development and Reform Commissionsupport from the National Science Foundation of China (NSFC, Nos. 11273028, 11333004, 11603035, 11603038 and 11503054)
文摘X-ray emission is an important indicator of stellar activity.In this paper,we study stellar Xray activity using the XMM-Newton and LAMOST data for different types of stars.We provide a sample including 1259 X-ray-emitting stars,of which 1090 have accurate stellar parameter estimations.Our sample size is much larger than those used in previous works.We find a bimodal distribution of the X-ray to optical flux ratio(log(fX/fV)) for G and K stars.We interpret that this bimodality is due to two subpopulations with different coronal heating rates.Furthermore,using the full widths at half maxima calculated from Hα and Hβ lines,we show that these stars in the inactive peaks have smaller rotational velocities.This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity.We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the Hα line,and find a tight relation between the coronal and chromospheric activity indicators.
基金supported by the Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences (Grant No. XDB09000000)the National Natural Science Foundation of China (NSFC, Grant No. 11333004)+1 种基金the scholarship awarded by the AMD companythe NSFC (Grant Nos. 11373032 and 11333003)
文摘The age of the Galactic halo is a critical parameter that can constrain the origin of the stellar halo. In general, the Galactic stellar halo is believed to be very old. However, different independent measurements and techniques based on various types of stars are required so that the age estimates of the Galactic halo are accurate, robust, and reliable. In this work, we provide a novel approach to determine the age of the halo with turn-off stars. We first carefully select 63 field halo turn-off stars from the literature. Then, we compare them with the GARSTEC model, which takes the process of atomic diffusion into account in the B - V vs. metallicity plane. Finally, we run Monte Carlo simulations to consider the uncertainty of the color index and obtain the age of 10.5 ± 1.5 Gyr. This result is in agreement with previous studies. Future works are needed to collect more turn-off samples with more accurate photometry to reduce the uncertainty of the age.
基金supported by the National Program on Key Research and Development Project (Grant No.2016YFA0400804)the National Natural Science Foundation of China (NSFC) (Grant Nos.11603038, 11333004, 11425313 and 11403056)+1 种基金STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts
文摘We take advantage of Gaia Data Release 2 to present 275 and 1774 ultraviolet luminous stars in the far ultraviolet(FUV) and near ultraviolet(NUV), respectively.These stars exceed their expected values by 5σ with respect to over one million ultraviolet stars in the log g vs.Teffdiagram.Galactic extinction is corrected with a 3 D dust map.In order to limit the Lutz-Kelker bias to an insignificant level, we select stars with relative uncertainties in luminosity less than 40% and trigonometric parallaxes less than 20%.We cross-identified our sample with the catalogs of RR Lyr stars and possible white dwarf main-sequence binaries, and find they compose ~62% and ~16% of our sample in the FUV and NUV, respectively.This catalog provides a unique sample to study stellar activity, spectrally unresolved compact main-sequence binaries and variable stars.
基金supported by the National Key R&D Program of China(Grant No.2021YFA1600401)the National Natural Science Foundation of China(NSFC)(Grant Nos.11925301+10 种基金12033006)supported by the NSFC(Grant Nos.11973002,and 12322303)supported by the NSFC(Grant No.12103041)supported by the NSFC(Grant Nos.11988101,and 11933004)supported by the NSFC(Grant No.U2031117)supported by the NSFC(Grant No.12033004)supported by the NSFC(Grant No.12273029)supported by the NSFC(Grant No.12221003)supported by the NSFC(Grant No.11933008)supported by the NSFC(Grant No.12090044)supported by the NSFC(Grant Nos.12041301,and 12121003)。
文摘The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily identified.It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes,the products of supernovae.However,neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/γ-ray emitters.Here we report the discovery of one of the nearest(127.7±0.3 pc)neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9(hereafter J2354).Utilizing the time-resolved ground-based spectroscopy and space photometry,we find that J2354 hosts an unseen compact object with M_(inv)being 1.4-1.6 M_(⊙).The follow-up Swift ultraviolet(UV)and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object.Hence,J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf.Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the 6σflux upper limit of 12.5μJy.Therefore,the neutron star candidate in J2354 can only be revealed via our time-resolved observations.Interestingly,the distance between J2354 and our Earth can be as close as~50 pc around 2.5 million years(Myrs)ago,as revealed by the Gaia kinematics.Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain,thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.
基金supported by the National Key R&D Program of China(Grant No.2018YFA0404703)the National Natural Science Foundation of China(Grant No.11225314)+6 种基金the Open Project Program of the Key Laboratory of FAST,NAOC,Chinese Academy of Sciencesthe Project of Chinese Academy of Sciences(CAS)supported by the Special Funding for Advanced Users,budgeted and administrated by Center for Astronomical Mega-Science,Chinese Academy of Sciences(CAMS)the Max-Planck-Society(MPS)Collaborationthe financial support by the European Research Council for the ERC Synergy Grant BlackHoleCam(Grant No.610058)supported by the National Key R&D Program of China(Grant No.2017YFA0402600)the Chinese Academy of Sciences "Light of West China" Program
文摘Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Fivehundred-meter Aperture Spherical radio Telescope(FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.
基金co-supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20133218120037)the National High-Tech Research & Development Program of China (No. 2012AA121602)the Fundamental Research Funds for the Central Universities of China (No. NS2014091)
文摘In order to expand the coverage area of satellite navigation systems, a combined navigation constellation which is formed by a global navigation constellation and a Lagrangian navigation constellation was studied. Only the crosslink range measurement was used to achieve long-term precise autonomous orbit determination for the combined navigation constellation, and the measurement model was derived. Simulations of 180 days based on the international global navigation satellite system(GNSS) service(IGS) ephemeris showed that the mentioned autonomous orbit determination method worked well in the Earth–Moon system. Statistical results were used to analyze the accuracy of autonomous orbit determination under the influences of different Lagrangian satellite constellations.
基金supported by the National Key R&D Program of China(Grant Nos.2018YFA0404703,and 2017YFA0402602)the National Natural Science Foundation of China(Grant Nos.11673002,and 11225314)+5 种基金the Open Project Program of the Key Laboratory of FAST,National Astronomical Observatories,Chinese Academy of Sciencesthe project of Chinese Academy of Sciences(CAS)supported by the Special Funding for Advanced Users,budgeted and administrated by Center for Astronomical Mega-Science,Chinese Academy of Sciences(CAMS)Chinese Academy of Sciences "Light of West China" Programthe Max-Planck-Society(MPS)collaborationsupported by the National Key R&D Program of China(Grant No.2017YFA0402600)
文摘With the largest dish Five-hundred-meter Aperture Spherical radio Telescope(FAST), both the mean and single pulses of PSR B2016+28, especially including the single-pulse structure, are investigated in detail in this study. The mean pulse profiles at different frequencies can be well fitted in a conal model, and the peak separation of intensity-dependent pulse profiles increases with intensity. The integrated pulses are obviously frequency dependent(pulse width decreases by ~20% as frequency increases from 300 to 750 MHz), but the structure of single pulses changes slightly(the corresponding correlation scale decreases by only~1%). This disparity between mean and single pulses provides independent evidence for the existence of the RS-type vacuum inner gap, indicating a strong bond between particles on the pulsar surface. Diffused drifting sub-pulses are analyzed. The results show that the modulation period along pulse series(P_3) is positively correlated to the separation between two adjacent sub-pulses(P_2). This correlation may hint a rough surface on the pulsar, eventually resulting in the irregular drift of sparks. All the observational results may have significant implications in the dynamics of pulsar magnetosphere and are discussed extensively in this paper.