检索结果-内蒙古大学图书馆

arXiv 2020年

作者： Wei, Dandan Wang, Bo Chen, Xuefei Chen, Hailiang Li, Lifang Jiang, Dengkai Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

While it is well known that mass transfer in binaries can pollute the surfaces of the accretors, it is still unclear whether this mechanism can reproduce the observed chemical inhomogeneities in globular clusters. We study the surface abundances of the accretors in low-mass binaries, as a first step towards understanding whether mass transfer in low-mass binaries is one of the potential origins of the aforementioned abundance anomalies in globular clusters. We use the Modules for Experiments in Stellar Astrophysics code to calculate binary evolutionary models with different initial donor masses between 0.9 and 1.9 M for an initial metallicity of Z = 0.0034. The results show that in some low-mass binary systems, the accretors exhibit peculiar chemical patterns when they are still unevolved stars, e.g. C and O depletion;Na and N enhancement;constant Mg, Al and C+N+O. The abundance patterns of the accretors are significantly different from their initial abundances (or that of normal single stars), and can match the observed populations. These abundance patterns strongly depend not only on the initial parameters of binaries (donor mass, mass ratio, and orbital period), but also on the assumptions regarding mass-transfer efficiency and angular momentum loss. These results support the hypothesis that mass transfer in low-mass binaries is at least partly responsible for the unevolved anomalous stars in globular clusters. More work on binary evolutionary models and binary population synthesis is required to fully evaluate the contribution of this scenario. Copyright © 2020, The Authors. All rights reserved.

关键词： Mass transfer

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Flares hunting in hot subdwarf and white dwarf stars from Cycles 1-5 of TESS photometry

arXiv

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arXiv 2024年

作者： Xing, keyu Zong, Weikai Silvotti, Roberto Fu, Jian-Ning Charpinet, Stéphane Cang, Tianqi Hermes, J.J. Ma, Xiao-Yu Wang, Haotian Wang, Xuan Wu, Tao Wang, Jiaxin Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China Department of Astronomy Beijing Normal University Beijing100875 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China INAF-Osservatorio Astrofisico di Torino strada dell’Osservatorio 20 Pino TorineseI-10025 Italy Institut de Recherche en Astrophysique et Planétologie CNRS Université de Toulouse CNES 14 Avenue Edouard Belin ToulouseF-31400 France Department of Astronomy Institute for Astrophysical Research Boston University 725 Commonwealth Avenue BostonMA02215 United States Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China College of Science Chongqing University of Posts and Telecommunications Chongqing400065 China

Stellar flares are critical phenomena on stellar surfaces, which are closely tied to stellar magnetism. While extensively studied in main-sequence (MS) stars, their occurrence in evolved compact stars, specifically hot subdwarfs and white dwarfs (WDs), remains scarcely explored. Based on Cycles 1-5 of TESS photometry, we conducted a pioneering survey of flare events in ∼12 000 compact stars, corresponding to ∼38 000 light curves with 2-minute cadence. Through dedicated techniques for detrending light curves, identifying preliminary flare candidates, and validating them via machine learning, we established a catalog of 1016 flares from 193 compact stars, including 182 from 58 sdB/sdO stars and 834 from 135 WDs, respectively. However, all flaring compact stars showed signs of contamination from nearby objects or companion stars, preventing sole attribution of the detected flares. For WDs, it is highly probable that the flares originated from their cool MS companions. In contrast, the higher luminosities of sdB/sdO stars diminish companion contributions, suggesting that detected flares originated from sdB/sdO stars themselves or through close magnetic interactions with companions. Focusing on a refined sample of 23 flares from 13 sdB/sdO stars, we found their flare frequency distributions were slightly divergent from those of cool MS stars;instead, they resemble those of hot B/A-type MS stars having radiative envelopes. This similarity implies the flares on sdB/sdO stars, if these flares did originate from them, may share underlying mechanisms with hot MS stars, which warrants further investigation. © 2024, CC BY.

关键词： Machine learning

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Velocity-resolved Reverberation Mapping of Changing-look Active Galactic Nucleus NGC 4151 During Outburst Stage: Evidence for Kinematics evolution of Broad-line Region

arXiv

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arXiv 2022年

作者： Li, Sha-Sha Feng, Hai-Cheng Liu, H.T. Bai, J.M. Li, Rui Lu, Kai-Xing Wang, Jian-Guo Huang, Ying-Ke Zhang, Zhi-Xiang Yunnan Observatories Chinese Academy of Sciences Yunnan Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650011 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Qian Xuesen Laboratory of Space Technology China Academy of Space Technology 104 Youyi Road Haidian District Beijing100094 China Multi-disciplinary Research Division Institute of High Energy Physics Chinese Academy of Sciences 19B Yuquan Road Beijing100049 China Department of Astronomy Xiamen University Fujian Xiamen361005 China

Changing-look active galactic nucleus NGC 4151, which has attracted a lot of attention, is undergoing the second dramatic outburst stage in its evolutionary history. To investigate the geometry and kinematics of the broad-line region (BLR), and measure the mass of supermassive black hole in NGC 4151, we perform a seven-month photometric and spectroscopic monitoring program in 2020–2021, using the 2.4 m telescope at Lijiang Observatory. We successfully measure the time lags of the responses from broad Hα, Hβ, Hγ, He I, and He II emission lines to continuum variation, which are 7.63+1.85−2.62, 6.21+1.41−1.13, 5.67+1.65−1.94, 1.59+0.86−1.11, and 0.46+1.22−1.06 days, respectively, following radial stratification. The ratios of time lags among these lines are 1.23: 1.00: 0.91: 0.26: 0.07. We find that the continuum lag between the ultraviolet and optical bands can significantly affect the lag measurements of He I and He II. Virial and infalling gas motions coexist in this campaign, which is different from previous results, implying the evolutionary kinematics of BLR. Based on our measurements and previous ones in the literature, we confirm that the BLR of NGC 4151 is basically virialized. Finally, we compute the black hole mass through multiple lines, and the measurement from Hβ to be 3.94+0.90−0.72 × 107Mo, which is consistent with previous results. The corresponding accretion rate is 0.02+0.01−0.01LEddc−2, implying a sub-Eddington accretor. © 2022, CC BY.

关键词： Active Galactic Nuclei

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Binary population synthesis

arXiv

引用

arXiv 2020年

作者： Han, Zhanwen Ge, Hongwei Chen, Xuefei Chen, Hailiang Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of the Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

Binary interactions lead to the formation of intriguing objects, such as compact binaries, supernovae, gamma ray bursts, X-ray binaries, pulsars, novae, cataclysmic variables, hot subdwarf stars, barium stars, and blue stragglers. To study the evolution of binary populations and the consequent formation of these objects, many methods have been developed over the years, of which a robust approach named binary population synthesis (BPS) warrants special attention. This approach has seen widespread use in many areas of astrophysics, including but not limited to analyses of the stellar content of galaxies, research on galactic chemical evolution, and studies concerning star formation and cosmic re-ionization. In this review, we discuss the role of BPS, its general picture, and the various components that comprise it. We pay special attention to the stability criteria for mass transfer in binaries, as this stability largely determines the fate of binary systems. We conclude with our perspectives regarding the future of this field. Copyright © 2020, The Authors. All rights reserved.

关键词： Supernovae

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The innermost jet in the hidden ultra-luminous X-ray source Cygnus X-3

arXiv

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arXiv 2023年

作者： Yang, Jun García, Federico Palacio, Santiago del Spencer, Ralph Paragi, Zsolt Segura, Noel Castro Gong, Biping Cao, Hongmin Chen, Wen Department of Space Earth and Environment Chalmers University of Technology Onsala Space Observatory OnsalaSE-439 92 Sweden C.C.5 Villa Elisa Buenos Aires Argentina Jodrell Bank Centre for Astrophysics Department of Physics and Astronomy The University of Manchester Oxford Rd. ManchesterM13 9PL United Kingdom Oude Hoogeveensedijk 4 Dwingeloo7991 PD Netherlands School of Physics and Astronomy University of Southampton SouthamptonSO17 1BJ United Kingdom School of Physics Huazhong University of Science and Technology Wuhan430074 China School of Electronic and Electrical Engineering Shangqiu Normal University 298 Wenhua Road Shangqiu Henan476000 China Yunnan Observatories Chinese Academy of Sciences Yunnan Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

Cygnus X-3 is a high-mass X-ray binary with a compact object accreting matter from a Wolf-Rayet donor star. Recently, it has been revealed by the Imaging X-ray Polarimetry Explorer (IXPE) as a hidden Galactic ultra-luminous X-ray (ULX) source with a luminosity above the Eddington limit along the direction of a narrow (opening angle ∼ 32◦) funnel. In between the IXPE observations, we observed Cyg X-3 with the European VLBI (very long baseline interferometry) Network at 22 GHz and the NICER X-ray instrument. To probe possible relations between the X-ray funnel and the potential radio jet from the ULX, we analyzed the simultaneous multi-wavelength data. Our high-resolution VLBI image reveals an elongated structure with a position angle of −3◦. 2 ± 0◦. 4, accurately perpendicular to the direction of the linear X-ray polarization. Because Cyg X-3 was in the radio quiescent state on 2022 November 10, we identify the mas-scale structure as the innermost radio jet. The finding indicates that the radio jet propagates along and within the funnel. Moreover, the jet is marginally resolved in the transverse direction. This possibly results from the strong stellar winds and the rapid orbital motion of the binary system. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars

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A time-dependent particle acceleration and emission model: Understanding the particle spectral evolution and blazar flares

arXiv

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arXiv 2020年

作者： Zheng, Y.G. Kang, Shi-Ju Yang, C.Y. Bai, J.M. Department of Physics Yunnan Normal University Kunming650092 China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences China School of Physics and Electrical Engineering Liupanshui Normal University Liupanshui Guizhou553004 China

The jets of blazars are renowned for their multi-wavelength flares and rapid extreme variability;however, there are still some important unanswered questions about the physical processes responsible for these spectral and temporal changes in emission properties. In this paper, we develop a time-dependent particle evolution model for the time-varying emission spectrum of blazars. In the model, we introduce time-dependent electric and magnetic fields, which consistently include the variability of relevant physical quantities in the transport equation. The evolution on the electron distribution is numerically solved from a generalized transport equation that contains the terms describing the electrostatic, first-order and second-order Fermi acceleration, escape of particles due to both advection and spatial diffusion, as well as energy losses due to the synchrotron emission and inverse-Compton scattering of both synchrotron and external ambient photon fields. We find that the light curve profiles of blazars are consistent with the particle spectral evolution resulting from time-dependent electric and magnetic fields, rather than the effects of the acceleration or the cooling processes. The proposed model is able to simultaneously account for the variability of both the energy spectrum and the light curve profile of the BL Lac object Mrk 421 with reasonable assumptions about the physical parameters. The results strongly indicate that the magnetic field evolution in the dissipated region of a blazar jet can account for the variabilities. Copyright © 2020, The Authors. All rights reserved.

关键词： Emission spectroscopy

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The afterglow emission from a stratified jet in GRB 170817A

arXiv

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arXiv 2021年

作者： Cheng, Kang-Fa Zhao, Xiao-Hong Zhang, Bin-Bin Bai, Jin-Ming Yunnan Observatories Chinese Academy of Sciences Kunming650216 China University of the Chinese Academy of Sciences Yuquan Road 19 Shijingshan Block Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China School of Astronomy and Space Science Nanjing University Nanjing210093 China Ministry of Education China Department of Physics and Astronomy University of Nevada Las VegasNV89154 United States

The afterglow of GRB 170817A has been detected for more than three years, but the origin of the multi-band afterglow light curves remains under debate. A classical top-hat jet model is faced with difficulties in producing a shallow rise of the afterglow light curves as observed (Fν ∝ T0.8). Here we reconsider the model of stratified ejecta with energy profile of E(> Γβ) = E0(Γβ)-k as the origin of the afterglow light curves of the burst, where Γ and β are the Lorentz factor and speed of the ejecta, respectively. k is the power-law slope of the energy profile. We consider the ejecta are collimated into jets. Two kinds of jet evolutions are investigated, including a lateral-spreading jet and a non-lateral-spreading jet. We fit the multi-band afterglow light curves, including the X-ray data at one thousand days post-burst, and find that both the models of the spreading and non-spreading jets can fit the light curves well, but the observed angular size of the source and the apparent velocity of the flux centroid for the spreading jet model are beyond the observation limits, while the non-spreading jet model meets the observation limits. Some of the best-fit parameters for the non-spreading jet model, such as the number density of the circumburst medium ∼ 10-2 cm-3 and the total jet kinetic energy E ∼ 4.8 × 1051 erg, also appear plausible. The best-fit slope of the jet energy profile is k ∼ 7.1. Our results suggest that the afterglow of GRB 170817A may arise from the stratified jet and that the lateral spreading of the jet is not significant. Copyright © 2021, The Authors. All rights reserved.

关键词： Kinetic energy

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Long-Term Light and Period Variations in the Supersoft X-Ray Source V617 Sgr

SSRN

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SSRN 2023年

作者： Zang, Lei Zhao, Ergang Fernández-Lajús, Eduardo Zubairi, Ahmed Waqas Sarotsakulchai, Nopphadon P. O. Box 110 Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China University of Chinese Academy of Sciences No.1 Yanqihu East Rd Huairou District Beijing101408 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Facultad de Ciencias Astronómicas y Geofísicas Universidad Nacional de La Plata Paseo del Bosque S/N La PlataB1900FWA Argentina La PlataB1900FWA Argentina National Astronomical Research Institute of Thailand 260 Moo 4 T. Donkaew A. Maerim Chiangmai50180 Thailand

V617 Sgr is one of the Galactic counterparts of supersoft X-ray sources as a member of the V Sagittae class, where a massive white dwarf is accreting material from its stellar companion and forming an accretion disk. Since 2014, we have monitored it for about nine years with the 2.15m telescope at CASLEO. It is found that the light curve shows obviously fluctuations and flickering, which imply the presence of actively hot spots on the accretion disk. Meanwhile, the flat-bottomed depressions can be explained by the presence of circumbinary material. By collecting all available eclipse times from the literature together with 149 newly determined times of light minimum, we constructed the O-C diagram and analyzed the variations in the orbital period of the eclipsing binary V617 Sgr. It is confirmed that the orbital period is increasing continuously with a rate of dP/dt=+1.68(3)E-7d/yr=+0.0145(3)s/yr. A cyclic variation is detected to be superimposed on the period increase with an amplitude of 4.6min and a period of 26yr. The continuous period increase is largely due to mass transfer from the donor secondary on its Kelvin–Helmholtz time-scale, while wind mass loss from the accretion disk surrounding the white dwarf may also contribute on the period change. In this case, the mass-transfer rate of V617 Sgr is estimated to be in the range of about 0.575E-6 to 2.25E-6Msun/yr and the mass-accretion rate is less than 1.59E-6Msun/yr. The cyclic change can be explained by the presence of a third body or magnetic activity cycles of the secondary. © 2023, The Authors. All rights reserved.

关键词： Mass transfer

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The formation of single neutron-stars from double white-dwarf mergers via accretion-induced collapse

arXiv

引用

arXiv 2020年

作者： Liu, D. Wang, B. Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

The merging of double white-dwarfs \(WDs\) may produce the events of accretion-induced collapse \(AIC\) and form single neutron stars \(NSs\). Meanwhile, it is also notable that the recently proposed WD+He subgiant scenario has a significant contribution to the production of massive double WDs, in which the primary WD grows in mass by accreting He-rich material from a He subgiant companion. In this work, we aim to study the binary population synthesis \(BPS\) properties of AIC events from the double WD mergers by considering the classical scenarios and also the contribution of the WD+He subgiant scenario to the formation of double WDs. Firstly, we provided a dense and large model grid of WD+He star systems for producing AIC events through the double WD merger scenario. Secondly, we performed several sets of BPS calculations to obtain the rates and single NS number in our Galaxy. We found that the rates of AIC events from the double WD mergers in the Galaxy are in the range of 1.4−8.9×10−3 yr−1 for all ONe/CO WD+ONe/CO WD mergers, and in the range of 0.3−3.8 × 10−3 yr−1 when double CO WD mergers are not considered. We also found that the number of single NSs from AIC events in our Galaxy may range from 0.382 × 107 to 1.072 × 108. The chirp mass of double WDs for producing AIC events distribute in the range of 0.55−1.25 Mo. We estimated that more than half of double WDs for producing AIC events are capable to be observed by the future space-based gravitational wave detectors. Copyright © 2020, The Authors. All rights reserved.

关键词： Merging

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Studies of extragalactic background light with TeV BL Lac objects

arXiv

引用

arXiv 2020年

作者： Qin, Longhua Wang, Jiancheng Gao, Quangui Na, Weiwei Li, Huaizhen Ma, Ju Yang, Jianping Physics Department Yuxi Normal University YuxiYunnan653100 China Yunnan Observatory Chinese Academy of Sciences KunmingYunnan650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences KunmingYunnan650011 China Yunnan Agricultural University KunmingYunnan650201 China

Very high energy (VHE;E ≽ 100GeV) γ−ray from cosmological distances are attenuated by the extragalactic background light (EBL) in the IR to UV band. By contrasting measured versus intrinsic emission, the EBL photon density can be derived. However, neither the intrinsic spectra nor the EBL is separately known - except their combined effect. Here we first present a flexible model-dependent optical depth method to study EBL by fitting the emission spectra of TeV BL Lacs objects via a one-zone leptonic synchrotron self-Compton model (SSC). We have little information about electron energy distributions (EEDs) in the jet, which is critically important to build spectral energy distributions (SEDs) in SSC scenario. Based on the current particle acceleration models, we use two types of EEDs, i,e., a power-law log-parabola (PLLP) EED and a broken power-law (BPL) EED to fit the observed spectra. We obtain that the upper limits of EBL density are around about 30 n W m−2 sr−1, which are similar to the published measurement. Furthermore, we propose an unprecedented method to test radiation mechanisms involved in TeV objects by simply comparing the reduced EBL density with the limit obtained by galaxy counts, and demonstrate that for some BL Lacs, at least, the one-zone SSC model should be reconsidered. Copyright © 2020, The Authors. All rights reserved.

关键词： Gamma rays

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