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arXiv 2024年

作者： Wang, Zhenyu Zhang, Jujia Er, Xinzhong Bai, Jinming Yunnan Observatories Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming50216 China South-Western Institute for Astronomy Research Yunnan University Kunming650500 China

The Multi-channel Photometric Survey Telescope (Mephisto) is a real-time, threecolor photometric system designed to capture the color evolution of stars and transients accurately. This telescope system can be crucial in cosmological distance measurements of low-redshift (low-z, z 0.1) Type Ia supernovae (SNe Ia). To optimize the capabilities of this instrument, we perform a comprehensive simulation study before its official operation is scheduled to start. By considering the impact of atmospheric extinction, weather conditions, and the lunar phase at the observing site involving the instrumental features, we simulate the light curves of SNe Ia obtained by the Mephisto. The best strategy in the case of SN Ia cosmology is to take the image at an exposure time of 130 s with a cadence of 3 days. In this condition, Mephisto can obtain hundreds of high-quality SNe Ia to achieve a distance measurement better than 4.5%. Given the on-time spectral classification and monitoring of the Lijiang 2.4 m Telescope at the same observatory, Mephisto, in the whole operation, can significantly enrich the well-calibrated sample of supernovae at low-z and improve the calibration accuracy of high-z SNe Ia. © 2024, CC BY.

关键词： Supernovae

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Constraining evolution of magnetic field strength in the dissipation region of two BL Lac objects

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Research in Astronomy and Astrophysics 2021年第12期21卷 351-356页

作者： Xu-Liang Fan Da-Hai Yan Qing-Wen Wu Xu Chen School of Mathematics Physics and StatisticsShanghai University of Engineering ScienceShanghai 201620China Yunnan Observatories Chinese Academy of SciencesKunming 650011China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650011China School of Physics Huazhong University of Science and TechnologyWuhan 430074China Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment Institute of Space SciencesShandong UniversityWeihai 264209China

With the assumption that the optical variability timescale is dominated by the cooling time of the synchrotron process for BL Lac objects,we estimate time dependent magnetic field strength of the emission region for two BL Lac *** average magnetic field strengths are consistent with those estimated from core shift measurement and spectral energy distribution *** of magnetic field strength in the dissipation region is *** of flux and magnetic field strength shows no clear correlation,which indicates the variation of magnetic field is not the dominant reason of the variability *** evolution of magnetic field strength can provide another approach to constrain the energy dissipation mechanism in jets.

关键词： BL Lacertae objects:general BL Lacertae objects:individual(S50716+714 BL Lacertae) galaxies:magnetic fields

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Simulating the Escaping Atmosphere of GJ436 b with two-fluid Magnetohydrodynamic Models-

arXiv

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arXiv 2024年

作者： Xing, Lei Guo, Jianheng Yan, Dongdong Yang, Chuyuan Yunnan Observatories Chinese Academy of Sciences P.0.Box110 Kunming650216 China Yuquan Road Shijingshan District Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.0.Box110 Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China

Observations of transmission spectra reveals that hot Jupiters and Neptunes are likely to possess escaping atmospheres driven by stellar radiation. Numerous models predict that magnetic fields may exert significant influences on the atmospheres of hot planets. Generally, the escaping atmospheres are not entirely ionized, and magnetic fields only directly affect the escape of ionized components within them. Considering the chemical reactions between ionized components and neutral atoms, as well as collision processes, magnetic fields indirectly impact the escape of neutral atoms, thereby influencing the detection signals of planetary atmospheres in transmission *** order to simulate this process, we developed a magneto-hydrodynamic multi-fluid model based on MHD code PLUTO. As an initial exploration, we investigated the impact of magnetic fields on the decoupling of H+ and H in the escaping atmosphere of the hot Neptune GJ436 b. Due to the strong resonant interactions between H and H+. The coupling between them is tight even if the magnetic field is strong. However, our simulation results indicate that under the influence of magnetic fields, there are noticeable regional differences in the decoupling of H+ and H. With the increase in magnetic field strength, the degree of decoupling also increases. For heavier particles such as O, the decoupling between O and H+ is more pronounced. our findings provide important insights for future studies on the decoupling processes of heavy atoms in the escaping atmospheres of hot Jupiters and hot Neptunes under the influence of magnetic fields. © 2024, CC BY-NC-ND.

关键词： Magnetohydrodynamics

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An Exposure Meter of Lijiang Fiber-fed High Resolution Spectrograph

arXiv

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arXiv 2024年

作者： Yu, Xiao-Guang Ji, Kai-Fan Zhang, Xi-Liang Chang, Liang Cai, Yun-Fang Qin, Ying Shang, Zhen-Hong Yunan Observatories Chinese Academy of Sciences Kunming650011 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 Faculty of Information Engineering and Automation Kunming University of Science and Technology Kunming650500 China

In 2016, an exposure meter was installed on the Lijiang Fiber-fed High-Resolution Spectrograph to monitor the coupling of starlight to the science fiber during observations. Based on it, we investigated a method to estimate the exposure flux of the CCD in real time by using the counts of the photomultiplier tubes (PMT) of the exposure meter, and developed a software to optimize the control of the exposure time. First, by using flat-field lamp observations, we determined that there is a linear and proportional relationship between the total counts of the PMT and the exposure flux of the CCD. Second, using historical observations of different spectral types, the corresponding relational conversion factors were determined and obtained separately. Third, the method was validated using actual observation data, which showed that all values of the coefficient of determination were greater than 0.92. Finally, software was developed to display the counts of the PMT and the estimated exposure flux of the CCD in real-time during the observation, providing a visual reference for optimizing the exposure time control. Copyright © 2024, The Authors. All rights reserved.

关键词： Exposure meters

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The fractions of post-binary-interaction stars and evolved blue straggler stars on the red giant branch of globular clusters

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Research in Astronomy and Astrophysics 2021年第9期21卷 101-110页

作者： Dan-Dan Wei Bo Wang Hai-Liang Chen Hai-Feng Wang Xiao-Bo Gong Dong-Dong Liu Deng-Kai Jiang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of ScienceKunming 650216China University of Chinese Academy of Science Beijing 100049China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China South-Western Institute for Astronomy Research Yunnan UniversityKunming 650500China LAMOST

The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in *** is well known that binary interactions are responsible for many exotic ***,it is important to understand what fraction of stars on the RGB of GCs is the result of binary *** this paper,we performed a binary population synthesis study to track the number of post-binary-interaction(post-BI)stars that appear on the RGB,with particular emphasis on the evolved blue straggler stars(E-BSSs).Assuming an initial binary fraction of nearly 50%,we find that about half of the objects on the RGB(called giants)underwent the binary interactions,and that E-BSSs account for around 10%of the giants in our standard *** also compare the properties of post-BI giants that evolved from different *** find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI *** results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs,which should be considered in future investigations of the origin of multiple stellar populations.

关键词： blue stragglers stars:chemically peculiar globular clusters:general binaries:general

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Opacity enhanced by the localization of electrons

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Science China(Physics,Mechanics & Astronomy) 2022年第3期65卷 131-131页

作者： Qian-Sheng Zhang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100012China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China University of Chinese Academy of Sciences Beijing 100049China

Plasmas absorbing and scattering photons are often described according to the conception of opacity. The opacity in hot, dense plasmas is crucial in many fields, including astrophysics and controlled nuclear fusion. It is a difficult problem because of many complex mechanisms involving,for instance, excited states, line broadenings, relativistic effects, and two-photon contributions. Studies on opacity.

关键词： excited instance relativistic

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He-shell flashes on the surface of oxygen-neon white dwarfs

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Research in Astronomy and Astrophysics 2021年第2期21卷 73-81页

作者： Yunlang Guo Dongdong Liu Chengyuan Wu Bo Wang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China University of Chinese Academy of Sciences Beijing 100049China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China Physics Department and Tsinghua Center for Astrophysics(THCA) Tsinghua UniversityBeijing 100084China

Accretion induced collapse(AIC)may be responsible for the formation of some interesting neutron star binaries(e.g.,millisecond pulsars,intermediate-mass binary pulsars,etc).It has been suggested that oxygen-neon white dwarfs(ONe WDs)can increase their mass to the Chandrasekhar limit by multiple He-shell flashes,leading to AIC ***,the properties of He-shell flashes on the surface of ONe WDs are still not well *** this article,we aim to study He-shell flashes on the surface of ONe WDs in a systematic *** investigated the long-term evolution of ONe WDs accreting He-rich material with various constant mass-accretion rates by time-dependent calculations with the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),in which the initial ONe WD masses range from 1.1 to 1.35 M_(⊙).We found that the mass-retention efficiency increases with the ONe WD mass and the mass-accretion rate,whereas both the nova cycle duration and the ignition mass decrease with the ONe WD mass and the mass-accretion *** also present the nuclear products in different accretion *** results presented in this article can be used in the future binary population synthesis studies of AIC events.

关键词： stars evolution-binaries close-supernovae general-white dwarfs

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A New Magnetically Active Binary System Discovered in Yunnan-Hong Kong Wide Field Survey

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Chinese Astronomy and Astrophysics 2021年第1期45卷 67-81页

作者： Jian-hua, W.A.N.G. Sheng-hong, G.U. Xiao-bin, W.A.N.G. YEUNG, Bill NG, Eric Yunnan Observatories Chinese Academy of Sciences Kunming 650216 Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650216 School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing 101408 Hong Kong Astronomical Society Hong Kong 999077

We present a newly discovered magnetically active binary system detected by Yunnan-Hong Kong wide field survey, with an orbital period of 0.60286 days. Two color photometry for the system was performed using the 1 m Cassegrain telescope of Yunnan Observatories with its CCD (Charge-Coupled Device) camera. In the observed light curves, there are clearly different light maxima existed in the out-of-eclipse regions. We made spectroscopic observations for the binary system using the 2.4 m telescope and YFOSC (Yunnan Faint object Spectrograph and Camera) of Lijiang station of Yunnan Observatories, China. The radial velocity curve was derived for primary star of the binary system. The primary star exhibited strong chromospheric activity, which confirms that the distortion of the light curves results from the starspot activity on the primary star. Through analyzing the light curves and RV (Radial Velocity) curve mentioned above by means of the W-D (Wilson-Devinney) code, orbital parameters and starspot configuration of the binary system are obtained. Finally, we have discussed the properties of the binary system, and given the prospects on the future work. © 2021

关键词： Binary: eclipsing Stars: activity stars: magnetic field starspots

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evolution of double oxygen-neon white dwarf merger remnant

arXiv

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arXiv 2023年

作者： Wu, Chengyuan Xiong, Heran Han, Zhanwen Wang, Bo Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Research School of Astronomy and Astrophysics The Australian National University CanberraACT2611 Australia

Double white dwarf (WD) merger process and their post-merger evolution are important in many fields of astronomy, such as supernovae, gamma-ray bursts, gravitational waves, etc. The evolutionary outcomes of double ultra-massive WD merger remnants are still a subject of debate, though the general consensus is that the merger remnant will collapse to form a neutron star. In this work, we investigate the evolution of a 2.20Mo merger remnant stemmed from the coalescence of double 1.10Mo ONe WDs. We find that the remnant ignites off-centre neon burning at the position near the surface of primary WD soon after the merger, resulting in the stable inwardly propagating oxygen/neon (O/Ne) flame. The final outcomes of the merger remnant are sensitive to the effect of convective boundary mixing. If the mixing cannot stall the O/Ne flame, the flame will reach the centre within 20 years, leading to the formation of super Chandrasekhar mass silicon core, and its final fate probably be neutron star (NS) through iron-core-collapse supernova. In contrast, if the convective mixing is effective enough to prevent the O/Ne flame from reaching the centre, the merger remnant will undergo electron capture supernova to form an ONeFe WD. Meanwhile, we find that the wind mass loss process may hardly alter the final fate of the remnant due to its fast evolution. Our results imply that the coalescence of double ONe WDs can form short lived giant like object, but the final outcomes (NS or ONeFe WD) are influenced by the uncertain convective mixing in O/Ne flame. © 2023, CC BY.

关键词： Oxygen

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Stellar Spectral Classification Based on Capsule Network

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Chinese Astronomy and Astrophysics 2021年第3期45卷 352-363页

作者： Li-ting, D.U. Li-hua, H.O.N.G. Jin-tao, Y.A.N.G. Ting-ting, X.U. Jing-min, ZHANG Lin-pin, A.I. Wei-hong, Z.H.O.U. School of Mathematics and Computer Science Yunnan Minzu University Kunming 650500 School of Software Engineering Xiamen Institute of Software Technology Xiamen 361000 Center for Astrophysics Guangzhou University Guangzhou 510006 Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011

The rapid development of large-scale sky survey project has produced a large amount of stellar spectral data, which make the automatic classification of stellar spectral data a challenging task. In this paper, we have proposed a stellar spectral classification method based on a capsule network. At first, by using the one-dimensional convolutional network and short-time Fourier transform (STFT), the one-dimensional spectra of the F5, G5, and K5 types selected from the LAMOST Data Release 5 (DR5) are converted into the two-dimensional Fourier spectrum images. Then, the two-dimensional Fourier spectrum images are classified automatically by the capsule network. Because the capsule network can preserve the hierarchical pose relationships among the entities in the image, and it does not need any pooling layers, the experimental results show that the capsule network has a better classification performance, for the classifications of the F5, G5, and K5-type stellar spectra, its classification accuracy is superior to other classification methods. © 2021

关键词： methods: data analysis Stars: fundamental parameters techniques: spectral analysis

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