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arXiv 2024年

作者： Cheng, Qiyuan Xiong, Jianping Ding, Xu Ji, Kaifan Li, Jiao Liu, Chao Li, Jiangdan Luo, Jingxiao Lyu, Xin Han, Zhanwen Chen, Xuefei Yunnan Observatories Chinese Academy of Sciences 396 YangFangWang Guandu District Kunming650216 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory of Space Astronomy and Technology National Astronomical Observatories CAS Beijing100101 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Key Laboratory of Radio Astronomy and Technolgoy Chinese Academy of Sciences A20 Datun Road Chaoyang District Beijing100101 China

Low mass-ratio (q) contact binary systems are progenitors of stellar mergers such as blue straggles (BS) or fast-rotating FK Com stars. In this study, we present the first light curve analysis of two newly identified low mass-ratio contact binary systems, TIC 55007847 and TIC 63597006, that are identified from TESS. Both stars are classified as A-subtype contact binaries. We obtained the precise orbit periods for the two objects by using the O-C method, i.e. P=0.6117108 d for TIC 55007847 and P=0.7008995 d for TIC 63597006, respectively, and found an obvious periodic signal in the O-C curve of TIC 63597006. We suggest that the periodic signal comes from a third body. We further use the Markov Chain Monte Carlo (MCMC) method with PHOEBE to derive the photometric solutions for the two binaries. The photometric solution for this object shows that the contribution of the third body is about 6%. Our analysis revealed that TIC 55007847 has an extremely low mass ratio of q = 0.08. By calculating the ratio of spin angular momentum to the orbital angular momentum Js/Jo, we found that TIC 55007847 is very close to the instability threshold with Js/Jo = 0.31, indicating that it may merge into a single, fast-rotating star in the future. For TIC 63597006, q = 0.14 and Js/Jo = 0.15. This object is in a relatively stable evolutionary status at present. Copyright © 2024, The Authors. All rights reserved.

关键词： Monte Carlo methods

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SN 2021dbg: A Luminous Type IIP-IIL Supernova Exploding from a Massive Star with a Layered Shell

arXiv

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arXiv 2024年

作者： Zhao, Zeyi Zhang, Jujia Li, Liping Zhai, Qian Cai, Yongzhi Srivastav, Shubham Wang, Xiaofeng Lin, Han Yang, Yi Filippenko, Alexei V. Brink, Thomas G. Zheng, WeiKang Kunming650216 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing101408 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast BelfastBT7 1NN United Kingdom Department of Physics Tsinghua University Beijing100084 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing210023 China Key Laboratory of Radio Astronomy and Technology CAS A20 Datun Road Chaoyang District Beijing100101 China Department of Astronomy University of California BerkeleyCA94720-3411 United States

We present extensive observations and analysis of supernova (SN) 2021dbg, utilizing optical photometry and spectroscopy. For approximately 385 days following the explosion, SN 2021dbg exhibited remarkable luminosity, surpassing most SNe II. This initial high luminosity is potentially attributed to the interaction between the ejected material and the surrounding circumstellar material (CSM), as evidenced by the pronounced interaction signatures observed in its spectra. The subsequent high luminosity is primarily due to the significant 56Ni (0.17 ± 0.05 M☉) produced in the explosion. Based on the flux of flash emission lines detected in the initial spectra, we estimate that the CSM mass near the progenitor amounted to ∼(1.0–2.0) ×10−3 M☉, likely resulting from intense stellar wind activity 2–3 yr preceding the explosion. Considering the bolometric light curve, nebular spectrum modeling, and mass-loss rate, we suggest that the progenitor of SN 2021dbg was a red supergiant (RSG) with a mass of ∼ 20 M☉ and a radius of 1200 R☉. This RSG featured a thick hydrogen shell, which may have contained a region with a sharp decrease in material density, electron density, and temperature, contributing to its layered structure. This object demonstrates mixed features of SNe IIP and SNe IIL, making it as a transitional event linking the above two subclasses of SNe II. Copyright © 2024, The Authors. All rights reserved.

关键词： Supernovae

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Magnetic-Reconnection-Heated Corona Model: Implication of Hybrid Electrons for Hard X-ray Emission of Luminous Active Galactic Nuclei

arXiv

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arXiv 2023年

作者： Liu, Jie-Ying Mao, Jirong Liu, B.F. Yunnan Observatories Chinese Academy of Sciences Yunnan Province Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China School of Astronomy and Space Sciences University of Chinese Academy of Sciences 19A Yuquan Road Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Key Laboratory of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China

It is widely accepted that X-ray emission in luminous active galactic nuclei (AGNs) originates from hot corona. To prevent the corona from over-cooling by strong X-ray emission, steady heating to the corona is essential, for which the most promising mechanisms is the magnetic reconnection. Detailed studies of the coupled disc and corona, in the frame of magnetic field transferring accretion-released energy from the disc to the corona, reveal that the thermal electrons can only produce X-ray spectrum with Γ2−10 keV > 2.1, which is an inevitable consequence of the radiative coupling of the thermal corona and disc. In the present work, we develop the magnetic-reconnection-heated corona model by taking into account the potential non-thermal electrons accelerated in the magnetic reconnection process, in addition to the thermal electrons. We show that the features of the structure and spectrum of the coupled disc and corona can be affected by the fraction of magnetic energy allocated to thermal electrons. Furthermore, we investigate the effects of the power-law index and energy range of non-thermal electrons and the magnetic field on the spectrum. It is found that the X-ray spectrum from the Comptonization of the hybrid electrons can be flatter than that from thermal electrons only, in agreement with observations. By comparing with the observed hard X-ray data, we suggest that a large fraction (> 40%) of the magnetic energy be allocated to the non-thermal electrons in the luminous and flat X-ray spectrum AGNs. Copyright © 2023, The Authors. All rights reserved.

关键词： Gamma rays

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The radius variations of accreting main-sequence stars and mass transfer instability

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Monthly Notices of the Royal Astronomical Society: Letters 2024年第1期531卷 L45-L51页

作者： Zhao, Zi-Qi Li, Zhen-Wei Xiao, Lin Ge, Hong-Wei Han, Zhan-Wen Department of Physics Hebei University Baoding 071002 China Hebei Key Laboratory of High-precision Computation and Application of Quantum Field Theory Baoding 071002 China Hebei Research Center of the Basic Discipline for Computational Physics College of Physics Science and Technology Hebei University Baoding 071002 China Yunnan Observatories Chinese Academy of Sciences Kunming 650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Science Kunming 650011 China International Centre of Supernovae Yunnan Key Laboratory Kunming 650216 China University of the Chinese Academy of Science Yuquan Road 19 Shijingshan Block Beijing 100049 China

Many previous works studied the dynamical time-scale mass transfer stability criteria based on the donor response with neglecting the stellar structure of the accretor. In this letter, we investigate the radial response of accretors with mass accumulation and its effect on the binary mass transfer stability. We perform a series of detailed stellar evolution simulations with different types of accretors and obtain the radial variations of stars accreting at different rates. Since the time within which the donor loses half of the original mass has a correlation with the donor mass, we approximately obtain the mean mass transfer rate as a function of mass ratio. Assuming that the common envelope (CE) phase occurs if the accretor radius exceeds the outer Roche lobe radius, we obtain the critical mass ratio of dynamically unstable mass transfer. We find the critical mass ratios for donors filling their Roche lobes at the Main Sequence (MS) and Hertzsprung Gap (HG) stages are smaller than that derived from the radial response of the donor in the traditional way. Our results may suggest that the binary is easier to enter into the CE phase for a donor star at the MS or HG stage than previously believed. © 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.

关键词： accretion, accretion discs binaries: close convection

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Photometric Analysis of the Dwarf Nova Su Uma Based on Tess

SSRN

引用

SSRN 2023年

作者： Liu, Wei Shi, Xiang-Dong Fang, Xiao-Hui Wang, Qi-Shan Yunnan Observatories 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 Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650216 China School of Mathematics Physics and Finance Anhui Polytechnic University Wuhu241000 China

We report the photometric analysis of SU UMa based on the observations ofthe Transiting Exoplanet Survey Satellite (TESS). TESS has released a large amount of data, which contain the light curves of a complete superoutburst and three normal outbursts of SU UMa. The evolution of superhumps during the superoutburst were analyzed. By using O - C method the three stages were determined and the superhump period for each stage were calculated. The mass ratio $q=0.137 (1)$ was estimated based on the stage A superhump method. A periodic oscillation with a period of 2.17(9) days was found in the superhump minimum O - C diagram, which is related to the precession of the accretion disk. We investigated the frequency information of QPOs in the light curves. An ultra-long period QPO of 0.18 days at the time of normal outburst and two ultra-long periods QPOs of 0.19 days and 0.285 days in quiescence were found. No QPO was found in the superoutburst. © 2023, The Authors. All rights reserved.

关键词： Stars

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Distribution and evolution of Li abundance in red clump stars can be explained by the internal gravity waves

arXiv

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arXiv 2024年

作者： Li, Xue-Feng Shi, Jian-Rong Li, Yan Yan, Hong-Liang Zhang, Jing-Hua Yunnan Observatories Chinese Academy of Sciences P.O.Box110 Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China CAS Key Laboratory of Optical Astronomy National Astronomical Observatories Beijing100101 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O.Box110 Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China

The study of Li phenomena in red clump (RC) stars can give us a deeper understanding of the structure and evolution of stars. Chanamé et al. (2022) explained the RC Li abundance distributions naturally using only standard post main sequence (MS) Li evolution models when the distribution of progenitor masses and the depletion of Li during the MS observed in MS stars were considered, thus neither extra Li depletion nor Li creation mechanism is required. Nevertheless, it is interesting to consider the effects of mixing caused by some extra mechanisms. By constructing different models, we find that the mixing caused by internal gravity waves can explain the observed Li abundances of RC stars with low mass progenitors. To explain that, we rely on the extra mixing induced by internal gravity waves that are excited at the bottom of the convective envelope at the red giant branch (RGB) stage. During the RGB stage, introducing the internal gravity waves can improve the diffusion coefficient and strengthen the mixing effect. The effective enrichment of Li occurs at the late RGB stage and requires the diffusion coefficient of H-burning shell to reach ∼ 108 cm2 s−1. Our models predict that the Li abundance decreases from ∼ 1.5 dex to ∼ 0.0 dex at the end of core He-burning stage, thereby revealing the ∼ 99% of the observed Li abundance distribution. The thermohaline mixing regulates the Li abundance of RGB stars, which combines with the internal gravity waves can explain the Li abundances of most giants. Copyright © 2024, The Authors. All rights reserved.

关键词： Diffusion

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Meridional Circulation. I. A Formation Channel for Lithium-rich and Super Lithium-rich Red Clump Stars

arXiv

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arXiv 2025年

作者： Li, Xue-Feng Shi, Jian-Rong Li, Yan Yan, Hong-Liang Zhang, Jing-Hua Yunnan Observatories Chinese Academy of Sciences P.O.Box110 Kunming650216 China CAS Key Laboratory of Optical Astronomy National Astronomical Observatories Beijing100101 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O.Box110 Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China South-Western Institute for Astronomy Research Yunnan University Chenggong District Kunming650500 China

Current observations indicate that stars with higher rotation rates appear to maintain more surface lithium, and the majority of lithium-rich giants are indeed red clump stars. Hence, we investigate the mechanisms behind lithium enrichment in rotating red clump stars and the pathways to forming lithium-rich red clump stars. Meridional circulation is prevalent in the radiative zone of rotating giants. We model its radial mixing as a diffusion process and derive the corresponding diffusion coefficient based on its material transfer effect. Due to uncertainties in numerical calculations, we consider an average diffusion effect. Additionally, certain limiting conditions for the radial velocity of meridional circulation are incorporated. With varying input rotation velocities, we simulate the lithium evolution for red clump stars with this model. Our results indicate that the material transfer effect due to meridional circulation can efficiently transport beryllium, produced by H burning, into the convective envelope. This meridional circulation can lead to lithium enrichment, with a maximum lithium abundance increment approaching 3.0 dex. Consequently, it is capable of forming both lithium-rich and super lithium-rich red clump stars. The degree of lithium enrichment exhibits a strong positive correlation with the rotation velocity, i.e., faster red clump stars show more surface lithium. Furthermore, our models indicate that lithium-rich red clump stars are relatively young (∼ 106 yr), which aligns with observation evidences. Copyright © 2025, The Authors. All rights reserved.

关键词： Giant stars

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Strong magnetic field inside degenerate relativistic plasma and the impacts on the neutrino transport in Core-Collapse Supernovae

arXiv

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arXiv 2024年

作者： Luo, Yudong Zha, Shuai Kajino, Toshitaka School of Physics Peking University Beijing100871 China Kavli Institute for Astronomy and Astrophysics Peking University Beijing100871 China Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China School of Physics Peng Huanwu Collaborative Center for Research and Education International Research Center for Big-Bang Cosmology and Element Genesis Beihang University Beijing100191 China Graduate School of Science The University of Tokyo Tokyo113-0033 Japan National Astronomical Observatory of Japan Tokyo181-8588 Japan

We study the impacts of magnetic field on the neutrino transport inside corecollapse supernovae (CCSNe). Magnetic field quantizes the momentum of electrons and positrons, resulting in the modification of weak-interaction cross sections and the chemical potentials of electrons and positrons. We include these changes in the leakage scheme of neutrino transport and perform 1D CCSN simulations with GR1D, assuming the postbounce magnetic field strength of 1016-17 G. The results show that the neutrino opacities are enhanced due to the amplified interaction rates, resulting in a larger neutrinosphere. This further reduces the peak value of neutrino luminosities and their decay rates since neutrinos stay longer inside the neutrinosphere. Meanwhile, the neutrino mean energies are smaller shortly after bounce and reach their peak values at later times. As these neutrino properties are crucial in subsequent nucleosynthesis processes, including the νp-process, ν-process, and r-process, our findings suggest that the magnetic field may leave discernible marks on the abundance pattern of nucleosynthesis in CCSN. Copyright © 2024, The Authors. All rights reserved.

关键词： Magnetic fields

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An investigation of the magnetic activity of HD 134319 based on TESS photometry and ground-based spectroscopy

arXiv

引用

arXiv 2022年

作者： Xu, Fukun Gu, Shenghong Ioannidis, Panogiotis Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing101408 China Hamburger Sternwarte Universität Hamburg Gojenbergsweg 112 HamburgD-21029 Germany

We present analysis of the starspot properties and chromospheric activity on HD 134319 using high precision photometry by TESS in sectors 14-16 (T1), 21-23 (T2) and high-resolution spectroscopy by OHP/ELODIE and Keck/HIRES during years 1995-2013. We applied a two-spot model with GLS determined period P = 4.436391 ± 0.00137 day to model chunks sliding over TESS light curve, and measured relative equivalent widths of Ca II H and K, Hβ and Hα emissions by subtracting overall spectrum from individual spectrum. It was found that a two-spot configuration, i.e. a primary, slowly evolving and long-lasting spot (P) plus a secondary and rapidly evolving spot S, was capable of explaining the data, although the actual starspot distribution is unable to derived from collected data. Despite the spot radius-latitude degeneracy revealed in the best-fit solutions, a sudden alternation between P and S radii followed by gradual decrease of S in T1 and the decrease of both P and S from T1 to T2 were significant, corresponding to the evolution of magnetic activity. Besides, S revealed rotation and oscillatory longitude migration synchronized to P in T1, but held much larger migration than P in T2. This might indicate the evolution of internal magnetic configuration. Chromospheric activity indicators were found to tightly correlated with each other and revealed rotational modulation as well as a long-term decrease of emissions, implying the existence and evolution of magnetic acitivity on HD 134319. © 2022, CC0.

关键词： Photometry

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Constraints on cosmic star formation history via a new modeling of the radio luminosity function of star-forming galaxies

arXiv

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arXiv 2023年

作者： Wang, Wenjie Yuan, Zunli Yu, Hongwei Mao, Jirong Department of Physics School of Physics and Electronics Hunan Normal University Changsha410081 China Key Laboratory of Low Dimensional Quantum Structures and Quantum Control Hunan Normal University Changsha410081 China Synergetic Innovation Center for Quantum Effects and Applications Institute of Interdisciplinary Studies Hunan Normal University Hunan Changsha410081 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

Context. Radio wavelengths offer a unique possibility to trace the total star-formation rate (SFR) in galaxies, both obscured and unobscured. To probe the dust-unbiased star-formation history, an accurate measurement of the radio luminosity function (LF) for star-forming galaxies (SFGs) is crucial. Aims. We make use of an SFG sample (5900 sources) from the Very Large Array (VLA) COSMOS 3 GHz data to perform a new modeling of the radio LF. By integrating the analytical LF, we aim to calculate the history of the cosmic SFR density (SFRD) from z ∼ 5 onwards. Methods. For the first time, we use both models of the pure luminosity evolution (PLE) and joint luminosity+density evolution (LADE) to fit the LFs directly to the radio data using a full maximum-likelihood analysis, considering the sample completeness correction. We also incorporate updated observations of local radio LFs and radio source counts into the fitting process to obtain additional constraints. Results. We find that the PLE model cannot be used to describe the evolution of the radio LF at high redshift (z > 2). By construct, our LADE models can successfully fit a large amount of data on radio LFs and source counts of SFGs from recent observations. The Akaike information criterion (AIC) also demonstrates that the LADE model is superior to the PLE model. We therefore conclude that density evolution is genuinely indispensable in modeling the evolution of SFG radio LFs. Our SFRD curve shows a good fit to the SFRD points derived by previous radio estimates. In view of the fact that our radio LFs are not biased, as opposed those of previous studies performed by fitting the 1/Vmax LF points, our SFRD results should be an improvement on these previous estimates. Below z ∼ 1.5, our SFRD matches a published multiwavelength compilation, while our SFRD turns over at a slightly higher redshift (2 © 2023, CC BY.

关键词： Luminance

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