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arXiv 2024年

作者： Zhai, Qian Zhang, Jujia Lin, Weili Mazzali, Paolo Pian, Elena Benetti, Stefano Tomasella, Lina Liu, Jialian Li, Liping Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Department of Astronomy Xiamen University Fujian Xiamen361005 China Tsinghua University Beijing100084 China Astrophysics Research Institute Liverpool John Moores University Liverpool Science Park 146 Brownlow Hill LiverpoolL3 5RF United Kingdom Max-Planck-Institut für Astrophysik Karl-Schwarzschild Straße 1 Garching85748 Germany INAF Astrophysics and Space Science Observatory Via P. Gobetti 101 Bologna40129 Italy INAF Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5 PadovaI-35122 Italy

We present photometric and spectroscopic observations of supernova (SN) 2014C, primarily emphasizing the initial month after the explosion at approximately daily intervals. During this time, it was classified as a Type Ib SN exhibiting a notably higher peak luminosity (Lpeak ≈ 4.3 × 1042erg s−1), a faster rise to brightness (trise ≈ 11.6 d), and a more gradual dimming (∆mV15 ≈ 0.48 mag) compared to typical SNe Ib. Analysis of the velocity evolution over the first ∼ 20 days after the explosion supports the view that the absorption near 6200Å is due to high-velocity Hα in the outer layers of the ejecta, indicating the presence of a small amount of hydrogen in the envelope of progenitor before the explosion. Assuming the peak luminosity is entirely attributed to radioactive decay, we estimate that 0.14 M☉ of 56Ni was synthesized in the explosion. However, this amount of nickel could no longer maintain observed brightness approximately ten days after peak luminosity, suggesting additional energy sources beyond radioactive decay. This supplementary energy likely originates from interaction with the circumstellar medium (CSM). Consequently, the timing of the SN-CSM interaction in SN 2014C may occur much earlier than the emergence of IIn-like features during the nebular phase. © 2024, CC BY.

关键词： Supernovae

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Photometric investigations on two totally eclipsing contact binaries:V342 UMa and V509 Cam

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Research in Astronomy and Astrophysics 2019年第10期19卷 75-86页

作者： Kai Li Qi-Qi Xia Jin-Zhong Liu Yu Zhang Xing Gao Shao-Ming Hu Di-Fu Guo Xu Chen Yuan Liu Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment Institute of Space Sciences Shandong University Weihai 264209 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650216 China Xinjiang Astronomical Observatory Chinese Academy of Sciences Urumqi 830011 China Qilu Institute of Technology Jinan 250200 China

By analyzing two sets of complete BV Rc Ic light curves for V342 UMa and three sets of complete BV Rc Ic light curves for V509 Cam, we determined that the two systems are both W-subtype contact binaries and that V342 UMa manifests a shallow contact configuration, while V509 Cam exhibits a medium contact configuration. Given that both of them are totally eclipsing binaries, the physical parameters derived only by the photometric light curves are reliable. Meanwhile, the period changes of the two targets were analyzed based on all available eclipsing times. We discovered that V342 UMa shows long-term period decrease with a rate of-1.02(±0.54)× 10^-7 d yr^-1 and that V509 Cam displays long-term period increase with a rate of 3.96(±0.90)× 10^-8 d yr^-1. Both the conservative mass transfer and angular momentum loss via magnetic stellar winds can be used to interpret the long-term period decrease of V342 UMa. The longterm period increase of V509 Cam can be explained by mass transfer from the less massive star to the more massive one. The absolute parameters of the two binaries were estimated according to their Gaia distances and our derived photometric solution results. This method can be extended to other contact binaries without radial velocities but with reliable photometric solutions. Their evolutionary states were investigated and we found that they reveal properties that are identical to other W-subtype contact systems.

关键词： stars binaries close-stars eclipsing-stars individual (V342UMa, V509Cam)

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Asteroseismic investigation on KIC 10526294 to probe convective core overshoot mixing

arXiv

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arXiv 2023年

作者： Zhang, Qian-Sheng Li, Yan Wu, Tao Jiang, Chen Yunnan Observatories 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 Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Institute of Theoretical Physics Shanxi University Taiyuan030006 China Max-Planck-Institut für Sonnensystemforschung Justus-von-Liebig-Weg 3 GöttingenD-37077 Germany

In the overshoot mixing model with an exponentially decreasing diffusion coefficient, the initial value of the diffusion coefficient plays a crucial role. According to the turbulent convective mixing model, the characteristic length of convection in the convection zone differs from that in the overshoot region, resulting in a rapid decrease of the diffusion coefficient near the convective boundary. To investigate this quick decrease, we conducted an asteroseismic study on the intermediate-mass SPB star KIC 10526294. We generated stellar models with varied input parameters, including the overshoot parameters, and compared the resulting stellar oscillation periods with observations. To mitigate the potential issue arising from large steps in the stellar parameters and stellar age, we employed a comprehensive interpolation scheme for the stellar oscillatory frequencies, considering all stellar parameters and stellar age. Our analysis revealed that the quick decreasing of the diffusion coefficient has discernible effects on the stellar oscillations and a quick decrease with 4 magnitude orders shows the best oscillatory frequencies compared with the observations. This provides weak evidence in support of the prediction made by the turbulent convective mixing model. Furthermore, we examined the residuals of the oscillation periods and discovered a potential association between abundance anomalies in the buoyancy frequency profile and the oscillation-like patterns observed in the residuals. © 2023, CC BY.

关键词： Diffusion

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Effect of Tidal Torques on Rotational Mixing in Close Binaries

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Chinese Physics Letters 2018年第7期35卷 139-143页

作者：李志宋汉峰彭卫国 College of Physics Guizhou University Geneva Observatory University of Geneva Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences

The effect of tidal torques on rotational mixing in close binaries is investigated. It is found that spin angular momentum can attain a high value due to a strong tidal torque. Nitrogen and helium enrichment occurs early in the binary system that is triggered by tides. The stellar radius can reach a high value in the single star model with high initial velocities at the early stage of the evolution, but efficient rotational mixing can inhibit stellar expanding at the subsequent evolution. Central compactness is increased by the centrifugal force at the early stage of evolution but is reduced by rotational mixing induced by strong tides. The binary models with weak tides have high values of central temperature and stellar radius. Rotational mixing in single stars can slow down the shrinkage of convective cores, while convective cores can be expanded by strong tides in the binary *** rotational mixing induced by tides can cause the star to evolve towards high temperature and luminosity.

关键词： Tides

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TYC∼2990-127-1: an Algol-type SB2 binary system of subgiant and red giant with a probable ongoing mass-transfer

arXiv

引用

arXiv 2022年

作者： Kovalev, Mikhail Li, Zhenwei Zhang, Xiaobin Li, Jiangdan Chen, Xuefei Han, Zhanwen Yunnan Observatories China Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Max Planck Institute for Astronomy Heidelberg D-69117 Germany Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China University of the Chinese Academy of Sciences Yuquan Road 19 Shijingshan Block Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

We present a study of the spectroscopic binary TYC 2990-127-1 from the LAMOST survey. We use full-spectrum fitting to derive radial velocities and spectral parameters. The high mass ratio indicates that the system underwent mass transfer in the past. We compute the orbital solution and find that it is a very close sub-giant/red giant pair on circular orbit, slightly inclined to the sky-plane. Fitting of the TESS photometrical data confirms this and suggests an inclination of i ∼ 39.8◦. The light curve and spectrum around Hα show signs of irregular variability, which supports ongoing mass transfer. The binary evolution simulations suggest that the binary may experience non-conservative mass transfer with accretion efficiency 0.3, and the binary will enter into common envelope phase in the subsequent evolution. The remnant product after the ejection of common envelope may be a detached double helium white dwarf (He WD) or a merger. Copyright © 2022, The Authors. All rights reserved.

关键词： Mass transfer

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The statistical properties of early-type stars from LAMOST DR8

arXiv

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arXiv 2022年

作者： Guo, Yanjun Liu, Chao Wang, Luqian Wang, Jinliang Zhang, Bo Ji, Kaifan Han, ZhanWen Chen, XueFei Yunnan observatories Chinese Academy of Sciences P.O. Box 110 Kunming650011 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 Key Laboratory of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

Context. Massive binary stars play a crucial role in many astrophysical fields. Investigating the statistical properties of massive binary stars is essential to trace the formation of massive stars and constrain the evolution of stellar populations. However, no consensus has been achieved on the statistical properties of massive binary stars, mainly due to the lack of a large and homogeneous sample of spectroscopic observations. Aims. We study the intrinsic binary fraction fbin and distributions of mass ratio f(q) and orbital period f(P) of early-type stars (comprised of O-, B-, and A-type stars) and investigate their dependences on effective temperature Teff, stellar metallicity [M/H], and the projection velocity v sin i, based on the homogeneous spectroscopic sample from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release Eight (DR8). Methods. We collected 886 early-type stars, each with more than six observations from the LAMOST DR8, and divided the sample into subgroups based on their derived effective temperature (Teff), metallicity ([M/H]), and projected rotational velocity (v sin i). Radial velocity measurements were archived from a prior study. A set of Monte Carlo simulations, following distributions of f(P) ∝ Pπ and f(q) ∝ qγ were applied to the observed binary fraction to correct for any observational biases. The uncertainties of the derived results induced by the sample size and observation frequency are examined systematically. Results. We found that fbin increases with increasing Teff. For stars in groups of B8-A, B4-B7, O-B3, the binary fractions are fbin = 48% ± 10%, 60% ± 10%, and 76% ± 10%, respectively. The binary fraction is positively correlated with metallicity for spectra in the sample, with derived values of fbin = 44% ± 10%, 60% ± 10%, and 72% ± 10% for spectra with metallicity ranges of [M/H]bin have constant values of ∼50%. It seems that the binary population is relatively evenly distributed over a wide rang

关键词： Monte Carlo methods

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Period investigation of Algol systems TZ Eri and TU Her

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Research in Astronomy and Astrophysics 2019年第8期19卷 11-18页

作者： Zhi-Hua Wang Li-Ying Zhu Lin-Jia Li Xiao-Man Tian Yunnan Observatories Chinese Academy of SciencesKunming650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing100101China University of Chinese Academy of Sciences Beijing100049China

TZ Eri and TU Her are both classic Algol-type systems(Algols). By observing and collecting times of minimum light, we constructed the O-C curves for the two systems. The long-time upward and downward parabolas shown in these diagrams are considered to be the result of the combination of mass transfer and angular momentum loss. The secular orbital period change rates are d P/dt = 4.74(±0.12) ×10-7 d yr-1 and d P/dt =-2.33(±0.01) × 10-6 d yr-1, respectively. There are also cyclic variations in their O-C curves which might be caused by the light-travel time effect(LTTE). A circumbinary star may exist in the TZ Eri system with a mass of at least 1.34 M⊙, while there are possibly two celestial bodies that almost follow a 2 : 1 resonance orbit around the TU Her binary pair. Their masses are at least 2.43 M⊙and 1.27 M⊙.

关键词： stars:binaries:close stars:binaries:eclipsing stars:individual (TZ Eri, TU Her)

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Gaussian process modeling Fermi-LAT γ-ray blazar variability: A sample of blazars with γ-ray quasi-periodicities

arXiv

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arXiv 2020年

作者： Yang, Shenbang Yan, Dahai Zhang, Pengfei Dai, Benzhong Zhang, Li School of Physics and Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatory Chinese Academy of Sciences Kunming650011 China

Blazar variability may be driven by stochastic processes. On the other hand, quasi-periodic oscillation (QPO) behaviors are recently reported to be detected in Fermi-LAT data of blazars. However, the significances of these QPO signals given by traditional Fourier-like methods are still questioned. We analyze γ-ray light curves of the QPO blazars with two Gaussian process methods, CARMA and celerite, to examine the appropriateness of Gaussian processes for characterizing γ-ray light curves of blazars and the existence of the reported QPOs. We collect a sample of 27 blazars with possible γ-ray periodicity and generate their ∼ 11 years Fermi-LAT light curves. We apply the Gaussian process models to the γ-ray light curves, and build their intrinsic power spectral densities (PSDs). The results show that in general the γ-ray light curves can be characterized by CARMA and celerite models, indicating that γ-ray variabilities of blazars are essentially Gaussian processes. The resulting PSDs are generally the red noise shapes with slopes between −0.6 and −1.7. Possible evidence for the γ-ray QPOs in PKS 0537−441 and PG 1553+113 are found in the Gaussian process modelings. © 2020, CC BY.

关键词： Gamma rays

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Broadening and redward asymmetry of Hα line profiles observed by LAMOST during a stellar flare on an M-type star

arXiv

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arXiv 2022年

作者： Wu, Yuchuan Chen, Hechao Tian, Hui Zhang, Liyun Shi, Jianrong He, Han Lu, Hongpeng Xu, Yu Wang, Haifeng School of Earth and Space Sciences Peking University Beijing100871 China National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China College of Physics Guizhou University Guiyang550025 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China CAS Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China University of Chinese Academy of Sciences Beijing100049 China GEPI Observatoire de Paris Université PSL CNRS Place Jules Janssen 92195 Meudon France

Stellar flares are characterized by sudden enhancement of electromagnetic radiation in stellar atmospheres. So far much of our understanding of stellar flares comes from photometric observations, from which plasma motions in flare regions could not be detected. From the spectroscopic data of LAMOST DR7, we have found one stellar flare that is characterized by an impulsive increase followed by a gradual decrease in the Hα line intensity on an M4-type star, and the total energy radiated through Hα is estimated to be on the order of 1033 erg. The Hα line appears to have a Voigt profile during the flare, which is likely caused by Stark pressure broadening due to the dramatic increase of electron density and/or opacity broadening due to the occurrence of strong non-thermal heating. Obvious enhancement has been identified at the red wing of the Hα line profile after the impulsive increase of the Hα line intensity. The red wing enhancement corresponds to plasma moving away from the Earth at a velocity of 100−200 km s−1. According to the current knowledge of solar flares, this red wing enhancement may originate from: (1) flare-driven coronal rain, (2) chromospheric condensation, or (3) a filament/prominence eruption that either with a non-radial backward propagation or with strong magnetic suppression. The total mass of the moving plasma is estimated to be on the order of 1015 kg. © 2022, CC BY.

关键词： Stars

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Mass-Ratio Distribution of Binaries From the LAMOST-MRS Survey

arXiv

引用

arXiv 2022年

作者： Li, Jiangdan Li, Jiao Liu, Chao Li, Chunqian Guo, Yanjun Wang, Luqian Chen, Xuefei Xing, Lifeng Hou, Yonghui Han, Zhanwen 396 Yangfangwang Guandu District Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Key Lab of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China CAS Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Nanjing Institute of Astronomical Optics & Technology National Astronomical Observatories Chinese Academy of Sciences Nanjing210042 China School of Astronomy and Space Science University of Chinese Academy of Sciences China

Binary evolution leads to the formation of important objects crucial to the development of astrophysics, but the statistical properties of binary populations are still poorly understood. The LAMOST-MRS has provided a large sample of stars to study the properties of binary populations, especially for the mass ratio distributions and the binary fractions. We have devised a Peak Amplitude Ratio (PAR) approach to derive the mass ratio of a binary system based on results obtained from its spectrum. By computing a cross-correlation function (CCF), we established a relationship between the derived mass ratio and the PARs of the binary systems. By utilizing spectral observations obtained from LAMSOT DR6 DR7, we applied the PAR approach to form distributions of the derived mass ratio of the binary systems to the spectral types. We selected the mass ratio within the range of 0.6 − 1.0 for investigating the mass-ratio distribution. Through a power-law fitting, we obtained the power index γ values of −0.42 ±0.27, 0.03 ±0.12, and 2.12 ±0.19 for A-, F-, and G-type stars identified in the sample, respectively. The derived γ-values display an increasing trend toward lower primary star masses, and G-type binaries tend to be more in twins. The close binary fractions (for P 150 d and q 0.6) in our sample for A, F and G binaries are 7.6 ± 0.5%, 4.9 ± 0.2% and 3.7 ± 0.1%, respectively. Note that the PAR approach can be applied to large spectroscopic surveys of stars. Copyright © 2022, The Authors. All rights reserved.

关键词： Surveys

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