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Magnetic activities on two single-lined RS Canum Venaticorum binaries IM Pegasi and σ Geminorum

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arXiv 2024年

作者： Cao, Dongtao Gu, Shenghong Grundahl, F. Pallé, P.L. 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 Stellar Astrophysics Centre Department of Physics and Astronomy Aarhus University NyMunkegade 120 Aarhus C8000 Denmark Instituto de Astrofísica de Canarias Tenerife La Laguna38205 Spain Universidad de La Laguna Departamento de Astrofísica Tenerife La Laguna38206 Spain

We present the study on continuous high-resolution spectroscopic observations of two long-period single-lined RS Canum Venaticorum (RS CVn) binary stars IM Pegasi (IM Peg) and σ Geminorum (σ Gem), obtained with the Hertzsprung SONG telescope during the 2015–2016 season. Chromospheric activity indicators Hα, Na i D1, D2 doublet, He i D3, and Hβ lines have been analyzed by using the spectral subtraction technique. The expected chromospheric emission features in the Hα, Na i D1, D2 doublet, and Hβ lines confirm that both of two stars are very active systems. In the spectra, the He i D3 line had been always detected in absorption feature. Although the behavior of chromospheric activity indicators is very similar for both stars, the activity level of IM Peg is much stronger than that of σ Gem. Moreover, the EW variations of the Hα, He i D3, and Hβ line subtractions correlate well and show different behavior among different orbital cycles, which indicates the presence and evolution of activity longitudes over the surface of two stars. Furthermore, the subtracted Hα line profile is usually asymmetric. The red-shifted excess absorption features could be interpreted as a strong down-flow of cool absorbing material, while the blue-shifted emission component is probably caused by up-flow of hot materials through microflare events. Copyright © 2024, The Authors. All rights reserved.

关键词： Stars

Physical Parameters of 11,100 Short-Period ASAS-SN Eclipsing Contact Binaries

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arXiv 2024年

作者： Li, Xu-Zhi Zhu, Qing-Feng Ding, Xu Xu, Xiao-Hui Zheng, Hang Qiu, Jin-Sheng Liu, Ming-Chao CAS Key Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei230026 China School of Astronomy and Space Sciences University of Science and Technology of China Hefei230026 China Deep Space Exploration Laboratory Hefei230088 China Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Yunnan Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China University of the Chinese Academy of Sciences Yuquan Road 19 Shijingshan Block Beijing100049 China

Starting from more than 11,200 short-period (less than 0.5 days) EW-type eclipsing binary candidates with the All-Sky Automated Survey for Supernovae (ASAS-SN) V-band light curves, we use MCMC and neural networks (NNs) to obtain the mass ratio (q), orbital inclination (incl), fill-out factor (f) and temperature ratio (Ts/Tp). After cross-matching with the Gaia DR3 database, the final sample contains parameters of 2,399 A-type and 8,712 W-type contact binaries (CBs). We present the distributions of parameters of these 11,111 short-period CBs. The mass ratio (q) and fill-out factor (f) are found to obey log-normal distributions, and the remaining parameters obey normal distributions. There is a significant period-temperature correlation of these CBs. Additionally, the temperature ratio (Ts/Tp) tends to increase as the orbital period decreases for W-type CBs. There is no significant correlation between them for A-type CBs. The mass ratio and fill-out factor (q − f) diagram suggest there is no significant correlation between these two parameters. A clear correlation exists between the mass ratio and radius ratio. The radius ratio increases with the mass ratio. Moreover, the deep fill-out CBs tend to fall on the upper boundary of the q−Rs/Rp distribution, while the shallow fill-out CBs fall on the lower boundary. © 2024, CC BY.

关键词： Normal distribution

Hawking-like radiation of charged particles via tunneling across the lightcylinder of a rotating magnetosphere

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arXiv 2021年

作者： Li, Huiquan Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

In rotating magnetospheres planted on compact objects, there usually exist light-cylinders (LC), beyond which the rotation speed of the magnetic field lines exceeds the speed of light. The LC is a close analog to the horizon in gravity, and is a casual boundary for charged particles that are restricted to move along the magnetic field lines. In this work, it is proposed that there should be Hawking-like radiation of charged particles from the LC of a rotating magnetosphere from the point of view of tunneling by using the field sheet metric. Copyright © 2021, The Authors. All rights reserved.

关键词： Charged particles

Influence of a mass transfer stability criterion on double white dwarf populations

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arXiv 2022年

作者： Zhenwei, Li Xuefei, Chen Hongwei, Ge Hai-Liang, Chen Zhanwen, Han Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Science China Center for Astronomical Mega-Science Chinese Academy of Science 20A Datun Road Chaoyang District Beijing100012 China University of the Chinese Academy of Sciences 19A Yuquan Road Shijingshan District Beijing100049 China

Context. Mass transfer stability is a key issue in studies of binary evolution. Critical mass ratios for dynamically stable mass transfer have been analyzed on the basis of an adiabatic mass loss model, finding that the donor stars on the giant branches tend to be more stable than that based on the composite polytropic stellar model. Double white dwarfs (DWDs) are of great importance in many fields and their properties would be significantly affected under the new mass transfer stability criterion. Aims. We seek to investigate the influence of mass transfer stability on the formation and properties of DWD populations and discuss the implications in supernova Type Ia (SN Ia) and gravitational wave (GW) sources. Methods. We performed a series of binary population synthesis, adopting the critical mass ratios from the adiabatic mass loss model (i.e., Ge’s model) and that of the composite polytropic model, respectively. In each simulation, 5 × 106 binaries were included and evolved from zero-age main sequence to the end of their evolution and the DWDs were gradually obtained. Results. For Ge’s model, most of the DWDs are produced from the stable non-conservative Roche lobe (RL) overflow, along with a common-envelope (CE) ejection channel (RL+CE channel), regardless of the CE ejection efficiency, αCE. Conversely, the results of the polytropic model strongly depend on the adopted value of αCE. We find DWDs produced from the RL+CE channel have comparable WD masses and the mass ratio distribution peaks at around 1. Based on the magnitude-limited sample of DWDs, the space densities for the detectable DWDs and those with extremely low-mass WD (ELM WD) companions in Ge’s model is: 1347 kpc−3 and 473 kpc−3, respectively, which is close to what has been shown in observations. On the other hand, the polytropic model overpredicts space density of DWDs by a factor of about 2-3. We also find that the results of DWD merger rate distribution per Galaxy in Ge’s model reproduce the obser

关键词： White dwarfs

The effect of aspherical stellar wind of giant stars on the symbiotic channel of type Ia supernovae

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arXiv 2021年

作者： Wu, Chengyuan Liu, Dongdong Wang, Xiaofeng Wang, Bo Tsinghua University Beijing100084 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories CAS Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China

The progenitor systems accounting for explosions of type Ia supernovae (SNe Ia) is still under debate. Symbiotic channel is one of the possible progenitor scenarios, in which the WDs in these systems increase in mass through wind accretion from their red giant companions. The mass-loss processes of the giants in the symbiotic systems could produce amount of circumstellar medium (CSM), and the detections of the interaction signals between SN ejecta and CSM can be used as an ideal way to distinguish the different progenitor models. However, the density distribution and geometric structure of the CSM around the symbiotic systems remain highly uncertain. By assuming that the tidal torque from binary interaction can increase the mass-loss rate of the red giant and cause the stellar wind concentrate towards the equatorial plane, we provide a simplified method to estimate the density and the degree of deviation from spherical symmetry of the CSM. Based on the calculations of the binary evolutions of symbiotic systems using stellar evolution code MESA, we obtained the parameter space for producing SNe Ia. We found that SNe Ia could originate from symbiotic systems with massive carbon-oxygen white dwarfs (CO WDs), while the half-opening angle of the stellar wind from red giant towards the WD varies with the binary evolution, resulting in the formation of surrounding CSM with different geometric structures. The corresponding properties of ejecta-CSM interactions may be examined by the spectropolarimetry observations in the future, from which one may find additional relationship between circumstellar environment of SNe Ia and their progenitor systems. © 2021, CC0.

关键词： White dwarfs

Pulsation Properties of Blazhko and Non-Blazhko RRab Stars

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arXiv 2025年

作者： Zong, Peng Fu, Jian-Ning Su, Jie Zhang, Bing-Kai Liu, Gao-Chao Sun, Weichao Wang, Jiaxin Zhang, Bo Hu, Xueying Bai, Zhongrui Zong, Weikai Key Laboratory of Functional Materials and Devices for Informatics Anhui Higher Education Institutes School of Physics and Electronic Engineering Fuyang Normal University Fuyang236037 China School of Physics and Astronomy Beijing Normal University Beijing100875 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Department of Physics Fuyang Normal University Fuyang236041 China Key Laboratory of Functional Materials and Devices for Informatics Anhui Higher Education Institutes Fuyang Normal University Fuyang236037 China Center for Astronomy and Space Sciences China Three Gorges University Yichang443002 China School of Science Chongqing University of Posts and Telecommunications Chongqing400065 China Key Laboratory of Space Astronomy and Technology National Astronomical Observatories of China Chinese Academy of Science Beijing100012 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China

In this study, we conduct a comparative analysis of the properties of Blazhko and non-Blazhko RRab stars. We identified 1054 non-Blazhko and 785 Blazhko RRab stars in the photometric data observed by K2 mission, which, combined with those 37 stars observed in the original Kepler field, constituted our study sample. Using the Fourier Decomposition method, we calculated the pulsation parameters, including phase differences and amplitude ratios, for these RRab stars, revealing significant discrepancies in the pulsation parameters between Blazhko and non-Blazhko RRab stars. However, distinguishing between Blazhko and Non-Blazhko RRab stars based on Fourier parameters remains challenging due to the significant overlap in their distributions. By cross-matching our sample with the LRS of LAMOST DR12, we identified 147 Blazhko and 111 non-Blazhko RRab stars, which exhibit similar metallicity distributions. Furthermore, cross-matching with Gaia DR3 data yielded 766 Blazhko and 950 non-Blazhko RRab stars, showing differences in color indices but not in absolute magnitudes. Our findings suggested the Blazhko effect is linked to pulsation parameters and colors, rather than metallicities or absolute magnitude. © 2025, CC BY-NC-SA.

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Multiwavelength Properties of Infrared-Faint Radio Sources Based on Spectral Energy Distribution Analysis

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arXiv 2024年

作者： Zhang, Yihang Fan, Lulu An, Tao Yang, Jun Sun, Weibin Yu, Haoran Han, Yunkun Department of Astronomy University of Science and Technology of China Hefei230026 China School of Astronomy and Space Science University of Science and Technology of China Hefei230026 China Deep Space Exploration Laboratory Hefei230088 China Key Laboratory of Radio Astronomy Shanghai Astronomical Observatory 80 Nandan Road Shanghai200030 China Department of Space Earth and Environment Chalmers University of Technology Onsala Space Observatory OnsalaSE-439 92 Sweden 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 International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China

Infrared-faint radio sources (IFRSs) are believed to be a rare class of radio-loud active galactic nuclei (RL AGN) characterized by their high radio-to-infrared flux density ratios of up to several thousands. Previous studies have shown that a fraction of IFRSs are likely to be hosted in dust-obscured galaxies (DOGs). In this paper, our aim was to probe the dust properties, star formation rate (SFR), and AGN activity of IFRSs by modeling the UV-to-infrared spectral energy distribution (SED) of 20 IFRSs with spectroscopic redshifts ranging from 1.2 to 3.7. We compare the Bayesian evidence of a three-component model (stellar, AGN and cold dust) with that of a two-component model (stellar and cold dust) for six IFRSs in our sample with far-infrared (FIR) photometry and find that the three-component model has significantly higher Bayesian evidence, suggesting that IFRSs are most likely to be AGN. The median SED of our IFRS sample shows similarities to AGN-starburst composite in the IR regime. The derived IR luminosities of IFRSs indicate that they are low-luminosity counterparts of high-redshift radio galaxies. We disentangle the contributions of AGN-heated and star-formation-heated dust to the IR luminosity of IFRSs and find that our sample is likely AGN-dominated. However, despite the evidence for significant impact of AGN on the host galaxy, the AGN luminosity of our sample does not show correlation with the SFR of the sources. © 2024, CC BY.

关键词： Stars

A possibly solar metallicity atmosphere escaping from HAT-P-32b revealed by Hα and He absorption

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arXiv 2024年

作者： Yan, Dongdong Guo, Jianheng Seon, Kwang-Il López-Puertas, Manuel Czesla, Stefan Lampón, Manuel Yunnan Observatories Chinese Academy of Sciences P.O. Box 110 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 Astronomy and Space Science University of Chinese Academy of Sciences Beijing China Korea Astronomy & Space Science Institute 776 Daedeokdae-ro Yuseong-gu Daejeon34055 Korea Republic of University of Science and Technology 217 Gajeong-ro Yuseong-gu Daejeon34113 Korea Republic of Glorieta de la Astronomía s/n Granda 18008 Spain Thüringer Landessternwarte Tautenburg Sternwarte 5 TautenburgD-07778 Germany

This paper presents a hydrodynamic simulation that couples detailed non-local thermodynamic equilibrium (NLTE) calculations of the hydrogen and helium level populations to model the Hα and He 10830 transmission spectra of the hot Jupiter HAT-P-32b. A Monte Carlo simulation is applied to calculate the number of Lyα resonance scatterings, which is the main process for populating H(2). In the examined parameter space, only the models with H/He ≥ 99.5/0.5, (0.5 ∼ 3.0) times the fiducial value of FXUV, βm = 0.16 ∼ 0.3, can explain the Hα and He 10830 lines simultaneously. We find a mass-loss rate of ∼ (1.0 ∼ 3.1)×1013 g s−1, consistent with previous studies. Moreover, we find that the stellar Lyα flux should be as high as 4 × 105 erg cm−2 s−1, indicating high stellar activity during the observation epoch of the two absorption lines. Despite the fact that the metallicity in the lower atmosphere of HAT-P-32b may be super-solar, our simulations tentatively suggest it is close to solar in the upper atmosphere. The difference in metallicity between the lower and upper atmospheres is essential for future atmospheric characterisations. © 2024, CC BY-NC-ND.

关键词： Monte Carlo methods

Synchrotron polarization of a hybrid distribution of relativistic thermal and nonthermal electrons in GRB prompt emission

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arXiv 2024年

作者： Cheng, Kangfa Mao, Jirong Zhao, Xiaohong Liu, Hongbang Kole, Merlin Produit, Nicolas Chen, Zhifu School of Mathematics and Physics Guangxi Minzu University Nanning530006 China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Science Kunming650011 China Center for Astronomical Mega-Science Chinese Academy of Science 20A Datun Road Chaoyang District Beijing100012 China School of Physical Science and Technology Guangxi University Nanning530004 China Space Science Center University of New Hampshire DurhamNH03824 United States Astronomy Department University of Geneva Versoix Switzerland

Synchrotron polarization of relativistic nonthermal electrons in gamma-ray bursts (GRBs) has been widely studied. However, recent numerical simulations of relativistic shocks and magnetic reconnection have found that a more realistic electron distribution consists of a power-law component plus a thermal component, which requires observational validation. In this paper, we investigate synchrotron polarization using a hybrid energy distribution of relativistic thermal and nonthermal electrons within a globally toroidal magnetic field in GRB prompt emission. Our results show that, compared to the case of solely non-thermal electrons, the synchrotron polarization degrees (PDs) in these hybrid electrons can vary widely depending on different parameters and that the PD decreases progressively with frequency in the γ-ray, X-ray, and optical bands. The time-averaged PD spectrum displays a significant bump in the γ-ray and X-ray bands with the PDs higher than ∼ 60% if the thermal peak energy of electrons is much smaller than the conjunctive energy of electrons between the thermal and non-thermal distribution. The high synchrotron PD ( 60%) in the γ-ray and X-ray bands, which generally can not be produced by solely non-thermal electrons with typical power-law slopes, can be achieved by the hybrid electrons and primarily originates from the exponential decay part of the thermal component. Moreover, this model can roughly explain the PDs and spectral properties of some GRBs, where GRB 110301A with a high PD ((Equation presented)) may be potential evidence for the existence of relativistic thermal electrons. Copyright © 2024, The Authors. All rights reserved.

关键词： Gamma rays