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Study of Advective Energy Transport in the Inflow and the Outflow of Super-Eddington Accretion Flows

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arXiv 2023年

作者： Jiao, Cheng-Liang 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

Photon trapping is believed to be an important mechanism in super-Eddington accretion, which greatly reduces the radiative efficiency as photons are swallowed by the central black hole before they can escape from the accretion flow. This effect is interpreted as the radial advection of energy in one-dimensional height-integrated models, such as the slim disk model. However, when multi-dimensional effects are considered, the conventional understanding may no longer hold. In this paper, we study the advective energy transport in super-Eddington accretion, based on a new two-dimensional inflow-outflow solution with radial self-similarity, in which the advective factor is calculated self-consistently by incorporating the calculation of radiative flux, instead of being set as an input parameter. We found that radial advection is actually a heating mechanism in the inflow due to compression, and the energy balance in the inflow is maintained by cooling via radiation and vertical (θ-direction) advection, which transports entropy upwards to be radiated closer to the surface or carried away by the outflow. As a result, less photons are advected inwards and more photons are released from the surface, so that the mean advective factor is smaller and the emergent flux is larger than those predicted by the slim disk model. The radiative efficiency of super-Eddington accretion thus should be larger than that of the slim disk model, which agrees with the results of some recent numerical simulations. Copyright © 2023, The Authors. All rights reserved.

关键词： Advection

Search for spectroscopic binaries using rotational velocities in five open clusters observed by ESO.

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arXiv 2023年

作者： Kovalev, Mikhail Ahmed, Mariyam Asa'd, Randa Yunnan Observatories China Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Sternberg Astronomical Institute Leninskie Gory Moscow119992 Russia International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Physics Department American University of Sharjah PO Box 26666 Sharjah United Arab Emirates

In this paper we detect double-lined spectroscopic binaries (SB2) in five open clusters: NGC 2243, NGC 2420, NGC 3532, NGC 6253 and NGC 6705 (M 11) using a method based on high values of the projected rotational velocity when they are fitted with single star spectral model. Observed spectra were obtained from ESO archive. The method was validated on sets of synthetic spectra for the single and binary stars. It is able to reliably select spectroscopic binaries without confusing them with single stars, if components in binary rotate slowly and radial velocity separation is sufficiently high. We found 60 SB2 candidates: two in NGC 2243, eight in NGC 2420 and NGC 3532, 17 in NGC 6253 and 25 in NGC 6705. Comparison with literature confirms 18 of them, thus we found 42 new SB2 candidates. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars

Does Nature allow formation of ultra-compact black hole X-ray binaries via accretion-induced collapse of neutron stars?

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arXiv 2023年

作者： Chen, Hai-Liang Tauris, Thomas M. Chen, Xuefei Han, Zhanwen Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Department of Materials and Production Aalborg University Skjernvej 4A Aalborg ØstDK-9220 Denmark University of the Chinese Academy of Sciences Yuquan Road 19 Shijingshan Block Beijing100049 China

The formation path to ultra-compact X-ray binaries (UCXBs) with black hole (BH) accretors is still unclear. In the classical formation scenario, it is difficult to eject the massive envelope of the progenitor star of the BH via common envelope process. Given that some neutron stars (NSs) in binary systems evidently have birth masses close to ∼ 2.0 M☉, we explore here the possibility that BH-UCXBs may form via accretion-induced collapse (AIC) of accreting NSs, assuming that these previously evolved in LMXBs to masses all the way up to the maximum limit of a NS. We demonstrate this formation path by modelling a few cases of NS-UCXBs with initial NS masses close to the maximum mass of a NS that evolve into BH-UCXBs after the NS accretes material from its He WD companion. We follow the evolution of the post-AIC BH-UCXB and, based on simple arguments, we anticipate that there is about one BH-UCXB with an AIC origin and a He WD donor within the current sample of known UCXBs and that 2-5 such BH-UCXBs may be detected in gravitational waves by LISA. In addition, we find that the X-ray luminosity of NS-UCXBs near their orbital period minimum exceeds ∼ 1039 erg s−1 and thus such systems may appear as ultraluminous X-ray sources. © 2023, CC BY.

关键词： Gravity waves

Heating or Cooling: Study of Advective Heat Transport in the Inflow and the Outflow of Optically Thin Advection-dominated Accretion Flows

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arXiv 2023年

Advection is believed to be the dominant cooling mechanism in optically thin advection-dominated accretion flows (ADAFs). When outflow is considered, however, the first impression is that advection should be of opposite sign in the inflow and the outflow, due to the opposite direction of radial motion. Then how is the energy balance achieved simultaneously? We investigate the problem in this paper, analyzing the profiles of different components of advection with self-similar solutions of ADAFs in spherical coordinates (rθf). We find that for n − n and γ is the heat capacity ratio, the radial advection is a heating mechanism in the inflow and a cooling mechanism in the outflow. It becomes 0 for n = 3γ/2 − 1, and turns to a cooling mechanism in the inflow and a heating mechanism in the outflow for n > 3γ/2 − 1. The energy conservation is only achieved when the latitudinal (θ direction) advection is considered, which takes an appropriate value to maintain energy balance, so that the overall effect of advection, no matter the parameter choices, is always a cooling mechanism that cancels out the viscous heating everywhere. For the extreme case of n = 3/2, latitudinal motion stops, viscous heating is balanced solely by radial advection, and no outflow is developed. Copyright © 2023, The Authors. All rights reserved.

关键词： Advection

Prominence detection and chromosphere feature on the prototype RS CVn of active binary systems

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arXiv 2024年

作者： Cao, Dongtao Gu, Shenghong Wolter, U. Mittag, M. Schmitt, J.H.M.M. Gao, Dongyang Hu, Shaoming 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 HamburgD-21029 Germany Shandong Provincial key Laboratory of Optical Astronomy and Solar-Terrestrial Environment Institute of Space Sciences Shandong University Weihai264209 China

We present a study of high-resolution spectra of RS Canum Venaticorum (RS CVn), a prototype of active binary systems. Our data were obtained from 1998 to 2017 using different telescopes. We analyze the chromospheric activity indicators Ca ii IRT, Hα, Na i D1, D2 doublet, He i D3, and Hβ using a spectral subtraction technique. The chromospheric emission stems mainly from the K2 IV primary star, while the F5 V secondary star only shows weak emission features in a few of our spectra. We find excess absorption features in the subtracted Hα lines and other activity indicators from spectra taken near primary eclipse, which we ascribe to prominence-like material associated with the primary star. We estimate size limits of these tentative prominences based on the geometry of the binary system, and investigate the physical properties of the strongest prominence. An optical flare, characterized by He i D3 line emission, together with stronger emission in other activity lines, was detected. The flare energy is roughly comparable to strong flares observed on other RS CVn-type stars. The chromospherically active longitudes of RS CVn most frequently appear near the two quadratures of the system and display changes between observing runs, which indicates an ongoing evolution of its active regions. Copyright © 2024, The Authors. All rights reserved.

关键词： Chromophores

ASTEROSEISMOLOGY OF THE DAV STAR L19-2

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arXiv 2022年

作者： Chen, Yanhui Institute of Astrophysics Chuxiong Normal University Chuxiong675000 China School of Physics and Electronical Science Chuxiong Normal University Chuxiong675000 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650011 China

L19-2 is a DAV star, which has been intermittently observed from 1976 to 2013. Five independent pulsation modes of 350 s, 192 s, 143 s, 118 s, and 113 s are identified. The five modes can be used to constrain the fitting models. The rates of period change can be obtained through the O-C method for modes of 192 s and 113 s, which can be used to study the evolution effect of DAV stars. Using the WDEC (2018 version), a large sample DAV star models are evolved. The theoretical modes are calculated and used to fit the observed modes. After fine model fittings, we obtain an optimal model with an absolute difference of Φ = 0.06 s. By parameterizing the core oxygen profile, the WDEC (2018 version) procedure can greatly reduce the fitting error of asteroseismological model. According to our optimal model, the distance obtained through the model luminosity is only 1% different from that reported by the Gaia Data Release 2. The L19-2 is a massive and hot DAV star with relatively a thick H atmosphere and a thick He layer. The stellar parameters and the rates of period change of our optimal model are a little modifications to that of the previous work. Our optimal model has a large central oxygen abundance. The central oxygen abundance is strongly correlated with the previous physical process of stellar evolution. A lot of asteroseismological work on white dwarfs have an opportunity to explore the progenitor stars. Copyright © 2022, The Authors. All rights reserved.

关键词： Oxygen

Hemispheric Distribution of Solar Active Regions During Solar Cycles 23-25

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arXiv 2025年

作者： Liu, Yuxia Xu, Tingting Wan, Miao Deng, Linhua Zhao, Xinhua Qi, Shiyang Xiang, Nanbin Zhou, Weihong School of Mathematics and Computer Science Yunnan Minzu University Yunnan Kunming650504 China State Key Laboratory of Space Weather National Space Science Center Chinese Academy of Sciences Beijing100190 China Sichuan Chengdu610041 China College of Science Henan Agricultural University Henan Zhengzhou450002 China Yunnan Observatories Chinese Academy of Sciences Yunnan Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650216 China

Solar active regions (ARs) are crucial for understanding the long-term evolution of solar activities and predicting eruptive phenomena, including solar flares and coronal mass ejections. However, the cycle-dependent properties in the north-south asymmetry of ARs have not been fully understood. In this study, we investigate the hemispheric distribution of ARs from Carrington Rotation 1909 to 2278 (between 1996 May and 2023 November) by using three parameters that describe the magnetic field distribution of ARs: number, area, and flux. The main findings are as follows: (1) The three AR parameters show significant hemispheric asymmetry in cycles 23-25. The strong correlation between AR area and flux indicates that they can better reflect the intrinsic properties of solar magnetic field. (2) The correlation between sunspot activity and AR parameters varies in the two hemispheres across the different cycles. The AR parameters provide additional information for the variations in sunspot activity, which can better predict the intensity and cyclical changes of solar activity. (3) The variation in the fitting slope sign of the asymmetry index for AR parameters reflects periodic changes in hemispheric ARs, providing valuable insights into the activity of other stars. (4) Both the dominant hemisphere and the cumulative trend of AR parameters display a cycle-dependent behavior. Moreover, the trend variations of AR area and flux are similar, reflecting the long-term evolutionary characteristics of solar magnetic field. Our analysis results are relevant for understanding the hemispheric coupling of solar magnetic activity and its cyclic evolutionary patterns. Copyright © 2025, The Authors. All rights reserved.

关键词： Aspherics

Correlations between γ-ray luminosity and magnetization of the jet as well as relativistic electron injection power:cases for Mrk 421, 3C 454.3 and 3C 279

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arXiv 2021年

作者： Hu, Wen Yan, Da-Hai Hu, Qiang-Lin Department of Physics Jinggangshan University Ji’anJiangxi Province343009 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories Chinese Academy of Sciences Kunming650011 China

By fitting high-quality and simultaneous multi-wavelength (MWL) spectral energy distributions (SEDs) at multiple epochs with a one-zone leptonic jet model, we study jet properties of the three famous blazars Mrk 421, 3C 454.3 and 3C 279. In the jet model, the emitting electron energy distributions (EEDs) are calculated by solving the kinetic equation of electron injection, escape, adiabatic and radiative energy losses. To explore multi-dimensional parameter space systematically, we employ a Markov chain Monte Carlo (MCMC) fitting technique. The properties of emission regions we derived here are consistent with those in previous studies, e.g., the particle-dominated and low-magnetization jet. The new finding is that there is a tight correlation between γ-ray luminosity and electron injection power and an anti-correlation between γ-ray luminosity and jet magnetization parameter. The results suggest that same energy-dissipative mechanism (like a shock) could be operating in the jets of different types of blazars, and the origin of γ-ray flares is associated with the particle acceleration process. Copyright © 2021, The Authors. All rights reserved.

关键词： Energy dissipation

Four Changing-Look Active Galactic Nuclei Found From Optical Variations

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arXiv 2024年

作者： Zhu, Li-Tao Li, Jie Wang, Zhongxiang Zhang, Ju-Jia Department of Astronomy School of Physics and Astronomy Yunnan University Kunming650091 China Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei230036 China School of Astronomy and Space Science University of Science and Technology of China Hefei230026 China Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai200030 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

We report the finding of four changing-look (CL) active galactic nuclei (AGN). We selected these sources due to their potential as interesting targets when considering their relatively-large optical flux variations and related mid-infrared flux variations. To identify their CL feature, we use archival spectra from the Sloan Digital Sky Survey (SDSS) taken at least 8 years ago as well as spectra taken recently from the Transient Name Server (TNS) and with the 2.4-m LiJiang telescope (LJT). We study the sources' spectral changes by fitting and determining the H_ and H_ components and verify their CL behavior. When comparing the TNS and/or LJT spectra to the SDSS ones, all four sources showed the appearance of a broad or a stronger broad H_ component and a relatively weak broad H_ component. As two of the four sources are established to have a brighter-and-bluer feature in the photometric data, during the time periods in which the TNS and LJT spectra were taken, this feature likely accompanied the turn-on of the broad components. Thus, we suggest that this brighter-and-bluer feature can be used as a criterion for efficiently finding CL sources among previously spectroscopically classified type 2 AGN, such as from among the sources provided by the SDSS. Copyright © 2024, The Authors. All rights reserved.

关键词： Active Galactic Nuclei