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Detection of 12426 SB2 candidates in the LAMOST-MRS, using a binary spectral model

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arXiv 2023年

作者： Kovalev, Mikhail Zhou, Zenghua 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 Sternberg Astronomical Institute Leninskie Gory Moscow119992 Russia Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

We use an updated method for the detection of double-lined spectroscopic binaries (SB2) using V sin i values from spectral fits. The method is applied to all spectra from LAMOST MRS. Using this method, we detect 12426 SB2 candidates, where 4321 are already known and 8105 are new discoveries. We check their spectra manually to minimise possible false positives. We also detect several cases of contamination of the spectra by solar light. Additionally, for candidates with multiple observations we compute mass ratios with systemic velocities and determine Keplerian orbits. We present an updated catalogue of all SB2 candidates together with additional information for some of them in separate data tables. Copyright © 2023, The Authors. All rights reserved.

关键词： Orbits

One Fits All: A Unified Synchrotron Model Explains GRBs with FRED-Shaped Pulses

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arXiv 2023年

作者： Yan, Zhen-Yu Yang, Jun Zhao, Xiao-Hong Meng, Yan-Zhi Zhang, Bin-Bin School of Astronomy and Space Science Nanjing University Nanjing210093 China Key Laboratory of Modern Astronomy and Astrophysics Nanjing University Ministry of Education China Yunnan Observatories Chinese Academy of Sciences Kunming China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China Purple Mountain Observatory Chinese Academy of Sciences Nanjing210023 China

The analysis of gamma-ray burst (GRB) spectra often relies on empirical models lacking a distinct physical explanation. Previous attempts to couple physical models with observed data focus on individual burst studies, fitting models to segmented spectra with independent physical parameters. However, these approaches typically neglect to explain the time evolution of observed spectra. In this study, we propose a novel approach by incorporating the synchrotron radiation model to provide a self-consistent explanation for a selection of single-pulse GRBs. Our study comprehensively tests the synchrotron model under a unified physical condition, such as a single injection event of electrons. By tracing the evolution of cooling electrons in a decaying magnetic field, our model predicts time-dependent observed spectra that align well with the data. Using a single set of physical parameters, our model successfully fits all time-resolved spectra within each burst. Our model suggests that the rising phase of the GRB light curve results from the increasing number of radiating electrons, while the declining phase is attributed to the curvature effect, electron cooling, and the decaying magnetic field. Our model provides a straightforward interpretation of the peak energy's evolution, linked to the decline of the magnetic field and electron cooling due to the expansion of the GRB emission region. Our findings strongly support the notion that spectral and temporal evolution in GRB pulses originates from the expansion of the GRB emission region, with an initial radius of approximately 1015 cm, and synchrotron radiation as the underlying emission mechanism. Copyright © 2023, The Authors. All rights reserved.

关键词： Synchrotron radiation

Two high-amplitude δ Scuti-γ Doradus hybrids constrained by the radial fundamental p and equally spaced g modes

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arXiv 2024年

作者： Chen, Xinghao Zhang, Xiaobin Li, Yan Su, Jie Yunnan Observatories Chinese Academy of Sciences P.O. Box 110 Kunming650216 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 Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

Based on 2-minute cadence TESS data, we investigate pulsations of TIC 65138566 and TIC 139729335 and discover them to be two new HADS stars with equally spaced g modes. We recognize the radial fundamental mode f1 = 18.3334 c/d and the first overtone f3 = 23.6429 c/d for TIC 65138566, and identify the highest peak f1 = 19.0955 c/d as the radial fundamental mode for TIC 139729335. For g modes, both stars display a regular period spacing of 2413 s. Through detailed seismological analysis, we deduce that these period spacing patterns correspond to modes with = 1. Moreover, our analysis reveals that with the increase in masses and metallicities, the star should display a higher degree of evolution to match a specific period spacing Π0. Conversely, the star should have a lower extent of evolution to match the radial fundamental mode. These two contradictory behaviors allow us to precisely obtain stellar physical parameters. TIC 65138566 and TIC 139729335 are determined to be two main sequence stars that have almost the same range of masses and metallicities, with M = 1.36 ± 0.06 M☉ and Z = 0.005 ± 0.002. The hydrogen abundance in the core of TIC 65138566 is estimated to be about 0.28, while TIC 139729335 has a slightly higher value of around 0.31. Finally, we suggest that the HADS δ Scuti-γ Doradus star TIC 308396022 is a main sequence star with M = 1.54 ± 0.08 M☉, Z = 0.007 ± 0.001, and Xc = 0.18 ± 0.02. Copyright © 2024, The Authors. All rights reserved.

关键词： Stars

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

Two Different Weak Modulations in ab-type RR Lyrae Variable V838 Cyg, and Potential Influence of Metal Abundance on Blazhko Modulation

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arXiv 2023年

作者： Li, L.-J. Qian, S.-B. Shi, X.-D. Zhu, L.-Y. Yunnan Observatories Chinese Academy of Sciences P.O. Box 110 Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects 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

Noting the weakest modulation and relatively high metal abundance of the ab-type RR Lyrae star V838 Cyg, we collected the photometric data of this star from several sky surveys to carry out an in-depth analysis. The O - C diagram shows that the pulsation period of V838 Cyg increases linearly over a long timescale. In a reanalysis of the high-precision Kepler data, we confirmed the modulation with a period of 59.45 ± 0.07 days found by Benko et al., (2014), and also found an additional weak modulation with a longer period (840±21 days). After a series of analyses, we incline to the view that the mechanisms causing the two modulations are different: the former is more similar to the typical Blazhko effect, while the mechanism leading to the latter may be an extrinsic factor. We also collected and compared the modulation and physical parameters of other Blazhko RR Lyrae stars from several works in the literature, and find that there is a potential negative correlation between the modulation amplitude (or upper limit of amplitude) and the metal abundance. We infer that the relatively high metal abundance will promote convection in the outer stellar atmosphere, and then inhibit those factors (turbulence, shock wave, etc.) that may cause Blazhko modulation. Future observations and research work can be carried out with reference to this viewpoint. We also introduce the moiré effects that appear in the Kepler long-cadence light curves and their possible interference in the previous analyses. © 2023, CC BY.

关键词： Shock waves

Mean-squared displacement and variance for confined Brownian motion

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arXiv 2023年

作者： Liao, Yi Hao, Yu-Zhou Gong, Xiao-Bo Department of Materials Science and Engineering College of Engineering Southern University of Science and Technology Shenzhen518055 China Department of Physics College of Science Southern University of Science and Technology Shenzhen518055 China State Key Laboratory for Mechanical Behavior of Materials School of Materials Science and Engineering Xi’an Jiaotong University Xi’an710049 China Yunnan Observatory Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

For one-dimension Brownian motion in the confined system with the size L, the mean-squared displacement(MSD) defined by 〈(x − x0)2〉 should be proportional to tα(t). The power α(t) should range from 1 to 0 over time, and the MSD turns from 2Dt to cL2, here the coefficient c independent of t, D being the diffusion coefficient. The paper aims to quantitatively solve the MSD in the intermediate confinement regime. The key to this problem is how to deal with the propagator and the normalization factor of the Fokker-Planck equation(FPE) with the Dirichlet Boundaries. Applying the Euler-Maclaurin approximation(EMA) and integration by parts for the small t, we obtain the MSD being (Formular presented), with (Formular presented), t and the power α(t) being 1-0.18√ξ /1-0.18√ξ. Further, we analysis the MSD and the power for the d-dimension system with γ-dimension confinement. In the case of γ 2〉. In the finite system, the variance is not necessarily the same as MSD. The initial conditions are essential to characterize the diffusion behavior described by the FPE, especially in the finite system. Under the initial condition referring to the different probability density function(PDF) being p0(x), MSD and PV should exhibit different dependencies on time, which reflect corresponding diffusion *** examples, the paper discusses the representative initial PDFs reading p0(x) = δ(x − x0), with the midpoint x0 = L/2 and the endpoint x0 = ∊(or 0+). In the case of midpoint, the MSD(equal to PV) reads 2Dt(1 − 5π3Dt)/L2 for the small t, which reflects a kind of sub-diffusion, with D being the diffusion coefficient. In the case of endpoint, the MSD(equal to PV) reads 4/π (2Dt)[1 + 2√πDt/L ] for the small t, which reflects a kind of super-diffusion. © 2023, CC BY.

关键词： Diffusion

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

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

Nine New Cataclysmic Variable Stars with Negative Superhumps

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arXiv 2023年

作者： Sun, Qi-Bin Qian, Sheng-Bang Zhu, Li-Ying Liao, Wen-Ping Zhao, Er-Gang Li, Fu-Xing Shi, Xiang-Dong Li, Min-Yu Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Yuquan Road Shijingshan District Beijing China

Negative superhumps (NSHs) are signals a few percent shorter than the orbital period of a binary star and are considered to originate from the reverse precession of the tilted disk. Based on TESS photometry, we find nine new cataclysmic variable stars (CVs) with NSHs. Three (ASAS J1420, TZ Per, and V392 Hya) of these stars similar to AH Her still have NSHs during dwarf nova outbursts, and the NSH amplitude varies with the outburst. The variation in the radius of the accretion disk partially explains this phenomenon. However, it does not explain the rebound of the NSH amplitude after the peak of the outburst and the fact that the NSH amplitude of the quiescence is sometimes not the largest, and it is necessary to combine the disk instability model (DIM) and add other ingredients. Therefore, we suggest that the variation of NSH amplitude with outburst can be an essential basis for studying the origin of NSHs and improving the DIM. The six (ASASSN-V J1137, ASASSN-V J0611, 2MASS J0715, LAMOST J0925, ASASSN-17qj, and ZTF18acakuxo) remaining stars have been poorly studied, and for the first time we determine their orbital periods, NSHs and Superorbital signal (SOR) periods. The NSH periods and amplitudes of ASASSN-V J1137 and ASASSN-17qj vary with the SOR, and based on the comparison of the observations with the theory, we suggest that a single change in tilted disk angle does not explain the observations of the SOR and that other ingredients need to be considered as well. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars