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The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b∗

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arXiv 2023年

作者： Xing, Lei Yan, Dongdong Guo, Jianheng Yunnan Observatories Chinese Academy of Sciences P.0.Box110 Kunming650216 China Yuquan Road Shijingshan District Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.0.Box110 Kunming650216 China

The absorption signals of metastable He in HD 209458b and several other exoplanets can be explained via escaping atmosphere model with a subsolar He/H ratio. The low abundance of helium can be a result of planet formation if there is a small amount of helium in their primordial atmosphere. However, another possibility is that the low He/H ratio is caused by the process of mass fractionation of helium in the atmosphere. In order to investigate the effect of the fractionation in the hydrogen-helium atmosphere, we developed a self-consistent multi-fluid 1D hydrodynamic model based on the well-known open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be produced spontaneously in the multi-fluid model. We further modeled the transmission spectra of He 10830 lines for HD 209458b in a broad parameter space. The transmission spectrum of the observation can be fitted in the condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen, FHe/FH, is 0.039. Our results indicate that the mass fractionation of helium to hydrogen can naturally interpret the low He/H ratio required by the observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the abundance of helium in the atmosphere is not needed even if its He abundance is similar to that of the Sun. The simulation presented in this work hints that in the escaping atmosphere, mass fractionation can also occur on other exoplanets, which needs to be explored further. © 2023, CC BY-NC-ND.

关键词： Helium

On the Detection and Characterization of Quasiperiodic Oscillations in Astronomical Time Series: Gamma-ray Burst X-ray Light Curves as a Test Case

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arXiv 2024年

作者： Song, Fei-Fan Mao, Jirong Yunnan Observatories Chinese Academy of Sciences Yunnan Province Kunming650011 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 Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

The study of temporal properties of variable sources can elucidate their physical processes. In this context, we present a critical study comparing three approaches to periodic or quasiperiodic behavior: Gaussian process, power spectrum, and wavelet analysis, using celerite, Lomb-Scargle periodograms, and weighted wavelet-Z transforms, respectively. We use 15 Swift-X-ray Telescope light curves of short gamma-ray bursts (sGRBs) as examples. A comprehensive analysis of two sGRB X-ray light curves is performed. The results reveal the importance of artifacts, largely in the form of false quasiperiodic oscillation signals, possibly introduced by preprocessing (such as detrending) or other aspects of the analysis. The exploration described in this paper can be helpful for future studies of variability in GRBs, active galactic nuclei, and other astronomical sources. Copyright © 2024, The Authors. All rights reserved.

关键词： Z transforms

evolution of double oxygen-neon white dwarf merger remnant

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arXiv 2023年

作者： Wu, Chengyuan Xiong, Heran Han, Zhanwen Wang, Bo Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Research School of Astronomy and Astrophysics The Australian National University CanberraACT2611 Australia

Double white dwarf (WD) merger process and their post-merger evolution are important in many fields of astronomy, such as supernovae, gamma-ray bursts, gravitational waves, etc. The evolutionary outcomes of double ultra-massive WD merger remnants are still a subject of debate, though the general consensus is that the merger remnant will collapse to form a neutron star. In this work, we investigate the evolution of a 2.20Mo merger remnant stemmed from the coalescence of double 1.10Mo ONe WDs. We find that the remnant ignites off-centre neon burning at the position near the surface of primary WD soon after the merger, resulting in the stable inwardly propagating oxygen/neon (O/Ne) flame. The final outcomes of the merger remnant are sensitive to the effect of convective boundary mixing. If the mixing cannot stall the O/Ne flame, the flame will reach the centre within 20 years, leading to the formation of super Chandrasekhar mass silicon core, and its final fate probably be neutron star (NS) through iron-core-collapse supernova. In contrast, if the convective mixing is effective enough to prevent the O/Ne flame from reaching the centre, the merger remnant will undergo electron capture supernova to form an ONeFe WD. Meanwhile, we find that the wind mass loss process may hardly alter the final fate of the remnant due to its fast evolution. Our results imply that the coalescence of double ONe WDs can form short lived giant like object, but the final outcomes (NS or ONeFe WD) are influenced by the uncertain convective mixing in O/Ne flame. © 2023, CC BY.

关键词： Oxygen

Formation of WNL stars for the MW and LMC based on the k-ω model

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arXiv 2024年

作者： Si, Jijuan Li, Zhi Li, Yan Yunnan Observatories Chinese Academy of Sciences P.O.Box 110 Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

We adopt a set of second-order differential equations (k − ω model) to handle core convective overshooting in massive stars, simulate the evolution of WNL stars with different metallicities and initial masses, both rotating and non-rotating models, and compare the results with the classical overshooting model. The results indicate that under the same initial conditions, the k − ω model generally produces larger convective cores and wider overshooting regions, thereby increasing the mass ranges and extending the lifetimes of WNL stars, as well as the likelihood of forming WNL stars. The masses and lifetimes of WNL stars both increase with higher metallicities and initial masses. Under higher-metallicity conditions, the two overshooting schemes significantly differ in their impacts on lifetimes of the WNL stars, but insignificant in the mass ranges of the WNL stars. Rotation may drive the formation of WNL stars in low-mass, metal-poor counterparts, with this effect being more pronounced in the OV model. The surface nitrogen of metal-rich WNL stars formed during the MS phase is likely primarily from the CN-cycle, while it may come from both the CN- and NO-cycles for relatively metal-poor counterparts. Our model can effectively explain the distribution of WNL stars in the Milky Way, but appears to have inadequacies in explaining the WNL stars in the LMC. Copyright © 2024, The Authors. All rights reserved.

关键词： Giant stars

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一颗大质量恒星在死亡前猛烈抛射出星周物质

Science Bulletin 2023年第21期68卷 2548-2554,M0005页

作者：张居甲林含王晓锋赵泽毅李丽萍刘嘉联闫圣钰向丹凤王汇娟白金明 Yunnan Observatories(YNAO) Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China International Centre of Supernovae Yunnan Key LaboratoryKunming 650216China Key Laboratory of Radio Astronomy and Technology CASBeijing 100101China Department of Physics Tsinghua UniversityBeijing 100084China Beijing Planetarium Beijing Academy of Science and TechnologyBeijing 100044China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 101408China

Ⅱ型超新星是宇宙中最常见的恒星爆炸,其富氢的大质量前身星最后阶段的演变让人捉摸不透.这类恒星晚期演化和由此产生的星周环境的差异导致了超新星丰富的观测多样性.为了建立Ⅱ型超新星爆炸与大质量恒星晚期演化之间的联系,有必要捕捉... 详细信息

Ⅱ型超新星是宇宙中最常见的恒星爆炸,其富氢的大质量前身星最后阶段的演变让人捉摸不透.这类恒星晚期演化和由此产生的星周环境的差异导致了超新星丰富的观测多样性.为了建立Ⅱ型超新星爆炸与大质量恒星晚期演化之间的联系,有必要捕捉超新星爆炸的第一缕光,即由激波爆发冷却产生的高能光子电离星周物质造成的闪亮光谱.近邻星系M 101中爆发的SN 2023ixf为探索这个问题提供了难得的机会.本文利用爆炸后1~5天内频繁拍摄地闪亮光谱,对这颗超新星周围物质的性质进行严格的约束.计算得出,SN 2023ixf前身星在爆炸前最后2~3年中以高达M≈6×10^(-4)M⊙a^(-1)速率损失物质.这些物质以55 km s^(-1)的速度运动,在距离前身星不到7×10^(14)cm的位置形成致密的星周物质壳层.考虑到如此高的质量损失率和相对较大的风速,以及20年前的前身星图像,SN2023ixf可能是刚从红超巨星演化而来的黄巨超巨星产生的超新星爆炸.

关键词：超新星爆炸星周物质前身星 Ⅱ型超新星红超巨星近邻星系质量损失率

The Application of Machine Learning in Tidal evolution Simulation of Star-Planet Systems

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arXiv 2024年

作者： Guo, Shuaishuai Guo, Jianheng Ji, KaiFan Liu, Hui Xing, Lei Yunnan Observatories Chinese Academy of Sciences P.O. Box 110 Kunming650011 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650011 China Yunnan Key Laboratory of SolarPhysics and Space Science 650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China

With the release of a large amount of astronomical data, an increasing number of close-in hot Jupiters have been discovered. Calculating their evolutionary curves using star-planet interaction models presents a challenge. To expedite the generation of evolutionary curves for these close-in hot Jupiter systems, we utilized tidal interaction models established on MESA to create 15,745 samples of star-planet systems and 7,500 samples of stars. Additionally, we employed a neural network (Multi-Layer Perceptron - MLP) to predict the evolutionary curves of the systems, including stellar effective temperature, radius, stellar rotation period, and planetary orbital period. The median relative errors of the predicted evolutionary curves were found to be 0.15%, 0.43%, 2.61%, and 0.57%, respectively. Furthermore, the speed at which we generate evolutionary curves exceeds that of model-generated curves by more than four orders of magnitude. We also extracted features of planetary migration states and utilized lightGBM to classify the samples into 6 categories for prediction. We found that by combining three types that undergo long-term double synchronization into one label, the classifier effectively recognized these features. Apart from systems experiencing long-term double synchronization, the median relative errors of the predicted evolutionary curves were all below 4%. Our work provides an efficient method to save significant computational resources and time with minimal loss in accuracy. This research also lays the foundation for analyzing the evolutionary characteristics of systems under different migration states, aiding in the understanding of the underlying physical mechanisms of such systems. Finally, to a large extent, our approach could replace the calculations of theoretical models. Copyright © 2024, The Authors. All rights reserved.

关键词： Stars

Constraints on Extragalactic Background Light using TeV Observations of BL Lacertae objects

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arXiv 2023年

作者： Qin, Longhua Wang, Jiancheng Gao, Quangui Na, Weiwei Li, Huaizhen Wang, Ao Yang, Chuyuan Yang, Jianping Department of Physics Yuxi Normal University Yunnan Yuxi653100 China Yunnan Observatory Chinese Academy of Sciences Yunnan Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650011 China Yunnan Agricultural University Yunnan Kunming650201 China

The extragalactic background light (EBL) in the IR to UV bands partly absorbs very high energy (VHE, E ≥ 100GeV) γ−ray photons travelling over cosmological distances via pair production. In this paper, to get stronger constraints on EBL, we use the deliberate selection of the EBL model and data of five BL Lacs with better statistics and the harder spectra to limit the EBL density and the radiation mechanism of BL Lacs. We constrain the upper limit of the EBL density by fitting the spectral energy distributions (SEDs) of TeV BL Lacs and find that our results are compatible with the published measurement, reaching 50 nWm−2sr−1. We also obtain that the EBL is not necessarily transparent to high VHE photons. We fix the intrinsic spectral index Γi of TeV BL Lacs as 1.0 and 1.5 under observation evidence and model assumption. Comparing the EBL density given by galaxy count and Spitzer observations, we then obtain that 1ES 1101-232 has Γi ≤ 1.0 and 1ES 0229+200 should have Γi not harder than 1.0. We demonstrate that the common radiation assumption of BL Lacs, in which the Γi is softer than 1.5, should be revisited. Furthermore, we propose that the upper EBL density could be given by fitting the hardest energy spectra of TeV BL Lacs. © 2023, CC BY.

关键词： Gamma rays

Investigation into the reflection properties of the neutron star low-mass X-ray binary 4U 1636-53

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Astronomy and Astrophysics 2023年 677卷

作者： Lyu, M. Zhang, G.B. Wang, H.G. García, F. Department of Physics Xiangtan University Xiangtan Hunan411105 China Key Laboratory of Stars and Interstellar Medium Xiangtan University Xiangtan Hunan411105 China Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Department of Astronomy School of Physics and Materials Science Guangzhou University Guangzhou510006 China Villa Elisa Buenos Aires Argentina

We present the spectroscopy of the neutron star low-mass X-ray binary 4U 1636-53 using six simultaneous XMM-Newton and Rossi X-ray Timing Explorer observations. We applied different self-consistent reflection models to explore the features when the disk is illuminated by either the corona or the neutron star surface. We found that the spectra could be well fitted by these two types of models, with the derived emissivity index below a typical value of 3. The relative low emissivity can be explained if the neutron star and the corona, working together as an extended illuminator, simultaneously illuminate and ionize the disk. Additionally, the derived ionization parameter in the lamppost geometry is larger than the theoretical prediction. This inconsistency likely suggests that the corona does not emit isotropically in a realistic context. Furthermore, we also found that there is a possible trend between the height of the corona and the normalization of the disk emission. This could be understood either as a variation in the reflected radiation pressure or in the context of a jet base. Finally, we found that the disk is less ionized if it is illuminated by the neutron star, indicating that the illuminating source has significant influence on the physical properties of the disk. © The Authors 2023.

关键词： Stars

Exploring variation of double-peak broad-line profile in strongly variable AGNs

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arXiv 2024年

作者： Wu, Jiancheng Wu, Qingwen Lu, Kaixing Cao, Xinwu Lei, Xiangli Wang, Mengye Fan, Xiao Department of Astronomy School of Physics Huazhong University of Science and Technology Luoyu Road 1037 Wuhan China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Institute for Astronomy School of Physics Zhejiang University 866 Yuhangtang Road Hangzhou310058 China

The geometry and kinematics of the broad-line region (BLR) in AGNs are still unclear, which is crucial for studying the physics and evolution of supermassive black holes (SMBHs) and AGNs. The broad-line profile provides valuable information on BLR geometry and kinematics. In this work, we explore the evolution of line profiles in variable AGNs based on the BLR model of Czerny & Hryniewicz, where the BLR is driven by the radiation pressure acting on dust at the surface layers of the accretion disk. The line profiles in the low-Eddington-ratio regime show a double-peak profile, which will become a single peak at high Eddington ratios. The high metallicity of Z 5Zo is required to reproduce the observational anti-correlation between the peak separation of broad lines and the Eddington ratio for a sample of AGNs. For the broad lines in variable AGNs, it will take several years to several decades to change their line profile if the disk luminosity suffers strong variation in a much shorter timescale. More monitoring of the broad line and continuum in strongly variable AGNs can shed special light on BLR physics. © 2024, CC BY.

关键词： Kinematics