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arXiv 2025年

作者： Jiang, Zhen Li, Cheng Zhang, Fenghui Zhou, Shuang Department of Astronomy Tsinghua University Beijing100084 China National Astronomical Observatories Chinese Academy of Sciences Beijing100101 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 INAF–Osservatorio Astronomico di Brera via Brera 28 Milano20159 Italy

UV-upturn galaxies are characterized by unusually excessive flux in the far-ultraviolet (FUV) band, observed in some elliptical galaxies and the bulges of disk galaxies. We examine UV-upturn galaxies within the semi-analytic model gabe, which embeds the formation of extreme horizontal branch (EHB) stars—proposed as key candidates responsible for the UV-upturn phenomenon. We have analyzed all related physical processes, including stellar evolution, initial mass functions (IMFs), dust attenuation, galaxy age, metallicity, and binary fractions, in an effort to determine which processes play significant roles. Our findings reveal two categories of UV-upturn galaxies in the semi-analytic model, each with distinct formation channels: old metal-rich quenched elliptical galaxies, which are intrinsic UV-upturn galaxies induced by EHB stars within their old stellar populations, and dusty star-forming galaxies, which are relatively young and may also be photometrically identified as UV-upturn galaxies when accounting for dust attenuation. Dust attenuation contributes to 20% − 60% of the UV-upturn galaxies, depending on the specific dust attenuation models adopted. With the binary star formation model of EHB stars, both of these formation channels exhibit strong preferences for high stellar metallicity. The high-mass end slope of the IMFs is found to have a marginal effect, indicating that a universal IMF is adequate for studying the UV-upturn phenomenon. Copyright © 2025, The Authors. All rights reserved.

关键词： Dust

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Relation between spectral indices and binary fractions in GCs

arXiv

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arXiv 2023年

作者： Zhang, Fenghui Li, L. Han, Z. Gong, X. Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 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

Context. We study the relation between the known binary fraction and spectral absorption feature index to judge whether (and potentially which) spectral absorption feature indices are suitable for determining the binary fraction. Aims. The determination of the binary fraction is important in studies of binary star formation, evolutionary population synthesis models, and other works. The number of binary stars is difficult to determine for nearly all stellar systems because the individual stars are need to be resolved photometrically or spectroscopically. By comparison, their integrated spectra or spectral absorption feature indices are relatively easy to obtain. Methods. We used Galactic globular clusters (GCs) as our sample since they have relatively accurate binary fraction measurements and spectroscopic observations along the radial direction. When studying the relation between binary fractions and the spectral absorption feature index, we used three types of binary fractions: one with a mass ratio of q>0.5 (f(q>0.5)) and two with a total binary fraction (the methods of counting (f(tot)mf) and fitting (f(tot)mc), calculated and obtained the equivalent widths or magnitudes of 46 spectral absorption feature indices at three spectral resolutions (FWHMLick/IDS, 5, and 15 Å). Since the regions for the binary fraction measurements (photometric) and the spectroscopic observations are different, we used the method of constructing the radial binary-fraction profile to get the binary fractions corresponding to the regions in the spectroscopic observations. The construction of the radial binary-fraction profile was obtained by using the python curve_fit module to fit the measured and analytic binary fraction values. The analytic value was expressed by taking advantage of the King surface-density profile and the assumed forms with respect to the radial binary-fraction profile (linear, quadratic, exponential, and Gaussian). Results. We find that the low-resolution (15 Å) spec

关键词： Stars

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Dark Matter (S)pins the Planet

arXiv

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arXiv 2025年

作者： Shi, Haihao Zhou, Junda Huang, Zhenyang Lü, Guoliang Chen, Xuefei Xinjiang Astronomical Observatory Chinese Academy of Sciences Urumqi830011 China College of Astronomy and Space Science University of Chinese Academy of Sciences Beijing101408 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China School of Physical Science and Technology Xinjiang University Urumqi830046 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China

Dark matter heating in planets has been proposed as a potential probe for dark matter detection. Assuming near-equilibrium, we find that dark matter energy input raises planetary temperature and accelerates rotation. The energy distribution depends on planetary properties and external input, suggesting that previous studies have overestimated its heating effect. When dark matter density is high, planetary rotation stabilizes earlier and is primarily governed by dark matter. For Earth, our model predicts a 0.015 K temperature increase and a 10−8 rad/s angular velocity increase over 100 years. Copyright © 2025, The Authors. All rights reserved.

关键词： Dark energy

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

arXiv

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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

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

arXiv

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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

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Detectability of neutrino-signal fluctuations induced by the hadron-quark phase transition in failing core-collapse supernovae

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Physical Review D 2024年第2期109卷 023005-023005页

作者： Zidu Lin Shuai Zha Evan P. O’Connor Andrew W. Steiner Department of Physics and Astronomy University of Tennessee Knoxville Knoxville 37996 USA Tsung-Dao Lee Institute Shanghai Jiao Tong University Shanghai 200240 China Yunnan Observatories Chinese Academy of Sciences (CAS) Kunming 650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming 650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming 650216 China The Oskar Klein Centre Department of Astronomy Stockholm University AlbaNova SE-106 91 Stockholm Sweden Physics Division Oak Ridge National Laboratory Oak Ridge 37831 USA

We introduce a systematic and quantitative methodology for establishing the presence of neutrino oscillatory signals due to the hadron-quark phase transition (PT) in failing core-collapse supernovae from the observed neutrino event rate in water- or ice-based neutrino detectors. The methodology uses a likelihood ratio in the frequency domain as a test-statistic; it is employed for quantitative analysis of neutrino signals without assuming the frequency, amplitude, starting time, and duration of the PT-induced oscillations present in the neutrino events and thus it is suitable for analyzing neutrino signals from a wide variety of numerical simulations. We test the validity of this method by using a core-collapse simulation of a 17 solar-mass star by Zha et al. [Astrophys. J. 911, 74 (2021) ]. Based on this model, we further report the presence of a PT-induced oscillations quantitatively for a core-collapse supernovae out to a distance of ∼10 kpc, ∼5 kpc for IceCube and to a distance of ∼10 kpc, ∼5 kpc, and ∼1 kpc for a 0.4 Mt mass water Cherenkov detector. This methodology will aid the investigation of a future galactic supernova and the study of hadron-quark phase in the core of core-collapse supernovae.

关键词： Nuclear astrophysics Nuclear physics of explosive environments

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

arXiv

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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

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Absolute physical parameters of three poorly studied detached eclipsing binaries

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Research in Astronomy and Astrophysics 2021年第1期21卷 220-228页

作者： Dao-Ye Yang Li-Fang Li Quan-Wang Han Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China University of Chinese Academy of Sciences Beijing 100049China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100012China Key Lab of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 10101China School of Physics and Electronics Qiannan Normal University for NationalitiesDuyun 558000China

The photometric and spectroscopic data for three double-lined detached eclipsing binaries were collected from the photometric and spectral *** light and radial velocity curves of each binary system were simultaneously analyzed using Wilson-Devinney(WD)code,and the absolute physical and orbital parameters of these binaries were *** masses of both components of ASASSN-V J063123.82+192341.9 were found to be M1=1.088±0.016 and M20.883±0.016 M⊙;those of ASAS J011416+0426.4 were determined to be M1=0.934±0.046 and M2=0.754±0.043 M⊙;and those of MW Aur were derived to be M1=2.052±0.196 and M21.939±0.193 M⊙.Finally,the evolutionary status of these detached binaries was discussed based on their absolute parameters and the theoretical stellar models.

关键词： stars:binaries:eclipsing stars:fundamental parameters stars:evolution stars:individual:ASASSN-V J063123.82+192341.9,ASAS J011416+0426.4 and MW Aur

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Type Ia Supernovae from First-generation Stars

arXiv

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arXiv 2024年

作者： Li, Zhenwei Wang, Lifan Han, Zhanwen Chen, Xuefei Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Science Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China George P. and Cynthia Woods Mitchell Institute for Fundamental Physics & Astronomy Texas A&M University Department of Physics and Astronomy 4242 TAMU College StationTX77843 United States

Type Ia Supernovae (SNe Ia) discovered at redshift z 2.5 are presumed to be produced from Population (Pop) I/II stars. In this work, we investigate the production of SNe Ia from Pop III binaries in the cosmological framework. We derive the SN Ia rate as a function of redshift under a theoretical context for the production of first generation stars and emanate the likelihood of their detection by the James Webb Space Telescope (JWST). Assuming the initial stellar mass function (IMF) favors low-mass stars as from recent numerical simulations, we found Pop III stars may give rise to a considerable amount of SNe Ia at high redshift and Pop III stars may even be the dominant SN Ia producer at z 6. In an optimistic scenario, we expect ∼ 1(2) SNe Ia from Pop III stars at z ≈ 4(5) for a survey of area 300 arcmin2 during a 3 yr period with JWST. The same survey may record more than ∼ 400 SNe Ia at lower redshift (z 2.5) but with only about one of them from Pop III progenitors. There will be ∼ 6 Pop III SNe Ia in the same field of view at redshifts of 5 − 10. Observational constraints on SN Ia rates at the redshift range of 5 − 10 can place crucial constraints on the IMF of Pop III stars. Copyright © 2024, The Authors. All rights reserved.

关键词： Supernovae

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

arXiv

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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

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