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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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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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A spectral hardening in the Fermi-LAT Data of 1ES 0502+675

arXiv

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arXiv 2022年

作者： Zeng, Yuhang Yan, Dahai Hu, Wen Wang, Jiancheng Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories Chinese Academy of Sciences Kunming650011 China University of Chinese Academy of Science Beijing100049 China Department of Physics Jinggangshan University Jiangxi Province Ji'An343009 China

The γ-ray spectral feature of the blazar 1ES 0502+675 is investigated by using Fermi Large Area Telescope (Fermi-LAT) Pass 8 data (between 100 MeV and 300 GeV) covering from 2008 August to 2021 April. A significant (∼ 4σ) hardening at ∼ 1 GeV is found in the γ-ray spectrum during a moderately flaring state (MJD 55050-55350). The photon index below and above the break energy is Γ1 = 2.36 ± 0.31 and Γ2 = 1.33 ± 0.11, respectively. In the rest of the observations, the γ-ray spectrum can be described by a power-law form with the photon index of ≈ 1.6. In the frame of a one-zone synchrotron self-Compton (SSC) model, the spectral hardening is interpreted as the transition between the synchrotron component and the SSC component. This could be the result of a slight increase of the break/maximum Lorentz factor of the electrons. Copyright © 2022, The Authors. All rights reserved.

关键词： Hardening

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The afterglow emission from a stratified jet in GRB 170817A

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Research in Astronomy and Astrophysics 2021年第7期21卷 223-233页

作者： Kang-Fa Cheng Xiao-Hong Zhao Bin-Bin Zhang Jin-Ming Bai Yunnan Observatories Chinese Academy of SciencesKunming 650216China University of the Chinese Academy of Sciences Beijing 100049China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China School of Astronomy and Space Science Nanjing UniversityNanjing 210093China Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University) Ministry of EducationNanjing 210046China Department of Physics and Astronomy University of Nevada Las VegasNV 89154USA

The afterglow of GRB 170817 A has been detected for more than three years,but the origin of the multi-band afterglow light curves remains under debate.A classical top-hat jet model is faced with difficulties in producing a shallow rise of the afterglow light curves as observed(E_(v) ∝ T^(0.8)).Here we reconsider the model of stratified ejecta with an energy profile of E(> Γβ)=E_0(Γβ)^(-k) as the origin of the afterglow light curves of the burst,where Γ and β are the Lorentz factor and speed of the ejecta,respectively.k is the power-law slope of the energy *** consider that the ejecta are collimated into *** kinds of jet evolutions are investigated,including a lateral-spreading jet and a non-lateral-spreading *** fit the multi-band afterglow light curves,including the X-ray data at one thousand days post-burst,and find that both the models of the spreading and non-spreading jets can fit the light curves well,but the observed angular size of the source and the apparent velocity of the flux centroid for the spreading jet model are beyond the observation limits,while the non-spreading jet model meets the observation *** of the best-fit parameters for the non-spreading jet model,such as the number density of the circumburst medium~10^(-2) cm^(-3) and the total jet kinetic energy E ~ 4.8 × 10^(51) erg,also appear *** best-fit slope of the jet energy profile is k ~*** results suggest that the afterglow of GRB 170817 A may arise from the stratified jet and that the lateral spreading of the jet is not significant.

关键词： gamma-ray burst:general stars:jets relativistic processes

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An upgraded interpolator of the radial basis function network for spectral calculation based on empirical stellar spectral library

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Research in Astronomy and Astrophysics 2020年第9期20卷 277-290页

作者： Lian-Tao Cheng Feng-Hui Zhang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega Science Chinese Academy of SciencesBeijing 100012China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China University of Chinese Academy of Sciences Beijing 100049China

Stellar population synthesis is an important method in galaxy and star-cluster *** stellar population synthesis models,a stellar spectral library is necessary for the integrated spectra of the stellar ***,the stellar spectral library is utilized for the transformation between the stellar atmospheric parameters and stellar *** empirical stellar spectral library has distinct advantages over the theoretical ***,for the empirical spectral library,the distribution of stars is irregular in the stellar atmospheric parameter space,which makes the traditional interpolator difficult to get accurate *** this work,we will provide an improved radial basis function interpolator which is implemented to obtain the interpolated stellar spectra based on the empirical stellar spectral *** this interpolator,we use the relation between the standard varianceσin the Gaussian radial basis function and the density distribution of stars in the stellar atmospheric parameter space to give the prior constraint on thisσ.Moreover,we also consider the anisotropic radial basis function by the advantage of the local dispersion of stars in the stellar atmospheric parameter ***,we use the empirical stellar spectral library MILES to test this *** the whole,the interpolator has a good performance except for the edge of the low-temperature *** last,we compare this interpolator with our work in 2018,and the interpolation result shows an obvious *** can apply this interpolator to retrieve the interpolated spectra based on the stellar spectral library quickly and easily.

关键词： stars:fundamental parameters stars:atmospheres (Galaxy:)globular clusters:general methods:numerical

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CCD astrometric observations of 2017 VR12, Camillo and Midas

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Research in Astronomy and Astrophysics 2019年第5期19卷 91-100页

作者： Zhen-Jun Zhang Yi-Gong Zhang Xiang-Ming Chen Jian-Cheng Wang Jie Su Yunnan Observatories Chinese Academy of Sciences Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences University of Chinese Academy of Sciences

We have observed three near-Earth objects(NEOs), 2017 VR12, Camillo and Midas, during *** observations were made with the 1-m telescope, operated by Yunnan Observatories, over two *** precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion laboratory(JPL) Horizons System and Institut de M′ecanique C′eleste et de Calcul des ′Eph′em′erides(IMCCE). The positions of three asteroids are measured with respect to stars in the Gaia DR2 star catalog. For 2017 VR12, the means(O-C) of right ascension and declination are -0.090′′and-0.623′′respectively based on the published JPL ephemeris, but the corresponding means(O-C) are 3.122′′and-0.636′′based on the published IMCCE ephemeris. The great difference in declination could be explained by several factors.(1) The degraded CCD images caused by the fast apparent motion of the objects lead to a reduction in positioning accuracy.(2) The poor timing system may introduce systematic errors, especially in the high speed direction.(3) The asteroid may be perturbed by Earth when it approaches the Earth too closely. These astrometric results demonstrate that the centroid centering method can reduce the dispersion of non-Gaussian images as compared with the PSF modeling *** Camillo and Midas, the astrometric results are consistent based on the two ephemerides. Implementing a high-precision timing system, and analyzing some astronomical effects and geometric distortions in CCD images should be carefully considered in future works.

关键词： astrometry:astrometric observation NEOs:individual(2017 VR12,Camillo,Midas)

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A possible explanation of W-type phenomena in V694 Peg

arXiv

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arXiv 2024年

作者： Xu, Hu-Shan Zhu, Li-Ying Physics Department Yuxi Normal University Yuxi653100 China 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 Graduate University of the Chinese Academy of Sciences Yuquan Road 19 Sijingshang Block Beijing City100049 China

Three sets of complete multi-color light curves of V694 Peg observed in 2013, 2015 and 2019 were presented and analyzed. Our photometric solutions show that this system is an A-type shallow contact binary in 2013 and 2015, while it converted to a W-type one in 2019. A large cool spot on the component of this binary could explain the conversion, implying the W-type phenomena may be caused by magnetic activity of the components. We have collected available data of this binary and calculated 505 times of light minimum, which span 17 years. The orbital period investigation based on these timings shows there is a long-term period increase at a rate of dP/dt = 4.3(± 0.3)× 10−9 d yr−1 superposed on a periodic variation with a period of 11.81(± 0.06) years. The cyclic orbital variation may be the result of magnetic activity cycles or the existence of a third body. Till now, only 8 transformed systems including V694 Peg have been reported. Compared with other converting contact systems between A-type and W-type, V694 Peg is recorded as the shortest-period one. All of these converting systems are late-type (later than F7) contact binaries with O’Connell effect and show cyclic period variation, which indicates that magnetic activity may be the reason for the conversion between the two types of contact binaries. For investigating the nature of A-type and W-type phenomena, the discovery of more converting contact binaries is essential. Copyright © 2024, The Authors. All rights reserved.

关键词： Stars

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Identification of temperature anomaly RR Lyrae stars in LAMOST survey,misclassification and binarities

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Research in Astronomy and Astrophysics 2020年第6期20卷 239-252页

作者： Lin-Jia Li Sheng-Bang Qian Jia Zhang Jia-Jia He Li-Ying Zhu Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key laboratory of the structure and evolution of celestial objects Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China

RR Lyrae stars,a well-known type of pulsating variable stars,have been known about for more than a century.A large amount of photometric data on RR Lyrae stars has been accumulated by space-and ground-based sky surveys,but the spectral data are relatively ***,the LAMOST sky survey project provides an opportunity to view them from the point of view of *** collect the atmospheric parameters of 1685 RR Lyrae stars provided by the LAMOST catalog,and carry out research by using the reliable *** find that there is a clear correlation between their Teff and pulsation periods,which is consistent with the pulsation and evolution theories of RR Lyrae *** addition,we focus on those RR Lyrae stars with abnormal *** analyzing the data from several photometric surveys,we find that some of these temperature anomalies are misclassified variable stars(e.g.,eclipsing binaries,pulsating stars on main sequence),and some are RR Lyrae binary *** the latter,the temperatures of potential companions should be lower and their luminosities should not be neglected(e.g.,red giant stars).We obtain that the ratio of temperature anomaly stars to all the sample stars is 4%,which means that the impact on the further analysis(e.g.,kinematics analysis)is *** also present the catalogs of spectral anomaly RR Lyrae stars.

关键词： techniques spectroscopic-techniques photometric-stars fundamental parameters-stars variables RR Lyrae

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Binary Population Synthesis

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Research in Astronomy and Astrophysics 2020年第10期20卷 207-220页

作者： Zhan-Wen Han Hong-Wei Ge Xue-Fei Chen Hai-Liang Chen Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China University of the Chinese Academy of Sciences Beijing 100049China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China

Binary interactions lead to the formation of intriguing objects,such as compact binaries,supernovae,gamma ray bursts,X-ray binaries,pulsars,novae,cataclysmic variables,hot subdwarf stars,barium stars and blue *** study the evolution of binary populations and the consequent formation of these objects,many methods have been developed over the years,for which a robust approach named binary population synthesis(BPS)warrants special *** approach has seen widespread application in many areas of astrophysics,including but not limited to analyses of the stellar content of galaxies,research on galactic chemical evolution and studies concerning star formation and cosmic *** this review,we discuss the role of BPS,its general picture and the various components that comprise *** pay special attention to the stability criteria for mass transfer in binaries,as this stability largely determines the fate of binary *** conclude with our perspectives regarding the future of this field.

关键词： stars evolution-star binaries(including multiple) close-stars statistics-supernovae general-galaxies stellar content-methods numerical

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Investigation of stellar magnetic activity using variational autoencoder based on low-resolution spectroscopic survey

arXiv

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arXiv 2022年

作者： Xiang, Yue Gu, Shenghong Cao, Dongtao 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

We apply the variational autoencoder (VAE) to the LAMOST-K2 low-resolution spectra to detect the magnetic activity of the stars in the K2 field. After the training on the spectra of the selected inactive stars, the VAE model can efficiently generate the synthetic reference templates needed by the spectral subtraction procedure, without knowing any stellar parameters. Then we detect the peculiar spectral features, such as chromospheric emissions, strong nebular emissions and lithium absorptions, in our sample. We measure the emissions of the chromospheric activity indicators, Hα and Ca ii infrared triplet (IRT) lines, to quantify the stellar magnetic activity. The excess emissions of Hα and Ca ii IRT lines of the active stars are correlated well to the rotational periods and the amplitudes of light curves derived from the K2 photometry. We degrade the LAMOST spectra to simulate the slitless spectra of the China Space Station Telescope (CSST) and apply the VAE to the simulated data. For cool active stars, we reveal a good agreement between the equivalent widths (EWs) of Hα line derived from the spectra with two resolutions. The result indicates the ability of identifying the magnetically active stars in the future CSST survey, which will deliver an unprecedented large database of low-resolution spectra as well as simultaneous multi-band photometry of stars. Copyright © 2022, The Authors. All rights reserved.

关键词： Stars

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