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arXiv 2022年

作者： Yuan, Zunli Zhang, Xibin Wang, Jiancheng Cheng, Xiangming Wang, Wenjie Department of Physics School of Physics and Electronics Hunan Normal University Changsha410081 China Key Laboratory of Low Dimensional Quantum Structures and Quantum Control Hunan Normal University Changsha410081 China Department of Econometrics and Business Statistics Monash University Australia Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China

We propose a generalization of our previous KDE (kernel density estimation) method for estimating luminosity functions (LFs). This new upgrade further extend the application scope of our KDE method, making it a very flexible approach which is suitable to deal with most of bivariate LF calculation problems. From the mathematical point of view, usually the LF calculation can be abstracted as a density estimation problem in the bounded domain of {Z1 2, L > flim(z)}. We use the transformation-reflection KDE method (φ) to solve the problem, and introduce an approximate method (φ1) based on one-dimensional KDE to deal with the small sample size case. In practical applications, the different versions of LF estimators can be flexibly chosen according to the Kolmogorov-Smirnov test criterion. Based on 200 simulated samples, we find that for both cases of dividing or not dividing redshift bins, especially for the latter, our method performs significantly better than the traditional binning method φbin. Moreover, with the increase of sample size n, our LF estimator converges to the true LF remarkably faster than φbin. To implement our method, we have developed a public, open-source Python Toolkit, called kdeLF. With the support of kdeLF, our KDE method is expected to be a competitive alternative to existing nonparametric estimators, due to its high accuracy and excellent stability. kdeLF is available at http://***/yuanzunli/kdeLF with extensive documentation available at http://***/en/latest . Copyright © 2022, The Authors. All rights reserved.

关键词： High level languages

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A New Stellar Spectral Feature Extraction Method Based on Two-dimensional Fourier Spectrum Image and Its Application in the Stellar Spectral Classification Based on Deep Network

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Chinese Astronomy and Astrophysics 2020年第3期44卷 334-344页

作者： Jing-min, ZHANG Chen-ye, M.A. Lu, Wang Li-ting, Du Ting-ting, X.U. Lin-pin, Ai Wei-hong, Z.H.O.U. School of Mathematics and Computer Sciences Yunnan Minzu University Kunming 650500 School of Economics and Business Administration Yunnan Vocational and Technical Collage of Agriculture Kunming 650031 School of Physics and Electronic Engineering Guangzhou University Guangzhou510006 Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011

The classification of celestial spectra is one of the important contents of astronomical research. The key is to select and extract the most effective feature for classification from spectra data. In this paper, we propose a new feature extraction method for astronomical spectra based on two-dimensional Fourier spectrum image, and apply the method to the classification study of LAMOST (the Large Sky Area Multi-object Fiber Spectroscopic Telescope) stellar spectral data. The spectra data are from LAMOST Data Release 5 (DR5). We select 30000 F, G, and K types of spectra data. The short-time Fourier transform (STFT) is used to transform the one-dimensional spectra data into two-dimensional Fourier spectrum images. We classify and test these two-dimensional Fourier spectrum images with a module based on deep convolution network, and the classification accuracy rate is 92.90%. The experimental result shows that the LAMOST stellar spectra data can be transformed into the two-dimensional Fourier spectrum images by the STFT. These spectral images inform new features, and build a new feature space, which is effective for classification. The method is a fully new attempt in spectra classification, which has certainly a pioneering significance for the classification and mining of massive celestial spectra. © 2020

关键词： Methods: data analysis Stars: fundamental parameters techniques: spectral analysis

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Formation of accreting millisecond X-ray pulsars

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Research in Astronomy and Astrophysics 2019年第8期19卷 45-55页

作者： Xiang He Xiang-Cun Meng Hai-Liang Chen Yunnan Observatories Chinese Academy of SciencesKunming650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming650216China University of Chinese Academy of Sciences Beijing100049China

Accreting millisecond X-ray pulsars(AMXPs) are an important subclass of low-mass X-ray binaries(LMXBs), in which coherent millisecond X-ray pulsations can be observed during outburst *** have dual characteristics of LMXBs and millisecond pulsars, providing a direct confirmation for the recycling scenario. However, their formation is not well understood. In this work, we simulate the evolution of LMXBs with the MESA code to explore the formation and evolution of AMXPs. Based on the binary evolutionary model of LMXBs and the model of accretion disk instability, we find that most of the observed AMXPs can be produced from LMXBs with orbital periods at the onset of Roche lobe overflow close to the bifurcation period and their observed properties can be explained by our models. The AMXPs with main sequence(MS) donors ultimately evolve into AMXPs with extremely low-mass He white dwarf ***, our results indicate that these AMXPs with MS donors are likely to have donor stars near the terminal-age main sequence.

关键词： binaries:close stars:evolution stars:neutron X-ray:binaries

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r-process Abundance Patterns in the Globular Cluster M92

arXiv

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arXiv 2023年

作者： Kirby, Evan N. Ji, Alexander P. Kovalev, Mikhail Department of Physics and Astronomy University of Notre Dame 225 Nieuwland Science Hall Notre DameIN46556 United States Department of Astronomy & Astrophysics University of Chicago 5640 S Ellis Avenue ChicagoIL60637 United States Kavli Institute for Cosmological Physics University of Chicago ChicagoIL60637 United States Yunnan Observatories China Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

Whereas light element abundance variations are a hallmark of globular clusters, there is little evidence for variation in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-capture dispersion in M92. We conducted an analysis of archival Keck/HIRES spectra of 35 stars in M92, 29 of which are giants, which we use exclusively for our conclusions. M92 conforms to the light element abundance variations typical of massive clusters. Like other globular clusters, its neutron-capture abundances were generated by the r-process. We confirm a star-to-star dispersion in the r-process. Unlike M15, the dispersion is limited to "first-generation" (low Na, high Mg) stars, and the dispersion is smaller for Sr, Y, and Zr than for Ba and the lanthanides. This is the first detection of a relation between light element and neutron-capture abundances in a globular cluster. We propose that a source of the main r-process polluted the cluster shortly before or concurrently with the first generation of star formation. The heavier r-process abundances were inhomogeneously distributed while the first-generation stars were forming. The second-generation stars formed after several crossing times (∼ 0.8 Myr);hence, the second generation shows no r-process dispersion. This scenario imposes a minimum temporal separation of 0.8 Myr between the first and second generations. © 2023, CC BY-NC-SA.

关键词： Stars

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Full-frame data reduction method: A data mining tool to detect the potential variations in optical photometry

arXiv

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arXiv 2023年

作者： Dai, Zhi-Bin Zhou, Hao Cao, Jin 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 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Yuquan Road Shijingshan District Beijing100049 China School of Information Science and Engineering of Yunnan University South Section East Outer Ring Road Chenggong District Kunming650500 China

A Synchronous Photometry Data Extraction (SPDE) program, performing indiscriminate monitors of all stars appearing at the same field of view of astronomical image, is developed by integrating several Astropy affiliated packages to make full use of time series observed by the traditional small/medium aperture ground-based telescope. The complete full-frame stellar photometry data reductions implemented for the two time series of cataclysmic variables: RX J2102.0+3359 and Paloma J0524+4244 produce 363 and 641 optimal light curves, respectively. A cross-identification with the SIMBAD finds 23 known stars, of which 16 red giant-/horizontal-branch stars, 2 W UMa-type eclipsing variables, 2 program stars, a X-ray source and 2 Asteroid Terrestrial-impact Last Alert System variables. Based on the data productions of the SPDE program, a followup Light Curve Analysis (LCA) program identifies 32 potential variable light curves, of which 18 are from the time series of RX J2102.0+3359, and 14 are from that of Paloma J0524+4244. They are preliminarily separated into periodical, transient, and peculiar types. By querying for the 58 VizieR online data catalogs, their physical parameters and multi-band brightness spanning from X-ray to radio are compiled for future analysis. Copyright © 2023, The Authors. All rights reserved.

关键词： Photometry

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Multi-epoch spectroscopy of Mg II broad absorption line transitions

arXiv

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arXiv 2021年

作者： Yi, Weimin Timlin, John Yunnan Observatories Kunming650216 China Department of Astronomy & Astrophysics The Pennsylvania State University 525 Davey Lab University ParkPA16802 United States Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

Built upon a sample of 134 quasars that was dedicated to a systematic study of Mg ii-BAL variability from Yi et al. (2019a), we investigate these quasars showing Mg ii-BAL disappearance or emergence with the aid of at least three epoch optical spectra sampled more than 15 yr in the observed frame. We identified 3/3 quasars undergoing pristine/tentative BAL transformations. The incidence of pristine BAL transformations in the sample is therefore derived to be 2.2+2−122%, consistent with that of high-ionization BAL transformations from the literature. Adopting an average Mg ii-BAL disappearance timescale of rest-frame 6.89 yr among the six quasars, the average characteristic lifetime of Mg ii BALs in the sample is constrained to be >160 yr along our line of sight. There is a diversity of BAL-profile variability observed in the six quasars, probably reflecting a variety of mechanisms at work. Our investigations of Mg ii-BAL transitions, combined with observational studies of BAL transitions from the literature, imply an overall FeLoBAL/LoBAL→HiBAL/non-BAL transformation sequence along with a decrease in reddening. This sequence is consistent with the evacuation models for the origin of commonly seen blue quasars, in which LoBAL quasars are in a shorted-lived, blowout phase. © 2021, CC BY-NC-SA.

关键词： Galaxies

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Helium enrichment during classical nova outbursts

arXiv

引用

arXiv 2021年

作者： Guo, Yunlang Wu, Chengyuan Wang, Bo Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Tsinghua University Beijing100084 China

Nova outbursts play an important role in the chemical evolution of galaxies, especially they are the main source of synthetic 13C, 15N, 17O and some radioactive isotopes like 22Na and 26Al. The enrichment of He in nova ejecta indicates that the accreted material may mix with the He-shell (He-mixing). The purpose of this work is to investigate how the He-mixing affects the nova outbursts in a systematic way. We evolved a series of accreting WD models, and found that the mass fraction of H and He in nova ejecta can be influenced by different He-mixing fractions significantly. We also found that both the nova cycle duration and ejected mass increase with the He-mixing fractions. Meanwhile, the nuclear energy generation rate of p-p chains decreases with the He-mixing fraction during the nova outbursts, whereas the CNO-cycle increases. The present work can reproduce the chemical abundances in the ejecta of some representative novae, such as GQ Mus, ASASSN-18fv, HR Del, T Aur and V443 Sct. This implies that the He-mixing process cannot be neglected when studying nova outbursts. This study also develops a He-mixing meter (i.e. He/H) that can be used to estimate the He-mixing fraction in classical nova systems. © 2021, CC0.

关键词： Mixing

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Convective Mixing: The Formation Channel of Li-rich Giants

arXiv

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arXiv 2024年

作者： Li, Xue-Feng Shi, Jian-Rong Li, Yan Yan, Hong-Liang Zhang, Jing-Hua Yunnan Observatories Chinese Academy of Sciences P.O.Box 110 Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China CAS Key Laboratory of Optical Astronomy National Astronomical Observatories Beijing100101 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O.Box 110 Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China South-Western Institute for Astronomy Research Yunnan University Chenggong District Kunming650500 China

Increasing observed data indicate that part of giants has abnormally high lithium (Li) inside their surface, and their proportion is around 1%. Instead of pursuing the feasible mechanisms for extra Li enrichment, we focus on how to inhibit Li depletion from the main sequence (MS) phase of giants. With this in mind, we find that convective mixing is capable of achieving this goal and forming Li-rich giants, which is mainly attributed to the convection model with the convective boundary defined by the Ledoux criterion. Another factor in the formation of Li-rich giants in our convection models is related to the Li abundances of their progenitors. If the Li abundances of the progenitors exceed the meteoritic value (3.3 dex), then the majority of giants will be rich in Li. This is the general pattern of stellar Li abundance evolution without factoring in extra Li depletion. We propose that other Li depletion processes should also be adopted in the future, as they may be the key to the 1% puzzle. Copyright © 2024, The Authors. All rights reserved.

关键词： Mixing

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Measuring the virial factor in SDSS DR5 quasars with redshifted Hβ and Fe II broad emission lines

arXiv

引用

arXiv 2022年

作者： Liu, H.T. Feng, Hai-Cheng Li, Sha-Sha Bai, J.M. 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 Yunnan Kunming650011 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Beijing Chaoyang District100012 China University of Chinese Academy of Sciences Beijing100049 China

Under the hypothesis of gravitational redshift induced by the central supermassive black hole, and based on line widths and shifts of redward shifted Hβ and Fe II broad emission lines for a sample of 1973 z © 20... 详细信息

关键词： Galaxies

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Type Ia supernova ejecta-donor interaction: explosion model comparison

arXiv

引用

arXiv 2022年

作者： McCutcheon, C. Zeng, Y. Liu, Z.-W. Izzard, R.G. Pan, K.-C. Chen, H.-L. Han, Z. Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Astrophysics Research Group Faculty of Engineering and Physics University of Surrey GuildfordGU2 7XH United Kingdom University of Chinese Academy of Sciences Beijing100049 China Department of Physics Institute of Astronomy National Tsing Hua University Hsinchu30013 Taiwan

In the single-degenerate scenario of Type Ia supernovae (SNe Ia), the interaction between high-speed ejected material and the donor star in a binary system is expected to lead to mass being stripped from the donor. A series of multi-dimensional hydrodynamical simulations of ejecta-donor interaction have been performed in previous studies most of which adopt either a simplified analytical model or the W7 model to represent a normal SN Ia explosion. Whether different explosion mechanisms can significantly affect the results of ejecta-donor interaction is still unclear. In this work, we simulate hydrodynamical ejecta interactions with a main-sequence (MS) donor star in two dimensions for two near-Chandrasekhar-mass explosion models of SNe Ia, the W7 and N100 models. We find that about 0.30 and 0.37 Mo of hydrogen-rich material are stripped from a 2.5 Mo donor star in a 2 day orbit by the SN Ia explosion in simulations with the W7 deflagration and N100 delayed-detonation explosion model, respectively. The donor star receives a kick of about 74 and 86 km s−1, respectively, in each case. The modal velocity, about 500 km s−1, of stripped hydrogen-rich material in the N100 model is faster than the W7 model, with modal velocity of about 350 km s−1, by a factor 1.4. Based on our results, we conclude that the choice of near-Chandrasekhar-mass explosion model for normal SNe Ia seems to not significantly alter the ejecta-donor interaction for a given main-sequence donor model, at least in 2D. Copyright © 2022, The Authors. All rights reserved.

关键词： Explosions

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