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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

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

Testing Colour-magnitude Pattern as A Method in the Search for Changing-Look AGNs

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arXiv 2024年

作者： Zhu, Li-Tao Wang, Zhongxiang Devanand, P.U. Gupta, Alok C. Dogra, Karan Li, Jie Zhang, Ju-Jia Ji, Shun-Hao Sun, Si-Si Department of Astronomy School of Physics and Astronomy Yunnan University Kunming650091 China Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai200030 China Manora Peak Nainital263001 India Department of Applied Physics/Physics Mahatma Jyotiba Phule Rohilkhand University Bareilly243006 India Key Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei230036 China School of Astronomy and Space Science University of Science and Technology of China Hefei230026 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

We develop a simple method to search for changing-look (CL) active galactic nucleus (AGN) candidates, and conduct a test run. In this method, optical variations of AGNs are monitored and CL-AGNs may appear to have a pattern of being bluer when in brightening flare-like events. Applying this method, previously-classified type 2 AGNs that show the bluer-when-brighter (BWB) pattern are selected. Among more than ten thousands type 2 AGNs classified in the Sloan Digital Sky Survey (SDSS), we find 73 candidates with possibly the strongest BWB pattern. We note that 13 of them have previously been reported as CL-AGNs. We have observed nine candidates, and found that five among them showed the CL transition from type 2 to type 1. In addition, we also test extending the selection to previously-classified type 1 AGNs in the SDSS by finding sources with a possible redder-when-brighter pattern, but none of the three sources observed by us is found to show the transition from type 1 to type 2. We discuss the variation properties in both the success and failure cases, and plan to observe more candidates selected with the method. From the observational results, a detailed comparison between the CL-AGNs and none CL-AGNs will help quantitatively refine the selection criteria and in turn allow us to configure the general properties of CLAGNs. © 2024, CC BY.

关键词： Active Galactic Nuclei

Multi-epoch spectroscopy of Mg II broad absorption line transitions

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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

r-process Abundance Patterns in the Globular Cluster M92

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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

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

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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

The Coude Echelle Spectrograph for the Lijiang 1.8 m telescope

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Research in Astronomy and Astrophysics 2020年第3期20卷 76-83页

作者： Xiao-Li Wang Liang Chang Lei Wang Hang-Xin Ji Hao Xian Zhen Tang Yu-Xin Xin Chuan-Jun Wang Shou-Sheng He Ju-Jia Zhang Bao-Li Lun Kai Wei Xi-Qi Li Xiao-Jun Jiang Hui-Juan Wang Hong-Bin Li Ji-Rong Mao Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China Nanjing Institute of Astronomical Optics&Technology National Astronomical ObservatoriesChinese Academy of SciencesNanjing 210042China The Institute of Optics and Electronics Chinese Academy of SciencesChengdu 610209China Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of ScienccsBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China

The Coude Echelle Spectrograph(CES)was originally mounted on Xinglong 2.16 m telescope in *** the High Resolution Fiber-fed Spectrograph(HRS)was commissioned at Xinglong 2.16 m telescope,the red path of CES was moved to Lijiang 1.8 m telescope,following some redesign and *** CES of Lijiang 1.8 m telescope has the spectral resolution(R=λ/?λ)ranging from 20000 to 50000 corresponding to different slit *** a 2 k×2 k PI CCD,CES has a wavelength coverage between 570 nm to 1030 *** particular,the resolution of 37000 at 0.5 mm slit corresponds to 1.3′′on the *** limiting magnitude is V=11.5 with the use of the tip-tilt feedback system,and the S/N is about 40 for 1 hour exposure at 600 nm(R=37000).During the installation of CES,the tip-tilt mirror technology had successfully fulfilled high precision guiding and tracking for high resolution spectral observation and significantly improved the observation efficiency.

关键词： Instrumentation:spectrographs methods:observational techniques:spectroscopic

Helium enrichment during classical nova outbursts

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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

Physical properties of hyperluminous, dust-obscured quasars at z ∼ 3: multiwavelength Spectral Energy Distribution analysis and cold gas content revealed by ALMA

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arXiv 2024年

作者： Sun, Weibin Fan, Lulu Han, Yunkun Knudsen, Kirsten K. Chen, Guangwen Zhang, Hong-Xin CAS Key Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei230026 China School of Astronomy and Space Science University of Science and Technology of China Hefei230026 China Deep Space Exploration Laboratory Hefei230088 China 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 Department of Space Earth and Environment Chalmers University of Technology Onsala Space Observatory OnsalaSE-439 92 Sweden

We present a UV to millimeter spectral energy distribution (SED) analysis of 16 hyperluminous, dust-obscured quasars at z ∼ 3, selected by the Wide-field Infrared Survey Explorer. We aim to investigate the physical properties of these quasars, with a focus on their molecular gas content. We decompose the SEDs into three components: stellar, cold dust, and active galactic nucleus (AGN). By doing so, we are able to derive and analyze the relevant properties of each component. We determine the molecular gas mass from CO line emission based on Atacama Large Millimeter/submillimeter Array (ALMA) observations. By including ALMA observations in the multiwavelength SED analysis, we derive the molecular gas fractions, gas depletion timescales, and star formation efficiencies (SFEs). Their sample median and 16th-84th quartile ranges are fgas ∼ 0.33+0.33−0.17, tdepl ∼ 39+85−28 Myr, SFE ∼ 297+659−195 K km s−1 pc−2. Compared to main-sequence galaxies, they have a lower molecular gas content and higher SFEs, similar to quasars in the literature. This suggests that the gas in these quasars is rapidly depleted, likely as the result of intense starburst activity and AGN feedback. The observed correlations between these properties and the AGN luminosities further support this scenario. Additionally, we infer the black hole to stellar mass ratio and black hole mass growth rate, which indicate a significant central black hole mass assembly over short timescales. Our results are consistent with the scenario that our sample represents a short transition phase toward unobscured quasars. Copyright © 2024, The Authors. All rights reserved.

关键词： Physical properties