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The spectroscopic binaries from LAMOST medium-resolution survey (MRS). I. Searching for double-lined spectroscopic binaries (SB2s) with convolutional neural network

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arXiv 2021年

作者： Zhang, Bo Jing, Ying-Jie Yang, Fan Wan, Jun-Chen Ji, Xin Fu, Jian-Ning Liu, Chao Zhang, Xiao-Bin Luo, Feng Tian, Hao Zhou, Yu-Tao Wang, Jia-Xin Guo, Yan-Jun Zong, Weikai Xiong, Jian-Ping Li, Jiao Department of Astronomy Beijing Normal University Beijing100875 China Key Laboratory for Computational Astrophysics National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Kuaishou Technology Beijing100085 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Key Laboratory of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Department of Astronomy School of Physics Peking University Beijing100871 China Kavli Institute for Astronomy and Astrophysics Peking University Beijing100871 China Yunnan observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

We developed a convolutional neural network (CNN) model to distinguish the double-lined spectroscopic binaries (SB2s) from others based on single exposure medium-resolution spectra (R ∼ 7, 500). The training set consists of a large set of mock spectra of single stars and binaries synthesized based on the MIST stellar evolutionary model and ATLAS9 atmospheric model. Our model reaches a novel theoretic false positive rate by adding a proper penalty on the negative sample (e.g., 0.12% and 0.16% for the blue/red arm when the penalty parameter Λ = 16). Tests show that the performance is as expected and favors FGK-type Main-sequence binaries with high mass ratio (q ≥ 0.7) and large radial velocity separation (∆v ≥ 50 km s−1). Although the real false positive rate can not be estimated reliably, validating on eclipsing binaries identified from Kepler light curves indicates that our model predicts low binary probabilities at eclipsing phases (0, 0.5, and 1.0) as expected. The color-magnitude diagram also helps illustrate its feasibility and capability of identifying FGK MS binaries from spectra. We conclude that this model is reasonably reliable and can provide an automatic approach to identify SB2s with period ≾ 10 days. This work yields a catalog of binary probabilities for over 5 million spectra of 1 million sources from the LAMOST medium-resolution survey (MRS), and a catalog of 2198 SB2 candidates whose physical properties will be analyzed in our following-up paper. Data products are made publicly available at the journal as well as our Github website. © 2021, CC BY.

关键词： Surveys

The synchrotron polarization in decaying magnetic field in gamma-ray bursts

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arXiv 2020年

作者： Cheng, Kangfa Zhao, X.H. Bai, J.M. Yunnan Observatories Chinese Academy of Sciences Kunming China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China University of the Chinese Academy of Sciences Yuquan Road 19 Shijingshan Block Beijing100049 China

Polarization can serve as a probe of the radiation mechanism and magnetic field (MF) configuration in gamma-ray bursts (GRBs). In the case of constant MF, the synchrotron polarization in the prompt phase of GRBs has been widely studied. In this paper, we consider the case of the decaying MF. We calculate the time-averaged and instantaneous synchrotron polarizations in a pulse for different viewing angles and for the large-scale decaying MF model, which can explain the so-called Band spectrum. We find that the on-axis time-averaged polarization degree (PD) in the energy band of 50-500 keV for the decaying large-scale MF model (∼ 0.6 for typical parameters) is higher than that in the constant MF model (∼ 0.5). An interesting result is the instantaneous PD in the off-axis case will experience a turnover, i.e., the PD will evolve from a positive value to a negative one. This suggests the polarization angle (PA) change by an angle of 90◦. Such a result is roughly consistent with the discovery of the PA evolution within a pulse in some bursts, such as GRB 170114A and GRB 160821A. Our result implies at least a part of bursts (off-axis bursts) should have the PA evolution in a pulse. Copyright © 2020, The Authors. All rights reserved.

关键词： Polarization

Automatic Detection of Solar Radio Burst using K-Means Clustering

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Automatic Detection of Solar Radio Burst using K-Means Clust...

2019第十一届数字图像处理国际会议

作者： Zexiao Cui Guowu Yuan Guannan Gao Liang Dong Hao Zhou Yun Gao Shaojie Guo Min Wang School of Information Science and Engineering Yunnan University Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Observatories Chinese academy of Sciences

With the development of solar radio spectrometer,a large number of observational data has been obtained and the manual detection is difficult to reach the research *** automatic detection method of solar radio burst using kmeans clustering was presented in this paper.K-means clustering is introduced to classify the burst points in solar radio spectrum,and it can do better in high spectral and time resolution *** experimental results show that the proposed method is effective.

关键词： Solar radio bursts outlier detection K-means clustering

Black hole immersed dark matter halo

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Physical Review D 2020年第2期101卷 024029-024029页

作者： Zhaoyi Xu Xiaobo Gong Shuang-Nan Zhang Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming 650216 China University of Chinese Academy of Sciences Beijing 100049 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming 650216 China National Astronomical Observatories of China Chinese Academy of Sciences Beijing 100012 China

In this work, based on the constant for the equation of state ω, we obtain the Schwarzschild-like black hole solutions in some dark matter halos. We also generalize these black hole metrics to Kerr-like black hole solutions with Newman-Janis algorithm. For an example, we derive the specific black hole space-time metrics in the case of the cold dark matter halo and Bose-Einstein condensation dark matter halo. Following the above two black hole metrics, we discuss how a dark matter halo changes the properties of black holes, including the event horizon structure (these results agree with that obtained by Liu and Zhang [Phys. Lett. B 679, 88 (2009).] in the case of gravitational collapse), stationary limit surfaces, ergosphere, and singularity structure. Our results may help us understand the interaction between the dark matter halo and supermassive black holes at the centers of galaxies.

关键词： Alternative gravity theories Astrophysical studies of gravity

An Automatic Detection Method of Solar Radio Burst based on Otsu Binarization

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An Automatic Detection Method of Solar Radio Burst based on ...

2019第十一届数字图像处理国际会议

作者： Menglin Jin Guowu Yuan Guannan Gao Liang Dong Hao Zhou Yun Gao Shaojie Guo Min Wang School Of Information Science And Engineering Yunnan University Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Observatories Chinese Academy of Sciences

With the development of solar radio spectrometer,it is difficult to process a large number of observed data quickly by manual detection *** automatic detection method of solar radio burst based on Otsu binarization is proposed in this *** this method,channel normalization is used to denoise the original solar radio *** experimental comparison,Otsu method is selected as a binary method of solar radio spectrum,and Open and Close operations are used to smooth the binary *** show that the proposed method for automatic detection of solar radio bursts is effective.

关键词： Solar radio spectrum image denoise binarization threshold setting method

Starspot evolution, differential rotation and correlation between chromospheric and photospheric activities on kepler-411

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arXiv 2020年

作者： Xu, Fukun Gu, Shenghong Ioannidis, Panos Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Hamburger Sternwarte Universität Hamburg Gojenbergsweg 112 Hamburg21029 Germany School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing101408 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time series photometry over 4 years from Kepler, and spectroscopic data from Keck I 10-m telescope and Lijiang 2.4-m telescope. We constructed the light curve by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software PyKE3. An efficient program, GEMC_LCM, was developed to apply a two-spots model to chosen light curve segments with three spot groups at fixed latitudes (30◦, 45◦), (30◦, 60◦) and (45◦, 60◦). We found a periodic variation of the starspots at period of about 660 days which independs on spot latitudes, and estimated the lower limit of SDR as Peq = 9.7810(0.0169) days and α = 0.1016(0.0023). Simultaneously, the relative variations of chromospheric activity indicators were derived by subtracting the overall mean spectrum from individual spectrum. It is found that Ca II H and K emissions are strongly correlated with each other, and there also exists a correlation between Hα and Ca II H & K emissions, with large dispersion, in accordance with previous results. Furthermore we find the correlation between Ca II H and K emissions is different in 2011 and 2012. The chromospheric emission variation shows a highly spatial anti-correlation with the light curve, suggesting a spatial connection between the chromospheric active region and spot region. Copyright © 2020, The Authors. All rights reserved.

关键词： Chromophores

Minute-Cadence Observations of the LAMOST Fields with the TMTS: II. Catalogues of Short-Period Variable Stars from the First Two-Year Surveys

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arXiv 2023年

作者： Lin, Jie Wang, Xiaofeng Mo, Jun Xi, Gaobo Filippenko, Alexei V. Yan, Shengyu Brink, Thomas G. Yang, Yi Wu, Chengyuan Németh, Péter Li, Gaici Guo, Fangzhou Guo, Jincheng Cai, Yongzhi Xiong, Heran Zheng, WeiKang Liu, Qichun Zhang, Jicheng Jiang, Xiaojun Chen, Liyang Xia, Qiqi Peng, Haowei Chen, Zhihao Li, Wenxiong Lin, Weili Xiang, Danfeng Ma, Xiaoran Liu, Jialian Physics Department Tsinghua Center for Astrophysics Tsinghua University Beijing100084 China Beijing Planetarium Beijing Academy of Sciences and Technology Beijing100044 China Department of Astronomy University of California BerkeleyCA94720-3411 United States Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Astronomical Institute of the Czech Academy of Sciences Fričova 298 Ondřejov25165 Czech Republic *** Fő tér 1 Malomsok8533 Hungary Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Research School of Astronomy & Astrophysics Australian National University Canberra2611 Australia Department of Astronomy Beijing Normal University Beijing100875 China National Astronomical Observatories of China Chinese Academy of Sciences Beijing100012 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China The School of Physics and Astronomy Tel Aviv University Tel Aviv69978 Israel

Over the past few years, wide-field time-domain surveys like ZTF and OGLE have led to discoveries of various types of interesting short-period stellar variables, such as ultracompact eclipsing binary white dwarfs, rapidly rotating magnetised white dwarfs (WDs), transitional cataclysmic variables between hydrogen-rich and helium accretion, and blue large-amplitude pulsators (BLAPs), which greatly enrich our understandings of stellar physics under some extreme conditions. In this paper, we report the first-two-year discoveries of short-period variables (i.e., P2, which started to monitor the LAMOST sky areas since 2020 and generated uninterrupted minute-cadence light curves for about ten million sources within 2 years. Adopting the Lomb-Scargle periodogram with period-dependent thresholds for the maximum powers, we identify over 1 100 sources that exhibit a variation period shorter than 2 hr. Compiling the light curves with the Gaia magnitudes and colours, LAMOST spectral parameters, VSX classifications, and archived observations from other prevailing time-domain survey missions, we identified 1 076 as δ Scuti stars, which allows us study their populations and physical properties in the short-period regime. The other 31 sources include BLAPs, subdwarf B variables (sdBVs), pulsating WDs, ultracompact/short-period eclipsing/ellipsoidal binaries, cataclysmic variables below the period gap, etc., which are highly interesting and worthy of follow-up investigations. Copyright © 2023, The Authors. All rights reserved.

关键词： White dwarfs

An explanation for 13 consecutive days activities of Mrk 421

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arXiv 2020年

作者： Zheng, Y.G. Yang, C.Y. Kang, Shi-Ju Bai, J.M. Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Department of Physics Yunnan Normal University Kunming650092 China Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment-Shandong University Weihai264209 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences China Department of Physics and Electronics Science Liupanshui Normal University LiupanshuiGuizhou553004 China

It is surprising to find a fact for migration in the peak positions of synchrotron spectra energy distribution component during in the activity epochs of Mrk 421, accompanying with an orphan flaring at the X-ray and GeV-TeV γ-ray bands. A geometric interpretation and standard shock or stochastic acceleration models of blazar emission have difficulty reproducing these observed behaviours. The present paper introduces a linear acceleration by integrating the reconnection electric field into the particle transport model for the observed behaviours of Mrk 421. We note that the strong evidence for evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency, accompanying with an orphan flaring at the X-ray and GeV-TeV γ-ray bands provides an important electrostatic acceleration diagnostic in blazar jet. Assuming suitable model parameters, we apply the results of the simulation to the 13-day flaring event in 2010 March of Mrk 421, concentrating on the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency. It is clear that the ratio of the electric field and magnetic field strength plays an important role in temporal evolution of the peak frequency of synchrotron spectral energy distribution component. We suggest the electrostatic acceleration responsible for the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency is reasonable. Based on the model results, we issue that the peak frequency of the synchrotron spectral energy distribution component may denote a temporary characteristic of blazars, rather than a permanent one. Copyright © 2020, The Authors. All rights reserved.

关键词： Spectroscopy

Morpho-Photometric Classification of KiDS DR5 Sources Based on Neural Networks: A Comprehensive Star-Quasar-Galaxy Catalog

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arXiv 2024年

作者： Feng, Hai-Cheng Li, Rui Napolitano, Nicola R. Li, Sha-Sha Bai, J.M. Li, Ran Liu, H.T. Lu, Kai-Xing Radovich, Mario Shan, Huan-Yuan Wang, Jian-Guo Xi, Wen-Zhe Xie, Ling-Hua Zhang, Yang-Wei Yunnan Observatories Chinese Academy of Sciences Yunnan Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Key Laboratory of Radio Astronomy and Technology Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100101 China Institude for Astrophysics School of Physics Zhengzhou University Zhengzhou450001 China School of Physics and Astronomy Sun Yat-sen University Zhuhai Campus 2 Daxue Road Xiangzhou District Zhuhai China CSST Science Center for Guangdong-Hong Kong-Macau Great Bay Area Zhuhai519082 China INAF Osservatorio Astronomico di Capodimonte Salita Moiariello 16 Napoli80131 Italy University of Chinese Academy of Sciences Beijing100049 China National Astronomical Observatories Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China INAF Osservatorio Astronomico di Padova via dell’Osservatorio 5 Padova35122 Italy Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai200030 China South-Western Institute for Astronomy Research Yunnan University Kunming650500 China

We present a novel multimodal neural network for classifying astronomical sources in multiband ground-based observations, from optical to near infrared, to separate sources in stars, galaxies and quasars. Our approach combines a convolutional neural network branch for learning morphological features from r-band images with an artificial neural network branch for extracting spectral energy distribution (SED) information. Specifically, we have used 9-band optical (ugri) and NIR (ZY HJKs) data from the Kilo-Degree Survey (KiDS) Data Release 5. The two branches of the network are concatenated and feed into fully-connected layers for final classification. We train the network on a spectroscopically confirmed sample from the Sloan Digital Sky Survey cross-matched with KiDS. The trained model achieves 98.76% overall accuracy on an independent testing dataset, with F1 scores exceeding 95% for each class. Raising the output probability threshold, we obtain higher purity at the cost of a lower completeness. We have also validated the network using external catalogs cross-matched with KiDS, correctly classifying 99.74% of a pure star sample selected from Gaia parallaxes and proper motions, and 99.74% of an external galaxy sample from the Galaxy and Mass Assembly survey, adjusted for low-redshift contamination. We apply the trained network to 27,334,751 KiDS DR5 sources with r ≤ 23 mag to generate a new classification catalog. This multimodal neural network successfully leverages both morphological and SED information to enable efficient and robust classification of stars, quasars, and galaxies in large photometric surveys. © 2024, CC BY.

关键词： Classification (of information)