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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

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

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

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

A Roche Lobe-filling hot Subdwarf and White Dwarf Binary: possible detection of an ejected common envelope

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arXiv 2022年

作者： Li, Jiangdan Onken, Christopher A. Wolf, Christian Németh, Péter Bessell, Mike Li, Zhenwei Zhang, Xiaobin Li, Jiao Wang, Luqian Li, Lifang Luo, Yangping Chen, Hailiang Ji, Kaifan Chen, Xuefei Han, Zhanwen 396 Yangfangwang Guandu District Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650011 China University of Chinese Academy of Sciences Beijing100049 China Research School of Astronomy and Astrophysics Australian National University Weston CreekACT2611 Australia Centre for Gravitational Astrophysics Australian National University CanberraACT2600 Australia Astronomical Institute of the Czech Academy of Sciences OndřejovCZ-25165 Czech Republic *** Fő tér 1 Malomsok8533 Hungary Key Laboratory of Optical Astronomy National Astronomical Observatories CAS Beijing100012 China Key Lab of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Department of Astronomy China West Normal University Nanchong637002 China

Binaries consisting of a hot subdwarf star and an accreting white dwarf (WD) are sources of gravitational wave radiation at low frequencies and possible progenitors of type Ia supernovae if the WD mass is large enough. Here, we report the discovery of the third binary known of this kind: it consists of a hot subdwarf O (sdO) star and a WD with an orbital period of 3.495 hours and an orbital shrinkage of 0.1 s in 6 yr. The sdO star overfills its Roche lobe and likely transfers mass to the WD via an accretion disk. From spectroscopy, we obtain an effective temperature of Teff = 54 240 ± 1 840 K and a surface gravity of log g = 4.841 ± 0.108 for the sdO star. From the light curve analysis, we obtain a sdO mass of MsdO = 0.55 M☉ and a mass ratio of q = MWD/MsdO = 0.738 ± 0.001. Also, we estimate that the disk has a radius of ∼ 0.41R☉ and a thickness of ∼ 0.18R☉. The origin of this binary is probably a common envelope ejection channel, where the progenitor of the sdO star is either an RGB star or, more likely, an early AGB star;the sdO star will subsequently evolve into a WD and merge with its WD companion, likely resulting in an R CrB star. The outstanding feature in the spectrum of this object is strong Ca H&K lines, which are blueshifted by ∼200 km/s and likely originate from the recently ejected common envelope, and we estimated that the remnant CE material in the binary system has a density ∼ 6 × 10−10g/cm3 Copyright © 2022, The Authors. All rights reserved.

关键词： White dwarfs

Synchrotron Radiation Dominates the Extremely Bright GRB 221009A

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arXiv 2023年

作者： Yang, Jun Zhao, Xiao-Hong Yan, Zhenyu Wang, Xiangyu Ivy Zhang, Yan-Qiu An, Zheng-Hua Cai, Ce Li, Xin-Qiao Li, Zihan Liu, Jia-Cong Liu, Zi-Ke Ma, Xiang Meng, Yan-Zhi Peng, Wen-Xi Qiao, Rui Shao, Lang Song, Li-Ming Tan, Wen-Jun Wang, Ping Wang, Chen-Wei Wen, Xiang-Yang Xiao, Shuo Xue, Wang-Chen Yang, Yu-Han Yin, Yihan Zhang, Bing Zhang, Fan Zhang, Shuai Zhang, Shuang-Nan Zheng, Chao Zheng, Shi-Jie Xiong, Shao-Lin Zhang, Bin-Bin School of Astronomy and Space Science Nanjing University Nanjing210093 China Key Laboratory of Modern Astronomy and Astrophysics Nanjing University Ministry of Education China 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 Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences 19B Yuquan Road Beijing100049 China University of Chinese Academy of Sciences Beijing100049 China College of Physics Hebei Key Laboratory of Photophysics Research and Application Hebei Normal University Hebei Shijiazhuang050024 China College of Physics Hebei Normal University Shijiazhuang050024 China Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing Guizhou Normal University Guiyang550001 China Department of Physics University of Rome "Tor Vergata" via della Ricerca Scientifica 1 RomeI-00133 Italy School of Physics Nanjing University Nanjing210093 China Department of Physics and Astronomy University of Nevada Las Vegas NV89154 United States Purple Mountain Observatory Chinese Academy of Sciences Nanjing210023 China

The brightest Gamma-ray burst, GRB 221009A, has spurred numerous theoretical investigations, with particular attention paid to the origins of ultra-high energy TeV photons during the prompt phase. However, analyzing the mechanism of radiation of photons in the ∼MeV range has been difficult because the high flux causes pile-up and saturation effects in most GRB detectors. In this letter, we present systematic modeling of the time-resolved spectra of the GRB using unsaturated data obtained from Fermi/GBM (precursor) and SATech-01/GECAM-C (main emission and flare). Our approach incorporates the synchrotron radiation model, which assumes an expanding emission region with relativistic speed and a global magnetic field that decays with radius, and successfully fits such a model to the observational data. Our results indicate that the spectra of the burst are fully in accordance with a synchrotron origin from relativistic electrons accelerated at a large emission radius. The lack of thermal emission in the prompt emission spectra supports a Poynting-flux-dominated jet composition. Copyright © 2023, The Authors. All rights reserved.

关键词： Synchrotron radiation

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

Flares hunting in hot subdwarf and white dwarf stars from Cycles 1-5 of TESS photometry

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arXiv 2024年

作者： Xing, Keyu Zong, Weikai Silvotti, Roberto Fu, Jian-Ning Charpinet, Stéphane Cang, Tianqi Hermes, J.J. Ma, Xiao-Yu Wang, Haotian Wang, Xuan Wu, Tao Wang, Jiaxin Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China Department of Astronomy Beijing Normal University Beijing100875 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China INAF-Osservatorio Astrofisico di Torino strada dell’Osservatorio 20 Pino TorineseI-10025 Italy Institut de Recherche en Astrophysique et Planétologie CNRS Université de Toulouse CNES 14 Avenue Edouard Belin ToulouseF-31400 France Department of Astronomy Institute for Astrophysical Research Boston University 725 Commonwealth Avenue BostonMA02215 United States 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 Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China College of Science Chongqing University of Posts and Telecommunications Chongqing400065 China

Stellar flares are critical phenomena on stellar surfaces, which are closely tied to stellar magnetism. While extensively studied in main-sequence (MS) stars, their occurrence in evolved compact stars, specifically hot subdwarfs and white dwarfs (WDs), remains scarcely explored. Based on Cycles 1-5 of TESS photometry, we conducted a pioneering survey of flare events in ∼12 000 compact stars, corresponding to ∼38 000 light curves with 2-minute cadence. Through dedicated techniques for detrending light curves, identifying preliminary flare candidates, and validating them via machine learning, we established a catalog of 1016 flares from 193 compact stars, including 182 from 58 sdB/sdO stars and 834 from 135 WDs, respectively. However, all flaring compact stars showed signs of contamination from nearby objects or companion stars, preventing sole attribution of the detected flares. For WDs, it is highly probable that the flares originated from their cool MS companions. In contrast, the higher luminosities of sdB/sdO stars diminish companion contributions, suggesting that detected flares originated from sdB/sdO stars themselves or through close magnetic interactions with companions. Focusing on a refined sample of 23 flares from 13 sdB/sdO stars, we found their flare frequency distributions were slightly divergent from those of cool MS stars;instead, they resemble those of hot B/A-type MS stars having radiative envelopes. This similarity implies the flares on sdB/sdO stars, if these flares did originate from them, may share underlying mechanisms with hot MS stars, which warrants further investigation. © 2024, CC BY.

关键词： Machine learning

A temperate 10-Earth-mass exoplanet around the Sun-like star Kepler-725

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Nature Astronomy 2025年 1-11页

作者： L. Sun S. Gu X. Wang J. H. M. M. Schmitt P. Ioannidis M. B. N. Kouwenhoven J. Dou G. Zhao Yunnan Observatories Chinese Academy of Sciences Kunming China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China International Centre of Supernovae Yunnan Key Laboratory Kunming China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing China Hamburger Sternwarte Universität Hamburg Hamburg Germany Department of Physics School of Mathematics and Physics Xi’an Jiaotong-Liverpool University Suzhou China Nanjing Institute of Astronomical Optics & Technology Chinese Academy of Sciences Nanjing China CAS Key Laboratory of Astronomical Optics & Technology Nanjing Institute of Astronomical Optics & Technology Nanjing China

The detection of low-mass exoplanets (≤10 Earth masses (M⊕)) yields fundamental inputs for current theories of planet formation and evolution, and supplies critical information for the planned direct-imaging missions that aim to detect and characterize Earth-like planets in the habitable zones around solar-like stars. However, the most efficient detection techniques available for low-mass exoplanets (that is, photometric transit and radial velocity methods) are heavily biased towards the detection of short-period planets (for example, ≤100 days) and strongly favour late-type stars. Here we report the discovery of Kepler-725 c, a 10 ± 3M⊕exoplanet within the habitable zone of the late G-type dwarf Kepler-725. Through analysis of the transit timing variations of the relatively short-period (39.64 days) warm Jupiter Kepler-725 b, we find that Kepler-725 c has a period of 207.5 days and travels in an eccentric orbit (with an eccentricity of 0.44 ± 0.02 and an orbital semi-major axis of 0.674 ± 0.002 au), receiving a time-averaged insolation of 1.4 times the Earth’s value. This discovery demonstrates that the transit timing variation method enables the detection and accurate mass measurement of a super-Earth/mini-Neptune within a solar-like star’s habitable zone. Similar searches for such exoplanets could be conducted in other exoplanetary systems in the era of the Transiting Exoplanet Survey Satellite mission and upcoming PLAnetary Transits and Oscillations of stars and Earth 2.0 missions.

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