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Unveiling Bifurcated Blue Straggler Sequences in NGC 2173: Insights from Binary evolution

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arXiv 2025年

作者： Wang, Li Jiang, Dengkai Li, Chengyuan Deng, Licai Milone, Antonino P. Wang, Long School of Physics and Astronomy Sun Yat-sen University Daxue Road Zhuhai519082 China CSST Science Center for the Guangdong–Hong Kong–Macau Greater Bay Area Zhuhai519082 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 Kunming650011 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for 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 Department of Astronomy School of Physics and Astronomy China West Normal University Nanchong637002 China Dipartimento di Fisica e Astronomia "Galileo Galilei" Univ. di Padova Vicolo dell’Osservatorio 3 PadovaIT-35122 Italy Istituto Nazionale di Astrofisica Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5 PadovaIT-35122 Italy

Identifying bifurcated blue straggler (BS) sequences in color-magnitude diagrams (CMDs) of star clusters has long been regarded as a powerful diagnostic for distinguishing different BS formation mechanisms. While such bifurcations are typically associated with core-collapsed clusters, their detection in dynamically young clusters raises new questions about their origins. In this study, using high-precision proper motion data derived from Hubble Space Telescope multi-epoch observations, we confirm the existence of two distinct BS sequences in the Large Magellanic Cloud cluster NGC 2173 (∼ 1.58 Gyr): a well-defined, narrow blue sequence and a sparser red sequence. The extended core region excludes collisional formation as a viable channel for BS formation. Our binary evolution models suggest that non-conservative mass transfer (MT) is essential for shaping the distribution of BS binaries in the CMD. The red sequence primarily comprises BS binaries formed through conservative ongoing MT. In contrast, the blue sequence BS binaries are formed through non-conservative post-MT processes, all involving white dwarf (WD) companions. These BS+WD binary systems may subsequently undergo a second MT phase, leading to the formation of double WD systems. © 2025, CC BY.

关键词： White dwarfs

Studies of extragalactic background light with TeV BL Lac objects

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arXiv 2020年

作者： Qin, Longhua Wang, Jiancheng Gao, Quangui Na, Weiwei Li, Huaizhen Ma, Ju Yang, Jianping Physics Department Yuxi Normal University YuxiYunnan653100 China Yunnan Observatory Chinese Academy of Sciences KunmingYunnan650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences KunmingYunnan650011 China Yunnan Agricultural University KunmingYunnan650201 China

Very high energy (VHE;E ≽ 100GeV) γ−ray from cosmological distances are attenuated by the extragalactic background light (EBL) in the IR to UV band. By contrasting measured versus intrinsic emission, the EBL photon density can be derived. However, neither the intrinsic spectra nor the EBL is separately known - except their combined effect. Here we first present a flexible model-dependent optical depth method to study EBL by fitting the emission spectra of TeV BL Lacs objects via a one-zone leptonic synchrotron self-Compton model (SSC). We have little information about electron energy distributions (EEDs) in the jet, which is critically important to build spectral energy distributions (SEDs) in SSC scenario. Based on the current particle acceleration models, we use two types of EEDs, i,e., a power-law log-parabola (PLLP) EED and a broken power-law (BPL) EED to fit the observed spectra. We obtain that the upper limits of EBL density are around about 30 n W m−2 sr−1, which are similar to the published measurement. Furthermore, we propose an unprecedented method to test radiation mechanisms involved in TeV objects by simply comparing the reduced EBL density with the limit obtained by galaxy counts, and demonstrate that for some BL Lacs, at least, the one-zone SSC model should be reconsidered. Copyright © 2020, The Authors. All rights reserved.

关键词： Gamma rays

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

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

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

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