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Doppler imaging and differential rotation of σ2Coronae Borealis using SONG

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arXiv 2020年

作者： Xiang, Yue Gu, Shenghong Collier Cameron, A. Barnes, J.R. Christensen-Dalsgaard, J. Grundahl, F. Antoci, V. Andersen, M.F. Pallé, P.L. Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China School of Astronomy and Space Sciences University of Chinese Academy of Sciences Beijing101408 China School of Physics and Astronomy University of St Andrews FifeKY16 9SS United Kingdom Department of Physical Sciences Open University Walton Hall Milton KeynesMK7 6AA United Kingdom Department of Physics and Astronomy Aarhus University Ny Munkegade 120 AarhusDK-8000 Denmark Instituto de Astrofísica de Canarias La Laguna TenerifeE-38205 Spain Departamento de Astrofísica Universidad de la Laguna La Laguna TenerifeE-38205 Spain

We present new Doppler images of both components of the double-lined binary σ2CrB, based on the high-resolution spectroscopic data collected during 11 nights in 2015 March-April. The observed spectra form two independent data sets with sufficient phase coverage. We apply the least-squares deconvolution to all observed spectra to obtain high signal-to-noise mean profiles, from which we derive the Doppler images of both components of σ2CrB simultaneously. The surfaces of both F9 and G0 components are dominated by pronounced polar spots. The F9 component exhibits a weak spot at latitude 30° and its mid-to-low latitudes are relatively featureless. The G0 star shows an extended spot structure at latitude 30°, and its surface spot coverage is larger than that of the F9 star, which suggests a higher level of magnetic activity. With the cross-correlation method, we derive a solar-like surface differential rotation on the G0 star of cr2CrB for the first time, and the surface shear rate is ΔΩ = 0.180 + 0.004 rad d-1and a = ΔΩ/Ωeq= 0.032 + 0.001. We do not obtain a clear surface shear law for the F9 star due to the lack of mid-to-low latitude features, but detect a systematic longitude shift of high-latitude spots, which indicates a slower rotation with respect to the co-rotating frame. Copyright © 2020, The Authors. All rights reserved.

关键词： Stars

Reddening of the blr and nlr in agn from a systematic analysis of balmer decrement

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arXiv 2018年

作者： Lu, Kai-Xing Zhao, Yinghe Bai, Jin-Ming Fan, Xu-Liang Chinese Academy of Sciences KunmingYunnan650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China School of Physics Huazhong University of Science and Technology Wuhan430074 China

We selected an active galactic nuclei (AGN) sample (0 b/Hβb) and narrow-line Balmer decrements (Hαn/Hβn) of 554 selected AGNs. We found that the distributions of Balmer decrements can be fitted by a Gaussian function and give the best estimates of Hαb/Hβb = 3.16 with a standard deviation 0.07 dex, and Hαn/Hβn = 4.37 with a standard deviation 0.10 dex. We inspected the distributions of Hαb/Hβb and Hαn/Hβn in the Baldwin−Phillips−Terlevich (BPT) diagram and found that only narrow-line Balmer decrements depend on the physical conditions of the narrow-line region (NLR). We tested the relationship between Hαb/Hβb and Hαn/Hβn, and found that Hαb/Hβb does not correlate with Hαn/Hβn. We investigated the relationship between Balmer decrements and Seyfert sub-type, and found that only broad-line Balmer decrements correlate with Seyfert sub-type, We also examined the dependency of Balmer decrements on AGN properties, and found that Balmer decrements have no correlation with optical luminosity, but show some dependence on accretion rate. These results indicate that the NLR is subject to more reddening by dust than the broad-line region (BLR). Copyright © 2018, The Authors. All rights reserved.

关键词： Statistics

Lijiang 2.4-meter Telescope and its Instruments∗

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arXiv 2019年

作者： Wang, Chuan-Jun Bai, Jin-Ming Fan, Yu-Feng Mao, Jirong Chang, Liang Xin, Yu-Xin Zhang, Ju-Jia Lun, Bao-Li Wang, Jian-Guo Zhang, Xi-Liang Ying, Mei Lu, Kai-Xing Wang, Xiao-Li Ji, Kai-Fan Xiong, Ding-Rong Yu, Xiao-Guang Ding, Xu Ye, Kai Xing, Li-Feng Yi, Wei-Min Xu, Liang Zheng, Xiang-Ming Feng, Yuan-Jie He, Shou-Sheng Wang, Xue-Li Liu, Zhong Chen, Dong Xu, Jun Qin, Song-Nian Zhang, Rui-Long Tan, Hui-Song Li, Zhi Lou, Ke Li, Jian Liu, Wei-Wei Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang GuanduKunming650216 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 Astrophysics Center of Guangzhou University Guangzhou510006 China

Lijiang 2.4-meter Telescope(LJT), the largest common-purpose optical telescope in China, has been applied to the world-wide astronomers since 2008. It is located at Gaomeigu site, Lijiang Observatory(LJO), the southwest of China. The site has very good observational conditions. Since 10-year operation, several instruments have been equipped on the LJT. Astronomers can perform both photometric and spectral observations. The main scientific goals of LJT include photometric and spectral evolution of supernova, reverberation mapping of active galactic nucleus, physical properties of binary star and near-earth object(comet and asteroid), identification of exoplanet, and all kinds of transients. Until now, the masses of 41 high accretion rate black holes have been measured, and more than 168 supernova have been identified by the LJT. More than 190 papers related to the LJT have been published. In this paper, the general observation condition of the Gaomeigu site is introduced at first. Then, the LJT structure is described in detail, including the optical, mechanical, motion and control system. The specification of all the instruments, and some detailed parameters of the YFOSC is also presented. Finally, some important scientific results and future expectations Copyright © 2019, The Authors. All rights reserved.

关键词： Photometry

GeV-TeV γ-ray energy spectral break of BL Lac objects

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arXiv 2018年

作者： Zhong, W. Liu, W.G. Zheng, Y.G. Department of Physics Yunnan Normal University Kunming650092 China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

In this paper, we compile the very-highenergy and high-energy spectral indices of 43 BL Lac objects from the literature. Based on a simple math model, ΔΓobs= αz + β, we present evidence for the origin of an observed spectral break that is denoted by the difference between the observed very-high-energy and high-energy spectral indices, ΔΓobs. We find by linear regression analysis that α ≠ 0 and β ≠ 0. These results suggest that the extragalactic background light attenuation and the intrinsic curvature dominate on the GeV-TeV γ-ray energy spectral break of BL Lac objects. We argue that the extragalactic background light attenuation is an exclusive explanation for the redshift evolution of the observed spectral break. Copyright © 2018, The Authors. All rights reserved.

关键词： Regression analysis

Photometric analysis of the eclipsing polar MN Hya

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Research in Astronomy and Astrophysics 2018年第7期18卷 11-20页

作者： Qi-Shan Wang Sheng-Bang Qian Zhong-Tao Han Miloslav Zejda Eduardo Fernandez-Lajus Li-Ying Zhu Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming650216China University of Chinese Academy of Sciences Beijing 100049China Department of Theoretical Physics and Astrophysics Masaryk UniversityKotlfirgkfi 2Bmo 611 37Czech Republic Facultad de Ciencias Astron6micas y Geoffsicas Universidad Nacional de La PlataPaseo del Bosque s/n1900La PlataPcia.Bs.As.Argentina Instituto de Astroffsica de La Plata(CCT La plata-CONICET/UNLP) Argentina

As an eclipsing polar with a 3.39 h orbital period, MN Hya was going through a state change when we observed it during 2009-2016. Ten new mid-eclipse times, along with others obtained from literature, allow us to give a new ephemeris. The residuals of a linear fit show that period decreased during the phase of state change, which means angular momentum was lost during this phase. The associated X-ray observation indicates the mass accretion rate was about 3.6 x 10^-9 Mo yr^-1. The period decrease indicates that at least 60% of mass being transferred from the secondary was lost, maybe in the form of spherically symmetric stellar wind. In the high state, the data show the intensity of flickering reduced when the system had a higher accretion rate, and that flickering sticks out with a primary timescale of about 2 min, which implies the position of the threading point was about 30 white dwarf radii above its surface. The trend of light curves for the system in its high state follows that of the low state for a large fraction of the phase interval from phase 0 to phase 0.4 since, starting at phase 0.4, the cyclotron feature is visible, and the primary intensity hump of the light curves near phase 0.7 when the system is in the high state did not appear on the curve when it was in the low state. Those facts contradict predictions of the two-pole model.

关键词： techniques photometric-stars cataclysmic variables eclipsing polars-stars individ-ual （MN Hya）

Multicolor optical monitoring of the blazar S5 0716+714 from 2017 to 2019

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arXiv 2020年

作者： Xiong, Dingrong Bai, Jinming Fan, Junhui Yan, Dahai Gu, Minfeng Fan, Xuliang Mao, Jirong Ding, Nan Xue, Rui Yi, Weimin 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 Center for Astrophysics Guangzhou University Guangzhou510006 China Astronomy Science and Technology Research Laboratory Department of Education of Guangdong Province Guangzhou510006 China Key Laboratory for Research in Galaxies and Cosmology Shanghai Astronomical Observatory Chinese Academy of Sciences 80 Nandan Road Shanghai200030 China School of Mathematics Physics and Statistics Shanghai University of Engineering Science Shanghai201620 China School of Astronomy and Space Science Nanjing University Nanjing Jiangsu210093 China Ministry of Education Nanjing210093 China Department of Astronomy and Astrophysics Pennsylvania State University 525 Davey Lab University ParkPA16802 United States

We continuously monitored the blazar S5 0716+714 in the optical g, r and i bands from Nov. 10, 2017 to Jun. 06, 2019. The total number of observations is 201 nights including 26973 data points. This is a very large quasi-simultaneous multicolor sample for the blazar. The average time spans and time resolutions are 3.4 hours and 2.9 minutes per night, respectively. During the period of observations, the target source in the r band brightens from 14m.16 to 12m.29 together with five prominent sub-flares, and then first becomes fainter to 14m.76 and again brightens to 12m.94 with seven prominent sub-flares. For the long-term variations, we find a strong flatter when brighter (FWB) trend at a low flux state and then a weak FWB trend at a higher flux state. A weak FWB trend at a low flux state and then a strong FWB trend at a higher flux state are also reported. Most of sub-flares show the strong FWB trends, except for two flares with a weak FWB trend. The particle acceleration and cooling mechanisms together with the superposition of different FWB-slopes from sub-flares are likely to explain the optical color behaviours. A scenario of bent jet is discussed. Copyright © 2020, The Authors. All rights reserved.

关键词： Galaxies

Physical properties and catalog of EW-type eclipsing binaries observed byLAMOST

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Research in Astronomy and Astrophysics 2017年第8期17卷 109-122页

作者： Sheng-Bang Qian Jia-Jia He Jia Zhang Li-Ying Zhu Xiang-Dong Shi Er-Gang Zhao Xiao Zhou Yunnan Observatories Chinese Academy of Sciences Kunming 650011 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing 100012 China University of the Chinese Academy of Sciences Beijing 100049 China

EW-type eclipsing binaries(hereafter called EWs)are strong interacting systems in which both component stars usually fill their critical Roche lobes and share a common *** EWs were discovered by several deep photometric surveys and there were about 40 785 EW-type binary systems listed in the international variable star index(VSX)by 2017 March 13.7938 of them were observed with LAMOST by 2016 November 30 and their spectral types were *** atmospheric parameters of 5363 EW-type binary stars were determined based on good spectroscopic *** the paper,those EWs are cataloged and their properties are *** distributions of orbital period(P),effective temperature(T),gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(RV)are presented for these observed EW-type *** is shown that about 80.6% of sample stars have metallicity below zero,indicating that EW-type systems are old stellar *** is in agreement with the conclusion that EW binaries are formed from moderately close binaries through angular momentum loss via magnetic braking that takes a few hundred million to a few billion *** unusually high metallicities of a few percent of EWs may be caused by contamination of material from the evolution of unseen neutron stars or black holes in the *** correlations between orbital period and effective temperature,gravitational acceleration and metallicity are presented and their scatters are mainly caused by(i)the presence of third bodies and(ii)sometimes wrongly determined *** is shown that some EWs contain evolved component stars and the physical properties of EWs mainly depend on their orbital *** is found that extremely short-period EWs may be older than their long-period cousins because they have lower *** reveals that they have a longer timescale of pre-contact evolution and their formation and evolution are mainly driven by angular momentum loss vi

关键词： stars binaries close—stars binaries spectroscopic—stars binaries eclipsing—stars evolution

Optical and ultraviolet monitoring of the black hole X-ray binary MAXI J1820+070/ASASSN-18ey for 18 months

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arXiv 2021年

作者： Sai, Hanna Wang, Xiaofeng Wu, Jianfeng Lin, Jie Feng, Hua Zhang, Tianmeng Li, Wenxiong Zhang, Jujia Mo, Jun Sun, Tianrui Ehgamberdiev, Shuhrat A. Mirzaqulov, Davron Rui, Liming Lin, Weili Zhao, Xulin Lin, Han Zhang, Jicheng Zhang, Xinghan Zhao, Yong Li, Xue Xiang, Danfeng Wang, Lingzhi Wu, Chengyuan Tsinghua University Beijing100084 China Beijing Planetarium Beijing Academy of Science and Technology Beijing100044 China Siming District Xiamen Fujian361005 China Department of Astronomy Tsinghua University Beijing100084 China Department of Engineering Physics Tsinghua University Beijing100084 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 Beijing101408 China Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing210008 China Chinese Center for Antarctic Astronomy Nanjing210008 China School of Astronomy and Space Science University of Science and Technology of China Hefei230026 China Ulugh Beg Astronomical Institute Uzbekistan Academy of Sciences Uzbekistan Tashkent100052 Uzbekistan School of Science Tianjin University of Technology Tianjin300384 China University of Chinese Academy of Sciences Beijing100049 China National Astronomical Observatory of China Chinese Academy of Sciences Beijing100012 China Chinese Academy of Sciences South America Center for Astronomy National Astronomical Observatories CAS Beijing100101 China

MAXI J1820+070 is a low-mass black hole X-ray binary system with high luminosity in both optical and X-ray bands during the outburst periods. We present extensive photometry in X-ray, ultraviolet, and optical bands, as well as densely-cadenced optical spectra, covering the phase from the beginning of optical outburst to ∼550 days. During the rebrightening process, the optical emission preceded the X-ray by 20.80 ± 2.85 days. The spectra are characterized by blue continua and emission features of Balmer series, He i, He ii lines and broad Bowen blend. The pseudo equivalent width (pEW) of emission lines are found to show anticorrelations with the X-ray flux measured at comparable phases, which is due to the increased suppression by the optical continuum. At around the X-ray peak, the full width at half maximums (FWHMs) of Hβ and He ii λ4686 tend to stabilize at 19.4 Angstrom and 21.8 Angstrom, which corresponds to the line forming region at a radius of 1.7 and 1.3 Ro within the disk. We further analyzed the absolute fluxes of the lines and found that the fluxes of Hβ and He ii λ4686 show positive correlations with the X-ray flux, favoring that the irradiation model is responsible for the optical emission. However, the fact that X-ray emission experiences a dramatic flux drop at t∼200 days after the outburst, while the optical flux only shows little variations suggests that additional energy such as viscous energy may contribute to the optical radiation in addition to the X-ray irradiation. © 2021, CC BY.

关键词： Stars

SPECTRAL PROPERTIES OF MAGNETOHYDRODNAMIC TURBULENCE REVEALED BY POLARIZATION SYNCHROTRON EMISSION WITH FARADAY ROTATION

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arXiv 2018年

作者： Zhang, Jian-Fu Lazarian, Alex Xiang, Fu-Yuan Department of Physics Xiangtan University Xiangtan Hunan411105 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Astronomy Department University of Wisconsin MadisonWI53711 United States

We investigate how to recover the spectral properties of underlying magnetohydrodynamic (MHD) turbulence using fluctuation statistics of synchrotron polarization radiation, based on the synthetic observations. Taking spatially coincident, separated, and compounded synchrotron emission and Faraday rotation regions into account, we extract the power spectrum of synchrotron polarization intensities integrated along the line of sight. Our results demonstrate that in the short wavelength range, the power spectra reflect fluctuation statistics of the perpendicular component of turbulent magnetic fields, and the spectra at long wavelengths reveal the fluctuation of the Faraday rotation density, which is a product of the parallel component of magnetic field and thermal electron density. We find that our numerical results (in the case of spatially coincident regions) are in agreement with the analytical prediction in Lazarian & Pogosyan (2016), and this theoretical prediction is applicable to more complicated settings, i.e., the spatially separated and compounded regions. We simulate telescopic observations that incorporate the effects of telescope angular resolution and noise, and find that statistics of underlying MHD turbulence can be recovered successfully. We expect that the technique can be applied to a variety of astrophysical environments, with existing synchrotron data cubes and a large number of forthcoming data sets from such as the LOw-Frequency Array for Radio astronomy (LOFAR), the Square Kilometer Array (SKA) and the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Copyright © 2018, The Authors. All rights reserved.

关键词： Power spectrum