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arXiv 2018年

作者： Jeong, Gwanghui Han, Inwoo Park, Myeong-Gu Hatzes, Artie P. Bang, Tae-Yang Gu, Shenghong Bai, Jinming Lee, Byeong-Cheol Korea Astronomy and Space Science Institute 776 Daedeokdae-Ro Youseong-Gu Daejeon34055 Korea Republic of Korea University of Science and Technology 217 Gajeong-ro Yuseong-gu Daejeon34113 Korea Republic of Department of Astronomy and Atmospheric Sciences Kyungpook National University Daegu41566 Korea Republic of Thüringer Landessternwarte Tautenburg Sternwarte 5 TautenburgD-07778 Germany Yunnan Observatories Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

We report the discovery of long-period radial velocity (RV) variations in six intermediate mass K giant stars using precise RV measurements. These discoveries are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey being conducted at the Bohyunsan Optical Astronomy Observatory (BOAO). The nature of the RV variations was investigated by looking for photometric and line shape variations. We can find no variability with the RV period in these quantities and conclude that RV variations are most likely due to unseen sub-stellar companions. Orbital solutions for the six stars yield orbital periods in the range 418 - 1065 d and minimum masses in the range 1.9 - 8.5 MJ. These properties are typical on planets around intermediate mass stars. Our SENS survey so far has about an 8% confirmed planet occurrence rate, and it will provide better statistics on planets around giant stars when the survey is completed. Copyright © 2018, The Authors. All rights reserved.

关键词： Extrasolar planets

Applications of the k-ω model in stellar evolutionary models

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arXiv 2017年

作者： Li, Yan Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

The k-ω model for turbulence was first proposed by Kolmogorov (1942). A new k-ω model for stellar convection was developed by Li (2012), which could reasonably describe turbulent convection not only in the convectively unstable zone but also in the overshooting regions. We have revised the k-ω model by improving several model assumptions (including the macro-length of turbulence, convective heat flux, and turbulent mixing diffusivity, etc.), making it applicable for not only convective envelopes but also convective cores. Eight parameters are introduced in the revised k-ω model. It should be noted that the Reynolds stress (turbulent pressure) is neglected in the equation of hydrostatic support. We have applied it into solar models and 5M stellar models, in order to calibrate the eight model parameters, as well as to investigate the effects of the convective overshooting on the sun and intermediate mass stellar models. Copyright © 2017, The Authors. All rights reserved.

关键词： Turbulence

The discrepancy between Einstein mass and dynamical mass for sis and power-law mass models

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arXiv 2018年

作者： Li, Rui Wang, Jiancheng Shu, Yiping Xu, Zhaoyi Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China University of Chinese Academy of Sciences Beijing100049 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 Purple Mountain Observatory Chinese Academy of Sciences 2 West Beijing Road Nanjing Jiangsu210008 China Institute of Astronomy Madingley Road CambridgeCB3 0HA United Kingdom

We investigate the discrepancy between the two-dimensional projected lensing mass and the dynamical mass for an ensemble of 97 strong gravitational lensing systems discovered by the Sloan Lens ACS (SLACS) Survey, the BOSS Emission-Line Lens Survey (BELLS), and the BELLS for GALaxy-Lyα EmitteR sYstems (BELLS GALLERY) Survey. We fit the lensing data to obtain the Einstein mass, and use the velocity dispersion of the lensing galaxies provided by the Sloan Digital Sky Survey (SDSS) to get the projected dynamical mass within the Einstein radius by assuming the power-law mass approximation. The discrepancy is found to be obvious and quantified by Bayesian analysis. For the singular isothermal sphere (SIS) mass model, we obtain that the Einstein mass is 20.7% more than the dynamical mass, and the discrepancy increases with the redshift of the lensing galaxies. For more general power-law mass model, the discrepancy still exists within 1σ credible region. The main reason of the the discrepancy could be mass contamination, including all invisible masses along the line of sight. In addition, the measurement errors and the approximation of the mass models could lead to part of the discrepancy. Copyright © 2018, The Authors. All rights reserved.

关键词： Galaxies

Multi-color blackbody emission in GRB 081221

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arXiv 2018年

作者： Hou, Shu-Jin Zhang, Bin-Bin Meng, Yan-Zhi Wu, Xue-Feng Liang, En-Wei Lu, Hou-Jun Liu, Tong Liang, Yun-Feng Lin, Lin Lu, Rui-Jing Huang, Jin-Shu Zhang, Bing College of Physics and Electronic Engineering Nanyang Normal University Nanyang Henan473061 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing210008 China Department of Physics GXU-NAOC Center for Astrophysics and Space Sciences Guangxi University Nanning530004 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China School of Astronomy and Space Science Nanjing University Nanjing210093 China Key Laboratory of Modern Astronomy and Astrophysics Nanjing University Ministry of Education China Department of Astronomy Xiamen University Xiamen Fujian361005 China Department of Astronomy Beijing Normal University Beijing100875 China Department of Physics and Astronomy University of Nevada Las VegasNV89154 United States

The radiation mechanism of the prompt emission of gamma-ray bursts (GRBs) remains an open question. Although their spectra are usually well fitted with the empirical Band function, which is widely believed to be fully nonthermal and interpreted as an optically thin synchrotron emission, accumulating evidence shows that a thermal component actually exists. In this paper, a multicolor blackbody (mBB) model is proposed for the time-integrated spectrum of GRB 081221 by assuming a power-law distribution of the thermal luminosities with temperature, which manifests photospheric emissions from a different radius and/or angle. The effects of the minimum temperature kTmin, the maximum temperature kTmax and the power law index m of the luminosity distribution of an mBB are discussed. The fitting to the time-integrated spectrum during the bright phase (from 20s to 30s since the trigger) of GRB 081221 by the mBB model yields kTmin = 4.4± 0.3 keV, kTmax = 57.0 +1.6-1.4 keV, and m =-0.46+0.05-0.06. When the time bin is small enough, the time-resolved spectra of GRB 081221 are well fitted with a series of single-temperature blackbodies. Our results imply the prompt emission of GRB 081221 is dominated by the photosphere emission and its time-integrated spectrum is a superposition of pure blackbody components at different times, indicating that some empirical Band spectra may be interpreted as mBB if the temperature is widely distributed. Copyright © 2018, The Authors. All rights reserved.

关键词： Gamma rays

Study of the X-ray properties of the neutron-star binary 4U 1728-34 from the soft to hard state

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arXiv 2019年

作者： Wang, Yanan Méndez, Mariano Altamirano, Diego Zhang, Guobao Belloni, T.M. Ribeiro, Evandro M. Linares, M. Sanna, Andrea Motta, S.E. Tomsick, John A. Kapteyn Astronomical Institute University of Groningen PO BOX 800 GroningenNL-9700 AV Netherlands Physics & Astronomy University of Southampton Southampton HampshireSO17 1BJ United Kingdom 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 Istituto Nazionale di Astrofisica Osservatorio Astronomico di Brera Via E. Bianchi 46 MerateI-23807 Italy Departament de Física EEBE Universitat Politècnica de Catalunya Av. Eduard Maristany 16 BarcelonaE-08019 Spain BarcelonaE-08034 Spain Dipartimento di Fisica Universitá degli Studi di Cagliari SP Monserrato-Sestu km 0.7 MonserratoI-09042 Italy University of Oxford Department of Physics Astrophysics Denys Wilkinson Building Keble Road OxfordOX1 3RH United Kingdom Space Sciences Laboratory University of California 7 Gauss Way BerkeleyCA94720-7450 United States

We studied five XMM-Newton observations of the neutron-star binary 4U 1728-34 covering the hard, intermediate and soft spectral states. By jointly fitting the spectra with several reflection models, we obtained an inclination angle of 25◦ − 53◦ and an iron abundance up to 10 times the solar. From the fits with reflection models, we found that the fluxes of the reflection and the Comptonised components vary inconsistently;since the latter is assumed to be the illuminating source, this result possibly indicates the contribution of the neutron star surface/boundary layer to the disc reflection. As the source evolved from the relatively soft to the intermediate state, the disc inner radius decreased, opposite to the prediction of the standard accretion disc model. We also explore the possible reasons why the supersolar iron abundance is required by the data and found that this high value is probably caused by the absence of the hard photons in the XMM-Newton data. Copyright © 2019, The Authors. All rights reserved.

关键词： Stars

Revealing two radio active galactic nuclei extremely near PSR J0437-4715

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arXiv 2018年

作者： Li, Zhixuan Yang, Jun An, Tao Paragi, Zsolt Deller, Adam Reynolds, Cormac Hong, Xiaoyu Wang, Jiancheng Ding, Hao Xia, Bo Yan, Zhen Guo, Li Yunnan Observatories Chinese Academy of Sciences Kunming Yunnan650216 China Department of Space Earth and Environment Chalmers University of Technology Onsala Space Observatory OnsalaSE-43992 Sweden Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai200030 China Postbus 2 DwingelooNL-7990 AA Netherlands Centre for Astrophysics & Supercomputing Swinburne University of Technology John St HawthornVIC3122 Australia CSIRO Astronomy and Space Science KensingtonWA6151 Australia University of Chinese Academy of Sciences 19A Yuquan Road Shijingshan District Beijing100049 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 Key Laboratory of Radio Astronomy Chinese Academy of Sciences Nanjing210009

Newton's gravitational constant G may vary with time at an extremely low level. The time variability of G will affect the orbital motion of a millisecond pulsar in a binary system and cause a tiny difference between the orbital period-dependent measurement of the kinematic distance and the direct measurement of the annual parallax distance. PSR J0437-4715 is the nearest millisecond pulsar and the brightest at radio. To explore the feasibility of achieving a parallax distance accuracy of one light-year, comparable to the recent timing result, with the technique of differential astrometry, we searched for compact radio sources quite close to PSR J0437-4715. Using existing data from the Very Large Array and the Australia Telescope Compact Array, we detected two sources with flat spectra, relatively stable flux densities of 0.9 and 1.0 mJy at 8.4 GHz and separations of 13 and 45 arcsec. With a network consisting of the Long Baseline Array and the Kunming 40-m radio telescope, we found that both sources have a point-like structure and a brightness temperature of >107K. According to these radio inputs and the absence of counterparts in the other bands, we argue that they are most likely the compact radio cores of extragalactic active galactic nuclei rather than Galactic radio stars. The finding of these two radio active galactic nuclei will enable us to achieve a sub-pc distance accuracy with the in-beam phase-referencing very-long-baseline interferometric observations and provide one of the most stringent constraints on the time variability of G in the near future. Copyright © 2018, The Authors. All rights reserved.

关键词： Geometrical optics

Linear polarization, circular polarization, and depolarization of gamma-ray bursts: A simple case of jitter radiation

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arXiv 2017年

作者： Mao, Jirong Wang, Jiancheng Yunnan Observatories Chinese Academy of Sciences Kunming Yunnan Province650011 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Beijing100012 Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011

Linear and circular polarizations of gamma-ray bursts (GRBs) have been detected during recent years. We adopt a simplified model to investigate GRB polarization characteristics in this paper. A compressed two-dimensional turbulent slab containing stochastic magnetic fields is considered, and jitter radiation can produce the linear polarization under this special magnetic field topology. Turbulent Faraday rotation measure (RM) of this slab makes strong wavelengthdependent depolarization. The jitter photons can also scatter with those magnetic clumps inside the turbulent slab, and a nonzero variance of the Stokes parameter V can be generated. Furthermore, the linearly and circularly polarized photons in the optical and radio bands may suffer heavy absorptions from the slab. Thus we consider the polarized jitter radiation transfer processes. Finally, we compare our model results with the optical detections of GRB 091018, GRB 121024A, and GRB 131030A. We suggest simultaneous observations of GRB multi-wavelength polarization in the future. Copyright © 2017, The Authors. All rights reserved.

关键词： Stars

DE CVn: An eclipsing post-common envelope binary with a circumbinary disk and a giant planet

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arXiv 2018年

作者： Han, Z.-T. Qian, S.-B. Zhu, L.-Y. Zhi, Q.-J. Dong, A.-J. Soonthornthum, B. Poshyachinda, S. Sarotsakulchai, T. Fang, X.-H. Wang, Q.-S. Voloshina, Irina P. O. Box 110 Kunming650216 China Guizhou Provincial Key Laboratory of Radio Data Processing School of Physics and Electronic Sciences Guizhou Normal University Guiyang550001 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China University of Chinese Academy of Sciences Yuquan Road 19# Sijingshang Block Beijing100049 China National Astronomical Research Institute of Thailand Ministry of Science and Technology Bangkok Thailand Sternberg Astronomical Institute Moscow State University Universitetskij prospect 13 Moscow119992 Russia

We present a timing analysis of the eclipsing post-common envelope binary (PCEB) DE CVn. Based on new CCD photometric observations and the published data, we found that the orbital period in DE CVn has a cyclic period oscillation with an amplitude of 28.08 s and a period of 11.22 years plus a rapid period decrease at a rate of P = -3.35 × 10-11ss-1. According to the evolutionary theory, secular period decreases in PCEBs arise from angular momentum losses (AMLs) driven by gravitational radiation (GR) and magnetic braking (MB). However, the observed orbital decay is too fast to be produced by AMLs via GR and MB, indicating that there could be other AML mechanism. We suggest that a circumbinary disk around DE CVn may be responsible for the additional AML. The disk mass was derived as a few × 10-4-10-3Mo, which is in agreement with that inferred from previous studies in the order of magnitude. The cyclic change is most likely result of the gravitational perturbation by a circumbinary object due to the Applegate's mechanism fails to explain such a large period oscillation. The mass of the potential third body is calculated as M3sin i′ = 0.011(±0.003)Mo. Supposing the circumbinary companion and the eclipsing binary is coplanar, its mass would correspond to a giant planet. This hypothetical giant planet is moving in a circular orbit of radius ∼ 5.75(±2.02) AU around its host star. Copyright © 2018, The Authors. All rights reserved.

关键词： Gravitation

New zz ceti stars from the lamost survey

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arXiv 2017年

作者： Su, Jie Fu, Jianning Lin, Guifang Chen, Fangfang Khokhuntod, Pongsak Li, Chunqian Department of Astronomy Beijing Normal University Beijing100875 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

The spectroscopic sky survey carried out by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) provides the largest stellar spectra library in the world until now. A large number of new DA white dwarfs had been identified based on the LAMOST spectra. The effective temperature (Teff) and surface gravity (log g) of most DA white dwarfs were determined and published in the catalogs, e.g. Zhao et al. (2013), Rebassa-Mansergas et al. (2015), Gentile Fusillo et al. (2015) and Guo et al. (2015). We selected ZZ Ceti candidates from the published catalogs by considering whether their Teff are situated in the ZZ Ceti instability strip. The follow-up time-series photometric observations for the candidates were performed in 2015 and 2016. Four stars: LAMOST J004628.31+343319.90, LAMOST J062159.49+252335.9, LAMOST J010302.46+433756.2 and LAMOST J013033.90+273757.9 are finally confirmed to be new ZZ Ceti stars. They show dominant peaks with amplitudes rising above the 99.9% confidence level in the amplitude spectra. As LAMOST J004628.31+343319.90 has an estimated mass of ∼ 0.40 M* and LAMOST J013033.90+273757.9 has a mass of ∼ 0.45 M* derived from their log g values, these two stars are inferred to be potential helium-core white dwarfs. Copyright © 2017, The Authors. All rights reserved.

关键词： White dwarfs

Strong-lensing measurement of the mass-density profile out to 3 effective radii for z ∼ 0.5 early-type galaxies

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arXiv 2018年

作者： Li, Rui Shu, Yiping Wang, Jiancheng Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China University of Chinese Academy of Sciences Beijing100049 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 Purple Mountain Observatory Chinese Academy of Sciences 2 West Beijing Road Nanjing Jiangsu210008 China Institute of Astronomy Madingley Road CambridgeCB3 0HA United Kingdom

We measure the total mass-density profiles out to three effective radii for a sample of 63 z ∼ 0.5, massive early-type galaxies (ETGs) acting as strong gravitational lenses through a joint analysis of lensing and stellar dynamics. The compilation is selected from three galaxy-scale strong-lens samples including the Baryon Oscillation Spectro- scopic Survey (BOSS) Emission-Line Lens Survey (BELLS), BELLS for GALaxy-Lya EmitteR sYstems Survey, and Strong Lensing Legacy Survey (SL2S). Utilizing the wide source-redshift coverage (0.8-3.5) provided by these three samples, we build a statistically significant ensemble of massive ETGs for which robust mass measurements can be achieved within a broad range of Einstein radii up to three effective radii. Char- acterizing the three-dimensional total mass-density distribution by a power-law profile as ρ ∞ r-γ, we find that the average logarithmic density slope for the entire sample is (γ) = 2.000+0.033-0.032 (68%CL) with an intrinsic scatter δ = 0.180+0.032-0.028. Further parame- terizing (γ) as a function of redshift z and ratio of Einstein radius to effective radius Rein/Reff, we find the average density distributions of these massive ETGs become steeper at larger radii and later cosmic times with magnitudes d(γ)/dz = -0.309+0.166-0.160 and d(γ)/d log10 Rein/Reff= 0.194+0.092-0.083. Copyright © 2018, The Authors. All rights reserved.

关键词： Galaxies