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A study of the relation between intensity oscillations and magnetic field parameters in a sunspot: Hinode observations

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research in Astronomy and Astrophysics 2014年第11期14卷 1458-1468页

作者： A.raja Bayanna Shibu K.Mathew Brajesh Kumar rohan E.Louis P.Venkatakrishnan Udaipur Solar Observatory Physical Research Laboratory Leibniz-institut für astrophysik Potsdam (AIP) An der Sternwarte 16 14482 PotsdamGermany

We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequency reveal reduction of power in the G band with an increase in photospheric magnetic field strength at all frequencies. In Ca II H, however, stronger fields exhibit more power at high frequen- cies, particularly in the 4.5-8.0 mHz band. Power distributions in different locations of the active region show that the oscillations in Ca II H exhibit more power compared to that of the G band. We also relate the power in intensity oscillations with differ- ent components of the photospheric vector magnetic field using near simultaneous spectro-polarimetric observations of the sunspot from the Hinode spectropolarime- ter. The photospheric umbral power is strongly anti-correlated with the magnetic field strength and its line-of-sight component but there is a good correlation with the trans- verse component. A reversal of this trend is observed in the chromosphere except at low frequencies （V≤ 1.5 mHz）. The power in sunspot penumbrae is anti-correlated with the magnetic field parameters at all frequencies （1.0 ≤ v ≤ 8.0 mHz） in both the photosphere and chromosphere, except that the chromospheric power shows a strong correlation in the frequency range 3-3.5 mHz.

关键词： Sun photosphere -- Sun chromosphere -- Sun oscillations -- Sun magnetic fields -- Sun Hinode

Type Ia Supernova Explosions in Binary Systems:A review

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research in Astronomy and Astrophysics 2023年第8期23卷 10-52页

作者： Zheng-Wei Liu friedrich K.röpke Zhanwen Han Yunnan Observatories Chinese Academy of Sciences(CAS)Kunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects CASKunming 650216China International Centre of Supernovae Yunnan Key LaboratoryKunming 650216China University of Chinese Academy of Sciences Beijing 100049China Zentrum für astronomie der Universität Heidelberg Institut für Theoretische AstrophysikPhilosophenweg 12D-69120 HeidelbergGermany Heidelberger institut für Theoretische Studien Schloss-Wolfsbrunnenweg 35D-69118 HeidelbergGermany

Type Ia supernovae(SNe Ia)play a key role in the fields of astrophysics and cosmology.It is widely accepted that SNe Ia arise from thermonuclear explosions of white dwarfs(WDs)in binary systems.However,there is no consensus on the fundamental aspects of the nature of SN Ia progenitors and their actual explosion mechanism.This fundamentally flaws our understanding of these important astrophysical objects.In this review,we outline the diversity of SNe Ia and the proposed progenitor models and explosion mechanisms.We discuss the recent theoretical and observational progress in addressing the SN Ia progenitor and explosion mechanism in terms of the observables at various stages of the explosion,including rates and delay times,pre-explosion companion stars,ejecta–companion interaction,early excess emission,early radio/X-ray emission from circumstellar material interaction,surviving companion stars,late-time spectra and photometry,polarization signals and supernova remnant properties.Despite the efforts from both the theoretical and observational sides,questions of how the WDs reach an explosive state and what progenitor systems are more likely to produce SNe Ia remain open.No single published model is able to consistently explain all observational features and the full diversity of SNe Ia.This may indicate that either a new progenitor paradigm or an improvement in current models is needed if all SNe Ia arise from the same origin.An alternative scenario is that different progenitor channels and explosion mechanisms contribute to SNe Ia.In the next decade,the ongoing campaigns with the James Webb Space Telescope,Gaia and the Zwicky Transient facility,and upcoming extensive projects with the Vera C.rubin Observatory's Legacy Survey of Space and Time and the Square Kilometre Array will allow us to conduct not only studies of individual SNe Ia in unprecedented detail but also systematic investigations for different subclasses of SNe Ia.This will advance theory and observations of SNe Ia sufficiently far to gain a deeper un

关键词： (stars:)binaries(including multiple) close-methods numerical-(stars )supernovae general

How to Build the Engine of and to Provide the fuel for Quasars

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天文研究与技术 2003年第S1期 147-150页

作者： Wolfgang J. Duschl institut für Theoretische astrophysik Tiergartenstr. 15 69121 Heidelberg Germany

We present a model in which a galaxy galaxy merger can provide not only the fuel for quasar activity, but can also build a super massive black hole, i.e., the engine.

关键词： viscosity Barnes

Metal Poor Accretion in the Early Universe

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天文研究与技术 2003年第S1期 151-154页

作者： Michael Mayer institut für Theoretische astrophysik Tiergartenstr. 15 69120 Heidelberg Germany

In the early Universe, the chemical composition of matter was different from the one today, as then the heavier elements present today were still missing. The structure, evolution and stability of accretion discs in AGNs depends on the chemical composition of the material. I will present first results of model calculations of such primordial accretion discs.for the calculations, I use a generalized viscosity prescription and newly computed opacities in the range 40-40000 K. I will discuss the influence of the primordial chemical composition on the structure and stability of AGN accretion disks and compare them to the present day Universe situation.

关键词： figure

The GeV emission of PSr B1259–63 during its last three periastron passages observed by fermi-LAT

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research in Astronomy and Astrophysics 2018年第12期18卷 89-94页

作者： Zhi Chang Shu Zhang Yu-Peng Chen Long Ji Ling-Da Kong Cong-Zhan Liu Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of SciencesBeijing 100049China institut fur astronomie und astrophysik Kepler Center for Astro and Particle PhysicsEberhard Karls UniversitatSand 172076 TubingenGermany University of Chinese Academy of Sciences Beijing 100049China

PSr B1259–63 is a γ-ray emitting high mass X-ray binary system, in which the compact object is a millisecond pulsar.The system has an orbital period of 1236.7 d and shows peculiar γ-ray flares when the neutron star moves out of the stellar disk of the companion star.The γ-ray flare events were firstly discovered by using fermi-LAT around the 2010 periastron passage, which was repeated for the 2014 and 2017 periastron passages.We analyze the fermi-LAT data for all the three periastron passages and found that in each flare the energy spectrum can be represented well by a simple power law.The γ-ray light curves show that in 2010 and 2014 after each periastron there are two main flares,but in 2017 there are four flares including one precursor about 10 d after the periastron passage.The first main flares in 2010 and 2014 are located at around 35 d after the periastron passage, and the main flare in 2014 is delayed by roughly 1.7 d with respect to that in 2010.In the 2017 flare, the source shows a precursor about 10 d after the periastron passage, but the following two flares become weaker and lag behind those in 2010 by roughly 5 d.The strongest flares in 2017 occurred 58 d and 70 d after the periastron passage.These results challenge the previous models.

关键词： binaries:general pulsars:general gamma rays:general

Gap formation around Ω_e/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory

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Earth and Planetary Physics 2020年第2期4卷 138-150页

作者： Konrad Sauer Klaus Baumgartel richard Sydora Max-Planck-institute for Solar System research GöttingenGermany(up to 2005 Leibnitz-institut für astrophysik(AIP) PotsdamGermany(up to 2008 institute for Geophysical research University of AlbertaEdmontonCanada

In this paper we show that two significant phenomena of magnetospheric chorus emission can be explained by the participation of beam-like electron structures,created by Landau-resonant interaction with growing oblique whistler waves.The first concerns the widely observed spectral gap near half the electron cyclotron frequency Ωe;the second is related to the observation of very obliquely propagating lower-band waves that cannot be directly generated by temperature anisotropy.Concerning the gap,kinetic dispersion theory reveals that interference of the beam-related cyclotron mode ω~Ωe-kVb with the conventional whistler mode leads to mode splitting and the appearance of a ’forbidden’ area in the ω-k space.Thereby the beam velocity appears as an essential parameter.It is directly related to the phase velocity of the most unstable whistler wave mode,which is close to VAe/2 for sufficiently hot electrons(VAe is the electron Alfven velocity).To clarify the second point,we show that Landau-resonant beams with Vb Vbrise in cold plasmas from unstable upper-band waves,are able to generate lower-band whistler mode waves at very oblique propagation(θ≥60°).Our studies demonstrate the important role of Landau-resonant electrons in nonlinear whistler wave generation in the magnetosphere.

关键词： important role play Landau-resonant electrons modification of the electron distribution function gap formation at half the electron cyclotron frequency

Nonlinear Variability Observed with Insight-HXMT in MAXI J1820+070 and MAXI J1535-571

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research in Astronomy and Astrophysics 2023年第8期23卷 346-354页

作者： Qi Ding Long Ji Qing-Cui Bu Tiekuang Dong Jin Chang Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210033China School of Astronomy and Space Sciences University of Science and Technology of ChinaHefei 230026China School of Physics and Astronomy Sun Yat-sen UniversityZhuhai 519000China institut für astronomie und astrophysik Kepler Center for Astro and Particle PhysicsEberhard KarlsUniversitätSand 1D-72076 TübingenGermany National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China

We present the timing analysis of the nonlinear variability in two black hole low mass X-ray binaries MAXI J1820+070 and MAXI J1535-571 by using the bicoherence,a measure of phase coupling at different fourier frequencies.We found different patterns,e.g.,“cross”and“hypotenuse,”for LfQPOs in different outburst states.When they can be clearly distinguished,bicoherence patterns are similar over a wide energy range of 1–100 keV.It is intriguing that in some type-C QPOs we found the patterns that are normally observed in type-B QPOs.On the contrary,the“hypotenuse”pattern,a characteristic of type-C QPOs,was detected in a type-B QPO.This suggests that different types of QPOs may originate from similar underlying mechanisms.In addition,we speculate that the nonlinear variability may be a promising approach to disentangle distinct QPO models which assume different interactions between the broadband noise and QPO components.

关键词： black hole physics-instrumentation detectors-methods data analysis-X-rays binaries

Characterization of Optical Aberrations Induced by Thermal Gradients and Vibrations via Zernike and Legendre Polynomials

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Optics and Photonics Journal 2016年第6期6卷 113-123页

作者： Igor Di Varano Leibniz institut für astrophysik Potsdam (AIP) Potsdam Germany

for every astronomical instrument, the operating conditions are undoubtedly different from those defined in a setup experiment. Besides environmental conditions, the drives, the electronic cabinets containing heaters and fans introduce disturbances that must be taken into account already in the preliminary design phase. Such disturbances can be identified as being mostly of two types: heat sources/sinks or cooling systems responsible for heat transfer via conduction, radiation, free and forced convection on one side and random and periodic vibrations on the other. for this reason, a key role already from the very beginning of the design process is played by integrated model merging the outcomes based on a finite Element Model from thermo-structural and modal analysis into the optical model to estimate the aberrations. The current paper presents the status of such model, capable of analyzing the deformed surfaces deriving from both thermo-structural and vibrational analyses and measuring their effect in terms of optical aberrations by fitting them by Zernike and Legendre polynomial fitting respectively for circular and rectangular apertures. The independent contribution of each aberration is satisfied by the orthogonality of the polynomials and mesh uniformity.

关键词： fEM Wavefront Error Zernike Legendre Polynomials Astronomical Instrumentation

BESTP——An automated Bayesian modeling tool for asteroseismology

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维普期刊数据库

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research in Astronomy and Astrophysics 2021年第9期21卷 135-145页

作者：姜晨 Laurent Gizon Max-Planck-institut für Sonnensystemforschung Justus-von-Liebig-Weg 337077 GöttingenGermany institut für astrophysik Georg-August-Universität GöttingenFriedrich-Hund-Platz 137077 GöttingenGermany School of Physics and Astronomy Sun Yat-Sen UniversityNo.135Xingang Xi RoadGuangzhou 510275China Center for Space Science NYUAD InstituteNew York University Abu DhabiAbu DhabiUAE

Asteroseismic observations are crucial to constrain stellar models with precision.Bayesian Estimation of STellar Parameters(BESTP)is a tool that utilizes Bayesian statistics and nested sampling Monte Carlo algorithm to search for the stellar models that best match a given set of classical and asteroseismic constraints from observations.The computation and evaluation of models are efficiently performed in an automated and multi-threaded way.To illustrate the capabilities of BESTP,we estimate fundamental stellar properties for the Sun and the red-giant star HD 222076.In both cases,we find models that are consistent with observations.We also evaluate the improvement in the precision of stellar parameters when the oscillation frequencies of individual modes are included as constraints,compared to the case when only the large frequency separation is included.for the solar case,the uncertainties of estimated masses,radii and ages are reduced by 0.7%,0.3%and 8%respectively.for HD 222076,they are reduced even more noticeably by 2%,0.5%and 4.7%respectively.We also note an improvement of 10%for the age of HD 222076 when the Gaia parallax is included as a constraint compared to the case when only the large separation is included as a constraint.

关键词： stars:interiors stars:oscillations methods:numerical asteroseismology