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  • Can we determine the filament chirality by the filament footpoint location or the barb-bearing?
  • We attempt to propose a method for automatically detecting the solar filament chirality and barb bearing. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm to recognize the filament spine. Then, we use the polarity inversion line(PIL) shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with Hα filtergrams from the Big Bear Solar Observatory(BBSO) Hα archive and magnetograms observed with the Helioseismic and Magnetic Imager(HMI) on board the Solar Dynamics Observatory(SDO). Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere(northern hemisphere) mainly have left-bearing(rightbearing) barbs and positive(negative) magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid.The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.
  • OO Aquilae: a solar-type contact binary with intrinsic light curve changes
  • New multi-color photometry of the solar-type contact binary OO Aql was obtained in 2012 and2013, using the 60 cm telescope at Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences. From two sets of light curves LC1 and LC2, photometric models were performed by using the 2003 version of the Wilson-Devinney code. The overcontact factor of the binary system was determined to be f = 37.0(±0.5)%. The intrinsic variability of this binary occurs in light maxima and minima, which could result from a possible third component and magnetic activity of the late type components. Based on all available light minimum times, the orbital period may change in a complicated mode,i.e., sudden period jumps or continuous period variations. The period of OO Aql may possibly undergo a secular period decrease with a rate of d P /dt =-3.63(±0.30) × 10-8d yr-1, superimposed by two possible cyclic variations in the O- C curve. The long-term period decrease may be interpreted as conserved mass transfer from the more massive component to the less massive one. The 21.5-yr oscillation may be attributed to cyclic magnetic activity, and the 69.3-yr one may result from the light-time effect of an unseen tertiary body.
  • Coupling of small- and large-scale filament eruptions
  • We present observations of the eruption of a large-scale quiescent filament(LF) that is associated with the formation and eruption of a miniature filament(MF). As a result of convergence and subsequent cancelation of opposite-polarity magnetic flux, MF was formed just below the spine of the LF’s right segment. Probably triggered by a nearby newly emerging flux, MF underwent a failed eruption immediately after its full development, which first ejected away from the spine of LF and then drained back to the Sun.This eruption no sooner started than the overlying LF’s right segment began to rise slowly and the LF’s other parts were also disturbed, and eventually the whole LF erupted bodily and quickly. These observations suggest that the MF can serve as an intermediary that links the photospheric small-scale magnetic-field activities to the eruption of the overlying large filament. It appears that, rather than directly interacting with the supporting magnetic field of LF, small-scale flux cancelation and emergence in the LF’s channel can manifest themselves as the formation and eruption of MF and so indirectly affect the stability of LF.
  • Global Mg/Si and Al/Si Distributions on the Lunar Surface Derived from Chang'E-2 X-ray Spectrometer
  • The technique of X-ray fluorescence remote sensing plays a significant role in research related to the chemical compositions of the Moon. Here we describe the data analysis method for China’s Chang’E-2 X-ray spectrometer in detail and present the preliminary results about the first global Mg/Si and Al/Si maps of the lunar surface. Our results show that the distributions of Mg/Si and Al/Si correlate well with terrains on the Moon. The higher Mg/Si ratio corresponds to the mare regions while the lower value corresponds to the highland terrains. The map of the Al/Si ratio shows a reversed distribution compared with the map of the Mg/Si ratio.
  • Solar flares with similar soft but different hard X-ray emissions: case and statistical studies
  • Progenitor model of cosmic ray knee
  • The primary energy spectrum of cosmic rays exhibits a knee at about 3 Pe V where a change in the spectral index occurs. Despite many efforts, the origin of such a feature in the spectrum is not satisfactorily solved yet. Here it is proposed that the steepening of the spectrum beyond the knee may be a consequence of the mass distribution of the progenitor of the cosmic ray source. The proposed speculative model can account for all the major observed features of cosmic rays without invoking any fine tuning to match flux or spectra at any energy point. The prediction of the proposed model regarding the primary composition scenario beyond the knee is quite different from most of the prevailing models of the knee, and thereby can be discriminated from precise experimental measurement of the primary composition.
  • Automatic generation of optical initial configuration based on Delano diagram
  • This paper presents a method to automatically initialize an optical system based on the Delano diagram. The process to generate the optical initial configuration is constrained by the control points, which are deduced from parameters related to basic design requirements. We present the theory and method to generate the optical initial configuration automatically when the basic design requirements are known. Two optical systems are taken as examples to demonstrate the proposed method.
  • Study of temporal evolution of emission spectrum in a steeply rising submillimeter burst
  • The temporal evolution of a spectrum during a steeply rising submillimeter(THz) burst that occurred on 2003 November 2 was investigated in detail for the first time.Observations show that the flux density of the THz spectrum increased steeply with frequency above 200 GHz.Their average rising rates reached a value of 235 sfu GHz-1(corresponding to spectral index α of 4.8) during the burst.The flux densities reached about 4 000 and 70 000 sfu at 212 and 405 GHz at the maximum phase,respectively.The emissions at 405 GHz maintained such a continuous high level that they largely exceeded the peak values of the microwave(MW) spectra during the main phase.Our studies suggest that only energetic electrons with a low-energy cutoff of 1 MeV and number density of 106-108 cm-3 can produce such a strong and steeply rising THz component via gyrosynchrotron radiation based on numerical simulations of burst spectra in the case of a nonuniform magnetic field.The electron number density N,derived from our numerical fits to the THz temporal evolution spectra,increased substantially from 8 ×106 to 4 × 108 cm-3,i.e.,the N value increased 50 times during the rise phase.During the decay phase it decreased to 7 ×107 cm-3,i.e.,it decreased by about five times from the maximum phase.The total electron number decreased an order of magnitude from the maximum phase to the decay phase.Nevertheless,the variation in amplitude of N is only about one time in the MW emission source during this burst,and the total electron number did not decrease but increased by about 20%during the decay phase.Interestingly,we find that the THz source radius decreased by about 24%while the MW source radius,on the contrary,increased by 28%during the decay phase.
  • Spindown of magnetars: quantum vacuum friction?
  • Magnetars are proposed to be peculiar neutron stars which could power their X-ray radiation by super-strong magnetic fields as high as > 1014 G.However,no direct evidence for such strong fields has been obtained till now,and the recent discovery of low magnetic field magnetars even indicates that some more efficient radiation mechanism than magnetic dipole radiation should be included.In this paper,quantum vacuum friction(QVF) is suggested to be a direct consequence of super-strong surface fields,therefore the magnetar model could then be tested further through QVF braking.The high surface magnetic field of a pulsar interacting with the quantum vacuum results in a significantly high spindown rate(P).It is found that a QVF dominates the energy loss of pulsars when the pulsar’s rotation period and its first derivative satisfy the relationship P3P > 0.63 ×10-16ξ-4 s2,whereξ is the ratio of the surface magnetic field over the dipole magnetic field.In the "QVF + magnetodipole" joint braking scenario,the spindown behavior of magnetars should be quite different from that in the pure magnetodipole model.We are expecting these results could be tested by magnetar candidates,especially low magnetic field cases,in the future.
  • Fabry-Perot based narrow band imager for solar filament observations
  • We have recently developed a narrow band imager(NBI) using an air gap based Fabry-P′erot(FP) interferometer at the Indian Institute of Astrophysics, Bangalore. Narrow band imaging is achieved by using an FP interferometer working in combination with an order sorting pre-filter. The NBI can be tuned to a different wavelength position on the line profile by changing the plate separation of the FP. The interferometer has a 50 mm clear aperture with a bandpass of ~247.8 m ?A and a free spectral range of~5.3 ?A at λ = 656.3 nm. The developed NBI is used to observe the solar filament in the Hα wavelength.The instrument is being used to image the Sun at chromospheric height and it is also able to scan the Hα spectral line profile at different wavelength positions. We have also made Doppler velocity maps at chromospheric height by taking the blue and red wing images at ±176 m ?A wavelength positions separately away from the line center of the spectral line. In this paper, we present a description of the NBI including lab test results of individual components and some initial observations carried out with this instrument.
  • Performance analysis of parallel gravitational N-body codes on large GPU clusters
  • We compare the performance of two very different parallel gravitational N-body codes for astrophysical simulations on large Graphics Processing Unit(GPU) clusters, both of which are pioneers in their own fields as well as on certain mutual scales- NBODY6++ and Bonsai. We carry out benchmarks of the two codes by analyzing their performance, accuracy and efficiency through the modeling of structure decomposition and timing measurements. We find that both codes are heavily optimized to leverage the computational potential of GPUs as their performance has approached half of the maximum single precision performance of the underlying GPU cards. With such performance we predict that a speed-up of200- 300 can be achieved when up to 1k processors and GPUs are employed simultaneously. We discuss the quantitative information about comparisons of the two codes, finding that in the same cases Bonsai adopts larger time steps as well as larger relative energy errors than NBODY6++, typically ranging from10- 50 times larger, depending on the chosen parameters of the codes. Although the two codes are built for different astrophysical applications, in specified conditions they may overlap in performance at certain physical scales, thus allowing the user to choose either one by fine-tuning parameters accordingly.
  • Optical light curve of GRB 121011A: a textbook for the onset of GRB afterglow in a mixture of ISM and wind-type medium
  • We report the optical observations of GRB 121011 A by the 0.8m TNT facility at Xinglong observatory, China. The light curve of the optical afterglow shows a smooth and featureless bump during the epoch of ~130 s and ~5000 s with a rising index of 1.57 ± 0.28 before the break time of 539 ± 44 s, and a decaying index of about 1.29 ± 0.07 up to the end of our observations. Moreover, the X-ray light curve decays in a single power-law with a slope of about 1.51 ± 0.03 observed by XRT onboard Swift from 100 s to about 10 000 s after the burst trigger. The featureless optical light curve could be understood as an onset process under the external-shock model. The typical frequency has been below or near the optical one before the deceleration time, and the cooling frequency is located between the optical and X-ray wavelengths. The external medium density has a transition from a mixed stage of ISM and wind-type medium before the peak time to the ISM at the later phase. The joint-analysis of X-ray and optical light curves shows that the emissions from both frequencies are consistent with the prediction of the standard afterglow model without any energy injections, indicating that the central engine has stopped its activity and does not restart anymore after the prompt phase.
  • The beaming effect and γ-ray emission for Fermi blazars
  • We study the γ-ray luminosity and beaming effect for Fermi blazars.Our results are as follows.(i) There are significant correlations between γ-ray luminosity and radio core luminosity,and between γ-ray luminosity and Rv,which suggests that the γ-ray emissions have a strong beaming effect,(ⅱ) Using the Lext/Mabs as an indicator of environment effects,we find that there is no significant correlation betweenγ-ray luminosity and Lext/Mabs for all sources when we remove the effect of redshift.Flat spectrum radio quasars considered alone also do not show a significant correlation,but BL Lacertae objects(BL Lacs) still show a significant correlation when we remove the effect of redshift.These results suggest that the γ-ray emission may be affected by the environment on a kiloparsec scale for BL Lacs.
  • Geoeffectiveness of the coronal mass ejections associated with solar proton events
  • The intensity-time profiles of solar proton events(SPEs) are grouped into three types in the present study. The Type-I means that the intensity-time profile of an SPE has one peak, which occurs shortly after the associated solar flare and coronal mass ejection(CME). The Type-II means that the SPE profile has two peaks: the first peak occurs shortly after the solar eruption, the second peak occurs at the time when the CME-driven shock reaches the Earth, and the intensity of the second peak is lower than the first one.If the intensity of the second peak is higher than the first one, or the SPE intensity increases continuously until the CME-driven shock reaches the Earth, this kind of intensity-time profile is defined as Type-III. It is found that most CMEs associated with Type-I SPEs have no geoeffectiveness and only a small part of CMEs associated with Type-I SPEs can produce minor(–50 n T ≤ Dst ≤–30 n T) or moderate geomagnetic storms(–100 n T≤ Dst ≤–50 n T), but never an intense geomagnetic storm(–200 n T ≤ Dst <-100 n T). However,most of the CMEs associated with Type-II and Type-III SPEs can produce intense or great geomagnetic storms(Dst ≤-200 n T). The solar wind structures responsible for the geomagnetic storms associated with SPEs with different intensity-time profiles have also been investigated and discussed.
  • Testing a solar coronal magnetic field extrapolation code with the Titov-Demoulin magnetic flux rope model
  • In the solar corona, the magnetic flux rope is believed to be a fundamental structure that accounts for magnetic free energy storage and solar eruptions. Up to the present, the extrapolation of the magnetic field from boundary data has been the primary way to obtain fully three-dimensional magnetic information about the corona. As a result, the ability to reliably recover the coronal magnetic flux rope is important for coronal field extrapolation. In this paper, our coronal field extrapolation code is examined with an analytical magnetic flux rope model proposed by Titov & D′emoulin, which consists of a bipolar magnetic configuration holding a semi-circular line-tied flux rope in force-free equilibrium. By only using the vector field at the bottom boundary as input, we test our code with the model in a representative range of parameter space and find that the model field can be reconstructed with high accuracy. In particular, the magnetic topological interfaces formed between the flux rope and the surrounding arcade, i.e., the "hyperbolic flux tube" and "bald patch separatrix surface," are also reliably reproduced. By this test, we demonstrate that our CESE–MHD–NLFFF code can be applied to recovering the magnetic flux rope in the solar corona as long as the vector magnetogram satisfies the force-free constraints.
  • f and g series solutions to a post-Newtonian two-body problem with parameters β and γ
  • Classical Newtonian f and g series for a Keplerian two-body problem are extended for the case of a post-Newtonian two-body problem with parameters β and γ. These two parameters are introduced to parameterize the post-Newtonian approximation of alternative theories of gravity and they are both equal to1 in general relativity. Up to the order of 30, we obtain all of the coefficients of the series in their exact forms without any cutoff for significant figures. The f and g series for the post-Newtonian two-body problem are also compared with a Runge-Kutta order 7 integrator. Although the f and g series have no superiority in terms of accuracy or efficiency at the order of 7, the discrepancy in the performances of these two methods is not quite distinct. However, the f and g series have the advantage of flexibility for going to higher orders.Some examples of relativistic advance of periastron are given and the effect of gravitational radiation on the scheme of f and g series is evaluated.
  • Mode coupling in solar spicule oscillations
  • In a real medium which has oscillations, the perturbations can cause an energy transfer between different modes. A perturbation, which is interpreted as an interaction between the modes, is inferred to be mode coupling. The mode coupling process in an inhomogeneous medium such as solar spicules may lead to the coupling of kink waves to local Alfv′en waves. This coupling occurs in practically any conditions when there is smooth variation in density in the radial direction. This process is seen as the decay of transverse kink waves in the medium. To study the damping of kink waves due to mode coupling, a 2.5-dimensional numerical simulation of the initial wave is considered in spicules. The initial perturbation is assumed to be in a plane perpendicular to the spicule axis. The considered kink wave is a standing wave which shows an exponential damping in the inhomogeneous layer after the mode coupling occurs.
  • A comparison study of a solar active-region eruptive filament and a neighboring non-eruptive filament
  • Solar active region(AR) 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE–MHD–NLFFF code reveals that two magnetic flux ropes(MFRs) exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface(BPSS) cospatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament(with a length of about 200 Mm), the eruptive MFR/filament is much smaller(with a length of about 20 Mm), but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.
  • Chemical abundance analysis of 19 barium stars
  • We aim at deriving accurate atmospheric parameters and chemical abundances of 19 barium(Ba) stars, including both strong and mild Ba stars, based on the high signal-to-noise ratio and high resolution Echelle spectra obtained from the 2.16 m telescope at Xinglong station of National Astronomical Observatories, Chinese Academy of Sciences. The chemical abundances of the sample stars were obtained from an LTE, plane-parallel and line-blanketed atmospheric model by inputting the atmospheric parameters(effective temperatures Teff, surface gravities log g, metallicity [Fe/H] and microturbulence velocity ξt) and equivalent widths of stellar absorption lines. These samples of Ba stars are giants as indicated by atmospheric parameters, metallicities and kinematic analysis about UVW velocity. Chemical abundances of 17 elements were obtained for these Ba stars. Their Na, Al, α- and iron-peak elements(O, Na, Mg, Al, Si, Ca,Sc, Ti, V, Cr, Mn, Ni) are similar to the solar abundances. Our samples of Ba stars show obvious overabundances of neutron-capture(n-capture) process elements relative to the Sun. Their median abundances of[Ba/Fe], [La/Fe] and [Eu/Fe] are 0.54, 0.65 and 0.40, respectively. The Y I and Zr I abundances are lower than Ba, La and Eu, but higher than the α- and iron-peak elements for the strong Ba stars and similar to the iron-peak elements for the mild stars. There exists a positive correlation between Ba intensity and [Ba/Fe].For the n-capture elements(Y, Zr, Ba, La), there is an anti-correlation between their [X/Fe] and [Fe/H]. We identify nine of our sample stars as strong Ba stars with [Ba/Fe]>0.6 where seven of them have Ba intensity Ba=2-5, one has Ba=1.5 and another one has Ba=1.0. The remaining ten stars are classified as mild Ba stars with 0.17<[Ba/Fe]<0.54.
  • Non-ballistic motion and precessing helical trajectory in quasar NRAO 150
  • NRAO 150 is a very special radio quasar in which prominent non-ballistic superluminal motion has been observed in its inner-jet region. We apply model-fittings to the kinematics of the superluminal knots(trajectory, distance from the core and apparent velocity) in terms of a helical precessing jet-nozzle model.Five cases are considered in which the angle between the jet axis and the line of sight is assumed to be 6?,3?, 1?, 0.6? and 0.12?, respectively. It is shown that the superluminal components have intrinsic acceleration in the innermost regions(≤0.2 mas from the core). The phenomenon of precessing nozzle/trajectory can be understood on the basis of relativistic magnetohydrodynamic theories for relativistic jets.
  • Instructions for authors
  • Can we determine the filament chirality by the filament footpoint location or the barb-bearing?(Qi Hao[1,2,3,4];Yang Guo[1,2];Cheng Fang[1,2];Peng-Fei Chen[1,2];Wen-Da Cao[3,4])
    OO Aquilae: a solar-type contact binary with intrinsic light curve changes(Hua-Li Li[1,2];Jian-Yan Wei;Yuan-Gui Yang;Hai-Feng Dai)
    Coupling of small- and large-scale filament eruptions(Jia-Yan Yang;Yun-Chun Jiang;Bo Yang[1,2];Jun-Chao Hong;Zhe Xu[1,2])
    Global Mg/Si and Al/Si Distributions on the Lunar Surface Derived from Chang'E-2 X-ray Spectrometer(Wu-Dong Dong;Xiao-Ping Zhang;Meng-Hua Zhu;Ao-Ao Xu;Ze-ShengTang)
    Solar flares with similar soft but different hard X-ray emissions: case and statistical studies(Ivan N. Sharykin;Alexei B. Struminskyl;Ivan V. Zimovets;Wei-Qun Gan)
    Progenitor model of cosmic ray knee(Biplab Bijay;Amnava Bhadra)
    Automatic generation of optical initial configuration based on Delano diagram(Kai-Yuan Zhang[1,2,3];Xiang-Yan Yuan[1,2];Xiang-Qun Cui[1,2])
    Study of temporal evolution of emission spectrum in a steeply rising submillimeter burst(Jian-Ping Li[1,2];Ai-Hua Zhou[1,2];Xin-Dong Wang)
    Spindown of magnetars: quantum vacuum friction?(Xue-Yu Xiong;Chun-Yuan Gao;Ren-Xin Xu)
    Fabry-Perot based narrow band imager for solar filament observations(Sajal Kumar Dhara;Belur Ravindra;Ravinder Kumar Banyal)
    Performance analysis of parallel gravitational N-body codes on large GPU clusters(Si-Yi Huang;Rainer Spurzem[1,2,4];Peter Berczik[1,3,4])
    Optical light curve of GRB 121011A: a textbook for the onset of GRB afterglow in a mixture of ISM and wind-type medium(Li-Ping Xin;Jian-Yan Wei;Yu-Lei Qiu;Jin-Song Deng;Jing Wang;Xu-Hui Han)
    The beaming effect and γ-ray emission for Fermi blazars(Yong-Yun Chen;Xiong Zhang;Ding-Rong Xiong;Si-Ju Wang;Xiao-Ling Yu)
    Geoeffectiveness of the coronal mass ejections associated with solar proton events(Gui-Ming Le[1,3];Chuan Li;Yu-Hua Tang;Liu-Guan Ding;Zhi-Qiang Yin;Yu-Lin Chen;Yang-Ping Lu[1,4];Min-Hao Chen[1,4];Zhong-Yi Li[1,4])
    Testing a solar coronal magnetic field extrapolation code with the Titov-Demoulin magnetic flux rope model(Chao-Wei Jiang;Xue-Shang Feng)
    f and g series solutions to a post-Newtonian two-body problem with parameters β and γ(Song-He Qin[1,2,3];Jing-Xi Liu[1,2,3];Ze-Hao Zhong[1,2,3];Yi Xie[1,2,3])
    Mode coupling in solar spicule oscillations(Zahra Fazel)
    A comparison study of a solar active-region eruptive filament and a neighboring non-eruptive filament(Chao-Wei Jiang[1,2];Shi-Tsan Wu[2,3];Xue-Shang Feng;Qiang Hu[2,4])
    Chemical abundance analysis of 19 barium stars(Guo-Chao Yang[1,2,3];Yan-Chun Liang;Monique Spite;Yu-Qin Chen;Gang Zhao;Bo Zhang[1,2];Guo-Qing Liu[2,5];Yu-Juan Liu;Nian Liu;Li-Cai Deng;Francois Spite;Vanessa Hill;Cai-Xia Zhang)
    Non-ballistic motion and precessing helical trajectory in quasar NRAO 150(Shan-Jie Qian)
    Instructions for authors
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