Comparison of chaos detection methods in the circular restricted three‐body problem     

O. Racoveanu 《Astronomische Nachrichten》2014,335(8):877-885

In this study, a sample of orbits is considered in the framework of the planar circular restricted three‐body problem. In order to separate ordered from chaotic orbits three numerical methods are compared: the Largest Lyapunov Characteristic Exponent (LLCE) and the Smaller Alignment Index (SALI) provide a fairly good characterization of the chaotic motions, while the computational time required is of the same order; the Correlation Dimension (CD) has the advantage of correctly classifying sticky orbits, but at the expense of a longer computational time. In order to classify a given orbit, any pair of the three methods can be considered, but LLCE and SALI are recommended due to their speed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Statistical properties of twin kilohertz quasi‐periodic oscillations in neutron star low‐mass X‐ray binaries     

D. H. Wang  L. Chen  C. M. Zhang  Y. J. Lei  J. L. Qu 《Astronomische Nachrichten》2014,335(2):168-177

We collect the data of twin kilohertz quasi‐periodic oscillations (kHz QPOs) published before 2012 from 26 neutron star (NS) low‐mass X‐ray binary (LMXB) sources, then we analyze the centroid frequency (ν) distribution of twin kHz QPOs (lower frequency ν₁ and upper frequency ν₂) both for Atoll and Z sources. For the data without shift‐and‐add, we find that Atoll and Z sources show different distributions of ν₁, ν₂ and ν₂/ν₁, but the same distribution of Δν (difference of twin kHz QPOs), which indicates that twin kHz QPOs may share the common properties of LXMBs and have the same physical origins. The distribution of Δν is quite different from a constant value, so is ν 2/ν₁ from a constant ratio. The weighted mean values and maxima of ν₁ and ν₂ in Atoll sources are slightly higher than those in Z sources. We also find that shift‐and‐add technique can reconstruct the distributions of ν₁ and Δν. The K‐S test results of ν₁ and Δν between Atoll and Z sources from data with shift‐and‐add are quite different from those without it, and we think that this may be caused by the selection biases of the sample. We also study the properties of the quality factor (Q) and the root‐meansquared (rms) amplitude of 4U 0614+09 with data from the two observational methods, but the errors are too big to make a robust conclusion. The NS spin frequency (ν_s) distribution of 28 NS‐LMXBs show a bigger mean value (∼408 Hz) than that (∼281 Hz) of the radio binary millisecond pulsars (MSPs), which may be due to the lack of the spin detections from Z sources (systematically lower than 281 Hz). Furthermore, on the relations between the kHz QPOs and NS spin frequency ν_s, we find the approximate correlations of the mean values of Δν with NS spin and its half, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Symbiotic stars with spectral indication of bipolar ejection and stellar wind     

N.A. Tomov  M.T. Tomova  D.V. Bisikalo 《Astronomische Nachrichten》2014,335(2):178-188

Four out of a total of five symbiotic systems whose optical spectral lines contain satellite components indicating collimated ejection have an additional absorption of P Cyg type with different velocity. These systems are Z And, Hen 3‐1341, StHα 190, and BF Cyg. It is shown that the line profiles of every of these systems can be interpreted in the framework of a model of a collimated stellar wind from the hot compact component proposed initially to interpret the line profiles of Z And, observed during its last active phase after 2000. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Time‐series high‐resolution spectroscopy and photometry of ε Aurigae from 2006–2013: Another brick in the wall     

K. G. Strassmeier  M. Weber  T. Granzer  L. Schanne  J. Bartus  I. Ilyin 《Astronomische Nachrichten》2014,335(9):904-934

We present continuous and time‐resolved R = 55 000 optical échelle spectroscopy of ε Aurigae from 2006–2013. Data were taken with the STELLA Echelle Spectrograph of the robotic STELLA facility at the Observatorio del Teide in Tenerife. Contemporaneous photometry with the Automatic Photoelectric Telescopes at Fairborn Observatory in Arizona is presented for the years 1996–2013. Spectroscopic observations started three years prior to the photometric eclipse and are still ongoing. A total of 474 high‐resolution échelle spectra are analyzed and made available in this paper. We identify 368 absorption lines of which 161 lines show the characteristic sharp disk lines during eclipse. Another 207 spectral lines appeared nearly unaffected by the eclipse. From spectrum synthesis, we obtained the supergiant atmospheric parameters T_eff = 7395 ± 70 K, log g ≈ 1, and [Fe/H] = +0.02 ± 0.2 with ξ_t = 9 km s^–1, ζ_RT = 13 km s^–1, and v sin i = 28 ± 3 km s^–1. The residual average line broadening expressed in km s^–1 varies with a period of 62.6 ± 0.7 d, in particular at egress and after the eclipse. Two‐dimensional line‐profile periodograms show several periods, the strongest with ≈110 d evident in optically thin lines as well as in the Balmer lines. Center‐of‐intensity weighted radial velocities of individual spectral lines also show the 110‐d period but, again, additional shorter and longer periods are evident and are different in the Balmer lines. The two main spectroscopic Hα periods, ≈ 116 d from the line core and ≈ 150 d from the center‐of‐intensity radial velocities, appear at 102 d and 139 d in the photometry. The Hβ and Johnson V I photometry on the other hand shows two well‐defined and phase‐coherent periods of 77 d and 132 d. We conclude that Hα is contaminated by changes in the circumstellar environment while the Hβ and V I photometry stems predominantly from the non radial pulsations of the F0 supergiant. We isolate the disk‐rotation profile from 61 absorption lines and found that low disk eccentricity generally relates to low disk rotational velocity (but not always) while high disk eccentricity always relates to high velocity. There is also the general trend that the disk‐absorption in spectral lines with higher excitation potential comes from disk regions with higher eccentricity and thus also with higher rotational velocity. The dependency on transition probability is more complex and shows a bi‐modal trend. The outskirts of the disk is distributed asymmetrically around the disk and appears to have been built up mostly in a tail along the orbit behind the secondary. Our data show that this tail continues to eclipse the F0 Iab primary star even two years after the end of the photometric eclipse. High‐resolution spectra were also taken of the other, bona‐fide, visual‐binary components of ε Aur (ADS 3605BCDE). Only the C‐component, a K3‐4‐giant, appears at the same distance than ε Aur but its radial velocity is in disagreement with a bound orbit. The other components are a nearby (≈ 7 pc) cool DA white dwarf, a G8 dwarf, and a B9 supergiant, and not related to ε Aur. The cool white dwarf shows strong DIB lines that suggest the existence of a debris disk around this star. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Seven years photometry of the W UMa‐type eclipsing binary V2612 Oph     

O. zdarcan  G. Ta 《Astronomische Nachrichten》2014,335(8):833-840

We present the first long‐term Johnson UBVR observations and comprehensive photometric analysis of the W UMa‐type eclipsing binary V2612 Oph. Observations in the time interval between 2003 and 2009 enabled us to reveal the seasonal and long‐term variations of the light curve. Hence, we found that the mean brightness level of the light curve shows a variation with a period of 6.7 years. Maximum and minimum brightness levels of the light curve exhibit a variation from year to year which we attribute to a solar‐like activity. The O – C variation of eclipse timings of the system shows a decreasing parabolic trend and reveals a period decrease at a rate of P = 6.27×10^‐7 day yr^‐1 with an additional low‐amplitude sinusoidal variation that has a similar period as the long‐term brightness variations. Our light curve analysis shows that the system is a W‐subtype W UMa eclipsing binary. We calculated masses and radii of the primary and secondary components as M₁ = 1.28 M_⊙, M₂ = 0.37 M_⊙ and R₁ = 1.31 R_⊙, R₂ = 0.75 R_⊙, respectively. The derived absolute photometric parameters allow us to calculate a distance of 140 pc, which confirms that the system is a foreground star in the sky field of the Galactic open cluster NGC 6633. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Distribution of CMEs with Different Angular Widths and Comparison with the Phase of Sunspot Number in the 23rd Solar Cycle     

MENG Wei-juan  LE Gui-ming  LIN Zhao-xiang  ZHANG Yong  YANG Xing-xing 《Chinese Astronomy and Astrophysics》2014

The variation of the number of coronal mass ejections (CMEs) with different angular widths in the period of 1996-2008 is analyzed statistically in this paper, together with a comparison of the feature of time variation between the number of CMEs with some typical angular widths and the number of sunspots.  相似文献   

A Preliminary Research on the Development of the Hard X-ray Imaging Telescope     

ZHENG Chun-xiao  CAI Ming-sheng  HU Yi-ming  HUANG Yong-yi  GONG Yi-zhong 《Chinese Astronomy and Astrophysics》2014

The hard X-ray imaging telescope based on the Fourier transform imaging technique is introduced. The double-layer parallel gratings are used to make the modulation and coding on the light emerging from a celestial X-ray source, the modulated light is acquired, to make the optoelectronic conversion by scintillation crystal detectors, and ?nally read out by the electronic system. The modulation collimator X-ray telescopes can be divided into two types: the spatial modulation and temporal modulation. The temporal modulation system requires the scanning motion of the detector system, but the spatial modulation system requires no motion. The technology of grating fabrication is investigated, and the basic structure design of the collimators is given. The principal compo- nents of the prototype hard X-ray imaging telescope of spatial modulation type are successfully developed, including the 8 CsI crystal detector modules (contain- ing photomultipliers or PMTs), 8-channel shaping ampli?ers (two of them are prepared for experiments), and the data acquisition system. And the preliminary test results of the electronic system are also given.  相似文献   

Long term optical variability of bright X-ray point sources in elliptical galaxies     

V.Jithesh  Ranjeev Misra  P.Shalima  K.Jeena  C.D.Ravikumar  B.R.S.Babu 《中国天文和天体物理学报》2014,(10)

We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array(ACIS-S) and observations from the Hubble Space Telescope(HST) Advanced Camera for Surveys.Out of the 46 bright(X-ray counts 60)sources that are in the common field of view of the Chandra and HST observations,34 of them have potential optical counterparts,while the rest of them are optically dark.After taking into account systematic errors,estimated using optical sources in the field as a reference,we find that four of the X-ray sources(three in NGC 1399 and one in NGC 1427) have variable optical counterparts at a high level of significance.The X-ray luminosities of these sources are ~ 10~(38) erg s~(-1) and are also variable on similar time scales.The optical variability implies that the optical emission is associated with the X-ray source itself rather than being the integrated light from a host globular cluster.For one source,the change in optical magnitude is 0.3,which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity.However,the optically variable sources in NGC 1399 have been reported to have blue colors(g- z 1).All four sources have been detected in the infrared(IR) by Spitzer as point sources,and their ratios of 5.8 to 3.6 μm flux are 0.63,indicating that their IR spectra are like those of Active Galactic Nuclei(AGNs).While spectroscopic confirmation is required,it is likely that all four sources are background AGNs.We find none of the X-ray sources having optical/IR colors different from AGNs to be optically variable.  相似文献   

样本输入方式对极端学习机预报日长变化的影响     

雷雨  蔡宏兵  赵丹宁 《天文研究与技术》2015,(3)

针对极端学习机(Extreme Learning Machine,ELM)用于日长(Length-Of-Day,LOD)变化预报过程中,样本输入方式对预报结果的影响进行了研究。采用跨度、连续和迭代3种样本输入方式对日长变化进行预报。结果表明,不同的样本输入方式对预报结果有很大影响,样本按跨度输入的预报精度最低;样本采用连续输入方式在短期和中长期预报中预报精度较高,但计算速度较慢,较适合中长期预报;样本按迭代输入方式的短期预报精度稍优于连续输入方式,而中长期预报精度则不如连续输入方式,但具有较高的预报效率。这对于日长变化的实时快速预报有着较高的现实意义。  相似文献   

Absolute parameters of southern eclipsing binary: MW Pup     

《New Astronomy》2015

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