共查询到20条相似文献，搜索用时 15 毫秒
1.
E. A. Evangelidis 《Astrophysics and Space Science》1988,143(1):113-121
It is proved that (1) electromagnetic fields with electric and magnetic components parallel to one another are solutions of Maxwell's equations; (2) the equationB(B)=0 (B is the magnetic field) is gauge and relativistically-invariant for systems of reference moving with velocityv/c=EB(1+v
2/c
2)/(E
2+B
2). 相似文献
2.
We present the results of modelling of the radio spectrum evolution and dispersion measure variations of PSR B1259–63, a pulsar in a binary system with Be star LS 2883.We base our model on a hypothesis that the observed variations of the spectrum are caused by thermal free-free absorption occurring in the pulsar surroundings. We reproduce the observed pulsar spectral shapes in order to examine the influence of the stellar wind of LS 2883 and the equatorial disc on the pulsar’s radiation.The simulations of the pulsar’s radio emission and its consequent free-free absorption give us an insight into the impact of stellar wind and equatorial disc of LS 2883 has on the shapes of PSR B1259–63 radio spectra, providing an evidence for the connection between gigahertz-peaked spectra phenomenon and the close environment of the pulsar. Additionally, we supplement our model with an external absorbing medium, which results in a good agreement between simulated and observational data. 相似文献
3.
S. Geier U. Heber H. Edelmann L. Morales-Rueda R. Napiwotzki 《Astrophysics and Space Science》2010,329(1-2):127-131
The formation of sdBs as well as the chemical composition of their atmospheres is still puzzling. While helium and other light elements are depleted relative to solar values, heavy elements are highly enriched. Diffusion processes in the hot, radiative atmosphere of these stars are the most likely explanation. Although several attempts have been made, it has not yet been possible to model all the observed features of sdB atmospheres. A drawback of most prior studies was the small sample size. We present a detailed abundance analysis of 139 sdBs. A general trend of enrichment was found with increasing temperature for most of the heavier elements. The lighter elements like carbon, oxygen and nitrogen are depleted and less affected by temperature. Although there is considerable scatter from one star to the other, the general abundance patterns in most sdBs are similar. An interplay between gravitational settling, radiative levitation and weak winds is most likely responsible. About 3% of the analysed stars show an enrichment in carbon and helium, which cannot be explained in the framework of diffusion alone. Nuclear processed material must have been transported to the surface somehow. 相似文献
4.
Jian-Ling Chen Hong-Guang Wang Wan-Hai Chen Hui Zhang Yi Liu Center for Astrophysics Guangzhou University Guangzhou National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2007,7(6):789-802
Based on dividing the profile into a number of absolute phase intervals,the phase-resolved spectra (PHRS) are derived from published time-aligned average profiles at radio frequencies over two decades for the classic conal-double pulsar B1133 16. The relative spectral index,defined as the difference between the spectral indices of a reference and the given arbitrary phase interval,is obtained by power-law fit at each phase interval. The derived phase-resolved spectra show an "M-like" shape,of which the leading part and trailing part are approximately symmetrical. The basic feature of the PHRS is that the spectrum first flat-tens then steepens as the pulse phase sweeps from the profile center to the profile edges. The PHRS provide a coherent explanation of the major features of profile evolution of B1133 16,namely,the pulse width shrinkage with increasing frequency and the frequency evolution of the relative intensity between the leading and trailing conal components,and the bridge emission. The PHRS may be an indicator for emission spectral variation across the pulsar magnetosphere. Possible mapping from PHRS to emission-location-dependent spectral vari-ation is presented,and some intrinsic mechanisms are discussed. 相似文献
5.
We used the Fourier decomposition technique to investigate the stability of the X-ray pulse profile of a young pulsar PSR B1509–58 by studying the relative amplitudes and phase differences of its harmonic components with respect to the fundamental using data from the Rossi X-Ray Timing Explorer. Like most young rotation powered pulsars, PSR B1509–58 has a high spin down rate. It also has less timing noise, allowing accurate measurement of higher order frequency derivatives which in turn helps in the study of the physics of pulsar spin down. Detailed investigation of pulse profiles over the years will help us establish any possible connection between the timing characteristics and the high energy emission characteristics for this pulsar.Furthermore, the study of pulse profiles of short period X-ray pulsars can also be useful when used as a means of interplanetary navigation. The X-ray pulse profile of this source has been analyzed for 15 yr(1996–2011). The long term average amplitudes of the first, second and third harmonics(and their standard deviation for individual measurements) compared to the fundamental are 36.9%(1.7%), 13.4%(1.9%) and 9.4%(1.8%) respectively. Similarly, the phases of the three harmonics(and standard deviations) with respect to the fundamental are 0.36(0.06), 1.5(0.2) and 2.5(0.3) radian respectively. We do not find any significant variation of the harmonic components of the pulse profile in comparison to the fundamental. 相似文献
7.
H. Hüseyİn Mentese 《Astrophysics and Space Science》1988,146(1):27-32
We have studied the interstellar column densities in the direction of the star Cas with the IUE high resolution SWP spectrum so as to see the relations of element depletions with condensation temperature and compare our results with the interstellar column densities in the directions of the other B-type stars obtained with the COPERNICUS satellite.Based on the observations made by the International Ultraviolet Explorer (IUEO, and collected at the Villafranca Satellite Tracking Station of European Space Agency. 相似文献
8.
H. Hüseyin Menteşe 《Astrophysics and Space Science》1994,220(2):279-287
We have investigated the star Ori with IUE high resolution SWP spectrum in order to derive curve of growth and column densities of Al II, Si II, S II, Fe II, Ni II and Zn II. It has been possible to fit these ions on one empirical curve of growth with a velocity parameterb = 11 km s–1 for the star studied.Based on observations made by the International Ultraviolet Explorer (IUE), and collected at the Villafranca Satellite Tracking Station of the European Space Agency. 相似文献
9.
Ren-Xin Xu Department of Astronomy School of Physics Peking University Beijing 《中国天文和天体物理学报》2006,6(5)
Efforts are made to understand the timing behaviors (e.g., the jumps in the projected pulsar semimajor axis at the periastron passages) observed in the 13-year monitoring of PSR B1259-63. Planet-like objects are suggested to orbit around the Be star, which may gravitationally perturb the (probably low mass) pulsar when it passes through periastron. An accretion disk should exist outside the pulsar's light cylinder, which creates a spindown torque on the pulsar due to the propeller effect. The observed negative braking index and the discrepant timing residuals close to periastron could be related to the existence of a disk with a varying accretion rate. A speculation is presented that the accretion rate may increase on a long timescale in order to explain the negative braking index. 相似文献
10.
High dispersion CCD spectra are used to study the profiles of the Hα and Hβ lines of 48 stars in early spectral classes in
the young diffuse binary cluster h/χ Per. In addition, moderate resolution spectra of 15 B and Be stars were taken over the
interval 4400–4960 Å. One or, possibly, two new Be stars are discovered. The major parameters of the Hα line are measured
for the observed B and Be stars. The spectra over 4400–4960 Å are used to estimate Teff, logg, and υsin i. No traces of emission are detected in the Hα line profiles for 28 of the stars and emission is observed in the Hα line
for 20. During our observations an absorption profile of the Hα line was observed for some of the stars, such as Oo146, Oo566,
Oo922, and Oo1268, although they have previously been identified as Be stars. A significant long-term variability of the Hα
line is discovered for the Be stars Oo1161 and Oo2242. Oo2371 manifests a variability in its faint emission spectrum which
is typical of close binary systems that include a Be star.
__________
Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008). 相似文献
11.
B. Rudak 《Journal of Astrophysics and Astronomy》2018,39(4):48
A review of observational properties of the Vela pulsar across a wide energy spectrum is given. Then current approaches to the modelling of pulsars and their wind zones are briefly presented. The challenges posed to the models by the diversity of Vela’s light curves in different energy ranges are discussed. 相似文献
12.
I. G. Richardson T. T. von Rosenvinge H. V. Cane E. R. Christian C. M. S. Cohen A. W. Labrador R. A. Leske R. A. Mewaldt M. E. Wiedenbeck E. C. Stone 《Solar physics》2014,289(8):3059-3107
Using observations from the High Energy Telescopes (HETs) on the STEREO A and B spacecraft and similar observations from near-Earth spacecraft, we summarize the properties of more than 200 individual >?25 MeV solar proton events, some detected by multiple spacecraft, that occurred from the beginning of the STEREO mission in October 2006 to December 2013, and provide a catalog of these events and their solar sources and associations. Longitudinal dependencies of the electron and proton peak intensities and delays to onset and peak intensity relative to the solar event have been examined for 25 three-spacecraft particle events. Expressed as Gaussians, peak intensities fall off with longitude with σ=47±14° for 0.7?–?4 MeV electrons, and σ=43±13° for 14?–?24 MeV protons. Several particle events are discussed in more detail, including one on 3 November 2011, in which ～?25 MeV protons filled the inner heliosphere within 90 minutes of the solar event, and another on 7 March 2012, in which we demonstrate that the first of two coronal mass ejections that erupted from an active region within ～?1 hour was associated with particle acceleration. Comparing the current Solar Cycle 24 with the previous cycle, the first >?25 MeV proton event was detected at Earth in the current solar cycle around one year after smoothed sunspot minimum, compared with a delay of only two months in Cycle 23. Otherwise, solar energetic particle event occurrence rates were reasonably similar during the rising phases of Cycles 23 and 24. However, the rate declined in 2013, reflecting the decline in sunspot number since the peak in the northern-hemisphere sunspot number in November 2011. Observations in late 2013 suggest that the rate may be rising again in association with an increase in the southern sunspot number. 相似文献
13.
We report results from a multi-wavelength study of the 3B/X1.2 two-ribbon disk flare (S15E44), which was well observed by both ground-based and space-borne instruments. Two pairs of conjugate kernels - K1 and K4, and K2 and K3 - in the Ha images are identified. These kernels are linked by two different systems of EUV loops. Kl and K4 correspond to the two 17 GHz and 34 GHz microwave sources observed by the Nobeyama Radioheliograph (NoRH), while K2 and K3 have no corresponding microwave sources. Optical spectroscopic observations suggest that all the four kernels are possible precipitating sites of non-thermal electrons. Thus the energy of electron deposited in K2 and K3 should be less than 100 keV. Two-dimensional distributions of the full widths at half maximum (FWHM) of the Ha profiles and the line-of-sight (LOS) velocities derived from the Ca Ⅱ 8542 (?) profiles indicate that the largest FWHM and LOS velocity tends to be located near the outer edges of Ha kernels, which is consistent with the scenario of current two-ribbon flare models and previous results. When non-thermal electron bombardment is present, the observed Ha and Ca Ⅱ 8542 (?) profiles are similar to previous observational and theoretical results, while the He I 10830 A profiles are different from the theoretical ones. This puts some constraints on future theoretical calculation of the He I 10830 (?) line. 相似文献
14.
On 2002 July23,a 2B/X4.8 flare was observed in the Hα line spec-tropolarimetrically by the Large Solar Vacuum Telescope of Baikal Astrophysical Observatory.Linear polarization of 3%-10% was detected in the Hα line,particu-larly where the line showed central reversal.The linear polarization is mainly radial on the solar disk and appears at the impulsive phase of the hard X-ray and γ-ray bursts.It is limited to some relatively small regions of the flare.The polarization in a limited small region(～4″-5″）changed its direction within a short period of time(～10s). 相似文献
15.
Yu. P. Ilyasov M. Imae Y. Hanado V. V. Oreshko V. A. Potapov A. E. Rodin M. Sekido 《Astronomy Letters》2005,31(1):30-36
We present the results from our timing of the millisecond pulsar B1937+21, performed jointly since 1997 on two radio telescopes: the RT-64 in Kalyazin (Russia) at a frequency of 0.6GHz and RT-34 in Kashima (Japan) at a frequency of 2.15 GHz. The rms value of the pulse time of arrival (TOA) residuals for the pulsar at the barycenter of the Solar system is 1.8 μs (the relative variation is ≈10?14 over the observing period). The TOA residuals are shown to be dominated by white phase noise, which allows this pulsar to be used as an independent time scale keeper. The upper limit for the gravitational background energy density Ωgh2 at frequencies ≈6.5 × 10?9 Hz is estimated to be no higher than 10?6. Based on the long-term timing of the pulsar, we have improved its parameters and accurately determined the dispersion measure and its time variation over the period 1984–2002, which was, on average, ?0.00114(3) pc cm?3 yr?1. 相似文献
16.
We present a multiwavelength analysis of a long-duration, white-light solar flare (M8.9/3B) event that occurred on 04 June 2007 from AR NOAA 10960. The flare was observed by several spaceborne instruments, namely SOHO/MDI, Hinode/SOT, TRACE, and STEREO/SECCHI. The flare was initiated near a small, positive-polarity, satellite sunspot at the center of the active region, surrounded by opposite-polarity field regions. MDI images of the active region show a considerable amount of changes in the small positive-polarity sunspot of δ configuration during the flare event. SOT/G-band (4305 Å) images of the sunspot also suggest the rapid evolution of this positive-polarity sunspot with highly twisted penumbral filaments before the flare event, which were oriented in a counterclockwise direction. It shows the change in orientation, and also the remarkable disappearance of twisted penumbral filaments (≈35?–?40%) and enhancement in umbral area (≈45?–?50%) during the decay phase of the flare. TRACE and SECCHI observations reveal the successive activation of two helically-twisted structures associated with this sunspot, and the corresponding brightening in the chromosphere as observed by the time-sequence of SOT/Ca?ii H line (3968 Å) images. The secondary, helically-twisted structure is found to be associated with the M8.9 flare event. The brightening starts six?–?seven minutes prior to the flare maximum with the appearance of a secondary, helically-twisted structure. The flare intensity maximizes as the secondary, helically-twisted structure moves away from the active region. This twisted flux tube, associated with the flare triggering, did not launch a CME. The location of the flare activity is found to coincide with the activation site of the helically-twisted structures. We conclude that the activation of successive helical twists (especially the second one) in the magnetic-flux tubes/ropes plays a crucial role in the energy build-up process and the triggering of the M-class solar flare without a coronal mass ejection (CME). 相似文献
17.
Rodolfo Batista Negri Antonio Fernando Bertachini de Almeida Prado Alexander Sukhanov 《Celestial Mechanics and Dynamical Astronomy》2017,129(3):269-284
The swing-by maneuver is a technique used to change the energy of a spacecraft by using a close approach in a celestial body. This procedure was used many times in real missions. Usually, the first approach to design this type of mission is based on the “patched-conics” model, which splits the maneuver into three “two-body dynamics.” This approach causes an error in the estimation of the energy variations, which depends on the geometry of the maneuver and the system of primaries considered. Therefore, the goal of the present paper is to study the errors caused by this approximation. The comparison of the results are made with the trajectories obtained using the more realistic restricted three-body problem, assumed here to be the “real values” for the maneuver. The results shown here describe the effects of each parameter involved in the swing-by. Some examples using bodies in the solar system are used in this part of the paper. The study is then generalized to cover different mass parameters, and its influence is analyzed to give an idea of the amount of the error expected for a given system of primaries. The results presented here may help in estimating errors in the preliminary mission analysis using the “patched-conics” approach. 相似文献
18.
19.
We present the pattern of the polar magnetic reversal for cycle 23 derived from H synoptic charts and have also included the reversals of the earlier cycles 18–22 for comparison. At the beginning of a new cycle (i.e., soon after the polar reversal) the zonal boundaries of unipolar magnetic regions of opposite polarities (seen as filament bands on the synoptic charts) appear close to and on either side of the equator continuing through the years of minimum indicating the onset of the cancellation of flux at these low latitudes. The cycle thus starts with cancellation of flux close to the equator and ends with the polar reversal or flux cancellation near the poles. The filament bands just below the polemost ones migrate and reach latitudes 35°–45° by the time of polar reversal and become the polemost, once the polar reversal has taken place. During the years of minimum that follow, these filament bands remain more or less stagnant at the latitudes 35°–45° except for occasional slow migration towards the equator. The migration to the poles starts at a low speed of 3 m s–1 only when the spot activity has risen to a significant level and then it accelerates to 30 m s–1 at the peak of the activity. It takes 3–4 years for the polemost bands to reach the poles moving at these high speeds. We quantify this possible cause and effect phenomenon by introducing the concept of the `strength of the solar cycle' and represent this by either of a set of three parameters. We show that the velocity of poleward migration is a linear function of the `strength of the solar cycle'. 相似文献
20.
L. Zaninetti 《中国天文和天体物理学报》2006,6(4):387-395
The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2,3),-2D cut of 3D Voronoi diagram-are explored, with the single-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated Vp(2,3) map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CfA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size. 相似文献