共查询到20条相似文献，搜索用时 31 毫秒
1.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
2.
3.
In the numerical integrations of the outer planets, when the inner planets are not considered, the initial conditions are determined by least square adjustment with a complete ephemeris. In the present work, we compute the resulting uncertainty on the initial conditions by the analysis of the very simple problem which consists in fitting by least squares a straight line to a sine curve. Explicit formulae for the computation of the error due to the fitting process are given. In particular, fitting over an integer number of periods is very close to the worst case. The determination of the initial conditions in the LONGSTOP project (Milani,et al., 1987) is analysed as an example. It is shown that the uncertainty on the main frequencies of the secular system due to the determination of the initial conditions is of the order of 0.01 arcsec/year. 相似文献
4.
Tapan K. Chatterjee 《Astrophysics and Space Science》1981,76(2):491-502
The tidal force effects of a spherical galaxy passing head-on through a disk galaxy have been studied at various regions of the disk galaxy and for various orientations of the disk galaxy with respect to the direction of relative motion of the two galaxies. The density distribution of the disk galaxy is taken to be, (r)=ce–4r/R
, where c is the central density andR is the radius of the disk. The density distribution of the spherical galaxy is taken to be that of a oolytrope of indexn=4. It is found that as a result of the collision, through the central parts and the outer parts of the disk galaxy remain intact, the region in between these two regions disrupts. Thus a ring galaxy with a nucleus embedded in the ring-i.e., a ring galaxy of the RN-type, is formed. 相似文献
5.
V. Batllo 《Celestial Mechanics and Dynamical Astronomy》1998,71(3):191-201
The objective of this paper is to develop a simple model of an encounter between a comet and a planet, with a subsequent capture
or an escape, and to study the potential consequences. The hypothetical scenario is as follows: a comet with a conic orbit
meets close to one of its vertices (located near the ecliptic plane), a jovian planet, and transforms its orbit. There are
two hypotheses which are made for the shock: this vertex becomes one of the final vertices and the orbital plane of the comet
is unchanged during the encounter as it was the case for Brooks 2 in 1886.
In this model, it was able to find an equation which was then used to obtain the pre‐ and post‐encounter orbits elements and
the kind of orbit (ellipse, hyperbola, parabola) with respect to the initial inclination. The numerical experiments with the
observed comets often provide pre‐encounter orbits with an aphelion point located near another jovian planet farther from
the Sun, and so on with sometimes several planets, or with an aphelion point located beyond the Pluto orbit.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
We formulate the problem of an infinitesimal particle moving in the space under the influence of the gravitational force induced
by a homogeneous annulus disk fixed on a plane. We compute using different coordinates and in terms of an elliptic integral
the potential associated to this problem. Also we study the symmetries of the associated potential. After that, we look at
the dynamics in some particular cases, namely: in the line perpendicular to the plane that contains the annulus disk and passes
through the center of the ring and on the plane that contains the massive annulus.
相似文献
7.
We present a quasar model with a rotating disk and a massive nucleus. We use this model in order to characterize the motion in the model (regular or chaotic) and to connect the extent of the chaotic regions to the physical parameters of the model. Numerical experiments suggest that, there are connections between the extent of the chaotic areas and the parameters of the system. Furthermore, it is shown that the form of numerically found relationships can be expressed analytically. Comparison to previous work is also made. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Xinwu Cao 《Astrophysics and Space Science》1995,226(1):165-168
The inclination of the field lines at the surface of the disc plays a crucial role on the nature of the magnetically driven flows. For the non-relativistic case, a centrifugally driven outflow of matter from the disc is possible, if the poloidal component of the magnetic field makes an angle of less than a critical 60° with the disc surface (Blandford and Payne 1982). We investigate the dynamical properties of the magnetically driven flows from the disc near a non-rotating black hole and find that the critical angle becomes larger than 60° when the flows start from the region near the black hole. 相似文献
9.
2009年11月,云南天文台射电天文研究团组采用40m射电望远镜以及基于DBBC（Digital Base Band Conveter）和Mark5B的VLBI记录系统对PSRJ08354510和PSRJ0332＋5434进行了观测。观测选用S波段右旋圆极化信号,起始频率为2206．99MHz,总带宽为32MHz。对数据进行相干消色散和平均后,得到PSRJ0332＋5434的单脉冲图像和两颗脉冲星的平均脉冲轮廓。由平均轮廓的展宽随时间的变化关系,对脉冲星的视周期作了一定修正后,得到信噪比更高的平均轮廓图。最后对轮廓的信噪比随时间的变化作了初步分析,由此可了解整个系统在观测时的稳定性。 相似文献
10.
Results of evolutionary calculations for a close binary system with a central helium burning He-star filling its Roche lobe and an accreting white dwarf are presented. Values for the mass of the components and the degree of central helium exhaustion before the filling of the Roche lobe are varied. It is shown that in such a system the mass accretion rate will remain for a long time (2–4) Ö 10–8
yr–1 ifq<1 (q=M
He,2/M
CO,1). The obtained results are discussed in connection with pre-supernova I phenomenon. 相似文献
11.
12.
H. Zirin 《Solar physics》1976,50(2):399-404
A large surge was observed on September 17, 1971, part of which, after travelling 200 000 km through the corona, returned to the surface to form a filament. The filament lasted about 30 min, then rose up and returned to the source of the surge. We interpret this as the filling of a semi-stable magnetic trap.The energetics of radio, X-ray, and surge expulsion are estimated. The radio spectrum and flux correspond to a thermal source of area 4 (arcmin)2, T 190 000 K, N
e
2
V 7 × 1048, which is optically deep at 8800 MHz.The soft X-ray source has T 12 × 106 K, N
e
2
V 3 × 1048; and if an equal mass is expelled in the surge, the kinetic energy of the surge is similar to the thermal energy of the X-ray source. 相似文献
13.
R.J. Strangeway 《Planetary and Space Science》1977,25(8):795-797
A spread in parallel beam velocity is found to have little effect on the previous results from the model by Dungey and Strangeway (1976). However, examination of the eigenfunctions for the same model indicates that perpendicular temperature may be the key to beam stability. 相似文献
14.
2009年11月,云南天文台射电天文研究团组采用40 m射电望远镜以及基于DBBC(Digital Base Band Conveter)和Mark 5B的VLBI记录系统对PSR J0835-4510和PSRJ0332+5434进行了观测。观测选用S波段右旋圆极化信号,起始频率为2 206.99 MHz,总带宽为32 MHz。对数据进行相干消色散和平均后,得到PSR J0332+5434的单脉冲图像和两颗脉冲星的平均脉冲轮廓。由平均轮廓的展宽随时间的变化关系,对脉冲星的视周期作了一定修正后,得到信噪比更高的平均轮廓图。最后对轮廓的信噪比随时间的变化作了初步分析,由此可了解整个系统在观测时的稳定性。 相似文献
15.
We investigate the motion, near the equilibrium configurations, of an initially spinless rigid body subject to an external
tidal field. Two cases are considered: when the center of mass of the body is at rest at the equilibrium point of the field
generated by a generic mass distribution, and when it is placed on a circular orbit subject to a spherically symmetric potential.
A complete analysis of the equilibrium configurations is carried out for both cases. First, we derive the conditions for the
stable equilibria, and then we analyze the frequencies of oscillations around the equilibrium positions. In view of these
results, we consider the problem of alignment of galaxies in clusters. After estimating the period of the oscillations induced
on the galaxies by the tidal field of the cluster, we discuss the possible effect of resonances between stellar orbits inside
the galaxy and the oscillations of the galaxy as a whole; this may be a mechanism responsible for producing an intracluster
stellar population.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
17.
18.
In a two-component cycle, the generation of the dipole field by a separate mechanism as well as the strong link occurring, with a 5–6-yr delay, between the sunspot cycle and the preceding dipole cycle, sets in new terms the problem of the mechanisms at the origin of the solar cycle. In this paper, from various series of synoptic solar data, we identify some of the mechanisms to incorporate in a model of a two-component solar cycle. The first one concerns the dipole field which is not a surface phenomenon. We establish the cyclic behaviour and the various properties of the dipole-field sources which are deep-seated in the solar interior and have a rigid rotation of about 27 days. We identify two cyclic phenomena which, in each hemisphere, link with a 5–6-yr delay, the dipole field generation which occurs at high latitudes, to the bipolar field emergence occurring at sunspot latitudes. They are the signatures of a coupling mechanism taking place deep in the solar interior. Then we study the constraints imposed on the mechanisms of the sunspot field generation both by a two-component cycle and by new observational results. These last ones concern the links occurring between the birth of new sunspot groups and the occurrence of pre-existing features of the photospheric field and of pivot-points in rigid rotation at 27.3 days.Our final discussion is devoted to a first sketch of the distribution of the relevant mechanisms among separate regions of the convective zone. Unfortunately neither the helioseismology, nor our data analysis has yet supplied us with appropriate pieces of information for building a physical model of this two-component cycle. 相似文献
19.
Olivier Thizy Christian Buil François Cochard Coralie Neiner 《Planetary and Space Science》2008,56(14):1878-1881
Amateur spectroscopists are getting organized to contribute to professional astronomy work. We present here the work done within the AUDE association to design, manufacture and distribute the Lhires III high-resolution Littrow spectrograph, which fits usual amateur telescopes and CCD cameras. We also review how the communication is organized through the ARAS distribution list (Spectro-L), forums, and workshops to develop and promote spectroscopic work among amateurs. Last but not least, we introduce the Be stars spectra (BeSS) Virtual Observatory-compatible database and its use for the monitoring of Be stars in association with the COROT satellite. 相似文献
20.
Up to now, 17 Neptune Trojan asteroids have been detected with their orbits being well determined by continuous observations. This paper analyzes systematically their orbital dynamics. Our results show that except for two temporary members with relatively short lifespans on Trojan orbits, the vast majority of Neptune Trojans located within their orbital uncertainties may survive in the solar system age. The escaping probability of Neptune Trojans, through slow diffusion in the orbital element space in 4.5 billion years, is estimated to be ～50%. The asteroid 2012 UW177 classified as a Centaur asteroid by the IAU Minor Planet Center currently is in fact a Neptune Trojan. Numerical simulations indicate that it is librating on the tadpole-shaped orbit around the Neptune's L4 point. It was captured into the current orbit approximately 0.23 million years ago, and will stay there for at least another 1.3 million years in the future. Its high inclination of i ≈ 54° not only makes it the most inclined Neptune Trojan, but also makes it exhibit the complicated and interesting co-orbital transitions between the leading and trailing Trojans via the quasi-satellite orbit phase. 相似文献