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《天文学进展》2019,(2)
周期修正项是长波授时信号的一个特征量,它通常与长波授时信号的跟踪点有关。在授时过程中,它是影响长波传播路径时延计算的重要因素。讨论了长波定时信号接收端感应电动势周期修正项与发射端电流信号周期修正项的不同,分析了磁天线和电天线对周期修正项的影响,计算了实际传播介质中周期修正项的大小。结果表明:当传播路径上的电参数恒定时,周期修正项与传播距离有关,传播距离越大,感应电动势的周期修正项也越大,并且两者呈线性关系。同时,周期修正项也受等效电导率等因素的影响,在恒定的距离上,等效电导率越小,周期修正项反而越大。授时用户可以利用感应电动势周期修正项的数值计算结果修正传播路径上的时延,有效地提高传播路径时延计算的精度,从而提高授时精度。 相似文献
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本文叙述了用CCD作重迭测量中,每片上量度坐标应作的大气折射较差修正和光行差较差修正,并推导了量度坐标的修正公式。 相似文献
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本文讨论了脉冲星磁偶极辐射模型所取得的成就和存在的困难,针对不足之处对磁偶极模型进行修正。从统计上得到修正因子与周期变率的幂律关系。由修正后的磁场强度得出其衰减时标大于108年,这与有关的理论研究结果一致。修正后的磁偶极模型给出周期变率和周期的新关系为р∝P-3,这恰好和р-P图中加速线以上的资料的统计拟合方程一致。 相似文献
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从球对称引力场中光子在赤道面上的运动微分方程出发,采用后牛顿近似方法,讨论了Reissner-Nordstr(o|¨)m度规场中雷达回波延迟实验的后后牛顿修正.通过计算给出了后牛顿以及后后牛顿的修正结果,当荷电量Q为零时,该结果适用于电中性天体,其后牛顿部分的修正与经典文献一致.文中采用的近似展开方法同样适用于讨论更高阶的修正.雷达回波的高阶修正对目前展开的高精度空间引力试验有着重要的参考价值. 相似文献
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本讨论了脉冲星磁偶极辐射模型所取得的成就和存在的困难,针对不足之处对磁偶极模型进行修正。从统计上得到修正因子与周期变率的幂律关系。由修正后的磁场强度得出其衰减时标大于10^8年,这与有关的理论研究结果一致。修正后的磁偶极模型给出周期变率和周期的新关系为P∝P^-3图中加速线以上的资料的统计拟合方程一致。 相似文献
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针对包含饱和样本数据的频数幂律分布拟合,提出一个新的幂律分布指数的极大似然估计方法的修正公式.对比研究显示,修正公式适用于剔除异常饱和值的幂律频数拟合.如果不剔除饱和值,幂律指数的估计只能使用修正前的公式,其误差随幂律指数变化,指数较小时误差较大.由此建议,对于包含饱和样本的频数分布拟合,首先剔除异常的饱和值,然后对剩余不含饱和值的子集使用修正公式进行参数估计. 相似文献
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望远镜静态指向模型的基本参数 总被引:5,自引:0,他引:5
对地平式望远镜静态指出模型的基本参数进行了讨论,给出了一种参数较少,模型稳定的望远镜修正模型,与常用的球谐函修正模型相比较,基本参数模型具有对观测资料分布不敏感,模型的系随资料分布变化较小和修正精度较高优点,并且其残差序列服从正态分布,基本上能够满足高精度定轨的需要。 相似文献
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Hong-Xing Yin Cheng-Min Zhang Yong-Heng Zhao Li-Ming Song Fan Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing Institute of High Energy Physics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(6):595-600
For the bright neutron star low-mass X-ray binary Sco X-1, we analyzed all updated frequencies of the twin kilohertz quasi-periodic oscillations (kHz QPOs), their correlations and distributions. We found that the frequency separation of the kHz QPO peaks appears not to be a constant, rather, it decreases with increasing inferred mass accretion rate. We show that the currently available data of Sco X-1 by Rossi X-ray Timing Explorer are inconsistent with the proposals of the beat model that the frequency separation is a constant. Our conclusions are consistent with those of some previous researchers and we discuss further implications for the kilohertz QPO models. 相似文献
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RXTE observations confirm that the X-ray light curve of V2400 Oph is pulsed at the beat cycle, as expected in a discless intermediate polar. There are no X-ray modulations at the orbital or spin cycles, but optical line profiles vary with all three cycles. We construct a model for line-profile variations in a discless accretor, based on the idea that the accretion stream flips from one magnetic pole to the other, and show that this accounts for the observed behaviour over the spin and beat cycles. The minimal variability over the orbital cycle implies that (1) V2400 Oph is at an inclination of only ≈10°, and (2) much of the accretion flow is not in a coherent stream, but is circling the white dwarf, possibly as a ring of denser, diamagnetic blobs. We discuss the light that this sheds on disc formation in intermediate polars. 相似文献
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SS433短周期变化中的拍现象 总被引:1,自引:0,他引:1
罗万前 《中国天文和天体物理学报》1989,(4)
本文用喷流模型计算SS433短周期变化的周期和振幅值。讨论短周期变化叠加成拍的条件。用此条件判断,很自然地得出:在短周期变化中可能存在拍现象。对于喷流模型,在一个进动周期内其拍频为2。 文中还利用了Margon,B·等人的SS433多普勒频移图作SS433多普勒频移的残差分布图。在分布图中,某些进动周期内显示出分布轮廓有双峰结构,分析产生双峰的原因,正是与章动有关的、短周期变化中的拍现象。因此,在SS433的163天多普勒频移图上,观测点始终存在10%的弥散,乃是163天进动曲线与不能消除的短周期中的拍叠加的结果。 这样,本文从理论和实测分析上都证认了SS433短周期变化中存在拍现象的可能性。 相似文献
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In this fourth paper in a series, we present a model of the remarkable temporal and azimuthal variability of the Io plasma torus observed during the Cassini encounter with Jupiter. Over a period of three months, the Cassini Ultraviolet Imaging Spectrograph (UVIS) observed a dramatic variation in the average torus composition. Superimposed on this long-term variation, is a 10.07-h periodicity caused by an azimuthal variation in plasma composition subcorotating relative to System III longitude. Quite surprisingly, the amplitude of the azimuthal variation appears to be modulated at the beat frequency between the System III period and the observed 10.07-h period. Previously, we have successfully modeled the months-long compositional change by supposing a factor of three increase in the amount of material supplied to Io's extended neutral clouds. Here, we extend our torus chemistry model to include an azimuthal dimension. We postulate the existence of two azimuthal variations in the number of superthermal electrons in the torus: a primary variation that subcorotates with a period of 10.07 h and a secondary variation that remains fixed in System III longitude. Using these two hot electron variations, our model can reproduce the observed temporal and azimuthal variations observed by Cassini UVIS. 相似文献
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Pulsating type IV solar radio bursts with beat structure are presented and analysed in this paper. Based upon the theory of whistler soliton emission we interpret the beat structure by the combination of two components with different pulsation frequencies due to radial oscillations of two legs of the magnetic loop. The large depth of pulsation is also explained in this model.Proceedings if the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.On leave from the Department of Astronomy, Nanjing University, Nanjing, The People's Republic of China. 相似文献
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Ermanno F. Borra 《Monthly notices of the Royal Astronomical Society》2008,389(1):364-370
Measurements of the spectrum of the fluctuations of the output current of the quadratic detector of a telescope can be used to find unresolved astronomical gravitational lenses and determine time delays between their image components. These time delays can be used for astronomical studies. The spatial correlation coefficient of a source is an important parameter that quantifies the loss of contrast, caused by the extendedness of the source, in the spectral modulation of the intensity fluctuations. This work shows that the correlation coefficient must not be evaluated at the frequency of observation, but must instead be evaluated at the much lower beat frequencies of the spectrum of the fluctuations. This opens up a powerful, novel technique to find unresolved gravitational lenses and to study the lensing event and the source. 相似文献
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Systematic measurements of the differential Doppler velocity of the Sun have been performed in Crimea from 1974 through 1988 (total 987 days, 6197 hours of observations). They confirm the presence of a long-term phase-coherent solar pulsation with a period of 160.010 min. On the other hand, the analysis of new data suggests that solar 160 min pulsation might, in frequency, have a multiplet fine structure. In particular, large changes of amplitude and phase of the pulsation over the years 1982–1986 may indicate that during the last few years we have been observing the solar 160 min oscillation of the second portion of the 22 year solar cycle.It is further noted that the beat period of the two closely spaced frequencies (periods are 160.0101 and 160.0126 min) equals 19.5 ± 1.1 year, which is in good agreement with the average length of the solar magnetic activity cycle, 20–22 years. Being verified, this unpredicted property of the pulsation can offer a novel possibility for probing the Sun's interior and perhaps for the study of the internal rotation and 11(22) year cycle of a star. 相似文献