Multiple frequency analysis of the large-amplitude SX Phoenicis star BL Camelopardalis     

Ai-Ying Zhou  E. Rodríguez  Shi-Yang Jiang  A. Rolland  Víctor Costa 《Monthly notices of the Royal Astronomical Society》1999,308(3):631-639

A multifrequency analysis of the SX Phoenicis star BL Camelopardalis is presented on the basis of new high-speed photometry, along with fitting a total of 136 maxima. BL Cam is a multiple periodic pulsator. We find f ₀=25.5768, f ₁=25.2982, f ₂=25.8622, f ₃=31.5912, f ₄=25.1065, f ₅=25.5147 and f ₆=25.6188 cycle d⁻¹ together with the harmonics 51.1513 and 76.7268 cycle d⁻¹ and combination frequencies f ₀+ f ₁, f ₀+ f ₂ and f ₀+ f ₃. The new frequency solution represents the light curves of BL Cam quite well. The observed minus calculated (O-C) analysis indicates that the fundamental frequency is in good agreement with the results of Fourier analysis.  相似文献   

Detection of high‐frequency optical oscillation during the flare phase of EV Lac in 1999     

M. E. Contadakis  S. Avgoloupis  J. Seiradakis  B. E. Zhilyaev  Ya. O. Romanyuk  I. A. Verlyuk  O. A. Svyatogorov  V. R. Khalack  A. V. Sergeev  R. K. Konstantinova‐Antova  A. P. Antov  R. S. Bachev  I. Y. Alekseev  V. E. Chalenko  D. N. Shakhovskoy 《Astronomische Nachrichten》2004,325(5):427-432

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Amplitude,frequency and drivers of Caspian Sea lake-level variations during the Early Pleistocene and their impact on a protected wave-dominated coastline     

Elisabeth L. Jorissen  Hemmo A. Abels  Frank P. Wesselingh  Sergei Lazarev  Vusala Aghayeva  Wout Krijgsman 《Sedimentology》2020,67(1):649-676

The Caspian Sea, the largest isolated lake in the world, witnessed drastic lake-level variations during the Quaternary. This restricted basin appears very sensitive to lake-level variations, due to important variations in regional evaporation, precipitation and runoff. The amplitude, frequency and drivers of these lake-level changes are still poorly documented and understood. Studying geological records of the Caspian Sea might be the key to better comprehend the complexity of these oscillations. The Hajigabul section documents sediment deposited on the northern margin of the Kura Basin, a former embayment of the Caspian Sea. The 2035 m thick, well-exposed section was previously dated by magneto-biostratigraphic techniques and provides an excellent record of Early Pleistocene environmental, lake-level and climate changes. Within this succession, the 1050 m thick Apsheronian regional stage, between ca 2·1 Ma and 0·85 Ma, represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes. Sequences are regressing from offshore to coastal, lagoonal or terrestrial settings and are bounded by abrupt flooding events. Sediment reveals a low energy, wave-dominated, reflective beach system. Wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean. Water depth estimations of the wave baselines allow reconstruction of a lake-level curve, recording oscillations of ca 40 m amplitude. Cyclostratigraphic analyses display lake-level frequency close to 41 kyr, pointing to allogenic forcing, dominated by obliquity cycles and suggesting a direct or indirect link with high-latitude climates and environments. This study provides a detailed lake-level curve for the Early Pleistocene Caspian Sea and constitutes a first step towards a better comprehension of the magnitude, occurrence and forcing mechanisms of Caspian Sea lake-level changes. Facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake-level fluctuations may form good analogues for other (semi-)isolated basins worldwide.  相似文献   

Internal co-seismic deformation and curvature effect based on an analytical approach          下载免费PDF全文

Jie Dong  Wenke Sun 《地震科学（英文版）》2017,30(1):47-56

In this study, we present a new method to compute internal co-seismic deformations of a homogeneous sphere, based on our previous approach (Dong et al. 2016). In practical numerical computations, we consider a strike-slip point source as an example, and compute the vertical co-seismic displacement on different internal spherical surfaces (including the Earth surface). Numerical results show that the internal co-seismic deformations are generally larger than that on the Earth surface; especially, the maximum co-seismic displacement appears around the seismic source. The co-seismic displacements are opposite in sign for the areas over and beneath the position of the seismic source. The results also indicate that the curvature effect of the internal deformation is pretty large, and larger than that on the Earth surface. The results indicate that the dislocation theory for a sphere is necessary in computing internal co-seismic deformations.  相似文献   

基于CHAMP卫星与地面矢量数据联合建立中国地磁模型          下载免费PDF全文

冯彦  孙涵  蒋勇  安振昌  姜乙  刘宝嘉  黄娅  张华  武业文 《地球物理学报》2017,60(7):2522-2533

首先对地面台站以及CHAMP卫星的矢量磁测数据进行预处理,结合12个子午工程台站最新的磁测数据,并利用第十二代国际地磁参考场模型(IGRF12)对不同数据归算至统一时间点,再结合第四代地磁场综合模型(CM4)计算并移除主磁场、磁层磁场、电离层磁场、感应磁场及较为微弱的环形场,最后通过球冠谐(SCH)模型联合建立了中国地区岩石圈磁场(地磁要素X、Y、Z和总强度F)的球冠谐模型(SCH2000),结合IGRF12得到了中国地磁模型(CGRF2000).建模同时考虑了测点数据海拔高度的影响,并讨论了截断阶数的选取以及边界效应的控制问题.通过比较均方偏差(RMS),认为8阶SCH2000模型可较好地反映中国地区岩石圈磁场,其分布与SCH1936、CM4以及Taylor多项式模型具有一定的相似性.从位置和强度来看,SCH2000模型所反映的岩石圈磁场更为准确,而与CM4存在一定差异,除了测点不同,截断阶数也是原因之一.通过验证,SCH2000模型各要素随高度的变化与CM4模型较为一致,所建立的CGRF2000与IGRF12模型的分布也较为相似.  相似文献   

基于非均一场源的球坐标大地电磁模拟方法   总被引：1，自引：0，他引：1       下载免费PDF全文

韩骑  胡祥云  彭荣华 《地球物理学报》2020,63(8):3154-3166

大地电磁测深理论与数据处理解释均假定平面电磁波垂直入射地下空间,但随着研究尺度的逐渐扩大,使得因地球弧度产生的影响难以忽略.此时,传统笛卡尔坐标体系及平面波场源不再适用于大尺度的大地电磁数据正反演解释.本文提出并实现了一种基于球坐标系的大地电磁交错网格有限差分三维正演算法,并对电场进行极向-环向分解,结合球谐函数和贝塞尔函数构建了可取代平面波的场源模型.首先利用经纬度信息构建三维地电模型,将场源设置于模型空间正上方,然后通过直接求解球坐标系下麦克斯韦方程来获得大地电磁响应.在此基础上,本文设计了球坐标下具有不同分辨率的多个三维地电模型,阐述了由球体模型到笛卡尔模型的转换方法,详细对比了两种坐标体系在计算效率、所求得的电场和视电阻率方面的差异.结果表明二者差异度主要与电性横向分布和地图投影方法有关,与周期并不存在明显的单调递增关系.  相似文献   

GSFC（9/80）地磁模型的评价和中国地磁台站异常值的确定          下载免费PDF全文

吴文京  白彤霞  任熙宪 《地球物理学报》1987,30(2):178-185

本文利用1960-1980年中国地磁台站资料检验了GSFC（9/80）地磁模型,结果表明该模型是成功的。据此通过地磁台站1960-1980年的观测值与GSFC（9/80）模型计算值的比较,确定了中国地磁台站的异常值。本文还建议在基本磁场的研究中从台站观测年均值中减去较精确测定的台站磁异常值,以提高资料的精确度。  相似文献   

Search for magnetic field oscillations in a sunspot umbra     

V. Landgraf 《Astronomische Nachrichten》1997,318(2):129-133

In order to search for oscillations in velocity and magnetic field strength within a sunspot umbra, a time series of spectra has been obtained through a circular analyzer and the Gregory-Coudé telescope at the Observatorio del Teide, Tenerife. The velocity oscillations clearly show peaks of power at periods between 2 and 7 minutes, with a maximum at 5 minutes. The apparent variations of the magnetic field strength, however, don't exhibit significant oscillations; these fluctuations are rather produced by the influence of parasitic stray light from the surrouding quiet sun which are also visible in the measured time variations of the umbral contrast of continuum intensity.  相似文献   

姿态卡尔曼滤波对FAST馈源舱 BDS/SINS组合导航位姿精度的提高          下载免费PDF全文

李明辉  姜鹏  于东俊  宋本宁  骆亚波  孙京海 《天文学报》2021,62(3):31

500 m球面射电望远镜(The Five-hundred-meter Aperture Spherical radio Telescope, FAST)馈源舱位置和姿态测量精度直接影响望远镜接收机的对准精度.为了提高馈源舱位姿精度,提出姿态卡尔曼滤波算法,采用北斗导航系统的多天线技术解算馈源舱姿态,将它与捷联惯导解算的馈源舱姿态对比,两者的差值作为姿态卡尔曼滤波的量测量.为了降低北斗导航系统解算姿态的复杂度,采用了罗德里格矩阵解算方法.以望远镜跟踪观测模式时,北斗导航系统和捷联惯导解算的实际导航结果作为测试数据,测试结果表明采用姿态卡尔曼滤波的组合导航结果精度优于传统卡尔曼滤波的组合导航结果,尤其在航向角和yf轴的位置精度上.  相似文献   

The correlations and anticorrelations in QPO data     

M. A. Abramowicz  D. Barret  M. Bursa  J. Hork  W. Klu niak  P. Rebusco  G. Trk 《Astronomische Nachrichten》2005,326(9):864-866

Double peak kHz QPO frequencies in neutron star sources varies in time by a factor of hundreds Hz while in microquasar sources the frequencies are fixed and located at the line ν ₂ = 1.5ν ₁ in the frequency‐frequency plot. The crucial question in the theory of twin HFQPOs is whether or not those observed in neutron‐star systems are essentially different from those observed in black holes. In black hole systems the twin HFQPOs are known to be in a 3:2 ratio for each source. At first sight, this seems not to be the case for neutron stars. For each individual neutron star, the upper and lower kHz QPO frequencies, ν ₂ and ν ₁, are linearly correlated, ν ₂ = Aν ₁ + B , with the slope A < 1.5, i.e., the frequencies definitely are not in a 1.5 ratio. In this contribution we show that when considered jointly on a frequency‐frequency plot, the data for the twin kHz QPO frequencies in several (as opposed to one) neutron stars uniquely pick out a certain preferred frequency ratio that is equal to 1.5 for the six sources examined so far. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献