Power spectrum of geomagneticK p-index detected at Misallat magnetic station     

A. A. Galal  H. A. Deebes  Maha S. Quassim  Shahinaz Yousef 《Earth, Moon, and Planets》1995,70(1-3):151-162

TheK _p-indices measured at Misallat station [ø = 29°45 N; = 30°54 E] during the period 1958–1989, have been compared with the data of two geomagnetic stations; one of them has similar longitude as Misallat and the second has almost similar latitude. The spectra of daily and hourly data of the three stations are compared together to define the latitude and longitude-effects on the detected periodicities. Daily periodicities ofK _p-index activities at the values 32.7, 21.2, 12.9, 11.6 and 9.2 days have been obtained to be common in the spectra of the three stations. The existence of 5-days periodicity in these stations has also been detected.  相似文献   

The third harmonic of type III solar radio bursts     

Takakura  Tatsuo  Yousef  Shahinaz 《Solar physics》1974,39(2):451-458

The harmonic ratios of a large sample of inverted-U bursts are found to be smaller at the turning frequency than at the starting frequency. Ratios <2.0 are explained by postulating that the lowest fundamental frequencies emitted are prevented from escaping from the corona by an evanescent region between the source and the observer. This concept is used to construct a source model for inverted-U bursts where the density is lower inside a magnetic flux tube than it is outside.  相似文献   

North and south major flare periodicities during solar cycle 20     

A. A. Galal  Shahinaz Yousef  E. Bebars 《Astrophysics and Space Science》1995,228(1-2):19-30

The periodicities of monthly values of major flare numbers and comprehensive major flare index (CFI) have been studied for the 20^th solar cycle. It has been proved that the periodicity 152 days exists also in the southern (S) solar hemisphere. This periodicity has been previously defined in the earlier cycles to be a northern (N) periodicity, but it has migrated to the southern hemisphere (S) during the cycles 19, 20, 21. For the whole solar disk data, it has been found that the periodicity at 78.43^d is much remarkable than its first harmonic at 156.86^d. We have also detected very strong periodicity at 548.96^d in N-hemisphere while a strong one has been found near 100^d in both solar hemispheres. The detected periodicities at 80±2^d and 101-⁺1^d seems to have a global origin . The 87.1^d periodicity is present and it is suggested that it is related to 88^d periodicity attributed to the tidal influence of the planet Mercury on sunspots. Both hemispheres present their periodicities independently.  相似文献   

Physical properties of three short period close binaries:KIC 2715417,KIC 6050116 and KIC 6287172     

Mahmoud AbdelFattah NegmEldin  Ahmed Essam Elsayed  Shahinaz Mostafa Yousef 《天文和天体物理学研究(英文版)》2019,(2)

We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-band). Our three systems are KIC 2715417, KIC 6050116 and KIC 6287172. The first system, KIC 2715417, is considered a semi-detached system with the secondary component filling its Roche lobe. The second system, KIC 6050116, is an overcontact system, while the third system, KIC 6287172, belongs to ellipsoidal variables as deduced from the Roche lobe geometry. For photometric analysis, we used the PHOEBE software package, which is based on the Wilson-Devinney code. Due to lack of spectroscopic data, the photometric mass ratios are determined from the analyses of light curves using the q-search method. The absolute parameters are determined using three different methods(Harmanec, Maceroni Van'tVeer and Gazeas Niarchos).  相似文献   

Type IIIb radio bursts: 80 MHz source position and theoretical model     

Tatsuo Takakura  Shahinaz Yousef 《Solar physics》1975,40(2):421-438

We present Culgoora spectrograph and radioheliograph observations as well as a model of type IIIb bursts; the latter are defined as chains of striae of slow or no frequency drift, the chain as a whole drifting like a normal type III burst.The 80 MHz source positions are studied for a group of IIIb bursts, a IIIb precursor and harmonic pairs of 1:2 frequency ratio. It is found that the IIIb position may vary in a IIIb group. No significant difference was found between the source positions of a IIIb precursor and the following III burst. For one event we found that the fundamental IIIb burst showed a high degree of circular polarization (46%), while its second harmonic, a normal type III burst, was unpolarized.We suggest that the main cause for the striae in type IIIb bursts is the existence of filamentary, density irregularities along the path of the electron stream. The denser filaments initially reduce the value of the density gradient along the electrons' path and thereby enhance their emissions over a small range of plasma frequencies. If the radio emission from the filaments dominates the emission from the ambient rarified plasma, striae appear in the spectrum and a type IIIb burst results. This condition is more easily satisfied at the fundamental frequency and for electron streams of relatively high density.Radiophysics Publication RPP 1758, October, 1974, (2nd version).On leave from the Dept. of Astronomy, University of Tokyo, Tokyo, Japan.On leave from the Dept. of Astronomy, Cairo University, Cairo, Egypt.  相似文献