Interpretation of a special fine structure in type-IV solar radio bursts     

G. Mann  K. Baumgaertel  G. P. Chernov  M. Karlický 《Solar physics》1989,120(2):383-391

A special fine structure (slowly drifting chains of narrowband fiber bursts), firstly observed during the solar type-IV radio burst on April 24, 1985, is interpreted as the radio signature of whistler waves periodically excited by a switch-on/switch-off process of a loss-cone instability in a localized wave packet of the fast magnetoacoustic mode.  相似文献   

Evolution of latitude zonal structure of the large-scale magnetic field in solar cycles     

V. I. Makarov  K. R. Sivaraman 《Solar physics》1989,119(1):35-44

Properties of a latitude zonal component of the large-scale solar magnetic field are analyzed on the basis of H charts for 1905–1982. Poleward migration of prominences is used to determine the time of reversal of the polar magnetic field for 1870–1905. It is shown that in each hemisphere the polar, middle latitude and equatorial zones of the predominant polarity of large-scale magnetic field can be detected by calculating the average latitude of prominence samples referred to one boundary of the large-scale magnetic field. The cases of a single and three-fold polar magnetic field reversal are investigated. It is shown that prominence samples referred to one boundary of the large-scale magnetic field do not have any regular equatorward drift. They manifest a poleward migration with a variable velocity up to 30 m s^-1 depending on the phase of the cycle. The direction of migration is the same for both low-latitude and high-latitude zones. Two different time intervals of poleward migration are found. One lasts from the beginning of the cycle to the time of polar magnetic field reversal and the other lasts from the time of reversal to the time of minimum activity. The velocity of poleward migration of prominences during the first period is from 5 m s^-1 to 30 m s^-1 and the second period is devoid of regular latitude drift.  相似文献   

Optical interferometric observations of a transient event of 1986 March 13 in the coma of Comet Halley     

C. Debi Prasad  T. Chandrasekhar  J. N. Desai  N. M. Ashok  Vinod Krishan 《Journal of Astrophysics and Astronomy》1989,10(1):1-20

During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H₂ O⁺ emission was recorded in thecoma at ～ 0^h UT on 1986 March 13. Observations were carried out using a special IHW filter for H₂ O⁺ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24?39’N,72? 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ～ 35km s^?1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet  相似文献   

The University of Durham Southern Hemisphere VHE gamma ray telescope     

K. T. Brazier  A. Carramiñana  P. M. Chadwick  T. R. Currell  N. A. Dipper  E. W. Lincoln  V. G. Mannings  T. J. L. McComb  K. J. Orford  S. M. Rayner  K. E. Turver 《Experimental Astronomy》1989,1(2):77-99

The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence guard ring technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes.  相似文献   

Fluctuations of CaFz(Eu) scintillator background     

Z. Dvořák  K. Štukheil 《Solar physics》1989,123(1):189-192

Background signal of the scintillation detector routinely used for atmospheric Kr-85 counting follows fluctuations, and their connection with cosmic ray variations is searched for. A strong correlation between the 27-day moving average of sunspot numbers and the background is obtained from the 1988 data.  相似文献   

Variable pulse profile and the accretion geometry in GX 1+4     

R. K. Manchanda 《Astrophysics and Space Science》1989,161(1):85-98

We suggest that the variable pulse profile of GX 1+4 in the low-energy X-ray region results from the superposition of polar and disk components. The anomalous appearance during the spin-down episode can then be explained, if we consider a transition from thin to thick accretion disk configuration which can develop at midly super-Eddington luminosity levels of the source. a close examination of the data suggests that the intrinsic period of the pulsar is 4 min. A switching disk geometry can provide a natural explanation to pulse profile variations in more luminous accreting binary pulsars and also account for the transition between high and low spectral states seen in the case of the Cyg X-1 and low-mass X-ray binary systems.  相似文献   

Finite-β effects on the radiative thermal instability in magnetized plasmas     

G. Murtaza  Hamid Saleem  P. K. Shukla  M. Y. Yu 《Astrophysics and Space Science》1989,154(2):311-319

The radiative thermal instability is investigated taking into account finite-, or electromagnetic, effects. The two-fluid model for magnetized plasmas together with the Maxwell equations are used to derive a general dispersion relation valid for compressional perturbations with frequency below the electron-cyclotron frequency. The growth rates of the radiative thermal instabilities involving fast magnetosonic flute-like and low-frequency hydromagnetic perturbations are presented.  相似文献   

Radiometry of near-earth asteroids     

Veeder GJ  Hanner MS  Matson DL  Tedesco EF  Lebofsky LA  Tokunaga AT 《The Astronomical journal》1989,97(4):1211-1219

We report 10 micrometers infrared photometry for 22 Aten, Apollo, and Amor asteroids. Thermal models are used to derive the corresponding radiometric albedos and diameters. Several of these asteroids appear to have surfaces of relatively high thermal inertia due to the exposure of bare rock or a coarse regolith. The Apollo asteroid 3103, 1982 BB, is recognized as class E. The Jupiter-crossing Amor asteroid 3552, 1983 SA, is confirmed as class D, but low albedos remain rare for near-Earth asteroids.  相似文献   

External radiation field in Rayleigh-Cabannes atmospheres with constant and linear sources     

Tōnu Viik 《Astrophysics and Space Science》1992,198(2):265-280

The external field of radiation in Rayleigh-Cabannes atmospheres with constant and linear sources is found using the resolvent matrix approach. If the internal sources are constant the external field may be described by theX-, Y-, andH-matrices. For the case with linear sources we need the derivatives of these matrices with respect to angular variable. The respective scheme for their determination is given.A set of integro-differential equations for theX- andY-matrices is derived and solved numerically. Some relations between the moments of theH-matrix are given and a sample of results for external fields are provided.  相似文献   

Radio observations of the M8.1 solar flare of 23 June, 1988: Evidence for energy transport by thermal processes     

T. S. Bastian  D. E. Gary 《Solar physics》1992,139(2):357-385

The Very Large Array (VLA) and the frequency agile interferometer at the Owens Valley Radio Observatory (OVRO) were used to observe the M8.1 flare of 23 June, 1988. The VLA obtained images prior to and during the flare at 333 MHz, and at 1.5 and 4.7 GHz. The frequency agile interferometer at Owens Valley obtained interferometer amplitude and total power spectra of the flare at 45 frequencies between 1 and 18 GHz. The observations were supplemented by radiometer measurements made by the USAF RSTN network site at Palehua, HI, by GOES soft X-ray observations, by USAF SOON H filtergrams, and by a KPNO photospheric magnetogram.The radio data reveal a wide variety of phenomena, including: (i) a multiply impulsive microwave burst that is essentially thermal in character; (ii) stationary discrete components at 1.5 GHz, associated temporally and spatially with distant brightenings in Ha; (iii) a dynamical component at 1.5 GHz associated with hot plasma moving subsonically into the corona; (iv) the appearance of intense, short-lived, decimetric burst activity near the lead sunspot in the active region at 1.5 GHz, indicative of a high degree of inhomogeneity in the source.The unusually complete radio coverage allows us to investigate the transport of energy from the initial site to sites of distant H brightenings. The transport of energy appears to be most consistent with slow, thermal processes, rather than rapid transport by nonthermal electron beams.  相似文献