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71.
K. S. Stankevich A. M. Aslanyan V. P. Ivanov R. M. Martirosyan Ye. Terzian 《Astrophysics》2003,46(4):429-433
Radio emission of the historical supernovae remnants Tycho (SNR1572) and Kepler (SNR1604) and evolution of their luminosity are considered. Measurement data of secular luminosity decrease rate, obtained earlier by the authors, were corrected with account of variation in time of the flux density of the reference sources. As a result, it is found that the SNR1604 luminosity at 1667 MHz is weakening with an annual mean rate equal to (0.2 ± 0.07)%. The corresponding rate for SNR1572 is (0.47 ± 0.05)%. Since the radio luminosity evolution, as well as energy densities of magnetic field and relativistic electrons inside SNR1604 and SNR1572 are essentially different, these remnants should be considered as different types of supernovae. Bandiera classified SN1604 as type SNIb or SNII. 相似文献
72.
A computer simulation of the sputtering of lunar soil by solar wind protons was performed with the TRIM program. The rate of the sputtering-induced erosion of regolith particles was shown to be less than 0.2 Å per year. A preferential sputtering of Ca, Mg, and O was found along with a less intense sputtering of Fe, Si, and Ti. However, with no other selection mechanisms, surface concentrations of the atoms would differ from the volume ones by no more than 6 %. The enrichment of rims of regolith particles with iron occurs as a result of selective removal of lighter atoms from the lunar surface because of different energies of escape from the Moon's gravity. The energy distributions proved to be the same for all sorts of the sputtered atoms, except for implanted hydrogen; thus, a greater fraction of the atoms left on the lunar surface corresponds to heavier elements. According to simulation results, the concentration of reduced iron observed in the mature regolith could be attained during the time of regolith particle exposure to the present flux of solar wind (105 years). Thus, sputtering can provide the concentration of Fe0 observed in regolith. On periphery of a cloud of impact vapor the temperature is too low for an irreversible selective removal of evaporation products; thus, a meteoritic bombardment contributes to the formation of composition of the rims of regolith particles mainly through enrichment of the rims with elements from the bulk of the particles. The estimates of fluxes of backscattered solar wind protons and of sputtered protons, earlier implanted to the regolith, demonstrated that their contribution to the proton flux near the poles is only 104 cm–2 s–1. This is by two orders of magnitude smaller than the proton flux from the Earth's magnetosphere which is, therefore, the main source of protons for permanently shaded polar craters of the Moon. 相似文献
73.
We present the results of our analysis of the RXTE observations for two transient sources, IGR J17091-3624 and IGR J18539+0727, in April 2003. The derived energy spectra of the sources and the power-density spectra of their light curves make it possible to classify them as low/hard-state X-ray binaries. The parameters of the power spectrum for IGR J18539+0727 lead us to tentatively conclude that the compact object in this binary is a black hole. 相似文献
74.
This paper describes the application of environmental isotopes and injected tracer techniques in estimating the contribution of storms as well as annual precipitation to groundwater recharge and its circulation, in the semi‐arid region of Bagepalli, Kolar district, Karnataka. Environmental isotopes 2H, 18O and 3H were used to study the effect of storms on the hydrological system, and an isotope balance was used to compute the contribution of a storm component to the groundwater. Some of the groundwater samples collected during the post‐storm periods were highly depleted in stable isotope content with higher deuterium excess relative to groundwater from the pre‐storm periods. Significant variation in deuterium excess in groundwater from the same area, collected in two different periods, indicates the different origin of air masses. The estimated recharge component of a storm event of 600 mm to the groundwater was found to be in the range of 117–165 mm. There was no significant variation in environmental tritium content of post‐storm and pre‐storm groundwater, indicating the fast circulation of groundwater in the system. After completion of the environmental isotope work, an injected radiotracer 3H technique was applied to estimate the direct recharge of total precipitation to the groundwater. The estimated recharge to the groundwater is 33 mm of the 550 mm annual precipitation during 1992. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
75.
In this paper we seek the origin of the axial component of the magnetic field in filaments by adapting theory to observations.
A previous paper (Mackay, Gaizauskas, and van Ballegooijen, 2000) showed that surface flows acting on potential magnetic fields
for 27 days – the maximum time between the emergence of magnetic flux and the formation of large filaments between the resulting
activity complexes – cannot explain the chirality or inverse polarity nature of the observed filaments. We show that the inclusion
of initial helicity, for which there is observational evidence, in the flux transport model results in sufficiently strong
dextral fields of inverse polarity to account for the existence and length of an observed filament within the allotted time.
The simulations even produce a large length of dextral chirality when just small amounts of helicity are included in the initial
configuration. The modeling suggests that the axial field component in filaments can result from a combination of surface
(flux transport) and sub-surface (helicity) effects acting together. Here surface effects convert the large-scale helicity
emerging in active regions into a smaller-scale magnetic-field component parallel to the polarity inversion line so as to
form a magnetic configuration suitable for a filament. 相似文献
76.
77.
Gopal C. Kilambi Praveen Nagar N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1992,13(2):175-194
Mid-ultraviolet and optical photometric analysis of helium stars are presented. A linear relation exists between the effective
temperature derived from model atmospheres and (1965-V)0 index. The effective temperatures derived from (1965-V)0 index are somewhat higher than that of MK spectral type estimates especially for late B-type helium objects. 相似文献
78.
R. A. JAMIESON N. G. CULSHAW N. WODICKA D. CORRIGAN J. W. F. KETCHUM 《Journal of Metamorphic Geology》1992,10(3):321-332
Systematic mapping of a transect along the well-exposed shores of Georgian Bay, Ontario, combined with the preliminary results of structural analysis, geochronology and metamorphic petrology, places some constraints on the geological setting of high-grade metamorphism in this part of the Central Gneiss Belt. Correlations within and between map units (gneiss associations) have allowed us to recognize five tectonic units that differ in various aspects of their lithology, metamorphic and plutonic history, and structural style. The lowest unit, which forms the footwall to a regional decollement, locally preserves relic pre-Grenvillian granulite facies assemblages reworked under amphibolite facies conditions during the Grenvillian orogeny. Tectonic units above the decollement apparently lack the early granulite facies metamorphism; out-of-sequence thrusting in the south produced a duplex-like structure. Two distinct stages of Grenvillian metamorphism are apparent. The earlier stage (c. 1160–1120 Ma) produced granulite facies assemblages in the Parry Sound domain and upper amphibolite facies assemblages in the Parry Island thrust sheet. The later stage (c. 1040–1020 Ma) involved widespread, dominantly upper amphibolite facies metamorphism within and beneath the duplex. Deformation and metamorphism recently reported from south and east of the Parry Sound domain at c. 1100–1040 Ma have not yet been documented along the Georgian Bay transect. The data suggest that early convergence was followed by a period of crustal thickening in the orogenic core south-east of the transect area, with further advance to the north-west during and after the waning stages of this deformation. 相似文献
79.
80.