Dispersion characteristics of low-latitude whistlers

The effect of ions on whistler dispersion characteristics has been studied. It is shown that the significant changes in the dispersion characteristics of low-latitude whistlers are brought about by the presence of ions. The dispersions for Nainital (geomagnetic lat. 19°1'N) and Gulmarg (geomagnetic lat. 24°10'N) are found to peak around 800 Hz. The short whistler sonograms recorded at Nainital and Gulmarg have been analysed, using the complete dispersion equation and the effect of ions has been shown. At higher frequencies the dispersion is found to decrease steadily and becomes independent of ions. Some examples of short whistlers have been found whose characteristics do not conform to the general trend of low-latitude whistlers, and, on the other hand, these whistlers show a constant dispersion unaffected by ions up to a fairly low frequency and thereafter decrease sharply at lower frequencies.     

H 187 - At the Onset of a New Eclipse

CCD photometry data of the T Tauri star H 187 are presented. They show that a new eclipse of this star began at the end of 2004. Since only one eclipse of this star has been observed previously with a duration of 3.5 years, our data indicate that the eclipses of this object are periodic with a period P=4.9 years between eclipses. Thus, in terms of the absolute duration of the eclipses and in terms of their relative length as a fraction of the period, H 187 is one of the most exotic objects in the sky. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 529–534 (November 2005).     

Estimation of sedimentary thickness in the Godavari basin

A major portion of the southern part of the Indian subcontinent is classified as a stable continental region. However, a few segments in this region are punctuated by rifts and shear zones that are seismically active. The Godavari rift that sutures the eastern Dharwar and the Bastar cratons is one such region, prone to seismic hazard. Estimation of the sedimentary thickness in these seismically active regions assumes importance since locales of thick and soft sediments are vulnerable to destruction due to surface waves generated by earthquakes. In the present study, data from five broadband seismological stations are utilized to estimate the average sedimentary thickness of the Godavari region using the difference in travel times of the direct S and converted Sp phases from local earthquakes. The thickness of sediments varies between 0.32 and 4.32 km. Also, the site-specific response in terms of the fundamental resonance frequency and the corresponding amplifications are estimated using the well-established Nakamura technique. The predominant frequencies are in the range of 1.3–4.61 Hz, and the amplifications are higher (>1.5) for the stations inside the Godavari basin. Both the thickness and amplification values clearly indicate that the sediments tend to get thicker toward the center of the basin, in good agreement with the geological distribution of the sedimentary units.     

Lunar Gravity-Assist Maneuver As a Way of Reducing the Orbit Amplitude in the Spectrum–Röntgen–Gamma Project

Spectrum–Röntgen–Gamma (SRG) is a space observatory designed to observe astrophysical objects in the X-ray range of the electromagnetic spectrum. SRG is planned to be launched in 2019 by a Proton-M launch vehicle with a DM3 upper stage. The spacecraft will be delivered to an orbit around the Sun–Earth collinear libration point L2 located at a distance of ~1.5 million km from the Earth. Although the SRG launch scheme has already been determined at present, in this paper we consider an alternative spacecraft transfer scenario using a lunar gravity-assist maneuver. The proposed scenario allows a oneimpulse transfer from a low Earth orbit to a small-amplitude orbit around the libration point to be performed while fulfilling the technical constraints and the scientific requirements of the mission.     

Jovian electron jets in interplanetary space

The COSPIN/KET experiment onboard Ulysses has been monitoring the flux of 3–20 MeV electrons in interplanetary space since the launch of Ulysses in October 1990. The origin of these electrons has been known for a long time to be the Jovian magnetosphere. Propagation models assuming interplanetary diffusion of these electrons in the ideal Parker magnetic field were successfully developed in the past. The average electron flux measured by our experiment agrees with these models for most of the times before and after the Jovian flyby of February 1992, i.e. in and out of the ecliptic down to 28° S of heliographic latitude for the last data presented here (end of March 1993).However, in addition to this average flux level well accounted for by diffusion in an ideal Parker field, we have found very short duration electron events which we call “jets”, characterized by: (i) a sharp increase and decrease of flux; (ii) a spectrum identical to the electron spectrum in the Jovian magnetosphere; and (iii) a strong first-order anisotropy. These jets only occur when the magnetic field at Ulysses lies close to the direction of Jupiter, and most of the time (86% of the events) points outwards from Jupiter, i.e. has the same polarity after the flyby as the Jovian dipole (North to South). These events are interpreted as crossings by Ulysses of magnetic flux tubes or sheets directly connected to the location of the Jovian magnetosphere from which electrons escape into interplanetary space. The average thickness of these sheets is 10¹¹cm or 14 Jovian radii. These jets are clearly identified up to 0.4 a.u. before the Jupiter flyby in the ecliptic plane, and up to 0.9 a.u. out of the ecliptic.Moreover, the characteristic rocking of the electron spectrum in the Jovian magnetosphere with a 10 h periodicity is found to be present during the jets, and predominantly during them. In the past, this modulation has been reported to be present in interplanetary space as far as 1 a.u. upwind of Jupiter, a fact which cannot be accounted for by diffusion in the average Parker magnetic field. Our finding gives a simple explanation to this phenomenon, the 10 h modulation being carried by the “jet” electrons which travel with no appreciable diffusion along magnetic field lines with a direction far from the ideal Parker spiral.     

Intrusion and differentiation of granitic magma at a high level in the crust: the Puscao pluton, Lima Province, Peru

Regression surface techniques have been used on partial whole-rockchemical analyses from the Puscao pluton to establish the three-dimensionalnature of the chemical variations within this body, which wasemplaced at a depth of between 4 km and 8 km within the crust.Block diagrams produced by the computer program are consistentwith the hypothesis that during the period preceding the totalconsolidation of the magma, the pluton has undergone in situdifferentiation to give a layered structure. Statistical analysis confirms that there is a large scale variationwithin the pluton and that local variation, such as might beexpected to result from the contamination of the Puscao magmaby assimilated volcanic material, did not contribute significantlyto the overall variation. Evidence is presented which suggests that the layering withinthe Puscao pluton was disturbed as a result of the emplacementof the much later Cañhas pluton, and that this disturbancehas the form of a simple doming centred upon the site of thepresent Cañas intrusion.