Infrared bursts from liller I/MXB 1730-333

The observation of infrared bursts from the globular cluster Liller I has been reported by Kulkarniet al. (1979) and confirmed by Joneset al. (1980). The infrared bursts which resemble Type I X-ray bursts in their characteristics are plausibly attributed to a cyclotron maser instability operating at few tens of neutron star radii above the poles of a magnetized neutron star in a binary system. It is suggested that similar infrared bursts should in general be observable from Type I X-ray burst sources.     

Path length distribution of cosmic rays from pulsar nebula complexes

Particles accelerated in the vicinity of pulsars have to traverse the nebular matter surrounding pulsars. Using the variation of pulsar luminosity and nebular expansion, the path length distribution for the particle radiation is deduced and compared with that obtained from experimental observation. It is found that a significant amount of matter traversed by cosmic rays can be in the source itself; but it is not possible to simultaneously account for the production of secondary electrons and secondary nuclei with the same set of parameters.     

Disappearence of equatorial Es, associated with magnetic field depressions

The phenomenon of the sudden disappearance of equatorial sporadic E at two stations, namely, Trivandrum and Kodaikanal is studied. It is established that whenever there is a sudden disappearance of E_s, there is a depression in the horizontal magnetic field (H) range. Electron velocities during the presence and absence of sporadic E have been estimated. These results show that the irregularities responsible for sporadic E are present even when the electron velocities are less than the ion thermal velocity.     

Granitic activity and crustal growth in the Indian shield

Granites and granite gneisses of polymetamorphic and igneous episodes occupy about three-quarters of the exposed area in the Indian shield. Most of these granites are similar in their chemistry and age of emplacement, whereas the gneisses show variation in their chemistry and age. Geochemical studies reveal that prior to the Proterozoic or Late Archaean, the acidic igeneous activity was dominated by Na-rich tonalites and trondhjemites while K-rich granites started only from the Proterozoic period. Available data on the basic and acidic rocks in the shield suggest that: (1) the primordial crust was basic and thin in nature; and (2) the crust has attained its present thickness by extensive granitic activity around 2.5 Ga ago, probably in a single phase.     

The stability of stratified shear flows of an inviscid compressible fluid in MHD

By the generalized progressing wave expansion method, the effect of a magnetic field on the linear stability of the stratified horizontal flow of an inviscid compressible fluid has been studied. It is found that the magnetic field stabilizes the system.     

Imaging and power generation strategies for chandrayaan-1

The Chandrayaan-1 mission proposes to put a 550 kg lunarcraft into Geostationary Transfer Orbit (GTO) using the Polar Satellite Launch Vehicle (PSLV) which will subsequently be transferred into a 100 km circular lunar polar orbit for imaging purposes. In this paper, we describe certain aspects of mission strategies which will allow optimum power generation and imaging of the lunar surface. The lunar orbit considered is circular and polar and therefore nearly perpendicular to the ecliptic plane. Unlike an Earth orbiting remote sensing satellite, the orbit plane of lunar orbiter is inertially fixed as a consequence of the very small oblateness of the Moon. The Earth rotates around the Sun once a year, resulting in an apparent motion of Sun around this orbit in a year. Two extreme situations can be identified concerning the solar illumination of the lunar orbit, noon/midnight orbit, where the Sun vector is parallel to the spacecraft orbit plane and dawn/dusk orbit, where the Sun vector is perpendicular to the spacecraft orbit plane. This scenario directly affects the solar panel configuration. In case the solar panels are not canted, during the noon/midnight orbit, 100% power is generated, whereas during the dawn/dusk orbit, zero power is generated. Hence for optimum power generation, canting of the panels is essential. Detailed analysis was carried out to fix optimum canting and also determine a strategy to maintain optimum power generation throughout the year. The analysis led to the strategy of 180‡ yaw rotation at noon/midnight orbits and flipping the solar panel by 180‡ at dawn/dusk orbits. This also resulted in the negative pitch face of the lunarcraft to be an anti-sun panel, which is very useful for thermal design, and further to meet cooling requirements of the spectrometers. In principle the Moon’s surface can be imaged in 28 days, because the orbit chosen and the payload swath provide adequate overlap. However, in reality it is not possible to complete the imaging in 28 days due to various mission constraints like maximum duration of imaging allowed keeping in view the SSR sizing and payloads data input rate, time required for downlinking the payload data, data compression requirements and visibility of the lunarcraft for the Bangalore DSN. In each cycle, all the latitudes are swept. Due to the constraints mentioned, only 60‡ latitude arc coverage is possible in each orbit. As Bangalore DSN is the only station, half of the orbits in a day are not available. The longitudinal gaps because of non-visibility are covered in the next cycle by Bangalore DSN. Hence, in the firstprime imaging season, only 25% of the prime imaging zones are covered, and an additional threeprime imaging seasons are required for a full coverage of the Moon in two years. Strategy is also planned to cover X-ray payload coverage considering swath and orbit shift.     

Convection in normal stars and metal-deficient stars

The depths at which convection starts have been calculated for main sequence stars and giant stars of various effective temperature and hydrogen-to-metal ratios. It is found that for late-type stars ofT _e4400 K convenction stars at 0.1. In metal-deficient stars convection starts at shallower optical depths compared to normal stars of the same spectral type. The larger the metal deficiency, the shallower is the depth at which convection starts. The importance of convection in the study of metal-deficient stars and late type stars are also discussed.     

Infra-red emission from galactic nuclei

It has been suggested by several authors that the infra-red emission from galactic nuclei is due to synchrotron process from compact objects or due to thermal processes. We have examined here the coherent and incoherent synchrotron mechanisms from compact objects and find that these are unlikely to explain the observed emission.     

Urban Ground Water Pollution: A Case Study in Cuttack City, India

A large number of ground water samples (360) was collected from 60 stations over six consecutive seasons to study the influence of the main sewerage drain on shallow ground water table beneath the municipal area of Cuttack, India. A majority of the samples collected from stations close to the drain exceeded the maximum permissible limits set by the World Health Organization (WHO). Almost all the samples near the drain exceeded the WHO limit for NO₃^- and Na⁺. However, the concentrations decreased as the distance from the drain increased. The winter season registered the maximum concentrations of NH₄⁺, NO₃^-, and SO₄^2- ions whereas the minimum values always coincided with the rainy season. R-mode factor analysis was conducted to find relationships amongst the 16 chemical parameters studied. Fluoride showed a negative correlation with Cl^-, Na⁺, NO₃^-, SO₄^2-, and PO₄^3-. The concentration of F^- may be lower in raw waste water than naturally occurs in the ground water. Therefore, a decrease in the concentration of F^- near the drain may be attributed to dilution by contributions of waste water to the ground water. The rest of the parameters were found to be directly related to the distance of collection points to the sewerage. The distribution of nutrients is strongly affected by leaching of waste water into the ground water.