New telescopes in India     

J. C. Bhattacharyya 《Astrophysics and Space Science》1986,118(1-2):45-49

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Mass accretion by the nuclei of disk galaxies,II     

Tara Bhattacharyya  Anuradha Saha  B. Basu 《Astrophysics and Space Science》1985,113(1):33-51

Repeated explosions in the nuclei of galaxies are now accepted as observationally established phenomena. Each explosion leads to the ejection of gas from the central region of a galaxy with velocities depending on the strength of the explosive event. In the process the nucleus temporarily becomes gas-deficient. It is suggested that the mass los is replenished by the accretion of the mass which is shed by those evolved stars in the galactic bulge that possess relatively low rotational velocities. The gas to be accreted is assumed to be magnetized. In the present model, the accretion rate has been assumed to be a function of both radial distance and time. The cross-radial equation of motion has been solved to derive the expression for the rotational velocity which is found to bealmost linear with the radial distance from the centre. The radial equation has been solved to calculate the time-scale over which the nucleus accumulates sufficient mass to undergo instability and suffer explosion. The calculated time-scale range from few multiples of 10⁷ to a few multiples of 10⁸ yr. This range agrees very well with that as has been suggested on the basis of observation in the case of our own Galaxy.  相似文献   

Massive Compact Halo Objects from the relics of the cosmic quark–hadron transition     

Shibaji Banerjee  Abhijit Bhattacharyya  Sanjay K. Ghosh  Sibaji Raha  Bikash Sinha  Hiroshi Toki 《Monthly notices of the Royal Astronomical Society》2003,340(1):284-288

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Short-wavelength drift dissipative instability in the presence of field-aligned currents     

A. Bhattacharyya  G.S. Lakhina 《Planetary and Space Science》1982,30(6):581-585

Sharp density gradients coupled with field-aligned currents can give rise to short wavelength (?15 m) drift waves due to collisional effects in the F-region of the auroral ionosphere. In this wavelength range, ion-ion collisions at altitudes of 300–450 km render the ions unmagnetized and a field-aligned current can drive a drift wave, propagating almost transverse to the magnetic field, unstable due to the resistance in electron parallel motion arising from electron collisions.  相似文献   

General relativistic spectra of accretion discs around rapidly rotating neutron stars: effect of light bending   总被引：1，自引：0，他引：1  

Sudip Bhattacharyya  Dipankar Bhattacharya  Arun V. Thampan 《Monthly notices of the Royal Astronomical Society》2001,325(3):989-994

We present computed spectra, as seen by a distant observer, from the accretion disc around a rapidly rotating neutron star. Our calculations are carried out in a fully general relativistic framework, with an exact treatment of rotation. We take into account the Doppler shift, gravitational redshift and light-bending effects in order to compute the observed spectrum. We find that light bending significantly modifies the high-energy part of the spectrum. Computed spectra for slowly rotating neutron stars are also presented. These results would be important for modelling the observed X-ray spectra of low-mass X-ray binaries containing fast-spinning neutron stars.  相似文献   

A note on the post-explosion gas depletion in the central region of normal spiral galaxies     

T. Bhattacharyya 《Astrophysics and Space Science》1980,68(2):459-467

The problem of post-explosive gas depletion in the central region of normal spiral galaxies like our own has been investigated. It has been calculated that with a plausible density law and with some restriction on gas temperature, a sufficient quantity of gas will be depleted from the central region over a time-scale ranging from a few times 10⁷ to a few times 10⁸ years, the exact time depending on the particular density law. Such a time-scale has been suggested by many authors as the period for one phase of activity in the nuclei of these galaxies. A similar time-scale has also been proposed by several authors as that for the formation and destruction of the spiral patterns of these galaxies.  相似文献   

In memoriam     

J. C. Bhattacharyya 《Astrophysics and Space Science》1983,91(1):3-4

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Fast Transients with the Square Kilometre Array and its Pathfinders: An Indian Perspective     

Yashwant Gupta  Poonam Chandra  Manjari Bagchi  Niruj M. Ramanujam  Yogesh Maan  Avinash A. Deshpande  Siddhartha Bhattacharyya 《Journal of Astrophysics and Astronomy》2016,37(4):37

In the rapidly developing field of study of the transient sky, fast radio transients are perhaps the most exciting objects of scrutiny at present. The SKA, with its wide field-of-view and significant improvement in sensitivity over existing facilities, is expected to detect a plethora of fast transients which, in addition to help resolve the mysteries surrounding their nature and origin, will also lead to other interesting applications in astrophysics. We explore some of these possibilities here, and also emphasize the current status and future plans of the Indian community working in this area, in the context of ongoing work and extension of this to the SKA.  相似文献   

Physico-chemical conditions of four calc-alkaline granitoid plutons of Chhotanagpur Gneissic Complex,eastern India: Tectonic implications     

B Goswami  P Roy  A Basak  S Das  C Bhattacharyya 《Journal of Earth System Science》2018,127(8):120

Petrography and mineralogy of four calc-alkaline granitoid plutons Agarpur, Sindurpur, Raghunathpur and Sarpahari located from west to east of northern Purulia of Chhotanagpur Gneissic Complex, eastern India, are investigated. The plutons, as a whole, are composed of varying proportions of Qtz–Pl–Kfs–Bt–Hbl±Px–Ttn–Mag–Ap–Zrn±Ep. The composition of biotite is consistent with those of calc-alkaline granitoids. Hornblende–plagioclase thermometry, aluminium-in-hornblende barometry and the assemblage sphene–magnetite–quartz were used to determine the P, T and \(f_{\mathrm{O}_2}\) during the crystallisation of the parent magmas in different plutons. The plutons are crystallised under varying pressures (6.2–2.4 kbar) and a wide range of temperatures (896–\(718{^{\circ }}\hbox {C}\)) from highly oxidised magmas (log \(f_{\mathrm{O}_2}\) \(-11.2\) to \(-15.4\) bar). The water content of the magma of different plutons varied from 5.0 to 6.5 wt%, consistent with the calc-alkaline nature of the magma. Calc-alkaline nature, high oxygen fugacity and high \(\hbox {H}_{2}\hbox {O}_{{\mathrm{melt}}}\) suggest that these plutons were emplaced in subduction zone environment. The depths of emplacement of these plutons seem to increase from west to east. Petrologic compositions of these granitoids continuously change from enderbite (opx-tonalite: Sarpahari) in the east to monzogranite (Raghunathpur) to syenogranite (Sindurpur) to alkali feldspar granite (Agarpur) in the west. The water contents of the parental magmas of different plutons also increase systematically from east to west. No substantial increase in the depth of emplacement is found in these plutons lying south and north of the major shear zone passing through the study area suggesting the strike-slip nature of the east–west shear zone.  相似文献   

Exclusion (and seclusion): geographies of disowned widows of India     

Rituparna Bhattacharyya  Suman Singh 《GeoJournal》2018,83(4):757-774

Geographies of disowned Indian widows are highly under-researched. This case study seeks to understand the lives of 21 of the many diverse widows across India. These 21 widows were driven out by their families, who sought refuge in the two Briddhha Ashrams (old-age hermitages) namely Rajkya and Birla, both located in the heritage city, Varanasi, Uttar Pradesh. Drawing upon ethnographic research and building on 21 semi-structured interviews, the research aims to understand the lives of these widows in the two ashrams and their everyday coping strategies. The findings suggest that each woman has negotiated with ‘widowhood’ in order to build individual identities as ‘self’. Using the threads of analysis, we urge for the passing of the draft Bill on widows’ protection, welfare and maintenance prepared by Dr. Bindeshwar Pathak, the architect of sanitation charity, Sulabh International, who has adopted widows of Varanasi and Vrindavan by providing a dole of INR2000/month.  相似文献