AR_final file_2018-19

Catalogue (VAGC) is carried out with the help of two methods of multivariate analysis. First, Inde- pendent Component Analysis (ICA) is used to de- termine a set of derived independent components that are linear combinations of 47 observed fea- tures (viz. ionized lines, Lick indices, photomet- ric and morphological properties, star formation rates, etc.) of the galaxies. Subsequently, a K- means cluster analysis is applied on the nine in- dependent components to obtain ten distinct and homogeneous groups. It appears that the nine in- dependent Components represent a complete physi- cal description of galaxies (velocity dispersion, ion- isation, metallicity, surface brightness, and struc- ture). We find that ten groups can be essentially placed into traditional and empirical classes (from colour-magnitude and emission-line diagnostic di- agrams, early- vs late-types) despite the classical corresponding features (colour, line ratios and mor- phology) being not significantly correlated with the nine independent components. The classification has been done in collaboration with Tanuka Chat- topadhyay, and with Tanuka Chattopadhyay, and D. Fraix-Burnel. Soumen Mondal Spectral properties of the accretion discs around ro- tating black holes. We study the radiation properties of an accretion disc around a rotating black hole. We solve the hydrodynamic equations, and calculate the tran- sonic solutions of accretion disc in the presence of shocks. Then we use these solutions to generate the radiation spectrum in the presence of radia- tive heating and cooling processes. We present the effect of spin parameter of the black hole on the emitted radiation spectrum. In addition, attention has also been paid to the variation in energy spec- tral index with Kerr parameter and accretion rate. We find that spectral index becomes harder as the spin parameter changes from negative (accretion disc is counter-rotating with respect to the black hole spin) to a positive value. Finally, we compute and compare the spectral characteristics due to a free-fall flow and a transonic flow. We notice signif- icant differences in high energy contributions from these two solutions. The classification has been done in collaboration with Samir Mandal. A pseudo-Newtonian approach to study the accre- tion processes around Kerr black holes A number of ways the potentials are proposed sim- ply to avoid the complexity of the general relativis- tic (GR) framework. The constraints and limita- tions, success and failure, have also been addressed. We find that the pseudo-Kerr potential in Mondal and Chakrabarti (MNRAS, 371 :1418, 2006) is one of the best for GR predictions. Using this pseudo- Kerr potential, the particle dynamics and the ac- cretion flow hydrodynamics have also been carried out. The results are compared with the GR and percentage of accuracy are also presented briefly. Pradip Mukherjee Galilean gauge theory from Poincare gauge theory A shift-symmetric Galileon model in presence of spacetime torsion has been constructed for the first time. This has been realized by localizing (or, gauging) the Galileon symmetry in flat spacetime in an appropriate manner. We have applied the above model to study the evolution of the universe at a cosmological scale. Interestingly, for a wide class of torsional structures, we have shown that the model leads to late time cosmic acceleration. Furthermore, as torsion vanishes, our model repro- duces the standard results. The classification has been done in collaboration with Rabin Banerjee. Constrained Hamiltonian analysis of a non rela- tivistic Schrodinger field copuled with C-S gravity We provide a constrained Hamiltonian analysis of a non relativistic Schrodinger field in 2+1 di- mensions, coupled with Chern - Simons gravity. The coupling is achieved by the recently advanced Galilean gauge theory. The calculations are re- peated with a truncated model to show that de- viation from Galilean gauge theory makes the the- ory untenable. The issue of non relativistic spatial diffeomorphism is discussed in this context. The classification has been done in collaboration with Abdus Sattar. Hemwati Nandan and Rashmi Uniyal Bending angle of light in equatorial plane of Kerr- Sen black hole We study the gravitational lensing by a Kerr-Sen black hole arising in heterotic string theory. A ( 202 )