AR-2019-2020

Shantanu Rastogi Seasonal heterogeneity in aerosol optical properties over the subtropical humid region of northern India First-ever measurements and study of aerosol op- tical properties from a subtropical humid region of the eastern part of the central Indo-Gangetic Plain (IGP), Gorakhpur (26.75N, 83.38E, 85m amsl) is presented. Four years, March 2014-February 2018, of columnar aerosol optical measurements, using a multi-wavelength solar radiometer (MWR), are analyzed to examine temporal and seasonal het- erogeneity in aerosol optical properties, and to as- certain aerosol types over the study region along with their seasonal contribution. Average colum- nar aerosol optical depth at 500 nm (AOD500) is 0.65 ± 0.27, with highest seasonal mean (0.73 ± 0.30) during pre-monsoon (PM) and lowest sea- sonal mean (0.59 ± 0.25) during monsoon (M) sea- son. During PM season, more than 50% of AOD500 values are greater than 0.7 indicating high aerosol loading over the study region. Large variability in Angstrom exponent ( α ) and atmospheric turbid- ity ( β ) from 0.12 to 2.26 and 0.05 to 1.34, with mean value of 0.92 ± 0.27 and 0.37 ± 0.14, re- spectively, indicates heterogeneous aerosol emission sources and turbid atmosphere over the study re- gion. Higher α ( > 1) during post-monsoon (PoM) and winter (W) seasons indicate predominance of fine mode aerosols, whereas lower α ( < 0.7) dur- ing PM season indicate prevalence of coarser mode aerosols, over the study region. Aerosols of ur- ban/industrial and biomass burning origins (UB) have maximum contribution during PoM (71.4%) and W (56.2%) seasons, while more than 25% of mixed type (MT) aerosols are observed throughout the study period with maximum contribution ob- served during M (63%) season. AOD retrieved from MWR and that from MODerate-resolution Imag- ing Spectroradiometer (MODIS) compare reason- ably well with a correlation coefficient of 0.66. This work has been done in collaboration with Prayagraj Singh, Aditya Vaishya, and Suresh Babu. C. D. Ravikumar Co-evolution of nuclear rings, bars and the central intensity ratio of their host galaxies We study a sample of 13 early-type spiral galax- ies hosting nuclear rings and report remarkable correlations between the properties of the nuclear rings, and the newly discoverd central intensity ra- tio (CIR) of their host galaxies. The CIR is a purely photometric quantity involving intensities of light within the central 1.5 and 3 arcsec region of a galaxy, and is found to be a vital parame- ter in galaxy evolution, as it shares strong corre- lations with many structural and dynamical prop- erties of early-type galaxies, including mass of the central supermassive black hole (SMBH). They ob- serve strong correlations of CIR with the relative sizes of nuclear rings and ring cluster surface den- sities, which suggest reduced star formation in the centres of galaxies hosting small and dense nuclear rings. There is signicant connection observed be- tween the CIR and bar strengths. In addition, we observe that the CIR is closely related with the in- tegrated properties of the stellar population in the nuclear rings, associating the rings hosting older and less massive star clusters with low values of CIR. Thus, the CIR serves as a crucial parameter in unfolding the coupled evolution of bars and rings in galaxies. This study has been done in collabo- ration with S. Aswathy. Saibal Ray Study on charged strange stars in f (R,T) gravity We investigate the effects of the modified f ( R, T ) gravity on the charged quark stars for the stan- dard choice of f ( R, T ) = R + 2 χ T . These types of stars are supposed to be made of strange quark matter (SQM), whose distribution is gov- erned by the phenomenological MIT bag EoS as p = 1 / 3( ρ − 4 B ), where B is the bag constant, while the form of charge distribution is chosen to be q ( r ) = Q ( r/R ) 3 = αr 3 with α as a constant. We derive the values of the unknown parameters by matching the interior spacetime to the exte- rior Reissner-Nordstr¨om metric followed by the ap- propriate choice of the values of the parameters χ and α . The study under the f ( R, T ) gravity reveals that besides SQM, a new kind of matter distribution originates due to the interaction be- tween the matter and the geometric term, while the modification of the Tolman-Oppenheimer-Volkoff (TOV) equation invokes the presence of a new force F c . The accumulation of the electric charge distribution reaches its maximum at the surface, and the predicted values of the corresponding elec- tric charge and electric field are in the order of 10 19 − 20 C and 10 21 − 22 V/cm, respectively. To ex-