AR-2019-2020

the earliest merging systems detected with cluster radio emissions. In MACSJ1931-2635 cluster, we found a radio mini-halo and an interesting highly bent pair of radio jets. Further, we present here a maiden study of low frequency (GMRT 235 and 610 MHz) spectral and morphological signatures of a previously known radio cluster MACSJ0014.3- 3022 (Abell 2744). This cluster hosts a relatively flat spectrum ( α 610 235 ∼ − 1 . 15), giant ( ∼ 1 . 6 Mpc each) halo-relic structure and a close-by high-speed (1769 ± 148 359 km s − 1 ) merger-shock ( M = 2 . 02 ± 0 . 17 0 . 41 ) originated from a possible second merger in the cluster. This work has been done in collaboration with Sameer Salunkhe, Abhirup Datta, and Huib Intema. Ananta Charan Pradhan A catalogue of 108 extended planetary nebulae ob- served by GALEX We present the ultraviolet (UV) imaging observa- tion of planetary nebulae (PNe) using archival data of Galaxy Evolution Explorer (GALEX). We found 358 PNe detected by GALEX in near-UV (NUV). We have compiled a catalogue of 108 extended PNe with sizes greater than 8 and provided the angu- lar diameters for all the 108 extended PNe in NUV and 28 in FUV from the GALEX images consid- ering 3 σ surface brightness level above the back- ground. Of the 108 PNe, 74 are elliptical, 24 are circular and 10 are bipolar in NUV with most be- ing larger in the UV than in the radio, H α or op- tical. We derived luminosities for 33 PNe in FUV (LFUV) and 89 PNe in NUV (LNUV) and found that most of the sources are very bright in UV. The FUV emission of the GALEX band includes contri- bution from prominent emission lines N IV] (1487 ˚A), C IV (1550 ˚A), and O III] (1661 ˚A) whereas the NUV emission includes C III] (1907 ˚A) and C II (2325 ˚A) for PNe of all excitation classes. The other emission lines seen in low excitation PNe are O IV] (1403 ˚A) and N III (1892 ˚A) in FUV, and O II (2470 ˚A) and Mg II (2830 ˚A) in NUV. Sim- ilarly the emission lines O V (1371 ˚A) and He II (1666 ˚A) strongly contribute in FUV for high and medium excitation PNe but not for low excitation PNe. A mixture of other emission lines seen in all excitation PNe. We have also provided images of 34 PNe in NUV and 9 PNe in FUV. This work has been done in collaboration with Swayamtrupta Panda, Mudumba Parthasarathy, Jayant Murthy, and Devendra K. Ojha. Study of atomic spectroscopy and hyperfine struc- ture of francium (Fr) isotopes using relativistic Fock space multireference coupled cluster method The electronic structure and properties of 210 Fr, 212 Fr, 221 Fr and 223 Fr isotopes have been stud- ied using the relativistic Fock space multirefer- ence coupled-cluster method. By employing this method, we have determined the magnetic hyper- fine constants for the loweset multiplets of francium (Fr) isotopes with Dirac-Fock orbitals. We have provided the data for the ionization potentials and excitation energies for the Fr isotopes. The discrep- ancies between our calculated values and the cor- responding measured experimental values are less than 2% (for energy). In addition, we also report the transition probabilities and oscillator strengths for the various allowed E1 transitions of Fr. The estimated properties are in very good agreement with the available experimental values. This work has been done in collaboration with Madhulita Das. Anirudh Pradhan Friedmann-Robertson-Walker accelerating Uni- verse with interactive dark energy In this work, we study a model based on the cos- mological principle which exhibits a transition from deceleration to acceleration. We consider baryonic matter, dark energy, and “curvature” energy. Both baryonic matter and dark energy (DE) have vari- able equations of state. It is assumed that dark en- ergy interacts with and transforms energy to bary- onic matter . An FRW universe filled with two flu- ids has been discussed. The model is shown to satisfy current observational constraints. This uni- verse is at present in a phantom phase after passing through a quintessence phase in the past. Various cosmological parameters regarding the accelerating universe have been presented. The evolution of DE, Hubble, and deceleration parameters, etc. have been described with the aid of figures. Our the- oretical results have been compared with the SNe Ia related union 2 . 1 compilation 581 data, and we have observed that our derived model is in good agreement with current observational constraints. We have also explored the physical properties of the model. This work has been done in collabo- ration with Gopi Kant Goswami and Aroonkumar Beesham