AR_final file_2018-19

With an absolute V band magnitude at peak of M V = − 18.86 ± 0.23 mag, SN 2014ad is fainter than Gamma Ray Burst (GRB) associated super- novae, and brighter than most of the normal and broad-line type Ic supernovae without an associ- ated GRB. The spectral evolution indicates the ex- pansion velocity of the ejecta, as measured using the Si ii line, to be as high as ∼ 33,500 km s − 1 around maximum, while during the post-maximum phase, it settles down at ∼ 15,000 km s − 1 . The ex- pansion velocity of SN 2014ad is higher than all other well observed broad-line type Ic supernovae except the GRB associated SN 2010bh. The explo- sion parameters, determined by applying the Ar- nett’s analytical light curve model to the observed bolometric light curve, indicate that it was an en- ergetic explosion with a kinetic energy of ∼ (1 ± 0.3) × 10 52 ergs, a total ejected mass of ∼ (3.3 ± 0.8) M ⊙ , and ∼ 0.24 M ⊙ of 56 Ni was synthesized in the explosion. The metallicity of the host galaxy near the supernova region is estimated to be ∼ 0.5 Z ⊙ . This work was carried out in collaboration with D. K. Sahu, G. C. Anupama, S. Srivastav, Masaomi Tanaka, Keiichi Maeda, and K. Nomoto. The Nainital Cape Survey Project The Nainital-Cape Survey is a dedicated search programme initiated in 1999 in coordination of as- tronomers from SAAO South Africa, ARIES Naini- tal and ISRO Bangaluru Over the last 17 years, a total of 345 chemically peculiar stars were moni- tored for photometric variability, making it one of the longest ground-based survey to search for pul- sation in chemically peculiar stars in terms of both time span and sample size. Under this survey, we discovered rapid pulsation in the Apstar HD12098, while δ Scuti-type pulsations were detected in seven Am stars. Those stars in which pulsations were not detected have also been tabulated along with their detailed astrophysical parameters for further inves- tigation. This work was carried out in collaboration with Santosh Joshi. Ramesh Chandra Observations of two successive EUV waves and their mode conversion In this work, we present the observations of two successive fast-mode extreme ultraviolet (EUV) wave events observed on 2016 July 23. Both fast- mode waves were observed by the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory satellite, with a travelling speed of ≈ 675 and 640 km s − 1 , respectively. These two wave events were associated with two filament eruptions and two GOES M-class solar flares from the NOAA active region 12565, which was located near the western limb. The EUV waves mainly move toward the south direction. We observed the interaction of the EUV waves with a helmet streamer further away to the south. When either or one of the EUV waves penetrates into the hel- met streamer, a slowly propagating wave with a traveling speed of ≈ 150 km s − 1 is observed along the streamer. We suggest that the slowly mov- ing waves are slow-mode waves, and interpret this phenomenon as the magnetohydrodynamic wave- mode conversion from the fast mode to the slow mode. Furthermore, we observed several stationary fronts to the north and south of the source region. This work has been done in collaboration with D.F. Chen, R. Joshi, B. Joshi, and B. Schmieder. Can high-mode magnetohydrodynamic waves prop- agating in a spinning macrospicule be unstable due to the Kelvin-Helmholtz instability? We investigate the conditions at which high-mode magnetohydrodynamic (MHD) waves propagating in a spinning solar macrospicule can become un- stable with respect to the Kelvin-Helmholtz insta- bility (KHI). We consider the macrospicule as a weakly twisted cylindrical magnetic flux tube mov- ing along and rotating around its axis. Our study is based on the dispersion relation (in complex vari- ables) of MHD waves obtained from the linearized MHD equations of an incompressible plasma for the macrospicule and cool ( β = 0, with β the plasma to the magnetic pressure) plasma for its environ- ment. This dispersion equation is solved numer- ically using appropriate input parameters to find out an instability region or window that accommo- dates suitable unstable wavelengths on the order of the macrospicule width. It is established that an m = 52 MHD mode propagating in a macrospicule with width of 6 Mm, axial velocity of 75 km/s, and rotating one of 40 km/s can become unsta- ble against the KHI with growth times of 2.2 and 0.57 min at 3 and 5 Mm unstable wavelengths, re- spectively. These growth times are much shorter than the macrospicule lifetime, which lasts about 15 min. An increase or decease in the width of the jet would change the KHI growth times, which ( 178 )