AR-2019-2020

are estimated as 43.17 ± 0.16 erg s − 1 , and 43.24 ± 0.11 erg s − 1 suggesting that 0.60 ± 0.20 M of 56 Ni was synthesized in the explosion of SN 2009ig, and 0.72 ± 0.31 M in SN 2012cg. This work was car- ried out in collaboration with Devendra K. Sahu, and G. C. Anupama. Ground-based photometric survey to search for the pulsational variability in Bp, Ap, and Am stars We present the analysis of time-series of photo- electric data of a Bp star and four new Ap stars observed photoelectrically under the Nainital-Cape survey programme. The project was started about two decades ago, aiming to search for new rapidly oscillating Ap stars. The frequency analysis of the time-series of these stars obtained on multiple nights did not reveal any pulsational variability. In addition to this, we have performed the analysis of time-series differential CCD photometry of the two pulsating Am stars HD 13038 and HD 13079, where we find some evidence of new periods. To expand and strengthen the ongoing survey work, we propose to build-up a tri-national collaboration of astronomers from India, South Africa and Bel- gium. This work was carried out in collaboration with Daniel Nhlapo, Santosh Joshi, Bruno Letarte, and Sanjeev Kumar Tiwari. Ramesh Chandra How rotating solar atmospheric jets become Kelvin- Helmholtz unstable ? The Kelvin-Helmholtz instability (KHI) is a ubiq- uitous phenomenon across the Universe. Over the past two decades, several space missions have en- abled our understanding of this phenomenon at the Sun’s atmosphere. Key results obtained by Hinode and Atmospheric Imaging Assembly on board the Solar Dynamics Observatory allowed us to get use- ful data concerning the physical parameters of var- ious solar jets and the characteristics of detected waves and instabilities in those structures. The ro- tating solar jets are among the most spectacular events in our Sun. They support the propagation of a number of magnetohydrodynamic (MHD) modes which, under some conditions, can become unstable and the developing instability is of the KH kind. In its non-linear stage, the KHI can trigger the occur- rence of wave turbulence, which is considered as one of the basic mechanisms of the coronal heat- ing. The modelling of tornado-like phenomena in solar chromosphere and corona as moving weakly twisted and spinning cylindrical flux tubes shows that the KHI rises at the excitation of high-mode MHD waves. The instability occurs within a wave number range/window whose width depends on the MHD mode number m, the plasma density contrast between the rotating jet and its environment, as well as on the twists of the internal magnetic field and jet’s velocity. We have studied KHI instability in a twisted solar polar coronal hole jet, in a twisted rotating jet emerging from a filament eruption, and in a rotating macrospicule. It has been established that good agreement between the theoretically cal- culated KHI developing times of a few minutes at wavelengths comparable to the half-widths of the jets, and those growth times detected from obser- vations can be achieved at the excitation of high (9 ≤ m ≤ 52) MHD modes only. This work has been done in collaboration with Ivan Zhelyazkov, and Reetika Joshi. Kinematics and energetics of the EUV waves on 11 April, 2013 In this study, we present the observations of extreme-ultraviolet (EUV) waves associated with an M6.5 flare on 11 April 2013. The event was ob- served by Solar Dynamics Observatory (SDO) in different EUV channels. The flare was also associ- ated with a halo CME and type II radio bursts. We observed both fast and slow components of the EUV wave. The speed of the fast component, which is identified as a fast-mode MHD wave, varies in the range from 600 to 640 km/s, whereas the speed of the slow-component is ≈ 140 km/s. We observed the unusual phenomenon that, as the fast- component EUV wave passes through two succes- sive magnetic quasi-separatrix layers (QSLs), two stationary wave fronts are formed locally. We pro- pose that part of the outward-propagating fast- mode EUV wave is converted into slow-mode mag- netohydrodynamic waves, which are trapped in lo- cal magnetic field structures, forming successive stationary fronts. Along the other direction, the fast-component EUV wave also creates oscillations in a coronal loop lying ≈ 225 Mm away from the flare site. We have computed the energy of the EUV wave to be of the order of 1020 J. This work was done in collaboration with Aarti Fulara, Peng Fei Chen, Ivan Zhelyazkov, Abhishek K. Srivastva, and W. Uddin.