AR_final file_2018-19

S. Dev New mixing schemes for (3+1) neutrinos We propose new mixing schemes for (3+1) neu- trinos, which describe mixing among active-active and active-sterile neutrinos. The mixing matrix in these mixing schemes can be factored into a zeroth order flavour symmetric part and another part rep- resenting small perturbations needed for generating non-zero U e 3 , non-maximal θ 23 , CP violation and active-sterile mixing. We find interesting correla- tions amongst various neutrino mixing angles, and also, calculate the parameter space for various pa- rameters. This work has been done in collabora- tion with Desh Raj, Radha Raman Gautam, and Lal Singh. Shanti Priya Devarapalli Low resolution spectroscopy of selected Algol sys- tems The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand the presence of mass transfer, a disk or circumstellar matter and chromospheric emis- sion. We also present the first spectroscopic and period study for a few Algols, and conclude that high resolution spectra within and outside the pri- mary minimum are needed for better understand- ing of these Algol type close binaries. This work has been done in collaboration with Jagirdar Ruk- mini, M. Parthasarathy, D. K. Sahu, Vijay Mohan, B. C. Bhat, et al. Photometric studies of two solar type marginal con- tact binaries in the Small Magellanic Cloud Using the Optical Gravitational Lensing Experi- ment catalogue, two contact binaries were studied using data in the V and I bands. The photomet- ric solutions for the V and I bands are presented for two contact binaries OGLE 003835.24-735413.2 (V1) and OGLE 004619.65-725056.2 (V2) in Small Maglellanic Cloud. The presented light curves are analyzed using the Wilson-Devinney code. The re- sults show that the variables are in good thermal and marginal geometrical contact with features like the O’Connell effect in V1. The absolute dimen- sions are estimated and its dynamical evolution is inferred. They tend to be solar type marginal con- tact binaries. The 3.6 m Devasthal Optical Tele- scope and the 4.0 m International Liquid Mirror Telescope of the Aryabhatta Research Institute of Observational Sciences (ARIES, Nainithal) can fa- cilitate the continuous monitoring of such kind of objects, which will help in finding the reasons be- hind their period changes and their impact on the evolution of the clusters. This work has been done in collaboration with Jagirdar Rukmini. Vijayakumar Honnappa Doddamani Formation and eruption of sigmoidal structure from a weak field region of NOAA 11942 Using observations from the Solar Dynamics Ob- servatory, we studied an interesting example of a sigmoid formation and eruption from small-scale flux-cancelling regions of active region (AR) 11942. Through an analysis of Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly obser- vations, we infer that initially the AR is compact and bipolar in nature, evolved to a sheared config- uration consisting of inverse J-shaped loops host- ing a filament channel over a couple of days. By tracking the photospheric magnetic features, shear- ing and converging motions are observed to play a prime role in the development of S-shaped loops and further flux cancellation leads to tether-cutting reconnection of J-loops. This phase is co-temporal with the filament rise motion, followed by sigmoid eruption at 21:32 UT on January 6. The flux rope rises in phases of slow ( v avg = 26 kms − 1 and fast ( a avg = 55 ms − 2 rise motion categorizing the coro- nal mass ejection (CME) as slow with an associated weak C1.0 class X-ray flare. The flare ribbon sep- aration velocity peaks at around the peak time of the flare at which the maximum reconnection rate (2.14 V cm − 1 occurs. Furthermore, the extreme ul- traviolet light curves of 131, 171 ˚A have delayed peaks of 130 minutes compared to 94 ˚A and are ex- plained by differential emission measure. Our anal- ysis suggests that the energy release is proceeded by a much longer time duration, manifesting the onset of the filament rise and an eventual eruption driven by converging and cancelling flux in the pho- tosphere. Unlike strong eruption events, the ob- served slow CME and weak flare are indications of slow runway tether-cutting reconnection, in which ( 187 )