AR-2019-2020

carried out in collaboration with Gazal Sharma. Investigating sterile neutrino flux in the solar neu- trino data There are compelling evidences for the existence of a fourth degree of freedom of neutrinos, i.e., sterile neutrino. In the recent studies, the role of ster- ile component of neutrinos has been found to be crucial, not only in particle physics, but also in as- trophysics and cosmology. This has been proposed to be one of the potential candidates of dark mat- ter. In this work, we investigate the updated solar neutrino data available from all the relevant ex- periments including Borexino and KamLAND so- lar phase in a model independent way, and obtain bounds on the sterile neutrino component present in the solar neutrino flux. The mystery of the miss- ing neutrinos is further deepening as subsequent experiments are coming up with their results. The energy spectrum of solar neutrinos, as predicted by Standard Solar Models (SSM), is seen by neutrino experiments at different parts as they are sensitive to various neutrino energy ranges. It is interesting to note that more than 98% of the calculated stan- dard model solar neutrino flux lies below 1 MeV. Therefore, the study of low energy neutrinos can give us better understanding and the possibility to know about the presence of antineutrino and ster- ile neutrino components in solar neutrino flux. As such, this work becomes interesting as we include the data from medium energy ( ∼ 1 MeV) experi- ments, i.e., Borexino and KamLAND solar phase. In our study, we retrieve the bounds existing in lit- erature, and rather provide more stringent limits on sterile neutrino ( ν s ) flux available in solar neu- trino data. This work has been carried out in col- laboration with Ankush, Rishu Verma, and Gazal Sharma. Himadri Sekhar Das Bok Globule CB17: Polarization, extinction and distance In this work, the results obtained from the polari- metric study of a Bok Globule CB17 in both optical and sub-millimeter wavelength are presented. The optical polarimetric observations in R-band ( λ = 630 nm, Δ λ = 120 nm) were conducted from 1.04- meter Sampurnanand Telescope, ARIES, Nainital, India on 9th March 2016, while the sub-mm po- larimetric data are taken from the SCUPOL data archive which has been reanalyzed. The contours of Herschel is an ESA space observatory with sci- ence instruments provided by European-led Princi- pal Investigator consortia and with important par- ticipation from NASA. SPIRE 500 μm dust con- tinuum emissions of CB17 (typically a cometary- shaped globule) are overlaid on the DSS image of CB17 along with polarization vectors (optical and sub-mm). The magnetic field strength at the core of the globule is estimated to be 99 μ G. Using the near-infrared photometric technique and Gaia data, the distance to CB17 is found to be 253 ± 43 parsec. A correlation between the various quan- tities of the globule is also studied. It is observed that the magnetic field in the cloud core as revealed by polarization measurements at the sub-mm dust emission is found to be almost aligned along the minor axis of the globule, which fits the magnet- ically regulated star formation model. The mis- alignment between core-scale magnetic field direc- tion and molecular outflow direction is also found. This work has been done in collaboration with G. B. Choudhury, Ajoy Barman, and Biman J. Medhi . Photometry, spectroscopy, and polarimetry of dis- tant comet C/2014 A4 (SONEAR) We present an analysis of spectroscopy, photome- try, and polarimetry of comet C/2014 A4 (SON- EAR), which were performed during November 5- 7, 2015, when its heliocentric distance was 4.2 au and phase angle was 4.7 ◦ . Long-slit spectra and photometric and linear polarimetric images were obtained using the focal reducer SCORPIO-2 at- tached to the prime focus of the 6m telescope BTA (SAO RAS, Russia). We simulated the behavi- uor of colour and polarization in the coma pre- senting the cometary dust as a set of polydisperse polyshapes rough spheroids. No emission features were detected in the 3800–7200 ˚A wavelength range. The continuum showed a reddening effect with the normalized gradient of reflectivity 21 . 6 ± 0 . 2% per 1000 ˚A within the 4650–6200 ˚A wavelength region. The fan-like structure in the sunward hemisphere was detected. The radial profiles of surface bright- ness differ for r-sdss and g-sdss filters, indicating a predominance of sub-micron and micron-sized par- ticles in the cometary coma. The dust colour (g–r) varies from 0 . 75 ± 0 . 05 m to 0 . 45 ± 0 . 06 m along the tail. For an aperture radius near 20,000 km, the dust productions in various filters were estimated