http://hdl.handle.net/2248/7555 2026-04-05T04:58:59Z 2026-04-05T04:58:59Z Ikonnikova, N. P Parthasarathy, M Shaposhnikov, Ivan A Hubrig, S Sarkar, Geetanjali http://hdl.handle.net/2248/8612 2024-12-17T06:07:40Z 2024-12-01T00:00:00Z

Title: High-resolution spectroscopy of the variable hot post-AGB star LS 4331 (IRAS 17381‑1616) Authors: Ikonnikova, N. P; Parthasarathy, M; Shaposhnikov, Ivan A; Hubrig, S; Sarkar, Geetanjali Abstract: An analysis of the high-resolution (R∼48000) optical spectrum of hot (B1Ibe) post-AGB star LS 4331 (IRAS 17381‑1616) is presented. The detailed identification of the observed absorption and emission features in the wavelength range 3700–9200 Å is carried out for the first time. The atmospheric parameters and chemical composition of the star are derived from the non-LTE analysis of absorption lines. We estimated Teff=20900±500 K, logg=2.57±0.08, Vr=-51.7±0.8 km s-1, ξt=24±4 km s-1 and vsini=30±5 km s-1. An abundance analysis for C, N, O, Mg, Al, S, and Si reveals that the N and O abundance is close to solar while metal underabundances relative to the solar value (i.e., [Mg/H]=-1.04 dex, [Al/H]=-1.20 dex, [Si/H]=-0.46 dex) are found. LS 4331 is a high galactic latitude metal-poor and carbon-deficient hot post-AGB star. The underabundance of carbon ([C/H]=-0.64 dex) is similar to that found in other hot post-AGB stars and indicates that the star's AGB phase of evolution was terminated before the third dredge-up. Plasma diagnostics are derived from the nebular emission lines. The presence of nebular emission lines in the spectrum of LS 4331 indicates that the photoionization of the circumstellar envelope has already started. The nebular parameters and expansion velocity of the nebula are derived. Using the Gaia DR3 distance, the absolute luminosity of the star is derived, and the star's position on the post-AGB evolutionary tracks suggests that its initial main sequence mass is about 1.2 M⊙. It is also reported that fast irregular brightness variations with an amplitude of up to 0.3 mag in the V band have been found in the star, typical of hot post-AGB objects. Description: Restricted Access; The original publication is available at springerlink.com

2024-12-01T00:00:00Z Nagabhushana, S Prasad, B. R Nagesh, Suresh Venkata Suresh, Narra Sandeep, D. S Kamath, P. U Misra, Shalab Hegde, Bhavana Utkarsha, D Sinha, Mrityunjay Kumar Kathiravan, S Natarajan, V Pawan, Kumar Amit Kumar http://hdl.handle.net/2248/8004 2024-05-31T06:23:58Z 2022-03-01T00:00:00Z

Title: Experimental Validation of a Novel Concept to Reduce Optical Surface Wave Front Errors by Using Deformable Bushes at Opto-Mechanical Interfaces Authors: Nagabhushana, S; Prasad, B. R; Nagesh, Suresh; Venkata Suresh, Narra; Sandeep, D. S; Kamath, P. U; Misra, Shalab; Hegde, Bhavana; Utkarsha, D; Sinha, Mrityunjay Kumar; Kathiravan, S; Natarajan, V; Pawan, Kumar; Amit Kumar Abstract: One of the major objectives of the optomechanics is to support large optics required for the purpose and also to maintain high dynamic stability in operation. This requirement calls for more number of supports, to support large optics. While addressing this issue, the mounting system tends to become non-kinematic and distorts the optical surface and leads to poor image quality. The distorted optical surfaces bring in increased RMS surface wavefront errors which will result in poor image quality. In this context, a new concept is proposed in our previous publication (Nagabhushana et al., 2021) which involves introduction of deformable bushes at the optomechanical interfaces. These are deformed by applied clamping forces and also enabling all degrees of freedom (DOF) to be arrested. This also ensures that the clamping force in axial DOF is limited to a minimal value. This technique enables to arrest of axial DOF without exerting the clamping force on the optomechanical assembly there by reduces optical aberrations and improves the mounting system’s dynamic stability. This is because deformable bushes absorb all the clamping forces and the strain has no impact on the mount and therefore does not lead deformation of the optical surface. The clamping forces are simulated by Finite Element (FE) methods. Further, in this paper, the concept is verified and validated by experiments. The simulation results are observed to be in close correlation with experiment results. Improved stability is also observed by additional constraints introduced to optomechanical mounts with no compromise in wavefront errors. Description: Restricted access

2022-03-01T00:00:00Z Cowsik, R (editor) http://hdl.handle.net/2248/7593 2021-02-07T04:41:29Z 1995-01-01T00:00:00Z

Title: International conference on Non-accelerator particle physics : proceedings of the international conference held at Indian Institute of Astrophysics, Bangalore, January 2-9, 1994 Authors: Cowsik, R (editor) Abstract: This international conference focussed on several exciting frontier areas of particle physics at energy scales not realizable in terrestrial accelerators and their significance in the fields of astrophysics and cosmology. The topics discussed included physics beyond the standard model, violations of discrete symmetries, neutrino physics, neutrino astronomy, experimental detection of dark matter, gravitation and feebler new forces, cosmic rays, etc. Some of the highlights are the latest results from the Kamiokande neutrino detector and status reports on experimental facilities under commission to detect solar and atmospheric neutrinos, WIMP's and dark matter candidates. Description: © World Scientific Publishing https://doi.org/10.1142/2402

1995-01-01T00:00:00Z Priest, E. R (editor) Krishan, V (editor) http://hdl.handle.net/2248/7592 2021-02-07T04:39:58Z 1990-01-01T00:00:00Z

Title: Basic plasma processes on the sun : proceedings of the 142th symposium of the International Astronomical Union held in Bangalore, India, December 1-5, 1989 Authors: Priest, E. R (editor); Krishan, V (editor) Abstract: Much of the excitement in modern Solar Physics has come from the realisation that the Sun is a plasma and that this plasma is interacting with the magnetic field in a wide variety of subtle ways. As well as being of great interest in their own right the observed plasma phenomena on the Sun are of much wider importance, since they reveal to us details of basic phenomena that are expected to be occurring throughout the universe. It was with this in mind that 173 solar physicists from 17 countries gathered together in Bangalore with an air of anticipation. We were not disappointed as we received the warmest of welcomes from our graceful and charming host,Vinod Krishan. She and her colleagues worked tirelessly to make our stay a most memorable one and to ensure that the meeting ran with calm and efficiency. In addition to being stimulated by an excellent series of talks on the up-to-the­ minute advances in our subject, it was a pleasure to make new friendships from so many countries and to learn, in particular, of the Solar Physics being done in India which has a great tradition and is of a high standard. Furthermore, we enjoyed hearing about Indian culture and appreciating its beauty, especially on our day's tour into the countryside to visit some Hindu and Jain temples. Description: © International Astronomical Union The original publication is available at Springer http://www.springer.com/us/book/9780792308799

1990-01-01T00:00:00Z