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Browsing by Author "Sankarasubramanian, K"

Browsing by Author "Sankarasubramanian, K"

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  • An efficient modulation scheme for dual beam polarimetry 
    Nagaraju, K; Ramesh, K. B; Sankarasubramanian, K; Rangarajan, K. E (Astronomical Society of India, 2007-09)
    An eight stage balanced modulation scheme for dual beam polarimetry is presented in this paper. The four Stokes parameters are weighted equally in all the eight stages of modulation resulting in total polarimetric efficiency ...
  • Elemental abundances in the solar corona as measured by the X-ray solar monitor onboard Chandrayaan-1 
    Narendranath, S; Sreekumar, P; Alha, L; Sankarasubramanian, K; Huovelin, J; Athiray, P. S (Springer, 2014-05)
    The X-ray Solar Monitor (XSM) on the Indian lunar mission Chandrayaan-1 was flown to complement lunar elemental abundance studies by the X-ray fluorescence experiment C1XS. XSM measured the ≈ 1.8 – 20 keV solar X-ray ...
  • Ellipsometry of Coelostat Coatings Using a Babinet Compensator: Simulation of the Experimental Accuracy 
    Sankarasubramanian, K; Venkatakrishnan, P (Kluwer Academic Publishers, 1996-08)
    The precise measurement of solar magnetic fields requires an accurate measurement of the Muller matrix of the optical components in the path of the light beam, which again requires a careful measurement of the optical ...
  • Estimation of polarization aberrations and its effect on the point spread function of the Thirty Meter Telescope 
    Ramya, M. Anche; Anupama, G. C; Sriram, S; Sankarasubramanian, K; Skidmore, W (SPIE--The International Society for Optical Engineering, 2018-07)
    The Thirty Meter Telescope (TMT) is a future generation telescope proposed to be located in Mauna Kea, Hawaii or in La Palma in the Canary Islands. The telescope will have a segmented primary and an inclined tertiary mirror. ...
  • The estimation of the instrumental polarization and crosstalk at the focus of the mid-infrared imaging system for the Thirty Meter Telescope 
    Ramya, M. Anche; Packham, Chris; Anupama, G. C; Sankarasubramanian, K; Maheswar, G; Manoj, P (SPIE--The International Society for Optical Engineering, 2018-07)
    The Thirty Meter Telescope (TMT) is a proposed future generation telescope which will be located on either Maunakea, Hawaii or La Palma in the Canary islands. A thermal-infrared (TIR) imager and spectrometer (MICHI) combined ...
  • Fast Iterative Techniques for Polarized Radiative Transfer in Spherically Symmetric Moving Media 
    Megha, A; Sampoorna, M; Nagendra, K. N; Anusha, L. S; Sankarasubramanian, K (IOP Publishing, 2020-11-01)
    For a more precise modeling of polarized spectral lines formed in extended and expanding stellar atmospheres, the solution of the radiative transfer equation for the Stokes vectors must be obtained in a spherical geometry ...
  • Hanle-Zeeman Scattering Matrix for Magnetic Dipole Transitions 
    Megha, A; Sampoorna, M; Nagendra, K. N; Sankarasubramanian, K (IOP Publishing, 2017-07)
    The polarization of the light that is scattered by the coronal ions is influenced by the anisotropic illumination from the photosphere and the magnetic field structuring in the solar corona. The properties of the coronal ...
  • The Horizontal Branch Population of NGC 1851 as Revealed by the Ultraviolet Imaging Telescope (UVIT) 
    Subramaniam, A; Snehalata Sahu; Postma, J; Cote, Patrick; Hutchings, J. B; Darukhanawalla, N; Chung, Chul; Tandon, S. N; Kameswara Rao, N; George, K; Ghosh, S. K; Girish, V; Murthy, J; Mohan, Rekhesh; Murthy, J; Pati, A. K; Sankarasubramanian, K; Stalin, C. S; Choudhury, S (IOP Publishing, 2017-12)
    The Horizontal Branch Population of NGC 1851 as Revealed by the Ultraviolet Imaging Telescope ( UVIT ) Annapurni Subramaniam 1 , Snehalata Sahu 1 , Joseph E. Postma 2 , Patrick Côté 3 , J. B. Hutchings 3 , ...
  • Hα full line spectropolarimetry as diagnostics of chromospheric magnetic field 
    Nagaraju, K; Sankarasubramanian, K; Rangarajan, K. E (Indian Academy of Sciences, 2020-12)
    Analysis of spectropolarimetric observations of two circular sunspots located close to disk centre in Hα (6562.8 Å) and Fe i (6569.22 Å) is presented in this paper. The corresponding active region numbers areNOAA 10940 and ...
  • In-orbit Calibrations of the Ultraviolet Imaging Telescope 
    Tandon, S. N; Subramaniam, A; Girish, V; Postma, J; Sankarasubramanian, K; Sriram, S; Stalin, C. S; Mondal, Chayan; Sahu, S; Joseph, P; Hutchings, J; Ghosh, S. K; Barve, Indrajit V; George, K; Kamath, P. U; Kathiravan, S; Kumar, A; Lancelot, J. P; Leahy, D; Mahesh, P. K; Mohan, Rekhesh; Nagabhushana, S; Pati, A. K; Kameswara Rao, N; Sreedhar, Yuvraj Harsha; Sreekumar, P (IOP Publishing, 2017-09)
    The Ultra-Violet Imaging Telescope (UVIT) is one of the payloads in ASTROSAT, the first Indian Space Observatory. The UVIT instrument has two 375 mm telescopes: one for the far-ultraviolet (FUV) channel (1300–1800 Å), ...
  • In-orbit performance of UVIT and first results 
    Tandon, S. N; Hutchings, J. B; Ghosh, S. K; Subramaniam, A; George, K|; Girish, V; Kamath, P. U; Kathiravan, S; Kumar, A; Lancelot, J.P; Mahesh, P. K; Mohan, Rekhesh; Murthy, J; Nagabhushana, S; Pati, A. K; Postma, J; Kameswara Rao, N; Sankarasubramanian, K; Sreekumar, P; Sriram, S; Stalin, C. S; Sutaria, F. K; Sreedhar, Yuvraj Harsha; Barve, Indrajit V; Mondal, Chayan; Snehalata Sahu (Indian Academy of Sciences, 2017-06)
    The performance of the ultraviolet telescope (UVIT) on-board AstroSat is reported. The performance in orbit is also compared with estimates made from the calibrations done on the ground. The sensitivity is found to be ...
  • In-orbit performance of UVIT over the past 5 years 
    Ghosh, S. K; Joseph, P; Kumar, A; Postma, J; Stalin, C. S; Subramaniam, A; Tandon, S. N; Barve, Indrajit V; Devaraj, A; George, K; Girish, V; Hutchings, J. B; Kamath, P. U; Kathiravan, S; Lancelot, J. P; Leahy, D; Mahesh, P. K; Mohan, R; Nagabhushana, S; Pati, A. K; Kameswara Rao, N; Sankarasubramanian, K; Sreekumar, P; Sriram, S (Indian Academy of Sciences, 2021-10)
    Over the last 5 years, UVIT has completed observations of more than 500 proposals with ∼800 unique pointings. In addition, regular planned monitoring observations have been made and from their analysis various key parameters ...
  • Issues with external occultation of a coronagraph 
    Bayanna, A. R; Mathew, S. K; Sankarasubramanian, K; Venkatakrishnan, P; Singh, J; Prasad, B. R (Springer, 2011-04)
    This paper addresses some of the issues related to externally occulted solar coronagraph; vignetting and achievable resolution due to an external occulter. The analytical expression by Evans (J Opt Soc Am 38:1083–1085, ...
  • Line-of-sight observables algorithms for the helioseismic and magnetic imager (HMI) Instrument Tested with Interferometric bidimensional spectrometer (IBIS) observations 
    Couvidat, S; Rajaguru, S. P; Wachter, R; Sankarasubramanian, K; Schou, J; Scherrer, P. H (Springer, 2012-05)
    The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory produces line-of-sight (LOS) observables (Doppler velocity, magneticfield strength, Fe I line width, line depth, and continuum ...
  • Local helioseismic and spectroscopic analyses of interactions between acoustic waves and a sunspot 
    Rajaguru, S. P; Wachter, R; Sankarasubramanian, K; Couvidat, S (IOP Publishing, 2010-10-01)
    Using a high-cadence imaging spectropolarimetric observation of a sunspot and its surroundings in magnetically sensitive (Fe I 6173 Å) and insensitive (Fe I 7090 Å) upper photospheric absorption lines, we map the instantaneous ...
  • Magnetic and velocity properties of G-band bright points around a pore 
    Rangarajan, K. E; Sankarasubramanian, K; Nagaraju, K (Astronomical Society of the Pacific, 2009-06)
    Physical properties of G-band bright points (GBPs) surrounding a pore are studied using observations spanning from photosphere to chromosphere. The magnetic field strengths obtained in these bright points are of the order ...
  • Measurement of instrumental polarisation of the Kodaikanal tunnel tower telescope 
    Sankarasubramanian, K; Samson, J. P. A; Venkatakrishnan, P (Kluwer Academic Publishers, 1999)
    The measurement of the instrumental polarization for any obliquely reflecting telescope is necessary to measure the polarization state of the input beam precisely. To find out the instrumental polarization of the reflecting ...
  • Multilayer Mirror Based High-Resolution Solar Soft X-Ray Spectrometer 
    Panini, S. S; Narendranath, S; Sreekumar, P; Sankarasubramanian, K (Frontiers Media S.A, 2021-07)
    Soft X-ray spectroscopy of the Sun is an important tool to understand the coronal dynamics and composition. The solar coronal X-ray spectrum below 1 keV is the least explored with high-resolution spectroscopy. Recent ...
  • A New Technique for Solar Imaging Spectro-polarimetry using Shack-Hartmann and Fabry-Perot 
    Gosain, S; Sankarasubramanian, K; Venkatakrishnan, P; Bayanna, A. R (Astronomical Society of the Pacific, 2012-12)
    A new technique for solar imaging spectro-polarimetry is presented. Using the combination of a Shack-Hartmann (SH) and a Fabry-Pérot (FP) interferometer, high-cadence spectroscopic observations can be obtained at discrete ...
  • Noise modeling and analysis of an IMU-based attitude sensor: improvement of performance by filtering and sensor fusion 
    Subramaniam, A; Sindhu, N; Tandon, S. N; Kameswara Rao, N; Postma, J; Cote, Patrick; Hutchings, J. B; Ghosh, S. K; George, K; Girish, V; Mohan, Rekhesh; Murthy, J; Sankarasubramanian, K; Stalin, C. S; Sutaria, F. K; Mondal, Chayan; Snehalata Sahu (SPIE-The International Society for Optical Engineering, 2016-07)
    We describe the characterization and removal of noises present in the Inertial Measurement Unit (IMU) MPU- 6050, which was initially used in an attitude sensor, and later used in the development of a pointing system for ...

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