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Browsing by Author "Nagendra, K. N"

Browsing by Author "Nagendra, K. N"

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  • Analysis of the Forward-scattering Hanle Effect in the Ca I 4227 Å Line 
    Anusha, L. S; Nagendra, K. N; Bianda, M; Stenflo, J. O; Holzreuter, R; Sampoorna, M; Frisch, H; Ramelli, R; Smitha, H. N (IOP Publishing, 2011-08-20)
    Coherent scattering of limb-darkened radiation is responsible for the generation of the linearly polarized spectrum of the Sun (the Second Solar Spectrum). This Second Solar Spectrum is usually observed near the limb of ...
  • Blend lines in the polarized spectrum of the Sun 
    Sowmya, K; Nagendra, K. N; Sampoorna, M (Wiley-Blackwell, 2012-07)
    Blend lines form an integral part of the theoretical analysis and modeling of the polarized spectrum of the Sun. Their interaction with other spectral lines needs to be explored and understood before we can properly use ...
  • Center-to-limb Observations and Modeling of the Ca I 4227 Å Line 
    Supriya, H. D; Smitha, H. N; Nagendra, K. N; Stenflo, J. O; Bianda, M; Ramelli, R; Ravindra, B; Anusha, L. S (IOP Publishing, 2014-09-20)
    The observed center-to-limb variation (CLV) of the scattering polarization in different lines of the Second Solar Spectrum can be used to constrain the height variation of various atmospheric parameters, in particular the ...
  • Collisional redistribution effects on line polarization in spherical atmospheres 
    Nagendra, K. N (Blackwell Publishing, 1995-05)
    The polarization of resonance and subordinate lines formed in spherically symmetric media is studied. The effect of collisions is shown by taking a combination of partial redistribution mechanisms represented by the functions ...
  • The combined effect of partial redistribution and non-coherent electron scattering on polarized resonance line transfer 
    Nagendra, K. N; Rangarajan, K. E; Mohan Rao, D (Royal Astronomical Society, 1993-06-15)
    The combined effect of partial frequency redistribution by atoms (PRD) and noncoherent electron scattering (NCES) on line formation is studied, taking account of the polarization state of the radiation field in resonance ...
  • Commission 36: theory of stellar atmospheres 
    Landstreet, J. D; Asplund, M; Spite, M; Balachandran, S. B; Berdyugina, S. V; Hauschildt, P. H; Ludwig, H. G; Mashonkina, L. I; Nagendra, K. N; Puls, J; Randich, M. S; Tautvaisiene, G (International Astronomical Union, 2008-12)
    Commission 36 covers the whole field of the physics of stellar atmospheres. The scientific activity in this large subject has been very intense during the last triennium and led to the publication of a large number of ...
  • Commission 36: theory of stellar atmospheres 
    Spite, M; Landstreet, J. D; Asplund, M; Ayres, T. R; Balachandran, S. C; Dravins, D; Hauschildt, P. H; Kiselman, D; Nagendra, K. N; Sneden, C; Tautvaišiené, G; Werner, K (International Astronomical Union, 2007-12)
    The business meeting of Commission 36 was held during the General Assembly in Prague on 16 August. It was attended by about 15 members. The issues presented included a review of the work made by members of Commission 36, ...
  • Coronal magnetic field measurements using forbidden emission lines 
    Megha, A; Sampoorna, M; Nagendra, K. N; Sankarasubramanian, K (Cambridge University Press, 2018-02)
    The polarization measurement of coronal forbidden emission lines is the most promising method of determining the direction of magnetic fields in the corona. A classical theory for the forbidden lines was presented in Megha ...
  • Effect of Cross-redistribution on the Resonance Scattering Polarization of O I Line at 1302 Å 
    Anusha, L. S; Nagendra, K. N; Uitenbroek, H (IOP Publishing, 2014-10-10)
    Oxygen is the most abundant element on the Sun after hydrogen and helium. The intensity spectrum of resonance lines of neutral oxygen, namely, O I (1302, 1305, and 1306 Å), has been studied in the literature for chromospheric ...
  • The effect of electron scattering redistribution on atomic line polarization 
    Supriya, H. D; Nagendra, K. N; Sampoorna, M; Ravindra, B (Wiley-Blackwell, 2012-09)
    The polarization of spectral lines is generated by the scattering of angularly anisotropic incident radiation field on the atoms in the stellar atmosphere. This atomic scattering polarization is modified by frequency ...
  • Effects of angle-dependent partial frequency redistrubtion on polarized line profiles 
    Sampoorna, M; Nagendra, K. N; Frisch, H; Stenflo, J. O (Astronomical Society of the Pacific, 2019-07)
    Scattering of solar limb darkened radiation field on atoms and molecules produces linearly polarized spectrum of the sun (Second Solar Spectrum). Partial frequency redistribution (PFR) plays a fundamental role in shaping ...
  • Effects on partial frequency redistribution R(II) on the level population ratios in a resonance line 
    Peraiah, A; Nagendra, K. N (Kluwer Academic Publishers, 1983-02)
    Simultaneous solutions of the radiative transfer equation in the comoving frame and the statistical equilibrium equation, for a non-LTE two-level atom, have been obtained by means of angle-averaged partial frequency ...
  • An efficient decomposition technique to solve angle-dependent Hanle scattering problems 
    Supriya, H. D; Sampoorna, M; Nagendra, K. N; Ravindra, B; Anusha, L. S (Elsevier, 2013-04)
    Hanle scattering is an important diagnostic tool to study weak solar magnetic fields. Partial frequency redistribution (PRD) is necessary to interpret the linear polarization observed in strong resonance lines. Usually ...
  • Electron Scattering Redistribution Effect on Atomic Line Polarization 
    Supriya, H. D; Nagendra, K. N; Ravindra, B; Sampoorna, M (Astronomical Society of the Pacific, 2014-10)
    The scattering of line photons on free electrons modifies the polarization of the atomic spectral lines. Hence it is important to treat scattering by electrons as a redistribution process and to study in detail its effect ...
  • 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 ...
  • Fast Numerical Methods for Polarized Line Radiative Transfer in the Presence of Hanle Effect 
    Faurobert, M; Frisch, H; Nagendra, K. N (Astronomical Society of the Pacific, 1999-09)
    The Hanle effect provides a diagnostic tool for weak magnetic fields which do not give rise to a measurable Zeeman effect, such as turbulent fields or magnetic canopies. The lines which are sensitive to the Hanle effect ...
  • Forward-scattering Hanle effect in the solar Ca i 4227 Å line 
    Frisch, H; Anusha, L. S; Bianda, M; Holzreuter, R; Nagendra, K. N; Ramelli, R; Sampoorna, M; Smitha, H. N; Stenflo, J. O (Cambridge University Press, 2012-06)
    High sensitivity spectropolarimetric observations of the four Stokes parameters of the solar Ca i 4227 Å line have been performed in October 2010 at IRSOL with the ZIMPOL polarimeter, near the disk center, outside an active ...
  • Generalization of the last scattering approximation for the second solar spectrum modeling: the Ca i 4227 å line as a case study 
    Anusha, L. S; Nagendra, K. N; Stenflo, J. O; Bianda, M; Sampoorna, M; Frisch, H; Holzreuter, R; Ramelli, R (IOP Publishing, 2010-08-01)
    To model the second solar spectrum (the linearly polarized spectrum of the Sun that is due to coherent scattering processes), one needs to solve the polarized radiative transfer (RT) equation. For strong resonance lines, ...
  • Generalized Voigt functions and their derivatives 
    Sampoorna, M; Nagendra, K. N; Frisch, H (Elsevier Ltd, 2007-03)
    This paper deals with a special class of functions called generalized Voigt functions H(n)(x,a) and G(n)(x,a) and their partial derivatives, which are useful in the theory of polarized spectral line formation in stochastic ...
  • Green's matrix for Compton reflection of polarized radiation from cold matter 
    Poutanen, J; Nagendra, K. N; Svensson, R (Royal Astronomical Society, 1996-12)
    The Compton-reflected spectrum from cold matter for incident X-rays and gamma-rays with arbitrary angular, spectral and polarization properties can be determined by a simple folding of Green's matrix with the incident ...

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