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Browsing IIAP Publications by Subject "Line: formation"

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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 ...
Azimuthal structures in the wind and chromosphere of the Herbig AE star AB Aurigae. Results from the MUSICOS 1992 campaign

Boehm, T; Catala, C; Donati, J. F; Welty, A; Baudrand, J; Butler, C. J; Carter, B; Collier-Cameron, A; Czarny, J; Foing, B; Ghosh, K; Hao, J; Houdebine, E; Huang, L; Jiang, S; Neff, J. E; Rees, D; Semel, M; Simon, T; Talavera, A; Zhai, D; Zhao, F (European Southern Observatory, 1996-12)

The observations of the MUSICOS 1992 campaign concerned three scientific programs, among which was the study of azimuthal structures in the wind and chromosphere of the pre-main sequence Herbig Ae star AB Aur. The He I ...
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 ...
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 ...
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 ...
Emission lines from X-ray illuminated accretion disc in black hole binaries

Mondal, Santanu; Adhikari, Tek P; Singh, Chandra B (Oxford University Press on behalf of the Royal Astronomical Society, 2021-07)

X-ray flux from the inner hot region around central compact object in a binary system illuminates the upper surface of an accretion disc and it behaves like a corona. This region can be photoionized by the illuminating ...
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, ...
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 ...
m-state Interference with Partial Frequency Redistribution for Polarized Line Formation in Arbitrary Magnetic Fields

Sampoorna, M (IOP Publishing, 2011-04-20)

The present paper concerns the derivation of polarized partial frequency redistribution (PRD) matrices for scattering on a two-level atom in arbitrary magnetic fields. We generalize the classical theory of PRD that is ...
The metal-poor end of the Spite plateau. II. Chemical and dynamical investigation

Pinto, A. M. Matas; Spite, M; Caffau, E; Bonifacio, P; Sbordone, L; Sivarani, T; Steffen, M; François, P; Di Matteo, P (EDP Sciences, 2021-10)

Context. The study of old, metal-poor stars deepens our knowledge on the early stages of the universe. In particular, the study of these stars gives us a valuable insight into the masses of the first massive stars and their ...
Multi-dimensional Radiative Transfer to Analyze Hanle Effect in Ca II K Line at 3933 Å

Anusha, L. S; Nagendra, K. N (IOP Publishing, 2013-04-20)

Radiative transfer (RT) studies of the linearly polarized spectrum of the Sun (the second solar spectrum) have generally focused on line formation, with an aim to understand the vertical structure of the solar atmosphere ...
Polarized line formation in Multi-dimensional media-I: Decomposition of Stokes parameters in arbitrary geometries

Anusha, L. S; Nagendra, K. N (IOP Publishing, 2011-01-01)

The solution of the polarized line radiative transfer (RT) equation in muti-dimensional geome- tries has been rarely addressed and only under the approximation that the changes of frequencies at each scattering are ...
Polarized line formation in multi-dimensional media-II: A fast method to solve problems with partial frequency redistribution

Anusha, L. S; Nagendra, K. N; Paletou, F (IOP Publishing, 2011-01-10)

In the previous paper of this series (Anusha & Nagendra 2010), we presented a formula- tion of the polarized radiative transfer equation for resonance scattering with partial frequency redistribution (PRD) in multi-dimensional ...
Polarized Line Formation in Multi-dimensional Media. III. Hanle Effect with Partial Frequency Redistribution

Anusha, L. S; Nagendra, K. N (IOP Publishing, 2011-09-01)

In two previous papers, we solved the polarized radiative transfer (RT) equation in multi-dimensional (multi-D) geometries with partial frequency redistribution as the scattering mechanism. We assumed Rayleigh scattering ...
Polarized Line Formation in Multi-dimensional Media. IV. A Fourier Decomposition Technique to Formulate the Transfer Equation with Angle-dependent Partial Frequency Redistribution

Anusha, L. S; Nagendra, K. N (IOP Publishing, 2011-09-20)

To explain the linear polarization observed in spatially resolved structures in the solar atmosphere, the solution of polarized radiative transfer (RT) equation in multi-dimensional (multi-D) geometries is essential. For ...
Polarized Line Formation in Multi-dimensional Media. V. Effects of Angle-dependent Partial Frequency Redistribution

Anusha, L. S; Nagendra, K. N (IOP Publishing, 2012-02-10)

The solution of polarized radiative transfer equation with angle-dependent (AD) partial frequency redistribution (PRD) is a challenging problem. Modeling the observed, linearly polarized strong resonance lines in the solar ...
Polarized line formation in spherically symmetric atmospheres with velocity fields

Megha, A; Sampoorna, M; Nagendra, K. N; Anusha, L. S; Sankarasubramanian, K (IOP Publishing, 2019-07-01)

The plane–parallel approximation of the stellar atmospheres cannot be applied to model the formation of optically thick lines formed in extended atmospheres. To a good approximation these atmospheres can be represented by ...
Polarized line formation with lower-level polarization and partial frequency redistribution

Supriya, H. D; Sampoorna, M; Nagendra, K. N; Stenflo, J. O; Ravindra, B (IOP Publishing, 2016-09-10)

In the well-established theories of polarized line formation with partial frequency redistribution (PRD) for a two-level and two-term atom, it is generally assumed that the lower level of the scattering transition is ...
Polarized Line Transfer with F-state Interference in a Non-magnetic Medium: Partial Frequency Redistribution Effects in the Collisionless Regime

Smitha, H. N; Sowmya, K; Nagendra, K. N; Sampoorna, M; Stenflo, J. O (IOP Publishing, 2012-10-20)

Quantum interference phenomena manifest themselves in several ways in the polarized solar spectrum formed due to coherent scattering processes. One such effect arises due to interference between the fine structure (J) ...

Browsing IIAP Publications by Subject "Line: formation"

Browsing IIAP Publications by Subject "Line: formation"

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