Theoretical study of the Fraunhofer lines polarization: The case of Ca i 4227

Dumont, Simone; Pecker, Jean‐Claude; Omont, A.

doi:10.1007/bf00152298

Cited by 25 publications

(21 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, these three spectral lines have the same polarisation factor E 1 = 0.5 as deduced from Dumont et al (1973). In Stenflo & Stenholm (1976), an optically thin transition region, at the limb, will produce a p = 0.17 for the Si iv line.…”

Section: Possible Importance Of Linear Polarisationmentioning

confidence: 62%

Evidence of scattering effects influenced by plasma flows in C VI 1548 Å, 1550 Å spectral lines emitted from the Sun

Gontikakis

Vial

2016

A&A

View full text Add to dashboard Cite

Aims. We search for, and study, individual spectral profiles where the complex shape of the C iv 1548 Å line is different from the shape of the simultaneously recorded C iv 1550 Å line. Such an asymmetry is not expected for line emission resulting from collisional excitation. Therefore we propose an explanation of these observations through the differential effect of velocity fields on resonant scattering. Methods. We analyse spectra recorded with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and Heliospheric Observatory (SOHO) over active region, NOAA 8541 as well as a second data set on the quiet Sun. We perform Gaussian fits on the individual profiles with two or three Gaussian functions. Moreover, we parameterize the profile asymmetries by calculating the intensity ratios I 1548 /I 1550 , from the derived Gaussian functions. We also calculate artificial spectral profiles emitted from two plasma volumes, which have different line of sight motions and where the plasma emission is influenced by resonant scattering. Results. We locate three small regions in NOAA 8541 which have spectral asymmetries. There the profiles have two or three spectral components, with different intensity ratios. Artificial profiles show that two plasma volumes, having distinct velocities relative to the observer, may reproduce the observed profiles, under the influence of resonant scattering. Conclusions. Asymmetric profiles, found in an active region, can be used as a diagnostic for the importance of resonant scattering in transition region plasma.

show abstract

Section: Possible Importance Of Linear Polarisationmentioning

confidence: 62%

Evidence of scattering effects influenced by plasma flows in C VI 1548 Å, 1550 Å spectral lines emitted from the Sun

Gontikakis

Vial

2016

A&A

View full text Add to dashboard Cite

show abstract

“…Dumont et al (1977) were the first to consider line polarization with angle-dependent PRD, using the Hummer (1962)'s type I redistribution function. McKenna (1985) used Hummer's types I, II, andIII, andFaurobert (1987, 1988) the type II 1 .…”

Section: Introductionmentioning

confidence: 99%

“…They differ rather strongly from previous methods used for angle-dependent PRD. In Dumont et al (1977), Faurobert (1987Faurobert ( , 1988, Nagendra et al (2002), Sampoorna et al (2008a), the radiation field is described by the two Stokes parameters I and Q and the transfer equations for I and Q are solved by Feautrier-type methods, sometimes associated with a perturbation method, or fully perturbative methods, which is based on the linear polarization created by resonance scattering being a few percent only. In McKenna (1985), the radiation field is also described by I and Q, but the radiative transfer equations are solved by a moment equation method.…”

Section: Introductionmentioning

confidence: 99%

Spectral line polarization with angle-dependent partial frequency redistribution

Sampoorna

Nagendra²,

Frisch³

2011

A&A

View full text Add to dashboard Cite

Context. The linear polarization of strong resonance lines observed in the solar spectrum is created by the scattering of the photospheric radiation field. This polarization is sensitive to the form of the partial frequency redistribution (PRD) function used in the line radiative transfer equation. Observations have been analyzed until now with angle-averaged PRD functions. With an increase in the polarimetric sensitivity and resolving power of the present-day telescopes, it will become possible to detect finer effects caused by the angle dependence of the PRD functions. Aims. We devise new efficient numerical methods to solve the polarized line transfer equation with angle-dependent PRD, in planeparallel cylindrically symmetrical media. We try to bring out the essential differences between the polarized spectra formed under angle-averaged and the more realistic case of angle-dependent PRD functions. Methods. We use a recently developed Stokes vector decomposition technique to formulate three different iterative methods tailored for angle-dependent PRD functions. Two of them are of the accelerated lambda iteration type, one is based on the core-wing approach, and the other one on the frequency by frequency approach suitably generalized to handle angle-dependent PRD. The third one is based on a series expansion in the mean number of scattering events (Neumann series expansion). Results. We show that all these methods work well on this difficult problem of polarized line formation with angle-dependent PRD. We present several benchmark solutions with isothermal atmospheres to show the performance of the three numerical methods and to analyze the role of the angle-dependent PRD effects. For weak lines, we find no significant effects when the angle-dependence of the PRD functions is taken into account. For strong lines, we find a significant decrease in the polarization, the largest effect occurring in the near wing maxima.

show abstract

“…Note that the polarization in the lines has been calculated previously [13][14][15] for a similar problem by direct solution of the transfer equation (1). In the case of 0 = β we can compare our calculations with that part of the results ( ) shows that our results agree with those of the earlier work [13][14][15].…”

Section: Calculating the Matrix ( ) Z : Resultsmentioning

confidence: 99%

Effect of continuum absorption on the polarization of resonance lines

Dementyev

2009

Astrophysics

View full text Add to dashboard Cite

Multiple resonance scattering of radiation in a spectrum line with absorption in the continuum isexamined. It is assumed that the scattering atmosphere is semi-infinite and that there is no magnetic field or continuum emission at the frequencies of the spectrum line. The polarization characteristics of the emerging radiation are determined for unpolarized primary radiation sources distributed uniformly within an atmosphere in the case of a Voigt absorption profile. The calculations employ an iterative solution of the Ambartsumyan-Chandrasekhar matrix integral equation.

show abstract

Theoretical study of the Fraunhofer lines polarization: The case of Ca i 4227

Cited by 25 publications

References 11 publications

Evidence of scattering effects influenced by plasma flows in C VI 1548 Å, 1550 Å spectral lines emitted from the Sun

Evidence of scattering effects influenced by plasma flows in C VI 1548 Å, 1550 Å spectral lines emitted from the Sun

Spectral line polarization with angle-dependent partial frequency redistribution

Effect of continuum absorption on the polarization of resonance lines

Contact Info

Product

Resources

About