Net circular polarization of sunspot penumbrae

Schlichenmaier, R.; Müller, D.; Steiner, O.; Stix, M.

doi:10.1051/0004-6361:20011706

Cited by 39 publications

(20 citation statements)

References 13 publications

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“…The photospheric Evershed flow is usually associated with velocities of approximately 5 km s −1 (Bellot Rubio et al 2003) which is well below our 20 km s −1 values. However, Schlichenmaier et al (2002) provide a model where photospheric Evershed flows may reach velocities up to 14 km s −1 , which is comparable with our findings after consideration of the errors involved in our analysis.…”

Section: Resultssupporting

confidence: 89%

High-frequency oscillations in a solar active region observed with the RAPID DUAL IMAGER

Jess

Andic²,

Mathioudakis³

et al. 2007

A&A

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High-cadence, synchronized, multiwavelength optical observations of a solar active region (NOAA 10794) are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system: the rapid dual imager. Wavelet analysis is undertaken to search for intensity related oscillatory signatures, and periodicities ranging from 20 to 370 s are found with significance levels exceeding 95%. Observations in the H-α blue wing show more penumbral oscillatory phenomena when compared to simultaneous G-band observations. The H-α oscillations are interpreted as the signatures of plasma motions with a mean velocity of 20 km s −1 . The strong oscillatory power over H-α blue-wing and G-band penumbral bright grains is an indication of the Evershed flow with frequencies higher than previously reported.

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Section: Resultssupporting

confidence: 89%

High-frequency oscillations in a solar active region observed with the RAPID DUAL IMAGER

Jess

Andic²,

Mathioudakis³

et al. 2007

A&A

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“…The area asymmetry in the circular polarization profiles, Stokes V, as well as its behavior with radial distance in the penumbra are also reproduced. The azimuthal variation of the NCP observed in both sets of spectral lines also finds a satisfactory explanation in terms of the uncombed model (see Müller et al 2002;Schlichenmaier et al 2002).…”

Section: Discussionsupporting

confidence: 55%

“…There is already considerable evidence pointing towards a magnetic structure of the sunspot penumbra in the form of uncombed magnetic fields: Martínez Pillet (2000Pillet ( , 2001, Schlichenmaier et al (2002), Müller et al (2002), Mathew et al (2003, Borrero et al (2004Borrero et al ( , 2005. The uncombed magnetic field was first employed by Solanki & Montavon (1993) to qualitatively reproduce the net circular polarization (NCP) observed in the sunspot penumbra.…”

Section: Introductionmentioning

confidence: 99%

On the fine structure of sunspot penumbrae

Borrero

Solanki²,

Lagg³

et al. 2006

A&A

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In this paper we study the fine structure of the penumbra as inferred from the uncombed model (flux tube embedded in a magnetic surrounding) when applied to penumbral spectropolarimetric data from the neutral iron lines at 6300 Å. The inversion infers very similar radial dependences in the physical quantities (LOS velocity, magnetic field strength etc.) as those obtained from the inversion of the Fe I 1.56 µm lines. In addition, the large Stokes V area asymmetry exhibited by the visible lines helps to constrain the size of the penumbral flux tubes. As we demonstrate here, the uncombed model is able to reproduce the area asymmetry with striking accuracy, returning flux tubes as thick as 100−300 kilometers in the vertical direction, in good agreement with previous investigations.

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“…In papers II and III, we used a simple (the flux tube cross section was assumed to be square) flux tube model where those large gradients in the inclination were produced at the lower and upper tube boundaries. In this manner, we successfully reproduced the observed NCP and the full polarization profiles (see also Schlichenmaier et al 2002;Müller et al 2002 andMüller et al 2006).…”

Section: Vertical Gradients In the Field Inclinationmentioning

confidence: 75%

The structure of sunspot penumbrae

Borrero

2007

A&A

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Aims. We study the magnetohydrostatic equilibrium of magnetic flux tubes with circular cross sections embedded in a magnetic surrounding atmosphere. Methods. We solve the static momentum equation in 2.5D to obtain the thermodynamics that are consistent with a prescribed velocity and magnetic fields. Results. We show that force balance is roughly satisfied if the flux tube's magnetic field is aligned with its axis. Equilibrium is guaranteed if this magnetic field possesses a transverse component. Several forms of this transverse field are investigated. The resulting magnetic field configurations are critically reviewed in terms of the results from spectropolarimetric observations. The thermodynamic structure that allows the flux tube to be in mechanical equilibrium is also calculated. We show that the inferred pressure, density, and temperature stratification reproduce intensity features similar to dark core penumbral filaments and penumbral grains.

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Net circular polarization of sunspot penumbrae

Cited by 39 publications

References 13 publications

High-frequency oscillations in a solar active region observed with the RAPID DUAL IMAGER

High-frequency oscillations in a solar active region observed with the RAPID DUAL IMAGER

On the fine structure of sunspot penumbrae

The structure of sunspot penumbrae

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