Retrieval of the full magnetic vector with the He I multiplet at 1083 nm

Lagg, A.; Woch, J.; Krupp, N.; Solanki, S. K.

doi:10.1051/0004-6361:20031643

Cited by 164 publications

(215 citation statements)

References 40 publications

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“…This code operates, with some modifications, under a LevenbergMarquardt non-linear minimization algorithm . We cannot exclude that other numerical schemes such as genetic (Lagg et al 2004) or Bayesian algorithms (Asensio Asensio Ramos 2009) are less affected by photon noise and therefore able to infer more accurately the distribution of the magnetic field vector.…”

Section: Discussionmentioning

confidence: 99%

Inferring the magnetic field vector in the quiet Sun

Borrero

Kobel

2012

A&A

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In a previous paper, we argued that the inversion of Stokes profiles applied to spectropolarimetric observations of the solar internetwork yield unrealistically large values of the inclination of the magnetic field vector (γ). This is because photon noise in Stokes Q and U are interpreted by the inversion code as valid signals, that leads to an overestimation of the transverse component B ⊥ , thus the inclination γ. However, our study was based on the analysis of linear polarization signals that featured only uncorrelated noise. In this paper, we develop this idea further and study this effect in Stokes Q and U profiles that also show correlated noise. In addition, we extend our study to the three components of the magnetic field vector, as well as the magnetic filling factor α. With this, we confirm the tendency to overestimate γ when inverting linear polarization profiles that, although non-zero, are still below the noise level. We also establish that the overestimation occurs mainly for magnetic fields that are nearly vertical γ 20 • . This indicates that a reliable inference of the inclination of the magnetic field vector cannot be achieved by analyzing only Stokes I and V. In addition, when inverting Stokes Q and U profiles below the noise, the inversion code retrieves a randomly uniform distribution of the azimuth of the magnetic field vector φ. To avoid these problems, we propose only inverting Stokes profiles for which the linear polarization signals are sufficiently above the noise level. However, this approach is also biased because, in spite of allowing for a very accurate retrieval of the magnetic field vector from the selected Stokes profiles, it selects only profiles arising from highly inclined magnetic fields.

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Section: Discussionmentioning

confidence: 99%

Inferring the magnetic field vector in the quiet Sun

Borrero

Kobel

2012

A&A

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“…The atmospheric parameters for the individual He components were retrieved by inverting the Stokes profiles, using the numerical code HeLIx+ (Lagg et al 2004(Lagg et al , 2009). The nine free parameters tuned by the code to fit the observed Stokes profiles were the magnetic field strength B and direction (inclination angle γ and azimuthal angle χ), the line-of-sight (LOS) velocity v LOS , the Doppler width Δλ D , the damping constant Γ, the ratio of the line centre to the continuum opacity η 0 , the gradient of the source function S 1 , and the filling factor α i , which defines the contribution of a given atmospheric component i to the total observed He profile.…”

Section: Observations and Data Analysismentioning

confidence: 99%

Magnetic structure of an activated filament in a flaring active region

Sasso

Lagg

Solanki

2014

A&A

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Aims. While the magnetic field in quiescent prominences has been widely investigated, less is known about the field in activated prominences. We report observational results on the magnetic field structure of an activated filament in a flaring active region. In particular, we studied its magnetic structure and line-of-sight flows during its early activated phase, shortly before it displayed signs of rotation.Methods. We inverted the Stokes profiles of the chromospheric He i 10 830 Å triplet and the photospheric Si i 10 827 Å line observed in this filament by the Vacuum Tower Telescope on Tenerife. Using these inversion results, we present and interpret the first maps of the velocity and magnetic field obtained in an activated filament, both in the photosphere and the chromosphere. Results. Up to five different magnetic components are found in the chromospheric layers of the filament, while outside the filament a single component is sufficient to reproduce the observations. Magnetic components displaying an upflow are preferentially located towards the centre of the filament, while the downflows are concentrated along its periphery. Moreover, the upflowing gas is associated with an opposite-polarity magnetic configuration with respect to the photosphere, while the downflowing gas is associated with a same-polarity configuration. Conclusions. The activated filament has a very complex structure. Nonetheless, it is compatible with a flux rope, albeit a distorted one, in the normal configuration. The observations are best explained by a rising flux rope in which part of the filament material is still stably stored (upflowing material, rising with the field), while the rest is no longer stably stored and flows down along the field lines.

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“…[5] Up to now, while many efforts have been devoted to the direct measurements of magnetic fields in the solar chromosphere and corona [e.g., Judge, 1998;Solanki et al, 2003;Lagg et al, 2004;Lin et al, 2004;Kramar et al, 2006;Trujillo Bueno and Asensio Ramos, 2007;Liu and Lin, 2008;Cargill, 2009;Frisch et al, 2009], the extrapolation based on NLFFF model is still a commonly used and necessary approach to understand the 3-D configuration of the coronal magnetic field. That is, the field can be reconstructed by solving the force-free and divergence-free differential equations (2) and (3) or equivalent equations (4) and (5), in which the observed photospheric vector magnetogram is taken as the bottom boundary condition.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

Wang

Yan

2011

J. Geophys. Res.

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[1] The Hinode satellite can obtain high-quality photospheric vector magnetograms of solar active regions and the simultaneous coronal loop images in soft X-ray and extreme ultraviolet (EUV) bands. In this paper, we continue the work of and apply the newly developed upward boundary integration computational scheme for the nonlinear force-free field (NLFFF) extrapolation of the coronal magnetic field to the

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Retrieval of the full magnetic vector with the He I multiplet at 1083 nm

Cited by 164 publications

References 40 publications

Inferring the magnetic field vector in the quiet Sun

Inferring the magnetic field vector in the quiet Sun

Magnetic structure of an activated filament in a flaring active region

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

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