Quiet-Sun Magnetic Fields at High Spatial Resolution

Cerdeña, I. Domínguez; Kneer, F.; Alméida, J. Sánchez

doi:10.1086/346199

Cited by 101 publications

(74 citation statements)

References 19 publications

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“…Unfortunately, the signals are barely above the noise level, thus it has not yet been possible to fully characterize the magnetic field vector in these regions. This has led to a long-standing controversy about the distribution of the module of the magnetic field vector in the internetwork (Domínguez Cerdeña et al 2003;Socas-Navarro & Lites 2004;Sánchez Almeida 2005;Martínez González et al 2006;Asensio Ramos et al 2007;López Ariste et al 2007;Socas-Navarro et al 2008; see also references therein).…”

Section: Introductionmentioning

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: Introductionmentioning

confidence: 99%

Inferring the magnetic field vector in the quiet Sun

Borrero

Kobel

2012

A&A

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“…Steiner 2003). Analyses based on visible lines suggest that the internetwork contains a sizeable fraction of fields in the kG range (Grossmann-Doerth et al 1996;Sánchez Almeida & Lites 2000;Socas-Navarro & Sánchez Almeida 2002;Domínguez Cerdeña et al 2003; but see Lites 2002). Analyses based on infrared spectral lines, on the contrary, indicate that strong fields are very rare and that weak fields dominate the PDF (Lin 1995;Khomenko et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Understanding internetwork magnetic fields as determined from visible and infrared spectral lines

Rubio

Collados

2003

A&A

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Abstract. We present numerical experiments aimed at understanding why near-infrared observations systematically deliver weak magnetic fields in the internetwork, whereas analyses based on visible lines indicate that kG fields are ubiquitous. Synthetic noisy Stokes V profiles of the iron lines at 6302 Å and 1.565 µm have been produced under varying conditions in an effort to simulate polarized spectra coming from the internetwork. An inversion technique has been applied to the profiles, as it is usually done with real observations, in order to derive the distribution of magnetic fields in the simulated region. Our results show that infrared lines yield distributions which are very similar to those used as input for the simulation, while visible lines are to a large extent affected by noise. Analyses based on the Fe I lines at 6302 Å may lead to an overabundance of kG fields if the signal-to-noise ratio in Stokes V is poorer than about 10. A particular example is shown where strong fields are retrieved in nearly 30% of the pixels of a simulated internetwork region in which only fields of 200 G exist.

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“…Viticchié et al (2009) studied their association with G-band bright points and used the SIR (Stokes inversions based on response function) approach (Ruiz Cobo & del Toro Iniesta 1992) to determine that their temporal evolution is related to the filling factor rather than to the magnetic field strength. Observations with high polarimetric sensitivity revealed that magnetic fields occupy approximately 45 % of the area in internetwork patches, predominantly in intergranular spaces (Domínguez Cerdeña et al 2003). Scrutinizing the intricate fine structure of granules, Steiner et al (2010) found evidence for horizontally oriented vortex tubes, i.e., striations with leading bright rim and a trailing dark edge, which migrate in unison from the periphery to the granule's interior.…”

Section: Science With Imaging Spectropolarimetersmentioning

confidence: 99%

The GREGOR Fabry‐Pérot Interferometer

et al. 2012

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The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard-and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50 ×38 is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25 ×38 . The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution of R ≈ 250 000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface.

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Quiet-Sun Magnetic Fields at High Spatial Resolution

Cited by 101 publications

References 19 publications

Inferring the magnetic field vector in the quiet Sun

Inferring the magnetic field vector in the quiet Sun

Understanding internetwork magnetic fields as determined from visible and infrared spectral lines

The GREGOR Fabry‐Pérot Interferometer

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