Inter-network magnetic fields observed with sub-arcsec resolution

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

doi:10.1051/0004-6361:20030892

Cited by 98 publications

(81 citation statements)

References 48 publications

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“…Previous studies of very quiet regions reported a polarity balance, even with smaller observed areas (e.g. Lites 2002;Domínguez Cerdeña et al 2003;Martínez González et al 2008c). This imbalance occurs for all signals, hence it cannot be a result of unipolar network patches or a unipolar weak component previously undetected.…”

Section: One Magnetic Structure Embedded In a Field-free Atmospherementioning

confidence: 66%

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Inference of magnetic fields in the very quiet Sun

González

Yabar

Lagg

et al. 2016

A&A

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Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution. Aims. We present high-precision spectro-polarimetric data with high spatial resolution (0.4 ) of the very quiet Sun at 1.56 µm obtained with the GREGOR telescope to shed some light on this complex magnetism. Methods. We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component. Results. Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak (∼150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area ∼50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised.

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Section: One Magnetic Structure Embedded In a Field-free Atmospherementioning

confidence: 66%

“…Khomenko et al 2003;Martínez González et al 2008c), other works used visible lines and derived kG fields (e.g. Socas-Navarro & Sánchez Almeida 2002;Domínguez Cerdeña et al 2003). Later, the Hinode satellite provided spectro-polarimetric data in the visible with improved spatial resolution.…”

Section: Introductionmentioning

confidence: 99%

Inference of magnetic fields in the very quiet Sun

González

Yabar

Lagg

et al. 2016

A&A

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“…IR spectra at 1.56 μm allow us to disentangle most of the ambiguities because the field strength can be inferred from the splitting of the polarization, or in some cases, even the intensity components of the spectral line for magnetic fields above around 400 G (Beck 2006;Beck et al 2007). It is thus unsurprising that studies before HINODE using solely VIS lines (Sánchez Almeida & Lites 2000;Domínguez Cerdeña et al 2003;Socas-Navarro & Sánchez Almeida 2003; or IR lines (Lin 1995;Khomenko et al 2003; Article published by EDP Sciences Martínez González et al 2006a;Domínguez Cerdeña et al 2006a) did not agree especially about the intrinsic field strength: the VIS observations indicated a significant fraction of strong kG fields, whereas the IR was dominated by weaker hG fields.…”

Section: Introductionmentioning

confidence: 99%

The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

Beck¹,

Rezaei²

2009

A&A

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Context. Observations made with the spectropolarimeter onboard the HINODE satellite have detected abundant horizontal magnetic fields in the internetwork quiet Sun. Aims. We compare the results for the horizontal fields obtained at 630 nm with ground-based observations at 1.56 μm, where the sensitivity to magnetic fields is higher than in the visible. Methods. We obtained 30-s integrated spectropolarimetric data of the quiet Sun on disc centre during a period of extremely stable and good seeing. The data have a rms noise in polarization of around 2 × 10 −4 of the continuum intensity. The low noise level allows the spectra to be inverted with the SIR code. We compare the inversion results with proxies to determine the magnetic flux. Results. We confirm the presence of the horizontal fields in the quiet Sun internetwork as reported for the satellite data, including voids without linear polarization signal that extend over an area of a few granules. Voids in the circular polarization signal are only of granular scale. More than 60% of the surface show polarization signals of above four times the rms noise level. We find that the total magnetic flux contained in the more inclined to horizontal fields (γ > 45 • ) is lower by a factor of around 2 than that of the less inclined fields. The proxies for flux determination are strongly affected by the thermodynamic state of the atmosphere, and hence, seem to be unreliable. Conclusions. During spells of good seeing conditions, adaptive optics can render ground-based slit-spectrograph observations at a 70-cm telescope equivalent to the seeing-free space-based data of half-meter class telescopes. We suggest that the difference in the ratio of horizontal to transversal flux between the ground-based infrared data and the satellite-based visible data is due to the different formation heights of the respective spectral lines. We emphasize that the true amount of magnetic flux cannot be derived directly from the spectra. For purely horizontal flux, one would need its vertical extension that has to be estimated by explicit modeling, using the observed spectra as boundary conditions, or be taken from MHD simulations. Time-series of the evolution of the magnetic flux and chromospheric diagnostics are needed to address its possible contribution to chromospheric heating.

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“…When averaged over the 30% of the FOV that we study, the mean unsigned flux density turns out to be 11 G in the visible, and 6 G in the IR. Due to the complexity of the IN magnetic fields, the observed unsigned flux is expected to increase with increasing angular resolution (see, e.g., Sánchez Domínguez Cerdeña et al 2003b). The fact that the IR, with higher resolution, has lower unsigned flux, seems to indicate that this is a true solar effect.…”

Section: Resultsmentioning

confidence: 99%

Simultaneous Visible and Infrared Spectropolarimetry of a Solar Internetwork Region

Alméida¹,

Cerdeña²,

Kneer³

2003

ApJ

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We present the first simultaneous infrared (IR) and visible spectro-polarimetric observations of a solar internetwork region. The Fe I lines at λ6301.5 Å, λ6302.5 Å, λ15648 Å, and λ15652 Å were observed, with a lag of only 1 min, using highly sensitive spectro-polarimeters operated in two different telescopes (VTT and THEMIS at the Observatorio del Teide). Some 30% of the observed region shows IR and visible Stokes V signals above noise. These polarization signals indicate the presence of kG magnetic field strengths (traced by the visible lines) co-existing with sub-kG fields (traced by the infrared lines). In addition, one quarter of the pixels with signal have visible and IR Stokes V profiles with opposite polarity. We estimate the probability density function of finding each longitudinal magnetic field strength in the region. It has a tail of kG field strengths that accounts for most of the (unsigned) magnetic flux of the region.

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Inter-network magnetic fields observed with sub-arcsec resolution

Cited by 98 publications

References 48 publications

Inference of magnetic fields in the very quiet Sun

Inference of magnetic fields in the very quiet Sun

The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

Simultaneous Visible and Infrared Spectropolarimetry of a Solar Internetwork Region

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