A two-component model of the solar photosphere   from the
inversion of spectral lines

Borrero, J. M.; Rubio, L. R. Bellot

doi:10.1051/0004-6361:20020176

Cited by 60 publications

(75 citation statements)

References 25 publications

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“…To that end we have determined the depth of the optical depth unity level as a function of wavelength z(τ λ = 1) for different atmospheric models: granular model from Borrero & Bellot Rubio (2002), hot and cool umbral models from Collados et al (1994), and finally the spatiallyaveraged penumbral model obtained from the inversions of NOAA 12049 described in Sect. 4.3.…”

Section: How Deep Are We Probing?mentioning

confidence: 99%

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Borrero

Ramos

Collados

et al. 2016

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Context. Some models for the topology of the magnetic field in sunspot penumbrae predict the existence of field-free or dynamically weak-field regions in the deep Photosphere. Aims. To confirm or rule out the existence of weak-field regions in the deepest photospheric layers of the penumbra. Methods. The magnetic field at log τ5 = 0 is investigated by means of inversions of spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45 ′′ . The data have been recorded using the GRIS instrument attached to the 1.5-meters GREGOR solar telescope at El Teide observatory. It includes three Fe i lines around 1565 nm, whose sensitivity to the magnetic field peaks at half a pressure-scale-height deeper than the sensitivity of the widely used Fe i spectral line pair at 630 nm. Prior to the inversion, the data is corrected for the effects of scattered light using a deconvolution method with several point spread functions. Results. At log τ5 = 0 we find no evidence for the existence of regions with dynamically weak (B < 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations done with Fe i lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, and also independent of the point spread function used to deconvolve the data, and does not depend on the amount of straylight (i.e. wide-angle scattered light) considered.

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Section: How Deep Are We Probing?mentioning

confidence: 99%

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Borrero

Ramos

Collados

et al. 2016

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“…The observations have provided some boundary conditions, like for instance the presence of the Evershed flow (Evershed 1909), an almost radial orientation of the magnetic field lines, a radial decrease in magnetic field strength, and a radial increase in the field inclination to the local vertical (e.g., Lites et al 1993;Westendorp Plaza et al 2001;Borrero & Bellot Rubio 2002;Solanki 2003;Bellot Rubio et al 2004;Langhans et al 2005;Beck 2008;Schlichenmaier 2009). With increasing spatial resolution, the Evershed flow could definitely be shown to be related to the penumbral filaments (Shine et al 1994;Tritschler et al 2004;Langhans et al 2005;Rimmele & Marino 2006).…”

Section: Introductionmentioning

confidence: 99%

An uncombed inversion of multiwavelength observations reproducing the net circular polarization in a sunspot’s penumbra

Beck

2010

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Context. The penumbra of sunspots has a complex magnetic field topology whose three-dimensional organization remains unclear after more than a century of investigation. Aims. I derive a geometrical model of the penumbral magnetic field topology from an uncombed inversion setup designed to reproduce the net circular polarization (NCP) of simultaneous spectra in near-infrared (IR; 1.56 μm) and visible (VIS; 630 nm) spectral lines. Methods. I inverted the co-spatial spectra of five photospheric lines with a model that mimicked vertically interlaced magnetic fields with two distinct components, labeled background field and flow channels because of their characteristic properties (flow velocity, field inclination). The flow channels were modeled as a perturbation of the constant background field with a Gaussian shape using the SIRGAUS code. The location and extension of the Gaussian perturbation in the optical depth scale retrieved by the inversion code were then converted to a geometrical height scale. By estimating the geometrical size of the flow channels, I investigated the relative amount of magnetic flux in the flow channels and the background field atmosphere.Results. The uncombed model is able to reproduce the NCP well on the limb side of the spot and less successfully on the center side; the VIS lines are better reproduced than the near-IR lines. I find that the Evershed flow happens along nearly horizontal field lines close to the solar surface given by optical depth unity. The magnetic flux that is related to the flow channels constitutes about 20−50% of the total magnetic flux in the penumbra. Conclusions. The gradients that can be produced by a Gaussian perturbation are too small for a perfect reproduction of the NCP in the IR lines with their small formation height range, where a step function seems to be required. Two peculiarities of the observed NCP, a sign change in the NCP of the VIS lines on the center side and a ring structure around the umbra with opposite signs of the NCP in the Ti i line at 630.37 nm and the Fe i line at 1565.2 nm, deserve closer attention in future modeling attempts. The large fraction of magnetic flux related to the flow channel component could suffice to replenish the penumbral radiative losses in the flux tube picture.

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“…Fig. 3 in Borrero & Bellot Rubio 2002), we could then have postulated a correlation between the magnetic field vector B and the gradient of the source function with optical depth S 1 , which is contained in T (Eq. (3)).…”

Section: Assumptions and Limitationsmentioning

confidence: 99%

Inferring the magnetic field vector in the quiet Sun

Borrero

Kobel

2013

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Recent investigations of the magnetic field vector properties in the solar internetwork have provided diverging results. While some works found that the internetwork is mostly pervaded by horizontal magnetic fields, other works argued in favor of an isotropic distribution of the magnetic field vector. Motivated by these seemingly contradictory results and by the fact that most of these works have employed spectropolarimetric data at disk center only, we have revisited this problem employing high-quality data (noise level σ ≈ 3 × 10 −4 in units of the quiet-Sun intensity) at different latitudes recorded with the Hinode/SP instrument. Instead of applying traditional inversion codes of the radiative transfer equation to retrieve the magnetic field vector at each spatial point on the solar surface and studying the resulting distribution of the magnetic field vector, we surmised a theoretical distribution function of the magnetic field vector and used it to obtain the theoretical histograms of the Stokes profiles. These histograms were then compared to the observed ones. Any mismatch between them was ascribed to the theoretical distribution of the magnetic field vector, which was subsequently modified to produce a better fit to the observed histograms. With this method we find that Stokes profiles with signals above 2 × 10 −3 (in units of the continuum intensity) cannot be explained by an isotropic distribution of the magnetic field vector. We also find that the differences between the histograms of the Stokes profiles observed at different latitudes cannot be explained in terms of line-of-sight effects. However, they can be explained by a distribution of the magnetic field vector that inherently varies with latitude. We note that these results are based on a series of assumptions that, although briefly discussed in this paper, need to be considered in more detail in the future.

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A two-component model of the solar photosphere from the inversion of spectral lines

Cited by 60 publications

References 25 publications

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

An uncombed inversion of multiwavelength observations reproducing the net circular polarization in a sunspot’s penumbra

Inferring the magnetic field vector in the quiet Sun

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