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

¹ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79110 Freiburg, Germany
e-mail: borrero@leibniz-kis.de
² Instituto de Astrofísica de Canarias, Avd. Vía Láctea s/n, 38205 La Laguna, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁴ Leibniz Institute for Astrophysics Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁵ Max Planck Institut for Solar System Reesearch, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁶ Georg-August-Universität Göttingen, Faculty of Physics, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁷ Astronomical Institute, Academy of Sciences of the Czech Republic, Fričova 298, 25165 Ondřejov, Czech Republic
⁸ School of Space Research, Kyung Hee University, Yongin, 446-701 Gyeonggi, Republic of Korea

Received: 15 February 2016
Accepted: 1 August 2016

Abstract

Context. Some models for the topology of the magnetic field in sunspot penumbrae predict regions free of magnetic fields or with only dynamically weak fields in the deep photosphere.

Aims. We aim to confirm or refute the existence of weak-field regions in the deepest photospheric layers of the penumbra.

Methods. We investigated the magnetic field at log τ₅ = 0 is by inverting 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-m solar telescope GREGOR at the El Teide observatory. The data include three Fe i lines around 1565 nm, whose sensitivity to the magnetic field peaks half a pressure scale height deeper than the sensitivity of the widely used Fe i spectral line pair at 630 nm. Before the inversion, the data were 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 of regions with dynamically weak (B< 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations made on Fe i lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, is independent of the point spread function used to deconvolve the data, and does not depend on the amount of stray light (i.e., wide-angle scattered light) considered.