Solar disk center shows scattering polarization in the Sr~{sc i} 4607~AA~line. (arXiv:2004.03679v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zeuner_F/0/1/0/all/0/1">Franziska Zeuner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sainz_R/0/1/0/all/0/1">Rafael Manso Sainz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Feller_A/0/1/0/all/0/1">Alex Feller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Noort_M/0/1/0/all/0/1">Michiel van Noort</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Solanki_S/0/1/0/all/0/1">Sami K. Solanki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Iglesias_F/0/1/0/all/0/1">Francisco A. Iglesias</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reardon_K/0/1/0/all/0/1">Kevin Reardon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pillet_V/0/1/0/all/0/1">Valentín Martínez Pillet</a>
Magnetic fields in turbulent, convective high-$beta$ plasma naturally
develop highly tangled and complex topologies—the solar photosphere being the
paradigmatic example. These fields are mostly undetectable by standard
diagnostic techniques with finite spatio-temporal resolution due to
cancellations of Zeeman polarization signals. Observations of resonance
scattering polarization have been considered to overcome these problems. But up
to now, observations of scattering polarization lack the necessary combination
of high sensitivity and high spatial resolution in order to directly infer the
turbulent magnetic structure at the resolution limit of solar telescopes. Here,
we report the detection of clear spatial structuring of scattering polarization
in a magnetically quiet solar region at disk center in the Sr~{sc i} 4607~AA
spectral line on granular scales, confirming theoretical expectations. We find
that the linear polarization presents a strong spatial correlation with the
local quadrupole of the radiation field. The result indicates that polarization
survives the dynamic and turbulent magnetic environment of the middle
photosphere and is thereby usable for spatially-resolved Hanle observations.
This is an important step towards the long-sought goal of directly observing
turbulent solar magnetic fields at the resolution limit and investigating their
spatial structure.
Magnetic fields in turbulent, convective high-$beta$ plasma naturally
develop highly tangled and complex topologies—the solar photosphere being the
paradigmatic example. These fields are mostly undetectable by standard
diagnostic techniques with finite spatio-temporal resolution due to
cancellations of Zeeman polarization signals. Observations of resonance
scattering polarization have been considered to overcome these problems. But up
to now, observations of scattering polarization lack the necessary combination
of high sensitivity and high spatial resolution in order to directly infer the
turbulent magnetic structure at the resolution limit of solar telescopes. Here,
we report the detection of clear spatial structuring of scattering polarization
in a magnetically quiet solar region at disk center in the Sr~{sc i} 4607~AA
spectral line on granular scales, confirming theoretical expectations. We find
that the linear polarization presents a strong spatial correlation with the
local quadrupole of the radiation field. The result indicates that polarization
survives the dynamic and turbulent magnetic environment of the middle
photosphere and is thereby usable for spatially-resolved Hanle observations.
This is an important step towards the long-sought goal of directly observing
turbulent solar magnetic fields at the resolution limit and investigating their
spatial structure.
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