Bibcode
Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
Bibliographical reference
Astronomy & Astrophysics, Volume 616, id.A46, 18 pp.
Advertised on:
8
2018
Journal
Description
The magnetism at the poles is similar to that of the quiet Sun in the
sense that no active regions are present there. However, the polar quiet
Sun is somewhat different from that at the activity belt as it has a
global polarity that is clearly modulated by the solar cycle. We study
the polar magnetism near an activity maximum when these regions change
their polarity, from which it is expected that its magnetism should be
less affected by the global field. To fully characterise the magnetic
field vector, we use deep full Stokes polarimetric observations of the
15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as
well as a quiet region at disc centre to compare their field
distributions. In order to calibrate the projection effects, we observe
an additional quiet region at the east limb. We find that the two limb
datasets share similar magnetic field vector distributions. This means
that close to a maximum, the poles look like typical limb, quiet-Sun
regions. However, the magnetic field distributions at the limbs are
different from the distribution inferred at disc centre. At the limbs,
we infer a new population of magnetic fields with relatively strong
intensities ( 600-800 G), inclined by 30° with respect to the line
of sight, and with an azimuth aligned with the solar disc radial
direction. This line-of-sight orientation interpreted as a single
magnetic field gives rise to non-vertical fields in the local reference
frame and aligned towards disc centre. This peculiar topology is very
unlikely for such strong fields according to theoretical considerations.
We propose that this new population at the limbs is due to the
observation of unresolved magnetic loops as seen close to the limb.
These loops have typical granular sizes as measured in the disc centre.
At the limbs, where the spatial resolution decreases, we observe them
spatially unresolved, which explains the new population of magnetic
fields that is inferred. This is the first (indirect) evidence of
small-scale magnetic loops outside the disc centre and would imply that
these small-scale structures are ubiquitous on the entire solar surface.
This result has profound implications for the energetics not only of the
photosphere, but also of the outer layers since these loops have been
reported to reach the chromosphere and the low corona.