92 research outputs found
Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 {\AA} line
It has so far proven impossible to reproduce all aspects of the solar plage
chromosphere in quasi-realistic numerical models. The magnetic field
configuration in the lower atmosphere is one of the few free parameters in such
simulations. The literature only offers proxy-based estimates of the field
strength, as it is difficult to obtain observational constraints in this
region. Sufficiently sensitive spectro-polarimetric measurements require a high
signal-to-noise ratio, spectral resolution, and cadence, which are at the limit
of current capabilities. We use critically sampled spectro-polarimetric
observations of the \cair line obtained with the CRISP instrument of the
Swedish 1-m Solar Telescope to study the strength and inclination of the
chromospheric magnetic field of a plage region. This will provide direct
physics-based estimates of these values, which could aid modelers to put
constraints on plage models. We increased the signal-to-noise ratio of the data
by applying several methods including deep learning and PCA. We estimated the
noise level to be . We then used STiC, a non-local
thermodynamic equilibrium (NLTE) inversion code to infer the atmospheric
structure and magnetic field pixel by pixel. We are able to infer the magnetic
field strength and inclination for a plage region and for fibrils in the
surrounding canopy. In the plage we report an absolute field strength of G, with an inclination of with respect to
the local vertical. This value for is roughly double of what was reported
previously, while the inclination matches previous studies done in the
photosphere. In the fibrillar region we found G, with an
inclination of .Comment: Accepted September 22t
Magnetic fields of opposite polarity in sunspot penumbrae
Context. A significant part of the penumbral magnetic field returns below the
surface in the very deep photosphere. For lines in the visible, a large portion
of this return field can only be detected indirectly by studying its imprints
on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe
a narrow layer in the very deep photosphere, providing the possibility of
directly measuring the orientation of magnetic fields close to the solar
surface.
Aims. We study the topology of the penumbral magnetic field in the lower
photosphere, focusing on regions where it returns below the surface.
Methods. We analyzed 71 spectropolarimetric datasets from Hinode and from the
GREGOR infrared spectrograph. We inferred the quality and polarimetric accuracy
of the infrared data after applying several reduction steps. Techniques of
spectral inversion and forward synthesis were used to test the detection
algorithm. We compared the morphology and the fractional penumbral area covered
by reversed-polarity and three-lobed Stokes V profiles for sunspots at disk
center. We determined the amount of reversed-polarity and three-lobed Stokes V
profiles in visible and infrared data of sunspots at various heliocentric
angles. From the results, we computed center-to-limb variation curves, which
were interpreted in the context of existing penumbral models.
Results. Observations in visible and near-infrared spectral lines yield a
significant difference in the penumbral area covered by magnetic fields of
opposite polarity. In the infrared, the number of reversed-polarity Stokes V
profiles is smaller by a factor of two than in the visible. For three-lobed
Stokes V profiles the numbers differ by up to an order of magnitude.Comment: 11 pages 10 figures plus appendix (2 pages 3 figures). Accepted as
part of the A&A special issue on the GREGOR solar telescop
Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to active
region filaments that follow the polarity inversion line. We used the GREGOR
Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral
lines Si I 1082.7 nm, He I 1083.0 nm, and Ca I 1083.9 nm. We focus on the
near-infrared calcium line to investigate the photospheric magnetic field and
velocities, and use the line core intensities and velocities of the helium line
to study the chromospheric plasma. The individual fibrils of the arch filament
system connect the sunspot with patches of magnetic polarity opposite to that
of the spot. These patches do not necessarily coincide with pores, where the
magnetic field is strongest. Instead, areas are preferred not far from the
polarity inversion line. These areas exhibit photospheric downflows of moderate
velocity, but significantly higher downflows of up to 30 km/s in the
chromospheric helium line. Our findings can be explained with new emerging flux
where the matter flows downward along the fieldlines of rising flux tubes, in
agreement with earlier results.Comment: Proceedings 12th Potsdam Thinkshop to appear in Astronomische
Nachrichte
Photospheric Magnetic Fields of the Trailing Sunspots in Active Region NOAA 12396
The solar magnetic field is responsible for all aspects of solar activity.
Sunspots are the main manifestation of the ensuing solar activity. Combining
high-resolution and synoptic observations has the ambition to provide a
comprehensive description of the sunspot growth and decay processes. Active
region NOAA 12396 emerged on 2015 August 3 and was observed three days later
with the 1.5-meter GREGOR solar telescope on 2015 August 6. High-resolution
spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS) are
obtained in the photospheric Si I 1082.7 nm and Ca I 1083.9
nm lines, together with the chromospheric He I 1083.0 nm triplet.
These near-infrared spectropolarimetric observations were complemented by
synoptic line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamics Observatory (SDO).Comment: 4 pages, 2 figures, to be published in "Solar Polarization Workshop
8", ASP Proceedings, Luca Belluzzi (eds.
A study of the capabilities for inferring atmospheric information from high-spatial-resolution simulations
In this work, we study the accuracy that can be achieved when inferring the
atmospheric information from realistic numerical magneto-hydrodynamic
simulations that reproduce the spatial resolution we will obtain with future
observations made by the 4m class telescopes DKIST and EST. We first study
multiple inversion configurations using the SIR code and the Fe I transitions
at 630 nm until we obtain minor differences between the input and the inferred
atmosphere in a wide range of heights. Also, we examine how the inversion
accuracy depends on the noise level of the Stokes profiles. The results
indicate that when the majority of the inverted pixels come from strongly
magnetised areas, there are almost no restrictions in terms of the noise,
obtaining good results for noise amplitudes up to 1 of . At
the same time, the situation is different for observations where the dominant
magnetic structures are weak, and noise restraints are more demanding.
Moreover, we find that the accuracy of the fits is almost the same as that
obtained without noise when the noise levels are on the order of
1of . We, therefore, advise aiming for noise values on the
order of or lower than 5 of if observers seek reliable
interpretations of the results for the magnetic field vector reliably. We
expect those noise levels to be achievable by next-generation 4m class
telescopes thanks to an optimised polarisation calibration and the large
collecting area of the primary mirror.Comment: 14 pages, 13 figure
Dissecting the long-term emission behaviour of the BL Lac object Mrk 421
We report on long-term multiwavelengthmonitoring of blazar Mrk 421 by the GLAST-AGILE
Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and
Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in
the period 2007â2015, characterized by several extreme flares. The ratio between the optical,
X-ray and Îł -ray fluxes is very variable. The Îł -ray flux variations show a fair correlation with
the optical ones starting from 2012.We analyse spectropolarimetric data and find wavelengthdependence
of the polarization degree (P), which is compatible with the presence of the
host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA).
Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of
the EVPA.We build broad-band spectral energy distributions with simultaneous near-infrared
and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite.
They show strong variability in both flux and X-ray spectral shape and suggest a shift of
the synchrotron peak up to a factor of âŒ50 in frequency. The interpretation of the flux and
spectral variability is compatible with jet models including at least two emitting regions that
can change their orientation with respect to the line of sight.http://10.0.4.69/mnras/stx2185Accepted manuscrip
Eyes Are Windows to the Chinese Soul: Evidence from the Detection of Real and Fake Smiles
How do people interpret the meaning of a smile? Previous studies with Westerners have found that both the eyes and the mouth are crucial in identifying and interpreting smiles, yet less is known about Easterners. Here we reported that when asking the Chinese to judge the Duchenne and non-Duchenne smiles as either real or fake, their accuracy and sensitivity were negatively correlated with their individualism scores but positively correlated with their collectivism scores. However, such correlations were found only for participants who stated the eyes to be the most useful references, but not for those who favored the mouth. Moreover, participants who favored the eyes were more accurate and sensitive than those who favored the mouth. Our results thus indicate that Chinese who follow the typical Eastern decoding process of using the eyes as diagnostic cues to identify and interpret others' facial expressions and social intentions, are particularly accurate and sensitive, the more they self-report greater collectivistic and lower individualistic values
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