1,461 research outputs found
The effect of isotopic splitting on the bisector and inversions of the solar Ca II 854.2 nm line
The Ca II 854.2 nm spectral line is a common diagnostic of the solar
chromosphere. The average line profile shows an asymmetric core, and its
bisector shows a characteristic inverse-C shape. The line actually consists of
six components with slightly different wavelengths depending on the isotope of
calcium. This isotopic splitting of the line has been taken into account in
studies of non-solar stars, but never for the Sun. We performed non-LTE
radiative transfer computations from three models of the solar atmosphere and
show that the asymmetric line-core and inverse C-shape of the bisector of the
854.2 nm line can be explained by isotopic splitting. We confirm this finding
by analysing observations and showing that the line asymmetry is present
irrespective of conditions in the solar atmosphere. Finally, we show that
inversions based on the Ca II 854.2 nm line should take the isotopic splitting
into account, otherwise the inferred atmospheres will contain erroneous
velocity gradients and temperatures.Comment: Accepted for ApJ
On chromospheric heating during flux emergence in the solar atmosphere
Context. The radiative losses in the solar chromosphere vary from
4~kW~m in the quiet Sun, to 20~kW~m in active regions. The
mechanisms that transport non-thermal energy to and deposit it in the
chromosphere are still not understood. Aims. We aim to investigate the
atmospheric structure and heating of the solar chromosphere in an emerging flux
region. Methods. We use observations taken with the CHROMIS and CRISP
instruments on the Swedish 1-m Solar Telescope in the Ca II K, Ca II 854.2 nm,
H, and Fe I 630.1 nm and 630.2 nm lines. We analyse the various line
profiles and in addition perform multi-line, multi-species, non-Local
Thermodynamic Equilibrium (non-LTE) inversions to estimate the spatial and
temporal variation of the chromospheric structure. Results. We investigate
which spectral features of Ca II K contribute to the frequency-integrated Ca II
K brightness, which we use as a tracer of chromospheric radiative losses. The
majority of the radiative losses are not associated with localized high-Ca II
K-brightness events, but instead with a more gentle, spatially extended, and
persistent heating. The frequency-integrated Ca II K brightness correlates
strongly with the total linear polarization in the Ca II 854.2 nm line, while
the Ca II K profile shapes indicate that the bulk of the radiative losses occur
in the lower chromosphere.
Non-LTE inversions indicate a transition from heating concentrated around
photospheric magnetic elements below to a more
space-filling and time-persistent heating above . The
inferred gas temperature at correlates strongly with
the total linear polarization in the Ca II 854.2 nm line, suggesting that that
the heating rate correlates with the strength of the horizontal magnetic field
in the low chromosphere.Comment: Accepted for publication by A&
Second-harmonic generation in vortex-induced waveguides
We study the second-harmonic generation and localization of light in a
reconfigurable waveguide induced by an optical vortex soliton in a defocusing
Kerr medium. We show that the vortex-induced waveguide greatly improves
conversion efficiency from the fundamental to the second harmonic field.Comment: 3 pages, 4 figures, submitted to Optics Letter
Three-dimensional modeling of the Ca II H&K lines in the solar atmosphere
CHROMIS, a new imaging spectrometer at the Swedish 1-m Solar Telescope (SST),
can observe the chromosphere in the H and K lines of Ca II at high spatial and
spectral resolution. Accurate modeling as well as an understanding of the
formation of these lines are needed to interpret the SST/CHROMIS observations.
Such modeling is computationally challenging because these lines are influenced
by strong departures from local thermodynamic equilibrium, three-dimensional
radiative transfer, and partially coherent resonance scattering of photons. We
aim to model the CaII H&K lines in 3D model atmospheres to understand their
formation and to investigate their diagnostic potential for probing the
chromosphere. We model the synthetic spectrum of Ca II using the radiative
transfer code Multi3D in three different radiation-magnetohydrodynamic model
atmospheres computed with the Bifrost code. We classify synthetic intensity
profiles according to their shapes and study how their features are related to
the physical properties in the model atmospheres. We investigate whether the
synthetic data reproduce the observed spatially-averaged line shapes,
center-to-limb variation and compare with SST/CHROMIS images. The
spatially-averaged synthetic line profiles show too low central emission peaks,
and too small separation between the peaks. The trends of the observed
center-to-limb variation of the profiles properties are reproduced by the
models. The Ca II H&K line profiles provide a temperature diagnostic of the
temperature minimum and the temperature at the formation height of the emission
peaks. The Doppler shift of the central depression is an excellent probe of the
velocity in the upper chromosphere.Comment: 19 pages, 20 figures, accepted for publication by A&
Chromospheric polarimetry through multi-line observations of the 850 nm spectral region
Future solar missions and ground-based telescopes aim to understand the
magnetism of the solar chromosphere. We performed a supporting study in
Quintero Noda et al. (2016) focused on the infrared Ca II 8542 A line and we
concluded that is one of the best candidates because it is sensitive to a large
range of atmospheric heights, from the photosphere to the middle chromosphere.
However, we believe that it is worth to try improving the results produced by
this line observing additional spectral lines. In that regard, we examined the
neighbour solar spectrum looking for spectral lines that could increase the
sensitivity to the atmospheric parameters. Interestingly, we discovered several
photospheric lines that greatly improve the photospheric sensitivity to the
magnetic field vector. Moreover, they are located close to a second
chromospheric line that also belongs to the Ca II infrared triplet, i.e. the Ca
II 8498 A line, and enhances the sensitivity to the atmospheric parameters at
chromospheric layers. We conclude that the lines in the vicinity of the Ca II
8542 A line not only increase its sensitivity to the atmospheric parameters at
all layers, but also they constitute an excellent spectral window for
chromospheric polarimetry.Comment: 11 pages, 8 figures, 1 tabl
Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations
Ellerman bombs and UV bursts are transient brightenings that are ubiquitously
observed in the lower atmospheres of active and emerging flux regions. Here we
present inversion results of SST/CRISP and CHROMIS, as well as IRIS data of
such transient events. Combining information from the Mg II h & k, Si IV and Ca
II 8542A and Ca II H & K lines, we aim to characterise their temperature and
velocity stratification, as well as their magnetic field configuration. We find
average temperature enhancements of a few thousand kelvin close to the
classical temperature minimum, but localised peak temperatures of up to
10,000-15,000 K from Ca II inversions. Including Mg II generally dampens these
temperature enhancements to below 8000 K, while Si IV requires temperatures in
excess of 10,000 K at low heights, but may also be reproduced with secondary
temperature enhancements of 35,000-60,000 K higher up. However, reproducing Si
IV comes at the expense of overestimating the Mg II emission. The line-of-sight
velocity maps show clear bi-directional jet signatures and strong correlation
with substructure in the intensity images, with slightly larger velocities
towards the observer than away. The magnetic field parameters show an
enhancement of the horizontal field co-located with the brightenings at similar
heights as the temperature increase. We are thus able to largely reproduce the
observational properties of Ellerman bombs with UV burst signature with
temperature stratifications peaking close to the classical temperature minimum.
Correctly modelling the Si IV emission in agreement with all other diagnostics
is, however, an outstanding issue. Accounting for resolution differences,
fitting localised temperature enhancements and/or performing spatially-coupled
inversions is likely necessary to obtain better agreement between all
considered diagnostics.Comment: Accepted for publication in Astronomy & Astrophysics. 24 pages, 17
figure
Chromospheric polarimetry through multi-line observations of the 850 nm spectral region II: A magnetic flux tube scenario
In this publication we continue the work started in Quintero Noda et al.
(2017) examining this time a numerical simulation of a magnetic flux tube
concentration. Our goal is to study if the physical phenomena that take place
in it, in particular, the magnetic pumping, leaves a specific imprint on the
examined spectral lines. We find that the profiles from the interior of the
flux tube are periodically dopplershifted following an oscillation pattern that
is also reflected in the amplitude of the circular polarization signals. In
addition, we analyse the properties of the Stokes profiles at the edges of the
flux tube discovering the presence of linear polarization signals for the Ca II
lines, although they are weak with an amplitude around 0.5% of the continuum
intensity. Finally, we compute the response functions to perturbations in the
longitudinal field and we estimate the field strength using the weak field
approximation. Our results indicate that the height of formation of the
spectral lines changes during the magnetic pumping process which makes the
interpretation of the inferred magnetic field strength and its evolution more
difficult. These results complement those from previous works demonstrating the
capabilities and limitations of the 850 nm spectrum for chromospheric Zeeman
polarimetry in a very dynamic and complex atmosphere.Comment: 12 pages, 12 figures, 0 tables, MNRAS main journal publicatio
Linear and nonlinear waveguides induced by optical vortex solitons
We study, numerically and analytically, linear and nonlinear waveguides
induced by optical vortex solitons in a Kerr medium. Both fundamental and
first-order guided modes are analyzed, as well as the cases of effectively
defocusing and focusing nonlinearity.Comment: 3 pages, 3 figures, changed conten
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