176 research outputs found
Simulation of a flux emergence event and comparison with observations by Hinode
We study the observational signature of flux emergence in the photosphere
using synthetic data from a 3D MHD simulation of the emergence of a twisted
flux tube. Several stages in the emergence process are considered. At every
stage we compute synthetic Stokes spectra of the two iron lines Fe I 6301.5
{\AA} and Fe I 6302.5 {\AA} and degrade the data to the spatial and spectral
resolution of Hinode's SOT/SP. Then, following observational practice, we apply
Milne-Eddington-type inversions to the synthetic spectra in order to retrieve
various atmospheric parameters and compare the results with recent Hinode
observations. During the emergence sequence, the spectral lines sample
different parts of the rising flux tube, revealing its twisted structure. The
horizontal component of the magnetic field retrieved from the simulations is
close to the observed values. The flattening of the flux tube in the
photosphere is caused by radiative cooling, which slows down the ascent of the
tube to the upper solar atmosphere. Consistent with the observations, the
rising magnetized plasma produces a blue shift of the spectral lines during a
large part of the emergence sequence.Comment: A&A Letter, 3 figure
Unusual Stokes V profiles during flaring activity of a delta sunspot
We analyze a set of full Stokes profile observations of the flaring active
region NOAA 10808 recorded with the Vector-Spectromagnetograph (VSM) of the
SOLIS facility. We aim to quantify transient and permanent changes in the
magnetic field and velocity field. The results are put in context with MDI
magnetograms and reconstructed RHESSI X-ray images. We find signs of
restructuring of the photospheric magnetic field during the flare close to the
polarity inversion line (PIL) at the flaring site. At two locations in the
umbra we encounter strong fields (approx. 3 kG), as inferred from the Stokes I
profiles which, however, exhibit a low polarization signal. During the flare we
observe in addition asymmetric Stokes V profiles at one of these sites. The
asymmetric Stokes V profiles appear co-spatial and co-temporal with a strong
apparent polarity reversal observed in MDI-magnetograms and a chromospheric
hard X-ray source. The two-component atmosphere fits of the asymmetric Stokes
profiles result in line-of-sight velocity differences in the range of approx.
12km/s to 14 km/s between the two components in the photosphere. Another
possibility is that local atmospheric heating is causing the observed
asymmetric Stokes V profile shape. In either case our analysis shows that a
very localized patch of approx. 5 arcsec in the photospheric umbra, co-spatial
with a flare footpoint, exhibits a sub-resolution fine structure.Comment: 13 pages, 10 figures, 1 tabl
Chemical Abundances from Inversions of Stellar Spectra: Analysis of Solar-Type Stars with Homogeneous and Static Model Atmospheres
Spectra of late-type stars are usually analyzed with static model atmospheres
in local thermodynamic equilibrium (LTE) and a homogeneous plane-parallel or
spherically symmetric geometry. The energy balance requires particular
attention, as two elements which are particularly difficult to model play an
important role: line blanketing and convection. Inversion techniques are able
to bypass the difficulties of a detailed description of the energy balance.
Assuming that the atmosphere is in hydrostatic equilibrium and LTE, it is
possible to constrain its structure from spectroscopic observations. Among the
most serious approximations still implicit in the method is a static and
homogeneous geometry. In this paper, we take advantage of a realistic
three-dimensional radiative hydrodynamical simulation of the solar surface to
check the systematic errors incurred by an inversion assuming a plane-parallel
horizontally-homogeneous atmosphere. The thermal structure recovered resembles
the spatial and time average of the three-dimensional atmosphere. Furthermore,
the abundances retrieved are typically within 10% (0.04 dex) of the abundances
used to construct the simulation. The application to a fairly complete dataset
from the solar spectrum provides further confidence in previous analyses of the
solar composition. There is only a narrow range of one-dimensional thermal
structures able to fit the absorption lines in the spectrum of the Sun. With
our carefully selected dataset, random errors are about a factor of two smaller
than systematic errors. A small number of strong metal lines can provide very
reliable results. We foresee no major difficulty in applying the technique to
other similar stars, and obtaining similar accuracies, using spectra with a
resolving power about 50,000 and a signal-to-noise ratio as low as 30.Comment: 65 pages, figures included; uses aastex; to appear in The
Astrophysical Journa
Biological indices applied to benthic macroinvertebrates at reference conditions of mountain streams in two ecoregions (Poland, the Slovak Republic)
Exploiting solar visible-range observations by inversion techniques: from flows in the solar subsurface to a flaring atmosphere
Observations of the Sun in the visible spectral range belong to standard
measurements obtained by instruments both on the ground and in the space.
Nowadays, both nearly continuous full-disc observations with medium resolution
and dedicated campaigns of high spatial, spectral and/or temporal resolution
constitute a holy grail for studies that can capture (both) the long- and
short-term changes in the dynamics and energetics of the solar atmosphere.
Observations of photospheric spectral lines allow us to estimate not only the
intensity at small regions, but also various derived data products, such as the
Doppler velocity and/or the components of the magnetic field vector. We show
that these measurements contain not only direct information about the dynamics
of solar plasmas at the surface of the Sun but also imprints of regions below
and above it. Here, we discuss two examples: First, the local time-distance
helioseismology as a tool for plasma dynamic diagnostics in the near subsurface
and second, the determination of the solar atmosphere structure during flares.
The methodology in both cases involves the technique of inverse modelling.Comment: 29 pages, 15 figures. Accepted for publication in the book "Reviews
in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds
Kabath, Jones and Skarka; publisher Springer Nature) funded by the European
Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul"
2017-1-CZ01-KA203-03556
Anaerobic metabolism at thermal extremes: A metabolomic test of the oxygen limitation hypothesis in an aquatic insect
Contains fulltext :
117110.pdf (publisher's version ) (Open Access
Alquimia, Ocultismo, Maçonaria: o ouro e o simbolismo hermético dos cadinhos (Séculos XVIII e XIX)
Este artigo apresenta a arqueologia das enigmáticas marcas impressas na base de cadinhos dos séculos XVIII e XIX recuperados nas escavações da Casa da Moeda do Rio de Janeiro, na década de 1980, e a explanação do seu significado simbólico à luz da alquimia, do ocultismo e da Maçonaria. Espraiando-se extraordinariamente mundo afora através de uma bem-sucedida estratégia de comunicação visual, a Maçonaria utilizou símbolos herméticos para a difusão de seus princípios nos mais diferentes suportes. Aparentemente estamos diante de um sinal de reconhecimento maçônico, o sinal exterior de uma organização oculta, só partilhado por iniciados e incompreensível para os demais, que contribuiu para difundir veladamente a doutrina maçônica por diferentes pontos do globo
- …