1,434 research outputs found
Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals
We present results from the analysis of Fe I 630 nm measurements of the quiet
Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets
with noise levels of 1.2{\times}10-3 and 3{\times}10-4 are employed. We
determine the distribution of field strengths and inclinations by inverting the
two observations with a Milne-Eddington model atmosphere. The inversions show a
predominance of weak, highly inclined fields. By means of several tests we
conclude that these properties cannot be attributed to photon noise effects. To
obtain the most accurate results, we focus on the 27.4% of the pixels in the
second data set that have linear polarization amplitudes larger than 4.5 times
the noise level. The vector magnetic field derived for these pixels is very
precise because both circular and linear polarization signals are used
simultaneously. The inferred field strength, inclination, and filling factor
distributions agree with previous results, supporting the idea that
internetwork fields are weak and very inclined, at least in about one quarter
of the area occupied by the internetwork. These properties differ from those of
network fields. The average magnetic flux density and the mean field strength
derived from the 27.4% of the field of view with clear linear polarization
signals are 16.3 Mx cm-2 and 220 G, respectively. The ratio between the average
horizontal and vertical components of the field is approximately 3.1. The
internetwork fields do not follow an isotropic distribution of orientations.Comment: To appear in APJ, Vol 749, 201
Power spectra of velocities and magnetic fields on the solar surface and their dependence on the unsigned magnetic flux density
We have performed power spectral analysis of surface temperatures,
velocities, and magnetic fields, using spectro-polarimetric data taken with the
Hinode Solar Optical Telescope. When we make power spectra in a field-of-view
covering the super-granular scale, kinetic and thermal power spectra have a
prominent peak at the granular scale while the magnetic power spectra have a
broadly distributed power over various spatial scales with weak peaks at both
the granular and supergranular scales. To study the power spectra separately in
internetwork and network regions, power spectra are derived in small
sub-regions extracted from the field-of-view. We examine slopes of the power
spectra using power-law indices, and compare them with the unsigned magnetic
flux density averaged in the sub-regions. The thermal and kinetic spectra are
steeper than the magnetic ones at the sub-granular scale in the internetwork
regions, and the power-law indices differ by about 2. The power-law indices of
the magnetic power spectra are close to or smaller than -1 at that scale, which
suggests the total magnetic energy mainly comes from either the granular scale
magnetic structures or both the granular scale and smaller ones contributing
evenly. The slopes of the thermal and kinetic power spectra become less steep
with increasing unsigned flux density in the network regions. The power-law
indices of all the thermal, kinetic, and magnetic power spectra become similar
when the unsigned flux density is larger than 200 Mx cm^-2.Comment: 9 pages, 6 figures, accepted for publication in Ap
Cuban immigrants in the United States: what determines their earnings distribution?
Este artículo analiza la distribución de ingresos condicionales de los inmigrantes cubanos en los Estados Unidos usando OLS y analizando una Regresión Cuantílica. Los datos usados en este estudio fueron tomados del American Community Survey (ACS) de los Estados Unidos y fueron suministrados por IPUMS (2011). Los resultados muestran que incrementos en los ingresos asociados a diferentes características socioeconómicas tales como: el sexo, estado civil, etnia, manejo del idioma inglés y educación varían entre las diferentes distribuciones de ingresos.In this paper the conditional earnings distribution of Cuban immigrants in the U.S. using OLS and Quantile Regression is analyzed. The data used in the study come from the 2011 American Community Survey (ACS) in the U.S. provided by IPUMS (2011). The results show that increments in earnings associated with different socioeconomic characteristics such as: sex, marital status, ethnicity, proficiency in English and education vary across the earnings distribution.Este artigo analisa a distribuição de ingressos condicionais dos imigrantes cubanos nos Estados Unidos usando OLS e analisando uma Regressão Quantílica. Os dados usados neste estudo foram tomados do American Community Survey (ACS) dos Estados Unidos e foram subministrados por IPUMS (2011). Os resultados mostram que incrementos nos ingressos associados a diferentes características socioeconômicas tais como: o sexo, estado civil, etnia, manejo do idioma inglês e educação variam entre as diferentes distribuições de ingressos
On the inversion of Stokes profiles with local stray-light contamination
Obtaining the magnetic properties of non-resolved structures in the solar
photosphere is always challenging and problems arise because the inversion is
carried out through the numerical minimization of a merit function that depends
on the proposed model. We investigate the reliability of inversions in which
the stray-light contamination is obtained from the same observations as a local
average. In this case, we show that it is fundamental to include the covariance
between the observed Stokes profiles and the stray-light contamination. The
ensuing modified merit function of the inversion process penalizes large
stray-light contaminations simply because of the presence of positive
correlations between the observables and the stray-light, fundamentally
produced by spatially variable systematics. We caution that using the wrong
merit function, artificially large stray-light contaminations might be
inferred. Since this effect disappears if the stray-light contamination is
obtained as an average over the full field-of-view, we recommend to take into
account stray-light contamination using a global approach.Comment: 5 pages, 3 figures, accepted for publication in Ap
The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He I 10830 A triplet
Context: The determination of the magnetic field vector in quiescent solar
prominences is possible by interpreting the Hanle and Zeeman effects in
spectral lines. However, observational measurements are scarce and lack high
spatial resolution. Aims: To determine the magnetic field vector configuration
along a quiescent solar prominence by interpreting spectropolarimetric
measurements in the He I 1083.0 nm triplet obtained with the Tenerife Infrared
Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio
del Teide. Methods. The He I 1083.0 nm triplet Stokes profiles are analyzed
with an inversion code that takes into account the physics responsible of the
polarization signals in this triplet. The results are put into a solar context
with the help of extreme ultraviolet observations taken with the Solar Dynamic
Observatory and the Solar Terrestrial Relations Observatory satellites.
Results: For the most probable magnetic field vector configuration, the
analysis depicts a mean field strength of 7 gauss. We do not find local
variations in the field strength except that the field is, in average, lower in
the prominence body than in the prominence feet, where the field strength
reaches 25 gauss. The averaged magnetic field inclination with respect to the
local vertical is 77 degrees. The acute angle of the magnetic field vector with
the prominence main axis is 24 degrees for the sinistral chirality case and 58
degrees for the dextral chirality. These inferences are in rough agreement with
previous results obtained from the analysis of data acquired with lower spatial
resolutions.Comment: Accepted in A&
Photospheric downward plasma motions in the quiet-Sun
We analyze spectropolarimetric data taken with the Hinode spacecraft in quiet
solar regions at the disk center. Distorted redshifted Stokes profiles are
found showing a characteristic evolution that always follows the same sequence
of phases. We have studied the statistical properties of these events using
spectropolarimetric data from Hinode/SP. We also examined the upper photosphere
and the low chromosphere using Mg i b2 and Ca ii h data from Hinode. Finally,
we have applied the SIRGAUSS inversion code to the polarimetric data in order
to infer the atmospheric stratification of the physical parameters. We have
also obtained these physical parameters taking into account dynamical terms in
the equation of motion.
The Stokes V profiles display a bump that evolves in four different time
steps, and the total process lasts 108 seconds. The Stokes I shows a strongly
bent red wing and the continuum signal exhibits a bright point inside an
intergranular lane. This bright point is correlated with a strong redshift in
the Mg i b2 line and a bright feature in Ca ii h images. The model obtained
from the inversion of the Stokes profiles is hotter than the average quiet-Sun
model, with a vertical magnetic field configuration and field strengths in the
range of kG values. It also presents a LOS velocity stratification with a
Gaussian perturbation whose center is moving to deeper layers with time.
We have examined a particular type of event that can be described as a
plasmoid of hot plasma that is moving downward from the top of the photosphere,
placed over intergranular lanes and always related to strong magnetic field
concentrations. We argue that the origin of this plasmoid could be a magnetic
reconnection that is taking place in the chromosphere.Comment: 18 pages, 14 figure
- …