405 research outputs found
He-D3 Polarization observed in Prominences
Spectro-polarimetric measurements of the D3-HeI 5876 A line profile in 35
prominences have been performed in 2003 with the Gregory-Coud\'e Telescope in
Locarno. Two different experimental techniques (ZIMPOL and Beam-exchange
method) have been successfully employed to determine all four Stokes
components. Both give compatible results. The preliminary results as well as
the measurement techniques are reported.Comment: 4 pages, 4 figures, Latex, Proceedings "Solar Magnetic Phenomena"
Summerschool & Workshop at the Kanzelhoehe Solar Observatory 200
Evidence for the two fluid scenario in solar prominences
This paper presents observational evidence of the different dynamical
behavior of neutral and ionized species in solar prominences. The analysis of a
time-series of Sr II 4078 A and Na D spectra in a quiescent prominence yields
systematically larger Doppler shifts (line-of-sight velocities) for the ions
V_LOS(Sr II)= 1.22 x V_LOS (Na D). Both lines show a 30 min oscillation of good
coherence. Sixteen hours later the same prominence underwent marked
morphological changes (with a rising dome), and the Sr II velocity excess drops
to V_LOS(Sr II)=1.11 x V_LOS(Na D). The same excess is found for the line pair
Fe II 5018 A and He I 5015 A. The widths of the ionic lines, mainly
non-thermally broadened, are not related to the macro velocities. The emission
ratio of Na D and Sr II, a measure of the electron density, yields n_e = 4 x
10^10 1/cm, shows no relation with the V_LOS variation or with height above the
limb, and seems to be reduced 16 hr later during the active phase. We apply a
new wavelength reference from aureola spectra, which is independent of
photospheric velocity fields
Origin of spatial variations of scattering polarization in the wings of the Ca {\sc i} 4227 \AA line
Polarization that is produced by coherent scattering can be modified by
magnetic fields via the Hanle effect. According to standard theory the Hanle
effect should only be operating in the Doppler core of spectral lines but not
in the wings. In contrast, our observations of the scattering polarization in
the Ca {\sc i} 4227 \AA line reveals the existence of spatial variations of the
scattering polarization throughout the far line wings. This raises the question
whether the observed spatial variations in wing polarization have a magnetic or
non-magnetic origin. A magnetic origin may be possible if elastic collisions
are able to cause sufficient frequency redistribution to make the Hanle effect
effective in the wings without causing excessive collisional depolarization, as
suggested by recent theories for partial frequency redistribution with coherent
scattering in magnetic fields. To model the wing polarization we apply an
extended version of the technique based on the "last scattering approximation".
This model is highly successful in reproducing the observed Stokes
polarization (linear polarization parallel to the nearest solar limb),
including the location of the wing polarization maxima and the minima around
the Doppler core, but it fails to reproduce the observed spatial variations of
the wing polarization in terms of magnetic field effects with frequency
redistribution. This null result points in the direction of a non-magnetic
origin in terms of local inhomogeneities (varying collisional depolarization,
radiation-field anisotropies, and deviations from a plane-parallel atmospheric
stratification).Comment: Accepted in May 2009 for publication in The Astrophysical Journa
Helium Emissions Observed in Ground-Based Spectra of Solar Prominences
The only prominent line of singly ionized helium in the visible spectral
range, helium-II 4686 A, is observed together with the helium-I 5015 A singlet
and the helium-I 4471 A triplet line in solar prominences. The sodium emission,
NaD2, is used as a tracer for helium-II emissions which are sufficiently bright
to exceed the noise level near 10^-6 of the disk-center intensity. The so
selected prominences are characterized by small non-thermal line broadening and
almost absent velocity shifts, yielding narrow line profiles without wiggles.
The reduced widths [Delta(lambda_D) / lambda] of helium-II 4686 A are 1.5 times
broader than those of helium-I 4471 A triplet and 1.65 times broader than those
of helium-I 5015 A singlet. This indicates that the helium lines originate in a
prominence--corona transition region with outwards increasing temperature.Comment: 12 pages, 5 figure, 3 table
Comparison of theoretical and observed Ca~{\sc ii}~8542 Stokes profiles in quiet regions at the centre of the solar disc
Interpreting the Stokes profiles observed in quiet regions of the solar
chromosphere is a challenging task. The Stokes Q and U profiles are dominated
by the scattering polarisation and the Hanle effect, and these processes can
only be correctly quantified if 3D radiative transfer effects are taken into
account. Forward-modelling of the intensity and polarisation of spectral lines
using a 3D model atmosphere is a suitable approach in order to statistically
compare the theoretical and observed line profiles. Our aim is to present novel
observations of the Ca 8542 line profiles in a quiet region at the centre of
the solar disc and to quantitatively compare them with the theoretical Stokes
profiles. We aim at estimating the reliability of the 3D model atmosphere using
not only the line intensity but the full vector of Stokes parameters. We used
data obtained with the ZIMPOL instrument at the IRSOL and compared the
observations with the theoretical profiles computed with the PORTA radiative
transfer code, using as solar model atmosphere a 3D snapshot taken from a
radiation-magnetohydrodynamics simulation. The synthetic profiles were degraded
to match the instrument and observing conditions. The degraded theoretical
profiles of the Ca 8542 line are qualitatively similar to the observed ones. We
confirm that there is a fundamental difference in the widths of all Stokes
profiles: the observed lines are wider than the theoretical lines. We find that
the amplitudes of the observed profiles are larger than those of the
theoretical ones, which suggests that the symmetry breaking effects in the
solar chromosphere are stronger than in the model atmosphere. This means that
the isosurfaces of temperature, velocity, and magnetic field strength and
orientation are more corrugated in the solar chromosphere than in the currently
available 3D radiation-magnetohydrodynamics simulation
PENGARUH LOGISTICS SERVICE QUALITY TERHADAP CUSTOMER SATISFACTION CAT EMCO PT SATRIAKARYA ADIYUDHA (PT SKAY)
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Calibration of the 6302/6301 Stokes V line ratio in terms of the 5250/5247 ratio
Four decades ago the Stokes V line ratio in the Fe I 5247.06 and 5250.22
{\AA} lines was introduced as a powerful means of exploring the intrinsic field
strengths at sub-pixel scales, which led to the discovery that most of the
photospheric flux is in intermittent kG form. The "green" 5247-5250 line pair
is unique because it allows the magnetic-field effects to be isolated from the
thermodynamic effects. No other line pair with this property has since been
identified. In recent years much of the magnetic-field diagnostics has been
based on the "red" Fe I 6301.5 and 6302.5 {\AA} line pair, since it was chosen
in the design of the Hinode space observatory. Although thermodynamic effects
severely contaminate the magnetic-field signatures for this line ratio, it is
still possible to use it to extract information on intrinsic magnetic fields,
but only after it has been "renormalized", since otherwise it produces
fictitious, superstrong fields everywhere. In the present work we explore the
joint behavior of these two line ratios to determine how the "contaminated" red
line ratio can be translated into the corresponding green line ratio, which
then allows for a direct interpretation in terms of intrinsic magnetic fields.
Our observations are mainly based on recordings with the ZIMPOL-3
spectro-polarimeter at IRSOL in Locarno, Switzerland, complemented by data from
the STOP telescope at the Sayan solar observatory (Irkutsk, Russia). The IRSOL
observations are unique by allowing both the green and red line pairs to be
recorded simultaneously on the same CCD sensor. We show how the line ratios
depend on both the measured flux densities and on the heliocentric distance
(the \mu\ value on the solar disk), and finally derive the calibration function
that enables the red line ratio to be translated to the green ratio for each
\mu\ value
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