434 research outputs found
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
Late Quaternary tectonic activity of the Meers Fault, southwest Oklahoma
Online access for this thesis was created in part with support from the Institute of Museum and Library Services (IMLS) administered by the Nevada State Library, Archives and Public Records through the Library Services and Technology Act (LSTA). To obtain a high quality image or document please contact the DeLaMare Library at https://unr.libanswers.com/ or call: 775-784-6945.The Meers fault in southwestern Oklahoma is an active fault capable of producing large, damaging earthquakes. The most recent large event is late Holocene, occurring some 1,200 - 1,300 years ago, and it was preceded by one or more earlier Quaternary events. Few faults in stable continental interior (SCI) areas are known to be active, so this fault holds many implications for seismic hazards in these poorly understood regions. Paleoseismic events probably had magnitudes of at least 6 3/4 to 7 1/4. Seismic events may be relatively larger in SCI regions and magnitudes of 7 1/2 or greater may be possible. The minimum scarp length is 37 km. Displacements have both left-lateral and high-angle reverse components. Vertical separation of the surface reaches about 5 m, while lateral separation exceeds vertical by a ratio of about 3:1 to 5:1, reaching approximately 20 m. Individual events appear to have had maximum surface displacements of several meters. This fault may be part of a larger active zone. The Washita Valley and Potter County faults also have surface expressions believed to indicate recent surface faulting. No additional active surface faults have been recognized in the Mers fault area, but activity may be concealed by poor preservation or non-brittle surface deformation. Active faults are likely to be sparse and to rupture infrequently
Center to limb observations and modeling of the Ca I 4227 A line
The observed center-to-limb variation (CLV) of the scattering polarization in
different lines of the Second Solar Spectrum can be used to constrain the
height variation of various atmospheric parameters, in particular the magnetic
fields via the Hanle effect. Here we attempt to model non-magnetic CLV
observations of the profiles of the Ca I 4227 A line recorded with the
ZIMPOL-3 at IRSOL. For modeling, we use the polarized radiative transfer with
partial frequency redistribution with a number of realistic 1-D model
atmospheres. We find that all the standard FAL model atmospheres, used by us,
fail to simultaneously fit the observed (, ) at all the limb distances
(). However, an attempt is made to find a single model which can provide a
fit at least to the CLV of the observed instead of a simultaneous fit to
the (, ) at all . To this end we construct a new 1-D model by
combining two of the standard models after modifying their temperature
structures in the appropriate height ranges. This new combined model closely
reproduces the observed at all the , but fails to reproduce the
observed rest intensity at different . Hence we find that no single 1-D
model atmosphere succeeds in providing a good representation of the real Sun.
This failure of 1-D models does not however cause an impediment to the magnetic
field diagnostic potential of the Ca I 4227 A line. To demonstrate this we
deduce the field strength at various positions without invoking the use
of radiative transfer.Comment: 20 pages, 10 figures, Accepted for publication in Ap
Atmospheric fluctuations below 0.1 Hz during drift-scan solar diameter measurements
Measurements of the power spectrum of the seeing in the range 0.001-1 Hz have
been performed in order to understand the criticity of the transits' method for
solar diameter monitoring.Comment: 3 pages, 3 figures, proc. of the Fourth French-Chinese meeting on
Solar Physics Understanding Solar Activity: Advances and Challenges, 15 - 18
November, 2011 Nice, Franc
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