190 research outputs found
Revisiting the Hugenholtz-Van Hove theorem in nuclear matter
An assessment of the magnitude of the rearrangement contribution to the Fermi
energy and to the binding energy per particle is carried out in symmetric
nuclear matter by extending the G-matrix framework. The restoration of the
thermodynamic consistency or, equivalently, the fulfillment of the
Hugenholtz-Van Hove theorem, is discussed.Comment: 14 pages, 3 figure
Width of Radio-Loud and Radio-Quiet CMEs
In the present paper we report on the difference in angular sizes between
radio-loud and radio-quiet CMEs. For this purpose we compiled these two samples
of events using Wind/WAVES and SOHO/LASCO observations obtained during
1996-2005. It is shown that the radio-loud CMEs are almost two times wider than
the radio-quiet CMEs (considering expanding parts of CMEs). Furthermore we show
that the radio-quiet CMEs have a narrow expanding bright part with a large
extended diffusive structure. These results were obtained by measuring the CME
widths in three different ways.Comment: Solar Physic, in pres
EIS/Hinode observations of Doppler flow seen through the 40 arcsec wide slit
The Extreme ultraviolet Imaging Spectrometer (EIS) on board Hinode is the
first solar telescope to obtain wide slit spectral images that can be used for
detecting Doppler flows in transition region and coronal lines on the Sun and
to relate them to their surrounding small scale dynamics. We select EIS lines
covering the temperature range 6x10^4 K to 2x10^6 K that give spectrally pure
images of the Sun with the 40 arcsec slit. In these images Doppler shifts are
seen as horizontal brightenings. Inside the image it is difficult to
distinguish shifts from horizontal structures but emission beyond the image
edge can be unambiguously identified as a line shift in several lines separated
from others on their blue or red side by more than the width of the
spectrometer slit (40 pixels). In the blue wing of He II, we find a large
number of events with properties (size and lifetime) similar to the
well-studied explosive events seen in the ultraviolet spectral range.
Comparison with X-Ray Telescope (XRT) images shows many Doppler shift events at
the footpoints of small X-ray loops. The most spectacular event observed showed
a strong blue shift in transition region and lower corona lines from a small
X-ray spot that lasted less than 7 min. The emission appears to be near a cool
coronal loop connecting an X-ray bright point to an adjacent region of quiet
Sun. The width of the emission implies a line-of-sight velocity of 220 km/s. In
addition, we show an example of an Fe XV shift with a velocity about 120 km/s,
coming from what looks like a narrow loop leg connecting a small X-ray
brightening to a larger region of X-ray emission.Comment: 12 pages, 8 figures, to be published in Solar Physic
Using an Ellipsoid Model to Track and Predict the Evolution and Propagation of Coronal Mass Ejections
We present a method for tracking and predicting the propagation and evolution
of coronal mass ejections (CMEs) using the imagers on the STEREO and SOHO
satellites. By empirically modeling the material between the inner core and
leading edge of a CME as an expanding, outward propagating ellipsoid, we track
its evolution in three-dimensional space. Though more complex empirical CME
models have been developed, we examine the accuracy of this relatively simple
geometric model, which incorporates relatively few physical assumptions,
including i) a constant propagation angle and ii) an azimuthally symmetric
structure. Testing our ellipsoid model developed herein on three separate CMEs,
we find that it is an effective tool for predicting the arrival of density
enhancements and the duration of each event near 1 AU. For each CME studied,
the trends in the trajectory, as well as the radial and transverse expansion
are studied from 0 to ~.3 AU to create predictions at 1 AU with an average
accuracy of 2.9 hours.Comment: 18 pages, 11 figure
Quasi-Periodic Releases of Streamer Blobs and Velocity Variability of the Slow Solar Wind near the Sun
We search for persistent and quasi-periodic release events of streamer blobs
during 2007 with the Large Angle Spectrometric Coronagraph on the \textit{Solar
and Heliospheric Observatory} and assess the velocity of the slow solar wind
along the plasma sheet above the corresponding streamer by measuring the
dynamic parameters of blobs. We find 10 quasi-periodic release events of
streamer blobs lasting for three to four days. In each day of these events, we
observe three-five blobs. The results are in line with previous studies using
data observed near the last solar minimum. Using the measured blob velocity as
a proxy for that of the mean flow, we suggest that the velocity of the
background slow solar wind near the Sun can vary significantly within a few
hours. This provides an observational manifestation of the large velocity
variability of the slow solar wind near the Sun.Comment: 14 pages, 5 figures, accepted by Soalr Physic
Streamer Wave Events Observed in Solar Cycle 23
In this paper we conduct a data survey searching for well-defined streamer
wave events observed by the Large Angle and Spectrometric Coronagraph (LASCO)
on-board the Solar and Heliospheric Observatory (SOHO) throughout Solar Cycle
23. As a result, 8 candidate events are found and presented here. We compare
different events and find that in most of them the driving CMEs ejecta are
characterized by a high speed and a wide angular span, and the CME-streamer
interactions occur generally along the flank of the streamer structure at an
altitude no higher than the bottom of the field of view of LASCO C2. In
addition, all front-side CMEs have accompanying flares. These common
observational features shed light on the excitation conditions of streamer wave
events.
We also conduct a further analysis on one specific streamer wave event on 5
June 2003. The heliocentric distances of 4 wave troughs/crests at various
exposure times are determined; they are then used to deduce the wave properties
like period, wavelength, and phase speeds. It is found that both the period and
wavelength increase gradually with the wave propagation along the streamer
plasma sheet, and the phase speed of the preceding wave is generally faster
than that of the trailing ones. The associated coronal seismological study
yields the radial profiles of the Alfv\'en speed and magnetic field strength in
the region surrounding the streamer plasma sheet. Both quantities show a
general declining trend with time. This is interpreted as an observational
manifestation of the recovering process of the CME-disturbed corona. It is also
found that the Alfv\'enic critical point is at about 10 R where the
flow speed, which equals the Alfv\'en speed, is 200 km s
TomograPy: A Fast, Instrument-Independent, Solar Tomography Software
Solar tomography has progressed rapidly in recent years thanks to the
development of robust algorithms and the availability of more powerful
computers. It can today provide crucial insights in solving issues related to
the line-of-sight integration present in the data of solar imagers and
coronagraphs. However, there remain challenges such as the increase of the
available volume of data, the handling of the temporal evolution of the
observed structures, and the heterogeneity of the data in multi-spacecraft
studies.
We present a generic software package that can perform fast tomographic
inversions that scales linearly with the number of measurements, linearly with
the length of the reconstruction cube (and not the number of voxels) and
linearly with the number of cores and can use data from different sources and
with a variety of physical models: TomograPy
(http://nbarbey.github.com/TomograPy/), an open-source software freely
available on the Python Package Index. For performance, TomograPy uses a
parallelized-projection algorithm. It relies on the World Coordinate System
standard to manage various data sources. A variety of inversion algorithms are
provided to perform the tomographic-map estimation. A test suite is provided
along with the code to ensure software quality. Since it makes use of the
Siddon algorithm it is restricted to rectangular parallelepiped voxels but the
spherical geometry of the corona can be handled through proper use of priors.
We describe the main features of the code and show three practical examples
of multi-spacecraft tomographic inversions using STEREO/EUVI and STEREO/COR1
data. Static and smoothly varying temporal evolution models are presented.Comment: 21 pages, 6 figures, 5 table
Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere
A method for the full three-dimensional (3-D) reconstruction of the
trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations
Observatory (STEREO) data is presented. Four CMEs that were simultaneously
observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and
Behind STEREO satellites were analysed. These observations were used to derive
CME trajectories in 3-D out to ~15Rsun. The reconstructions using COR1/2 data
support a radial propagation model. Assuming pseudo-radial propagation at large
distances from the Sun (15-240Rsun), the CME positions were extrapolated into
the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in
the different fields-of-view. It was found that CMEs slower than the solar wind
were accelerated, while CMEs faster than the solar wind were decelerated, with
both tending to the solar wind velocity.Comment: 17 pages, 10 figures, 1 appendi
Large-space shell-model calculations for light nuclei
An effective two-body interaction is constructed from a new Reid-like
potential for a large no-core space consisting of six major shells and is used
to generate the shell-model properties for light nuclei from =2 to 6. (For
practical reasons, the model space is partially truncated for =6.) Binding
energies and other physical observables are calculated and compare favorably
with experiment.Comment: prepared using LaTex, 21 manuscript pages, no figure
Prediction Space Weather Using an Asymmetric Cone Model for Halo CMEs
Halo coronal mass ejections (HCMEs) are responsible of the most severe
geomagnetic storms. A prediction of their geoeffectiveness and travel time to
Earth's vicinity is crucial to forecast space weather.
Unfortunately coronagraphic observations are subjected to projection effects
and do not provide true characteristics of CMEs. Recently, Michalek (2006, {\it
Solar Phys.}, {\bf237}, 101) developed an asymmetric cone model to obtain the
space speed, width and source location of HCMEs. We applied this technique to
obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO
experiment during a period from the beginning of 2001 until the end of 2002
(solar cycle 23). These parameters were applied for the space weather forecast.
Our study determined that the space speeds are strongly correlated with the
travel times of HCMEs within Earth's vicinity and with the magnitudes related
to geomagnetic disturbances
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