334 research outputs found
New EUV Fe IX emission line identifications from Hinode/EIS
Four Fe IX transitions in the wavelength range 188--198 A are identified for
the first time in spectra from the EUV Imaging Spectrometer on board the Hinode
satellite. In particular the emission line at 197.86 A is unblended and close
to the peak of the EIS sensitivity curve, making it a valuable diagnostic of
plasma at around 800,000 K - a critical temperature for studying the interface
between the corona and transition region. Theoretical ratios amongst the four
lines predicted from the CHIANTI database reveal weak sensitivity to density
and temperature with observed values consistent with theory. The ratio of
197.86 relative to the 171.07 resonance line of Fe IX is found to be an
excellent temperature diagnostic, independent of density, and the derived
temperature in the analysed data set is log T=5.95, close to the predicted
temperature of maximum ionization of Fe IX.Comment: 10 pages, 3 figures, 2 tables, submitted to ApJ Letter
CHIANTI - An atomic database for emission lines. XI. EUV emission lines of Fe VII, Fe VIII and Fe IX observed by Hinode/EIS
A detailed study of emission lines from Fe VII, Fe VIII and Fe IX observed by
the EUV Imaging Spectrometer on board the Hinode satellite is presented.
Spectra in the ranges 170-212 A and 246-292 A show strongly enhanced lines from
the upper solar transition region (temperatures 5.4 <= log T <= 5.9) allowing a
number of new line identifications to be made. Comparisons of Fe VII lines with
predictions from a new atomic model reveal new plasma diagnostics, however
there are a number of disagreements between theory and observation for emission
line ratios insensitive to density and temperature, suggesting improved atomic
data are required. Line ratios for Fe VIII also show discrepancies with theory,
with the strong 185.21 and 186.60 lines under-estimated by 60-80 % compared to
lines between 192 and 198 A. A newly-identified multiplet between 253.9 and
255.8 A offers excellent temperature diagnostic opportunities relative to the
lines between 185-198 A, however the atomic model under-estimates the strength
of these lines by factors 3-6. Two new line identifications are made for Fe IX
at wavelengths 176.959 A and 177.594 A, while seven other lines between 186 and
200 A are suggested to be due to Fe IX but for which transition identifications
can not be made. The new atomic data for Fe VII and Fe IX are demonstrated to
significantly modify models for the response function of the TRACE 195 A
imaging channel, affecting temperature determinations from this channel. The
data will also affect the response functions for other solar EUV imaging
instruments such as SOHO/EIT, STEREO/EUVI and the upcoming AIA instrument on
the Solar Dynamics Observatory.Comment: 51 pages, submitted to Ap
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
On the nature of spectral line broadening in solar coronal dimmings
We analyze the profiles of iron emission lines observed in solar coronal
dimmings associated with coronal mass ejections, using the EUV Imaging
Spectrometer on board Hinode. We quantify line profile distortions with
empirical coefficients (asymmetry and peakedness) that compare the fitted
Gaussian to the data. We find that the apparent line broadenings reported in
previous studies are likely to be caused by inhomogeneities of flow velocities
along the line of sight, or at scales smaller than the resolution scale, or by
velocity fluctuations during the exposure time. The increase in the amplitude
of Alfv\'en waves cannot, alone, explain the observed features. A
double-Gaussian fit of the line profiles shows that, both for dimmings and
active region loops, one component is nearly at rest while the second component
presents a larger Doppler shift than that derived from a single-Gaussian fit.Comment: 16 pages, 11 figures - Accepted for publication in Ap
Process of Producing Equine Viral Arteritis Vaccine and Product Thereof
A process is disclosed for producing an avirulent attenuated live virus vaccine for use in immunizing horses against equine viral arteritis and for simultaneously obviating the transmission of the disease from a vaccinated horse to a non-vaccinated horse. The invention also includes the product derived from practice of the process and typical examples of the efficacy of the product are disclosed
EUV spectral line formation and the temperature structure of active region fan loops: observations with Hinode/EIS and SDO/AIA
With the aim of studying AR fan loops using Hinode/EIS and SDO/AIA, we
investigate a number of inconsistencies in modeling the absolute intensities of
Fe VIII and Si VII lines, and address why their images look very similar
despite the fact that they have significantly different formation temperatures
in ionization equilibrium: log T/K = 5.6 and 5.8. These issues are important to
resolve because confidence has been undermined in their use for DEM analysis,
and Fe VIII is the main contributor to the AIA 131A channel at low
temperatures. Furthermore, they are the best EIS lines to use for velocity
studies, and for assigning the correct temperature to velocity measurements in
the fans. We find that the Fe VIII 185.213A line is particularly sensitive to
the slope of the DEM, leading to disproportionate changes in its effective
formation temperature. If the DEM has a steep gradient in the log T/K = 5.6 to
5.8 range, or is strongly peaked, Fe VIII 185.213A and Si VII 275.368A will be
formed at the same temperature. We show that this effect explains the
similarity of these images in the fans. Furthermore, we show that the most
recent ionization balance compilations resolve the discrepancies in absolute
intensities. We then combine EIS and AIA to determine the temperature structure
of a number of fan loops and find that they have peak temperatures of
0.8--1.2MK. The EIS data indicate that the temperature distribution has a
finite (but narrow) width < log sigma/K = 5.5 which, in one case, is found to
broaden substantially towards the loop base. AIA and EIS yield similar results
on the temperature, emission measure, and thermal distribution in the fans,
though sometimes the AIA data suggest a relatively larger thermal width. The
result is that both the Fe VIII 185.213A and Si VII 275.368A lines are formed
at log T/K ~ 5.9 in the fans, and the AIA 131A response also shifts to this
temperature.Comment: To be published in ApJ. Figure 6 is reduced resolution to meet size
limits. The abstract has been significantly shortened (original in PDF file
Updated Atomic Data and Calculations for X-ray Spectroscopy
We describe the latest release of AtomDB, version 2.0.2, a database of atomic
data and a plasma modeling code with a focus on X-ray astronomy. This release
includes several major updates to the fundamental atomic structure and process
data held within AtomDB, incorporating new ionization balance data,
state-selective recombination data, and updated collisional excitation data for
many ions, including the iron L-shell ions from Fe to Fe and
all of the hydrogen- and helium-like sequences. We also describe some of the
effects that these changes have on calculated emission and diagnostic line
ratios, such as changes in the temperature implied by the He-like G-ratios of
up to a factor of 2.Comment: Submitted to ApJ, 12 pages, 9 figure
Optimal spectral lines for measuring chromospheric magnetic fields
This paper identifies spectral lines from X-ray to infrared wavelengths which
are optimally suited to measuring vector magnetic fields as high as possible in
the solar atmosphere. Instrumental and Earth's atmospheric properties, as well
as solar abundances, atmospheric properties and elementary atomic physics are
considered without bias towards particular wavelengths or diagnostic
techniques. While narrowly-focused investigations of individual lines have been
reported in detail, no assessment of the comparative merits of all lines has
ever been published. Although in the UV, on balance the Mg+ h and k lines near
2800 Angstroms are optimally suited to polarimetry of plasma near the base of
the solar corona. This result was unanticipated, given that longer-wavelength
lines offer greater sensitivity to the Zeeman effect. While these lines sample
optical depths photosphere to the coronal base, we argue that cores of multiple
spectral lines provide a far more discriminating probe of magnetic structure as
a function of optical depth than the core and inner wings of a strong line.
Thus, together with many chromospheric lines of Fe+ between 2585 and the h line
at 2803 Angstrom, this UV region promises new discoveries concerning how the
magnetic fields emerge, heat, and accelerate plasma as they battle to dominate
the force and energy balance within the poorly-understood chromosphere.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 2
figures, and 1 tabl
Dielectronic Recombination of Argon-Like Ions
We present a theoretical investigation of dielectronic recombination (DR) of
Ar-like ions that sheds new light on the behavior of the rate coefficient at
low-temperatures where these ions form in photoionized plasmas. We provide
results for the total and partial Maxwellian-averaged DR rate coefficients from
the initial ground level of K II -- Zn XIII ions. It is expected that these new
results will advance the accuracy of the ionization balance for Ar-like M-shell
ions and pave the way towards a detailed modeling of astrophysically relevant
X-ray absorption features. We utilize the AUTOSTRUCTURE computer code to obtain
the accurate core-excitation thresholds in target ions and carry out
multiconfiguration Breit-Pauli (MCBP) calculations of the DR cross section in
the independent-processes, isolated-resonance, distorted-wave (IPIRDW)
approximation. Our results mediate the complete absence of direct DR
calculations for certain Ar-like ions and question the reliability of the
existing empirical rate formulas, often inferred from renormalized data within
this isoelectronic sequence
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