Author name code: landi
ADS astronomy entries on 2022-09-14
author:"Landi, Enrico"
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Title: Manifestation of Gravitational Settling in Coronal Mass
Ejections Measured in the Heliosphere
Authors: Rivera, Yeimy J.; Raymond, John C.; Landi, Enrico; Lepri,
Susan T.; Reeves, Katharine K.; Stevens, Michael L.; Alterman, B. L.
Bibcode: 2022ApJ...936...83R
Altcode:
Elemental composition in the solar wind reflects the fractionation
processes at the Sun. In coronal mass ejections (CMEs) measured in
the heliosphere, the elemental composition can vary between plasma
of high and low ionization states as indicated by the average Fe
charge state, <QFe>. It is found that CMEs with
higher ionized plasma, <QFe> greater than 12, are
significantly more enriched in low first ionization potential (FIP)
elements compared to their less ionized, <QFe> less
than 12, counterparts. In addition, the CME elemental composition
has been shown to vary along the solar cycle. However, the processes
driving changes in elemental composition in the plasma are not well
understood. To gain insight into this variation, this work investigates
the effects of gravitational settling in the ejecta to examine how
that process can modify signatures of the FIP effect found in CMEs. We
examine the absolute abundances of C, N, O, Ne, Mg, Si, S, and Fe in
CMEs between 1998 and 2011. Results show that the ejecta exhibits some
gravitational settling effects in approximately 33% of all CME periods
in plasma where the Fe abundance of the ejecta compared to the solar
wind (Fe/HCME:Fe/HSW) is depleted compared to
the C abundance (C/HCME:C/HSW). We also find
gravitational settling is most prominent in CMEs during solar minimum;
however, it occurs throughout the solar cycle. This study indicates
that gravitational settling, along with the FIP effect, can become
important in governing the compositional makeup of CME source regions.
Title: A novel inversion method to determine the coronal magnetic
field including the impact of bound-free absorption
Authors: Martinez-Sykora, Juan; Hansteen, Viggo H.; De Pontieu, Bart;
Landi, Enrico
Bibcode: 2022arXiv220813984M
Altcode:
The magnetic field governs the corona; hence it is a crucial parameter
to measure. Unfortunately, existing techniques for estimating its
strength are limited by strong assumptions and limitations. These
techniques include photospheric or chromospheric field extrapolation
using potential or non-linear-force-free methods, estimates based on
coronal seismology, or by direct observations via, e.g., the Cryo-NIRSP
instrument on DKIST which will measure the coronal magnetic field,
but only off the limb. Alternately, in this work we investigate a
recently developed approach based on the magnetic-field-induced (MIT)
transition of the \fex~257.261~Å. In order to examine this approach,
we have synthesized several \fex\ lines from two 3D magnetohydrodynamic
simulations, one modeling an emerging flux region and the second an
established mature active region. In addition, we take bound-free
absorption from neutral hydrogen and helium and singly ionised
helium into account. The absorption from cool plasma that occurs at
coronal heights has a significant impact on determining the magnetic
field. We investigate in detail the challenges of using these \fex\
lines to measure the field, considering their density and temperature
dependence. We present a novel approach to deriving the magnetic field
from the MIT using inversions of the differential emission measure as a
function of the temperature, density, and magnetic field. This approach
successfully estimates the magnetic field strength (up to \%18 relative
error) in regions that do not suffer from significant absorption and
that have relatively strong coronal magnetic fields ($>250$~G). This
method allows the masking of regions where absorption is significant.
Title: Depletion of Heavy Ion Abundances in Slow Solar Wind and Its
Association with Quiet Sun Regions
Authors: Zhao, Liang; Landi, Enrico; Lepri, Susan T.; Carpenter, Daniel
Bibcode: 2022Univ....8..393Z
Altcode:
The exact coronal origin of the slow-speed solar wind has been
under debate for decades in the Heliophysics community. Besides the
solar wind speed, the heavy ion composition, including the elemental
abundances and charge state ratios, are widely used as diagnostic tool
to investigate the coronal origins of the slow wind. In this study,
we recognize a subset of slow speed solar wind that is located on the
upper boundary of the data distribution in the O7+/O6+ versus C6+/C5+
plot (O-C plot). In addition, in this wind the elemental abundances
relative to protons, such as N/P, O/P, Ne/P, Mg/P, Si/P, S/P, Fe/P,
He/P, and C/P are systemically depleted. We compare these winds
("upper depleted wind" or UDW hereafter) with the slow winds that
are located in the main stream of the O-C plot and possess comparable
Carbon abundance range as the depletion wind ("normal-depletion-wind",
or NDW hereafter). We find that the proton density in the UDW is about
27.5% lower than in the NDW. Charge state ratios of O7+/O6+, O7+/O,
and O8+/O are decreased by 64.4%, 54.5%, and 52.1%, respectively. The
occurrence rate of these UDW is anti-correlated with solar cycle. By
tracing the wind along PFSS field lines back to the Sun, we find that
the coronal origins of the UDW are more likely associated with quiet
Sun regions, while the NDW are mainly associated with active regions
and HCS-streamer.
Title: AWSoM Magnetohydrodynamic Simulation of a Solar Active Region
with Realistic Spectral Synthesis
Authors: Shi, Tong; Manchester, Ward, IV; Landi, Enrico; van der
Holst, Bart; Szente, Judit; Chen, Yuxi; Tóth, Gábor; Bertello,
Luca; Pevtsov, Alexander
Bibcode: 2022ApJ...928...34S
Altcode:
For the first time, we simulate the detailed spectral line emission
from a solar active region (AR) with the Alfvén Wave Solar Model
(AWSoM). We select an AR appearing near disk center on 2018 July 13
and use the National Solar Observatory's Helioseismic and Magnetic
Imager synoptic magnetogram to specify the magnetic field at the
model's inner boundary. To resolve small-scale magnetic features, we
apply adaptive mesh refinement with a horizontal spatial resolution
of 0°.35 (4.5 Mm), four times higher than the background corona. We
then apply the SPECTRUM code, using CHIANTI spectral emissivities,
to calculate spectral lines forming at temperatures ranging from 0.5
to 3 MK. Comparisons are made between the simulated line intensities
and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer
where we find close agreement across a wide range of loop sizes and
temperatures (about 20% relative error for both the loop top and
footpoints at a temperature of about 1.5 MK). We also simulate and
compare Doppler velocities and find that simulated flow patterns are
of comparable magnitude to what is observed. Our results demonstrate
the broad applicability of the low-frequency AWSoM for explaining the
heating of coronal loops.
Title: Charge State Calculation for Global Solar Wind Modeling
Authors: Szente, J.; Landi, E.; van der Holst, B.
Bibcode: 2022ApJ...926...35S
Altcode:
The charge state composition of the solar wind carries information about
the electron temperature, density, and velocity of plasma in the solar
corona that cannot always be measured with remote sensing techniques,
due to limitations in instrumental sensitivity and field of view as
well as line-of-sight integration issues. However, in situ measurements
of the wind charge state distribution only provide the end result
of the solar wind evolution from the source region to the freeze-in
point. By using 3D global modeling it is possible to follow solar wind
plasma parcels of different origin along the path of their journey
and study the evolution of their charge states as well as the driving
physical processes. For this purpose, we implemented nonequilibrium
ionization calculations within the Space Weather Modeling Framework's
solar corona and inner heliosphere modules, to the Alfvén Wave Solar
Model (AWSoM). The charge state calculations are carried out parallel
to the AWSoM calculations, including all the elements and ions whose
ionization-recombination rates are included in the CHIANTI database,
namely, from H to Zn. In this work, we describe the implementation
of the charge state calculation, and compare simulation results to in
situ measurements from the Advanced Composition Explorer and Ulysses
spacecraft, and study charge state evolution of plasma parcels along
different wind trajectories and wind types.
Title: ACE SWICS observations of solar cycle variations of the
solar wind
Authors: Cardenas-O'Toole, A.; Landi, E.
Bibcode: 2022arXiv220105535C
Altcode:
In the present work we utilize ACE/SWICS in-situ measurements of
the properties of the solar wind outside ICMEs in order to determine
whether, and to what extent are the solar wind properties affected
by the solar cycle. We focus on proton temperatures and densities,
ion temperatures and differential speeds, charge state distributions
and both relative and absolute elemental abundances. We carry out
this work dividing the wind in velocity bins to investigate how
winds at different speeds react to the solar cycle. We also repeat
this study, when possible, to the subset of SWICS measurements less
affected by Coulomb collisions. We find that with the only exception
of differential speeds (for which we do not have enough measurements)
all wind properties change as a function of the solar cycle. Our
results point towards a scenario where both the slow and fast solar
wind are accelerated by waves, but originate from different sources
(open/closed magnetic structures for the fast/slow wind, respectively)
whose relative contribution changes along the solar cycle. We also
find that the signatures of heating and acceleration on one side,
and of the FIP effect on the other, indicate that wave-based plasma
heating, acceleration and fractionation remain active throughout the
solar cycle, but decrease their effectiveness in all winds, although
the slow wind is much affected than the fast one.
Title: Ion temperature diagnostics at the off-limb coronal hole
boundary and post-flare loops
Authors: Zhu, Yingjie; Landi, Enrico; Szente, Judit
Bibcode: 2021AGUFMSH45B2380Z
Altcode:
Physical quantities, such as ion temperature and non-thermal
velocity, provide critical information about the heating mechanism
of the million-degree solar corona. In this study, we measure both
quantities from spectroscopic observations of two very different
coronal structures: the coronal hole boundary observed by Hinode/EIS and
SOHO/SUMER, and post-flare loops observed by SUMER. In our measurements,
we only assume that the plasma non-thermal velocity is the same for
all ions. At the coronal hole boundary, we find the ion temperature
is much higher than the formation temperature of the line. Also,
the measured ion temperature first decreases with the charge-to-mass
ratio to 0.25 and then slightly increases with the charge-to-mass
ratio. We run the Alfvén Wave Solar Model (AWSoM) and SPECTRUM module
to investigate the physical properties of the coronal hole boundary
and compare the synthetic line profiles with the observed spectrum. In
the post-flare loops, we find significant flare-related Lyman beta
and Ly gamma emission enhancement from SUMER observations which allow
us to determine the neutral hydrogen temperature in the lower solar
corona for the first time. We also estimate ion temperature for other
species in the post-flare loops. Our study provides new constraints
to the coronal heating and cooling models.
Title: First Images from the Upgraded Coronal Multi-channel
Polarimeter (UCoMP)
Authors: Tomczyk, Steven; Landi, Enrico; Berkey, Ben; Burkepile,
Joan; Cotter, Marc; Gallaher, Dennis; Galloy, Michael D.; Graves,
Rob; Oakley, Philip; Perez-Gonzalez, Lisa; Sewell, Scott; de Toma,
Giuliana; Zmarzly, Patrick
Bibcode: 2021AGUFMSH15G2089T
Altcode:
The Upgraded Coronal Multi-channel Polarimeter (UCoMP) is a coronal
polarimeter with a narrow-band tunable birefringent filter capable
of imaging the intensity, full Stokes polarization, and Doppler shift
across the coronal emission lines of FeXIV 530.3 nm, FeX 637.4 nm, ArXI
691.8, FeXV 706.2 nm, FeXI 789.4, FeXIII 1074.7 and 1079.8 nm and the
chromospheric emission lines of HI 656.3 and HeI 1083 nm. The UCoMP is
an upgrade of the CoMP instrument. It has a broader wavelength range
(530 - 1083 nm) than CoMP (1074 - 1083 nm) increasing the number of
available emission lines in order to observe the corona over a wide
range of temperatures, a larger field-of-view (+/- 2 Rsun) compared
to CoMP (+/- 1.3 Rsun), and higher spatial resolution (6 arcseconds)
compared to CoMP (9 arcseconds). The UCoMP demonstrates the technology
of a large aperture (50 mm) tunable birefringent filter based on Lithium
Niobate crystals and is a pathfinder instrument for the Coronal Solar
Magnetism Observatory. The instrument was shipped to Mauna Loa Solar
Observatory in December of 2020, installed in the Spring of 2021, and
started taking data May 26, 2021, followed by four months of instrument
commissioning. This talk will describe the instrument and present the
first images taken with the UCoMP.
Title: First Imaging Spectroscopy of 92-115 Angstrom Solar Soft
X-rays by EUNIS: Implications for Solar Coronal Heating
Authors: Brosius, Jeffrey; Daw, Adrian; Rabin, Douglas; Landi, Enrico;
Schmit, Donald
Bibcode: 2021AGUFMSH12B..04B
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket waslaunched from White Sands Missile Range, NM, on
May 18, 2021. The instrumentcomprised a pair of coaligned imaging
spectrographs, one of which observed solarline emission in first
order at wavelengths between 525 and 639 A, and the secondof which
observed line emission in third order at wavelengths between 92 and
115 Aand in first order between 277 and 345 A. Images of AR 12824,
quiet-sun area, andoff-limb area were obtained by rastering the slits
over the selected targets. Thisis the first time that solar imaging
spectroscopy has been performed in the 92-115A soft X-ray range. This
waveband was selected to (1) observe Fe XVIII 93.932 and103.948 A
and Fe XIX 108.355 A line emission in a quiescent active region, and
(2)explore a relatively unobserved portion of the solar electromagnetic
spectrum. Theinstrument performed well during its 6-minute observing
run. We report preliminaryresults on observations of Fe XVIII and Fe
XIX in the quiescent active region, anddiscuss implications for the
nanoflare model of solar coronal heating. EUNIS wassupported by NASA
Heliophysics Low Cost Access to Space award 13-HTIDS13_2-0074.
Title: AWSoM MHD simulation of a solar active region with realistic
spectral synthesis
Authors: Manchester, Ward; Shi, Tong; Landi, Enrico; Szente, Judit;
van der Holst, Bart; Chen, Yuxi; Toth, Gabor; Bertello, Luca; Pevtsov,
Alexander
Bibcode: 2021AGUFMSH12B..02M
Altcode:
For the first time, we simulate the detailed spectral line emission
from a solar active region (AR) with the Alfven Wave Solar Model
(AWSoM). We select an active region appearing near disk center on
2018 July 13 and use an NSO-HMI synoptic magnetogram to specify the
magnetic field at the model's inner boundary. To resolve smaller-scale
magnetic features, we apply adaptive mesh refinement to resolve the
AR with a spatial resolution of 0.37 degrees, four times higher than
the background corona. We then apply the SPECTRUM code informed with
Chianti spectral emissivities to calculate more than a dozen spectral
lines forming at temperatures ranging from 0.5 to 3+ MK. Comparisons
are made between these simulated line profiles and those observed by
the Hinode/EIS instrument where we find close agreement (within a
20% margin of error of peak intensity) across a wide range of loop
sizes and temperatures. We also compare the differential emission
measure calculated from both the simulation and EIS observation to
further show the model's ability to capture the plasma temperature and
density. Finally, we simulate and compare Doppler velocities and find
that simulated flow patterns to be of comparable magnitude to what
is observed. Our results demonstrate the broad applicability of the
low-frequency Alfven wave balanced turbulence theory for explaining
the heating of coronal loops.
Title: Constraining charge exchange between solar wind He2+ and
circumsolar dust
Authors: Rivera, Yeimy; Landi, Enrico; Lepri, Susan; Gilbert, Jason;
Raymond, John; Reeves, Katharine; Stevens, Michael
Bibcode: 2021AGUFMSH24C..07R
Altcode:
As the solar wind accelerates from the Sun, ions in the plasma
experience ionization and recombination processes whose net effect
results in the ion composition measured in the heliosphere. The ion
evolution is governed by collisions with electrons and, to a lesser
extent, interaction with the radiation field. Additionally, charge
exchange can occur between solar wind ions and dust neutrals that
surround the Sun which is not well understood. Recent observations
from ACE/SWICS near the Earth measure elevated densities of solar He+
believed to have been formed from He2+ solar wind ions undergoing
charge exchange with dust neutrals. However, there is still much
uncertainty surrounding how and where charge exchange occurs as the
solar wind propagates through the inner heliosphere. To investigate
this interaction, we simulate charge exchange processes between solar
He2+ and neutral particles from dust using a nonequilibrum ionization
code. To probe the effects of charge exchange, we constrain the
simulations with a combination of in situ observations from ACE/SWICS
and remote observations of the inner heliosphere from WISPR on Parker
Solar Probe and SOHO/UVCS. A better understanding of the solar wind and
dust interaction will provide a more complete picture of the ionization
and recombination processes governing the radial evolution of the
solar wind and the distribution of dust in the vicinity of the Sun.
Title: Charge State Simulations with the Alfven Wave Solar Model
Authors: Szente, Judit; Landi, Enrico; van der Holst, Bart
Bibcode: 2021AGUFMSH45B2359S
Altcode:
AWSoM is a physically driven 3D Solar Corona and Inner Heliosphere
model, which solves for the extended magnetohydrodynamics with
electron-, parallel and perpendicular temperatures and includes
radiative losses, collisional and collisionless heat conduction. The
solar wind is heated by Alfvén-wave turbulence and the wind is
accelerated by wave pressure gradients. We implemented heavy ion
charge state calculation to the Alfvén Wave Solar Model (AWSoM). The
implementation allows to calculate non-equilibrium charge state
distributions over time in the 3d domain for steady-state and time
dependent simulations for all ions with ionization and recombination
rates recorded in SolarSoft's CHIANTI. The coronal model is calculating
the charge states and plasma status simultaneously everywhere in the
domain. We show AWSoM simulations performed with GONG magnetogram
data that coincides with the Ulysses passing and ACE observations
and resulting comparisons of synthetic to observed charge states at
various parts of the heliosphere.
Title: Measurements of Coronal Magnetic Field Strengths in Solar
Active Region Loops
Authors: Brooks, David H.; Warren, Harry P.; Landi, Enrico
Bibcode: 2021ApJ...915L..24B
Altcode: 2021arXiv210610884B
The characteristic electron densities, temperatures, and thermal
distributions of 1 MK active region loops are now fairly well
established, but their coronal magnetic field strengths remain
undetermined. Here we present measurements from a sample of coronal
loops observed by the Extreme-ultraviolet Imaging Spectrometer on
Hinode. We use a recently developed diagnostic technique that involves
atomic radiation modeling of the contribution of a magnetically
induced transition to the Fe X 257.262 Å spectral line intensity. We
find coronal magnetic field strengths in the range of 60-150 G. We
discuss some aspects of these new results in the context of previous
measurements using different spectropolarimetric techniques, and their
influence on the derived Alfvén speeds and plasma β in coronal loops.
Title: A Theoretical Investigation of the Magnetic-field-induced
Transition in Fe X, of Importance for Measuring Magnetic Field
Strengths in the Solar Corona
Authors: Li, W.; Li, M.; Wang, K.; Brage, T.; Hutton, R.; Landi, E.
Bibcode: 2021ApJ...913..135L
Altcode:
The use of the magnetic-field-induced transition
(MIT) $3{{\rm{p}}}^{4}3{\rm{d}}{}^{4}{D}_{7/2}\to
3{{\rm{p}}}^{5}\,{}^{2}{P}_{3/2}^{{\rm{o}}}$ in Fe X for the measurement
of the magnetic field strength in the solar corona has been discussed
and demonstrated in a number of recent studies. This diagnostic
technique depends on, among other conditions, the accuracy of the
atomic data for Fe X. In the present work, we carry out a large-scale
calculation for the atomic properties needed for the determination
of the MIT rate using the multiconfiguration Dirac-Hartree-Fock
method. Four computational schemes are employed to study the convergence
of the atomic properties of interest. Comparison with other experimental
and theoretical sources are performed and recommended values are
suggested for important properties, e.g., the magnetic induced
transition probabilities as a function of magnetic field strengths. The
present calculations affect magnetic field measurements by decreasing
the magnetic field strengths by 10%-15%, leading to differences in
magnetic energy up to 30%. We recommend that the current data should
be employed in magnetic field measurements in the future.
Title: Gyroresonance and Free-Free Radio Emissions from Multithermal
Multicomponent Plasma
Authors: Fleishman, Gregory D.; Kuznetsov, Alexey A.; Landi, Enrico
Bibcode: 2021ApJ...914...52F
Altcode: 2021arXiv210407655F
The solar atmosphere contains thermal plasma at a wide range of
temperatures. This plasma is often quantified, in both observations
and models, by a differential emission measure (DEM). The DEM
is a distribution of the thermal electron density squared over
temperature. In observations, the DEM is computed along a line of
sight, while in the modeling it is over an elementary volume element
(voxel). This description of the multithermal plasma is convenient
and widely used in the analysis and modeling of extreme ultraviolet
emission, which has an optically thin character. However, there is
no corresponding treatment in the radio domain, where the optical
depth of emission can be large, more than one emission mechanism
is involved, and plasma effects are important. Here, we extend the
theory of thermal gyroresonance and free-free radio emissions in
the classical single-temperature Maxwellian plasma to the case of a
multitemperature plasma. The free-free component is computed using
the DEM and temperature-dependent ionization states of coronal ions,
contributions from collisions of electrons with neutral atoms, the
exact Gaunt factor, and the magnetic field effect. For the gyroresonant
component, another measure of the multitemperature plasma is used,
which describes the distribution of the thermal electron density over
temperature. We give representative examples demonstrating important
changes in the emission intensity and polarization due to the effects
considered. The theory is implemented in available computer code.
Title: Hinode/EIS Coronal Magnetic Field Measurements at the Onset
of a C2 Flare
Authors: Landi, E.; Li, W.; Brage, T.; Hutton, R.
Bibcode: 2021ApJ...913....1L
Altcode: 2021arXiv210206072L
We study Hinode/EIS observations of an active region taken before,
during, and after a small C2.0 flare in order to monitor the evolution
of the magnetic field and its relation to the flare event. We find that
while the flare left the active region itself unaltered, the event
included a large magnetic field enhancement (MFE), which consisted
of a large magnetic field strength increase to values just short of
500 G in a rather small region where no magnetic field was measured
before. This MFE is observed during the impulsive phase of the flare
at the footpoints of flare loops, its magnetic energy is sufficient
to power the radiative losses of the entire flare, and has completely
dissipated after the flare. We argue that the MFE might occur at the
location of the reconnection event triggering the flare, and note
that it formed within 22 minutes of the flare start (as given by the
EIS raster return time). These results open the door to a new line
of studies aimed at determining whether MFEs can be flare precursor
events or used for Space Weather forecasts, what advance warning
time they could provide and if this time is long enough to allow for
mitigation procedures to be implemented; as well as to explore which
physical processes lead to MFE formation and dissipation, whether such
processes are the same in both long-duration and impulsive flares,
and whether they can be predicted by theoretical models.
Title: Fe XII and Fe XIII Line Widths in the Polar Off-limb Solar
Corona up to 1.5 R⊙
Authors: Zhu, Yingjie; Szente, Judit; Landi, Enrico
Bibcode: 2021ApJ...913...74Z
Altcode: 2020arXiv200914640Z
The nonthermal broadening of spectral lines formed in the solar corona
is often used to seek evidence of Alfvén waves propagating in the
corona. To have a better understanding of the variation of line widths
at different altitudes, we measured the line widths of the strong Fe
XII 192.4, 193.5, and 195.1 Å and Fe XIII 202.0 Å in an off-limb
southern coronal hole up to 1.5 R⊙ observed by the Extreme
Ultraviolet Spectrometer on board the Hinode satellite. We compared
our measurements to the predictions from the Alfvén Wave Solar Model
(AWSoM) and the SPECTRUM module. We found that the Fe XII and Fe XIII
line widths first increase monotonically below 1.1 R⊙
and then keep fluctuating between 1.1 and 1.5 R⊙. The
synthetic line widths of Fe XII and Fe XIII below 1.3 R⊙
are notably lower than the observed ones. We found that the emission
from a streamer in the line of sight significantly contaminates the
coronal hole line profiles even up to 1.5 R⊙ both in
observations and simulations. We suggest that either the discrepancy
between the observations and simulations is caused by insufficient
nonthermal broadening at the streamer in the AWSoM simulation or the
observations are less affected by the streamer. Our results emphasize
the importance of identifying the origin of the coronal EUV emission
in off-limb observations.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: Codes for computing the solar gyroresonance and free-free
radio emissions: the first release
Authors: Kuznetsov, Alexey; Fleishman, Gregory; Landi, Enrico
Bibcode: 2021zndo...4625572K
Altcode:
Codes for computing the solar gyroresonance and free-free radio
emissions; both the isothermal plasma and the sources described
by the differential emission measure (DEM) and differential density
metric (DDM) are supported. The codes are implemented as Windows/Linux
libraries callable from IDL (via call_external function). See the files
CallingConventions.pdf and Diagram.pdf for more details and calling
conventions, and the folder Examples for the usage examples. The folder
Binaries contains the compiled Windows DLL and Linux SO libraries. This
is the first release of the codes (21 March 2021).
Title: CHIANTI—An Atomic Database for Emission Lines. XVI. Version
10, Further Extensions
Authors: Del Zanna, G.; Dere, K. P.; Young, P. R.; Landi, E.
Bibcode: 2021ApJ...909...38D
Altcode: 2020arXiv201105211D
We present version 10 of the CHIANTI package. In this release, we
provide updated atomic models for several helium-like ions and for
all the ions of the beryllium, carbon, and magnesium isoelectronic
sequences that are abundant in astrophysical plasmas. We include rates
from large-scale atomic structure and scattering calculations that
are in many cases a significant improvement over the previous version,
especially for the Be-like sequence, which has useful line diagnostics
to measure the electron density and temperature. We have also added
new ions and updated several of them with new atomic rates and line
identifications. Also, we have added several improvements to the IDL
software, to speed up the calculations and to estimate the suppression
of dielectronic recombination.
Title: Fe VII Emission Lines in the Wavelength Range 193-197 Å
Authors: Young, Peter R.; Ryabtsev, Alexander N.; Landi, Enrico
Bibcode: 2021ApJ...908..104Y
Altcode: 2020arXiv201208027Y
The identifications of Fe VII emission lines in the wavelength range
193-197 Å are discussed in the light of new measurements of laboratory
spectra and atomic data calculations. This region is of importance to
studies of solar spectra from the EUV Imaging Spectrometer (EIS) on
board the Hinode spacecraft, which has its peak sensitivity at these
wavelengths. Ten lines are measured, arising from seven fine structure
levels in the 3p53d3 configuration. Two lines have
not previously been reported and lead to new experimental energies for
the ${({a}^{2}D)}^{3}{F}_{\mathrm{2,3}}$ levels. Updated experimental
energies are obtained for the remaining levels. The new atomic model
is used to compute theoretical values for the two density diagnostic
ratios λ196.21/λ195.39 and λ196.21/λ196.06, and densities are
derived from EIS spectra of coronal loop footpoints.
Title: Modeling the interaction between the solar wind and
interplanetary dust
Authors: Rivera, Yeimy; Lepri, Susan; Landi, Enrico
Bibcode: 2021cosp...43E.937R
Altcode:
After leaving the relatively cool photosphere, solar material
experiences a rapid increase in temperature as it travels through the
transition region. This rise in temperature is expected to significantly
ionize the majority of the material and is enough to fully ionize H and
He. After entering the tenuous corona, collisions decrease and ions
reach a fixed charge state where they are expected to remain as they
propagate through the heliosphere. In the heliosphere, low ionized
charge states are uncommon outside of pick up ions and occasional
prominence material; however, measurements from ACE/SWICS routinely
observe He$^{+}$ throughout solar cycle 23 that are potentially of solar
origin. Our work investigates the possible connection of the He$^{+}$
detected in the heliosphere to the interaction between the solar wind
and surrounding dust by modeling charge exchange of solar wind alphas
with neutral H, and H$_{2}$ from the dust. We use an ionization code
that includes impact ionization, and photo-ionization, experienced by
the solar wind with an additional term to account for charge exchange
with the neutrals to test if dust could be a viable source of solar
He$^{+}$ population. This process will be further constrained and tested
with the heliospheric imagers on Parker Solar Probe and Solar Orbiter,
as well as the Heavy Ion Sensor on Solar Orbiter.
Title: On the production of singly ionized He in the solar wind from
the first observations of Solar Orbiter's Heavy Ion Sensor
Authors: Rivera, Y.; Landi, E.; Lepri, S. T.; Gilbert, J. A.; Bruno,
R.; Dewey, R. M.; Galvin, A. B.; Horbury, T. S.; Livi, S. A.; Louarn,
P.; Owen, C. J.; Raines, J. M.
Bibcode: 2020AGUFMSH035..06R
Altcode:
The He+ ion is expected to be rare in the solar wind, and it is usually
associated with material from the interstellar medium, interplanetary
dust, comets, or planetary atmospheres that originate as neutral,
undergo ionization, and are subsequently picked up by the interplanetary
magnetic field. The newly picked up ions can be differentiated from
typical solar wind ions through their characteristic non-thermal
velocity distribution functions that contrasts the narrowly peaked
Maxwellian profile of the solar wind. However, through inspection of
He+ measurements from ACE/SWICS throughout solar cycle 23 (1998-2011),
we find a significant population of He+ of solar origin that are
unaccounted for with current ionization modeling. The population of
He+ observed is independent of wind speed, composition, and source
region suggesting the He+ is formed after leaving the Sun, making the
interaction with dust a likely source. Through nonequilibrium ionization
modeling, we find charge exchange with low energy neutrals outgassed
from dust to be effective in creating solar He+ from He2+. We compare
the present He+ of solar origin to first light measurements from the
Heavy Ion Sensor on Solar Orbiter in the inner heliosphere to further
constrain the solar wind-dust interaction.
Title: Hinode/EIS Measurements of Active-region Magnetic Fields
Authors: Landi, E.; Hutton, R.; Brage, T.; Li, W.
Bibcode: 2020ApJ...904...87L
Altcode: 2020arXiv200803532L
The present work illustrates the potential of a new diagnostic technique
that allows the measurement of the coronal magnetic field strength
in solar active regions by utilizing a handful of bright Fe X and Fe
XI lines commonly observed by the high-resolution Hinode/EUV Imaging
Spectrometer (EIS). The importance of this new diagnostic technique is
twofold: (1) the coronal magnetic field is probably the most important
quantity in coronal physics, being at the heart of the processes
regulating space weather and the properties of the solar corona,
and (2) this technique can be applied to the existing EIS archive
spanning from 2007 to 2020, including more than one full solar cycle
and covering a large number of active regions, flares, and even coronal
mass ejections. This new diagnostic technique opens the door to a whole
new field of studies, complementing the magnetic field measurements
from the upcoming DKIST and UCoMP ground-based observatories, and
extending our reach to active regions observed on the disk and until
now only sampled by radio measurements. In this work, we present a
few examples of the application of this technique to EIS observations
taken at different times during the EIS mission, and we discuss its
current limitations and the steps to improve its accuracy. We also
present a list of EIS observing sequences whose data include all of
the lines necessary for the application of this diagnostic technique,
to help the solar community navigate the immense set of EIS data and
to find observations suitable for measuring the coronal magnetic field.
Title: Fe XII and Fe XIII Line Widths in a Southern Coronal Hole up
to 1.5 Solar Radii
Authors: Zhu, Y.; Szente, J.; Landi, E.
Bibcode: 2020AGUFMSH0290011Z
Altcode:
The non-thermal broadening of spectral lines formed in the solar corona
are often regarded as the evidence of Alfvé n waves propagating in
the corona. To have a better understanding of the variation of line
widths at different altitudes, we measured the strongest Fe XII 192.4
Å, 193.5Å, 195.1Å and Fe XIII 202.0Å line widths in an off-limb
southern coronal hole up to 1.5 solar radii observed by Extreme
Ultraviolet Spectrometer (EIS) on board the Hinode satellite with a
total exposure time of ~30000 s. We compared our measurements to the
predictions from the Alfvé n Wave Solar Model (AWSoM) and the SPECTRUM
module. We found the Fe XII and Fe XIII line widths first increase
monotonically below 1.1 solar radii, then keep fluctuating between 1.1
- 1.5 solar radii. The synthetic line widths of Fe XII and Fe XIII
below 1.3 solar radii are notably lower than the observed ones. We
suggested that some other heating mechanisms besides the dissipation
of the Alfvé n waves are required to understand the coronal heating
and solar wind acceleration of the heavy minor ions in corona holes
below 1.3 solar radii.
Title: Introduction of Zeeman splitting in CHIANTI
Authors: Giarrusso, M.; Landi, E.; Del Zanna, G.; Leone, F.
Bibcode: 2020JPlPh..86e8402G
Altcode:
High-resolution spectra emitted by laboratory plasmas provide invaluable
diagnostic tools for the measurement of plasma properties. To be
implemented, they require a large amount of atomic data and transition
rates, which are available in several spectral codes. In this paper we
present a new feature added to the CHIANTI code, which allows us to
calculate the Zeeman splitting of spectral lines in the presence of
a magnetic field with known intensity and orientation. When combined
with the CHIANTI database and software to calculate level populations
and line emissivities, this new feature returns the emissivities in
all four Stokes parameters, that can be utilized for the measurement of
the magnetic field inside laboratory plasma chambers, along with other
plasma parameters. This new feature can be applied to the analysis of
the emission of laboratory plasmas created in different devices.
Title: SUMER Measurement of the Fe X 3p43d
4D5/2,7/2 Energy Difference
Authors: Landi, E.; Hutton, R.; Brage, T.; Li, W.
Bibcode: 2020ApJ...902...21L
Altcode:
Recent studies have shown that magnetic fields in the solar corona
are strong enough to significantly mix the two 3p43d
4D5/2,7/2 levels in Cl-like Fe X. This
mixing gives rise to a magnetically induced transition (MIT)
component in the bright Fe X 257.3 Å line, commonly observed by
current instrumentation, that can be used for coronal magnetic field
diagnostics. This line, commonly observed by the still operational
EIS spectrometer on board the Hinode satellite since 2007, opens a
new window into the coronal magnetic field. However, the strength of
this MIT transition depends on the square of the energy difference
ΔE of the two ${}^{4}{{\rm{D}}}_{5/\mathrm{2,7}/2}$ levels, so
that an accurate determination of ΔE is of critical importance to
accurately measure coronal magnetic field strengths. In the present
work we present a new measurement of ΔE obtained determining the
separation of the two component of the Fe X doublet close to 1603.3 Å
from deep-exposure spectra of a quiescent streamer at the solar limb
taken with the SUMER instrument on board SoHO. Our measurement of ΔE =
2.29 ± 0.50 cm-1 agrees with, and improves upon, an earlier
measurements by Judge et al. by decreasing its uncertainty from 80%
to approximately 20%, improving the attainable accuracy of magnetic
field strength measurements obtainable with the Fe X 257.26 Å line.
Title: On the Production of He+ of Solar Origin in the
Solar Wind
Authors: Rivera, Yeimy J.; Landi, Enrico; Lepri, Susan T.; Gilbert,
Jason A.
Bibcode: 2020ApJ...899...11R
Altcode: 2020arXiv200704402R
Solar wind measurements in the heliosphere predominantly comprise
protons, alphas, and minor elements in a highly ionized state. The
majority of low-charge states, such as He+, measured in situ
are often attributed to pick-up ions of nonsolar origin. However,
through inspection of the velocity distribution functions of
near-Earth measurements, we find a small but significant population
of He+ ions in the normal solar wind whose properties
indicate that it originated from the Sun and has evolved as part of
the normal solar wind. Current ionization models, largely governed by
electron impact and radiative ionization and recombination processes,
underestimate this population by several orders of magnitude. Therefore,
to reconcile the singly ionized He observed, we investigate the
recombination of solar He2+ through charge exchange with
neutrals from circumsolar dust as a possible formation mechanism of
solar He+. We present an empirical profile of neutrals
necessary for charge exchange to become an effective vehicle to
recombine He2+ to He+ such that it meets
observational He+ values. We find that the formation of
He+ is not only sensitive to the density of neutrals but also
to the inner boundary of the neutral distribution encountered along
the solar wind path. However, further observational constraints are
necessary to confirm that the interaction between solar α particles and
dust neutrals is the primary source of the He+ observations.
Title: Evidence for Solar Coronal Heating by Nanoflares Based on
Coordinated EUV Spectra Observed with the EUNIS Sounding Rocket
and Hinode/EIS
Authors: Brosius, J. W.; Daw, A. N.; Landi, E.
Bibcode: 2019AGUFMSH53B3373B
Altcode:
The nanoflare model of solar coronal heating has been widely viewed with
increasing favor over the last 5-10 years. According to this model,
the solar atmosphere is heated by numerous impulsive heating events
that are currently too small to be detected individually. Collectively,
however, they produce the corona's 2-3 MK plasma. Widespread faint
emission from lines formed at flare-like temperatures (6-10 MK) is
considered to be strong, "smoking gun" evidence for the nanoflare
model. Previously we reported such evidence in the form of faint
Fe XIX emission observed throughout an active region during the 2013
flight of the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket instrument. The instrument recorded spectra in 300-370
and 530-635 A wavebands. Here we present an analysis of coordinated
spectra of that same active region obtained with both EUNIS and the
Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. EIS
records spectra in 170-210 and 250-290 A wavebands. We investigate
the emission measure of the faint, high-temperature component, slopes
within the emission measure curve, element abundances, nonthermal line
broadening, and bulk velocity flows. This work helps pave the way for
the next EUNIS flight, which records spectra and spectroheliograms
in 90-115 and 530-635 A wavebands. These include, in particular,
strong emission lines of Fe XVIII and Fe XIX, which are among the best
candidates for nanoflare emission identification and analysis.
Title: Implementation of the Sun Radio Interferometer Space Experiment
(SunRISE) Mission Concept
Authors: Lazio, J.; Kasper, J. C.; Romero-Wolf, A.; Bastian, T.; Cohen,
C.; Landi, E.; Manchester, W.; Hegedus, A. M.; Schwadron, N.; Sokolov,
I.; Bain, H. M.; Cecconi, B.; Hallinan, G.; Krupar, V.; Maksimovic,
M.; Moschou, S. P.; Zaslavsky, A.; Lux, J. P.; Neilsen, T. L.
Bibcode: 2019AGUFMSH31C3328L
Altcode:
The Sun Radio Interferometer Space Experiment (SunRISE) would provide
an entirely new view on particle acceleration and transport in the
heliosphere by obtaining spatially and temporally resolved observations
of Decametric-Hectometric (DH, < 15 MHz) Type II and Type III
radio bursts. In order to obtain the required angular resolution,
SunRISE would be a free-flying interferometer. Building on more than 50
years of experience from ground-based very long baseline interferometry
(VLBI), SunRISE would fly six small spacecraft in a supersynchronous
geosynchronous orbit (GEO) in a passive formation. Their orbits
are designed to keep them within approximately 6 km of each other. A
space-based interferometer is required because most of the DH band does
not penetrate the Earth's ionosphere, due to ionospheric absorption. Each 6U spacecraft would carry only a single science radio designed
to operate in the DH band. The radio would form spectra on-board,
with pre-selected sub-bands identified for downlink. This science
payload radio would be integrated into a Global Positioning System
(GPS) receiver, allowing precise time to be measured on board the
spacecraft as well. The spacecraft would be independent of each other,
as is the practice for ground-based VLBI arrays. On a regular
basis, both science data and GPS timing would be downlinked. NASA's
Deep Space Network antennas would be used for the downlink, with an
efficient multiple spacecraft per aperture (MSPA) mode enabling the
data from three spacecraft to be downlinked simultaneously. After orbit
determination, the interferometric data processing would form images of
Type II and Type III solar radio bursts and identify the locations of
radio emission relative to the structures of CMEs. SunRISE would
leverage advances in software-defined radios, GPS navigation and timing,
and small spacecraft technologies that have been demonstrated over
the past few years. An Extended Phase A study of the SunRISE mission
concept is scheduled to be completed in 2019 September. Part
of this research was carried out at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration. Some of the information presented
is pre-decisional and for planning and discussion purposes only.
Title: Identification of spectral lines to study CMEs with ground-
and space-based observatories
Authors: Rivera, Y.; Lepri, S. T.; Landi, E.
Bibcode: 2019AGUFMSH33B3383R
Altcode:
Many studies of coronal mass ejections (CMEs) suggest that the plasma
experiences rapid and significant heating as it travels away from the
Sun. However, the dynamic and multi-thermal nature of the eruption
makes it difficult to study the plasma's temporal evolution with
a single EUV channel or spectral line. Therefore, in this work,
we identify useful spectral lines for CME diagnostics. We include
lines spanning the extreme ultraviolet to near-Infrared, 100-14400
Å, that range between log Te (K) = 4 - 6.7 in equilibrium
formation temperature to study the eruption. Many lines tested in our
analysis will be observed by future ground based solar telescopes;
DKIST, and UCoMP, and space-based EUV spectrometer SPICE on Solar
Orbiter. The synthetic intensities for each line were computed
between 1.05-2Rsun from a CME comprised of a prominence,
prominence-coronal transition region (PCTR), and coronal plasma: an
empirical model of their thermodynamic properties was developed in a
previous study. We find many of the lines from the prominence material
maintain strong signal and remain in ionization equilibrium throughout
the field of view considered. The intensities formed within the strongly
heated, tenuous PCTR plasma peak and subsequently dim following the
rapid ionization of the corresponding emitting ion while evolving far
from ionization equilibrium. Furthermore, we find each component can
be observed by multiple instruments providing the opportunity to make
coordinated plasma measurements. We include a summary of spectral
lines that are predicted to be visible from each CME component and
discuss their diagnostic potential
Title: The Sun Radio Interferometer Space Experiment (SunRISE)
Mission Concept
Authors: Kasper, J. C.; Lazio, J.; Romero-Wolf, A.; Bain, H. M.;
Bastian, T.; Cohen, C.; Landi, E.; Manchester, W.; Hegedus, A. M.;
Schwadron, N.; Sokolov, I.; Cecconi, B.; Hallinan, G.; Krupar, V.;
Maksimovic, M.; Moschou, S. P.; Zaslavsky, A.; Lux, J. P.; Neilsen,
T. L.
Bibcode: 2019AGUFMSH33A..02K
Altcode:
The Sun Radio Interferometer Space Experiment (SunRISE) would provide
an entirely new view on particle acceleration and transport in the
inner heliosphere by obtaining spatially and temporally resolved
observations of solar Decametric-Hectometric (DH, < 15 MHz) radio
bursts. These bursts are produced by electrons energized near expanding
CMEs (Type II) and released by solar flares (Type III). SunRISE would
track DH bursts from 2 RS to 20 RS in order to
achieve two science objectives. The first objective is to discriminate
competing hypotheses for the source mechanism of CME-associated SEPs by
measuring the location of Type II bursts relative to expanding CMEs. By
locating Type II emission relative to the overall structure of CMEs,
SunRISE would reveal where particle acceleration occurs and determine
if specific properties of CMEs lead to DH bursts. The second objective
is to determine if a broad magnetic connection between active regions
and interplanetary space is responsible for the wide longitudinal extent
of some SEPs by imaging the field lines traced by Type III bursts from
active regions through the corona. By tracing the radio emission from
energetic electrons as they travel along magnetic field lines, SunRISE
would reveal the field line topology, and its time variation, from
active regions into interplanetary space. SunRISE would consist
of six 6U small spacecraft in a supersynchronous geosynchronous orbit
(GEO) in a passive formation. Forming a synthetic aperture and observing
at frequencies that cannot be observed on Earth due to ionospheric
absorption, SunRISE would leverage advances in software-defined radios,
GPS navigation and timing, and small spacecraft technologies. These
advances have been flown over the past few years, making this concept
finally affordable and low-risk. An Extended Phase A study
of the SunRISE mission concept is scheduled to be completed in 2019
September. This paper presents a summary of the concept study. Part
of this research was carried out at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration. Some of the information presented
is pre-decisional and for planning and discussion purposes only.
Title: Coronal Solar Magnetism Observatory Science Objectives
Authors: Gibson, S. E.; Tomczyk, S.; Burkepile, J.; Casini, R.;
DeLuca, E.; de Toma, G.; de Wijn, A.; Fan, Y.; Golub, L.; Judge,
P. G.; Landi, E.; McIntosh, S. W.; Reeves, K.; Seaton, D. B.; Zhang, J.
Bibcode: 2019AGUFMSH11C3395G
Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
Title: Investigating the role of solar wind-dust interaction in the
production of He+
Authors: Rivera, Y.; Landi, E.; Lepri, S. T.; Spitzer, S. A.
Bibcode: 2019AGUFMSH31B..14R
Altcode:
After leaving the relatively cool photosphere, solar material
experiences a rapid increase in temperature as it travels through
the dense transition region. This rise in temperature is expected to
significantly ionize the majority of the material and is enough to
fully ionize H and He. After entering the tenuous corona, collisions
decrease and ions reach a fixed charge state where they are expected to
remain as they propagate through the heliosphere. However, many eclipse
observations suggest the presence low ionized and neutral material in
the corona said to be due to the interaction of the solar wind with
circumsolar dust. In the heliosphere, low ionized charge states are
uncommon outside ICMEs; still, measurements from ACE/SWICS routinely
show enhancements of He+/He2+ throughout solar cycle 23 that are
potentially of solar origin, and cannot be explained with standard
solar wind ionization models. Our work investigates the possible
connection of the He+ enhancements detected in the heliosphere to
the interaction between solar wind and circumsolar dust by modeling
charge exchange of solar wind alphas with neutral H, and H2
from the dust. This process can be further constrained and tested with
coordinated observations of future DKIST and the Heavy Ion Sensor on
Solar Orbiter.
Title: Nonequilibrium ionization effects on coronal plasma diagnostics
and elemental abundance measurements
Authors: Shi, T.; Landi, E.; Manchester, W.
Bibcode: 2019AGUFMSH11C3402S
Altcode:
Plasma diagnostics and elemental abundance measurements are crucial
to help us understand the formation and dynamics of the solar
wind. Here we use a theoretical solar wind model to study the effect
of non-equilibrium ionization (NEI) on plasma diagnostic techniques
applied to line intensities emitted by the fast solar wind. We find
that NEI almost always changes the spectral line intensities with up to
120% difference for the lighter elements and for higher charge states
of Fe even below 1.5 solar radii (Rs). The measured plasma density,
temperature, and differential emission measure (DEM) are only slightly
affected by NEI. However, NEI significantly affects the first ionization
potential (FIP) bias and abundance ratio measurements, producing up to
a factor of 4 error at 1.5 Rs for Mg/Ne, Fe/S, and Ar/Fe ratios when
assuming EI. We conclude that it is very important to consider the
NEI effect when synthesizing spectral line intensities and measuring
the FIP bias and elemental abundance.
Title: Investigating Coronal Magnetism with COSMO: Science on
the Critical Path To Understanding The ``Weather'' of Stars and
Stellarspheres
Authors: McIntosh, Scott; Tomczyk, Steven; Gibson, Sarah E.; Burkepile,
Joan; de Wijn, Alfred; Fan, Yuhong; deToma, Giuliana; Casini, Roberto;
Landi, Enrico; Zhang, Jie; DeLuca, Edward E.; Reeves, Katharine K.;
Golub, Leon; Raymond, John; Seaton, Daniel B.; Lin, Haosheng
Bibcode: 2019BAAS...51g.165M
Altcode: 2019astro2020U.165M
The Coronal Solar Magnetism Observatory (COSMO) is a unique ground-based
facility designed to address the shortfall in our capability to measure
magnetic fields in the solar corona.
Title: Nonequilibrium Ionization Effects on Coronal Plasma Diagnostics
and Elemental Abundance Measurements
Authors: Shi, Tong; Landi, Enrico; Manchester, Ward, IV
Bibcode: 2019ApJ...882..154S
Altcode:
Plasma diagnostics and elemental abundance measurements are crucial to
help us understand the formation and dynamics of the solar wind. Here we
use a theoretical solar wind model to study the effect of nonequilibrium
ionization (NEI) on plasma diagnostic techniques applied to line
intensities emitted by the fast solar wind. We find that NEI almost
always changes the spectral line intensities with up to 120% difference
for the lighter elements and for higher charge states of Fe even below
1.5 solar radii (R s ). The measured plasma density,
temperature, and differential emission measure are only slightly
affected by NEI. However, NEI significantly affects the first-ionization
potential (FIP) bias and abundance ratio measurements, producing an
error of up to a factor 4 at 1.5 R s for the Mg-to-Ne,
Fe-to-S, and Ar-to-Fe ratios when EI is assumed. We conclude that it is
very important to consider the NEI effect when spectral line intensities
are synthesized and the FIP bias and elemental abundance are measured.
Title: Tomography of the Solar Corona with Multiple Instruments:
First Steps
Authors: Lloveras, D. G.; Vásquez, A. M.; Landi, E.; Frazin, R. A.
Bibcode: 2019BAAA...61...35L
Altcode:
Solar rotational tomography is an observational technique of the solar
corona that allows the reconstruction of the global three-dimensional
distribution of some of its fundamental physical parameters, such
as electron density. EUV tomography is routinely applied to data
provided by spaceborne telescopes, typically covering the range of
heliocentric heights . This range partially overlaps with the field of
view of the white light K-coronagraph (KCOR) instrument, at the High
Altitude Observatory (HAO), which covers the range . In this work
we show preliminary results of the first comparison of tomographic
reconstruction of the coronal electron density based on EUV images,
with the reconstruction based on white light images. The results are
discussed in terms of the diverse characteristics of the used data sets,
as well as the different physical factors that affect each analysis.
Title: Identifying Spectral Lines to Study Coronal Mass Ejection
Evolution in the Lower Corona
Authors: Rivera, Yeimy J.; Landi, Enrico; Lepri, Susan T.
Bibcode: 2019ApJS..243...34R
Altcode:
As prominences propagate away from the Sun via a coronal mass ejection
(CME), they expand, accelerate, and are strongly heated. The heating
is substantial enough to continuously ionize the prominence plasma,
making it difficult to follow its dynamic evolution with a single
extreme ultraviolet (EUV) narrow-band channel or a white light
instrument. In this work, we identify useful spectral lines that
can be utilized to study the prominence during the early stages of
propagation. We generate nonequilibrium ion fractions from a previously
studied multi-thermal component CME using the Michigan Ionization Code
to compute synthetic intensities along the CME path. We test several
emission lines produced by the multi-thermal evolution of the CME that
span the EUV to the visible and infrared wavelength range, 100-14400 Å,
and equilibrium formation temperatures between log(T e )
= 4.3-6.7. We assess the visibility and diagnostic potential up to 2
solar radii of many lines in a wavelength range encompassing the EUV
to the near-infrared, including those observed by many existing and
past instruments, as well as upcoming observatories, such as the Daniel
K. Inouye Solar Telescope, Upgraded Coronal Multi-channel Polarimeter,
and Solar Orbiter/Spectral Imaging of the Coronal Environment.
Title: Latest updates to the CHIANTI atomic database
Authors: Young, Peter R.; Dere, Kenneth P.; Del Zanna, Giulio; Landi,
Enrico; Sutherland, Ralph
Bibcode: 2019AAS...23431402Y
Altcode:
CHIANTI is a database of atomic data parameters and a software
package for computing the radiative emissions from optically-thin
astrophysical plasmas. CHIANTI is freely available to the community
(http://chiantidatabase.org),
and is very widely used in the Heliophysics and Astrophysics
communities. The papers describing CHIANTI have been cited over
3500 times in the 22-year lifetime of the project. Version 9 of
CHIANTI was released in March 2019, and this presentation summarizes
the new updates and highlights important applications. The key change
for CHIANTI 9 was the implementation of a new method to account for
recombination and dielectronic capture in the level balance equations
through new, two-ion models that fully capture the state-to-state
transitions between ions. The models are needed for the calculation
of X-ray satellite lines and, for the first time, enable density
sensitivity to be modeled. A number of the standard atomic
data-sets have been updated, including recombination rates for several
important coronal iron ions. New software routines have been written
for computing the differential emission measure of a plasma, and for
computing the response functions of the Atmospheric Imaging Assembly
on board NASA's Solar Dynamics Observatory .
Title: Upgraded Coronal Multi-channel Polarimeter (UCoMP)
Authors: Tomczyk, Steven; Landi, Enrico
Bibcode: 2019shin.confE.131T
Altcode:
The Coronal Multi-channel Polarimeter (CoMP) is a coronal polarimeter
with a narrow-band tunable Lyot filter capable of imaging the intensity,
polarization and Doppler shift in the coronal emission lines of FeXIII
1074.7 and 1079.8 nm and HeI 1083 nm. We are currently in the process
of upgrading the CoMP instrument to 1) broaden the wavelength range
to 530 - 1083 nm to increase of emission lines that can be observed
to 9 in order to enhance the plasma diagnostic capabilities of the
CoMP, 2) increase the field-of-view to 1 degree, and 3) increase the
spatial resolution. This poster will describe the upgrade and focus
on the enhanced scientific capabilities of the UCoMP. The UCoMP will
be deployed in September of 2019.
Title: SPECTRUM: Synthetic Spectral Calculations for Global Space
Plasma Modeling
Authors: Szente, J.; Landi, E.; Manchester, W. B., IV; Toth, G.;
van der Holst, B.; Gombosi, T. I.
Bibcode: 2019ApJS..242....1S
Altcode:
High-resolution spectroscopy is the most accurate tool for measuring
the properties of the solar corona. However, interpreting measured
line intensities and line profiles emitted by the optically thin solar
corona is complicated by line-of-sight (LOS) integration, which leads to
measuring weighted averages of the plasma properties along the LOS. LOS
integration effects can be removed by combining CHIANTI spectral
emissivities with a 3D global model of the solar corona to calculate
the contribution of all structures along the LOS to the measured
intensities. In this paper, we describe SPECTRUM, a postprocessing tool
that can calculate the emission from the optically thin solar corona
by combining 3D magnetohydrodynamic (MHD) space plasma simulation
results with the CHIANTI database. Doppler-shifted, nonthermal line
broadening due to low-frequency Alfvén waves and anisotropic proton
and isotropic electron temperatures can be individually taken into
account during calculations. Synthetic spectral calculations can then
be used for model validation, for interpretation of solar observations,
and for forward modeling purposes. SPECTRUM is implemented within the
Space Weather Modeling Framework (SWMF) and is therefore publicly
available. In this paper, we describe the SPECTRUM module and show
its applications by comparing synthetic spectra using simulation data
by the 3D MHD Alfvén Wave Solar Model with observations done by the
Hinode/Extreme-ultraviolet Imaging Spectrometer during Carrington
rotations 2063 and 2082.
Title: COSMO Science
Authors: Gibson, Sarah; Tomczyk, Steven; Burkepile, Joan; Casini,
Roberto; Deluca, Ed; de Toma, Giuliana; deWijn, Alfred; Fan, Yuhong;
Golub, Leon; Judge, Philip; Landi, Enrico; Lin, Haosheng; McIntosh,
Scott; Reeves, Kathy; Seaton, Dan; Zhang, Jie
Bibcode: 2019shin.confE..32G
Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
Title: Predicted intensities formed by a simulated coronal mass
ejection (CME) using a non-equilibrium ionization model
Authors: Rivera, Yeimy Johanna; Landi, Enrico; Lepri, Susan
Bibcode: 2019shin.confE..67R
Altcode:
Prominences, as referred to while appearing on the Sun’s limb, and
filaments, on the solar disk, are typically observed in H? and 304Å at
the Sun. However, once they are released into the interplanetary medium
via coronal mass ejections (CMEs), the plasma may experience heating
which can significantly ionize the plasma causing it to radiate at
higher temperatures. Therefore, in order to capture the rapid evolution
of the prominence and adjacent structures that form the CME, we need
to identify new spectral lines that may become bright as a result
of the heating. Determining CME evolution near the Sun is important
to quantify the injection of energy to the system which can provide
insight to the heating mechanism. In this work, we investigate potential
spectral lines that can be used for diagnostics of the thermodynamic
evolution of CME plasma to study the eruption process. We generate
synthetic intensities formed by four plasma components evolving within
a previously studied CME to test spectral lines spanning the Extreme
Ultraviolet to Infrared, 100-50000Å, with a range of temperatures
between Log Te [K] = 4.3-6.7. Intensities are generated as a function of
distance out to 2Rs. We find that many of the lines will be observable
with future instruments; ground-based telescopes, DKIST and UCoMP,
and space-based spectrograph SPICE on Solar Orbiter, which together,
can capture the multi-thermal CME evolution.
Title: Nonequilibrium ionization effects on coronal plasma diagnostics
and elemental abundance measurements
Authors: Shi, Tong; Landi, Enrico; Manchester, Ward
Bibcode: 2019shin.confE..71S
Altcode:
Plasma diagnostics and elemental abundance measurements are crucial to
help us understand the formation and dynamics of the solar wind. It
is commonly assumed that the solar wind is in equilibrium ionization
(EI). Here we use a theoretical solar wind model to study whether the
non-equilibrium ionization (NEI) has any effect on the fast solar
wind. We find that the measured plasma density and temperature are
only slightly affected, but NEI systematically shifts the differential
emission measure (DEM) towards lower temperature on all heights. In
addition, NEI significantly affects the first ionization potential
(FIP) bias and abundance measurements. The EI assumption can lead
up to a factor of 4 error at 1.5 solar radii for Mg/Ne, Fe/S, and
Ar/Fe line pairs. Therefore, it is very important to consider the NEI
effect when doing the DEM diagnostics and measuring the FIP bias and
elemental abundance.
Title: CHIANTI—An Atomic Database for Emission Lines. XV. Version 9,
Improvements for the X-Ray Satellite Lines
Authors: Dere, K. P.; Del Zanna, G.; Young, P. R.; Landi, E.;
Sutherland, R. S.
Bibcode: 2019ApJS..241...22D
Altcode: 2019arXiv190205019D
CHIANTI contains a large quantity of atomic data for the analysis
of astrophysical spectra. Programs are available in IDL and
Python to perform calculation of the expected emergent spectrum
from these sources. The database includes atomic energy levels,
wavelengths, radiative transition probabilities, rate coefficients
for collisional excitation, ionization, and recombination, as well
as data to calculate free-free, free-bound, and two-photon continuum
emission. In Version 9, we improve the modeling of the satellite
lines at X-ray wavelengths by explicitly including autoionization
and dielectronic recombination processes in the calculation of level
populations for select members of the lithium isoelectronic sequence
and Fe XVIII-XXIII. In addition, existing data sets are updated,
new ions are added, and new total recombination rates for several Fe
ions are included. All data and IDL programs are freely available at http://www.chiantidatabase.org
or through SolarSoft, and the Python code
ChiantiPy is also freely available at https://github.com/chianti-atomic/ChiantiPy.
Title: Empirical Modeling of CME Evolution Constrained to ACE/SWICS
Charge State Distributions
Authors: Rivera, Yeimy J.; Landi, Enrico; Lepri, Susan T.; Gilbert,
Jason A.
Bibcode: 2019ApJ...874..164R
Altcode:
It is generally accepted that coronal mass ejections (CMEs) undergo
rapid heating as they are released from the Sun. However, to date,
the heating mechanism remains an open question. To gain insight into
the plasma heating, we derive the density, temperature, and velocity
evolution of the 2005 January 9 interplanetary CME event from launch
to ion freeze-in distance by examining ion distributions collected
within the ejecta near the Earth. We use the Michigan Ionization Code
to simulate the ion evolution and determine thermodynamic properties
through an extensive iterative search that finds agreement between
simulated and observed ion populations. The final results show that the
ion distributions can be effectively reconstructed using a combination
of ions generated within four distinct plasma structures traveling
together. Three of the modeled plasma components derived originate
from the prominence and the prominence-corona transition region (PCTR)
structures, while a fourth plasma shares features common to the ambient
corona. The absolute abundances computed for each plasma reveal that
the prominence material contains photospheric composition, while the
remaining PCTR and warmer plasma have coronal abundances. Furthermore,
we computed an energy release rate for each plasma structure that
includes the kinetic, potential, and thermal energy rates, along
with the radiative cooling, thermal conduction, and adiabatic cooling
rates. We found the prominence material’s energy release rate to be
consistently larger compared to the other components. In future work,
the energy results will be used to investigate the feasibility of a
proposed heating mechanism in an effort to gain a more comprehensive
understanding of the eruption process.
Title: Investigating properties of Coronal Mass Ejections (CMEs)
near the Sun using in-situ charge state distributions
Authors: Rivera, Yeimy; Landi, Enrico; Lepri, Susan T.; Gilbert, Jason
Bibcode: 2019EGUGA..21..172R
Altcode:
Coronal Mass Ejections (CMEs) are highly energetic eruptions that
release massive amounts of solar material into the interplanetary
medium. Previous work has shown CMEs undergo rapid heating as they are
released from the Sun, however the energy mechanism remains an open
question. To investigate the heating we have determined the thermal
history of CME plasma from in-situ composition observations collected
within the ejecta near the Earth. The ion distributions, unlike density
or temperature, remain unaltered early along its propagation. This
occurs as the expanding plasma reaches an altitude where the ionization
and recombination processes stop as the collisional frequency rapidly
decreases rendering the ionization level fixed. As a result, the
ion distributions retain information of their thermodynamics history
from below the freeze-in distance providing a method of probing plasma
properties near the Sun. We investigate a specific ICME event by using
the Michigan Ionization Code (MIC) that simulates the evolution of these
ions. We constrain the ejecta's thermodynamic history to match observed
ion distributions of Carbon, Oxygen and Iron from the January 9th 2005
Interplanetary CME (ICME) measured by ACE/SWICS. Final results show that
the ion distributions can be reconstructed using a combination of ions
generated from four plasma structures traveling together. The derived
plasma components resemble the main prominence core and surrounding
prominence coronal transition region (PCTR) plasma, as well as a warmer
structure possibly originating from the surrounding ambient corona. The
electron density, temperature and velocity derived from our modeling
results are used to compute energetics. We found that the energy
deposited to the prominence plasma is consistently higher compared
to all other components. In future work, we plan use our results to
constrain the necessary plasma heating and evolution timescales for
proposed heating mechanisms to assess their potential viability.
Title: Testing Models of the Fast Solar Wind using Spectroscopic
and In Situ Observations
Authors: Fludra, Andrzej; Landi, Enrico
Bibcode: 2018IAUS..335...87F
Altcode:
We present a new technique to study joint observations of EUV spectral
line intensities and in situ charge states of the fast solar wind. We
solve the time-dependent equation for ionization and recombination
for a chosen element and calculate the charge state evolution along
the open magnetic fields for elements such as C, O, Ne, Mg, Si and
Fe. Comparing predicted spectral lines intensities above the limb and in
situ charge states to observations from SOHO/SUMER and Ulysses/SWICS,
we test how well the modelled thermodynamic parameters of the solar
wind reproduce observations. We outline the application of this method
to Solar Orbiter data.
Title: Estudio del balance de energía en la corona solar con tres
y cuatro bandas de SDO/AIA
Authors: Mac Cormack, C.; Nuevo, F. A.; Vásquez, A. M.; López
Fuentes, M.; Frazin, R. A.; Landi, E.
Bibcode: 2018BAAA...60..204M
Altcode:
A semi-empirical technique was developed to estimate the energy flux
input required at the coronal base of magnetic loops in the quiet
corona so that they are thermodynamically stable. This technique
combines three-dimensional reconstructions of electronic density
and temperature, based on differential emission measure tomography
(DEMT), with potential extrapolations of the magnetic field measured
in the photosphere. This technique was applied using three EUV bands
with thermal sensitivities in the range of characteristic coronal
temperatures, from to 2 MK. We expand the observed temperature range
using a fourth band, whose range of sensitivity reaches MK.
Title: The Coronal Solar Magnetism Observatory
Authors: Thompson, Michael J.; Tomczyk, Steven; Gibson, Sarah E.;
McIntosh, Scott W.; Landi, Enrico
Bibcode: 2018IAUS..335..359T
Altcode:
The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new
facility led by the High Altitude Observatory and a consortium of
partners to measure magnetic field and plasma properties in a large
(one degree) field of view extending down to the inner parts of the
solar corona. CoSMO is intended as a research facility that will
advance the understanding and prediction of space weather. The
instrumentation elements of CoSMO are: a white-light coronagraph
(KCor), already operational at the Mauna Loa Solar Observatory
(MLSO); the Chromosphere and Prominence Magnetometer (ChroMag), due
for deployment to MLSO next year; and the CoSMO Large Coronagraph (LC)
which has completed Preliminary Design Review.
Title: First Empirical Determination of the Fe 10+ and Fe 13+
Freeze-in Distances in the Solar Corona
Authors: Boe, Benjamin Reid; Habbal, Shadia; Druckmuller, Miloslav;
Landi, Enrico; Kourkchi, Ehsan; Ding, Adalbert; Starha, Pavel;
Hutton, Joseph
Bibcode: 2018shin.confE..36B
Altcode: 2018arXiv180503211B
Heavy ions are markers of the physical processes throughout the fine
scale magnetic structures that define the shape of the solar corona. One
property of the heavy ions, whose value has yet to be empirically
determined in the corona, is the 'freeze-in' distance (Rf) where
they reach fixed ionization states that are adhered to during their
expansion with the solar wind into interplanetary space. We present
the first empirical inference of Rf for Fe10+ and Fe13+ derived from
multi-wavelength imaging observations of the corresponding Fe XI (Fe10+)
789.2 nm and Fe XIV (Fe13+) 530.3 nm emission acquired during the 2015
March 20 total solar eclipse. We find that the two ions freeze-in at
variable distances, even within the same coronal structures. In polar
coronal holes Rf is around 1.45 Rs for Fe10+ and below 1.25 Rs for Fe
13+. Along open field lines in streamer regions Rf ranges from 1.4 to
2 Rs for Fe10+ and from 1.5 to 2.2 Rs for Fe13+. These first empirical
Rf values: (1) reflect the differing plasma parameters between coronal
holes and streamers and structures within them, including prominences
and Coronal Mass Ejections (CMEs); (2) are well below the currently
quoted values derived from empirical model studies; and (3) place doubt
on the reliability of plasma diagnostics based on the assumption of
ionization equilibrium beyond 1.2 Rs.
Title: Empirical modeling of a CME constrained to ion distributions
detected by ACE/SWICS
Authors: Rivera, Yeimy Johanna; Landi, Enrico; Lepri, Susan; Gilbert,
Jason
Bibcode: 2018shin.confE.198R
Altcode:
Coronal Mass Ejections (CMEs) are large scale eruptions that propel
massive amounts of solar material into the interplanetary medium. It is
generally accepted that CMEs undergo heating as they are released from
the Sun, however, the mechanism itself remains largely unknown. This
work aims to quantify the heating of a CME event, to compare with
proposed heating sources, using in-situ ions as tracers to the
thermal history of the plasma. The ions are a powerful diagnostic
due to the frozen-in process which renders the ionization level
of the expanding plasma fixed as it reaches an altitude where the
ionization and recombination processes stop due to a rapid decrease in
density. The frozen-in ions detected near the Earth retain information
of the local thermodynamic environment at their freeze-in altitude,
providing a manner of probing plasma properties near the Sun. Using
the Michigan Ionization Code (MIC), we empirically determined the
thermodynamic evolution of Earth bound ejecta constrained to in-situ
ion distributions from Carbon, Oxygen and Iron of the January 9th 2005
Interplanetary CME (ICME) detected by ACE/SWICS. Final results show
that the distributions are made up of four distinct plasma structures
that resemble plasma originating from the main prominence core and
surrounding prominence coronal transition region (PCTR) of the CME,
as well as, a warmer plasma structure possibly originating from the
nearby corona. The electron density, temperature and velocity derived
from our modeling results are used to compute a heating rate that we
compare to the energy deposition from wave heating computed using a
magnetohydrodynamic (MHD) CME simulation.
Title: EUV Diagnostics of Optically Thick Plasmas using the 304
Å channel
Authors: Kocher, Manan; Landi, Enrico; Lepri, Susan T.
Bibcode: 2018shin.confE.124K
Altcode:
A fundamental limitation of current EUV diagnostic techniques is
the need to neglect the He II emission contribution in the 304 Å
channel. This limits our ability to use strong observations available
to us and increases uncertainties in the measurements made. A new
EUV diagnostic technique is introduced that accounts for absorption
as well as emission contributions from emitting channels such as
304 Å. This new technique can be equally applied to emitting and
non-emitting channels, paving the way for more realistic discussion of
the heating and energetics of transient plasmas using a wider range of
observations. The diagnostic technique is used to compute the dynamics
and energetics of a filament eruption observed in the high-cadence
SDO/AIA and the associated ICME is observed by ACE/SWICS. The analysis
gives us robust measurements of filament dynamics, energetics and
its ionization history in the low solar corona. A comparison of these
results with results calculated with techniques where He II emission
in 304 Å is not considered allowed us to quantify the contribution
from emission and comment on the robustness of our method.
Title: Bright Network, UVA, and the Physical Modeling of Solar
Spectral and Total Irradiance in Recent Solar Cycles
Authors: Fontenla, J. M.; Landi, E.
Bibcode: 2018ApJ...861..120F
Altcode:
In this paper we study the total solar irradiance (TSI) and the spectral
solar irradiance (SSI) by applying the solar disk image decomposition
algorithm (SDIDA) and solar irradiance synthesis algorithm (SISA)
methods. These methods were applied to space-based observations in
previous works, but in this work, they are applied to ground-based
observations from various observatories, which allows for a long-term
determination of TSI and SSI. We discuss the results of the SDIDA
and SISA methods for the areas of solar features and the synthesized
TSI and SSI. We find that SDIDA decompositions based on Ca II K line
images from various sources are all in good agreement between them
and with previous space results when cross-calibration is performed,
and consequently yield essentially the same TSI and SSI when SISA
is applied. This paper shows the synthesized TSI and SSI, as well
as the contributions from various feature types, during the recent
solar cycles 23 and 24 and suggest further work can provide historical
extended coverage using archival ground-based observations. The results
demonstrate the presence of a significant variable bright network
contribution during the cycle maximum, and of a reduced one at solar
minimum, and that such a presence and variability affect both the SSI
and TSI. We also find that all activity features are loosely correlated
over solar cycle variations, but this correlation is nonlinear, and we
show differences between cycles 23 and 24. Furthermore, we find that
the SISA method can be successfully applied to determine the TSI and SSI
for any particular state of the solar disk, and that the results depend
not only on the total areas on the disk for each feature, but also on
the relative distances from disk center of the active region features.
Title: A Survey of Singly Charged Ions within ICMEs
Authors: Gilbert, Jason Andre; Landi, Enrico; Lepri, Susan T.
Bibcode: 2018shin.confE.205G
Altcode:
Interplanetary coronal mass ejections (ICMEs) observed near Earth
sometimes contain remnants of the cold, low charge state filament
material present at their eruptions. To determine the prevalence of
this material within ICMEs, a survey was conducted using ACE/SWICS
data from 1998-2011 on the ions C+ and O+. Events were catalogued
based on various criteria, and were compared to a standard list of
ICMEs. The results are presented here, along with discussion regarding
the implications for formation and evolution of the filamentary material
through the heliosphere.
Title: Temperature Anisotropy in Synthetic Spectroscopic Observations
Authors: Szente, Judit; Landi, Enrico; van der Holst, Bart
Bibcode: 2018shin.confE.253S
Altcode:
The Alfvén Wave Solar Atmosphere Model (AWSoM), a module within the
Space Weather Modeling Framework (SWMF), simulates the entire solar
corona in 3D, providing the user with the option of carrying out the
calculations assuming either a single plasma temperature, or separate
electron and proton (isotropic) temperatures, or separate electron
and anisotropic proton temperature (a 3-temperature model). SPECTRUM
is a post-processing tool within SWMF, which performs a full
synthetic spectral calculation at any wavelength range, with any
user-defined spectral resolution. In this work, we investigate the
effects of different choices of temperatures (single, 2-temperature,
3-temperature), on the predicted synthetic spectra. The comparison of
results will indicate possible diagnostics of temperature anisotropies,
which can be observed by solar coronal spectra observed by Hinode/EIS,
SoHO/CDS and SUMER, as well as the upcoming SPICE spectrometer on
board Solar Orbiter.
Title: The First Empirical Determination of the Fe10+
and Fe13+ Freeze-in Distances in the Solar Corona
Authors: Boe, Benjamin; Habbal, Shadia; Druckmüller, Miloslav; Landi,
Enrico; Kourkchi, Ehsan; Ding, Adalbert; Starha, Pavel; Hutton, Joseph
Bibcode: 2018ApJ...859..155B
Altcode:
Heavy ions are markers of the physical processes responsible
for the density and temperature distribution throughout the
fine-scale magnetic structures that define the shape of the solar
corona. One of their properties, whose empirical determination
has remained elusive, is the “freeze-in” distance (R
f ) where they reach fixed ionization states that are
adhered to during their expansion with the solar wind. We
present the first empirical inference of R f for
{Fe}}{10+} and {Fe}}{13+}
derived from multi-wavelength imaging observations of the
corresponding Fe XI ({Fe}}{10+}) 789.2 nm and
Fe XIV ({Fe}}{13+}) 530.3 nm emission acquired
during the 2015 March 20 total solar eclipse. We find that the two
ions freeze-in at different heliocentric distances. In polar coronal
holes (CHs) R f is around 1.45 R ⊙ for
{Fe}}{10+} and below 1.25 R ⊙ for
{Fe}}{13+}. Along open field lines in streamer
regions, R f ranges from 1.4 to 2 R ⊙ for
{Fe}}{10+} and from 1.5 to 2.2 R ⊙
for {Fe}}{13+}. These first empirical R
f values: (1) reflect the differing plasma parameters between
CHs and streamers and structures within them, including prominences
and coronal mass ejections; (2) are well below the currently quoted
values derived from empirical model studies; and (3) place doubt on the
reliability of plasma diagnostics based on the assumption of ionization
equilibrium beyond 1.2 R ⊙.
Title: Tracking Filament Evolution in the Low Solar Corona Using
Remote Sensing and In Situ Observations
Authors: Kocher, Manan; Landi, Enrico; Lepri, Susan. T.
Bibcode: 2018ApJ...860...51K
Altcode: 2017arXiv171204556K
In the present work, we analyze a filament eruption associated with
an interplanetary coronal mass ejection that arrived at L1 on 2011
August 5. In multiwavelength Solar Dynamic Observatory/Advanced Imaging
Assembly (AIA) images, three plasma parcels within the filament were
tracked at high cadence along the solar corona. A novel absorption
diagnostic technique was applied to the filament material traveling
along the three chosen trajectories to compute the column density
and temperature evolution in time. Kinematics of the filamentary
material were estimated using STEREO/Extreme Ultraviolet Imager and
STEREO/COR1 observations. The Michigan Ionization Code used inputs of
these density, temperature, and speed profiles for the computation of
ionization profiles of the filament plasma. Based on these measurements,
we conclude that the core plasma was in near ionization equilibrium,
and the ionization states were still evolving at the altitudes where
they were visible in absorption in AIA images. Additionally, we report
that the filament plasma was heterogeneous, and the filamentary material
was continuously heated as it expanded in the low solar corona.
Title: Plasma Properties of the Corona and Sources of the Solar Wind
as Derived from Total Solar Eclipse Observations
Authors: Habbal, Shadia R.; Druckmuller, Miloslav; Ding, Adalbert;
Starha, Pavel; Landi, Enrico; Arndt, Martina B.; Hoderova, Jana;
Johnson, Judd; Starha, Petr
Bibcode: 2018tess.conf32104H
Altcode:
Total solar eclipses provide unique observing opportunities for the
inference of the plasma properties of the corona and establishing
the sources of the solar wind, starting from the solar surface out
to several solar radii. Properties that are critical for exploring
coronal heating and plasma acceleration processes are the distribution
of the electron temperature in the corona, the ionic composition of
the corona, and the freeze-in distances of different ions in the
solar wind. These properties can be readily inferred from imaging
in coronal forbidden lines in the visible wavelength range. On the
other hand, broad band white light eclipse images, which at present
yield the highest resolution depiction of coronal structures, capture
the sources of the solar wind as well as the dynamics of the coronal
plasma. Examples drawn from our most recent eclipse observations in
broadband white light and narrowband imaging in coronal forbidden
lines will be presented. These observations underscore the urgency
for the next generation of space-based instrumentation to carry out
such measurements, to achieve significant progress in understanding
the coronal heating processes and for uncovering the different origins
of the solar wind.
Title: EUV Emission and Scattered Light Diagnostics of Equatorial
Coronal Holes as Seen by Hinode/EIS
Authors: Wendeln, Carolyn; Landi, Enrico
Bibcode: 2018ApJ...856...28W
Altcode: 2017arXiv171203042W
Spectroscopic diagnostics of solar coronal plasmas critically depends
on the uncertainty in the measured line intensities. One of the
main sources of uncertainty is instrumental scattered light, which
is potentially most important in low-brightness areas. In the solar
corona, such areas include polar and equatorial coronal holes, which
are the source regions of the solar wind; instrument-scattered light
must thus pose a significant obstacle to studies of the source regions
of the solar wind. In this paper, we investigate the importance of
instrument-scattered light on observations of equatorial coronal holes
made by the Hinode/EIS spectrometer in two different phases of the solar
cycle. We find that the instrument-scattered light is significant at
all temperatures, and in both regions it amounts to approximately 10%
of the average intensity of the neighboring quiet-Sun regions. Such
contribution dominates the measured intensity for spectral lines formed
at temperatures larger than Log T = 6.15 K, and has deep implications
for spectroscopic diagnostics of equatorial coronal hole plasmas and
studies of the source regions of a large portion of the solar wind that
reaches Earth. Our results suggest that the high-temperature tail in
the coronal hole plasma distribution with temperature, however small,
is an artifact due to the presence of scattered light.
Title: Magnetic field extrapolation with MHD relaxation using AWSoM
Authors: Shi, T.; Manchester, W.; Landi, E.
Bibcode: 2017AGUFMSH13A2458S
Altcode:
Coronal mass ejections are known to be the major source of disturbances
in the solar wind capable of affecting geomagnetic environments. In
order for accurate predictions of such space weather events,
a data-driven simulation is needed. The first step towards such a
simulation is to extrapolate the magnetic field from the observed field
that is only at the solar surface. Here we present results of a new
code of magnetic field extrapolation with direct magnetohydrodynamics
(MHD) relaxation using the Alfvén Wave Solar Model (AWSoM) in the Space
Weather Modeling Framework. The obtained field is self-consistent with
our model and can be used later in time-dependent simulations without
modifications of the equations. We use the Low and Lou analytical
solution to test our results and they reach a good agreement. We also
extrapolate the magnetic field from the observed data. We then specify
the active region corona field with this extrapolation result in the
AWSoM model and self-consistently calculate the temperature of the
active region loops with Alfvén wave dissipation. Multi-wavelength
images are also synthesized.
Title: Empirical Modeling of ICMEs Using ACE/SWICS Ionic Distributions
Authors: Rivera, Y.; Landi, E.; Lepri, S. T.; Gilbert, J. A.
Bibcode: 2017AGUFMSH11B2439R
Altcode:
Coronal Mass Ejections (CMEs) are some of the largest, most energetic
events in the solar system releasing an immense amount of plasma and
magnetic field into the Heliosphere. The Earth-bound plasma plays a
large role in space weather, causing geomagnetic storms that can damage
space and ground based instrumentation. As a CME is released, the plasma
experiences heating, expansion and acceleration; however, the physical
mechanism supplying the heating as it lifts out of the corona still
remains uncertain. From previous work we know the ionic composition of
solar ejecta undergoes a gradual transition to a state where ionization
and recombination processes become ineffective rendering the ionic
composition static along its trajectory. This property makes them
a good indicator of thermal conditions in the corona, where the CME
plasma likely receives most of its heating. We model this so-called
`freeze-in' process in Earth-directed CMEs using an ionization code
to empirically determine the electron temperature, density and bulk
velocity. `Frozen-in' ions from an ensemble of independently modeled
plasmas within the CME are added together to fit the full range of
observational ionic abundances collected by ACE/SWICS during ICME
events. The models derived using this method are used to estimate the
CME energy budget to determine a heating rate used to compare with a
variety of heating mechanisms that can sustain the required heating
with a compatible timescale.
Title: A Spectroscopic Study of the Energy Deposition in the Low
Corona: Connecting Global Modeling to Observations
Authors: Szente, J.; Landi, E.; Toth, G.; Manchester, W.; van der
Holst, B.; Gombosi, T. I.
Bibcode: 2017AGUFMSH41C..06S
Altcode:
We are looking for signatures of coronal heating process using a
physically consistent 3D MHD model of the global corona. Our approach is
based on the Alfvén Wave Solar atmosphere Model (AWSoM), with a domain
ranging from the upper chromosphere (50,000K) to the outer corona,
and the solar wind is self-consistently heated and accelerated by the
dissipation of low-frequency Alfvén waves. Taking into account separate
electron and anisotropic proton heating, we model the coronal plasma
at the same time and location as observed by Hinode/EIS, and calculate
the synthetic spectra that we compare with the observations. With
the obtained synthetic spectra, we are able to directly calculate
line intensities, line width, thermal and nonthermal motions, line
centroids, Doppler shift distributions and compare our predictions
to real measurements. Our results directly test the extent to which
Alfvénic heating is present in the low corona.
Title: Tomographic Validation of the AWSoM Model of the Inner Corona
During Solar Minima
Authors: Manchester, W.; Vásquez, A. M.; Lloveras, D. G.; Mac Cormack,
C.; Nuevo, F.; Lopez-Fuentes, M.; Frazin, R. A.; van der Holst, B.;
Landi, E.; Gombosi, T. I.
Bibcode: 2017AGUFMSH51C2512M
Altcode:
Continuous improvement of MHD three-dimensional (3D) models of the
global solar corona, such as the Alfven Wave Solar Model (AWSoM) of
the Space Weather Modeling Framework (SWMF), requires testing their
ability to reproduce observational constraints at a global scale. To
that end, solar rotational tomography based on EUV image time-series
can be used to reconstruct the 3D distribution of the electron density
and temperature in the inner solar corona (r < 1.25 Rsun). The
tomographic results, combined with a global coronal magnetic model, can
further provide constraints on the energy input flux required at the
coronal base to maintain stable structures. In this work, tomographic
reconstructions are used to validate steady-state 3D MHD simulations
of the inner corona using the latest version of the AWSoM model. We
perform the study for selected rotations representative of solar
minimum conditions, when the global structure of the corona is more
axisymmetric. We analyse in particular the ability of the MHD simulation
to match the tomographic results across the boundary region between the
equatorial streamer belt and the surrounding coronal holes. The region
is of particular interest as the plasma flow from that zone is thought
to be related to the origin of the slow component of the solar wind.
Title: Tracking Energetics of a CME Core in the Low Solar Corona
Authors: Kocher, M.; Landi, E.; Lepri, S. T.
Bibcode: 2017AGUFMSH53A2538K
Altcode:
In order to understand the processes that generate CMEs, and develop
the ability to predict their evolution and geoeffectiveness, it is
very important to determine how the plasma properties within coronal
mass ejections (CME) evolve through their journey from the low
corona through the solar environment. This study uses a combination
of remote-sensing and in-situ observations of a filament eruption
(that later formed the core of the CME) that left the Sun on August
4th, 2011 - shortly after an M-class flare. Separate absorption and
emission diagnostic techniques are utilized to compute time-evolution
estimates of the density and temperature of multiple plasma parcels
within the filament using SDO/AIA EUV images. Twin STEREO spacecraft
observations are used to estimate the height, speed, and acceleration
of the CME at corresponding times. These observation-based densities,
temperatures, and speeds allowed us to use the Michigan Ionization
Code to compute the ionization history of this CME in the low solar
corona. Along with the thermal and kinetic properties of this CME,
we present a comparison with existing CME evolution models and draw
inferences on its heating and acceleration.
Title: The Sun Radio Imaging Space Experiment (SunRISE) Mission
Authors: Kasper, J. C.; Lazio, J.; Alibay, F.; Amiri, N.; Bastian,
T.; Cohen, C.; Landi, E.; Hegedus, A. M.; Maksimovic, M.; Manchester,
W.; Reinard, A.; Schwadron, N.; Cecconi, B.; Hallinan, G.; Krupar, V.
Bibcode: 2017AGUFMSH41B2760K
Altcode:
Radio emission from coronal mass ejections (CMEs) is a direct tracer
of particle acceleration in the inner heliosphere and potential
magnetic connections from the lower solar corona to the larger
heliosphere. Energized electrons excite Langmuir waves, which then
convert into intense radio emission at the local plasma frequency,
with the most intense acceleration thought to occur within 20 R_S. The
radio emission from CMEs is quite strong such that only a relatively
small number of antennas is required to detect and map it, but many
aspects of this particle acceleration and transport remain poorly
constrained. Ground-based arrays would be quite capable of tracking
the radio emission associated with CMEs, but absorption by the Earth's
ionosphere limits the frequency coverage of ground-based arrays (nu >
15 MHz), which in turn limits the range of solar distances over which
they can track the radio emission (< 3 R_S). The state-of-the-art
for tracking such emission from space is defined by single antennas
(Wind/WAVES, Stereo/SWAVES), in which the tracking is accomplished by
assuming a frequency-to-density mapping; there has been some success
in triangulating the emission between the spacecraft, but considerable
uncertainties remain. We describe the Sun Radio Imaging Space Experiment
(SunRISE) mission concept: A constellation of small spacecraft in a
geostationary graveyard orbit designed to localize and track radio
emissions in the inner heliosphere. Each spacecraft would carry a
receiving system for observations below 25 MHz, and SunRISE would
produce the first images of CMEs more than a few solar radii from
the Sun. Part of this research was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under a contract with
the National Aeronautics and Space Administration.
Title: Detecting Spectroscopic Signatures of Magnetic Reconnection
Along the Boundary of Coronal Holes
Authors: Wendeln, C. N.; Landi, E.
Bibcode: 2017AGUFMSH11B2435W
Altcode:
Magnetic reconnection is an essential release mechanism of energy
proposed for the highly variable solar wind and plays a direct role
in leading to many astrophysical phenomena such as space weather
events. Reconnection between open and closed magnetic field lines
(i.e. along the boundary of coronal holes) releases coronal loop
plasma into the heliosphere as the reconfiguration of the magnetic
field accelerates plasma along two reconnection beams. In this
investigation we will look for spectral signatures of reconnection
occurring along the edges of coronal holes using observations from the
EUV Imaging Spectrometer (EIS) onboard Hinode. We will use a novel
direct observational method, which we have developed, for detecting
magnetic reconnection in the solar atmosphere. Furthermore we will
provide a constraint on the energetics at which reconnection occurs. Our
preliminary results indicates the presence of spectral lines due to
a magnetic reconnection event. Moreover, our preliminary diagnostics
indicates that the amount of stray light contamination for the EIS
instrument is greater than previously measured.
Title: Comparison between two models of energy balance in coronal
loops
Authors: Mac Cormack, C.; López Fuentes, M.; Vásquez, A. M.; Nuevo,
F. A.; Frazin, R. A.; Landi, E.
Bibcode: 2017BAAA...59..142M
Altcode:
In this work we compare two models to analyze the energy balance along
coronal magnetic loops. For the first stationary model we deduce an
expression of the energy balance along the loops expressed in terms
of quantities provided by the combination of differential emission
measure tomography (DEMT) applied to EUV images time series and
potential extrapolations of the coronal magnetic field. The second
applied model is a 0D hydrodynamic model that provides the evolution of
the average properties of the coronal plasma along the loops, using as
input parameters the loop length and the heating rate obtained with the
first model. We compare the models for two Carrington rotations (CR)
corresponding to different periods of activity: CR 2081, corresponding
to a period of minimum activity observed with the Extreme Ultraviolet
Imager (EUVI) on board of the Solar Terrestrial Relations Observatory
(STEREO), and CR 2099, corresponding to a period of activity increase
observed with the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO). The results of the models are consistent
for both rotations.
Title: On the Relation between the In Situ Properties and the Coronal
Sources of the Solar Wind
Authors: Zhao, L.; Landi, E.; Lepri, S. T.; Gilbert, J. A.; Zurbuchen,
T. H.; Fisk, L. A.; Raines, J. M.
Bibcode: 2017ApJ...846..135Z
Altcode:
We categorize the types of solar wind using a new classification scheme
based on the location of the wind’s coronal source regions in the
solar atmosphere and near-solar heliosphere. We first trace the solar
wind measured by ACE/SWEPAM and SWICS from 1998 to 2011 at 1 au back
to a 2.5{R}{{s}} solar surface using ballistic mapping
at constant proton speed; then we map them back to their magnetic
footpoints on the 1{R}{{s}} solar surface via the potential
field source surface (PFSS) model. Coronal structures are identified
using a classification scheme based on the pixel brightness in the
SOHO or STEREO EUV Carrington images. The angular distances between
each mapped solar wind footpoint to the different coronal structure
pixels are calculated and used as a criterion to identify the type of
solar wind source region. Depending on the proximity of the solar wind
footpoints to a given coronal or heliospheric structure, we classify the
solar wind into six types: active region (AR), AR-boundary, quiet Sun
(QS), coronal hole (CH), CH-boundary, and helmet-streamer associated
wind. The in situ properties of these six types of solar winds are
then examined and compared, and their solar cycle dependences are
also discussed.
Title: Alfvén Wave Turbulence as a Coronal Heating Mechanism:
Simultaneously Predicting the Heating Rate and the Wave-induced
Emission Line Broadening
Authors: Oran, R.; Landi, E.; van der Holst, B.; Sokolov, I. V.;
Gombosi, T. I.
Bibcode: 2017ApJ...845...98O
Altcode:
We test the predictions of the Alfvén Wave Solar Model (AWSoM),
a global wave-driven magnetohydrodynamic (MHD) model of the solar
atmosphere, against high-resolution spectra emitted by the quiescent
off-disk solar corona. AWSoM incorporates Alfvén wave propagation and
dissipation in both closed and open magnetic field lines; turbulent
dissipation is the only heating mechanism. We examine whether this
mechanism is consistent with observations of coronal EUV emission by
combining model results with the CHIANTI atomic database to create
synthetic line-of-sight spectra, where spectral line widths depend
on thermal and wave-related ion motions. This is the first time
wave-induced line broadening is calculated from a global model with a
realistic magnetic field. We used high-resolution SUMER observations
above the solar west limb between 1.04 and 1.34 R ⊙ at
the equator, taken in 1996 November. We obtained an AWSoM steady-state
solution for the corresponding period using a synoptic magnetogram. The
3D solution revealed a pseudo-streamer structure transversing the
SUMER line of sight, which contributes significantly to the emission;
the modeled electron temperature and density in the pseudo-streamer
are consistent with those observed. The synthetic line widths and
the total line fluxes are consistent with the observations for five
different ions. Further, line widths that include the contribution from
the wave-induced ion motions improve the correspondence with observed
spectra for all ions. We conclude that the turbulent dissipation assumed
in the AWSoM model is a viable candidate for explaining coronal heating,
as it is consistent with several independent measured quantities.
Title: Determining CME Evolution Near the Sun by Modeling the Charge
State Distribution of CME plasmas
Authors: Rivera, Yeimy; Landi, Enrico; Lepri, Susan; Gilbert, Jason
Bibcode: 2017shin.confE..21R
Altcode:
Coronal Mass Ejections (CMEs) are some of the largest, most energetic
events in the solar system expelling a significant amount of charged
particles and magnetic field into the Heliosphere. Earth-bound
plasma can trigger geomagnetic storms causing damage to satellites,
disrupting communication signals and navigation systems. As a CME
launches through the interplanetary medium it undergoes heating,
expansion and acceleration. How the plasma is heated as it lifts out
of the corona is significant to its evolution and geoeffectiveness,
and yet is still not well understood. Previous work has shown that
the ions in the plasma 'freeze-in' to their final charge state at
distances within a few solar radii from the Sun, and stay unaltered
until they reach Earth. This property makes them a good indicator of
thermal conditions in the corona, where the CME plasma likely receives
most of its heating. We model the evolution of the ionization states of
Carbon, Oxygen, Magnesium and Iron in an Earth-directed CME to derive
empirical models of the plasma heating and evolution. We focus on the
event on January 9th 2005 using the ionic abundances collected with
the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced
Composition Explorer (ACE) spacecraft. We empirically determine the
electron temperature, density and bulk velocity of plasma along its
trajectory by iteratively adjusting ion abundances predicted by a plasma
ionization code to match the observed charge state distributions. In
future work, the models developed from this research will be used to
estimate many components of the energy budget to gain insight on the
heating near the Sun.
Title: Detecting Spectroscopic Signatures of Magnetic Reconnection
Along the Boundary of Coronal Holes
Authors: Wendeln, Carolyn; Landi, Enrico
Bibcode: 2017shin.confE..41W
Altcode:
Magnetic reconnection is an essential release mechanism of energy
proposed for the highly variable solar wind and plays a direct role
in leading to many astrophysical phenomena such as space weather
events. Reconnection between open and closed magnetic field lines
(i.e. along the boundary of coronal holes) releases coronal loop
plasma into the heliosphere as the reconfiguration of the magnetic
field accelerates plasma along two reconnection beams. In this
investigation we will look for spectral signatures of reconnection
occurring along the edges of coronal holes using observations from the
EUV Imaging Spectrometer (EIS) onboard Hinode. We will use a novel
direct observational method, which we have developed, for detecting
magnetic reconnection in the solar atmosphere. Furthermore we will
provide a constraint on the energetics at which reconnection occurs. Our
preliminary results indicates the presence of spectral lines due to
a magnetic reconnection event. Moreover, our preliminary diagnostics
indicates that the amount of stray light contamination for the EIS
instrument is greater than previously measured.
Title: Energy Input Flux in the Global Quiet-Sun Corona
Authors: Mac Cormack, Cecilia; Vásquez, Alberto M.; López Fuentes,
Marcelo; Nuevo, Federico A.; Landi, Enrico; Frazin, Richard A.
Bibcode: 2017ApJ...843...70M
Altcode: 2017arXiv170600365M
We present first results of a novel technique that provides, for the
first time, constraints on the energy input flux at the coronal base
(r ∼ 1.025 R ⊙) of the quiet Sun at a global scale. By
combining differential emission measure tomography of EUV images,
with global models of the coronal magnetic field, we estimate the
energy input flux at the coronal base that is required to maintain
thermodynamically stable structures. The technique is described in
detail and first applied to data provided by the Extreme Ultraviolet
Imager instrument, on board the Solar TErrestrial RElations Observatory
mission, and the Atmospheric Imaging Assembly instrument, on board
the Solar Dynamics Observatory mission, for two solar rotations
with different levels of activity. Our analysis indicates that the
typical energy input flux at the coronal base of magnetic loops
in the quiet Sun is in the range ∼0.5-2.0 × 105 (erg
s-1 cm-2), depending on the structure size and
level of activity. A large fraction of this energy input, or even its
totality, could be accounted for by Alfvén waves, as shown by recent
independent observational estimates derived from determinations of
the non-thermal broadening of spectral lines in the coronal base of
quiet-Sun regions. This new tomography product will be useful for the
validation of coronal heating models in magnetohydrodinamic simulations
of the global corona.
Title: Spectral Analysis of Heating Processes in the Alfvén Wave
Driven Global Corona Model
Authors: Szente, Judit; Toth, Gabor; Landi, Enrico; Manchester, Ward;
van der Holst, Bart; Gombosi, Tamas
Bibcode: 2017shin.confE..78S
Altcode:
Among numerous theories explaining the existence of the hot solar
corona and continuous solar wind, one of the most successful one is
based on wave heating. This approach describes Alfvén waves traveling
along the magnetic field lines carrying sufficient energy to heat the
corona and accelerate the solar wind. The wave energy is deposited
through turbulent dissipation, which leaves identifiable traces in the
plasma. Spectral observations have suggested the existence of wave
heating: via the decrease of non-thermal spectral line broadening,
and via charge state ratios of specific minor-ions reflecting the
heating history of the solar wind plasma. We determine the extent
to which Alfvén-waves drive the solar corona using a combination of
spectral modeling and observational techniques. In this study,
we reevaluate observational evidence of the coronal heating process:
we simulate observations of the global corona and its spectral line
emission with the Alfvén Wave Solar Model (AWSoM) and compare the
synthetic data with observations.
Title: Numerical Modeling of the Lower Corona during the Total
Solar Eclipses
Authors: Mukhopadhyay, Agnit; Landi, Enrico; van der Holst, Bart
Bibcode: 2017shin.confE..50M
Altcode:
We perform and analyze the results of a global magnetohydrodynamic
(MHD) simulation of the lower solar corona and compare with
observations taken during the total solar eclipse that occurred on
2010 July 11 and 2008 August 1. Total eclipses serve as the primary
sources to study the lower corona, and the thermodynamics of the
eclipses of July 11 and August 1 was extensively studied by Habbal
et al (2011, 2010a, 2010b), which included an in-depth analysis
of multi-wavelength coronal observations. In this study, we use the
three dimensional Alfven Wave Solar Model (AWSoM), which addresses the
coronal heating and solar wind acceleration with low frequency Alfven
wave turbulence, to simulate solar wind properties, broadband white
light and multi-wavelength extreme ultraviolet images and compare
with the observations from SOHO/LASCO C2 coronagraph, STEREO/EUVI
and the Solar Dynamics Observatory/AIA instruments, in addition to
performing comparisons of 1 AU solar wind properties with observations
from STEREO A/B and the OMNIWeb dataset. We also simulate white light
images with an occultation of 1 radius of Sun resembling an eclipse
image, for comparison with white-light total eclipse images. We find
good agreement of the morphology of the lower corona with both white
light and EUV images. The model is sparsely able to capture the dynamic
structures observed during the eclipse.
Title: Tracking Properties of an Erupting Filament in the Low
Solar Corona
Authors: Kocher, Manan; Landi, Enrico; Lepri, Susan T.
Bibcode: 2017shin.confE..32K
Altcode:
In order to understand the processes that generate CMEs, and develop
the ability to predict their evolution and geoeffectiveness, it is very
important to determine how the plasma properties within coronal mass
ejections (CME) evolve through their journey from the low corona through
the solar environment. This study uses a combination of remote-sensing
and in-situ observations of a filament eruption (that later formed the
core of the CME) that left the Sun on August 4th, 2011 - shortly after
an M-class flare. We use the absorption diagnostic technique described
in Landi and Reale (2013) to compute time-evolution estimates of the
column density and temperature of multiple plasma parcels within the
filament using SDO/AIA EUV images. Twin STEREO spacecraft observations
are used to estimate the height, speed, and acceleration of the CME at
corresponding times. These observation-based densities, temperatures,
and speeds allowed us to use the Michigan Ionization Code to compute
the ionization history of this CME in the low solar corona. Along with
the thermal and kinetic properties of this CME, we present a comparison
with existing CME evolution models and draw inferences on its heating
and acceleration.
Title: Simulating the Initiation and Liftoff Phases of CMEs
Authors: Shi, Tong; Manchester, Ward; Landi, Enrico
Bibcode: 2017shin.confE..15S
Altcode:
Coronal mass ejections (CMEs) are known to be the major source of
disturbances in the solar wind capable of affecting geomagnetic
environments. However, we are currently lacking in key information
during the early stage of the CMEs, including the nature of the
triggering mechanisms, that we are unable to accurately predict CME
onset, initial propagation, and possible impact on the planetary
systems. Here we will present preliminary results on a data-driven
CME simulation with the Space Weather Modeling Framework. Performing
such a simulation involves several steps: extrapolating the coronal
magnetic field from active region vector magnetogram observations
with nonlinear force free field model; using this field as the initial
condition for a steady state simulation; and then driving the eruption
by applying converging motion at the polarity inversion line at the
lower boundary. This data-driven simulation will help us to support
or restrict the mechanisms that provide reliable magnetic, kinematics,
and thermal properties of a CME in its early stage, and is a required
first step towards an accurate space weather forecast.
Title: CME Plasma Dynamics Using In-situ and Remote-sensing
Observations
Authors: Kocher, Manan; Lepri, Susan; Landi, Enrico
Bibcode: 2017EGUGA..19.9608K
Altcode:
The thermal and kinetic energy of Coronal Mass Ejections [CMEs] can
be best reconstructed if the plasma density, temperature and dynamics
of each of their components are known. During periods of quadrature,
we use a combination of in-situ measurements from ACE/SWICS and
remote sensing observations from SDO/AIA and STEREO/EUVI to present
several case studies of geo-effective halo-CMEs. We carry out density
diagnostics and Differential Emission Measure [DEM] profile calculations
to reconstruct a 3D picture of the CME plasma for the selected cases
in the low solar corona. We then discuss these results in the context
of models of CME initiation and release.
Title: The Sun Radio Imaging Space Experiment (SunRISE) Mission
Authors: Lazio, Joseph; Kasper, Justin; Maksimovic, Milan; Alibay,
Farah; Amiri, Nikta; Bastian, Tim; Cohen, Christina; Landi, Enrico;
Manchester, Ward; Reinard, Alysha; Schwadron, Nathan; Cecconi,
Baptiste; Hallinan, Gregg; Hegedus, Alex; Krupar, Vratislav; Zaslavsky,
Arnaud
Bibcode: 2017EGUGA..19.5580L
Altcode:
Radio emission from coronal mass ejections (CMEs) is a direct tracer
of particle acceleration in the inner heliosphere and potential
magnetic connections from the lower solar corona to the larger
heliosphere. Energized electrons excite Langmuir waves, which then
convert into intense radio emission at the local plasma frequency,
with the most intense acceleration thought to occur within 20 RS. The
radio emission from CMEs is quite strong such that only a relatively
small number of antennas is required to detect and map it, but many
aspects of this particle acceleration and transport remain poorly
constrained. Ground-based arrays would be quite capable of tracking
the radio emission associated with CMEs, but absorption by the Earth's
ionosphere limits the frequency coverage of ground-based arrays (ν
≳ 15 MHz), which in turn limits the range of solar distances over
which they can track the radio emission (≲ 3RS). The state-of-the-art
for tracking such emission from space is defined by single antennas
(Wind/WAVES, Stereo/SWAVES), in which the tracking is accomplished by
assuming a frequency-to-density mapping; there has been some success
in triangulating the emission between the spacecraft, but considerable
uncertainties remain. We describe the Sun Radio Imaging Space Experiment
(SunRISE) mission concept: A constellation of small spacecraft in a
geostationary graveyard orbit designed to localize and track radio
emissions in the inner heliosphere. Each spacecraft would carry a
receiving system for observations below 25 MHz, and SunRISE would
produce the first images of CMEs more than a few solar radii from
the Sun. Part of this research was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under a contract with
the National Aeronautics and Space Administration.
Title: The Deflection of the Cartwheel CME: ForeCAT Results
Authors: Capannolo, Luisa; Opher, Merav; Kay, Christina; Landi, Enrico
Bibcode: 2017ApJ...839...37C
Altcode:
We analyze the Cartwheel coronal mass ejection's (CME; 2008 April 9)
trajectory in the low corona with the ForeCAT model. This complex event
presented a significant rotation in the low corona and a reversal
in its original latitude direction. We successfully reproduce the
observed CME’s trajectory (latitude and longitude deflection) and
speed. Through a {χ }2 test, we are able to constrain the
CME’s mass to (2.3-3.0) × 1014 g and the CME’s initial
shape. We are able to constrain the expansion of the CME as well: the
angular width linearly increases until 2.1 {R}⊙ , and is
constant afterward. In order to match the observed latitude, we include
a non-radial initial speed of -42 km s-1. Despite allowing
the CME to rotate in the model, the magnetic forces of the solar
background are not able to reproduce the observed rotation. We suggest
that the complex reversal in latitude and the significant rotation of
the Cartwheel CME can be justified with an asymmetrical reconnection
event that ejected the CME non-radially and also initiated its rotation.
Title: Coronal Jets Simulated with the Global Alfvén Wave Solar Model
Authors: Szente, J.; Toth, G.; Manchester, W. B., IV; van der Holst,
B.; Landi, E.; Gombosi, T. I.; DeVore, C. R.; Antiochos, S. K.
Bibcode: 2017ApJ...834..123S
Altcode:
This paper describes a numerical modeling study of coronal jets to
understand their effects on the global corona and their contribution
to the solar wind. We implement jets into a well-established
three-dimensional, two-temperature magnetohydrodynamic (MHD) solar
corona model employing Alfvén-wave dissipation to produce a realistic
solar-wind background. The jets are produced by positioning a compact
magnetic dipole under the solar surface and rotating the boundary plasma
around the dipole's magnetic axis. The moving plasma drags the magnetic
field lines along with it, ultimately leading to a reconnection-driven
jet similar to that described by Pariat et al. We compare line-of-sight
synthetic images to multiple jet observations at EUV and X-ray
bands, and find very close matches in terms of physical structure,
dynamics, and emission. Key contributors to this agreement are the
greatly enhanced plasma density and temperature in our jets compared
to previous models. These enhancements arise from the comprehensive
thermodynamic model that we use and, also, our inclusion of a dense
chromosphere at the base of our jet-generating regions. We further
find that the large-scale corona is affected significantly by the
outwardly propagating torsional Alfvén waves generated by our polar
jet, across 40° in latitude and out to 24 R⊙. We estimate
that polar jets contribute only a few percent to the steady-state
solar-wind energy outflow.
Title: Anatomy of Depleted Interplanetary Coronal Mass Ejections
Authors: Kocher, M.; Lepri, S. T.; Landi, E.; Zhao, L.; Manchester,
W. B., IV
Bibcode: 2017ApJ...834..147K
Altcode:
We report a subset of interplanetary coronal mass ejections (ICMEs)
containing distinct periods of anomalous heavy-ion charge state
composition and peculiar ion thermal properties measured by ACE/SWICS
from 1998 to 2011. We label them “depleted ICMEs,” identified
by the presence of intervals where C6+/C5+
and O7+/O6+ depart from the direct correlation
expected after their freeze-in heights. These anomalous intervals within
the depleted ICMEs are referred to as “Depletion Regions.” We find
that a depleted ICME would be indistinguishable from all other ICMEs in
the absence of the Depletion Region, which has the defining property
of significantly low abundances of fully charged species of helium,
carbon, oxygen, and nitrogen. Similar anomalies in the slow solar wind
were discussed by Zhao et al. We explore two possibilities for the
source of the Depletion Region associated with magnetic reconnection
in the tail of a CME, using CME simulations of the evolution of two
Earth-bound CMEs described by Manchester et al.
Title: An Anomalous Composition in Slow Solar Wind as a Signature
of Magnetic Reconnection in its Source Region
Authors: Zhao, L.; Landi, E.; Lepri, S. T.; Kocher, M.; Zurbuchen,
T. H.; Fisk, L. A.; Raines, J. M.
Bibcode: 2017ApJS..228....4Z
Altcode:
In this paper, we study a subset of slow solar winds characterized by
an anomalous charge state composition and ion temperatures compared
to average solar wind distributions, and thus referred to as an
“Outlier” wind. We find that although this wind is slower and denser
than normal slow wind, it is accelerated from the same source regions
(active regions and quiet-Sun regions) as the latter and its occurrence
rate depends on the solar cycle. The defining property of the Outlier
wind is that its charge state composition is the same as that of normal
slow wind, with the only exception being a very large decrease in the
abundance of fully charged species (He2+, C6+,
N7+, O8+, Mg12+), resulting in a
significant depletion of the He and C element abundances. Based on
these observations, we suggest three possible scenarios for the origin
of this wind: (1) local magnetic waves preferentially accelerating
non-fully stripped ions over fully stripped ions from a loop opened by
reconnection; (2) depleted fully stripped ions already contained in the
corona magnetic loops before they are opened up by reconnection; or
(3) fully stripped ions depleted by Coulomb collision after magnetic
reconnection in the solar corona. If any one of these three scenarios
is confirmed, the Outlier wind represents a direct signature of slow
wind release through magnetic reconnection.
Title: Five Years of Synthesis of Solar Spectral Irradiance from
SDID/SISA and SDO/AIA Images
Authors: Fontenla, J. M.; Codrescu, M.; Fedrizzi, M.; Fuller-Rowell,
T.; Hill, F.; Landi, E.; Woods, T.
Bibcode: 2017ApJ...834...54F
Altcode:
In this paper we describe the synthetic solar spectral irradiance (SSI)
calculated from 2010 to 2015 using data from the Atmospheric Imaging
Assembly (AIA) instrument, on board the Solar Dynamics Observatory
spacecraft. We used the algorithms for solar disk image decomposition
(SDID) and the spectral irradiance synthesis algorithm (SISA) that
we had developed over several years. The SDID algorithm decomposes
the images of the solar disk into areas occupied by nine types of
chromospheric and 5 types of coronal physical structures. With this
decomposition and a set of pre-computed angle-dependent spectra for
each of the features, the SISA algorithm is used to calculate the
SSI. We discuss the application of the basic SDID/SISA algorithm to a
subset of the AIA images and the observed variation occurring in the
2010-2015 period of the relative areas of the solar disk covered by the
various solar surface features. Our results consist of the SSI and total
solar irradiance variations over the 2010-2015 period. The SSI results
include soft X-ray, ultraviolet, visible, infrared, and far-infrared
observations and can be used for studies of the solar radiative forcing
of the Earth’s atmosphere. These SSI estimates were used to drive
a thermosphere-ionosphere physical simulation model. Predictions of
neutral mass density at low Earth orbit altitudes in the thermosphere
and peak plasma densities at mid-latitudes are in reasonable agreement
with the observations. The correlation between the simulation results
and the observations was consistently better when fluxes computed by
SDID/SISA procedures were used.
Title: The Sun Radio Interferometer Space Experiment (SunRISE)
Authors: Alibay, F.; Lazio, J.; Kasper, J. C.; Amiri, N.; Bastian,
T.; Cohen, C.; Landi, E.; Manchester, W.; Reinard, A.; Schwadron, N.;
Hegedus, A. M.; Maksimovic, M.; Zaslavsky, A.; Cecconi, B.; Hallinan,
G.; Krupar, V.
Bibcode: 2016AGUFMSH41B2540A
Altcode:
Radio emission from coronal mass ejections (CMEs) is a direct tracer
of the particle acceleration in the inner heliosphere and potential
magnetic connections from the lower solar corona to the larger
heliosphere. However, many aspects of this particle acceleration
remain poorly constrained. The radio emission from CMEs is quite
strong such that only a relatively small number of antennas is
required to map it. However, the state-of-the-art for tracking
such emission is only defined by single antennas (Wind/WAVES,
Stereo/SWAVES) in which the tracking is accomplished by assuming
a frequency-to-density mapping. These are limited to tracking CMEs
to only a few solar radii before the frequencies of radio emission
drop below the Earth's ionospheric cutoff. Triangulation between the
STEREO/SWAVES and Wind/WAVES instruments have provided some initial
constraints on particle acceleration sites at larger distances (lower
frequencies), but the uncertainties remain considerable. We present
the Sun Radio Imaging Space Experiment (SunRISE) mission concept:
a space-based array designed to localize such radio emissions. This
low-cost constellation is composed of small spacecraft placed in a
geostationary graveyard orbit, each carrying an HF radio receiver. In
this concept, each spacecraft would perform concurrent observations
below 25 MHz, which would then be correlated on the ground to produce
the first images of CMEs more than a few solar radii from the Sun. Part
of this research was carried out at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration.
Title: Studying the thermodynamics of coronal jets through modeling-
and observational diagnostics techniques
Authors: Szente, J.; Manchester, W.; Landi, E.; Toth, G.; van der
Holst, B.; Gombosi, T. I.; DeVore, C. R.; Antiochos, S. K.
Bibcode: 2016AGUFMSH21E2577S
Altcode:
We present a comprehensive study of simulated and observed coronal jets
using EUV and soft X-ray narrow-band images and EUV high resolution
spectra. The goal of our study is to understand the thermodynamics
and time evolution of jets and their impact on the coronal plasma. We
simulate jets with a full 3D MHD coronal model with separate electron
and proton temperatures and heating due to Alfvén wave turbulence. Due
to the fast dynamics of the small-scale eruptive reconnections at the
footpoint of the jet, it is essential to undertake this effort with a
model with separate electron and proton temperatures to interpret the
observed signatures in EUV and soft X-ray bands. The obtained synthetic
images are compared to observations done by the instrumentations of
SDO, STEREO and Hinode space crafts. The turbulence in this model is
ideally suited to analyze the spectroscopic signatures, such as line
broadening. The 3-hour long simulation of jets interacting with the
global solar corona shows plasma responses potentially being observed
with the upcoming Solar Probe Plus mission.
Title: CME Plasma Dynamics using Remote Sensing & In-situ
Observations
Authors: Kocher, M.; Lepri, S. T.; Landi, E.
Bibcode: 2016AGUFMSH13B2297K
Altcode:
The thermal and kinetic energy of Coronal Mass Ejections [CMEs] can
be best reconstructed if the plasma density, temperature and dynamics
of each of their components are known. During periods of quadrature,
we use a combination of in-situ measurements from ACE/SWICS and
remote sensing observations from SDO/AIA and STEREO/EUVI to present
several case studies of geo-effective halo-CMEs. We carry out density
diagnostics and Differential Emission Measure [DEM] profile calculations
to reconstruct a 3D picture of the CME plasma for the selected cases
in the low solar corona. We then discuss these results in the context
of models of CME initiation and release.
Title: Coronal response to EUV jets modeled with the Alfvén Wave
Solar Model
Authors: Szente, Judith; Toth, Gabor; Manchester, Ward B., IV; van der
Holst, Bartholomeus; Landi, Enrico; Gombosi, Tamas; DeVore, Carl R.;
Antiochos, Spiro K.
Bibcode: 2016usc..confE..72S
Altcode:
We study the thermodynamics of jet phenomena with the use of multiple
wavelength SDO-AIA observations [e.g. Adams (2014) and Moore (2015)]
combined with advanced numerical simulations made with AWSoM coronal
model [van der Holst (2014)]. AWSoM provides a fully three-dimensional,
magnetohydrodynamic description of the solar atmosphere heated by the
dissipation of kinetic Alfvén waves in a self-consistent manner. In
addition, the model's multi-species thermodynamics with electron
heat conduction provides for the accurate construction of synthetic
line-of-sight images of phenomena. We implement our jets in the solar
wind with a magnetic dipole twisted about axis, resulting in EUV jets
similar in topology and dynamics as being observed. We show that the
coronal atmosphere responds at a large-scale as torsional Alfvén waves
propagate into the outer corona (up to 24 solar radii and 40 degrees in
latitude), introduced by the small-scale eruptive reconnection events
at the footpoint of the jet.
Title: On Solar Wind Origin and Acceleration: Measurements from ACE
Authors: Stakhiv, Mark; Lepri, Susan T.; Landi, Enrico; Tracy, Patrick;
Zurbuchen, Thomas H.
Bibcode: 2016ApJ...829..117S
Altcode:
The origin and acceleration of the solar wind are still debated. In this
paper, we search for signatures of the source region and acceleration
mechanism of the solar wind in the plasma properties measured in situ
by the Advanced Composition Explorer spacecraft. Using the elemental
abundances as a proxy for the source region and the differential
velocity and ion temperature ratios as a proxy for the acceleration
mechanism, we are able to identify signatures pointing toward possible
source regions and acceleration mechanisms. We find that the fast
solar wind in the ecliptic plane is the same as that observed from the
polar regions and is consistent with wave acceleration and coronal-hole
origin. We also find that the slow wind is composed of two components:
one similar to the fast solar wind (with slower velocity) and the
other likely originating from closed magnetic loops. Both components
of the slow solar wind show signatures of wave acceleration. From
these findings, we draw a scenario that envisions two types of wind,
with different source regions and release mechanisms, but the same
wave acceleration mechanism.
Title: Coronal plasma diagnostics from ground-based observations
Authors: Landi, E.; Habbal, S. R.; Tomczyk, S.
Bibcode: 2016JGRA..121.8237L
Altcode:
In this paper we discuss the potential of ground-based visible
observations of the solar corona to address the key open problems in
the physics of the solar atmosphere and of solar activity. We first
compare the diagnostic potential of visible observations with those of
high-resolution spectrometers and narrowband imagers working in the
EUV and X-ray wavelength ranges. We then review the main diagnostic
techniques (and introduce a few new ones) that can be applied to
line and continuum emission in the solar atmosphere, and the physical
problems that they enable us to address. Finally, we briefly review the
main features of ground-based coronographic instrumentation currently
being developed and planned.
Title: Energy budget in the magnetic loops of the quiet Sun
Authors: Mac Cormack, C.; Nuevo, F. A.; Vásquez, A. M.; López
Fuentes, M.; Frazin, R. A.; Landi, E.; Mandrini, C. H.
Bibcode: 2016BAAA...58..275M
Altcode:
The characteristic temperature of the solar corona is hotter than that
of the photosphere. The causes for such heating are of a magnetic nature
and several possible mechanisms have been proposed. Most studies on
coronal heating focus on active regions, but the so called quiet sun,
or diffuse corona, is also subject to heating phenomena. By combining
differential emission measure tomography applied to EUV (Extreme
Ultraviolet) images time series, with potential extrapolations of the
coronal magnetic field, it is possible to estimate the radiative loss
energy along coronal loops of the diffuse corona, and the energy flux at
their foot-points that is required to maintain thermodynamically stable
structures. In this work we show the first results of this technique.
Title: Scientific objectives and capabilities of the Coronal Solar
Magnetism Observatory
Authors: Tomczyk, S.; Landi, E.; Burkepile, J. T.; Casini, R.; DeLuca,
E. E.; Fan, Y.; Gibson, S. E.; Lin, H.; McIntosh, S. W.; Solomon,
S. C.; Toma, G.; Wijn, A. G.; Zhang, J.
Bibcode: 2016JGRA..121.7470T
Altcode:
Magnetic influences increase in importance in the solar atmosphere
from the photosphere out into the corona, yet our ability to routinely
measure magnetic fields in the outer solar atmosphere is lacking. We
describe the scientific objectives and capabilities of the COronal Solar
Magnetism Observatory (COSMO), a proposed synoptic facility designed
to measure magnetic fields and plasma properties in the large-scale
solar atmosphere. COSMO comprises a suite of three instruments chosen
to enable the study of the solar atmosphere as a coupled system: (1)
a coronagraph with a 1.5 m aperture to measure the magnetic field,
temperature, density, and dynamics of the corona; (2) an instrument
for diagnostics of chromospheric and prominence magnetic fields and
plasma properties; and (3) a white light K-coronagraph to measure
the density structure and dynamics of the corona and coronal mass
ejections. COSMO will provide a unique combination of magnetic field,
density, temperature, and velocity observations in the corona and
chromosphere that have the potential to transform our understanding
of fundamental physical processes in the solar atmosphere and their
role in the origins of solar variability and space weather.
Title: A Study of Slow Solar Wind Origin and Acceleration using
Measurements from ACE
Authors: Stakhiv, Mark; Lepri, Sue; Landi, Enrico; Tracy, Patrick;
Zurbuchen, Thomas
Bibcode: 2016shin.confE..83S
Altcode:
The origin and acceleration of the slow solar wind is still debated. In
this work we investigate the solar wind using elemental abundances,
differential velocity, and ion temperatures measured with the SWICS
instrument on the ACE spacecraft. Using these measurements we are able
to identify signatures of possible source regions and acceleration
mechanisms. We find that the slow wind is composed of two components,
one similar to the fast solar wind and the other originating from
closed magnetic loops. We also find that these two types of wind
show signatures of wave acceleration. Given these measurements a
scenario is laid out which envisions two types of wind, with different
source regions and release mechanisms, but the same wave acceleration
mechanism.
Title: Anatomy of Depleted Interplanetary Coronal Mass Ejections
Authors: Kocher, Manan; Lepri, Susan T.; Landi, Enrico; Zhao, Liang;
Machester, Ward B., IV
Bibcode: 2016shin.confE..50K
Altcode:
We report a subset of ICMEs containing distinct periods of anomalous
charge state composition and distinguished ion thermal properties using
ACE/SWICS measurements from 1998-2011. We label them 'Depleted ICMEs',
identified by the presence of intervals where the expected correlation
between C6+/C5+ and O7+/O6+ violates the traditional picture of ionic
composition freeze-in. These anomalous intervals within the Depleted
ICMEs are referred to as 'Depletion Regions'. We find that the Depleted
ICME would be indistinguishable from all other ICMEs outside of the
Depletion Region, which has the defining property of significantly
low abundances of fully charged species of Helium, Carbon, Oxygen,
and Nitrogen. Similar anomalies were discussed by Zhao et al. 2016
in a population of slow solar wind. We propose a scenario of magnetic
reconnection in the tail of a CME as the source of the Depletion Region,
and make preliminary energy estimates to investigate the feasibility of
this theory using a 3D MHD model of the evolution of an Earth-bound CME,
described by Manchester et al. 2003. If this scenario is confirmed,
the Depletion Region plasma that we find within a large population of
ICMEs could be an excellent diagnostic of the magnetic reconnection
mechanism in a CME tail in the low solar corona.
Title: Prevalence and Characteristics of ICME Filament Material
Measured In Situ
Authors: Gilbert, Jason A.; Lepri, Susan T.; Landi, Enrico
Bibcode: 2016shin.confE.169G
Altcode:
Filaments are commonly observed at the Sun in conjunction with erupting
coronal mass ejections. As the CME travels into interplanetary space,
however, the filament material becomes tenuous. In situ observations
of filament material have previously been made at 1 AU in a systematic
survey of heavy ion composition data from the ACE/SWICS sensor. This
study extends that survey using a recalibrated data set, different
criteria, and full ion charge states when available. The characteristics
of each event, including the charge state distribution are given within
the context of the surrounding solar wind. The ICMEs found using these
criteria are compared with published ICME lists. Results are also shown
for modeled results of initial coronal conditions that could result
in the measured charge state distributions of the eruptive filament.
Title: The deflection of the 'Cartwheel' CME: ForeCAT results
Authors: Capannolo, Luisa; Opher, M.; Kay, C. C.; Landi, E.
Bibcode: 2016shin.confE..48C
Altcode:
Coronal Mass Ejections (CMEs) are of high scientific interest as
they represent the major cause of geomagnetic activity at Earth. In
this work, we examine the CME that occurred on April 9th, 2008,
during the solar minimum of solar cycle 24. This CME is referred to
as the 'Cartwheel CME' due to its unusual motion in the coronagraph
observations: the CME clearly rotates as it propagates outward. The CME
also shows a reversal in its latitudinal direction: the CME is ejected
at -20 degrees and moves southward to -30 degrees, then turns and
deflects northward to -20 degrees until it begins propagating radially
at 5-6 solar radii. Longitudinally, the CME is essentially stable. We
model the trajectory of the CME in the low corona with the ForeCAT model
(Kay et al., 2013; Kay et al., 2015). ForeCAT is based on magnetic
forces that act on CMEs as they propagate in the solar wind. Given a
magnetic background and initial parameters, ForeCAT provides the CME
trajectory, including any deflection or rotation, as a function of
time and distance from the Sun. We compare the results of the model
to available data of latitude and longitude of the CME (Landi et al.,
2010). ForeCAT successfully predicts the reversal in the latitudinal
deflection of the Cartwheel CME. To match the data, we constrain the
initial mass of the CME to 3.5 10^14 g in the low corona, the initial
CME size and the angular width expansion law of the CME (linear as a
function of distance until 2.10 solar radii and constant onwards).
Title: Erratum: "Modeling the Chromosphere of a Sunspot and the
Quiet Sun" (2015, ApJ, 811, 87)
Authors: Avrett, E.; Tian, H.; Landi, E.; Curdt, W.; Wuelser, J. -P.
Bibcode: 2016ApJ...821...70A
Altcode:
No abstract at ADS
Title: The CHIANTI atomic database
Authors: Young, P. R.; Dere, K. P.; Landi, E.; Del Zanna, G.; Mason,
H. E.
Bibcode: 2016JPhB...49g4009Y
Altcode: 2015arXiv151205620Y
The freely available CHIANTI atomic database was first released
in 1996 and has had a huge impact on the analysis and modeling of
emissions from astrophysical plasmas. It contains data and software
for modeling optically thin atom and positive ion emission from low
density (≲1013 cm-3) plasmas from x-ray to
infrared wavelengths. A key feature is that the data are assessed
and regularly updated, with version 8 released in 2015. Atomic data
for modeling the emissivities of 246 ions and neutrals are contained
in CHIANTI, together with data for deriving the ionization fractions
of all elements up to zinc. The different types of atomic data are
summarized here and their formats discussed. Statistics on the impact
of CHIANTI to the astrophysical community are given and examples of
the diverse range of applications are presented.
Title: Energy Balance in Magnetic Loops of the Quiet Sun
Authors: van der Holst, B.; Mac Cormack, C.; Nuevo, F. A.; Vásquez,
A. M.; Lopez-Fuentes, M.; Frazin, R. A.; Landi, E.; Mandrini, C. H.
Bibcode: 2015AGUFMSH21A2369V
Altcode:
Most coronal heating studies focus in active regions, but heating
phenomena also take place in the quiet diffuse corona. Using
differential emission measure tomography (DEMT) of EUV image time
series, in combination with potential extrapolations of the global
coronal magnetic field, it is possible to estimate the energy flux
in the lower corona required to maintain thermodynamically stable
structures. We present results of this type of analysis based on both
EUVI/STEREO and AIA/SDO EUV data, and MDI/SOHO synoptic magnetograms. We
discuss the implications of our results to coronal heating models.
Title: The Coronal Solar Magnetism Observatory
Authors: Tomczyk, S.; Landi, E.; Zhang, J.; Lin, H.; DeLuca, E. E.
Bibcode: 2015AGUFMSH43B2460T
Altcode:
Measurements of coronal and chromospheric magnetic fields are
arguably the most important observables required for advances in
our understanding of the processes responsible for coronal heating,
coronal dynamics and the generation of space weather that affects
communications, GPS systems, space flight, and power transmission. The
Coronal Solar Magnetism Observatory (COSMO) is a proposed ground-based
suite of instruments designed for routine study of coronal and
chromospheric magnetic fields and their environment, and to understand
the formation of coronal mass ejections (CME) and their relation to
other forms of solar activity. This new facility will be operated by
the High Altitude Observatory of the National Center for Atmospheric
Research (HAO/NCAR) with partners at the University of Michigan, the
University of Hawaii and George Mason University in support of the
solar and heliospheric community. It will replace the current NCAR
Mauna Loa Solar Observatory (http://mlso.hao.ucar.edu). COSMO will
enhance the value of existing and new observatories on the ground and
in space by providing unique and crucial observations of the global
coronal and chromospheric magnetic field and its evolution. The design
and current status of the COSMO will be reviewed.
Title: Coronal plasma diagnostics from eclipse observations
Authors: Landi, E.; Habbal, S. R.; Tomczyk, S.
Bibcode: 2015AGUFMSH51C2456L
Altcode:
In this talk we will discuss the diagnostic potential of observationsof
visible spectral lines formed in the extended solar corona that
canbe obtained during eclipses. We will discuss the possible
diagnosticapplications of visible eclipse observations to measure the
physicalparameters of the extended corona, to understand solar wind
origin andacceleration, and to determine the evolution of Coronal
Mass Ejectionsduring onset.We will first review the mechanisms of
formation of spectral lineintensities, we will then illustrate their
diagnostic applications,and show some results from recent eclipse
observations. We will alsoreview the spectral lines that are most
likely to be observed inthe extended solar corona during the upcoming
2017 eclipse in thecontinental United States.
Title: A Unified Scenario for the Solar Wind Phenomenon
Authors: Stakhiv, M.; Lepri, S. T.; Landi, E.
Bibcode: 2015AGUFMSH21A2381S
Altcode:
The solar wind was traditionally divided into two types: a fast, coronal
hole associated wind and a slow, streamer associated wind. Previously,
in Stakhiv et al. 2015, this bimodal view of the solar wind was expanded
to include a subclass of fast solar wind called boundary wind emanating
from the edge of coronal holes. Here we expand upon this work using
ACE data. Using compositional data we investigate the solar wind with
velocity less than 450 km/s and present arguments for the presence
of multiple source regions: coronal holes and closed loops opened by
reconnection. Finally, we find that the compositional and kinetic
properties of the solar wind point to Alfvén wave acceleration in
both the fast and slow solar wind. Thus, we develop the Unified Wind
Scenario, where the solar wind has two different source regions -
open magnetic field regions in coronal holes, and closed quiescent
loops opened be reconnection, and one single acceleration mechanism:
Alfvén wave acceleration.
Title: Anomalous Ion Charge State Behavior In Interplanetary Coronal
Mass Ejections
Authors: Kocher, M.; Lepri, S. T.; Landi, E.; Zhao, L.
Bibcode: 2015AGUFMSH21A2387K
Altcode:
A recent analysis of solar wind charge state composition measurements
from the ACE/SWICS instrument showed that the expected correlation
between the frozen-in values of the O7/O6 and C6/C5 ratios was
violated in ~5% of the slow solar wind in the 1998-2011 period (Zhao
et al. 2015). In this work we determine that such anomalous behavior
is also found in over 40% of Interplanetary Coronal Mass Ejections
(ICMEs), as identified by Richardson and Cane (2010). An analysis
of the plasma composition during these events reveals significant
depletions in densities of fully stripped ions of Carbon, Oxygen, and
Nitrogen. We argue that these events are indicators of ICME plasma
acceleration via magnetic reconnection near the freeze-in region of
Carbon and Oxygen above the solar corona.
Title: Dynamics of Polar Jets from the Chromosphere to the Corona:
Mass, Momentum and Energy Transfer
Authors: Szente, J.; Toth, G.; Manchester, W.; van der Holst, B.;
Landi, E.; DeVore, C. R.; Gombosi, T. I.
Bibcode: 2015AGUFMSH23D..05S
Altcode:
Coronal jets, routinely observed by multiple instruments at
multiple wavelengths, provide a unique opportunity to understand
the relationships between magnetic field topology, reconnection, and
solar wind heating and acceleration. We simulate coronal jets with the
Alfvén Wave Solar Model (AWSoM) [van der Holst (2014)] and focus our
study on the thermodynamical evolution of the plasma. AWSoM solves
the two-temperature MHD equations with electron heat conduction,
which not only addresses the thermodynamics of individual species,
but also allows for the construction of synthetic images from the EUV
and soft X-ray wavelength range. Our jet model takes the form of a
slowly rotating bipole field imbedded in the open magnetic field of
a coronal hole; a topology suggested by observations. We follow the
formation and evolution of polar jets starting from the chromosphere
and extending into the outer corona. The simulations show small-scale
eruptive reconnection events that self-consistently heat and accelerate
the solar wind. Our results provide a quantitative comparison to
observations made in the EUV and X-ray spectrum.
Title: Photoionization in the Solar Wind
Authors: Landi, E.; Lepri, S. T.
Bibcode: 2015ApJ...812L..28L
Altcode:
In this work we investigate the effects of photoionization on the charge
state composition of the solar wind. Using measured solar EUV and X-ray
irradiance, the Michigan Ionization Code and a model for the fast
and slow solar wind, we calculate the evolution of the charge state
distribution of He, C, N, O, Ne, Mg, Si, S, and Fe with and without
including photoionization for both types of wind. We find that the solar
radiation has significant effects on the charge state distribution
of C, N, and O, causing the ionization levels of these elements to
be higher than without photoionization; differences are largest for
oxygen. The ions commonly observed for elements heavier than O are
much less affected, except in ICMEs where Fe ions more ionized than
16+ can also be affected by the solar radiation. We also show that the
commonly used O7+/O6+ density ratio is the most
sensitive to photoionization; this sensitivity also causes the value
of this ratio to depend on the phase of the solar cycle. We show that
the O7+/O6+ ratio needs to be used with caution
for solar wind classification and coronal temperature estimates, and
recommend the C6+/C4+ ratio for these purposes.
Title: Modeling the Chromosphere of a Sunspot and the Quiet Sun
Authors: Avrett, E.; Tian, H.; Landi, E.; Curdt, W.; Wülser, J. -P.
Bibcode: 2015ApJ...811...87A
Altcode:
Semiempirical atmospheric modeling attempts to match an observed
spectrum by finding the temperature distribution and other physical
parameters along the line of sight through the emitting region such
that the calculated spectrum agrees with the observed one. In this
paper we take the observed spectrum of a sunspot and the quiet Sun
in the EUV wavelength range 668-1475 Å from the 2001 SUMER atlas
of Curdt et al. to determine models of the two atmospheric regions,
extending from the photosphere through the overlying chromosphere into
the transition region. We solve the coupled statistical equilibrium
and optically thick radiative transfer equations for a set of 32 atoms
and ions. The atoms that are part of molecules are treated separately,
and are excluded from the atomic abundances and atomic opacities. We
compare the Mg ii k line profile observations from the Interface
Region Imaging Spectrograph with the profiles calculated from the two
models. The calculated profiles for the sunspot are substantially
lower than the observed ones, based on the SUMER models. The only
way we have found to raise the calculated Mg ii lines to agree with
the observations is to introduce illumination of the sunspot from the
surrounding active region.
Title: Multimodal Differential Emission Measure in the Solar Corona
Authors: Nuevo, Federico A.; Vásquez, Alberto M.; Landi, Enrico;
Frazin, Richard
Bibcode: 2015ApJ...811..128N
Altcode: 2015arXiv150302473N
The Atmospheric Imaging Assembly (AIA) telescope on board the Solar
Dynamics Observatory provides coronal extreme ultraviolet imaging
over a broader temperature sensitivity range than the previous
generations of instruments (Extreme Ultraviolet Imager; EUVI, EIT, and
TRACE). Differential emission measure tomography (DEMT) of the solar
corona based on AIA data is presented here for the first time. The
main product of DEMT is the three-dimensional distribution of the
local differential emission measure (LDEM). While in previous studies,
based on EIT or EUVI data, there were three available EUV bands, the
present study is based on the four cooler AIA bands (aimed at studying
the quiet sun). The AIA filters allow exploration of new parametric
LDEM models. Since DEMT is better suited for lower activity periods,
we use data from Carrington Rotation 2099, when the Sun was in its
most quiescent state during the AIA mission. Also, we validate the
parametric LDEM models by using them to perform a bi-dimensional
differential emission measure (DEM) analysis on sets of simultaneous
AIA images, and comparing results with those obtained using other
methods. Our study reveals a ubiquitous bimodal LDEM distribution in
the quiet diffuse corona, characterized by two well-defined average
centroid temperatures < {T}{0,1}> =(1.47+/- 0.05)
{MK} and < {T}{0,2}> =(2.57+/- 0.05) {MK}. We argue
that the nanoflare heating scenario is less likely to explain these
results, and that alternative mechanisms, such as wave dissipation,
appear better supported by our results.
Title: CHIANTI - An atomic database for emission lines. Version 8
Authors: Del Zanna, G.; Dere, K. P.; Young, P. R.; Landi, E.; Mason,
H. E.
Bibcode: 2015A&A...582A..56D
Altcode: 2015arXiv150807631D
We present version 8 of the CHIANTI database. This version includes
a large amount of new data and ions, which represent a significant
improvement in the soft X-ray, extreme UV (EUV) and UV spectral
regions, which several space missions currently cover. New data for
neutrals and low charge states are also added. The data are assessed,
but to improve the modelling of low-temperature plasma the effective
collision strengths for most of the new datasets are not spline-fitted
as previously, but are retained as calculated. This required a change
of the format of the CHIANTI electron excitation files. The format
of the energy files has also been changed. Excitation rates between
all the levels are retained for most of the new datasets, so the data
can in principle be used to model high-density plasma. In addition,
the method for computing the differential emission measure used in
the CHIANTI software has been changed.
Title: In situ observations of fundamental characteristics of the
Sun and astrophysical plasmas
Authors: Zurbuchen, Thomas H.; Landi, Enrico
Bibcode: 2015IAUGA..2255340Z
Altcode:
This presentation will focus on in situ observations of the solar wind
and how these data can be used to deduce key properties of the Sun and
derive properties of plasmas in the solar atmosphere and wind. First
we will focus on novel measurements of the elemental composition in
the solar wind, and discuss the constraints thy place on the solar
metallicity, a measure of the Sun’s proportion of elements heavier
than He, and their consequences for solar EUV and X-ray irradiance. The
composition of the solar photosphere and upper atmosphere has been
debated recently, mainly due to the results from novel inversion models
applied to spectroscopic observations of the photosphere.The second
part of the presentation will focus on the dynamic properties of solar
wind in the atmosphere, especially the issue of energy distribution in
plasmas among the components and field. We will first focus on some key
results of ionic composition and their relation to the dynamic processes
in the corona. Second, we will look at the distribution of energy among
the ion components of these plasmas, reflecting both collisional effects
and wave-particle interactions near the Sun and in the heliosphere.
Title: Solar Spectral Irradiance, Solar Activity, and the
Near-Ultra-Violet
Authors: Fontenla, J. M.; Stancil, P. C.; Landi, E.
Bibcode: 2015ApJ...809..157F
Altcode:
The previous calculations of the Solar Spectral Irradiance (SSI)
by the Solar Radiation Physical Modeling, version 2 system, are
updated in this work by including new molecular photodissociation
cross-sections of important species, and many more levels and lines in
its treatment of non-LTE radiative transfer. The current calculations
including the new molecular photodissociation opacities produce a
reduced over-ionizaton of heavy elements in the lower chromosphere and
solve the problems with prior studies of the UV SSI in the wavelength
range 160-400 nm and now reproduce the available observations with much
greater accuracy. Calculations and observations of the near-UV at 0.1
nm resolution and higher are compared. The current set of physical
models includes four quiet-Sun and five active-region components,
from which radiance is computed for ten observing angles. These
radiances are combined with images of the solar disk to obtain the
SSI and Total Solar Irradiance and their variations. The computed SSI
is compared with measurements from space at several nm resolution and
agreement is found within the accuracy level of these measurements. An
important result is that the near-UV SSI increase with solar activity
is significant for the photodissociation of ozone in the terrestrial
atmosphere because a number of highly variable upper chromospheric
lines overlap the ozone Hartley band.
Title: The Coherent Relation between the Solar Wind in situ
Composition and its Coronal Source
Authors: Zhao, Liang; Landi, Enrico
Bibcode: 2015shin.confE..57Z
Altcode:
We analyze the solar wind dynamic properties and heavy ion composition
measured by ACE (SWICS and SWEPAM) from 1998 to 2011 at 1AU. By
applying a two-step mapping technique, we link the solar wind
properties at 1 AU to the images of the solar corona observed by
SOHO and STEREO, in which we identify different plasma structures
(such as active regions, coronal holes and quiet Sun regions) by
using a classification scheme based on pixel brightness. Using this
combination, we determine from which regions in the solar corona the
solar wind streams observed by ACE originate. Using the results of
this identification, we examine the in-situ properties of the solar
wind streams associated to coronal-holes, to active regions and to
quiet Sun regions. We find that about 54% of coronal hole associated
wind is actually slow wind. Further, we measure the minimum distance
from the solar wind coronal foot point to active regions and coronal
holes in the solar corona, and find that the solar wind O7+/O6+ charge
state ratio is anticorrelated with the distance from active regions,
and correlated with the distance to coronal holes. On the contrary,
a similar study carried out on the proton speed provides much weaker
correlations. We conclude that the O7+/O6+ ratio is a much more
effective discriminator to identify solar wind source region in the
corona than proton speed. The implications and constrains of this work
to the solar wind acceleration models will be discussed.
Title: Conceptual and Hydrodynamic Models of Mass-Fractionation in
Coronal Loops
Authors: Weberg, Micah J.; Lepri, Susan T.; Landi, Enrico; Zurbuchen,
Thomas H.
Bibcode: 2015shin.confE..60W
Altcode:
In previous presentations and papers (Weberg et al. 2012; 2015) we
described the identification and compositional properties of a new class
of solar wind events called 'heavy ion dropouts'. These dropouts are
thought to originate from large, closed coronal loops which have been
gravitationally settled before reconnecting and releasing the previously
confined plasma into the solar wind. In this work we further develop
a theoretical model for strong, mass-dependent elemental fractionation
within coronal loops. Our primary goal is to perform a few illustrative
calculations that can be directly compared with in-situ observations
of heavy ion dropouts. Our results provide new information concerning
the heights and rates at which magnetic reconnection occurs in large
coronal loops and may, in the future, serve as an interpretive aid
for analyzing unusually fractionated solar wind.
Title: Anomalous Ion Charge State Behaviour in a Population of
Interplanetary Coronal Mass Ejections
Authors: Kocher, Manan; Lepri, Susan T.; Landi, Enrico; Zhao, Liang;
Weberg, Micah
Bibcode: 2015shin.confE..63K
Altcode:
Anomalous solar wind measurements are analysed where the O^(7+)/O^(6+)
and C^(6+)/C^(5+) density ratios do not adequately correlate after
their freeze-in in a similar region above the corona. It is found
that 56% of these events coincide with ICME observations. Our study
focuses on these events. Analysis of SWICS/ACE heavy ion data shows
depletion in fully stripped ions of C, O, N, Fe, Mg, Si, S and Ne during
these events. It is argued that these enhanced event observations are
indicators of solar wind acceleration via magnetic reconnection.
Title: Differentiating sources of low latitude slow solar wind
Authors: Stakhiv, Mark; Lepri, Sue; Landi, Enrico
Bibcode: 2015shin.confE..61S
Altcode:
The solar wind has traditionally been divided into two classes based
on wind speed: fast and slow. In addition to being differentiated
by their velocity, the two classes of wind also have been shown to
exhibit distinctly different ion charge state ratios and elemental
composition. In a recent paper, Stakhiv et al. 2015, showed, using
Ulysses' in-situ solar wind observations, that this classification of
the solar was an over simplification and there existed a sub-set of
slower solar wind that exhibits fast solar wind elemental composition
and higher ion charge states. This wind was dubbed the 'boundary
wind'. The boundary wind is thought to originate along open fields near
the boundary of coronal holes, but expands from a higher density region,
thus explaining its compositional properties. In this work, we expand
upon the previous study and investigate the near ecliptic solar wind
using measurements of heavy ions from ACE SWICS. Our findings reveal
the presence of this "boundary wind" at low latitudes. We investigate
the differences between the "boundary wind" and the slowest wind
observed at ACE and attempt to separate the sources of the wind based
on properties expected from interchange reconnection with closed
coronal loops and the flow out of the boundary of coronal holes. We
find evidence of both sources in the slowest wind and discuss the
implications of these results.
Title: The Evolution of 1 AU Equatorial Solar Wind and its Association
with the Morphology of the Heliospheric Current Sheet from Solar
Cycle 23 to 24
Authors: Zhao, Liang; Landi, Enrico
Bibcode: 2015shin.confE..56Z
Altcode:
The solar wind can be categorized into three types based on its
"freeze-in" temperature in the coronal source: low freeze-in-temperature
wind mostly from coronal holes, high freeze-in-temperature wind
mostly from regions outside of coronal holes, including streamers
(helmet streamer and pseudostreamer), active regions, etc., and
transient interplanetary coronal mass ejections (ICMEs) usually
possessing the hottest freeze-in temperature. The global distribution
of these three types of wind has been investigated by examining the
most effective freeze-in temperature indicator, the O7+/O6+ ratio,
as measured by the Solar Wind Ion Composition Spectrometer on board
the ACE during 1998-2008 by Zhao et al 2009. In Zhao et al. 2014, we
extend the previous investigation to 2011 June. We find that during
the entire solar cycle, from the ascending phase of cycle 23 in 1998
to the ascending phase of cycle 24 in 2011, the average fractions
of the low O7+/O6+ ratio (LOR) wind, the high O7+/O6+ ratio (HOR)
wind, and ICMEs at 1 AU are 50.3%, 39.4%, and 10.3%, respectively;
the contributions of the three types of wind evolve with time in very
different ways. In addition, we compare the evolution of the HOR wind
with two heliospheric current sheet (HCS) parameters, which indicate
the latitudinal standard deviation (SD) and the slope (SL) of the HCS
on the synoptic Carrington maps at 2.5 solar radii surface. We find
that the fraction of HOR wind correlates with SD and SL very well
(slightly better with SL than with SD), especially after 2005. This
result verifies the link between the production of HOR wind and the
morphology of the HCS, implying that at least one of the major sources
of the HOR wind must be associated with the HCS.
Title: A Steady-state Picture of Solar Wind Acceleration and Charge
State Composition Derived from a Global Wave-driven MHD Model
Authors: Oran, R.; Landi, E.; van der Holst, B.; Lepri, S. T.;
Vásquez, A. M.; Nuevo, F. A.; Frazin, R.; Manchester, W.; Sokolov,
I.; Gombosi, T. I.
Bibcode: 2015ApJ...806...55O
Altcode: 2014arXiv1412.8288O
The higher charge states found in slow (<400 km s-1)
solar wind streams compared to fast streams have supported the
hypothesis that the slow wind originates in closed coronal loops
and is released intermittently through reconnection. Here we examine
whether a highly ionized slow wind can also form along steady and open
magnetic field lines. We model the steady-state solar atmosphere using
the Alfvén Wave Solar Model (AWSoM), a global MHD model driven by
Alfvén waves, and apply an ionization code to calculate the charge
state evolution along modeled open field lines. This constitutes the
first charge state calculation covering all latitudes in a realistic
magnetic field. The ratios {{O}+7}/{{O}+6}
and {{C}+6}/{{C}+5} are compared to in situ
Ulysses observations and are found to be higher in the slow wind, as
observed; however, they are underpredicted in both wind types. The
modeled ion fractions of S, Si, and Fe are used to calculate
line-of-sight intensities, which are compared to Extreme-ultraviolet
Imaging Spectrometer (EIS) observations above a coronal hole. The
agreement is partial and suggests that all ionization rates are
underpredicted. Assuming the presence of suprathermal electrons improved
the agreement with both EIS and Ulysses observations; importantly,
the trend of higher ionization in the slow wind was maintained. The
results suggest that there can be a sub-class of slow wind that is
steady and highly ionized. Further analysis shows that it originates
from coronal hole boundaries (CHBs), where the modeled electron
density and temperature are higher than inside the hole, leading to
faster ionization. This property of CHBs is global and observationally
supported by EUV tomography.
Title: Element Abundances in the Sun and Solar Wind Along the
Solar Cycle
Authors: Landi, Enrico
Bibcode: 2015TESS....110805L
Altcode:
Element abundances are a critical parameter in almost every aspect of
solar physics, from regulating the energy flow and the structure of the
solar interior, to shaping the energy losses of the solar atmosphere,
ruling the radiative output of the UV, EUV and X-rays solar radiation
which impacts the Earth's upper atmosphere, and determining the
composition of the solar wind.In this work we study the evolution of
the element abundances in the solar corona and in the solar wind from
1996 to date using data from SoHO, Hinode, Ulysses and ACE satellites,
in order to determine their variability along the solar cycle, and the
relationship between solar abundance variations in the solar wind and
in its source regions in the solar atmosphere. We study all the most
abundant elements, with a special emphasis on Ne and O. We discuss
our results in light of the source region of the solar wind, and of
the radiative output of the solar corona.
Title: On the Origin of Mid-latitude Fast Wind: Challenging the
Two-state Solar Wind Paradigm
Authors: Stakhiv, Mark; Landi, Enrico; Lepri, Susan T.; Oran, Rona;
Zurbuchen, Thomas H.
Bibcode: 2015ApJ...801..100S
Altcode:
The bimodal paradigm of solar wind describes a slow solar wind situated
near the heliospheric current sheet while a fast wind overexpands from
the poles to fill in the remainder of the heliosphere. In this paper, we
challenge this paradigm and focus here on mid-latitude wind using three
fast-latitude passes completed by the Ulysses spacecraft. Based on its
composition and dynamic properties, we discuss how this wind differs
from both the fast, polar coronal hole wind and the low latitude,
streamer-associated slow solar wind. Using a detailed analysis of ionic
and elemental abundances, as well as solar wind dynamic properties,
we conclude that there is a third quasi-stationary solar wind state,
called the boundary wind. This boundary wind is characterized by a
charge-state distribution that is similar to slow wind, but with an
elemental composition that is coronal hole like. Based on these data,
we present arguments for the location of the origin of this wind. We
conclude that the boundary wind is a subset of the fast wind emanating
from regions close to the boundaries of coronal holes and is accelerated
by a similar process.
Title: Neon and Oxygen Abundances and Abundance Ratio in the Solar
Corona
Authors: Landi, E.; Testa, P.
Bibcode: 2015ApJ...800..110L
Altcode:
In this work we determine the Ne/O abundance ratio from Solar and
Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) off-disk observations of quiescent streamers over
the 1996-2008 period. We find that the Ne/O ratio is approximately
constant over solar cycle 23 from 1996 to 2005, at a value of 0.099
± 0.017 this value is lower than the transition region determinations
from the quiet Sun used to infer the neon photospheric abundance from
the oxygen photospheric abundance. Also, the Ne/O ratio we determined
from SUMER is in excellent agreement with in situ determinations
from ACE/SWICS. In 2005-2008, the Ne/O abundance ratio increased with
time and reached 0.25 ± 0.05, following the same trend found in the
slowest wind analyzed by ACE/SWICS. Further, we measure the absolute
abundance in the corona for both oxygen and neon from the data set
of 1996 November 22, obtaining A o = 8.99 ± 0.04 and
A Ne = 7.92 ± 0.03, and we find that both elements are
affected by the first ionization potential (FIP) effect, with oxygen
being enhanced by a factor of 1.4-2.1 over its photospheric abundance,
and neon being changed by a factor of 0.75-1.20. We conclude that the
Ne/O ratio is not constant in the solar atmosphere, both in time and
at different heights, and that it cannot be reliably used to infer
the neon abundance in the photosphere. Also, we argue that the FIP
effect was less effective during the minimum of solar cycle 24, and
that the Ne/O = 0.25 ± 0.05 value measured at that time is closer to
the true photospheric value, leading to a neon photospheric abundance
larger than assumed by ≈40%. We discuss the implications of these
results for the solar abundance problem, for the FIP effect, and for
the identification of the source regions of the solar wind.
Title: Bright Hot Impacts by Erupted Fragments Falling Back on the
Sun: UV Redshifts in Stellar Accretion
Authors: Reale, F.; Orlando, S.; Testa, P.; Landi, E.; Schrijver, C. J.
Bibcode: 2014ApJ...797L...5R
Altcode: 2014arXiv1410.7193R
A solar eruption after a flare on 2011 June 7 produced EUV-bright
impacts of fallbacks far from the eruption site, observed with the
Solar Dynamics Observatory. These impacts can be taken as a template
for the impact of stellar accretion flows. Broad redshifted UV lines
have been commonly observed in young accreting stars. Here we study
the emission from the impacts in the Atmospheric Imaging Assembly's
UV channels and compare the inferred velocity distribution to stellar
observations. We model the impacts with two-dimensional hydrodynamic
simulations. We find that the localized UV 1600 Å emission and its
timing with respect to the EUV emission can be explained by the
impact of a cloud of fragments. The first impacts produce strong
initial upflows. The following fragments are hit and shocked by these
upflows. The UV emission comes mostly from the shocked front shell of
the fragments while they are still falling, and is therefore redshifted
when observed from above. The EUV emission instead continues from the
hot surface layer that is fed by the impacts. Fragmented accretion
can therefore explain broad redshifted UV lines (e.g., C IV 1550 Å)
to speeds around 400 km s-1 observed in accreting young
stellar objects.
Title: Counter-streaming alpha proton plasmas in an eroding magnetic
cloud: new insights into space plasma evolution from Wind
Authors: Szente, J.; Toth, G.; Manchester, W.; van der Holst, B.;
Landi, E.; DeVore, C. R.; Gombosi, T. I.
Bibcode: 2014AGUFMSH23D..05S
Altcode:
Coronal jets, routinely observed by multiple instruments at
multiple wavelengths, provide a unique opportunity to understand
the relationships between magnetic field topology, reconnection, and
solar wind heating and acceleration. We simulate coronal jets with the
Alfvén Wave Solar Model (AWSoM) [van der Holst (2014)] and focus our
study on the thermodynamical evolution of the plasma. AWSoM solves
the two-temperature MHD equations with electron heat conduction,
which not only addresses the thermodynamics of individual species,
but also allows for the construction of synthetic images from the EUV
and soft X-ray wavelength range. Our jet model takes the form of a
slowly rotating bipole field imbedded in the open magnetic field of
a coronal hole; a topology suggested by observations. We follow the
formation and evolution of polar jets starting from the chromosphere
and extending into the outer corona. The simulations show small-scale
eruptive reconnection events that self-consistently heat and accelerate
the solar wind. Our results provide a quantitative comparison to
observations made in the EUV and X-ray spectrum.
Title: Coronal Hole Boundaries as Source Regions of a Steady
Slow Solar Wind: Global Modeling of Charge State Composition and
Sun-to-Earth Observations
Authors: Oran, R.; Landi, E.; van der Holst, B.; Lepri, S. T.;
Manchester, W.; Frazin, R. A.; Nuevo, F.; Vásquez, A. M.; Sokolov,
I.; Gombosi, T. I.
Bibcode: 2014AGUFMSH33A4122O
Altcode:
We combine the results from a global MHD model of the solar atmosphere
with a charge state evolution code in order to predict the large-scale
variation of charge state composition in the fast and slow solar wind
during solar minimum. The model captures the well-known increase in
charge state ratios C+6/ C+5 and O+7/O+6 in the slow wind, inline with
Ulysses observations. We present a theoretical picture explaining
the formation of these increases, which are related to regions of
higher electron density and temperature near the boundaries of coronal
holes. We verify the existence of these regions using a 3D tomographic
reconstruction of the lower corona. This work establishes that a steady
slow wind flowing along open magnetic field lines can carry high charge
states without invoking reconnection with closed field regions. This
subset of slow wind can play a role explaining the properties of the
non-steady slow wind, and complement dynamic models of slow solar
wind formation.
Title: Solar Corona/Wind Composition and Origins of the Solar Wind
Authors: Lepri, S. T.; Gilbert, J. A.; Landi, E.; Shearer, P.; von
Steiger, R.; Zurbuchen, T.
Bibcode: 2014AGUFMSH33A4129L
Altcode:
Measurements from ACE and Ulysses have revealed a multifaceted solar
wind, with distinctly different kinetic and compositional properties
dependent on the source region of the wind. One of the major outstanding
issues in heliophysics concerns the origin and also predictability of
quasi-stationary slow solar wind. While the fast solar wind is now
proven to originate within large polar coronal holes, the source of
the slow solar wind remains particularly elusive and has been the
subject of long debate, leading to models that are stationary and
also reconnection based - such as interchange or so-called S-web based
models. Our talk will focus on observational constraints of solar wind
sources and their evolution during the solar cycle. In particular,
we will point out long-term variations of wind composition and dynamic
properties, particularly focused on the abundance of elements with low
First Ionization Potential (FIP), which have been routinely measured on
both ACE and Ulysses spacecraft. We will use these in situ observations,
and remote sensing data where available, to provide constraints for
solar wind origin during the solar cycle, and on their correspondence
to predictions for models of the solar wind.
Title: Sources of the Mid-Latitude Fast Solar Wind
Authors: Stakhiv, M.; Landi, E.; Lepri, S. T.; Zurbuchen, T.; Oran, R.
Bibcode: 2014AGUFMSH33A4125S
Altcode:
The traditional paradigm of the solar wind is bimodal: a fast, coronal
hole associated wind and a slow, streamer associated wind. We address
this bimodal solar wind view using a detailed analysis of ionic and
elemental abundances, as well as solar wind dynamic properties. From
this analysis we conclude that there is a subclass of fast solar wind
characterized by a charge state distribution that is similar to slow
wind, but with an elemental composition which is coronal-hole like. We
present arguments for origin and acceleration of this wind using
compositional and kinetic properties. Finally, we conclude that the
existence of this wind explains the continuum of velocity and charge
states seen between the fast and slow solar wind.
Title: The Coronal Solar Magnetism Observatory (COSMO)
Authors: Tomczyk, S.; Landi, E.; Lin, H.; Zhang, J.
Bibcode: 2014AGUFMSH53B4212T
Altcode:
Measurements of coronal and chromospheric magnetic fields are arguably
the most important observables required in our understanding of the
emergence of magnetic flux into the solar atmosphere and the processes
responsible for the production of solar activity, coronal heating
and coronal dynamics. However, routine observations of the strength
and orientation of coronal and chromospheric magnetic fields are
not currently available. COSMO is a proposed ground-based suite of
instruments designed for routine study of coronal and chromospheric
magnetic fields and their environment. We will present an overview
of the COSMO and show recent progress in development of the COSMO
observatory.
Title: The Evolution of 1 AU Equatorial Solar Wind and its Association
with the Morphology of the Heliospheric Current Sheet from Solar
Cycles 23 to 24
Authors: Zhao, L.; Landi, E.; Zurbuchen, T. H.; Fisk, L. A.; Lepri,
S. T.
Bibcode: 2014ApJ...793...44Z
Altcode:
The solar wind can be categorized into three types based on its
"freeze-in" temperature (T freeze-in) in the coronal
source: low T freeze-in wind mostly from coronal holes,
high T freeze-in wind mostly from regions outside of coronal
holes, including streamers (helmet streamer and pseudostreamer), active
regions, etc., and transient interplanetary coronal mass ejections
(ICMEs) usually possessing the hottest T freeze-in. The
global distribution of these three types of wind has been investigated
by examining the most effective T freeze-in indicator, the
O7 +/O6 + ratio, as measured by the Solar Wind
Ion Composition Spectrometer on board the Advanced Composition Explorer
(ACE) during 1998-2008 by Zhao et al. In this study, we extend the
previous investigation to 2011 June, covering the unusual solar minimum
between solar cycles 23 and 24 (2007-2010) and the beginning of solar
cycle 24. We find that during the entire solar cycle, from the ascending
phase of cycle 23 in 1998 to the ascending phase of cycle 24 in 2011,
the average fractions of the low O7 +/O6 + ratio
(LOR) wind, the high O7 +/O6 + ratio (HOR)
wind, and ICMEs at 1 AU are 50.3%, 39.4%, and 10.3%, respectively;
the contributions of the three types of wind evolve with time in very
different ways. In addition, we compare the evolution of the HOR wind
with two heliospheric current sheet (HCS) parameters, which indicate
the latitudinal standard deviation (SD) and the slope (SL) of the HCS
on the synoptic Carrington maps at 2.5 solar radii surface. We find
that the fraction of HOR wind correlates with SD and SL very well
(slightly better with SL than with SD), especially after 2005. This
result verifies the link between the production of HOR wind and the
morphology of the HCS, implying that at least one of the major sources
of the HOR wind must be associated with the HCS.
Title: VizieR Online Data Catalog: UV spectrum of the quiet Sun
above the limb (Warren+, 2014)
Authors: Warren, H. P.; Ugarte-Urra, I.; Landi, E.
Bibcode: 2014yCat..22130011W
Altcode:
First, we compare full-disk mosaics constructed by scanning the EIS slot
over the Sun with irradiance observations made by the EUV Variability
Experiment (EVE; Woods et al. 2012SoPh..275..115W) on the Solar
Dynamics Observatory (SDO) mission. These comparisons provide a means
of establishing the absolute calibration for EIS. Second, we combine
extended EIS observations from above the limb in the quiet Sun with a
simple temperature model to simultaneously determine the differential
emission measure (DEM) distribution and the time-dependent changes
to the effective areas that best fit all of the available spectral
lines. In Figure 2 we show the average spectrum from an observation
of seven consecutive runs of ELFULLCCDWSUMER. The
observations began on 2007 November 4 19:12 and ended on the same date
at 23:51 UT. The EIS field of view was centered at (990", -50") about
22" above the limb of the Sun. The central 129 pixels along the slit
have been averaged over 38 exposures (11 exposures were corrupted in
transmission to the ground) for a total of 4902 intensity measurements
at each wavelength. Since each exposure is 300s, the spectrum represents
1470600 pixels of effective exposure time and allows weak lines at
the ends of the detector to be measured. (1 data file).
Title: Charge State Evolution in the Solar Wind. III. Model Comparison
with Observations
Authors: Landi, E.; Oran, R.; Lepri, S. T.; Zurbuchen, T. H.; Fisk,
L. A.; van der Holst, B.
Bibcode: 2014ApJ...790..111L
Altcode:
We test three theoretical models of the fast solar wind with a
set of remote sensing observations and in-situ measurements taken
during the minimum of solar cycle 23. First, the model electron
density and temperature are compared to SOHO/SUMER spectroscopic
measurements. Second, the model electron density, temperature, and wind
speed are used to predict the charge state evolution of the wind plasma
from the source regions to the freeze-in point. Frozen-in charge states
are compared with Ulysses/SWICS measurements at 1 AU, while charge
states close to the Sun are combined with the CHIANTI spectral code to
calculate the intensities of selected spectral lines, to be compared
with SOHO/SUMER observations in the north polar coronal hole. We find
that none of the theoretical models are able to completely reproduce
all observations; namely, all of them underestimate the charge state
distribution of the solar wind everywhere, although the levels of
disagreement vary from model to model. We discuss possible causes
of the disagreement, namely, uncertainties in the calculation of the
charge state evolution and of line intensities, in the atomic data,
and in the assumptions on the wind plasma conditions. Last, we discuss
the scenario where the wind is accelerated from a region located in
the solar corona rather than in the chromosphere as assumed in the
three theoretical models, and find that a wind originating from the
corona is in much closer agreement with observations.
Title: The Absolute Calibration of the EUV Imaging Spectrometer
on Hinode
Authors: Warren, Harry P.; Ugarte-Urra, Ignacio; Landi, Enrico
Bibcode: 2014ApJS..213...11W
Altcode: 2013arXiv1310.5324W
We investigate the absolute calibration of the EUV Imaging Spectrometer
(EIS) on Hinode by comparing EIS full-disk mosaics with irradiance
observations from the EUV Variability Experiment on the Solar Dynamics
Observatory. We also use extended observations of the quiet corona above
the limb combined with a simple differential emission measure model
to establish new effective area curves that incorporate information
from the most recent atomic physics calculations. We find that changes
to the EIS instrument sensitivity are a complex function of both time
and wavelength. We find that the sensitivity is decaying exponentially
with time and that the decay constants vary with wavelength. The EIS
short wavelength channel shows significantly longer decay times than
the long wavelength channel.
Title: The Solar Wind Neon Abundance Observed with ACE/SWICS and
Ulysses/SWICS
Authors: Shearer, Paul; von Steiger, Rudolf; Raines, Jim M.; Lepri,
Susan T.; Thomas, Jonathan W.; Gilbert, Jason A.; Landi, Enrico;
Zurbuchen, Thomas H.
Bibcode: 2014ApJ...789...60S
Altcode:
Using in situ ion spectrometry data from ACE/SWICS, we determine the
solar wind Ne/O elemental abundance ratio and examine its dependence
on wind speed and evolution with the solar cycle. We find that Ne/O
is inversely correlated with wind speed, is nearly constant in the
fast wind, and correlates strongly with solar activity in the slow
wind. In fast wind streams with speeds above 600 km s-1,
we find Ne/O = 0.10 ± 0.02, in good agreement with the extensive polar
observations by Ulysses/SWICS. In slow wind streams with speeds below
400 km s-1, Ne/O ranges from a low of 0.12 ± 0.02 at solar
maximum to a high of 0.17 ± 0.03 at solar minimum. These measurements
place new and significant empirical constraints on the fractionation
mechanisms governing solar wind composition and have implications for
the coronal and photospheric abundances of neon and oxygen. The results
are made possible by a new data analysis method that robustly identifies
rare elements in the measured ion spectra. The method is also applied
to Ulysses/SWICS data, which confirms the ACE observations and extends
our view of solar wind neon into the three-dimensional heliosphere.
Title: Accretion impacts studied on the Sun
Authors: Reale, F.; Orlando, S.; Testa, P.; Peres, G.; Landi, E.;
Schrijver, C.
Bibcode: 2014xru..confE.169R
Altcode:
Accretion in star-forming regions is a hot topic. The Sun has recently
offered an interesting opportunity to study accretion impacts observed
in great detail at high energies (Reale et al. 2013, Science, 341,
6143, 251). After the eruption of a dense filament triggered by an
energetic flare on June 7, 2011 part of the ejected material falls
back onto the solar surface. The impact of the downfalling plasma is
similar to that of accretion flows on young stellar objects, and was
imaged in the EUV by the Atmospheric Imaging Assembly (AIA) on-board
the Solar Dynamics Observatory (SDO). Hydrodynamic simulations confirm
that the high energy emission is produced by the impact of high-density
plasma at the highest free-fall speeds and show the importance of
the absorption in reducing the X-ray emission and of fragmentation
in explaining the line broadenings. Impacts such as these present
a laboratory for stellar astronomers to study the impact of dense
(accreting) circumstellar material in unique detail.
Title: Scientific Validation of the AWSoM Model using Novel
Observational Tests
Authors: Oran, Rona; Sokolov, Igor; van der Holst, Bart; Landi,
Enrico; Frazin, Rich; Gombosi, Tamas
Bibcode: 2014shin.confE..97O
Altcode:
As part of the SHINE/CCMC model validation effort, a global simulation
of the solar environment was performed for CR2058, using the Alfven
Wave Solar Model (AWSoM), extending from the chromosphere to 1AU. We
present the scientific validation of these results, using both the
automated validation system, currently at place at CCMC, and other
validation products and techniques. Heliophysical models are
commonly validated by comparing the model results to in-situ and
remote observations. These comparisons reflect how accurately a model
can reproduce the observed properties of the solar corona and solar
wind. From the point of view of scientific validation, it is
desirable to also be able to test the underlying model assumptions -
the physical processes and input parameters that were invoked in order
to reproduce the observations. Observational tests of this kind are
model specific and may be hard or even impossible to obtain. However,
recent developments show possible new directions that could be adopted
by the community in the future. We will present results from several of
these techniques that are relevant to the AWSoM, and possibly other,
heliophysical models. These include synthetic emission line profiles,
tomography of the lower corona, and charge state composition in both
the corona and in the solar wind. We discuss how these techniques can be
used to examine the model assumptions and predictions in greater detail.
Title: Ulysses Measurements of the Continuum of Solar Wind States
Authors: Stakhiv, Mark; Lepri, Susan T.; Landi, Enrico; Zurbuchen,
Thomas H.
Bibcode: 2014shin.confE..22S
Altcode:
The solar wind has long been divided into two types: fast and
slow. These types of solar wind have been differentiated by their
velocity, heavy ion charge state ratios, and composition. The slow solar
wind has a low velocity, high charge states, and higher Fe/O ratio
while the fast solar wind has a high velocity, lower charge states,
and lower Fe/O ratio. In reality the solar wind is more complicated than
this. In addition to the bimodal nature there exists another population
of solar wind. This wind has slow wind velocity and charge states but
is compositionally similar to fast solar wind. In this presentation we
present data from three Ulysses fast latitude scans using compositional
data from the SWICS and SWOOPS instruments. We argue that there exists
a population of the solar wind which originates from the same region
as the fast solar wind but has slow solar wind properties.
Title: Charge State Evolution in the Fast and Slow Wind Predicted
by a Global Wave-Driven Solar Model
Authors: Oran, Rona; Landi, Enrico; van der Holst, Bart; Lepri, Susan;
Vásquez, Alberto; Nuevo, Federico; Frazin, Richard; Manchester,
Ward; Sokolov, Igor; Gombosi, Tamas
Bibcode: 2014shin.confE..66O
Altcode:
The mechanisms responsible for the formation of the slow solar wind are
a subject of vigorous debate in the heliospheric community. The heavy
ion charge state composition measured in-situ at 1AU and beyond depend
on the plasma conditions along the wind trajectory close to the Sun,
and are known to be significantly different when measured in either
the fast or slow solar wind. As such, heavy ion charge states have
played an important role in testing the various theories concerning
the formation of the fast and slow wind, and in determining the source
region of the slow solar wind. We will present results from a
global MHD model of the solar atmosphere, in which the wind is heated
and accelerated by Alfven waves. The global model results are used to
drive a charge state evolution code along open magnetic field lines at
all heliographic latitudes. The resulting charge state distributions of
several ions are compared to in-situ Ulysses measurements at 1-2AU as
well as to high resolution spectra observed in the lower corona. We
find that the large scale latitudinal variation in charge states
is captured by the model. In particular, the model can reproduce
and explain the increase in the O+7/O+6, C+6/C+5 ratios in the slow
(steady) solar wind compared to the fast wind. We demonstrate that these
increases are associated with a higher plasma density at the base of
open field lines whose foot-points are located near the boundary of
the coronal holes. We show that this density enhancement as predicted
by the model is consistent with EUV tomographic reconstructions of the
lower corona. We discuss the possible interpretations and implications
of our results to our understanding of solar wind formation.
Title: Further Analysis of Active Region Thermal Structure from
EUNIS-13
Authors: Rabin, Douglas M.; Landi, Enrico; Daw, Adrian N.; Brosius,
Jeffrey W.
Bibcode: 2014AAS...22432339R
Altcode:
The 2013 April 23 flight of the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument returned high-quality
spectra in two wavelength bands, 30.0-37.0 nm and 52.7-63.5 nm, sampling
three active regions (11723, 11724, and 11726). The spectral lines
in these bands probe a wide temperature range, 0.03 MK to 8 MK. We
have demonstrated that the differential emission measure (DEM) varies
significantly between different sub-regions of AR 11726. We extend
this analysis to ARs 11723 and 11724 and include a wider selection of
spectral lines to delineate better the variations in thermal structure.
Title: Evidence for Impulsive Coronal Heating from EUNIS 2013
Authors: Daw, Adrian N.; Brosius, Jeffrey W.; Rabin, Douglas M.;
Landi, Enrico; Klimchuk, James A.
Bibcode: 2014AAS...22431204D
Altcode:
Pervasive, faint Fe XIX 592 Å line emission was observed in active
regions by the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket instrument on 23 April 2013. The broad spectral coverage
(303-370 Å, 527-635 Å) and unprecedented dynamic range of the EUNIS
observations includes emission lines of ionization stages from He I to
Fe XX, and thus a wide temperature range of 0.03 to 10 MK. Comparison
of observed line intensities with calculations demonstrates that the
Fe XIX emission, formed at temperatures around 8 MK, is evidence of
the faint hot emission predicted by impulsive heating models of the
solar corona (such as nanoflares).
Title: Latitudinal Dependence of Coronal Hole-Associated Fast
Solar Wind
Authors: Zhao, L.; Landi, E.
Bibcode: 2014ASPC..484..263Z
Altcode:
The fast solar wind can have at least two different coronal sources:
high-latitude, polar coronal holes (PCH) and low-latitude, equatorial
coronal holes (ECH). The in-situ differences in the PCH and ECH winds
have not been well studied, nor have the differences in their evolution
over the solar cycles. Ulysses' 19 years of observations from 1990 to
2009, combined with ACE observations from 1998 to the present, provide
us with measurements of solar wind properties that span two entire solar
cycles, which allow us to study the in-situ properties and evolution
of the coronal hole-associated solar wind at different latitudes. In
this work, we focus on the PCH and ECH solar winds during the minima
between solar cycles 22-23 and 23-24. We use data from SWICS, SWOOPS,
and VHM/FGM on board Ulysses, and SWICS, SWEPAM, and MAG on board
ACE to analyze the proton dynamics, heavy ion composition, elemental
abundance, and magnetic field properties of the PCH wind and ECH wind,
with a special focus on their differences during the recent two solar
minima. We also include the slow and hot, streamer-associated (ST)
wind as a reference in the comparison. The comparison of PCH and ECH
wind shows that: 1) the in-situ properties of ECH and PCH winds are
significantly different during the two solar minima, and 2) the two
types of coronal hole-associated solar wind respond differently to
changes in solar activity strength from cycle 23 to cycle 24.
Title: The Temperature of Quiescent Streamers during Solar Cycles
23 and 24
Authors: Landi, E.; Testa, P.
Bibcode: 2014ApJ...787...33L
Altcode:
Recent in-situ determinations of the temporal evolution of the charge
state distribution in the fast and slow solar wind have shown a general
decrease in the degree of ionization of all the elements in the solar
wind along solar cycles 23 and 24. Such a decrease has been interpreted
as a cooling of the solar corona which occurred during the decline and
minimum phase of solar cycle 23 from 2000 to 2010. In the present work,
we investigate whether spectroscopic determinations of the temperature
of the quiescent streamers show signatures of coronal plasma cooling
during cycles 23 and 24. We measure the coronal electron density and
thermal structure at the base of 60 quiescent streamers observed from
1996 to 2013 by SOHO/SUMER and Hinode/EIS and find that both quantities
do now show any significant dependence on the solar cycle. We argue
that if the slow solar wind is accelerated from the solar photosphere
or chromosphere, the measured decrease in the in-situ wind charge
state distribution might be due to an increased efficiency in the wind
acceleration mechanism at low altitudes. If the slow wind originates
from the corona, a combination of density and wind acceleration changes
may be responsible for the in-situ results.
Title: Evolution of Solar Wind Heavy Ions over the Solar Cycle
Authors: Lepri, S. T.; Landi, E.; Zurbuchen, T. H.
Bibcode: 2014ASPC..484..104L
Altcode:
Solar wind composition has been shown to effectively discriminate
between different types of solar wind, including slow, fast and ICME
related wind. The composition reflects the properties of the source
regions of the wind in the corona and their evolution. We present
the systematic and comprehensive analysis of the ionic and elemental
composition observed on ACE over solar cycle 23 from 2000 until
2010. During this period, the Sun evolved through solar maximum to
solar minimum. We find significantly lower C, O, and Fe charge states
as well as a 50% decrease in heavy ion abundances (He, C, O, Si, Fe)
relative to H during this transition towards solar minimum. We also
examined the FIP bias. We consider the implications of these findings
for solar wind models and for identification of the fast and slow wind.
Title: Far- and Extreme-UV Solar Spectral Irradiance and Radiance
from Simplified Atmospheric Physical Models
Authors: Fontenla, J. M.; Landi, E.; Snow, M.; Woods, T.
Bibcode: 2014SoPh..289..515F
Altcode:
This article describes an update of the physical models that we use to
reconstruct the FUV and EUV irradiance spectra and the radiance spectra
of the features that at any given point in time may cover the solar disk
depending on the state of solar activity. The present update introduces
important modifications to the chromosphere-corona transition region of
all models. Also, the update introduces improved and extended atomic
data. By these changes, the agreement of the computed and observed
spectra is largely improved in many EUV lines important for the modeling
of the Earth's upper atmosphere. This article describes the improvements
and shows detailed comparisons with EUV/FUV radiance and irradiance
measurements. The solar spectral irradiance from these models at
wavelengths longer than ≈ 200 nm is discussed in a separate article.
Title: Polar and Equatorial Coronal Hole Winds at Solar Minima:
From the Heliosphere to the Inner Corona
Authors: Zhao, L.; Landi, E.
Bibcode: 2014ApJ...781..110Z
Altcode:
Fast solar wind can be accelerated from at least two different sources:
polar coronal holes and equatorial coronal holes. Little is known about
the relationship between the wind coming from these two different
latitudes and whether these two subcategories of fast wind evolve
in the same way during the solar cycle. Nineteen years of Ulysses
observations, from 1990 to 2009, combined with ACE observations from
1998 to the present provide us with in situ measurements of solar wind
properties that span two entire solar cycles. These missions provide
an ideal data set to study the properties and evolution of the fast
solar wind originating from equatorial and polar holes. In this work,
we focus on these two types of fast solar wind during the minima between
solar cycles 22 and 23 and 23 and 24. We use data from SWICS, SWOOPS,
and VHM/FGM on board Ulysses and SWICS, SWEPAM, and MAG on board ACE
to analyze the proton kinetic, thermal, and dynamic characteristics,
heavy ion composition, and magnetic field properties of these two
fast winds. The comparison shows that: (1) their kinetic, thermal,
compositional, and magnetic properties are significantly different at
any time during the two minima and (2) they respond differently to the
changes in solar activity from cycle 23 to 24. These results indicate
that equatorial and polar fast solar wind are two separate subcategories
of fast wind. We discuss the implications of these results and relate
them to remote-sensing measurements of the properties of polar and
equatorial coronal holes carried out in the inner corona during these
two solar minima.
Title: Observations of Energetic Particles between a Pair of
Corotating Interaction Regions
Authors: Wu, Z.; Chen, Y.; Li, G.; Zhao, L. L.; Ebert, R. W.; Desai,
M. I.; Mason, G. M.; Lavraud, B.; Zhao, L.; Liu, Y. C. -M.; Guo, F.;
Tang, C. L.; Landi, E.; Sauvaud, J.
Bibcode: 2014ApJ...781...17W
Altcode: 2014arXiv1401.2214W
We report observations of the acceleration and trapping of energetic
ions and electrons between a pair of corotating interaction regions
(CIRs). The event occurred in Carrington Rotation 2060. Observed by
the STEREO-B spacecraft, the two CIRs were separated by less than 5
days. In contrast to other CIR events, the fluxes of the energetic ions
and electrons in this event reached their maxima between the trailing
edge of the first CIR and the leading edge of the second CIR. The radial
magnetic field (Br ) reversed its sense and the anisotropy
of the flux also changed from Sunward to anti-Sunward between the two
CIRs. Furthermore, there was an extended period of counterstreaming
suprathermal electrons between the two CIRs. Similar observations for
this event were also obtained with the Advanced Composition Explorer
and STEREO-A. We conjecture that these observations were due to a
U-shaped, large-scale magnetic field topology connecting the reverse
shock of the first CIR and the forward shock of the second CIR. Such
a disconnected U-shaped magnetic field topology may have formed due
to magnetic reconnection in the upper corona.
Title: Alfvén Wave Turbulence as a Coronal Heating Mechanism:
Simultaneously Predicting the Heating Rate and the Wave-Induced
Emission Line Broadening
Authors: Oran, R.; Landi, E.; van der Holst, B.; Sokolov, I. V.;
Gombosi, T. I.
Bibcode: 2014arXiv1401.0565O
Altcode:
In the present work, we test the predictions of the AWSoM model,
a global extended-MHD model capable of calculating the propagation
and turbulent dissipation of Alfvén waves in any magnetic topology,
against high resolution spectra of the quiescent off-disk solar
corona. Wave dissipation is the only heating mechanism assumed in this
model. Combining 3D model results with the CHIANTI atomic database, we
were able to create synthetic line-of-sight spectra which include the
effects of emission line broadening due to both thermal and wave-related
non-thermal motions. To the best of our knowledge this is the first
time a global model is used to obtain synthetic non-thermal line
broadening. We obtained a steady-state solution driven by a synoptic
magnetogram and compared the synthetic spectra with SUMER observations
of a quiescent area above the solar west limb extending between 1.04
and 1.34 solar radii at the equator. Both the predicted line widths
and the total line fluxes were consistent with the observations for
5 different ions. Using the 3D solution, we were able to locate the
region that contributes the most to the emission used for measuring
electron properties; we found that region to be a pseudo-streamer,
whose modeled electron temperature and density are consistent with the
measured ones. We conclude that the turbulent dissipation assumed in
the AWSoM model can simultaneously account for the observed heating
rate and the non-dissipated wave energy observed in this region.
Title: Density Diagnostics of Coronal Mass Ejection Cores with the
Solar Dynamics Observatory/Atmospheric Imaging Assembly
Authors: Landi, E.; Miralles, M. P.
Bibcode: 2014ApJ...780L...7L
Altcode:
In this Letter, we investigate the application of the intensity ratio
from pairs of narrow-band images from the Atmospheric Imaging Assembly
(AIA) on the Solar Dynamics Observatory, the Extreme Ultraviolet (EUV)
Imager (EUVI) on board the Sun Earth Connection Coronal and Heliospheric
Investigation, and the EUV Imaging Telescope (EIT) on board the Solar
and Heliospheric Observatory, to density diagnostics of optically thin
plasmas. By inspecting the filtered spectra allowed by each instrument's
effective area, we find that ratios between AIA images in the 171 Å and
193 Å channels can be used to determine the plasma electron density
at transition region temperatures. This diagnostic potential is due
to a pair of O V transitions which dominate the effective spectra of
these two channels at temperatures around ≈2.5-3.0 × 105
K. The temperature and electron density ranges where the 171/193 ratio
is density sensitive are relevant for the cores of accelerating coronal
mass ejections (CMEs) in the inner solar corona. We discuss how AIA
series of images can be used for simultaneous temperature and density
diagnostics of CME cores.
Title: From Forbidden Coronal Lines to Meaningful Coronal Magnetic
Fields
Authors: Judge, P. G.; Habbal, S.; Landi, E.
Bibcode: 2013SoPh..288..467J
Altcode: 2013arXiv1304.3863J
We review methods to measure magnetic fields within the corona using
the polarized light in magnetic-dipole (M1) lines. We are particularly
interested in both the global magnetic-field evolution over a solar
cycle, and the local storage of magnetic free energy within coronal
plasmas. We address commonly held skepticisms concerning angular
ambiguities and line-of-sight confusion. We argue that ambiguities are,
in principle, no worse than more familiar remotely sensed photospheric
vector fields, and that the diagnosis of M1 line data would benefit
from simultaneous observations of EUV lines. Based on calculations and
data from eclipses, we discuss the most promising lines and different
approaches that might be used. We point to the S-like [Fe XI] line
(J=2 to J=1) at 789.2 nm as a prime target line (for the Advanced
Technology Solar Telescope (ATST) for example) to augment the hotter
1074.7 and 1079.8 nm Si-like lines of [Fe XIII] currently observed by
the Coronal Multi-channel Polarimeter (CoMP). Significant breakthroughs
will be made possible with the new generation of coronagraphs, in three
distinct ways: i) through single-point inversions (which encompasses
also the analysis of MHD wave modes), ii) using direct comparisons of
synthetic MHD or force-free models with polarization data, and iii)
using tomographic techniques.
Title: Determining the Coronal Origin of the Slow Solar Wind Using
Remote Sensing and In Situ Observations
Authors: Miralles, M. P.; Landi, E.; Cranmer, S. R.; Raymond, J. C.;
Cohen, O.; Oran, R.
Bibcode: 2013AGUFMSH32A0005M
Altcode:
We study the origin of the slow solar wind by characterizing the
physical properties of the slow solar wind plasma with multi-spacecraft
and ground-based observations. We compare the characteristics of
coronal-streamer wind streams obtained during solar cycle 24 with
results from the previous solar cycle. In order to investigate slow
solar wind heating and acceleration, we also compare our measurements
with predictions from theoretical models. We aim to use the empirical
measurements to distinguish between different proposed physical
processes for slow wind acceleration (e.g., waves/turbulence versus
reconnection). This work is supported by NASA grant NNX10AQ58G
to the Smithsonian Astrophysical Observatory.
Title: Calculated Resonance Line Profiles of [Mg II], [C II], and
[Si IV] in the Solar Atmosphere
Authors: Avrett, E.; Landi, E.; McKillop, S.
Bibcode: 2013ApJ...779..155A
Altcode:
NASA's Interface Region Imaging Spectrograph space mission, launched
2013 June 27, is intended to study the structure of the solar
chromosphere and the transition region between the chromosphere and
corona. The spectral lines to be observed include the Mg II k line at
2796.5 Å, the C II 1334.5 Å line, and the Si IV line at 1393.8 Å,
which are formed in the middle chromosphere, the upper chromosphere,
and the lower transition region, respectively. Here we calculate the
profiles of these lines from four models of the solar atmosphere,
intended to represent the faint and mean internetwork, a network lane,
and bright network. We show how the profiles change from the center of
the solar disk toward the limb of the Sun and in response to outflows
and inflows. These results are intended to cover the range of expected
quiet-Sun observations and assist in their interpretation. We expect
that the observations will lead to improvements in the models, which
can then be used to estimate the required non-radiative heating in
the different regions.
Title: A Global Wave-driven Magnetohydrodynamic Solar Model with a
Unified Treatment of Open and Closed Magnetic Field Topologies
Authors: Oran, R.; van der Holst, B.; Landi, E.; Jin, M.; Sokolov,
I. V.; Gombosi, T. I.
Bibcode: 2013ApJ...778..176O
Altcode: 2013arXiv1307.4510O
We describe, analyze, and validate the recently developed Alfvén
Wave Solar Model, a three-dimensional global model starting from
the top of the chromosphere and extending into interplanetary space
(out to 1-2 AU). This model solves the extended, two-temperature
magnetohydrodynamics equations coupled to a wave kinetic equation
for low-frequency Alfvén waves. In this picture, heating and
acceleration of the plasma are due to wave dissipation and to wave
pressure gradients, respectively. The dissipation process is described
by a fully developed turbulent cascade of counterpropagating waves. We
adopt a unified approach for calculating the wave dissipation in both
open and closed magnetic field lines, allowing for a self-consistent
treatment in any magnetic topology. Wave dissipation is the only
heating mechanism assumed in the model; no geometric heating functions
are invoked. Electron heat conduction and radiative cooling are
also included. We demonstrate that the large-scale, steady state
(in the corotating frame) properties of the solar environment are
reproduced, using three adjustable parameters: the Poynting flux of
chromospheric Alfvén waves, the perpendicular correlation length of
the turbulence, and a pseudoreflection coefficient. We compare model
results for Carrington rotation 2063 (2007 November-December) with
remote observations in the extreme-ultraviolet and X-ray ranges from
the Solar Terrestrial Relations Observatory, Solar and Heliospheric
Observatory, and Hinode spacecraft and with in situ measurements by
Ulysses. The results are in good agreement with observations. This is
the first global simulation that is simultaneously consistent with
observations of both the thermal structure of the lower corona and
the wind structure beyond Earth's orbit.
Title: Hot Plasma Associated with a Coronal Mass Ejection
Authors: Landi, E.; Miralles, M. P.; Raymond, J. C.; Hara, H.
Bibcode: 2013ApJ...778...29L
Altcode:
We analyze coordinated observations from the EUV Imaging Spectrometer
(EIS) and X-Ray Telescope (XRT) on board Hinode of an X-ray Plasma
Ejection (XPE) that occurred during the coronal mass ejection (CME)
event of 2008 April 9. The XPE was trailing the CME core from behind,
following the same trajectory, and could be identified both in EIS
and XRT observations. Using the EIS spectrometer, we have determined
the XPE plasma parameters, measuring the electron density, thermal
distribution, and elemental composition. We have found that the XPE
composition and electron density were very similar to those of the
pre-event active region plasma. The XPE temperature was higher, and its
thermal distribution peaked at around 3 MK also, typical flare lines
were absent from EIS spectra, indicating that any XPE component with
temperatures in excess of 5 MK was likely either faint or absent. We
used XRT data to investigate the presence of hotter plasma components
in the XPE that could have gone undetected by EIS and found that—if
at all present—these components have small emission measure values
and their temperature is in the 8-12.5 MK range. The very hot plasma
found in earlier XPE observations obtained by Yohkoh seems to be
largely absent in this CME, although plasma ionization timescales
may lead to non-equilibrium ionization effects that could make bright
lines from ions formed in a 10 MK plasma not detectable by EIS. Our
results supersede the XPE findings of Landi et al., who studied the
same event with older response functions for the XRT Al-poly filter;
the differences in the results stress the importance of using accurate
filter response functions.
Title: Two Novel Parameters to Evaluate the Global Complexity of
the Sun's Magnetic Field and Track the Solar Cycle
Authors: Zhao, L.; Landi, E.; Gibson, S. E.
Bibcode: 2013ApJ...773..157Z
Altcode:
Since the unusually prolonged and weak solar minimum between solar
cycles 23 and 24 (2008-2010), the sunspot number is smaller and the
overall morphology of the Sun's magnetic field is more complicated
(i.e., less of a dipole component and more of a tilted current sheet)
compared with the same minimum and ascending phases of the previous
cycle. Nearly 13 yr after the last solar maximum (~2000), the monthly
sunspot number is currently only at half the highest value of the
past cycle's maximum, whereas the polar magnetic field of the Sun
is reversing (north pole first). These circumstances make it timely
to consider alternatives to the sunspot number for tracking the Sun's
magnetic cycle and measuring its complexity. In this study, we introduce
two novel parameters, the standard deviation (SD) of the latitude of
the heliospheric current sheet (HCS) and the integrated slope (SL)
of the HCS, to evaluate the complexity of the Sun's magnetic field
and track the solar cycle. SD and SL are obtained from the magnetic
synoptic maps calculated by a potential field source surface model. We
find that SD and SL are sensitive to the complexity of the HCS:
(1) they have low values when the HCS is flat at solar minimum,
and high values when the HCS is highly tilted at solar maximum;
(2) they respond to the topology of the HCS differently, as a higher
SD value indicates that a larger part of the HCS extends to higher
latitude, while a higher SL value implies that the HCS is wavier;
(3) they are good indicators of magnetically anomalous cycles. Based
on the comparison between SD and SL with the normalized sunspot number
in the most recent four solar cycles, we find that in 2011 the solar
magnetic field had attained a similar complexity as compared to the
previous maxima. In addition, in the ascending phase of cycle 24,
SD and SL in the northern hemisphere were on the average much greater
than in the southern hemisphere, indicating a more tilted and wavier
HCS in the north than the south, associated with the early reversal
of the polar magnetic field in the north relative to the south.
Title: Prominence Plasma Diagnostics through Extreme-ultraviolet
Absorption
Authors: Landi, E.; Reale, F.
Bibcode: 2013ApJ...772...71L
Altcode: 2012arXiv1209.2934L
In this paper, we introduce a new diagnostic technique that uses EUV
and UV absorption to determine the electron temperature and column
emission measure, as well as the He/H relative abundance of the
absorbing plasma. If a realistic assumption on the geometry of the
latter can be made and a spectral code such as CHIANTI is used, then
this technique can also yield the absorbing plasma hydrogen and electron
density. This technique capitalizes on the absorption properties of
hydrogen and helium at different wavelength ranges and temperature
regimes. Several cases where this technique can be successfully applied
are described. This technique works best when the absorbing plasma is
hotter than 15,000 K. We demonstrate this technique on AIA observations
of plasma absorption during a coronal mass ejection eruption. This
technique can be easily applied to existing observations of prominences
and cold plasmas in the Sun from almost all space missions devoted to
the study of the solar atmosphere, which we list.
Title: Comparison of Coronal Streamer Properties to Solar Wind Models
For The Last Two Solar Cycle Minima
Authors: Miralles, Mari Paz; Landi, E.; Cranmer, S. R.; Raymond,
J. C.; Cohen, O.; Oran, R.
Bibcode: 2013SPD....44...28M
Altcode:
We characterize the physical properties of two coronal streamers
during Earth/Ulysses quadrature configurations for the previous two
solar minimum periods. Comparisons between coronal remote-sensing
observations and in situ measurements of solar wind plasma properties
are being used to characterize the origin of slow wind streams. In order
to investigate slow solar wind heating and acceleration, we compare
the measurements with predictions from MHD models. We aim to use
the empirical measurements to distinguish between different proposed
physical processes for the slow solar wind. This work is supported by
NASA grant NNX10AQ58G to the Smithsonian Astrophysical Observatory.
Title: Progress toward high resolution EUV spectroscopy
Authors: Korendyke, C.; Doschek, G. A.; Warren, H.; Young, P. R.;
Chua, D.; Hassler, D. M.; Landi, E.; Davila, J. M.; Klimchuck, J.;
Tun, S.; DeForest, C.; Mariska, J. T.; Solar C Spectroscopy Working
Group; LEMUR; EUVST Development Team
Bibcode: 2013SPD....44..143K
Altcode:
HIgh resolution EUV spectroscopy is a critical instrumental technique
to understand fundamental physical processes in the high temperature
solar atmosphere. Spectroscopic observations are used to measure
differential emission measure, line of sight and turbulent flows,
plasma densities and emission measures. Spatially resolved, spectra of
these emission lines with adequate cadence will provide the necessary
clues linking small scale structures with large scale, energetic
solar phenomena. The necessary observations to determine underlying
physical processes and to provide comprehensive temperature coverage
of the solar atmosphere above the chromosphere will be obtained by the
proposed EUVST instrument for Solar C. This instrument and its design
will be discussed in this paper. Progress on the VEry high Resolution
Imaging Spectrograph (VERIS) sounding rocket instrument presently under
development at the Naval Research Laboratory will also be discussed.
Title: EUNIS 2013 and Beyond: Resolving the AIA 94 and 131 Å
Bandpasses
Authors: Daw, Adrian N.; Brosius, J. W.; Haas, J. P.; Landi, E.;
Plummer, T.; Rabin, D. M.; Wang, T.
Bibcode: 2013SPD....44...10D
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument is a two-channel imaging spectrograph that observes
the solar corona and transition region with high spectral resolution
and a rapid cadence made possible by unprecedented sensitivity. The
2013 flight on 23 April at 17:30 UT incorporated a new wavelength
channel covering the range 525-630 Å, the previously-flown 300-370
Å channel, and the first flight demonstration of cooled active
pixel sensor (APS) arrays, resulting in high-signal-to-noise spectral
coverage spanning a wide temperature range of 0.025 to 10 MK. Absolute
radiometric calibration of the two channels is performed using a hollow
cathode discharge lamp and NIST-calibrated AXUV-100G photodiode. For
the 2013 flight, EUNIS co-observed dynamic coronal phenomena with
DST/IBIS, SoHO/CDS, SDO/AIA and Hinode/EIS and contributes to the
absolute radiometric calibrations of these instruments. Plans for
future wavelength channels to cover the AIA 94 and 131 Å bandpasses
and address the currently unresolved spectral lines (and therefore
temperature responses) within them are presented.
Title: Bright Hot Impacts by Erupted Fragments Falling Back on the
Sun: A Template for Stellar Accretion
Authors: Reale, Fabio; Orlando, Salvatore; Testa, Paola; Peres,
Giovanni; Landi, Enrico; Schrijver, Carolus J.
Bibcode: 2013Sci...341..251R
Altcode:
Impacts of falling fragments observed after the eruption of a filament
in a solar flare on 7 June 2011 are similar to those inferred for
accretion flows on young stellar objects. As imaged in the ultraviolet
(UV)-extreme UV range by the Atmospheric Imaging Assembly onboard
the Solar Dynamics Observatory, many impacts of dark, dense matter
display uncommonly intense, compact brightenings. High-resolution
hydrodynamic simulations show that such bright spots, with plasma
temperatures increasing from ~104 to ~106
kelvin, occur when high-density plasma (>>1010
particles per cubic centimeter) hits the solar surface at several
hundred kilometers per second, producing high-energy emission as in
stellar accretion. The high-energy emission comes from the original
fragment material and is heavily absorbed by optically thick plasma,
possibly explaining the lower mass accretion rates inferred from x-rays
relative to UV-optical-near infrared observations of young stars.
Title: Heating of Coronal Streamers: a Combined Study Using a 3D
Alfven Wave Solar Model and SUMER Observations
Authors: Oran, Rona; van der Holst, Bart; Landi, Enrico; Gombosi, Tamas
Bibcode: 2013shin.confE.121O
Altcode:
The temperature of coronal ions is an important observable that can help
us test our understanding of coronal heating processes: by measuring
the broadening of coronal emission lines, the effective temperature
profiles of the different ion species can be determined. Several
efforts have studied the effective temperature profiles in polar
coronal holes, but only a few have focused on the closed field lines
of helmet streamers, which are the target of the present work. In
this work, we combine model predictions of non-thermal broadening
with detailed SUMER observations of spectral line profiles in the
corona at heights between 1.04 and 1.3 solar radii inside a coronal
streamer. A synoptic map of the photospheric magnetic field at the
time of the SUMER observations is used as a boundary condition to the
model. By taking into account the modeled wave amplitude in the region
observed by SUMER, the non-thermal contribution to the line broadening
are calculated so that the ion temperatures can be estimated from the
observed line profiles.
Title: Two Novel Parameters to Evaluate the Global Complexity of
the Sun's Magnetic Field and to Track the Solar Cycle
Authors: Zhao, Liang; Landi, E.
Bibcode: 2013shin.confE..59Z
Altcode:
Since the unusually prolonged and weak solar minimum between the solar
cycles 23 and 24 (2008-2010), the sunspot number is smaller and the
overall morphology of the Sun's magnetic field is more complicated
(i.e. less of a dipole component and a more tilted current sheet)
compared with the same minimum and ascending phases of the previous
cycle. Nearly twelve years after the last solar maximum ( 2000),
the monthly sunspot number is currently only at half the highest
value of the past cycle's maximum, whereas the polar magnetic field
of the Sun is reversing (north pole first). These circumstances make
it timely to consider alternatives to sunspot number for tracking the
Sun's magnetic cycle and measuring its complexity. In this study, we
introduce two novel parameters, the Standard Deviation of the latitude
of the Heliospheric Current Sheet (HCS) (SD) and the integrated SLope
of the HCS (SL), to evaluate the complexity of the Sun's magnetic field
and to track the solar cycle. SD and SL are obtained from the magnetic
synoptic maps calculated by a Potential Field Source Surface model
(PFSS). We find that SD and SL are sensitive to the complexity of the
HCS: 1) they have low values when the HCS is flat at solar minimum,
and high values when the HCS is highly tilted at solar maximum; 2)
they respond to the topology of the HCS differently, as higher SD value
indicates a larger part of HCS extends to higher latitude, while a
higher SL value implies the HCS is wavier; 3) they are good indicators
of magnetically anomalous cycles. Based on the comparison between SD
and SL with the normalized sunspot number in the recent four cycles,
we find that in 2011 the solar magnetic field had attained a similar
complexity as compared to the previous maxima. In addition, in the
ascending phase of cycle 24, SD and SL in the northern hemisphere
are on the average much greater than in the southern hemisphere,
indicating a more tilted and wavier HCS in the north than the south,
associated with the early reversal of the polar magnetic field in the
north relative to the south.
Title: Polar- and Equatorial-coronal-hole Wind at Solar Minima:
ACE and Ulysses Observations
Authors: Zhao, Liang; Landi, E.
Bibcode: 2013shin.confE...1Z
Altcode:
The fast solar wind can be accelerated from at least two different
sources: polar coronal holes and equatorial coronal holes. Little is
known about the relationship between the wind coming from these two
different latitudes, and whether these two sub-categories of wind evolve
in the same way along the solar cycle. Ulysses 19-year observations
from 1990 to 2009, combined with ACE observations from 1998 to present,
provide us with in-situ measurements of solar wind properties that span
two entire solar cycles. These missions allow us to study the evolution
of the properties of the solar wind at different latitudes and provide
an ideal dataset to compare the properties and evolution of the fast
wind coming from equatorial and polar holes. In this work, we focus
on the evolution and properties of the PCH and ECH solar wind during
the minima of solar cycle 23 and 24. We use data from SWICS, SWOOPS,
VHM/FGM on board Ulysses, and SWICS, SWEPAM, and MAG on board ACE to
analyze the dynamic, composition, and magnetic field properties of
the PCH wind and ECH wind, with a special focus on their differences
during the minima of solar cycles 23 and 24. The comparison of PCH
and ECH wind shows that: 1) the dynamic, compositional and magnetic
properties of ECH wind and PCH are significantly different at any time
during the solar cycle, and 2) the two types of solar wind respond
differently to the changes in solar activity from cycle 23 to cycle
24. We discuss the implications of these results, and relate them to
remote sensing measurements of the properties of polar and equatorial
coronal holes carried out during the minima of cycles 23 and 24.
Title: Solar Wind Heavy Ions over Solar Cycle 23: ACE/SWICS
Measurements
Authors: Lepri, S. T.; Landi, E.; Zurbuchen, T. H.
Bibcode: 2013ApJ...768...94L
Altcode:
Solar wind plasma and compositional properties reflect the physical
properties of the corona and its evolution over time. Studies comparing
the previous solar minimum with the most recent, unusual solar minimum
indicate that significant environmental changes are occurring globally
on the Sun. For example, the magnetic field decreased 30% between
the last two solar minima, and the ionic charge states of O have
been reported to change toward lower values in the fast wind. In this
work, we systematically and comprehensively analyze the compositional
changes of the solar wind during cycle 23 from 2000 to 2010 while the
Sun moved from solar maximum to solar minimum. We find a systematic
change of C, O, Si, and Fe ionic charge states toward lower ionization
distributions. We also discuss long-term changes in elemental abundances
and show that there is a ~50% decrease of heavy ion abundances (He,
C, O, Si, and Fe) relative to H as the Sun went from solar maximum to
solar minimum. During this time, the relative abundances in the slow
wind remain organized by their first ionization potential. We discuss
these results and their implications for models of the evolution of
the solar atmosphere, and for the identification of the fast and slow
wind themselves.
Title: CHIANTI 7.1: a new database release for SDO data analysis
Authors: Young, P. R.; Landi, E.; Del Zanna, G.; Dere, K. P.; Mason,
H. E.
Bibcode: 2013enss.confE..58Y
Altcode:
Version 7.1 of the CHIANTI atomic database was released in October 2012
and contains a number of improvements to better model data returned by
the AIA and EVE instruments on board SDO. Specifically the models for
the important iron ions Fe VIII to Fe XIV have been greatly expanded,
yielding many thousands of new transitions in the 50-170 angstrom
range that enable the irradiance spectra obtained by EVE to be modeled
more accurately. A lack of available atomic data meant that the AIA 94
angstrom channel was not well modeled at low temperatures in earlier
versions of CHIANTI. New data for Fe VIII, Fe X and Fe XIV added to
CHIANTI 7.1 give important contributions to the channel and greatly
improve comparisons with theory.
Title: CHIANTI—An Atomic Database for Emission Lines. XIII. Soft
X-Ray Improvements and Other Changes
Authors: Landi, E.; Young, P. R.; Dere, K. P.; Del Zanna, G.; Mason,
H. E.
Bibcode: 2013ApJ...763...86L
Altcode:
The CHIANTI spectral code consists of two parts: an atomic database
and a suite of computer programs in Python and IDL. Together, they
allow the calculation of the optically thin spectrum of astrophysical
objects and provide spectroscopic plasma diagnostics for the analysis
of astrophysical spectra. The database includes atomic energy levels,
wavelengths, radiative transition probabilities, collision excitation
rate coefficients, ionization, and recombination rate coefficients,
as well as data to calculate free-free, free-bound, and two-photon
continuum emission. Version 7.1 has been released, which includes
improved data for several ions, recombination rates, and element
abundances. In particular, it provides a large expansion of the
CHIANTI models for key Fe ions from Fe VIII to Fe XIV to improve the
predicted emission in the 50-170 Å wavelength range. All data and
programs are freely available at http://www.chiantidatabase.org and
in SolarSoft, while the Python interface to CHIANTI can be found at
http://chiantipy.sourceforge.net.
Title: Multi-modal DEM in the solar corona
Authors: Nuevo, F. A.; Vásquez, A. M.; Frazin, R. A.; Landi, E.
Bibcode: 2013BAAA...56..395N
Altcode:
Differential emission measure tomography (DEMT) uses time series of
coronal EUV images covering a full solar rotation to determine the
three-dimensional (3D) distribution of the local differential emission
measure (LDEM). The LDEM of each tomographic voxel is a measure of the
thermal distribution of the plasma within the cell. The LDEM inversion
problem is under-determined and solved by modeling the LDEM as a
function with free parameters. In this work we implemented unimodal
and non-unimodal LDEM models constrained by data of 3 to 4 bands of
the Atmospheric Imaging Assembly (AIA) instrument on board the Solar
Dynamics Observatory (SDO) mission. Our study reveals a multi-modal
nature of the LDEM distribution of the global coronal plasma at the
tomographic resolution level.
Title: Sources of Solar Wind at Solar Minimum: Constraints from
Composition Data
Authors: Zurbuchen, Thomas H.; von Steiger, Rudolf; Gruesbeck, Jacob;
Landi, Enrico; Lepri, Susan T.; Zhao, Liang; Hansteen, Viggo
Bibcode: 2013mspc.book...41Z
Altcode:
No abstract at ADS
Title: Charge State Evolution in the Solar Wind. II. Plasma Charge
State Composition in the Inner Corona and Accelerating Fast Solar Wind
Authors: Landi, E.; Gruesbeck, J. R.; Lepri, S. T.; Zurbuchen, T. H.;
Fisk, L. A.
Bibcode: 2012ApJ...761...48L
Altcode:
In the present work, we calculate the evolution of the charge state
distribution within the fast solar wind. We use the temperature,
density, and velocity profiles predicted by Cranmer et al. to calculate
the ionization history of the most important heavy elements in the solar
corona and solar wind: C, N, O, Ne, Mg, Si, S, and Fe. The evolution
of each charge state is calculated from the source region in the lower
chromosphere to the final freeze-in point. We show that the solar
wind velocity causes the plasma to experience significant departures
from equilibrium at very low heights, well inside the field of view
(within 0.6 R sun from the solar limb) of nearly all the
available remote-sensing instrumentation, significantly affecting
observed spectral line intensities. We also study the evolution of
charge state ratios with distance from the source region, and the
temperature they indicate if ionization equilibrium is assumed. We
find that virtually every charge state from every element freezes in
at a different height, so that the definition of freeze-in height is
ambiguous. We also find that calculated freeze-in temperatures indicated
by charge state ratios from in situ measurements have little relation
to the local coronal temperature of the wind source region, and stop
evolving much earlier than their correspondent charge state ratio. We
discuss the implication of our results on plasma diagnostics of coronal
holes from spectroscopic measurements as well as on theoretical solar
wind models relying on coronal temperatures.
Title: The thermal and spatial structure of the solar corona over
the cycle and its implication for the coronae of inactive stars
Authors: Testa, P.; Landi, E.; Saar, S.
Bibcode: 2012AGUFMSH42A..05T
Altcode:
We use spectral (SOHO/SUMER and Hinode/EIS) and imaging (Hinode/XRT
and SDO/AIA) solar coronal data to systematically measure the thermal
structure of different types of solar features (coronal hole, quiet
Sun, X-ray bright points, active regions...), and how they vary over
the solar cycle. We use a combination of these structures to construct
a model for the quiet corona of the inactive G8V star tau Ceti, which
is a candidate stellar analog of a solar magnetic minimum. Since tau
Ceti is significantly metal-poor relative to the Sun, we reconstruct
the solar results with corresponding lower metallicities to generate
more appropriate coronal structures.
Title: Coronal Streamers and Their Associated Solar Wind Streams
Authors: Miralles, M. P.; Landi, E.; Cranmer, S. R.; Cohen, O.;
Raymond, J. C.
Bibcode: 2012AGUFMSH53A2268M
Altcode:
We use the EUV spectrometers aboard SOHO and Hinode and white-light
coronagraphs to characterize the physical properties of coronal
streamers during Earth/Ulysses quadrature configurations for the
previous two solar minimum periods. In addition, comparisons between
coronal observations and in situ measurements of solar wind plasma
properties are being used to further characterize the origins of slow
wind streams. In order to investigate slow solar wind heating and
acceleration, we also compare with predictions from three-dimensional
MHD models. We aim to use the empirical measurements to distinguish
between different proposed physical processes for slow wind acceleration
(e.g., waves/turbulence versus reconnection). This work is supported
by NASA grant NNX10AQ58G to the Smithsonian Astrophysical Observatory.
Title: Using the Low Freeze-in Height of Heavy Elements to Validate
a Global 3D Solar Model with an Upper Chromospheric Boundary
Authors: Oran, R.; van der Holst, B.; Landi, E.; Gruesbeck, J. R.;
Sokolov, I.; Manchester, W. B.; Gombosi, T. I.
Bibcode: 2012AGUFMSH33B2229O
Altcode:
We present results from a global 3D magnetohydrodynamic (MHD) model
extending from the top of the chromosphere to the inner heliosphere,
combined with an ionic charge state evolution model for Carbon,
Oxygen, Silicon and Iron ions. The MHD model is driven by Alfvenic
turbulence, which is the sole source of heating. The inner boundary of
the model is set at the top of the chromosphere with a temperature of
20,000K. Non ideal-MHD processes such as radiative cooling and electron
heat conduction are included, as well as separate electron and proton
temperatures. The speed, electron temperature and density distribution
along magnetic field lines are extracted from the MHD solution and
used as input to a charge state evolution model (Michigan Ionization
Code, Landi et al. [2012]). Compared to similar analysis based on MHD
models starting at the coronal base, where the electron temperature
is already in the 1MK range, setting the inner boundary at 20,000K
will allow us to fully characterize the evolution of the charge state
distribution of the heavy elements accelerated into the slow and fast
solar wind. In fact, the transition region is critical to the evolution
of elements like Carbon and Oxygen, which are the most abundant heavy
species observed by in-situ mass spectrometers. The predicted charge
state distribution will be used to validate the global model in two
ways. First, the predicted frozen-in charge state distribution can
be directly compared to in-situ measurements in the heliosphere made
by the SWICS instrument on board ACE and Ulysses. Second, the charge
state values predicted in the inner corona (below 1.5 solar radii)
can be combined with the CHIANTI database and the global model's 3D
temperature and density distributions to calculate spectral line
intensities and narrow-band images along any line of sight, to be
compared with observations from the SOHO/EIT, STEREO/EUVI, Hinode/EIS
and SDO/AIA instruments. We analyze both the solar minimum and maximum
cases, by using synoptic magnetograms to constrain the radial magnetic
field at the inner boundary.
Title: Exploring Small Spatial Scales in the Transition Region
and Solar Corona with the Very High Angular Resolution Imaging
Spectrometer (VERIS)
Authors: Chua, D. H.; Korendyke, C. M.; Vourlidas, A.; Brown, C. M.;
Tun-Beltran, S.; Klimchuk, J. A.; Landi, E.; Seely, J.; Davila, J. M.;
Hagood, R.; Roberts, D.; Shepler, E.; Feldman, R.; Moser, J.; Shea, J.
Bibcode: 2012AGUFMSH33A2217C
Altcode:
Theoretical and experimental investigations of the transition region
and coronal loops point to the importance of processes occurring on
small spatial scales in governing the strong dynamics and impulsive
energy release in these regions. As a consequence, high spatial,
temporal, and temperature resolution over a broad temperature range,
and accuracy in velocity and density determinations are all critical
observational parameters. Current instruments lack one or more of these
properties. These observational deficiencies have created a wide array
of opposing descriptions of coronal loop heating and questions such
as whether or not the plasma within coronal loops is multi-thermal or
isothermal. High spectral and spatial resolution spectroscopic data
are absolutely required to resolve these controversies and to advance
our understanding of the dynamics within the solar atmosphere. We
will achieve this with the Very High Angular Resolution Imaging
Spectrometer (VERIS) sounding rocket payload. VERIS consists of an
off-axis paraboloid telescope feeding a very high angular resolution,
extreme ultraviolet (EUV) imaging spectrometer that will provide
the first ever, simultaneous sub-arcsecond (0.16 arcsecond/pixel)
spectra in bright lines needed to study plasma structures in the
transition region, quiet corona, and active region core. It will do
so with a spectral resolution of >5000 to allow Doppler velocity
determinations to better than 3 km/s. VERIS uses a novel two-element,
normal incidence optical design with highly reflective, broad wavelength
coverage EUV coatings to access a spectral range with broad temperature
coverage (0.03-15 MK) and density-sensitive line ratios. Combined with
Hinode Solar Optical Telescope (SOT) and ground based observatories,
VERIS will deliver simultaneous observations of the entire solar
atmosphere from the photosphere to the multi-million degree corona
at sub-arcsecond resolution for the first time ever, allowing us to
understand the missing link between chromospheric structures and the
corona. VERIS will be launched from White Sands Missile Range in early
2013. This paper presents a progress report on the VERIS payload and
a summary of observations planned to further our understanding of
the fine-scale structure of individual coronal loops and the heating
mechanisms operating within them.
Title: Sources of Solar Wind at Solar Minimum: Constraints from
Composition Data
Authors: Zurbuchen, Thomas H.; von Steiger, Rudolf; Gruesbeck, Jacob;
Landi, Enrico; Lepri, Susan T.; Zhao, Liang; Hansteen, Viggo
Bibcode: 2012SSRv..172...41Z
Altcode: 2012SSRv..tmp...25Z
In this discussion of observational constraints on the source regions
and acceleration processes of solar wind, we will focus on the
ionic composition of the solar wind and the distribution of charge
states of heavy elements such as oxygen and iron. We first focus on
the now well-known bi-modal nature of solar wind, which dominates
the heliosphere at solar minimum: Compositionally cool solar wind
from polar coronal holes over-expands, filling a much larger solid
angle than the coronal holes on the Sun. We use a series of remote and
in-situ characteristics to derive a global geometric expansion factor of
∼5. Slower, streamer-associated wind is located near the heliospheric
current sheet with a width of 10-20°, but in a well-defined band with
a geometrically small transition width. We then compute charge states
under the assumption of thermal electron distributions and temperature,
velocity, and density profiles predicted by a recent solar wind model,
and conclude that the solar wind originates from a hot source at around
1 million K, characteristic of the closed corona.
Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere
Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico
Bibcode: 2012uxss.book.....P
Altcode:
1. The solar atmosphere; 2. Fundamentals of solar radiation;
3. Fundamentals of atomic physics; 4. Mechanisms of formation of the
solar spectrum; 5. Plasma diagnostic techniques; 6. Ultraviolet and
X-ray emission lines; 7. Spectrometers and imagers for observing the
solar ultraviolet and X-ray spectrum; 8. Quiet Sun and coronal holes;
9. Active regions; 10. Solar flares; 11. Element abundances; Appendices;
References; Index.
Title: Charge State Evolution in the Solar Wind. Radiative Losses
in Fast Solar Wind Plasmas
Authors: Landi, E.; Gruesbeck, J. R.; Lepri, S. T.; Zurbuchen, T. H.;
Fisk, L. A.
Bibcode: 2012ApJ...758L..21L
Altcode:
We study the effects of departures from equilibrium on the radiative
losses of the accelerating fast, coronal hole-associated solar wind
plasma. We calculate the evolution of the ionic charge states in the
solar wind with the Michigan Ionization Code and use them to determine
the radiative losses along the wind trajectory. We use the velocity,
electron temperature, and electron density predicted by Cranmer et
al. as a benchmark case even though our approach and conclusions
are more broadly valid. We compare non-equilibrium radiative losses
to values calculated assuming ionization equilibrium at the local
temperature, and we find that differences are smaller than 20% in
the corona but reach a factor of three in the upper chromosphere and
transition region. Non-equilibrium radiative losses are systematically
larger than the equilibrium values, so that non-equilibrium wind
plasma radiates more efficiently in the transition region. Comparing
the magnitude of the dominant energy terms in the Cranmer et al. model,
we find that wind-induced departures from equilibrium are of the same
magnitude as the differences between radiative losses and conduction
in the energy equation. We investigate which ions are most responsible
for such effects, finding that carbon and oxygen are the main source of
departures from equilibrium. We conclude that non-equilibrium effects
on the wind energy equation are significant and recommend that they
are included in theoretical models of the solar wind, at least for
carbon and oxygen.
Title: Temperature and Extreme-ultraviolet Intensity in a Coronal
Prominence Cavity and Streamer
Authors: Kucera, T. A.; Gibson, S. E.; Schmit, D. J.; Landi, E.;
Tripathi, D.
Bibcode: 2012ApJ...757...73K
Altcode:
We analyze the temperature and EUV line emission of a coronal cavity and
surrounding streamer in terms of a morphological forward model. We use a
series of iron line ratios observed with the Hinode Extreme-ultraviolet
Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature
as a function of altitude in a morphological forward model of the
streamer and cavity. We also compare model predictions to the EIS EUV
line intensities and polarized brightness (pB) data from the Mauna
Loa Solar Observatory (MLSO) Mark 4 K-coronameter. This work builds
on earlier analysis using the same model to determine geometry of
and density in the same cavity and streamer. The fit to the data
with altitude-dependent temperature profiles indicates that both
the streamer and cavity have temperatures in the range 1.4-1.7
MK. However, the cavity exhibits substantial substructure such
that the altitude-dependent temperature profile is not sufficient to
completely model conditions in the cavity. Coronal prominence cavities
are structured by magnetism so clues to this structure are to be found
in their plasma properties. These temperature substructures are likely
related to structures in the cavity magnetic field. Furthermore,
we find that the model overestimates the EUV line intensities by a
factor of 4-10, without overestimating pB. We discuss this difference
in terms of filling factors and uncertainties in density diagnostics
and elemental abundances.
Title: Newly Discovered Global Temperature Structures in the Quiet
Sun at Solar Minimum
Authors: Huang, Zhenguang; Frazin, Richard A.; Landi, Enrico;
Manchester, Ward B.; Vásquez, Alberto M.; Gombosi, Tamas I.
Bibcode: 2012ApJ...755...86H
Altcode: 2012arXiv1207.6661H
Magnetic loops are building blocks of the closed-field corona. While
active region loops are readily seen in images taken at EUV and
X-ray wavelengths, quiet-Sun (QS) loops are seldom identifiable and
are therefore difficult to study on an individual basis. The first
analysis of solar minimum (Carrington Rotation 2077) QS coronal
loops utilizing a novel technique called the Michigan Loop Diagnostic
Technique (MLDT) is presented. This technique combines Differential
Emission Measure Tomography and a potential field source surface
(PFSS) model, and consists of tracing PFSS field lines through the
tomographic grid on which the local differential emission measure
is determined. As a result, the electron temperature Te
and density Ne at each point along each individual field
line can be obtained. Using data from STEREO/EUVI and SOHO/MDI, the
MLDT identifies two types of QS loops in the corona: so-called up
loops in which the temperature increases with height and so-called
down loops in which the temperature decreases with height. Up loops
are expected, however, down loops are a surprise, and furthermore,
they are ubiquitous in the low-latitude corona. Up loops dominate the
QS at higher latitudes. The MLDT allows independent determination of
the empirical pressure and density scale heights, and the differences
between the two remain to be explained. The down loops appear to be
a newly discovered property of the solar minimum corona that may shed
light on the physics of coronal heating. The results are shown to be
robust to the calibration uncertainties of the EUVI instrument.
Title: The role of radiative losses in the late evolution of
pulse-heated coronal loops/strands
Authors: Reale, F.; Landi, E.
Bibcode: 2012A&A...543A..90R
Altcode: 2012arXiv1205.4553R
Context. Radiative losses from optically thin plasma are an important
ingredient in modeling confined plasma in the solar corona. Spectral
models are continuously updated to include the emission from more
spectral lines, with significant effects on radiative losses, especially
around 1 MK.
Aims: We investigate the effect of changes to the
radiative-loss temperature dependence caused by upgrading spectral
codes on the predictions obtained when modeling confined plasma in the
solar corona.
Methods: We revisit the hydrodynamic simulation
of a pulse-heated loop strand by comparing results obtained using an
old and a recent radiative-loss function.
Results: We find that
significant changes occur in the plasma evolution during the late phases
of plasma cooling: when the more recent radiative-loss curve is used,
the plasma cooling rate indeed increases significantly when temperatures
reach 1-2 MK. This more rapid cooling occurs when the plasma density
is higher than a threshold value, which in impulsive heating models
leads to the loop plasma becoming overdense. This rapid cooling has the
effect of steepening the slope in the emission measure distribution of
coronal plasmas with temperature, at temperatures lower than ~2 MK, and
of reducing the visibility of warm (1 MK) loops.
Conclusions:
The effects of changes to the radiative-loss curves can be important
when modeling the late phases of the evolution of pulse-heated coronal
loops, and, in general, of thermally unstable optically thin plasmas.
Title: Evidence of Wave Damping at Low Heights in a Polar Coronal Hole
Authors: Hahn, M.; Landi, E.; Savin, D. W.
Bibcode: 2012ApJ...753...36H
Altcode: 2012arXiv1202.1743H
We have measured the widths of spectral lines from a polar coronal
hole using the Extreme Ultraviolet Imaging Spectrometer on board
Hinode. Polar coronal holes are regions of open magnetic field and the
source of the fast solar wind. We find that the line widths decrease
at relatively low heights. Previous observations have attributed such
decreases to systematic effects, but we find that such effects are
too small to explain our results. We conclude that the line narrowing
is real. The non-thermal line widths are believed to be proportional
to the amplitude of Alfvén waves propagating along these open field
lines. Our results suggest that Alfvén waves are damped at unexpectedly
low heights in a polar coronal hole. We derive an estimate on the upper
limit for the energy dissipated between 1.1 R ⊙ and 1.3
R ⊙ and find that it is enough to account for up to 70%
of that required to heat the polar coronal hole and accelerate the
solar wind.
Title: Complete Heavy Ion Charge State Distributions of Solar Wind
Heavy Ions Associated With ICMEs
Authors: Gilbert, Jason A.; Lepri, Susan T.; Landi, Enrico; Zurbuchen,
Thomas H.
Bibcode: 2012shin.confE..78G
Altcode:
The complete charge state distributions of certain heavy ions observed
in interplanetary coronal mass ejections have been measured, from singly
charged to fully ionized. To find all charge states, a novel analysis
technique is used, which requires the combination and cross-calibration
of two different data sets from ACE-SWICS. The first contains ions of
higher charge states, and includes an identification of their mass,
mass-per-charge, and energy-per-charge. The second data set contains
singly and low-charge ions, and identifies only their mass-per-charge
and energy-per-charge. Focusing on C, O, and Fe, we find ionic charge
states representative of temperatures from ≈60,000 K to over 5,000,000
K contained within interplanetary coronal mass ejections observed near 1
AU. We interpret these data in the context of near-Sun observations of
filament material associated with coronal mass ejections. We find that
singly charged ions are embedded within selected interplanetary coronal
mass ejections, and we examine their densities and durations. These
data thus provide the most unambiguous in situ diagnostic of solar
prominence plasma in the heliosphere.
Title: Solar wind diagnostic using both in-situ and spectroscopic
measurements
Authors: Landi, Enrico
Bibcode: 2012shin.confE...5L
Altcode:
We developed a new diagnostic technique that simultaneouslyutilizes
two completely different types of observations - in-situdeterminations
of solar wind charge states, and high-resolutionspectroscopy of the
inner solar corona - to determine the temperature,density and velocity
of the solar wind as a function of height in theinner corona, below
the plasma freeze-in point. This techniquerelies on the ability to
calculate the evolution of the ion chargecomposition as the solar
wind escapes the Sun given wind temperature,density and velocity
profiles as a function of distance. The resultingcharge composition
can be used to predict frozen-in charge statesas well as spectral
line intensities, to be compared with in-situ andremote sensing
observations.Such a comparison can be used in two ways. If the input
profilesare predicted by a theoretical solar wind model, this technique
allowsbenchmarking of the model. Otherwise, an empirical determination
ofthe velocity, temperature and density profile can be achieved below
theplasma freeze-in point applying a trial-and-error procedure to
initial,user-specified profiles. To demonstrate this methodology,
we have appliedthis technique to a state-of-the-art coronal hole and
equatorial streamermodel. We also show that line intensity profiles
depart from thoseobtained using the common ionization equilibrium
assumption.
Title: The Newly Discovered Global Temperature Structures in Different
Solar Rotation
Authors: Huang, Zhenguang; Frazin, Richard A.; Landi, Enrico;
Manchester, W. B., IV; Vásquez, Alberto M.; Gombosi, Tamas I.
Bibcode: 2012shin.confE..99H
Altcode:
We recently studied the quiet solar (QS) corona for Carrington
Rotation 2077 with the Michigan Loop Diagnostic Technique (MLDT). The
MLDT combines Differential Emission Measure Tomography (DEMT) and a
potential field source surface (PFSS) to provide the electron density
(Ne) and electron temperature (Te) along magnetic field lines through
the tomographic grid where the local differential emission measure
(LDEM) is determined. We identify two types of QS loops with the data
from STEREO/EUVI and SOHO/MDI:
Title: Evidence for Wave Damping at Low Heights in a Polar Coronal
Hole
Authors: Hahn, Michael; Landi, Enrico; Savin, Daniel W.
Bibcode: 2012shin.confE...4H
Altcode:
Polar coronal holes are regions of open magnetic field and are the
source of the fast solar wind. We have measured the widths of spectral
lines from a polar coronal hole using the Extreme Ultraviolet Imaging
Spectrometer onboard the Hinode satellite. Non-thermal broadening in
polar coronal holes is believed to be proportional to the amplitude
of Alfven waves propagating along these open field lines. We find that
line widths decrease at relatively low heights. Previous observations
have attributed such decreases to systematic effects, but we find
that such effects are too small to explain our results. We conclude
that the line narrowing is real, which suggests that Alfven waves are
damped at unexpectedly low heights in a polar coronal hole. We derive
an estimate for the upper limit for the energy dissipated between 1.1
and 1.3 solar radii and find that it is enough to account for up to
70% of that required to heat the polar coronal hole and accelerate
the solar wind.
Title: Newly Discovered Global Temperature Structures in the Quiet
Sun at Solar Minimum
Authors: Frazin, Richard A.; Huang, Zhenguang; Landi, Enrico;
Manchester, W. B., IV; Vásquez, Alberto M.; Gombosi, Tamas I.
Bibcode: 2012shin.confE.104F
Altcode:
Magnetic loops are building blocks of the closed-field corona. While
active region loops are readily seen in images taken at EUV and X-ray
wavelengths, quiet Sun loops are seldom identifiable and therefore
difficult to study on an individual basis. The first analysis of solar
minimum (Carrington Rotation 2077) quiet Sun (QS) coronal loopsutilizing
a novel technique called the Michigan Loop Diagnostic Technique (MLDT)
is presented. This technique combines Differential Emission Measure
Tomography (DEMT) and a potential field source surface (PFSS) model,
and consists of tracing PFSS field lines through the tomographic grid on
which the local differential emission measure (LDEM) is determined. As
a result, the electron temperature T_e and density N_e at each point
along each individual field line can be obtained.Using data from
STEREO/EUVI and SOHO/MDI, the MLDT identifies two types of QS loops:
so-called ``up'' loops in which the temperature increases with height,
and so-called "down"
Title: Coordinated Visible, EUV and White Light Observations of the
Extended Corona During the 2010 July 11 Total Solar Eclipse
Authors: Habbal, Shadia R.; Landi, E.; Morgan, H.; Druckmuller, M.;
Ding, A.
Bibcode: 2012AAS...22042303H
Altcode:
Eclipse observations of coronal forbidden lines emitted by highly
ionized elements are unique as they extend the field of view of
space-borne high-resolution EUV spectrometers and narrow-band EUV
imagers up to several solar radii. Furthermore, they combine in one
single dataset the two main features of space-borne instrumentation:
high spatial resolution 2D images of the solar corona and
full temperature resolution and diagnostic potential allowed by
monochromatic imaging of individual spectral lines. The limitation
of the published eclipse results, however, has been the absence of
an absolute calibration. In the present work, we combine the 2010
July 11 eclipse observations with simultaneous observations carried
out with the Hinode/EIS instrument. Such a combination allows us to
calibrate the eclipse images and to use them to carry out detailed
plasma diagnostics in the extended corona out to a few solar radii
using a variety of techniques.
Title: First Measurements of the Complete Heavy-ion Charge State
Distributions of C, O, and Fe Associated with Interplanetary Coronal
Mass Ejections
Authors: Gilbert, J. A.; Lepri, S. T.; Landi, E.; Zurbuchen, T. H.
Bibcode: 2012ApJ...751...20G
Altcode:
We present the first analysis of the complete charge state distributions
of heavy ions in interplanetary coronal mass ejections (CMEs),
from singly charged to fully ionized. We develop a novel analysis
technique that requires the combination and cross-calibration of two
different data sets from the Solar Wind Ion Composition Spectrometer
on the Advanced Composition Explorer. The first contains ions of
higher charge states, and includes an identification of their mass,
mass-per-charge, and energy-per-charge. The second data set contains
singly and low-charge ions, and identifies only their mass-per-charge
and energy-per-charge. Focusing on C, O, and Fe, we find ionic
charge states representative of temperatures from <=60,000 K to
over 5,000,000 K contained within interplanetary CMEs observed near 1
AU. We interpret these data in the context of near-Sun observations of
filament material associated with CMEs. We find that singly charged ions
are embedded within selected interplanetary CMEs, and we examine their
densities and durations. These data thus provide the most unambiguous
in situ diagnostic of solar prominence plasma in the heliosphere.
Title: Post-Coronal Mass Ejection Plasma Observed by Hinode
Authors: Landi, E.; Raymond, J. C.; Miralles, M. P.; Hara, H.
Bibcode: 2012ApJ...751...21L
Altcode:
In the present work we study the evolution of an active region after
the eruption of a coronal mass ejection (CME) using observations from
the EIS and XRT instruments on board Hinode. The field of view includes
a post-eruption arcade, a current sheet, and a coronal dimming. The
goal of this paper is to provide a comprehensive set of measurements
for all these aspects of the CME phenomenon made on the same CME
event. The main physical properties of the plasma along the line of
sight—electron density, thermal structure, plasma composition, size,
and, when possible, mass—are measured and monitored with time for
the first three hours following the CME event of 2008 April 9. We find
that the loop arcade observed by EIS and XRT may not be related to the
post-eruption arcade. Post-CME plasma is hotter than the surrounding
corona, but its temperature never exceeds 3 MK. Both the electron
density and thermal structure do not show significant evolution with
time, while we found that the size of the loop arcade in the Hinode
plane of the sky decreased with time. The plasma composition is the same
in the current sheet, in the loop arcade, and in the ambient plasma,
so all these plasmas are likely of coronal origin. No significant
plasma flows were detected.
Title: New Solar Wind Diagnostic Using Both in Situ and Spectroscopic
Measurements
Authors: Landi, E.; Gruesbeck, J. R.; Lepri, S. T.; Zurbuchen, T. H.
Bibcode: 2012ApJ...750..159L
Altcode:
We develop a new diagnostic technique that utilizes, at the same time,
two completely different types of observations—in situ determinations
of solar wind charge states and high-resolution spectroscopy of the
inner solar corona—in order to study the temperature, density,
and velocity of the solar wind as a function of height in the inner
corona below the plasma freeze-in point. This technique relies on the
ability to calculate the evolution of the ion charge composition as
the solar wind escapes the Sun given the wind temperature, density,
and velocity profiles as a function of distance. The resulting charge
state composition can be used to predict frozen-in charge states
as well as spectral line intensities. The predicted spectra and
ion charge compositions can be compared with observations carried
out when spectrometers and in situ instruments are in quadrature
configuration to quantitatively test a set of assumptions regarding
density, temperature, and velocity profiles in the low corona. Such
a comparison can be used in two ways. If the input profiles are
predicted by a theoretical solar wind model, this technique allows
the benchmarking of the model. Otherwise, an empirical determination
of the velocity, temperature, and density profiles can be achieved
below the plasma freeze-in point applying a trial-and-error procedure
to initial, user-specified profiles. To demonstrate this methodology,
we have applied this technique to a state-of-the-art coronal hole and
equatorial streamer model.
Title: Evidence for Wave Damping at at Low Heights in a Polar
Coronal Hole
Authors: Hahn, Michael; Landi, E.; Savin, D. W.
Bibcode: 2012AAS...22020103H
Altcode:
Polar coronal holes are regions of open magnetic field and are the
source of the fast solar wind. We have measured the widths of spectral
lines from a polar coronal hole using the Extreme Ultraviolet Imaging
Spectrometer onboard the Hinode satellite. Non-thermal broadening in
polar coronal holes is believed to be proportional to the amplitude
of Alfven waves propagating along these open field lines. We find that
line widths decrease at relatively low heights. Previous observations
have attributed such decreases to systematic effects, but we find
that such effects are too small to explain our results. We conclude
that the line narrowing is real, which suggests that Alfven waves are
damped at unexpectedly low heights in a polar coronal hole. We derive
an estimate for the upper limit for the energy dissipated between 1.1
and 1.3 solar radii and find that it is enough to account for up to
70% of that required to heat the polar coronal hole and accelerate
the solar wind.
Title: Temperature Structure of a Coronal Cavity and Streamer
Authors: Kucera, Therese A.; Gibson, S. E.; Schmit, D. J.; Landi,
E.; Tripathi, D.
Bibcode: 2012AAS...22052113K
Altcode:
We analyze the temperature and EUV line emission of a coronal cavity and
surrounding streamer in terms of a morphological forward model. We use a
series of iron line ratios observed with the Hinode Extreme-ultraviolet
Imaging Spectrograph (EIS) on 2007 Aug. 9 to constrain temperature
as a function of altitude in a morphological forward model of the
streamer and cavity. We also compare model prediction of the EIS EUV
line intensities and polarized brightness (pB) data from the Mauna Loa
Solar Observatory (MLSO) MK4. This work builds on earlier analysis using
the same model to determine geometry of and density in the same cavity
and streamer (Gibson et al. 2010 and Schmit and Gibson 2011). The fit
to the data with altitude dependent temperature profiles indicates that
both the streamer and cavity have temperatures in the range 1.4-1.7
MK. However, the cavity exhibits substantial substructure such that the
altitude dependent temperature profile is not sufficient to completely
model conditions in the cavity. This work is supported in part by the
NASA SHP program
Title: Monte Carlo Markov chain DEM reconstruction of isothermal
plasmas
Authors: Landi, E.; Reale, F.; Testa, P.
Bibcode: 2012A&A...538A.111L
Altcode: 2011arXiv1112.2857L
Context. Recent studies carried out with SOHO and Hinode high-resolution
spectrometers have shown that the plasma in the off-disk solar corona is
close to isothermal. If confirmed, these findings may have significant
consequences for theoretical models of coronal heating. However,
these studies have been carried out with diagnostic techniques whose
ability to reconstruct the plasma distribution with temperature has
not been thoroughly tested.
Aims: In this paper, we carry out
tests on the Monte Carlo Markov chain (MCMC) technique with the aim
of determining: 1) its ability to retrieve isothermal plasmas from a
set of spectral line intensities, with and without random noise; 2)
to what extent can it discriminate between an isothermal solution and a
narrow multithermal distribution; and 3) how well it can detect multiple
isothermal components along the line of sight. We also test the effects
of 4) atomic data uncertainties on the results, and 5) the number of
ions whose lines are available for the DEM reconstruction.
Methods: We first use the CHIANTI database to calculate synthetic
spectra from different thermal distributions: single isothermal
plasmas, multithermal plasmas made of multiple isothermal components,
and multithermal plasmas with a Gaussian DEM distribution with variable
width. We then apply the MCMC technique on each of these synthetic
spectra, so that the ability of the MCMC technique at reconstructing
the original thermal distribution can be evaluated. Next, we add a
random noise to the synthetic spectra, and repeat the exercise, in
order to determine the effects of random errors on the results. We
also we repeat the exercise using a different set of atomic data from
those used to calculate synthetic line intensities, to understand the
robustness of the results against atomic physics uncertainties. The
size of the temperature bin of the MCMC reconstruction is varied in
all cases, in order to determine the optimal width.
Results: We
find that the MCMC technique is unable to retrieve isothermal plasmas to
better than Δlog T ≃ 0.05. Also, the DEM curves obtained using lines
calculated with an isothermal plasma and with a Gaussian distribution
with FWHM of log T ≃ 0.05 are very similar. Two near-isothermal
components can be resolved if their temperature separation is Δlog
T = 0.2 or larger. Thus, DEM diagnostics has an intrinsic resolving
power of log T = 0.05. Atomic data uncertainties may significantly
affect both temperature and peak DEM values, but do not alter our
conclusions. The availability of small sets of lines also does not
worsen the performance of the MCMC technique, provided these lines are
formed in a wide temperature range.
Conclusions: Our analysis
shows the present limitations in our ability to identify the presence
of strictly isothermal plasmas in stellar and solar coronal spectra.
Title: Post-flare Ultraviolet Light Curves Explained with Thermal
Instability of Loop Plasma
Authors: Reale, F.; Landi, E.; Orlando, S.
Bibcode: 2012ApJ...746...18R
Altcode: 2011arXiv1111.3579R
In the present work, we study the C8 flare that occurred on 2000
September 26 at 19:49 UT and observed by the Solar and Heliospheric
Observatory/Solar Ultraviolet Measurement of Emitted Radiation
spectrometer from the beginning of the impulsive phase to well
beyond the disappearance in the X-rays. The emission first decayed
progressively through equilibrium states until the plasma reached
2-3 MK. Then, a series of cooler lines, i.e., Ca X, Ca VII, Ne VI,
O IV, and Si III (formed in the temperature range log T = 4.3-6.3
under equilibrium conditions), are emitted at the same time and all
evolve in a similar way. Here, we show that the simultaneous emission
of lines with such a different formation temperature is due to thermal
instability occurring in the flaring plasma as soon as it has cooled
below ~2 MK. We can qualitatively reproduce the relative start time
of the light curves of each line in the correct order with a simple
(and standard) model of a single flaring loop. The agreement with the
observed light curves is greatly improved, and a slower evolution of the
line emission is predicted, if we assume that the model loop consists
of an ensemble of subloops or strands heated at slightly different
times. Our analysis can be useful for flare observations with the
Solar Dynamics Observatory/Extreme ultraviolet Variability Experiment.
Title: Testing EUV/X-Ray Atomic Data for the Solar Dynamics
Observatory
Authors: Testa, Paola; Drake, Jeremy J.; Landi, Enrico
Bibcode: 2012ApJ...745..111T
Altcode: 2011arXiv1110.4611T
The Atmospheric Imaging Assembly (AIA) and the Extreme-ultraviolet
Variability Experiment (EVE) on board the Solar Dynamics Observatory
(SDO) include spectral windows in the X-ray/EUV band. Accuracy and
completeness of the atomic data in this wavelength range is essential
for interpretation of the spectrum and irradiance of the solar corona,
and of SDO observations made with the AIA and EVE instruments. Here,
we test the X-ray/EUV data in the CHIANTI database to assess their
completeness and accuracy in the SDO bands, with particular focus on the
94 Å and 131 Å AIA passbands. Given the paucity of solar observations
adequate for this purpose, we use high-resolution X-ray spectra of the
low-activity solar-like corona of Procyon obtained with the Chandra Low
Energy Transmission Grating Spectrometer (LETGS). We find that while
spectral models overall can reproduce quite well the observed spectra
in the soft X-ray range λ <~ 50 Å, and at the EUV wavelengths λ
>~ 130 Å, they significantly underestimate the observed flux in the
50-130 Å wavelength range. The model underestimates the observed flux
by a variable factor ranging from ≈1.5, at short wavelengths below
~50 Å, up to ≈5-7 in the ~70-125 Å range. In the AIA bands covered
by LETGS, i.e., 94 Å and 131 Å, we find that the observed flux can be
underestimated by large factors (~3 and ~1.9, respectively, for the case
of Procyon presented here). We discuss the consequences for analysis
of AIA data and possible empirical corrections to the AIA responses
to model more realistically the coronal emission in these passbands.
Title: A Global Two-temperature Corona and Inner Heliosphere Model:
A Comprehensive Validation Study
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Gruesbeck,
J. R.; Frazin, R. A.; Landi, E.; Vasquez, A. M.; Lamy, P. L.; Llebaria,
A.; Fedorov, A.; Toth, G.; Gombosi, T. I.
Bibcode: 2012ApJ...745....6J
Altcode:
The recent solar minimum with very low activity provides us a unique
opportunity for validating solar wind models. During CR2077 (2008
November 20 through December 17), the number of sunspots was near
the absolute minimum of solar cycle 23. For this solar rotation,
we perform a multi-spacecraft validation study for the recently
developed three-dimensional, two-temperature, Alfvén-wave-driven
global solar wind model (a component within the Space Weather Modeling
Framework). By using in situ observations from the Solar Terrestrial
Relations Observatory (STEREO) A and B, Advanced Composition Explorer
(ACE), and Venus Express, we compare the observed proton state (density,
temperature, and velocity) and magnetic field of the heliosphere with
that predicted by the model. Near the Sun, we validate the numerical
model with the electron density obtained from the solar rotational
tomography of Solar and Heliospheric Observatory/Large Angle and
Spectrometric Coronagraph C2 data in the range of 2.4 to 6 solar
radii. Electron temperature and density are determined from differential
emission measure tomography (DEMT) of STEREO A and B Extreme Ultraviolet
Imager data in the range of 1.035 to 1.225 solar radii. The electron
density and temperature derived from the Hinode/Extreme Ultraviolet
Imaging Spectrometer data are also used to compare with the DEMT as
well as the model output. Moreover, for the first time, we compare
ionic charge states of carbon, oxygen, silicon, and iron observed in
situ with the ACE/Solar Wind Ion Composition Spectrometer with those
predicted by our model. The validation results suggest that most of the
model outputs for CR2077 can fit the observations very well. Based on
this encouraging result, we therefore expect great improvement for the
future modeling of coronal mass ejections (CMEs) and CME-driven shocks.
Title: CHIANTI—An Atomic Database for Emission Lines. XII. Version
7 of the Database
Authors: Landi, E.; Del Zanna, G.; Young, P. R.; Dere, K. P.; Mason,
H. E.
Bibcode: 2012ApJ...744...99L
Altcode:
The CHIANTI spectral code consists of an atomic database and
a suite of computer programs to calculate the optically thin
spectrum of astrophysical objects and carry out spectroscopic plasma
diagnostics. The database includes atomic energy levels, wavelengths,
radiative transition probabilities, collision excitation rate
coefficients, and ionization and recombination rate coefficients,
as well as data to calculate free-free, free-bound, and two-photon
continuum emission. Version 7 has been released, which includes
several new ions, significant updates to existing ions, as well as
Chianti-Py, the implementation of CHIANTI software in the Python
programming language. All data and programs are freely available at
http://www.chiantidatabase.org, while the Python interface to CHIANTI
can be found at http://chiantipy.sourceforge.net.
Title: Carbon Ionization Stages as a Diagnostic of the Solar Wind
Authors: Landi, E.; Alexander, R. L.; Gruesbeck, J. R.; Gilbert,
J. A.; Lepri, S. T.; Manchester, W. B.; Zurbuchen, T. H.
Bibcode: 2012ApJ...744..100L
Altcode:
Oxygen charge states measured by in situ instrumentation have
long been used as a powerful diagnostic of the solar corona and
to discriminate between different solar wind regimes, both because
they freeze in very close to the Sun, and because the oxygen element
abundance is comparatively high, allowing for statistically relevant
measures. Like oxygen, carbon is also rather abundant and freezes in
very close to the Sun. Here, we show an analysis of carbon and oxygen
ionic charge states. First, through auditory and Fourier analysis of
in situ measurements of solar wind ion composition by ACE/SWICS we show
that some carbon ion ratios are very sensitive to solar wind type, even
more sensitive than the commonly used oxygen ion ratios. Then we study
the evolution of the ionization states of carbon and oxygen by means
of a freeze-in code, and find that carbon ions, commonly found in the
solar wind, freeze in at comparable coronal distances, while oxygen ions
evolve over a much larger range of coronal distances. Finally, we show
that carbon and oxygen ion abundance ratios have similar sensitivity
to the electron plasma temperature, but the carbon ratios are more
robust against atomic physics uncertainties and a better indicator of
the temperature of the solar wind source regions.
Title: Characterization of Slow Solar Wind Sources
Authors: Miralles, M. P.; Landi, E.; Cranmer, S. R.; Raymond, J. C.
Bibcode: 2011AGUFMSH33B2055M
Altcode:
The slow wind is a sizable component of the solar wind and plays a
fundamental role in shaping the interplanetary environment and its
variability. Coronal streamers are the prime source of slow solar
wind plasma. We use the EUV spectrometers aboard SOHO and Hinode to
characterize the physical properties of streamers and other candidate
coronal source regions of slow wind. In addition, comparisons between
coronal observations and in situ measurements of solar wind plasma
properties are being used to further characterize the origins of slow
wind streams. In order to investigate slow solar wind heating and
acceleration, we also compare with predictions from three-dimensional
models. We aim to use the empirical measurements to distinguish between
different proposed physical processes for slow wind acceleration (e.g.,
waves/turbulence versus reconnection). This work is supported by NASA
grant NNX10AQ58G to the Smithsonian Astrophysical Observatory.
Title: Modeling Solar Wind and Coronal Mass Ejection During Carrington
Rotation 2107
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Gruesbeck,
J. R.; Frazin, R. A.; Landi, E.; Vasquez, A. M.; Toth, G.; Gombosi,
T. I.
Bibcode: 2011AGUFMSH53C..08J
Altcode:
With the starting of solar cycle 24, the Sun begins to show more
activity. New observations from Solar Dynamics Observatory (SDO) give
us a great opportunity to test and validate our solar corona model
for space weather forecasts. During Carrington Rotation 2107, an M3.7
flare occurred in NOAA 11164 on 2011 March 7 with a fast CME (> 2000
km/s). There is also a Solar Energetic Particle (SEP) event associated
with this CME. In this study, we will first model the steady state solar
wind using a newly developed three-dimensional Alfven-wave-driven global
solar wind model within the Space Weather Modeling Framework (SWMF),
which includes counter propagating Alfven waves. The magnetic field of
the inner boundary is set up using the magnetogram from SDO/HMI. The
inner boundary condition for density and temperature are specified
from the Differential Emission Measure Tomography (DEMT) of SDO/AIA
data. A flux rope is then applied to the active region NOAA 11164 to
initiate the CME event. The properties of CME-driven shocks in the
model output are studied in detail, which will be used to simulate the
related SEP event in the future. By using multispacecraft observations,
we perform a validation study for the model results.
Title: A large-scale R-matrix calculation for electron-impact
excitation of the Ne2 +, O-like ion
Authors: McLaughlin, B. M.; Lee, Teck-Ghee; Ludlow, J. A.; Landi,
E.; Loch, S. D.; Pindzola, M. S.; Ballance, C. P.
Bibcode: 2011JPhB...44q5206M
Altcode: 2011arXiv1102.5127M
The five JΠ levels within an np2 or np4
ground-state complex provide an excellent testing ground for the
comparison of theoretical line ratios with astrophysically observed
values, in addition to providing valuable electron temperature
and density diagnostics. The low-temperature nature of the line
ratios ensures that the theoretically derived values are sensitive
to the underlying atomic structure and electron-impact excitation
rates. Previous R-matrix calculations for the O-like Ne ion, Ne2
+, exhibit spurious structure in the cross sections at higher
electron energies, which may affect Maxwellian averaged rates even at
low temperatures. Furthermore, there is an absence of comprehensive
excitation data between the excited states that may provide newer
diagnostics to complement the more established lines discussed in
this paper. To resolve these issues, we present both a small-scale
56-level Breit-Pauli calculation and a large-scale 554-level R-matrix
intermediate coupling frame transformation calculation that extends the
scope and validity of earlier JAJOM calculations both in terms of the
atomic structure and scattering cross sections. Our results provide a
comprehensive electron-impact excitation data set for all transitions
to higher n-shells. The fundamental atomic data for this O-like ion are
subsequently used within a collisional radiative framework to provide
the intensity line ratios across a range of electron temperatures and
densities of interest in astrophysical observations.
Title: Differential Emission Measure Analysis of a Polar Coronal
Hole during the Solar Minimum in 2007
Authors: Hahn, M.; Landi, E.; Savin, D. W.
Bibcode: 2011ApJ...736..101H
Altcode:
We have performed a differential emission measure (DEM) analysis
for a polar coronal hole observed during solar minimum in 2007. Five
observations are analyzed spanning the coronal hole from the central
meridian to the boundary with the quiet-Sun corona. The observed
heights ranged from 1.05 to 1.20 R sun. The analysis shows
that the plasma is not strictly isothermal anywhere, but rather has a
high-temperature component that extends up to log T(K) = 6.2-6.3. The
size and importance of this component depend on location, and its
evolving magnitude with height marks the boundary between the coronal
hole and the quiet corona, where it becomes dominant. The DEM of the
coronal hole plasma below log T(K) = 6.0 decreases faster with height
than that of the high-temperature component. We discuss the possible
nature of the high-temperature component. Our results highlight the
potential limitations of isothermal analyses. Such methods actually
measure a DEM-weighted average temperature and as a result can infer
artificial temperature gradients. Assuming the gas is isothermal along
the line of sight can also yield incorrect electron densities. By
revealing structures along the line of sight, a DEM analysis can also
be used to more reliably interpret electron temperature and density
measurements.
Title: Carbon ionization stages as a diagnostic of the solar wind
Authors: Landi, Enrico; Alexander, R. L.; Gruesbeck, J. R.; Gilbert,
J.; Lepri, S. T.; Manchester, W. B.; Zurbuchen, T. H.
Bibcode: 2011shin.confE..67L
Altcode:
Oxygen ion charges measured by in-situ instrumentation have long been
used as a powerful
Title: Differential Emission Measure Analysis of a Polar Coronal
Hole During the Recent Solar Minimum
Authors: Hahn, Michael; Landi, E.; Savin, D. W.
Bibcode: 2011shin.confE.162H
Altcode:
We have performed a differential emission measure (DEM) analysis for
a polar coronal hole observed during the solar minimum in 2007. The
analysis was performed for the above-limb portions of five observations
from the EUV Imaging Spectrometer on Hinode. The slit pointings also
included quiet Sun corona near the boundary with the coronal hole. The
analysis shows that the plasma is not strictly isothermal anywhere,
but rather has a high-temperature component that extends up to log T(K)
= 6.2-6.3. The size and importance of this component depend on location
and its evolving magnitude marks the boundary between the coronal hole
and the quiet corona, where it becomes dominant. Our results highlight
the potential limitations of isothermal analyses. Such methods actually
measure a DEM-weighted average temperature and as a result can infer
artificial temperature gradients. The isothermal analyses also do not
detect different structures along the line-of-sight, which can affect
the interpretation of density diagnostic line ratios.
Title: The X-ray Sun
Authors: Landi, Enrico
Bibcode: 2011APS..DMP.B1003L
Altcode:
The X-ray emission of the Sun is one of the main avenues through which
we can make progress in our understanding of the physical processes
that drive solar activity, heat and accelerate solar coronal plasmas,
and influence the interplanetary environment and the Earth itself. The
last decade has seen the launch of several space missions carrying
X-ray instrumentation, that have helped us to greatly advance our
understanding of our star. These missions have also boosted our need of
accurate atomic data for the interpretation of the observations. In this
talk I will review the main results delivered by X-ray solar missions,
and will highlight the challenges that still lie ahead of us and the
atomic data we need to face them.
Title: Coronal Bright Points and Quiet Sun Areas Observed with
EUNIS-07 and EIS
Authors: Brosius, Jeffrey W.; Wang, T. J.; Rabin, D. M.; Thomas,
R. J.; Landi, E.
Bibcode: 2011SPD....42.1828B
Altcode: 2011BAAS..43S.1828B
The Extreme-Ultraviolet Normal-Incidence Spectrograph is a
sounding rocket instrument with two independent but co-pointing
imaging spectrographs. One spectrograph observes emission lines in a
long-wavelength (LW) channel (300-370 A), while a second observes lines
in a short-wavelength (SW) channel (170-205 A). The instrument was last
flown on 6 November 2007 (EUNIS-07), when there were no active regions
on the solar disk. After the flight, the absolute radiometric responses
of both channels were derived from laboratory measurements obtained
in the same facility used for pre-flight calibrations of SOHO/CDS and
Hinode/EIS. Coordinated EUNIS-07 and EIS observations of quiet sun area
near disk center reveal that the sensitivity of both EIS wavebands had
diminished to 82% of their pre-launch values (Wang et al. 2011). Here
we use the combined EUNIS-07 and EIS spectra to investigate quiet sun
areas and small bright points observed by both instruments, as well
as a larger, brighter bright point that was observed only by EUNIS-07.
Title: Differential Emission Measure Analysis of a Polar Coronal
Hole During the Recent Solar Minimum
Authors: Hahn, Michael; Landi, E.; Savin, D. W.
Bibcode: 2011SPD....42.1827H
Altcode: 2011BAAS..43S.1827H
We have performed a differential emission measure (DEM) analysis
for a polar coronal hole observed during the solar minimum in
2007. The analysis was performed for the above-limb portions of five
observations from the EUV Imaging Spectrometer on Hinode. The slit
pointings also included quiet Sun corona near the boundary with the
coronal hole. Our DEM analysis showed that none of the positions
were completely isothermal. Instead the emitting material appeared
to have a significant high-temperature tail and was consistent with
being composed of two plasmas at different temperatures, as measured
in K, of log T = 5.95 and log T = 6.15. The lower temperature peak
was dominant in the coronal hole and the higher temperature peak
dominant in the quiet Sun corona. We used our DEM curves to model
isothermal analyses and found that relatively small deviations from
isothermality can distort the results inferred using an isothermal
analysis method. Isothermal temperature analyses actually measure a
DEM-weighted average and can infer artificial temperature gradients
if the high and low temperature parts of the DEM curve do not change
uniformly with position. The isothermal analyses also do not detect
different structures along the line-of-sight, which can affect the
interpretation of density diagnostic line ratios.
Title: First Results from Differential Emission Measure Tomography
with SDO/AIA
Authors: Frazin, Richard; Vásquez, A. M.; Landi, E.; Manchester,
W., IV; Huang, Z.
Bibcode: 2011SPD....42.2105F
Altcode: 2011BAAS..43S.2105F
We present, for the first time, the results of 3D differential emission
measure tomography (DEMT) applied to AIA data. The procedure has only be
applied to STEREO/EUVI data previously (ApJ 701, 547). The tomographic
reconstruction of 30.4 nm channel data provides a convenient tool for
qualitative mapping of filaments, whereas combining the tomographic
reconstructions from the bands dominated by coronal Fe lines yields
a 3D determination of the electron density and temperature as well
as higher order information. Compared to DEMT with EUVI, AIA provides
enhanced temperature coverage and opportunity for testing assumptions
used in the DEM inversion. Furthermore, we discuss the importance to
stray light reduction and atomic physics uncertainties to DEMT science.
Title: Temperature Distribution of a Non-flaring Active Region from
Simultaneous Hinode XRT and EIS Observations
Authors: Testa, Paola; Reale, Fabio; Landi, Enrico; DeLuca, Edward E.;
Kashyap, Vinay
Bibcode: 2011ApJ...728...30T
Altcode: 2010arXiv1012.0346T
We analyze coordinated Hinode X-ray Telescope (XRT) and Extreme
Ultraviolet Imaging Spectrometer (EIS) observations of a non-flaring
active region to investigate the thermal properties of coronal plasma
taking advantage of the complementary diagnostics provided by the
two instruments. In particular, we want to explore the presence of
hot plasma in non-flaring regions. Independent temperature analyses
from the XRT multi-filter data set, and the EIS spectra, including
the instrument entire wavelength range, provide a cross-check of the
different temperature diagnostics techniques applicable to broadband and
spectral data, respectively, and insights into cross-calibration of the
two instruments. The emission measure distributions, (EM(T)), we derive
from the two data sets have similar width and peak temperature, but
show a systematic shift of the absolute values, the EIS (EM(T)) being
smaller than the XRT (EM(T)) by approximately a factor two. We explore
possible causes of this discrepancy, and we discuss the influence of the
assumptions for the plasma element abundances. Specifically, we find
that the disagreement between the results from the two instruments
is significantly mitigated by assuming chemical composition closer
to the solar photospheric composition rather than the often adopted
"coronal" composition. We find that the data do not provide conclusive
evidence on the high temperature (log T(K) >~ 6.5) tail of the
plasma temperature distribution, however, suggesting its presence to
a level in agreement with recent findings for other non-flaring regions.
Title: Properties of a Polar Coronal Hole During the Solar Minimum
in 2007
Authors: Hahn, M.; Bryans, P.; Landi, E.; Miralles, M. P.; Savin, D. W.
Bibcode: 2010ApJ...725..774H
Altcode: 2010arXiv1010.4277H
We report measurements of a polar coronal hole during the recent
solar minimum using the Extreme Ultraviolet Imaging Spectrometer on
Hinode. Five observations are analyzed that span the polar coronal hole
from the central meridian to the boundary with the quiet-Sun corona. We
study the observations above the solar limb in the height range of
1.03-1.20 R sun. The electron temperature T e
and emission measure (EM) are found using a geometric mean emission
measure method. The EM derived from the elements Fe, Si, S, and Al
are compared in order to measure relative coronal-to-photospheric
abundance enhancement factors. We also studied the ion temperature
T i and the non-thermal velocity v nt using the
line profiles. All these measurements are compared to polar coronal hole
observations from the previous (1996-1997) solar minimum and to model
predictions for relative abundances. There are many similarities in the
physical properties of the polar coronal holes between the two minima at
these low heights. We find that the electron density, T e,
and T i are comparable in both minima. T e shows
a comparable gradient with height. Both minima show a decreasing T
i with increasing charge-to-mass ratio q/M. A previously
observed upturn of T i for ions above q/M>0.25 was not
found here. We also compared relative coronal-to-photospheric elemental
abundance enhancement factors for a number of elements. These ratios
were ~1 for both the low first ionization potential (FIP) elements Si
and Al and the marginally high FIP element S relative to the low FIP
element Fe, as is expected based on earlier observations and models
for a polar coronal hole. These results are consistent with no FIP
effect in a polar coronal hole.
Title: Fast Solar Wind Streams From the Sun to 1 AU During the Recent
Solar Minimum
Authors: Miralles, M. P.; Simunac, K. D.; Strachan, L.; Galvin, A. B.;
Landi, E.; Lee, C. O.; Luhmann, J. G.; McIntosh, P. S.
Bibcode: 2010AGUFMSH41A1773M
Altcode:
The origin and evolution of the solar wind from coronal holes is
studied by characterizing the physical properties of the solar wind
plasma (temperature, density, outflow velocity, and composition) with
multi-spacecraft and ground-based observations. PFSS modeling is also
used to confirm interpretation of the source regions and in wind-stream
boundary mapping. We discuss the results for the fast solar wind from
polar and low-latitude coronal-hole wind streams. We also compare the
characteristics of these wind streams with results from the previous
solar minimum.
Title: Hinode, STEREO and SOHO obervations of a CME event
Authors: Landi, E.; Raymond, J. C.; Miralles, M. P.; Hara, H.
Bibcode: 2010AGUFMSH31D..01L
Altcode:
Coronal Mass Ejections (CMEs) are among the most dramatic and violent
dynamic events occurring in the solar atmosphere, and have significant
impact on the near-Earth environment. So far, the physical processes
responsible for their release and acceleration have not been completely
understood, in part because of the lack of direct measurements of the
CME plasma phycical parameters and evolution during the CME onset. Here
we describe the analysis of multiwavelength observations from Hinode,
SOHO and STEREO of the very early phases of a CME observed during the
Whole Heliospheric Interval campaign. SECCHI/EUVI, SECCHI/COR1, SOHO/EIT
and SOHO/LASCO images are used to reconstruct the 3D trajectory,
velocity and acceleration up to 20 solar radii. Hinode/EIS, Hinode/XRT
and SOHO/UVCS high resolution EUV spectra and X-ray images are used to
measure the physical properties and the thermal structure of the core
of the CME ejecta as a function of time up to 2.0 solar radii. The
physical properties of the current sheet that formed after the CME
erupted are also measured as a function of time.
Title: Differential Emission Tomography of AIA Images
Authors: Frazin, R. A.; Vasquez, A. M.; Landi, E.
Bibcode: 2010AGUFMSH11A1598F
Altcode:
Differential Emission Measure Tomography (DEMT) uses a time series
of EUV images to determine the 3D distribution of the differential
emission measure in the solar corona, from which the electron density
and temperature, and other information, can be derived. Here we
present the first DEMT results based on data from the AIA instrument
on SDO. We use a 28-day time series of data from AIA’s six EUV bands,
and compare the results to those from the three STEREO-EUVI bands over
the same period. We will emphasize what we are learning from increased
spectral coverage of AIA and discuss uncertainties and future work.
Title: Science Objectives for an X-Ray Microcalorimeter Observing
the Sun
Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M;
Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse,
N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.;
DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra,
A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg,
C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.;
Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska,
J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres,
G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.;
Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz,
J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.;
Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B.
Bibcode: 2010arXiv1011.4052L
Altcode:
We present the science case for a broadband X-ray imager with
high-resolution spectroscopy, including simulations of X-ray spectral
diagnostics of both active regions and solar flares. This is part of
a trilogy of white papers discussing science, instrument (Bandler et
al. 2010), and missions (Bookbinder et al. 2010) to exploit major
advances recently made in transition-edge sensor (TES) detector
technology that enable resolution better than 2 eV in an array that
can handle high count rates. Combined with a modest X-ray mirror, this
instrument would combine arcsecondscale imaging with high-resolution
spectra over a field of view sufficiently large for the study of
active regions and flares, enabling a wide range of studies such as
the detection of microheating in active regions, ion-resolved velocity
flows, and the presence of non-thermal electrons in hot plasmas. It
would also enable more direct comparisons between solar and stellar
soft X-ray spectra, a waveband in which (unusually) we currently have
much better stellar data than we do of the Sun.
Title: On the Isothermality of Solar Plasmas
Authors: Landi, E.; Klimchuk, J. A.
Bibcode: 2010ApJ...723..320L
Altcode:
Recent measurements have shown that the quiet unstructured solar corona
observed at the solar limb is close to isothermal, at a temperature
that does not appear to change over wide areas or with time. Some
individual active region loop structures have also been found to
be nearly isothermal both along their axis and across their cross
section. Even a complex active region observed at the solar limb has
been found to be composed of three distinct isothermal plasmas. If
confirmed, these results would pose formidable challenges to the current
theoretical understanding of the thermal structure and heating of the
solar corona. For example, no current theoretical model can explain
the excess densities and lifetimes of many observed loops if the loops
are in fact isothermal. All of these measurements are based on the
so-called emission measure (EM) diagnostic technique that is applied
to a set of optically thin lines under the assumption of isothermal
plasma. It provides simultaneous measurement of both the temperature and
EM. In this work, we develop a new method to quantify the uncertainties
in the technique and to rigorously assess its ability to discriminate
between isothermal and multithermal plasmas. We define a formal measure
of the uncertainty in the EM diagnostic technique that can easily be
applied to real data. We here apply it to synthetic data based on a
variety of assumed plasma thermal distributions and develop a method
to quantitatively assess the degree of multithermality of a plasma.
Title: Ultraviolet Coronagraph Spectroscopy: A Key Capability for
Understanding the Physics of Solar Wind Acceleration
Authors: Cranmer, S. R.; Kohl, J. L.; Alexander, D.; Bhattacharjee,
A.; Breech, B. A.; Brickhouse, N. S.; Chandran, B. D. G.; Dupree,
A. K.; Esser, R.; Gary, S. P.; Hollweg, J. V.; Isenberg, P. A.; Kahler,
S. W.; Ko, Y. -K.; Laming, J. M.; Landi, E.; Matthaeus, W. H.; Murphy,
N. A.; Oughton, S.; Raymond, J. C.; Reisenfeld, D. B.; Suess, S. T.;
van Ballegooijen, A. A.; Wood, B. E.
Bibcode: 2010arXiv1011.2469C
Altcode:
Understanding the physical processes responsible for accelerating the
solar wind requires detailed measurements of the collisionless plasma
in the extended solar corona. Some key clues about these processes
have come from instruments that combine the power of an ultraviolet
(UV) spectrometer with an occulted telescope. This combination enables
measurements of ion emission lines far from the bright solar disk,
where most of the solar wind acceleration occurs. Although the UVCS
instrument on SOHO made several key discoveries, many questions remain
unanswered because its capabilities were limited. This white paper
summarizes these past achievements and also describes what can be
accomplished with next-generation instrumentation of this kind.
Title: Arcetri Spectral Code for Thin Plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 2010ascl.soft07005L
Altcode:
The Arcetri spectral code allows to evaluate the spectrum of the
radiation emitted by hot and optically thin plasmas in the spectral
range 1 - 2000 Angstroms. The database has been updated including atomic
data and radiative and collisional rates to calculate level population
and line emissivities for a number of ions of the minor elements;
a critical compilation of the electron collision excitation for these
elements has been performed. The present version of the program includes
the CHIANTI database for the most abundant elements, the minor elements
data, and Fe III atomic model, radiative and collisional data.
Title: Highly Ionized sodium X-ray line emission from the solar
corona and the abundance of sodium
Authors: Phillips, K. J. H.; Aggarwal, K. M.; Landi, E.; Keenan, F. P.
Bibcode: 2010A&A...518A..41P
Altcode: 2010arXiv1005.4375P
Context. The Na X X-ray lines between 10.9 and 11.2 Å have attracted
little attention but are of interest since they enable an estimate
of the coronal abundance of Na to be made. This is of great interest
in the continuing debate on the nature of the FIP (first ionization
potential) effect.
Aims: Observations of the Na X lines with
the Solar Maximum Mission Flat Crystal Spectrometer and a rocket-borne
X-ray spectrometer are used to measure the Na/Ne abundance ratio,
i.e. the ratio of an element with very low FIP to one with high
FIP.
Methods: New atomic data are used to generate synthetic
spectra which are compared with the observations, with temperature
and the Na/Ne abundance ratio as free parameters.
Results:
Temperature estimates from the observations indicate that the line
emission is principally from non-flaring active regions, and that the
Na/Ne abundance ratio is 0.07 ± 50%.
Conclusions: The Na/Ne
abundance ratio is close to a coronal value for which the abundances
of low-FIP elements (FIP < 10 eV) are enhanced by a factor of 3 to 4
over those found in the photosphere. For low-temperature (Te
≤slant 1.5 MK) spectra, the presence of Fe XVII lines requires that
either a higher-temperature component is present or a revision of
ionization or recombination rates is needed.
Title: Properties of the Solar Corona above a Polar Coronal Hole
during the Solar Minimum in 2007
Authors: Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M. P.; Savin,
D. W.
Bibcode: 2010shin.confE.150H
Altcode:
Observations have shown that the latest solar minimum differs from the
previous one in 1996-1997. Here we present the analysis of EUV spectra
of the north polar coronal hole observed during the recent minimum 16
November 2007. The data were taken using the Extreme ultraviolet Imaging
Spectrometer (EIS) on Hinode. Five observations span the coronal hole
in the longitudinal direction from the center to the boundary with
the quiet sun corona and extend radially from the solar disk to about
1.2 Rsun. We use the geometric mean emission measure (GEM) approach to
determine the plasma emission measure (EM) and electron temperature. The
GEM analysis shows that the observations are nearly isothermal, but
there are indications of a small contribution from higher temperature
plasma along the line of sight. To investigate the temperature structure
in more detail we are performing a differential emission measure (DEM)
analysis. The upper and lower bounds on the ion temperature are also
measured using line widths. Our results are compared to spectroscopic
measurements of polar coronal holes obtained from observations carried
out during the previous solar minimum in 1996-1997.
Title: Physical Conditions in a CME from Hinode, STEREO, and SOHO
Observations
Authors: Landi, E.; Raymond, J. C.; Miralles, M. P.; Hara, H.
Bibcode: 2010ASPC..428..201L
Altcode:
In the present work we analyze multiwavelength observations from
Hinode, SOHO, and STEREO of the early phases of a CME. We use EIS,
UVCS, and XRT to measure the physical properties of the CME ejecta as
a function of time at 1.1 and 1.9 Rsun. EUVI, COR 1, EIT,
and LASCO images are used to measure the CME trajectory, velocity, and
acceleration in 3D up to 5 Rsun. The diagnostic results are
used to determine the energy budget of the CME plasma and the heating
rate, and to compare it to theoretical predictions.
Title: Ion Temperatures in the Low Solar Corona: Polar Coronal Holes
at Solar Minimum
Authors: Landi, E.; Cranmer, S. R.
Bibcode: 2010ASPC..428..197L
Altcode:
We use a SUMER spectrum of a polar coronal hole to measure the
ion temperatures Ti of many ions between 0.03 and 0.17
Rsun above the limb. We find that the measured Ti
are almost always larger than the electron temperatures (Te)
and exhibit a non-monotonic dependence on the charge-to-mass ratio. We
use these measurements to provide empirical constraints to a theoretical
model of ion heating and acceleration based on gradually replenished
ion-cyclotron waves and anisotropic magnetohydrodynamic turbulence. We
find that the empirical heating model and the turbulent cascade model
agree with one another and with observations for charge-to-mass (Z/A)
ratios smaller than about 0.25. Ions with Z/A > 0.25 disagree with
the model.
Title: The Relative Intensity Calibration of Hinode/EIS and SOHO/SUMER
Authors: Landi, E.; Young, P. R.
Bibcode: 2010ApJ...714..636L
Altcode:
In this work, we have used simultaneous observations of the quiet Sun
above the solar west limb obtained with the Hinode/Extreme ultraviolet
Imaging Spectrograph and SOHO/SUMER instruments to determine their
relative intensity calibration. We used two different methods: intensity
ratios of lines emitted by the same upper level and observed in the
spectral ranges of the two spectrometers, and the determination of
the differential emission measure and total emission measure of the
plasma. We review the uncertainties in our analysis and conclude
that the relative calibration of the two instruments, as it can be
determined from the standard data reduction software of each of them,
is correct within uncertainties.
Title: Testing Atomic Data for the SDO AIA and EVE Missions
Authors: Testa, Paola; Landi, E.; Drake, J.
Bibcode: 2010AAS...21640203T
Altcode: 2010BAAS...41..873T
The Solar Dynamic Observatory carries two instruments, AIA and EVE, that
include spectral windows in the X-ray/EUV band ( 15-170A). Accuracy
in the atomic data in this wavelength range is essential for the
interpretation of the solar EUV irradiance data from EVE and of
the variability of the high temperature corona. Here we carry out a
detailed benchmark of X-ray/EUV data in the CHIANTI 6.0.1 database
to assess their completeness and accuracy. Given the paucity of solar
observations, we use high-resolution X-ray spectra of the low-activity
corona of Procyon obtained with the Low Energy Transmission Grating
Spectrometer onboard Chandra.
Title: Elemental Abundance Variations in a Decaying EUV-Bright Region
Authors: Ko, Yuan-Kuen; Landi, E.; Feldman, U.; Young, P.
Bibcode: 2010AAS...21640515K
Altcode: 2010BAAS...41..891K
The EIS instrument on Hinode observed an EUV-bright region at N15 as it
evolved during a course of four days on December 7-11, 2009. Although
containing no sunspots, this region was associated with a weak magnetic
concentration and exhibited large variations in loop and footpoint
brightening. It was in a decay phase with dispersing magnetic field
and weakening high-temperature emission. We present the variations of
elemental abundances in this region among different spatial structures
and with time. Implications in factors that can be associated with
the First Ionization Potential (FIP) effect will be discussed.
Title: Properties of the Solar Corona above a Polar Coronal Hole
during the Recent Solar Minimum
Authors: Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M.; Savin, D.
Bibcode: 2010AAS...21640105H
Altcode: 2010BAAS...41..857H
Recent observations have shown that the latest solar minimum differs
from the previous one in 1996-1997. Here we present the analysis of
EUV spectra of the north polar coronal hole observed in November 2007,
during the current minimum. The data were taken using the Extreme
Ultraviolet Imaging Spectrometer (EIS) on Hinode. Five observations
span the coronal hole in the longitudinal direction from the center
to the boundary with the quiet sun corona and extend radially from
the solar disk to about 1.2 solar radii to. We use the geometric mean
emission measure (GEM) approach to determine the plasma emission measure
(EM) and electron temperature. From the EM we estimate the relative
elemental abundances. We also determine upper and lower bounds on the
ion temperature using measured line widths. We then compare our results
to spectroscopic measurements of polar coronal holes obtained from
observations carried out during the previous solar minimum in 1996-1997.
Title: New Fe VIII Line Identifications using Observations of the
Quiet Sun
Authors: Landi, E.; Young, P. R.
Bibcode: 2010ApJ...713..205L
Altcode:
In this work, we study Fe VIII lines emitted in the 1000-1200 Å
wavelength range that originate from levels that also emit transitions
observed in the 190-200 Å wavelength range. The intensity ratios
between such lines depend on atomic physics parameters only and not
on the physical parameters of the emitting plasma: they are excellent
tools to verify the relative intensity calibration of instruments
operating in those wavelength ranges. We first carry out extensive
atomic physics calculations to improve the accuracy of the predicted
intensity ratios of those lines. We then compare the results with
simultaneous Hinode/Extreme Ultraviolet Imaging Spectrometer and
SOHO/SUMER observations of an off-disk quiet-Sun region, identify
four new lines in the 1000-1200 Å range, and discuss their use for
instrument calibration purposes.
Title: Physical Conditions in a Coronal Mass Ejection from Hinode,
Stereo, and SOHO Observations
Authors: Landi, E.; Raymond, J. C.; Miralles, M. P.; Hara, H.
Bibcode: 2010ApJ...711...75L
Altcode:
In the present work, we analyze multiwavelength observations from
Hinode, Solar and Heliospheric Observatory (SOHO), and STEREO of the
early phases of a coronal mass ejection (CME). We use Hinode/EIS
and SOHO/UVCS high-resolution spectra to measure the physical
properties of the CME ejecta as a function of time at 1.1 and 1.9
solar radii. Hinode/XRT images are used in combination with EIS
spectra to constrain the high temperature plasma properties of the
ejecta. SECCHI/EUVI, SECCHI/COR 1, SOHO/EIT, and SOHO/LASCO images are
used to measure the CME trajectory, velocity, and acceleration. The
combination of measurements of plane of the sky velocities from two
different directions allows us to determine the total velocity of the
CME plasma up to 5 solar radii. Plasma properties, dynamical status,
thermal structure, and brightness distributions are used to constrain
the energy content of the CME plasma and to determine the heating
rate. We find that the heating is larger than the kinetic energy,
and compare it to theoretical predictions from models of CME plasma
heating and acceleration.
Title: A new approach for deriving the solar irradiance from
nonflaring solar upper atmosphere plasmas at 2 × 104
≤ T ≤ 2 × 107 K
Authors: Feldman, U.; Brown, C. M.; Seely, J. F.; Dammasch, I. E.;
Landi, E.; Doschek, G. A.; Colgan, J.; Abdallah, J.; Fontes, C. J.;
Sherrill, M. E.
Bibcode: 2010JGRA..115.3101F
Altcode: 2010JGRA..11503101F
We propose a new approach for deriving the solar irradiance due to the
emission by solar upper atmosphere plasmas at 2 × 104 ≤
T ≤ 2 × 107 K for wavelengths shorter than 800 Å. Our
approach is based on a new understanding of the properties of the solar
upper atmosphere; specifically, the discovery that the majority of
emission from the nonflaring solar upper transition region and corona in
the temperature range 3 × 105 ≤ T ≤ 3 × 106
K arises from isothermal plasmas that have four distinct temperatures:
0.35, 0.9, 1.4, and 3 × 106 K. Although the lower transition
region (2 × 104 ≤ T ≤ 2 × 105 K) of coronal
holes, quiet regions or active regions, is multithermal and variable
in brightness, the shape of emission measure versus temperature curves
in this region is almost constant. At any given time, flaring plasmas
are for the most part isothermal, although their emission measure and
temperature continuously change. In this paper we review these recent
results and propose a set of simple spectrometers for recording the
solar spectrum in several narrow bands. The solar emission measure,
average plasma temperature, and composition can be derived using the
measured line fluxes. By combining the emission measure and other
plasma properties with the output of a suite of atomic physics codes,
which are also described here, the solar irradiance at wavelengths
shorter than 800 Å can be calculated.
Title: Bright Points and Jets in Polar Coronal Holes Observed by
the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Landi, E.; Warren, H. P.; Harra, L. K.
Bibcode: 2010ApJ...710.1806D
Altcode:
We present observations of polar coronal hole bright points (BPs)
made with the Extreme-ultraviolet Imaging Spectrometer (EIS) on the
Hinode spacecraft. The data consist of raster images of BPs in multiple
spectral lines from mostly coronal ions, e.g., Fe X-Fe XV. The BPs
are observed for short intervals and thus the data are snapshots of
the BPs obtained during their evolution. The images reveal a complex
unresolved temperature structure (EIS resolution is about 2''), with the
highest temperature being about 2 × 106 K. Some BPs appear
as small loops with temperatures that are highest near the top. But
others are more point-like with surrounding structures. However, the
thermal time evolution of the BPs is an important factor in their
appearance. A BP may appear quite different at different times. We
discuss one BP with an associated jet that is bright enough to allow
statistically meaningful measurements. The jet Doppler speed along the
line of sight is about 15-20 km s-1. Electron densities of
the BPs and the jet are typically near 109 cm-3,
which implies path lengths along the line of sight on the order of a
few arcsec. We also construct differential emission measure curves for
two of the best observed BPs. High spatial resolution (significantly
better than 1'') is required to fully resolve the BP structures.
Title: The Structure and Dynamics of the Upper Chromosphere and Lower
Transition Region as Revealed by the Subarcsecond VAULT Observations
Authors: Vourlidas, A.; Sanchez Andrade-Nuño, B.; Landi, E.;
Patsourakos, S.; Teriaca, L.; Schühle, U.; Korendyke, C. M.;
Nestoras, I.
Bibcode: 2010SoPh..261...53V
Altcode: 2009arXiv0912.2272V
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a
sounding rocket payload built to study the crucial interface between
the solar chromosphere and the corona by observing the strongest line
in the solar spectrum, the Ly α line at 1216 Å. In two flights, VAULT
succeeded in obtaining the first ever subarcsecond ( 0.5\hbox{$^''$}
) images of this region with high sensitivity and cadence. Detailed
analyses of those observations contributed significantly to new
ideas about the nature of the transition region. Here, we present
a broad overview of the Ly α atmosphere as revealed by the VAULT
observations and bring together past results and new analyses from the
second VAULT flight to create a synthesis of our current knowledge
of the high-resolution Ly α Sun. We hope that this work will serve
as a good reference for the design of upcoming Ly α telescopes and
observing plans.
Title: The Electron Temperature of the Solar Transition Region as
Derived from EIS and SUMER
Authors: Muglach, K.; Landi, E.; Doschek, G. A.
Bibcode: 2010ApJ...708..550M
Altcode:
We use UV and extreme-UV emission lines observed in quiet regions on the
solar disk with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) instrument and the Extreme Ultraviolet Imaging Spectrometer
(EIS) to determine the electron temperature in solar transition region
plasmas. Prominent emission lines of O IV and O VI are present in
the solar spectrum, and the measured intensity line ratios provide
electron temperatures in the range of log T = 5.6-6.1. We find that the
theoretical O IV and O VI ion formation temperatures are considerably
lower than our derived temperatures. The line ratios expected from
a plasma in ionization equilibrium are larger by a factor of about
2-5 than the measured line ratios. A careful cross-calibration of
SUMER and EIS has been carried out, which excludes errors in the
relative calibration of the two instruments. We checked for other
instrumental and observational effects, as well as line blending,
and can exclude them as a possible source of the discrepancy between
theoretical and observed line ratios. Using a multi-thermal quiet-Sun
differential emission measure changes the theoretical line ratio by
up to 28% which is not sufficient as an explanation. We also explored
additional excitation mechanisms. Photoexcitation from photospheric
blackbody radiation, self-absorption, and recombination into excited
levels cannot be a possible solution. Adding a second Maxwellian to
simulate the presence of non-thermal, high-energy electrons in the
plasma distribution of velocities also did not solve the discrepancy.
Title: New Fe IX Line Identifications Using Solar and Heliospheric
Observatory/Solar Ultraviolet Measurement of Emitted Radiation and
Hinode/EIS Joint Observations of the Quiet Sun
Authors: Landi, E.; Young, P. R.
Bibcode: 2009ApJ...707.1191L
Altcode:
In this work, we study joint observations of Hinode/EUV Imaging
Spectrometer (EIS) and Solar and Heliospheric Observatory/Solar
Ultraviolet Measurement of Emitted Radiation of Fe IX lines emitted
by the same level of the high energy configuration 3s 23p
54p. The intensity ratios of these lines are dependent on
atomic physics parameters only and not on the physical parameters of
the emitting plasma, so that they are excellent tools to verify the
relative intensity calibration of high-resolution spectrometers that
work in the 170-200 Å and 700-850 Å wavelength ranges. We carry out
extensive atomic physics calculations to improve the accuracy of the
predicted intensity ratio, and compare the results with simultaneous
EIS-SUMER observations of an off-disk quiet Sun region. We were
able to identify two ultraviolet lines in the SUMER spectrum that
are emitted by the same level that emits one bright line in the EIS
wavelength range. Comparison between predicted and measured intensity
ratios, wavelengths and energy separation of Fe IX levels confirms the
identifications we make. Blending and calibration uncertainties are
discussed. The results of this work are important for cross-calibrating
EIS and SUMER, as well as future instrumentation.
Title: Chianti—An Atomic Database for Emission
Lines. XI. Extreme-Ultraviolet Emission Lines of Fe VII, Fe VIII,
and Fe IX Observed by Hinode/EIS
Authors: Young, P. R.; Landi, E.
Bibcode: 2009ApJ...707..173Y
Altcode: 2009arXiv0907.3488Y
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 Å and 246-292
Å 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 λ185.21 and λ186.60 lines
underestimated by 60%-80% compared to lines between 192 and 198 Å. A
newly identified multiplet between 253.9 and 255.8 Å offers excellent
temperature diagnostic opportunities relative to the lines between 185
and 198 Å, however the atomic model underestimates the strength of
these lines by factors of 3-6. Two new line identifications are made
for Fe IX at wavelengths 176.959 Å and 177.594 Å, while seven other
lines between 186 and 200 Å are suggested to be due to Fe IX but
for which transition identifications cannot be made. The new atomic
data for Fe VII and Fe IX are demonstrated to significantly modify
models for the response function of the Transition Region And Coronal
Explorer 195 Å 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.
Title: CHIANTI—An Atomic Database for Emission Lines. X. Spectral
Atlas of a Cold Feature Observed with Hinode/EUV Imaging Spectrometer
Authors: Landi, E.; Young, P. R.
Bibcode: 2009ApJ...706....1L
Altcode: 2009arXiv0907.3490L
In this work, we report on a cold, bright portion of an active region
observed by the Hinode/EUV Imaging Spectrometer. The emitting plasma
was very bright at transition region temperatures, and the intensities
of lines of ions formed between 105 and 106
K were enhanced over normal values. The data set constitutes an
excellent laboratory where the emission of transition region ions can
be tested. We first determine the thermal structure of the observed
plasma, and then we use it (1) to develop a spectral atlas, and (2)
to assess the quality of CHIANTI atomic data by comparing predicted
emissivities with observed intensities. We identify several lines
never observed before in solar spectra, and find an overall very good
agreement between CHIANTI-predicted emissivities and observations.
Title: Solar transition region above sunspots
Authors: Tian, H.; Curdt, W.; Teriaca, L.; Landi, E.; Marsch, E.
Bibcode: 2009A&A...505..307T
Altcode: 2009arXiv0906.2211T
Aims: We study the transition region (TR) properties above sunspots and
the surrounding plage regions, by analyzing several sunspot reference
spectra obtained by the SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) instrument in March 1999 and November 2006.
Methods:
We compare the SUMER spectra observed in the umbra, penumbra, plage,
and sunspot plume regions. The hydrogen Lyman line profiles averaged
in each of the four regions are presented. For the sunspot observed
in 2006, the electron densities, differential emission measure (DEM),
and filling factors of the TR plasma in the four regions are also
investigated.
Results: The self-reversals of the hydrogen Lyman
line profiles are almost absent in sunspots at different locations (at
heliocentric angles of up to 49°) on the solar disk. In the sunspot
plume, the Lyman lines are also not reversed, whilst the lower Lyman
line profiles observed in the plage region are obviously reversed, a
phenomenon found also in the normal quiet Sun. The TR densities of the
umbra and plume are similar and one order of magnitude lower than those
of the plage and penumbra. The DEM curve of the sunspot plume exhibits
a peak centered at log(T / K) ~ 5.45, which exceeds the DEM of other
regions by one to two orders of magnitude at these temperatures. We
also find that more than 100 lines, which are very weak or not observed
anywhere else on the Sun, are well observed by SUMER in the sunspot,
especially in the sunspot plume.
Conclusions: We suggest that the
TR above sunspots is higher and probably more extended, and that the
opacity of the hydrogen lines is much lower above sunspots, compared to
the TR above plage regions. Our result indicates that the enhanced TR
emission of the sunspot plume is probably caused by a large filling
factor. The strongly enhanced emission at TR temperatures and the
reduced continuum ensure that many normally weak TR lines are clearly
distinctive in the spectra of sunspot plumes. Tables 5 and 6 are
only available in electronic form at http://www.aanda.org
Title: The thermal structure of the solar upper atmosphere
Authors: Landi, Enrico; Feldman, Uri
Bibcode: 2009AIPC.1161..142L
Altcode:
In the present work we review the thermal structure of the solar
atmosphere. We first discuss the main diagnostic techniques used
to measure it, outlining their pitfalls and limitations. Then, we
review the recent measurements of the thermal structure of the solar
atmosphere carried out with the SOHO spectrometers CDS and SUMER. The
review shows that the solar upper atmosphere is made by an ensemble of
few, nearly isothermal plasmas with fixed temperatures, disconnected
from the colder, thermally continuous lower atmosphere.
Title: CHIANTI - an atomic database for emission lines. IX. Ionization
rates, recombination rates, ionization equilibria for the elements
hydrogen through zinc and updated atomic data
Authors: Dere, K. P.; Landi, E.; Young, P. R.; Del Zanna, G.; Landini,
M.; Mason, H. E.
Bibcode: 2009A&A...498..915D
Altcode:
Aims: The goal of the CHIANTI atomic database is to provide a set of
atomic data for the interpretation of astrophysical spectra emitted by
collisionally dominated, high temperature, optically thin sources.
Methods: A complete set of ground level ionization and recombination
rate coefficients has been assembled for all atoms and ions of the
elements of H through Zn and inserted into the latest version of the
CHIANTI database, CHIANTI 6. Ionization rate coefficients are taken from
the recent work of Dere (2007, A&A, 466, 771) and recombination
rates from a variety of sources in the literature. These new rate
coefficients have allowed the calculation of a new set of ionization
equilibria and radiative loss rate coefficients. For some ions, such
as Fe VIII and Fe IX, there are significant differences from previous
calculations. In addition, existing atomic parameters have been revised
and new atomic parameters inserted into the database.
Results:
For each ion in the CHIANTI database, elemental abundances, ionization
potentials, atomic energy levels, radiative rates, electron and proton
collisional rate coefficients, ionization and recombination rate
coefficients, and collisional ionization equilibrium populations are
provided. In addition, parameters for the calculation of the continuum
due to bremsstrahlung, radiative recombination and two-photon decay are
provided. A suite of programs written in the Interactive Data Language
(IDL) are available to calculate line and continuum emissivities
and other properties. All data and programs are freely available at
http://wwwsolar.nrl.navy.mil/chianti
Title: CHIANTI Version 6.0 - Inclusion of Ionization and Recombination
Rates
Authors: Dere, Kenneth P.; Landi, E.; Young, P.; Del Zanna, G.; Mason,
H.; Landini, M.
Bibcode: 2009SPD....40.1504D
Altcode:
A new version of the CHIANTI atomic database for astrophysical
spectroscopy is being prepared for imminent release. This will
constitute Version 6.0. The main focus of this release is the inclusion
of ionization cross-sections and rate coefficients from Dere (2007)
and recombination rate coefficients from the literature, in particular,
the calculations of Badnell and colleagues. A new set of ionization
equilibria have been calculated from these rate coefficients. These
show some significant differences from previous calculations. Atomic
data for many ions have been revised and new calculations are included
that enable the calculation of spectra of ions new to the CHIANTI
database. The radiative loss function has been calculated based on
the CHIANTI Version 6 database for both coronal and photospheric
abundances. A paper describing CHIANTI Version 6.0 in detail has
been accepted for publication in Astronomy and Astrophysics.
Title: Improved Atomic Models for EUV Imaging Instruments
Authors: Young, Peter R.; Landi, E.
Bibcode: 2009SPD....40.1506Y
Altcode:
A combination of new atomic data and new line identifications made
from Hinode/EIS spectra have expanded and improved atomic models for
Fe VII and Fe IX emission lines in the extreme ultraviolet wavelength
range. These have a significant effect on the response functions of
EUV imaging instruments, particularly the 195 angstrom filters used
by SOHO/EIT, TRACE, STEREO/EUVI and SDO/AIA, and will be discussed.
Title: Physical Properties of Cooling Plasma in Quiescent Active
Region Loops
Authors: Landi, E.; Miralles, M. P.; Curdt, W.; Hara, H.
Bibcode: 2009ApJ...695..221L
Altcode:
In the present work, we use SOHO/SUMER, SOHO/UVCS, SOHO/EIT, SOHO/LASCO,
STEREO/EUVI, and Hinode/EIS coordinated observations of an active
region (AR 10989) at the west limb taken on 2008 April 8 to study the
cooling of coronal loops. The cooling plasma is identified using the
intensities of SUMER spectral lines emitted at temperatures in the
4.15 <= log T <= 5.45 range. EIS and SUMER spectral observations
are used to measure the physical properties of the loops. We found that
before cooling took place these loops were filled with coronal hole-like
plasma, with temperatures in the 5.6 <= log T <= 5.9 range. SUMER
spectra also allowed us to determine the plasma temperature, density,
emission measure, element abundances, and dynamic status during the
cooling process. The ability of EUVI to observe the emitting region
from a different direction allowed us to measure the volume of the
emitting region and estimate its emission measure. Comparison with
values measured from line intensities provided us with an estimate
of the filling factor. UVCS observations of the coronal emission
above the active region showed no streamer structure associated with
AR 10989 at position angles between 242°and 253fdg EIT, LASCO, and
EUVI-A narrowband images and UVCS spectral observations were used to
discriminate between different scenarios and monitor the behavior
of the active region in time. The present study provides the first
detailed measurements of the physical properties of cooling loops,
a very important benchmark for theoretical models of loop cooling
and condensation.
Title: The Emission Measure of the Solar Lower Transition Region
(2 × 104-2 × 105 K)
Authors: Feldman, U.; Dammasch, I. E.; Landi, E.
Bibcode: 2009ApJ...693.1474F
Altcode:
We analyze Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectra in the 750-790 Å wavelength range from 12 different solar
regions on the disk to measure the thermal structure of the lower
transition region (LTR). We considered four coronal hole (CH), four
quiet Sun (QS), and four active region (AR) data sets observed by
SUMER during the rising phase of the solar cycle, and we analyzed the
emission of seven different ions formed between 2 × 104
and 2 × 105 K. We study the spatial variation of line
radiances along the slit within each observation, as well as their
relative radiances in different data sets. We also use them to determine
the differential emission measure of the LTR. We find that all lines
behave in the same way both along the slit within the same observation,
and between different data sets from different regions of the Sun. We
also find that while the absolute value of the differential emission
measure of LTR plasmas changes from region to region, its distribution
with temperature is fairly constant, suggesting that the thermal
structure of LTR plasmas is the same in CH, QS, and AR regions, and as
a function of time along the solar cycle. We discuss the implications
of our results for studies of coronal heating and of the solar cycle.
Title: A New Approach to Analyzing Solar Coronal Spectra and
Updated Collisional Ionization Equilibrium Calculations. II. Updated
Ionization Rate Coefficients
Authors: Bryans, P.; Landi, E.; Savin, D. W.
Bibcode: 2009ApJ...691.1540B
Altcode: 2008arXiv0805.3302B
We have re-analyzed Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) observations of a parcel of coronal gas using new
collisional ionization equilibrium (CIE) calculations. These improved
CIE fractional abundances were calculated using state-of-the-art
electron-ion recombination data for K-shell, L-shell, Na-like, and
Mg-like ions of all elements from H through Zn and, additionally, Al-
through Ar-like ions of Fe. They also incorporate the latest recommended
electron impact ionization data for all ions of H through Zn. Improved
CIE calculations based on these recombination and ionization data are
presented here. We have also developed a new systematic method for
determining the average emission measure (EM) and electron temperature
(Te ) of an isothermal plasma. With our new CIE data and
a new approach for determining average EM and Te , we have
re-analyzed SUMER observations of the solar corona. We have compared
our results with those of previous studies and found some significant
differences for the derived EM and Te . We have also
calculated the enhancement of coronal elemental abundances compared to
their photospheric abundances, using the SUMER observations themselves
to determine the abundance enhancement factor for each of the emitting
elements. Our observationally derived first ionization potential factors
are in reasonable agreement with the theoretical model of Laming.
Title: Ion Temperatures in the Low Solar Corona: Polar Coronal Holes
at Solar Minimum
Authors: Landi, E.; Cranmer, S. R.
Bibcode: 2009ApJ...691..794L
Altcode: 2008arXiv0810.0018L
In the present work we use a deep-exposure spectrum taken by the
SUMER spectrometer in a polar coronal hole in 1996 to measure the ion
temperatures of a large number of ions at many different heights above
the limb between 0.03 and 0.17 solar radii. We find that the measured
ion temperatures are almost always larger than the electron temperatures
and exhibit a nonmonotonic dependence on the charge-to-mass ratio. We
use these measurements to provide empirical constraints to a theoretical
model of ion heating and acceleration based on gradually replenished
ion-cyclotron waves. We compare the wave power required to heat the ions
to the observed levels to a prediction based on a model of anisotropic
magnetohydrodynamic turbulence. We find that the empirical heating model
and the turbulent cascade model agree with one another, and explain
the measured ion temperatures, for charge-to-mass ratios smaller than
about 0.25. However, ions with charge-to-mass ratios exceeding 0.25
disagree with the model; the wave power that they require to be heated
to the measured ion temperatures shows an increase with charge-to-mass
ratio (i.e., with increasing frequency) that cannot be explained by
a traditional cascade model. We discuss possible additional processes
that might be responsible for the inferred surplus of wave power.
Title: Observations and analysis of the April 9, 2008 CME using
STEREO, Hinode TRACE and SoHO data
Authors: Reeves, K. K.; Patsourakos, S.; Stenborg, G.; Miralles, M.;
Deluca, E.; Forbes, T.; Golub, L.; Kasper, J.; Landi, E.; McKenzie,
D.; Narukage, N.; Raymond, J.; Savage, S.; Su, Y.; van Ballegooijen,
A.; Vourlidas, A.; Webb, D.
Bibcode: 2008AGUFMSH12A..04R
Altcode:
On April 9, 2008 a CME originating from an active region behind the limb
was well-observed by STEREO, Hinode, TRACE and SoHO. Several interesting
features connected to this eruption were observed. (1) The interaction
of the CME with open field lines from a nearby coronal hole appeared
to cause an abrupt change in the direction of the CME ejecta. (2) The
prominence material was heated, as evidenced by a change from absorption
to emission in the EUV wavelengths. (3) Because the active region was
behind the limb, the X-Ray Telescope on Hinode was able to take long
enough exposure times to observe a faint current- sheet like structure,
and it was able to monitor the dynamics of the plasma surrounding this
structure. This event is also being studied in the context of activity
that occurred during the Whole Heliosphere Interval (WHI).
Title: The Off-Disk Thermal Structure of a Polar Coronal Hole
Authors: Landi, Enrico
Bibcode: 2008ApJ...685.1270L
Altcode:
The thermal structure of the coronal portion of coronal holes is a
key factor in the modeling of the source regions and acceleration
mechanisms of the fast solar wind. Studies aimed at this region
are best carried out on observations outside the disk, where the
chromosphere and transition region are not included in the line of
sight. In the past, many off-disk studies measured the line-of-sight
temperature using line intensity ratios, a method that cannot provide
information on the distribution of material with temperature; a few
off-disk DEM determinations are also available, which are limited
to a few heights only. No EM loci study has been carried out to the
best of our knowledge. In this paper we use SOHO SUMER deep-exposure
spectra of a polar coronal hole observed in 1996 to carry out a
systematic investigation of the thermal structure of the emitting
plasma as a function of distance from the limb, making use of the EM
loci technique. Instrument-scattered light limits our investigation
to distances in the 1.03-1.17 R⊙ range, where we find
that the plasma is close to isothermal along the line of sight, with
temperature slowly increasing with distance from the limb.
Title: Nonthermal Electron Measurements in Solar Flares with
Hinode EIS
Authors: Feldman, Uri; Ralchenko, Yuri; Landi, Enrico
Bibcode: 2008ApJ...684..707F
Altcode:
The spectral range of the Hinode EIS (EUV Imaging Spectrometer)
instrument is 170-211 Å and 245-291 Å lines emitted by low-energy
levels in highly ionized Mn, Fe, Co, and Ni, as well as the very
energetic 1s2s3S1-1s2p3P2
transition in Fe XXV, appear in the EIS range. In this paper, we
investigate the use of these lines for detecting the presence of
nonthermal, high-energy electrons in flares. We first calculate line
fluxes among the various lines expected in the EIS range, assuming
that the electron velocity distribution is strictly Maxwellian. Then,
we calculate line fluxes using a velocity distribution composed of a
Maxwellian distribution plus an additional population of electrons with
a temperature of 10 keV (1.2 × 108 K) providing 1%, 2%, 4%,
7%, and 10% of the total free electrons. The calculations indicate that
flux ratios between the highly excited Fe XXV line and lines originating
in low-lying levels of other highly ionized ions in the EIS range could
shed light on the electron velocity distribution in hot flare plasmas.
Title: He-like Ar XVII triplet observed by RESIK
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Landi, E.
Bibcode: 2008AdSpR..42..833S
Altcode:
We present the observations of He-like Ar triplet lines obtained by
RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios
between triplet lines of lower Z elements is known to provide useful
diagnostics of plasma conditions within the emitting source. Here, we
investigate whether triplet line ratios are useful for interpretation
of higher Z element spectra. A high sensitivity, low background and
precise absolute calibration of RESIK allow to consider in addition
also the continuum contribution. This provides a way to determine
the Ar absolute abundance from the observed triplet component
ratios. The method is presented and the results are shown for two
selected flares. Derived values of Ar absolute abundance for these
flares are found to be similar: 2.6 × 10 -6 and 2.9 × 10
-6. They fall in the range between presently accepted Ar
photospheric and coronal abundances.
Title: Physical parameters along the boundaries of a mid-latitude
streamer and in its adjacent regions
Authors: Susino, R.; Ventura, R.; Spadaro, D.; Vourlidas, A.; Landi, E.
Bibcode: 2008A&A...488..303S
Altcode:
Context: Coronal streamers appear to be strictly associated with the
generation of the slow solar wind, even if a firm identification of
the sources of the particle flux within these structures is still an
unresolved issue.
Aims: The purpose of this work is to contribute
to a better knowledge of the physical characteristics of streamers and
of their surroundings in a wide range of heliocentric distances and
at both high radial and latitudinal resolutions.
Methods: The
analysis is based on spectral observations of a narrow, mid-latitude
streamer performed with UVCS/SOHO during one week in May 2004: H i
Lyα and O vi resonance doublet line intensities and profiles were
obtained at different heliocentric distances and latitudes. In addition,
white-light polarized brightness images were taken in the same days
of observation, through the LASCO/SOHO C2 coronagraph.
Results:
The radial variations in electron density and temperature, H i and O
vi kinetic temperatures, and outflow velocities were derived from the
observed line intensities, profiles, and O vi line intensity ratios
between 1.6 and 5.0 R_⊙, in two regions, 2-3 arcmin wide, located
along the boundaries and in a narrow strip (5-10 arcmin) outside
the streamer structure. Significantly high kinetic temperatures and
outflow velocities were found in the out-of-streamer region above 3.0
R_⊙ for the O vi ions and, for the first time, H i atoms, compared
to those obtained along the streamer boundaries. Moreover, the O vi
kinetic temperatures and velocities turn out much higher than the H
i ones at any heliocentric distance in all the observed regions. A
higher anisotropy is also noticed for the O vi kinetic temperature
in the region flanking the streamer.
Conclusions: The slow
coronal wind is found to flow with significantly different speeds and
kinetic temperatures along the boundaries of the streamer and in the
out-of-streamer regions at all heights, above 3.0-3.5 R_⊙. This fact,
consistent with previous studies, indicates that two components of
slow wind probably form in the observed regions: one originates just
above the streamer cusp and flows with velocities a little higher than
100 km s-1, while the other flows along the open magnetic
field lines flanking the streamer with velocities slightly lower than
the slow wind asymptotic heliospheric value of ~400 km s-1,
around 5.0 R_⊙.
Title: Determination of K, Ar, Cl, S, Si and Al flare abundances
from RESIK soft X-ray spectra
Authors: Sylwester, J.; Sylwester, B.; Landi, E.; Phillips, K. J. H.;
Kuznetsov, V. D.
Bibcode: 2008AdSpR..42..838S
Altcode:
The RESIK is a high sensitivity, uncollimated bent crystal spectrometer
which successfully operated aboard Russian CORONAS-F solar mission
between 2001 and 2003. It measured for the first time in a systematic
way solar soft X-ray spectra in the four wavelength channels from 3.3
Å to 6.1 Å. This range includes characteristic strong lines of H-
and He-like ions of K, Ar, Cl, Si, S and Al in the respective spectral
channels. A distinguishing feature of RESIK is its possibility
of making reliable measurements of the continuum radiation in
flares. Interpretation of line and the continuum intensities observed
in vicinity of respective strong lines provides diagnostics of plasma
temperature and absolute abundances of K, Ar, Cl, S, Si and Al in
several flares. We analyzed the observed intensities of spectral
lines and the nearby continuum using the CHIANTI v5.2 atomic data
package. A specific, so-called “locally isothermal” approach has
been used in this respect allowing us to make not only flare-averaged
abundance estimates, but also to look into a possible variability of
plasma composition during the course of flares.
Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere
Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico
Bibcode: 2008uxss.book.....P
Altcode:
1. The solar atmosphere; 2. Fundamentals of solar radiation;
3. Fundamentals of atomic physics; 4. Mechanisms of formation of the
solar spectrum; 5. Plasma diagnostic techniques; 6. Ultraviolet and
X-ray emission lines; 7. Spectrometers and imagers for observing the
solar ultraviolet and X-ray spectrum; 8. Quiet Sun and coronal holes;
9. Active regions; 10. Solar flares; 11. Element abundances; Appendices;
References; Index.
Title: Line Intensity Ratios in the EIS Range Sensitive to Electron
Densities in 107 K Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
Bibcode: 2008ApJ...679..843F
Altcode:
Electron density variations during the rise, maximum, and decay phases
of flaring plasmas at T simeq 10 MK are important quantities to be
used to test flare models. To date, electron density values measured
in solar flares are, with few exceptions, only lower limits. With the
launch of the EUV Imaging Spectrometer (EIS) on Hinode, it has become
possible for the first time to measure electron densities and their
time evolution during flares. In this paper we discuss electron density
diagnostics in the 1010-1013 cm-3
range by means of intensity ratios of lines emitted by Ti, Cr, and Mn
ions within the Hinode/EIS wavelength range.
Title: The Electron Temperature of the Solar Transition Region
Authors: Muglach, K.; Landi, E.; Doschek, G. A.
Bibcode: 2008AGUSMSP43C..05M
Altcode:
There are few spectroscopic measurements of electron temperature
in the solar transition region (the temperature region from about
2×104 K to 8×105 K). This is because UV and EUV spectral lines
from which temperature sensitive intensity ratios can be formed
are usually far separated in wavelength and cannot be observed
by a single instrument. Therefore, temperatures inferred for the
transition region are usually obtained from experimentally untested
theory that furthermore depends on the assumption of ionization
equilibrium. However, between 30 March 2007 and 14 April 2007 there
was a joint campaign between the SUMER spectrometer on SOHO and the
EIS spectrometer on Hinode. The EIS spectrometer operates in two
narrow wavelength bands: 170 — 210 and 250 — 290 Å. The SUMER
spectrometer operates roughly between about 500 and 1610 Å. Both SUMER
and EIS jointly observed portions of quiet Sun and active regions and
obtained spectra that include lines from a number of the same transition
region ions. The ratios of some of these lines from the same ion are
temperature sensitive and provide an unprecedented opportunity to
measure the temperatures of ion formation in the transition region and
to compare these temperatures with the values obtained from theoretical
ionization equilibrium calculations. A good example is the lines of
O VI at 183.94, 184.12 Å (EIS) and 1031.92, 1037.61 Å (SUMER). We
discuss temperatures derived for quiet Sun and active region transition
regions from joint spectra obtained during the SUMER/EIS campaign.
Title: The temperature structure of solar coronal plasmas
Authors: Feldman, Uri; Landi, Enrico
Bibcode: 2008PhPl...15e6501F
Altcode:
In the early 1940s it was at last accepted that the temperature of
the solar corona is at least 1 MK and varies considerably from region
to region throughout the solar activity cycle. It was recognized that
during solar minimum periods the electron temperatures of plasmas in
polar regions do not exceed 1 MK, but during solar maximum periods
the plasma temperatures of highly active regions could be as high as 3
MK. Nevertheless, until recently the consensus among the solar physics
community was that coronal temperatures vary among the different
regions in a continuous manner. In the present paper we review the
evidence showing that solar coronal plasmas (Te>0.7 MK)
are isothermal and their temperature can have only a small set of
fixed values.
Title: Analysis of EUV, UV, and H-alpha Emission from Two Very
Different Prominences
Authors: Kucera, T. A.; Landi, E.
Bibcode: 2008AGUSMSP43B..03K
Altcode:
Analysis of EUV, UV, and H-alpha Emission from Two Very Different
Prominences T. Kucera (NASA/GSFC), E. Landi (Artep Inc.) We analyze the
properties of a pair of prominences observed the UV and EUV in April
2004. One was a generally quiet prominence which exhibited a period of
activation. Another was a large "coronal cloud" type prominence. Both
were observed in by SOHO/SUMER, TRACE, and in Hα by BBSO and MLSO. The
quiet promince was also observed by the SOHO/CDS instrument. TRACE
and Hα data provide 2D images on with time cadences on the order of 1
minute. The SUMER data was taken from a single slit location with a 90
second cadence and included a number of lines spanning the temperature
range 80,000 to 1.6 million K. This observing program was designed
to allow us to study prominence dynamics. CDS raster data was taken
with a slower cadence, in lines formed at temperatures from 20,000
- 1 million K. We combine these different data sets to analyze the
thermal properties, including differential emission measures (DEMs),
of these very different prominences, and compare the results to those
of prominences previously analyzed by ourselves and others. This
work was partly funded through a NASA Heliophysics GI RTOP and NASA
award NNH04AA12
Title: The Status of Collisional Ionization Equilibrium Calculations
and a New Approach to Emission Eeasure Determinations
Authors: Bryans, Paul; Laming, J. M.; Landi, E.; Savin, D. W.
Bibcode: 2008AAS...212.0302B
Altcode: 2008BAAS...40Q.184B
We have calculated improved collisional ionization equilibrium (CIE)
fractional abundances using state-of-the-art dielectronic recombination
(DR) and radiative recombination (RR) rate coefficients for K-shell,
L-shell, Na-like, and Mg-like ions of all elements from H through Zn and
M-shell ions of Fe. These data have been compared with other published
state-of-the-art DR and RR data and found to agree within 35% and 10%,
respectively, in the temperature range where the ion forms in CIE. Where
DR measurements exist, theory and experiment agree to within 35% in this
temperature range. We have also investigated recent improvements to
the recommended electron impact ionization rate coefficient database,
concluding that differences of up to a factor of 4 between recent
compilations implies that significant additional experimental
and theoretical work is required. Using our new CIE calculations we
have re-analyzed solar coronal observations of an isothermal parcel
of coronal gas. We have also developed a mathematically rigorous
method for determining the average emission measure and temperature
of the emitting plasma. Using our new CIE data and our new approach
to determining the average emission measure, we use the observations
to quantify the first ionization potential effect on the coronal
abundances of the emitting elements. We present the results of this
analysis and compare our conclusions with those of previous works.
Title: Diagnostics of the Thermal Structure of Off-Disk Quiet
Sun Plasmas
Authors: Testa, P.; Landi, E.
Bibcode: 2008AGUSMSP51A..02T
Altcode:
It has been suggested recently that the quiet solar corona, when
observed outside the solar disk, is isothermal or near isothermal. If
true, this result has profound consequences for any theoretical model
trying to explain the thermal structure and the temperature of the
quiet solar corona. In this work we study the thermal structure of
the solar corona by combining simultaneous, long-exposure SOHO/SUMER
and Hinode/EIS observations of the quiet solar corona that include
the entire wavelength range of both instruments. We also analyze
simultaneous Hinode/XRT observations of the study region. This
comprehensive dataset includes lines emitted by many different types
of transitions and by a very large number of ions, that enable us to
obtain a very accurate determination of the thermal structure of the
quiet solar corona.
Title: Analysis of a Solar Coronal Bright Point Extreme Ultraviolet
Spectrum from the EUNIS Sounding Rocket Instrument
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.;
Landi, Enrico
Bibcode: 2008ApJ...677..781B
Altcode:
We present a well-calibrated EUV spectrum of a solar coronal bright
point observed with the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument on 2006 April
12. The coronal bright point brightened around 06:30 UT during a
period of emerging magnetic flux and remained bright at least until
the rocket flight around 18:12 UT, while the magnetic flux merged
and canceled. Density-sensitive line intensity ratios yield mutually
consistent coronal electron densities (Ne in cm-3)
of log Ne ≈ 9.4. The differential emission measure
(DEM, in cm-5 K-1) curve derived from the
spectrum yields a peak of log DEM ≈ 20.70 at log T ≈ 6.15 and a
local minimum of log DEM ≈ 20.15 at log T ≈ 5.35. Photospheric
(not coronal) element abundances are required to achieve equality
and consistency in the DEM derived from lines of Mg V, Mg VI, Mg VII,
and Ca VII (with a low first ionization potential, or FIP) and lines
from Ne IV and Ne V (with a high FIP) formed at transition region
temperatures. The bright point's photospheric abundance is likely
produced by reconnection-driven chromospheric evaporation, a process
that is not only central to existing bright point models, but also
consistent with measurements of relative Doppler velocities.
Title: An EUV narrow band imaging technique for diagnosing 10-30
keV ITER plasmas
Authors: Feldman, U.; Seely, J. F.; Landi, E.; Ralchenko, Y.
Bibcode: 2008AIPC..988..205F
Altcode:
In this paper we investigate the use of lines from tungsten (W)
ions to measure the properties of W impurities in ITER plasmas. We
calculate the intensities of the brightest spectral lines expected to
be radiated by W ions with wavelengths longer than 45 Å, abundance of
10-4 and at densities of 1020 m3. Using
the calculated wavelengths and intensities we propose a concept for
segmented multilayer-coated imaging telescopes that could be used to
investigate the properties of W impurities as a function of time and
space using spectral lines from highly ionized W
Title: The Quiet-Sun Differential Emission Measure from Radio and
UV Measurements
Authors: Landi, E.; Chiuderi Drago, F.
Bibcode: 2008ApJ...675.1629L
Altcode:
In the present work we combine UV and radio observations of the quiet
Sun to determine the differential emission measure (DEM) of the average
quiet solar atmosphere from the photosphere (5600 K) to the corona. UV
line intensities have been used to constrain the DEM above 30,000 K, and
the radio spectrum from 1.5 to 345 GHz has been used to extend the DEM
determination down to 5600 K. Radio observations are shown to provide
a much more reliable diagnostic tool for DEM determination than UV and
EUV lines at T < 30,000 K. The resulting average quiet-Sun DEM that
we found is in excellent agreement with curves from the literature
for temperatures larger than 60,000 K, but is lower than previous
determinations by more than 1 order of magnitude in the 10,000-30,000
K temperature range. The present work determines the DEM below 10,000
K for the first time, in a temperature region where UV and EUV lines
cannot be used.
Title: The Status of Collisional Ionization Equilibrium Calculations
and a New Approach to Emission Measure Determinations
Authors: Bryans, Paul; Laming, J. M.; Landi, E.; Savin, D. W.
Bibcode: 2008HEAD...10.1313B
Altcode:
We have calculated improved collisional ionization equilibrium (CIE)
fractional abundances using state-of-the-art dielectronic recombination
(DR) and radiative recombination (RR) rate coefficients for K-shell,
L-shell, Na-like, and Mg-like ions of all elements from H through Zn and
M-shell ions of Fe. These data have been compared with other published
state-of-the-art DR and RR data and found to agree within 35% and 10%,
respectively, in the temperature range where the ion forms in CIE. Where
DR measurements exist, theory and experiment agree to within 35% in this
temperature range. We have also investigated recent improvements to
the recommended electron impact ionization rate coefficient database,
concluding that differences of up to a factor of 5 between recent
compilations implies that significant additional experimental and
theoretical work is required. Using our new CIE calculations we
have re-analyzed solar coronal observations of an isothermal parcel
of coronal gas. We have also developed a mathematically rigorous
method for determining the average emission measure and temperature
of the emitting plasma. Using our new CIE data and our new approach
to determining the average emission measure, we use the observations
to quantify the first ionization potential effect on the coronal
abundances of the emitting elements. We present the results of this
analysis and compare our conclusions with those of previous works.
Title: An Observation of Low-Level Heating in an Erupting Prominence
Authors: Kucera, T. A.; Landi, E.
Bibcode: 2008ApJ...673..611K
Altcode:
Here we present multiwavelength observations of low-level heating in
an erupting prominence observed in the UV and EUV over a wide range of
temperatures and wavelengths by the Solar and Heliospheric Observatory
(SOHO) Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
instrument and the Transition Region and Coronal Explorer (TRACE),
and also in Hα by the Yunnan Astronomical Observatory. The eruption
occurred on 2004 April 30. The heating is relatively mild, leading
only to the ionization of hydrogen and helium. It is also localized,
occurring along the bottom edge of the erupting prominence and in
a kinklike feature in the prominence. The heating is revealed as
a decrease in the Lyman absorption relative to other parts of the
prominence. This decrease results in an apparent increase in emission in
all the lines observed by SUMER, especially those formed at temperatures
of ~105 K. However, this is due to the disappearance of
cooler absorbing material in the prominence rather than to an increase
in these higher temperature species. These observations suggest that
there may be low-level heating occurring in other erupting prominences
that do not show heating to coronal temperatures. They also indicate
that the prominence-corona transition region is best modeled with two
or more structures along the line of sight. We discuss the results in
terms of models of heating in erupting prominences and observations
of Lyman absorption in prominences.
Title: The Thermal Structure of an Active Region Observed Outside
the Solar Disk
Authors: Landi, E.; Feldman, U.
Bibcode: 2008ApJ...672..674L
Altcode:
In the present work we analyze an extensive active region spectrum
observed by the SUMER instrument on board SOHO with the aim of
determining the thermal structure of the emitting plasma. We found
that the plasma is made of three distinct, isothermal components,
whose physical properties are similar to coronal hole, quiet-Sun,
and active region plasmas. The temperatures of the coronal hole-like
and quiet-Sun-like plasmas are in excellent agreement with previous
measurements obtained outside active regions. We also used a DEM
diagnostic technique to check the robustness of our results and
found that the DEM curves are compatible with the presence of three
distinct nearly isothermal plasmas if the individual DEM measurements
are smoothed over a small temperature interval. Larger intervals lead
the resulting DEM curves to a more multithermal behavior, raising the
question of whether multithermal active region DEM curves available in
the literature are real or an artifact of oversmoothing. The results
are compared with measurements of the temperature of individual loop
structures in the literature and discussed in light of a new picture
of the solar corona.
Title: A proposed new method for the determination of the solar
irradiance at EUV wavelength range
Authors: Feldman, Uri; Doschek, G. A.; Seely, J. F.; Landi, E.;
Dammasch, I.
Bibcode: 2008cosp...37..866F
Altcode: 2008cosp.meet..866F
The solar irradiance in the far ultraviolet (FUV) and extreme
ultraviolet (EUV) and its time variability are important inputs to
geospace models. It provides the primary mechanism for heating the
earth's upper atmosphere and creating the ionosphere. Understanding
various space weather phenomena requires reliable detailed knowledge
of the solar EUV irradiance. Ideally one would like to have a single
well-calibrated, high-resolution spectrometer that can continuously
monitor the solar irradiance over the relevant wavelengths range. Since
this is much too difficult to accomplish, a number of monitoring
instruments were constructed in the past, each covering a fraction
of the required wavelength range. Assembling solar irradiance from
measurements by a number of instruments is extremely difficult and
is usually plagued by large uncertainties. To overcome some of the
difficulties resulting from such procedures, empirical models have
been developed that rely in large part on solar activity levels as
proxies. In recent years a different approach has been established for
the determination of the solar irradiance, an approach independent
of irradiance observations. The new approach is based on the line
intensities calculated from emission measure (EM) distributions across
the solar surface. The EM distributions are derived from spatially and
spectrally resolved measurements of line intensities and describe the
temperature and density structure of the basic large scale features of
the solar atmosphere, specifically coronal holes, quiet Sun, and active
regions. Recently, as a result of detailed analysis of solar upper
atmosphere (SUA) spectra recorded by SUMER/SoHO it was discovered that,
in contrast to earlier beliefs, the solar EM in 3x105 -4x106 K plasmas
does not appear to vary continuously with temperature as previously
assumed. Instead it appears to be composed of isothermal structures
where each can attain but one of the following four main temperatures:
5x105 , 9x105 , 1.4x106 and 3x106 K. At the transition region (2x104
-2x105 K) where the structures are not isothermal the slopes of the
emission measure vs. temperature stay the same independent of the solar
activity. In our talk we will propose a variation to the EM method for
the determination of the solar irradiance described above. The modified
method will be based on line intensity calculations from the actual
solar EM values at the above specified discrete temperatures. The
EM in those temperatures could in principle be derived from solar
observations spanning a fairly limited wavelengths range.
Title: Continuum emission in the 1-2000 Å range
Authors: Landi, E.
Bibcode: 2007A&A...476..675L
Altcode:
Context: Continuum emission is a fundamental component of the solar
and stellar spectra between 1 Å and 2000 Å and has important
applications to plasma diagnostics. However, the importance of X-ray
free-bound continuum radiation has been overlooked in recent years,
and no assessment of the accuracy of different data and approximations
underlying the calculation of continuum emissivity has been carried out
to understand the reliability of diagnostic results.
Aims: The
importance of free-bound radiation in the X-rays will be demonstrated
and its effects on plasma diagnostics will be discussed. The importance
of user-chosen parameters such as ion and element abundances, necessary
to the calculation of continuum emissivity, will be assessed. The
uncertainties in the atomic data underlying continuum calculations will
be investigated.
Methods: We will use the CHIANTI spectral code
to investigate the relative importance of the free-free, free-bound
and two-photon radiation as a function of wavelength in the 1-2000 Å
spectral range, and to assess the effects of user-chosen parameters
on the calculation of the continuum emission. A comparison between
continuum emissivity of two of the most widely used spectral codes,
developed using very different atomic data and approximations, will
give us an indication of their reliability.
Results: The effects
of element abundances and of the neglect of free-bound radiation in
the X-rays are shown to be significant, with important consequences
for plasma diagnostics results. The total continuum emissivities
of the two spectral codes we compared are found to be in agreement
to better than 40% at all wavelengths and temperatures of interest,
with only a few exceptions.
Title: Physical parameters of a mid-latitude streamer during the
declining phase of the solar cycle
Authors: Spadaro, D.; Susino, R.; Ventura, R.; Vourlidas, A.; Landi, E.
Bibcode: 2007A&A...475..707S
Altcode:
Context: Investigating the physical properties of solar coronal
streamers is important for understanding their role in the global
magnetic structure of the extended solar atmosphere, as well as in the
generation of the slow solar wind.
Aims: We hope to contribute as
completely as possible to the ongoing SOHO instruments campaign devoted
to the study of the physical characteristics of coronal streamers at
various heliocentric distances.
Methods: We analyzed ultraviolet
H I Lyα and O VI resonance doublet lines observed by UVCS/SOHO in
a narrow, mid-latitude streamer structure along different lines
of sight during a week in May 2004 and made nearly simultaneous
white-light polarized brightness measurements from the LASCO/SOHO C2
coronagraph.
Results: Electron densities and temperatures, H
I and O VI kinetic temperatures, and outflow velocities were derived
from the line intensities and widths, as well as from the O VI line
intensity ratio in the 1.6-5 R⊙ range of heights, limited
to the central region of the streamer. To our knowledge, the H I outflow
velocities obtained in this work are the first ones determined inside a
streamer structure. They are significantly lower than those of the O VI
ions. This, together with the O VI kinetic temperatures that are much
higher than the H I ones, suggest that the absorption of Alfvén waves
at the ion cyclotron frequency might also occur inside streamers.
Conclusions: In comparison with other streamers described in the
literature, the structure examined in this work generally exhibits lower
electron density and neutral hydrogen kinetic temperature. Conversely,
the O VI kinetic temperature and outflow velocity radial profiles are
consistent with the results for the other examined streamers.
Title: EUV Emission Lines and Diagnostics Observed with Hinode/EIS
Authors: Young, Peter R.; Del Zanna, Giulio; Mason, Helen E.; Dere,
Ken P.; Landi, Enrico; Landini, Massimo; Doschek, George A.; Brown,
Charles M.; Culhane, Len; Harra, Louise K.; Watanabe, Tetsuya; Hara,
Hirohisa
Bibcode: 2007PASJ...59S.857Y
Altcode: 2007arXiv0706.1857Y
Quiet Sun and active region spectra from the Hinode/EIS instrument are
presented, and the strongest lines from different temperature regions
discussed. A list of emission lines recommended to be included in EIS
observation studies is presented based on analysis of blending and
diagnostic potential using the CHIANTI atomic database. In addition
we identify the most useful density diagnostics from the ions covered
by EIS.
Title: Application of CHIANTI to Solar-B
Authors: Dere, K.; Landi, E.; Del Zanna, G.; Young, P.; Mason, H.;
Landini, M.
Bibcode: 2007ASPC..369...35D
Altcode:
CHIANTI (http://wwwsolar.nrl.navy.mil/chianti.html) has been developed
to support the interpretation of solar and astrophysical spectroscopic
measurements. The most recent release, version 5.0 (Landi et al. 2005)
presents an improvement over previous versions by including new
large scale datasets for Fe ions from Fe XVII to Fe XXIV for X-ray
emission and improved atomic data for EUV line emission. We will
demonstrate how this can be applied to the analysis of XRT and EIS
data, in particular. For example, new excitation rates for Fe XII have
resolved a long standing problem in the use of Fe XII line ratios as
accurate density diagnostics. Current work involves improvements to
ionization and recombination rates which will also be useful in the
interpretation of Solar-B data
Title: Ion Temperatures in the Quiet Solar Corona
Authors: Landi, E.
Bibcode: 2007ApJ...663.1363L
Altcode:
We measure the upper and lower limits of the temperatures Ti
for a number of ions observed in the quiescent solar corona from 1996
to 2000, in order to compare with the measured electron temperature
Te and test the assumption Ti=Te
commonly adopted to measure the plasma nonthermal velocity
vnth. We use a diagnostic technique that relaxes all
assumptions on Ti and only requires that the plasma
nonthermal velocity be the same for all ions; this provides a
measurement of the upper limit on vnth and of a range of
Ti-values compatible with observations. The measurements
were carried out using spectra observed outside the solar limb in 1996,
1999, and 2000, spanning the rising phase of the solar cycle, and are
repeated at different heights above the solar photosphere for each data
set. We find that in the 2000 data set Ti>Te
in the majority of cases, while the differences are smaller in the 1999
data set and nearly absent in the 1996 data set. We also investigate
the correlation of the measured values of Ti with line
wavelength, ion charge, charge-to-mass ratio, and temperature of maximum
abundance, line intensity and width, and atomic weight, finding none.
Title: Progress Toward A Very High Angular Resolution Imaging
Spectrometer (VERIS)
Authors: Korendyke, Clarence M.; Vourlidas, A.; Landi, E.; Seely,
J.; Klimchuck, J.
Bibcode: 2007AAS...210.2604K
Altcode: 2007BAAS...39Q.324K
Recent imaging at arcsecond (TRACE) and sub-arcsecond (VAULT) spatial
resolution clearly show that structures with fine spatial scales
play a key role in the physics of the upper solar atmosphere. Both
theoretical and observational considerations point to the importance
of small spatial scales, impulsive energy release, strong dynamics,
and extreme plasma nonuniformity. Fundamental questions regarding the
nature, structure, properties and dynamics of loops and filamentary
structures in the upper atmosphere have been raised. To address
these questions, we are developing a next generation, VEry high
angular Resolution Imaging Spectrometer (VERIS) as a sounding rocket
instrument. VERIS will obtain the necessary high spatial resolution,
high fidelity measurements of plasma temperatures, densities and
velocities. With broad simultaneous temperature coverage, the VERIS
observations will directly address unresolved issues relating to
interconnections of various temperature solar plasmas. VERIS will
provide the first ever subarcsecond spectra of transition region and
coronal structures. It will do so with a sufficient spectral resolution
of to allow centroided Doppler velocity determinations to better than 3
km/s. VERIS uses a novel two element, normal incidence optical design
with highly reflective EUV coatings to access a spectral range with
broad temperature coverage (0.03-15 MK) and density-sensitive line
ratios. Finally, in addition to the spectra, VERIS will simultaneously
obtain spectrally pure slot images (10x150 arcsec) in the +/-1 grating
orders, which can be combined to make instantaneous line-of-sight
velocity maps with 8km/s accuracy over an unprecedented field of
view. The VERIS program is beginning the second year of its
three year development cycle. All design activities and reviews are
complete. Fabrication of all major components has begun. Brassboard
electronics cards have been fabricated, assembled and tested. The paper
presents the essential scientific characteristics of the instrument.
Title: Implications for Atomic Physics from New Ionization Balance
Calculations and Solar Physics Observations
Authors: Bryans, Paul; Landi, Enrico; Savin, Daniel
Bibcode: 2007APS..DMP.R1107B
Altcode:
We have used state-of-the-art electron-ion recombination data
for K-shell, L-shell, and Na-like ions of H through Zn to calculate
improved collisional ionization equilibrium (CIE) fractional abundances
for ions of all these elements. We present the implications of these
new CIE results for observations of the solar atmosphere and discuss
a number of atomic systems showing puzzling discrepancies between
observations and solar models. These discrepancies suggest errors in
the underlying atomic data. Based on this, we highlight those atomic
processes that require improved theoretical or experimentally-derived
rate coefficients.
Title: The Transition Region Above Sunspots
Authors: Curdt, W.; Landi, E.
Bibcode: 2007ASPC..370...40C
Altcode:
We present results from spectroscopic observations of sunspots in the
vacuum ultraviolet wavelength range obtained by SUMER on SOHO. The
atmospheric conditions above sunspots are very special and remarkably
different compared to other parts of the solar atmosphere. The
transition region, which is normally a thin layer extends above sunspots
very high in altitude and is filled with rather cold, low-density
plasma. Sunspot plumes are sites of systematic downflow into a bottom
layer, which is coherently oscillating with a 3-minute period.
Title: Observation of Low Level Heating in an Erupting Prominence
Authors: Kucera, Therese A.; Landi, E.
Bibcode: 2007AAS...210.2905K
Altcode: 2007BAAS...39..138K
We present multi-wavelength observations of low level heating in an
erupting prominence observed in the UV and EUV over a wide range of
temperatures and wavelengths by SOHO's SUMER instrument, TRACE and
also in H-alpha by the Yunnan Astronomical Observatory. The eruption
occurred on 2004 April 30. The heating is relatively mild, leading only
to the ionization of neutral hydrogen and probably helium. It is also
localized, occurring along the bottom edge of the erupting prominence
and in a kink-like feature in the prominence. The heating is revealed
as a decrease in the Lyman absorption. This decrease results in an
apparent increase in emission in all the lines observed by SUMER,
especially those formed at temperatures ∼10^5 K. However, this is
due to the disappearance of cooler absorbing material in the prominence
rather than an increase in these higher temperature species. This
project was funded by the NASA SEC GI RTOP 955518.02.01.01.15 and NASA
awards NNG06EA14I and NNH06CD24C.
Title: Diagnostics of Suprathermal Electrons in Active-Region Plasmas
Using He-like UV Lines
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
Bibcode: 2007ApJ...660.1674F
Altcode:
In the present paper we use UV lines emitted by He-like ions as a
tool to test the presence of nonthermal high-energy electrons and
to quantify their number and energy. The He-like lines we consider
are the He-like 1s2s3S-1s2p3P lines observed
in the UV, and their use capitalizes on the high excitation energies
for the 1s2p3P levels and on the near-unity ion abundances
of the He-like ions for large temperature ranges. We investigate the
presence of nonthermal high-energy electrons in solar active regions,
placing upper limits on the presence of electrons capable of exciting
the upper levels of Ne IX, Mg XI, and Si XIII.
Title: Neon and Oxygen Absolute Abundances in the Solar Corona
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2007ApJ...659..743L
Altcode:
In the present work we use the UV spectrum of a solar
flare observed with SOHO SUMER to measure the absolute
abundance of Ne in the solar atmosphere. The measurement
is carried out using the intensity ratio between the allowed
1s2s3S1-1s2p3P2 Ne IX
line at 1248.28 Å and the free-free continuum radiation observed
close to the Ne IX line. We find a value of the absolute Ne abundance
ANe=8.11+/-0.12, in agreement with previous estimates
but substantially higher than the very recent estimate by Asplund et
al. based on the oxygen photospheric abundance and the Ne/O relative
abundance. Considering our measured ANe value, we argue
that the absolute oxygen abundance of Asplund et al. is too low by a
factor 1.9. This result has important consequences for models of the
solar interior based on helioseismology measurements, as well as on
the FIP bias determination of the solar upper atmosphere, solar wind,
and solar energetic particles.
Title: 2006 LWS TR & T Solar Wind Focused Science Topic Team:
The Beginnings
Authors: Miralles, M. P.; Bhattacharjee, A.; Landi, E.; Markovskii,
S.; Cranmer, S. R.; Doschek, G. A.; Forbes, T. G.; Isenberg, P. A.;
Kohl, J. L.; Ng, C.; Raymond, J. C.; Vasquez, B. J.
Bibcode: 2006AGUFMSH11A0371M
Altcode:
The Solar Wind Focused Science Topic (FST) team was created to
apply a combination of theoretical studies, numerical simulations,
and observations to the understanding of how the fast and slow solar
wind are heated and accelerated. Four proposals were selected for this
FST team. They will investigate the role of energy sources and kinetic
mechanisms responsible for the heating and acceleration of the solar
wind. In particular, the FST team will examine magnetic reconnection
and turbulence as possible heating mechanisms. Plasma properties and
their evolution over the solar cycle, determined from the analysis of
remote and in situ measurements, will be used to put firm constraints
on the models. The work of the Solar Wind FST team is in its initial
stages. The organization, planning, and findings resulting from the
first FST team meeting will be reported.
Title: CHIANTI-An Atomic Database for Emission Lines. VIII. Comparison
with Solar Flare Spectra from the Solar Maximum Mission Flat Crystal
Spectrometer
Authors: Landi, E.; Phillips, K. J. H.
Bibcode: 2006ApJS..166..421L
Altcode:
In the present work we describe the comparison of the fluxes
predicted by the latest version of the CHIANTI database (version
5.2) with the observed X-ray spectra of two solar flares from the
Flat Crystal Spectrometer on board the Solar Maximum Mission on
1980 August 25 and 1985 July 2. The two flares were of GOES classes
M1.5 and M4.5, respectively, and were observed in the 7.47-18.97 Å
wavelength range. The aim of the present work is to benchmark the
CHIANTI database in this range in an effort to assess its accuracy
and completeness. Very good agreement is found at all wavelengths,
except for Fe XVIII and Fe XIX lines between 14.7 and 16.4 Å. These
discrepancies are discussed. A list of lines recommended for future
diagnostic studies of X-ray sources is presented.
Title: The Transition Region Above Sunspots
Authors: Curdt, W.; Landi, E.
Bibcode: 2006ESASP.617E..56C
Altcode: 2006soho...17E..56C
No abstract at ADS
Title: Plasma Diagnostics of the Large-Scale Corona with SUMER
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2006ESASP.617E..12L
Altcode: 2006soho...17E..12L
No abstract at ADS
Title: Ultraviolet Observations of Prominence Activation and Cool
Loop Dynamics
Authors: Kucera, T. A.; Landi, E.
Bibcode: 2006ApJ...645.1525K
Altcode:
In this paper we investigate the thermal and dynamic properties of
dynamic structures in and around a prominence channel observed on
the limb on 2003 April 17. Observations were taken with the Solar and
Heliospheric Observatory's Solar Ultraviolet Measurements of Emitted
Radiation (SOHO SUMER) in lines formed at temperatures from 80,000 K
to 1.6 MK. The instrument was pointed to a single location and took
a series of 90 s exposures. Two-dimensional context was provided by
the Transition Region and Coronal Explorer (TRACE) in the UV and EUV
and the Kanzelhöhe Solar Observatory in Hα. Two dynamic features
were studied in depth: an activated prominence and repeated motions
in a loop near the prominence. We calculated three-dimensional
geometries and trajectories, differential emission measures, and
limits on the mass, pressure, average density, and kinetic and thermal
energies. These observations provide important tests for models of
dynamics in prominences and cool (~105 K) loops, which
will ultimately lead to a better understanding of the mechanism(s)
leading to energy and mass flow in these solar features.
Title: Plasma Diagnostics of the Large-Scale Corona with
SUMER. I. Measurements at the West Limb
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2006ApJ...643.1258L
Altcode:
In the present work we analyze the physical properties of the quiet-Sun
plasma measured in a 0.5×1.8 Rsolar region above the west
solar limb (Rsolar=solar radius). We make use of large
scans obtained with the SUMER spectrometer on board SOHO to construct
two-dimensional spatial maps of line intensities, electron temperature,
emission measure, element abundances, line widths and nonthermal
velocities, and photoexcitation effects covering the entire field
of view. Electron densities were measured in a more limited portion
of the field of view. The aim of the paper is to identify tracers of
coronal hole and quiet-Sun plasma at high altitudes that allow us to
measure the position of the coronal hole/quiet-Sun boundaries, and
to provide a comprehensive, empirical picture of the off-limb solar
corona that can provide theoreticians with experimental constraints
to their models of the large-scale coronal structure, coronal heating,
and solar wind acceleration.
Title: Thermal Analysis of Post-eruption Loops From 80,000 to 1.6
Million K
Authors: Kucera, Therese A.; Landi, E.
Bibcode: 2006SPD....37.0802K
Altcode: 2006BAAS...38..230K
We analyze the thermal properties of a set of post eruptive loops
which appeared after a prominence eruption on April 30, 2004. The event
was observed by TRACE and SOHO/SUMER. The SUMER data was taken from a
single slit location with a 90 second cadence and included a number
of lines spanning the temperature range 80,000 to 1.6 million K. We
perform a differential emission measure analysis of the loops in order
to study their thermal evolution.This work was partly funded through
a NASA SEC GI RTOP andNASA grants NNH04AA12I, W10,232 and NNG04ED07P
Title: Atomic Data for High-Energy Configurations in Fe XVII-XXIII
Authors: Landi, E.; Gu, M. F.
Bibcode: 2006ApJ...640.1171L
Altcode:
In the present work we calculate energy levels, oscillator
strengths, A-values, and electron-ion excitation collision
strengths for high-energy configurations for the iron ions Fe XVII
to Fe XXIII. Collision rate coefficients are calculated using the
distorted-wave approximation; the contribution of resonant excitation
is taken into account by using the isolated-resonance approximation
for configurations with principal quantum numbers n=2 and 3. Results
are compared with R-matrix calculations available in the literature
for the lowest configurations; our results are the first ever published
for highly excited configurations with n>=4 for most ions. Synthetic
spectra are calculated from the resulting rate coefficients and compared
to available spectral codes. Some applications of the results of the
present calculation to solar physics are discussed. These data will
be part of the next version of the CHIANTI database.
Title: He-like triplets observed by RESIK
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Landi, E.
Bibcode: 2006cosp...36.2877S
Altcode: 2006cosp.meet.2877S
The RESIK is a high sensitivity uncollimated bent crystal spectrometer
which successfully operated aboard Russian CORONAS-F solar mission
between 2001 and 2003 It measured systematically for the first time
solar soft X-ray spectra in the four wavelength channels from 3 3 AA to
6 1 AA This range includes characteristic triplet lines of He-like ions
of K Ar Cl and S in the respective spectral channels Interpretation of
observed line ratios within each triplet provides diagnostics of plasma
conditions in the emitting source We reduced the observed spectra for
a number of flares using the absolute RESIK calibration software We
analyzed the observed intensities of spectral line components comprising
the triplets and investigated their time variability The evolution of
important plasma parameters like temperature and emission measure have
been studied for selected events Flaring plasma densities were measured
from these parameters using X-ray brightness maps as determined from
the RHESSI observations The CHIANTI v5 1 atomic data package was used
as a consistent tool for spectral data analysis
Title: Determination of K, Ar, Cl, S and Si flare abundances from
RESIK soft X-ray spectra
Authors: Sylwester, J.; Sylwester, B.; Landi, E.; Phillips, K. J. H.;
Kuznetsov, V. D.
Bibcode: 2006cosp...36.2871S
Altcode: 2006cosp.meet.2871S
We investigate possible variability of coronal plasma composition
during flares based on the analysis of spectra measured by RESIK bent
crystal spectrometer aboard the CORONAS-F solar mission We fit the
measured spectra with synthesized theoretical ones in the vicinity of
the observed He-like ions The spectral synthesis is performed based on
CHIANTI v5 1 spectral code in so-called locally isothermal approximation
with the aim to reproduce observed line-to-continuum ratios Influence
of possible multitemperaure plasma structure is considered and discussed
based on respective differential emission measure calculations
Title: Atomic data and spectral line intensities for Mg V
Authors: Bhatia, A. K.; Landi, E.; Eissner, W.
Bibcode: 2006ADNDT..92..105B
Altcode:
Electron impact collision strengths, energy levels, oscillator
strengths, and spontaneous radiative decay rates are calculated
for Mg V. The configurations used are 2s22p4,
2s2p5, 2p6, 2s22p33s,
2s22p33p, and 2s22p33d,
giving rise to 86 fine-structure levels in intermediate
coupling. Collision strengths are calculated at five incident
energies, 10, 20, 30, 40, and 50 Ry, in the distorted wave
approximation. Excitation rate coefficients (not tabulated here)
are calculated as a function of electron temperature by assuming a
Maxwellian electron velocity distribution. To calculate excitation
rate coefficients, collision strengths at low and high energy limits
are calculated by a method described by Burgess and Tully. Using
the excitation rate coefficients and the radiative transition rates,
statistical equilibrium equations for level populations are solved at
electron densities covering the range of 108 1014
cm-3 at an electron temperature of log Te
= 5.4, corresponding to the maximum abundance of Mg V. Fractional
level populations and relative spectral line intensities are also
calculated. Our calculated intensities are compared with the active
region observations from the solar EUV rocket telescope and spectrograph
(SERTS) and the diagnostic properties of Mg V are discussed. This
dataset will be made available in the next version of the CHIANTI
database.
Title: CHIANTI-An Atomic Database for Emission Lines. VII. New Data
for X-Rays and Other Improvements
Authors: Landi, E.; Del Zanna, G.; Young, P. R.; Dere, K. P.; Mason,
H. E.; Landini, M.
Bibcode: 2006ApJS..162..261L
Altcode:
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities, and collisional excitation data for
a large number of ions of astrophysical interest. CHIANTI also includes
a suite of IDL routines to calculate synthetic spectra and carry out
plasma diagnostics. Version 5 has been released, which includes several
new features, as well as new data for many ions. The new features in
CHIANTI are as follows: the inclusion of ionization and recombination
rates to individual excited levels as a means to populate atomic
levels; data for Kα and Kβ emission from Fe II to Fe XXIV; new data
for high-energy configurations in Fe XVII to Fe XXIII; and a complete
reassessment of level energies and line identifications in the X-ray
range, multitemperature particle distributions, and photoexcitation
from any user-defined radiation field. New data for ions already in
the database, as well as data for ions not present in earlier versions
of the database, are also included. Version 5 of CHIANTI represents a
major improvement in the calculation of line emissivities and synthetic
spectra in the X-ray range and expands and improves theoretical spectra
calculations in all other wavelength ranges.
Title: Atomic data and spectral line intensities for Ca XIII
Authors: Landi, E.; Bhatia, A. K.
Bibcode: 2005A&A...444..305L
Altcode:
Electron impact collision strengths, energy levels, oscillator
strengths and spontaneous radiative decay rates are calculated for Ca
xiii. The configurations used are {2s2} {2p4},
{2s2p5}, {2p6}, {2s2}
{2s3 3s}, {2s2} {2p3 3p} and
{2s2}{2p3 3d} giving rise to 86 fine-structure
levels in intermediate coupling. Collision strengths are calculated at
five incident energies (40, 80, 120, 160 and 200 Ry) in the distorted
wave approximation. Excitation rate coefficients are calculated as a
function of electron temperature by assuming a Maxwellian electron
velocity distribution. Using the excitation rate coefficients and
the radiative transition rates, statistical equilibrium equations for
level populations are solved at electron densities covering the range
of 108-1014 cm-3 at an electron
temperature of log Te(K)=6.5, corresponding to maximum
abundance of Ca xiii. Relative and absolute spectral line intensities
are calculated, and their diagnostic relevance is discussed. This
dataset will be made available in the next version of the CHIANTI
database.
Title: Observing the Solar atmosphere with the Extreme Ultraviolet
Imaging Spectrometer on Solar B
Authors: Korendyke, C. M.; Brown, C.; Dere, K.; Doschek, G.; Klimchuk,
J.; Landi, E.; Mariska, J.; Warren, H.; Lang, J.
Bibcode: 2005AGUFMSH41B1124K
Altcode:
The Extreme Ultraviolet Imaging Spectrometer (EIS) is part of the
instrument complement on the Solar B satellite, scheduled for launch
in the summer of 2006. The instrument has been calibrated and is
presently mounted on the spacecraft. EIS is the most sensitive EUV
solar spectrometer to be flown. The instrument is the first of a new
generation of two optical element, solar spectrographs. Preliminary
results from the laboratory focussing and calibration of the
instrument will be shown. The instrument wavelength coverage includes
reasonably bright spectral lines emitted by plasmas from 0.1 to 20 MK
in temperature. The wavelength range also provides coronal density
diagnostics. Temperature, density and velocity diagnostics will be
discussed. An example observing program for exploring active region
evolution and dynamics will be discussed.
Title: Application of CHIANTI to High Resolution Solar Spectra
Authors: Dere, K. P.; Landi, E.
Bibcode: 2005AGUFMSH44A..02D
Altcode:
CHIANTI has been developed to support the interpretation of solar and
astrophysical spectroscopic measurements. The most recent release,
version 5.0 (Landi et al., 2005) presents an improvement over previous
versions by including new large scale datasets for Fe ions from Fe XVII
to Fe XXIV for X-ray emission and improved atomic data for EUV line
emission. We will show examples of its use in the analysis of X-ray
spectra from SMM, ultraviolet spectra from SOHO and the interpretation
of broadband instruments such as EIT and TRACE. Current work involves
the analysis of ionization and recombination rates based on recent
laboratory measurements and calculations with the Flexible Atomic
Code. The incorporation of ionization and recombination rates into
CHIANTI will allow us to explore such effects as the effect of finite
densities on ionization balance and transient and nonthermal ionization
populations.
Title: VizieR Online Data Catalog: A-values + oscillator strength
of Ca XIII (Landi+, 2005)
Authors: Landi, E.; Bhatia, A. K.
Bibcode: 2005yCat..34440305L
Altcode:
Atomic data, energy levels, radiative transition rate and electron-ion
collision rate coefficients have been calculated for Ca XIII using
the distorted wave approximation. They have been compared with data
available in the literature and with observations. (2 data files).
Title: Modeling X-ray Emission from Planetary Nebulae
Authors: Steffen, M.; Schönberner, D.; Warmuth, A.; Schwope, A.;
Landi, E.; Perinotto, M.; Bucciantini, N.
Bibcode: 2005AIPC..804..161S
Altcode:
Recent observations using the Chandra X-ray Observatory and XXM Newton
revealed without doubt diffuse X-ray emission from the shock-heated
wind gas in planetary nebula (PN) interiors. Typical properties
of the emitting gas are temperatures of a few 106 K and
electron densities of the order of 100 cm-3. According
to current hydrodynamical models, the shocked gas becomes too
hot (T ~ 107-108 K) and too tenuous (ne ~
1 cm-3) to produce the observed X-ray emission. However,
the hot gas is confined by the rather cool (T ~ 10 000K) nebular gas,
and thermal heat conduction across the interface between the hot
and cool gas becomes important. It changes the contact discontinuity
into a more extended transition layer covering the temperature range
where the observed X-ray emission is thought to arise. To date, only
similarity solutions for the hydrodynamical problem of PN evolution
with heat conduction have been derived (Zhekov & Perinotto
1996). We present first results from new numerical simulations of the
PN evolution including thermal conduction by electrons. We confront
the X-ray luminosities predicted by these models with those derived
from XMM/Chandra observations.
Title: Properties of a Sunspot Plume Observed With the Coronal
Diagnostic Spectrometer Aboard the Solar and Heliospheric Observatory
Authors: Brosius, Jeffrey W.; Landi, Enrico
Bibcode: 2005ApJ...632.1196B
Altcode:
We used three instruments (CDS, EIT, MDI) aboard the Solar and
Heliospheric Observatory spacecraft to observe the large sunspot in
NOAA Active Region 8539 on 1999 May 9 and 13. The spot contained
a bright plume, most easily seen in EUV emission lines formed
at 5.2<~logT<~5.7 (where T is the temperature in K), in its
umbra on both dates. The plume's differential emission measure (DEM)
exhibited one and only one broad peak, centered around logT~5.8 on May
9 and around logT~5.6 on May 13, and exceeded the DEM of the quiet
Sun by more than an order of magnitude at these temperatures. The
high-temperature portion of the plume's DEM resembled that of nearby
quiet-Sun areas. Intensity ratios of the O IV lines at 625.8 and 554.5
Å yield logne (where ne is the electron density
in cm-3) of 9.6+0.3-0.6 in the plume
on May 9 and 9.7+0.2-0.2 on May 13; values of
9.4+0.3-0.9 and 9.4+0.2-0.3
were obtained in the quiet-Sun areas on the same dates. Based on
abundance enhancements derived from transition region emission lines of
Ca, an element with low first ionization potential, elemental abundances
in the plume appear to be coronal rather than photospheric. The plume
plasma reveals a bipolar Doppler velocity flow pattern, in which
maximum downflows in excess of 37 km s-1 are observed in
the northeast portion of the plume, and maximum upflows that exceed
52 km s-1 are observed in the northwest.
Title: A new method for in-flight intensity calibration of
high-resolution EUV and FUV spectrometers
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2005A&A...441.1211F
Altcode:
We introduce a new technique for the measurement of the in-flight
relative intensity calibration of high resolution spectrometers. This
technique makes use of the free-free radiation in hot, dense active
regions and flares, and combines it with spectral line intensities
in an iterative procedure. After a few iterations, the relative
intensity calibration and the temperature of the emitting plasma are
determined. The application of this technique to the EIS instrument
on board the Solar-B satellite (launch in 2006) is discussed.
Title: Diagnostics of Two X-Ray Flares Using CHIANTI
Authors: Landi, E.; Phillips, K. J. H.
Bibcode: 2005ESASP.592..499L
Altcode: 2005ESASP.592E..91L; 2005soho...16E..91L
No abstract at ADS
Title: Evidence for In Situ Heating in Active Region Loops
Authors: Curdt, W.; Landi, E.; Wang, T. J.; Feldman, U.
Bibcode: 2005ESASP.592..475C
Altcode: 2005soho...16E..85C; 2005ESASP.592E..85C
No abstract at ADS
Title: Observations and Models of Solar Active Region Loops
Authors: Landi, E.; Landini, M.
Bibcode: 2005ESASP.592..495L
Altcode: 2005soho...16E..90L; 2005ESASP.592E..90L
No abstract at ADS
Title: Spectral Atlas of X-Ray Lines Emitted during Solar Flares
Based on CHIANTI
Authors: Landi, E.; Phillips, K. J. H.
Bibcode: 2005ApJS..160..286L
Altcode:
A spectral atlas of X-ray lines in the wavelength range 7.47-18.97 Å is
presented, based on high-resolution spectra obtained during two M-class
solar flares (on 1980 August 25 and 1985 July 2) with the Flat Crystal
Spectrometer on board the Solar Maximum Mission. The physical properties
of the flaring plasmas are derived as a function of time using strong,
unblended lines. From these properties, predicted spectra using the
CHIANTI database have been obtained, which were then compared with
wavelengths and fluxes of lines in the observed spectra to establish
line identifications. Identifications for nearly all the observed lines
in the resulting atlas are given, with some significant corrections
to previous analyses of these flare spectra. Line ratios allowed
us to determine temperature and density; in the 1985 July 2 flare,
very high densities (Ne~=1013 cm-3)
were measured.
Title: On the sources of fast and slow solar wind
Authors: Feldman, U.; Landi, E.; Schwadron, N. A.
Bibcode: 2005JGRA..110.7109F
Altcode: 2005JGRA..11007109F
The slow speed solar wind as measured at the Earth orbit and beyond
is characterized by its velocity of ≃400 km s-1, by its
coronal composition and by its frozen-in temperature (from carbon
charge-states) of 1.4-1.6 × 106 K. In contrast the
fast speed solar wind is characterized by its velocity of ≃750
km s-1, its nearly photospheric composition and its
frozen-in temperature of ≃8 × 105 K. The solar wind is
believed to originate very close to the solar surface, but since it
is accelerated significantly above the solar surface, its velocity
cannot be correlated with remote observations to trace its origin. In
contrast, elemental abundances and freeze-in temperatures can be used
as tracers for locating the sources from which the slow and fast solar
winds emerge. By comparing remote observations with properties of the
solar wind observed in situ, the most likely structures from which solar
wind plasmas emerge can be identified. In the present paper we review
the current understanding of the morphological features present in the
solar upper atmosphere and their physical properties such as electron
temperature, electron density and elemental abundances. In addition, we
discuss these observations in the context of recent theories describing
the emergence of new magnetic flux to power the solar wind, and more
traditional models that treat the background field and solar wind as
a steady phenomenon.
Title: The High-Temperature Response of the TRACE 171 Å and 195
Å Channels
Authors: Phillips, K. J. H.; Chifor, C.; Landi, E.
Bibcode: 2005ApJ...626.1110P
Altcode:
The CHIANTI spectral code is used to estimate line and continuum
intensity contributions to the TRACE 171 and 195 Å channels, widely
used for imaging a variety of solar features and phenomena, including
quiet-Sun and active region loops and solar flares. It is shown that
the 171 Å channel has a high-temperature response due to continuum
and Fe XX line emission, so high-temperature (~10-20 MK) features in
flares, prominent in TRACE 195 Å images as well as in X-ray images
from Yohkoh and RHESSI, are sometimes visible in images made in
the 171 Å channel. Such features consist of hot loop-top emission,
either confined spots or ``spine'' structures in loop arcades. This
is illustrated with TRACE and X-ray flare images.
Title: Dielectronic Satellites Near the 1s2 - 1snp (n >
2) Lines of He-like Ions in Solar X-ray Spectra
Authors: Landi, E.; Phillips, K. J. H.; Sylwester, J.; Sylwester,
B.; Dennis, B. R.; Dubau, J.
Bibcode: 2005AIPC..774..173L
Altcode:
We discuss the importance of dielectronic satellites with transitions
1s22l - 1s2l3p on the long-wavelength side of He-like ion
lines 1s2 - 1snp (n > 2). Their intensity ratios with
the He-like ion lines have an inverse temperature dependence, making
them useful as diagnostics. This is examined in the case of Si and
Fe satellites.
Title: Recent developments of the CHIANTI database in the X-ray
wavelength range
Authors: Landi, E.; Dere, K. P.; Young, P. R.; del Zanna, G.; Mason,
H. E.; Landini, M.
Bibcode: 2005AIPC..774..409L
Altcode:
CHIANTI is a database of atomic data and transition probabilities that
allows the calculation of synthetic spectra and plasma diagnostics of
optically thin plasmas. It is primarily suited for wavelengths shorter
than 2000 Å but in principle can also be used at longer wavelengths. In
the present paper we illustrate the latest development of the CHIANTI
database, that include a huge expansion of the database in the X-ray
wavelength range, the renewal of several data in the EUV range, and
the inclusion of ionization and recombination in the level population
calculation. This enhanced database will constitute the Version 5
of CHIANTI.
Title: Structure and Organization of the Upper Chromosphere
Authors: Korendyke, C. M.; Landi, E.; Vourlidas, A.
Bibcode: 2005AGUSMSH12A..05K
Altcode:
Over its past two flights, the VAULT sounding rocket instrument
obtained a series of subarcsecond resolution images of the solar
disk. These Lyman alpha images resolve and separate structures in
the upper chromosphere. The observed plasmas are concentrated in
larger diameter, optically thick loops. The images taken near the limb
unambiguously identify the height of the upper chromosphere in the quiet
sun. An unexpected level of evolution and activity is present in the
"quiet sun" at small spatial scales. The third flight of the payload
will investigate the interconnectivity of the observed structures with
the photosphere.
Title: Properties of the Solar Corona Outside the West Solar Limb
Authors: Doschek, G. A.; Feldman, U.; Landi, E.
Bibcode: 2005AGUSMSP21B..08D
Altcode:
We discuss the analysis of 36 spectral observations recorded by the
SUMER spectrometer on SOHO on April 22-23, 1998, at the onset of the
new solar cycle. The observations were made with the 4" x 300" slit,
and are distributed over the west hemisphere between 1.02 and 1.5 solar
radii along the equatorial direction and between -0.9 solar radii south
of the equator and +0.9 solar radii north of it. At the far corners of
the studied region the solar distance was 1.74 solar radii. We have
found that the physical characteristics of the central part of the
region are typical of quiet Sun coronal plasmas. The regions furthest
from the equator resemble coronal hole plasmas and the intermediate
regions are consistent with a transition between the two. We believe
that this is the most comprehensive work of its kind undertaken thus
far using UV spectral lines. We use the recorded line intensities
and line shapes to describe, as a function of coronal position,
electron temperatures, electron densities, elemental abundances,
line-of-sight emission measures (EM), nonthermal mass motions, and
mass dependent elemental settling. By using intensity ratios between
the two component resonance lines of Li-like O VI, Ne VIII and Mg X,
we determine the fractional excitation in the Li-like lines produced
by electron collisions and the fractional excitation produced by
photo-excitation of transition region radiation emitted just above
the photosphere.
Title: Thermal and Kinetic Properties of Motions in a Prominence
Activation and Nearby Loop
Authors: Kucera, T. A.; Landi, E. E.
Bibcode: 2005AGUSMSP21B..01K
Altcode:
We perform a quantitative analysis of the thermal properties of
a prominence activation and motions in a nearby loop. In order to
make measurements of the quickly moving features seen in loops and
prominences in the UV we use the SOHO/SUMER spectrograph to take a
time series of exposures from a single pointing position, providing
a measurement of spectral line properties as a function of time and
position along the slit. The lines observed cover a broad range
of temperatures from 80,000 - 1.6 million K. These measurements
are combined with TRACE movies in transition region and coronal
temperature bands to obtain more complete information concerning
prominence structure and motions. The resulting observations allow
us to analyze the thermal and kinetic energy of the moving sources as
functions of time. The loop and prominence are most apparent in lines
formed at temperatures below 250,000 K. We find that in most cases
the temperature distribution of plasma in a moving feature changes
relatively little over time periods of about 20 minutes.
Title: Elemental Abundances in a Sunspot Plume Observed With SERTS
Authors: Brosius, J. W.; Landi, E.; Thomas, R. J.
Bibcode: 2005AGUSMSP11A..03B
Altcode:
We present an EUV spectrum of a sunspot plume obtained with the SERTS
sounding rocket experiment. The spectrum contains emission lines from
various ionization stages of elements with a low (less than 10 eV) first
ionization potential (low FIP: Al, Ca, Fe, Mg, Ni, Si) and a high FIP
(C, He, Ne, O). The plume appears much brighter than its surroundings
in lines formed at log T around 5.6, i.e., lines of high-FIP Ne VI
and low-FIP Mg VI. Based upon the differential emission measure (DEM)
derived from all of the lines available, we are able to compare the
abundances of low-FIP and high-FIP elements in the plume. Results
indicate whether plume plasma abundances are photospheric or coronal.
Title: Coronal Element Comparison Observed by SOHO SUMER in the
Quiet Southeast and Northwest Limb Regions at 1.04 Rsolar
above the Solar Disk
Authors: Widing, K. G.; Landi, E.; Feldman, U.
Bibcode: 2005ApJ...622.1211W
Altcode:
The composition in an isothermal region at 1.04 Rsolar above
a diffuse, quiet coronal region on the northwest limb is studied and
compared with a similar region above the southeast limb analyzed by
Warren in 1999. Elemental abundances relative to H in the corona are
measured and normalized to the abundance ratios in the photosphere. The
enrichment factors of the low first ionization potential elements are
comparable above both limbs, but are significantly smaller than the
factor of 4 in SUMER spectra obtained 2 years earlier at solar minimum
in a diffuse, quiet equatorial region.
Title: Radiative transition probabilities in the O-like sequence
Authors: Landi, E.
Bibcode: 2005A&A...434..365L
Altcode:
In the present work a complete set of radiative transition rates is
calculated for all for the O-like ions with Z=11{-}30. Energy levels,
oscillator strengths and A values are computed for all transitions
within the n=2 complex and are compared with previous calculations,
where available. Calculations are carried out using the Superstructure
code. The present work provides for the first time a self-consistent,
complete set of A values necessary for the calculation of line
emissivities and synthetic spectra for all the ions considered, filling
several gaps in the existing literature. The present data are especially
suited for the analysis of spectral lines emitted by the less-abundant
elements in the universe, for which few if any data were available in
the literature.
Title: Helium Abundance in High-Temperature Solar Flare Plasmas
Authors: Feldman, U.; Landi, E.; Laming, J. M.
Bibcode: 2005ApJ...619.1142F
Altcode:
In the present work we use emission from dense plasmas late in the decay
phase of flares, while the plasmas are still hot [(2-4)×106
K], to determine the absolute helium abundance in flaring solar
corona. To achieve this, we make use of intensity ratios of H I
and He II lines and of intensity ratios between the He II lines
and the bremsstrahlung continuum radiation emitted by the local
postflare plasmas. These ratios are very sensitive to the electron
temperature, which is measured by using two different techniques:
intensity ratios from lines emitted by heavier elements and from the
line width of H I and He II lines. The latter method is made possible
by the low atomic weight of H and He and by the high temperature of
the plasma, which causes the widths of these lines to exceed 0.6 Å
(He) and 1.1 Å (H). Such values significantly exceed the broadening
due to nonthermal mass motions, so line widths can provide accurate
temperature measurements. The average helium absolute abundance was
found to be 12.2%+/-2.4%.
Title: Models for Solar Magnetic Loops. V. A New Diagnostic Technique
to Compare Loop Models and Observations
Authors: Landi, E.; Landini, M.
Bibcode: 2005ApJ...618.1039L
Altcode:
We present a new diagnostic technique to compare theoretical models
with observations of quiescent magnetic loops from high-resolution
imaging spectrometers. The diagnostic technique is primarily suited
for the analysis of high-resolution, spatially resolved spectra, but
it can also be applied to narrowband images. The diagnostic technique
is based on a steady state, dynamic loop model and allows us to
unambiguously determine whether the model reproduces the observations
and to determine the plasma heating, velocities, footpoint conductive
flux, and pressure in the loop.
Title: The CHIANTI database
Authors: Landi, E.; Dere, K. P.; Young, P. R.; Landini, M.; Mason,
H. E.; Del Zanna, G.
Bibcode: 2005HiA....13..653L
Altcode:
CHIANTI is a database of atomic data and transition rates necessary for
calculating synthetic spectra and carrying out plasma diagnostics of
astrophysical sources in the X-ray EUV and UV wavelength ranges. CHIANTI
includes both line and continuum emission from all astrophysically
abundant elements in the universe. All data are taken from refereed
literature and are critically assessed. CHIANTI also includes a suite
of IDL programs that allow spectroscopic analysis to be carried
out. CHIANTI data and software are freely distributed over the
internet. In the present talk I will describe the contents of
the CHIANTI database its current status and the areas where CHIANTI
is being developed and I will also present a comparison of CHIANTI
predictions with the X-ray emission from astrophysical sources.
Title: In-Situ Heating in Active Region Loops
Authors: Curdt, W.; Landi, E.; Wang, T.; Feldman, U.
Bibcode: 2005HvaOB..29..157C
Altcode:
We report new observational results and insights in the energy release
during transient events on sub-flare level in active region coronal
loops. Our work is based on multi-temperature observations obtained
high above the limb by the SUMER spectrometer on SOHO. We conclude
that the energy is impulsively injected into the loop system from
one and only one foot point. This asymmetric injection does not seem
to be connected with any bulk flow and there is no indication that
the plasma in the loop is replenished or replaced. Therefore the
chromospheric evaporation model is not applicable for this type of
events. The electron density, Ne, however, increases by up
to two orders of magnitude during such events. If no new material is
added to the local plasma, then the Ne increase can only be
explained by a rapid volume decrease, i.e., by a in-situ pinch effect,
compressing and heating the affected plasma.
Title: The SUMER spectral atlas of solar coronal features
Authors: Curdt, W.; Landi, E.; Feldman, U.
Bibcode: 2004A&A...427.1045C
Altcode:
We present a spectral atlas of the solar corona in the far-ultraviolet
(FUV) and extreme ultraviolet (EUV) wavelength range. The atlas is based
on observations obtained between 670 Å and 1609 Å in first order of
diffraction and between 465 and 670 Å in second order with the SUMER
(Solar Ultraviolet Measurements of Emitted Radiation) spectrograph
on SOHO (Solar and Heliospheric Observatory). This paper complements
the SUMER Spectral Atlas of Solar Disk Features, also published in
A&A. The atlas contains off-limb spectra of the corona above a
coronal hole, a quiet region, the active corona, and a flare. We provide
wavelengths of all detected lines and identification, if available; 311
out of 507 coronal emission lines could be identified or reconfirmed,
including several new identifications. Brief descriptions of the
data reduction and calibration procedures are given. The spectral
radiances are determined with a relative uncertainty of 0.15 to 0.40
(1σ) and the wavelength scale is accurate to typically ≃30 mÅ. The
atlas is also available in a machine readable format. Table
\ref{tab3} and Fig. \ref{fig3} are only available in electronic form
at http://www.edpsciences.org
Title: Models for Solar Magnetic Loops. IV. On the Relation between
Coronal and Footpoint Plasma in Active Region Loops
Authors: Landi, E.; Feldman, U.
Bibcode: 2004ApJ...611..537L
Altcode:
In the present work we analyze several SUMER intensity maps of active
region solar loops in order to compare the relative brightnesses of
the footpoints and the coronal section of active region loops. We
find that the former are barely distinguishable from the background
emission of the active region, while the coronal emission of loops is
confined in well-identifiable structures that are significantly brighter
than the background. This result means that the vast majority of the
active region emission in chromospheric and transition region lines
is generated by plasma not directly connected with the coronal plasma
that constitutes the observed coronal loops. We determine the observed
intensities of coronal lines relative to the observed transition
region and chromospheric emission and compare them with predictions
from loop models having uniform cross section and different heating
functions. We find that the loop models overestimate the footpoint
emission by orders of magnitude. We discuss the discrepancy in light
of the heating function and of the loop cross section. We speculate
that nonuniformity in the loop cross section, more specifically a
significant decrease of the cross section near the footpoints, is the
most likely solution to the discrepancy.
Title: Observations Indicating That ~1 × 107 K Solar
Flare Plasmas May Be Produced in Situ from ~1 × 106
K Coronal Plasma
Authors: Feldman, U.; Dammasch, I.; Landi, E.; Doschek, G. A.
Bibcode: 2004ApJ...609..439F
Altcode:
We discuss a set of flare observations obtained at a position of
0.10 Rsolar above the solar northwest limb. The data
were acquired by the Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) spectrometer on the Solar and Heliospheric
Observatory (SOHO). We derive time-dependent comparisons of
physical properties, such as electron temperature and density,
between flare plasma and background coronal plasma observed along
the same lines of sight. In addition to temperature and density,
we discuss emission measures, elemental abundances, nonthermal mass
motions (from line widths), and bulk mass motions (from Doppler
shifts). The observations appear to indicate that the flaring plasmas
(4×106K<=Te<=1×107K)
along the lines of sight were formed by in situ heating
and possibly by compression of the ambient coronal material
(Te<=2×106 K).
Title: Models for Solar Magnetic Loops. III. Dynamic Models and
Coronal Diagnostic Spectrometer Observations
Authors: Landi, E.; Landini, M.
Bibcode: 2004ApJ...608.1133L
Altcode:
In the present work SOHO Coronal Diagnostic Spectrometer (CDS)
observations of a quiescent active region loop are compared to a
steady state, dynamic loop model. Three different heating functions
are adopted: uniform, concentrated at the top, and concentrated at the
footpoints. Predicted temperature and density profiles of the selected
loop are compared with those obtained from CDS observations using
line ratios and an emission measure analysis. The latter method also
allows us to measure the loop filling factor. The space of parameters
of the model is investigated in an effort to achieve agreement with
observations. The effects of uncertainties and of CDS instrumental
limitations on the results are assessed. We find that no agreement can
be found between model predictions and observations. Possible causes of
the disagreement and areas of further investigation are discussed. This
work also demonstrates the potential of high-resolution spectroscopy
in loop studies, even in the presence of moderate spatial resolution.
Title: Newly Identified Forbidden Transitions within the Ground
Configuration of Ions of Very Low Abundance P, Cl, K, and Co
Authors: Feldman, U.; Landi, E.; Curdt, W.
Bibcode: 2004ApJ...607.1039F
Altcode:
Forbidden lines from transitions within the ground configuration
of highly ionized atoms occupy an important role in diagnosing the
properties of astrophysical plasmas. In this paper we report the
identification of forbidden lines in the 500-1500 Å range from
transitions within the ground configuration of highly ionized ions
of the very low abundance phosphorus, chlorine, potassium, and
cobalt recorded by SOHO SUMER. For the newly identified lines we
provide upper level fractional populations multiplied by relevant
spontaneous decay rates. Aided by the newly identified lines, the
coronal composition of elements with photospheric abundances of
5×10-7-1×10-8 relative to hydrogen could
be established.
Title: Atomic Data and Spectral Line Intensities for Ca VIII
Authors: Landi, E.; Storey, P. J.; Zeippen, C. J.
Bibcode: 2004ApJ...607..640L
Altcode:
In the present work a complete set of energy levels, spontaneous
radiative decay rates, and thermally averaged collision strengths
are calculated for the first time for the five lowest electron
configurations of Ca VIII, corresponding to 40 fine-structure energy
levels. Collision data are calculated using the R-matrix approximation,
and results are compared with earlier computations. The potential of Ca
VIII lines for plasma diagnostics is shown. Ca VIII line emissivities
are calculated and compared to observations of the Sun obtained with
high-resolution spectrometers on board the Solar and Heliospheric
Observatory (SOHO). Excellent agreement between predictions and
observations is found, and Ca VIII is able to provide accurate
measurements of Ca/Ne abundance, relevant for studies of the first
ionization potential effect.
Title: Prominence energetics measured with SOHO/SUMER and TRACE
Authors: Kucera, T. A.; Landi, E.
Bibcode: 2004AAS...204.5501K
Altcode: 2004BAAS...36Q.760K
The mechanisms by which solar prominences are filled with plasma are
still undetermined. In this study we perform a quantitative analysis
of the thermal properties of moving features in prominences in order
to put constraints on models of prominence formation and dynamics. In
order to make such measurements of the quickly moving features seen
in prominences in the UV we use the SOHO/SUMER spectrograph to
take a time series of exposures from a single pointing position,
providing a measurement of spectral line properties as a function
of time and position along the slit. The line observed cover a broad
range of temperatures from 80,000 - 1.6 million K. These measurements
are combined with TRACE movies in transition region and coronal
temperature bands to obtain more complete information concerning
prominence structure and motions. The resulting observations allow
us to analyze the thermal and kinetic energy of the moving prominence
sources as functions of time. This work was partly funded through
NASA SR&T RTOP 432-03-52-17
Title: Recent development of the CHIANTI database in the X-ray
wavelength range
Authors: Landi, E.; Dere, K. P.; Mason, H. E.; Del Zanna, G.; Landini,
M.; Young, P. R.
Bibcode: 2004AAS...204.7310L
Altcode: 2004BAAS...36R.801L
CHIANTI consists of a database of critically assessed atomic data
and transition rates to calculate line and continuum emission
from astrophysical plasmas. During the last year the CHIANTI
database has been substantially expanded in the X-ray wavelength
region by including a large number of new configurations and lines,
and by including ionization and recombination processes in the level
population calculations. We will describe these improvements,
the data we used, and illustrate examples of 1) their effects on
predicted emissivities and on plasma diagnostics 2) applications to
the study of flares in solar active regions
Title: The Differential Emission Measure Distribution of EQ Pegasi
Observed by BeppoSAX
Authors: Landini, M.; Landi, E.; Del Zanna, G.; Risaliti, G.
Bibcode: 2004IAUS..219..893L
Altcode: 2003IAUS..219E.126L
Broad band BeppoSAX observation of EQ Pegasi is analyzed using the
CHIANTI spectral database and a differential emission measure versus
temperature distribution of coronal matter. Comparison is performed
with the two temperature modelling usually performed in the data
reduction of broad band observations of active stars.
Title: Abundances of Potassium, Argon, and Sulphur in Solar Flares
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.
Bibcode: 2004IAUS..219..176P
Altcode:
No abstract at ADS
Title: Active Region Loop Models and Observations
Authors: Landi, E.; Landini, M.
Bibcode: 2004IAUS..219..557L
Altcode: 2003IAUS..219E.125L
The analysis of broad band images from EIT and TRACE and spectra
from SUMER and CDS have triggered a heated debate on 1) whether
the loops are isothermal for most of their length 2) whether they
are multithermal across their section and 3) what is the shape of
their heating function. Our work describes a detailed comparison
between SOHO-CDS observations of an active region loop with a standard
RTV-like loop model developed assuming a temperature-independent
heating function in the energy balance equation and a variable loop
cross-section. Observations of an active region loop recorded by
CDS have been analyzed. Additional data from EIT MDI and Yohkoh-SXT
have been considered. Electron density temperature and pressure along
the selected loop structure have been measured by means of line ratio
techniques and an emission measure analysis. Comparison with CDS
data has shown that 1) the RTV-like model is not able to reproduce
the observations 2) the loop is isothermal along most of its length 3)
the loop is isothermal across its section.
Title: Detection of H- and He-like resonance lines of chlorine in
solar flare spectra
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Phillips,
K. J. H.; Landi, E.
Bibcode: 2004IAUS..223..671S
Altcode: 2005IAUS..223..671S
Preliminary analysis of spectra collected with the RESIK Bragg bent
crystal X-ray spectrometer aboard CORONAS-F indicates the presence
of many spectral features which until recently were unidentified. We
present RESIK spectra in which the H-like Cl XVII Lyalpha line at 4.182
Å and He-like Cl XVI triplet components in the range 4.43 Å-4.45 Å
are identified.
Title: FIP Effect and FIP-Dependent Bias in the Solar Corona
Authors: Dwivedi, B. N.; Mohan, A.; Landi, E.
Bibcode: 2004IAUS..219..493D
Altcode: 2003IAUS..219E.129D
Using EUV spectra of an active region observed off the solar disk
by SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
spectrograph on the SOHO spacecraft we investigate the dependence of
the FIP effect on the height above the photosphere and its relation
to plasma magnetic structures present in the field of view. We also
investigate the possibility of the FIP bias in the low-FIP elements to
be FIP-dependent so that different abundance anomalies must be found
even within the low-FIP class of elements which can provide important
constraints on the FIP effect models.
Title: Thermal Properties of Prominence Motions as Observed in the UV
Authors: Kucera, T. A.; Landi, E.
Bibcode: 2003AGUFMSH42B0538K
Altcode:
The mechanisms by which solar prominences are filled with plasma are
still undetermined. In this study we perform a quantitative analysis of
the thermal properties of moving features in prominences in order to put
constraints on models of prominence formation and dynamics. In order to
make such measurements of moving features seen in prominences in the
UV we use the SOHO spectrometers SUMER and CDS to take a time series
of exposures at a single pointing position, providing a measurement
of spectral line properties as a function of time and position along
the slit. The resulting observations in spectral lines in a range of
"transition region" temperatures allow us to analyze the evolution of
thermal properties of quickly moving prominence features as a function
of time.
Title: Atomic Data and Spectral Line Intensities for S XI
Authors: Landi, E.; Bhatia, A. K.
Bibcode: 2003ApJS..149..251L
Altcode:
Electron impact collision strengths, energy levels, oscillator
strengths, and spontaneous radiative decay rates are calculated for S
XI. The configurations included are 2s22p2,
2s2p3, 2p4, 2s22p3l, and
2s22p4l (l=s, p, d), giving rise to 72 fine-structure
levels in intermediate coupling. Collision strengths are calculated
at five incident energies, 32, 60, 90, 120, and 150 ryd. Excitation
rate coefficients are calculated as a function of electron temperature
by assuming a Maxwellian electron velocity distribution. Using the
excitation rate coefficients and the radiative transition rates,
statistical equilibrium equations for level populations are solved. The
effects of resonances, proton rates, photoexcitation, and cascades
on level populations have been investigated. The predicted S XI line
intensities are compared with EUV and UV observations of the quiet
and active Sun.
Title: CHIANTI -- An Atomic Database for UV and X-ray Cool star
spectroscopy
Authors: Young, P. R.; Landi, E.; Bromage, G. E.; del Zanna, G.;
Dere, K. P.; Landini, M.; Mason, H. E.
Bibcode: 2003csss...12.1119Y
Altcode:
The CHIANTI atomic database was first released in 1996 and has since
become the standard resource for the interpretation of UV spectra
from the transition regions and coronae of the Sun and other cool
stars. We describe the contents of the most recent release (v.3)
and some of the uses that have been found for the database.
Title: Free-Free Emission in the Far-Ultraviolet Spectral Range:
A Resource for Diagnosing Solar and Stellar Flare Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Dammasch, I.;
Curdt, W.
Bibcode: 2003ApJ...593.1226F
Altcode:
We report the detection of free-free (bremsstrahlung) emission near 1200
Å from a flare at the solar limb observed with the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) spacecraft. The observations
consist of a time series of slit spectra at a fixed pointing that
lasted almost 2 hr, during which the observed solar region produced
a C8 flare. Using the free-free continuum intensities in conjunction
with intensities of high-temperature (106-107
K) emission lines that appear in the same wavelength range, we
derive the flare plasma electron density, electron temperature,
emission measure, and nonthermal mass motions before, during, and
after the flare. We describe a new diagnostic method for determining
the temperature of cooling plasmas. Because the free-free radiation
is emitted primarily by the interaction of electrons with nuclei of
H and He atoms, we are also able to derive the Fe/H, Al/H, and Ca/H
abundance ratios from the line intensities of highly ionized Fe, Al,
and Ca lines and the intensities of the free-free emission, assuming
a He abundance. The present work demonstrates the exceptional plasma
diagnostic potential of ultraviolet free-free continuum radiation when
coupled with emission-line intensities. We demonstrate that a similar
technique could be employed to diagnose plasma properties of stellar
flares using a high-resolution spectrometer with a sufficiently large
effective collecting area.
Title: Atomic Data and Spectral Line Intensities for S X
Authors: Bhatia, A. K.; Landi, E.
Bibcode: 2003ApJS..147..409B
Altcode:
Electron impact collision strengths, energy levels, oscillator
strengths and spontaneous radiative decay rates are calculated for
S X. The configurations included are 2s22p3,
2s2p4, 2p5, 2s22p23s,
2s22p23p, and 2s22p23d
giving rise to 72 fine-structure levels in intermediate
coupling. Collision strengths are calculated at five incident
energies, 25, 50, 75, 100, and 125 ryd. Excitation rate coefficients
are calculated as a function of electron temperature by assuming a
Maxwellian electron velocity distribution. Using the excitation rate
coefficients and the radiative transition rates, statistical equilibrium
equations for level populations are solved. Proton excitation rates
between the levels of the ground configuration have also been calculated
and included in the statistical equilibrium equations. The predicted S X
line intensities are compared with SUMER observations of the quiet Sun.
Title: Properties of Solar Plasmas near Solar Maximum above Two
Quiet Regions at Distances of 1.02-1.34 Rsolar
Authors: Landi, E.; Feldman, U.
Bibcode: 2003ApJ...592..607L
Altcode:
In the present work we have analyzed the spectra emitted by two quiet
solar regions observed off the solar disk by the SUMER instrument on
board the SOHO satellite. The two complete spectra were recorded when
the SOHO north-south axis was rotated relative to the Sun north-south
axis by ~=150° clockwise. As a result, the SUMER slit could be placed
so that it is perpendicular to the solar limb in an intermediate
orientation between the equator and the poles. The SUMER fields of
view consisted of two 1" wide radial strips of the solar corona from
1.02 to 1.34 Rsolar. The aim of the present work was to
measure the physical properties of the emitting plasma, namely, the
electron density and temperature, the plasma emission measure, and
the nonthermal mass motions, as a function of the distance from the
solar limb. The measurement of the plasma absolute element abundances
is deferred to a future paper. In measuring the nonthermal velocities
of both source regions, we have discovered a residual instrumental
systematic effect to line widths. The plasma in the SUMER field of
view is nearly isothermal. The measurements of electron density and
temperature allow us to check the hydrostatic assumption commonly
adopted in the literature and to find that the plasma is denser than
predicted. The wide wavelength range covered by the SUMER instrument
includes several Li-like ions, allowing us to investigate the relative
contribution of the radiative and collisional excitation mechanisms
in the Li-like resonance doublet formation. We confirm the earlier
findings that a significant radiative excitation occurs for O VI and
Ne VIII resonance lines even at low altitudes.
Title: Atomic Data and Emission-Line Intensities for Ca VII
Authors: Landi, E.; Bhatia, A. K.
Bibcode: 2003ApJ...589.1075L
Altcode:
In the present work we calculate energy levels, transition
probabilities, and electron-ion collisional excitation rates for the
3s23p2, 3s3p3, and 3s23p3d
configurations of the silicon-like ion Ca VII. The total number of
intermediate coupling levels considered is 27. Collision strengths
are calculated at seven incident electron energies: 8, 10, 15,
20, 30, 40, and 60 ryd, using the distorted-wave approximation
and a five-configuration model. Excitation rate coefficients are
calculated by assuming a Maxwellian distribution of velocities and
are used to calculate level populations and line emissivities under
the assumption of statistical equilibrium. Line intensity ratios are
calculated and compared with observed values measured from SERTS and
SOHO CDS spectra. The diagnostic potential of Ca VII is demonstrated,
with particular emphasis on the possibility of measuring the Ne/Ca
relative abundance through simultaneous observations of Ca VII and Ne
VI lines. Ca VII proves to be an excellent tool for the study of the
first ionization potential effect in the solar transition region.
Title: SOHO-Ulysses Spring 2000 Quadrature: Coronal Diagnostic
Spectrometer and SUMER Results
Authors: Parenti, S.; Landi, E.; Bromage, B. J. I.
Bibcode: 2003ApJ...590..519P
Altcode:
We present results from SOHO/CDS and SOHO/SUMER coordinated observations
of coronal streamers made during the spring 2000 quadrature of SOHO,
the Sun, and Ulysses. These observations form part of the JOP 112,
which is primarily aimed at investigating the composition of the
regions of the corona and the solar wind observed by both SOHO and
Ulysses. SUMER and CDS observed the low corona from the limb up
to about 1.3 Rsolar from the Sun center. The physical
parameters of the plasma, such as electron density, temperature,
emission measure, and composition, are measured along the radial
direction, toward Ulysses. The variation in these parameters over the
6 day series of observations was examined, and no significant change
was seen. The dependence of these parameters on the solar latitude was
also investigated. The results indicate that the observed streamers
are homogeneous, of coronal composition, and nearly in hydrostatic
equilibrium. The structures remained almost stable during the whole
period of the observations.
Title: Solving the Discrepancy between the Extreme-Ultraviolet and
Microwave Observations of the Quiet Sun
Authors: Landi, E.; Chiuderi Drago, F.
Bibcode: 2003ApJ...589.1054L
Altcode:
The aim of the present work is to understand the origin of the
long-standing discrepancy between the EUV/UV-based predictions of
the quiet-Sun microwave spectrum and the observed one. We compare
accurate measurements of the quiet-Sun microwave brightness temperature
(Tb) with theoretical calculations obtained by using the
differential emission measure (DEM) of the plasma derived from UV and
EUV spectral line intensities observed by the SUMER and CDS instruments
on board the Solar and Heliospheric Observatory (SOHO). No agreement
can be found between the observed Tb and calculations
carried out using the standard DEM curves obtained from the EUV/UV
observations. In order to obtain agreement, it is necessary (1) to
modify the temperature range in which the DEM is usually defined in
order to take into account the presence of an isothermal corona, (2)
to separate the contribution of the cell and the network structures
in the transition region, and (3) to substitute the EUV/UV-based DEM
values at very low temperature (logT<=4.3) with values based on
the Vernazza, Avrett, & Loeser model. In the present work we are
able to solve a long-standing discrepancy between microwave and EUV/UV
results, and we demonstrate the great potential of the simultaneous
use of observations in these two spectral ranges.
Title: Solar Flare Abundances of Potassium, Argon, and Sulphur
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.
Bibcode: 2003ApJ...589L.113P
Altcode:
The absolute abundance of potassium has been determined for the first
time from X-ray solar flare line and continuum spectra. The absolute
and relative abundances of Ar and S have also been determined. Assuming
that the flare plasma is coronal, and since potassium has the lowest
first ionization potential (FIP) of any common element on the Sun,
this determination is of importance in the continuing debate concerning
the nature of the coronal/photospheric element abundance ratios, which
are widely considered to depend on the FIP. The measurements were made
with the RESIK crystal spectrometer on the Coronas-F spacecraft. A
differential emission measure DEM~exp(-βTe) was found to
be the most consistent with the data of three models considered. We
find that the K/H abundance ratio is (3.7+/-1.0)×10-7,
a factor of 3 times photospheric. Our measured values of the
Ar/H ratio, (2.8+/-0.2)×10-6, and of the S/H ratio,
(2.2+/-0.4)×10-5, are equal to previous coronal and
photospheric determinations to within uncertainties. These measurements
therefore fit a pattern in which low-FIP elements are enriched in
the corona by a factor 3 and in which high-FIP elements (including S)
have equal coronal and photospheric abundances.
Title: Solar Flare Abundances of Potassium, Argon, and Sulphur
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.
Bibcode: 2003SPD....34.1622P
Altcode: 2003BAAS...35..837P
The absolute coronal abundances of potassium, argon, and sulphur
are determined from X-ray solar flare spectra using the RESIK
bent crystal spectrometer on the Coronas-F space observatory. A
differential emission measure of the form exp(-α Te) was
found to be appropriate for describing the fluxes of the lines due
to K XVIII (λ 3.53Å), Ar XVIII (λ 3.73Å), Ar XVII (λ 3.95Å),
S XV (λ λ 4.09, 4.30Å), Si XIV (λ 5.22Å), and Si XIII (λ λ
5.40, 5.68Å) which are observed by RESIK over a period of several
hours in four long-duration flares. The continuum in two of the four
RESIK channels appears to be uncontaminated by crystal fluorescence
or other instrumental effects, allowing abundances relative to H to
be determined. We estimate the following abundances relative to H:
[K/H] = 4.7 X 10-7; [S/H] = 2.9 X 10-5; [Ar/H] =
2.0 X 10-6. These values agree with a pattern that depends
on the first ionization potential (FIP) of an element in which the
coronal abundances of low-FIP elements (like K) are enhanced over
their photospheric abundances by a factor 3 and high-FIP elements
(like Ar) are depleted by a factor 2. The coronal abundance of sulphur
(medium-FIP) is slightly enhanced (factor of 1.5) compared with its
photospheric abundance. The exponential temperature dependence of the
differential emission measure is applied to simultaneous X-ray data
from the RHESSI mission which sees a thermal spectrum (continuum plus
Fe lines at 6.7 keV) for some of these flares. Results of this will
be discussed. We acknowledge support for this research from the
National Research Council (KJHP), Polish Committee for Scientific
Research (JS, BS), and from the Office of Naval Research (EL).
Title: DEM measurements of moving UV features in prominences
Authors: Kucera, T. A.; Landi, E.
Bibcode: 2003SPD....34.0412K
Altcode: 2003BAAS...35Q.812K
Multi-thermal features with speeds of 5-70 km/s perpendicular to the
line of sight are common in the prominences which showed traceable
motions. These speeds are noticeably higher than the typical speeds of
5-20 km/s observed in H-alpha data from ``quiet" prominences and are
more typical of ``activated" prominences in which H-alpha blob speeds of
up to 40 km/s have been reported. In order to make a more quantitative
determination of the thermal properties of the moving features seen
in the UV, we use the SOHO Coronal Diagnostic Spectrometer to take a
time series of exposures from a single pointing position, providing
a measurement of spectral line properties as a function of time and
position along the slit. The resulting observations in lines of O III,
O IV, O V, Ne IV, Ne V, Ne VI, and Ne VII allow us to calculate the
differential emission measure of moving features and provide a test
of models of flows in prominences. Support for this work was partially
provided by NASA RTOP 432-03-52-17.
Title: Nonthermal Mass Motions within the High-Temperature Plasmas
above a Complex Solar Active Region
Authors: Feldman, U.; Landi, E.; Curdt, W.
Bibcode: 2003ApJ...585.1087F
Altcode:
We report on mass motions in high-temperature plasmas at
radial distances of 1.06-1.20 Rsolar corresponding
to 3.3×104-1.3×105 km above the west
solar limb. The observations were conducted over a 53 hr time
period while a complex active region moved across the west
solar limb. We found that the nonthermal mass motions in the
2.6×106-6.6×106 K plasmas that were
imaged along the slit were in the 20-35 km s-1
velocity range. The magnitude of the nonthermal mass motions
was independent of the plasma temperature or its height above the
limb. We also found that the emission measure distribution within the
2.6×106-6.6×106 K plasma regimes did not change
during most of the observations, an indication that on the average
the temperature distribution among the various plasma volumes along
the line of sight stayed unchanged.
Title: Atomic Data and Spectral Line Intensities for Si VII
Authors: Bhatia, A. K.; Landi, E.
Bibcode: 2003ApJ...585..587B
Altcode:
Electron impact collision strengths, energy levels, oscillator
strengths, and spontaneous radiative decay rates are calculated
for the Si VII configurations 2s22p4,
2s2p5, 2p6, 2s22p33s,
2s22p33p, and 2s22p33d,
giving rise to 86 fine-structure levels in intermediate
coupling. Collision strengths are calculated at five incident
energies, 15, 30, 45, 60, and 75 ryd, using the distorted wave
approximation. Excitation rate coefficients are calculated as a
function of electron temperature by assuming a Maxwellian electron
velocity distribution. Using the excitation rate coefficients and the
radiative transition rates, statistical equilibrium equations for level
populations are solved at electron densities covering the range of
108-1014 cm-3 assuming an electron
temperature of logTe(K)=5.8, corresponding to maximum
ionic abundance of Si VII. Relative spectral line intensities are
calculated. Proton excitation rates between the lowest three levels
have been included in the statistical equilibrium equations. The
predicted Si VII line intensities are compared with Solar EUV Rocket
Telescope and Spectrograph (SERTS) observations in NOAA Active Region
5464 and Solar Ultraviolet Measurement of Emitted Radiation (SUMER)
observations of the quiet Sun.
Title: The Solar Transition Region from UV and microwave observations
Authors: Chiuderi Drago, F.; Landi, E.
Bibcode: 2003MmSAI..74..691C
Altcode:
The quiet sun chromosphere-corona transition region is analyzed by
comparing the ultraviolet line intensities (observed by the SOHO
satellite) with the radio emission in the microwave range. Results
from the two wavelength ranges seem to be in strong disagreement
when standard techniques are applied to UV data. A more careful
analysis of the line intensities done separately in the network and
in the cell decreases the disagreement, but it does not remove it. It is finally shown that the most important reason of disagreement
comes from the lowest portion of the transition region, at log T <
4.5, where the plasma parameters derived from the UV lines (no more
optically thin) are very uncertain. The radio emission puts therefore
important constraints on the physical parameters of this portion of
the solar atmosphere.
Title: On the Extreme-Ultraviolet/Ultraviolet Plasma Diagnostics
for Nitrogen-like Ions from Spectra Obtained By SOHO/SUMER
Authors: Mohan, A.; Landi, E.; Dwivedi, B. N.
Bibcode: 2003ApJ...582.1162M
Altcode:
In this work we discuss the potential for plasma diagnostics of
forbidden transitions from the ground levels in the nitrogen-like
ions: Al VII, Si VIII, P IX, S X, Ar XII, K XIII, and Ca XIV. We also
study the lines emitted by n=3 levels of Si VIII. These transitions
fall in the UV spectral range and have been recently observed by
the SOHO/SUMER instrument in the solar spectrum. Some of the lines
considered in the present study have been measured by SUMER for the
first time. We investigate the effects of photospheric radiation, proton
collisional excitation, additional configurations, and resonances on
level populations, in order to assess the importance of these processes
in the calculation of line emissivities. We compare line ratios with
observations from SUMER on quiet-Sun and active regions and measure the
electron density and temperature of the emitting plasma. We show that
in a few cases current atomic data are still not able to reproduce the
observations and that further work is required to solve inconsistencies
between observations and theoretical predictions.
Title: Properties of the base of streamers from UV and EUV
observations
Authors: Parenti, S.; Landi, E.; Bromage, B. J. I.
Bibcode: 2003MmSAI..74..717P
Altcode:
In this paper we investigate the physical parameters of a streamer
observed during the Spring 2000 quadrature of SOHO, the Sun and
Ulysses. The analysis was carried out using SOHO/CDS and SOHO/SUMER
coordinated observations of the low corona. We analysed six days
of observations of the same region, deriving electron temperature,
density, emission measure and composition. We found full agreement
in the results from the two instruments. We conclude that we were
observing an omogeneus streamer, with coronal composition and not
completely isothermal.
Title: CHIANTI-An Atomic Database for Emission Lines. VI. Proton
Rates and Other Improvements
Authors: Young, P. R.; Del Zanna, G.; Landi, E.; Dere, K. P.; Mason,
H. E.; Landini, M.
Bibcode: 2003ApJS..144..135Y
Altcode: 2002astro.ph..9493Y
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities, and electron excitation data for
a large number of ions of astrophysical interest. Version 4 has been
released, and proton excitation data are now included, principally
for ground configuration levels that are close in energy. The fitting
procedure for excitation data, both electrons and protons, has been
extended to allow nine-point spline fits in addition to the previous
five-point spline fits. This allows higher quality fits to data from
close-coupling calculations where resonances can lead to significant
structure in the Maxwellian-averaged collision strengths. The effects
of photoexcitation and stimulated emission by a blackbody radiation
field in a spherical geometry on the level balance equations of
the CHIANTI ions can now be studied following modifications to the
CHIANTI software. With the addition of H I, He I, and N I, the first
neutral species have been added to CHIANTI. Many updates to existing
ion data sets are described, while several new ions have been added
to the database, including Ar IV, Fe VI, and Ni XXI. The two-photon
continuum is now included in the spectral synthesis routines, and a
new code for calculating the relativistic free-free continuum has been
added. The treatment of the free-bound continuum has also been updated.
Title: CHIANTI - An Atomic Database for XUV Emission Lines
Authors: Landi, Enrico; Dere, Ken P.; Landini, Massimo; Young, Peter
R.; Mason, Helen E.; del Zanna, Giulio
Bibcode: 2003IAUJD..17E..10L
Altcode:
CHIANTI is a database of atomic data and transition rates necessary for
calculating synthetic spectra and carrying out plasma diagnostics of
astrophysical sources in the X-ray EUV and UV wavelength ranges. CHIANTI
includes both line and continuum emission from all astrophysically
abundant elements in the universe. All data are taken from refereed
literature and are critically assessed. CHIANTI also includes a suite
of IDL programs that allow spectroscopic analysis to be carried
out. CHIANTI data and software are freely distributed over the
internet. In the present talk I will describe the contents of
the CHIANTI database its current status and the areas where CHIANTI
is being developed and I will also present a comparison of CHIANTI
predictions with the X-ray emission from astrophysical sources.
Title: Mass Motions and Plasma Properties in the 107
K Flare Solar Corona
Authors: Landi, E.; Feldman, U.; Innes, D. E.; Curdt, W.
Bibcode: 2003ApJ...582..506L
Altcode:
In the present work, we analyze Solar Ultraviolet Measurement of
Emitted Radiation (SUMER) observations of a solar limb flare that
occurred on 1999 May 9. The analyzed data cover a time span of around
6.4 hr, during which an M-7.6 flare erupted and decayed in the field of
view. Two selected regions along the SUMER slit have been considered
for quantitative analysis. The main purpose of the present analysis
is to measure the mass motions and the nonthermal velocities of the
postflare plasmas and their temporal evolution. To achieve this we
use lines having formation temperatures in the 2.5×106
to 2×107 K range from which we derive net mass motions
and nonthermal velocities and compare them with the properties of the
surrounding plasma not affected by the flare activity. To understand
the physical conditions of the flaring plasma and of the surrounding
material, we derive electron temperature, electron density, and emission
measures of the emitting plasma. We find that bulk motions, initially
of the order of several hundreds of kilometers per second in both
directions, decay within 10 minutes from the flare onset; nonthermal
velocities decay to preflare values of around 30 km s-1 in
less than 2 hr from the maximum value of around 100 km s-1
at flare onset. The measured electron density does not seem to change
during activity, while the flare plasma temperature steadily decays
to preflare values. The temperature evolution is consistent with a
radiatively cooling plasma, although the uncertainties associated to
the measurement of the variation of thermal energy of the flare plasma
prevent a definitive conclusion on possible continuous heating of the
flaring plasma.
Title: EUV plasma diagnostics for nitrogen-like ions from spectra
obtained by SUMER/SOHO
Authors: Dwivedi, B. N.; Mohan, A.; Landi, E.
Bibcode: 2002ESASP.505..397D
Altcode: 2002IAUCo.188..397D; 2002solm.conf..397D
We discuss the potential for plasma diagnostics of forbidden transitions
from the ground levels in the nitrogen-like ions: Al VII, Si VIII,
P IX, S X, Ar XII, K XIII and Ca XIV. These transitions fall in the
UV spectral range and have been recently observed by the SOHO/SUMER
instrument in the solar spectrum. Some of the lines used in the present
study have been measured by SUMER for the first time: higher resolution
and sensitivity allow for the identification and measurement of weaker
lines than previously, at positions higher off the solar limb. We
show that current atomic data are still not able to reproduce the
observations and that further work is required to solve inconsistencies
between observations and theoretical predictions.
Title: Measurements of Three-dimensional Coronal Magnetic Fields
from Coordinated Extreme-Ultraviolet and Radio Observations of a
Solar Active Region Sunspot
Authors: Brosius, Jeffrey W.; Landi, Enrico; Cook, John W.; Newmark,
Jeffrey S.; Gopalswamy, N.; Lara, Alejandro
Bibcode: 2002ApJ...574..453B
Altcode:
We observed NOAA Active Region 8108 around 1940 UT on 1997 November 18
with the Very Large Array and with three instruments aboard the NASA/ESA
Solar and Heliospheric Observatory satellite, including the Coronal
Diagnostic Spectrometer, the EUV Imaging Telescope, and the Michelson
Doppler Imager. We used the right-hand and left-hand circularly
polarized components of the radio observing frequencies, along with
the coordinated EUV observations, to derive the three-dimensional
coronal magnetic field above the region's sunspot and its immediate
surroundings. This was done by placing the largest possible harmonic
(which corresponds to the smallest possible magnetic field strength)
for each component of each radio frequency into appropriate atmospheric
temperature intervals such that the calculated radio brightness
temperatures at each spatial location match the corresponding
observed values. The temperature dependence of the derived coronal
magnetic field, B(x,y,T), is insensitive to uncertainties on the
observed parameters and yields field strengths in excess of 580 G
at 2×106 K and in excess of 1500 G at 1×106
K. The height dependence of the derived coronal magnetic field,
B(x,y,h), varies significantly with our choice of magnetic scale height
LB. Based on LB=3.8×109 cm derived
from the relative displacements of the observed radio centroids, we
find magnetic field strengths in excess of 1500 G at heights of 15,000
km and as great as 1000 G at 25,000 km. By observing a given target
region on several successive days, we would obtain observations at a
variety of projection angles, thus enabling a better determination of
LB and, ultimately, B(x,y,h). We compare coronal magnetic
fields derived from our method with those derived from a potential
extrapolation and find that the magnitudes of the potential field
strengths are factors of 2 or more smaller than those derived from our
method. This indicates that the sunspot field is not potential and that
currents must be present in the corona. Alfvén speeds between 25,000
and 57,000 km s-1 are derived for the 1×106
K plasma at the centroids of the radio observing frequencies. Filling
factors between 0.003 and 0.1 are derived for the 1×106
K plasma at the centroids of the radio observing frequencies.
Title: A Comparison between Coronal Emission Lines from an Isothermal
Spectrum Observed with the Coronal Diagnostic Spectrometer and
CHIANTI Emissivities
Authors: Landi, E.; Feldman, U.; Dere, K. P.
Bibcode: 2002ApJ...574..495L
Altcode:
The present paper compares off-disk spectral observations of the
solar corona in the ranges 307-379 and 513-633 Å with theoretical
emissivities calculated using the CHIANTI database. The observed spectra
were recorded by the Coronal Diagnostic Spectrometer instrument on
board the Solar and Heliospheric Observatory using the normal-incidence
portion of the instrument. Using line-ratio techniques, we first measure
the electron temperature and density in the emitting region, verifying
that it is nearly isothermal. Next, we use an emission-measure analysis
to compare measured spectral line intensities with predictions from the
CHIANTI database. This comparison allows us to assess the quality of
the CHIANTI data for the brightest coronal lines in the 307-379 and
513-633 Å spectral ranges. As a result, we are able to (1) select
lines and ions for which the agreement between theory and observation
is good, (2) identify a few lines that are blended, and (3) stress
inconsistencies between a few lines and theory, thus showing where
improvements to atomic data and transition probabilities are necessary.
Title: SOHO/CDS and SUMER coordinated observations of coronal streamer
Authors: Parenti, Susanna; Landi, Enrico; Bromage, B. J. I.
Bibcode: 2002ESASP.508..399P
Altcode: 2002soho...11..399P
In June 2000 the SOHO and Ulysses satellites reached the quadrature
configuration with respect to the Sun. On this occasion the JOP 112
was run, with the aim of studying the coronal and solar wind physical
parameters, with particular attention to the element composition. In
this paper we present preliminary results from SOHO/SUMER and CDS/NIS
data. The two instruments were pointed off-limb and observed the
lower solar corona in the Ulysses direction (-58.2 deg in the S-E
quadrant). During the period of observations (12-17 June) the observed
corona was filled with streamers. From each instrument the electron
density, temperature and element composition of the studied areas have
been derived. A comparison of the results from the two instruments is
then presented.
Title: New Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; White, S. M.; Landi, E.; Cook, J. W.; Newmark,
J. S.; Gopalswamy, N.; Lara, A.
Bibcode: 2002AAS...200.0307B
Altcode: 2002BAAS...34..642B
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of NOAA
regions 8108 (N21E18 on 1997 November 18) and 8539 (N20W12 on 1999 May
13). The EUV spectra and images, obtained with the Coronal Diagnostic
Spectrometer (CDS) and the Extreme-ultraviolet Imaging Telescope (EIT)
aboard the Solar and Heliospheric Observatory (SOHO) satellite, were
used to derive the differential emission measure (DEM) and the plasma
electron density for each spatial pixel (along each line of sight)
within both regions. These were subsequently used to calculate maps
of the expected thermal bremsstrahlung brightness temperature at the
Very Large Array (VLA) radio observing frequencies of 1.4, 4.9, 8.4,
and 15 GHz. The thermal bremsstrahlung maps reproduce neither the
structure nor the intensity of the observed maps, and indicate that
thermal gyroemission must dominate the observed radio emission. The
radio observations were used to constrain the magnetic scale height and
the gross temperature structure of the atmosphere. These, along with
the DEM, electron density, and observed radio brightness temperature
maps, were used to derive the temperature distribution of the coronal
magnetic field strength B(T) that reproduced simultaneously the observed
right-hand and left-hand circularly polarized emission at the radio
observing frequencies for each spatial pixel in the images. Magnetic
field strengths corresponding to 3rd harmonic gyroemission at 4.9 GHz
(580 Gauss) are found in coronal plasmas at temperatures as high as
3.2 MK, while magnetic field strengths corresponding to 3rd harmonic
gyroemission at 15 GHz (1800 Gauss) are found in coronal plasmas at
temperatures as high as 1.6 MK. B(T) was ultimately converted to B(h)
and compared with extrapolations from photospheric magnetograms.
Title: The Prominence - Corona and the Filament - Corona Transition
Region: is There any Difference?
Authors: Chiuderi Drago, F.; Landi, E.
Bibcode: 2002SoPh..206..315C
Altcode:
The ratio between the Extreme Ultraviolet emission of the
prominence-corona transition region and that of the quiet Sun (QS)
transition region is measured using observations from the CDS and SUMER
instruments on board the SOHO Satellite. These results are compared with
those obtained in an earlier paper, analysing the same prominence as
a filament on the disk. Theoretical models predict a difference in the
emission of the prominence-corona transition region when it is observed
at the limb and on the disk as a filament; the aim of the present work
is to provide an observational check of this difference. SUMER and
CDS data provide fairly good agreement if the prominence intensity
measured by SUMER is compared with the average quiet-Sun intensity,
measured near the disk center; the prominence intensity relative to
the average quiet-Sun level measured on the same rasters results in
disagreement with CDS, due to the smaller size of the disk portion
and to the very strong limb brightening present in SUMER rasters. The
relative prominence to quiet-Sun intensity ratio varies from 0.2 to
0.4, depending on the line formation temperature. This value leads to
a discrepancy with the results obtained in a previous study when the
same prominence was observed as a filament. This discrepancy indicates
that the prominence-corona transition region emission is different
when emitted by different sides of the prominence.
Title: The Arcetri Spectral Code for optically thin plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 2002A&A...384.1124L
Altcode:
The Arcetri Spectral Code allows one to evaluate the spectrum of
the radiation emitted by hot and optically thin plasmas in the
spectral range 1-2000 Å. The Arcetri Code consists of a series of
files that contain the emissivity of the plasma as a function of
electron temperature and density. Both line and continuum emission
are considered. These quantities are calculated using a database
of atomic data and transition probabilities, mostly taken from the
CHIANTI database. In the present work we describe the updates to the
spectrum and present the new results. A comparison with the previous
version of the code allows us to assess the improvements to the
spectrum; comparison with other spectral codes allows us to assess
the completeness of the Arcetri Code and of the CHIANTI database.
Title: CHIANTI-An Atomic Database for Emission Lines. V. Comparison
with an Isothermal Spectrum Observed with SUMER
Authors: Landi, E.; Feldman, U.; Dere, K. P.
Bibcode: 2002ApJS..139..281L
Altcode:
CHIANTI is a database consisting of critically evaluated atomic data and
transition probabilities necessary to analyze spectral observations
of optically thin plasmas. Previous papers described the content
of the database and compared it to a solar active region spectrum
between 170 and 450 Å. The aim of the present paper is to compare
CHIANTI predictions to off-disk spectral observations of the solar
corona between 500 and 1500 Å. The observed spectra were recorded by
the SUMER instrument on board the Solar and Heliospheric Observatory
using the full spectral range allowed by the instrument. Earlier works
have demonstrated that the particular emitting plasma is isothermal
at a temperature of 1.35×106 K, making it ideal for the
assessment of the accuracy of the CHIANTI database. This assessment of
the CHIANTI database allowed us (1) to select lines and ions for which
the agreement between theory and observation is good, (2) to identify
several lines which are blended, and (3) to stress inconsistencies
between a few lines and theory, thus showing where improvements to
atomic data and transition probabilities are necessary.
Title: Models for solar magnetic loops. II. Comparison with SOHO-CDS
observations on the solar disk
Authors: Brković, A.; Landi, E.; Landini, M.; Rüedi, I.; Solanki,
S. K.
Bibcode: 2002A&A...383..661B
Altcode:
The present work describes a detailed comparison between SOHO-CDS
observations of active region loops with a static, isobaric loop
model developed assuming a temperature-independent heating function
in the energy balance equation and a variable loop cross-section. The
loop model is described in Landini & Landi (2002). Observations
of an active region recorded by CDS have been analyzed. Additional
data from the EIT and MDI instruments on board the SOHO satellite,
and broad band soft X-rays images from the Yohkoh satellite, have
been used to complement the CDS dataset. CDS monochromatic images
from lines at different temperatures have been co-aligned with EIT,
MDI and Yohkoh images and a loop structure has been identified. Two
other loop structures are visible but their footpoints are not clearly
identified, and have not been analyzed. Electron density, temperature
and pressure along the selected loop structure have been measured by
means of line ratio techniques. These quantities have been used to test
the assumption of constant pressure adopted in the theoretical model,
and to compare their values with its predictions. The loop filling
factor has also been estimated from the CDS data after assumptions on
the loop geometry have been made. Comparison with CDS data has shown
that a classical model is not able to reproduce the observations;
despite the large uncertainties, mainly given by the limited CDS
spatial resolution, indications suggest that agreement occurs only if an
``ad hoc'' isothermal region is added on top of the loop and a large
conductive flux at the base is assumed. Suggestions for improvements
of theoretical loop models and further studies with the EIS instrument
on Solar-B, due for launch in 2005, are given.
Title: Fe XIII line intensities in solar plasmas observed by SERTS
Authors: Landi, E.
Bibcode: 2002A&A...382.1106L
Altcode:
Extreme-Ultraviolet spectral observations of \ion[Fe xiii] lines,
obtained during the 1989 and 1995 flights of the SERTS instrument,
are compared with line emissivities derived from two different sets
of atomic data and transition probabilities. One dataset is based
upon calculations involving the Close-Coupling approximation, and
the other is based upon the Distorted Wave approximation. Emission
line ratios that are insensitive to density and temperature are used
to assess both the quality of the transition rates and possible line
blending. Density-sensitive line ratios are used to measure the electron
density. The comparison between the observed and the theoretical line
ratios yields a set of lines, free of blends, that is recommended for
plasma diagnostic studies. Both theoretical datasets yield the same
set of lines, which includes wavelengths of 200.02, 201.13, 202.04,
203.16, 203.82, 209.67, 209.92, 256.43, 312.17, 312.87, 320.80,
348.18, 359.64 and 413.00 Å. Electron densities derived from line
ratios calculated with each theoretical dataset differ by a factor =~
2, comparable to the scatter in density measurements from other ions
formed at similar temperatures, as well as to the uncertainties on some
of the individual density measurements. This precludes determining
which of the two datasets is more accurate. Ambiguities in a few of
the line intensity ratios suggest that new, more accurate calculations
of transition rates are needed.
Title: Models for solar magnetic loops. I. A simple theoretical
model and diagnostic procedure
Authors: Landini, M.; Landi, E.
Bibcode: 2002A&A...383..653L
Altcode:
In the present paper the quasi-static model of Landini & Monsignori
Fossi (\cite{Landini75}) for coronal loops is improved and a simple
diagnostic procedure is developed to compare the most important
physical properties of the model with a set of spectral observations
of loops such as those obtained by the CDS and SUMER instruments
on SOHO. The model assumes quasi-static and isobaric conditions and
solves the energy equation among radiative losses, a constant heating
function and heat conduction. The model is allowed to have a variable
loop section. To better match the latest observational results, an
isothermal section of the loop is added at the top of the loop model;
its effects on the diagnostic technique and on the shape of the unknown
heating function are discussed. A numerical simulation is shown and
the effect of the isothermal region is discussed. In a second paper
(Brković et al. \cite{Brkovic01}, Paper II) the present model will
be compared with observations from the SOHO satellite.
Title: The CHIANTI Atomic Database and Instrument Calibration:
a Symbiosis
Authors: Mason, H. E.; Del Zanna, G.; Dere, K. P.; Landi, E.; Landini,
M.; Young, P. R.
Bibcode: 2002ISSIR...2..271M
Altcode: 2002ESASR...2..271M; 2002rcs..conf..271M
The CHIANTI atomic database comprises a comprehensive, accurate and
up-to-date database of atomic parameters, necessary for emission-line
spectroscopy. The suite of user-friendly software allows plasma
diagnostics to be carried out. Since its release in 1996, CHIANTI has
become a standard resource for the analysis of solar spectra. Accurate
atomic data can provide the foundation for in-flight instrument
calibrations. Conversely, an accurate instrument calibration can provide
a check on atomic parameters. The internal consistency of spectral-line
intensities can be used to highlight specific anomalies. In this paper,
we illustrate how CHIANTI has been used to validate the calibration of
solar EUV instruments: SOHO-CDS, -SUMER, -EIT and SERTS. In addition,
we show how anomalous spectral-line intensities indicate the need for
more accurate atomic calculations.
Title: Coronal and solar wind elemental abundances
Authors: Raymond, J. C.; Mazur, J. E.; Allegrini, F.; Antonucci, E.;
Del Zanna, G.; Giordano, S.; Ho, G.; Ko, Y. -K.; Landi, E.; Lazarus,
A.; Parenti, S.; Poletto, G.; Reinard, A.; Rodriguez-Pacheco, J.;
Teriaca, L.; Wurz, P.; Zangrilli, L.
Bibcode: 2001AIPC..598...49R
Altcode: 2001sgc..conf...49R
Coronal elemental abundances, as compared with abundances in the solar
wind and solar energetic particles, provide the means for connecting
solar wind gas with its coronal source. Comparison of coronal abundances
with photospheric values shows fractionation with the ionization
potential of the atom, providing important, though not yet fully
understood, information about the exchange of material between corona
and chromosphere. Fractionation due to gravitational settling provides
clues about flows within the corona. In this paper, we discuss the
uncertainties of abundance determinations with spectroscopic techniques
and in situ measurements, we survey the ranges of abundance variations
in both the corona and solar wind, and we discuss the progress in
correlating solar wind features with their coronal sources. .
Title: Solar EUV spectroscopic observations with SOHO/CDS. I. An
in-flight calibration study
Authors: Del Zanna, G.; Bromage, B. J. I.; Landi, E.; Landini, M.
Bibcode: 2001A&A...379..708D
Altcode:
An in-flight calibration study of the Coronal Diagnostic Spectrometer
(CDS) instrument on board SOHO (Solar and Heliospheric Observatory) is
presented. The relative intensity calibration of CDS is a fundamental
requirement for deriving important physical parameters of the solar
transition region and corona from the observations. This comprehensive
study provides the first complete in-flight relative calibration
of all nine CDS channels, first and second order. This has been
achieved with the use of a spectroscopic calibration method, mainly
based on the comparison between observed line ratios and theoretical
predictions provided by the CHIANTI atomic database. The calibration
method has been applied to a large number of observations (on-disc,
off-limb, quiet sun, active region), to enable the use of a wide
range of spectral lines from low to high temperatures of formation. The
results are compared to the pre-launch calibration and other post-launch
studies. Significant differences with the ground calibration results are
found, while there is good agreement with the post-launch studies, based
on rocket flights. It is also shown that the relative calibration has
not significantly changed over a long period of time, thus confirming
the excellent stability of the CDS instrument.
Title: Stokes profile measurements in each sodium D-line using single
and dual band magneto-optical filters on board Solar Orbiter
Authors: Cacciani, A.; Rapex, P.; Dolci, M.; Reale, F.; Landi, E.;
Stenflo, J.; Bianda, M.; Moses, D.
Bibcode: 2001ESASP.493..177C
Altcode: 2001sefs.work..177C
No abstract at ADS
Title: CHIANTI - An atomic database for X-EUV spectral lines
Authors: Dere, K. P.; Landi, E.
Bibcode: 2001tysc.confE..64D
Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for
a large number of ions of astrophysical interest. It also includes
a suite of Interactive Data Language (IDL) programs to calculate
optically thin synthetic spectra and to perform spectral analysis
and plasma diagnostics. This database allows the calculation of
theoretical line emissivities necessary for the analysis of optically
thin emission line spectra. The first version (1.01) of the CHIANTI
database was released in 1996 h paper1. The second version, released
in 1999, included continuum emission and data for additional ions
(Landi et al. 1999). Both versions of the CHIANTI database have been
used extensively by the astrophysical and solar communities to analyze
emission line spectra from astrophysical sources. Now the CHIANTI
database has been extended to wavelengths shorter than 50Å by including
atomic data for the hydrogen and helium isoelectronic sequences,
inner-shell transitions and satellite lines and several other ions. In
addition, some of the ions already present in the database have been
updated and extended with new atomic data from published calculations.
Title: Spectral windows of the solar atmosphere
Authors: Curdt, W.; Landi, E.
Bibcode: 2001ESASP.493..199C
Altcode: 2001sefs.work..199C
No abstract at ADS
Title: Intensity Ratios between the 2s2
1S0-2s2p 3P1
and 2s2p 1P1-2p2
1D2 Transitions in Be-like Ions as Electron
Temperature Indicators for Solar Upper Atmosphere Plasmas
Authors: Landi, E.; Doron, R.; Feldman, U.; Doschek, G. A.
Bibcode: 2001ApJ...556..912L
Altcode:
We investigate the relative intensities of
the two moderately bright Be-like 2s2
1S0-2s2p 3P1 and 2s2p
1P1-2p2 1D2
lines as a function of electron temperature. We show that the intensity
ratios of the lines in the beryllium isoelectronic sequence from C
III to Ni XXV ions can serve as sensitive temperature indicators for
a large variety of solar plasmas. While the C III-Ne VII lines can be
used to diagnose unresolved fine structures in relatively cold solar
atmosphere plasmas [(1-5)×105 K], the Na VIII-Ar XV ions
can be used to diagnose coronal plasmas [(0.8-3)×106
K], and Ca XVII-Ni XXV lines are useful to measure the temperature
in flaring plasmas [(5-16)×107 K]. We investigate the
effects on the temperature determination caused by varying the number of
energy levels that are included in the atomic model for the considered
ions. It is found that a model that includes the 2l2l'
and 2l3l' configurations is sufficient for adequately
describing the relevant level populations of the Be-like ions in
coronal conditions. We compare theoretical ratios obtained using
collisional cross section and transition probability values derived
by different theoretical methods. The atomic data are obtained from
the CHIANTI database, the Hebrew University Lawrence Livermore Atomic
Code (HULLAC) suite of programs, and other available sources in the
literature. Finally, we use spectra of an apparently isothermal
coronal plasma observed by the Solar Ultraviolet Measurement of
Emitted Radiation instrument on the Solar and Heliospheric Observatory
to determine the electron temperature of streamer plasma using the
HULLAC and CHIANTI atomic data sets. The result is compared with the
temperature derived in an earlier study using different methods.
Title: CHIANTI-An Atomic Database for Emission Lines. IV. Extension
to X-Ray Wavelengths
Authors: Dere, K. P.; Landi, E.; Young, P. R.; Del Zanna, G.
Bibcode: 2001ApJS..134..331D
Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities, and electron excitation data for
a large number of ions of astrophysical interest. It also includes a
suite of Interactive Data Language programs to calculate optically
thin synthetic spectra and to perform spectral analysis and plasma
diagnostics. This database allows the calculation of theoretical line
emissivities necessary for the analysis of optically thin emission-line
spectra. The first version (1.01) of the CHIANTI database was released
in 1996 and published by Dere et al. in 1997 as Paper I in this
series. The second version, released in 1999 by Landi et al., included
continuum emission and data for additional ions. Both versions of the
CHIANTI database have been used extensively by the astrophysical and
solar communities to analyze emission-line spectra from astrophysical
sources. Now the CHIANTI database has been extended to wavelengths
shorter than 50 Å by including atomic data for the hydrogen and helium
isoelectronic sequences, inner-shell transitions and satellite lines,
and several other ions. In addition, some of the ions already present
in the database have been updated and extended with new atomic data
from published calculations.
Title: A comparison between theoretical and solar FeXII UV line
intensity ratios UV line intensity ratios
Authors: Binello, A. M.; Landi, E.; Mason, H. E.; Storey, P. J.;
Brosius, J. W.
Bibcode: 2001A&A...370.1071B
Altcode:
A new set of radiative and electron collisional data for Fe XII
was presented in two earlier papers. In the present work, we derive
level populations and theoretical line intensities for a range of
plasma densities and temperatures. Observations of Fe XII lines
obtained with the Solar EUV Rocket Telescope and Spectrograph are
analysed both as a check the quality of the new atomic data and
to determine the electron density in active regions and the quiet
Sun. The discrepancy between the electron density values determined
from Fexii line intensity ratios and those obtained from other ions
is investigated. Tables 2-5 are also available in electronic form
at the CDS via anonymous ftp to cdarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/370/1071}
Title: Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; Landi, E.; Cook, J. W.; Newmark, J.;
Gopalswamy, N.; Lara, A.
Bibcode: 2001AGUSM..SH32C02B
Altcode:
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of
NOAA region 8108 (N21 E18) on 1997 November 18. The EUV spectra
and images, obtained with the Coronal Diagnostic Spectrometer (CDS)
and the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar
and Heliospheric Observatory (SOHO) satellite, were used to derive
differential emission measure (DEM) distributions for each spatial
pixel (i.e., along each line of sight) of the region's images. These
were subsequently used to calculate maps of the expected thermal
bremsstrahlung brightness temperature at the Very Large Array
(VLA) radio observing frequencies of 4.9 and 8.4 GHz. The thermal
bremsstrahlung maps reproduce neither the structure nor the intensity
of the observed maps, and indicate that thermal gyroemission must
also contribute to the observed radio emission. Under the assumptions
of a monotonic increase in temperature and a monotonic decrease in
magnetic field strength with height above the sunspot, we derived
the temperature distribution of the coronal magnetic field strength
that reproduced simultaneously the observed right-hand and left-hand
circularly polarized radio emission at 4.9 and 8.4 GHz for each
spatial pixel in the sunspot maps. This was done by placing harmonics
of the radio observing frequencies in appropriate plasma temperature
intervals, integrating along the line of sight, and iterating until
a solution was obtained. Magnetic field strengths corresponding to
3rd harmonic gyroemission at 4.9 GHz (580 Gauss) are found in coronal
plasmas at temperatures as high as 2.2*E6 K, while magnetic
field strengths corresponding to 2nd harmonic gyroemission at 8.4 GHz
(1500 Gauss) are found in coronal plasmas at temperatures as high as
1.1*E6 K.
Title: CHIANTI - an atomic database for emission lines, Paper 4:
Extension to X-ray Wavelengths
Authors: Dere, K. P.; Landi, E.; Young, P. R.; Del Zanna, G.
Bibcode: 2001AGUSM..SP21B08D
Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for
a large number of ions of astrophysical interest. It also includes
a suite of Interactive Data Language (IDL) programs to calculate
optically thin synthetic spectra and to perform spectral analysis and
plasma diagnostics. This database allows the calculation of theoretical
line emissivities necessary for the analysis of optically thin emission
line spectra. The first version of the CHIANTI database was released
in 1996 (Dere et al., 1996). The second version, released in 1999,
included continuum emission and data for additional ions (Landi
et al. 1999). Both versions of the CHIANTI database have been used
extensively by the astrophysical and solar communities to analyze
emission line spectra from astrophysical sources. Now the CHIANTI
database has been extended to wavelengths shorter than 50Å by including
atomic data for the hydrogen and helium isoelectronic sequences,
inner-shell transitions and satellite lines and several other ions. In
addition, some of the ions already present in the database have been
updated and extended with new atomic data from published calculations.
Title: VizieR Online Data Catalog: Fe XII UV line intensity ratios
(Binello+, 2001)
Authors: Binello, A. M.; Landi, E.; Mason, H. E.; Storey, P. J.;
Brosius, J. W.
Bibcode: 2001yCat..33701071B
Altcode:
A new set of radiative and electron collisional data for Fe XII
was presented in two earlier papers. In the present work, we derive
level populations and theoretical line intensities for a range of
plasma densities and temperatures. Observations of Fe XII lines
obtained with the Solar EUV Rocket Telescope and Spectrograph are
analysed both as a check on the quality of the new atomic data and
to determine the electron density in active regions and the quiet
Sun. The discrepancy between the electron density values determined
from Fe XII line intensity ratios and those obtained from other ions
is investigated. (2 data files).
Title: Looking for the FIP Effect in EUV Spectra
Authors: Dwivedi, B. N.; Landi, E.; Mohan, A.
Bibcode: 2001IAUS..203..356D
Altcode:
We present results from a study of extreme-ultraviolet (EUV) off-limb
spectra obtained with the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) on the spacecraft SOHO. Using EUV line intensities,
we deduce plasma temperatures and densities in the off-limb solar
plasma. We make use of this information to study the FIP effect
in the solar corona. We have looked for FIP effect in EUV spectra
obtained by SUMER in a considerable detail. In particular, we report
K/Ar, Si/Ar and S/Ar relative element abundances and investigate the
height dependence of the FIP bias in the solar corona. Also, we study
the relative Mg/Ne abundance in an active region at the solar limb
to investigate the correlation of the FIP bias with magnetic loop
structures in the field of view.
Title: The Effect of Different Ion Fraction Datasets on FIP Effect
Studies (CD-ROM Directory: contribs/gianetti)
Authors: Gianetti, D.; Landi, E.; Landini, M.
Bibcode: 2001ASPC..223..643G
Altcode: 2001csss...11..643G
No abstract at ADS
Title: Statistical Features of the Quiet Sun in EUV
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
Schühle, U.
Bibcode: 2001IAUS..203..416P
Altcode:
The frequency distribution of the extreme ultraviolet (EUV) intensities
in the quiet Sun has in the past usually been modelled using two
Gaussians. Here we test this and other distribution functions against
observed distributions with exceptional statistics. The data were
obtained in a number of spectral lines observed with two extreme
ultraviolet spectrometers, CDS (Coronal Diagnostic Spectrometer)
and SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on
board the Solar and Heliospheric Observatory (SOHO). We show that the
frequency distribution of the radiance is best modelled by a lognormal
distribution or by a sum of a lognormal and a Gaussian. The fact that
the radiance distribution of the quiet Sun including the network and
the intranetwork is better reproduced by a single lognormal distribution
function than by two Gaussians suggests that the same heating processes
are acting in both types of features. The shape of the distribution
function shows a clear temperature dependence.
Title: Spectroscopic features in the EUV emission of a M8 flare
observed by SUMER
Authors: Curdt, W.; Landi, E.; Feldman, U.; Innes, D.; Dwivedi, B.;
Wilhelm, K.
Bibcode: 2001IAUS..203..260C
Altcode:
On May 9, 1999 a flare of size M8 occurred while SUMER obtained a
spectral scan above the active region NOAA 8537 at the west limb. We
recorded spectra during the pre-flare phase, at flare onset, and during
the decay phase. More than 60 flare lines were observed during this
event, which include Fe XVIII - Fe XXIII lines that provide evidence
of 107 K plasmas. We also recorded lines from He-like ions,
such as Ne IX, Na X, Mg XI or Si XIII. Accurate wavelength measurements
of such lines are of interest in basic atomic physics studies. Using
plasma diagnostic techniques, we investigated the temporal evolution
of the electron densities and temperatures during the event. Since
the spectra contain lines from many different elements, we were able
to determine elemental abundances in the flaring plasma.
Title: DEM Study of Selected Quiet Sun Regions
Authors: Gontikakis, C.; Landi, E.; Dara, H. C.; Alissandrakis, C. E.;
Vial, J. -C.
Bibcode: 2001IAUS..203..390G
Altcode:
In the present work EUV spectra of quiet Sun regions, observed with
the Coronal Diagnostic Spectometer (CDS), are analysed in order to
determine the Differential Emission Measure (DEM) of selected areas
of the field of view. In particular, we study the differences between
the DEM curves of the quiet Sun cell center areas, network areas and
cell-network boundaries. The results are discussed in the light of
theoretical models for the solar upper atmospheres.
Title: An Empirical Test of Different Ionization Balance Calculations
in an Isothermal Solar Plasma (CD-ROM Directory: contribs/allen)
Authors: Allen, R.; Landi, E.; Landini, M.; Bromage, G. E.
Bibcode: 2001ASPC..223..563A
Altcode: 2001csss...11..563A
No abstract at ADS
Title: BEPPOSAX Observation of EQ Pegasi (CD-ROM Directory:
contribs/landi)
Authors: Landi, E.; Landini, M.; Dere, K.; Risaliti, G.
Bibcode: 2001ASPC..223..991L
Altcode: 2001csss...11..991L
No abstract at ADS
Title: FIP effect measurements in the off-limb corona observed by
SUMER on SOHO
Authors: Mohan, A.; Landi, E.; Dwivedi, B. N.
Bibcode: 2000A&A...364..835M
Altcode:
Systematic differences between elemental abundances in the corona and in
the photosphere have been long acknowledged in the Sun; these abundance
anomalies are correlated with the first ionization potentials (FIPs)
of the elements. This correlation is called FIP effect. Using spectra
obtained from the SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric
Observatory), we investigate electron density, temperature and the
abundance anomalies in the off-limb solar corona. In particular, we
present the behaviour of the solar FIP effect with height above an
active region observed at the solar limb, with K/Ar, Si/Ar and S/Ar
ratios of lines present in the recorded UV spectra. We find that the
K FIP bias seems to be higher than for the other low-FIP elements,
and that the Si and K FIP biases are dependent on the distance from the
photosphere. Studying the Ne/Mg line ratio in the active region, we also
investigate the presence of the FIP effect in active region structures.
Title: Analysis of a Solar Active Region Extreme-Ultraviolet Spectrum
from SERTS-97
Authors: Brosius, Jeffrey W.; Thomas, Roger J.; Davila, Joseph M.;
Landi, Enrico
Bibcode: 2000ApJ...543.1016B
Altcode:
Goddard Space Flight Center's Solar EUV Research Telescope and
Spectrograph was flown on 1997 November 18, carrying an intensified
CCD detector and a multilayer-coated toroidal diffraction grating
with enhanced sensitivity over that of a standard gold-coated grating
throughout the instrument's 299-353 Å spectral bandpass. Spectra
and spectroheliograms of NOAA Active Region 8108 (N21°, E18°)
were obtained with a spectral resolution (instrumental FWHM) of
115 mÅ. Nearly 100 emission lines were observed in the spatially
averaged active region spectrum. Spectra and spectroheliograms of
quiet areas south of the region were also obtained. An end-to-end
radiometric calibration of the rocket instrument was carried out at
the Rutherford-Appleton Laboratory in the same facility that was used
to calibrate the Coronal Diagnostic Spectrometer experiment on SOHO
and using the same EUV light source. The accuracy of this calibration
is confirmed by the excellent agreement between the measured and
theoretical values of density- and temperature-insensitive line
intensity ratios. Nine emission lines of Fe XV are identified in
our spectrum; however, large differences between wavelengths in the
CHIANTI database and some of the measured solar wavelengths, as well
as inconsistencies of various theoretical intensity ratios, suggest
a need for improvement in the Fe XV atomic physics parameters and/or
the presence of unidentified blending lines. Density-sensitive line
intensity ratios of Fe XI λλ308.55/352.67, Fe XII λλ338.27/352.11,
Fe XIII λλ320.80/312.17, and Fe XV λλ321.78/327.03 yield logarithmic
electron densities (in cm-3) of 9.92+/-0.28, 9.74+/-0.28,
9.52+/-0.30, and 9.62+/-0.26, respectively. Using the strongest emission
line observed for each ionization stage of Fe from X through XVI and Ni
XVIII, we find that all of the measured nonthermal line widths yield
velocities consistent with 35 km s-1. The differential
emission measure curve derived from the observed line intensities
exhibits a relative minimum at logT~5.7, a broad maximum centered
around logT~6.3, and a rapid decline for temperatures above logT~6.6.
Title: Identification of Spectral Lines in the 500-1600 Å Wavelength
Range of Highly Ionized Ne, Na, Mg, Ar, K, Ca, Ti, Cr, Mn, Fe, Co,
and Ni Emitted by Flares (Te>=3×106 K)
and Their Potential Use in Plasma Diagnostics
Authors: Feldman, U.; Curdt, W.; Landi, E.; Wilhelm, K.
Bibcode: 2000ApJ...544..508F
Altcode:
On 1999 May 9 the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) recorded spectra from a high-temperature region located
in the solar corona above the west limb. These spectra contain
lines from rather less-abundant elements in solar plasmas. In
this paper we present identifications of the high-temperature
(Te>=3×106 K) Ne, Na, Mg, Ar, K, Ca, Ti,
Cr, Mn, Fe, Co, and Ni lines that were detected in the 500-1600 Å
spectral range of SUMER. In addition, accurate wavelength measurements
have been obtained with uncertainties varying between 0.015 and 0.040
Å (1 σ). Making use of the newly measured wavelengths, we derive
energy levels in the ground configuration of a number of highly
charged ions. We present intensity ratio calculations of lines in
the SUMER range that could be used to measure electron densities in
high-temperature solar plasmas. We also provide emissivities for Ca
XIII-Ca XV and Fe XVIII-Fe XXIII lines that could be used to determine
emission measures and electron temperatures of high-temperature
plasmas. We discuss a method for measuring elemental abundance
variations in high-temperature solar plasmas using lines presented
in the paper. A list of spectral lines spanning the 300-30000 Å
wavelength range and their branching ratios that are suitable for
efficiency calibration of space-borne spectrographs is provided.
Title: Statistics of quiet Sun extreme ultraviolet intensities
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
Schühle, U.
Bibcode: 2000A&A...362..737P
Altcode:
The frequency distribution of the extreme ultraviolet (EUV) emission
line intensities in the quiet Sun has in the past often been modelled
using two Gaussians. This gives adequate fits to observed distributions
of average statistical significance. In this paper we test this
and other distribution functions against observed distributions with
exceptional statistical significance. The data were obtained in a number
of spectral lines observed with two extreme ultraviolet spectrometers
on board the Solar and Heliospheric Observatory (SOHO). In this way,
the influence of spatial resolution and other instrument-specific
parameters can be identified. The observations span a period of
more than two years and provide a very large data set of radiance
measurements of the quiet Sun at or near solar disk centre. We show
that the frequency distribution of the radiance is best modelled by
a lognormal distribution. The fact that the radiance distribution of
the quiet Sun including the network and the intranetwork is better
reproduced by a single lognormal distribution function than by two
Gaussians suggests that the same heating processes are acting in both
types of features. The parameters of the lognormal fit show a clear
temperature dependence, with the transition region lines exhibiting the
largest skewness of the distribution and the chromospheric intensity
distributions being the most symmetric.
Title: Wavelength measurements of heliumlike 1s2s
3S1-1s2p 3P0,2
transitions in Ne8+, Na9+, Mg10+,
and Si12+ emitted by solar flare plasmas
Authors: Curdt, W.; Landi, E.; Wilhelm, K.; Feldman, U.
Bibcode: 2000PhRvA..62b2502C
Altcode:
With the Solar Ultraviolet Measurements of Emitted Radiation
instrument-a high-resolution normal-incidence telescope and spectrometer
on board the Solar and Heliospheric Observatory-heliumlike 1s2s
3S1-1s2p 3P0,2 transitions
in the highly ionized species Ne8+, Na9+,
Mg10+, and Si12+ were observed. The spectral
lines were emitted by high-temperature solar flare plasmas. In this
paper, we report on wavelength measurements of the He-like lines
identified in the recorded spectra. The wavelength uncertainties
we obtained from the solar measurements are <=20 mÅ(1σ),
and in one case <=30 mÅ. This is comparable to or better than
the best determinations so far achieved for these heliumlike 1s2s
3S1-1s2p 3P0,2 transitions
with instrumentation in the laboratory. For the Na9+
3S1-3P2 transition we
report what is to our knowledge the first wavelength measurement. The
knowledge of the accurate wavelengths can provide important checks on
atomic structure calculations.
Title: The effect of different ion fraction datasets on plasma
diagnostics
Authors: Gianetti, D.; Landi, E.; Landini, M.
Bibcode: 2000A&A...360.1148G
Altcode:
In the present work the element abundances in an active region observed
on the solar disk are studied using EUV spectral lines observed by
the Coronal Diagnostic Spectrometer (CDS) on board of SOHO. Making
use of the large number of lines identified in the CDS spectral
range and of the instrument imaging capability, the abundances of
several elements having First Ionization Potential (FIP) smaller
and greater than 10eV have been determined in different parts of the
observed active region. Also, the differential emission measure of the
selected emitting regions have been determined. This study has been
carried out assuming ionization equilibrium in the emitting plasma,
and adopting three different ion fraction datasets to interpret the
observed intensities. This has permitted a detailed check of the impact
of differences in the ion fraction datasets on the element abundances
measurements and DEM determination and to assess the reliability of
the use of EUV line intensities for such studies. Our results show that
the use of different ion fractions may alter significantly the measured
abundances and DEM curves, and have large effects on quantitative FIP
effect studies.
Title: Electron Density and Temperature Measurements, and Abundance
Anomalies in the Solar Atmosphere
Authors: Mohan, A.; Dwivedi, B. N.; Landi, E.
Bibcode: 2000JApA...21..407M
Altcode:
No abstract at ADS
Title: An empirical test of different ionization balance calculations
in an isothermal solar plasma
Authors: Allen, R.; Landi, E.; Landini, M.; Bromage, G. E.
Bibcode: 2000A&A...358..332A
Altcode:
By examining solar observations using the Normal Incidence Spectrometer
(NIS) within the Coronal Diagnostic Spectrometer (CDS) on board SOHO,
an isothermal region in the lower solar corona was chosen for analysis
by three different temperature diagnostic techniques. These techniques
are the line-ratio method, the Differential Emission Measure and the
Emission Measure analysis. All three methods should in theory yield
the same temperature. Using these powerful diagnostic methods, the
reliability of all widely used ionisation balance calculations, namely
those of Shull & Van Steenberg (1982), Arnaud & Rothenflug
(1985) (with revisions by Arnaud & Raymond 1992) and Mazzotta
et al. (1998) have been empirically tested. It has been found that
the temperature obtained does not depend on the ionization balance
calculation used. It is also concluded that the three ionization balance
calculations give the same results, within their uncertainties. A
new variant Emission Measure analysis is presented. This provides a
diagnostic tool that is stable against any distorting effects arising
when a few lines have large deviations from the mean.
Title: CHIANTI--An Atomic Database for EUV Emission Lines
Authors: Landi, E.
Bibcode: 2000RMxAC...9..140L
Altcode:
CHIANTI consists of a critically evaluated set of atomic data and
transition probabilities necessary to calculate the emission line
spectrum of astrophysical plasmas. The data consist of atomic energy
levels, atomic radiative data such as wavelengths, weighted oscillator
strengths and A values, and electron collisional excitation rates. A set
of programs that use these data to calculate the spectrum in a desired
wavelength range as a function of temperature and density is also
provided. A suite of programs has been developed to carry out plasma
diagnostics of astrophysical plasmas. The state-of-the-art contents of
the CHIANTI database will be described and some of the most important
results obtained from the use of the CHIANTI database will be reviewed.
Title: SUMER observations of transition region fine structures
Authors: Landi, E.; Mason, H. E.; Lemaire, P.; Landini, M.
Bibcode: 2000A&A...357..743L
Altcode:
The SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
instrument on SOHO (Solar and Heliospheric Observatory) provides an
opportunity to observe and study the solar transition region with
high spatial and spectral resolution. We present new evidence to
confirm that the emission from the quiet Sun at 2x 105 K
is dominated by cool loop-like fine structures which cluster across
the chromospheric network boundaries. The electron density of these
structures is found to be around 1010 cm-3. The
red-shifts in spectral line profiles and the non-thermal widths from
lines formed at this temperature are found to be correlated with
intensity. The properties of explosive events with irregular profiles
are explored. A large jet-like structure is analysed. The results of
our analysis are compared with recent predictions from numerical models.
Title: A study of opacity in SOHO-SUMER and SOHO-CDS spectral
observations. I. Opacity deduction at the limb
Authors: Brooks, D. H.; Fischbacher, G. A.; Fludra, A.; Harrison,
R. A.; Innes, D. E.; Landi, E.; Landini, M.; Lang, J.; Lanzafame,
A. C.; Loch, S. D.; McWhirter, R. W. P.; Summers, H. P.
Bibcode: 2000A&A...357..697B
Altcode:
A study is presented of the optical thickness of spectral lines of
carbon, nitrogen and oxygen ions in the quiet sun. The observations
consist of cross limb scans by the SUMER and CDS spectrometers on
the SOHO spacecraft. A maximum likelihood spectral line fitting code
has been adapted to analyse the multiplet profiles and to provide an
assessment of errors in the count rates, especially of close lying
components. Branching multiplet component ratios are presented as a
function of position across the limb and contrasted with theoretical
ratios in the optically thin case. The emergent fluxes are analysed
in an escape probability model to deduce the optical thicknesses in
the various spectral lines. Different specifications of the escape
probability are examined. These are used to compare the observations
with a geometric model of the emitting layer thickness across the limb
and the thinning of the emitting layer above the limb. Classification
of the deviations of quiet sun spectral line intensities from the
optically thin case is given to assist in the critical selection of
lines for differential emission measure analysis. This is linked to
a general purpose code for the calculation of the influence of the
line radiation fields on the local excited state population structure
of the selected ions so that the fluxes in any spectral lines can be
predicted. The Atomic Data and Analysis Structure (ADAS) was used for
the atomic calculations and data of the paper.
Title: Analysis of an Active Region EUV Spectrum from SERTS-97
Authors: Brosius, J. W.; Thomas, R. J.; Davila, J. M.; Landi, E.
Bibcode: 2000SPD....31.0214B
Altcode: 2000BAAS...32..813B
Goddard Space Flight Center's Solar EUV Research Telescope and
Spectrograph (SERTS) was flown on 1997 November 18, carrying
a CCD-intensified detector and a multilayer-coated toroidal
diffraction grating that enhanced the sensitivity over that of a
standard gold-coated grating throughout the instrument's first-order
waveband (299 -- 353 Angstroms). Spectra and spectroheliograms of NOAA
active region 8108 (N21 E18) were obtained with a spectral resolution
(instrumental FWHM) ~ 118 m Angstroms. Spectra and spectroheliograms
of quiet areas southeast of the active region were also obtained. An
end-to-end radiometric calibration of the rocket instrument was
carried out at Rutherford-Appleton Laboratory in the same facility
used to calibrate the Coronal Diagnostic Spectrometer (CDS) on the
Solar and Heliospheric Observatory (SOHO) satellite, using the same
EUV light source. The accuracy of this calibration is confirmed by
the excellent agreement between measured and theoretical values of
density- and temperature-insensitive line intensity ratios among some
of the nearly 100 spectral lines observed in the spatially averaged
active region spectrum. We present the spectrum itself, and discuss
measurements of the plasma density, non-thermal mass motions, relative
wavelength shifts, and the differential emission measure. This work
is supported by NASA through RTOP grants and contract NAS5-99145.
Title: An Empirical Test of Different Ionization Balance Calculations
in an Isothermal Solar Plasma
Authors: Allen, R.; Landi, E.; Landini, M.; Bromage, G. E.
Bibcode: 1999ESASP.448..563A
Altcode: 1999ESPM....9..563A; 1999mfsp.conf..563A
No abstract at ADS
Title: The Effect of Different Ion Fraction Datasets on FIP Effect
Studies
Authors: Gianetti, D.; Landi, E.; Landini, M.
Bibcode: 1999ESASP.448..599G
Altcode: 1999mfsp.conf..599G; 1999ESPM....9..599G
No abstract at ADS
Title: CHIANTI: A database for astrophysical emission line
spectroscopy
Authors: Del-Zanna, Giulio; Young, Peter; Dere, Ken; Landini, Massimo;
Landi, Enrico; Mason, Helen
Bibcode: 1999ascl.soft11004D
Altcode:
CHIANTI consists of a critically evaluated set of atomic data necessary
to calculate the emission line spectrum of astrophysical plasmas. The
data consists of atomic energy levels, atomic radiative data such as
wavelengths, weighted oscillator strengths and A values, and electron
collisional excitation rates. A set of programs that use these data to
calculate the spectrum in a desired wavelength range as a function of
temperature and density are also provided. These programs have been
written in Interactive Data Language (IDL) and descriptions of these
various programs are provided on the website.
Title: Comparison Between Euv And Radio Observations : A Powerful
Diagnostic For The Upper Solar Atmosphere
Authors: Chiuderi Drago, F.; Landi, E.; Fludra, A.; Delouis, J. M.;
Kerdraon, A.
Bibcode: 1999ESASP.446..287C
Altcode: 1999soho....8..287C
In the present work we show that EUV and radio observation can provide a
very powerful plasma diagnostics when combined together. The intensity
of EUV lines formed in the range of temperature corresponding to
the Chromosphere-Corona Transition Region, supplies the DEM function
defined as DEM(T)=Ne2 dh/dT. Above the temperature where no
more lines are detected, the DEM can be either truncated or arbitrarily
extrapolated to a very low value at a very high temperature. The DEM
derived with both assumptions reproduce of course very well the observed
line intensities, being derived from a best fit of these lines. We have
used the DEM, derived from a set of EUV lines observed by CDS in an
equatorial Coronal Hole using both assumptions, to compute the radio
brightness temperature. The comparison of the computed Tb
with the values observed by the Nancay Radiheliograph in the same hole,
shows that both DEM assumptions are unable to reproduce the observations
and that it is necessary to add the contribution of an isothermal
Corona above the region where the DEM is defined. From the fit of
the radio observations at four frequencies between 164 and 410 MHz,
the coronal hole Emission Measure and an upper limit of the coronal
electron temperature (T < 9. 105) are derived. Using this coronal
model, together with the DEM up to T < 9.105, we have computed the
theoretical EUV line intensities, obtaining a very good agreement with
the observations for T > 8x105 K, thus providing also a lower limit
to the hole temperature.
Title: A Direct Comparison Between EUV Coronal Flux And He Resonance
Line Photon Flux From SOHO/CDS Data
Authors: Andretta, V.; Landi, Enrico; Del Zanna, Giulio; Jordan,
Stuart D.
Bibcode: 1999ESASP.446..123A
Altcode: 1999soho....8..123A
In the wealth of EUV spectroscopic and imaging data gathered by the
SOHO and TRACE missions, a prominent role is played by the helium
resonance emission. For example, He I lines are among the most intense
features in CDS/NIS spectra, while the EIT 304 waveband (dominated by
He II emission) is routinely employed to map the structure of the solar
chromosphere and transition region. However, no 'standard' model has
emerged so far that is able to interpret observed He spectra/images
to a satisfactory degree of self-consistency. Recent research on
the problem of the formation of the solar helium spectrum tends to
rule out a dominant role of coronal radiation in exciting He resonance
lines. However, while evidence for this result is strong, it is based on
indirect tests. Here we present a more direct assessment of this issue
by directly measuring the photon photoionizing EUV flux measured with
CDS/GIS-NIS1. This measure can be directly compared with the observed
flux in the main He I and He II resonance lines observed with CDS/NIS2.
Title: Plasma Flows In Coronal Hole Regions
Authors: Landi, E.; Mullan, D.; Poletto, G.; Wilhelm, K.
Bibcode: 1999ESASP.446..417L
Altcode: 1999soho....8..417L
More than two decades after coronal holes (CH) had been recognized
to be the source regions of solar wind, we still do not know which
structures, within CH, most contribute to the solar wind mass flux. In
a recent work, Hassler et al. (1999) obtained velocity maps of a
coronal hole region, in the Ne VIII 770 Angstrom line, which suggest
that localized areas within the network might be sources of the solar
wind. On the opposite, an earlier work of Dupree et al. (1996), from
an analysis of the He I 10830 Angstrom line, suggested cell regions
as sources of the solar wind. In the present work, we reinvestigate
this issue analysing SUMER data taken in an equatorial and in a polar
coronal hole, observed respectively on 29 August 1996 and 21 September
1996. We study the behavior of Si II, C IV, O V, N V, Ne VIII, Mg X and
Fe XII ions, whose temperatures of formation range from chromospheric
(around 2x104 K) to coronal values (around 1.5x105
K). In particular, we analysed intensity and velocity distributions
of these lines, and illustrate changes in the plasma velocity pattern
as a function of the temperature regime where lines form.
Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brkovic, A.; Landi, E.; Rüedi, I.; Solanki, S.
Bibcode: 1999ESASP.446..423L
Altcode: 1999soho....8..423L
SOHO CDS, GIS and NIS, observations are used to evaluate the
electron temperature, density and pressure of active region loops. The
measurements are used to constrain empirical models of loops, which are
compared with an improved version of theoretical models from Landini
and Monsignori Fossi 1975. Energy balance is investigated to evaluate
temperature, pressure and heating release along the loop.
Title: Electron density and temperature structure of two limb active
regions observed by SOHO-CDS
Authors: Mason, H. E.; Landi, E.; Pike, C. D.; Young, P. R.
Bibcode: 1999SoPh..189..129M
Altcode:
The analysis of two active regions on the limb using observations from
SOHO-CDS allows us to determine the electron density and temperature
distribution of the coronal emission. We find that the active regions
have hot cores (3×106 K) with larger cooler (106
K) loop structures extending above the limb. The electron number
density, determined using the Si X diagnostic line ratio, is found to
be highest in the active region core (greater than 2.3×109
cm−3). Electron number density values are determined for a
range of spectral lines from different ions and are found to increase
with temperature between 0.8 and 2.5×106 K. These results
are consistent with recent models of enhanced heating along the compact
core of active regions, where the magnetic field shear is strongest.
Title: EUV and radio observations of an equatorial coronal hole
Authors: Chiuderi Drago, F.; Landi, E.; Fludra, A.; Kerdraon, A.
Bibcode: 1999A&A...348..261C
Altcode:
EUV and radio data of an equatorial coronal hole, observed in October
1996 at its central meridian transit, are compared. EUV lines were
observed by the CDS instrument onboard SOHO and the radio emission
by the Nancay Radioheliograph (France) in the frequency range 164-410
MHz. Using the Differential Emission Measure (DEM), derived from EUV
line intensities, we have computed the radio brightness temperature T_b,
leaving the coronal temperature (upper limit of the DEM definition)
and pressure as free parameters, to be determined from the comparison
with the observations. This analysis has shown that radio data,
contrarily to EUV line intensities, cannot be fitted without the
presence of isothermal plasma above the region where the DEM is
defined, independently of the choice of parameters. A model, nicely
fitting both sets of data, is derived, in which the coronal temperature
and density are T_c <= 9 x 10(5) K and N_e(0) =~ 3x 10(8 cm(-3))
respectively. The assumption of hydrostatic equilibrium with a scale
height derived from the electron temperature is discussed.
Title: Radiative losses of optically thin coronal plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 1999A&A...347..401L
Altcode:
In the present work the total radiative losses and the total emissivity
curve are calculated for an optically thin plasma using the Arcetri
Spectral Code in the 10(4-10^8) temperature range. Checks have been
made on the effects of changes in the parameters involved in the
calculations, such as element abundances, ion fractions, electron
density and transition probabilities on the resulting curves. Parametric
fits are given for the resulting radiative losses curves and comparison
is made with previous results.
Title: The quiet Sun extreme ultraviolet spectrum observed in normal
incidence by the SOHO coronal diagnostic spectrometer
Authors: Brooks, D. H.; Fischbacher, G. A.; Fludra, A.; Harrison,
R. A.; Innes, D. E.; Landi, E.; Landini, M.; Lang, J.; Lanzafame,
A. C.; Loch, S. D.; McWhirter, R. W. P.; Summers, H. P.; Thompson,
W. T.
Bibcode: 1999A&A...347..277B
Altcode:
The extreme ultraviolet quiet Sun spectrum, observed at normal incidence
by the Coronal Diagnostic Spectrometer on the SOHO spacecraft, is
presented. The spectrum covers the wavelength ranges 308-381 Ä and
513-633 Ä and is based on data recorded at various positions on the
solar disk between October 1996 and February 1997. Datasets at twelve
of these `positions' were judged to be free from active regions and
data faults and selected for detailed study. A constrained maximum
likelihood spectral line fitting code was used to analyse the spectral
features. In all over 200 spectrum lines have been measured and about
50% identified. The line identification process consisted of a number
of steps. Firstly assignment of well known lines was made and used to
obtain the primary wavelength calibration. Variations of wavelengths
with position were used to assess the precision of calibration
achievable. Then, an analysis method first used in studies with the
CHASE experiment, was applied to the new observations. The behaviour
of the intensities of lines from like ions over the twelve positions,
called `position patterns', were used to distinguish probable emitters
of weaker lines and extend the identifications. Spectral line widths
and expected multiplet intensities were examined to identify lines and
probable blends. The product of the study is a table which includes all
clearly observed emission lines, their measured wavelengths, widths
and count rates. Adopted laboratory wavelengths, ion and transition
designations are also presented for identified lines. The table has an
estimate of the uncertainty of the count rates based on a statistical
analysis of the variability of each line. A marked spectrum is also
provided.
Title: CHIANTI - an atomic database for emission lines. III. Continuum
radiation and extension of the ion database
Authors: Landi, E.; Landini, M.; Dere, K. P.; Young, P. R.; Mason,
H. E.
Bibcode: 1999A&AS..135..339L
Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for a
large number of ions of astrophysical interest. This database allows
the calculation of theoretical line emissivities necessary for the
analysis of optically thin emission line spectra, and includes also
a suite of IDL (Interactive Data Language) programs to calculate
optically thin synthetic spectra and to perform spectral analysis and
plasma diagnostics. The first version (1.0) of the CHIANTI database was
released in 1996 te[(Dere et al. 1997)]{Der97} and has been extensively
used for analysis of line spectra from astrophysical sources by the
scientific community. The present paper describes the first major update
to the CHIANTI database which will subsequently be labeled version
2.0. The update consists of the addition of a large number of new ions,
the revision of existing data for some ions and the inclusion of an
IDL procedure to calculate the continuum. The CHIANTI atomic database
and supporting IDL routines are freely available through the internet.
Title: Relative intensity calibration of CDS-GIS detectors on SOHO
using a plasma diagnostic technique
Authors: Landi, E.; Del Zanna, G.; Breeveld, E. R.; Landini, M.;
Bromage, B. J. I.; Pike, C. D.
Bibcode: 1999A&AS..135..171L
Altcode:
The internal intensity calibration of the Coronal Diagnostic
Spectrometer (CDS) - Grazing Incidence Spectrometer (GIS) is studied
using the Arcetri diagnostic method. A large number of spectral lines
observed by the four GIS detectors in solar active and quiet regions is
analysed in order to determine the relative intensity calibration curve
of the instrument. The plasma diagnostic method developed in Arcetri
allows the measurement of the correction factors to the pre-flight
CDS - GIS internal intensity calibration curves and of the relative
calibration between different detectors. No gross deviations from the
pre-flight calibration are found. Also the GIS 3 and GIS 4 second order
sensitivites are measured. The problems of fixed patterning, ghosting,
anomalous line profiles and widths are also discussed, and a list of
lines suitable for further diagnostic studies with GIS is presented.
Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brković , A.; Landi, E.; Rüedi, I.; Solanki, S.
Bibcode: 1999SSRv...87..245L
Altcode:
The Coronal Diagnostic Spectrometer (CDS) on SOHO is a grazing/normal
incidence spectrograph, aimed to produce stigmatic spectra of selected
regions of the solar surface in six spectral windows of the extreme
ultraviolet from 150 Å to 785 Å (Harrison et al. 1995). In the
present work, CDS, EIT, MDI and Yohkoh observations of active region
lops have been analyzed. These observations are part of JOP 54. CDS
monochromatic images from lines at different temperatures have been
co-aligned with EIT and MDI images, and loop structures have been
clearly identified using Fe XVI emission lines. Density sensitive
lines and lines from adjacent stages of ionization of Fe ions have
been used to measure electron density and temperature along the loop
length; these measurements have been used to determine the electron
pressure along the loop and test the constant pressure assumption
commonly used in loop modeling. The observations have been compared
with a static, isobaric loop model (Landini and Monsignori Fossi 1975)
assuming a temperature-constant heating function in the energy balance
equation. Good agreement is found for the temperature distribution
along the loop at the coronal level. The model pressure is somewhat
higher than obtained from density sensitive line ratios.
Title: EUV and Radio Observations of an Equatorial Coronal Hole
Authors: Chiuderi-Drago, F.; Kerdraon, A.; Landi, E.; Fludra, A.
Bibcode: 1999SSRv...87..141C
Altcode:
An equatorial coronal hole has been observed on 18 and 19 October 1996
with SOHO-CDS and with the Nancąy Radioheliograph (RH). The CDS EUV
line intensities are used to determine the coronal hole Differential
Emission Measure (DEM); in turn this is used to compute the radio
brightness temperature Tb at the observed frequencies,
leaving the coronal electron temperature and density as free
parameters. EUV line intensities, calculated from the derived models,
show a good agreement with EUV observations.
Title: Observation of Transition Region Fine Structures with
Soho/Sumer
Authors: Landi, E.; Mason, H. E.; Landini, M.
Bibcode: 1999SSRv...87..241L
Altcode:
We present a preliminary analysis of two quiet Sun transition
region areas observed with the SOHO/SUMER spectrometer, using lines
from oxygen, nitrogen and silicon. The average quiet Sun physical
parameters are studied as a function of line intensity. Systematic
variations of line position and width with increasing intensity are
found. A large number of small-scale active points have been observed,
and preliminary analysis of the physical properties and dynamics of
these active features is presented. A jet-like structure, found in an
active point, is also investigated and its velocity along the line of
sight determined.
Title: Temperature and density diagnostics of quiet Sun and active
regions observed with CDS NIS
Authors: Landi, E.; Landini, M.
Bibcode: 1998A&A...340..265L
Altcode:
We study the Differential Emission Measure distribution of two pairs of
active and quiet regions of the solar atmosphere, observed by CDS Normal
Incidence Spectrometer (NIS) on SOHO, and investigate their temperature
and density structure . Use is made of the Arcetri Method (Landi &
Landini 1997) for DEM and density diagnostics. An iterative method
for determining the DEM is presented; it allows to select physically
meaningful DEM distributions having a definite top temperature along
the line of sight. Density sensitive lines are identified and density
diagnostics is performed for all the four different spectra. Comments
are made on the density versus temperature curves obtained for each
region. Simple constant pressure models are not satisfactory and
constraints on temperature and density distributions are discussed.
Title: The Arcetri spectral code for thin plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 1998A&AS..133..411L
Altcode:
The Arcetri spectral code allows to evaluate the spectrum of the
radiation emitted by hot and optically thin plasmas in the spectral
range 1 - 2000 Angstroms. The database has been updated including atomic
data and radiative and collisional rates to calculate level population
and line emissivities for a number of ions of the minor elements;
a critical compilation of the electron collision excitation for these
elements has been performed. The present version of the program includes
the CHIANTI database for the most abundant elements, the minor elements
data, and Fe III atomic model, radiative and collisional data.
Title: CHIANTI: an atomic database for emission lines. II. Comparison
with the SERTS-89 active region spectrum
Authors: Young, P. R.; Landi, E.; Thomas, R. J.
Bibcode: 1998A&A...329..291Y
Altcode:
The CHIANTI database was described by Dere et al. (1997, hereafter
Paper I) and the present paper applies the atomic data to the study
of extreme ultra-violet emission lines found in the SERTS-89 active
region spectrum published by Thomas & Neupert (1994). Firstly,
the emission line ratios that are insensitive to density and
temperature are used to check both the quality of the atomic data and
the calibration of the instrument. Secondly, we use, where possible,
ratios that are sensitive to density to estimate the electron density
from different ions. In general we find excellent agreement between
theory and observation, providing confidence in both the atomic data
in the CHIANTI database and the quality of the SERTS-89 spectrum. Where
inconsistencies between theory and observation exist we try to explain
them in terms of either inaccuracies in the atomic data or blending of
the lines. One consistent discrepancy was that all observed lines that
we analysed in the lambr{430}{450} region were uniformly a factor of
1.5--2.0 weaker than predicted, suggesting that the SERTS-89 calibration
may need adjustment in this spectral interval. Serious problems were
also found in some of the theoretical predictions for a few ions,
especially ion{Fe}{xiv}.
Title: CHIANTI - an Atomic Database For Emission Lines Paper I:
Wavelengths Greater than 50 Angstroms
Authors: Dere, K. P.; Landi, E.; Mason, H. E.; Fossi, B. C. M.; Young,
P. R.
Bibcode: 1998ASPC..143..390D
Altcode: 1998sigh.conf..390D
No abstract at ADS
Title: The EUV Spectrum of kappa Ceti in a Quiescent Phase
Authors: Landi, E.; Landini, M.; Del Zanna, G.
Bibcode: 1998ASPC..154.1105L
Altcode: 1998csss...10.1105L
The spectrum of kappa Cet in the region 80-370 AA observed by EUVE
Spectrometers is discussed to investigate the transition region and the
corona of the star. The medium wavelength spectrum of the star appears
to be very similar to a moderately active Sun and no evidence exists
of flare-like lines observed in many active stars by EUVE. Several
emission lines of moderately ionized iron (from Fe 9 to Fe 18) are
identified and used together with IUE observations to evaluate the
differential emission measure (DEM). The DEM peaks at about 3 x 10^6 K,
a value typical of solar active regions. Comparison of observed and
synthetic spectra are performed using Arcetri code, including both
Arcetri and CHIANTI databases.
Title: The Arcetri Spectral Code for Thin Plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 1998ESASP.417..251L
Altcode: 1998cesh.conf..251L
No abstract at ADS
Title: Temperature and density diagnostics of quiet Sun and active
regions observed with CDS NIS on SOHO
Authors: Landi, E.; Landini, M.
Bibcode: 1998ESASP.421..287L
Altcode: 1998sjcp.conf..287L
No abstract at ADS
Title: The Arcetri spectral code for thin plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 1998ESASP.421..293L
Altcode: 1998sjcp.conf..293L
No abstract at ADS
Title: Simultaneous temperature and density diagnostics of optically
thin plasmas
Authors: Landi, E.; Landini, M.
Bibcode: 1997A&A...327.1230L
Altcode:
A method is given for performing simultaneous temperature and density
diagnostics of an optically thin plasma by means of all the available
observations of lines of the same ions. The density and differential
emission measure at selected temperatures may be measured and the
chemical composition verified. The method is applied to line emission
measured by SERTS 89 for an active region of the solar corona and
use is made of the Arcetri spectral code and the CHIANTI atomic data
base to evaluate the theoretical expected intensities. Lines of He II,
C IV, Ne V and VI, Mg VI,VII,VIII and IX, Si VIII,IX,X and XI, S XIII
and XIV, Cr XIII and XIV, Fe X,XI,XII,XIII XIV,XV,XVI and XVII and Ni
XVIII are used to put constraints on the model of the density versus
temperature and on the Differential Emission Measure, and suggestions
are given on how to use the method to verify intensity calibrations
and identify lines for which atomic physics must be improved.
Title: CHIANTI - an atomic database for emission lines
Authors: Dere, K. P.; Landi, E.; Mason, H. E.; Monsignori Fossi,
B. C.; Young, P. R.
Bibcode: 1997A&AS..125..149D
Altcode:
A comprehensive set of accurate atomic data is required for analyses of
astrophysical and solar spectra. CHIANTI provides a database of atomic
energy levels, wavelengths, radiative data and electron excitation
data for ions which are abundant in cosmic plasmas. The most recent
electron excitation data have been assessed and stored following
the method of \cite[Burgess \& Tully (1992)]{bur92}. The current
version is essentially complete for specifying the emission spectrum
at wavelengths greater than 50 Angstroms. A list of observed lines in
the spectral region between 50 and 1100 Angstroms has been compiled
and compared with the lines predicted by the CHIANTI database. The
CHIANTI database reproduces the vast majority of lines observed at
these wavelengths. CHIANTI includes IDL (Interactive Data Language)
routines to calculate optically thin synthetic spectra for equilibrium
conditions. IDL routines to calculate theoretical line intensities
required for electron density or temperature diagnostics and emission
measure studies are also included. The CHIANTI atomic database and
supporting IDL routines are available by anonymous FTP.
Title: Soho Cds nis in-flight intensity calibration using a plasma
diagnostic method
Authors: Landi, E.; Landini, M.; Pike, C. D.; Mason, H. E.
Bibcode: 1997SoPh..175..553L
Altcode:
The internal intensity calibration of the Coronal Diagnostic
Spectrometer (CDS) - Normal Incidence Spectrometer (NIS) is studied
using the Arcetri diagnostic method. A large number of spectral lines
observed by the CDS-NIS 1 and NIS 2 windows in a solar active region
is analysed in order to determine the intensity calibration curve for
both channels.
Title: The EUV spectrum of κ Ceti: an active Sun.
Authors: Landi, E.; Landini, M.; Del Zanna, G.
Bibcode: 1997A&A...324.1027L
Altcode:
The spectrum of κ Cet in the region 80-370Å observed by EUVE
Spectrometers is analyzed to investigate the transition region and the
corona of the star. The star appears to be in a rather quiet condition
and no evidence exists of flare-like lines observed in many active
stars. Several emission lines of moderately ionized iron (from Fe IX
to Fe XVIII) are identified and used together with I.U.E. observations
to evaluate the differential emission measure (DEM). The DEM peaks
at about 3x10^6^K, a value typical of solar active regions. This is
confirmed by a comparison with the spectrum of an Active Region of
the Solar Corona measured by the Coronal Diagnostic Spectrometer on
SOHO showing very similar features.
Title: VizieR Online Data Catalog: CHIANTI - An Atomic Database For
Emission Lines I. (Dere+ 1997)
Authors: Dere, K. P.; Landi, E.; Mason, H. E.; Monsignori Fossi,
B. C.; Young, P. R.
Bibcode: 1997yCat..41250149D
Altcode:
A comprehensive set of accurate atomic data is required for analyses of
astrophysical and solar spectra. CHIANTI provides a database of atomic
energy levels, wavelengths, radiative data and electron excitation
data for ions which are abundant in cosmic plasmas. The most recent
electron excitation data have been assessed and stored following
the method of Burgess & Tully (1992A&A...254..436B). The
current version is essentially complete for specifying the emission
spectrum at wavelengths greater than 50Å. A list of observed lines
in the spectral region between 50 and 1100Å has been compiled
and compared with the lines predicted by the CHIANTI database. The
CHIANTI database reproduces the vast majority of lines observed at
these wavelengths. CHIANTI includes IDL (Interactive Data Language)
routines to calculate optically thin synthetic spectra for equilibrium
conditions. IDL routines to calculate theoretical line intensities
required for electron density or temperature diagnostics and emission
measure studies are also included. The CHIANTI atomic database and
supporting IDL routines are available by anonymous FTP. (1 data file).
Title: GIS Calibration Study with a Plasma Diagnostic Method
Authors: Landi, E.; Del Zanna, G.; Landini, M.; Bromage, B. J. I.;
Breeveld, E. R.; Pike, C. D.
Bibcode: 1997ESASP.404..501L
Altcode: 1997cswn.conf..501L
No abstract at ADS
Title: Temperature and Density Diagnostics of Active Region Observed
with CDS NIS
Authors: Landi, E.; Landini, M.
Bibcode: 1997ESASP.404..495L
Altcode: 1997cswn.conf..495L
No abstract at ADS
Title: Density diagnostic of astrophysical plasmas
Authors: Landini, Massimo; Landi, Enrico
Bibcode: 1997AIPC..386..419L
Altcode:
The Arcetri Spectral Code, that evaluates XUV line and continuum
emission of thin plasmas in the range 1-2000 Å, has been recently
updated and includes detailed computation of levels populations for
the Iron lines from Fe IX to Fe XXIII and the most important Be-like,
C-like, and N-like ions (1). A new technique is developed to evaluate
the electron density, comparing observations and theoretical predictions
for a set of density dependent lines of selected ions. Examples are
given for Fe XIII and Si IX using recent observations of the solar
corona with the S.E.R.T.S. spectrometers.
Title: The XUV spectral code of Arcetri
Authors: Landini, Massimo; Landi, Enrico; Fossi, Brunella Monsignori
Bibcode: 1997AIPC..386..421L
Altcode:
The Arcetri Spectral Code evaluates lines and continuum emission of
thin thermal plasmas in the temperature range from 104
K to 108 K and for electron number density lower than
1012 cm-3, in the spectral range 1-2000 Å. For
each ion of the most common elements the ionization balance is
evaluated and the population level is computed assuming statistical
equilibrium between excitation and decay processes. A sampling
of the code, that is in the way of upgrading, is available on
Mosaic(http://www.arcetri.astro.it).
Title: CHIANTI - an Atomic Database for Emission Line Spectroscopy:
Version 1 - Wavelengths greater than 50 Angstroms
Authors: Dere, K. P.; Monsignori-Fossi, B. C.; Landi, E.; Mason,
H. E.; Young, P. R.
Bibcode: 1996AAS...188.8501D
Altcode: 1996BAAS...28..961D
A comprehensive set of accurate atomic data is required for analyses of
astrophysical and solar spectra. CHIANTI provides an atomic database of
energy levels (wavelengths), radiative data and electron excitation data
for ions which are abundant in astrophysical plasmas. The most recent
electron excitation data have been assessed and stored following the
method of Burgess and Tully (1992). CHIANTI includes IDL (Interactive
Data Language) routines to produce optically thin synthetic spectra
for lambda > 50 Angstroms, assuming equilibrium conditions. It also
includes IDL routines to calculate theoretical line intensities required
for electron density or temperature diagnostics and emission measure
studies. The CHIANTI atomic database and supporting IDL routines are
available by anonymous FTP.
Title: Comparison of temperature and density diagnostics in the
coronae of a Centauri and the sun
Authors: Del Zanna, G.; Landini, M.; Landi, E.; Monsignori Fossi, B. C.
Bibcode: 1996ASPC..109..259D
Altcode: 1996csss....9..259D
No abstract at ADS