Author name code: schmelz
ADS astronomy entries on 2022-09-14
author:"Schmelz, Joan T."
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Title: Gaussian Decomposition of λ21 cm H I profiles, the Critical
Ionization Velocity, and the Interstellar Helium Abundance
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 2022ApJ...934..187V
Altcode:
Following an established protocol of science-that results must be
reproducible-we examine the Gaussian fits to Galactic λ21 cm (H I)
emission profiles obtained by two seemingly complementary methods using
data from the Leiden-Argentine-Bonn all-sky survey. One is based on
the method used by Verschuur, the other by Nidever et al. (2008). The
comparisons led to the identification of four problems that might arise
when an algorithm is applied to huge databases without close monitoring:
(1) different methods of calculating ${\tilde{\chi }}^{2}$ measuring
the goodness of fit; (2) an ultra-broad component found to imperfectly
bridge the gap between low- and intermediate-velocity gas; (3) the lack
of an imposed spatial coherence allowing different components to appear
and disappear in profiles separated by a fraction of a beamwidth; and
(4) multiple, fundamentally different solutions for profiles at both
the north and south Galactic poles. Confirming evidence emerges from
this study of an underlying component with a line width of an order
34 km s-1. If this feature is the result of the critical
ionization velocity effect acting on interstellar helium, it can be
used to calculate its interstellar abundance. Analysis of H I profiles
in an area in the southern Galactic hemisphere using multitelescope
data gives a helium abundance of 0.094 ± 0.035, in excellent agreement
with the accepted cosmic abundance of 0.085.
Title: The Origin and Distance of the High-Velocity Cloud MI
Authors: Schmelz, J. T.; Verschuur, G. L.
Bibcode: 2022arXiv220708707S
Altcode:
The high-velocity, neutral hydrogen feature known as MI may be
the result of a supernova that took place about 100,000 years ago
at a distance of 163 pc. Low-velocity HI data show a clear cavity,
a structure indicative of regions evacuated by old exploding stars,
centered on the spatial coordinates of MI, (l,b) = (165o, 65.o5). The
invisible companion of the yellow giant star, 56 Ursae Majoris, may
be the remains of the supernova that evacuated the cavity and blasted
MI itself outward at 120 km/s. The mass and energy of MI are easily in
line with what is expected from a supernova. The X-rays seen by ROSAT
are consistent with an origin in the resulting bow shock. Ironically,
this scenario for MI only came together because we were exploring
low-velocity gas in the direction of high-velocity clouds.
Title: The Effect of Shear Flows on the Davis-Chandrasekhar-Fermi
Approximation
Authors: Guerra Aguilera, Jordan; Lopez-Rodriguez, Enrique; Chuss,
David; Butterfield, Natalie; Schmelz, Joan
Bibcode: 2022AAS...24014309G
Altcode:
The Davis-Chandrasekhar-Fermi (DCF) method is one of the most common
means to estimate the magnetic field strength from dust polarimetric
observations. Its physical foundation lies on the idea that the speed of
an Alfvén wave is determined by the amplitude of the turbulent motions
in the gas. However, this scenario does not consider the large-scale
motions of the gas such as shear flows, which often is evident in
polarimetric data. We extended the DCF method to include such effects
by studying the propagation of an Alfvén wave in a medium with a
background structured flow. The new approximation was first tested
on synthetic polarization in order to determine the range of physical
variables (i.e. mass density, turbulent velocity, shear-flow amplitude)
in which it is valid. Finally, the extended DCF approximation was used
to determined the strength of magnetic field in the Circus-nuclear Disk
(CND) in the galactic center for which polarimetric data was obtained
with HAWC+/SOFIA.
Title: Episodic Accretion in High-Mass Protostars
Authors: De Buizer, James; Schmelz, Joan
Bibcode: 2022SSNew...7....4D
Altcode:
No abstract at ADS
Title: SOFIA Science: Remarkable Results
Authors: Schmelz, Joan; Proudfit, Leslie
Bibcode: 2021ssrr.rept....1S
Altcode:
No abstract at ADS
Title: Episodic Accretion in Massive Star Formation
Authors: Schmelz, Joan; Jackson, James
Bibcode: 2021SSNew...6....5S
Altcode:
No abstract at ADS
Title: The Strength and Structure of the Magnetic Field in the
Galactic Outflow of Messier 82
Authors: Lopez-Rodriguez, Enrique; Guerra, Jordan A.; Asgari-Targhi,
Mahboubeh; Schmelz, Joan T.
Bibcode: 2021ApJ...914...24L
Altcode: 2021arXiv210203362L
Galactic outflows driven by starbursts can modify the galactic
magnetic fields and drive them away from the galactic planes. Here,
we quantify how these fields may magnetize the intergalactic medium
(IGM). We estimate the strength and structure of the fields
in the starburst galaxy M82 using thermal polarized emission
observations from the Stratospheric Observatory for Infrared
Astronomy/High-resolution Airborne Wideband Camera-plus and a potential
field extrapolation commonly used in solar physics. We modified the
Davis-Chandrasekhar-Fermi method to account for the large-scale flow
and the turbulent field. Results show that the observed magnetic
fields arise from the combination of a large-scale ordered potential
field associated with the outflow and a small-scale turbulent field
associated with bow-shock-like features. Within the central 900 pc
radius, the large-scale field accounts for 53 ± 4% of the observed
turbulent magnetic energy with a median field strength of 305 ± 15 μG,
while small-scale turbulent magnetic fields account for the remaining
40 ± 5% with a median field strength of 222 ± 19 μG. We estimate
that the turbulent kinetic and turbulent magnetic energies are in
close equipartition up to ~2 kpc (measured), while the turbulent
kinetic energy dominates at ~7 kpc (extrapolated). We conclude that
the fields are frozen into the ionized outflowing medium and driven
away kinetically. The magnetic field lines in the galactic wind of
M82 are open, providing a direct channel between the starburst core
and the IGM. Our novel approach offers the tools needed to quantify
the effects of outflows on galactic magnetic fields as well as their
influence on the IGM and evolution of energetic particles.
Title: λ21-cm Interstellar HI Profiles, Critical Ionization
Velocities, and Derived Electron Densities
Authors: Verschuur, Gerrit L.; Schmelz, Joan T.; Asgari-Targhi,
Mahboubeh
Bibcode: 2021ITPS...49.1669V
Altcode:
No abstract at ADS
Title: Magnetic Field of the Galaxy M82
Authors: Guerra Aguilera, J.; Lopez Rodriguez, E.; Schmelz, J.;
Asgari Targhi, M.
Bibcode: 2021AAS...23722805G
Altcode:
We use far-infrared (FIR) dust polarimetric data from HAWC+/SOFIA at
53 micron to study the magnetic field orientations in the starburst
galaxy Messier 82 (M82). Combining the analysis of polarization-angle
dispersion with the traditional Davis-Chandrasekhar-Fermi (DCF)
method, a plane-of-sky (POS) magnetic field strength of BPOS ~ 1.0
mG is estimated. However, considering that in the M82 the bulk of
polarized dust emission is located within the outflow-dominated region,
the BPOS is overestimated by the presence of large-scale flows. Thus,
a modification to the DCF method was performed and a corrected BPOS ~
0.8 mG was estimated. Using the estimated magnetic field strength and
energy balance considerations, we construct a two-dimensional map of
BPOS that resembles the FIR surface brightness distribution. Finally,
using this map and the estimated magnetic field orientations, we
are able to construct and visualize the magnetic fields to radial
distances of ~ 5 kpc. We find that a large volume of the magnetic
fields in the galactic outflow of M82 can be considered as force-free
with a dipole-like overall appearance. With this extended magnetic
field structure we will be able to determine whether the magnetic
field is strong enough to form close field lines facilitating feedback
from/to the ongoing star formation, or open field lines magnetizing
the intergalactic medium.
Title: Where is the Missing Galactic Hydrogen?
Authors: Schmelz, J. T.; Verschuur, G. L.
Bibcode: 2021AAS...23711007S
Altcode:
All-sky surveys of neutral hydrogen at 21 cm give us an opportunity to
study the interstellar medium and galactic structure in new ways. Here,
we use the Leiden/Argentine/Bonn data to investigate the differences
in the neutral hydrogen structure between the northern and southern
hemispheres at high galactic latitudes. Examining longitude-velocity
planes of the latitude-longitude-velocity data cube at high negative
latitudes shows the expected distribution of low-velocity galactic gas
as we look through the galactic plane toward the relative emptiness
of intergalactic space. Comparison with the equivalent images at
high positive latitudes shows the well-known anomalous-velocity
features, dramatically illustrating a north-south asymmetry in the
high-latitude hydrogen distribution. Another thing to notice are
the gaps in the northern hemisphere low-velocity gas. Where is this
missing hydrogen? It could be shifted to either a different velocity or
a neighboring position. We can check both these options by integrating
along the line of sight at the specific longitudes where the gaps occur
and integrating over the entire longitude range of the disturbance. If
we use the equivalent southern hemisphere data as the "standard," we
find that column densities in the south are about three time higher
than these northern directions, not supporting either conjecture. A
third possibility is that the missing hydrogen is ionized. Assuming
a scale height of about 1 kpc, the resulting electron density is in
good agreement with results from pulsar dispersion measures.
Title: The neutral hydrogen structure of an interstellar H-alpha
filament
Authors: Verschuur, G.; Schmelz, J.
Bibcode: 2021AAS...23711202V
Altcode:
The neutral hydrogen (HI) structure of a straight segment of an Hα
filament discovered by Ogden & Reynolds (1985) has been studied
using Effelsberg-Bonn HI survey data. The HI structure is directly
associated with the Hα and is found at the same velocity, -62 km/s,
and with the same line width, 26 km/s. If interpreted as thermal
broadening, a line width of 26 km/s implies a temperature of 15,000
K at which temperature the hydrogen would be ionized and rendered
invisible to 21-cm observations. Having cold hydrogen capable of
producing 21-cm emission so closely associated with the Hα filament,
which is believed to be evidence of a warm ionized medium (8000 K),
poses challenges to thermodynamic models. An alternative model for
this association will be proposed.
Title: The Geometry of the Magnetic Field in the Central Five Parsecs
of the Galaxy
Authors: Morris, Mark R.; Dowell, C. Darren; Chuss, David T.; Schmelz,
Joan T.
Bibcode: 2021cosp...43E1251M
Altcode:
The far-infrared camera and polarimeter HAWC+, mounted on the
Stratospheric Observatory for Infrared Astronomy (SOFIA), has been used
to measure the polarized emission at 53 and 214 µm from the Galaxy's
circumnuclear disk (CND) and its immediate surroundings. Significant
detections (> 3$\sigma$) of polarization have been made at over 600
independent positions in this region. Assuming that the polarization
E-vectors result from thermal emission from spinning, magnetically
aligned dust grains, we find that the magnetic field is highly ordered,
showing an apparently spiral-shaped projected geometry. The field
geometry is consistent with having a toroidal component in the CND, as
had previously been reported, but the polarization vectors are strongly
influenced by emission from the "wings" - point-reflection-symmetric
linear protrusions from the ends of the projected major axis of
the tilted CND that appear in radio images to have a filamentary
character. We interpret the wings as streams of outflowing gas resulting
from collimated outflows from the central parsec (presumably SgrA*)
that have entrained dusty material from the CND. The magnetic field
is aligned with the filamentation of these streams, perhaps by sheared
motion along the streams. Throughout the measured region, small local
dispersion of the polarization vector directions leads to estimates
of the magnetic field strength of several milligauss.
Title: The Dominance of the Magnetic Field in the Central Five
Parsecs of the Galaxy
Authors: Schmelz, J.; Dowell, C.; Chuss, D.; Morris, M.; Guerra, J.;
HAWC+ Science Team
Bibcode: 2020AAS...23630606S
Altcode:
Using polarimetric and photometric data from the HAWC+ instrument
on the Stratospheric Observatory for Infrared Astronomy (SOFIA),
we have estimated the value of the plasma β, the ratio of the
thermal-to-magnetic pressure. This value is used traditionally as an
indicator of whether magnetic or thermodynamic processes dominate
in an environment. If the thermal pressure is greater than the
magnetic pressure, β > 1, referred to as a high-β plasma, the
gas dynamics will control the structure of the environment, e.g.,
the solar photosphere. If the thermal pressure is less than the
magnetic pressure, β < 1, referred to as a low-β plasma, the
magnetic field will control the structure of the environment, e.g.,
the solar corona. Using values of temperature and density from the
literature and the magnetic field value of B = 5 mG obtained from the
Davis-Chandrasekhar-Fermi method, we find that β ~ 0.001. Since the
widths of all molecular, atomic, and ionized gas lines are quite large
in and around this region, we might want to include all forms of kinetic
energy, including turbulence, to determine if the magnetic pressure
really dominates. Defining β' as the ratio of the turbulent pressure
over the magnetic pressure and using an equivalent temperature from
the literature, we find that β' ~ 0.03. These values are clearly in
the low-β regime where the magnetic pressure dominates. They indicate
that, like the solar corona, the magnetic field is channeling the plasma
and appears to be a significant force on the matter in this region.
Title: Gaussian Decomposition of {\lambda}21-cm Interstellar HI
profiles
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 2020arXiv200409328V
Altcode:
Following an established protocol of science, that results must
be reproducible, we examine the Gaussian fits to Galactic 21-cm
emission profiles obtained by two seemingly complementary methods:
the semi-automated approach based on the method used by Verschuur
(2004) and the automated technique of Nidever et al. (2008). Both
methods use data from the Leiden/Argentine/Bonn all-sky survey. The
appeal of an automated routine is great, if for no other reason than
the time saved over semi-automated fits. The pitfalls, however, are
often unanticipated, and the most important aspect of any algorithm
is the reproducibility of the results. The comparisons led to the
identification of four problems with the Nidever et al. (2008) analysis:
(1) different methods of calculating the reduced chi-squared measuring
the goodness of fit; (2) an ultra-broad component found bridging the
gap between low and intermediate velocity gas; (3) the lack of an
imposed spatial coherence allowing different components to appear and
disappear in profiles separated by a fraction of a beam width; and (4)
multiple, fundamentally different solutions for the profiles at both
the North and South Galactic Poles. A two-step method would improve the
algorithm, where an automated fit is followed by a quality-assurance,
visual inspection. Confirming evidence emerges from this study of a
pervasive component with a line width of order 34 km/s, which may be
explained by the Critical Ionization Velocity (CIV) of helium. Since
the Nidever et al. (2008) paper contains the only result in the refereed
literature that contradicts the CIV model, it is important to understand
the flaws in the analysis that let to this contradiction.
Title: The Role of the Critical Ionization Velocity Effect in
Interstellar Space and the Derived Abundance of Helium
Authors: Verschuur, Gerrit L.; Schmelz, Joan T.; Asgari-Targhi,
Mahboubeh
Bibcode: 2020arXiv200405257V
Altcode:
Gaussian analysis of new, high-angular-resolution interstellar 21-cm
neutral hydrogen emission profile structure more clearly reveals the
presence of the previously reported signature of the critical ionization
velocity ({\it CIV}) of Helium (34 km s$^{-1}$). The present analysis
includes 1496 component line widths for 178 neutral hydrogen profiles
in two areas of sky at galactic latitudes around $-$50$^\circ$, well
away from the galactic plane. The new data considered here allow the
interstellar abundance of Helium to be calculated, and the derived
value of 0.095 $\pm$ 0.020 compares extremely well with the value of
0.085 for the cosmic abundance based on solar data. Although the precise
mechanisms that give rise to the {\it CIV} effect in interstellar space
are not yet understood, our results may provide additional motivation
for further theoretical study of how the mechanism operates.
Title: Hydrogen, Helium, and Magnetic Fields in Interstellar Space
Authors: Schmelz, Joan T.; Verschuur, Gerrit L.
Bibcode: 2019AAS...23431602S
Altcode:
Analysis by multiple authors of a variety of interstellar neutral
hydrogen features studied over many decades using data from different
telescopes reveals a pervasive 34 km/s wide component. The traditional
explanation, that the line width results from a kinetic temperature,
would mean that T = 24,000 K, high enough to ionize the gas so it could
not contribute to the 21-cm profile. Turbulent motions could explain
a pervasive broad component, but not why it has the same numerical
value in so many different types of HI features. Confusion due to
telescope side lobes has been proposed as a possible explanation,
but the broad feature persists in side-lobe-corrected survey data. The
critical ionization velocity is a well-studied plasma phenomenon where
atoms become ionized in the presence of a magnetic field when their
kinetic energy relative to the plasma is equivalent to the ionization
potential. The critical ionization velocity for helium is 34 km/s,
which could account for the pervasiveness of this component. This result
supports other evidence that the neutral hydrogen in the interstellar
medium is tightly coupled to the galactic magnetic field (Clark et
al. 2014; 2015). Strong support for this interpretation stems from the
resulting abundance of interstellar helium, which can be estimated from
the column density fraction of the 34 km/s component with respect to
the entire emission profile. A derived value of 0.28 is within one σ
of the cosmic abundance of helium.
Title: The Spiral Magnetic Field in the Central 5 Parsecs of the
Galaxy
Authors: Dowell, C. Darren; Chuss, David T.; Guerra, Jordan A.; Houde,
Martin; Michail, Joseph M.; Morris, Mark; Schmelz, Joan T.; Staguhn,
Johannes; Werner, Michael W.
Bibcode: 2019AAS...23431605D
Altcode:
At λ ≈ 50 microns, the most prominent feature in the inner parsecs
of the Milky Way is the rotating, irregular Circum-Nuclear Ring (CNR)
which demarcates the inner boundary of the molecular gas that is likely
spiraling in toward the supermassive black hole. The gas is magnetized,
with previous estimates of field strength exceeding 1 milliGauss. We
present new observations of the polarization and inferred magnetic field
structure of the CNR and vicinity, made at λ = 53 microns with the
HAWC+ instrument on SOFIA. These observations show a spiral magnetic
field on scales of 0.5 - 5 pc, with organized components, but mostly
lacking the 180 degree symmetry of existing magnetized accretion disk
models. We discuss estimates of the magnetic field strength from the 53
micron data, the relationship of these data to observations at shorter
and longer far-infrared wavelengths, and interpretation of several of
the magnetic features observed.
Title: Introduction to Magnetic Fields and Filaments in Star Formation
Authors: Schmelz, Joan T.
Bibcode: 2019AAS...23312701S
Altcode:
Magnetic field extrapolations and filamentary loop substructure have
been key results in understanding the solar atmosphere and coronal
heating. Arecibo’s 21-cm neutral hydrogen data reveal pervasive
interstellar filaments that follow the galactic magnetic field lines
revealed by Planck’s all-sky dust polarization maps. The small
scales of the solar coronal and the large scales of interstellar
matter hint that there may be a role for magnetic fields and filaments
at every step of the star formation process. Herschel observations
established that molecular filaments are the preferred sites of
star formation. SOFIA’s new instrument, HAWC+, studies the role of
magnetic fields in filaments on sub-parsec scales. ALMA polarization
observations probe regions surrounding young protostars. Sub-orbital
platforms, such as BLASTPOL and BLAST-TNG, deliver a wealth of data on
magnetic fields in the interstellar medium. This talk sets the stage,
allowing the session components to knits the big and small pictures
together to provide a better understanding of galactic magnetic fields
and filaments in star forming regions.
Title: Interstellar HI: Filaments and threads
Authors: Verschuur, Gerrit; Schmelz, Joan T.; Asgari-Targhi, Mahboubeh
Bibcode: 2019AAS...23311107V
Altcode:
A very long and nearly straight HI filament at about -60 km s-1
in the southern galactic hemisphere, seen nearly normal to the
line-of-sight and well separated from low velocity gas, has been
studied in several ways in order to understand its physics, structure,
and morphology. Gaussian analysis of 1800 profiles show an underlying
HI component, which is at least 15 deg. long and about 1 deg. wide,
has a typical line width of 21 km/s. At a distance of 100 pc it
would be confined by a magnetic field of 18 μG. Examination of 140
declination-velocity cross-sections revealed evidence for narrow,
elongated features (threads) unresolved in width within the boundaries
of the filament. These cooler components have an average density of
29 cu.cm. and may be confined by a magnetic field of 5 μG. These
results, taken together, suggest that interstellar HI filaments may
have magnetic substructure.
Title: Interstellar Matters: Neutral Hydrogen and the Galactic
Magnetic Field
Authors: Verschuur, G. L.; Schmelz, J. T.; Asgari-Targhi, M.
Bibcode: 2018ApJ...867..139V
Altcode:
A very long and nearly straight H I filament at about -60 km
s-1 in the southern Galactic hemisphere, seen nearly normal
to the line of sight and well separated from low-velocity gas, has been
studied in several ways in order to understand its physics, structure,
and morphology. Gaussian analysis of 1800 profiles and examination
of 140 declination-velocity cross sections shows that an underlying
H I component, which is at least 15° long and about 1° wide, has a
typical line width of 21 km s-1. It does not appear to be
in thermal pressure equilibrium with its surroundings; rather, it may
be confined by a magnetic field of 18 μG. Narrow, elongated features
(threads), probably unresolved in the 4‧ H I observations, have
been identified within the boundaries of the filament. In general,
each of these threads has two emission components, with line widths
of the order of 8 and 3 km s-1, which may wind around each
other. Analysis suggests that these cooler components have an average
density of 29 cm-3 and may be confined by a magnetic field
of 5 μG. These results, taken together, can be explained if this
southern filament has magnetic substructure.
Title: Arecibo weathers the storm
Authors: Rivera-Valentín, Edgard G.; Schmelz, Joan T.
Bibcode: 2018NatAs...2..264R
Altcode:
Hurricane Maria was 2 mph short of category 5 when it made landfall
on Puerto Rico on 20 September 2017. The 305 m radio telescope at
the Arecibo Observatory withstood the storm, suffering only minor
structural damage. Staff have worked diligently to return the site to
full operations and provide vital services to the surrounding Puerto
Rican community.
Title: The Complexities of Interstellar Dust and the Implications
for the Small-scale Structure in the Cosmic Microwave Background
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 2018ApJ...853..137V
Altcode:
A detailed comparison of the full range of PLANCK and Wilkinson
Microwave Anisotropy Probe data for small (2° × 2°) areas of sky
and the Cosmic Microwave Background Internal Linear Combination (ILC)
maps reveals that the structure of foreground dust may be more complex
than previously thought. If 857 and 353 GHz emission is dominated
by galactic dust at a distance < few hundred light years, then it
should not resemble the cosmological ILC structure originating at a
distance ∼13 billion light years. In some areas of sky, however,
we find strong morphological correlations, forcing us to consider the
possibility that the foreground subtraction is not complete. Our data
also show that there is no single answer for the question: “to what
extent does dust contaminate the cosmologically important 143 GHz
data?” In some directions, the contamination appears to be quite
strong, but in others, it is less of an issue. This complexity needs
to be taken in account in order to derive an accurate foreground mask
in the quest to understand the Cosmic Microwave Background small-scale
structure. We hope that a continued investigation of these data will
lead to a definitive answer to the question above and, possibly, to
new scientific insights on interstellar matter, the Cosmic Microwave
Background, or both.
Title: The Implications of Interstellar Dust for the Cosmic Microwave
Background
Authors: Schmelz, Joan T.; Verschuur, Gerrit
Bibcode: 2018AAS...23111606S
Altcode:
A detailed comparison of the full range of PLANCK and WMAP data for
small (2 deg by 2 deg) areas of sky and the Cosmic Microwave Background
(CMB) ILC maps reveals that the structure of foreground dust may be
more complex than previously thought. If 857 and 353 GHz emission is
dominated by galactic dust at a distance < few hundred light years,
then it should not resemble the cosmological ILC structure originating
at a distance ~13 billion light years. In some areas of sky, however,
we find strong morphological correlations, forcing us to consider
the possibility that the foreground subtraction is not complete. Our
data also show that there is no single answer for the question,
“To what extent does dust contaminate the cosmologically important
143 GHz data?” In some directions, the contamination appears to be
quite strong, but in others, it is less of an issue. This complexity
needs to be taken in account in order to derive an accurate foreground
mask in the quest to understand the CMB small-scale structure. We hope
that a continued investigation of these data will lead to a definitive
answer to the question above and, possibly, to new scientific insights
on interstellar matter, the CMB, or both.
Title: Interstellar Matters: Neutral Hydrogen and the Galactic
Magnetic Field
Authors: Verschuur, Gerrit; Schmelz, Joan T.; Asgari-Targhi
asgari-Targhi, M.
Bibcode: 2018AAS...23121208V
Altcode:
The physics of the interstellar medium was revolutionized by the
observations of the Galactic Arecibo L-Band Feed Array (GALFA) HI survey
done at the Arecibo Observatory. The high-resolution, high-sensitivity,
high-dynamic- range images show complex, tangled, extended filaments,
and reveal that the fabric of the neutral interstellar medium is deeply
tied to the structure of the ambient magnetic field. This discovery
prompts an obvious question - how exactly is the interstellar {\it
neutral} hydrogen being affected by the galactic magnetic field? We
look into this question by examining a set of GALFA-HI data in great
detail. We have chosen a long, straight filament in the southern
galactic sky. This structure is both close by and isolated in velocity
space. Gaussian analysis of profiles both along and across the filament
reveal internal structure - braided strands that can be traced through
the simplest part, but become tangled in more complex segments. These
braids do not resemble in any way the old spherical HI clouds and
rudimentary pressure balance models that were used to explain the
pre-GALFA- HI interstellar medium. It is clear that these structures
are created, constrained, and dominated by magnetic fields. Like many
subfields of astronomy before it, e.g., physics of the solar coronal,
extragalactic radio jets, and pulsar environment, scientists are
confronted with observations that simply cannot be explained by simple
hydrodynamics and are forced to consider magneto-hydrodynamics.
Title: Arecibo Under the Gun
Authors: Schmelz, Joan T. Verschuur, Gerrit L.
Bibcode: 2017S&T...133e..84S
Altcode:
No abstract at ADS
Title: A Comparison of EIT and TRACE Loop Widths
Authors: Chastain, S. I.; Schmelz, J. T.
Bibcode: 2017arXiv170506776C
Altcode:
In this study we have compared coronal loops in the Extreme ultraviolet
Imaging Telescope (EIT) on-board the Solar and Heliospheric Observatory
(SOHO) with coronal loops from the Transition Region and Coronal
Explorer (TRACE). The purpose of which is to quantitatively and
qualitatively examine the effects of spatial resolution on the width of
coronal loops and implications for how a coronal loop is defined. Out
of twenty-two loop sections analyzed, we find that none of them were
resolved in EIT and none of them were close to the width of the TRACE
loops. These findings suggest that coronal loops are unresolved in
EIT. We also find examples of how unresolved loops can be quite
misleading. We have also found that many of the TRACE loops that
we have analyzed may be unresolved as well. Our findings emphasize
the importance of studying loop width in order to better understand
coronal loops and also emphasize the need for instruments with higher
spatial resolution.
Title: Cutting-Edge Science from Arecibo Observatory: Introduction
Authors: Schmelz, Joan T.
Bibcode: 2017AAS...22910901S
Altcode:
The Arecibo Observatory is home to the largest radio telescope in
the world operating above 2 GHz, where molecule emission pertaining
to the origins of life proliferate. It also houses the most powerful
radar system on the planet, providing crucial information for the
assessment of impact hazards of near-Earth asteroids (NEA). It was
built to study the ionosphere with a radar system that can also
monitor the effects of Space Weather and climate change. Arecibo
has a proven track record for doing excellent science, even after
50 years of operations. This talk will include brief summaries of
several Arecibo astronomy topics including the (1) latest attempts to
resolve the Pleiades distance controversy, which include VLBI and Gaia;
(2) galactic and extragalactic molecules; and (3) Arecibo 3D orbit
determinations of potentially hazardous asteroids, and the crucial
observation required to select Bennu as the target for the recently
launched NASA OSIRIS-REx mission. This introduction will set the stage
for the invited talks in this session, which include such topics as
Fast Radio Bursts, galactic and extragalactic HI results, the pulsar
emission problem, and NANOGrav. This work is supported by NSF and NASA.
Title: Cosmic Microwave Background Small-Scale Structure:
I. Observations of the Foreground Emission
Authors: Schmelz, Joan T.; Verschuur, Gerrit L.
Bibcode: 2017AAS...22932305S
Altcode:
The derivation of the small-scale structure in the cosmic microwave
background (CMB) relies on an accurate subtraction of foreground
signals from the Milky Way Galaxy. Known sources include thermal
emission from interstellar cirrus, galactic synchrotron emission
resulting from interactions between cosmic ray electrons and magnetic
fields, and electron-ion free-free emission from interstellar H II
regions. Additional sources include spinning and spinning-wobbling
dust grains, and emission from rotational transitions of carbon
monoxide. Verschuur (2015 and references therein) showed many examples
of connections, associations, and overlaps of galactic HI and CMB
structure. Clark et al. (2014) showed that the long, thin filamentary
features seen in the high sensitivity, high dynamic range Galactic
Arecibo L-Band Feed Array (GALFA) HI survey appear to be aligned
along magnetic field directions, which are inferred from the optical
polarization of star light. Clark et al. (2015) took this important
discovery a step further, relating those magnetic field orientations
to the polarized PLANCK 353 GHz dust emission. These results imply
that the neutral hydrogen in the interstellar medium is tightly
coupled to the galactic magnetic field, which requires a population
of electrons. Taken together, these HI results suggest a candidate
for a previously unidentified foreground component that may need to
be understood in order to improve our ability to measure and interpret
the CMB small-scale structure. This work is supported by NASA and NSF.
Title: Cosmic Microwave Background Small-Scale Structure: II. Model
of the Foreground Emission
Authors: Verschuur, Gerrit L.; Schmelz, Joan T.
Bibcode: 2017AAS...22932306V
Altcode:
We have investigated the possibility that a population of galactic
electrons may contribute to the small-scale structure in the cosmic
microwave background (CMB) found by WMAP and PLANCK. Model calculations
of free-free emission from these electrons which include beam dilution
produce a nearly flat spectrum. Data at nine frequencies from 22 to
100 GHz were fit with the model, which resulted in excellent values
of reduced chi squared. The model involves three unknowns: electron
excitation temperature, angular extent of the sources of emission, and
emission measure. The resulting temperatures agree with the observed
temperatures of related HI features. The derived angular extent of the
continuum sources corresponds well with the observed angular extent
of HI filamentary structures in the areas under consideration. The
derived emission measures can be used to determine the fractional
ionization along the path lengths through the emitting volumes of
space. Understanding the role that free-free emission plays in the
small-scale features observed by PLANCK and WMAP should allow us
to create better masks of the galactic foreground. Pursuing such
discoveries may yet transform our understanding of the origins of
the universe.
Title: On the Nature of the Small-scale Structure in the Cosmic
Microwave Background Observed by PLANCK and WMAP
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 2016ApJ...832...98V
Altcode:
Small-scale features observed by Wilkinson Microwave Anisotropy Probe
(WMAP) and PLANCK in the frequency range of 22-90 GHz show a nearly
flat spectrum, which meets with expectations that they originate in
the early universe. However, free-free emission from electrons in small
angular scale galactic sources that suffer beam dilution very closely
mimic the observed spectrum in this frequency range. Fitting such a
model to the PLANCK and WMAP data shows that the angular size required
to fit the data is comparable to the angular width of associated H
I filaments found in the Galactic Arecibo L-Band Feed Array-H isurvey
data. Also, the temperature of the electrons is found to be in the range
of 100-300 K. The phenomenon revealed by these data may contribute to
a more precise characterization of the foreground masks required to
interpret the cosmological aspect of PLANCK and WMAP data.
Title: Hot Plasma from Solar Active-Region Cores: Constraints from
the Hinode X-Ray Telescope
Authors: Schmelz, J. T.; Christian, G. M.; Matheny, P. O.
Bibcode: 2016ApJ...833..182S
Altcode:
Mechanisms invoked to heat the solar corona to millions
of degrees kelvin involve either magnetic waves or magnetic
reconnections. Turbulence in the convection zone produces MHD waves,
which travel upward and dissipate. Photospheric motions continuously
build up magnetic energy, which is released through magnetic
reconnection. In this paper, we concentrate on hot non-flaring
plasma with temperatures of 5 MK < T < 10 MK because it is one
of the few observables for which wave and reconnection models make
different predictions. Wave models predict no (or little) hot plasma,
whereas reconnection models predict it, although in amounts that are
challenging to detect with current instrumentation. We used data from
the X-ray Telescope (XRT) and the Atmospheric Imaging Assembly (AIA). We
requested a special XRT observing sequence, which cycled through the
thickest XRT filter several times per hour so we could average these
images and improve the signal-to-noise. We did differential emission
measure (DEM) analysis using the time-averaged thick-filter data as
well as all available channels from both the XRT and AIA for regions
observed on 2014 December 11. Whereas our earlier work was only able to
determine that plasma with a temperature greater than 5 MK was present,
we are now able to find a well-constrained DEM distribution. We have
therefore added a strong observational constraint that must be explained
by any viable coronal heating model. Comparing state-of-the-art wave
and reconnection model predictions, we can conclude that reconnection
is heating the hot plasma in these active regions.
Title: The Coronal Loop Inventory Project: Expanded Analysis and
Results
Authors: Schmelz, J. T.; Christian, G. M.; Chastain, R. A.
Bibcode: 2016ApJ...831..199S
Altcode: 2017arXiv170509360S
We have expanded upon earlier work that investigates the relative
importance of coronal loops with isothermal versus multithermal
cross-field temperature distributions. These results are important
for determining if loops have substructure in the form of unresolved
magnetic strands. We have increased the number of loops targeted for
temperature analysis from 19 to 207 with the addition of 188 new loops
from multiple regions. We selected all loop segments visible in the
171 Å images of the Atmospheric Imaging Assembly (AIA) that had a
clean background. Eighty-six of the new loops were rejected because
they could not be reliably separated from the background in other AIA
filters. Sixty-one loops required multithermal models to reproduce
the observations. Twenty-eight loops were effectively isothermal,
that is, the plasma emission to which AIA is sensitive could not be
distinguished from isothermal emission, within uncertainties. Ten
loops were isothermal. Also, part of our inventory was one small
flaring loop, one very cool loop whose temperature distribution could
not be constrained by the AIA data, and one loop with inconclusive
results. Our survey can confirm an unexpected result from the pilot
study: we found no isothermal loop segments where we could properly
use the 171-to-193 ratio method, which would be similar to the analysis
done for many loops observed with TRACE and EIT. We recommend caution
to observers who assume the loop plasma is isothermal, and hope that
these results will influence the direction of coronal heating models
and the effort modelers spend on various heating scenarios.
Title: Multiwavelength Characteristics of Microflares
Authors: Poduval, Bala; Schmelz, J. T.
Bibcode: 2016usc..confE.116P
Altcode:
We present the multiwavelength characteristic of microflare detected in
the SDO/AIA and IRIS images using the Automated Microevent-finding Code
(AMC). We have catalogued independent events with information such as
location on the disk, size, lifetime and peak flux, and obtained their
frequency distribution. We mapped these events to other wavelengths,
using their location information, to study their associated features,
and infer the temperature characteristics and evolution. Moreover, we
obtained their magnetic topologies by mapping the microflare locations
on to the HMI photospheric magnetic field synoptic maps. Further, we
analyzed the filtered brightness profiles and light curves for each
event to classify them. Finally, we carried out a differential emission
measure (DEM) analysis to study their temperature characteristics.
Title: The Arecibo Observatory Space Academy: 4 Years of STEAM
Engagement
Authors: Zambrano Marin, L. F.; Rivera-Valentin, E. G.; Schmelz, J.;
Rodriguez-Ford, L. A.; Aponte, B.; Ortiz, A. M.
Bibcode: 2016LPI....47.2617Z
Altcode:
The Arecibo Observatory Space Academy (AOSA) is an intense ten (10)
week research program, for highly qualified pre-college students
residing in Puerto Rico.
Title: The Arecibo Observatory Planetary Radar System
Authors: Taylor, P. A.; Nolan, M. C.; Rivera-Valentin, E. G.;
Richardson, J. E.; Rodriguez-Ford, L. A.; Zambrano-Marin, L. F.;
Howell, E. S.; Schmelz, J. T.
Bibcode: 2016LPI....47.2534T
Altcode:
Arecibo Observatory houses the largest and most sensitive single-dish
radio telescope and the most active and powerful planetary radar
facility in the world.
Title: Radar Observations of Near-Earth Asteroids from Arecibo
and Goldstone
Authors: Taylor, P. A.; Richardson, J. E.; Rivera-Valentin, E. G.;
Rodriguez-Ford, L. A.; Zambrano-Marin, L. F.; Nolan, M. C.; Howell,
E. S.; Benner, L. A. M.; Brozovic, M.; Naidu, S. P.; Jao, J. S.; Lee,
C. G.; Giorgini, J. D.; Busch, M. W.; Marshall, S. E.; Margot, J. L.;
Greenberg, A. H.; Ghigo, F. D.; Shepard, M. K.; Schmelz, J. T.
Bibcode: 2016LPI....47.2772T
Altcode:
We will present a subset of radar results from the 108 near-Earth
asteroids detected with Arecibo and Goldstone in 2015 from spheroids
to peanuts and binaries.
Title: Modeling of magnetically confined plasma in hot coronal loops
Authors: Asgari-Targhi, M.; Imada, S.; Schmelz, J. T.
Bibcode: 2015AGUFMSH13C2452A
Altcode:
In this talk, we present results of three-dimensional MHD modeling
for the Alfvén wave turbulence within loops with high temperatures
⩾ 5 MK. One of our findings is that for the Alfvén waves to create
enough turbulence to heat the loops in the core of the active region,
the footpoint velocity must be 5-6 km/s. We also present the results of
the non-thermal line broadenings in these loops and draw a comparison
between the observations and modeling.
Title: The Coronal Loop Inventory Project
Authors: Schmelz, J. T.; Pathak, S.; Christian, G. M.; Dhaliwal,
R. S. S.; Paul, K. S.
Bibcode: 2015ApJ...813...71S
Altcode:
Most coronal physicists now seem to agree that loops are composed of
tangled magnetic strands and have both isothermal and multithermal
cross-field temperature distributions. As yet, however, there is no
information on the relative importance of each of these categories,
and we do not know how common one is with respect to the other. In
this paper, we investigate these temperature properties for all loop
segments visible in the 171-Å image of AR 11294, which was observed
by the Atmospheric Imaging Assembly (AIA) on 2011 September 15. Our
analysis revealed 19 loop segments, but only 2 of these were clearly
isothermal. Six additional segments were effectively isothermal,
that is, the plasma emission to which AIA is sensitive could not
be distinguished from isothermal emission, within measurement
uncertainties. One loop had both isothermal transition region and
multithermal coronal solutions. Another five loop segments require
multithermal plasma to reproduce the AIA observations. The five
remaining loop segments could not be separated reliably from the
background in the crucial non-171-Å AIA images required for temperature
analysis. We hope that the direction of coronal heating models and the
efforts modelers spend on various heating scenarios will be influenced
by these results.
Title: Modeling of Hot Plasma in the Solar Active Region Core
Authors: Asgari-Targhi, M.; Schmelz, J. T.; Imada, S.; Pathak, S.;
Christian, G. M.
Bibcode: 2015ApJ...807..146A
Altcode:
Magnetically confined plasma with temperatures ≥slant 5 {MK} are a
feature of hot coronal loops observed in the core of active regions. In
this paper, using observations and MHD modeling of coronal loops,
we investigate whether wave heating (Alternating Current) models can
describe the high temperature loops observed in the active region
of 2012 September 7. We construct three-dimensional MHD models for
the Alfvén wave turbulence within loops with high temperature. We
find that for the Alfvén waves to create enough turbulence to
heat the corona, the rms velocity at the footpoints must be 5-6 {km}
{{{s}}}-1. We conclude that the Alfvén wave turbulence model
may be a candidate for explaining how the hot loops are heated, provided
the loops have a high velocity at their photospheric footpoints.
Title: Hot Plasma from Solar Active Region Cores: a Test of AC and
DC Coronal Heating Models?
Authors: Schmelz, J. T.; Asgari-Targhi, M.; Christian, G. M.; Dhaliwal,
R. S.; Pathak, S.
Bibcode: 2015ApJ...806..232S
Altcode:
Direct current (DC) models of solar coronal heating invoke magnetic
reconnection to convert magnetic free energy into heat, whereas
alternating current (AC) models invoke wave dissipation. In both
cases the energy is supplied by photospheric footpoint motions. For
a given footpoint velocity amplitude, DC models predict lower average
heating rates but greater temperature variability when compared to AC
models. Therefore, evidence of hot plasma (T > 5 MK) in the cores
of active regions could be one of the ways for current observations
to distinguish between AC and DC models. We have analyzed data from
the X-Ray Telescope (XRT) and the Atmospheric Imaging Assembly for 12
quiescent active region cores, all of which were observed in the XRT
Be_thick channel. We did Differential Emission Measure (DEM) analysis
and achieved good fits for each data set. We then artificially truncated
the hot plasma of the DEM model at 5 MK and examined the resulting
fits to the data. For some regions in our sample, the XRT intensities
continued to be well-matched by the DEM predictions, even without the
hot plasma. This truncation, however, resulted in unacceptable fits
for the other regions. This result indicates that the hot plasma is
present in these regions, even if the precise DEM distribution cannot
be determined with the data available. We conclude that reconnection
may be heating the hot plasma component of these active regions.
Title: What can observations tell us about coronal heating?
Authors: Schmelz, J. T.; Winebarger, A. R.
Bibcode: 2015RSPTA.37340257S
Altcode:
The actual source of coronal heating is one of the longest standing
unsolved mysteries in all of astrophysics, but it is only in
recent years that observations have begun making significant
contributions. Coronal loops, their structure and sub-structure,
their temperature and density details, and their evolution with time,
may hold the key to solving this mystery. Because spatial resolution
of current observatories cannot resolve fundamental scale lengths,
information about the heating of the corona must be inferred from
indirect observations. Loops with unexpectedly high densities and
multi-thermal cross-field temperatures were not consistent with results
expected from steady uniform heating models. The hot (T>5 MK) plasma
component of loops may also be a key observation; a new sounding rocket
instrument called the Marshall Grazing Incidence X-ray Spectrometer
will specifically target this observable. Finally, a loop is likely
to be a tangle of magnetic strands. The High Resolution Coronal Imager
observed magnetic braids untwisting and reconnecting, dispersing enough
energy to heat the surrounding plasma. The existence of multi-thermal,
cooling loops and hot plasma provides observational constraints that
all viable coronal heating models will need to explain.
Title: Hot Topic, Warm Loops, Cooling Plasma? Multithermal Analysis
of Active Region Loops
Authors: Schmelz, J. T.; Pathak, S.; Brooks, D. H.; Christian, G. M.;
Dhaliwal, R. S.
Bibcode: 2014ApJ...795..171S
Altcode:
We have found indications of a relationship between the differential
emission measure (DEM) weighted temperature and the cross-field DEM
width for coronal loops. The data come from the Hinode X-ray Telescope,
the Hinode EUV Imaging Spectrometer, and the Solar Dynamics Observatory
Atmospheric Imaging Assembly. These data show that cooler loops tend to
have narrower DEM widths. If most loops observed by these instruments
are composed of bundles of unresolved magnetic strands and are only
observed in their cooling phase, as some studies have suggested,
then this relationship implies that the DEM of a coronal loop narrows
as it cools. This could imply that fewer strands are seen emitting
in the later cooling phase, potentially resolving the long standing
controversy of whether the cross-field temperatures of coronal loops
are multithermal or isothermal.
Title: The Flow-chart Loop: Temperature, Density, and Cooling
Observables Supporting Nanoflare Coronal Heating Models
Authors: Schmelz, J. T.; Pathak, S.; Dhaliwal, R. S.; Christian,
G. M.; Fair, C. B.
Bibcode: 2014ApJ...795..139S
Altcode:
We have tested three controversial properties for a target loop
observed with the Atmospheric Imaging Assembly: (1) overdense loops; (2)
long-lifetime loops; and (3) multithermal loops. Our loop is overdense
by a factor of about 10 compared to results expected from steady uniform
heating models. If this were the only inconsistency, our loop could
still be modeled as a single strand, but the density mismatch would
imply that the heating must be impulsive. Moving on to the second
observable, however, we find that the loop lifetime is at least an
order of magnitude greater than the predicted cooling time. This
implies that the loop cannot be composed of a single flux tube, even
if the heating were dynamic, and must be multi-stranded. Finally,
differential emission measure analysis shows that the cross-field
temperature of the target loop is multithermal in the early and middle
phases of its lifetime, but effectively isothermal before it fades from
view. If these multithermal cooling results are found to be widespread,
our results could resolve the original coronal loop controversy of
"isothermal" versus "multithermal" cross-field temperatures. That is,
the cross-field temperature is not always "multithermal" nor is it
always "isothermal," but might change as the loop cools. We find that
the existence and evolution of this loop is consistent with predictions
of nanoflare heating.
Title: Grand Unified Speculation: Coronal Cooling & Multi-thermal
Analysis of AIA Loops
Authors: Schmelz, Joan T.
Bibcode: 2014AAS...22432327S
Altcode:
We have tested three controversial properties for a target loop
observed with the Atmospheric Imaging Assembly: (1) overdense loops;
(2) long-lifetime loops; and (3) multithermal loops. Our loop is
overdense by a factor of about 10 compared to results expected from
steady uniform heating models. If this were the only inconsistency, our
loop could still be modeled as a single strand, but the density mismatch
would imply that the heating must be impulsive. Moving on to the second
observable, however, we find that the loop lifetime is at least an order
of magnitude greater than the predicted cooling time. This implies that
the loop cannot be composed of a single flux tube, even if the heating
were dynamic, and must be multi-stranded. Finally, differential emission
measure analysis shows that the cross-field temperature of the target
loop is multithermal in the early and middle phases of its lifetime,
but isothermal before it fades from view. If these multithermal cooling
results are found to be widespread, our results could resolve the
original coronal loop controversy of isothermal versus multithermal
cross-field temperatures. That is, the cross-field temperature is not
always multithermal nor is it always isothermal, but changes as the
loop cools.
Title: Bright Points: Multithermal Analysis as a Test of Steady
Heating Models
Authors: Schmelz, J. T.; Winebarger, A. R.; Kimble, J. A.; Pathak,
S.; Golub, L.; Jenkins, B. S.; Worley, B. T.
Bibcode: 2013ApJ...770..160S
Altcode:
X-ray bright points are small, million-degree features in the solar
atmosphere composed of short coronal loops. They are magnetically
driven structures associated with photospheric magnetic bipoles. Their
relatively small size and simple structure suggest they are ideal
candidates for comparisons with coronal heating models. In this paper,
we present the analysis of 12 bright points using data from the EUV
Imaging Spectrometer on Hinode and the Michelson Doppler Imager on
Solar and Heliospheric Observatory. Using the spectroscopy data, we
construct differential emission measure (DEM) curves, calculate the
electron density, and find DEM-weighted temperatures. In addition,
we determine the most likely ionization balance. Using the magnetic
field observations, we complete potential field extrapolations of the
magnetograms and estimate the loop lengths. Using this information,
we construct models assuming the bright points are formed of hundreds
of strands, each heated steadily and uniformly. We formulate the models
so that the observed emission measure distribution is matched within a
few percent. We then compare the densities determined from the models,
(1.4-5.0) × 109, to those calculated from spectral data,
(0.6-2.0) × 109. We find the majority of bright points
do not agree with steady uniform heating models; instead they are
underdense relative to their expected density by a factor of 0.16-0.82.
Title: Multithermal Analysis of Coronal Loops Using SDO-AIA Data
Authors: Schmelz, Joan T.; Pathak, S.
Bibcode: 2013AAS...22211603S
Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
is designed to provide an unprecedented view of the solar corona. The
six coronal filters peak at different temperatures and cover the entire
active region temperature range, making AIA ideal for multi-thermal
analysis. Temperature analysis relies on the instrument response
functions, sensitivity of each filter with respect to temperature. These
response functions are constructed by convolving the instrument
effective areas with a synthetic coronal spectrum calculated at each
relevant temperature. Each coronal spectrum relies on the data tabulated
in the CHIANTI atomic physics database. Recent upgrades to CHIANTI
have resulted in more complete calculations of the synthetic spectra in
the AIA wavelength bands, especially near 94 and 131 angstroms. These
advances have led to improved results for the Differential Emission
Measure analysis of coronal loop cross-field temperatures calculated
from AIA data. These improved results will be presented.
Title: Atmospheric Imaging Assembly Observations of Coronal Loops:
Cross-field Temperature Distributions
Authors: Schmelz, J. T.; Jenkins, B. S.; Pathak, S.
Bibcode: 2013ApJ...770...14S
Altcode:
We construct revised response functions for the Atmospheric Imaging
Assembly (AIA) using the new atomic data, ionization equilibria, and
coronal abundances available in CHIANTI 7.1. We then use these response
functions in multithermal analysis of coronal loops, which allows us
to determine a specific cross-field temperature distribution without
ad hoc assumptions. Our method uses data from the six coronal filters
and the Monte Carlo solutions available from our differential emission
measure (DEM) analysis. The resulting temperature distributions are not
consistent with isothermal plasma. Therefore, the observed loops cannot
be modeled as single flux tubes and must be composed of a collection
of magnetic strands. This result is now supported by observations from
the High-resolution Coronal Imager, which show fine-scale braiding of
coronal strands that are reconnecting and releasing energy. Multithermal
analysis is one of the major scientific goals of AIA, and these results
represent an important step toward the successful achievement of that
goal. As AIA DEM analysis becomes more straightforward, the solar
community will be able to take full advantage of the state-of-the-art
spatial, temporal, and temperature resolution of the instrument.
Title: Atmospheric Imaging Assembly Response Functions: Solving the
Fe VIII Problems with Hinode EIS Bright Point Data
Authors: Schmelz, J. T.; Jenkins, B. S.; Kimble, J. A.
Bibcode: 2013SoPh..283..325S
Altcode: 2013arXiv1301.1929S
The Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory is a state-of-the-art imager with the potential to
perform an unprecedented time-dependent multi-thermal analysis at
every pixel on scales that are short compared to the radiative and
conductive cooling times. Recent results, however, have identified
missing spectral lines in the CHIANTI atomic physics database, which
is used to construct the instrument response functions. This is not
surprising since the wavelength range from 90 Å to 140 Å has rarely
been observed with solar spectrometers, and atomic data for many of
these ions are simply not available in the literature. We have performed
a differential emission measure analysis using simultaneous AIA and
Hinode/EIS observations of six X-ray bright points. Our results not
only support the conclusion that CHIANTI is incomplete near 131 Å,
but more importantly, suggest that the peak temperature of the Fe
VIII emissivity/response is likely to be closer to log T=5.8 than to
the current value of log T=5.7. Using a revised emissivity/response
calculation for Fe VIII, we find that observed AIA 131-Å flux can
be underestimated by ≈ 1.25, lower than previous comparisons. With
these adjustments, not only the AIA 131-Å data, but also the EIS Fe
VIII lines, match the remainder of the bright-point data better. In
addition, we find that CHIANTI is reasonably complete in the AIA
171- and 193-Å bands. For the AIA 211-, 335-, and 94-Å channels,
we recommend that more work be done with AIA-EIS DEM comparisons using
observations of active-region cores, i.e. coronal structures with more
emission measure at warmer temperatures than our bright points. Then
a variety of EIS iron lines could be directly compared with AIA data.
Title: Point-spread Functions for the Extreme-ultraviolet Channels
of SDO/AIA Telescopes
Authors: Poduval, B.; DeForest, C. E.; Schmelz, J. T.; Pathak, S.
Bibcode: 2013ApJ...765..144P
Altcode:
We present the stray-light point-spread functions (PSFs) and their
inverses we characterized for the Atmospheric Imaging Assembly (AIA) EUV
telescopes on board the Solar Dynamics Observatory (SDO) spacecraft. The
inverse kernels are approximate inverses under convolution. Convolving
the original Level 1 images with them produces images with improved
stray-light characteristics. We demonstrate the usefulness of
these PSFs by applying them to two specific cases: photometry and
differential emission measure (DEM) analysis. The PSFs consist
of a narrow Gaussian core, a diffraction component, and a diffuse
component represented by the sum of a Gaussian-truncated Lorentzian
and a shoulder Gaussian. We determined the diffraction term using the
measured geometry of the diffraction pattern identified in flare images
and the theoretically computed intensities of the principal maxima of
the first few diffraction orders. To determine the diffuse component,
we fitted its parameterized model using iterative forward-modeling of
the lunar interior in the SDO/AIA images from the 2011 March 4 lunar
transit. We find that deconvolution significantly improves the contrast
in dark features such as miniature coronal holes, though the effect
was marginal in bright features. On a percentage-scattering basis,
the PSFs for SDO/AIA are better by a factor of two than that of the
EUV telescope on board the Transition Region And Coronal Explorer
mission. A preliminary analysis suggests that deconvolution alone does
not affect DEM analysis of small coronal loop segments with suitable
background subtraction. We include the derived PSFs and their inverses
as supplementary digital materials.
Title: Deeper by the Dozen: Understanding the Cross-field Temperature
Distributions of Coronal Loops
Authors: Schmelz, J. T.; Pathak, S.; Jenkins, B. S.; Worley, B. T.
Bibcode: 2013ApJ...764...53S
Altcode:
Spectroscopic analysis of coronal loops has revealed a variety
of cross-field temperature distributions. Some loops appear to be
isothermal while others require multithermal plasma. The EUV Imaging
Spectrometer on Hinode has the spatial resolution and temperature
coverage required for differential emission measure (DEM) analysis
of coronal loops. Our results also use data from the X-Ray Telescope
on Hinode as a high-temperature constraint. Of our 12 loops, two
were post-flare loops with broad temperature distributions, two were
narrow but not quite isothermal, and the remaining eight were in the
mid range. We consider our DEM methods to be a significant advance over
previous work, and it is also reassuring to learn that our findings are
consistent with results available in the literature. For the quiescent
loops analyzed here, 10 MK plasma, a signature of nanoflares, appears to
be absent at a level of approximately two orders of magnitude down from
the DEM peak. We find some evidence that warmer loops require broader
DEMs. The cross-field temperatures obtained here cannot be modeled
as single flux tubes. Rather, the observed loop must be composed of
several or many unresolved strands. The plasma contained in each of
these strands could be cooling at different rates, contributing to
the multithermal nature of the observed loop pixels. An important
implication of our DEM results involves observations from future
instruments. Once solar telescopes can truly resolve X-ray and
EUV coronal structures, these images would have to reveal the loop
substructure implied by our multithermal results.
Title: Deriving Plasma Densities and Elemental Abundances from SERTS
Differential Emission Measure Analysis
Authors: Schmelz, J. T.; Kimble, J. A.; Saba, J. L. R.
Bibcode: 2012ApJ...757...17S
Altcode:
We use high-resolution spectral emission line data obtained by the SERTS
instrument during three rocket flights to demonstrate a new approach
for constraining electron densities of solar active region plasma. We
apply differential emission measure (DEM) forward-fitting techniques
to characterize the multithermal solar plasma producing the observed
EUV spectra, with constraints on the high-temperature plasma from the
Yohkoh Soft X-ray Telescope. In this iterative process, we compare line
intensities predicted by an input source distribution to observed line
intensities for multiple iron ion species, and search a broad range
of densities to optimize χ2 simultaneously for the many
available density-sensitive lines. This produces a density weighted
by the DEM, which appears to be useful for characterizing the bulk
of the emitting plasma over a significant range of temperature. This
"DEM-weighted density" technique is complementary to the use of
density-sensitive line ratios and less affected by uncertainties in
atomic data and ionization fraction for any specific line. Once the
DEM shape and the DEM-weighted density have been established from the
iron lines, the relative elemental abundances can be determined for
other lines in the spectrum. We have also identified spectral lines
in the SERTS wavelength range that may be problematic.
Title: The Cold Shoulder: Emission Measure Distributions of Active
Region Cores
Authors: Schmelz, J. T.; Pathak, S.
Bibcode: 2012ApJ...756..126S
Altcode:
The coronal heating mechanism for active region core loops is difficult
to determine because these loops are often not resolved and cannot
be studied individually. Rather, we concentrate on the "inter-moss"
areas between loop footpoints. We use observations from the Hinode
EUV Imaging Spectrometer and the X-Ray Telescope to calculate the
emission measure distributions of eight inter-moss areas in five
different active regions. The combined data sets provide both high-
and low-temperature constraints and ensure complete coverage in the
temperature range appropriate for active regions. For AR 11113, the
emission can be modeled with heating events that occur on timescales
less than the cooling time. The loops in the core regions appear to
be close to equilibrium and are consistent with steady heating. The
other regions studied, however, appear to be dominated by nanoflare
heating. Our results are consistent with the idea that active region age
is an important parameter in determining whether steady or nanoflare
heating is primarily responsible for the core emission, that is,
older regions are more likely to be dominated by steady heating,
while younger regions show more evidence of nanoflares.
Title: Spatial and Thermal Study of an Isolated Loop with XRT and EIS
Authors: Saar, S. H.; Schmelz, J. T.; Kashyap, V. L.
Bibcode: 2012ASPC..454..241S
Altcode:
We use multi-filter contemporaneous XRT and EIS observations of a
small active region to study the spatial and thermal properties of an
isolated quiescent loop. We study the loop as a whole, in segments,
in transverse cuts, and point-by-point, always with some form of
"background" subtraction. We find the loop DEM is not-isothermal, but
is also not extremely broad, with ≍96% of the EM between 6.2 ≤ log
T ≤ 6.7, and an EM-weighted average temperature of log T = 6.48 ±
0.16. There is some evidence for a gradual change in temperature along
the loop, with log T increasing by ≍0.1 from the foot points to the
peak. Including EIS data helps better constrain the EM at low T. Future
work includes combining the analysis with contemporaneous RHESSI data
and to explore XRT-EIS-RHESSI cross-calibration at AR temperatures.
Title: Composition of the Solar Corona, Solar Wind, and Solar
Energetic Particles
Authors: Schmelz, J. T.; Reames, D. V.; von Steiger, R.; Basu, S.
Bibcode: 2012ApJ...755...33S
Altcode:
Along with temperature and density, the elemental abundance is a basic
parameter required by astronomers to understand and model any physical
system. The abundances of the solar corona are known to differ from
those of the solar photosphere via a mechanism related to the first
ionization potential of the element, but the normalization of these
values with respect to hydrogen is challenging. Here, we show that the
values used by solar physicists for over a decade and currently referred
to as the "coronal abundances" do not agree with the data themselves. As
a result, recent analysis and interpretation of solar data involving
coronal abundances may need to be revised. We use observations from
coronal spectroscopy, the solar wind, and solar energetic particles
as well as the latest abundances of the solar photosphere to establish
a new set of abundances that reflect our current understanding of the
coronal plasma.
Title: SDO-AIA Response Functions: Insights and Updates from Hinode
EIS Bright Point Data
Authors: Schmelz, Joan T.; Jenkins, B. S.
Bibcode: 2012AAS...22030902S
Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
is a state-of-the-art imager with the potential to do unprecedented
time-dependent multithermal analysis at every pixel on scales short
compared to the radiative and conductive cooling times. Recent results,
however, have identified shortcomings in the CHIANTI atomic physics data
base, which is used to construct the instrument response functions. We
have done Differential Emission Measure analysis using simultaneous AIA
and Hinode EIS observations of six X-ray bright points. Our results
not only support the conclusion that CHIANTI is incomplete near 131
A, but more importantly, suggest that the peak temperature of the
Fe VIII ionization fraction is likely to be closer to Log T = 5.8
than to the current value of Log T = 5.7. Using a revised ionization
balance calculation for Fe VIII, we find that the observed AIA 131-A
flux can be underestimated by 1.25, which is smaller than previous
comparisons. Making these adjustments brings not only the AIA 131-A
data but also the EIS Fe VIII lines into better agreement with the
remainder of the bright point data. In addition, we find that CHIANTI
is reasonably complete in the AIA 171- and 193-A bands.
Title: Fix Up Your AIA Images: A Complete Empirically Determined
Set of PSFs And Their Inverses for the AIA EUV Channels
Authors: DeForest, Craig; Poduval, B.; Schmelz, J.
Bibcode: 2012AAS...22020704D
Altcode:
All EUV imagers to date have had significant stray "light" in the
instrument point-spread function, taking the form of very broad,
low-level wings that disperse low, hard-to-measure amounts of radiance
into pixels far from the core of the PSF -- but whose integrated
intensity is a significant fraction of total received energy. This
results in a hazy appearance to EUV images of the Sun. Thus, to obtain
quantitative results from any EUV imager it is necessary to characterize
the PSF via forward modeling of a distributed object rather than only
(as is done on the ground) with a bright point source. We have
prepared and tested empirical PSF functions for each of the six EUV
channels in the SDO/AIA instrument, and present them here. We have
also prepared inverse PSFs that can be used for simple deconvolution
of stray light from Level 1 AIA data: simply convolve the subject data
with the inverse PSF to improve its stray light characteristics. We present our results and some sample images, together with the
imaging improvements afforded by known-PSF deconvolution. The bottom
line: AIA performs notably better than past instruments but still
requires care when interpreting "diffuse" brightness in the images. We
will demonstrate how deconvolution affects a particular photometric
application: DEM determination of different coronal features.
Title: Temperature Analysis of an Active Region Core Loop Using AIA
and XRT Data
Authors: Garst, Jennifer W.; Schmelz, J.; Kimble, J.
Bibcode: 2012AAS...22020208G
Altcode:
Data obtained on December 10, 2010 by both the Atmospheric Imaging
Assembly (AIA) and the X-Ray Telescope (XRT) are co-aligned and
appropriately scaled in order to do a differential emission measure
analysis of the combined data. This project uses Hybrid abundances
from Fludra & Schmelz and atomic data from the CHIANTI atomic
physics database to analyze an active region core loop and report on the
multithermal analysis of the combined data set. The loop being analyzed
is visible in the 94, 131, 171, 193, 211, 335 Å passbands on AIA;
and the Al-thick, Ti-poly, Al-mesh, Al-poly/Ti-poly, C-Poly/Ti-poly,
C-poly, Be-thin, Be-med, Al-med, and Al-poly filters on XRT. Solar
physics research at the University of Memphis is supported by NSF
ATM-0402729 as well as a Hinode subcontract from NASA/SAO.
Title: Multithermal Analysis of EIS Coronal Loops
Authors: Worley, Brian T.; Schmelz, J. T.; Pathak, S.
Bibcode: 2012AAS...22020116W
Altcode:
Four separate active regions containing multiple coronal loops were
selected for Differential Emission Measure (DEM) analysis from Hinode
Extreme ultraviolet Imaging Spectrometer (EIS) data. Each loop was
chosen based on its location and our ability to find a clean nearby area
for background subtraction. Our analysis uses iron lines with ionization
stages from Fe VIII to Fe XVI in the wavelength ranges 170 - 210 and
250 - 290 A. The twelve selected loops were then analyzed to determine
if their cross-field temperature was isothermal or multithermal. This
was accomplished by averaging the intensities of ten individual pixels
along the length of each loop and subtracting the average intensity of
ten nearby background pixels. We then used these background-subtracted
values, the density from a density-sensitive line ratio, and the
atomic data from the CHIANTI database to create a DEM curve for each
loop. Solar physics research at the University of Memphis is supported
by NSF ATM-0402729 as well as a Hinode subcontract from NASA/SAO.
Title: Combined XRT and AIA Differential Emission Measure Analysis
of Active Region Loops and Weak Flares
Authors: Saar, S. H.; Schmelz, J. T.
Bibcode: 2012ASPC..455..353S
Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) provides excellent new tools for exploring the thermal properties
of active regions at high cadence. The thick filters of the Hinode X-ray
Telescope (XRT), however, can add important additional constraints on
high temperature plasma, particularly in flares. We demonstrate the
power of combined AIA and XRT studies by conducting a joint AIA+XRT
differential emission measure analysis of an active region loop and
a weak flare.
Title: AIA Multithermal Analysis of Coronal Loops
Authors: Jenkins, Ben; Schmelz, J.
Bibcode: 2012AAS...22020715J
Altcode:
Simultaneous SDO Atmospheric Imaging Assembly (AIA) and Hinode EUV
Imaging Spectrometer (EIS) data of coronal bright points were used to
investigate the completeness of the CHIANTI atomic physics data base
near the wavelengths of the AIA coronal filters. Our results not only
support the conclusion that CHIANTI is incomplete near 131 A and 94 A,
but more importantly, suggest that the peak temperature of the Fe VIII
ionization fraction is closer to Log T = 5.8 than to Log T = 5.7. This
change affects both the 131-A and 171-A AIA response functions. These
empirically adjusted response functions were applied to loops that had
previously been analyzed using the default response functions. As a
result, the differential emission measure curves showed a more realistic
shape, with no significant response around Log T = 7.0. Similarly,
new loops have also been analyzed and similar results were obtained.
Title: Defining the "Blind Spot" of Hinode EIS and XRT Temperature
Measurements
Authors: Winebarger, Amy R.; Warren, Harry P.; Schmelz, Joan T.;
Cirtain, Jonathan; Mulu-Moore, Fana; Golub, Leon; Kobayashi, Ken
Bibcode: 2012ApJ...746L..17W
Altcode:
Observing high-temperature, low emission measure plasma is key to
unlocking the coronal heating problem. With current instrumentation,
a combination of EUV spectral data from Hinode Extreme-ultraviolet
Imaging Spectrometer (EIS; sensitive to temperatures up to 4 MK)
and broadband filter data from Hinode X-ray Telescope (XRT; sensitive
to higher temperatures) is typically used to diagnose the temperature
structure of the observed plasma. In this Letter, we demonstrate that a
"blind spot" exists in temperature-emission measure space for combined
Hinode EIS and XRT observations. For a typical active region core with
significant emission at 3-4 MK, Hinode EIS and XRT are insensitive
to plasma with temperatures greater than ~6 MK and emission measures
less than ~1027 cm-5. We then demonstrate that
the temperature and emission measure limits of this blind spot depend
upon the temperature distribution of the plasma along the line of sight
by considering a hypothetical emission measure distribution sharply
peaked at 1 MK. For this emission measure distribution, we find that
EIS and XRT are insensitive to plasma with emission measures less
than ~1026 cm-5. We suggest that a spatially and
spectrally resolved 6-24 Å spectrum would improve the sensitivity to
these high-temperature, low emission measure plasma.
Title: Using a Differential Emission Measure and Density Measurements
in an Active Region Core to Test a Steady Heating Model
Authors: Winebarger, Amy R.; Schmelz, Joan T.; Warren, Harry P.;
Saar, Steve H.; Kashyap, Vinay L.
Bibcode: 2011ApJ...740....2W
Altcode: 2011arXiv1106.5057W
The frequency of heating events in the corona is an important
constraint on the coronal heating mechanisms. Observations indicate
that the intensities and velocities measured in active region cores are
effectively steady, suggesting that heating events occur rapidly enough
to keep high-temperature active region loops close to equilibrium. In
this paper, we couple observations of active region (AR) 10955 made
with the X-Ray Telescope and the EUV Imaging Spectrometer on board
Hinode to test a simple steady heating model. First we calculate the
differential emission measure (DEM) of the apex region of the loops in
the active region core. We find the DEM to be broad and peaked around
3 MK. We then determine the densities in the corresponding footpoint
regions. Using potential field extrapolations to approximate the loop
lengths and the density-sensitive line ratios to infer the magnitude
of the heating, we build a steady heating model for the active region
core and find that we can match the general properties of the observed
DEM for the temperature range of 6.3 < log T < 6.7. This model,
for the first time, accounts for the base pressure, loop length,
and distribution of apex temperatures of the core loops. We find that
the density-sensitive spectral line intensities and the bulk of the
hot emission in the active region core are consistent with steady
heating. We also find, however, that the steady heating model cannot
address the emission observed at lower temperatures. This emission may
be due to foreground or background structures, or may indicate that the
heating in the core is more complicated. Different heating scenarios
must be tested to determine if they have the same level of agreement.
Title: Isothermal and Multithermal Analysis of Coronal Loops Observed
with Atmospheric Imaging Assembly. II. 211 Å Selected Loops
Authors: Schmelz, J. T.; Worley, B. T.; Anderson, D. J.; Pathak, S.;
Kimble, J. A.; Jenkins, B. S.; Saar, S. H.
Bibcode: 2011ApJ...739...33S
Altcode:
An important component of coronal loop analysis involves conflicting
results on the cross-field temperature distribution. Are loops
isothermal or multithermal? The Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamics Observatory was designed in part to
answer this question. AIA has a series of coronal filters that peak at
different temperatures and cover the entire active region temperature
range. These properties should make AIA ideal for multithermal analysis,
but recent results have shown that the response functions of two of
the filters, AIA 94 and 131 Å, are missing a significant number of
low-temperature emission lines. Here we analyze coronal loops from
several active regions that were chosen in the 211 Å channel of AIA,
which has a peak response temperature of log T = 6.3. The differential
emission measure (DEM) analysis of the 12 loops in our sample reveals
that using data from the 131 Å AIA filter distorts the results, and
we have no choice but to do the analysis without these data. The 94
Å data do not appear to be as important, simply because the chosen
loops are not visible in this channel. If we eliminate the 131 Å data,
however, we find that our DEM analysis is not well constrained on the
cool temperature end of six of our loops. The information revealed
by our 211 selected loops indicates that additional atomic data are
required in order to pin down the cross-field temperature distribution.
Title: Warm and Fuzzy: Temperature and Density Analysis of an Fe XV
EUV Imaging Spectrometer Loop
Authors: Schmelz, J. T.; Rightmire, L. A.; Saar, S. H.; Kimble, J. A.;
Worley, B. T.; Pathak, S.
Bibcode: 2011ApJ...738..146S
Altcode:
The Hinode EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) were
designed in part to work together. They have the same spatial resolution
and cover different but overlapping coronal temperature ranges. These
properties make a combined data set ideal for multithermal analysis,
where EIS provides the best information on the cooler corona (log T
< 6.5) and XRT provides the best information on the hotter corona
(log T > 6.5). Here, we analyze a warm non-flaring loop detected in
images made in a strong EIS Fe XV emission line with a wavelength of
284.16 Å and peak formation temperature of log T = 6.3. We perform
differential emission measure (DEM) analysis in three pixels at
different heights above the footpoint and find multithermal results
with the bulk of the emission measure in the range 6.0 < log T <
6.6. Analysis with the EIS lines alone gave a DEM with huge amounts of
emission measure at very high temperatures (log T >7.2) analysis
with XRT data alone resulted in a DEM that was missing most of the
cooler emission measure required to produce many of the EIS lines. Thus,
both results were misleading and unphysical. It was only by combining
the EIS and XRT data that we were able to produce a reasonable result,
one without ad hoc assumptions on the shape and range of the DEM itself.
Title: Observing Isothermal and Multithermal Coronal Loops using
SDO-AIA
Authors: Pathak, Sankaet; Schmelz, J.
Bibcode: 2011AAS...21822418P
Altcode: 2011BAAS..43G22418P
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) is designed to provide an unprecedented view of the solar
corona. The six coronal filters peak at different temperatures and
cover the entire active region temperature range, making AIA ideal for
multi-thermal analysis. Here, we chose several loops in different active
regions using images in the 211-A filter, which has a peak response
temperature of Log T = 6.3 K. The purpose of this analysis was to
determine if the loops were isothermal or multithermal. A few of our
12 loops have narrow temperature distributions, which appear consistent
with isothermal plasma. Other loops have intermediate-width temperature
distributions and must, therefore, be multi-stranded. The remaining
loops have unrealistically broad temperature distributions. However,
after a series of tests we found that this problem was the result of
missing low-temperature lines in the AIA 131-A channel. We, therefore,
repeated the analysis without the 131-A data; these loops then appeared
well constrained and multi-stranded.
Title: Resolving the Coronal Loop Controversy with AIA
Authors: Schmelz, Joan T.
Bibcode: 2011AAS...21821302S
Altcode: 2011BAAS..43G21302S
An important component of the coronal loop controversy involves
conflicting results on the diagnostic of one of the fundamental
properties: the cross-field temperature distribution. Are loops
isothermal or multithermal? Is the observed loop a single flux tube or
a collection of tangled magnetic strands? Resolving this controversy
has important implications for the coronal heating problem. The
coronal filters in the Atmospheric Imaging Assembly (AIA) aboard the
Solar Dynamics Observatory peak at different temperatures; the series
covers the entire active region temperature range, making AIA ideal for
multithermal analysis. Here we analyze coronal loops from several active
regions that have been observed by AIA. We find that a few of our loops
have narrow temperature distributions, which may be consistent with
isothermal plasma and can be modeled with a single flux tube. Other
loops, however, have broader temperature distributions, and are not
well-modeled by isothermal plasma; these appear to be multi-stranded.
Title: Analysis of Full Coronal Loops Observed with the Atmospheric
Imaging Assembly
Authors: Jenkins, Ben; Schmelz, J.
Bibcode: 2011AAS...21822419J
Altcode: 2011BAAS..43G22419J
Using EUV image data from the Atmospheric Imaging Assembly (AIA) on the
Solar Dynamics Observatory, we have done multi-thermal analysis along
the entire length of a collection of coronal loops. The six coronal
filters of AIA peak at different temperatures to produce data that
span the entire range of temperatures found in these loops. We have
selected cooler loops for this analysis that were chosen from images
taken with the 171-A filter, which has a peak response temperature
around 0.63 MK. The object of this investigation is to determine if
the plasma is isothermal or multi-thermal either (a) along the line
of sight or (b) along the length of the loop. We have used both an
automatic and a manual method to determine the Differential Emission
Measure (DEM) distribution at the loop apex and the foopoints. We find
that the temperature distribution is narrow, but not consistent with
isothermal plasma. In addition, the DEM-weighted temperature changes
much less along the loop length than predicted by standard RTV models.
Title: Cross-calibration Of EIS And XRT Using Coronal Bright Points
Authors: Kimble, Jason; Schmelz, J. T.
Bibcode: 2011AAS...21822421K
Altcode: 2011BAAS..43G22421K
The Extreme Ultraviolet Imaging Spectrometer and the X-Ray Telescope
aboard Hinode are designed to complement one another. This study
uses X-Ray Bright Points, simple emission features in the Solar
Corona, as sources of emission data for the purpose of obtaining a
cross-calibration factor for the two instruments. After calibrating
and co-aligning the data from each instrument individually, pixels
are selected within several coronal Bright Points. By analyzing this
equivalent data from both instruments, separate Differential Emission
Measures and Emission Measure Loci Plots are produced. These results
are then used to produce the desired instrument cross calibrations. The
use of Bright Points eliminates the need for prolonged and uncertain
background subtraction. Due to the simple thermal characteristics
of the Bright Points, this method could be used to calibrate other
instruments as well.
Title: Temperature Analysis of 171-A Coronal Loops
Authors: Worley, Brian T.; Schmelz, J. T.
Bibcode: 2011AAS...21822417W
Altcode: 2011BAAS..43G22417W
We searched the Atmospheric Imaging Assembly (AIA) database for
observations of active region coronal loops seen in the 171-A
images, which have a peak response temperature of Log T = 5.8. The
twelve resulting loops were then analyzed to determine whether the
cross-field temperature was isothermal or multithermal. A few of the
twelve loops could be recognized as isothermal based on the narrowness
of the resulting Differential Emission Measure (DEM) curves. These loops
could then be modeled as a single magnetic flux tube. Most of the loops,
however, were classified as multithermal as they have relatively broad
DEM curves. These loops were more likely composed of several or even
many magnetic strands, which might be tangled but are still able to
confine plasma of different temperatures.
Title: Isothermal and Multithermal Analysis of Coronal Loops Observed
with AIA
Authors: Schmelz, J. T.; Jenkins, B. S.; Worley, B. T.; Anderson,
D. J.; Pathak, S.; Kimble, J. A.
Bibcode: 2011ApJ...731...49S
Altcode:
The coronal filters in the Atmospheric Imaging Assembly (AIA) aboard
the Solar Dynamics Observatory peak at different temperatures; the
series covers the entire active region temperature range, making
AIA ideal for multithermal analysis. Here, we analyze coronal loops
from several active regions that have been observed by AIA. We have
specifically targeted cool loops (or at least loops with a cool
component) that were chosen in the 171 Å channel of AIA, which has a
peak response temperature of log T = 5.8. We wanted to determine if
the loops could be described as isothermal or multithermal. We find
that several of our 12 loops have narrow temperature distributions,
which may be consistent with isothermal plasma; these can be
modeled with a single flux tube. Other loops have intermediate-width
temperature distributions, appear well-constrained, and should be
multi-stranded. The remaining loops, however, have unrealistically
broad differential emission measures. We find that this problem is the
result of missing low-temperature lines in the AIA 131 Å channel. If
we repeat the analysis without the 131 Å data, these loops also appear
to be well-constrained and multi-stranded.
Title: SDO-AIA DEM: Initial Results
Authors: Schmelz, Joan T.
Bibcode: 2011AAS...21731903S
Altcode: 2011BAAS...4331903S
The Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics
Observatory has state-of-the-art spatial resolution and shows the
most detailed images of coronal loops ever observed. The series of
coronal filters peak at different temperatures, which span the range
of active regions. These features represent a significant improvement
over earlier coronal imagers and make AIA ideal for multi-thermal
analysis. Here we targeted a 171-A coronal loop in AR 11092 observed by
AIA on 2010 August 3. Isothermal analysis using the 171-to-193 ratio
gave a temperature of Log T = 6.1, similar to the results of EIT and
TRACE. Differential Emission Measure analysis, however, showed that the
plasma was multithermal, not isothermal, with a distribution that peaked
between Log T = 6.3 and 6.4. The result from the isothermal analysis,
which is the average of the true plasma distribution weighted by the
instrument response functions, appears to be deceptively low. These
results have potentially serious implications: EIT and TRACE results,
which use the same isothermal method, show substantially smaller
temperature gradients than predicted by standard models for loops
in hydrodynamic equilibrium and have been used as strong evidence in
support of footpoint heating models. These implications may have to
be re-examined in the wake of new results from AIA.
Title: Atmospheric Imaging Assembly Multithermal Loop Analysis:
First Results
Authors: Schmelz, J. T.; Kimble, J. A.; Jenkins, B. S.; Worley, B. T.;
Anderson, D. J.; Pathak, S.; Saar, S. H.
Bibcode: 2010ApJ...725L..34S
Altcode:
The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory has state-of-the-art spatial resolution and shows the most
detailed images of coronal loops ever observed. The series of coronal
filters peak at different temperatures, which span the range of active
regions. These features represent a significant improvement over earlier
coronal imagers and make AIA ideal for multithermal analysis. Here,
we targeted a 171 Å coronal loop in AR 11092 observed by AIA on
2010 August 3. Isothermal analysis using the 171-to-193 ratio gave
a temperature of log T ≈ 6.1, similar to the results of Extreme
ultraviolet Imaging Spectrograph (EIT) and TRACE. Differential emission
measure analysis, however, showed that the plasma was multithermal, not
isothermal, with the bulk of the emission measure at log T > 6.1. The
result from the isothermal analysis, which is the average of the true
plasma distribution weighted by the instrument response functions,
appears to be deceptively low. These results have potentially serious
implications: EIT and TRACE results, which use the same isothermal
method, show substantially smaller temperature gradients than predicted
by standard models for loops in hydrodynamic equilibrium and have been
used as strong evidence in support of footpoint heating models. These
implications may have to be re-examined in the wake of new results
from AIA.
Title: Multi-stranded and Multi-thermal Solar Coronal Loops: Evidence
from Hinode X-ray Telescope and EUV Imaging Spectrometer Data
Authors: Schmelz, J. T.; Saar, S. H.; Nasraoui, K.; Kashyap, V. L.;
Weber, M. A.; DeLuca, E. E.; Golub, L.
Bibcode: 2010ApJ...723.1180S
Altcode:
Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer
(EIS) on the Japanese/USA/UK Hinode spacecraft were used to investigate
the spatial and thermal properties of an isolated quiescent coronal
loop. We constructed differential emission measure (DEM) curves
using Monte Carlo based, iterative forward fitting algorithms. We
studied the loop as a whole, in segments, in transverse cuts, and
point-by-point, always with some form of background subtraction, and
find that the loop DEM is neither isothermal nor extremely broad, with
approximately 96% of the EM between 6.2 <=log T<= 6.7, and an
EM-weighted temperature of log T = 6.48 ± 0.16. We find evidence for
a gradual change in temperature along the loop, with log T increasing
only by ≈0.1 from the footpoints to the peak. The combine XRT-EIS
data set does a good job of constraining the temperature distribution
for coronal loop plasma. Our studies show that the strong constraints
at high and low temperatures provided by the combined data set are
crucial for obtaining reasonable solutions. These results confirm
that the observations of at least some loops are not consistent with
isothermal plasma, and therefore cannot be modeled with a single flux
tube and must be multi-stranded.
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: Automated Coronal-Loop Detection based on Contour Extraction
and Contour Classification from the SOHO/EIT Images
Authors: Durak, Nurcan; Nasraoui, Olfa; Schmelz, Joan
Bibcode: 2010SoPh..264..383D
Altcode: 2010SoPh..tmp...93D
Arch-shaped coronal loops that are isolated from the background are
typically acquired manually from massive online image databases to
be used in solar coronal research. The manual search for special
coronal loops is not only subject to human mistakes but is also time
consuming and tedious. In this study, we propose a completely automated
image-retrieval system that identifies coronal-loop regions located
outside of the solar disk from 17.1 nm EIT images. To achieve this
aim, we first apply image-preprocessing techniques to bring out loop
structures from their background and to reduce the effect of undesired
patterns. Then we extract principal contours from the solar image
regions. The geometrical attributes of the extracted principal
contours reveal the existence of loops in a given region. Our
completely automated decision-making procedure gives promising
results in separating the regions with loops from the regions without
loops. Based on our loop-detection procedure, we have developed an
automated image-retrieval tool that is capable of retrieving images
containing loops from a collection of solar images.
Title: A Pervasive Broad Component in H I Emission Line Profiles:
Temperature, Turbulence, or a Helium Signature?
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 2010AJ....139.2410V
Altcode:
Gaussian analysis of interstellar neutral hydrogen emission profiles
has revealed a pervasive broad component with a width on the order of
34 km s-1. When present, this component can most readily be
identified in high galactic latitude directions where the H I profiles
are either intrinsically weak or simple. Examination of published
data reveals that this characteristic line width has been found
in a variety of other H I features including compact high-velocity
clouds, very-high-velocity clouds, and the Magellanic Stream. When
its presence is accounted for in the analysis of H I profiles, other
families of line widths at 14 and 6 km s-1 are clearly
revealed. Possible mechanisms for producing this broad background
component are discussed, including temperature, turbulence, and the
critical ionization velocity effect. A line width on the order of
34 km s-1 would imply a kinetic temperature of 24,000 K,
too high to keep the gas neutral; hence it should not be observed
in H I emission spectra. Turbulent motions could explain a pervasive
broad component, but not why it always has the same numerical value in
various classes of H I emission line features. The critical ionization
velocity effect hypothesis is intriguing because 34 km s-1
is the value for helium. Clearly, this could be a coincidence but
the other prominent distribution peaks correspond to two families
of critical ionization velocities of abundant interstellar elements
including C, N, and O (about 14 km s-1) and metals (about 6
km s-1). Unfortunately, the mechanism by which this effect
operates, even in laboratory situations, is not clearly understood. It
is suggested that further investigation of the distribution of H I
component line widths by allowing for the existence of a pervasive
broad underlying component may cast a clearer light on this intriguing
phenomenon.
Title: Steady Heating Model of an Active Region Core
Authors: Winebarger, Amy R.; Schmelz, J. T.; Saar, S. H.; Kashyap,
V. L.; Warren, H. P.
Bibcode: 2010AAS...21640711W
Altcode: 2010BAAS...41R.861W
If the heating in an active region core is steady, the base pressure of
loop as well as its loop length determines exactly the apex temperature,
density and required heating rate. In this research, we analyze data
of an active region core that is observed with both Hinode XRT and
EIS instruments. We use the density sensitve Fe XII line ratios to
determine the base pressure of the loops and geometrical constraints
to determine the loop lengths. We use the hotter spectral lines coupled
with the XRT filter intensities to determine the differential emission
measure (DEM) of the core plasma. Using the base pressures and loop
lengths, we populate loops in a model active region to determine a
model DEM. We then compare this emission measure distribution to the
observed distribution.
Title: Introduction to Unconscious Bias
Authors: Schmelz, Joan T.
Bibcode: 2010AAS...21620201S
Altcode:
We all have biases, and we are (for the most part) unaware of them. In
general, men and women BOTH unconsciously devalue the contributions
of women. This can have a detrimental effect on grant proposals,
job applications, and performance reviews. Sociology is way ahead
of astronomy in these studies. When evaluating identical application
packages, male and female University psychology professors preferred
2:1 to hire "Brian” over "Karen” as an assistant professor. When
evaluating a more experienced record (at the point of promotion to
tenure), reservations were expressed four times more often when the
name was female. This unconscious bias has a repeated negative effect
on Karen's career. This talk will introduce the concept of unconscious
bias and also give recommendations on how to address it using an example
for a faculty search committee. The process of eliminating unconscious
bias begins with awareness, then moves to policy and practice, and
ends with accountability.
Title: Hinode XRT and EIS Multithermal Analysis of a Coronal Loop
Authors: Schmelz, Joan T.; Saar, S.; Kashyap, V.
Bibcode: 2010AAS...21640713S
Altcode: 2010BAAS...41..861S
Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer
(EIS) on Hinode were used to investigate the spatial and thermal
properties of an isolated quiescent coronal loop. We constructed
Differential Emission Measure (DEM) curves using Monte Carlo based
reconstruction algorithms. We studied the loop as a whole, in
segments, in transverse cuts, and point-by-point, always with some
form of background subtraction, and find that the loop DEM is neither
isothermal nor extremely broad, with 96% of the EM between 6.2 <
log T < 6.7, and an EM weighted average temperature of log T =
6.48 +/- 0.16. We find evidence for a gradual change in temperature
along the loop, with log T increasing by 0.1 from the footpoints to
the peak. The combined XRT-EIS data can do a good job of constraining
the temperature distribution for coronal loop plasma, but strong high-
and low- temperature constraints are crucial. Solar physics research
at the University of Memphis is supported by a Hinode subcontract from
NASA/SAO as well as NSF ATM-0402729.
Title: SDO-AIA Multithermal Analysis of Solar Coronal Features
Authors: Schmelz, Joan
Bibcode: 2010cosp...38.2861S
Altcode: 2010cosp.meet.2861S
Data from the Atmospheric Imaging Assembly (AIA) on the Solar
Dynamics Observatory (SDO) will be used to investigate the multithermal
properties of coronal features, including active regions, coronal loops,
and bright points. AIA takes full-Sun images in multiple wave-lengths
nearly simultaneously, with a spatial resolution of about 1 arcsec and a
cadence of about 10 seconds. The eight AIA passbands cover temperatures
from 20 thousand to 20 million de-grees, which allows us to image,
analyze, and model evolving coronal plasma with the best combination of
spatial, temporal, and thermal resolution ever achieved. Differential
Emission Measure analysis will be used to investigate the temperature
distributions of different coronal features. These results will be
presented and discussed.
Title: Coronal Loop Temperatures Obtained with Hinode XRT: A
Toothpaste-Tube Analogy
Authors: Schmelz, J. T.; Saar, S. H.; Weber, M. A.; Deluca, E. E.;
Golub, L.
Bibcode: 2009ASPC..415..299S
Altcode:
Multi-filter data observed by the Hinode X-Ray Telescope on 10 and
2007 July 13 were used to investigate the thermal properties of
coronal loops. At several positions along the loops, differential
emission measure analysis revealed a strong peak at log T = 6.1 (which
would predict the presence of a TRACE loop) and a much weaker hot
component (which we speculated might be a nanoflare signature). TRACE
observations, however, did not reveal the predicted loop, so we were
forced to re-examine our assumptions. Good differential emission measure
results require high- and low-temperature constraints, but our data sets
did not contain images from the thinnest and thickest filters, which
would be most likely to provide these constraints. Since differential
emission measure programs aim to match observed intensities and get
low values of χ2, they may place emission measure in high-
and low-temperature bins where it does not belong. We draw an analogy to
squeezing the toothpaste tube in the middle. Our analysis was repeated
for a loop observed on 2007 May 13 when the instrument acquired data
in 11 filters and filter combinations, including both the thinnest and
thickest filters. These results show that the loop is multi-thermal,
with significant emission measure in the range 6.0 < log T < 6.5.
Title: Some Like It Hot: Coronal Heating Observations from Hinode
X-ray Telescope and RHESSI
Authors: Schmelz, J. T.; Kashyap, V. L.; Saar, S. H.; Dennis, B. R.;
Grigis, P. C.; Lin, L.; De Luca, E. E.; Holman, G. D.; Golub, L.;
Weber, M. A.
Bibcode: 2009ApJ...704..863S
Altcode:
We have used Hinode X-Ray Telescope observations and RHESSI upper
limits together to characterize the differential emission measure
(DEM) from a quiescent active region. We find a relatively smooth DEM
curve with the expected active region peak at log T = 6.4. We also
find a high-temperature component with significant emission measure
at log T gsim 7. This curve is consistent with previous observations
of quiescent active regions in that it does not produce observable Fe
XIX lines. It is different from that generated with X-Ray Telescope
(XRT) data alone—RHESSI rules out the possibility of a separate
high-temperature component with a peak of approximately log T = 7.4. The
strength and position of the high-temperature peak in this XRT-only
analysis was, however, poorly determined; adding RHESSI flux upper
limits in the 4-13 keV energy range provide a strong high-temperature
constraint which greatly improves the multi-thermal findings. The
results of the present work as well as those from a growing number
of papers on this subject imply that our previous understanding of
the temperature distribution in active regions has been limited. Hot
plasma (log T ≈ 7) appears to be prevalent, although in relatively
small quantities as predicted by nanoflare models. Other models may
need to be adjusted or updated to account for these new results.
Title: Hinode X-Ray Telescope Detection of Hot Emission from Quiescent
Active Regions: A Nanoflare Signature?
Authors: Schmelz, J. T.; Saar, S. H.; DeLuca, E. E.; Golub, L.;
Kashyap, V. L.; Weber, M. A.; Klimchuk, J. A.
Bibcode: 2009ApJ...693L.131S
Altcode: 2009arXiv0901.3122S
The X-Ray Telescope (XRT) on the Japanese/USA/UK Hinode (Solar-B)
spacecraft has detected emission from a quiescent active region
core that is consistent with nanoflare heating. The fluxes from 10
broadband X-ray filters and filter combinations were used to construct
differential emission measure (DEM) curves. In addition to the expected
active region peak at log T = 6.3-6.5, we find a high-temperature
component with significant emission measure at log T > 7.0. This
emission measure is weak compared to the main peak—the DEM is down
by almost three orders of magnitude—which accounts of the fact
that it has not been observed with earlier instruments. It is also
consistent with spectra of quiescent active regions: no Fe XIX lines
are observed in a CHIANTI synthetic spectrum generated using the XRT
DEM distribution. The DEM result is successfully reproduced with a
simple two-component nanoflare model.
Title: Are Coronal Loops Isothermal or Multithermal?
Authors: Schmelz, J. T.; Nasraoui, K.; Rightmire, L. A.; Kimble,
J. A.; del Zanna, G.; Cirtain, J. W.; DeLuca, E. E.; Mason, H. E.
Bibcode: 2009ApJ...691..503S
Altcode: 2009arXiv0901.3281S
Surprisingly few solar coronal loops have been observed simultaneously
with TRACE and SOHO/Coronal Diagnostics Spectrometer (CDS), and even
fewer analyses of these loops have been conducted and published. The
SOHO Joint Observing Program 146 was designed in part to provide the
simultaneous observations required for in-depth temperature analysis of
active region loops and determine whether these loops are isothermal
or multithermal. The data analyzed in this paper were taken on 2003
January 17 of AR 10250. We used TRACE filter ratios, emission measure
loci, and two methods of differential emission measure analysis to
examine the temperature structure of three different loops. TRACE and
CDS observations agree that Loop 1 is isothermal with log T = 5.85,
both along the line of sight as well as along the length of the loop
leg that is visible in the CDS field of view. Loop 2 is hotter than
Loop 1. It is multithermal along the line of sight, with significant
emission between 6.2 < log T< 6.4, but the loop apex region
is out of the CDS field of view so it is not possible to determine
the temperature distribution as a function of the loop height. Loop
3 also appears to be multithermal, but a blended loop that is just
barely resolved with CDS may be adding cool emission to the Loop
3 intensities and complicating our results. So, are coronal loops
isothermal or multithermal? The answer appears to be yes.
Title: May Day! Coronal Loop Temperatures from the Hinode EUV
Imaging Spectrometer
Authors: Schmelz, J. T.; Scott, J.; Rightmire, L. A.
Bibcode: 2008ApJ...684L.115S
Altcode:
Data from the EUV Imaging Spectrometer on Hinode taken on 2007
May 1 (May Day) are used to investigate the thermal properties of
a coronal loop in AR 10953. For background subtraction, we have
taken cuts across the loop near the apex and the footpoint where the
background is relatively simple. Three density-sensitive line ratios
give statistically different answers, and emission measure loci plots
indicate that the loop plasma in not isothermal. Therefore, we have
done differential emission measure analysis on these data and found
a two-component model that can reproduce the background-subtracted
intensities. Since both of these components are broadened, they
cannot simply represent two isothermal strands of the EIS loop or
two isothermal loops along the line of sight. They could, however,
represent either two dominant ensembles of strands for the observed
EIS loop or the dominant ensemble of strands for two individual loops
along the line of sight. The TRACE image of the active region can
help us determine which of these models best describes the data. It
shows what appears to be two distinct loops that cross, one behind
the other, at the approximate position of our cut near the EIS loop
apex. It seemed natural to conclude, therefore, that the two-component
DEM distribution represents two ensembles of strands, one for each of
the loops seen in the TRACE image.
Title: Thermal Analysis of CDS Coronal Loops
Authors: Kimble, J. A.; Schmelz, J. T.; Nasraoui, K.; Rightmire,
L. A.; Andrews, J. M.; Cirtain, J. W.
Bibcode: 2008AGUSMSP31C..03K
Altcode:
The coronal loop data used for this analysis was obtained using the
Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric
Observatory on 2003 January 17 at 14:24:43 UT. We use the Chianti
atomic physics database and the hybrid coronal abundances to determine
temperatures and densities for positions along several loops. We
chose six pixels along each loop as well as background pixels. The
intensities of the background pixels are subtracted from each loop
pixel to isolate the emission from the loop pixel, and then spectral
lines with significant contributions to the loop intensities are
selected. The loops were then analyzed with a forward folding process
to produce differential emission measure (DEM) curves. Emission measure
loci plots and DEM automatic inversions are then used to verify those
conclusions. We find different results for each of these loops. One
appears to be isothermal at each loop position, and the temperature does
not change with height. The second appears to be multithermal at each
position and the third seems to be consistent with two DEM spikes,
which might indicate that there are two isothermal loops so close
together, that they are not resolved by CDS. Solar physics research
at the University of Memphis is supported by a Hinode subcontract from
NASA/SAO as well as NSF ATM-0402729.
Title: Coronal Loop Temperatures Obtained with Hinode EIS and XRT Data
Authors: Schmelz, J. T.
Bibcode: 2008AGUSMSP41C..01S
Altcode:
Data from the EUV Imaging Spectrometer (EIS) and the X-Ray Telescope
(XRT) on Hinode are used to investigate the thermal properties of
coronal loops. For background subtraction, we take a cut across the
loop in areas where the background is relatively simple. EIS gives
us density-sensitive line ratios, some of which give statistically
different answers for the same background-subtracted plasma. In many
cases, emission measure loci plots indicate that the loop plasma in
not isothermal. Therefore, we have used two methods of differential
emission measure analysis on these data. The first uses a forward
folding method with a manual manipulation of the curve to evaluate
the DEM based. Although this method is time-consuming, it forces
the user to understand both the limitations of the data as well as
the assumptions going into the analysis. The user has control of the
final DEM shape and no smoothing is required beyond that imposed by the
resolution of the G(T) functions (0.1 dex). The second method uses the
automatic inversion technique where the DEM curve is represented with
a series of spline knots that are repositioned interactively for more
control over the smoothness of the DEM curve. This method represents
the best of both worlds: the quickness of automatic inversion and
the control of manual manipulation. In both cases, the best fit is
determined from a chi-sq minimization of the differences between the
observed and predicted intensities. We test three different models and
compare the results: (1) an isothermal model; (2) a two-spike model;
and (3) a broad DEM. When available, we also use TRACE images to help
distinguish among these models. Solar physics research at the University
of Memphis is supported by a Hinode subcontract from NASA/SAO as well
as NSF ATM-0402729.
Title: HINODE-EIS: Thermal and Density Analysis of Coronal Loops
Authors: Rightmire, L. A.; Schmelz, J. T.; Scott, J.
Bibcode: 2008AGUSMSP31C..01R
Altcode:
Data was obtained using the EUV Imaging Spectrometer (EIS) instrument
on Hinode. The loop being analyzed was observed by EIS on 2007 May
1. The goal of this project is to analyze the data obtained by the
EIS instrument in order to determine the temperature and density
of the coronal loop. The background intensity was subtracted from
the loop pixel intensity in order to isolate the emission from the
loop. The spectral line intensities of each loop pixel were analyzed
to determine which spectral lines had any significant contribution to
the loop intensity. The observed intensities of these significant lines
were then used to create a differential emission measure (DEM) curve
to best fit the loop pixel emission. Density analysis was done using
the CHIANTI atomic physics database along with the measured intensity
ratios of density-sensitive lines. The DEM curves and density analysis
for the loop pixel indicate a multi-thermal temperature profile. Solar
physics research at the University of Memphis is supported by NSF
ATM-0402729 with Hinode subcontracted from NASA/SAO.
Title: Temperature and Density Analysis of a Coronal Loop Using EIS
Authors: Garst, J. W.; Schmelz, J. T.
Bibcode: 2008AGUSMSP31C..02G
Altcode:
The temperature analysis of coronal loops has produced contradictory
results. Image ratios from TRACE show substantially smaller temperature
gradients than predicted by standard models for loops in hydrodynamic
equilibrium. TRACE has state-of-the-art spatial resolution but limited
temperature coverage. On the other hand, the pixels of the Coronal
Diagnostics Spectrometer (CDS) on SOHO are larger but its temperature
resolution is state-of-the-art. Loop results from differential emission
measure analyses from CDS data have been questioned due to the resolving
power. Loop analysis could benefit greatly from observations by an
instrument with the spatial resolution of TRACE and the temperature
coverage of CDS. A spectrometer with (almost) these characteristics was
launched in September 2006 on the Japanese/USA/UK Hinode mission. The
EUV Imaging Spectrometer (EIS) is similar to CDS, observing emission
lines originating from the solar corona and upper transition region at
wavelength intervals in the extreme ultraviolet, but with a spatial
resolution that is almost as good as TRACE. Differential emission
measure and density analysis is done on the coronal loop data observed
by EIS on 01 June 2007. Results from CDS and TRACE analysis are compared
and discussed qualitatively. Solar physics research at the University
of Memphis is supported by a Hinode subcontract from NASA/SAO as well
as NSF ATM-0402729.
Title: Coronal Loop Temperatures Obtained with Hinode EIS and XRT Data
Authors: Schmelz, Joan
Bibcode: 2008cosp...37.2772S
Altcode: 2008cosp.meet.2772S
Data from the EUV Imaging Spectrometer (EIS) and the X-Ray Telescope
(XRT) on Hinode are used to investigate the thermal properties of
coronal loops. For background subtraction, we take a cut across the
loop in areas where the background is relatively simple. EIS gives
us densitysensitive line ratios, some of which give statistically
different answers for the same backgroundsubtracted plasma. In many
cases, emission measure loci plots indicate that the loop plasma in
not isothermal. Therefore, we have used two methods of differential
emission measure analysis on these data. The first uses a forward
folding method with a manual manipulation of the curve to evaluate
the DEM. Although this method is time-consuming, it forces the user to
understand both the limitations of the data as well as the assumptions
going into the analysis. The user has control of the final DEM shape
and no smoothing is required beyond that imposed by the resolution
of the G(T) functions (0.1 dex). The second method uses the automatic
inversion technique where the DEM curve is represented with a series of
spline knots that are repositioned interactively for more control over
the smoothness of the DEM curve. This method represents the best of both
worlds: the quickness of automatic inversion and the control of manual
manipulation. In both cases, the best fit is determined from a chi-sq
minimization of the differences between the observed and predicted
intensities. We test three different models and compare the results: (1)
an isothermal model; (2) a two-spike model; and (3) a broad DEM. When
available, we also use TRACE images to help distinguish among these
models. Solar physics research at the University of Memphis is supported
by a Hinode subcontract from NASA/SAO as well as NSF ATM-0402729.
Title: Coronal Loops: Isothermal or Multithermal?
Authors: Kimble, Jason; Schmelz, J. T.; Nasraoui, K.; Cirtain, J. W.;
Del Zanna, G.; DeLuca, E. E.; Mason, H. E.
Bibcode: 2007AAS...210.9120K
Altcode: 2007BAAS...39..207K
The coronal loop data used for this analysis were taken on 2003 January
17 at 14:24:45 UT by the Coronal Diagnostic Spectrometer (CDS) aboard
the Solar and Heliospheric Observatory. We use the Chianti atomic
physics data base and the hybrid coronal abundances to determine
temperatures and densities for positions along several loops. The
traditional method used to create our differential emission measure
(DEM) curves has been forward folding, but we are now using both
emission measure loci plots and DEM automatic inversion to support
and confirm the original conclusions. In this poster, we will look
specifically at the emission measure loci analysis of three loops
visible in the CDS data set. We find different results for each of
these loops. One of the loops seems to be composed of isothermal
plasma with Log T = 5.8 MK. The temperature does not appear to change
with position, from the footpoint to the loop leg. Unfortunately,
the loop top is outside the CDS field of view. Each pixel examined in
the second loop seems to require a multithermal DEM distribution. For
the third loop, the temperature increases and the density appears
to decrease with loop height, reminiscent of traditional hydrostatic
loop models. Solar physics research at the University of Memphis is
supported by NSF ATM-0402729 and NASA NNG05GE68G.
Title: SOHO-CDS: Thermal and Density Analysis of Coronal Loops
Authors: Rightmire, Lisa; Schmelz, J. T.; Cirtain, J. W.; Del Zanna,
G.; DeLuca, E. E.; Mason, H. E.
Bibcode: 2007AAS...210.9121R
Altcode: 2007BAAS...39..207R
Data was obtained using the Coronal Diagnostic Spectrometer (CDS)
instrument on the Solar and Heliospheric Observatory (SOHO). The goal
of this project is to analyze the data obtained by the CDS instrument
in order to determine the behavior of temperature and density of the
coronal loop progressing from the foot point and moving up the loop. The
loop being analyzed was observed by CDS on 2003 January 17 and the foot
point was located at solar coordinates (585,-472) arcsecs. A background
pixel and several pixels on the loop were selected. The background pixel
intensity was then subtracted from each loop pixel intensity in order to
isolate the emission from each loop pixel. The spectral line intensities
of each loop pixel were analyzed to determine which spectral lines
had any significant contribution to the loop intensity. The predicted
and observed intensities of these significant lines were then used to
create a differential emission measure (DEM) curve to best fit each
loop pixel emission. Comparison of the DEM curves for each loop pixel
indicates that the temperature increases and the density decreases,
while progressing up the loop. Solar physics research at the University
of Memphis is supported by NSF ATM-0402729 and NASA NNG05GE68G.
Title: Coronal Heat: Solar Loop Temperatures from TRACE Triple-Filter
Data
Authors: Schmelz, J. T.; Kashyap, V. L.; Weber, M. A.
Bibcode: 2007ApJ...660L.157S
Altcode:
The Transition Region and Coronal Explorer (TRACE) has state-of-the-art
spatial resolution and shows the most detailed images of coronal loops
ever observed. The temperatures of these loops are primarily derived
from the 171 to 195 Å filter ratio, with data from the third filter at
284 Å used by several authors to improve the precision of the derived
temperatures. Most of these studies assume that the plasma is isothermal
and model the loops primarily as uniform temperature structures with
footpoint-dominated heating. However, these triple-filter data are
insufficient to constrain the plasma temperature and cannot be used to
determine the isothermality or otherwise of coronal loop structures. We
show this explicitly by constructing differential emission measures
with these same triple-filter data using a sophisticated Markov-chain
Monte Carlo-based reconstruction algorithm. We find that these TRACE
data cannot, in general, limit the temperature distribution for coronal
loop plasma. In other words, many different temperature distributions
(isothermal, broad, sloped, etc.) can reproduce the observed fluxes,
and the TRACE coronal data alone cannot determine which of these
distributions represents the actual coronal plasma.
Title: Are Coronal Loops Isothermal Or Multithermal? Yes!
Authors: Schmelz, Joan T.; Nasraoui, K.; Rightmire, L.; Garst, J.;
Kimble, J.; Cirtain, J.; DeLuca, E. E.; Del Zanna, G.; Mason, H.
Bibcode: 2007AAS...210.9431S
Altcode: 2007BAAS...39..222S
Analysis of loops observed with the Coronal Diagnostics Spectrometer
(CDS) and the Transition Region and Coronal Explorer (TRACE) reveal
examples of both isothermal and multithermal plasma. These data
were taken on 2003 January 17, and since the loops are on the disk,
a lot of work was done on the details of background subtraction. The
background-subtracted CDS intensities were analyzed using three
methods: (1) Emission Measure Loci, (2) Forward-Folding DEM, and (3)
Automatic-Inversion DEM. The first loop appears to be isothermal,
with Log T = 5.8 MK. The forward-folding DEM shows a spike at this
temperature and the EM Loci curves all intersect at this point. The
automatic-inversion DEM results are broadened, however, as a result
of the smoothing required for this method. This loop has a uniform
temperature along the segment visible in the CDS field of view,
and this result is confirmed using the TRACE data. The pixels along
the second loop do not appear to be isothermal. The EM Loci curves
do not intersect at a single point and both DEM methods show a broad
curve. Other loops in this data set as well as loop evolution will be
investigated if time permits. Solar physics research at the University
of Memphis is supported by NSF ATM-0402729 and NASA NNG05GE68G.
Title: Differential Emission Measurements on Sparse Raster Data
from SOHO-CDS
Authors: Garst, Jennifer W.; Schmelz, J. T.; Nasraoui, K.; Cirtain,
J. W.; DeLuca, E. E.; Del Zanna, G.; Mason, H. E.
Bibcode: 2007AAS...210.2517G
Altcode: 2007BAAS...39..133G
Two types of rasters were taken on 2003 January 17 with the Solar and
Heliospheric Observatory’s Coronal Diagnostic Spectrometer. The
first type contains a continuous image of coronal loops under
investigation while the second, the ‘sparse raster,’ was taken at
spatial intervals in order to simulate enhanced time resolution. With
this technique, intensities in 14 passbands were collected at fixed
positions on the solar disk every 7 minutes. The start time for the
CDS observations was 06:51:27 UT and the observing sequences ran for
7 hours. The continuous rasters were interspersed with the sparse
rasters. All the rasters were then co-aligned and a loop pixel and a
background pixel were selected for detailed analysis. Differential
emission measure was performed on the background-subtracted CDS
intensities to determine the temporal evolution of the loop pixel
plasma. Solar physics research at the University of Memphis is supported
by NSF ATM-0402729 and NASA NNG05GE68G.
Title: Coronal Diagnostics Spectrometer Observations of Coronal Loops
Authors: Nasraoui, Kaouther; Schmelz, J. T.; Cirtain, J. W.; Del Zanna,
G.; DeLuca, E. E.; Mason, H. E.
Bibcode: 2007AAS...210.9122N
Altcode: 2007BAAS...39..207N
Two side by side loops from the solar disk were analyzed. These two
loops were observed with the Coronal Diagnostics Spectrometer on
SOHO on 2003 January 17. The first loop was best seen in Mg IX at
a wavelength of 368 angstroms and a peak formation temperature of
Log T = 6.0. Seven pixels on the loop and one background pixel were
chosen. The intensity of the background pixel was subtracted from each
of the loop pixels. Only the lines that had a significant intensity
after background subtraction were considered. A differential emission
measure (DEM) curve was constructed for the background subtracted data
using the forward folding technique. The DEM for most of these pixels
had a spike shape at Log T equal to 5.85. This result shows that the
loop is isothermal at most of these pixels. The second loop was best
seen in Si XII at a wavelength of 520 angstroms and a peak formation
temperature of Log T = 6.3. The same procedure was followed for the
data analysis. After background subtraction only some hot lines had a
significant intensity and a DEM curve was constructed for each loop
pixel. This time the DEM is broader with a shape that shows that
the loop plasma is multithermal with a log temperature range of 6.1
to 6.5. Solar physics research at the University of Memphis is
supported by NSF ATM-0402729 and NASA NNG05GE68G.
Title: Coronal Diagnostic Spectrometer Observations of Isothermal
and Multithermal Coronal Loops
Authors: Schmelz, J. T.; Nasraoui, K.; Del Zanna, G.; Cirtain, J. W.;
DeLuca, E. E.; Mason, H. E.
Bibcode: 2007ApJ...658L.119S
Altcode:
A data set obtained on 2003 January 17 with the Coronal Diagnostic
Spectrometer (CDS) shows two loops sitting side by side on the solar
disk. These loops are oriented along the CDS slit, so all pixels in
each loop were observed simultaneously. So, although the instrument
has a relatively slow time cadence, changes as a function of time
that may occur during the CDS raster buildup will not affect the loop
temperature results. Differential emission measure (DEM) analysis
using a forward-folding technique shows different results for the
two loops. For the first loop, the intensities of the lines that
remain after background subtraction are well fit with a DEM curve that
collapses to a single spike. In other words, the loop plasma at this
location is isothermal. This analysis is confirmed with an emission
measure loci method and agrees with the results obtained recently
by other authors that show that the moderate spatial resolution
of CDS can detect isothermal structures. For the second loop, the
background-subtracted line intensities require a broad DEM, not
consistent with isothermal plasma. This conclusion is confirmed with
an automatic-inversion DEM method. In this Letter, we specifically
address some of the concerns raised about CDS temperature analysis:
the slow CDS temporal resolution, the moderate CDS spatial resolution,
the inherent smoothing associated with DEM inversion, and line-of-sight
effects on the DEM distribution.
Title: Active Region Loops: Temperature Measurements as a Function
of Time from Joint TRACE and SOHO CDS Observations
Authors: Cirtain, J. W.; Del Zanna, G.; DeLuca, E. E.; Mason, H. E.;
Martens, P. C. H.; Schmelz, J. T.
Bibcode: 2007ApJ...655..598C
Altcode:
In this paper, we aim to quantitatively investigate the structure
and time variation of quiescent active region loop structures. We
coordinated a joint program of observations (JOP 146) using TRACE, to
obtain high-cadence EUV images, and SOHO CDS, to obtain spectroscopic
data. Loop intensities are used to determine temperature as a function
of time for a single loop, taking full account of the background
emission. In many locations, the emission measure loci are consistent
with an isothermal structure. However, the results indicate significant
changes in the loop temperature (between 1 and 2 MK) over the 6 hr
observing period. It is possible that the loop structures are composed
of multiple, independently heated strands with sizes less than the
resolution of the imager and spectrometer.
Title: The coronal loop controversy: TRACE analysis
Authors: Schmelz, J. T.; Roames, J. K.; Nasraoui, K.
Bibcode: 2007AdSpR..39.1497S
Altcode:
The temperature distribution along coronal loops provides an important
clue for solving the coronal heating problem. Recent analysis, however,
has produced conflicting results. Here, we analyze in detail one
component of this analysis - the effect of background subtraction
on the temperature of loops observed with the Transition Region
and Coronal Explorer ( TRACE). Specifically, we selected 10 coronal
loops that were visible in the TRACE 171 Å and 195 Å passbands. We
chose between 20 and 30 pixel along each loop and background pixels
to correspond with the loop pixels. Temperature analysis was done in
three different ways: (1) standard TRACE analysis of the loop pixels
with no background subtraction; (2) constant background subtraction
for each TRACE image; (3) pixel pair background subtraction. Each
method produced a temperature estimate for the selected pixels. We find
that a flat line is an excellent fit to the temperature results - the
analysis indicates that the temperature of the loop is uniform along
the length visible by TRACE. However, if we select random pixels and
plot the temperature results in the same way, these pixels indicate
that the temperature of this "structure" is also uniform. We conclude
therefore, that in the cases considered here, the image ratio analysis
does not produce a physically meaningful value of plasma temperature;
in addition, background subtraction makes no significant difference
to the temperatures results.
Title: Neon Lights Up a Controversy
Authors: Lippner, Lindsey; Schmelz, J. T.; Nasraoui, K.; Roames,
J. K.; Garst, J. W.
Bibcode: 2006SPD....37.0111L
Altcode: 2006BAAS...38..217L
The standard solar model and helioseismology measurements were
in goodagreement until recently when new, three-dimensional
hydrodynamiccalculations apparently reduced the metal content in the
solarphotosphere by a factor of 2. To once again reconcile theory
andobservation, it has been suggested that the solar Ne/O abundance
ratiocould be increased to 0.52 from the accepted value of 0.15. Since
neonis not observed in the solar photosphere, this suggestion could
not betested directly. However, a recent study of 21 stars observed by
theChandra X-ray telescope supported this correction with a value of
0.41for stellar Ne/O abundance. We have analyzed old data from the FCS
(FlatCrystal Spectrometer on board NASA's Solar Maximum Mission) archive
tosee if the results supported this new enhanced neon hypothesis. We
alsoexamined full-Sun X-ray spectra from the 1960's which show the
Sun as astar. Both of our analyses show that Ne/O abundance ratio
is consistentwith the currently accepted value of 0.15. We conclude
that the enhancedneon hypothesis cannot be used to reconcile theory
and observation.Solar physics research at the University of Memphis
is supported bygrants from NSF and NASA.
Title: Is TRACE's High Spatial Resolution High Enough for Isothermal
Temperature Analysis?
Authors: Garst, Jennifer W.; Schmelz, J. T.; Lippner, L. A.; Roames,
J. K.
Bibcode: 2006SPD....37.0118G
Altcode: 2006BAAS...38..218G
It has been suggested that TRACE may be able to resolve individual
isothermal coronal loop strands. If this is true, then isothermal
temperature analysis using filter ratios from TRACE data could provide
accurate measurements of the temperature of coronal loops. In this case,
it follows that EIT, with significantly lower spatial resolution, would
provide statistically different results for the same loop since the EIT
pixel would have to contain some flux from the background. We analyze
several loops for which data from both instruments are available in the
171, 195, and 284 A passbands and compare EIT and TRACE temperature
analysis results from both the 171:195 and 195:284 filter ratios. Do
our results suggest that TRACE's 0.5 arcsec spatial resolution is
substantial enough to provide accurate temperature analysis? Solar
physics research at the University of Memphis is supported by grants
from NSF and NASA.
Title: The Coronal Loop Controversy: Resolved!
Authors: Schmelz, Joan T.; Nasraoui, K.; Cirtain, J.; DeLuca, E.;
Del Zanna, G.; Mason, H.
Bibcode: 2006SPD....37.1701S
Altcode: 2006BAAS...38..245S
Critics have pointed out the shortcomings of CDS coronal loop
temperature analysis - the large pixel size and the slow time
cadence. It is these limitations, some say, that have produced
multithermal results for the loop observed with CDS on 1998 April
20, both along the line of sight and along the loop length. Analysis
of the CDS observations of AR 10250 from 2003 January 17, however,
seem to contradict these critics. Two loops sit side-by-side right
along the slit in this raster, so all pixels in each loop were
observed at the same time. As a result changes as a function of time
will not affect the temperature results. The first loop is observed
primarily in Mg IX (Log T = 6.0) and the second in Si XII (Log T =
6.3). Differential Emission Measure (DEM) analysis of background
subtracted line intensities of pixels in each loop show distinctly
different results. For the first loop, the intensities of the lines
that remain after background subtraction are well fit with a DEM that
collapses to a single spike. In other words, the loop plasma at this
location is isothermal. This proves that it is neither the DEM method
nor the CDS pixel size that produced the multithermal distributions
for the 1998 April 20 loop plasma. In addition the DEM distribution for
the second loop is similar to those produced for the 1998 April 20 loop
and is clearly inconsistent with isothermal plasma. Both distributions
change as a function of position along the loop, with the temperatures
increasing with loop height. Solar physics research at the University
of Memphis is supported by grants from NSF and NASA.
Title: Does TRACE Resolve Isothermal Coronal Loops?
Authors: Weber, Mark A.; Schmelz, J.; Kashyap, V.; Roames, J.
Bibcode: 2006SPD....37.0115W
Altcode: 2006BAAS...38..217W
Historically, increasing resolution of solar data has revealed ever
smaller length scales for both the thermodynamics and the magnetic
structure of the corona. Furthermore, the dynamics there are governed
by magnetohydrodynamic processes which are difficult to observe or
model. Recent results in the literature suggest that some coronal loops
with cross-sections near the resolution limits of the Transition Region
and Coronal Explorer (pixel size = 0.5 arc-seconds, or approx. 360 km)
are, in fact, isothermally homogeneous and thus may be identified as
elementary loop strands. This poster presents some ongoing work that
applies state-of-the-art estimation of differential emission measures in
order to evaluate these claims for a sample of loops. We find that the
data give no evidence to prefer the "isothermal" hypothesis over the
"multithermal" hypothesis. The authors are supported by the following
funds: contract SP02H820IR to the Lockheed-Martin Corp.; NSF grant
ATM-0402729; NASA grant NNG05GE68G; and NASA contracts NAS8-39073
and NAS8-03060.
Title: Multithermal Analysis of a SOHO/CDS Coronal Loop
Authors: Schmelz, J. T.; Martens, P. C. H.
Bibcode: 2006ApJ...636L..49S
Altcode: 2005astro.ph.11487S
The observations from 1998 April 20 taken with the Coronal Diagnostics
Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) of
a coronal loop on the limb have shown that the plasma was multithermal
along each line of sight investigated, both before and after background
subtraction. The latter result relied on emission measure (EM) loci
plots, but in this Letter, we used a forward-folding technique to
produce differential emission measure (DEM) curves. We also calculate
DEM-weighted temperatures for the chosen pixels and find a gradient
in temperature along the loop as a function of height that is not
compatible with the flat profiles reported by numerous authors for
loops observed with the EUV Imaging Telescope (EIT) on SOHO and
the Transition Region and Coronal Explorer (TRACE). We also find
discrepancies in excess of the mathematical expectation between some
of the observed and predicted CDS line intensities. We demonstrate
that these differences result from well-known limitations in our
knowledge of the atomic data and are to be expected. We further show
that the precision of the DEM is limited by the intrinsic width of
the ion emissivity functions that are used to calculate the DEM, which
for the EUV lines considered is of the order dlogT = 0.2-0.3. Hence,
we conclude that peaks and valleys in the DEM, while in principle not
impossible, cannot be confirmed from the data.
Title: The Cinderella loop project
Authors: Schmelz, J. T.; Beene, J.; Coyle, T.; Douglass, J.; Nasraoui,
K.; O'Connor, J.; Roames, J.; Scott, M.
Bibcode: 2006AdSpR..38.1529S
Altcode:
The solar loop that formed off the northeast limb of the Sun on 1999
November 6 (a.k.a. the Cinderella loop) is one of the few examples of
a loop on the limb observed with all three of the following imaging
instruments: the Transition Region and Coronal Explorer (TRACE), the
SOHO Extreme-ultraviolet Imaging Telescope (EIT), and the Yohkoh Soft
X-ray Telescope (SXT). In this project we investigate the temperature
differences that result when examining the Cinderella loop with
one instrument compared with another. For example, what temperature
differences result from the increased spatial resolution between the
two EUV imagers? More specifically, given that TRACE and EIT have
almost identical temperature response to coronal plasma, does the
different spatial resolution of TRACE (with 0.5″ pixels) and EIT
(with 2.6″ pixels) produce statistically different results? We
find that the answer is no, and that our results do not change after
background subtraction. In addition, the spatial resolution of EIT and
SXT is similar, but the temperature responses of the two instruments are
quite different. The two instruments do not seem to be viewing the same
loop strands, and the plasma temperature differences are significant.
Title: The Transparency of Solar Coronal Active Regions
Authors: Brickhouse, N. S.; Schmelz, J. T.
Bibcode: 2006ApJ...636L..53B
Altcode: 2005astro.ph.11683B
Resonance scattering has often been invoked to explain the disagreement
between the observed and predicted line ratios of Fe XVII λ15.01 to Fe
XVII λ15.26 (the ``3C/3D'' ratio). In this process photons of λ15.01,
with its much higher oscillator strength, are preferentially scattered
out of the line of sight, thus reducing the observed line ratio. Recent
laboratory measurements, however, have found significant inner-shell
Fe XVI lines at 15.21 and 15.26 Å, suggesting that the observed
3C/3D ratio results from blending. Given our new understanding of the
fundamental spectroscopy, we have reexamined the original solar spectra,
identifying the Fe XVI λ15.21 line and measuring its flux to account
for the contribution of Fe XVI to the λ15.26 flux. Deblending brings
the 3C/3D ratio into good agreement with the experimental ratio; hence,
we find no need to invoke resonance scattering. Low opacity in Fe XVII
λ15.01 also implies low opacity for Fe XV λ284.2, ruling out resonance
scattering as the cause of the fuzziness of TRACE and SOHO-EIT 284 Å
images. The images must, instead, be unresolved due to the large number
of structures at this temperature. Insignificant resonance scattering
implies that future instruments with higher spatial resolution could
resolve the active region plasma into its component loop structures.
Title: Neon Lights up a Controversy: The Solar Ne/O Abundance
Authors: Schmelz, J. T.; Nasraoui, K.; Roames, J. K.; Lippner, L. A.;
Garst, J. W.
Bibcode: 2005ApJ...634L.197S
Altcode: 2005astro.ph.10230S
The standard solar model was so reliable that it could predict the
existence of the massive neutrino. Helioseismology measurements
were so precise that they could determine the depth of the
convection zone. This agreement between theory and observation was
the envy of all astrophysics-until recently, when sophisticated
three-dimensional hydrodynamic calculations of the solar atmosphere
reduced the metal content by a factor of almost 2. Antia &
Basu suggested that a higher value of the solar neon abundance,
ANe/AO=0.52, would resolve this controversy. Drake
& Testa presented evidence in favor of this idea from a sample
of 21 Chandra stars with enhanced values of the neon abundance,
ANe/AO=0.41. In this Letter, we have analyzed
solar active region spectra from the archive of the Flat Crystal
Spectrometer on the Solar Maximum Mission, a NASA mission from the
1980s, as well as full-Sun spectra from the pioneering days of X-ray
astronomy in the 1960s. These data are consistent with the standard
neon-to-oxygen abundance value, ANe/AO=0.15
(Grevesse & Sauval). We conclude, therefore, that the enhanced-neon
hypothesis will not resolve the current controversy.
Title: Isothermal Bias of the ``Filter Ratio'' Method for Observations
of Multithermal Plasma
Authors: Weber, M. A.; Schmelz, J. T.; DeLuca, E. E.; Roames, J. K.
Bibcode: 2005ApJ...635L.101W
Altcode:
An early result from the Transition Region and Coronal Explorer
(TRACE) was that the EUV filter ratios for many narrow coronal loops
(widths of a few arcseconds) were found to cluster within the small
range 0.50-1.70, as functions of position along loop length. The
most common interpretation is that the temperature along the
loop is in fact nearly constant with a value between 1.1 and 1.3
MK. This interpretation has resulted in a class of TRACE loop models
with heating close to the footpoints. We analyze the filter ratio
method to show that the constant TRACE 195 Å/173 Å ratios can be
reproduced by multithermal differential emission measures (DEMs)
along the line of sight over a wide range of peak temperatures, so
long as the distribution is relatively flat and spans the temperature
response of both channels. Furthermore, in the limit of flat (i.e.,
very multithermal) DEMs, the filter ratio method is biased toward the
ratio of the integrals of the temperature response functions. This
result is general to any measurement of intensity ratios that are
formed over a nonzero temperature range (e.g., narrow passbands and
ion emission lines).
Title: All Coronal Loops Are the Same: Evidence to the Contrary
Authors: Schmelz, J. T.; Nasraoui, K.; Richardson, V. L.; Hubbard,
P. J.; Nevels, C. R.; Beene, J. E.
Bibcode: 2005ApJ...627L..81S
Altcode: 2005astro.ph..5593S
The 1998 April 20 spectral line data from the Coronal Diagnostic
Spectrometer on the Solar and Heliospheric Observatory show a coronal
loop on the solar limb. Our original analysis of these data showed
that the plasma was multithermal, both along the length of the loop and
along the line of sight. However, more recent results by other authors
indicate that background subtraction might change these conclusions,
so we consider the effect of background subtraction on our analysis. We
show emission measure (EM) loci plots of three representative pixels:
loop apex, upper leg, and lower leg. Comparisons of the original
and background-subtracted intensities show that the EM loci are more
tightly clustered after background subtraction, but that the plasma
is still not well represented by an isothermal model. Our results
taken together with those of other authors indicate that a variety of
temperature structures may be present within loops.
Title: EM Loci of CDS Loop Data
Authors: Schmelz, J. T.; Nasraoui, K.
Bibcode: 2005AGUSMSP13B..04S
Altcode:
Our original analysis of the 1998 April 20 SOHO-CDS spectral line
data for a coronal loop on the solar limb showed that the plasma was
multi-thermal, both along the length of the loop as well as along the
line of sight. Here we consider the effect of background subtraction
on our analysis, and show EM Loci plots of three representative
pixels, one near the loop apex, a second at the upper loop leg,
and a third at the lower loop leg. Comparisons of the original and
background-subtracted intensities show that the EM Loci are more tightly
clustered after background subtraction, but that the plasma is still not
well represented by an isothermal model. Possible explanations include
a series of isothermal loops contributing along the line of sight, or
multiple adjacent isothermal strands at different temperatures within
the resolution element. Solar physics research at the University of
Memphis is supported by NASA grants NAG5-9783 and NAG5-12096.
Title: Why Does TRACE See So Many Isothermal Loops?
Authors: Weber, M.; Deluca, E.; Schmelz, J.
Bibcode: 2005AGUSMSP13B..03W
Altcode:
The Transition Region and Coronal Explorer (TRACE) has advanced our
view of the dynamics of solar active regions. TRACE brings the highest
spatial resolution and reasonable temporal coverage to bear on the
evolution and structure of coronal plasma; temperature discrimination
is achieved with three narrowband EUV filters and the filter ratio
method. Many thin coronal loops have been observed to have near-constant
filter ratios along their length, which has commonly been interpreted
as evidence for isothermal structure. We discuss and quantify how the
TRACE filter response ratios are biased to estimate relatively constant
isothermal temperatures in the observed range when the plasma along
the line-of-sight is multithermal.
Title: How does Background Subtraction Affect SXT Loop Temperatures?
Authors: Roames, J. K.; Schmelz, J. T.
Bibcode: 2005AGUSMSP41A..09R
Altcode:
We have chosen a sample of 10 coronal loops that were visible on the
limb and disk using SXT data. Our analysis was limited to Al1 and AlMg
image observations taken when the instrument cycles through different
filters during routine operations. The structures of the loop did
not appear to change significantly during the cycle. We chose a range
of twenty to thirty pixels along each loop and background pixels to
correspond with the loop pixels. Temperature analysis was performed in
three different ways: (1) standard SXT analysis of the loop pixels with
no background subtraction; (2) constant background subtraction for each
SXT image; (3) pixel pair background subtraction. Each method produced
a temperature estimate for the selected pixels. We are interested
specifically in how these results may differ from the EIT and TRACE
loop temperature analysis that we have already completed. These results
showed that background subtraction did not affect the EIT or TRACE
temperatures. Solar physics research at the University of Memphis is
supported by NASA grants NAG5-9783 and NAG5-12096.
Title: EUV Observations of Active Region Dynamics
Authors: Deluca, E. E.; Cirtain, J. W.; del Zanna, G.; Mason, H. E.;
Martens, P. C.; Schmelz, J.; Golub, L.
Bibcode: 2005AGUSMSP33A..03D
Altcode:
Data collected during SoHO JOP 146, in collaboration with TRACE, is
used to investigate the physical characteristics of coronal active
region loops as a function of time and position along and across
loop structures. These data include TRACE images in all three EUV
passbands, and simultaneous CDS spectroscopic observations. Preliminary
measurements of the loop temperature both along the loop half-length
and loop cross-section are presented as a function of time. We will
show the temperature and density profiles of several structures as a
function of position, show changes in temperature and density with time
and characterize the coronal background emission. Questions raised
by these results will be greatly advanced with the high resolution
spectra available from the EIS on Solar-B.
Title: CDS Observations of Oxygen-V Loops
Authors: Prozny, T. E. K.; Schmelz, J. T.
Bibcode: 2004AAS...204.5605P
Altcode: 2004BAAS...36..762P
Central to solving the coronal heating problem is an understanding
of the temperature structure and loop dynamics of coronal loops. It
is thought that the great amounts of energy needed to heat the
corona could be dumped into the lower solar atmosphere via these
small magnetic loops that spring up and then disappear. Thus, by
determining such characteristics as temperatures, abundances, and
densities, and observing the time evolution of these loops, one can
address the question of how the corona is heated. These are some of
the goals focused on by The Coronal Diagnostic Spectrometer (CDS). We
chose to analyze and compare CDS loops that are brightly visible in the
Oxygen V line at 629.73 Angstroms with a peak formation temperature
of Log T = 5.4. Our particular data set was from 2000 October 25 at
06:54 UT. Six pixels were chosen along the loop with corresponding
background pixels inside and outside the loop structure. Emission lines
were fit and background subtraction was performed for each pixel. We
have also studied the loop dynamics and time evolution using imaging
data from TRACE, EIT on SOHO, and SXT on Yohkoh. We want to compare
the properties of this loop with other O V loops, including the one
observed on 1999 June 30 at 19:28 UT, which we have already studied in
detail. We hope to determine if the O V loops are a relative rarity,
or perhaps a phase in the standard loop evolution, or even a different
class of solar loop altogether. Solar physics research at the University
of Memphis is supported by NASA grants NAG5-9783 and NAG5-12096.
Title: SOHO-CDS Coronal Loops: More deeply into Background Subtraction
Authors: Nasraoui, K.; Schmelz, J. T.
Bibcode: 2004AAS...204.5607N
Altcode: 2004BAAS...36..762N
Analyzing two CDS data sets from two loops on the solar limb showed
that the plasma was multi-thermal, both along the length of the loop as
well as along the line of sight. Background subtraction is the latest
step in our analysis. We chose three loop pixels: one at the south
footpoint, one on the south leg, and one at the top of the loop. We also
selected a pair of background pixels associated with each loop pixel:
one inside the loop and one outside. At these locations there were
no structures contaminating the emission, and it was as close to pure
diffuse background corona as we could get given the CDS resolution. We
then fit the spectral lines in these pixels with Gaussian profiles
and determined the intensities. Both background intensities were
averaged and subtracted from the associated loop pixel intensity,
and the differential emission measure curves were reevaluated with
these adjusted values. These two loops have several things in common
- an event occurred several hours earlier, triggering activity in
the general area. Both loops are relatively isolated at the time of
the CDS observations, but a companion loop emerges near the primary
target. There are also properties that are quite different. Our analysis
indicates that the loop observed on 1998 April 20 is hotter and stable;
it formed in place as hot plasma filled the magnetic flux tube from
the southern footpoint. The 1999 June 30 loop is cooler and dynamic;
it emerges from an unresolved knot of activity and grows substantially
over the course of the next several hours. It does not appear that
these two loops are simply different `snapshots' of the same overall
time evolutionary process, i.e., a cool loop evolving to a hotter phase
of vise versa. Solar physics research at the University of Memphis is
supported by NASA grants NAG5-9783 and NAG5-12096.
Title: How does Background Subtraction Affect TRACE Loop Temperatures?
Authors: Roames, J. K.; Schmelz, J. T.; Beene, J. E.
Bibcode: 2004AAS...204.5604R
Altcode: 2004BAAS...36..762R
We have chosen a sample of 10 coronal loops that were visible in
the 171 A and 195 A passband of TRACE, five on the limb and five on
the disk. Our analysis was limited to 171/195 image observations
taken when the instrument cycles through the different passbands
during routine operations. The cycle takes only a few minutes,
so each of these nonflaring structures did not appear to change
significantly during the cycle. We chose between twenty to thirty
pixels along each loop and background pixels to correspond with the loop
pixels. Temperature analysis was done three different ways: (1) standard
TRACE analysis of the loop pixels with no background subtraction;(2)
constant background subtraction for each TRACE image; (3) pixel pair
background subtraction. Each method produced a temperature estimate
for the selected pixels. We are interested specifically in how these
results may differ from he EIT loop temperature analysis that we have
already completed. These results showed that background subtraction did
not affect the EIT temperatures. EIT and TRACE have nearly identical
temperature responses, but TRACE has high spatial resolution (0.5 arcsec
pixels) compared with EIT (2.6 arcsec pixels). Does the higher spatial
resolution change the results? Solar physics research at the University
of Memphis is supported by NASA grants NAG5-9783 and NAG5-12096.
Title: Isothermal or Multithermal Loop Plasma: to See or not to See
Authors: Kim, T.; Schmelz, J. T.
Bibcode: 2004AAS...204.5606K
Altcode: 2004BAAS...36..762K
Solar coronal imagers like TRACE, EIT on SOHO, and SXT on Yohkoh use
a ratio of images taken through different passbands to determine
the plasma temperature. This standard analysis uses an isothermal
approximation and is used widely throughout the solar community. The
accuracy and usefulness of this method depends in part on the nature of
the observed plasma and, in particular, how truly isothermal it actually
is. We have investigated this aspect of the temperature analysis by
folding known plasma differential emission measure distributions through
the various instrument responses provided in Solarsoft. We began with
noiseless, strongly peaked Gaussian distributions, which represented
the close-to-ideal case of an essentially isothermal plasma. We
found that the standard analysis did an excellent job of reproducing
the temperatures at the peak of the input distribution, even if this
value was well off the peak of the instrument response function. This
neat result begins to disappear, however, when we slowly broaden
the Gaussian distributions or add a second peak to the differential
emission measure distributions. For example, a broadened distribution
produces temperature that is shifted by a small, yet noticeable
amount from the center of the Gaussian. Introducing a second peak,
of equal intensity as the first one, but at a different temperature,
also recreates temperature different from the peak positions. Indeed,
the temperatures that the instruments see lie somewhere in between
where the Gaussian peaks actually occur. In the case where one peak is
significantly more dominant than the other, the instruments seem to
favor the temperature of the stronger peak. All in all, our results
indicate that the standard analysis struggles to provide reliable
temperature values for multithermal plasma. Solar physics research
at the University of Memphis is supported by NASA grants NAG5-9783
and NAG5-12096.
Title: The Cinderella Loop Project
Authors: O'Connor, J.; Coyle, T.; Douglass, J.; Schmelz, J. T.
Bibcode: 2004AAS...204.5603O
Altcode: 2004BAAS...36..762O
On 1999 Nov 6 at 02:30 UT, a solar loop (dubbed Cinderella) on the
northeast limb was simultaneously observed by TRACE, EIT on SOHO,
and SXT on Yohkoh. This project investigates differences among the
data sets from the three instruments. For example, EIT and TRACE have
nearly identical temperature responses, but does the high resolution
TRACE imager (0.5 arcsec pixels) produce results that match those from
the lower resolution EIT imager (2.6 arcsec pixels)? Furthermore,
EIT and SXT have similar spatial resolutions, but their temperature
responses are much farther apart. Do these two instruments observe the
same structures within the loop, and if so, how do their temperature
and emissions measures compare? What are the effects of background
subtraction on all three data sets? This presentation will address
these questions. Solar physics research at the University of Memphis
is supported by NASA grants NAG5-9783 and NAG5-12096.
Title: Coronal Energetics and Loop Dynamics
Authors: Schmelz, J. T.
Bibcode: 2004AAS...204.9505S
Altcode: 2004BAAS...36R.826S
To understand the overall energetics of the solar corona, one must
consider the various energy reservoirs, for example, thermal plasma,
microscopic "turbulence," bulk kinetic motions, shock fronts,
non-potential magnetic field configurations, and non-equilibrium
ionization states. Other crucial inputs include the methods of
energy transfer and the detailed processes of energy release and
dissipation. In the actual corona, there are different kinds of energy
reservoirs, transfer mechanisms, and release/dissipation processes
(sometimes present or operating simultaneously), and their roles vary,
depending largely on the nature of the local magnetic field. In this
project, we focused on one component of the coronal energy storage
system - the active region loop (which may also be taken to mean
an unresolved ensemble of strands). The heated coronal loop plasma
is a transitional storage medium of the coronal energy reservoir. In
particular, we will examine the temperature profile, density structure,
and temporal evolution of active region loops. With this information -
and using estimates of the coronal magnetic field, elemental abundances,
bulk flows, waves, and turbulent motions from previous measurements -
we can evaluate the conductive and radiative loss rates, investigate
the conditions under which other energy transport mechanisms are
important, and begin to determine the dominant energy loss mechanism(s)
for different (and possibly different types of) coronal loops. These
loop studies will characterize a key link in the complicated chain that
comprises the transition from energy storage to energy dissipation
in the corona. With a better handle on the thermal content of active
coronal loops, one can begin to assess the importance of these prolific
structures to other aspects of the coronal energy storage system and
the relation of loops to different methods of energy transfer, release,
and dissipation. Solar physics research at the University of Memphis
is supported by NASA grants NAG5-9783 and NAG5-12096.
Title: The Coronal Loop Controversy
Authors: Schmelz, J.
Bibcode: 2004cosp...35.1475S
Altcode: 2004cosp.meet.1475S
Recent images of the solar atmosphere in the X-ray and EUV have revealed
the spectacular structure of coronal loops. These loops are connected
with such crucial solar physics questions as the coronal heating
problem, the flare trigger, and the effects of solar irradiance on the
Earth. Recent results, however, have left the study of these fundamental
structures in a somewhat confused state. The solar community cannot
currently agree on the answers to some of the most basic questions
concerning the physical structure and temporal behavior of loops. Ratios
of loop images taken through different instrument passbands have been
used to determine the plasma temperature distribution along these
loops. Are these loops isothermal? The analysis of SXT ratios of
broadband coronal loop data shows that the temperatures increase from
the footpoints to the loop top. But a similar ratio-type analysis
of narrowband TRACE or EIT data shows that loops have a constant
temperature. This temperature distribution, according to theoretical
model calculations, should be sensitive to the mechanism that heats
the solar atmosphere to several million degrees Kelvin. Is the coronal
heating uniform? Analysis of the same SXT loop data by three different
groups has produced three different answers: the heating is (1) uniform;
(2) concentrated at the loop footpoints; (3) concentrated at the loop
apex. Is the heating episodic? The properties of a set of coronal loops
observed with SXT are compatible with steady heating, but those same
loops were also compatible with nanoflare heating occurring randomly
in thousands of unresolved loop strands. How important is background
subtraction? Each of these questions will be addressed. Solar physics
research at the University of Memphis is supported by NASA grants
NAG5-9783 and NAG5-12096.
Title: The Cinderella Loop Project
Authors: Schmelz, J.; Beene, J.; Buchanan, J.; Coyle, T.; Douglass,
J.; Nasraoui, K.; O'Connor, J.; Roames, J.; Scott, M.
Bibcode: 2004cosp...35.1476S
Altcode: 2004cosp.meet.1476S
The solar loop observed off the northeast limb on 1999 Nov 6 (a.k.a. the
Cinderella Loop) is one of the few examples of a loop on the limb
observed with all three of the following imaging instruments: TRACE,
EIT on SOHO, and SXT on Yohkoh. In this project we investigate the
differences that result when examining the Cinderella Loop with one
instrument compared with another. For example, what are the loop
temperature and emission measure differences that result from the
increased special resolution between the two EUV imagers? More
specifically, TRACE and EIT have almost identical temperature
responses to coronal plasma. Do the observations taken with the
higher-resolution TRACE instrument (with 0.5 arcsec pixels) produce
statistically different results than those observations taken with the
lower-resolution EIT instrument (with 2.6 arcsec pixels)? In addition,
the special resolution of EIT and SXT is similar, but the temperature
responses of the two instruments are quite different. Are the two
instruments even seeing the same loop strands? If they are, what are
the temperatures and emission measures that result from the analysis
of the two data sets? How do these results change after background
subtraction? This presentation will answer these questions. Solar
physics research at the University of Memphis is supported by NASA
grants NAG5-9783 and NAG5-12096.
Title: The Effect of Background Subtraction on the Temperature of
EIT Coronal Loops
Authors: Schmelz, J. T.; Beene, J. E.; Nasraoui, K.; Blevins, H. T.;
Martens, P. C. H.; Cirtain, J. W.
Bibcode: 2003ApJ...599..604S
Altcode:
We have selected a sample of 10 coronal loops that were clearly
visible in the 171 Å passband of the SOHO EIT, five on the limb
and five on the disk. Our analysis was limited to 171/195/284 image
``triplets''-observations taken when the instrument cycles through
the different passbands during routine operations. This cycle takes
only a few minutes, so each of these nonflaring structures did not
change significantly during the cycle. We chose five pixels along
each loop and five carefully selected background pixels. Temperature
analysis was done four different ways: (1) standard EIT analysis on
the five loop pixels with no background subtraction; (2) constant
background subtraction for each EIT image; (3) pixel pair background
subtraction; and (4) radial background array subtraction (this method
works only for loops observed above the limb). Each method produced
two estimates of temperature for each loop pixel, one from the 171:195
ratio and the second for the 195:284 ratio. Both ratios produced loops
with a uniform temperature, but each ratio results in a statistically
different temperature value, perhaps indicating that the plasma along
the line of sight was not isothermal. Background subtraction did
not affect the EIT temperature analysis, i.e., the results were the
same with and without background subtraction. The results for loops
on the limb were ``cleaner'' i.e., had less scatter, than for loops
on the disk. Finally, we did a similar temperature analysis with five
randomly chosen pixels for each data set. The results were the same as
for the loop pixels: two statistically different, uniform temperature
``structures.'' These findings indicate that EIT ratio analysis does
not generate a physically meaningful value for the electron temperature.
Title: Coronal loops: Isothermal OR multithermal?
Authors: Schmelz, J. T.; Cirtain, J. W.; Beene, J. E.; Blevins, H. T.;
Ellis, D.; Medlin, D. A.; Nasraoui, K.; Nevels, C.
Bibcode: 2003AdSpR..32.1109S
Altcode:
Are coronal loops isothermal? A controversy over this question has
arisen recently because different investigators using different
techniques have obtained very different answers. Analysis of data
using narrowband filter ratios to obtain temperature maps has
produced several key publications that suggest that coronal loops
may be isothermal. We have constructed a multi-thermal distribution
for several pixels along a relatively isolated coronal loop on the
southwest limb of the solar disk using spectral line data from the
Coronal Diagnostics Spectrometer (CDS), on SOHO taken on 1998 April
20. These distributions are clearly inconsistent with isothermal
plasma along either the line of sight or the length of the loop, and
suggested rather that the temperature increases from the footpoints to
the loop top. We convolved these Differential Emission Measure curves
with two of the Soft X-ray Telescope (SXT) response functions. This
gives us the intensity (in Data Numbers/sec) of what the instrument
would "see" in these filters if it were observing the same loop. We
then took a ratio of these values, and used the regular Yohkoh
software to calculate a temperature at each pixel. The instrument
"sees" a loop that is marginally consistent with an almost uniform
temperature, but a linear or quadratic model is a much better fit to
the data. These results are different from those of a similar analysis
with narrow-passband instruments that produced data consistent with a
uniform temperature loop, even though the actual temperature input was
multi-thermal both along the line of sight and along the length of the
loop. We suspect that these apparent uniform-temperature loops may be
an unfortunate byproduct of the simplistic filter-ratio method that is
used for temperature analysis. Our results are consistent with earlier
analysis of Yohkoh data, where there were strong indications that the
SXT temperatures were a kind of Differential Emission Measure-weighted
temperature. There is a problem, however, when we compare these
temperatures with those calculated with the actual SXT data, which
are much higher than even the hottest plasma observed by CDS.
Title: Why stellar astronomers should be interested in the sun
Authors: Schmelz, J. T.
Bibcode: 2003AdSpR..32..895S
Altcode:
By all accounts, the Sun is a garden-variety star with an average age,
a standard size, a regular temperature, norormal mass, an ordinary
structure, and a typical chemical composition. Only one feature
makes it special - the Sun is our star. It is located in the center
of our solar system, and therefore, is responsible for all life on
Earth. Astronomically speaking, the Sun is the only star in the sky
that we can study up-close and personal. The unaided human eye does
a better job of resolving the Sun than the finest telescope does for
any other star. Stellar astronomers issue a press release whenever
they can lay a few pixels of some state-of-the-art instrument across
a nearby supergiant. The resolution of the Sun, however, is something
we can see routinely in the magnificent images that are downloaded
every day from the Transition Region and Coronal Explorer (TRACE)
spacecraft. In a very real sense, the Sun is the Rosetta Stone of
the Stars. Observations of the Sun deflecting starlight ushered in
a new way of thinking about gravity. Zeeman effect observations of
the Sun showed that stellar atmospheres were controlled by magnetic
fields. The discovery of solar helium founded the science of stellar
spectroscopy. Measurements of the solar mass, radius, and temperature
allowed scientists to probe the interiors of stars for the first
time. tim ancient age of the Sun implied that stars shine as a result
of thermonuclear fusion. Observations of solar flares flamulated
developments in rapid magnetic reconnection theory. The study of solar
coronal holes led to a deeper understanding of the role that mass
loss plays in the evolution of stars. Detailed analysis of the solar
activity cycle inspired the development of Magneto-Hydrodynamic (MHD)
dynamo theory. The detection and understanding; of the solar corona
uncovered one of the longest unsolved mysteries in all of astrophysics
— the coronal-heating problem. And the list goes on. The Sun is indeed
a Laboratory for Astrophysics, but it is more than that. The Sun is a
Laboratory for all of Physics. This paper describes 20th century physics
discoveries that are directly attributable to solar observations. It is
in the form of a Top Ten List, and was inspired originally by a talk
given by Dr. Eugene N. Parker; subsequent discussions with Dr. Parker
have molded it into its present form.
Title: The Coronal Loop Controversy
Authors: Schmelz, J. T.
Bibcode: 2003SPD....34.1005S
Altcode: 2003BAAS...35..825S
Coronal loops are connected with such crucial solar physics questions
as the coronal heating problem, the flare trigger, and the effects of
solar irradiance on the Earth. Recent results, however, have left the
study of these fundamental structures in a somewhat confused state. The
solar community cannot currently agree on the answers to some of the
most basic questions concerning the physical structure and temporal
behavior of loops. Are coronal loops isothermal? The analysis of
SXT ratios of broadband coronal loop data show that the temperatures
increase from the footpoints to the loop top. But a similar ratio-type
analysis of narrowband TRACE or EIT data shows that loops have a
constant temperature. Is the coronal heating uniform? Analysis of
the same SXT loop data by three different groups has produced three
different answers: the heating is (1) uniform; (2) concentrated
at the loop footpoints; (3) concentrated at the loop apex. Is the
heating episodic? The properties of a set of coronal loops observed
with SXT are compatible with steady heating, but those same loops
were also compatible with nanoflare heating occurring randomly in
thousands of unresolved loop strands. One of the important analysis
unknowns to emerge from these controversial results is the effect
of 'background subtraction' on loop properties. Proper or improper
background subtraction can cause results to flip-flop - from isothermal
to multi-thermal, from footpoint heating to apex heating, from steady
heating to episodic heating, and vise versa. Here we summarize our
background subtraction results for EIT, CDS, and SXT data for both
limb and disk loops. Is background subtraction important? Well, yes
. . . and no. Solar physics research at the University of Memphis is
supported by NASA grants NAG5-9783 and NAG5-12096.
Title: SOHO-CDS Coronal Loops: Multi-thermal Analysis and Background
Subtraction
Authors: Nasraoui, K.; Schmelz, J. T.; Nevels, C. R.
Bibcode: 2003SPD....34.1709N
Altcode: 2003BAAS...35..838N
Our original analysis of the 20 April 1998 and 30 June 1999 SOHO-CDS
spectral line data for two loops on the solar limb showed that
the plasma was multi-thermal, both along the length of the loop as
well as along the line of sight. But this analysis did not consider
background subtraction. Here, we add this additional step to our
analysis and compare the background-subtracted results with our original
results. First, we selected a `background pixel' for each loop. This
pixel was inside the loop at a location where no structures contaminated
the emission - it was as close to pure diffuse background corona as we
could get given the CDS resolution. We then fit the spectral lines in
this pixel with Gaussian profiles and determined the intensities. These
were then subtracted from the intensities of the 'loop pixels' and the
differential emission measure (DEM) curves were reevaluated with these
adjusted values. Second, a pair of background pixels was selected for
each loop pixel, one inside the loop and one outside the loop. The
line intensities were measured at each of these locations, averaged,
and subtracted from the associated loop pixel intensity. A third
set of DEM curves was constructed. These results will be compared
and contrasted with both the original results as well as those from
phase one. Does background subtraction make a difference? Of course:
the intensities of all lines are smaller so the DEMs are lower in
every temperature bin. But does the multi-thermal distribution from
the original result simplify to an isothermal one reminiscent of the
results seen in TRACE and EIT loops? We're still working on the answer
to that question. Solar physics research at the University of Memphis
is supported by NASA grants NAG5-9783 and NAG5-12096.
Title: Limb Looking: The effects of background subtraction on the
temperature of SXT loops.
Authors: Medlin, D. A.; Blevins, H. T.; Schmelz, J. T.
Bibcode: 2003SPD....34.1708M
Altcode: 2003BAAS...35..838M
Knowing the temperature distribution along a loop is one possible
test for the coronal heating models. The matter of how background
subtraction may or may not affect the temperature distribution
of loops could also play a crucial role in this analysis. Several
instruments are currently available for loop studies, and numerous
techniques are used to determine the temperature distributions along
the loops. This has lead to many different, and mostly conflicting
temperature results. We have chosen the Soft X-ray Telescope (SXT),
aboard the Japanese satellite Yohkoh, for this study. The SXT data
archives were searched for possible loop candidates. A set of loops
on the limb, as well as a set of loops on the disk, were chosen for
analysis. Temperature maps were generated for each loop with and without
background subtraction. For each loop, we used both a uniform background
subtraction as well as a pixel-by-pixel background subtraction. Once
the temperature as a function of arc length has been found, it is
then compared to the predictions made by different models. The Solar
physics research at the University of Memphis is supported by NASA
grants NAG5-9783 and NAG5-12096.
Title: To BG or not to BG: Background Subtraction for EIT Coronal
Loops
Authors: Beene, J. E.; Schmelz, J. T.
Bibcode: 2003SPD....34.1711B
Altcode: 2003BAAS...35..839B
One of the few observational tests for various coronal heating models
is to determine the temperature profile along coronal loops. Since
loops are such an abundant coronal feature, this method originally
seemed quite promising - that the coronal heating problem might
actually be solved by determining the temperature as a function of
arc length and comparing these observations with predictions made by
different models. But there are many instruments currently available
to study loops, as well as various techniques used to determine
their temperature characteristics. Consequently, there are many
different, mostly conflicting temperature results. We chose data
for ten coronal loops observed with the Extreme ultraviolet Imaging
Telescope (EIT), and chose specific pixels along each loop, as well
as corresponding nearby background pixels where the loop emission was
not present. Temperature analysis from the 171-to-195 and 195-to-284
angstrom image ratios was then performed on three forms of the data:
the original data alone, the original data with a uniform background
subtraction, and the original data with a pixel-by-pixel background
subtraction. The original results show loops of constant temperature,
as other authors have found before us, but the 171-to-195 and 195-to-284
results are significantly different. Background subtraction does not
change the constant-temperature result or the value of the temperature
itself. This does not mean that loops are isothermal, however, because
the background pixels, which are not part of any contiguous structure,
also produce a constant-temperature result with the same value as
the loop pixels. These results indicate that EIT temperature analysis
should not be trusted, and the isothermal loops that result from EIT
(and TRACE) analysis may be an artifact of the analysis process. Solar
physics research at the University of Memphis is supported by NASA
grants NAG5-9783 and NAG5-12096.
Title: Are Coronal Loops Isothermal?
Authors: Schmelz, J. T.
Bibcode: 2002ApJ...578L.161S
Altcode:
A controversy over the temperature distribution of coronal loops
has arisen recently because different investigators using different
techniques have obtained very different answers. Analysis of Solar and
Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope
(EIT) and Transition Region and Coronal Explorer (TRACE) data using
narrowband ratios to obtain temperature maps has produced several key
publications that suggest that coronal loops may be isothermal. On the
other hand, our analysis of the SOHO Coronal Diagnostics Spectrometer
(CDS) spectral line data taken on 1998 April 20 for several pixels
along a relatively isolated coronal loop on the southwest limb of
the solar disk is clearly inconsistent with isothermal plasma along
either the line of sight or the length of the loop. We have constructed
a differential emission measure (DEM) distribution for each pixel;
these distributions, taken together, suggested that the DEM-weighted
temperature increases from the footpoints to the loop top. We convolved
these DEM curves with the three different EIT coronal response
functions. This gives us the intensity (in units of DN s-1)
of what EIT would ``see'' in the 171, 195, and 284 Å passbands if it
were observing the CDS loop. We take a ratio of these values (171 Å/195
Å and 195 Å/284 Å), and use the regular EIT software to calculate a
temperature at each pixel for each ratio. EIT ``sees'' a loop with an
almost uniform temperature, but the derived temperatures are different
for the different ratios. These uniform-temperature loops arise even
though the actual temperature input is multithermal both along the
line of sight and along the length of the loop. We suspect that these
apparent uniform-temperature loops may be an unfortunate by-product
of the simplistic filter-ratio method that is used for both EIT and
TRACE temperature analysis. Our results indicate that narrow-passband
EUV observations must be used in conjunction with other diagnostics
to draw quantitative conclusions about the properties of coronal plasma.
Title: The Inadequacy of Temperature Measurements in the Solar Corona
through Narrowband Filter and Line Ratios
Authors: Martens, P. C. H.; Cirtain, J. W.; Schmelz, J. T.
Bibcode: 2002ApJ...577L.115M
Altcode:
We analyze the determination of coronal line-of-sight temperatures
with the technique of narrowband filter ratios that is currently
employed for data obtained with the Transition Region and Coronal
Explorer and the EUV Imaging Telescope on board the Solar and
Heliospheric Observatory. We demonstrate that the simple fact that
the observed differential emission measure curves in coronal loops
have a broad plateau everywhere along the length of the loop leads to
the finding of isothermal loops with different temperatures for each
pair of filters. We show that none of the temperatures thus obtained
correctly describe the state of the loop plasma, which instead must be
characterized by the full differential emission measure per pixel. We
conclude that the recent discovery of a new class of isothermal loops
is probably a mere artifact of the narrowband filter ratio method and
show that the shift in the location of the plateau in the differential
emission measure along the loop indicates significant heating near
the loop tops.
Title: Coronal abundances obtained from serts and Yohkoh-SXT data
Authors: Schmelz, J. T.; Winter, H. D.; Marino, C. P.
Bibcode: 2002AdSpR..30...61S
Altcode:
Coronal abundances for active region AR 7563 were obtained using a
combination of broad-band filter data from Yohkoh SXT and simultaneous
spectral line data from the SERTS rocket taken during its flight on
1993 August 17. We have used a forward-folding technique to determine
the emission measure distribution of the active region plasma using only
the SERTS iron lines and the SXT filters (which are sensitive primarily
to iron and used mainly to constrain the high-temperature end of the
emission measure distribution). We then adjusted the abundances of the
other elements to achieve the best agreement with this curve. Magnesium,
aluminum, silicon, sulfur, and nickel were changed to 110%, 88%, 80%,
80%, and 115%, respectively from standard published values.
Title: Coronal Loops: Evolving Beyond the Isothermal Approximation
Authors: Schmelz, J. T.; Cirtain, J. W.; Allen, J. D.
Bibcode: 2002AAS...200.1604S
Altcode: 2002BAAS...34..667S
Are coronal loops isothermal? A controversy over this question
has arisen recently because different investigators using different
techniques have obtained very different answers. Analysis of SOHO-EIT
and TRACE data using narrowband filter ratios to obtain temperature maps
has produced several key publications that suggest that coronal loops
may be isothermal. We have constructed a multi-thermal distribution
for several pixels along a relatively isolated coronal loop on the
southwest limb of the solar disk using spectral line data from SOHO-CDS
taken on 1998 Apr 20. These distributions are clearly inconsistent
with isothermal plasma along either the line of sight or the length
of the loop, and suggested rather that the temperature increases from
the footpoints to the loop top. We speculated originally that these
differences could be attributed to pixel size -- CDS pixels are larger,
and more `contaminating' material would be expected along the line
of sight. To test this idea, we used CDS iron line ratios from our
data set to mimic the isothermal results from the narrowband filter
instruments. These ratios indicated that the temperature gradient along
the loop was flat, despite the fact that a more complete analysis of
the same data showed this result to be false! The CDS pixel size was
not the cause of the discrepancy; rather, the problem lies with the
isothermal approximation used in EIT and TRACE analysis. These results
should serve as a strong warning to anyone using this simplistic
method to obtain temperature. This warning is echoed on the EIT web
page: ``Danger! Enter at your own risk!'' In other words, values
for temperature may be found, but they may have nothing to do with
physical reality. Solar physics research at the University of Memphis
is supported by NASA grant NAG5-9783. This research was funded in part
by the NASA/TRACE MODA grant for Montana State University.
Title: Methods of Temperature and Emission Measure Determination of
Coronal Loops
Authors: Cirtain, J. W.; Schmelz, J. T.; Martens, P. C. H.
Bibcode: 2002AAS...200.1605C
Altcode: 2002BAAS...34..667C
Recent observational results from both SOHO-EIT and TRACE indicate that
coronal loops are isothermal along their length (axially). These results
are obtained from a narrowband filter ratio method that assumes that
the plasma is isothermal along the line of sight (radially). However,
these temperatures vary greatly from those derived from differential
emission measure (DEM) curves produced from spectral lines recorded by
SOHO-CDS. The DEM results indicate that the loops are neither axially
nor radially isothermal. This discrepancy was investigated by Schmelz
et al. (2001). They chose pairs of iron lines from the same CDS data
set to mimic the EIT and TRACE loop results. Ratios of different
lines gave different temperatures, indicating that the plasma was not
radially isothermal. In addition the results indicated that the loop
was axially isothermal, even though the DEM analysis of the same data
showed this result to be false. Here we have analyzed the EIT data for
the CDS loop published by Schmelz et al. (2001). We took the ratios of
the 171-to-195 and 195-to-284 filter data, and made temperature maps
of the loop. The results indicate that the loop is axially isothermal,
but different temperatures were found for each pair of filters. Both
ratio techniques force the resultant temperature to lie within the range
where the response functions (for filters) or the emissivity functions
(for lines) overlap; isothermal loops are therefore a byproduct of
the analysis. This conclusion strengthens support for the idea that
temperature and emission measure results from filter ratio methods may
be misleading or even drastically wrong. This research was funded in
part by the NASA/TRACE MODA grant for Montana State University. Solar
physics research at the University of Memphis is supported by NASA
grant NAG5-9783.
Title: How to `Subtract' Spectrally Determined Intensities from a
Coronal Loop on the Limb
Authors: Martens, P. C. H.; Cirtain, J. W.; Schmelz, J. T.
Bibcode: 2002AAS...200.0206M
Altcode: 2002BAAS...34..640M
There are two main problems in the determination of plasma emissions
within a coronal loop. First, the line of sight adds the ambient
background to the measurement. Second, scattering elevates the intensity
for pixels close to a structure (i.e. a loop) by counting photons that
actually are emitted from that structure. Here we have a possible
solution for these two problems. We show that the intensities for
the spectral lines are shown to have scale height dependence when the
plasma is not confined to a structure. Accordingly, at any distance
greater than its scale height, the ion will not have a statistically
significant contribution to the measure of intensity. Additionally,
an isolated coronal structure will have a maximum intensity value along
an exposure and within a range of pixels that effectively slice a leg
of the loop. The maximum is the location of the pixel that is most
likely the one containing the loop. All other pixels are considered
scatter until the point spread function can deconvolve the true value
for intensity per pixel. The resulting values for intensity have then
been reduced to approximate the value for intensity for the plasma
within the loop. Now the intensity has been reduced to the intensity
of the ion within the loop and the analysis of an accurate DEM is now
possible. This research was funded in part by the NASA/TRACE MODA grant
for Montana State University. Solar physics research at the University
of Memphis is supported by NASA grant NAG5-9783.
Title: Using Differential Emission Measure Techniques to Compare
Plasma Parameters in Active Regions
Authors: Medlin, D. A.; Schmelz, J. T.; Beene, J. E.
Bibcode: 2002AAS...200.0203M
Altcode: 2002BAAS...34S.639M
If one is to study solar active regions and the processes that drive
them, one must accurately describe the temperature distributions and the
elemental abundances of the emitting plasma. The best way to determine
these vital parameters is with multi-thermal analysis techniques,
which do not have as many initial assumptions as their isothermal
counterparts. The accuracy of these emission measure distributions
depends on spectroscopic observations of emitting ions that cover a
broad temperature range. The Solar EUV Rocket Telescope and Spectrograph
(SERTS) is well suited for studying multi-thermal coronal structures. It
provides observations of numerous emission lines with excellent spectral
resolution. Observations taken with the Soft X-ray Telescope (SXT) were
combined with data from SERTS in order to constrain the high-temperature
end of the multi-thermal distribution. Three active regions (AR 7563,
AR 7870, and AR 8108) were chosen for this investigation. All three
regions were observed simultaneously with both instruments. We generated
a differential emission measure (DEM) curve for each region using the
SERTS iron lines and the SXT data. Therefore, we were interested to
see the results for the other (non-iron) lines when the same DEM curve
was used to model the plasma. Initially the hybrid abundance values
were used for the elements in each separate SERTS data set. Then these
abundances were adjusted so that the predicted intensities agreed with
the observed as closely as possible. The results show how the elemental
abundances vary from one region to the next. Solar physics research
at the University of Memphis is supported by NASA grant NAG5-9783.
Title: Coronal Densities from SERTS Differential Emission Measure
Analysis
Authors: Nevels, C. R.; Schmelz, J. T.; Richardson, V. L.
Bibcode: 2002AAS...200.0202N
Altcode: 2002BAAS...34..639N
A measurement of density is essential when trying to understand the
fundamental physics of complex phenomena such as coronal heating
and loop dynamics. Plasma densities are usually determined from the
ratio of intensities of two spectral lines, ideally from the same
element and ionization state in order to eliminate the uncertainties
inherent in elemental abundances and the ionization fractions. Instead,
we have used the spectral lines of iron observed in active regions
during the 1993, 1995, and 1997 SERTS rocket flights. With these
data, we produced differential emission measure curves that model the
multi-thermal plasma in the field of view. We then varied the density
in the range 5 x 108 cm-3 < ne <
5 x 1010 cm-3 in order to minimize the difference
between the line intensities observed by the instrument and those
predicted by our differential emission measure model. In all three
cases, it appeared that a mean electron density could characterize
the emitting loops of the stable active regions under study over a
fairly large range in temperature. This method of determining density
is complementary to standard line-ratio diagnostics. Because it uses
a large number of spectral lines simultaneously, it is not weighted
heavily by the potential atomic data uncertainties inherent in any
given line ratio. Our results lead us to postulate that, at least
for stable, quiescent regions, there might in fact be a narrow range
of characteristic mean densities over a broad temperature regime. We
suggest that this technique might be a powerful new density diagnostic
tool. Solar physics research at the University of Memphis is supported
by NASA grant NAG5-9783.
Title: Differential Emission Measure: Forward Folding vs. Automatic
Inversion
Authors: Allen, J. D.; Schmelz, J. T.
Bibcode: 2002AAS...200.0204A
Altcode: 2002BAAS...34..639A
When attempting to compare models and observations of the solar corona,
an accurate determination of the multi-thermal distribution of the
plasma along the line of sight is clearly superior to the single value
of temperature obtained from an isothermal approximation. But methods
of determining the Differential Emission Measure (DEM) are fraught
with pitfalls. Forward Folding is subjective and time consuming: an
initial model DEM curve is convolved with the emissivity function of
the spectral lines. This produces a set of predicted intensities that
are compared with the observed values. The emission measure distribution
is then adjusted manually to improve the agreement between the observed
and predicted intensities while keeping the curve as smooth a function
of temperature as possible. The process is repeated until, ideally,
the predicted and observed intensities agree to within approximately
1-2 sigma. Automatic inversion techniques are mathematically ill posed,
so small changed in the observed spectral line intensities can result
in large differences in the DEM solution. The programs are too often
used as a 'black box,' and the physical relevance of these solutions
has (rightfully so) been questioned. We attempt to minimize these
pitfalls by comparing and contrasting the temperature distributions
obtained from forward folding with two different automatic inversion
techniques. We used three different data sets: (1) SERTS iron line
intensities of an active region from the 1993 Aug 17 rocket flight;
(2) Solar Maximum Mission Flat Crystal Spectrometer data for a flare
on 1980 Aug 30; and (3) XSST spectral data of a flare from the 1982
Jul 13 rocket flight. Solar physics research at the University of
Memphis is supported by NASA grant NAG5-9783.
Title: SOHO-EIT Temperature Analysis of Active Region Loops
Authors: Blevins, H. T.; Schmelz, J. T.
Bibcode: 2002AAS...200.0207B
Altcode: 2002BAAS...34..640B
In an attempt to determine the thermal nature of coronal loops, data
from SOHO-EIT have been analyzed with isothermal approximations from
narrow-band filter ratios: 171 (Fe IX-X; T = 1.3 MK) to 195 (Fe XII;
T = 1.6 MK) angstroms and 195 (Fe XII; T = 1.6 MK) to 284 (Fe XV; T =
2.0 MK) angstroms. Numerous loops along the solar limb were selected
and corresponding temperature maps were created. Uniform background
subtraction was also applied in an attempt to remove any potential
contamination from the loop data. Initial results indicate a discrepancy
between the results produced by the two filter ratios. First, the
temperatures that result from the 171-to-195 ratio are significantly
lower than those that result from the 195-to-284 ratio, indicating
that there may be plasma of different temperatures along the line
of sight. Second, the 171-to-195 ratio seems to indicate that the
temperature is uniform along the length of the loop, while the
195-to-284 ratio indicates that the temperature increases from the
base of the loop to the top. Further investigation will be conducted
to determine potential sources for these discrepancies. Solar physics
research at the University of Memphis is supported by NASA grant
NAG5-9783.
Title: Multi-Thermal Analysis of SOHO-CDS Coronal Loops
Authors: Hubbard, P. J.; Schmelz, J. T.
Bibcode: 2002AAS...200.0208H
Altcode: 2002BAAS...34..640H
Our analysis of the 20 April 1998 SOHO-CDS spectral line data for a
loop on the solar limb showed that the plasma was multi-thermal, both
along the length of the loop as well as along the line of sight. We
have now completed analysis for two additional loops and find similar
results, which are in stark contrast to those obtained recently by
several groups who used EIT and TRACE data. They used a standard
narrowband filter ratio technique to obtain temperature maps that
assumes, a priori, that the plasma observed along the line of sight is
isothermal. Perhaps both types of loops exist in the corona; or perhaps
the isothermal loops are an artifact of the somewhat simplistic filter
ratio temperature analysis; or perhaps the multi-thermal loops are
the result of contamination from background structures of different
temperatures in the same field of view. We present here the first step
in an attempt to reconcile these seemingly disparate results. We have
taken the differential emission measure curves generated for the CDS 20
April 1998 loop, and folded these temperature distributions through the
Al.1 and AlMg response functions of SXT. This produced predicted values
(in DN/sec) for Al.1 and AlMg filters of SXT at each pixel. We then
calculated the temperature from these predictions using the normal SXT
filter ratio method, and compared these temperatures with those obtained
from the SXT observations. We hope to expand this project in the future
to include SOHO-EIT and TRACE observations. Solar physics research at
the University of Memphis is supported by NASA grant NAG5-9783.
Title: Coronal loops: isothermal or multithermal?
Authors: Schmelz, J.; Cirtain, J.
Bibcode: 2002cosp...34E1226S
Altcode: 2002cosp.meetE1226S
Are coronal loops isothermal? A controversy over this question
has arisen recently because different investigators using different
techniques have obtained very different answers. Analysis of SOHO-EIT
and TRACE data using narrowband filter ratios to obtain temperature maps
has produced several key publications that suggest that coronal loops
may be isothermal. We have constructed a multi-thermal distribution
for several pixels along a relatively isolated coronal loop on the
southwest limb of the solar disk using spectral line data from SOHO-CDS
taken on 1998 Apr 20. These distributions are clearly inconsistent
with isothermal plasma along either the line of sight or the length
of the loop, and suggested rather that the temperature increases from
the footpoints to the loop top. We speculated originally that these
differences could be attributed to pixel size -- CDS pixels are larger,
and more `contaminating' material would be expected along the line
of sight. To test this idea, we used CDS iron line ratios from our
data set to mimic the isothermal results from the narrowband filter
instruments. These ratios indicated that the temperature gradient along
the loop was flat, despite the fact that a more complete analysis of the
same data showed this result to be false! The CDS pixel size was not the
cause of the discrepancy; rather, the problem lies with the isothermal
approximation used in EIT and TRACE analysis. These results should serve
as a strong warning to anyone using this simplistic method to obtain
temperature. This warning is echoed on the EIT web page: ``Danger! Enter
at your own risk!'' In other words, values for temperature may be found,
but they may have nothing to do with physical reality.
Title: Determining coronal heating of plasma loops through
differential emission measure analysis
Authors: Schmelz, J. T.; Scopes, R. T.; Cirtain, J. W.
Bibcode: 2002AdSpR..30..507S
Altcode:
Insights into the nature of the heating mechanism in coronal plasmas
can be gained through the analysis of differential emission measure
curves localized along coronal loops. This technique is especially
desirable since it does not require the isothermal approximation
for potentially dynamic loop plasmas. Of particular interest are
the parameters describing the heating rate per unit volume in the
corona as a function of radial height and/or arc length along loop
structures. Using simultaneous observations taken on 20 April 98 with
the Solar and Heliospheric Observatory Coronal Diagnostics Spectrometer
and the Yohkoh Soft X-ray Telescope, plasma temperature distributions
were constructed in the relevant temperature domain (Log T = 5.5-7.5)
along an isolated coronal loop on the west limb, ranging from one
footpoint to the loop top. Subsequent analysis of the differential
emission measure curves using abundance values from Fludra and Schmelz
(1999) at each pixel combined with knowledge of the loop geometry
helped to pin down the coronal heating mechanism using the method
described by Priest et al. (1998).
Title: Isothermal Approximation vs. Differential Emission Measure
Analysis: How Hot are Hot Loops?
Authors: Cirtain, J. W.; Schmelz, J. T.
Bibcode: 2002mwoc.conf...79C
Altcode:
Isothermal Approximation vs. Differential Emission Measure Analysis:
How Hot are Hot LoopsNULL J. W. Cirtain and J. T. Schmelz Department
of Physics, University of Memphis, Memphis, TN 38152 USA Abstract
Analysis of EUV data from both EIT and TRACE suggests that active
region loops may be isothermal. These results are in sharp contrast
to the multi-thermal loops obtained from the analysis of X-ray data
from SXT. The analysis of all these observations uses an isothermal
approximation, but the EUV results are derived from narrow-band
filter ratios while the X-ray results use a broad-band ratio. We
have incorporated CDS data into the mix in two different ways: (a)
we have used an isothermal approximation with different iron line
ratios to determine temperatures at various pixels along a couple of
(relatively) isolated coronal loops on the limb; and (b) we have used
multiple spectral lines from the same data sets to produce differential
emission measure distributions at these pixels. The data sets were
obtained from observations taken on 13 Nov 1997 and 20 Apr 1998 by
both CDS and SXT. We find that different instruments and/or different
methods of analysis give different results. In some sense, this is
not surprising since the limitations of the isothermal approximation
are well understood. What is surprising, however, is that we sometimes
forget these limitations.
Title: Why stellar astronomers should be interested in the sun
Authors: Schmelz, J.
Bibcode: 2002cosp...34E1222S
Altcode: 2002cosp.meetE1222S
By all accounts, the Sun is a garden-variety star with an average age,
a standard size, a regular temperature, a normal mass, an ordinary
structure, and a typical chemical composition. Only one feature makes
it special - the Sun is our star. It is located in the center of our
solar system, and therefore, is responsible for all l fe on Earth.i
Astronomically speaking, the Sun is the only star in the sky that we
can study up- close and personal. The unaided human eye does a better
job of resolving the Sun than the finest telescope does for any other
star. Stellar astronomers issue a press release whenever they can
lay a few pixels of some state-of the-art instrument across a nearby
supergiant. The resolution of the Sun, however, is something we can see
routinely in the magnificent images that are downloaded every day from
the TRACE spacecraft. In a very real sense, the Sun is the Rosetta Stone
of the Stars. It was observations of the Sun deflecting starlight that
ushered in a new way of thinking about gravity. Zeeman observations of
the Sun showed that stellar atmospheres were controlled by magnetic
fields. Models of the solar chromosphere required the development of
more complex non-LTE analysis. The discovery of solar helium founded
the science of stellar spectroscopy. Measurements of the solar mass,
radius, and temperature allowed scientists to probe the interiors of
stars for the first time. The ancient age of the Sun implied that
stars shine as a result of thermonuclear fusion. Observations of
solar flares stimulated developments in rapid magnetic reconnection
theory. The study of solar coronal holes lead to a deeper understanding
of the role that mass loss plays in the evolution of stars. Detailed
analysis of the solar activity cycle inspired the development of MHD
dynamo theory. The detection and understanding of the solar corona u
covered one of the longest unsolvedn mysteries in all of astrophysics -
the coronal-heating problem. And the list goes on. The Sun is indeed
a Laboratory for Astrophysics, but it is more than that. The Sun is
a Laboratory for All of Physics.
Title: Observational Constraints on Coronal Heating Models Using
Coronal Diagnostics Spectrometer and Soft X-Ray Telescope Data
Authors: Schmelz, J. T.; Scopes, R. T.; Cirtain, J. W.; Winter, H. D.;
Allen, J. D.
Bibcode: 2001ApJ...556..896S
Altcode:
We have constructed a multithermal differential emission measure
distribution for several pixels along a relatively isolated coronal loop
on the southwest limb of the solar disk using spectral line data from
the Solar and Heliospheric Observatory coronal diagnostics spectrometer
(CDS) and broadband data from the Yohkoh soft X-ray telescope. The
temperature distributions are clearly inconsistent with isothermal
plasma along either the line of sight or the length of the loop. These
conclusions disagree with some recent results that used an isothermal
approximation derived from narrowband filter ratios to calculate
loop temperature profiles. The differences between their results
and ours could be attributed to pixel size-CDS pixels are larger,
and more ``contaminating'' material would be expected along the line
of sight. To test this idea, we used CDS iron line ratios from our
data set to mimic the isothermal results from the narrowband filter
instruments. The results gave temperature gradients that were almost
flat, indicating that the larger CDS pixel size is not the cause of
the discrepancy. A significant intensity was measured for the O V
line about 8 scale heights above the limb. In order to account for
these observed values, the cool end (below 1 mK) of the emission
measure curves must turn up again, even for the pixels at the top
of the loop. Plasma densities fell off with loop height producing a
relatively constant pressure, and radiative losses were greater than,
but did not overwhelm, conductive losses.
Title: Are Active Region Loops Isothermal?
Authors: Schmelz, J. T.; Edwards, C. R.; Blevins, H. T.
Bibcode: 2001AGUSM..SH41B02S
Altcode:
Recent results from both EIT and TRACE data suggest that active region
loops may be isothermal. The analysis of these observations uses
an isothermal approximation derived from narrow-band filter ratios -
either 171 (Fe IX; T = .63 MK) to 195 (Fe XII; T = 1.6 MK) angstroms or
195 (Fe XII; T = 1.6 MK) to 284 (Fe XV; T = 2.0 MK) angstroms. These
findings imply that the loops cannot be in quasi-static equilibrium
unless very strict, possibly unphysical restrictions are met. These
results are in sharp contrast to the multi-thermal loops obtained
from the analysis of: (a) SXT data, which also uses an isothermal
approximation, but one derived from a broad-band filter ratio; (b)
CDS data, where individual spectral lines have been used to produce
a differential emission measure distribution at multiple pixels
along several loops. One possible reason for the discrepancy is the
larger pixel size of both SXT and CDS - it is possible that neither
instrument is observing a single, isolated loop, but rather a loop
bundle which is not resolved. Each individual loop could be isothermal,
but the unresolved collection could mimic a multi-thermal loop that is
both hydrostatic and in quasi-static equilibrium. To test this idea,
we do two related analyses: we do the EIT and TRACE analysis with
bigger pixels that match the size of SXT and CDS pixels; and we do an
isothermal approximation with different iron line ratios from CDS.
Title: Comparing Active Region Plasma Parameters Using Differential
Emission Measure Techniques
Authors: Winter, H. D.; Schmelz, J. T.; Medlin, D. A.
Bibcode: 2001AGUSM..SH41B22W
Altcode:
In order to study solar active regions and the processes that drive
them, it is necessary to accurately describe the elemental abundances,
electron densities, and temperature distributions of the emitting
plasma. The best way to determine these vital parameters is with
multi-thermal analysis techniques, which have fewer initial assumptions
than their isothermal counterparts. The reliability of these emission
measure distributions depends on spectroscopic observations of a large
sample of emitting ions over a wide temperature range. The Solar EUV
Rocket Telescope and Spectrograph (SERTS) is well suited for studying
multi-thermal coronal structures. It provides observations of numerous
emission lines with excellent spectral resolution. Simultaneous
observations taken with the Soft X-ray Telescope were combined with
the SERTS data in order to constrain the high-temperature end of the
multi-thermal distribution. Three active regions (AR 7563, AR 7870,
and AR 8108) observed with both instruments were chosen for this
investigation. The results of our analysis show how certain plasma
parameters -- emission measure distributions, electron densities,
and elemental abundances -- vary from region to region.
Title: Relative Coronal Abundances from Yohkoh SXT and SERTS Data
Authors: Marino, C. P.; Schmelz, J. T.; Winter, H. D.
Bibcode: 2000SPD....31.0224M
Altcode: 2000BAAS...32.1290M
There is strong evidence documented in the literature to suggest
that elemental abundances vary not only from the photosphere to the
corona, but also from flare to flare and even active region to active
region. In this study, coronal abundances for Active Region 7563 were
obtained using a combination of broad-band filter data from Yohkoh
SXT and simultaneous spectral line data from the SERTS rocket taken
during its flight on 1993 August 17. We have used a forward-folding
technique to determine the emission measure distribution of the active
region plasma using the SERTS iron lines and the SXT filters. The
response of these filters is dominated by the numerous iron lines of
various ionization states in the X-ray portion of the spectrum. The
SXT data are used primarily to constrain the high-temperature end of
the emission measure distribution. The abundances of elements other
than iron were then adjusted to achieve the best agreement with the
original curve. Preliminary results suggest that lowering the abundance
of silicon and raising the abundance of magnesium from the values found
by Fludra & Schmelz (1999, A&A, 348, 286) will significantly
improve the agreement with the original curve. This work is supported
by NASA grant NAG5-7197.
Title: Diagnostic Constraints for Loop Dynamics Models
Authors: Schoepke, B. H.; Schmelz, J. T.; Scopes, R. T.; Cirtain,
J. W.; Edwards, C. R.
Bibcode: 2000SPD....31.0213S
Altcode: 2000BAAS...32R.813S
An accurate determination of the temperature distribution of a coronal
loop is an essential first step to understanding the plasma emission
measure, density, and filling factor. These quantities are important
inputs in determining, for example, the energy balance and heating
requirements, the stability, as well as the radiative losses and
conductive cooling times. These loops are a basic and abundant type of
coronal feature. Because they are inherently bright, they are a target
of choice to learn more about the coronal structure in general. Despite
much progress in recent years, the physical properties of loops are not
fully understood. In fact, seemingly contradictory observations from
different instruments have created conflicting ideas about their true
physical properties. We have used high-resolution EUV spectral line data
from SOHO-CDS and imaging data gathered simultaneously with Yohkoh-SXT
to determine the temperature height structure of selected quiescent
active region loops. Combining these simultaneous plasma measurements in
different wavebands using different observing techniques will lead to
an improved understanding of the properties and structures of coronal
loops as well as provide an effective temperature cross-calibration of
these two instruments. This work is supported by NASA grant NAG5-7197.
Title: Using the Results of Multi-Thermal Analysis to Constrain
Coronal Heating Models
Authors: Scopes, R. T.; Schmelz, J. T.
Bibcode: 2000SPD....31.0212S
Altcode: 2000BAAS...32Q.813S
Despite recent progress in understanding the solar corona, there are
still important parameters and processes that remain elusive. Chief
among them is the coronal heating problem, i.e., the precise
physical mechanism(s) by which the solar atmosphere is heated to
its million-degree temperatures. Although there is a rich database of
theoretical models described in the literature, there are few diagnostic
constraints that can help determine which of these possible models, if
any, is correct. Insights into the nature of the heating mechanism can
be gained through the analysis of differential emission measure curves
localized along isolated coronal loops. Simultaneous observations of
such a loop were taken on 20 April 98 with the SOHO-CDS and YOHKOH-SXT
instruments. Plasma temperature distributions in the range log T =
4.5-7.5 at various positions along to loop were constructed using
a forward-folding technique. This analysis used elemental abundance
values from Fludra & Schmelz (1999, A & A, 348, 286) and
ionization fractions from Arnaud & Raymond (1992, ApJ, 398, 394) for
iron and from Arnaud & Rothenflug (1985, ApJS, 60, 425) for other
elements. The differential emission measure curve at each pixel combined
with knowledge of the loop geometry helped to pin down the coronal
heating mechanism using the method described by Priest et al.(1998,
Nature, 393, 545). This work is supported by NASA grant NAG5-7197.
Title: Using Forward-Folding of SERTS and Yohkoh SCT Data to Estimate
the Electron Densities of Coronal Plasma
Authors: Schmelz, J. T.; Winter, H. D.
Bibcode: 1999ESASP.446..593S
Altcode: 1999soho....8..593S
No abstract at ADS
Title: Use of Experimental Multi-Thermal Plasma Distributions as a
Constraint for Coronal Heating Models
Authors: Schmelz, J. T.; Scopes, R. T.; Wülser, J. -P.
Bibcode: 1999ESASP.446..589S
Altcode: 1999soho....8..589S
No abstract at ADS
Title: The Elemental Composition of the Solar Corona: Abundance
Normalization and Possible Abudance Variability
Authors: Schmelz, J. T.
Bibcode: 1999ESASP.446..585S
Altcode: 1999soho....8..585S
Knowledge of the abundances of trace elements relative to hydrogen
-- absolute abundances -- in solar coronal plasma is essential for
the understanding of plasma conditions. Both spectroscopic and solar
energetic particle data agree that the coronal-to-photospheric abundance
ratios of elements with low First Ionization Potential (FIP < 10
eV) seem to be enhanced by about a factor of four relative to those
with high FIP (> 11 eV). The observations, however, do not agree
on the normalization of the trace elements with respect to hydrogen,
a result which is problematic in both the spectroscopic and particle
data analysis. Two different empirical models have been suggested
in the literature: (1) low-FIP elements may be enhanced by about
a factor of four with respect to their photospheric values while
high-FIP elements are the same in the corona and the photosphere; or
(2) low-FIP elements may be the same in the corona and the photosphere
while high-FIP elements are depleted by about a factor of four with
respect to their photospheric values. Unfortunately, however, neither of
these two empirical models accurately represents the data. We have used
the absolute coronal abundance results from several groups using both
spectroscopic and energetic particle data to show that a much better
representation is achieved with a 'hybrid' set of abundances. In this
empirical model, there is both low-FIP enhancement as well as high-FIP
depletion, each by about a factor of two. The data clearly show that
it is impossible for one model to satisfy all observations. It is
also vital to account for the possibility of abundance variability
when analyzing any data set. However, it is often useful to begin
the analysis with an assumed set of coronal abundances. The hybrid
abundances represent the best average values for all available data.
Title: Emission Measure Distribution for an Active Region Using
Coordinated SERTS and YOHKOH SXT Observations
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Winter, H. D.;
Brosius, J. W.
Bibcode: 1999ApJ...523..432S
Altcode:
Often the derived temperature of an active region reflects the
method and the nature of the instrument used in its measurement. The
emission measure (i.e., the amount of emitting material) derived
from spectroscopic observations usually depends on assumptions about
the absolute elemental abundances and ionization fractions of the
emitting ions. Yet establishing the distribution of emission measure
with temperature is the first step needed to proceed with most of the
interesting physics of active regions--including heating processes,
cooling timescales, and loop stability. Accurately characterizing
the thermal distribution of the coronal plasma requires data which
can resolve multithermal features and constrain both low- and
high-temperature emission. To model the temperature distribution
of NOAA Active Region 7563, we have combined broadband filter
data from the Yohkoh Soft X-Ray Telescope (SXT) with simultaneous
spectral line data from the Goddard Solar EUV Rocket Telescope and
Spectrograph (SERTS) taken during its flight on 1993 August 17. We
have used a forward-folding technique to determine the emission
measure distribution of the active region loops. We have found that
(1) the SXT response functions are sensitive to both the elemental
abundances and the ionization fractions assumed to compute the solar
spectrum that is folded through the instrument effective area; (2) the
relative calibration between the SERTS and the SXT instruments must
be adjusted by a factor of 2 (a value consistent with the absolute
measurement uncertainty of the 1993 SERTS flight) no matter which
abundances or iron ionization fractions are used; (3) the two-peaked
differential emission measure previously determined using SERTS data
alone is not consistent with the SXT data: including the SXT data
as a high-temperature constraint in the analysis requires that the
emission above about 3 MK drop off steeply rather than extending out to
6 MK. The sensitivity of the SXT filter response functions to elemental
abundance and iron ionization fraction could have a major impact on
many routine analyses of SXT data. The emission measures can be greatly
affected (up to a factor of 7) and temperatures derived from filter
ratios can be significantly altered (up to at least 40%) by adopting
different sets of commonly used elemental and ionic abundances. The
results of our multithermal analysis imply that using broadband SXT
data or a comparable high-temperature constraint in conjunction with
high-resolution spectra covering a wide lower temperature range to study
solar active regions can significantly improve the information derived
from either data set alone. In this study, the revised multithermal
distribution reduces the thermal energy content of the region by about
a factor of 2 and the required heating by about a factor of 5, which
in turn relaxes some constraints on possible heating models.
Title: The absolute coronal abundances of sulfur, calcium, and iron
from Yohkoh-BCS flare spectra
Authors: Fludra, A.; Schmelz, J. T.
Bibcode: 1999A&A...348..286F
Altcode:
Using X-ray spectra from the Bragg Crystal Spectrometer on Yohkoh,
we have derived the absolute coronal abundances of sulfur, calcium,
and iron using the ratio of the flux in the S XV, Ca XIX and Fe XXV
resonance lines to the continuum near the Ca XIX and S XV resonance
lines. For the 57 flares analyzed here, multi-thermal effects have been
taken into account using a differential emission measure analysis. We
compare these abundances of S, Ca, and Fe with their photospheric values
and with values derived for coronal plasma from both spectral and solar
energetic particle data. The mean Yohkoh abundance of sulfur relative
to hydrogen is 7.9 x 10(-6) , smaller than the photospheric value by
over a factor of two. The mean abundance of calcium is 3.4 x 10(-6)
, about 50% greater than the photospheric value. The mean abundance
of iron shows greater scatter around its mean value of 4.5 x 10(-5) ,
but is still higher than the accepted photospheric value. Comparison of
these results with others already in the literature, suggests that the
coronal abundance-normalization problem does not have a simple solution.
Title: A New Diagnostic Constraint for Coronal Heating Models
Authors: Scopes, R. T.; Schmelz, J. T.; Wuelser, J. -P.
Bibcode: 1999AAS...194.7809S
Altcode: 1999BAAS...31..962S
Despite recent progress in understanding the solar corona, there are
still important parameters and processes that remain elusive. Chief
among them is the coronal heating problem, the precise physical
mechanism(s) by which the solar atmosphere is heated to its
million-degree (or greater) temperatures. It is not yet known how
this energy is stored, released, and dissipated. Theoretical arguments
classify coronal heating mechanisms as either dissipation of MHD waves
or dissipation of field-aligned electric currents. When reasonable
estimates of the current density and wave amplitudes are combined with
the classical coefficients of resistively and viscosity, the derived
heating rates are too low to balance the energy losses through radiation
and conduction. Fortunately, there is a rich database of theoretical
models described in the literature that attempts to explain how the
dissipation rates are enhanced over the classical estimates. Since
many of these theoretical models can produce enough energy to balance
the observed losses from both radiation and conduction, the coronal
heating problem is then to determine which of these possible models,
if any, is correct. We are involved in a joint analysis of plasma
parameter measurements obtained from high-resolution EUV spectral line
data from the SOHO Coronal Diagnostics Spectrometer, and imaging data
gathered simultaneously with the Yohkoh Soft X-ray Telescope. These data
were used to determine the multi-thermal distribution at each pixel
along a set of quasi-stable coronal loops using the forward-folding
technique. Specifically, our focus has been comparison of measurements
taken form coronal loop footpoints with those of their respective
peaks. We are currently comparing our observational results with the
temperature profiles predicted by various coronal heating mechanisms
to determine which of these mechanisms, if any, is responsible for the
loop heating (Priest et al. 1998, Nature, 393, 545). This research is
supported through NASA grant NASG5-7197.
Title: Estimating Electron Densities of Coronal Plasma Using
Forward-Folding
Authors: Winter, H. D., III; Schmelz, J. T.; Saba, J. L. R.
Bibcode: 1999AAS...194.1604W
Altcode: 1999BAAS...31..850W
Understanding features and phenomena on the Sun requires knowledge
of the basic plasma parameters, such as composition, temperature,
emission measure, electron density, filling factors, and their
distributions. Establishing the distribution of emission measure
(the amount of emitting material) with temperature is the first step
needed to proceed with most of the interesting physics of active
regions -- including heating processes, cooling timescales, and loop
stability. The reliability of emission measure distributions derived
from spectroscopic observations usually depends upon the validity of
the assumptions about the absolute elemental abundances, ionization
fractions of the emitting ions, and the electron density. Inaccuracies
in the electron density assumptions can lead to emission measure
distributions that do not correctly describe the observed plasma. To
model the temperature distribution of NOAA Active Region 7563, we have
combined broad-band filter data from the Yohkoh Soft X-ray Telescope
(SXT) with simultaneous spectral data of iron lines from the Goddard
Solar EUV Rocket Telescope and Spectrograph (SERTS) taken during its
flight on 1993 August 17. We have used a forward-folding technique to
determine an emission measure distribution of the active region loops
using different assumptions for the electron density while holding
other assumptions about the plasma constant. We have found that: (1)
Assuming an electron density of 10(9) cm(-3) yields a good degree
of agreement between theoretical and observed results. (2) With an
electron density of 10(10) cm(-3) it becomes impossible to derive an
emission measure with good agreement between theoretical and observed
results. The results of our multithermal analysis imply that an average
electron density of 10(9) cm(-3) is a satisfactory assumption for the
plasma of NOAA Active Region 7563 as viewed by the SXT and the SERTS
instruments. Solar physics research at the University of Memphis is
supported through NASA grant NAG5-7197.
Title: The Hybrid Set of Absolute Coronal Abundances
Authors: Schmelz, J. T.; Fludra, A.
Bibcode: 1999AAS...19410001S
Altcode: 1999BAAS...31..996S
Knowledge of the abundances of trace elements relative to hydrogen
-- absolute abundances -- in the solar corona is essential for the
understanding of plasma conditions. Both spectroscopic and solar
energetic particle data agree that the coronal-to-photospheric abundance
ratios of elements with low First Ionization Potential (FIP <10
eV) seem to be enhanced by about a factor of four relative to those
with high FIP (>11 eV). The observations, however, do not agree
on the normalization of the trace elements with respect to hydrogen,
a result which is problematic in both the spectroscopic and particle
data analysis. Two different empirical models have been suggested
in the literature: (1) low-FIP elements may be enhanced by about
a factor of four with respect to their photospheric values while
high-FIP elements are the same in the corona and the photosphere; or
(2) low-FIP elements may be the same in the corona and the photosphere
while high-FIP elements are depleted by about a factor of four with
respect to their photospheric values. Unfortunately, however, neither of
these two empirical models accurately represents the data. We have used
the absolute coronal abundance results from several groups using both
spectroscopic and energetic particle data to show that a much better
representation is achieved with a 'hybrid' set of abundances. In this
empirical model, there is both low-FIP enhancement as well as high-FIP
depletion, each by about a factor of two. The data clearly show that
it is impossible for one model to explain all observations. It is
also vital to account for the possibility of abundance variability
when analyzing any data set. However, it is often useful to begin
the analysis with an assumed set of coronal abundances. The hybrid
abundances represent the best average values for all available data.
Title: Fe XVII Soft X-Ray Lines: Theory and Data Comparisons
Authors: Saba, J. L. R.; Schmelz, J. T.; Bhatia, A. K.; Strong, K. T.
Bibcode: 1999ApJ...510.1064S
Altcode:
Fe XVII soft X-ray spectral emission lines are examined using data
from the Flat Crystal Spectrometer (FCS) on the Solar Maximum Mission
satellite. Results are compared with theoretical calculations and with
other recent observational results. Disparate findings from different
studies on the inferred opacity of the bright resonance line at 15.01 Å
and on its center-to-limb behavior are reviewed. Present limitations on
the use of resonance scattering to infer coronal plasma densities and
absolute elemental abundances are discussed. An analysis is made of the
temperature-insensitive ratio of the 15.01 Å line of Fe XVII to the
optically thin 16.78 Å line. This analysis shows that approximately
half of the photons expected in the 15.01 Å line are missing from the
bright emission cores of quiescent active regions on the solar disk;
the missing fraction increases at most by 50% near the solar limb. If
the missing flux has been resonantly scattered out of the line of sight,
then the equivalent optical depth at line center of the 15.01 Å line
is τ0~2 on the disk, based on a simple escape probability
treatment for a slab geometry. This suggests that the effects of
resonance scattering for other FCS lines, with the possible exception
of the O VIII doublet at 18.97 Å, should be negligible for quiescent
active region conditions. This is consistent with the lack of systematic
center-to-limb dependence found previously for FCS lines other than
Fe XVII at 15.01 Å. Yohkoh Soft X-ray Telescope measurements of the
expected lines of sight for active regions as a function of location
on the solar disk, and resonance scattering results from other soft
X-ray active region data sets all support a trend of increased opacity
at the limb compared to disk center.
Title: The many faces of the sun : a summary of the results from
NASA's Solar Maximum Mission
Authors: Strong, Keith T.; Saba, Julia L. R.; Haisch, Bernhard M.;
Schmelz, Joan T.
Bibcode: 1999mfs..conf.....S
Altcode:
No abstract at ADS
Title: The Solar Maximum Mission
Authors: Strong, K. T.; Schmelz, J. T.
Bibcode: 1999mfs..conf....1S
Altcode:
The Origins of the Mission Scientific Objectives of the Mission The SMM
Instrument Package The γ-Ray Spectrometer (GRS) The Hard X-Ray Burst
Spectrometer (HXRBS) The Hard X-Ray Imaging Spectrometer (HXIS) The
Bent Crystal Spectrometer (BCS) The Flat Crystal Spectrometer (FCS) The
Ultraviolet Spectrometer/Polarimeter (UVSP) The Coronagraph/Polarimeter
(C/P) The Active Cavity Radiometer Irradiance Monitor (ACRIM) Scientific
Discoveries Concluding Remarks
Title: Clarifying the Picture of Fe XVII Opacity in the Solar Corona
Authors: Saba, J. L. R.; Strong, K. T.; Schmelz, J. T.
Bibcode: 1997SPD....28.0145S
Altcode: 1997BAAS...29..887S
Several recent studies of opacity in the bright resonance line of Fe
XVII at 15.01 Angstroms have yielded disparate results. Discrepancies
include the magnitude of the inferred resonance scattering effects,
the amount of center-to-limb variation, and even the sign of the
center-to-limb change. The larger optical depths inferred by Waljeski
et al. (1994 ApJ 429, 909) compared to those found by Schmelz,
Saba, & Strong (1992 ApJ 398, L115) and by Saba et al. (1997, in
prep.) in active region data from the Solar Maximum Mission Flat Crystal
Spectrometer (FCS) could be explained by allowing for an estimated 20%
relative uncertainty in the calculated emissivities of pairs of Fe XVII
lines (A.K. Bhatia, private communication). The lower values of optical
depth are supported by a demonstrated lack of measurable opacity in
other potentially affected FCS lines (Schmelz et al. 1997 ApJ 477,
509). On the other hand, it is impossible to reconcile the report by
Phillips et al. (1997 ApJ 469, L57) of a large decrease in opacity
from disk center to the limb, with the more usual behavior found by
Schmelz et al. (1997) and Saba et al. (1997), i.e., a slight increase
in opacity for regions at or near the limb due to the increased line
of sight. A reality check can be made with Yohkoh SXT intensities
and with other soft X-ray spectroscopic data sets. We will also
discuss the use and abuse of resonance scattering as a coronal plasma
diagnostic tool. Resonance scattering is likely to be relevant for SOHO
observations, for some bright EUV resonance lines with high elemental
abundance, large ionization fraction, and moderate oscillator strength,
such as Fe XV at 284 Angstroms. This work was supported by NASA contract
NASW-4814 and the Lockheed-Martin Independent Research Program.
Title: Measuring Active Region Temperatures with SERTS and YOHKOH
(SXT) Data
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1997SPD....28.0139S
Altcode: 1997BAAS...29..886S
Often the derived temperature of an active region reflects the
method and the nature of the instrument used in its measurement. Yet
establishing the temperature is the first step needed to proceed
with most of the interesting physics of active regions -- including
heating processes, loop stability, and cooling timescales. Accurately
characterizing the thermal distribution of the coronal plasma requires
data which can resolve multi-thermal features and which also constrain
both low- and high-temperature emission. To model the temperature
distribution of NOAA Active Region 7563, we have combined broad-band
filter data from the Yohkoh Soft X-ray Telescope (SXT) with simultaneous
spectral line data from the Goddard Solar EUV Rocket Telescope and
Spectrograph (SERTS) taken during its flight on 17 August 1993. From
the SERTS data alone, Brosius et al. (1996) produced a double-peaked
differential emission measure (DEM) distribution (see their Figure
8), but the higher-temperature ( 4 MK) peak was at the extreme end of
the SERTS range of sensitivity, and so was uncertain. But the higher
temperature response of SXT can be used to cross-check the reality of
this high-temperature feature -- we adjusted the response functions
of the three SXT filters available for this observation by replacing
the Meyer (1985) elemental abundances normally used in SXT analysis
with the coronal abundance set of Feldman (1992), which was used by
Brosius et al. (1996). We then folded the SERTS DEM curve through the
adjusted SXT responses, and found that the high-temperature DEM peak
was NOT consistent with the SXT data. The SERTS and SXT data sets
could be reconciled only if the high-temperature peak was eliminated
from the DEM curve. We also discuss how the SXT responses change with
the assumed set of elemental abundances. In particular, a change in the
normalization of heavy elements with respect to hydrogen does NOT yield
a simple scaling factor in the emission measure, and the temperature
responses of filter ratios are also affected. Brosius et al. 1996,
ApJ Suppl., 106, 143. Feldman 1992, Phys. Scr., 46, 202. Meyer 1985,
ApJ Suppl., 57,173.
Title: Investigating the effect of Opacity in Soft X-Ray Spectral
Lines Emitted by Solar Coronal Active Regions
Authors: Schmelz, J. T.; Saba, J. L. R.; Chauvin, J. C.; Strong, K. T.
Bibcode: 1997ApJ...477..509S
Altcode:
Current literature suggests that several lines in the soft X-ray portion
of the coronal spectrum may not be optically thin. Here, we wish to
check this possibility for five of the brightest resonance lines in
this part of the spectrum--O VIII at 18.97 Å, Fe XVII at 15.25 Å, Fe
XVII at 15.01 Å, Ne IX at 13.45 Å, and Mg XI at 9.17 Å. A comparison
is made between each of these resonance lines and an optically thin
``reference'' line produced by the same element in the same ionization
state--O VIII at 16.01 Å, Fe XVII at 16.78 Å, Ne IX at 13.70 Å,
and Mg XI at 9.31 Å. In the latter two cases, the comparison line is
the forbidden line of the He-like triplet. The spectra are from
the Solar Maximum Mission Flat Crystal Spectrometer, which had a FWHM
field of view of 15" and could scan the soft X-ray resonance lines
of prominent ions in the 1.5-20.0 Å portion of the spectrum. Here
33 spectra are analyzed, all of which were obtained from nonflaring,
quasi-stable active regions. For the quiescent regions selected,
the data for the Fe XVII line at 15.01 Å are clearly consistent with
resonance scattering, with an increasing trend from Sun center to the
limb. For the other lines tested, however, we find neither significant
opacity effects nor center-to-limb variations.
Title: Opacity effects in soft X-ray spectral lines of the solar
corona
Authors: Schmelz, J. T.; Chauvin, J. C.; Saba, J. L. R.
Bibcode: 1997AdSpR..20.2259S
Altcode:
Current literature suggests that several lines in the soft X-ray
portion of the coronal spectrum may not be optically thin. Here, we
confirm the results of Schmelz et al. (1996) who find no significant
opacity effects for three of the brightest non-iron resonance lines
in this part of the spectrum - O VIII at 18.97A˚, Ne IX at 13.45A˚,
and Mg XI at 9.17A˚. A comparison is made between each of these lines
and an optically thin ``reference'' line produced by the same element
in the same ionization state - O VIII at 15.18A˚, Ne IX at 13.55A˚,
and Mg XI at 9.23A˚. In the latter two cases, the comparison line
is the intersystem line of the He-like triplet. 33 spectra from the
Solar Maximum Mission Flat Crystal Spectrometer are analyzed, all of
which were obtained from non-flaring, quasi-stable active regions.
Title: Ne/O, Mg/O and Fe/O abundances derived from spectroscopic
and SEP analysis
Authors: Schmelz, J. T.; Saba, J. L. R.; Islam, B.
Bibcode: 1997AdSpR..20...87S
Altcode:
The relative abundances Ne/O, Mg/O, and Fe/O derived from 33 Solar
Maximum Mission Flat Crystal Spectrometer spectra are compared with
those derived from the in situ Solar Energetic Particle analysis of
Reames (1995). The spectra were obtained from non-flaring, quasi-stable
active regions and include lines of the ions Mg XI (9.17 A˚), Ne IX
(13.45 A˚), Fe XVIII (14.22 A˚), Fe XVII (15.25 A˚), Fe XVII (16.78
A˚), and O VIII (18.97 A˚) which were used in this study. With a
characteristic temperature determined from the ratio of the Fe XVIII
to Fe XVII (16.78 A˚) line fluxes, the abundance ratios are obtained
using the fluxes and emissivity functions of lines from these different
elements.
Title: Anomalous Coronal Neon Abundances in Quiescent Solar Active
Regions
Authors: Schmelz, J. T.; Saba, J. L. R.; Ghosh, D.; Strong, K. T.
Bibcode: 1996ApJ...473..519S
Altcode:
The systematic differences between the solar photo spheric and coronal
composition are generally thought to be related to the first ionization
potential (FIP) of the trace elements. While there are ample data
showing that this is a significant factor, there is a growing body of
observational evidence that a simple, FIP-based formula is not the whole
story for coronal abundances. One of the most troubling problems for
the Fl P-based models is the apparent abundance variation of high-FIP
(>11 eV) elements with respect to one another. We describe abundance
variations of (high-FIP) neon relative to (high-FIP) oxygen, and
(low-FIP) iron and magnesium, in solar active region observations made
by the Flat Crystal Spectrometer on the Solar Maximum Mission. We show
that, even in quiescent active regions, Ne/O can vary inconsistently
with simple empirical FIP models: it shows values about a factor of
2 both above and below the "standard" coronal value of 0.15 obtained
from solar energetic particle measurements of long-duration events
(Reames). McKenzie & Feldman have recently invoked photoionization
of O I by EUV radiation to explain low measurements of the Ne/O
abundance ratio. Photoionization by a long-lived bath of soft
X-rays and chromospheric evaporation have been suggested as being
responsible for the anomalous behavior of neon in flares, but flare
conditions should not apply in the quiescent regions of the present
study. A complex picture involving the detailed dynamics, geometry,
and radiation environment in the differentiation layer(s) may be
required to understand coronal composition and its variability.
Title: Opacity Effects in Soft X-Ray Spectral Lines of the Solar
Corona
Authors: Schmelz, J. T.; Chauvin, J. C.
Bibcode: 1996AAS...188.3606S
Altcode: 1996BAAS...28..874S
Current literature suggests that several lines in the soft X-ray
portion of the coronal spectrum may not be optically thin. Here,
we wish to confirm the results of Schmelz, et al (1996, Submitted
to Ap.J.) who find no significant opacity effects for three of the
brightest non-iron resonance lines in this part of the spectrum --
O VIII at 18.97 Angstroms, Ne IX at 13.45 Angstroms, and Mg XI at
9.17 Angstroms . A comparison is made between each of these lines
and an optically thin ``reference'' line produced by the same element
in the same ionization state -- O VIII at 15.18 Angstroms, Ne IX at
13.55 Angstroms, and Mg XI at 9.23 Angstroms. In the latter two cases,
the comparison line is the intersystem line of the He-like triplet. 33
spectra from the Solar Maximum Mission Flat Crystal Spectrometer are
analyzed, all of which were obtained from non-flaring, quasi-stable
active regions.
Title: Ne/O, Mg/O, and Fe/O Abundances Derived from Spectroscopic
and SEP Analysis
Authors: Islam, B.; Schmelz, J. T.
Bibcode: 1996AAS...188.7017I
Altcode: 1996BAAS...28..941I
Ne/O. Mg/O, and Fe/O abundances derived from 33 Solar Maximum Mission
Flat Crystal Spectrometer spectra are compared with those derived
from the in situ Solar Energetic Particle analysis of Reames (1995,
Adv. Space Res., 15 (7)41). The spectra were obtained from non-flaring,
quasi-stable active regions and include lines of the Mg XI (9.17
Angstroms), Ne IX (13.45 Angstroms), Fe XVIII (14.22 Angstroms),
Fe XVII (16.78 Angstroms), and O VIII (18.97 Angstroms) which were
used in this study. With a temperature determined from the ratio
of the Fe XVIII to Fe XVII line fluxes, the abundance ratios are
obtained using: $ {F_{Ne,Mg,Fe} / FO} = {{A_{Ne,Mg,Fe} \
G_{Ne,Mg,Fe}(T_e)} / {AO \ GO(T_e)}} => {
{A_{Ne,Mg,Fe} / AO}} where F is the line flux, A is the
abundance, and G(T)$ is the emissivity function.
Title: Absolute Abundances of Flaring Coronal Plasma Derived from
SMM Spectral Observations
Authors: Fludra, A.; Schmelz, J. T.
Bibcode: 1995ApJ...447..936F
Altcode:
X-ray spectra simultaneously observed by the Flat Crystal Spectrometer
and Bent Crystal Spectrometer on Solar Maximum Mission have been
analyzed for two solar flares. Elemental abundances for O, Ne, Mg, Si,
S, Ca, and Fe with respect to hydrogen have been derived with the aid
of a differential emission measure analysis. Absolute abundances of
elements with a high first ionization potential (FIP) are depleted in
the corona relative to their photospheric values. An indication for
a gradual change in the coronal-to-photospheric abundance ratio as a
function of FIP is found, rather than the step-function distribution
associated with solar energetic particles. The coronal abundance of
low-FIP calcium is enhanced by a factor of 1.5-2.0, while the high-FIP
oxygen is depleted by a factor of 0.25, with respect to photospheric
abundances. Anomalous values of neon and argon abundances are discussed.
Title: Abundances from SMM spectroscopic observations for non-flaring
coronal plasma
Authors: Schmelz, J. T.
Bibcode: 1995AdSpR..15g..77S
Altcode: 1995AdSpR..15R..77S
Plots of the Emission Measure vs. Temperature are used to look
for deviations from the ``standard'' coronal abundance values for
Oxygen, Neon, and Magnesium. The fluxes of three strong, relatively
simple soft X-ray emission lines (O VIII at 18.97 Angstroms, Ne IX
at 13.45 Angstroms, and Mg XI at 9.17 Angstroms) from spectra taken
of quiescent active regions are analyzed. For four of the active
regions investigated, the ``standard'' values of the abundances seem
appropriate but, in the cases of four others variations from these
values are required. The data indicate that the most likely source of
these differences is a variation of the Neon abundance.
Title: Abundance Variations from SMM Spectroscopic Observations of
Non-Flaring Plasma
Authors: Ghosh, D.; Schmelz, J. T.
Bibcode: 1995SPD....26..608G
Altcode: 1995BAAS...27..962G
No abstract at ADS
Title: Testing the Optically Thin Assumption for Soft X-Ray Spectral
Lines of the Solar Corona
Authors: Chauvin, J. C.; Schmelz, J. T.
Bibcode: 1995SPD....26..710C
Altcode: 1995BAAS...27..967C
No abstract at ADS
Title: Ne/O, Mg/O, and Fe/O Abundances Derived Spectroscopically
for Coronal Plasma
Authors: Schmelz, J. T.; Miller, T. R.; Saba, J. L. R.
Bibcode: 1995SPD....26..709S
Altcode: 1995BAAS...27R.967S
No abstract at ADS
Title: Coronal Magnetic Structures Observing Campaign. III. Coronal
Plasma and Magnetic Field Diagnostics Derived from Multiwaveband
Active Region Observations
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Willson, R. F.
Bibcode: 1994ApJ...434..786S
Altcode:
Simultaneous soft X-ray, microwave, and photospheric magnetic
field observations were taken during the Coronal Magnetic Structures
Observing Campaign (CoMStOC '87). The plasma electron temperature and
emission measures determined from the X-ray data are used to predict the
free-free emission expected at 20 and 6 cm. Comparing these predictions
with the microwave observations, it is found that the predicted 20 cm
brightness temperatures are higher than the observed, requiring cool
absorbing material between the hot X-ray plasma and the observer. The
model that is most consistent with all the observations and minimizes
the required coronal fields indicates that this 20 cm emission is
either free-free or a combination of free-free and fourth harmonic
cyclotron emanating from the X-ray plasma with an electron temperature
of approximately 3.1 x 106 K and an emission measure of
approximately 1.3 x 1029/cm5. The observed 20
cm polarization requires a field strength of greater than or equal
to 150 G. In addition, the 6 cm emission is free-free, emanating
from cooler plasma with an electron temperature of approximately
1.5 x 106 K and an emission measure of approximately 3-6
x 1029/cm5. This model is consistent with the
rather unusual combination of high 20 cm and low 6 cm polarization as
well as the low extrapolated coronal fields.
Title: A review of results from CoMStOC '87
Authors: Schmelz, J. T.
Bibcode: 1994smf..conf..384S
Altcode:
No abstract at ADS
Title: Unique SMM observations of an impulsive double solar flare:
Enhanced neon abundance
Authors: Schmelz, J. T.; Fludra, A.
Bibcode: 1993AdSpR..13i.325S
Altcode: 1993AdSpR..13..325S
The Solar Maximum Mission Flat Crystal Spectrometer observed a GOES
M5 double impulsive flare on 05 November 1980. Simultaneous spectra
of seven bright soft X-ray resonance lines provide information
over a broad temperature range (2-35 × 106 K) and are
available throughout the event. A differential emission measure
analysis reveals that the flux of the Ne IX resonance line is larger
than expected. Various sources of contamination, non-equilibrium and
multi-thermal effects, and possible errors in the atomic physics
calculations are investigated and eliminated as the source of the
unexpected flux, and it is suggested, rather, that the neon abundance
is enhanced in this flare.
Title: A Study of the Solar Active Regions Using Simultaneous VLA
and Yohkoh Soft X-ray Imaging: CoMStOC `92
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Schmelz, J. T.
Bibcode: 1993BAAS...25R1213G
Altcode:
No abstract at ADS
Title: Yohkoh Observations During the CoMStOC'92 Campaign
Authors: Strong, K.; Holman, G.; Schmelz, J.
Bibcode: 1993BAAS...25R1223S
Altcode:
No abstract at ADS
Title: Is Hydrogen Acting Like a High FIP or a Low FIP Element in
the Solar Corona?
Authors: Schmelz, J. T.; Strong, K. T.; Lemen, J. R.
Bibcode: 1993BAAS...25R1201S
Altcode:
No abstract at ADS
Title: Elemental Abundances of Flaring Solar Plasma: Enhanced Neon
and Sulfur
Authors: Schmelz, J. T.
Bibcode: 1993ApJ...408..373S
Altcode:
Elemental abundances of two flares observed with the SMM Flat Crystal
Spectrometer are compared and contrasted. The first had a gradual rise
and a slow decay, while the second was much more impulsive. Simultaneous
spectra of seven bright soft X-ray resonance lines provide information
over a broad temperature range and are available throughout both flares,
making these events unique in the SMM data base. For the first flare,
the plasma seemed to be characterized by coronal abundances but, for
the second, the plasma composition could not be coronal, photospheric,
or a linear combination of both. A good differential emission measure
fit required enhanced neon such that Ne/O = 0.32 +/- 0.02, a value
which is inconsistent with the current models of coronal abundances
based on the elemental first-ionization potential. Similar values of
enhanced neon are found for flaring plasma observed by the SMM gamma-ray
spectrometer, in (He-3)-rich solar energetic particle events, and in
the decay phase of several long duration soft X-ray events. Sulfur
is also enhanced in the impulsive flare, but not as dramatically
as neon. These events are compared with two models which attempt to
explain the enhanced values of neon and sulfur.
Title: Book-Review - the Sun - a Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.; Rutten, R. J.
Bibcode: 1993SSRv...65..370S
Altcode:
No abstract at ADS
Title: Book-Review - the Sun - a Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.; Staude, J.
Bibcode: 1992AN....313..348S
Altcode:
No abstract at ADS
Title: Coronal Magnetic Structures Observing Campaign. II. Magnetic
and Plasma Properties of a Solar Active Region
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Gonzalez, R. D.
Bibcode: 1992ApJ...399..733S
Altcode:
Simultaneous soft X-ray, microwave, and photospheric magnetic field
observations were taken during the Coronal Magnetic Structures
Observing Campaign. The plasma electron temperatures and emission
measures determined from the X-ray data are used to predict the
intensity and structure of the thermal bremsstrahlung emission at 20
and 6 cm. Comparing these predictions with the microwave observations,
it is found that the 20 cm structure is very similar to that expected
from the X-rays, but a substantial amount of the 6 cm emission was
resolved out. The predicted 20 cm brightness temperatures are higher
than the observed, requiring cool absorbing material (not greater
than 500,000 K) between the hot X-ray plasma and the observer. The
absorption mechanism in the cool plasma at 20 cm is most likely
thermal bremsstrahlung, requiring coronal magnetic fields as high as
150 G. 'Coronal Magnetograms', made by extrapolating the photospheric
longitudinal field using the Sakurai code, show that appropriate values
of the total field are reached at heights of 6000-10,000 km above the
photosphere (at many but not all locations).
Title: Resonance Scattering of Fe xvii: A Density Diagnostic
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1992ApJ...398L.115S
Altcode:
Resonance scattering of the 15.01 A Fe XVII line, found to be important
by Rugge & McKenzie, provides a new density diagnostic for solar
active regions that is not subject to the lower density limit of the
competing diagnostic. For a 'typical' active region, over 50 percent
of the photons for this resonance line could be scattered out of the
line of sight. The effect is much stronger for this line than for
any other line in the soft X-ray part of the spectrum used routinely
to determine active region electron temperatures, emission measures,
or densities. Once understood and accounted for in the analysis, the
resonance scattering of the 15.01 A Fe XVII line leads to a direct
measurement of the density of the active region plasma. In the four
active regions studied here, the derived densities range is 1-4 x 10
exp 9/cu cm.
Title: CoMStOC '92: The Coronal Magnetic Structures Observing Campaign
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.
Bibcode: 1992AAS...180.4511S
Altcode: 1992BAAS...24..804S
A primary goal of CoMStOC '92 is to directly measure the magnetic
field strength and determine its structure in the solar corona,
especially for pre- and post-flare active regions. New instrumentation
and analysis techniques were combined with experience gained during
a previous campaign to improve the observing strategies and data
interpretation. 15 days of VLA observation were scheduled between 03
April -- 12 May 1992. Observations were also obtained by the instruments
on the Japanese Yohkoh spacecraft, ground-based magnetographs, and
the Owens Valley Radio Observatory. At the time of writing, the Solar
Plasma Diagnostics Experiment rocket payload (M. Bruner, Lockheed)
planned to launch and the Tunable Filter (T. Tarbell, Lockheed)
planned to observe during the campaign. The basic CoMStOC method
for determining the magnetic field is as follows: When the microwave
emission is dominated by gyroresonance, the magnetic field strength
is B(Gauss) = 357times nu (GHz)/n, where nu is the microwave observing
frequency and n is the harmonic. When thermal bremsstrahlung dominates,
the field is determined by the microwave polarization. Maps of the
electron temperature and emission measure of the coronal plasma are
made from images taken with the Soft X-ray Telescope on Yohkoh; these
maps are then used to calculate which microwave emission mechanism
dominates. Once this dominant mechanism is known, the magnetic field
strength can be calculated. The values obtained using this method are
then compared with extrapolations photospheric magnetograms into the
corona. (*) NAS/NRC Resident Research Associate
Title: A Multi-Thermal Analysis of Two Solar Flares Observed with SMM
Authors: Schmelz, J. T.; Fludra, A.
Bibcode: 1992AAS...180.1804S
Altcode: 1992BAAS...24Q.755S
Two flares observed with the Solar Maximum Mission Flat Crystal
Spectrometer are compared and contrasted. The first (a GOES M1.5 flare)
had a gradual rise and a slow decay, while the second (a GOES M5 flare)
was much more impulsive. Spectra taken simultaneously of seven bright
resonance lines provide information over a broad temperature range
(2 - 35 MK) and are available throughout both flares. Simultaneous
data from the Bent Crystal Spectrometer are also available, making
these events unique in the Solar Maximum Mission database. Elemental
abundance variations, non-thermal line broadening, and Superhot
component existence are investigated with the aid of a differential
emission measure analysis. (*) NAS/NRC Resident Research Associate
Title: Coronal Magnetic Structures Observing
Campaign. IV. Multiwaveband Observations of Sunspot and
Plage-associated Coronal Emission
Authors: Brosius, Jeffrey W.; Willson, Robert F.; Holman, Gordon D.;
Schmelz, Joan T.
Bibcode: 1992ApJ...386..347B
Altcode:
Results of simultaneous observations of an active region located near
the central meridian obtained on December 18, 1987, are presented. An
asymmetric looplike structure connects the strong leading sunspot
with a nearby region of opposite polarity. Both 6- and 20-cm emission
lie along this structure, rather than over the sunspot, with higher
frequency emission originating closer to the footpoint inside the
sunspot. The 20-cm emission is due to a superposition of second- and
third-harmonic gyroemission, where the field strength is 160-300 G,
while the 6-cm emission is due to third-harmonic gyroemission from a
region where the magnetic field strength ranges from 547 to 583 G. X-ray
data associated with an area of trailing plage are used to predict
the brightness temperature structure due to thermal bremsstrahlung
emission in the 6- and 20-cm wavebands.
Title: CoMStOC 4: Multiwaveband observations of sunspot and
plage-associated coronal emission
Authors: Brosius, Jeffrey W.; Willson, Robert F.; Holman, Gordon D.;
Schmelz, Joan T.
Bibcode: 1992tuft.rept.....B
Altcode:
Simultaneous observations of an active region located near the central
meridian were obtained with the Very Large Array, the Solar Maximum
Mission X-ray Polychromator, and the Beijing Observatory magnetograph
on 18 December 1987, during the Coronal Magnetic Structures Observing
Campaign (COMSTOC). An asymmetric loop-like structure connects the
strong leading sunspot with a nearby region of opposite polarity. Both
6 and 20 cm emission lies along this structure, rather than over
the sunspot, with higher frequency emission originating closer to
the footpoint inside the sunspot. The 20 cm emission is due to a
superposition of 2nd and 3rd harmonic gyroemission, where the field
strength is 16- G- 300 G, while the 6 cm emission is due to the 3rd
harmonic gyroemission from a region where the magnetic field strength
ranges from 547 583 G. A high value of the Alfven speed of 40,000
km/sec, is obtained at the location of the 6 cm source, with somewhat
lower values of 10,000 - 20,000 km/sec, at the location of the 20 cm
emission. At the location of the 6 cm source, the plasma temperature
diminishes with height from 2,500,000 K at 5000 km to 1,300,000 K at
15,000 km.
Title: The Sun: A Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.
Bibcode: 1992ASIC..373.....S
Altcode: 1992sla..conf.....S
No abstract at ADS
Title: Microwave polarization inversion observed
Authors: Brosius, Jeffrey W.; Holman, Gordon D.; Schmelz, Joan T.
Bibcode: 1991EOSTr..72..449B
Altcode:
Observations of an inversion of solar-active-region microwave
polarization are described as they occurred during the Coronal
Magnetic Structures Observing Campaign. Data regarding the microwave
frequencies, soft X-ray emissions, brightness temperatures, and column
emissions are obtained with the observations. The data are employed
in the potential-field extrapolation procedure by Sakurai (1982)
to calculate the coronal magnetic-field vector, and the microwave
polarization observations yield reasonable coronal densities and
evidence of an inversion.
Title: Multi--Wave Band SMM--VLA Observations of an M2 Flare and an
Associated Coronal Mass Ejection
Authors: Willson, Robert F.; Schmelz, Joan T.; Gonzalez, Raymond D.;
Lang, Kenneth R.; Smith, Kermit L.
Bibcode: 1991ApJ...378..360W
Altcode:
Results are presented of observations of an M2 flare and an associated
coronal mass ejection CME by instruments on the SMM as well as by the
VLA and other ground-based observatories on September 30, 1988. The
multiwave band data show a gradual slowly changing event which lasted
several hours. The microwave burst emission was found to originate in
compact moderately circularly polarized sources located near the sites
of bright H-alpha and soft X-ray emission. These data are combined
with estimates of an electron temperature of 1.5 x 10 to the 7th K
and an emission measure of about 2.0 x 10 to the 49th/cu cm obtained
from Ca XIX and Fe XXV spectra to show that the microwave emission
can be attributed to thermal gyrosynchrotron radiation in regions
where the magnetic field strength is 425-650 G. The CME acceleration
at low altitudes is measured on the basis of ground- and space-based
coronagraphs.
Title: Coronal Magnetic Structures Observing Campaign. I. Simultaneous
Microwave and Soft X-Ray Observations of Active Regions at the
Solar Limb
Authors: Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman,
G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1991ApJ...374..374N
Altcode:
Using simultaneous microwave and soft X-ray measurements made with
the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator
(XRP) aboard the Solar Maximum Mission (SMM), we have studied two
active regions near the solar limb. These observations were taken as
part of the Coronal Magnetic Structures Observing Campaign (CoMStOC),
a collaboration designed to study the magnetic field in the solar
corona. The images in soft X-rays and at 20 cm wavelength are similar:
both show peaks above the active regions and extended bridge of
emission 200,000 km long connecting the two regions. The brightness
temperature of the 20 cm emission is lower than that predicted from the
X-ray emitting material, however; it can be attributed to free-free
emission in cooler (<106 K) plasma not visible to XRP,
with an optical depth ∼1. The 6 cm emission is concentrated at lower
altitudes and in a ∼160,000 km long bundle of loops in the northern
active region. Comparison of the 6 cm map with the potential magnetic
field lines computed from photospheric magnetic fields (measured 2 days
earlier) indicates that the 6 cm emission is associated with fields
of less than ∼200 G. Such fields would be too weak to attribute the
observed 6 cm emission to gyroresonance radiation. Analysis of the
6 cm loop bundle indicates that it is strongly asymmetric, with the
magnetic field in the northern leg ∼2 times stronger than in the
southern leg; the 6 cm emission most likely arises from a combination
of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm
emission becomes optically thick in the cooler (∼9 × 103
K) plasma. We estimate an Alfvén speed ∼7000 km s-1
and ratio of electron gyrofrequency to plasma frequency ∼1.0 in the
northern leg of the 6 cm loop.
Title: On the Polarization of Microwave Emission from Active Regions:
Results from CoMStOC
Authors: Holman, G. D.; Brosius, J. W.; Schmelz, J. T.; Willson, R. F.
Bibcode: 1991BAAS...23.1045H
Altcode:
No abstract at ADS
Title: CoMStOC III: Measuring Magnetic Fields in Active Region
Coronal Plasma
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Willson, R. F.
Bibcode: 1991BAAS...23R1045S
Altcode:
No abstract at ADS
Title: Microwave polarization inversion observed
Authors: Brosius, J. W.; Holman, G. D.; Schmelz, J. T.
Bibcode: 1991EOSTr..72R.449B
Altcode:
No abstract at ADS
Title: Results from CoMStOC: The coronal magnetic structures
observing campaign
Authors: Schmelz, J. T.; Holman, G. D.
Bibcode: 1991AdSpR..11a.109S
Altcode: 1991AdSpR..11..109S
The Coronal Magnetic Structures Observing Campaign (CoMStOC) was
designed to measure the magnetic field strength and determine its
structure in the solar corona. Simultaneous soft X-ray and microwave
observations were taken by the Solar Maximum Mission's X-Ray
Polychromator (XRP) and the Very Large Array (VLA) on four days in
the campaign period (25 Nov to 21 Dec 1987). XRP maps in soft X-ray
resonance lines formed at different coronal temperatures provide
accurate temperature and emission measure diagnostics. VLA maps at
several frequencies in the 20 cm and 6 cm bands yield information
on microwave structure, spectrum and polarization. The combined
data set separates contributions from the two dominant microwave
emission mechanisms, thermal bremsstrahlung and gyroresonance. Where
gyroresonance dominates, the coronal magnetic field strength has been
determined with the aid of theoretical modeling.
Title: CoMStOC vs. International Solar Month: Experience gained and
lessons learned from SMM campaigns
Authors: Schmelz, J. T.
Bibcode: 1991AdSpR..11e..41S
Altcode: 1991AdSpR..11...41S
The scientific success and achievements of a solar observing campaign
depend on many factors. Seven points that should be addressed by
the organizers as the campaign begins to take shape are outlined and
described: 1. Scientific Focus, 2. Organization, 3. Communication,
4. Solar Conditions, 5. Instruments, 6. Analysis, 7. Results. Using
these points as a guide, two recent solar observing campaigns are
compared and discussed in detail. The Coronal Magnetic Structures
Observing Campaign (CoMStOC) was organized to measure the magnetic field
strength and determine its structure in the solar corona. International
Solar Month was a worldwide campaign to observe the Sun with emphasis
on simultaneous, stereoscopic observations of the solar corona by soft
X-ray imagers on NASA's Solar Maximum Mission satellite and the Soviet
Phobos-1 spacecraft. Lessons learned from these and other campaigns
involving the Solar Maximum Mission satellite are discussed briefly
and advice for future campaigns is offered.
Title: Accurate positions of OH/IR stars.
Authors: Lewis, B. M.; Chengalur, J. N.; Schmelz, J.; Terzian, Y.
Bibcode: 1990MNRAS.246..523L
Altcode:
We have observed a total of 57 OH/IR stars with the VLA and detected
46. Their positions, accurate to ≤ 1 arcsec, are listed. These
positions are in substantial agreement with the positions determined
by IRA S. This formally confirms the identification of each 161 2-MHz
maser with its IRAS source. The 161 2-MHz fluxes of the stars detected
correlate quite strongly (ρ = 0.88), with those measured 18 months
previously. The non-detections are primarily sources with lower than
average 1612-MHz fluxes.
Title: Microwave and X-Ray Observations of a Major Confined Solar
Flare
Authors: Schmahl, E. J.; Schmelz, J. T.; Saba, J. L. R.; Strong,
K. T.; Kundu, M. R.
Bibcode: 1990ApJ...358..654S
Altcode:
Observations of an X4 flare of May 19, 1984 using the VLA and the
SMM X-ray Polychromator are discussed. The 6 cm radio source remained
stationary throughout the decay phase. Combined with other evidence,
this indicates that the flare was magnetically confined and did not
disrupt the complex structure of its region. The observed structures
may be associated with a neutral sheet connecting the two bipoles.
Title: CoMStOCI: Physical Properties of an Active Region Loop Observed
at the Solar Limb
Authors: Holman, G. D.; Brosius, J. W.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1990BAAS...22..899H
Altcode:
No abstract at ADS
Title: CoMStOCIV: Interpretation of Multiwavelength Observations of
a Sunspot and Plage
Authors: Brosius, J. W.; Holman, G. D.; Willson, R. F.; Schmelz, J. T.
Bibcode: 1990BAAS...22..794B
Altcode:
No abstract at ADS
Title: Comstoc - the Coronal Magnetic Structures Observing Campaign
Authors: Schmelz, J. T.
Bibcode: 1990IAUS..140...20S
Altcode:
No abstract at ADS
Title: CoMStOC II: Multi-Waveband Observations of a Solar Active
Region
Authors: Schmelz, J. T.
Bibcode: 1989BAAS...21Q1186S
Altcode:
No abstract at ADS
Title: High-Resolution Studies of 21 CM Emission Profiles
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 1989AJ.....98..267V
Altcode:
High-resolution (4-arcmin beamwidth, 1.22-kHz bandwidth),
high-sensitivity observations of 21-cm emission profiles have been
decomposed into Gaussians. The peak in the histogram of linewidth
distribution occurs at 3 km/s, corresponding to T(k) = 200 K, similar
to that found in absorption-line studies. The new data on line widths
are compared with the results of other studies and reveal that the
characteristic width of the narrow component is dependent on angular
resolution. No evidence for a component related to a warm neutral
'intercloud' medium around 5000-10,000 K is found. A pervasive broad
component with linewidth from 30 to 50 km/s may be due to stray
radiation.
Title: Interpretation of Multiwavelength Observations of Solar Active
Regions Obtained During CoMStOC
Authors: Brosius, J. W.; Holman, G. D.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. R. L.; Willson, R.
Bibcode: 1989BAAS...21..838B
Altcode:
No abstract at ADS
Title: Simultaneous Microwave and Soft X-ray Observations of Active
Regions at the Solar Limb
Authors: Nitta, N.; White, S.; Kundu, M.; Gopalswamy, N.; Holman,
G.; Brosius, J.; Schmelz, J.; Saba, J.; Strong, K.
Bibcode: 1989BAAS...21..828N
Altcode:
No abstract at ADS
Title: Multiple Wavelength SMM-VLA Observations of an M2-Class
X-ray Flare
Authors: Willson, R. F.; Lang, K. R.; Schmelz, J. T.; Smith, K. L.
Bibcode: 1989BAAS...21Q.835W
Altcode:
No abstract at ADS
Title: Plasma parameters and structures of the X4 flare of 19 May
1984 as observed by SMM-XRP.
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1989sasf.confP.165S
Altcode: 1988sasf.conf..165S; 1989IAUCo.104P.165S
The eruption of a large flare on the east limb of the Sun was
observed by the X-ray Polychromator (XRP) on board the Solar Maximum
Mission (SMM) on 19 May 1984. The XRP Flat Crystal Spectrometer (FCS)
made polychromatic soft X-ray images during the preflare, flare and
postflare phases. The XRP Bent Crystal Spectrometer (BCS) provided
information on the temperature and dynamics of the hot (Te
> 8×106K) coronal plasma from spectra integrated
spatially over the whole region.
Title: Largescale Magnetic Field Phenomena
Authors: Harrison, R. A.; Bentley, R. D.; Brosius, J.; Dwivedi,
B. N.; Jardine, M.; Klimchuk, J. A.; Kundu, M. R.; Pearce, G.; Saba,
J.; Sakurai, T.; Schmahl, E. J.; Schmelz, J.; Sime, D. G.; Steele,
C. D. C.; Sun, M. T.; Tappin, S. J.; Waljeski, K.; Wang, A. H.; Wu,
S. T.
Bibcode: 1989tnti.conf....1H
Altcode:
No abstract at ADS
Title: The Megamaser Galaxy Markarian 273. II. VLA Observations of
the Neutral Hydrogen Absorption
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.
Bibcode: 1988ApJ...329..142S
Altcode:
The high-resolution A-array of the VLA was used to observe the wide
neutral hydrogen absorption in the OH megamaser galaxy Mrk 273. The
nuclear continuum of this galaxy is extended at 21 cm; Ulvestadt and
Wilson find a double structure at 6 cm where the stronger component
is resolved into a triple at 2 cm. The H I absorption is marginally
resolved both spatially and spectrally and different features can be
identified. These features are distinguishable as basically Gaussian
components of the absorption but are probably not independent; several
of these may form a rotating disk with a velocity gradient of 1.89
km s^-1^ per parsec. Assuming a typical rotational velocity of ~200
km s^-1^, the radius of this disk would be R = 106 pc and the total
internal mass can be estimated at M = 10^9^ M_sun_. These parameters,
when compared with the same values of other extragalactic H I absorption
disks, are not highly unusual and are, possibly, quite believable.
Title: A Search for Thermal Hydroxyl Emission in Nearby Galaxies
Authors: Schmelz, J. T.; Baan, W. A.
Bibcode: 1988AJ.....95..672S
Altcode:
A survey of 63 nearby spiral galaxies for hydroxyl emission has been
completed using the 305 m telescope of the Arecibo Observatory. We were
hoping to detect the main lines at 1667 and 1665 MHz in LTE emission as
observed in dark clouds and most GMCs in our own galaxy. No OH emission
was detected, but limits have been set on the OH column densities of
these galaxies.
Title: International solar month-September 1988
Authors: Schmelz, J.
Bibcode: 1988EOSTr..69..738S
Altcode:
Solar Maximum Mission (SMM) scientists plan to participate in
a worldwide campaign to observe the Sun in September 1988. It is
hoped that solar physicists from the Soviet Union and several European
countries with experiments on the Soviet spacecraft PHOBOS (a mission to
Mars which will carry solar instruments) will also be involved. PHOBOS
will be launched in July; the TEREK instruments (a soft X ray imager,
and ultrasoft X ray imager and a white light coronograph) will image
the Sun twice every 5 days. Other instruments will obtain nonimaging
solar data much more frequently. Now that the rapid rise phase of the
new solar cycle is well under way, such joint observations of the Sun
should be particularly fruitful.
Title: Preliminary results from the coronal magnetic structures
observing campaign (CoMStOC)
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Holman, G. D.
Bibcode: 1988AdSpR...8k.189S
Altcode: 1988AdSpR...8..189S
The object of the Coronal Magnetic Structures Observing Campaign
(CoMStOC) was to measure the electron density and the magnetic
field strength in coronal loops, quantities which are poorly known
but essential to the understanding of the solar corona. Simultaneous
soft X-ray and microwave observations were taken by the Solar Maximum
Mission's (SMM) X-Ray Polychromator (XRP) and the Very Large Array (VLA)
on four days in the campaign period (25 Nov to 21 Dec 1987). Supporting
multi-waveband observations were used to choose target regions,
understand morphology, track evolution, and co-register images. XRP maps
in soft X-ray resonance lines formed at different coronal temperatures
provide accurate temperature and emission measure diagnostics. VLA
maps at several frequencies in the 20 cm and 6 cm bands and Owens
Valley spectra yield information on microwave structure, spectrum and
polarization. The combined data set separates contributions from the
two dominant microwave emission mechanisms, thermal bremsstrahlung
and gyroresonance. Where gyroresonance is important, the coronal
magnetic field strength can be determined with the aid of theoretical
modeling. CoMStOC has provided an unprecedented set of coordinated
multi-waveband observations of five new cycle active regions, offering
a varied sample of intensity, activity, complexity, and projection
angle. Whatever the final scientific return from the detailed studies
now in progress, CoMStOC has already provided a wealth of experience
in obtaining coordinated, multi-waveband observations of solar active
regions.
Title: The Megamaser Galaxy Markarian 273. I. VLA Observations of
the Hydroxyl Emission
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.
Bibcode: 1987ApJ...321..225S
Altcode:
The hydroxyl megamaser emission in Mrk 273 was observed with the VLA in
its high-resolution A array. The radio continuum source is extended
at 18 cm; observations published by Ulvestad and Wilson (1984)
reveal a double at 6 cm where the stronger component is resolved
into a triple at 2 cm. The OH emission is certainly associated only
with the stronger component of the 6-cm double and possibly only
with the stongest component of the 2-cm triple. Unfortunately, the
three velocity-resolved components of the OH line are not spatially
resolved, and no information on the molecular disk rotation properties
of this galaxy can be determined. This is very different from the VLA
results of the megamaser prototype in IC 4553, where the emission is
associated with all the continuum components and actually mimics the
spatial structure of the radio continuum. Relevant properties of the
known megamasers are listed and compared.
Title: The Effect of a Large Flare on the Solar Corona
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Schmahl,
E. J.; Kundu, M. R.
Bibcode: 1987BAAS...19S1122S
Altcode:
No abstract at ADS
Title: A Study of Solar Preflare Activity Using Two-Dimensional
Radio and Smm/xrp Observations
Authors: Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.; Schmelz,
J. T. S.; Strong, K. T.
Bibcode: 1987SoPh..114..273K
Altcode:
We present a study of type III activity at meter- decameter wavelengths
in the preflare phase of the 1986 February 3 flare using data obtained
with the Clark Lake Multifrequency Radioheliograph. We compare this
activity with similar type III burst activity during the impulsive
phase and find that there is a displacement of burst sources between the
onset and end times of the activity. A comparison of this displacement
at three frequencies suggests that the type III emitting electrons gain
access progressively to diverging and different field lines relative
to the initial field lines. The energetics of the type III emitting
electrons are inferred from observations and compared with those of
the associated hard X-ray emitting electrons. The soft X-ray data from
SMM-XRP shows enhanced emission measure, density and temperature in
the region associated with the preflare type III activity.
Title: The Leo Triplet Spiral Galaxy NGC 3628. II. VLA Observations
of the Hydroxyl Absorption
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.
Bibcode: 1987ApJ...320..145S
Altcode:
The VLA-A has been used to observe the hydroxyl absorption against
the nuclear continuum region of NGC 3628, an edge-on spiral galaxy
in the Leo Triplet. The stronger 1667 MHz component is resolved into
eight spatial and velocity features. The weaker 1667 MHz transition is
seen in all of these, but three are between 3 and 5 sigma. A rotating
molecular disk with a radius of about 168 pc is consistent with the
observations and strongly supports the disk interpretation of the
H I features presented elsewhere by the authors. Several additional
features at lower velocities form a second structure which is expanding
away from this disk. A tidal interaction between NGC 3627 and NGC 3628
probably caused the H I extensions called the plume and the bridge
and possibly caused the nuclear radio source to turn on.
Title: Microwave Observations of the X-Flare of May 19, 1984
Authors: Schmahl, E. J.; Kundu, M. R.; Schmelz, J. T.; Saba, J.;
Strong, K. T.
Bibcode: 1987BAAS...19R1122S
Altcode:
No abstract at ADS
Title: The Leo Triplet Spiral Galaxy NGC 3628. I. VLA Observations
of the Neutral Hydrogen Absorption
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.
Bibcode: 1987ApJ...315..492S
Altcode:
Hydrogen absorption is observed against the nuclear region of NGC 3628,
an edge-on spiral galaxy in the Leo Triplet. VLA observations against
the extended continuum reveal approximately 10 individual H I features
which are resolved both spatially and in velocity space. A circular,
rotating disk is identified as well as several lower velocity features
which seem to form a second structure. This may be an expanding spiral
arm, similar to the 3 kpc arm in the Galaxy, or a second disk which
is either expanding with respect to the primary disk or elliptical in
shape. All of the features are optically thick with tau roughly 1 in
many cases.Estimated densities are high with n(HI+) greater than 100/cu
cm and M roughly 100,000 solar masses for a typical feature. The high
degree of activity in this galaxy, which includes complex hydroxyl
absorption and H I extensions in the form of plumes and bridges,
may have been triggered by a tidal encounter with NGC 3627, a second
spiral in the triplet.
Title: Megamaser Comparisons: IC 4553 and Mrk 273
Authors: Schmelz, J. T.
Bibcode: 1987BAAS...19S.711S
Altcode: 1987BAAS...19..711S
No abstract at ADS
Title: The Peculiar Galaxy IC 4553. II. VLA Observations of the
Neutral Hydrogen
Authors: Baan, Willem A.; van Gorkom, J. H.; Schmelz, Joan T.; Mirabel,
I. Felix
Bibcode: 1987ApJ...313..102B
Altcode:
The nuclear H I absorption of IC 4553 (Arp 220) was scanned with the
30 km VLA-A array and a search was made for extended H I emission
with the 3 km VLA-C array. The observations were made at 6.26 MHz on
different dates in 1982-1984. No extended H I emission was detected at
levels above 1 mJy per beam scales from 1-20 arcsec with the A array
and from 30 arcsec-4 arcmin with the C configuration. The nuclear H
I disk coincided with a previously mapped OH emitting disk, but had a
center velocity 77 km/sec higher. The H I disk is about 1.5 kpc across,
is contained within the OH disk, is noncircular in shape, and has a
mass of about 400 million solar masses. Reasons for the lack of an
extended H I feature are discussed.
Title: High Resolution Studies of 21-cm Emission Profiles Observed
at Arecibo Observatory
Authors: Verschuur, G. L.; Schmelz, J. T.
Bibcode: 1987BAAS...19..649V
Altcode:
No abstract at ADS
Title: Investigations of Extragalactic Hydroxyl.
Authors: Schmelz, Joan T.
Bibcode: 1987PhDT.........2S
Altcode: 1987DiAbI..48.1072S
Observations of extragalactic hydroxyl (OH) probe the physical
conditions of galactic nuclear regions. The four 18 cm spectral
lines of OH are known to respond differently to various conditions,
possibly making hydroxyl a better probe then CO and HI in certain
galaxies. First, OH must be detected; this thesis presents the results
of an extensive survey for extragalactic hydroxyl using the Arecibo
telescope. The OH is observed in absorption and in Megamaser emission
but not in thermal emission despite low noise values. This survey
was used as the basis for a statistical study between OH content
and other parameters of the parent galaxy. Statistical methods for
samples with upper limits were used to find correlations between
(tau)(,OH) and the Hubble Type, IRAS colors, infrared luminosity,
and IR-to -blue luminosity ratio of the galaxy. Two galaxies were then
studied in detail using the Very Large Array (VLA) interferometer. The
first was NGC 3628, an edge-on spiral galaxy in the Leo Triplet. The
OH and HI absorption maps reveal a rotating disk which may follow
the inner portion of the galaxy's rotation curve. A second structure
which is expanding with respect to the disk is also revealed and may
be similar to the three kpc arm in our own Galaxy. The second galaxy
studied with the VLA was Mrk 273, a Seyfert with HI absorption and OH
Megamaser emission. Although the continuum is resolved at 18 cm (and is
a double at six cm), the absorption and emission are associated only
with one component and, therefore, not resolved. So, unfortunately,
no information on the disk rotation properties of this galaxy could
be determined. This is very different from the VLA results for the
prototype Megamaser in IC 4553 where the OH emission actually mimics
the resolved continuum structure. Therefore, these observations could
not be used to support the present Megamaser model.
Title: An Arecibo survey for extragalactic hydroxyl
absorption. I. Presentation of results.
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.; Eder, J.
Bibcode: 1986AJ.....92.1291S
Altcode:
A survey of 240 galaxies for hydroxyl absorption has been completed
using the Arecibo Observatory. New results include five previously
unpublished strong lines in NGC 2339, IC 860, IC 883, NGC 5859, and UGC
11905. Six additional possible lines where the signal-to-noise ratio
is ⪉3 are also included. Spectra of the 1667 and 1665 MHz transition
of OH are accompanied by 21 cm neutral-hydrogen spectra for these 11
galaxies. H I absorption appears at the same velocity as the hydroxyl
features. In general, these galaxies are luminous IRAS sources and
many are tidally interacting with a close companion or classified as
mergers. Optical depths for the stronger 1667 MHz transition range
from 0.004 to 0.27 and the hyperfine ratio is generally within the
LTE limits. A large fraction of the lines (≡50%) are skewed toward
the red, indicating an unusual velocity structure for the absorbing
molecular disk.
Title: Is OH abundance enhanced in tidally distorted galaxies?
Authors: Schmelz, J. T.
Bibcode: 1986inpr.conf..107S
Altcode:
An extensive survey of 240 galaxies for hydroxyl absorption has been
completed using the Arecibo Observatory. These galaxies were used to
compile a sample to test for statistical correlations between the
optical depth of the 1667 MHz hydroxyl line and various parameters
of the parent galaxy. To be included in the sample, the radio flux
density of the galaxy at 1667 MHz had to be between 20 mjy and 1000 mjy
and the galactic declination between 0 and 38 deg. Since this sample
contains mainly non-detections, statistical methods for astronomical
data with upper limits as previously described were used to obtain
correlation and regression information. Preliminary studies indicate
a strong correlation between OH optical depth and infrared to blue
luminosity ratio (LIR/L sub B), where the infrared data
were obtained from the Cataloged Galaxies and Quasars Observed in the
IRAS Survey. A second correlation is seen between the optical depth
of the 1667 MHz line and galactic type, where a number from 1 to 15
(Elliptical to peculiar, distorted, or interacting) has been assigned to
each galaxy. So, stable, isolated galaxies tend not to have detectable
hydroxyl. On the other hand, galaxies with more gas and dust, galaxies
with a more peculiar or distorted appearance, and galaxies which are
more tidally interacting tend to have much more detectable OH. These
findings could indicate that these dusty, peculiar, distorted, and
interacting galaxies could be the site of large amounts of shocked
material where OH is likely to form. Hence, the hydroxyl abundance
could be enhanced in these regions of shocked material making the
detection of OH in these tidally distorted galaxies much more likely.
Title: VLA Observations of the H1 and OH Absorption in the Leo
Triplet Spiral Galaxy NGC 3628
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.
Bibcode: 1986BAAS...18..916S
Altcode:
No abstract at ADS
Title: A VLA survey of unidentified HEAO-1 X-ray sources.
Authors: Schmelz, J. T.; Feigelson, E. D.; Schwartz, D. A.
Bibcode: 1986AJ.....92..585S
Altcode:
The authors have employed a new technique to uncover candidates for
unidentified bright X-ray sources where traditional methods have
proved unsuccessful. The C configuration VLA was used at 20 cm to
search for 47 unidentified sources detected in the HEAO-1 all-sky X-ray
survey. Approximate pointing positions were obtained by superimposing
the large error boxes from the NRL experiment and the grid of small
diamonds from the Scanning Modulation Collimator. Radio maps of
the 30arcmin primary beam were made and 238 radio sources (with
flux densities as small as 1 - 3 mJy) were detected in or near the
diamond-shaped error boxes. A search was made for the associated optical
objects on POSS prints, and tentative classifications of the resulting
radio/optical candidates were made. The candidate X-ray identifications
include five possible RS CVn systems, three active galactic nuclei,
three galaxy or cluster sources, and two X-ray binaries.
Title: The fourth OH megamaser : Markarian 273.
Authors: Baan, W. A.; Haschick, A. D.; Schmelz, J. T.
Bibcode: 1985ApJ...298L..51B
Altcode:
A fourth OH megamaser has been found in the luminous IR galaxy Mrk 273
(= U08696). The characteristics of this masing galaxy are similar to
those of the other powerful extragalactic masers in NGC 3690, IC 4553,
and Mrk 231. The 1667 MHz line luminosity of Mrk 273 is 335 L solar
luminosities. The IR photon-to-OH photon conversion efficiency is
calculated for all OH megamasers and is found to be close to 1 percent.
Title: Hydroxyl absorption in NGC 520, NGC 2623, 6240.
Authors: Baan, W. A.; Haschick, A. D.; Buckley, D.; Schmelz, J. T.
Bibcode: 1985ApJ...293..394B
Altcode:
Extragalactic absorption of hydroxyl is reported for the galaxies NGC
520, NGC 2623, and NGC 6240. H I absorption has also been detected in
these galaxies. The properties of the H I and OH absorption features
are compared for these galaxies and for other galaxies with absorption
in both OH and H I. the hyperfine ratio for the 1667 and 1665 MHz
hydroxyl transitions for most extragalactic absorption lines falls
within LTE range. The characteristics of extragalactic OH absorption
lines are consistent with the existence of dense molecular disks in the
inner parts of the galaxies. An asymmetry in a number of extragalactic
OH absorption lines suggests a peculiar velocity structure for the
absorbing molecular disk.
Title: An Arecibo Survey for Extragalactic Hydroxyl
Authors: Schmelz, J. T.; Baan, W. A.; Haschick, A. D.
Bibcode: 1985BAAS...17..549S
Altcode:
No abstract at ADS
Title: Newly Discovered BL Lacertae Objects Identified as Bright
X-ray Source Counterparts by HEAO-1
Authors: Schwartz, D. A.; Roberts, W.; Murray, S.; Huchra, J.;
Remillard, R.; Bradt, H.; McClintock, J.; Tuohy, I.; Buckley, D.;
Tapia, S.; Feigelson, E.; Schmelz, J.
Bibcode: 1985BAAS...17..608S
Altcode:
No abstract at ADS
Title: Some systematic trends in the color variations of T Tauri
stars at visible wavelengths.
Authors: Vrba, F. J.; Rydgren, A. E.; Zak, D. S.; Schmelz, J. T.
Bibcode: 1985AJ.....90..326V
Altcode:
The dependence of U - B, B - V, and V - I color on V magnitude is
examined for ten well-observed T Tauri stars, based on photometry from
numerous sources. It is found that the 'color slopes' d(B - V)/dV
and d(V - I)/dV, due to variability, differ significantly between
stars and tend to be larger for T Tauri stars of later spectral
type. Furthermore, when the color slopes are small, the B - V color
slope is significantly less than the V - I color slope. All of these
results are in accord with the hypothesis that the primary source of
large-amplitude brightness variations in T Tauri stars is a changing
mix of photospheric regions, hot plage regions, and dark spots on
the stellar surface. In addition, the large scatter observed in U -
B is consistent with flare-like events.
Title: OH Megamasers
Authors: Baan, W. A.; Haschick, A. D.; Schmelz, J. T.
Bibcode: 1984IAUC.3993....2B
Altcode: 1984IAUC.3993....0B; 1984IAUC.3993....1B
W. A. Baan, A. D. Haschick and J. T. Schmelz write: "Recent observations
at the 91-m telescope of the National Radio Astronomy Observatory
resulted in the detection of three new powerful OH masers in the
disturbed galaxies NGC 3690, Mrk 231 and Arp 238. The maser in Mrk
231 has an isotropic luminosity of 2500 LO if the galaxy is at 227
Mpc. This makes it 3.5 times more luminous in the 1667-MHz OH-maser
line than the megamaser source IC 4553 (= Arp 220; Baan and Haschick
1984, Ap.J. 279, 541). NGC 3690 (56 Mpc) and Arp 238 (170 Mpc) have
isotropic luminosities of 85 LO and 290 LO, respectively. Almost all
extragalactic OH and H2O megamaser sources can be interpreted with a
maser amplification model where inverted foreground molecular gas in
an edge-on disk amplifies the central continuum source. The infrared
radiation field is likely to be the cause of the population inversion
of the OH and H2O needed for these molecular image-processing systems."
Title: VLA Observations of Unidentified HEAO-1 X-Ray Sources
Authors: Schmelz, J. T.; Feigelson, E. D.; Schwartz, D. A.
Bibcode: 1984BAAS...16R.472S
Altcode:
No abstract at ADS
Title: An investigation of T Tauri variability.
Authors: Schmelz, J. T.
Bibcode: 1984AJ.....89..108S
Altcode:
Three mechanisms have been suggested to account for the photometric
variability in T Tauri stars: (1) changes in the effective photospheric
spectral type; (2) changes in the optical thickness of the chromosphere;
and (3) changes in the optical thickness of the dust shell. The author
investigates these processes with color-color diagrams and energy
distribution plots of 14 stars located in the Taurus-Auriga dark cloud
complex. A relationship between a strong chromosphere and chromospheric
variability was found as well as a similar relationship between a
thick dust shell and dust shell variability. There is some evidence
that the stellar photosphere becomes more stable with increasing age
during the T Tauri phase.
Title: An investigation of T Tauri variability.
Authors: Schmelz, J.
Bibcode: 1983RMxAA...7Q.197S
Altcode:
No abstract at ADS
Title: Periodic Light Variability in Four Late Type Pre Main-Sequence
Stars
Authors: Vrba, F. J.; Rydgren, A. E.; Schmelz, J. T.
Bibcode: 1983ards.proc..503V
Altcode: 1983IAUCo..71..503V
No abstract at ADS
Title: Periodic Light Variability in Four Late-Type Pre-Main-Sequence
Stars
Authors: Vrba, F. J.; Rydgren, A. E.; Schmelz, J. T. Download PDF
(264KB)
Bibcode: 1983ASSL..102..503V
Altcode:
While the T Tauri stars are the best known of the late-type
pre-main-sequence (PMS) stars, there are also some late-type PMS stars
with only weak line emission in their visible spectra. Several years ago
we noted that the weak-emission PMS stars have B-V colors too blue for
their V-I colors and suggested that their surfaces might have regions of
differing temperature. During October 1981 we used the USNO 40-inch and
Kitt Peak National Observatory No. 4 16-inch telescopes to monitor, over
a 7 night interval with UBVRI photometry, four of these weak-emission
PMS stars: HD 283447, V410 Tau, and X-ray stars 1 and 2 of Feigelson
and Kriss (1981). The PMS nature of these stars is established from
(1) their membership in the Taurus dark cloud T-association and (2)
their location within the T Tauri band region of the H-R diagram.
Title: Evidence for a characteristic maximum temperature in the
circumstellar dust associated with T Tau stars.
Authors: Rydgren, A. E.; Schmelz, J. T.; Vrba, F. J.
Bibcode: 1982ApJ...256..168R
Altcode:
Evidence is found for a correlation between the color excess E(V-I)
and the IR color H-K for T Tauri stars in the Taurus and NGC 2264
regions, through nearly-simultaneous BVRI and JHKL photometry. This
phenomenon may be understood as a circumstellar reddening effect,
and suggests that some of the observed V-I reddening in typical T
Tauri stars is not interstellar in origin. Very narrow intrinsic
loci of the Taurus region T Tauri stars in the (J-H, H-K) and (H-K,
K-L) diagrams are found upon correction for interstellar reddening,
consistent with circumstellar dust shell models with maximum dust
temperatures of about 1300 K. No hot interstellar dust is found in
two late-type pre-main sequence stars with weak line emission first
noted by Feigelson and DeCampi (1981) as X-ray sources.
Title: On the Sources of Variability in T Tauri Stars
Authors: Schmelz, J. T.; Rydgren, A. E.; Vrba, F. J.
Bibcode: 1982BAAS...14R.629S
Altcode:
No abstract at ADS
Title: Evidence for Starspots on Several Non-T Tauri Pre-Main-Sequence
K Stars
Authors: Rydgren, A. E.; Schmelz, J. T.; Vrba, F. J.
Bibcode: 1982BAAS...14..629R
Altcode:
No abstract at ADS
Title: Circumstellar dust shells associated with T Tauri stars:
another progress report.
Authors: Rydgren, A. E.; Schmelz, J. T.; Vrba, F. J.
Bibcode: 1982ASNYN...2a..13R
Altcode:
No abstract at ADS
Title: An investigation of T Tauri variability.
Authors: Schmelz, J.
Bibcode: 1982ASNYN...2b...9S
Altcode:
No abstract at ADS