explanation      blue bibcodes open ADS page with paths to full text
Author name code: bryans
ADS astronomy entries on 2022-09-14
author:"Bryans, Paul" 

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Title: Exploration of the Physical and Spectroscopic Characteristics
    of Coronal Rain
Authors: Tyson, Kalista; Lacatus, Daniela; Paraschiv, Alin; Bryans,
   Paul
2021AGUFMSH45B2381T    Altcode:
  The correlation between the phenomenon known as coronal rain and the
  origin of the Suns heating and cooling mechanisms has become a popular
  area for exploration in recent years. In this study, we explored the
  specifics of how plasma flows are triggered and how material moves
  along closed magnetic field entities. Using spectroscopic data from the
  Interface Region Imaging Spectrograph (IRIS), we analyzed the Mg II,
  Si IV and C II emission lines in relation to the different magnetic
  structures, allowing us to study plasma under different emitting
  regimes. We have extracted spectroscopic characteristics of these
  emission lines for an off-limb prolonged coronal rain event taking place
  above a quiescent active region system. Additionally, we augmented our
  dataset with SDO/AIA coronal observations, highlighting corresponding
  higher temperature structures. We report a case where recurring coronal
  rain episodes occur over timescales of several hours. Our work reveals
  a multitude of complex, differently oriented, and turbulent, structures
  under what appeared to be a standard coronal rain event.

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Title: Measuring the Magnetic Origins of Solar Flares, Coronal Mass
    Ejections, and Space Weather
Authors: Judge, Philip; Rempel, Matthias; Ezzeddine, Rana; Kleint,
   Lucia; Egeland, Ricky; Berdyugina, Svetlana V.; Berger, Thomas; Bryans,
   Paul; Burkepile, Joan; Centeno, Rebecca; de Toma, Giuliana; Dikpati,
   Mausumi; Fan, Yuhong; Gilbert, Holly; Lacatus, Daniela A.
2021ApJ...917...27J    Altcode: 2021arXiv210607786J
  We take a broad look at the problem of identifying the magnetic
  solar causes of space weather. With the lackluster performance
  of extrapolations based upon magnetic field measurements in the
  photosphere, we identify a region in the near-UV (NUV) part of the
  spectrum as optimal for studying the development of magnetic free energy
  over active regions. Using data from SORCE, the Hubble Space Telescope,
  and SKYLAB, along with 1D computations of the NUV spectrum and numerical
  experiments based on the MURaM radiation-magnetohydrodynamic and
  HanleRT radiative transfer codes, we address multiple challenges. These
  challenges are best met through a combination of NUV lines of bright Mg
  II, and lines of Fe II and Fe I (mostly within the 4s-4p transition
  array) which form in the chromosphere up to 2 × 10<SUP>4</SUP>
  K. Both Hanle and Zeeman effects can in principle be used to derive
  vector magnetic fields. However, for any given spectral line the τ
  = 1 surfaces are generally geometrically corrugated owing to fine
  structure such as fibrils and spicules. By using multiple spectral
  lines spanning different optical depths, magnetic fields across nearly
  horizontal surfaces can be inferred in regions of low plasma β, from
  which free energies, magnetic topology, and other quantities can be
  derived. Based upon the recently reported successful sub-orbital space
  measurements of magnetic fields with the CLASP2 instrument, we argue
  that a modest space-borne telescope will be able to make significant
  advances in the attempts to predict solar eruptions. Difficulties
  associated with blended lines are shown to be minor in an Appendix.

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Title: Hinode and IRIS Synoptic Observations of Solar Cycle Transition
    at Mid-Latitudes
Authors: Egeland, R.; Centeno, R.; Lacatus, D.; de Toma, G.; Bryans,
   P.; McIntosh, S.
2021AAS...23811324E    Altcode:
  Recent observations by McIntosh et al. using SDO/AIA coronal bright
  point density and the magnetogram-derived large scale open magnetic
  flux "g-nodes" have traced out extended solar cycle activity bands
  that originate at ~55 degrees latitude and propagate toward the
  equator. When the opposite hemisphere bands "terminate" at the equator,
  this event corresponds with the rapid rise of new cycle flux and active
  regions at mid-latitudes, ~35 degrees. We present weekly synoptic
  high-resolution observations of mid-latitude (35-40 degrees) magnetic
  flux and chromospheric emission from Hinode SOT/SP and IRIS starting
  from March 2017 until today, covering the end of cycle 24 and the
  beginnings of cycle 25. After carefully correcting for instrumental
  shifts, noise, and solar B-angle effects, we analyze time series
  of mean magnetic flux, chromospheric line intensity, and statistical
  properties of magnetic regions for signals of a developing cycle 25 and
  the passage of the activity bands in these typically quiet mid-latitude
  regions. Initial results show that the statistical properties of our
  activity metrics are roughly constant over the four year period, with
  a step function increase in activity that corresponds to a change to a
  lower observation latitude. Finally, we investigate the correspondence
  of SDO/AIA coronal bright points in our observational field of view
  to chromospheric emission and photospheric magnetic features.

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Title: Investigating the Chromospheric Footpoints of the Solar Wind
Authors: Bryans, Paul; McIntosh, Scott W.; Brooks, David H.; De
   Pontieu, Bart
2020ApJ...905L..33B    Altcode:
  Coronal holes present the source of the fast solar wind. However,
  the fast solar wind is not unimodal—there are discrete, but subtle,
  compositional, velocity, and density structures that differentiate
  different coronal holes as well as wind streams that originate within
  one coronal hole. In this Letter we exploit full-disk observational
  "mosaics" performed by the Interface Region Imaging Spectrograph
  (IRIS) spacecraft to demonstrate that significant spectral variation
  exists within the chromospheric plasma of coronal holes. The spectral
  differences outline the boundaries of some—but not all—coronal
  holes. In particular, we show that the "peak separation" of the Mg
  II h line at 2803 Å illustrates changes in what appear to be open
  magnetic features within a coronal hole. These observations point
  to a chromospheric source for the inhomogeneities found in the fast
  solar wind. These chromospheric signatures can provide additional
  constraints on magnetic field extrapolations close to the source,
  potentially on spatial scales smaller than from traditional coronal hole
  detection methods based on intensity thresholding in the corona. This
  is of increased importance with the advent of Parker Solar Probe and
  Solar Orbiter and the ability to accurately establish the connectivity
  between their in situ measurements and remote sensing observations of
  the solar atmosphere.

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Title: A New Facility for Airborne Solar Astronomy: NASA's WB-57 at
    the 2017 Total Solar Eclipse
Authors: Caspi, Amir; Seaton, Daniel B.; Tsang, Constantine C. C.;
   DeForest, Craig E.; Bryans, Paul; DeLuca, Edward E.; Tomczyk,
   Steven; Burkepile, Joan T.; Casey, Thomas "Tony"; Collier, John;
   Darrow, Donald "DD"; Del Rosso, Dominic; Durda, Daniel D.; Gallagher,
   Peter T.; Golub, Leon; Jacyna, Matthew; Johnson, David "DJ"; Judge,
   Philip G.; Klemm, Cary "Diddle"; Laurent, Glenn T.; Lewis, Johanna;
   Mallini, Charles J.; Parent, Thomas "Duster"; Propp, Timothy; Steffl,
   Andrew J.; Warner, Jeff; West, Matthew J.; Wiseman, John; Yates,
   Mallory; Zhukov, Andrei N.; NASA WB-57 2017 Eclipse Observing Team
2020ApJ...895..131C    Altcode: 2020arXiv200409658C
  NASA's WB-57 High Altitude Research Program provides a deployable,
  mobile, and stratospheric platform for scientific research. Airborne
  platforms are of particular value for making coronal observations
  during total solar eclipses because of their ability both to follow the
  Moon's shadow and to get above most of the atmospheric air mass that
  can interfere with astronomical observations. We used the 2017 August
  21 eclipse as a pathfinding mission for high-altitude airborne solar
  astronomy, using the existing high-speed visible-light and near/midwave
  infrared imaging suite mounted in the WB-57 nose cone. In this paper,
  we describe the aircraft, the instrument, and the 2017 mission;
  operations and data acquisition; and preliminary analysis of data
  quality from the existing instrument suite. We describe benefits and
  technical limitations of this platform for solar and other astronomical
  observations. We present a preliminary analysis of the visible-light
  data quality and discuss the limiting factors that must be overcome
  with future instrumentation. We conclude with a discussion of lessons
  learned from this pathfinding mission and prospects for future research
  at upcoming eclipses, as well as an evaluation of the capabilities of
  the WB-57 platform for future solar astronomy and general astronomical
  observation.

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Title: Novel Measurements of Solar Corona during the July 2 2019
    Total Eclipse over Chile
Authors: Monaghan, A.; Bryans, P.; Berkey, B.; Rivera, Y.
2019AGUFMSA33B3153M    Altcode:
  Physical features of the solar corona such as temperature, density,
  and magnetic field, have been demonstrated to affect the polarization
  of coronal light making polarimetry one of the most crucial diagnostic
  tools for solar research. Although the history of polarimetry in solar
  physics is long, the ever-advancing world of technology continually
  provides opportunities for implementation with new instruments and
  new methods. The pursuit of new measurements could shed light on
  long-standing unsolved problems of the solar corona, and increase our
  understanding of the corona, solar weather, and our sun. The PolarCam
  snapshot micropolarizer camera from 4D Technologies could hold the
  potential for novel exploration of the solar corona. Developed for
  use in interferometric measurements, the PolarCam is sensitive
  to linearly polarized light on a pixel scale and has the unique
  potential for size- and weight-constrained measurements such as CubeSat
  deployment. Similarly, the relatively unexplored Si X emission line
  (1.43 microns) could provide novel measurements of the solar corona,
  and shows great promise for magnetometry. <P />The 2019 Total Solar
  Eclipse in Chile provided an opportunity for the exploration of the
  Si X line as well as an investigation into the potential of PolarCam
  and similar technology. A team from the High Altitude Observatory
  (HAO) in Boulder observed the eclipse from Cerro Tololo Inter-American
  Observatory, taking measurements of Si X (1.43 micron) and white-light
  (734 nm) polarization. PolarCam observations, taken during total solar
  eclipse, were quantitatively compared with ground-based white-light
  coronagraph measurements, demonstrating the capabilities and limitations
  of such a detector for coronal measurements. The instrument's potential
  for future deployment in expeditions or cubesat missions is also
  evaluated. Finally, preliminary data from the Si X experiment is
  presented and possible avenues for further exploration are proposed.

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Title: Probing the solar corona with Sun-grazing comets: comparing
    MHDsimulations with EUV observations
Authors: Jia, Y. D.; Pesnell, W. D.; Liu, W.; Downs, C.; Bryans, P.
2019AGUFMSH13A..03J    Altcode:
  Sun -grazing comets can dive within one solar radii of the Sun
  's surface. The cometary materials expand along the comet's orbit,
  and undergo various stages of fierce thermal-chemical reactions on
  the scales of seconds to minutes. These reactions ionize cometary
  ions through successive charge states , which is revealed by certain
  emission lines in the AIA images. Such plasma reaction processes are
  significantly affected by the transient structures in the corona, and
  thus these structures are revealed by the structures and shapes of the
  comet tail. We combine three numerical models: a global corona model,
  particle transportation model, and cometary plasma interaction model
  into one framework to simulate the interaction of Sun -grazing comets
  in the low corona. In our framework, cometary ejecta are vaporized
  and then ionized via multiple channels, and then confined by the
  coronal magnetic field. Constrained by imaging observations of the
  and cometary interaction images, we apply our framework to trace back
  to the local condition of the ambient corona, and its spatiotemporal
  variation. Previously, our model confirmed the importance of the
  ambient magnetic field vector in shaping the tail. In this study,
  we use the C/2011 W3 (Lovejoy) perihelion to determine the local
  plasma and field conditions in the corona. Our framework is capable of
  resolving structures from thousands of meters to tens of million meters,
  so we can identify the fine spatial variations in plasma density and
  magnetic field intensity, which may be visible in future/on-going
  close-up coronal observations.

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Title: Coronal Hole Variation from Chromosphere to Solar Wind
Authors: Bryans, P.
2019AGUFMSH53B3369B    Altcode:
  Coronal holes (CHs) are most commonly defined as long-lived regions
  of reduced intensity in EUV images, and known to be the source of the
  fast solar wind. Recent analysis of the spectral characteristics of CHs,
  using data from the Interface Region Imaging Spectrograph (IRIS) and the
  Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode, belies their
  apparent uniformity in imaging data. Despite the typical assertion
  that CHs are the source of the fast solar wind, EIS measurements
  show regions within a CH with indications of slow-wind composition
  in the corona. The spectral signatures of these regions extend to the
  chromosphere, as evidenced in the Mg II lines measured by IRIS, with
  the possibility that differences in the coronal composition could also
  have signatures in the lower solar atmosphere. In this presentation we
  will explore what these spectroscopic measurements reveal about the
  underlying magnetic field and discuss the implications of variations
  in the chromosphere and corona on the solar wind.

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Title: Novel observations of the middle corona during the 2017 total
    solar eclipse
Authors: Caspi, A.; Seaton, D. B.; Tsang, C.; DeForest, C.; Bryans,
   P.; Samra, J.; DeLuca, E.; Tomczyk, S.; Burkepile, J.; Gallagher,
   P.; Golub, L.; Judge, P. G.; Laurent, G. T.; West, M.; Zhukov, A.
2019AGUFMSH13A..10C    Altcode:
  Total solar eclipses offer rare opportunities to study the middle
  corona. This intriguing region contains complex interfaces and
  transitions between physical regimes, but has historically been
  under-observed due to the challenges of observing its dim emission so
  close to the bright inner corona and blinding solar disk. The unique
  circumstances of a total solar eclipse coupled with a high-altitude
  observing platform provide nearly space-quality observing conditions,
  including for wavelengths inaccessible by ground-based observatories,
  but with availability of ground-quality resources, including high-speed,
  high-resolution, wide-field coronography typically inaccessible
  from space. We used the 2017 August 21 "Great American" total solar
  eclipse to observe the solar corona from ~1.02 to ~3 R<SUB>Sun</SUB>
  in both visible (533.9 ± 4.75 nm) and medium-wave infrared (3-5
  μm) light using stabilized telescopes on two of NASA's WB-57F
  high-altitude research aircraft. This pathfinding mission utilized
  existing instrumentation to evaluate the platform performance, guide
  instrumentation development, and explore new discovery space for
  future studies of the middle corona. <P />We present the high-speed
  (30 Hz), high-resolution (3 arcsec/pixel) visible and IR observations
  obtained during the eclipse, and analysis of these observations
  in the context of coronal structure and dynamics. We discuss the
  limitations of the prototype data and pathways forward for future
  instrumentation and missions optimized for the range of observable
  parameters in the middle corona. We also discuss the benefits of
  such eclipse studies to an understanding of the corona as a single,
  unified system, from its origins at the solar surface to its extension
  into the heliosphere, particularly within the context of a developing
  multi- and inter-disciplinary research collaboration, COHERENT (the
  "Corona as a Holistic Environment" Research Network).

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Title: Solar Eclipse Observations from the Ground and Air from 0.31
    to 5.5 Microns
Authors: Judge, Philip; Berkey, Ben; Boll, Alyssa; Bryans, Paul;
   Burkepile, Joan; Cheimets, Peter; DeLuca, Edward; de Toma, Giuliana;
   Gibson, Keon; Golub, Leon; Hannigan, James; Madsen, Chad; Marquez,
   Vanessa; Richards, Austin; Samra, Jenna; Sewell, Scott; Tomczyk,
   Steven; Vera, Alysha
2019SoPh..294..166J    Altcode:
  We present spectra and broad-band polarized light data from a novel
  suite of instruments deployed during the 21st August 2017 total solar
  eclipse. Our goals were to survey solar spectra at thermal infrared
  wavelengths during eclipse, and to test new technology for measuring
  polarized coronal light. An infrared coronal imaging spectrometer,
  flown at 14.3 km altitude above Kentucky, was supported on the ground
  by observations from Madras, Oregon (elevation 683 m) and Camp Wyoba
  on Casper Mountain, Wyoming (2402 m). In Wyoming we deployed a new
  infrared Fourier Transform Spectrometer (FTS), three low-dispersion
  spectrometers loaned to us by Avantes, a novel visible-light camera
  PolarCam, sensitive to linear polarization, and one of two infrared
  cameras from FLIR Systems, the other operated at Madras. Circumstances
  of eclipse demanded that the observations spanned 17:19 to 18:26
  UT. We analyze spectra of the limb photosphere, the chromosphere,
  prominences, and coronal lines from 310 nm to 5.5 μm. We calibrated
  data photometrically using the solar disk as a source. Between different
  spectrometers, the calibrations were consistent to better than 13%. But
  the sensitivities achieved were insufficient to detect coronal lines
  from the ground. The PolarCam data are in remarkable agreement with
  polarization data from the K-Cor synoptic instrument on Mauna Loa, and
  with FLIR intensity data acquired in Madras. We discuss new results,
  including a detection of the He I 1083 nm multiplet in emission during
  the whole of totality. The combination of the FTS and AIR-Spec spectra
  reveals for the first time the effects of the telluric extinction
  on the infrared coronal emission lines, to be observed with upcoming
  Daniel K. Inouye Solar Telescope.

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Title: Instrument Calibration of the Interface Region Imaging
    Spectrograph (IRIS) Mission
Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell,
   T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.;
   Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.;
   Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M.
2018SoPh..293..149W    Altcode:
  The Interface Region Imaging Spectrograph (IRIS) is a NASA small
  explorer mission that provides high-resolution spectra and images of
  the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The
  IRIS data are archived in calibrated form and made available to the
  public within seven days of observing. The calibrations applied to
  the data include dark correction, scattered light and background
  correction, flat fielding, geometric distortion correction, and
  wavelength calibration. In addition, the IRIS team has calibrated the
  IRIS absolute throughput as a function of wavelength and has been
  tracking throughput changes over the course of the mission. As a
  resource for the IRIS data user, this article describes the details
  of these calibrations as they have evolved over the first few years
  of the mission. References to online documentation provide access to
  additional information and future updates.

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Title: Interaction between cool material from Sun-grazing comets
    and the low corona
Authors: Jia, Yingdong; Pesnell, William; Liu, Wei; Downs, Cooper;
   Bryans, Paul
2018cosp...42E1613J    Altcode:
  Sun-grazing comets dive into altitudes lower than 1 solar radius from
  the chromosphere. Cool materials of temperature lower than 10 ^{3}K
  explode from the comet into the 10 ^{6} K corona. These materials
  undergone various stages of rapid chemical reactions in scales of
  seconds to minutes. Such reactions Structures in such images of
  various wavelengths indicate strong variation in ambient conditions
  of the corona. We combine three numerical models: low corona model,
  particle transportation model, and cometary plasma interaction model
  into one framework to model the interaction of Sun-grazing comets in the
  low corona. In our framework, cometary vapor are ionized via multiple
  channels, and then detained by the coronal magnetic field. In seconds,
  these ions are further ionized into their highest charge state, which
  is revealed by certain emission lines. Constrained by coronal graphs
  and cometary interaction images, we apply our framework to trace back
  to the local condition of the ambient corona, and its spatial/time
  variation. Our frame work is able to resolve structures of sub-million
  meters to tens of million meters. Once trained by multiple stages of
  the comet's journey in the low corona, this framework can identify the
  fine spatial variations in plasma density and magnetic field intensity,
  which may be visible to future close-up observations.

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Title: New Coronal Science from NASA WB-57F High-Altitude Aircraft
    Observations of the 2017 Total Solar Eclipse
Authors: Caspi, Amir; DeLuca, . Edward; Tomczyk, Steven; DeForest,
   Craig; Bryans, Paul; Seaton, Daniel; Tsang, Constantine
2018cosp...42E.526C    Altcode:
  Total solar eclipses present rare opportunities to study the
  complex solar corona, down to altitudes of just a few percent of
  a solar radius above the surface, using ground-based and airborne
  observatories that would otherwise be dominated by the intense solar
  disk and high sky brightness. Studying the corona is critical to
  gaining a better understanding of physical processes that occur on
  other stars and astrophysical objects, as well as understanding the
  dominant driver of space weather that affects human assets at Earth and
  elsewhere. For example, it is still poorly understood how the corona
  is heated to temperatures of 1-2 MK globally and up to 5-10 MK above
  active regions, while the underlying chromosphere is 100 times cooler;
  numerous theories abound, but are difficult to constrain due to the
  limited sensitivities and cadences of prior measurements. The stability
  of large-scale coronal structures and the extent of their reach to the
  middle and outer corona are also not well known, limited in large part
  by sensitivities and fields of view of existing observations.Airborne
  observations during a total eclipse provide unique advantages. By
  flying in the stratosphere at altitudes of 50 kft or higher, they
  avoid all weather, the seeing quality is enormously improved, and
  additional wavelengths such as near-IR also become available due to
  significantly reduced water absorption. An airborne observatory can
  also follow the Moon's shadow, increasing the total observing time by
  50% or more.We present current results of solar coronal measurements
  from airborne observations of the 2017 Great American Total Solar
  Eclipse using two of NASA's WB-57 high-altitude research aircraft,
  each equipped with two 8.7" telescopes feeding high-sensitivity visible
  (green line and nearby continuum) and medium-wave IR (3-5 {μ}m) cameras
  operating at high cadence (30 Hz) with ∼3 arcsec/pixel platescale and
  ±3 R_{sun} fields of view. The aircraft flew along the eclipse path,
  separated by ∼110 km, to observe a summed ∼7.5 minutes of totality
  in both visible and MWIR. These observations enable groundbreaking
  studies of high-speed coherent motion - including possible Alfvén
  waves and nanojets - in the lower and middle corona that could shed
  light on coronal heating processes and the formation and stability of
  coronal structures. Our MWIR observations of a cool prominence and
  hot coronal active region plasma will be combined with spectra from
  the AIR-Spec instrument, flown concurrently on NCAR's HIAPER GV. We
  review the WB-57 eclipse mission and the current results of analysis
  on the visible and IR coronal measurements, along with an outlook for
  future analysis and missions.

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Title: Eclipse Science from 50,000 Feet: New Coronal Results from
    NASA WB-57F High-Altitude Aircraft Observations of the 2017 Total
    Solar Eclipse
Authors: Caspi, Amir; Tsang, Constantine; Seaton, Daniel B.; DeForest,
   Craig; Bryans, Paul; DeLuca, Edward; Tomczyk, Steven; Burkepile,
   Joan; Casey, Thomas Anthony; Collier, John; Darrow, Donald DD; Del
   Rosso, Dominic; Durda, Daniel D.; Gallagher, Peter; Gascar, Jasmine;
   Golub, Leon; Jacyna, Matthew; Johnson, David DJ; Judge, Philip G.;
   Klemm, Cary; Laurent, Glenn Thomas; Lewis, Johanna; Mallini, Charles;
   Parent, Thomas Duster; Propp, Timothy; Steffl, Andrew; Warner, Jeff;
   West, Matthew John; Wiseman, John; Yates, Mallory; Zhukov, Andrei
2018tess.conf31302C    Altcode:
  Total solar eclipses present rare opportunities to study the complex
  solar corona, down to altitudes of just a few percent of a solar
  radius above the surface. Studying the corona is critical to gaining
  a better understanding of the dominant driver of space weather that
  affects human assets on Earth and elsewhere. For example, it is still
  poorly understood how the corona is heated to temperatures of 1-2 MK
  globally and up to 5-10 MK above active regions, while the underlying
  chromosphere is 100 times cooler. The stability of large-scale coronal
  structures and the extent of their reach to the middle and outer corona
  are also not well known, limited in large part by sensitivities and
  fields of view of existing observations. <P />Airborne observations
  during a total eclipse provide unique advantages. By flying in the
  stratosphere at altitudes of 50 kft or higher, they avoid all weather,
  the seeing quality is enormously improved, and additional wavelengths
  such as near-IR also become available due to significantly reduced
  water absorption. An airborne observatory can also follow the Moon's
  shadow, increasing the total observing time by 50% or more. <P />We
  present current results of solar coronal measurements from airborne
  observations of the 2017 Great American Total Solar Eclipse using two
  of NASA's WB-57 high-altitude research aircraft, each equipped with
  two 8.7-inch telescopes feeding high-sensitivity visible (green line
  and nearby continuum) and medium-wave IR (3-5 μm) cameras operating
  at high cadence (30 Hz) with ∼3 arcsec/pixel platescale and ±3
  R<SUB>sun</SUB> fields of view. The two aircraft flew along the eclipse
  path, separated by ∼110 km, to observe a total of ∼7.5 minutes
  of totality in both visible and MWIR. These observations enable
  groundbreaking studies of high-speed coherent motion - including
  possible Alfvén waves and nanojets - in the lower and middle corona
  that could shed light on coronal heating processes and the formation
  and stability of coronal structures. Our MWIR observations of a cool
  prominence and hot coronal active region plasma will be combined with
  spectra from the AIR-Spec instrument, flown concurrently on NCAR's
  HIAPER GV. We review the WB-57 eclipse mission and the current results
  of analysis on the visible and IR coronal measurements, along with an
  outlook for future analysis and missions.

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Title: Chasing the Great American 2017 Total Solar Eclipse: Coronal
    Results from NASA's WB-57F High-Altitude Research Aircraft
Authors: Caspi, A.; Tsang, C.; DeForest, C. E.; Seaton, D. B.; Bryans,
   P.; Burkepile, J.; Casey, T. A.; Collier, J.; Darrow, D.; DeLuca,
   E.; Durda, D. D.; Gallagher, P.; Golub, L.; Judge, P. G.; Laurent,
   G. T.; Lewis, J.; Mallini, C.; Parent, T.; Propp, T.; Steffl, A.;
   Tomczyk, S.; Warner, J.; West, M. J.; Wiseman, J.; Zhukov, A.
2017AGUFMSH24A..05C    Altcode:
  Total solar eclipses present rare opportunities to study the complex
  solar corona, down to altitudes of just a few percent of a solar
  radius above the surface, using ground-based and airborne observatories
  that would otherwise be dominated by the intense solar disk and high
  sky brightness. Studying the corona is critical to gaining a better
  understanding of physical processes that occur on other stars and
  astrophysical objects, as well as understanding the dominant driver of
  space weather that affects human assets at Earth and elsewhere. For
  example, it is still poorly understood how the corona is heated to
  temperatures of 1-2 MK globally and up to 5-10 MK above active regions,
  while the underlying chromosphere is 100 times cooler; numerous theories
  abound, but are difficult to constrain due to the limited sensitivities
  and cadences of prior measurements. The origins and stability of coronal
  fans, and the extent of their reach to the middle and outer corona,
  are also not well known, limited in large part by sensitivities and
  fields of view of existing observations. Airborne observations during
  the eclipse provide unique advantages; by flying in the stratosphere
  at altitudes of 50 kft or higher, they avoid all weather, the seeing
  quality is enormously improved, and additional wavelengths such as
  near- IR also become available due to significantly reduced water
  absorption. For an eclipse, an airborne observatory can also follow the
  shadow, increasing the total observing time by 50% or more. We present
  results of solar coronal measurements from airborne observations of
  the 2017 Great American Total Solar Eclipse using two of NASA's WB-57
  high-altitude research aircraft, each equipped with two 8.7" telescopes
  feeding high-sensitivity visible (green-line) and medium-wave IR (3-5
  μm) cameras operating at high cadence (30 Hz) with 3 arcsec/pixel
  platescale and ±3 R_sun fields of view. The aircraft flew along the
  eclipse path, separated by 110 km, to observe a summed 7.5 minutes of
  totality in both visible and NIR, enabling groundbreaking studies of
  high-speed wave motions and nanojets in the lower corona, the structure
  and extent of coronal fans, and constraints on a potential primordial
  dust ring around the Sun. We review the mission, and the results of
  analysis on the visible and IR coronal measurements.

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Title: Multi-wavelength observations of the solar atmosphere from
    the August 21, 2017 total solar eclipse
Authors: Tomczyk, S.; Boll, A.; Bryans, P.; Burkepile, J.; Casini,
   R.; DeLuca, E.; Gibson, K. L.; Judge, P. G.; McIntosh, S. W.; Samra,
   J.; Sewell, S. D.
2017AGUFMSH24A..04T    Altcode:
  We will conduct three experiments at the August 21, 2017 total
  solar eclipse that we call the Rosetta Stone experiments. First,
  we will obtain narrow-bandpass images at infrared wavelengths of the
  magnetically sensitive coronal emission lines of Fe IX 2855 nm, Mg VIII
  3028 nm and Si IX 3935 nm with a FLIR thermal imager. Information on the
  brightness of these lines is important for identifying the optimal lines
  for coronal magnetometry. These images will also serve as context images
  for the airborne AirSpec IR coronal spectroscopy experiment (Samra et
  al). Second, we will obtain linear polarization images of the visible
  emission lines of Fe X 637 nm and Fe XI 789 nm as well as the continuum
  polarization near 735 nm. These will be obtained with a novel detector
  with an integral array of linear micro-polarizers oriented at four
  different angles that enable polarization images without the need for
  liquid crystals or rotating elements. These measurements will provide
  information on the orientation of magnetic fields in the corona and
  serve to demonstrate the new detector technology. Lastly, we will obtain
  high cadence spectra as the moon covers and uncovers the chromosphere
  immediately after 2nd contact and before third contact. This so-called
  flash spectrum will be used to obtain information about chromospheric
  structure at a spatial resolution higher than is possible by other
  means. In this talk, we will describe the instrumentation used in these
  experiments and present initial results obtained with them. This work
  is supported by a grant from NASA, through NSF base funding of HAO/NCAR
  and by generous loans of equipment from our corporate partners, FLIR,
  4D Technologies and Avantes.

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Title: Digging into the corona: A modeling framework trained with
    Sun-grazing comet observations
Authors: Jia, Y. D.; Pesnell, W. D.; Bryans, P.; Downs, C.; Liu, W.;
   Schwartz, S. J.
2017AGUFMSH11B2437J    Altcode:
  Images of comets diving into the low corona have been captured a few
  times in the past decade. Structures visible at various wavelengths
  during these encounters indicate a strong variation of the ambient
  conditions of the corona. We combine three numerical models: a global
  coronal model, a particle transportation model, and a cometary plasma
  interaction model into one framework to model the interaction of such
  Sun-grazing comets with plasma in the low corona. In our framework,
  cometary vapors are ionized via multiple channels and then captured
  by the coronal magnetic field. In seconds, these ions are further
  ionized into their highest charge state, which is revealed by certain
  coronal emission lines. Constrained by observations, we apply our
  framework to trace back to the local conditions of the ambient corona,
  and their spatial/time variation over a broad range of scales. Once
  trained by multiple stages of the comet's journey in the low corona,
  we illustrate how this framework can leverage these unique observations
  to probe the structure of the solar corona and solar wind.

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Title: Surveying the IR corona during the 2017 solar eclipse
Authors: Bryans, P.; Hannigan, J. W.; Sewell, S. D.; Judge, P. G.
2017AGUFMSH13B2479B    Altcode:
  The spectral emission of the infrared solar corona is the most
  promising direct diagnostic of the coronal magnetic field, and
  yet remains poorly measured. During the 2017 total solar eclipse,
  we will perform the first spectral survey of the IR corona using
  the NCAR Airborne Interferometer. This Fourier Transform Infrared
  Spectrometer is configured to observe the coronal spectrum from 1.5
  to 5.5 microns at R 10,000 from a ground-based site. The location
  is atop Casper Mountain, Wyoming (42.73ºN, 106.32ºW, 2400 masl),
  8 km from the center-line of totality. In this presentation, we will
  outline the need for such measurements, describe the instrument design
  and adaptation for the eclipse measurement, observation scheme, and
  present preliminary results. We will also discuss implications for
  observing infrared coronal lines from the ground, for example with
  the upcoming DKIST facility.

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Title: ASPIRE - Airborne Spectro-Polarization InfraRed Experiment
Authors: DeLuca, E.; Cheimets, P.; Golub, L.; Madsen, C. A.; Marquez,
   V.; Bryans, P.; Judge, P. G.; Lussier, L.; McIntosh, S. W.; Tomczyk, S.
2017AGUFMSH13B2480D    Altcode:
  Direct measurements of coronal magnetic fields are critical for
  taking the next step in active region and solar wind modeling and
  for building the next generation of physics-based space-weather
  models. We are proposing a new airborne instrument to make these key
  observations. Building on the successful Airborne InfraRed Spectrograph
  (AIR-Spec) experiment for the 2017 eclipse, we will design and build a
  spectro-polarimeter to measure coronal magnetic field during the 2019
  South Pacific eclipse. The new instrument will use the AIR-Spec optical
  bench and the proven pointing, tracking, and stabilization optics. A new
  cryogenic spectro-polarimeter will be built focusing on the strongest
  emission lines observed during the eclipse. The AIR-Spec IR camera,
  slit jaw camera and data acquisition system will all be reused. The
  poster will outline the optical design and the science goals for ASPIRE.

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Title: First results from the NASA WB-57 airborne observations of
    the Great American 2017 Total Solar Eclipse
Authors: Caspi, Amir; Tsang, Constantine; DeForest, Craig; Seaton,
   Daniel B.; Bryans, Paul; Tomczyk, Steven; Burkepile, Joan; Judge,
   Phil; DeLuca, Edward E.; Golub, Leon; Gallagher, Peter T.; Zhukov,
   Andrei; West, Matthew; Durda, Daniel D.; Steffl, Andrew J.
2017SPD....4810701C    Altcode:
  Total solar eclipses present rare opportunities to study the complex
  solar corona, down to altitudes of just a few percent of a solar
  radius above the surface, using ground-based and airborne observatories
  that would otherwise be dominated by the intense solar disk and high
  sky brightness. Studying the corona is critical to gaining a better
  understanding of physical processes that occur on other stars and
  astrophysical objects, as well as understanding the dominant driver of
  space weather that affects human assets at Earth and elsewhere. For
  example, it is still poorly understood how the corona is heated to
  temperatures of 1-2 MK globally and up to 5-10 MK above active regions,
  while the underlying chromosphere is 100 times cooler; numerous theories
  abound, but are difficult to constrain due to the limited sensitivities
  and cadences of prior measurements. The origins and stability of coronal
  fans, and the extent of their reach to the middle and outer corona,
  are also not well known, limited in large part by sensitivities and
  fields of view of existing observations.Airborne observations during
  the eclipse provide unique advantages; by flying in the stratosphere
  at altitudes of 50 kft or higher, they avoid all weather, the seeing
  quality is enormously improved, and additional wavelengths such
  as near-IR also become available due to significantly reduced water
  absorption. For an eclipse, an airborne observatory can also follow the
  shadow, increasing the total observing time by 50% or more.We present
  the first results from airborne observations of the 2017 Great American
  Total Solar Eclipse using two of NASA's WB-57 research aircraft, each
  equipped with two 8.7" telescopes feeding high-sensitivity visible
  (green-line) and near-IR (3-5 µm) cameras operating at high cadence
  (30 Hz) with ~3 arcsec/pixel platescale and ±3 R_sun fields of
  view. The aircraft will fly along the eclipse path, separated by ~90
  km, to observe a summed ~8 minutes of totality in both visible and
  NIR, enabling groundbreaking studies of high-speed wave motions and
  nanojets in the lower corona, the structure and extent of coronal fans,
  and constraints on a potential primordial dust ring around the Sun.

---------------------------------------------------------
Title: On the Connection between Propagating Solar Coronal
    Disturbances and Chromospheric Footpoints
Authors: Bryans, P.; McIntosh, S. W.; De Moortel, I.; De Pontieu, B.
2016ApJ...829L..18B    Altcode:
  The Interface Region Imaging Spectrograph (IRIS) provides an
  unparalleled opportunity to explore the (thermal) interface between the
  chromosphere, transition region, and the coronal plasma observed by the
  Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory
  (SDO). The SDO/AIA observations of coronal loop footpoints show
  strong recurring upward propagating signals—“propagating coronal
  disturbances” (PCDs) with apparent speeds of the order of 100-120 km
  s<SUP>-1</SUP>. That signal has a clear signature in the slit-jaw images
  of IRIS in addition to identifiable spectral signatures and diagnostics
  in the Mg iih (2803 Å) line. In analyzing the Mg iih line, we are able
  to observe the presence of magnetoacoustic shock waves that are also
  present in the vicinity of the coronal loop footpoints. We see there is
  enough of a correspondence between the shock propagation in Mg iih, the
  evolution of the Si IV line profiles, and the PCD evolution to indicate
  that these waves are an important ingredient for PCDs. In addition, the
  strong flows in the jet-like features in the IRIS Si IV slit-jaw images
  are also associated with PCDs, such that waves and flows both appear
  to be contributing to the signals observed at the footpoints of PCDs.

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Title: Post Flare Giant Arches and Run-Away Reconnection
Authors: West, Matthew; Seaton, Daniel B.; Savage, Sabrina; Bryans,
   Paul
2016SPD....4740206W    Altcode:
  The nature of post-flare giant arches and their relation to regular
  post flare loops has long been debated, especially in the context of
  how post-flare giant arches can sustain their growth for such long
  periods. In this presentation we discuss how magnetic reconnection can
  be sustained to such great heights, and the role the background corona
  plays in maintaining this growth. We use observations from 14 October
  2014, when the SWAP EUV solar telescope on-board the PROBA2 spacecraft
  observed an eruption that led to the formation of perhaps the largest
  post-eruptive loop system seen in the solar corona in solar cycle
  24. These loops grew to a height of approximately 400000 km (&gt;0.5
  solar-radii). We provide evidence of on-going reconnection, through
  observations spanning from the chromosphere to the middle corona,
  and discuss how only certain conditions can maintain prolonged growth.

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Title: Measuring the IR solar corona during the 2017 eclipse
Authors: Bryans, Paul; Hannigan, James; Philip, Judge; Larson, Brandon;
   Sewell, Scott; McIntire, Lauren
2016SPD....4730105B    Altcode:
  On 21 August 2017 a total solar eclipse will pass across the continental
  United States, offering a unique opportunity to conduct scientific
  research of the solar atmosphere. With the light from the Sun eclipsed,
  the solar corona becomes visible in a way not possible when swamped
  by the light from the photosphere. The infrared (IR) spectrum of
  the corona, in particular, is predicted to contain some of the most
  magnetically sensitive spectral lines. However, no comprehensive survey
  of this spectral range has been carried out to date. Here, we describe
  a Fourier Transform Spectrometer, currently under construction at NCAR,
  to measure the IR spectrum from 2 to 12 microns. We will discuss the
  operation of the experiment, which will be deployed along the path of
  totality in Wyoming, and the scientific results we hope to obtain.

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Title: On the Absence of EUV Emission from Comet C/2012 S1 (ISON)
Authors: Bryans, Paul; Pesnell, W. Dean
2016ApJ...822...77B    Altcode:
  When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage
  within two solar radii of the Sun’s surface, it was expected to be
  a bright emitter at extreme ultraviolet (EUV) wavelengths. However,
  despite solar EUV telescopes repointing to track the orbit of the comet,
  no emission was detected. This “null result” is interesting in
  its own right, offering the possibility of placing limits on the size
  and composition of the nucleus. We explain the lack of detection by
  considering the properties of the comet and the solar atmosphere that
  determine the intensity of EUV emission from sungrazing comets. By
  comparing these properties with those of sungrazing comet C/2011 W3
  (Lovejoy), which did emit in the EUV, we conclude that the primary
  factor resulting in non-detectable EUV emission from C/2012 S1 (ISON)
  was an insufficiently large nucleus. We conclude that the radius
  of C/2012 S1 (ISON) was at least a factor of four less than that of
  C/2011 W3 (Lovejoy). This is consistent with white-light observations
  in the days before perihelion that suggested the comet was dramatically
  reducing in size on approach.

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Title: Observed Variability of the Solar Mg II h Spectral Line
Authors: Schmit, D.; Bryans, P.; De Pontieu, B.; McIntosh, S.;
   Leenaarts, J.; Carlsson, M.
2015ApJ...811..127S    Altcode: 2015arXiv150804714S
  The Mg ii h&amp;k doublet are two of the primary spectral lines observed
  by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These
  lines are tracers of the magnetic and thermal environment that spans
  from the photosphere to the upper chromosphere. We use a double-Gaussian
  model to fit the Mg ii h profile for a full-Sun mosaic data set taken
  on 2014 August 24. We use the ensemble of high-quality profile fits to
  conduct a statistical study on the variability of the line profile as
  it relates the magnetic structure, dynamics, and center-to-limb viewing
  angle. The average internetwork profile contains a deeply reversed
  core and is weakly asymmetric at h2. In the internetwork, we find a
  strong correlation between h3 wavelength and profile asymmetry as well
  as h1 width and h2 width. The average reversal depth of the h3 core
  is inversely related to the magnetic field. Plage and sunspots exhibit
  many profiles that do not contain a reversal. These profiles also occur
  infrequently in the internetwork. We see indications of magnetically
  aligned structures in plage and network in statistics associated with
  the line core, but these structures are not clear or extended in the
  internetwork. The center-to-limb variations are compared to predictions
  of semi-empirical model atmospheres. We measure a pronounced limb
  darkening in the line core that is not predicted by the model. The
  aim of this work is to provide a comprehensive measurement baseline
  and preliminary analysis on the observed structure and formation of
  the Mg ii profiles observed by IRIS.

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Title: Full-Sun IRIS observations and what they reveal about
    chromosphere and transition region variation across the disk
Authors: Bryans, Paul; McIntosh, Scott W.
2015TESS....120313B    Altcode:
  The recent launch of the Interface Region Imaging Spectrometer
  (IRIS) has resulted in the first high-resolution spectroscopy of the
  chromosphere and transition region. The wavelength range sampled by IRIS
  allows us to measure emission and absorption lines across a range of
  heights in the lower solar atmosphere. However, the IRIS field-of-view
  is limited to 175 arcsec<SUP>2</SUP>, so simultaneous observations of
  these spectral lines is not possible across the entire disk. To overcome
  this problem we have performed full-disk mosaics, where we build up
  observations of the entire Sun using 184 different IRIS pointings. An
  analysis of these mosaics has highlighted interesting variations in
  the spectral line profiles across the disk. In this presentation we
  will summarize these findings and speculate on what physical insights
  they reveal.

---------------------------------------------------------
Title: Coronal Diagnostics from Cometary Emission
Authors: Bryans, Paul; Pesnell, William D; Seaton, Daniel B; West,
   Matthew J
2014AAS...22442203B    Altcode:
  The extreme ultraviolet (EUV) emission observed from sungrazing comets
  as they pass through the solar atmosphere can be used to infer the
  properties of the corona. In this paper we will discuss several of these
  properties that can be estimated from the EUV observations of Comet
  Lovejoy from AIA/SDO and SWAP/PROBA2. The longevity of the emission
  allows us to constrain the coronal electron density through which
  the comet passes. We will also discuss how dispersion of the emitting
  cometary material we can be used to estimate the local Alfven speed in
  the corona. Finally, measuring the deformation of the magnetic field
  as it is impacted by the comet can be used to estimate the magnetic
  field strength in this location. In the absence of the comet, none
  of these parameters are directly measurable in the corona. Sungrazing
  comets are thus unique probes of the solar atmosphere.

---------------------------------------------------------
Title: The Time-dependent Chemistry of Cometary Debris in the
    Solar Corona
Authors: Pesnell, W. D.; Bryans, P.
2014ApJ...785...50P    Altcode:
  Recent improvements in solar observations have greatly progressed the
  study of sungrazing comets. They can now be imaged along the entirety
  of their perihelion passage through the solar atmosphere, revealing
  details of their composition and structure not measurable through
  previous observations in the less volatile region of the orbit further
  from the solar surface. Such comets are also unique probes of the solar
  atmosphere. The debris deposited by sungrazers is rapidly ionized and
  subsequently influenced by the ambient magnetic field. Measuring the
  spectral signature of the deposited material highlights the topology
  of the magnetic field and can reveal plasma parameters such as the
  electron temperature and density. Recovering these variables from the
  observable data requires a model of the interaction of the cometary
  species with the atmosphere through which they pass. The present paper
  offers such a model by considering the time-dependent chemistry of
  sublimated cometary species as they interact with the solar radiation
  field and coronal plasma. We expand on a previous simplified model by
  considering the fully time-dependent solutions of the emitting species'
  densities. To compare with observations, we consider a spherically
  symmetric expansion of the sublimated material into the corona and
  convert the time-dependent ion densities to radial profiles. Using
  emissivities from the CHIANTI database and plasma parameters derived
  from a magnetohydrodynamic simulation leads to a spatially dependent
  emission spectrum that can be directly compared with observations. We
  find our simulated spectra to be consistent with observation.

---------------------------------------------------------
Title: What EUV Observations of Comet ISON Reveal About the Solar
    Corona
Authors: Bryans, P.; Pesnell, W. D.
2013AGUFM.P31A1787B    Altcode:
  Recent advances in space-based solar observations have greatly
  progressed the study of sungrazing comets. They can now be imaged along
  the entirety of their perihelion passage, revealing details of their
  composition, structure, and size. Such comets are also unique probes
  of the solar corona. The debris deposited by sungrazers is rapidly
  ionized and subsequently forced to follow the ambient magnetic field. In
  this paper we present preliminary results from EUV observations of
  Comet ISON. We estimate the size of the comet nucleus based on the
  EUV radiance and compare with independent estimates. The variation
  of the EUV emission with wavelength provides limits on the density of
  the ambient corona, and the motion of ionized debris will be used to
  infer the coronal magnetic field structure.

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Title: Time-dependent chemisty of outgassed cometary detritus in
    the solar corona
Authors: Bryans, Paul; Pesnell, W. D.
2013SPD....44...32B    Altcode:
  Recent observations of sungrazing comets have opened an exciting novel
  methof of probing the solar atmosphere. As well as providing valuable
  insight on the magnetic field of the lower corona, sungrazing comets
  also promise the potential of measuring the solar wind as their detritus
  follows the open field lines of the corona. In this work, we model the
  chemisty of the material sublimated from comets as they skim across
  the Sun. This material, largely water ice, is rapidly dissociated and
  ionized by the solar radiation field and coronal electrons. We track
  the evolution of the ionizing material as it expands into the corona
  using a generalized Haser-like model. Based on these results, we have
  predicted the emission resulting from these ions in different regions
  of the corona and compared the results with SDO/AIA observations.

---------------------------------------------------------
Title: What Will Comet ISON Debris Teach Us About the Sun?
Authors: Pesnell, W. D.; Bryans, P.
2013SPD....44...34P    Altcode:
  Comet ISON is a large sun-grazing comet due to pass perihelion on
  November 28, 2013. It will go through the corona 2.7 Rsun above
  the surface, much higher than earlier EUV comets. We will use our
  time-dependent models of cometary debris to discuss how the trail of
  Comet ISON can be used to probe the solar corona. The debris trail left
  behind as a sun-grazing comet passes by the Sun undergoes different
  chemical processes at different distances from the Sun. Near the Sun
  the material is rapidly converted to atomic ions and becomes part of
  the solar corona. Far from the Sun the evaporated material can remain in
  molecular form for a long time, while the grains of asteroidal material
  can exist long enough to become meteors in planetary atmospheres. The
  larger fragments may survive as independent comets, until the next
  perihelion passage. In between those limits the material moves in the
  solar wind acceleration region. The debris could become entrained in
  the solar wind and be measured by satellites far from the Sun. This
  material would be observed as abundance anomalies in the solar wind. We
  will describe the fate of the cometary debris trail left by Comet ISON
  and what the trail can tell us about the solar corona and solar wind.

---------------------------------------------------------
Title: EUV Emission from Sungrazing Comets
Authors: Bryans, Paul; Pesnell, W. Dean
2013enss.confE..33B    Altcode:
  The EUV emission resulting from comets' passage through the solar
  atmosphere has opened many exciting avenues of study. The observations
  show the sublimated cometary material to interact with ambient magnetic
  field and highlight magnetic features that are not normally visible with
  EUV telescopes. The first step, however, is to explain why the comet
  produces the EUV emission. In this talk, I will outline a model that
  describes the interaction of the cometary atmosphere with the quiescent
  solar background and results in such emission. In particular, the model
  accurately predicts the temporal and wavelength response of the emission
  detected by SDO/AIA. After describing the emission process, I will go on
  to discuss what we can learn about the corona from these observations.

---------------------------------------------------------
Title: Can we use comets as solar probes?
Authors: Bryans, P.
2012AGUFMSH13B2251B    Altcode:
  The EUV emission resulting from comets' passage through the solar
  atmosphere has opened many exciting avenues of study. The observations
  show the sublimated cometary material to interact with ambient magnetic
  field and highlight magnetic features that are not normally visible with
  EUV telescopes. The first step, however, is to explain why the comet
  produces the EUV emission. In this talk, I will outline a model that
  describes the interaction of the cometary atmosphere with the quiescent
  solar background and results in such emission. In particular, the model
  accurately predicts the temporal and wavelength response of the emission
  detected by SDO/AIA. After describing the emission process, I will go on
  to discuss what we can learn about the corona from these observations.

---------------------------------------------------------
Title: Investigating Coronal Activity by Release Using Sublimation
Authors: Moore, T. E.; Bryans, P.; Pesnell, W. D.; Thompson, B. J.
2012AGUFMSH21D..05M    Altcode:
  Plasma tails left by sun-grazing comets are visible in EUV, expanding
  their traditional role as "windsocks" into the low corona and serving
  as natural "chemical release" experiments. SDO obtained spectrally
  resolved video imagery of passages as close as 0.15 Rs to the solar
  photosphere at 12 sec frame cadence. Vaporized cometary materials
  form sublimation trails or "subtrails" that persist as long as 20
  min. in 13.1 and 17.1 nm channels. Striation along local magnetic flux
  tubes implies filamentation of the visible plasma, and the subtrails
  exhibit substantial deviations from the comet orbital track. These
  reveal coronal winds and shears with velocities that are comparable to
  the comet velocity of up to 600 km/s. We analyze the likely origins
  and directionality of these winds and their implications for coronal
  heating in the altitude range where ion-neutral collision mean free
  paths are longer than the gyro radius but shorter than the atmospheric
  scale height, that is, the solar transition region. With active impact
  or photo-ionization, and charge exchange, the inferred super-thermal,
  sub-Alfvenic ion-neutral relative velocities will lead to ion pick-up
  distributions that decay or relax into "kappa" distributions with
  super-thermal power law tails that are relevant to the formation of
  the corona.

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Title: Time-dependent Chemistry of Detritus from Sun-grazing Comets
Authors: Pesnell, W. D.; Bryans, P.
2012AGUFMSH13B2253P    Altcode:
  As a sun-grazing comet passes the Sun at perihelion it leaves behind
  a trail of water vapor and detritus. The latter are grains of stony
  material that rapidly heat and vaporize in the intense radiation field
  of the solar photosphere. A large amount of O is produced from both the
  water and the stony material. The atomic material does not continue
  along the comet's orbital path but appears to move along the ambient
  magnetic field. This requires an ionization mechanism that rapidly
  converts the neutral atoms into ions. We propose two models of the
  time-dependent chemistry that can be used to calculate the ionization
  balance of O and Fe. One is an extension of the Haser model to include
  many stages of ionization but without recombination. The advantage
  is that an analytic solution can be derived for an arbitrary numbers
  of ionization stages. Once the time dependence is known it can be
  converted to the radial profile in either spherical or cylindrical
  symmetry. The other model integrates in time the equations describing
  ionization/recombination balance. Both types of solutions can be
  numerically inverted to estimate the radiance profiles. The models give
  the same sequence to the ionization stages, but the time dependence
  and radial profiles are shown to differ. Although we concentrate on
  the O and Fe chemistry because it is observed from SDO/AIA, any atom
  can be considered.

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Title: The Extreme-ultraviolet Emission from Sun-grazing Comets
Authors: Bryans, P.; Pesnell, W. D.
2012ApJ...760...18B    Altcode: 2012arXiv1209.5708B
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  has observed two Sun-grazing comets as they passed through the solar
  atmosphere. Both passages resulted in a measurable enhancement of
  extreme-ultraviolet (EUV) radiance in several of the AIA bandpasses. We
  explain this EUV emission by considering the evolution of the cometary
  atmosphere as it interacts with the ambient solar atmosphere. Molecules
  in the comet rapidly sublimate as it approaches the Sun. They are
  then photodissociated by the solar radiation field to create atomic
  species. Subsequent ionization of these atoms produces a higher
  abundance of ions than normally present in the corona and results in
  EUV emission in the wavelength ranges of the AIA telescope passbands.

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Title: The Journey of Sungrazing Comet Lovejoy
Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.;
   Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson,
   H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse,
   C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.;
   Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson,
   W.; Weissman, P.; Comet Lovejoy Collaboration Team
2012AAS...22052507B    Altcode:
  Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed
  by space-based instruments, to survive perihelion passage. First
  observed by ground-based telescopes several weeks prior to perihelion,
  its journey towards the Sun was subsequently recorded by several solar
  observatories, before being observed in the weeks after perihelion by
  a further array of space- and ground-based instruments. Such a surfeit
  of wide-ranging observations provides an unprecedented insight into
  both sungrazing comets themselves, and the solar atmosphere through
  which they pass. This paper will summarize what we have learnt from the
  observations thus far and offer some thoughts on what future sungrazing
  comets may reveal about comets, the Sun, and their interaction.

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Title: The EUV Emission from Sun-Grazing Comets
Authors: Bryans, Paul; Pesnell, W. D.
2012AAS...22042305B    Altcode:
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  (SDO) has, to date, viewed two Sun-grazing comets as they passed
  through the solar corona. Both passages resulted in the significant
  enhancement of Extreme Ultraviolet (EUV) emission in several of
  the AIA bandpasses. We explain this EUV emission by considering the
  evolution of the cometary atmosphere as it interacts with the ambient
  solar atmosphere. Water ice in the comet rapidly sublimates as it
  approaches the Sun. This water vapor is then photodissociated by
  the solar radiation field to create atomic H and O. Other molecules
  present in the comet also evaporate and dissociate to give atomic
  Fe and other metals. Subsequent ionization of these atoms produces a
  high abundance of ions not normally present at the temperature of the
  corona and results in EUV emission in the wavelength ranges of the
  AIA telescopes. Understanding the EUV emission places constraints on
  the cometary composition and provides valuable insight to the nature
  of the upper solar atmosphere.

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Title: The EUV Emission in Comet-Solar Corona Interactions
Authors: Bryans, P.; Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.;
   Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H. S.
2011AGUFMSH34B..05B    Altcode:
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  (SDO) viewed a comet as it passed through the solar corona on 2011 July
  5. This was the first sighting of a comet by a EUV telescope. For 20
  minutes, enhanced emission in several of the AIA wavelength bands marked
  the path of the comet. We explain this EUV emission by considering
  the evolution of the cometary atmosphere as it interacts with the
  ambient solar atmosphere. Water ice in the comet rapidly sublimates
  as it approaches the Sun. This water vapor is then photodissociated,
  primarily by Ly-α, by the solar radiation field to create atomic H and
  O. Other molecules present in the comet also evaporate and dissociate
  to give atomic Fe and other metals. Subsequent ionization of these
  atoms can be achieved by a number of means, including photoionization,
  electron impact, and charge exchange with coronal protons and other
  highly-charged species. Finally, particles from the cometary atmosphere
  are thermalized to the background temperature of the corona. Each step
  could cause emission in the AIA bandpasses. We will report here on
  their relative contribution to the emission seen in the AIA telescopes.

---------------------------------------------------------
Title: New Collisional Ionization Equilibrium Calculations for
    Optically Thin Plasmas
Authors: Savin, D. W.; Bryans, P.; Mitthumsiri, W.; Badnell, N. R.;
   Gorczyca, T. W.; Laming, J. M.
2011nlaw.confC...5S    Altcode:
  Reliably interpreting spectra from electron-ionized laboratory and
  cosmic plasmas requires accurate ionization balance calculations for
  the plasma in question. However, much of the atomic data needed for
  these calculations have not been generated using modern theoretical
  methods and their reliability are often highly suspect. We have carried
  out state-of-the-art calculations of dielectronic recombination (DR)
  rate coefficients for the hydrogenic through Mg-like ions of all
  elements from He to Zn as well as for Al- like to Ar-like ions of
  Fe. We have also carried out state-of-the-art radiative recombination
  (RR) rate coefficient calculations for the bare through Na-like ions
  of all elements from H to Zn. Using our data and the most recently
  recommended electron impact ionization data, we present improved
  collisional ionization equilibrium (CIE) calculations. Here, as an
  example, we present our calculated fractional ionic abundances for
  iron using these data and compare them with those from the previously
  recommended CIE calculations.

---------------------------------------------------------
Title: Comparison of Vector Magnetograms from the Solenoidal and
    Irrotational Components of the Magnetic Field
Authors: Bryans, Paul; Pesnell, W. D.
2011SPD....42.2108B    Altcode: 2011BAAS..43S.2108B
  According to the Helmholtz Theorem, the solar magnetic field can be
  defined in terms of an irrotational and a solenoidal component. We will
  discuss the partitioning of the field into these components as a means
  of attributing elements of the magnetic field to its vorticity and
  divergence. We will then discuss the advantages of this decomposition
  as a metric for comparing vector magnetograms of varying spatial and
  temporal resolution.

---------------------------------------------------------
Title: Properties of a Polar Coronal Hole During the Solar Minimum
    in 2007
Authors: Hahn, M.; Bryans, P.; Landi, E.; Miralles, M. P.; Savin, D. W.
2010ApJ...725..774H    Altcode: 2010arXiv1010.4277H
  We report measurements of a polar coronal hole during the recent
  solar minimum using the Extreme Ultraviolet Imaging Spectrometer on
  Hinode. Five observations are analyzed that span the polar coronal hole
  from the central meridian to the boundary with the quiet-Sun corona. We
  study the observations above the solar limb in the height range of
  1.03-1.20 R <SUB>sun</SUB>. The electron temperature T <SUB>e</SUB>
  and emission measure (EM) are found using a geometric mean emission
  measure method. The EM derived from the elements Fe, Si, S, and Al
  are compared in order to measure relative coronal-to-photospheric
  abundance enhancement factors. We also studied the ion temperature
  T <SUB>i</SUB> and the non-thermal velocity v <SUB>nt</SUB> using the
  line profiles. All these measurements are compared to polar coronal hole
  observations from the previous (1996-1997) solar minimum and to model
  predictions for relative abundances. There are many similarities in the
  physical properties of the polar coronal holes between the two minima at
  these low heights. We find that the electron density, T <SUB>e</SUB>,
  and T <SUB>i</SUB> are comparable in both minima. T <SUB>e</SUB> shows
  a comparable gradient with height. Both minima show a decreasing T
  <SUB>i</SUB> with increasing charge-to-mass ratio q/M. A previously
  observed upturn of T <SUB>i</SUB> for ions above q/M&gt;0.25 was not
  found here. We also compared relative coronal-to-photospheric elemental
  abundance enhancement factors for a number of elements. These ratios
  were ~1 for both the low first ionization potential (FIP) elements Si
  and Al and the marginally high FIP element S relative to the low FIP
  element Fe, as is expected based on earlier observations and models
  for a polar coronal hole. These results are consistent with no FIP
  effect in a polar coronal hole.

---------------------------------------------------------
Title: Properties of the Solar Corona above a Polar Coronal Hole
    during the Solar Minimum in 2007
Authors: Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M. P.; Savin,
   D. W.
2010shin.confE.150H    Altcode:
  Observations have shown that the latest solar minimum differs from the
  previous one in 1996-1997. Here we present the analysis of EUV spectra
  of the north polar coronal hole observed during the recent minimum 16
  November 2007. The data were taken using the Extreme ultraviolet Imaging
  Spectrometer (EIS) on Hinode. Five observations span the coronal hole
  in the longitudinal direction from the center to the boundary with
  the quiet sun corona and extend radially from the solar disk to about
  1.2 Rsun. We use the geometric mean emission measure (GEM) approach to
  determine the plasma emission measure (EM) and electron temperature. The
  GEM analysis shows that the observations are nearly isothermal, but
  there are indications of a small contribution from higher temperature
  plasma along the line of sight. To investigate the temperature structure
  in more detail we are performing a differential emission measure (DEM)
  analysis. The upper and lower bounds on the ion temperature are also
  measured using line widths. Our results are compared to spectroscopic
  measurements of polar coronal holes obtained from observations carried
  out during the previous solar minimum in 1996-1997.

---------------------------------------------------------
Title: Multiple Component Outflows in an Active Region Observed with
    the EUV Imaging Spectrometer on Hinode
Authors: Bryans, P.; Young, P. R.; Doschek, G. A.
2010ApJ...715.1012B    Altcode: 2010arXiv1004.5085B
  We have used the Extreme Ultraviolet Imaging Spectrometer on the
  Hinode spacecraft to observe large areas of outflow near an active
  region. These outflows are seen to persist for at least 6 days. The
  emission line profiles suggest that the outflow region is composed of
  multiple outflowing components, Doppler-shifted with respect to each
  other. We have modeled this scenario by imposing a double-Gaussian fit
  to the line profiles. These fits represent the profile markedly better
  than a single-Gaussian fit for Fe XII and XIII emission lines. For
  the fastest outflowing components, we find velocities as high as 200
  km s<SUP>-1</SUP>. However, there remains a correlation between the
  fitted line velocities and widths, suggesting that the outflows are
  not fully resolved by the double-Gaussian fit and that the outflow
  may be comprised of further components.

---------------------------------------------------------
Title: Properties of the Solar Corona above a Polar Coronal Hole
    during the Recent Solar Minimum
Authors: Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M.; Savin, D.
2010AAS...21640105H    Altcode: 2010BAAS...41..857H
  Recent observations have shown that the latest solar minimum differs
  from the previous one in 1996-1997. Here we present the analysis of
  EUV spectra of the north polar coronal hole observed in November 2007,
  during the current minimum. The data were taken using the Extreme
  Ultraviolet Imaging Spectrometer (EIS) on Hinode. Five observations
  span the coronal hole in the longitudinal direction from the center
  to the boundary with the quiet sun corona and extend radially from
  the solar disk to about 1.2 solar radii to. We use the geometric mean
  emission measure (GEM) approach to determine the plasma emission measure
  (EM) and electron temperature. From the EM we estimate the relative
  elemental abundances. We also determine upper and lower bounds on the
  ion temperature using measured line widths. We then compare our results
  to spectroscopic measurements of polar coronal holes obtained from
  observations carried out during the previous solar minimum in 1996-1997.

---------------------------------------------------------
Title: Coronal Active Region Loop Variability Observed with Hinode/EIS
Authors: Bryans, Paul
2010AAS...21640720B    Altcode:
  Using the Extreme Ultraviolet Spectrometer (EIS) on the Hinode
  spacecraft, we have studied the properties of active region loops
  along their length. Here, we present results of the variation of the
  temperature, density and filling factor with respect to height in
  the loop. In particular, we find differences in the electron density
  between loop footpoints that provide important constraints on models
  used to explain coronal loop heating.

---------------------------------------------------------
Title: Updated Collisional Ionization Equilibrium Calculated for
    Optically Thin Plasmas
Authors: Savin, Daniel Wolf; Bryans, P.; Badnell, N. R.; Gorczyca,
   T. W.; Laming, J. M.; Mitthumsiri, W.
2010HEAD...11.1504S    Altcode: 2010BAAS...42..678S
  Reliably interpreting spectra from electron-ionized cosmic plasmas
  requires accurate ionization balance calculations for the plasma
  in question. However, much of the atomic data needed for these
  calculations have not been generated using modern theoretical methods
  and their reliability are often highly suspect. We have carried out
  state-of-the-art calculations of dielectronic recombination (DR) rate
  coefficients for the hydrogenic through Na-like ions of all elements
  from He to Zn as well as for Al-like to Ar-like ions of Fe. We have
  also carried out state-of-the-art radiative recombination (RR) rate
  coefficient calculations for the bare through Na-like ions of all
  elements from H to Zn. Using our data and the recommended electron
  impact ionization data of Dere (2007), we present improved collisional
  ionization equilibrium calculations (Bryans et al. 2006, 2009). We
  compare our calculated fractional ionic abundances using these data
  with those presented by Mazzotta et al. (1998) for all elements from
  H to Ni. This work is supported in part by the NASA APRA and SHP
  SR&amp;T programs.

---------------------------------------------------------
Title: Deriving the coronal hole electron temperature: electron
    density dependent ionization / recombination considerations
Authors: Doyle, John Gerard; Chapman, Steven; Bryans, Paul;
   Pérez-Suárez, David; Singh, Avninda; Summers, Hugh; Savin,
   Daniel Wolf
2010RAA....10...91D    Altcode: 2009arXiv0909.3195D
  Comparison of appropriate theoretically derived line ratios with
  observational data can yield estimates of a plasma's physical
  parameters, such as electron density or temperature. The usual practice
  in the calculation of the line ratio is the assumption of excitation
  by electrons/protons followed by radiative decay. Furthermore, it
  is normal to use the so-called coronal approximation, i.e. one only
  considers ionization and recombination to and from the ground-state. A
  more accurate treatment is to include ionization/recombination to and
  from metastable levels. Here, we apply this to two lines from adjacent
  ionization stages, Mg IX 368 Å and Mg X 625 Å, which has been shown to
  be a very useful temperature diagnostic. At densities typical of coronal
  hole conditions, the difference between the electron temperature derived
  assuming the zero density limit compared with the electron density
  dependent ionization/recombination is small. This, however, is not
  the case for flares where the electron density is orders of magnitude
  larger. The derived temperature for the coronal hole at solar maximum
  is around 1.04 MK compared to just below 0.82 MK at solar minimum.

---------------------------------------------------------
Title: Multiple Component Outflows in Active Regions observed by EIS
Authors: Bryans, Paul; Doschek, G. A.; Young, P. R.
2009SPD....40.1221B    Altcode:
  We have used the Extreme Ultraviolet Imaging Spectrometer (EIS) on
  the Hinode spacecraft to observe large areas of outflow near an active
  region. These outflows are seen to persist for a number of days. The
  emission line profiles suggest that the outflow region is composed of
  multiple outflowing components, Doppler-shifted with respect to each
  other. We have modelled this scenario by imposing a double-Gaussian fit
  to the line profiles; these fits represent the profile markedly better
  than a single Gaussian fit. For the fastest outflowing components,
  we find velocities as high as 200 km/s. However, there remains a
  correlation between the fitted line velocities and widths, suggesting
  that the outflows are not fully resolved by the double-Gaussian fit
  and that the outflow may be comprised of further components.

---------------------------------------------------------
Title: Molecular Cloud Chemistry and the Importance of Dielectronic
    Recombination
Authors: Bryans, P.; Kreckel, H.; Roueff, E.; Wakelam, V.; Savin, D. W.
2009ApJ...694..286B    Altcode: 2008arXiv0809.4504B
  Dielectronic recombination (DR) of singly charged ions is a
  reaction pathway that is commonly neglected in chemical models of
  molecular clouds. In this study we include state-of-the-art DR data
  for He<SUP>+</SUP>, C<SUP>+</SUP>, N<SUP>+</SUP>, O<SUP>+</SUP>,
  Na<SUP>+</SUP>, and Mg<SUP>+</SUP> in chemical models used to simulate
  dense molecular clouds, protostars, and diffuse molecular clouds. We
  also update the radiative recombination (RR) rate coefficients
  for H<SUP>+</SUP>, He<SUP>+</SUP>, C<SUP>+</SUP>, N<SUP>+</SUP>,
  O<SUP>+</SUP>, Na<SUP>+</SUP>, and Mg<SUP>+</SUP> to the current
  state-of-the-art values. The new RR data have little effect on the
  models. However, the inclusion of DR results in significant differences
  in gas-grain models of dense, cold molecular clouds for the evolution
  of a number of surface and gas-phase species. We find differences of
  a factor of 2 in the abundance for 74 of the 655 species at times
  of 10<SUP>4</SUP>-10<SUP>6</SUP> yr in this model when we include
  DR. Of these 74 species, 16 have at least a factor of 10 difference
  in abundance. We find the largest differences for species formed on
  the surface of dust grains. These differences are due primarily to the
  addition of C<SUP>+</SUP> DR, which increases the neutral C abundance,
  thereby enhancing the accretion of C onto dust. These results may
  be important for the warm-up phase of molecular clouds when surface
  species are desorbed into the gas phase. We also note that no reliable
  state-of-the-art RR or DR data exist for Si<SUP>+</SUP>, P<SUP>+</SUP>,
  S<SUP>+</SUP>, Cl<SUP>+</SUP>, and Fe<SUP>+</SUP>. Modern calculations
  for these ions are needed to better constrain molecular cloud models.

---------------------------------------------------------
Title: A New Approach to Analyzing Solar Coronal Spectra and
    Updated Collisional Ionization Equilibrium Calculations. II. Updated
    Ionization Rate Coefficients
Authors: Bryans, P.; Landi, E.; Savin, D. W.
2009ApJ...691.1540B    Altcode: 2008arXiv0805.3302B
  We have re-analyzed Solar Ultraviolet Measurement of Emitted
  Radiation (SUMER) observations of a parcel of coronal gas using new
  collisional ionization equilibrium (CIE) calculations. These improved
  CIE fractional abundances were calculated using state-of-the-art
  electron-ion recombination data for K-shell, L-shell, Na-like, and
  Mg-like ions of all elements from H through Zn and, additionally, Al-
  through Ar-like ions of Fe. They also incorporate the latest recommended
  electron impact ionization data for all ions of H through Zn. Improved
  CIE calculations based on these recombination and ionization data are
  presented here. We have also developed a new systematic method for
  determining the average emission measure (EM) and electron temperature
  (T<SUB>e</SUB> ) of an isothermal plasma. With our new CIE data and
  a new approach for determining average EM and T<SUB>e</SUB> , we have
  re-analyzed SUMER observations of the solar corona. We have compared
  our results with those of previous studies and found some significant
  differences for the derived EM and T<SUB>e</SUB> . We have also
  calculated the enhancement of coronal elemental abundances compared to
  their photospheric abundances, using the SUMER observations themselves
  to determine the abundance enhancement factor for each of the emitting
  elements. Our observationally derived first ionization potential factors
  are in reasonable agreement with the theoretical model of Laming.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Plasma Recombination rate
    coefficients (Bryans+, 2006)
Authors: Bryans, P.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.;
   Mitthumsiri, W.; Savin, D. W.
2008yCat..21670343B    Altcode:
  Reliably interpreting spectra from electron-ionized cosmic plasmas
  requires accurate ionization balance calculations for the plasma in
  question. However, much of the atomic data needed for these calculations
  have not been generated using modern theoretical methods and are often
  highly suspect. This translates directly into the reliability of the
  collisional ionization equilibrium (CIE) calculations. We make use
  of state-of-the-art calculations of dielectronic recombination (DR)
  rate coefficients for the hydrogenic through Na-like ions of all
  elements from He up to and including Zn. Where measurements exist,
  these published theoretical DR data agree with recent laboratory work
  to within typically 35% or better at the temperatures relevant for
  CIE. We also make use of state-of-the-art radiative recombination
  (RR) rate coefficient calculations for the bare through Na-like ions
  of all elements from H through to Zn. Here we present improved CIE
  calculations for temperatures from 104 to 109 K using our data and the
  recommended electron impact ionization data of Mazzotta et al. (1998,
  Cat. ) for elements up to and including Ni and Mazzotta (2000, private
  communication) for Cu and Zn. DR and RR data for ionization stages
  that have not been updated are also taken from these two additional
  sources. <P />(2 data files).

---------------------------------------------------------
Title: The Status of Collisional Ionization Equilibrium Calculations
    and a New Approach to Emission Eeasure Determinations
Authors: Bryans, Paul; Laming, J. M.; Landi, E.; Savin, D. W.
2008AAS...212.0302B    Altcode: 2008BAAS...40Q.184B
  We have calculated improved collisional ionization equilibrium (CIE)
  fractional abundances using state-of-the-art dielectronic recombination
  (DR) and radiative recombination (RR) rate coefficients for K-shell,
  L-shell, Na-like, and Mg-like ions of all elements from H through Zn and
  M-shell ions of Fe. These data have been compared with other published
  state-of-the-art DR and RR data and found to agree within 35% and 10%,
  respectively, in the temperature range where the ion forms in CIE. Where
  DR measurements exist, theory and experiment agree to within 35% in this
  temperature range. We have also investigated recent improvements to
  the recommended electron impact ionization rate coefficient database,
  concluding that differences of up to a factor of 4 between recent
  compilations implies that significant additional <P />experimental
  and theoretical work is required. Using our new CIE calculations we
  have re-analyzed solar coronal observations of an isothermal parcel
  of coronal gas. We have also developed a mathematically rigorous
  method for determining the average emission measure and temperature
  of the emitting plasma. Using our new CIE data and our new approach
  to determining the average emission measure, we use the observations
  to quantify the first ionization potential effect on the coronal
  abundances of the emitting elements. We present the results of this
  analysis and compare our conclusions with those of previous works.

---------------------------------------------------------
Title: Electron-Impact Ionization of Be-like C III, N IV, and O V
Authors: Fogle, M.; Bahati, E. M.; Bannister, M. E.; Vane, C. R.; Loch,
   S. D.; Pindzola, M. S.; Ballance, C. P.; Thomas, R. D.; Zhaunerchyk,
   V.; Bryans, P.; Mitthumsiri, W.; Savin, D. W.
2008ApJS..175..543F    Altcode:
  We present recent measurements of absolute electron-impact ionization
  cross sections for Be-like C III, N IV, and O V forming Li-like C IV,
  N V, and O VI. The measurements were taken using the crossed-beams
  apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation
  method was used to independently measure the metastable fractions
  present in the ion beams. The measured ionization cross sections were
  compared with calculations using the R-matrix with pseudostates and
  distorted-wave theoretical methods. Best agreement is found with the
  R-matrix with pseudostates cross sections results that account for the
  metastable fractions inferred from the gas attenuation measurements. We
  present a set of recommended rate coefficients for electron-impact
  single ionization from the ground state and metastable term of each ion.

---------------------------------------------------------
Title: The Status of Collisional Ionization Equilibrium Calculations
    and a New Approach to Emission Measure Determinations
Authors: Bryans, Paul; Laming, J. M.; Landi, E.; Savin, D. W.
2008HEAD...10.1313B    Altcode:
  We have calculated improved collisional ionization equilibrium (CIE)
  fractional abundances using state-of-the-art dielectronic recombination
  (DR) and radiative recombination (RR) rate coefficients for K-shell,
  L-shell, Na-like, and Mg-like ions of all elements from H through Zn and
  M-shell ions of Fe. These data have been compared with other published
  state-of-the-art DR and RR data and found to agree within 35% and 10%,
  respectively, in the temperature range where the ion forms in CIE. Where
  DR measurements exist, theory and experiment agree to within 35% in this
  temperature range. We have also investigated recent improvements to
  the recommended electron impact ionization rate coefficient database,
  concluding that differences of up to a factor of 5 between recent
  compilations implies that significant additional experimental and
  theoretical work is required. Using our new CIE calculations we
  have re-analyzed solar coronal observations of an isothermal parcel
  of coronal gas. We have also developed a mathematically rigorous
  method for determining the average emission measure and temperature
  of the emitting plasma. Using our new CIE data and our new approach
  to determining the average emission measure, we use the observations
  to quantify the first ionization potential effect on the coronal
  abundances of the emitting elements. We present the results of this
  analysis and compare our conclusions with those of previous works.

---------------------------------------------------------
Title: Implications for Atomic Physics from New Ionization Balance
    Calculations and Solar Physics Observations
Authors: Bryans, Paul; Landi, Enrico; Savin, Daniel
2007APS..DMP.R1107B    Altcode:
  We have used state-of-the-art electron-ion recombination data
  for K-shell, L-shell, and Na-like ions of H through Zn to calculate
  improved collisional ionization equilibrium (CIE) fractional abundances
  for ions of all these elements. We present the implications of these
  new CIE results for observations of the solar atmosphere and discuss
  a number of atomic systems showing puzzling discrepancies between
  observations and solar models. These discrepancies suggest errors in
  the underlying atomic data. Based on this, we highlight those atomic
  processes that require improved theoretical or experimentally-derived
  rate coefficients.

---------------------------------------------------------
Title: Collisional Ionization Equilibrium for Optically Thin
    Plasmas. I. Updated Recombination Rate Coefficients for Bare through
    Sodium-like Ions
Authors: Bryans, P.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.;
   Mitthumsiri, W.; Savin, D. W.
2006ApJS..167..343B    Altcode: 2006astro.ph..4363B
  Reliably interpreting spectra from electron-ionized cosmic plasmas
  requires accurate ionization balance calculations for the plasma in
  question. However, much of the atomic data needed for these calculations
  have not been generated using modern theoretical methods and are often
  highly suspect. This translates directly into the reliability of the
  collisional ionization equilibrium (CIE) calculations. We make use
  of state-of-the-art calculations of dielectronic recombination (DR)
  rate coefficients for the hydrogenic through Na-like ions of all
  elements from He up to and including Zn. Where measurements exist,
  these published theoretical DR data agree with recent laboratory work
  to within typically 35% or better at the temperatures relevant for
  CIE. We also make use of state-of-the-art radiative recombination
  (RR) rate coefficient calculations for the bare through Na-like ions
  of all elements from H through to Zn. Here we present improved CIE
  calculations for temperatures from 10<SUP>4</SUP> to 10<SUP>9</SUP>
  K using our data and the recommended electron impact ionization data
  of Mazzotta et al. for elements up to and including Ni and Mazzotta
  for Cu and Zn. DR and RR data for ionization stages that have not
  been updated are also taken from these two additional sources. We
  compare our calculated fractional ionic abundances using these data
  with those presented by Mazzotta et al. for all elements from H to
  Ni. The differences in peak fractional abundance are up to 60%. We
  also compare with the fractional ionic abundances for Mg, Si, S, Ar,
  Ca, Fe, and Ni derived from the modern DR calculations of Gu for the
  H-like through Na-like ions, and the RR calculations of Gu for the bare
  through F-like ions. These results are in better agreement with our
  work, with differences in peak fractional abundance of less than 10%.

---------------------------------------------------------
Title: Updated Ionization Balance Calculations for Collisionally
    Ionized Plasmas
Authors: Bryans, Paul; Badnell, N. R.; Gorczcya, T. W.; Laming, J. M.;
   Mitthumsiri, W.; Savin, D. W.
2006HEAD....9.1835B    Altcode: 2006BAAS...38R.387B
  Reliably interpreting spectra from electron-ionized cosmic plasmas
  requires accurate ionization balance calculations for the plasma
  in question. However, much of the atomic data needed for these
  calculations have not been generated using modern theoretical methods
  and their reliability are often highly suspect. We have carried out
  state-of-the-art calculations of dielectronic recombination (DR)
  rate coefficients for the hydrogenic through Na-like ions of all
  elements from He to Zn. We have also carried out state-of-the-art
  radiative recombination (RR) rate coefficient calculations for the
  bare through Na-like ions of all elements from H to Zn. Using our data
  and the recommended electron impact ionization data of [1], we present
  improved collisional ionization equilibrium calculations. We compare
  our <P />calculated fractional ionic abundances using these data with
  those presented <P />by [1] for all elements from H to Ni, and with the
  fractional abundances derived from the modern DR and RR calculations of
  [2] for Mg, Si, S, Ar, Ca, Fe, and Ni. <P />[1] Mazzotta, P. et al.,
  1998, A&amp;AS, 133, 403 <P />[2] Gu, M. F., 2003a, ApJ, 590, 1131;
  2003b, 589, 1085; 2004, 153, 389 <P />This work is supported in part
  by NASA.

---------------------------------------------------------
Title: Updated Coronal Equilibrium Calculations
Authors: Bryans, Paul; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.;
   Mitthumsiri, W.; Savin, D. W.
2006SPD....37.0101B    Altcode: 2006BAAS...38..215B
  Reliably interpreting solar spectra requires accurate ionization
  balance calculations. However, much of the atomic data needed for
  these calculations have not been generated using modern theoretical
  methods and are often highly suspect. This translates directly
  into the reliability of the collisional ionization equilibrium
  (CIE) calculations. We make use of state-of-the-art calculations of
  dielectronic recombination (DR) rate coefficients for the hydrogenic
  through Na-like ions of all elements from He through to Zn. We
  also make use of state-of-the-art radiative recombination (RR)
  rate coefficient calculations for the bar e through Na-like ions of
  all elements from H to Zn. Here we present improved CIE calculations
  for temperatures from 1e4 to 1e9 K using our data and the recommended
  electron impact ionization data of Mazzotta et al. (1998, A&amp;AS, 133,
  403) for elements up through Ni and Mazzotta (private communication)
  for Cu and Zn. DR and RR data for ionization stages that have not
  been updated are also taken from these two additional sources. We
  compare our calculated fractional ionic abundances using these data
  with those presented by Mazzotta et al. for all elements from H to
  Ni. The differences in peak fractional abundance are up to 60%. We
  also compare with the fractional ionic abundances for Mg, Si, S, Ar,
  Ca, Fe, and Ni derived from the modern DR calculations of Gu (2003a,
  ApJ, 590, 1131; 2004, ApJ, 153, 389) for the H-like through Na-like
  ions, and the RR calculations of Gu (2003b, ApJ, 589, 1085) for the
  bare through F-like ions. These results are in better agreement with
  our work, with differences in peak fractional abundance of less than
  10%. <P />This work was supported in part by the NASA Solar SR&amp;T
  and LWS programs, theOffice of Naval Research, and PPARC.

---------------------------------------------------------
Title: A Plasma Mechanism explaining the Asymmetric X-ray Emission
    from the Supernova
Authors: Kellett, B. J.; Bingham, R.; Bryans, P.; Torney, M.; Summers,
   H.; Shapiro, V.; Spicer, Ds
2006sgrb.confE..31K    Altcode:
  The interaction of the expanding shock from a supernova explosion
  with thesurrounding environment is a powerful source of radiation in
  variousspectral bands at different stages in the development of the
  supernovaremnant. Studying the X-rays generated by such objects is
  therefore likelyto reveal details of these on going interactions. For
  example, the X-rayemission from the relatively old supernova remnant
  PKS1209-52 is highlyasymmetric - 75% of the total emission arises from
  the eastern side of theshock. We describe a possible model that can
  explain this extra emissionfrom the eastern lobe of the remnant as
  resulting from a recent encounterbetween the shock front and a small,
  dense, interstellar cloud. Theparticular mechanism is a plasma streaming
  instability known as themodified two-stream instability. The presence
  of the cloud makes itpossible to extract some of the kinetic energy
  of the shock wave andconvert this into X-ray emission via high-energy
  electrons generated fromlower hybrid waves in the plasma interaction
  region. We have carried out2-D fluid simulation of the interaction
  which agrees very well with theobserved geometry of the source. Finally,
  the neutron star remnant of theoriginal supernova explosion is seen to
  generate cyclotron absorptionfeatures in its X-ray emission spectrum
  that reveal the detailed dynamicsof the magnetic field of the neutron
  star itself. Planned laboratoryexperiments to study the results will
  be outlined.

---------------------------------------------------------
Title: Collisional Ionization Equilibrium for Optically Thin Plasmas
Authors: Bryans, P.; Mitthumsiri, W.; Savin, D. W.; Badnell, N. R.;
   Gorczyca, T. W.; Laming, J. M.
2006nla..conf..166B    Altcode:
  Reliably interpreting spectra from electron-ionized cosmic plasmas
  requires accurate ionization balance calculations for the plasma in
  question. However, much of the atomic data needed for these calculations
  have not been generated using modern theoretical methods and their
  reliability are often highly suspect. We have utilized state-of-the-art
  calculations of dielectronic recombination (DR) rate coefficients
  for the hydrogenic through Na-like ions of all elements from He to
  Zn. We have also utilized state-of-the-art radiative recombination
  (RR) rate coefficient calculations for the bare through Na-like ions
  of all elements from H to Zn. Using our data and the recommended
  electron impact ionization data of tet{Mazz98a}, we have calculated
  improved collisional ionization equilibrium calculations. We compare
  our calculated fractional ionic abundances using these data with those
  presented by tet{Mazz98a} for all elements from H to Ni, and with the
  fractional abundances derived from the modern DR and RR calculations
  of tet{Gu03a,Gu03b,Gu04a} for Mg, Si, S, Ar, Ca, Fe, and Ni.

---------------------------------------------------------
Title: Evidence for explosive event activity originating in the
    chromosphere
Authors: Doyle, J. G.; Ishak, B.; Ugarte-Urra, I.; Bryans, P.; Summers,
   H. P.
2005A&A...439.1183D    Altcode:
  We report on a joint SUMER, CDS, TRACE study, concentrating on
  a region which shows prolonged EUV explosive event (EE) activity
  in the transition region line N v 1238 Å, yet little evidence of
  such activity in another transition region line O v 629 Å (formed
  at a similar temperature) which was observed simultaneously. A
  possible explanation for the lack of major activity in the O v line
  in several explosive events could be that they originate in the lower
  chromosphere. This is consistent with the enhancements in the C i 1249
  Å line and with the findings of another study which reported time
  delays between the chromospheric and transition region lines in some
  EE's using high cadence observations (10 s exposure time) obtained
  with the SUMER spectrometer in H i Ly 6 (20 000 K) and S vi (200 000
  K). Using the generalized collisional-radiative picture, including
  the population of metastable levels, we derive the density dependent
  contribution function for both N v 1238 and O v 629 for four values
  of the electron density; 10<SUP>6</SUP> cm<SUP>-3</SUP> representing
  the low density limit, 10<SUP>9</SUP> cm<SUP>-3</SUP> for a typical
  quiet Sun electron density plus 10<SUP>11</SUP> cm<SUP>-3</SUP> and
  10<SUP>12</SUP> cm<SUP>-3</SUP> for an active region. These calculations
  show that with increasing electron density, both lines shift to slightly
  lower temperatures. However, the major difference is in the relative
  increase in the line flux with increasing density. For N v, increasing
  the density to 10<SUP>11</SUP> cm<SUP>-3</SUP> results in a 60%
  increase in the line flux, while O v shows a 30% decrease. Increasing
  the electron density to 10<SUP>12</SUP> cm<SUP>-3</SUP> results in a
  factor of two decrease in the O v flux, thus making it difficult to
  detect explosive event activity in this line if the event is formed
  in the chromosphere. Other explosive events which show simultaneous
  activity in both lines are probably formed in the transition region. In
  one such event, activity is observed in both N v and O v, yet nothing
  in C i. In this event we also observe an increase in the TRACE 173
  emission, delayed by ≈40 s compared to the transition region lines.

---------------------------------------------------------
Title: X-Ray Emission from Comets and Nonmagnetic Planets. Theory
    and Comparison with CHANDRA Observations
Authors: Shapiro, V. D.; Bingham, R.; Kellett, B. J.; Quest, K.;
   Mendis, D. A.; Bryans, P.; Torney, M.; Summers, H. P.
2005PhST..116...83S    Altcode:
  Mass loading of the solar wind by newly created cometary photoions as
  well as counterstreaming fluxes of protons in the mantle regions at
  the ionospheric boundaries of nonmagnetic planets Mars, Venus result in
  the modified two stream instability MTSI and excitation of the intense
  lower hybrid wave turbulence. Electrons are efficiently energized by
  these waves in the magnetic field aligned direction up to KeV energies
  confirmed by in situ observations and interacting with cometary
  or planetary atmospheres producing X-Ray emission by combination
  of Bremsstrahlung and line K-shell radiation. Analytical study of
  the nonlinear evolution of MTSI as well as numerical simulations
  of instability development in the mantle regions of nonmagnetic
  planets has been performed and it basically confirms the scenario of
  electron acceleration. Using the above described mechanism of X-ray
  emission produced in impacts of energetic electrons with ions and
  neutrals we employed ADAS atomic data code to analyze X-ray spectrum
  emitted by comet Linear and obtained a good fit with recent CHANDRA
  observations. The theoretical model also predicts strong x-ray emission
  from nonmagnetic planets such as Mars and Venus.

---------------------------------------------------------
Title: The effect of metastable level populations on the ionization
    fraction of Li-like ions
Authors: Doyle, J. G.; Summers, H. P.; Bryans, P.
2005A&A...430L..29D    Altcode:
  Lines from Li-like ions have been known to produce theoretical
  intensities under-estimated compared to lines of a similar formation
  temperature. Here we investigate this anomalous behaviour whereby the
  ionization fractions are calculated using the ADAS code considering
  the electron density dependence of dielectronic recombination coupled
  with collisional ionization from metastable levels. For the lines
  investigated, the line contribution functions show a clear dependence
  with increasing electron density. For example, C IV 1548 Å shows
  over a factor of three enhancement for N<SUB>e</SUB> = 10<SUP>12</SUP>
  cm<SUP>-3</SUP>. The increase in the higher temperature lines is lower,
  but are still in the range of 30 to 60%. Furthermore, all the lines have
  their peak contribution shifted to lower temperature. Calculating the
  total radiative power output at an electron density of 10<SUP>11</SUP>
  cm<SUP>-3</SUP>, we find that the difference in the transition region
  is 10-15% while above 10<SUP>6</SUP> K the difference is around 30%
  compared to the low density value.

---------------------------------------------------------
Title: A New Mechanism Explaining the Asymmetric X-Ray Emission from
    Supernova Remnant PKS 1209-52
Authors: Bingham, R.; Kellett, B. J.; Bryans, P.; Summers, H. P.;
   Torney, M.; Shapiro, V. D.; Spicer, D. S.; O'Brien, M.
2004ApJ...601..896B    Altcode:
  The interaction of a supernova remnant with its surrounding environment
  is a powerful source of radiation in various spectral regions and at
  different stages in its development. The study of these emissions can
  therefore help to investigate the interstellar medium surrounding a
  supernova. For example, the highly asymmetric X-ray emission from PKS
  1209-52 has previously been described as resulting from the supernova
  shock front on the eastern side of the remnant interacting with a small,
  dense interstellar cloud (or cloud core). In this paper we describe a
  possible mechanism through which the kinetic energy of the expanding
  shock is converted to energetic electrons. The particular interaction
  is a plasma streaming instability known as the modified two-stream
  instability that creates plasma waves in the lower hybrid frequency
  range that can then go on to accelerate electrons to high energy. A
  Fokker-Planck equation describing the diffusion of the electrons
  to high energies by lower hybrid waves is solved for both Gaussian
  and Lorentzian wave spectral distributions. We also simulate the
  interaction between the supernova remnant with the dense interstellar
  cloud using a two-dimensional fluid code. The nonthermal electrons
  can then generate X-ray emission via bremsstrahlung and also line
  radiation through interactions with the ambient medium. The maximum
  energy of these electrons is limited to the few keV energy range and
  therefore does not lead to any synchrotron radio emission that would
  otherwise lead to a radio asymmetry in the remnant that is not seen.

---------------------------------------------------------
Title: X-ray Emission From Planets Venus and Mars: Theoretical Model
    and Numerical Simulations
Authors: Bryans, P.; Quest, K. B.; Shapiro, V. D.; Bingham, R.;
   Tourner, M.
2003AGUFMSM31C1122B    Altcode:
  Recently X-ray emission from non-magnetic planets Venus and Mars
  have been discovered by Chandra X-ray telescopes [1,2]. Analysis
  of observational data shows that either charge exchange model or
  fluorescent scattering of solar x-rays cannot explain the whole
  set of observational data. The premise of this paper is that x-ray
  emission of both planets is a combination of line k-shell radiation
  and Bremmstrahlung produced by energetic electrons interacting
  with planetary atmospheres. Due to the absence of their planetary
  magnetospheres, planetary bow shocks are located quite close to the
  ionospheres and on both planets their ionospheres are directly exposed
  to the shocked solar wind flow. In situ observations revealed the
  existence at the ionospheric boundaries of strongly turbulent layer --
  the so-called plasma mantle. Previous hybrid simulations (kinetic ions
  and hydro dynamical electrons) have shown that mantle turbulence is
  produced by interaction of counterstreaming ion populations of the solar
  wind and planetary ionospheres. Recently developed particle in cell
  (fully kinetic) code demonstrated that mantle turbulence is responsible
  for electron acceleration in an agreement with in-situ observations
  that revealed the presence in mantle electrons with energies up to
  several hundred eV.[3] In the present paper we incorporated energetic
  electron distribution obtained by numerical simulations into ADAS
  code [4] and compared results with observations. <P />1. K. Dennerl
  et.al. A&amp;A 286, 319 (2002). 2. K. Dennerl, A&amp;A 394, 1119-1128
  (2002). 3. K. Szego et.al. J6R 112, 2175 (1997) 4. http: adas.phystretch
  ac.uk

---------------------------------------------------------
Title: X-ray Emission from Planets Venus and Mars. Theoretical Model
    and Numerical Simulations.
Authors: Bryans, Paul; Quest, Kevin; Shapiro, Vitali; Bingham, Robert;
   Torney, Martin
2003APS..DPPGP1136B    Altcode:
  Recently X-ray emission from non-magnetic planets Venus and Mars
  have been discovered by Chandra X-ray telescopes [1,2]. Analysis
  of observational data shows that either charge exchange model or
  fluorescent scattering of solar x-rays cannot explain the whole
  set of observational data. The premise of this paper is that x-ray
  emission of both planets is a combination of line k-shell radiation
  and Bremmstrahlung produced by energetic electrons interacting
  with planetary atmospheres. Due to the absence of their planetary
  magnetospheres, planetary bow shocks are located quite close to the
  ionospheres and on both planets their ionospheres are directly exposed
  to the shocked solar wind flow. In situ observations revealed the
  existence at the ionospheric boundaries of strongly turbulent layer --
  the so-called plasma mantle. Previous hybrid simulations (kinetic ions
  and hydro dynamical electrons) have shown that mantle turbulence is
  produced by interaction of counterstreaming ion populations of the solar
  wind and planetary ionospheres. Recently developed particle in cell
  (fully kinetic) code deomonstrated that mantle turbulence is responsible
  for electron acceleration in an agreement with in-situ observations
  that revealed the presence in mantle electrons with energies up to
  several hundred eV.[3] In the present paper we incorporated energetic
  electron distribution obtained by numerical simulations into ADAS code
  and compared results with observations. 1. K. Dennerl et. al. A, 286,
  319 (2002) 2. K. Dennerl et. al. A, 394, 1119-1128 (2002 3. K. Szego
  et. al., JGR, 112, 2175 (1997) 4. http: adas.phystretch ac.uk

---------------------------------------------------------
Title: A Plasma Mechanism Explaining the Asymmetric X-ray Emission
    from the Supernova Remnant PKS1209-52.
Authors: Kellett, Barry; Bingham, Robert; Bryans, Paul; Torney,
   Martin; Summers, Hugh; Shapiro, Vitali; Spicer, Daniel
2003APS..DPPGP1149K    Altcode:
  The interaction of the expanding shock from a supernova explosion with
  the surrounding environment is a powerful source of radiation in various
  spectral bands at different stages in the development of the supernova
  remnant. Studying the X-rays generated by such objects is therefore
  likely to reveal details of these on going interactions. For example,
  the X-ray emission from the relatively old supernova remnant PKS1209-52
  is highly asymmetric - 75arises from the eastern side of the shock. We
  describe a possible model that can explain this extra emission from
  the eastern lobe of the remnant as resulting from a recent encounter
  between the shock front and a small, dense, interstellar cloud. The
  particular mechanism is a plasma streaming instability known as the
  modified two-stream instability. The presence of the cloud makes it
  possible to extract some of the kinetic energy of the shock wave and
  convert this into X-ray emission via high-energy electrons generated
  from lower hybrid waves in the plasma interaction region. We have
  carried out 2-D fluid simulation of the interaction which agree very
  well with the observed geometry of the source. Finally, the neutron
  star remnant of the original supernova explosion is seen to generate
  cyclotron absorption features in its X-ray emission spectrum that reveal
  the detailed dynamics of the magnetic field of the neutron star itself.

---------------------------------------------------------
Title: Coronal dimming and the coronal mass ejection onset
Authors: Harrison, R. A.; Bryans, P.; Simnett, G. M.; Lyons, M.
2003A&A...400.1071H    Altcode:
  A set of five observations of extreme-ultraviolet (EUV) coronal dimming
  associated with coronal mass ejection (CME) activity is examined. Using
  spectroscopic data, plasma characteristics across a broad range of
  temperatures from 20 000 K to 2 million K are determined. The dimming
  events are found to coincide in time, and to coincide spatially, with
  the projected onset times and locations of the associated CMEs. The
  spectral data confirm that the dimming is due to mass-loss, and not
  temperature variations. The actual mass-loss calculated from the degree
  of dimming, using two different methods, shows that the extracted
  mass in each case, is of the same order as the mass of the associated
  CME. In some cases, the EUV observations are limited to relatively small
  regions under the CME events and it is expected that we do not witness
  the mass-loss associated with the entire event, for these. However,
  we believe that this analysis has provided a method for locating the
  source region of the trigger for a CME eruption, and that the dimming
  characteristics can be used to distinguish between onset processes of
  the CME. In particular, the gradual nature of the dimming process,
  which takes place over several hours, suggests that either the CME
  has a continuous driver rather than a sudden impulsive onset, or the
  low coronal response to a CME extends over a long period.

---------------------------------------------------------
Title: EUV Sprays: Jet-like eruptive activity on the solar limb
Authors: Harrison, R. A.; Bryans, P.; Bingham, R.
2001A&A...379..324H    Altcode:
  Jet-like eruptive events have been detected in the extreme ultraviolet
  (EUV) observations from the Solar and Heliospheric Observatory
  (SOHO) spacecraft. Some jet-like events are shown and for one event,
  that of January 22 2000, we provide a detailed analysis of the EUV
  observations. The January 22 observation was part of an on-going
  campaign to observe the onset of coronal mass ejections (CMEs) using
  extreme ultraviolet spectroscopy. A high-temperature fan-like jet
  was first detected in emission lines from plasmas at one million K
  and over, and it appears to be the onset of a narrow mass ejection
  identified later in coronagraph data. This was followed by a dramatic
  jet or finger of cool (&lt;=250 000 K), rotating plasma which extended
  vertically, high into the corona. It extended well beyond the field of
  view of the instrument and appears to relate to a small ejected cloud
  which is detected in subsequent coronagraph data. The spectroscopic
  characteristics are used to provide plasma diagnostic information for
  these two events, and this combined with images for a wide range of
  temperatures allows a thorough investigation of the processes leading
  to such eruptions. A simple accreting magnetic field model is used to
  descibe the basic features of the jet activity.