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A Rapid, Manual Method to Map Coronal-Loop Structures of an Active Region Using Cubic Bezier Curves and Its Applications to Misalignment Angle Analysis  

G. Allen Gary   Submitted: 2013-07-08 09:15

A rapid and flexible manual method is described which maps individual coronal loops of a 2D EUV image as Bezier curves using only four points per loop. Using the coronal loops as surrogates of magnetic-field lines, the mapping results restrict the magnetic-field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. We outline explicitly how the coronal loops can be employed in constraining competing magnetic-field models by transforming 2D coronal-loop images into 3D field lines. The magnetic-field extrapolations must satisfy not only the lower boundary conditions of the vector field, the vector magnetogram, but also must have a set of field lines that satisfies the mapped coronal loops in the volume, analogous to an upper boundary condition. This method uses the minimization of the misalignment angles between the magnetic-field model and the best set of 3D field lines that match a set of closed coronal loops. The presented method is an important tool in determining the fitness of magnetic-field models for the solar atmosphere. The magnetic-field structure is crucial in determining the overall dynamics of the solar atmosphere.

Authors: Gilmer A. Gary, Qiang Hu, and Jong Kwan Lee
Projects: None

Publication Status: Accepted
Last Modified: 2013-07-10 13:34
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Future Possibilities for Doppler and Magnetic Field Measurements in the Extended Solar Atmosphere  

G. Allen Gary   Submitted: 2008-07-08 08:44

For the first time, a vacuum ultraviolet telescope can be built to observe magnetic fields, plasma flows, and heating events in the Sun's atmosphere. These observations can provide key data for space weather models. The vacuum ultraviolet (VUV) region allows remote sensing of the upper levels of the solar atmosphere where the magnetic field dominates the physics. A VUV Fabry-Perot interferometer (FPI) will allow us to observe the magnetic field, flows, and heating events in the mid-transition region (between the chromosphere and corona). Observations of this region are needed to directly probe the magnetic structure and activity at the base of the corona where the magnetic field is approximately force-free, i.e., where gas pressures are very small. This is a key element in developing accurate models of the Sun's dynamics for space weather. The specific region of interest is the 100 km thick transition region, between the chromosphere and the much hotter corona, which strongly emits at 155 nm from triply ionized carbon (CIV) at 100,000 K. This is best observed by an imaging interferometer that combines the best attributes of a spectrograph and an imager. We present the latest results from the NASA Marshall Space Flight Center (MSFC) FPI. The major elements of thetunable CIV VUV FP interferometer are the 35mm MgF2 etalon plates with a plate finesse of F>25 at 155 nm, the pi-dielectric coatings, a Hansen mechanical mount in a pressurize canister, and the piezoelectric control system. The control system for the etalon is a capacitance-stabilized Hovemere Ltd. standard system. The special Cascade Optical Corporation reflectance coatings are 25 pi-multilayers of high-low refractive layers paired in phase. This CIV interferometer, when flown above Earth's atmosphere, will obtain narrow-passband images, magnetograms, and Dopplergrams of the transition region in the CIV 155 nm line at a rapid cadence. We recently measured the MSFC VUV FPI using the University of Toronto's fluoride excimer laser as a proxy for CIV 155 nm. The test demonstrated the first tunable interferometer with the passband required for a VUV filter magnetograph. The measured values have a full-width half-maximum (FWHM) passband of 10 pm, a free-spectral range (FSR) of 61pm, and a transmittance of 58% at 157 nm. The resulting VUV interferometer finesse is 5.9. With this success, we are developing an instrument suitable for a flight on an orbiting solar observatory. A description of the interferometer for this mission is described.

Authors: G. Allen Gary (CSPAR), John M. Davis (MSFC), and Edward A. West (MSFC)
Projects: None

Publication Status: Submitted to Journal of Advances in Space Research (Elservier 2008)
Last Modified: 2008-09-23 20:57
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SOLAR CONFOCAL INTERFEROMETERS FOR SUB-PICOMETER-RESOLUTION SPECTRAL FILTERS  

G. Allen Gary   Submitted: 2007-03-07 06:20

The confocal Fabry-Perot interferometer allows sub-picometer spectral resolution of Fraunhofer line profiles. Such high spectral resolution is needed to keep pace with the higher spatial resolution of the new set of large-aperture solar telescopes. The line-of-sight spatial resolution derived for line profile inversions would then track the improvements of the transverse spatial scale provided by the larger apertures. In particular, profile inversion allows improved velocity and magnetic field gradients to be determined independent of multiple line analysis using different energy levels and ions. The confocal interferometer's unique properties allow a simultaneous increase in both etendue and spectral power.The higher throughput for the interferometer provides significant decrease in the aperture, which is important in spaceflight considerations. We have constructed and tested two confocal interferometers. A slow-response thermal-controlled interferometer provides a stable system for laboratory investigation, while a piezoelectric interferometer provides a rapid response for solar observations. In this paper we provide design parameters, show construction details, and report on the laboratory test for these interferometers. The field of view versus aperture for confocal interferometers is comparedwith other types of spectral imaging filters. We propose a multiple etalon system for observing with these units using existing planar interferometers as pre-filters.The radiometry for these tests established that high spectral resolution profiles can be obtained with imaging confocal interferometers. These sub-picometer spectral data of the photosphere in both the visible and near-infrared can provide important height variation information. However, at the diffraction-limited spatial resolution of the telescope, the spectral data is photon starved due to the decreased spectral passband.

Authors: Gary, G. A., Pietraszewski, C., West, E. A. and Dines, T. C.
Projects: None

Publication Status: A&A (in press)
Last Modified: 2007-03-07 09:45
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CIV Vacuum Ultraviolet Fabry-Perot Interferometer for Solar Research  

G. Allen Gary   Submitted: 2006-10-16 18:14

A tunable, high spectral resolution, high effective finesse, vacuum ultraviolet (VUV) Fabry-Perot interferometer (FPI) is described for obtaining narrow-passband images, magnetograms, and Dopplergrams of the transition region emission line of CIV (155nm). The integral parts of the CIV narrow passband filter package (2-10pm FWHM) consists of a multiple etalon system composed of a tunable interferometer that provides high-spectral resolution and a static low-spectral resolution interferometer that allows a large effective free spectral range. The prefilter for the interferometers is provided by a set of four mirrors with dielectric high-reflective coatings. A tunable interferometer, a VUV piezoelectric-control etalon, has undergone testing using the surrogate F2 eximer laser line at 157nm for the CIV line. We present the results of the tests with a description of the overall concept for a complete narrow-band CIV spectral filter. The fixed-gap interferometer of the filter is envisioned as being built using the coating-test MgF2 plates after being superpolished and recoated. The four-mirror prefilter would have dielectric multilayer Pi-stacks following the design concept used in the Ultraviolet Imager of NASA?s Polar Spacecraft. A dual etalon system allows the effective free spectral range to be commensurate with the prefilter profile. With an additional etalon, a triple etalon system would allow a spectrographic resolution of 2pm. The basic strategy has been to combine the expertise of spaceflight etalon manufacturing with VUV coating technology to build a VUV FPI which combines the best attributes of imagers and spectrographs into a single compact instrument. Spectro-polarimetry observations of the transition region CIV emission will allow an increased understanding of the magnetic forces, mass motion, evolution, and energy release within the solar atmosphere at the base of the corona where mainly the magnetic field is approximately force-free. The 2D imaging of the full vector magnetic field at the height of maximum magnetic influence (minimum plasma beta) can be accomplished, albeit difficult, by measuring the Zeeman splitting of the CIV resonance pair. Our designs of multiple VUV FPIs are being developed to integrate within the future orbiting solar observatories to obtain the necessary CIV observations.

Authors: G. Allen Gary, Edward A. West, David Rees, Jack McKay, Maumer Zukic, and Peter Herman
Projects: None

Publication Status: Accepted/Forthcoming
Last Modified: 2006-10-17 10:57
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Automated Detection of Solar Loops by the Orientated Connectivity Method  

G. Allen Gary   Submitted: 2004-03-22 08:38

An automated technique to segment solar coronal loops from intensity images of the Sun’s corona is introduced. It exploits physical characteristics of the solar magnetic field to enable robust extraction from noisy images. The technique is a constructive curve detection approach, constrained by collections of estimates of the magnetic field’s orientation. Its effectiveness is evaluated through experiments on synthetic and real coronal images.

Authors: Jong K. Lee (UAH), Timothy S. Newman (UAH), and G. Allen Gary (MSFC)
Projects: TRACE

Publication Status: Accepted for the 17th International Conference on Pattern Recognition
Last Modified: 2004-03-22 08:38
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ERUPTION OF A MULTIPLE-TURN HELICAL MAGNETIC FLUX TUBE IN A LARGE FLARE: EVIDENCE FOR EXTERNAL AND INTERNAL RECONNECTION THAT FITS THE BREAKOUT MODEL OF SOLAR MAGNETIC ERUPTIONS  

G. Allen Gary   Submitted: 2003-11-26 11:28

We present observations and an interpretation of a unique multiple-turn spiral flux tube eruption from AR10030 on 2002 July 15. The TRACE CIV observations clearly show a flux tube that is helical and that is erupting from within a sheared magnetic field. These observations are interpreted in the context of the breakout model for magnetic field explosions. The initiation of the helix eruption starts 25 seconds after the peak of the flare’s strongest impulsive spike of microwave gryosynchrotron radiation early in the flare’s explosive phase, implying that the sheared core field is not the site of the initial reconnection. Within the quadrupolar configuration of the active region, the external and internal reconnection sites are identified in each of two consecutive eruptive flares that produce a double CME. The first external breakout reconnection apparently releases an underlying sheared core field and allows it to erupt, leading to internal reconnection in the wake of the erupting helix. This internal reconnection heats the two-ribbon flare and might or might not produce the helix. These events lead to the first CME and are followed by a second breakout that initiates a second and larger halo CME. The strong magnetic shear in the region is associated with rapid proper motion and evolution of the active region. The multiple-turn helix originates from above a sheared-field magnetic inversion line within a filament channel, and starts to erupt only after fast breakout reconnection has started. These observations are counter to the standard flare model and support the breakout model for eruptive flare initiation. However, the observations are compatible with internal reconnection in a sheared magnetic arcade in the formation and eruption of the helix.

Authors: G. ALLEN GARY and R. L. MOORE
Projects: TRACE

Publication Status: Submitted to The Astrophysical Journal
Last Modified: 2003-12-02 13:24
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Plasma Beta above a Solar Active Region  

G. Allen Gary   Submitted: 2001-08-01 13:29

In this paper, we present a model of the plasma beta above an active region and discuss its consequences in terms of coronal magnetic field modeling. The beta-plasma model is representative and derived from a collection of sources. The resulting beta variation with height is used to emphasize the assumption that the magnetic pressure dominates over the plasma pressure must be carefully considered depending on what part of the solar atmosphere is being considered. This paper points out (1) that the paradigm that the coronal magnetic field can be constructed from a force-free magnetic field must be used in the correct context, since the force-free region is sandwiched between two regions which have beta>1, (2) that the chromospheric MgII-CIV magnetic measurements occur near the beta-minimum, and (3) that, moving from the photosphere upwards, beta can return to 1 at relatively low coronal heights, e.g. R~1.2Rs.

Authors: G. Allen Gary
Projects:

Publication Status: in press
Last Modified: 2001-08-01 13:31
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Abstracts by Author
A Rapid, Manual Method to Map Coronal-Loop Structures of an Active Region Using Cubic Bezier Curves and Its Applications to Misalignment Angle Analysis
Future Possibilities for Doppler and Magnetic Field Measurements in the Extended Solar Atmosphere
SOLAR CONFOCAL INTERFEROMETERS FOR SUB-PICOMETER-RESOLUTION SPECTRAL FILTERS
CIV Vacuum Ultraviolet Fabry-Perot Interferometer for Solar Research
Automated Detection of Solar Loops by the Orientated Connectivity Method
ERUPTION OF A MULTIPLE-TURN HELICAL MAGNETIC FLUX TUBE IN A LARGE FLARE: EVIDENCE FOR EXTERNAL AND INTERNAL RECONNECTION THAT FITS THE BREAKOUT MODEL OF SOLAR MAGNETIC ERUPTIONS
Plasma Beta above a Solar Active Region

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