Scholarly Work - Physics
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/3458
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Item First Flight of the EUV Snapshot Imaging Spectrograph (ESIS)(American Astronomical Society, 2022-10) Parker, Jacob D.; Smart, Roy T.; Kankelborg, Charles; Winebarger, Amy; Goldsworth, NelsonThe Extreme-ultraviolet Snapshot Imaging Spectrograph (ESIS) launched on a sounding rocket from White Sands Missile Range on 2019 September 30. ESIS is a computed tomography imaging spectrograph (CTIS) designed to map emission line profiles across a wide field of view, revealing the structure and dynamics of small-scale transient events that are prevalent at transition region temperatures. In this paper, we review the ESIS instrument, mission, and data captured. We demonstrate how this unique data set can be interpreted qualitatively and further present some initial quantitative inversions of the data. Using a multiplicative algebraic reconstruction technique, we combine information from all four ESIS channels into a single spatial–spectral cube at every exposure. We analyze two small explosive events in the O v 629.7 Å spectral line with jets near ±100 km s−1 that evolve on 10 s timescales and vary significantly over small spatial scales. Intriguingly, each of these events turns out to be a bimodal (red+blue) jet with outflows that are asymmetric and unsynchronized. We also present a qualitative analysis of a small jetlike eruption captured by ESIS and draw comparisons to previously observed mini-filament eruptions. In 5 minutes of observing time, ESIS captured the spatial and temporal evolution of tens of these small events across the ∼11.′5 field of view, as well as several larger extended eruptions, demonstrating the advantage of CTIS instruments over traditional slit spectrographs in capturing the spatial and spectral information of dynamic solar features across large fields of view.Item Instrument Calibration of the Interface Region Imaging Spectrograph (IRIS) Mission(2018-11) Wulser, J. P.; Jaeggli, Sarah A.; De Pontieu, Bart; Tarbell, Ted D.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, Sean R.; Kankelborg, Charles; Madsen, C.; McKillop, Sean; Prchlik, J.; Saar, Steven; Schanche, N.; Bryans, P.; Wiesmann, M.The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer mission that provides high-resolution spectra and images of the Sun in the 133-141nm and 278-283nm 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.Item The Unresolved Fine Structure Resolved: IRIS Observations of the Solar Transition Region(2014-10) Hansteen, Viggo H.; De Pontieu, B.; Carlsson, Mats; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; Pereira, Tiago M. D.; De Luca, E.E.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Kankelborg, Charles; Jaeggli, Sarah; Kleint, Lucia; Martínez-Sykora, J.The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a longstanding problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, lowlying loops or loop segments at transitionregion temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a longstanding observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.Item A PSF equalization technique for the Multi-Order Solar Extreme-ultraviolet Spectrograph (MOSES)(2015-10) Atwood, Shane; Kankelborg, CharlesThe Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) is a rocket-borne slitless imaging spectrometer, designed to observe He II (30.4 nm) emission in the solar transition region. This instrument forms three simultaneous images at spectral orders m=−1, 0, +1 over an extended field of view (FOV). A multi-layer coating on the grating and thin film filters in front of the detectors defines the instrument passband. Each image contains a unique combination of spectral and spatial information. Our overarching goal in analyzing these data is to estimate a spectral line profile at every point in the FOV. Each spectral order has different image geometry, and therefore different aberrations. Since the point spread function (PSF) differs between any two images, systematic errors are introduced when we use all three images together to invert for spectral line profiles. To combat this source of systematic error, we have developed a PSF equalization scheme. Determination of the image PSFs is impractical for several reasons, including changes that may occur due to vibration during both launch and recovery operations. We have therefore developed a strategy using only the solar images obtained during flight to generate digital filters that modify each image so that they have the same effective PSF. Generation of the PSF equalization filters does not require that the PSFs themselves be known. Our approach begins with the assumption that there are only two things that cause the power spectra of our images to differ: (1) aberrations; and (2) the FOV average spectral line profile, which is known in principle from an abundance of historical data. To validate our technique, we generate three synthetic images with three different PSFs. We compare PSF equalizations performed without knowledge of the PSF to corrections performed with that knowledge. Finally, we apply PSF equalization to solar images obtained in the 2006 MOSES flight and demonstrate the removal of artifacts.Item Using local correlation tracking to recover solar spectral information from a slitless spectrograph(2015-10) Courrier, Hans T.; Kankelborg, CharlesThe Multi-Order Solar EUV Spectrograph (MOSES) is a sounding rocket instrument that utilizes a concave spherical diffraction grating to form simultaneous solar images in the diffraction orders m = 0, +1, and −1. The large 2D field of view allows a single exposure to capture spatial and spectral information for large, complex solar features in their entirety. Most of the solar emission within the instrument passband comes from a single bright emission line. The m = 0 image is simply an intensity as a function of position, integrated over the passband of the instrument. Dispersion in the images at m = ±1 leads to a field-dependent displacement that is proportional to Doppler shift. Our goal is to estimate the Doppler shift as a function of position for every exposure. However, the interpretation of the data is not straightforward. Imaging an extended object such as the Sun without an entrance slit results in the overlapping of spectral and spatial information in the two dispersed images. We demonstrate the use of local correlation tracking as a means to quantify the differences between the m = 0 image and either one of the dispersed images. The result is a vector displacement field that may be interpreted as a measurement of the Doppler shift. Since two dispersed images are available, we can generate two independent Doppler maps from the same exposure. We compare these to produce an error estimate.Item Simultaneous imaging and spectroscopy of the solar atmosphere: advantages and challenges of a 3‐order slitless spectrograph(2001-12-10) Kankelborg, Charles; Thomas, Roger J.The dynamic solar atmosphere poses a severe observational challenge for imaging spectroscopy in EUV. The traditional method of building up images by rastering a slit spectrograph has so far proven too slow to keep up with the Sun's rapidly changing transition region and corona. We describe a new approach, using a slitless imaging spectrograph operating in a narrow band, with imaging detectors at three orders. This arrangement offers cotemporal imaging and spectroscopy at high spatial, spectral, and temporal resolution. The prospect of disentangling spatial and spectral information is greatly improved by choosing a narrow band containing only two spectral lines, and by imaging at several spectral orders. This paper discusses several advantages and challenges of the multiorder slitless approach. We derive a mathematical description of the null space of spatialspectral signatures to which an ideal threeorder slitless spectrograph has zero response. An exploration of the null space helps to clarify the capabilities and limitations of this instrument type. We infer that the threeorder slitless spectrograph is sensitive to line intensity, doppler shift and line width; but insensitive to line asymmetry. Strategies are developed to minimize the ambiguity in interpreting the multiorder data. A proof of concept sounding rocket payload, the MultiOrder Solar EUV Spectrograph (MOSES), is under development with an anticipated launch in Spring, 2004.Item Data inversion for the Multi‐Order Solar Extreme‐Ultraviolet Spectrograph(2003-11-05) Fox, J. Lewis; Kankelborg, Charles; Metcalf, Tomas R.The Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) is a high resolution, slitless imaging spectrometer that will observe the Sun in extreme ultraviolet near 304A. MOSES will fly on a NASA sounding rocket launch in spring 2004. The instrument records spatial and spectral information into images at three spectral orders. To recover the source spectrum, an illposed inversion must be performed on these data. We will explore two of the techniques by which this may be accomplished: Fourier backprojection and Pixons, constrained by the spatially integrated spectrum of the Sun. Both methods produce good results, including doppler shifts measured to 1/3pixel accuracy. The Pixon code better reproduces the line widths.Item Narrow‐band EUV multilayer coating for the MOSES sounding rocket(2005-09-08) Owens, Scott M.; Gum, Jeffery S.; Tarrio, Charles; Grantham, Steven; Dvorak, Joseph; Kjornrattanawanich, Benjawan; Keski-Kuha, Ritva; Thomas, Roger J.; Kankelborg, CharlesThe Multiorder Solar EUV Spectrograph (MOSES) is a slitless spectrograph designed to study solar He II emission at 303.8 Å (1 Å = 0.1 nm), to be launched on a sounding rocket payload. One difference between MOSES and other slitless spectrographs is that the images are recorded simultaneously at three spectral orders, m = 1, 0, +1. Another is the addition of a narrowband multilayer coating on both the grating and the fold flat, which will reject outofband lines that normally contaminate the image of a slitless instrument. The primary metrics for the coating were high peak reflectivity and suppression of Fe XV and XVI emission lines at 284 Å and 335 Å, respectively. We chose B4C/Mg2Si for our material combination since it provides excellent peak reflectivity and rejection of outofband wavelengths. Measurements of witness flats at NIST indicate the peak reflectivity at 303.8 is 39.0% for a 15 bilayer stack, while suppression ranges from 7.5x to 12.9x at 284 Å and from 3.4x to 15.1x at 335 Å for the individual reflections in the optical path. We present the results of coating the MOSES flight gratings and fold flat, including the spectral response of the fold flat and grating as measured at NIST's SURF III and Brookhaven's X24C beamline, respectively.Item Reconnectionless CME Eruption: Putting the Aly‐Sturrock Conjecture to Rest(2009-03-09) Rachmeler, L.A.; DeForest, C.E.; Kankelborg, CharlesWe demonstrate that magnetic reconnection is not necessary to initiate fast Coronal mass ejections (CMEs). The AlySturrock conjecture states that the magnetic energy of a given forcefree boundary field is maximized when the field is open. This is problematic for CME initiation because it leaves little or no magnetic energy to drive the eruption, unless reconnection is present to allow some of the flux to escape without opening. Thus, it has been thought that reconnection must be present to initiate CMEs. This theory has not been subject to rigorous numerical testing because conventional magnetohydrodynamics (MHD) numerical models contain numerical diffusion, which introduces uncontrolled numerical reconnection. We use a quasiLagrangian simulation technique to run the first controlled experiments of CME initiation in the complete lack of reconnection. We find that a flux rope confined by an arcade, when twisted beyond a critical amount, can escape to an open state, allowing some of the surrounding arcade to shrink, and releasing magnetic energy from the global field. This mechanism includes a true ideal MHD instability. We conclude that reconnection is not a necessary trigger for fast CME eruptions.Item CORONAL LOOP EXPANSION PROPERTIES EXPLAINED USING SEPARATORS(2009-10-27) Plowman, Joseph; Kankelborg, Charles; Longcope, Dana W.One puzzling observed property of coronal loops is that they are of roughly constant thickness along their length. Various studies have found no consistent pattern of width variation along the length of loops observed by TRACE and SOHO. This is at odds with expectations of magnetic flux tube expansion properties, which suggests that loops are widest at their tops, and significantly narrower at their footpoints. Coronal loops correspond to areas of the solar corona which have been preferentially heated by some process, so this observed property might be connected to the mechanisms that heat the corona. One means of energy deposition is magnetic reconnection, which occurs along field lines called separators. These field lines begin and end on magnetic null points, and loops forming near them can therefore be relatively wide at their bases. Thus, coronal energization by magnetic reconnection may replicate the puzzling expansion properties observed in coronal loops. We present results of a Monte Carlo survey of separator field line expansion properties, comparing them to the observed properties of coronal loops.
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