Engineering topics

Thomas, R. J.

Publications and source records attributed to Thomas, R. J..

At least 19 records

NASA NTRS2007

Absolute Radiometric Calibration of EUNIS-06

The Extreme-Ultraviolet Normal-Incidence Spectrometer (EUNIS) is a soundingrocket payload that obtains imaged high-resolution spectra of individual solar features, providing information about the Sun's corona and upper transition region. Shortly after its successful initial flight last year, a complete end-to-end calibration was carried out to determine the instrument's absolute radiometric response over its Longwave bandpass of 300 - 370A. The measurements were done at the Rutherford-Appleton Laboratory (RAL) in England, using the same vacuum facility and EUV radiation source used in the pre-flight calibrations of both SOHO/CDS and Hinode/EIS, as well as in three post-flight calibrations of our SERTS sounding rocket payload, the precursor to EUNIS. The unique radiation source provided by the Physikalisch-Technische Bundesanstalt (PTB) had been calibrated to an absolute accuracy of 7% (l-sigma) at 12 wavelengths covering our bandpass directly against the Berlin electron storage ring BESSY, which is itself a primary radiometric source standard. Scans of the EUNIS aperture were made to determine the instrument's absolute spectral sensitivity to +- 25%, considering all sources of error, and demonstrate that EUNIS-06 was the most sensitive solar E W spectrometer yet flown. The results will be matched against prior calibrations which relied on combining measurements of individual optical components, and on comparisons with theoretically predicted 'insensitive' line ratios. Coordinated observations were made during the EUNIS-06 flight by SOHO/CDS and EIT that will allow re-calibrations of those instruments as well. In addition, future EUNIS flights will provide similar calibration updates for TRACE, Hinode/EIS, and STEREO/SECCHI/EUVI.

Thomas, R. J.↗

NASA NTRS2006

First Results from EUNIS-06

The Extreme Ultraviolet Normal-Incidence Spectrograph (EUNIS) sounding rocket experiment successfully completed its first flight on 12 April 2006 from White Sands Missile Range, obtaining 145 science images in each of two wavelength channels. EUNIS is designed to investigate the energetics of the solar corona and hotter transition region through high-resolution imaging spectroscopy with a rapid (2-3 second) cadence. The two independent optical systems of EUNIS simultaneously record spectra over two passbands (170-205 Angstroms and 300-370 Angstroms), each spatially resolved along slit lengths of about 660 arcsec. The longwave channel includes He II 304 Angstroms and strong lines from Fe XI-XVI. The shortwave passband has a sequence of very strong Fe IX-XIII lines. Together, the EUNIS telescopes furnish a wide range of temperature and density diagnostics and enables underflight calibration of instrumental passbands on the SOHO, TRACE, Solar-B and STEREO missions. We present an overview of the science images from the first flight with emphasis on transient phenomena. The target was active region NOAA 10871 and adjacent quiet areas. Spectra were recorded with exposure times as short as 0.1 s, demonstrating that EUNIS is the most sensitive solar EUV spectrograph in operation, with over 100 times the throughput of its predecessor, the Solar Extreme ultraviolet Research Telescope and Spectrograph (SERTS). EUNIS is supported by the NASA Heliophysics Division's Solar & Heliospheric Physics Supporting Research and Technology and Low Cost Access to Space Program.

Rabin, Douglas M.↗

NASA NTRS2003

The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)

EUNIS (Extreme Ultraviolet Normal Incidence Spectrograph) is a high-efficiency extreme ultraviolet spectrometer that is expected to fly for the first time in 2004 as a sounding rocket payload. Using two independent optical systems, EUNIS will probe the structure and dynamics of the inner solar corona high spectral resolution in two wavelength regions: 17-21 nm with 3.5 pm resolution and 30-37 nm with 7 pm resolution. The long wavelength channel includes He II 30.4 nm and strong lines from Fe XI-XVI; the short wavelength channel includes strong lines of Fe IX-XIII. Angular resolution of 2 arcsec is maintained along a slit covering a full solar radius. EUNIS will have 100 times the throughput of the highly successful SERTS payloads that have preceded it. There are only two reflections in each optical channel, from the superpolished, off-axis paraboloidal primary and the toroidal grating. Each optical element is coated with a high-efficiency multilayer coating optimized for its spectral bandpass. The detector in each channel is a microchannel plate image intensifier fiber- coupled to three 1K x 1K active pixel sensors. EUNIS will obtain spectra with a cadence as short as 1 sec, allowing unprecedented studies of the physical properties of evolving and transient structures. Diagnostics of wave heating and reconnection wil be studied at heights above 2 solar radii, in the wind acceleration region. The broad spectral coverage and high spectral resolution will provide superior temperature and density diagnostics and will enable underflight calibration of several orbital instruments, including SOHO/CDS and EIT, TRACE, Solar-B/EIS, and STEREO/EUVI. EUNIS is supported by NASA through the Low Cost Access to Space Program in Solar and Heliospheric Physics.

Oegerle, William↗

NASA NTRS2003

SUMI - The Solar Ultraviolet Magnetograph Investigation

Solar physics has been successful in characterizing the full vector magnetic field in the photosphere, where the ratio of gas pressure to magnetic pressure (Beta) is >1. However, at higher levels in the atmosphere, where Beta <<1 and flares and CMEs are believed to be triggered, observations are difficult, severely limiting the understanding of these processes. In response to this situation, we are developing SUMI (the Solar Ultraviolet Magnetograph Investigation) a unique instrument designed to measure the circular and linear polarization of upper chromospheric Mg II lines (280 nm) and circular polarization of transition region C IV lines (155 nm). To date the telescope mirrors have been built, tested and coated with dielectric stacks designed to reflect only the wavelengths of interest. We have also developed a unique UV polarimeter and completed the design of a high-resolution spectrograph that uses dual toroidal varied- line-space (TVLS) gratings. Incorporating measurements of those components developed so far, the revised estimate of the system throughput exceeds our original estimate by more than an order of magnitude. A sounding rocket flight is anticipated in 2006. Our objectives and progress are detailed in this presentation.

Porter, J. G.↗

NASA NTRS2002

Atomic Data and Spectral Line Intensities for Ne III

A number of satellites and rockets have been launched to observe radiation from the Sun and other astrophysical objects. Line radiation is emitted when the electron impact excited levels decay to the lower levels by photon emission. From this radiation, the physical parameters such as electron temperature and density of the astrophysical plasma, elemental abundance, and opacity can be inferred. Ne III lines have been observed in H II regions, Ne-rich filaments in supernovae, and planetary nebulae. The allowed line at 489.50 Angstroms due to the transition 2s(sup 2) 2p(sup 5) (sup 3) P2 (goes to) 2s(sup 2)2p(sup 4)(sup 3)P2 has been identified in the solar spectrum by Vernazza and Reeves using Skylab observations. Other Ne III lines in the solar EUV spectrum have been reported by Thomas and Neupert based on observations from the Solar EUV Rocket Telescope and Spectrograph (SERTS) instrument. Atomic data for Ne III have been calculated by using a set of programs developed at, University College, London. The Superstructure and Distorted Wave (DW) programs have been updated over the years. In the Superstructure program, configuration interaction can be taken into account and radial functions are calculated in a modified Thomas-Fermi-Amaldi potential. This is a statistical potential and depends on parameters lambda 1 which are determined by optimizing the weighted sum of term energies. They are found to be lambda(sub 0)=1.2467, lambda(sub 1)=1.1617, and lambda(sub 2)=1.0663. The relativistic corrections are included by using the Breit-Pauli Hamiltonian as a perturbation to the nonrelativistic Hamiltonian. The same potential is used to calculate reactance matrices in the DW approximation in LS coupling. Collision strengths in intermediate coupling are obtained by using term coupling coefficients obtained from the Superstructure program. In this calculation, the configurations used are 2s(sup 2)2p(sup 4), 2s2p(sup 5), 2s(sup 2)2p(sup 3)3s, 2s(sup 2)p(sup 3)3d giving rise to 57 fine-structure levels in intermediate coupling.

Bhatia, A. K.↗

NASA NTRS2001

Atomic Data and Spectral Line Intensities for Ne III

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ne III. The configurations used are 2s(sup 2) 2p(sup 4),2s2p(sup 5),2s(sup 2) 2p(sup 3)3s, and 2s(sup 2)3p(sup 3)3d giving rise to 57 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 5, 10, 15, 20, and 25 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of logT,(K)=5.0, corresponding to maximum abundance of Ne III. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14) per cubic centimeter. Relative spectral line intensities are calculated. Proton excitation rates between the lowest three levels have been included in the statistical equilibrium equations. The predicted Ne III line intensities are compared with SERTS rocket measurements of a solar active region and of a laboratory EUV light source.

Bhatia, A. K.↗

NASA NTRS2000

SUMI: The Solar Ultraviolet Magnetograph Investigation

A major focus of solar physics is the measurement of the temporal and spatial variability of solar magnetic fields from the photosphere into the lower corona, together with the study of how their behavior produces the dynamic phenomena in this region such as flares and Coronal Mass Injection (CMEs). Considerable success has been achieved in the characterization of the full vector field in the photosphere, where P, the ratio of the gas pressure to the magnetic pressure, is greater than or equal to 1. At higher levels in the atmosphere where beta is less than 1, the magnetic field (through the Lorentz force) controls the structure and dynamics of the solar atmosphere, and rapid changes in structure with release of energy become possible. However, observations of the field at these higher levels have proven to be difficult, placing a serious limitation on our understanding of the physical processes occurring there. This poster will discuss the Solar Ultraviolet Magnetograph Investigation (SUMI), a hardware development study for an instrument capable of measuring the polarization in ultraviolet lines of C IV and Mg II formed in the transition region and upper chromosphere. We are currently developing optical technologies necessary to build an instrument that will achieve a major advance in performance over that of earlier attempts (e.g., SMM/UVSP). Initially configured as a sounding rocket payload, such a UV magnetograph would allow us to make exploratory measurements extending the observation of solar magnetic fields into new and dynamic regimes. This work is supported by NASA through the SEC Program in Solar Physics and the program for Technology Development for Explorer Missions and Sofia.

Davis, John M.↗

NASA NTRS1997

EUV line intensities above the limb measured by CDS

The extreme ultraviolet (EUV) above the limb observed with the coronal diagnostic spectrometer (CDS) are discussed. The CDS spectra were obtained up to 0.3 solar radii above the east and west limb, and above the polar coronal holes. A large data set was acquired during the campaign in August 1996. The intensities of the chromospheric, transition region and coronal lines were derived as a function of the radial distance. The density-sensitive line ratios of Si IX 350/342 A and Si X 356/347 A were used to derive an average electron density. The temperature and density in the coronal holes were found to be lower than in the closed field regions.

Fludra, A.↗

NASA NTRS1995

A conceptual framework for evaluating variable speed generator options for wind energy applications

Interest in variable speed generating technology has accelerated as greater emphasis on overall efficiency and superior dynamic and control properties in wind-electric generating systems are sought. This paper reviews variable speed technology options providing advantages and disadvantages of each. Furthermore, the dynamic properties of variable speed systems are contrasted with synchronous operation. Finally, control properties of variable speed systems are examined.

Reddoch, T. W.↗

NASA NTRS1994

EUV and infra-red lines of Fe 13

New level population calculations for Fe-XIII are presented, and line intensities predicted. The extreme ultraviolet (EUV) lines are compared with the recent observations of the solar extreme ultraviolet rocket telescope and spectrograph (SERTS), and density estimates for the active region are given. Uses of the Fe-XIII lines are suggested, both for the sun and other stars, and the possibility of coordinating SOHO studies of EUV lines with ground based observations of Fe-XIII infrared lines is discussed.

Young, P. R.↗

NASA NTRS1994

Solar Mesosphere Explorer satellite measurements of el Chichon stratospheric aerosols. 1: Cloud morphology

Data from the Solar Mesosphere Explorer (SME) is used to track the time, latitude, and altitude (above 18 km) development of the aerosol cloud injected into the stratosphere by the eruption of el Chichon. This unique data set, using scattering data from the near-infrared (1.27 and 1.87 microns) and visible (440 nm) spectrometers on SME, covers the period from the initial injection in April 1982 through the end of 1986. Although the bulk of the mass is contained in the latitude band from 10 deg S to 30 deg N for the entire duration of the measurements, transport of material to high latitudes is apparent in the data in the post eruption period. The times aerosol density maxima vary greatly as a function of altitude and latitude.

Rusch, D. W.↗

NASA NTRS1994

Evidence of mass outflow in the low corona over a large sunspot

An extreme ultraviolet (EUV) imaging spectrograph designed for sounding rocket flight has been used to search for velocity fields in the low solar corona. During a flight in May, 1989, we obtained emission line profile measurements along a chord through an active region on the Sun. Relative Doppler velocities were measured in emission lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km/s at 350 A. The only Doppler shift appreciably greater than this level was observed in the line of Mg IX at 368.1 A over the umbra of the large sunspot. The maximum shift measured at that location corresponded to a velocity toward the observer of 14 plus or minus 3 km/s relative to the mean of measurements in that emission line made elsewhere over the active region. The magnetic field in the low corona was aligned to within 10 deg of the line of sight at the location of maximum Doppler shift. Depending on the magnetic field geometry, this mass outflow could either re-appear as a downflow of material in distant footprints of closed coronal loops or, if along open field lines, could contribute to the solar wind. The site of the sunspot was near a major photospheric magnetic field boundary. Such boundaries have been associated with low-speed solar winds as observed in interplanetary plasmas.

Neupert, W. M.↗

NASA NTRS1994

Abundance determination in solar active region

An improved method has been developed to evaluate element abundances from emission line intensities of thin plasmas, depending on the differential emission measure (DEM) of the source. Observations made by the Solar EUV Rocket Telescope and Spectrograph (SERTS) Rocket EUV Spectrograph are used to perform a detailed analysis of the DEM distribution for temperatures larger than 10(exp 5) K in a solar active region. Comparison of the DEM distributions obtained by means of lines from different elements allows the verification of relative abundances for the most common elements of the solar corona, and gives an abundance estimates for the minor components, such as Na, Al, Ar, Cr, Mn and Zn.

Monsignori Fossi, B. C.↗

NASA NTRS1994

Mg IX emission lines in an active region spectrum obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical electron-temperature-sensitive Mg IX emission line ratios are presented for R(sub 1) = I(443.96 A)/I(368.06 A), R(sub 2) = I(439.17 A)/I(368.06 A), R(sub 3) = I(443.37 A)/I(368.06 A), R(sub 4) = I(441.22 A)/I(368.06 A), and R(sub 5) = I(448.28 A)/I(368.06 A). A comparison of these with observational data for a solar active region, obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals excellent agreement between theory and observation for R(sub 1) through R(sub 4), with discrepancies that average only 9%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on board Skylab. However in the case of R(sub 5), the theoretical and observed ratios differ by almost a factor of 2. This may be due to the measured intensity of the 448.28 A line being seriously affected by instrumental effects, as it lies very close to the long wavelength edge of the SERTS spectral coverage (235.46-448.76 A).

Keenan, F. P.↗

NASA NTRS1993

Correlation of He II Lyman alpha with He I 10830 A, and with chromospheric and EUV coronal emission

This paper describes the results of comparing Solar EUV Rocket Telescope and Spectrograph (SERTS-3) images obtained in the transition region line of He II 304 A with chromospheric He I 10830 A absorption; with strong coronal lines of Mg IX 368 A, Fe XV 284 A and 417 A, and Fe XVI 335 A and 31 A; with H-alpha; with Ca II 8542 A; and with magnetograms in Fe I 8688H-alpha. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the He II 304 A and He I 10830 A images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 A than in 304 A. In active regions, the 304 A line follows more closely the behavior of H-alpha and Ca II 8542 A than the 10830 A line.

Thompson, W. T.↗

NASA NTRS1993

Solar coronal observations and formation of the He II 304 A line

Although a large body of recent work supports the formation of the He II 304 A resonance line by collisional excitation in the quiet sun, the formation mechanism is less clear in strong coronal active regions and flares. The 1989 May 5 flight of the Goddard Solar Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS-3) provided a data set that is well suited to addressing this question. This paper develops a method of assessment of the line formation mechanism that is based on simple non-LTE theory and is applied to these data. The results support the conclusion of other authors that the 304 A line is formed by collisional excitation in the quiet sun, but that photoionization-recombination (p-r) may play a significant role in coronal active regions, and that p-r is important, and may even be predominant, in many flares.

Jordan, S. D.↗

NASA NTRS1993

A comparison of theoretical CIV emission line strengths with active region observations obtained with the solar EUV rocket telescope and spectrograph (SERTS)

Theoretical line ratios involving 2s 2S - 3p 2P, 2p 2p - 3s 2S, and 2p 2S - 3d 2D transitions in C IV between 312 and 420 A are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22 percent. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on board Skylab. The potential usefulness of the C IV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed.

Keenan, F. P.↗

NASA NTRS1992

Observations of the solar corona with a high resolution EUV imaging spectrograph

An extreme ultraviolet imaging spectrograph was used to obtain coronal observations with high spectral and spatial resolution. The imaging properties of the instrument enable measurements of spectral line shapes and positions in discrete spatial elements of a region, so that the dynamic characteristics of the coronal plasma, as well as the distribution of emission measure with temperature and well known density diagnostics, can be studied for specific features. The instrumentation is described and several results of a sounding rocket flight on 5 May 1989, when the corona over NOAA Region 5464 including emission over the umbra of the region's largest sunspot and the pre-impulsive phase emission of a small flare was recorded, are summarized.

Neupert, Werner M.↗