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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Magnetospheric and exospheric imaging in the extreme ultraviolet

Extreme ultraviolet line emissions by exospheric oxygen ions and neutrals of ionospheric origin can be used to form images of the dynamic magnetospheric regions with sufficient speed to provide a new global means of observing the dynamics of magnetosphere-ionosphere coupling processes. Computer simulations of such exospheric images based on the latest measurements of ion outflow, on known or estimated solar fluxes, and on known emission and excitation rates are shown. An evaluation of the current and foreseeable EUV imaging technology relevant to magnetospheric imaging is also given.

Chiu, Y. T.↗
NASA NTRS1987

Ultraviolet and extreme ultraviolet response of charge-coupled-device detectors

Results of a program to enhance the ultraviolet and extreme ultraviolet response of charge-coupled devices are presented. The ultimate goal of the program is to develop a large format device with both high and stable quantum efficiency from 100 to 3000 A that can be used as a windowless imaging detector in a space environment. Ultraviolet quantum efficiency measurements have been made for several ion-implanted and laser-annealed test CCDs. Quantum efficiencies as high as 22 percent at 2500 A, where the absorption depth in silicon is about 55 A, have been observed in one such test CCD. Quantum efficiency measurements of standard back-illuminated CCDs are also presented.

Stern, R. A.↗
NASA NTRS2002

Silicon Lightweight Mirrors (SLMS) for Ultraviolet and Extreme Ultraviolet Imaging Mirrors

Subtopic 01-S1.06 requires mirrors with a diameter of 0.5-2.4 meters, areal density less than 20 kg/sq m, a figure specification of 0.02-0.005 waves root mean square (rms) at 633 nanometers, a surface roughness 0.5-1 nanometers rms, and a midfrequency error of 1.0-2.5 nanometers rms for use in the infrared (IR) to extreme ultra violet (EUV) waveband. Schafer's Phase II objective is to use Silicon Lightweight Mirrors (SLMS), a novel, all-silicon, foam-core, lightweight mirror technology, to build three imaging mirrors for the Next Generation Space Telescope Near Infrared Camera (NIRCam) Engineering Test Unit: M0 (a flat), M2 (a concave sphere) and M3R (an oblate spheroid). The surface figure error specification for the NIRCam imaging mirrors is 8 nanometers rms (0.013 waves rms at 633 nanometers), equivalent to that required for ultraviolet (UV) and EUV mirrors, and this figure must be maintained at the 35 K operational temperature of NGST. The surface roughness required is 30 A rms since NIRCam operates in the visible to infrared (VIS/IR) (0.65-5 microns). We will produce mounts for mirrors M2 and M3R using the complementary thermally matched C/SiC material demonstrated by Schafer under another NASA SBIR, NAS8-98137.

Goodman, W. A.↗
NASA NTRS1992

Far ultraviolet and extreme ultraviolet rocket instrumentation for measuring the solar spectral irradiance and terrestrial airglow

A sounding-rocket experiment is being developed for the study of EUV spectral irradiance and its effects on the upper atmosphere, using three solar EUV instruments devised by the Laboratory for Atmospheric and Space Physics. These include a 25-cm Rowland circle EUV spectrograph, an array of Si X-UV photodiodes, and an X-UV imager with 20 arcsec resolution of the sun.

Woods, Thomas N.↗
NASA NTRS2003

The Solar Chromosphere/Corona Interface. I. Far-Ultraviolet to Extreme-Ultraviolet Observations and Modeling of Unresolved Coronal Funnels

A coronal funnel model, developed by D. Rabin, was tested against a calibrated spectroheliogram recorded in the 170-1 75 A bandpass. This image was recorded on board a sounding-rocket experiment flown on 1994 November 3, called the Multi-Spectral Solar Telescope Array II (MSSTA II). MSSTA, a joint project of Stanford University, the NASA Marshall Space Flight Center, and the Lawrence Livermore National Laboratory' is an observing platform composed of a set of normal-incidence, multilayer-coated optics designed to obtain narrow-bandpass, high-resolution images (1 sec.- 3 sec.) at selected far-ultraviolet (FUV), extreme-ultraviolet (EUV), and soft X-ray wavelengths (44-1550 A). Using full disk images centered at 1550 A (C IV) and 173 A (Fe IX/X), the funnel model, which is based on coronal back-heating, was tested against the data incorporating observed constraints on global coverage and measured flux. Found was a class of funnel models that could account for the quiescent, globally diffuse and unresolved emission seen in the 171-175 A bandpass, where the funnels are assumed to be rooted in the C IV supergranular network. These models, when incorporated with the CHIANTI spectral code, suggest that this emission is mostly of upper transition region origin and primarily composed of Fe IX plasma. The funnels are found to have constrictions, Gamma approx. 6-20, which is in good agreement with the observations. Further, the fitted models simultaneously satisfy global areal constraints seen in both images; namely,that a global network of funnels must cover approx. 700 - 95% of the total solar surface area seen in the 171-175 A image, and a 5% of the disk area seen in the 1550 A bandpass. These findings support the configuration of the EUV magnetic network as suggested by Reeves et al. and put forth in more detail by Gabriel. Furthermore, the models are in good agreement with differential emission measure estimates made of the transition region by J. C. Raymond & J. G. Doyle for temperatures 250,000 K less than or = T less than or = 650,000 K, based on full-disk observations made on board Skylab.

Martinez-Galarce, Dennis S.↗
NASA NTRS1976

A rocket measurement of the extreme ultraviolet dayglow

Extreme ultraviolet spectra of the mid-latitude dayglow in the wavelength range of 550 to 1250A have been obtained with a rocket borne grating spectrometer at a resolution of 20A. Spectra were obtained in the altitude range of 140 to 280 km. The spectra are dominated by emissions from atomic multiplets and no molecular bands have been identified with certainty. The strongest emissions other than H Lyman-alpha are OI (989) and OII (834). Other prominent emissions include He I(584), N II(916) and N II(1085). An unexpected feature near 612A has an intensity comparable to He I(584).

Christensen, A. B.↗
NASA NTRS1980

The equatorial aurora in the extreme ultraviolet

The extreme ultraviolet telescope on the Apollo-Soyuz mission observed the equatorial aurora from an altitude of 220 km on four separate occasions in July 1975, in quiet geomagnetic conditions (Ap = 6). In all cases signals well above ambient background in the 50-150, 114-150, 170-600, and 500-780 A bands were recorded as the spacecraft moved across the equator and the instrument viewed the atmosphere below it. The observed emissions are confined to a band roughly 10 to 20 deg in width with the peak emission occurring in the range -15 to +2 deg magnetic latitude. No enhancement on the 1350-1550 A channel was noted. The observed signals are interpreted as recombination radiation of energetic helium and, possibly, oxygen ions originating in the terrestrial ring current.

Paresce, F.↗
NASA NTRS1994

Astronomy and the Extreme Ultraviolet Explorer satellite

The extreme ultraviolet wave band (100 to 912 angstroms) was thought until recently to be useless to astronomy, primarily because the opacity of the interstellar medium would prevent observations at these wavelengths. However, the interstellar medium has been found to be markedly inhomogeneous in both density and ionization state and the sun is fortunately located in a region of low extreme ultraviolet opacity. The Extreme Ultraviolet Explorer, launched in June 1992, has surveyed the sky in this wave band and has detected a wide variety of astronomical sources at considerable distances, including some extragalactic objects. Studies in the extreme ultraviolet band have already begun to increase our understanding of the contents of the universe.

EUVE Project↗
NASA NTRS1982

The Extreme Ultraviolet Explorer

The Extreme Ultraviolet Explorer Mission is described. The purpose of this mission is to search the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation (100 to 1000 A). The search will be accomplished with the use of three EUV telescopes, each sensitive to different bands within the EUV band. A fourth telescope will perform a higher sensitivity search of a limited sample of the sky in a single EUV band. In six months, the entire sky will be scanned at a sensitivity level comparable to existing surveys in other more traditional astronomical bandpasses.

Malina, R. F.↗
NASA NTRS1974

Observations of the extreme ultraviolet nightglow

An extreme ultraviolet telescope system was flown on an Aerobee 170 rocket from the White Sands Missile Range on Oct. 22, 1971. Measurements of extreme ultraviolet radiation from the night sky were made with a set of Parylene, aluminum, and tin filters behind a grazing incidence concentrator. If the aluminum and tin filter data are interpreted as being due to only the He I 584-A and He II 304-A lines, the nightglow flux at 25 deg zenith angle and 270 deg azimuth angle at 180-km altitude was I(584) = 4.4 plus or minus 1.9 R and I(304) = 1.3 plus or minus 0.5 R.

Riegler, G. R.↗
NASA NTRS1990

The extreme ultraviolet explorer

The Extreme Ultraviolet Explorer (EUVE) mission, currently scheduled for launch in September 1991, is described. The primary purpose of the mission is to survey the celestial sphere for astronomical sources of Extreme Ultraviolet (EUV) radiation. The survey will be accomplished with the use of three EUV telescopes, each sensitive to a different segment of the EUV band. A fourth telescope will perform a high sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all sky survey will be carried out in the first six months of the mission and will be made in four bands, or colors. The second phase of the mission, conducted entirely by guest observers selected by NASA, will be devoted to spectroscopic observations of EUV sources. The performance of the instrument components is described. An end to end model of the mission, from a stellar source to the resulting scientific data, was constructed. Hypothetical data from astronomical sources processed through this model are shown.

Bowyer, Stuart↗
NASA NTRS2013

Ultraviolet and Extreme-Ultraviolet Emissions at the Flare Footpoints Observed by Atmosphere Imaging Assembly

A solar flare is composed of impulsive energy release events by magnetic reconnection, which forms and heats flare loops. Recent studies have revealed a two-phase evolution pattern of UV 1600 A emission at the feet of these loops: a rapid pulse lasting for a few seconds to a few minutes, followed by a gradual decay on timescales of a few tens of minutes. Multiple band EUV observations by the Atmosphere Imaging Assembly further reveal very similar signatures. These two phases represent different but related signatures of an impulsive energy release in the corona. The rapid pulse is an immediate response of the lower atmosphere to an intense thermal conduction flux resulting from the sudden heating of the corona to high temperatures (we rule out energetic particles due to a lack of significant hard X-ray emission). The gradual phase is associated with the cooling of hot plasma that has been evaporated into the corona. The observed footpoint emission is again powered by thermal conduction (and enthalpy), but now during a period when approximate steady-state conditions are established in the loop. UV and EUV light curves of individual pixels may therefore be separated into contributions from two distinct physical mechanisms to shed light on the nature of energy transport in a flare.We demonstrate this technique using coordinated, spatially resolved observations of UV and EUV emissions from the footpoints of a C3.2 thermal flare.

Flares↗
NASA NTRS1991

The Extreme Ultraviolet Explorer Mission

The Extreme Ultraviolet Explorer (EUVE) mission, currently scheduled from launch in September 1991, is described. The primary purpose of the mission is to survey the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation with the use of three EUV telescope, each sensitive to a different segment of the EUV band. A fourth telescope is planned to perform a high-sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all-sky survey is planned to be carried out in the first six months of the mission in four bands, or colors, 70-180 A, 170-250 A, 400-600 A, and 500-700 A. The second phase of the mission is devoted to spectroscopic observations of EUV sources. A high-efficiency grazing-incidence spectrometer using variable line-space gratings is planned to provide spectral data with about 1-A resolution. An end-to-end model of the mission, from a stellar source to the resulting scientific data, is presented. Hypothetical data from astronomical sources were processed through this model and are shown.

Bowyer, S.↗