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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Extreme UV measurements of a varied line-space Hitachi reflection grating - Efficiency and scattering

The first extreme UV measurements of a grating mechanically ruled with smooth variations in the grating constant are presented. The grating characteristics are summarized and a schematic of the testing apparatus is shown and described. The procedure for obtaining the absolute grating efficiency is given. The results for that efficiency as a function of wavelengths of 68, 170, 256, 304, 584, and 1216 A are reported and discussed. Efficiency measurements were also made as a function of position across the ruled width at 256 A and 87 deg incident angle, and the results are discussed. Scattering measurements performed via computer acquisition of diffracted image profiles are reported.

Edelstein, J.↗
NASA NTRS1984

Analysis of the magnetic field configuration of a filament-associated flare from X-ray, UV, and optical observations

X-ray and ultraviolet observations from SMM of a filament-associated event on November 22, 1980 are examined in conjunction with ground-based optical observations, in order to determine the magnetic field configuration involved in the flaring process. Evidence that the flare was produced by gradual energy release in a large sheared magnetic loop which interacted with another smaller loop is found. Nonthermal processes, as indicated by hard X-ray emission and impulsive UV kernels, were produced in the interaction of the two loops. Although this flare shared some of the characteristics of Long Duration (class II) Events, no indication of a helmet-type configuration, as generally envisaged for class II events, was found. On the contrary, the magnetic configuration of the November 22, 1980 event was more similar to that of a compact (class I) flare, although on a much larger spatial scale and longer time scale.

Cheng, C.-C.↗
NASA NTRS1985

The geometric extent of C II (UV 0.01) emitting regions around luminous, late-type stars

A method is presented by which the geometric extent of the chromospheres around late-type stars can be estimated from measurements of the total emission-line flux and line ratios within the C II (UV 0.01) multiplet. Application of this technique to a sample of 15 late-type stars indicates a clear difference in the radial extent of the chromospheres around coronal and noncoronal stars. The former stars appear to have very thin chromospheres (of no more than 0.1 percent of the photospheric radius), while the latter stars have chromospheres extending, on average, out to 2.5 photospheric radii. This, in principle, provides information for understanding structural differences between late-type giant and supergiant stars with and without coronae, and could lead to an understanding of the mass-loss mechanisms involved.

Carpenter, K. G.↗
NASA NTRS1985

A study of flare buildup from simultaneous observations in microwave, H-alpha, and UV wavelengths

The results of high-resolution observations of the solar preflare activity of June 25, 1980 are analyzed. The observations were carried out simultaneously in the UV microwave, and H-alpha wavelengths using the VLA, the Ottawa River photoheliograph, and the Solar Max spectrometer and polarimeter instruments. Increases were observed in the intensitiy and polarization of compact sources at a wavelength of 6-cm during the preflare hour. The increases were associated with rising and twisting motions in the magnetic loops near the sight of the subsequent flare. Consistent with this process, analysis of the transverse and Doppler motions observed in the H-alpha filament before disruption showed that the filament was activated internally by the motions of evolving magnetic flux patterns. Ultraviolet data for C IV brightenings and upflows at the first appearance of the H-alpha filament indicated the presence of rising magnetic loops and material rising within the loops. The complete VLA, microwave and H-alpha data sets are given.

Kundu, M. R.↗
NASA NTRS1985

Time-resolved UV spectroscopy of BE Ursae Majoris

Far-ultraviolet spectra have been obtained of the eclipsing, hot subdwarf binary, BE UMa, with phase coverage in the 2.3-day orbital period concentrated near minimum light. No clearly phase-related spectra changes were found, but the UV continuum appeared to be in a highly variable state, with changes of a factor of two occurring on a time scale of hours. The hot star in this system may be one of the few known PG1159-035 variables, which show nonradial pulsations. If so, this is the first such star known in a binary system and thus should be important for determining the physical properties of these stars.

Hutchings, J. B.↗
NASA NTRS1985

Potential of CCDs for UV and X-ray plasma diagnostics

A program is under way to develop charge-coupled device (CCD) sensors for space-based X-ray astronomy imaging spectrometers. To date, laboratory line-emission spectra have been acquired throughout the range of 277 to 8000 eV (carbon through copper K-alpha emission) and CCD sensitivity has been demonstrated throughout the range of 1.1 through 8000 eV. Image resolution is excellent, limited almost entirely by the 15 micron pixel size. These results are presented and specialized techniques are described which permit such low energy response, high spectral resolution, and efficient charge collection. Finally, analysis is presented of one particular CCD characteristic which currently limits UV and X-ray performance: charge diffusion.

Janesick, J. R.↗
NASA NTRS1985

A summary of the UV, optical and IR properties of disks in CV's

The available observations of dwarf novae and novalike systems that are relevant to the study of accretion in cataclysmic variables are reviewed. This includes UV data from IUE and optical spectroscopy and infrared photometry. The flux distributions are compared to available steady state models to obtain an estimate of the mass accretion and the range of this parameter among the dwarf novae (U Gem, Z Cam and SU UMa types) and the novalikes (UX UMa, AM Her, DQ Her types). The normal and abnormal range of variation in the continuum and line fluxes is discussed.

Szkody, P.↗
NASA NTRS1985

Balloon in-situ measurements of ozone with the NASA-JSC UV photometer

Details of the design and performance of a UV absorption photometer used to measure ozone in the stratosphere from large balloons are given. Mechanisms which might cause a loss of ozone in the instrument are shown to be negligible. An analysis of errors obtains an instrumental precision that is better than 3 percent and an accuracy less than 5 percent. Improvements are being made that will increase the precision to about 1 percent and the accuracy to 3 percent. The NASA-JSC photometer has been intercompared with other techniques during several balloon campaigns. Agreement with other in-situ techniques was usually within 1 to 5 percent, while agreement with remote techniques was typically in the range 10 to 15 percent.

Robbins, D. E.↗
NASA NTRS1986

UV-T-RH combined environmental testing

A combined environmental aging chamber was developed at the Jet Propulsion Laboratory (JPL). The chamber has an ultraviolet (UV) light source that can be varied between 1 to 2 suns, temperature control from -40 to +175 C, and adjustable humidity. Results from two initial aging experiments (Tedlar and amorphous silicon colar cells) were presented.

Gonzalez, C. C.↗
NASA NTRS1986

IUE observations of Comet Halley: Evolution of the UV spectrum between September 1985 and July 1986

The ultraviolet spectrum of comet P/Halley was monitored with the IUE between 12 September 1985 and 8 July 1986 (r <2.6 AU pre and post-perihelion) at regular time intervals except for a two-month period around the time of perihelion. A complete characterization of the UV spectrum of the comet was obtained to derive coma abundances and to study the light emission mechanisms of the observed species. The Fine Error Sensor (FES) camera of the IUE was used to photometrically investigate the coma brightness variation on time scales of the order of hours. Spectroscopic observations as well as FES measurements show that the activity of the nucleus is highly variable, particularly at the end of December 1985 and during March and April 1986. The production rates of OH, CS and dust are derived for the entire period of the observations. The total water loss rate for this period is estimated to be 150 million metric tons.

Feldman, P. D.↗
NASA NTRS1987

Submillimeter and Far-Infrared Spectroscopy of M17 and S106: UV-Heated, Quiescent Molecular Gas?

Measurements of CO line emission toward the interface between molecular cloud and HII region in M17, and the center of the bipolar nebula S106 are discussed. The warm quiescent molecular gas is in the interface between the exciting OB stars and the surrounging molecular cloud. Comparison of the submillimeter, far-IR, and millimeter CO line intensities and profiles suggests a model in which clumps of relatively cool gas (T = 50 K) have warm surfaces or are embedded in a warm surrounding medium. Heating of the warm, quiescent molecular gas by collisions with dust grains can be excluded. Slow shocks or heating by photoelectrons are possible. The most promising mechanism is photoelectric heating. The existence of a substantial amount of warm, quiescent molecular gas in UV illuminated regions may be of importance locally in most OB star formation regions and globally in external galaxies with large rates of star formation.

Harris, A. I.↗
NASA NTRS1986

X-ray, UV, and optical observations of the dwarf nova BV Puppis

Exosat, IUE, optical spectroscopic, and broad-band photometric data on BV Pup are presented and analyzed in order to study the system characteristics and their relation to the high excitation of the emission lines. It is observed that: (1) at quiescence and outburst, the He II 4686 A/H-beta ratio for the star is larger than for other observed dwarf novae; (2) the X-ray flux is high for a system at outbursts and the X-ray flux correlates with an increased He II flux over the quiescent values; (3) the flat slope of the flux distribution at quiescence implies relatively low accretion rate; and (4) the abnormal UV line spectrum suggests a different geometry/opacity for the line emission zone compared to normal dwarf novae.

Szkody, Paula↗
NASA NTRS1987

Dynamic spectrum of a radio flare on UV Ceti

The dMe flare star UV Ceti (L726-8B) was observed at four frequencies simultaneously in the 1385-1652 MHz band using the Very Large Array. A flare lasting 10 minutes was observed with 6.67 s time resolution 'Dynamic spectrum'-type images in the Stokes parameters I and V show considerable complexity in the frequency-time domain; some features show a positive frequency drift with time, while others are more complex, involving both positive and negative frequency drifts. The positive drift features would be consistent with disturbances traveling downward in the star's corona.

Jackson, Peter D.↗
NASA NTRS1987

Stellar occultation probes of the Uranian rings at 0.1 and 2.2 microns - A comparison of Voyager UVS and earth-based results

A comparison between Voyager 2 UV spectrometer data for stellar occultations of the Uranian ring system obtained at 0.11 microns and 2.2-micron earth-based occultation data reveals the anticipated factor-of-two reduction in observed optical depths relative to those observed from earth. This is due to Voyager's proximity to the rings, which allows light diffracted out of the direct beam by ring particles to be replaced by light diffracted into the direct beam light from other particles, and further permits the placing of firm lower limits on typical particle sizes of 0.3 and 1 cm for the epsilon and delta rings, respectively. As a function of true anomaly, the epsilon ring profile is noted to remain very similar in shape and essentially constant in equivalent depth, even very near periapse.

Holberg, J. B.↗
NASA NTRS1987

What's needed in the UV and EUV

High spectral and spatial resolution UV and EUV spectroscopy is discussed with emphasis on the spectroscopic observations that are required in order to increase the understanding of the physics of the lower transition region. The properties of the lower transition region are reviewed, and the available lower transition region plasma diagnostics are reviewed for the wavelength range between about 1150 and 2000 A. One important conclusion is that comprehensive spectroscopic coverage over a rather broad temperature range is necessary in order to observe satisfactorily small transition region structures. This is illustrated by two examples from the recent NRL Spacelab 2 HRTS experiment.

Doschek, G. A.↗
NASA NTRS1987

Some diatomic molecules from comet P/Halley's UV spectra near spacecraft flybys

The abundances of diatomic molecules seen in the UV both give clues to the parent compounds and help unravel the gas and ion mass spectrometry. From IUE spectra of comet Halley, upper limits on SH and CS(+) column densities and estimates of probable NO, S2, and SO are found. In particular, judged from the 226-nm gamma band, NO was relatively abundant at 2-8 x 10 to the 13th/sq cm on March 9-14. The production rate of S2 was around 1 x 10 to the 27th molecules/s at that time, but both showed day-to-day variability by 2-3 times.

Wallis, Max K.↗
NASA NTRS1988

An example of the association of X-ray and UV emission with H-alpha surges

From H-alpha UV, and X-ray data, the nature of a well-observed surge on November 12, 1980 has been studied to try to understand the relationships between the mechanical motions and the high-temperature emissions. The cool (H-alpha) and the hot (O v) parts of the surge plasma both show velocities in the range of 100-120 km/s. The kinetic and potential energies of the surge are two orders of magnitude higher than the radiative energy. The observations suggest that the surge occurs in open structures parallel to one leg of a large scale coronal magnetic loop. The energy is released principally in the open structure (surge) and only a small amount heats the coronal loop (X-ray signature). This energy division should probably not be treated as a general characteristic of surge events. Different events are expected to exhibit a different energy balance, and this can account for the lack of a consensus in the previous literature regarding surge/X-ray associations.

Schmieder, B.↗
NASA NTRS1988

Fluorescence processes and line identifications in the UV spectra of cool stars

Fluorescence processes active in the outer atmospheres of noncoronal cool stars and the UV lines they produce are summarized. Eight pumping processes and 21 fluorescent line products are discussed. The processes, which produce 12 lines, involves energy levels not previously known to be radiatively populated. Four of these are examples of self-fluorescence, whereby one or more lines of Fe II photo-excite through coincident lines the upper levels of other Fe II lines lines seen in emission, while two others explain the selective excitation of solitary Ni II and Si I lines. Nine of the line products are decays from levels in Fe I and Fe II already known to be radiatively populated.

Carpenter, Kenneth G.↗