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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

The 0.8 day orbit of the precataclysmic binary EUVE J1016-053

The optical counterpart of the new extreme ultraviolet source EUVE J1016-053 (=RE 1016-053) is known to show intermittent sharp Balmer and HE I emission and traces of an M dwarf associated with a white dwarf optical spectrum. We present extensive optical spectroscopy showing the emission lines vary in velocity and intensity on a period of 0d.78929 +/- 0d.00003. The phase of the emission-line strengths lags that of the velocities by 0.237 +/- 0.013 cycle, consistent with the quarter-cycle offset expected if emission arises from the side of the secondary facing the hot white dwarf. EUVE J1016-053 is another example of an extreme ultraviolet illumination-effect binary, which only recently emerged from a common-envelope phase of binary evolution. Based on spectroscopic measurements and new BVR photometry, we find that the M dwarf secondary's contribution to the combined light is smaller than previously reported, probably because of the difficulty of avoiding contamination from a third star 3".2 distant. The velocity of the weak H II absorption is in antiphase to the emission, suggesting that it originates in the white dwarf photosphere. The mass function implied by the emission-line motion is f(M) = 0.28 +/- 0.08 M solar. Assuming the He II absorption does follow the white dwarf, the mass ratio MWD/MdM is 1.8 +/- 0.5, and the gravitational redshift is 45 +/- 14 km s-1. The modulation of the emission lines suggests the inclination i > 40 degrees, but plausible masses demand this inclination be well above the value.

Non-NASA Center↗
NASA NTRS1974

Possibility of using sources of vacuum ultraviolet irradiation to solve problems of space material science

An urgent problem in space materials science is simulating the interaction of vacuum ultraviolet (VUV) of solar emission with solids in space conditions, that is, producing a light source with a distribution that approximates the distribution of solar energy. Information is presented on the distribution of the energy flux of VUV of solar radiation. Requirements that must be satisfied by the VUV source used for space materials science are formulated, and a critical evaluation is given of the possibilities of using existing sources for space materials science. From this evaluation it was established that none of the sources of VUV satisfies the specific requirements imposed on the simulator of solar radiation. A solution to the problem was found to be in the development of a new type of source based on exciting a supersonic gas jet flowing into vacuum with a sense electron beam. A description of this gas-jet source, along with its spectral and operation characteristics, is presented.

Verkhoutseva, E. T.↗
NASA NTRS1976

The interpretations of ultraviolet observations of comets

The paper summarizes recent cometary UV observations, most of which were made in Ly-alpha light with instruments aboard earth-orbiting satellites. These include OAO-2 observations of comets Bennett and Tago-Sato-Kosaka, OGO-5 observations of comets Bennett and Encke, and numerous observations of comet Kohoutek. Models for the production of cometary hydrogen atoms are described, including the fountain, syndyname, and parent-daughter models. Calculations of emission line profiles and multiple-scattering effects are also discussed. Results of observations and interpretations are reviewed for each cited comet, far-UV observations in other emission lines are noted, and the use of comets as solar-wind probes is considered. It is concluded that the results of the present cometary Ly-alpha observations strongly support the concept of an icy conglomerate solid cometary nucleus and suggest water to be one of the most abundant molecules in comets.

Keller, H. U.↗
NASA NTRS1985

Measurements of HO2 chemical kinetics with a new detection method

In this research program, HO2 was detected by the OH(A-X) photofragment from dissociative excitation of HO2 at 147 nm. This detection method was applied to measure the reaction rate constant of HO2 + O3. This reaction rate constant is needed for the understanding of stratospheric chemistry. Since C12 was used in the flow system, photoexcitation of C12 may produce fluorescence to interfere with the measurements. Thus, the photoexcitation process of C12 in the vacuum ultraviolet region was also examined in this research period using synchrotron radiation as a light source. The research results are summarized.

Lee, L. C.↗
NASA NTRS1994

Analysis of Voyager spectra of the beta Cephei star nu Eridani

Voyager 500-1700 A spectrophotometric observations of the beta Cephei star nu Eri are presented and discussed. The Voyager observations were obtained in 1981 and cover six pulsation cycles of the star. These data are supplemented with a set of nine International Ultraviolet Explorer (IUE) SWP high-resolution observations covering one, earlier epoch, pulsation cycle. Light curves are derived from the Voyager data at 1055 and 1425 A. These light curves are found to be consistent in both shape and period with published optical curves. The 1055 A light curve also exhibits a phenomenon not seen in the optical curves: a small but highly significant systematic increase in the flux of the maximum light phases while maintaining a constant minimum light level over the interval of observation. Substantially larger errors in the longer wavelength data preclude discussion of this phenomenon in the 1425 A light curve. Examination of the far-UV continuum in nu Eri during this period shows that the color temperature is lower for the brighter maxima. Analysis of the far-UV continuum at maximum and minimum light yields an effective temperature difference between these two phases of 2200 + or - 750 K. Spectroscopically, three prominent features are seen in the Voyager data: a feature at 985 A mostly due to a blend of C III 977 A, H I Ly gamma 972 A, and N III 990 A; a feature at 1030 A due to H I Ly beta 1026 A and C II 1037 A; and the Si IV resonance doublet near 1400 A. A comparison of the 912-1700 A spectral region in nu Eri with a set of standard, i.e., nonpulsating stars, shows that nu Eri closely resembles the standard both in continuum shape and spectral line strengths with the possible exception of a slight flux excess between 912 and 975 A. The equivalent width of the 985 A feature is shown to vary in strength over the pulsation cycle in antiphase with the light curve and variations seen in the C IV 1548-1551 lines from the IUE data. This behavior of the 985 A feature is most likely caused by variations in the strength of the Ly gamma component of the blend. Comparisons are also made between nu Eri and the only other beta Cephei star studied in the far-UV, BW Vul, with the most notable differences between the two stars being the much larger delta(T(sub eff)) for BW Vul and the almost total absence of abnormalities in observed spectrum of nu Eri.

Porri, A.↗
NASA NTRS2002

Space-Age Shades

Silhouette's Titan Minimal Art frames possess a super elasticity that ensures a slip-free fit for wearing comfort, without causing irritating pressure points. The titanium alloy used in the frames also prevents allergic reactions. This technology is available to both NASA astronauts and public consumers in either corrective eyewear or sunglass models. The only difference between the sunwear used by NASA astronauts and the commercial models is the lens. Silhouette and Dr. Keith Manuel, the "official" optometrist overseeing the NASA Space Shuttle, the International Space Station, and various other vision-related space projects, brought NASA a lens that is considerably darker (5.5 percent overall light transmittance), with a thin gold coating that offers total protection, not only against ultraviolet (UV) radiation, but also against the harmful infrared radiation in space.

Source record↗
NASA NTRS2000

Intensive HST, RXTE, and ASCA Monitoring of NGC 3516: Evidence against Thermal Reprocessing

During 1998 April 1316, the bright, strongly variable Seyfert 1 galaxy NGC 3516 was monitored almost continuously with HST for 10.3 hr at ultraviolet wavelengths and 2.8 days at optical wavelengths, and simultaneous RXTE and ASCA monitoring covered the same period. The X-ray fluxes were strongly variable with the soft (0.5-2 keV) X-rays showing stronger variations (approx. 65% peak to peak) than the hard (2-10 keV) X-rays (approx. 50% peak to peak). The optical continuum showed much smaller but still highly significant variations: a slow approx. 2.5% rise followed by a faster approx. 3.5% decline. The short ultraviolet observation did not show significant variability. The soft and hard X-ray light curves were strongly correlated, with no evidence for a significant interband lag. Likewise, the optical continuum bands (3590 and 5510 A) were also strongly correlated, with no measurable lag, to 3(sigma) limits of approx. less than 0.15 day. However, the optical and X-ray light curves showed very different behavior, and no significant correlation or simple relationship could be found. These results appear difficult to reconcile with previous reports of correlations between X-ray and optical variations and of measurable lags within the optical band for some other Seyfert 1 galaxies. These results also present serious problems for "reprocessing" models in which the X-ray source heats a stratified accretion disk, which then reemits in the optical/ultraviolet : the synchronous variations within the optical would suggest that the emitting region is approx. less than 0.3 It-day across, while the lack of correlation between X-ray and optical variations would indicate, in the context of this model, that any reprocessing region must be approx. greater than 1 It-day in size. It may be possible to resolve this conflict by invoking anisotropic emission or special geometry, but the most natural explanation appears to be that the bulk of the optical luminosity is generated by some mechanism other than reprocessing.

Edelson, Rick↗
NASA NTRS1991

OSL - Orbiting Solar Laboratory: Our Window on the Sun

The Sun, the nearest star, is crucial for life on Earth and has always been an object of intense study. Indeed, many of the fundamental principles of astrophysics, which seek to understand the physical nature of the universe, have been established through study of the Sun. Magnetic activity with the Sun drives powerful events on its surface and in its atmosphere. From the the Earth, these events can be seen as active region with their sunspots and solar flares. But to observe such phenomena in detail require more finely-tuned and powerful instruments, operating in space, across a broader range of the electomagnetic spectrum, than have ever been available in the past. Earth's atmosphere has always blurred the images received by visible-light telescopes on the ground. The atmosphere also acts as a barrier to the ultraviolet, extreme ultraviolet, and x rays that are similarly emitted from the Sun. All these wavelengths need to be captured, at the same moment in time, before the complex interrelationships of solar activity can be truly understood. The Orbiting Solar Laboratory (OSL), the prime NASA solar mission for the 1990's, is uniquely designed to 'see' across the wavelengths and so observe the fine evolving details of a wide range of phenomena on the surface of the Sun. By the turn of the century, OSL will enable scientists to solve mysteries that humankind has sought to unravel for thousands of years.

Source record↗
NASA NTRS1974

Ultraviolet photometry from the orbiting astronomical observatory. XV - The strongly magnetic variable HD 215441

The Wisconsin Experiment Package on OAO-2 was used to obtain light curves of the strongly magnetic, variable Ap star HD 215441 over the wavelength range 1550 to 4250 A. This star is characterized by a lack of outstanding spectrum variability at wavelengths accessible from the ground, while undergoing UBV photometric variations of large amplitude. The observations of HD 215441 demonstrate that an Ap star need not be a striking spectrum variable at blue-visible wavelengths for its photometric variations to be controlled by opacity variations in the ultraviolet.

Leckrone, D. S.↗
NASA NTRS2010

Large-Format AlGaN PIN Photodiode Arrays for UV Images

A large-format hybridized AlGaN photodiode array with an adjustable bandwidth features stray-light control, ultralow dark-current noise to reduce cooling requirements, and much higher radiation tolerance than previous technologies. This technology reduces the size, mass, power, and cost of future ultraviolet (UV) detection instruments by using lightweight, low-voltage AlGaN detectors in a hybrid detector/multiplexer configuration. The solar-blind feature eliminates the need for additional visible light rejection and reduces the sensitivity of the system to stray light that can contaminate observations.

Aslam, Shahid↗
NASA NTRS1972

Testing to determine the vacuum-ultraviolet degradation rate of thermal control coatings

Samples of S-13G that had been exposed to the salt air environment of Cape Kennedy, Florida were irradiated with simulated solar ultraviolet radiation after various cleaning treatments. In both of the the tests conducted two of the salt air exposed samples were not cleaned, two were lightly cleaned with water and detergent (i.e. rinsed), and two were vigorously scrubbed. Several other white thermal control coatings were also irradiated. The solar absorptance values of these coatings before and as a result of the ultraviolet irradiation are reported for exposure levels up to approximately 2000 ESH.

Gilligan, J. E.↗
NASA NTRS1974

Differential transmission of sunlight on Mars - Biological implications

A euphotic zone seems to exist at about 1 cm subsurface in the Martian epilith. At this depth, visible light is still intense enough to be utilized by conceivable photosynthetic organisms; but the germicidal ultraviolet intensities at the Martian surface have been reduced to values manageable by terrestrial life. Such euphotic zone organisms would experience moderately high Martian temperatures at equatorial latitudes and can be dispersed readily during global dust storms. During such storms the Martian euphotic zone may reach the surface. The aerosol content of the Martian atmosphere can be monitored by multiband single-line scans of the sun at large zenith angles by the Viking lander camera; and the postulated euphotic zone organisms can be searched for with the Viking lander sample arm and biology experiments.

Sagan, C.↗
NASA NTRS1975

On the origin of ultraviolet constrasts on Venus

Models for the origin of the contrasts in the ultraviolet images of Venus are examined in an attempt to determine the physical differences between light and dark regions fundamental to a clear understanding of the apparent cloud motions. To evaluate the meaning of the wavelength dependence of the contrasts, an improved determination of the spherical albedo curve for Venus in the 0.225-1.06 micron range is made by fitting appropriate theoretical models to the observations of monochromatic magnitudes as a function of phase angle. It is shown that, because of differences between the spectral dependences of spherical albedo and contrasts, at least one major absorber other than the one causing the contrasts is almost certainly required. Several classes of models are compatible with present observational evidence. The contrasts and the absorption associated with them may in fact be occurring below, within or above the main visible cloud layer, and thus an unambiguous interpretation of the apparent cloud motions is not possible.

Travis, L. D.↗
NASA NTRS1979

Pressure and temperature dependence kinetics study of the NO + BrO yielding NO2 + Br reaction - Implications for stratospheric bromine photochemistry

The reactivity of NO with BrO radicals over a wide range of pressure (100-700 torr) and temperature (224-398 K) is investigated using the flash photolysis-ultraviolet absorption technique. The flash photolysis system consists of a high-pressure xenon arc light source, a reaction cell/gas filter/flash lamp combination, and a 216.5 half-meter monochromator/polychromator/spectrography for wavelength selectivity. The details of the reaction and its corresponding Arrhenius expression are identified. The results are compared with previous measurements, and atmospheric implications of the reaction are discussed. The NO + BrO yielding NO2 + Br reaction is shown to be important in controlling the concentration ratios of BrO/Br and BrO/HBr in the stratosphere, but this reaction does not affect the catalytic efficiency of BrOx in ozone destruction.

Watson, R. T.↗
NASA NTRS1982

Observations and analysis of the R Aquarii jet

Ultraviolet, optical and radio observations of the symbiotic star R Aquarii are discussed in the light of the discovery of a bright radio and optical jet from this star. The star is probably a binary with a period of 44 years. The VLA maps of the jet reveal a protruding structure extending approximately 10 arc sec from the central radio source with a position angle virtually identical to that of the optical jet observed at Lick. The observations of R Aqr are interpreted as indicating the existence of an accretion disk around an unseen companion. The hot subdwarf has effective temperature approximately 65,000 K. It is suggested that the Mira primary and the hot secondary are in orbit around each other with a high eccentricity. At periastron the hot subdwarf accretes at super critical rates and a jet forms. It is difficult to understand how an accretion disk would have eclipsed the Mira in 1928-1935 and 1974-1980. The suppression of maximum light in these two periods is interpreted as due to a distortion of the Mira envelope at periastron by the tidal interaction with the secondary. The jet may help to explain the excitation of the R Aqr nebula. It is possible that R Aqr flared up as a nova approximately 1000 years ago forming the nebula.

Kafatos, M.↗
NASA NTRS1982

Observations of RR Lyrae with the ANS satellite

Photometric observations of RR Lyr in the ultraviolet have been obtained using the Astronomical Netherlands Satellite. The observations are compared with theoretical light curves calculated using synthetic spectra and angular diameters determined as a function of phase for RR Lyr by Manduca et al. from photometry at longer wavelengths. A good agreement is found. A bump in the observed light curves in the phase range 0.6 to 0.8 supports the existence of a shock as predicted by Hutchinson, Hill, and Lillie.

Bonnell, J.↗
NASA NTRS1990

Narrow circumstellar emission lines in SN 1987A

Low and high dispersion short wavelength prime (SWP) spectra of SN 1987A show that the supernova's progenitor was in a post red giant branch stage of evolution at the time of its demise in February 1987. The development of narrow high temperature emission lines of N 5, N 4, N 3, C 3, He 2 and O 3 were followed since May 1987. Observations through April 1990 are presented. The lines are interpreted as arising in a low density gas surrounding the supernova which was photoionized by the extreme UV pulse at shock breakout. In this picture, their temporal evolution is determined primarily by light travel time effects and recombination. Comparison of models of circumstellar environment with the International Ultraviolet Explorer (IUE) observations are discussed.

Sonneborn, George↗
NASA NTRS1991

High-resolution absorption cross sections of carbon monoxide bands at 295 K between 91.7 and 100.4 nanometers

Theoretical descriptions of the abundance and excitation of carbon monoxide in interstellar clouds require accurate data on the vacuum-ultraviolet absorption spectrum of the molecule. The 6.65 m spectrometer at the Photon Factory synchrotron light source was used to measure photoabsorption cross sections of CO features between 91.2 and 100.4 nm. These data were recorded at a resolving power of 170,000, more than 20 times greater than that used in previous work.

Stark, G.↗