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Results for “ULTRAVIOLET SPECTRA”

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Ultraviolet stellar spectra obtained with Skylab Experiment S019

Ultraviolet stellar spectra in the wavelength region from 130 to 500 nm were photographed during the three manned Skylab missions using a 15-cm-aperture objective-prism telescope mounted on the antisolar scientific airlock. Data at wavelengths of 200 nm or shorter were obtained for 1400 stars in 166 fields. Approximately 300 stars show absorption lines of Si IV, C IV, or C II in which the strengths and profiles show striking variations with stellar temperature and luminosity. Numerous weak lines are also observed in supergiant stars, shell stars, peculiar A stars, and Wolf-Rayet stars. Observations of comet Kohoutek show interesting variations in the strength of the OH 3090 A band.

Henize, K. G.↗
NASA NTRS1998

Detailed Mid- and Far- Ultraviolet Model Spectra for Accretion Disks in Cataclysmic Binaries

We present a large grid of computed far- and mid-ultraviolet spectra (850-2000 A) of the integrated light from steady-state accretion disks in luminous cataclysmic variables. The spectra are tabulated at 0.25 A intervals with an adopted FWHM resolution of 1.0 A, so they are suitable for use with observed spectra from a variety of modern space-borne observatories. Twenty-six different combinations of white dwarf mass M(sub wd) and mass accretion rate dot-m are considered, and spectra are presented for six different disk inclinations i. The disk models are computed self-consistently in the plane-parallel approximation, assuming LTE and vertical hydrostatic equilibrium, by solving simultaneously the radiative transfer, hydrostatic equilibrium, and energy balance equations. Irradiation from external sources is neglected. Local spectra of disk annuli are computed taking into account line transitions from elements 1-28 (H through Ni). Limb darkening as well as Doppler broadening and blending of lines are taken into account in computing the integrated disk spectra. The radiative properties of the models are discussed, including the dependence of ultraviolet fluxes and colors on M(sub wd), dot-m, and i. The appearance of the disk spectra is illustrated, with regard to changes in the same three parameters. Finally, possible future improvements to the present models and spectra are discussed.

Wade, Richard A.↗
NASA NTRS1983

Ultraviolet absorption spectra of FNO3 and HOF

Ultraviolet absorption cross sections of gas phase FNO3 and HOF have been measured over the wavelength range 180 to 400 nm at 295 K. The maximum photolysis lifetime for FNO3 in the stratosphere is calculated to be in the order of days, and for HOF in the order of hours.

Elliott, S.↗
NASA NTRS1992

The composite nature of the peculiar star HR 6560 (HD 159870)

Ground-based high-dispersion photographic spectra and ultraviolet spectra obtained with the IUE satellite are described and employed to determine the nature of the peculiar star HR 6560 (HD 159870). Previously this object had been described as both a composite system and as a strong Fm star. The UBVRI, Stromgren, and ultraviolet colors of HR 6560 are compared with objects classified composite from the Bright Star Catalogue and normal dwarfs and giants. The colors of HR 6560 are not unusual for a composite and are consistent with a late-A dwarf, combined with a late-G or early-K giant. The ultraviolet satellite clearly shows the presence of an A component, but its precise spectral type is difficult to assign. The IUE and TD-1 data suggest that the ultraviolet is dominated by light from an A5 V secondary and the visual from a GO III primary. This does not agree well with the most plausible model that fits the visual photometry. The peculiar nature of HR 6560's spectrum is most likely due to its composite nature.

Wegner, Gary↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - Cool stars with hot secondaries

A hot companion to the G5 III star HR 3080, a single-line spectroscopic binary, has been discovered from spectra in the vacuum-ultraviolet. The companion must be a subdwarf or pre-white dwarf. A list of previously known systems of the zeta Aur and VV Cep type observed with the ultraviolet spectrograph on Skylab is also given.

Parsons, S. B.↗
NASA NTRS1992

Spherically symmetric, expanding, non-LTE model atmospheres for novae during their early stages

In the continuum and line-blanketed models presented here, nova atmospheres are characterized by a very slow decrease of density with increasing radius. This feature leads to very large geometrical extensions so that there are large temperature differences between the inner and outer parts of the line-forming regions. The theoretical spectra show a large IR excess and a small Balmer jump which may be either in absorption or in emission. For the parameters considered (effective temperature of about 10 exp 4 K, L = 2 x 10 exp 4 solar luminosities, outer boundary density of about 3 x 10 exp -15 g cm exp -3, mass-loss rate of 10 exp -5 solar masses/yr), most lines are in absorption. The effects of changes in the abundances of the heavy elements on the emergent spectra are discussed. The strong unidentified features observed in ultraviolet spectra of novae are found in actuality to be regions of transparency within the Fe 'forest'. Ultraviolet spectra obtained from the IUE archives are displayed, and spectral synthesis of these spectra is done using the theoretical atmospheres.

Hauschildt, P. H.↗
NASA NTRS1978

Extreme ultraviolet composite spectra of representative solar features

The spectral identifications and absolute intensities of lines in the EUV spectrum for various solar features, such as the quiet sun, active regions, coronal holes, and the off-limb corona, are presented and discussed. Composite spectra have been assembled and processed from the ATM ultraviolet spectrometer data with a spectral resolution of 1.6 A over the range 280-1350 A. These spectra represent a self-consistent set of observations with good photometric calibration, in which intercomparison of intensities from different regions is used to assist in line identifications and to draw general conclusions on average physical conditions in the solar atmosphere. The quiet-sun line intensities obtained near solar minimum are compared with OSO 6 results near solar maximum to provide an estimate for the changes over the solar cycle.

Vernazza, J. E.↗
NASA NTRS1972

The human, primate and rabbit ultraviolet action spectra

A 5000 watt xenon-mercury high pressure lamp was used to produce a continuous ultraviolet spectrum. Human and animal exposures were made to establish the photokeratitis threshold and abiotic action spectrum. The lower limit of the abiotic action spectrum was 220 nm while the upper limit was 310 nm. The radiant exposure threshold at 270 nm was 0.005 watts/sq cm for the rabbit, 0.004 watts/sq cm for the primate, and 0.004 watts/ sq cm for the human. The rabbit curve was bi-peaked with minimums at 220 nm, 240 nm and 270 nm. The primate curve was tri-peaked with minimums at 220 nm, 240 nm and 270 nm. The human data showed a rather shallow curve with a minimum at 270 nm. Formulas and calculations are given to predict minimum exposure times for ocular damage to man in outer space, to establish valid safety criteria, and to establish protective design criteria.

Pitts, D. G.↗
NASA NTRS2003

Characterizing the Oxidizing Properties of Mars' Polar Regions

We investigate the oxidizing properties of Mars polar regions using disk-resolved ultraviolet spectra from the Ultraviolet Spectrometer (UVS) on Mariner 9. We detect the spectral characteristic of hydrogen peroxide (H2O2), which has already been found to exist on the icy galilean satellites. The Mariner 9 UVS data have been archived at NASA s Planetary Data System (PDS) Atmospheric Node and are also available at http://lasp.colorado.edu/Mariner_9_data/. A software visualization tool, Albatross, provides database access (http://lasp.colorado.edu/albatross/) and enables the user to view reflectance spectra for desired latitude/longitude regions and mission phases. It displays the UVS field-of-view (FOV) tracks along with the corresponding reflectance spectrum for a chosen FOV against a background showing the Mars surface image, or a user specified alternate dataset, such as a thermal, geologic or topographic map.

A R Hendrix↗
NASA NTRS1976

A study of meteor spectroscopy and physics from earth-orbit: A preliminary survey into ultraviolet meteor spectra

Preliminary data required to extrapolate available meteor physics information (obtained in the photographic, visual and near ultraviolet spectral regions) into the middle and far ultraviolet are presented. Wavelength tables, telluric attenuation factors, meteor rates, and telluric airglow data are summarized in the context of near-earth observation vehicle parameters using moderate to low spectral resolution instrumentation. Considerable attenuation is given to the problem of meteor excitation temperatures since these are required to predict the strength of UV features. Relative line intensities are computed for an assumed chondritic composition. Features of greatest predicted intensities, the major problems in meteor physics, detectability of UV meteor events, complications of spacecraft motion, and UV instrumentation options are summarized.

Meisel, D. D.↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - Emission lines from the Beta Lyrae system

Observations of Beta Lyr with the Skylab S-019 ultraviolet objective-prism spectrograph show numerous emission lines in the region from 1400 to 2300 A. Some variations in line strength between phases 0.25 and 0.50 are seen, which probably explain the shallowness of the OAO-2 light curve at 1910 A. Many of the emission lines are probably due to intercombination transitions, thus confirming the concept that the emission is produced by collisional excitation in low-density clouds of hot gas.

Kondo, Y.↗