Search NASA⌕ Search

SEARCH · Search NASA

Results for “ULTRAVIOLET DETECTION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
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 NTRS2013

On Inferring Extinction Laws in Z -approximately 6 Quasars as Signatures of Supernova Dust

Unusual extinction curves of high-redshift QSOs have been taken as evidence that dust is primarily produced by supernovae at high redshift. In particular, the 3000 ˚A Todini-Ferrara-Maiolino kink in the extinction curve of the z = 6.20 SDSS J1048+4637 has been attributed to supernova dust. Here we discuss the challenges in inferring robust extinction curves of high-redshift QSOs and critically assess previous claims of detection of supernova dust. In particular, we address the sensitivity to the choice of intrinsic QSO spectrum, the need for a long wavelength baseline, and the drawbacks in fitting theoretical extinction curves. In a sample of 21 QSOs at z ∼ 6 we detect significant ultraviolet extinction using existing broad-band optical, near-infrared, and Spitzer photometry. The median extinction curve is consistent with a Small Magellanic Cloud curve with A1450 ∼ 0.7 mag and does not exhibit any conspicuous (restframe) 2175 ˚A or 3000 ˚A features. For two QSOs, SDSS J1044−0125 at z = 5.78 and SDSS J1030+0524 at z = 6.31, we further present X-shooter spectra covering the wavelength range 0.9-2.5 μm. The resulting non-parametric extinction curves do not exhibit the 3000 ˚A kink. Finally, in a re-analysis of literature spectra of SDSS J1048+4637, we do not find evidence for a conspicuous kink. We conclude that the existing evidence for a 3000 ˚A feature is weak and that the overall dust properties at high and low redshift show no significant differences. This, however, does not preclude supernovae from dominating the dust budget at high redshift.

Extinction↗
NASA NTRS2019

The Young Age of the LAMP-Observed Frost in Lunar Polar Cold Traps

The Lunar Reconnaissance Orbiter/Lyman Alpha Mapping Project (LAMP) ultraviolet instrument detected a 0.5–2% icy regolith mix on the floor of some of the southern pole permanently shadowed craters of the Moon. We present calculations indicating that most or all of this icy regolith detected by LAMP (sensed to a depth of <1 μm) has to be relatively young—less than 2,000 years old—due to the surface erosional loss by plasma sputtering (external ionized gas‐surface interactions), meteoric impact vaporization, and meteoric impact ejection. These processes, especially meteoric impact ejection, will disperse water along the crater floor, even onto warm regions where it will then undergo desorption. We have determined that there should be a water exosphere over polar craters (e.g., like Haworth crater) and calculated that a model 40‐km‐diameter crater should emit ~10(exp 19) H2O per second into the exosphere in the form of free molecules and ice‐embedded particulates.

Farrell, W. M.↗
NASA NTRS1997

Evidence for a New Class of Extreme Ultraviolet Sources

Most of the sources detected in the extreme ultraviolet (EUV; 100-600 A) by the ROSAT/WFC and EUVE all-sky surveys have been identified with active late-type stars and hot white dwarfs that are near enough to the Earth to escape absorption by interstellar gas. However, about 15 per cent of EUV sources are as yet unidentified with any optical counterparts. We examine whether the unidentified EUV sources may consist of the same population of late-type stars and white dwarfs. We present B and R photometry of stars in the fields of seven of the unidentified EUV sources. We detect in the optical the entire main-sequence and white dwarf population out to the greatest distances where they could still avoid absorption. We use color-magnitude diagrams to demonstrate that, in most of the fields, none of the observed stars has the colours and magnitudes of late-type dwarfs at distances less than 100 pc. Similarly, none of the observed stars is a white dwarf within 500 pc that is hot enough to be a EUV emitter. The unidentified EUV sources we study are not detected in X-rays, while cataclysmic variables, X-ray binaries, and active galactic nuclei generally are. We conclude that some of the EUV sources may be a new class of nearby objects, which are either very faint at optical bands or which mimic the colours and magnitudes of distant late-type stars or cool white dwarfs. One candidate for optically faint objects is isolated old neutron stars, slowly accreting interstellar matter. Such neutron stars are expected to be abundant in the Galaxy, and have not been unambiguously detected.

Maoz, Dan↗
NASA NTRS2014

The Broad-Lined Type Ic SN 2012ap and the Nature of Relativistic Supernovae Lacking a Gamma-Ray Burst Detection

We present ultraviolet, optical, and near-infrared observations of SN2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from −13 to +272 days past the B-band maximum of −17.4 +/- 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of v approx. 20,000 km s(exp. −1) that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (v approx. greater than 27,000 km s(exp. −1)). We use these observations to estimate explosion properties and derive a total ejecta mass of 2.7 Solar mass, a kinetic energy of 1.0×1052 erg, and a (56)Ni mass of 0.1−0.2 Solar mass. Nebular spectra (t > 200 d) exhibit an asymmetric double-peaked [O I] lambda lambda 6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN2012ap joins SN2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black-hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable properties including above-average environmental metallicities of Z approx. greater than Solar Z, moderate to high levels of host-galaxy extinction (E(B −V ) > 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] > 1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae.

nature↗
NASA NTRS1981

Ozone flow visualization techniques

Flow visualization techniques using ozone for tracing gas flows are proposed whereby ozone is detected through its strong absorption of ultraviolet light, which is easily made visible with fluorescent materials, or through its reaction with nitric oxide to form excited nitrogen dioxide, which in relaxing emits detectable light. It is shown that response speeds in the kHz range are possible with an ultraviolet detection system for initial ozone concentrations of about 1%.

Dickerson, R. R.↗
NASA NTRS1980

The detection of a companion star to the Cepheid variable Eta Aquilae

Ultraviolet spectra have been obtained with IUE of the classical Cepheid Eta Aquilae at several phases in the 7.18 day period. Significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1600 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the nonvariable emission is consistent with the flux expected from a main-sequence companion star with an effective temperature of about 9500 K (A0 V). The observed ultraviolet flux and spectral type are used to compute a distance of 300 pc to the system, in agreement with the distance predicted using the period luminosity relation.

Mariska, J. T.↗
NASA NTRS2010

AlGaN Ultraviolet Detectors for Dual-Band UV Detection

This innovation comprises technology that has the ability to measure at least two ultraviolet (UV) bands using one detector without relying on any external optical filters. This allows users to build a miniature UVA and UVB monitor, as well as to develop compact, multicolor imaging technologies for flame temperature sensing, air-quality control, and terrestrial/counter-camouflage/biosensing applications.

Miko, Laddawan↗
NASA NTRS1981

The detection of companion stars to the Cepheid variables ETA Aquilae and T Monocerotis

Ultraviolet spectra of the classical Cepheid variables eta Aq1 and T Mon at several phases in their periods were obtained with IUE. For eta Aq1 significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1600 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the nonvariable emission is consistent with the flux expected from a main sequence companion star with an effective temperature of about 9500 K (AO V - A1 V). For T Mon a nonvarying component to the ultraviolet emission is observed for wavelengths less than 2600 A. Comparison with model atmosphere flux distributions suggests that the companion has an effective temperature of around 10,000 K (AO) and is near the main sequence.

Mariska, J. T.↗
NASA NTRS1988

The interstellar light echoes around SN 1987A

The observed light echoes around SN 1987A are modeled by dust in planar clouds roughly 120 and 330 pc in front of the supernova. The expected echo profiles depend on the observed light curve and on the cloud thicknesses. The surface brightness and colors of the echoes are modeled using a mix of silicate and graphite grains appropriate to the Large Magellanic Cloud (LMC). The model colors approximately agree with the observed ones. The observed surface brightness suggests that the dust column density in the echo clouds is comparable to the total dust column density in the LMC toward SN 1987A. The model predicts the presence of a narrow ultraviolet echo outside the visual echo; it should be detectable with future ultraviolet observatories and will give information on the supernova near the phase of shock breakout.

Chevalier, Roger A.↗
NASA NTRS1966

Sensor detects hydrocarbon oil contaminants in fluid lines

Sensor with ultraviolet light monitors and detects hydrocarbon oil contaminants present in fluid lines. The light causes the oil particles to fluoresce. This light emitted by the oil particle is detected by a photocell which is relatively insensitive to ultraviolet radiation.

Roth, B.↗
NASA NTRS1983

The ultraviolet spectra of three N-type carbon stars

The paper reports the successful detection of the ultraviolet spectra of three N-type carbon stars: BL Ori, TX Psc, and T Ind. Exposures of approximately 2-3 hours with the LWR camera of the IUE Satellite at low dispersion were necessary to record the ultraviolet flux. The shortward extension of the photospheric continuum is well exposed down to about 2800 A, with strong molecular and atomic absorption features. The spectrum appears not to be seriously affected by the unknown opacity source which blankets N stars (especially redder ones) in the violet. Emission lines of Mg II (h and k) and C II (2325 A) are conspicuous, indicating the presence of chromospheres in the stars. The ratios of integrated fluxes in the Mg II lines and C II lines to bolometric flux are respectively much smaller and slightly smaller than values observed in oxygen-rich M giants and supergiants.

Johnson, H. R.↗
NASA NTRS2003

Computed Tomography Imaging Spectrometer (CTIS) with 2D Reflective Grating for Ultraviolet to Long-Wave Infrared Detection Especially Useful for Surveying Transient Events

The optical system of this invention is an unique type of imaging spectrometer, i.e. an instrument that can determine the spectra of all points in a two-dimensional scene. The general type of imaging spectrometer under which this invention falls has been termed a computed-tomography imaging spectrometer (CTIS). CTIS's have the ability to perform spectral imaging of scenes containing rapidly moving objects or evolving features, hereafter referred to as transient scenes. This invention, a reflective CTIS with an unique two-dimensional reflective grating, can operate in any wavelength band from the ultraviolet through long-wave infrared. Although this spectrometer is especially useful for events it is also for investigation of some slow moving phenomena as in the life sciences.

Daniel W Wilson↗
NASA NTRS2003

Computed tomography imaging spectrometer (CTIS) with 2D reflective grating for ultraviolet to long-wave infrared detection especially useful for surveying transient events

The optical system of this invention is an unique type of imaging spectrometer, i.e. an instrument that can determine the spectra of all points in a two-dimensional scene. The general type of imaging spectrometer under which this invention falls has been termed a computed-tomography imaging spectrometer (CTIS). CTIS's have the ability to perform spectral imaging of scenes containing rapidly moving objects or evolving features, hereafter referred to as transient scenes. This invention, a reflective CTIS with an unique two-dimensional reflective grating, can operate in any wavelength band from the ultraviolet through long-wave infrared. Although this spectrometer is especially useful for rapidly occurring events it is also useful for investigation of some slow moving phenomena as in the life sciences.

Wilson, Daniel W.↗
NASA NTRS1984

Line identifications in the ultraviolet (2590-3230 A) spectrum of the hydrogen-deficient carbon star HD 182040

Identifications for absorption features detected in the ultraviolet spectrum of the hydrogen-deficient supergiant carbon star HD 182040 observed at high resolution with the IUE satellite are presented. The spectrum in this range is filled with blended lines of the iron-peak elements, with Fe I and Cr II dominating the spectrum. Spectra definitely and probably detected are given, as well as those searched for and not detected. In the investigated range, the spectrum resembles that of a middle-G supergiant. The absorption-line spectrum is similar to the spectra of the sun and other late-type stars, but neutral metal lines are weaker than in K and M giants. The level of ionization is significantly higher than in the sun, Zeta Cap, and Epsilon Gem.

Johnson, H. R.↗
NASA NTRS1997

IUE's View of Callisto: Detection of an SO2 Absorption Correlated to Possible Torus Neutral Wind Alterations

Observations taken with the International Ultraviolet Explorer (IUE) detected a 0.28 micron absorption feature on Callisto's leading and Jupiter-facing hemispheres. This feature is similar to Europa's 0.28 micron feature, however it shows no correlation with magnetospheric ion bombardment. The strongest 0.28 micron signature is seen in the region containing the Valhalla impact. This absorption feature also shows some spatial correlation to possible neutral wind interactions, suggestive of S implantation (rather than S(sub x)) into Callisto's water ice surface, Indications of possible temporal variations (on the 10% level) are seen at other wavelengths between the 1984-1986 and the 1996 observations.

Lane, Arthur L.↗