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Moos, H. W.

Publications and source records attributed to Moos, H. W..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

IUE spectrum of the IO torus - Identification of the 5S2-3P2,1 transition of S III

A spectrum of a much higher quality than previously available has been obtained which shows emission features arising from S(+), S(++), S(+++), and an upper limit for O(++). The well-defined splitting of the 1729 A feature is seen as confirming its tentative identification as semiforbidden S III 5S2(0)-3P2,1. The lower contamination of S III 1199 A by H I 1216 A than in most previous IUE spectra of the Io torus makes possible an estimate of the S III 1729 A collision strength. The variation of these features with temperature and their possible presence in spectra of nebulae are discussed.

Moos, H. W.↗
NASA NTRS1983

Temporal variation of the Jovian H I Lyman-alpha emission /1979-1982/

Observations of the Jovian H I Lyman-alpha emission have been made with the International Ultraviolet Explorer (IUE) observatory beginning in 1978 December, just before the time of the Voyager encounters, and extending through 1982 January. A nearly constant disk center brightness of about 8.5 kilorayleighs is observed for the central meridian longitude range lambda(III) = 200 to 360 deg and a variable brightness of between 9 and 15 kilorayleighs is found for the range lambda(III) = 50 to 150 deg. These brightness values have persisted throughout the three years of observation, and the hydrogen bulge near lambda(III) = 100 deg appears to be a fixed feature of the Jovian atmosphere. These results indicate that no substantial changes in the Jovian atomic hydrogen concentration or the average atmospheric conditions have taken place between the time immediately preceding the Voyager encounters and the present. The question of Jovian Lyman-alpha variability prior to 1978 is reexamined in the light of the IUE results.

Skinner, T. E.↗
NASA NTRS1982

Intense Ly-alpha emission from Uranus

The existence of intense atomic hydrogen Ly-alpha emission from Uranus is demonstrated here by utilizing the monochromatic imaging capabilities of the International Ultraviolet Explorer (IUE) spectrograph. Observations show increased emission in the vicinity of Uranus superimposed on the geocoronal/interplanetary background. If resonant scattering of solar Ly-alpha is the source of the 1.6 + or - 0.4 kR disk averaged brightness, then very high column densities of atomic H above the absorbing methane are required. Precipitation of trapped charged particles, i.e., aurora, could explain the emissions. This would imply a planetary magnetic field.

Durrance, S. T.↗
NASA NTRS1982

The spectrum of the Jovian Aurora 1150-1700 A

A series of observations of the northern hemisphere of Jupiter was made in January 1981 using the International Ultraviolet Explorer short-wavelength spectrograph. Exposures of 15 minutes each were made at regular intervals of about 45 minutes around the time when Jupiter's north magnetic pole was tilted toward the earth. The auroral emissions of H Lyman-alpha, and the H2 Lyman- and Werner-bands are seen to emanate from a localized region near the north pole. Their intensity increases and decreases in a periodic way as the planet rotates with the maximum occurring at lambda sub III approximately equal to 185 deg. Using the three observations nearest the observed maximum, a composite spectrum of the aurora is obtained with about 8 A resolution and high signal-to-noise ratio, and many of the H2 Lyman- and Werner-bands in this spectral region (1150-1700 A) are identified. This spectrum is compared with a laboratory H2 spectrum and with photoabsorption cross sections for CH4 and C2H6. An upper limit to the slant column density of these hydrocarbons above the auroral emissions is found to be approximately 2 x 10 to the 17th/sq cm.

Durrance, S. T.↗
NASA NTRS1982

The far-ultraviolet spectra and geometric albedos of Jupiter and Saturn

Spectra and geometric albedoes in the range 1200 to 1940 A are compiled for Jupiter and Saturn on the basis of IUE observations. The spectra of both planets are dominated by H Lyman-alpha emission line at 1216 A, although absorption bands of C2H2 are apparent at longer wavelengths, particularly in the spectrum of Saturn, and the C I line at 1657 A is also observed. Geometric albedoes show emission features corresponding to the weak H2 Lyman and Werner bands around 1230-1280 A, auroral Lyman band emission, C I emission, and C2H2 absorption from 1600 to 1900 A. A model of atmospheric absorption in homogeneously mixed atmospheres of H2 and trace molecular absorbers is then presented and fit to the Jupiter albedo, resulting in a predicted atmosphere containing C2H2 and an unidentified molecular or particulate absorber. Finally, north-south maps of Jupiter continuum emission show limb darkening, and a comparison of equatorial and polar spectra indicates a polar increase in C2H2 absorption and weaker polar H2 emissions than previously reported.

Clarke, J. T.↗
NASA NTRS1982

A photon-counting photodiode array detector for far ultraviolet (FUV) astronomy

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location.

Hartig, G. F.↗
NASA NTRS1982

IUE observations of the Jovian HI Lyman alpha emission (1979 - 1982)

Observations of the Jovian H ion Lyman emission made with the IUE observatory beginning in December 1978 just before the time of the Voyager encounters and extending through January 1982 are presented. A constant disk center brightness of about 8 kR is observed for the central meridian longitude range wavelength III approximately equal 200 deg to 360 deg and a variable brightness 9-15 kR is found for the range lambda III approximately 50 deg to 150 deg. These brightness values persisted throughout the three years of observation. The hydrogen bulge near wavelength III approximately equal 100 deg appears to be a permanent feature of the Jovian atmosphere, and no long term change of the planetary Lyman emission is seen. Since the early IUE observations were made near the two Voyager encounters, this indicates that no substantial changes in the atomic hydrogen concentration or the average atmospheric conditions took place between then and now.

Skinner, T. E.↗
NASA NTRS1982

Ultraviolet spectroscopy of the Jovian and Saturnian auroras

The results of a series of IUE observations of the north polar aurora obtained during a substantial fraction of one complete rotation of Jupiter are presented. From these data a spectrum of the aurora with high signal to noise ratio, and a resolution of about 8 A was obtained, making possible the identification of many H2 Lyman and Werner bands. The spectrum is of sufficient quality to provide reliable quantative data for a comparison with the model atmosphere calculations. The lack of an observable absorption signature makes it possible to set an upper limit on the column density of CH4 and C2H6 above the auroral emissions and hence an upper limit on the primary particle energies. A comparison of this spectrum with a laboratory spectrum of discharge excited H2 shows a remarkable similarity. The results of several IUE observations of the full disk of Saturn are also examined. The exposures were of approximately 2 hours each, and the H2 Lyman and Werner bands were observed near the north pole in two of them.

Durrance, S. T.↗
NASA NTRS1982

Photon counting photodiode array detector for far ultraviolet (FUV) astronomy

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location. Previously announced in STAR as N82-19118

Hartig, G. F.↗
NASA NTRS1981

Far-ultraviolet fluorescence of carbon monoxide in the red giant Arcturus

Evidence is presented that many of the weak features observed with International Ultraviolet Explorer (IUE) in the far-ultraviolet (1150-2000 A) spectrum of the archetype red giant Arcturus (K2 III) are A-X fourth positive bands of carbon monoxide excited by chromospheric emissions of O I, C I, and H I. The appearance of fluorescent CO bands near the wavelength of commonly used indicators of high-temperature (T greater than 20,000 K) plasma, such as C II at wavelength 1335 and C IV at wavelength 1548, introduces a serious ambiguity in diagnosing the presence of hot material in the outer atmospheres of the cool giants by means of low-dispersion IUE spectra.

Ayres, T. R.↗
NASA NTRS1981

Ultraviolet observations of the Io torus from the IUE observatory

The short wavelength spectrograph on the International Ultraviolet Explorer (IUE) has been used to obtain 11 A resolution spectra of the Io torus from 1175-1950 A. The four spectra, obtained in the springs of 1979 and 1980, show emissions (about 40R) of S II A1256A and S III A1199A. An unidentified feature is also present at 1729 A; a tentative identification as an intercombination line of S III is proposed. Weak features, probably due to O III A1664A and S IV A1406A, appear in some of the spectra. Abundances of the ions are determined from the brightnesses of the observed features. Upper limits are also set for the abundances of a number of ionic and neutral species. An observation of Io itself does not show any additional or enhanced spectral features, permitting upper limits to be set on the injection rate for a number of species.

Moos, H. W.↗
NASA NTRS1981

IUE monitoring of the spatial distribution of the H Ly-alpha emission from Jupiter

North-south spatial maps of the Jovian H Lyman-alpha emission observed with the IUE satellite support the identification of a marked longitudinal asymmetry in the equatorial brightness, with the peak around lambda III(1965) = 50-100 deg longitude, and show a weaker planet-wide equatorial brightening above the level predicted by a plane-parallel layer model. IUE observations made 18 months after the initial discovery of the localized emission bulge establish that it is fixed with respect to Jupiter's magnetic longitude (lambda III system) and not with respect to atmospheric longitude (lambda II system). In addition, a decrease in brightness of 20% in the region of the emission bulge has been observed over a one yr interval, while the rest of the planet remained roughly constant in brightness. This decrease is more than would be expected as a result of changes in the incident solar Lyman-alpha flux, indicating a real decrease in reflectivity in this region of Jupiter's upper atmosphere.

Clarke, J. T.↗
NASA NTRS1981

IUE detection of bursts of H Ly-alpha emission from Saturn

A new investigation is reported of the potential sources of Ly-alpha emission in a series of observations of the Saturnian system carried out between January and July 1980 using the short wavelength spectrograph of the IUE Observatory. It is noted that north-south maps of the Ly-alpha emission across the planet disk show pronounced spatial asymmetries in emission brightness. These asymmetries vary to a marked extent on a time scale of days and are interpreted as bursts of Ly-alpha emission of as much as 1 kR brightness averaged over a 6 x 10 arcsec area, above a constant planetary emission level of 700-800 R. In fact, the Ly-alpha emission peaks manifest themselves as essentially point source features in these data; it is pointed out that if the emitting region is smaller than the 6 x 10 arcsec instrumental resolution, the surface brightness must be proportionally higher.

Clarke, J. T.↗
NASA NTRS1981

Spatial imaging of UV emission from Jupiter and Saturn

Spatial imaging with the IUE is accomplished both by moving one of the apertures in a series of exposures and within the large aperture in a single exposure. The image of the field of view subtended by the large aperture is focussed directly onto the detector camera face at each wavelength; since the spatial resolution of the instrument is 5 to 6 arc sec and the aperture extends 23.0 by 10.3 arc sec, imaging both parallel and perpendicular to dispersion is possible in a single exposure. The correction for the sensitivity variation along the slit at 1216 A is obtained from exposures of diffuse geocoronal H Ly alpha emission. The relative size of the aperture superimposed on the apparent discs of Jupiter and Saturn in typical observation is illustrated. By moving the planet image 10 to 20 arc sec along the major axis of the aperture (which is constrained to point roughly north-south) maps of the discs of these planets are obtained with 6 arc sec spatial resolution.

Clarke, J. T.↗
NASA NTRS1981

Observations of polar aurora on Jupiter

North-south spatial maps of Jupiter were obtained with the SWP camera in IUE observations of 10 December 1978, 19 May 1979, and 7 June 1979. Bright auroral emissions were detected from the north and south polar regions at H Ly alpha (1216 A) and in the H2 Lyman bands (1250-1608 A) on 19 May 1979; yet no enhanced polar emission was detected on the other days. The relationship between the IUE observing geometry and the geometry of the Jovian magnetosphere is discussed.

Lane, A. L.↗
NASA NTRS1981

Observations of the Io plasma torus

The short wavelength spectrography on the IUE satellite was used to obtain spectra of the plasma torus near the orbit of Io about Jupiter. Three exposures of about 8 hours each taken in March and May 1979 show emission features due to SII, SIII, and OIII. The absence of features at other wavelengths permits upper limits to be other species in the torus.

Lane, A. L.↗
NASA NTRS1981

Extracting spatial information from large aperture exposures of diffuse sources

The spatial properties of large aperture exposures of diffuse emission can be used both to investigate spatial variations in the emission and to filter out camera noise in exposures of weak emission sources. Spatial imaging can be accomplished both parallel and perpendicular to dispersion with a resolution of 5-6 arc sec, and a narrow median filter running perpendicular to dispersion across a diffuse image selectively filters out point source features, such as reseaux marks and fast particle hits. Spatial information derived from observations of solar system objects is presented.

Clarke, J. T.↗