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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

A survey of interstellar C I - Insights on carbon abundances, UV grain albedos, and pressures in the interstellar medium

Interstellar atomic carbon has been sampled over 33 different paths with visual extinctions ranging from about 0.15 to 1.5 mag. The trend of C I vs different forms of hydrogen is found to be steep and somewhat erratic. It is concluded that the observed behavior can be explained by strong differences in the responses of C I, H I, and H2 equilibria to physical conditions, together with marked variations of these conditions within different interstellar clouds.

Jenkins, E. B.↗
NASA NTRS1979

Upper limits on argon isotope abundances in the Venus thermosphere

On December 9, 1978 the neutral gas mass spectrometer aboard the NASA Pioneer Venus multiprobe bus has measured density, composition, and temperature of the Venus dayside thermosphere. There was no positive identification of argon down to the lowest measuring altitude of 130 km. For the altitude level of 135 km the following upper limits for the number densities of argon isotopes were derived: n(Ar-36) less than 1.3 times 10 to the 6th power per cu cm and n(Ar-40) less than 2.8 times 10 to the 6th power per cu cm. From our upper atmosphere observations we infer for the troposphere of Venus the following upper limits for the mixing ratios: n(Ar-36)/total number density less than 9 times 10 to the minus 6th power and n(Ar-40)/total number density less than 20 times 10 to the minus 6th power.

Mauersberger, K.↗
NASA NTRS1979

New observations of interstellar abundances and depletions of boron, vanadium, chromium, and cobalt

New observations of interstellar lines of boron, vanadium, chromium, and cobalt in the spectra of Zeta Oph and Xi Per have been obtained with the Copernicus satellite. Chromium has been detected for the first time toward a reddened star, and cobalt has been seen for the first time in any interstellar line of sight. New limits have been obtained for boron and vanadium. These new data, along with limits on scandium and other species from the literature, have been compared with models for the depletion process. No fully conclusive test of depletion models is yet possible, but the new data on boron appear to favor the hypothesis that the depletions are dominated by accretion of gas-phase particles onto grains, rather than being due to grain condensation under pressure equilibrium. The impact of these new data on the study of grain surface properties is described.

Snow, T. P., Jr.↗
NASA NTRS1980

Elemental abundances in a Type I supernova remnant

The solid-state spectrometer (SSS) on the HEAO 2 (Einstein) X-ray observatory observed the X-ray spectrum of Tycho's SNR. The observations show a relative excess of line emission from Si, S, and Ar by not less than 6 compared to that expected from a plasma of solar composition in collisional equilibrium and by a factor of not less than 3 compared to Cas A. Similar excesses are not found for line emission from Mg and Fe. The data suggest that the SN observed by Tycho in 1572 produced significant amounts of Si group elements but did not eject large amounts of Fe as predicted by some models of Type I SN events.

Becker, R. H.↗
NASA NTRS1979

A measurement of the cosmic-ray source abundance of Ca-40

The measured charge composition of the galactic cosmic rays from Ar to Ni and the isotopic composition of the elements Ca and Sc are presented. It is found that the ratio Ca-40/Fe at the cosmic-ray source is (5.9 plus or minus 1.9)%. This result is in good agreement with the meteoritic value (6.8 plus or minus 1.0)%.

Tarle, G.↗
NASA NTRS1980

The helium abundance of Jupiter from Voyager

Full disk measurements recorded 31 days before the Voyager 1 encounter with Jupiter by the radiometer of the infrared instrument, IRIS, indicate a geometric albedo of 0.274 + or - 0.013. Combining this measurement with the Pioneer derived phase integral of 1.25 and our error estimate of 0.1 yields a Jovian Bond albedo of 0.343 + or - 0.032. Infrared spectra recorded at the same time by the Michelson interferometer, along with a model extrapolation to low wave numbers not covered by the instrument, yield a thermal emission of (1.359 + or - 0.014) .001 W cm to the (-2) power. As in the case of the albedo measurement, the quoted errors in the emission measurement reflect estimates of systematic effects and are uncertain while the random component is negligible. From these measurements the internal heat flux of Jupiter is estimated to be (5.444 + or - 0.425) .0001 W cm to the (-2) power, and the energy balance defined as the ratio of emitted thermal to absorbed solar energy is 1.668 + or - 0.085.

Gautier, D.↗
NASA NTRS1980

Some isotopic abundances in the cosmic radiation

Cosmic ray nuclei with Z not less than 10 have been observed in a detector which measures charge with a double scintillator-Cherenkov array and mass by combining the Cherenkov signal with residual range measured in nuclear emulsions. Results are presented for the isotopic analyses of Al, Ca, Sc, Mn, Fe, Co, Ni and Cu in the energy range 300-800 MeV/amu.

Young, J. S.↗
NASA NTRS1980

Abundance ratios of He-4/2+//He-3/2+/ in the solar wind

The ion composition experiment aboard the Isee 3 spacecraft has been used to measure the He-4(2+)/He-3(2+) ratio in the solar wind. Using 4334 observations made between Aug. 18 and Nov. 24, 1978, and March 24 and Aug. 25, 1979, the average ratio He-4(2+)/He-3(2+) was 2.1 + or - 0.2 x 1000, in agreement with previous foil measurements. Individual observations vary widely from the average and the low He-4(2+)/He-3(2+) ratios occur at times of low He-4(2+) flux.

Ogilvie, K. W.↗
NASA NTRS1980

Abundances and excitation of interstellar methyl formate

The detection of methyl formate (HCOOCH3) in four transitions toward Orion KL, in two transitions toward Sagitarrius B2, and in one transition toward W51 is reported. The column densities of HCOOCH3 are found to be surprisingly large (2-5 x 10 to the 14th per sq cm) in all three clouds. Stimulated emission in the 18 cm K doublet of HCOOCH3 toward Sagittarius B2 is clearly demonstrated. The relatively large column densities of HCOOCH3 in clouds outside the galactic-center region probably imply that this molecule is widely distributed in the galaxy, but the negative results in other clouds require lower column densities than in Orion by a factor of 0.5 or less. Two unidentified lines were detected in Orion, at approx. 91 and 99 GHz.

Churchwell, E.↗
NASA NTRS1980

The abundance of CO in diffuse interstellar clouds - An ultraviolet survey

CO was detected in 17 directions and its upper limits were estimated in 21 directions by a UV survey carried out with the Copernicus satellite in the C-X 1088 A and E-X 1076 A lines toward 48 bright stars. The CO column densities range from 10 to the 12th to 10 to the 17th/sq cm and correlate with C I and H2. The tendency of the C I/CO ratio to be about 10 follows the ratio of particular atomic and molecular cross-sections and the physical parameters of interstellar clouds. Finally, the connection between UV observations in diffuse clouds and radio observations of (C-13)O in dark clouds is discussed.

Federman, S. R.↗
NASA NTRS1981

EUV flux variations during solar cycle 21 from AE-E He/+/ abundances

The ionization rate of helium in the thermosphere is inferred from AE-E ion and neutral particle composition measurements, made on several days during solar cycle 21, in the context of a steady state photochemical model for helium ions. The inferred ionization rate varies by a factor of 4 between July 1976 and January 1979, a value consistent with the variation in the flux measured during the same period by the EUV spectrometer on board the AE-E satellite.

Oppenheimer, M.↗