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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Neutral hydrogen in cometary comas.

The strong L alpha radiation observed recently in comets Tago-Sato-Kosaka and Bennett can be explained in terms of the resonant scattering of solar L alpha radiation on neutral hydrogen formed by the photodissociation of H2O which is vaporized from a nucleus having an ice core. A complete hydrodynamic description of an atmosphere composed of H2O and its daughter products OH, H and O coupled through frictional interaction as well as production and loss processes is given. Numerical results are computed in a typical case, and it is found that a temperature of about 3000 K for the cometary atmosphere provides the best fit with observation.

Mendis, D. A.↗
NASA NTRS1974

Cometary coma ions

For comets whose nuclei are composed of water ice conglomerates it is shown that the ion H3O(+) can predominate to distances of 5000 km in the subsolar direction. Beyond this distance H2O(+) is the most important ion. The crossover point is a sensitive function of the rate of evaporation from the nucleus. The presence of ammonia or metals such as sodium, in concentrations greater than 0.1% H2O, can lead to NH4(+) and Na(+) ions.

Aikin, A. C.↗
NASA NTRS1974

Cometary coma ions

For comets whose nuclei are composed of water ice conglomerates it is shown that the ion H3O(+) can predominate to distances of 5000 km in the subsolar direction. Beyond this distance H2O(+) is the most important ion. The crossover point is a sensitive function of the rate of evaporation from the nucleus. The presence of ammonia or metals such as sodium, in concentrations greater than 0.1% H2O, can lead to NH4(+) and Na(+) ions.

Aikin, A. C.↗
NASA NTRS1976

On the cometary hydrogen coma and far UV emission

Cometary hydrogen observations are reviewed with emphasis on observations of comet Bennett. The results are theoretically interpreted and a brief summary of ultraviolet observations other than Lyman alpha is given.

Keller, H. U.↗
NASA NTRS1976

The neutral coma of comets: A review

The hypothesis that water snow controls the vaporization of the nucleus of some comets seems verified from the general order of magnitude of the size of their nucleus and of their nuclear albedo; the largest observed production rates are H and OH which both seem to originate from the photodissociation of H2O, as also confirmed by the scale length of the invisible parent molecule producing OH. However, comet Encke is not uniformly covered by water snow, as it produces only one tenth of the expected vaporization. Early results on comet Kohoutek suggest that the conclusions could be slightly different for some of the new comets in Oort's sense. If the far ultraviolet observations confirm the early assessments of the production rates of C, O and H, then at least another major constituent competing with water has not yet been detected. Such a major constituent is suggested by the ratios C/O = 0.24 and H/O = 2.5.

Delsemme, A. H.↗
NASA NTRS1976

MX 1313+29 - A compact source of very low energy X-rays in Coma Berenices

A compact X-ray source near the North Galactic Pole has been detected with the low-energy X-ray telescope aboard the SAS-3 satellite. The spectral temperature of the source is less than 1 million K, and the energy flux at the earth is 3 by 10 to the -10th power erg/sq cm/sec above 0.1 keV. The flux appeared to be constant both on short time scales (10-1000 s), and over the interval from the first SAS-3 observation (June 12, 1975) to the latest (July 15, 1975). The possible identification of this source with the hot white dwarf HZ 43 is discussed.

Hearn, D. R.↗