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Kim, Y. H.

Publications and source records attributed to Kim, Y. H..

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The chemistry of hydrocarbon ions in the Jovian ionosphere

We have modeled the chemistry of hydrocarbon ions in the jovian ionosphere. We find that a layer of hydrocarbon ions is formed in the altitude range 300-400 km above the ammonia cloud tops, due largely to direct ionization of hydrocarbons by photons in the wings of the H2 absorption lines in the 912- to 1100-A region that penetrate to below the methane homopause. We have explicitly included in the model 156 ion-neutral reactions involving hydrocaron ions with up to two carbon atoms. Larger hydrocarbon ions are included as two pseudoions, C3Hn(+) and C4Hn(+). The model shows that 15 reactions of H(+), CH3(+), CH5(+), C2H3(+), C2H5(+), and C2H6(+) with hydrocarbon neutrals are the major processes that are responsible for the production and growth of C1-, C2- and C3- or C4-ions in the hydrocarbon ion layer. The model also shows that ions initially produced in the hydrocarbon ion layer are converted into hydrocarbon ions with more than two carbon atoms with very little loss by recombination. It is likely that successive hydrocarbon ion-neutral reactions continue to produce even larger hydrocarbon ions, so the terminal ions probably have more than three or four carbon atoms. In the auroral regions, the chemistry of hydrocarbon ions may modify the densities of neutral hydrocarbons, especially C2H2 in the upper mesosphere, and may play a major role in the production of polar haze particles.

Kim, Y. H.↗
NASA NTRS1994

Jovian auroral ovals inferred from infrared H3(+) images

Detailed analyses have been carried out of infrared H3(+) images of Jupiter's polar regions observed with the ProtoCam camera on the Infrared Telescope Facility (IRTF) on March 3-6, 1992. The images were obtained at 3.5 microns, where H3(+) emission is strong and the jovian disk is dark. By carefully examining the H3(+) emission over the limb of the polar regions, we find that the H3(+) emission extended significantly above Jupiter's limb in the north polar region and to a lesser degree in the south polar region. This could be due to either a highly extended thermosphere or a broad energy spectrum of precipitating particles in the auroral regions. After we applied a new technique to the H3(+) images to remove limb brightening, we found auroral ovals in both polar regions. The northern oval appears to be close to the L = 30 footprint in the magnetospheric spot locations derived from previous analyses. One intrinsically bright area is found in the northern oval approximately at 150 deg longitude (System III) and 70 deg latitude, where the oval is also wider than elsewhere. The intensity of the bright area varies with a time scale as short as 50 min. The southern oval seems to occur at latitudes higer by a few degrees than the L = 30 footprint, although L = 30 is within the uncertainty of latitude determination. One or two localized intensity maxima are found in the southern oval between 0 deg and 70 deg longitude.

Kim, Y. H.↗
NASA NTRS1992

Densities and vibrational distribution of H(3+) in the Jovian auroral ionosphere

The assumption that H(3+) is in LTE in the region of the Jovian ionosphere from which the emissions originate is tested by calculating the vibrational distribution of H(3+) over the altitude range of 350 to 1500 km above the methane cloud tops. A model of the Jovian auroral ionosphere is constructed in which the neutral temperatures are enhanced over those of the midlatitude ionosphere, as suggested by observations and models of the auroral region. The energy and energy flux were found to be less than those involved in the production of the UV aurora. A computation of the densities and vibrational distribution shows that the distribution of the six lowest states of H(3+) can be determined fairly well in spite of uncertainties in the atomic and molecular data. The computed altitude profiles and vibrational distributions of H(3+) and H2 are consistent with the observations of IR emission in the 2- and 4-micron regions.

Kim, Y. H.↗
NASA NTRS1991

The Jovian ionospheric E region

A model of the Jovian ionosphere was constructed, that includes direct photoionization of hydrocarbon molecules. A high-resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N), and high-resolution cross sections for photoabsorption by H2 bands in the range 842 to 1116 A were constructed. Two strong solar lines and about 30 percent of the continuum flux between 912 and 1116 A penetrate below the methane homopause despite strong absorption by CH4 and H2. It is found that hydrocarbons (mainly C2H2 are ionized at a maximum rate of 55/cu cm per sec at 320 km above the ammonia cloud tops. The hydrocarbon ions produced are quickly converted to more complex hydrocarbon ions through reactions with CH4, C2H2, C2H6, and C2H4. It is found that a hydrocarbon ion layer is formed near 320 km that is about 50 km wide with a peak density in excess of 10,000/cu cm.

Kim, Y. H.↗
NASA NTRS1990

Search for interstellar methane

Researchers searched for interstellar methane in the spectra of infrared sources embedded in molecular clouds. New observations of several lines of the P and R branches of the nu 3 band of CH4 near 3.3 microns give column densities in the range N less than 1(-2) times 10 to the minus 16th power cm(-2). Resulting abundance ratios are (CH4)/(CO) less than 3.3 times 10 to the minus 2nd power toward GL961 in NGC 2244 and less than 2.4 times 10 to the minus 3rd power toward GL989 in the NGC 2264 molecular cloud. The limits, and those determined in earlier observations of BN in Orion and GL490, suggest that there is little methane in molecular clouds. The result agrees with predictions of chemical models. Exceptions could occur in clouds where oxygen may be depleted, for example by H2O freezing on grains. The present observations probably did not sample such regions.

Knacke, R. F.↗
NASA NTRS1988

The ice band in IRAS 09371 + 1212

Spectra from 2 to 4 microns of the unusual IRAS source 09371 + 1212, a bipolar nebula, reveal a deep H2O ice absorption band near 3.1 microns. No long-wavelength wing is present, implying that the absorbing grain mantles are of high purity. The structure of the absorption feature is reasonably well modeled by a mixture of amorphous and crystalline H2O ice mantles on silicate grains, but discrepancies remain that could indicate other absorbers also.

Geballe, T. R.↗