We have constructed a synthetic spectrum of the 2.5 micron C2H C2H bands and compared them with diminutive structures in the near-infrared spectra of Comets P/Halley and West (1976 VI). We found that the Q branches of the C2H C2H bands coincide with two small emission peaks in the spectra of the comets. We undertook Monte Carlo simulations using observed emission intensities of C2 C2 and possibly C2H C2H in Comet P/Halley in order to derive a lifetime range of C2H C2H and a production rate at the time of observations of P/Halley. We obtained a C2H C2H production rate of 1×1027sec−1 1×1027sec−1 for P/Halley on December 20, 1985, assuming the 2.5 micron features are due to C2H C2H . We derived a very short lifetime (<100 seconds) of C2H C2H at 1AU heliocentric distance, assuming that the only parent molecule for C2H C2H and C2 C2 is C2H C2H . Using this short lifetime we were unable to fit our C2 C2 distribution model to C2 C2 distribution curves observed by O'Dell et al.(1988), because our curve shows a steep slope compared with the observed one. We conclude that there must be significant additional source(s) for C2H C2H and C2 C2 other than C2H2 C2H2 .

Recent discovery of an Io-related feature in Jupiter's auroral regions prompted us to search for an or multiplet at 1304Å in IUE aurora spectra. In three independent IUE spectra taken on January 18, 1981, we found an emission structure at 1304Å , with a signal-to-noise of about three. If the structure is due to the OI emission, then it is a direct evidence of oxygen ion precipitation, which may originate from Io and Io torus. The emission rates of the H2 H2 band systems and the or multiplet are about 50 kR and 150 R, respectively. We have constructed high resolution model spectra with the estimated emission rates of H2 H2 , OI and SI for the Goddard High Resolution Spectrograph (GHRS) onboard the Hubble Space Telescope. The model spectra clearly show the or and SI mulitplets separated from crowded H2 H2 Lyman and Werner band lines, and therefore it is promising to detect the OI and SI multiplets with the GHRS. Given the possibility that the lo-related feature may be caused by ion precipitations from the Io flux tube, it is likely that the OI emission may be detected in the footprint area of the IO flux tube.

Theoretical calculations of the combined radiative transfer and statistical equilibrium equation including the charge-particle conservations have been earned out for a multilevel hydrogen atom in quiescent prominences. Cool and dense models show the steep changes of population and radiation field in the vicinity of the surface, while these physical quantities remain unchanged for models with temperature of 7,300K, regardless of total densities. Ionization rate of hydrogen atom related with metallic line formation varies in considerable amounts from the surface to the center of model prominences cooler than 6,300K. However, such cool models cannot release enough hydrogen line emissions to explain observed intensities. Prominence models with a temperature higher than 8,000K can yield the centrally reversed Lyman line profiles confirmed by satellite EUV observations. We find that queiscent prominence with a density between 2 × 10 11 and 10 12 c m − 3 should be in temperature range between 6,300K and 8,300K, in order to explain consistently observed H alpha, beta line emissions and n p / n l ratio.