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| Paper: |
Ices Under Conditions of Planetary Nebulae |
| Volume: |
511, Non-Stable Universe: Energetic Resources, Activity Phenomena and Evolutionary Processes |
| Page: |
98 |
| Authors: |
Yeghikyan, A. G. |
| Abstract: |
A large number of molecules are observed in planetary nebulae, both simple, the most common (H2, CO and OH), and more complex (H2O, SiO, HCN, HNC, HCO+), and even the polycyclic aromatic hydrocarbons and fullerenes containing a few dozen and more atoms. The water molecules are observed, as a rule, in the young objects, in the gas phase (water "fountains" and related water masers) and solid phase (emission of crystalline ice particles), and, regardless of the C/O ratio, water and carbon-containing molecules may be linked to the same object. On the other hand, the results of calculations by the well known Cloudy computer program given in this paper for stationery models, show that the abundance of water ice in planetary nebulae, other conditions being equal, is dependent on the ionization rate of hydrogen, which depends in turn on the flux of energetic particles (protons and alpha particles) in the range of MeV energies and higher. The possibility of the increased flux of such particles in planetary nebulae under conditions of the standard interacting stellar winds scenario is discussed, when the flux may locally exceed by 1-3 orders of magnitude that of caused by galactic cosmic rays. Calculated water ice column densities reach values up to 1018–1019 cm–2 at the usual average ISM H2 ionisation rate of 10–16s–1 and sharply decrease for the thousands times larger rates. Known observed results of NGC 6302 show for the column density of crystalline ice about 1019cm–2 close to the calculated one. |
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