Table 5
Proposed H2O formation mechanisms and the type of H2O produced.
| H2O formation mechanism | Type | Ṁg/ ν∞,g | nH2O/nH2 | R ⋆ | R i | R o | T f | Ref. | Comments |
(
)
|
(10-7) | (1013 cm) | (R⋆) | (R⋆) | (K) | ||||
|
|
|||||||||
| Evaporation of icy bodies | cold | 1.4–3.4 ×10-6 | 4–24 | 7.65 | 15 | / | < 500 | 1, 2, 10 | Ruled out |
| Radiative association H2 + O | cold | 2.1 ×10-6 | 1 | 6.5 | 150 | 750 | < 200 | 4, 9 | Ruled out |
| Fischer-Tropsch catalysis | intermediate | 3.4 ×10-6 | 1–100 | 7.0 | 15 | 45 | < 500 | 3 | ~Fe-grain density |
| Shock chemistry | warm | 1.0–4.0 ×10-6 | 1–7 | 6.5 | 1.2 | 3.0 | > 850 | 7, 8 | ~shock strength |
| UV photodissociation | warm | 1.4 ×10-6 | 2 | 5.1 | 2 | 20 | > 300 | 5 | ~degree of clumping |
| 6.7 ×10-7 | 2 | 5.0 | 2 | 12 | > 300 | 6 | ~degree of clumping | ||
| 6.7 ×10-8 | 2 | 5.0 | 2 | 8 | > 300 | 6 | ~degree of clumping | ||
| 6.7 ×10-9 | 10 | 5.0 | 2 | 5 | > 300 | 6 | ~degree of clumping | ||
Notes. Typical values for a set of stellar and circumstellar parameters are given: Ṁg/ ν∞,g the predicted H2O abundance, radius Ri at which H2O formation is expected to begin, radius Ro from which the H2O abundance is expected to remain constant, a typical temperature range Tf for each mechanism, the original literature references (given below the table), and finally additional comments.
Reference.
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