Limits on the D:H ratio in the interstellar medium from molecular observations

Frost, R. L.; Beckman, J. E.; Watt, G. D.; White, G. J.; Phillips, J. P.
Referencia bibliográfica

IN: Submillimetre wave astronomy (A84-29251 12-89). Cambridge and New York, Cambridge University Press, 1982, p. 253-259.

Fecha de publicación:
0
1982
Número de autores
5
Número de autores del IAC
0
Número de citas
0
Número de citas referidas
0
Descripción
The abundance ratio of D:H in the interstellar medium can be derived either more directly from the UV absorption measurements of HD and H2 in the spectra of early-type stars, or less directly from millimeter-wave emission in the rotational lines of a variety of molecules. The latter method is applicable over a much larger portion of the galaxy, but is subject to the uncertainty inherent in chemical fractionation. It is shown here how the basic assumptions of temperature distribution and geometry within a single source can cause the derived ratio HDO:H2O to vary between 0.05 and 0.0025, a comparable range to that found with three different molecules DCN:HCN, DNC:HNC, and DCO(+):HCO(+) in the same source. This result should lead to caution in the interpretation of such abundance ratios and of their gradients within the galaxy.