Nitrogen hydrides and the H2 ortho-to-para ratio in dark clouds (Dislaire et al.)

Vol. 537
In section 6. Interstellar and circumstellar matter

Nitrogen hydrides and the H_2 ortho-to-para ratio in dark clouds

by V. Dislaire et al., A&A 537, A20

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The ortho-para ratio of molecular hydrogen is a significant unknown in many studies of the thermodynamics of cold potentially star-forming clouds. It is, however, extremely difficult to determine directly at temperatures below 30 K. In this paper, Dislaire et al. show that in many conditions, this ratio is sensitive to the abundance ratio [NH]/[NH2] which is becoming accessible with observations from HIFI on the Herschel satellite. They find that an o/p ratio of 10-3 fits the available data towards the protostar IRAS 16293-2422 where the temperature is close to 10 K.