A Survey of Deuterated Ammonia in Galactic Protostars

Details A Survey of Deuterated Ammonia in Galactic Protostars A Survey of Deuterated Ammonia in Galactic Protostars

Oct 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999alma.confe..58s&link_type=abstract

Science with the Atacama Large Millimeter Array (ALMA), Associated Universities, Inc., held October 6-8, 1999 at Carnegie Instit

Mathematics

Logic

Nh2, Protostellar, Core, Star Formation, Gas, Radiation, Protostars

Scientific paper

We report on a survey of NH2D towards protostellar cores in low--mass star formation regions in the Galaxy. Twenty--three out of thirty observed sources have significant (> 5 sigma) detections. Ion--molecule chemistry, which preferentially enhances deuterium in molecules above its cosmological value of 2 x 10-5, primarily through exchange reactions with H2D+, sufficiently explains these abundances. These gas--phase reactions produce molecules which deplete onto grains and later (>106 yrs) reappear in the gas as the radiation from protostars evaporates icy mantles. Predictions of ``early-time'' gas-phase chemical networks, though qualitatively correct, underpredict the fractionation in the coldest (10-20 K) sources. This suggests that evolution of sources, branching ratios, alternative reaction pathways, or abundances have not been accurately taken into account by current models.

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