Doubly Deuterated Molecular Species in Protostellar Environments

Abstract

We report the detection of the doubly deuterated forms of ammonia (ND 2 H) and formaldehyde (D 2 CO) toward 16293E, a newly identified low-luminosity protostar in the ρ Ophiucus molecular complex. The abundances of ND 2 H and D 2 CO compared with their hydrogenated counterparts NH 3 and H 2 CO are ∼3% and 40% ± 20%, respectively. To date, 16293E is thus the source with the highest levels of multiple deuteration: [ND 2 H]/[NH 3 ] is 5-6 times larger there than in the only other astronomical source where ND 2 H has ever been found, the dense ammonia core of L134N; and [D 2 CO]/[H 2 CO] is more than 5 times higher than in the proto-binary system IRAS 16293-2422. The relative abundances of doubly deuterated molecules in low-luminosity protostars are much higher than their current gas-phase [D] /[H] ratios would suggest and, therefore, likely reflect active grain surface chemistry followed by some desorption process.