Search for solid HDO in low-mass protostars

Abstract

We present ground-based 2.1 to 4.2 μm observations of four low-mass protostars. We searched for the 4.1 μm OD stretch band, characteristic of solid HDO in grain mantles. We did not detect solid HDO in any of the four sources, but we derive 3σ upper limits from 0.5% to 2% for the HDO/H 2O ratio depending on the source. These ratios provide strong constraints to solid-state deuteration models when compared to deuterium fractionation values observed in the gas phase. We discuss various scenarios that could lead to such a low water deuteration compared to the high formaldehyde and methanol deuteration observed in the gas-phase.