  The HDO/H2O abundance ratio is thought to be a key diagnostic on the
evolution of water during the star- and planet-formation process and thus on
its origin on Earth. We here present millimeter-wavelength high angular
resolution observations of the deeply embedded protostar NGC1333-IRAS4B from
the Submillimeter Array targeting the 3(1,2)-2(2,1) transition of HDO at 225.6
GHz (Eu = 170 K). We do not (or only very tentatively) detect the HDO line
toward the central protostar, contrasting the previous prominent detection of a
line from another water isotopologue, H2-18-O, with similar excitation
properties using the IRAM Plateau de Bure Interferometer. The non-detection of
the HDO line provides a direct, model independent, upper limit to the HDO/H2O
abundance ratio of 6e(-4) (3sigma) in the warm gas associated with the central
protostar. This upper limit suggests that the HDO/H2O abundance ratio is not
significantly enhanced in the inner 50 AU around the protostar relative to what
is seen in comets and Earth's oceans and does not support previous suggestions
of a generally enhanced HDO/H2O ratio in these systems.
