Water deuterium fractionation in the inner regions of two solar type
  protostars
  The [HDO]/[H2O] ratio is a crucial parameter for probing the history of water
formation. So far, it has been measured for only three solar type protostars
and yielded different results, possibly pointing to a substantially different
history in their formation. In the present work, we report new interferometric
observations of the HDO 4 2,2 - 4 2,3 line for two solar type protostars,
IRAS2A and IRAS4A, located in the NGC1333 region. In both sources, the detected
HDO emission originates from a central compact unresolved region. Comparison
with previously published interferometric observations of the H218$O 3 1,3 - 2
2,0 line shows that the HDO and H$_2$O lines mostly come from the same region.
A non-LTE LVG analysis of the HDO and H218$O line emissions, combined with
published observations, provides a [HDO]/[H2O] ratio of 0.3 - 8 % in IRAS2A and
0.5 - 3 % in IRAS4A.
  First, the water fractionation is lower than that of other molecules such as
formaldehyde and methanol in the same sources. Second, it is similar to that
measured in the solar type protostar prototype, IRAS16293-2422, and,
surprisingly enough, larger than that measured in NGC1333 IRAS4B. {The
comparison of the measured values towards IRAS2A and IRAS4A with the
predictions of our gas-grain model GRAINOBLE gives similar conclusions to those
for IRAS 16293, arguing that these protostars {share} a similar chemical
history, although they are located in different clouds.
