Turn-off of Deuterium Astration in the Recent Star Formation of the
  Galaxy Disk
  Chemical features of the local stellar disk have firmly established that
long-term, continuous star formation has been accompanied by a steady rate of
accretion of low-metallicity gas from the halo. We now argue that the recent
discovery of an enhanced deuterium (D) fraction in the Galaxy is consistent
with this picture. We consider two processes: the destruction of D in the
interior of stars (astration) and the supply of nearly primordial D associated
with the gas infall. Conventional Galactic chemical evolution models predict a
monotonic decrease in D/H with time with a present-day D/H abundance which is
much lower than the local value recently revealed. This predicted feature is
the result of high levels of deuterium astration involved in the formation of
the local metal-enhanced disk. Here we propose a new channel to explain the
observed enhancement in D/H. Our model, which invokes ongoing gaseous infall
and a star formation rate that declines over the past several Gyr, predicts
that the D astration is suppressed over the same time interval.
