Hydroxyl as a Tracer of H2 in the Envelope of MBM40
  We observed 51 positions in the OH 1667 MHz main line transitions in the
translucent, high latitude cloud MBM40. We detected OH emission in 8 out of 8
positions in the molecular core of the cloud and 24 out of 43 in the
surrounding, lower extinction envelope and periphery of the cloud. Using a
linear relationship between the integrated OH line intensity and E(B-V), we
estimate the mass in the core, the envelope, and the periphery of the cloud to
be 4, 8, and 5 solar masses. As much as a third of the total cloud mass may be
found in the in the periphery (E(B-V) $<$ 0.12 mag) and about a half in the
envelope (0.12 $\le$ E(B-V) $\le$ 0.17 mag). If these results are applicable to
other translucent clouds the OH 1667 MHz line is an excellent tracer of gas in
very low extinction regions and high-sensitivity mapping of the envelopes of
molecular clouds may reveal the presence of significant quantities of molecular
mass.
