Molecular cloud in the local, hot interstellar medium

Echelle spectra recorded at the D lines of Na I are reported for nine A or F stars. Lying at approximate distances ranging from 25 to 230 pc, the stars are projected on or near the high-latitude molecular cloud MBM 12 at l = 159 deg, b = -34 deg. Among a subgroup of five of these stars separated by no more than 1.2 deg on the sky, four which are located at distances d more than 70 pc show strong interstellar D line absorption near the radial velocity of the CO emission observed in this general direction. The fifth star, at roughly 60 pc, shows no detectable absorption. MBM 12 therefore probably lies at roughly 65 pc, within the local region filled primarily by very hot, low-density gas, a conclusion supported by the large internal velocity dispersion of the molecular cloud complex. 15 references