The high-latitude cloud MBM 7 I Hi and CO observations

The high-latitude cloud (HLC) MBM 7 has been observed in the 21 cm H I line and the (CO)-C-12(1-0) and (CO)-C-13(1-0) lines with similar spatial resolutions. The data reveal a total mass similar to 30 M. for MBM 7 and a complex morphology. The cloud consists of a cold dense core of 5 M. surrounded by atomic and molecular gas with about 25 M., which is embedded in hotter and more diffuse H I gas. We derive a total column density N(H I + 2H(2)) of 1 x 10(21) cm(-2) toward the center and 1 x 10(20) cm(-3) toward the envelope of MBM 7. The CO line indicates the existence of dense cores [n(H-2) greater than or equal to 2000 cm(-3)] of size (FWHM) similar to 0.5 pc. The morphology suggests shock compression from the southwest direction, which can form molecular cores along the direction perpendicular to the H I distribution. The H I cloud extends to the northeast, and the velocity gradient appears to be about 2.8 km s(-1) pc(-1) in this direction, which indicates a systematic outward motion which will disrupt the cloud in similar to 10(6) yr. The observed large line widths of similar to 2 km s(-1) for CO suggest that turbulent motions exist in the cloud, and hydrodynamical turbulence may dominate the line broadening. Considering the energy and pressure of MBM 7, the dense cores appear not to be bound by gravity, and the whole cloud including the dense cores seem to be expanding. The distance to HLCs suggest that they belong to the galactic plane, since the scale height of the cloud is less than or similar to 100 pc. Compared to the more familiar dense dark clouds, HLCs may differ only in their small mass and low density, with their proximity reducing the filling factor and enhancing the contrast of the core and envelope structure.