A high-latitude cloud with increased hydroxyl abundance
V. Grossmann, H. Meyerdierks, U. Mebold, A. Heithausen;
AaA, 1990, 240, 400
ABSTRACT:Observations are presented of the (C-12)O, (C-13)O, OH, and H2CO ground state transitions in a small molecular cloud in the Polaris Flare - a
huge cloud complex covering 40 square degrees probably at a distance of
about 200 pc.
The appearance of the cloud in visual, far infrared and (C-12)O
emission is consistent with a collision between the cloud and an expanding
shell.
OH and (C-13)O column densities are well correlated with the IRAS
100-micron dust emission.
If (C-13)O is converted to H2 column density assuming a
conversion factor of 500,000, these relations indicate that the OH abundance is
higher than in dark clouds and even somewhat higher than in diffuse
clouds.
Also the H2CO abundance is similar or larger than in dark clouds.
As a
further result the observations of the 1667 MHz and 1665 MHz OH transitions show
main line anomalies in this high-latitude cloud i.e., non-LTE conditions
for the levels involved.
KEYWORDS: abundance, hydroxyl radicals, molecular clouds, carbon monoxide, cosmic dust, emission spectra, formaldehyde, gravitational effects
CODE: grossmann90