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Interstellar Medium

R. Allen, McKellar (NRC Ottawa), Loinard, and Lequeux (Paris), have carried out a search for the CO-H2 dimer in the ISM near 3 mm wavelength using frequencies computed from IR-absorption cell data supplied by McKellar. Since the binding energy of this ``van der Waals" complex is very low it is easily destroyed by collisions, and the abundance of this dimer may be a sensitive tracer of low temperatures in the ISM. The search was carried out using the 30m IRAM radio telescope; several different Galactic cold molecular clouds were examined for traces of emission, and an absorption experiment was done using the (presumed) extragalactic source 2013+370. No detections were recorded, and useful upper limits were obtained. A paper describing the experiment is in preparation.

J. Kingdon and Williams completed a revision of Williams' Emission Line Chart, which was based on an extensive grid of photoionization models. The results of this grid were used to identify those line ratios which are insensitive to conditions in the gas and which are therefore good for deriving abundances in emission-line objects.

Kingdon is continuing his investigation into temperature fluctuations in gaseous nebulae in order to explain the observed discrepancy between abundances derived from recombination and collisionally excited lines. He is currently studying whether radial variations in abundances can resolve the discrepancy.

B. Lasker, in collaboration with J. Walsh (ESO), D. Garnett (MN), Y.-H. Chu (IL), and others, continued an HST program of parallel observations of nebulae in the Magellanic Clouds. Recent results on spatially resolved structure too fine for study from the ground include fine filaments ( or less), wind-blown bubbles, and one small () dust globule; a report was presented at the Paris HST meeting.

Harry Payne
Copyright © 1996 American Astronomical Society
Tue Dec 17 14:37:25 EST 1996