Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985a%26a...142..131m&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 142, no. 1, Jan. 1985, p. 131-142.
Astronomy and Astrophysics
Astronomy
23
Formaldehyde, Interstellar Masers, Molecular Clouds, Radio Sources (Astronomy), Astronomical Maps, Centimeter Waves, H Ii Regions, Stellar Evolution, Water Masers
Scientific paper
One arcminute resolution measurements of the 2(11)-2(12) line of H2CO, at 2 cm, are presented. The observations were made toward nineteen OH and/or H2O maser centers and compact H II regions. In addition, limited maps were made toward eight H II regions; these are shown for 3 sources, W 31, W 43, and W 51, which are extended relative to the telescope beam. Absorption line optical depths were combined with appropriate 6 cm line data to estimate H2 densities. These agree with previous estimates, to a factor of 2-3. The lowest ratio of optical depths at 6 and 2 cm, tan(6)/tan(2) = 0.6, and hence the highest implied density, 10-million/cu cm, were obtained for the molecular cloud toward G 10.6-0.4. For the H2CO maser source in NGC 7538, the lower limit for the ratio of brightness temperatures at 6 cm to 2 cm is greater than 50. A critical discussion of the H2CO excitation model is given.
Gardner Frank F.
Henkel Carsten
Martín-Pintado Jesús
Wilson Thomas L.
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