Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....98..149b&link_type=abstract
Astronomy and Astrophysics, vol. 98, no. 1, May 1981, p. 149-154. Research supported by the Nederlandse Organisatie voor Zuiver
Astronomy and Astrophysics
Astrophysics
43
Astronomical Models, Formaldehyde, Hydrogen Ions, Interstellar Gas, Interstellar Masers, Molecular Clouds, Abundance, Astronomical Spectroscopy, H Ii Regions, Molecular Energy Levels, Molecular Excitation, Population Theory, Radiative Transfer, Transition Probabilities
Scientific paper
Considering the fact that the level population of the H2CO molecule is extremely sensitive to derivations from blackbody radiation at mm wavelengths and in view of the proximity of the ultra-compact H II region, it is proposed that the H2CO maser near NGC 7538-IRS 1 is pumped by the free-free continuum radiation of the H II region. Formaldehyde molecules are considered in a molecular hydrogen cloud in the presence of a strong radio continuum radiation field. To find the H2CO level populations, the equations of radiative transfer are solved, assuming that the thermal velocities of the molecules are much smaller than the large scale velocities in the cloud. The model described is found to be able to explain the maser amplification required to reproduce the observed brightness temperatures. From the calculations, it is also found that the induced emission rate in the maser transition is approximately equal to the rate of population exchange in the mm lines so that the maser is close to saturation. It is noted that the model can also be used to predict a brightness temperature of the 2(11)-2(12) line of formaldehyde.
Boland Wilfried
de Jong Teije
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