Bibcode
                                    
                            Hippelein, H. H.; Anderegg, M.; Beckman, J. E.; Moorwood, A. F. M.; Baluteau, J. P.; Coron, N.; Bussoletti, E.
    Bibliographical reference
                                    Astronomische Gesellschaft, Wissenschaftliche Tagung, Oberkochen, West Germany, Mar. 10-12, 1976. Astronomische Gesellschaft, Mitteilungen, no. 40, 1976, p. 216-220. In German.
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                        1976
            
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                            Description
                                    The importance of forbidden line radiation is considered, taking into
account lines in the visible and the infrared range. The result of a
theoretical study conducted by Petrosian (1970) is shown in a graph
which indicates the intensities of the IR lines predicted for M42. The
predicted values were found later to be one order of magnitude too high.
A description is given of a spectrometer which was designed for
extraterrestrial observations. The spectrometer was used together with a
91-cm telescope which is installed in a NASA Convair 141 aircraft.
Several observational flights were conducted in November and December of
1975. The results of the studies are discussed, taking into account the
detection of the forbidden line at 18.7 micrometers in M42.