Microwave spectroscopic mapping of gaseous nebulae. III. Hydrogen, helium, and carbon in Orion A

Recombination lines of hydrogen and helium have been detected at five locations distributed throughout the interior portion of Ori A. The average values of 9200 K for the temperature and of 0.10 for the relative ionized helium abundance are essentially constant throughout the region mapped. Carbon recombination lines that are thought to originate in a partially ionized region have also been mapped at five locations. Carbon-line emission is found to be most intense near the dark dust lane toward the northeast. Subject headings: abundances, nebular - nebulae - Orion Nebula - radio lines