Far-infrared hydrogen lasers in the peculiar star MWC 349A

Far-infrared hydrogen recombination lines H15 alpha (169.4 micrometers), H12 alpha (88.8 micrometers), and H10 alpha (52.5 micrometers) were detected in the peculiar luminous star MWC 349A from the Kuiper Airborne Observatory. Here it is shown that at least H15 alpha is strongly amplified, with the probable amplification factor being greater than or about equal to 10(3) and a brightness temperature that is greater than or about equal to 10(7) kelvin. The other two lines also show signs of amplification, although to a lesser degree. Beyond H10 alpha the amplification apparently vanishes. The newly detected amplified lines fall into the laser wavelength domain. These lasers, as well as the previously detected hydrogen masers, may originate in the photoionized circumstellar disk of MWC 349A and constrain the disk's physics and structure.