On Sunday January 21, 2024, we observed several OH maser sources with the Dwingeloo telescope.
Masers – like their more familiar visible light counterparts lasers – operate on the principle of stimulated emission. Similar to how lasers emit an intense beam of light of a single colour by amplifying light at a certain wavelength, masers are powerful radio sources amplifying microwaves at a very specific frequency. In order for stimulated emission to occur, the right atoms or molecules need to be present and a constant supply of energy is needed to “pump” these molecules to higher energy levels. Masers commonly occur in gas clouds in outer space, in particular in star forming regions and in the atmospheres of some stars. OH masers are a particular type, emitting bright, amplified spectral lines of the hydroxyl (OH) molecule at frequencies of 1612, 1665, 1667 and 1720 MHz.
The current front-end of the Dwingeloo telescope is designed for the 23 cm amateur band (1296 MHz) and the 21 cm hydrogen line (1420 MHz), and is thus not optimised for the 1.6-1.7 GHz band. Despite this limitation we wanted to see whether it was possible to detect the brightest OH maser sources with the Dwingeloo telescope, even though the sensitivity would be reduced at these higher frequencies. This test was a success: we successfully detected eight different maser sources in total. We detected six sources at 1612 MHz: these all belong to the class of “circumstellar masers” which are found around red giant stars. The other two sources are located in star forming regions, and were detected at 1665 and 1667 MHz.