Thomas TelkampMeasuring Radio Recombination Lines (RRL) with the Dwingeloo telescope (@radiotelescoop ), in the Omega Nebula (M17/W38).
These are spectral lines in the radio spectrum that arise from the transitions of electrons between high energy levels in atoms (n>90), when electrons recombine with ions in ionized gas regions, like HII regions. They are essentially the radio counterparts of the Balmer series of lines (n=2), which are visible light lines. In L-band we can detect 4 of these lines, from different energy levels.
These lines are weak and take a long integration time (30 minutes+) to become visible. For comparison, this is the H167⍺ RRL at the same scale as the neutral Hydrogen (HI) profile at M17.
At even higher excitation levels (n=252) we can measure the radio emission in the UHF band (408 MHz).
