Vol. 551
In section 1. Letters

LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A

The Letter by Askegar et al. represents an important demonstration of the ability of the LOFAR array to carry out low-frequency spectroscopic observations with high-angular resolution. It is also important because it opens a new avenue towards studying the diffuse interstellar medium by observing high-n (~ 540) radio recombination lines.