The 26.13 MHz absorption line in the direction of Cassiopeia A.

It has recently been suggested1 that the absorption line v = 26.13 MHz that we had detected2 in the direction of Cassiopeia A might be a recombination line due either to carbon (C631α) present in H I clouds or to heavier elements of hot gas. Observations reported here taken in February 1981 suggest that the low-frequency attenuation in the spectrum of Cas A is due to the presence of a cold cloud of ionized carbon.