Cometary heavy ions can resonantly excite hydromagnetic wave activity with spacecraft frequency spectra strongly deviating from the ion cyclotron frequency (Goldstein and Wong, 1987). We assess the influence of the newborn particle temperature on this effect, discuss its relevance to the interpretation of the observations, and suggest an alternative, more efficient mechanism to generate spacecraft frequencies of the order of the proton cyclotron frequency. ¿ American Geophysical Union 1988