Radio data obtained over more than 13 years of monitoring give detailed spectra of the youngest known protostars in the young star formation region Cepheus A. Two sources, namely HW 2 and HW 3(d), increase in flux density from 15 to 43 GHz, as previously known. The data confirm that HW 2 appears to be thermal, producing two ionized jets, and these jets show an averaged separation speed of 95 km.s–1, in comparison with the difference in the red and blue HCO+ outflow velocities of 54 km.s–1. The jets appear to be acting as pistons to produce the molecular outflows. HW 3(c) has time-dependent spectra which decrease between 1.4 and 4.9 GHz, rise to a peak near to 15 GHz, and then fall rapidly to 43.3 GHz. The low-frequency emission appears to be synchrotron radiation from a jet, and the high-frequency emission indicates gyrosynchrotron radiation. HW 3(d) is somewhat similar at the lower frequencies but at the higher frequencies is doubly peaked. One component has a steeply rising spectrum, as for HW 2. HW 3(d) is similar to the double source of L1551 NW but is unlikely to be a double protostar. The data from the whole region, including previous analyses, show time-dependent events that are less than 1000 yr old. The events consist of variations in both flux density and spectra and involve high-energy electrons. These time-dependent variations, together with measured proper motions, indicate that extremely energetic events occur in protostars before they reach the Class 0 stage and could play an important part in dispersing the surrounding gas. Caution must be observed when interpreting processes in protostar-forming regions if they are observed only in the snapshot mode.
open clusters and associations: individual (Cepheus A) - Radio Continuum: Stars - Stars: Formation - Stars: Pre-Main-Sequence