CEPHEUS-A HW2 - A POWERFUL THERMAL RADIO JET

At angular resolution of approximately 1'' the Cepheus A East radio so urce is known to consist of 16 compact components clustered within a 2 5'' radius region, most of which are aligned in stringlike structures. We present multifrequency VLA radio continuum observations of Cep A H W2, the elongated radio object believed to be associated with the most luminous (approximately 10(4) L.) source in the region. In the freque ncy range from 1.5 to 43 GHz, we find that its flux density increases with frequency as nu0.69, while the angular size of its major axis dec reases with frequency as nu-0.57. The above frequency dependences are very close to the theoretical values of nu0.6 and nu-0.7 expected for a biconical thermal jet and make Cep A HW2 the best example known of t his type of object. We suggest that Cep A HW2 is responsible for at le ast part of the complex outflow and excitation phenomena observed in t he region. The estimated ionized mass-loss rate in this source, approx imately 8 x 10(-7) M. yr-1, is about 100 times larger than the value e xpected for a star of the same luminosity in the main sequence.