ON JET RESPONSE TO A DRIVING FREQUENCY AND THE JETS IN 3C-449

Hydrodynamical simulations of the response of an expanding slab jet to different driving frequencies have been performed. Amplitude growth o f the resulting sinusoidal jet oscillation occurs when the driving fre quency is lower than the resonant frequency at which sinusoidal wave g rowth associated with the Kelvin-Helmholtz instability is a maximum. I n general, conditions leading to jet expansion result in the driving f requency being above the resonant frequency at some point along an exp anding jet. At larger distances where the driving frequency is above t he resonant frequency, growth ceases. If by this point sufficient ampl itude growth of sinusoidal oscillations has not occurred, the jet is n ot decollimated. A consequence for astrophysical jets is that observed large-scale jet oscillation can be at wavelengths longer than to slig htly less than the wavelength corresponding to the jet's lowest resona nt frequency. This places an upper limit on a precessional frequency, orbital frequency, or random perturbation frequency at the central eng ine to which an astrophysical jet can helically respond at large scale s. This result is applied to the radio source 3C 449 whose morphology suggests that orbital motion of the central engine is responsible for jet bending and an upper limit to the orbital frequency is obtained. A dditionally, the observed trajectory of the southern jet along with in formation about the galaxy's atmosphere is used to estimate the orbita l period and jet velocity.