Intermediate teeth in pulsed jets: A motivation for high-resolution observations

Supersonic jets often contain a series of knots which can be interpreted as arising from a pulsating energy source. The pulsation model is here examined for uniquely-identifying signatures. Formulae are presented for the number, intensity and distribution of knots. Our numerical and analytical calculations confirm that the classical sawtooth velocity structure contains intermediate teeth. The intermediate teeth are shown to possess high-velocity gradients, between 1.6 to 3 times the sawtooth gradient for models ranging between adiabatic and isothermal. Both sets of teeth weaken with distance with only positive gradients allowed. The leading shock of one pulse can catch up with the reflected shock of the pulse ahead. Then, the intermediate teeth form a new weaker sawtooth structure, with about half the original jump, upon which new teeth are weaned. This gives rise to a relatively long-period beat-type pattern. The associated velocity and spatial structures should soon be observable in protostellar jets.