The mass-velocity and position-velocity relations in episodic outflows

While observational evidence for the episodic nature of young stellar outflows continues to mount, existing numerical and theoretical models of molecular outflows assume that they are formed by the interaction of a nonepisodic wind from a young stellar object with an ambient cloud. In this Letter, we estimate and discuss the effects of episodicity on the mass-velocity and position-velocity relations observed in molecular outflows. We explain how many recent observational results disagree with the predictions of nonepisodic outflow models, and we offer simple explanations for the discrepancies. In particular, we discuss how an episodic stellar outflow can steepen the power-law slope of the mass-velocity relation in a molecular outflow. And we illustrate how an episodic outflow can produce multiple Hubble wedges in the position-velocity distribution of a molecular outflow. With a little more information than we have now, it may be possible to use the fossil record embedded in a molecular outflow's mass-velocity and position-velocity relations to reconstruct the history of a young stellar object's mass ejection episodes.