Bow Shocks, Wiggling Jets, and Wide-Angle Winds: A High-Resolution Study of the Entrainment Mechanism of the PV Cephei Molecular (CO) Outflow

摘要

We present a new set of high-resolution molecular-line maps of the gas immediately surrounding various Herbig-Haro (HH) knots of the giant HH flow HH 315 from the young star PV Cephei. The observations, aimed at studying the entrainment mechanism of the 2.6 pc-long HH 315 flow, include IRAM 30 m maps of the 12CO (2-1), 12CO (1-0), and 13CO (1-0) lines, with beam sizes of 11'', 21'', and 22'', respectively. We compare the morphology and the kinematics of the outflow gas, as well as the temperature and momentum distribution of the molecular outflow, with those predicted by different entrainment models. With our detailed study we are able to conclude that jet bow shock entrainment by an episodic stellar wind, with a time-varying axis, produces most of the high-velocity molecular outflow observed far from the source. In addition, near PV Cep we find evidence for a poorly collimated, wide-angle molecular outflow and a collimated, wiggling jet-like molecular outflow. We propose that the poorly collimated component is entrained by a wide-angle wind and the collimated component is entrained by a variable jet with internal working surfaces. If this picture is true, then a stellar wind model that allows for the coexistence of a wide-angle component and a collimated (jetlike) stellar wind component is needed to explain the observed properties of the PV Cep outflow. The wiggling axis of the redshifted molecular outflow lobe indicates that the outflow ejection axis is changing over time. We find that the timescale of the axis variation shown by the molecular outflow lobe is about a factor of 10 less than that shown by the large-scale optical HH knots.