Abstract
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.
Highlights
In order to better understand the effects of winds from young stars on the ambient molecular cloud, it is essential to study how the wind interacts with its surrounding medium
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
A velocity increase at the position of the optical HH knots A, B, C, and D is observed in the large-scale 12CO (2–1) p-v diagram of the HH 315 outflow (Fig. 13 in Paper I). Such morphology and velocity distribution in the molecular outflow gas is not expected if the underlying stellar wind responsible for the creation of the molecular outflow were made of a continuous constant flow of ejected mass
Summary
In order to better understand the effects of winds from young stars on the ambient molecular cloud, it is essential to study how the wind interacts with its surrounding medium. The mechanism by which a wind from a young stellar object entrains and accelerates the ambient gas, thereby producing a molecular outflow, is still a matter of debate, even though several models have been proposed. The jet carves into the cloud, and the bow shock moves away from the star, interacting with the ambient gas, thereby producing a molecular outflow around the jet. In the wide-angle–wind model (Shu et al 1991; Li & Shu 1996; Matzner & McKee 1999; Lee et al 2000, 2001), the outflow is produced when a momentum-conserving wideangle wind from a young stellar object interacts with the ambient gas.
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