2025A&A...693A..79M

Context. We continue to study the structure and kinematics of Herbig-Haro (HH) flows. HH flows exhibit a large variety of morphological and kinematical structures. Proper motion (PM) and radial velocity investigations are essential for understanding the physical nature of these structures.
Aims. We investigated the kinematics and PM of spectrally separated structures in the PV Cep HH flow HH 215.
Methods. We present observational results we obtained with a 6 m telescope (in Russia) using the SCORPIO multi-mode focal reducer with a scanning Fabry-Perot interferometer. Two epochs of the observations of the PV Cep region in Hα and [SII] emission (2003 and 2020-2021) allowed us to study the morphology of the HH 215 jet in detail and to measure the PM and radial velocities for its inner structures.
Results. We studied previously known emission knots in the HH 215 flow and new features. Moreover, a newly formed HH knot was revealed. It presumably formed during the large maximum of PV Cep in 1976-1977. We found the high-velocity inner channel in the HH 215 ionized outflow, oriented in the mean direction of the whole HH outflow, and the symmetry axis of the reflection nebula. The position angle of the HH knots located along the axis of the high-velocity channel coincide with its axis (about 325°), but others have a completely different value (about 25°). This supports the idea that these knots were formed by oblique shocks. We derived a value of i ≈ 30° ± 5° for the inclination angle between the flow axis and the line of sight. The total length of the HH 215 outflow probably is about 0.2 pc, and the full length of the bipolar outflow from PV Cep (HH 315 + HH 215) can be estimated as 3.6 pc, assuming that the inclination angle is approximately stable.