High‐Velocity Collimated Outflows in Planetary Nebulae: NGC 6337, He 2‐186, and K4‐47

Abstract

We have obtained narrowband images and high-resolution spectra of the planetary nebulae NGC 6337, He 2-186, and K4-47 with the aim of investigating the relation between their main morpho- logical components and several low-ionization features present in these nebulae. The data suggest that NGC 6337 is a bipolar PN seen almost pole-on, with polar velocities of 200 km s~1. The bright inner ring of the nebula is interpreted to be the ii equatorial ˇˇ density enhancement. It contains a number of low-ionization knots and outward tails that we ascribe to dynamical instabilities leading to fragmenta- tion of the ring or transient density enhancements due to the interaction of the ionization front with previous density —uctuations in the interstellar medium. The lobes show a pronounced point-symmetric morphology and two peculiar low-ionization —laments, the nature of which remains unclear. The most notable characteristic of He 2-186 is the presence of two high-velocity ( 135 km s~1) knots from which an S-shaped lane of emission departs toward the central star. K4-47 is composed of a compact core and two high-velocity, low-ionization blobs. We interpret the substantial broadening of line emission from the blobs as a signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman, we derive a shock velocity of D 150 km s~1 and a mild inclination of the out—ow on the plane of the sky. We discuss possible scenarios for the formation of these nebulae and their low-ionization features. In particular, the morphology of K4-47 hardly —ts into any of the usually adopted mass-loss geometries for single asymptotic giant branch stars. Finally, we discuss the possibility that point-symmetric morphol- ogies in the lobes of NGC 6337 and the knots of He 2-186 are the result of precessing out—ows from the central stars. Subject headings: ISM: jets and out—owsISM: kinematics and dynamics ¨ planetary nebulae: individual (NGC 6337, He 2-186, K4-47)