Stalled Winds: Interactions Between Nebulae and Stellar Winds

Abstract

Spectra of the nuclei of two planetaries show what appear to be features caused by fast stellar winds as they encounter the surrounding nebulae. Superimposed upon the high velocity (3670 km s⁻¹) ultraviolet P Cygni profiles of Abell 78 are low velocity absorption lines that likely arise from a density enhancement in the wind as it brakes and builds up against the inner edge of the nebula. The deepest portions of these narrow absorptions fall at −78 km s⁻¹ for N V and O V and −26 km s⁻¹ for C IV, which implies a gradient in the decelerating wind, as does the profile of the strongest C IV line. The lower value may be related to the expansion velocity of the inner helium-rich nebulosity, which we associate with a sharp absorption feature. Another density enhancement, evidenced only by absorption lines, appears at −250 km s⁻¹, and may be caused by a rebound shock of the sort envisioned by Kahn (IAU Symposium No. 103, Planetary Nebulae, 1983, 305) and Okorokov et al. (Astr. Ap., 1985, 142, 441).