Planetary nebulae with emission-line central stars

Abstract

Received ; accepted Abstract. The kinematic structure of a sample of planetary nebulae, consisting of 23 (WR) central stars, 21 weak emission line stars (wels) and 57 non-emission line central stars, is studied. The (WR) stars are shown to be surrounded by turbulent nebulae, a characteristic shared by some wels but almost completely absent from the non-emission line stars. The fraction of objects showing turbulence for non-emission-line stars, wels and (WR) stars is 7%, 24% and 91%, respectively. The (WR) stars show a distinct IRAS 12-micron excess, indicative of small dust grains, which is not found for wels. The (WR)-star nebulae are on average more centrally condensed than those of other stars. On the age-temperature diagram, the wels are located on tracks of both high and low stellar mass, while (WR) stars trace a narrow range of intermediate masses. Emission-line stars are not found on the cooling track. One group of wels may form a sequence wels-(WO) stars with increasing temperature. For the other groups both the wels and the (WR) stars appear to represent several, independent evolutionary tracks. We find a discontinuity in the (WR) stellar temperature distribution and suggest different evolutionary sequences above and below the temperature gap. One group of cool (WR) stars has no counterpart among any other group of PNe and may represent binary evolution. A prime factor distinguishing wels and (WR) stars appears to be stellar luminosity. We find no evi dence for an increase of nebular expansion velocity with time.