Planetary nebulae with emission-line central stars

¹ Centrum Astronomii UMK, ul. Gagarina 11, 87-100  Torun, Poland e-mail: [Krzysztof.Gesicki;Krzysztof.Gozdziewski]@astri.uni.torun.pl
² School of Physics and Astronomy, University of Manchester, PO Box 88, Manchester M60 1QD, UK e-mail: a.zijlstra@umist.ac.uk
³ Observatoire astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: acker@astro.u-strasbg.fr
⁴ Copernicus Astronomical Center, ul.Rabianska 8, 87-100 Torun, Poland e-mail: skg@ncac.torun.pl
⁵ Space Telescope European Co-ordinating Facility, ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany e-mail: jwalsh@eso.org

Received: 12 September 2005
Accepted: 29 December 2005

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 evidence for an increase in the nebular expansion velocity with time.