S. Medina

Expansion Velocities From Different Ions of Planetary Nebulae with [WC]-Type Central Stars

About 50 PNe in our Galaxy are known to have central stars of the carbon sequence Wolf-Rayet ([WC]) type stars and their atmospheres are almost pure helium and carbon. It has been suggested that the spectral sequence of [WC] stars and the “weak emission line stars” (WELS, as defined by Tylenda et al. 1993) corresponds to the following evolutionary sequence: late-[WC] → early-[WC] → WELS → PG 1159 type stars. This suggestion is based upon both the analysis of the stellar atmospheres and the nebular properties of the planetary nebulae around [WC] stars (WRPNe) (e.g., Parthasarathy et al. 1998). This suggestion is controversial (Gorny & Tylenda 2000; Peña et al. 2001) and in order to study the nature and evolution of WRPNe and WELS, we have obtained a homogeneous high spectral resolution (echelle) data set of 30 planetary nebulae and their nuclei using the 2.1-m telescope at the Observatorio Astronómico Nacional, San Pedro Mártir, México. High resolution is essential to estimate the expansion velocities of the nebular envelopes and in the present work we present preliminary results of the kinematic analysis of these objects from several nebular lines of different ionization degrees in order to map the kinematics along the ionization structure of the nebula. We have analyzed the expansion velocities (Vexp) of different ionization species and we have found no systematic trends. In each object, high and low ionization species show the same Vexp. Although Vexp(H I) vs. Vexp(low ionization stages) diagrams show larger spreading than Vexp(H I) vs. V (high ionization stages) diagrams. In general, expansion velocities show no correlation with nebular physical conditions (Te, Ne, excitation class) nor with stellar [WC]-type. This latter result seems to un-favor the stellar evolutionary sequence previously proposed. Another result is that no correlation has been found between the [O II]/[O III] expansion velocity ratios and the nebular parameters. A few objects, BD+30 3639, K2-16 and IC1747, show an anomalous behavior. In the cases of BD+30 3639 and K2-16, they show Vexp in [O III] higher than in H I by a factor of two, while IC1747 shows a higher Vexp in H I than in [O II]. A thorough study is needed to explain such anomalies.

Spectroscopy of planetary nebulae with [WR] nuclei

We have started an extensive program of systematic observations of planetary nebulae excited by [WR] nuclei with the aim of understanding the evolutionary status of the central stars. Detailed analysis of the nebular and stellar properties might reveal the presence of abundance variations across the nebulae, and allows to detect possible interactions between the massive stellar wind and the nebula. Such an analysis requires spatially resolved spectra, together with a reliable procedure to derive chemical abundances. This is best achieved by constructing individual photo-ionization models that reproduce the main observed properties. Here we present the spectroscopic analysis made for different knots of PB6, NGC2452, NGC2867, NGC6905 and He2–55. All these nebulae are ionized by [WC 2–3] stars and present very high ionization degrees.

Spectrophotometric Studies of Planetary Nebulae with [WR] Central Stars

We present the first results of a project on PNe with [WR] nuclei whose aim is twofold. One is to search for possible spatial abundance variations inside the nebula. The other is to check whether, for each object, one can build a self-consistent photoionization model (with the code PHOTO, Stasinska 1990, A&AS, 83, 501) using, as an input, the ionizing radiation field from an expanding model atmosphere reproducing the observed stellar lines of He, C and O (Koesterke et al., these proceedings).