In the present paper I review some important facts regarding the similarities and differences between Galactic planetary nebulae and Galactic Wolf-Rayet (WR) nebulae within the scope of stellar mass-loss history and its subsequent impact on the nebular dynamics and morphology. The case of planetary nebulae with [WR] nuclei, which allows one to perform a more direct comparison with WR nebulae, is emphasized. In particular, I describe the apparently ubiquitous turbulent-like phenomena originating in [WR] stellar atmospheres and the surrounding nebulae, and discuss the possible impact of turbulence on planetary nebula studies.

Many astrophysical flows occur in inhomogeneous media. We present results of a hydrodynamic numerical study of the interaction of a steady, planar shock/supersonic postshock flow with a system of embedded cylindrical clouds in a two-dimensional geometry and describe an analytical model of the evolution of such systems. Finally we discuss mass-loading in such systems and the applicability of the results to the planetary nebulae (PNe).

The most recent results and animations of the numerical experiments described in this paper can be found at www.pas.rochester.edu/~wma.

Wolf-Rayet type central stars have been analyzed with adequate model atmospheres. The obtained stellar parameters and chemical abundances allow for a discussion of their evolutionary origin.

Results of a spectroscopic investigation of central stars of old planetary nebulae (PNe) are reported. The evolutionary status of the central stars is discussed and it is shown that most are in good agreement with standard post-AGB evolution, but some are best explained as descendents from the first RGB after binary interaction. The distance scale of PNe is discussed.

The chemical abundances of Wolf-Rayet ([WC]) central stars are reviewed. Although the evolutionary connection between cooler (late) and hotter (early) [WC] central stars and PG1159 central stars is now on solid ground, several issues still remain. In particular, hydrogen and oxygen abundances, that could provide a way of discriminating between different evolutionary channels, are affected by large uncertainties. Following the ground-breaking discovery that cool [WC] central stars harbor hot carbon- as well as hot oxygen-rich dust, current theories of their origin have been put in serious doubt. Observations of three cool [WC] central stars are presented here which, while confirming the deficiency of our theoretical understanding, hint at the possibility of alternative scenarios, such as dust-storing disks.

In this review I present the binary model for the shaping of planetary nebulae (PNe) as I view it, in the context of historical evolution of other models for the shaping of PNe over more than 30 years. In describing the binary model, I concentrate on works published since the last IAU meeting on PNe. I think stellar companions are behind the shaping of bipolar PNe, i.e., having two lobes with an equatorial waist between them, and extreme elliptical PNe, e.g., having a dense equatorial ring, but no lobes. The question of whether a planet is required to spin the progenitor in order to form a moderate elliptical PN, or whether single stars can form moderate elliptical PNe, I consider to be an open question.

The effects of planetary systems around pre-AGB and AGB stars on their pulsations, optical spectra and on the shape of future planetary nebulae are discussed. The physical phenomena considered include include gas drag on the planet embedded in the ever denser circumstellar gas of a red giant and shock waves arising. intensity of the H2O The lack of variability in many red giants may be due to their low metallicity and absence of planetary systems around them.

We report on a study of 3 post common-envelope binary systems; EC 11575-1845, V644 Cas (the central star of the PN HFG 1), and VW Pyx (the central star of K 1–2). These 3 have similar photometric and spectroscopic characteristics. Emission lines from the heated face of the cool star move with different velocities, and the H I lines are very broad with deep absorption component(s) visible at all phases.

SuWt2 has been found to contain a double lined and eclipsing binary system. Surprisingly, both components appear to be A-type stars with masses of about 3 M⊙ moving in essentially circular orbits with a period of 4.9 days. We see no indications of a hotter component in the optical or IUE spectra. We discuss the possibility that this is a triple system.

Deep Hα + [N II] images show the nebula to be an inclined ring (≃600 to the line of sight) while spectra show anomalous line ratios (eg I([N II] 6584) ≥≥ I(Hα)) which maybe indicative of recombination in a changing radiation field. Further modeling is ongoing.

In this paper, we study the evolution of the weak emission line central stars of planetary nebula (WELS), which are similar to the H-deficient Wolf-Rayet central stars except for systematically weaker emission lines. Our attempts at finding an evolutionary sequence for the WELS similar to what was established for Wolf-Rayet central stars, were unsuccessful. No correlation was found between any of the analysed quantities: emission and absorption line fluxes or stellar and nebular parameters from the literature. It does appear, however, that WELS have intermediate stellar temperatures (30–80 kK), and do not reside in the middle of Type I planetary nebulae, possibly indicating lower mass precursors.

A new class of variable star is proposed. These are variable central stars of young Planetary Nebulae exhibiting roughly sinusoidal (semi)regular photometric and/or radial velocity variations with time scales of several hours. Fourteen of these objects have been identified. Their temperatures are between 25000 and 50000 K and most show hydrogen-rich spectra. The most likely reason for the variability is stellar pulsation. Another possibility would be variable stellar mass loss, but in that case the mechansism causing it must be different from that operating in massive O stars. We speculate that it actually is the stellar pulsations which cause mass loss mdulations.

FUSE high resolution spectra of two PG1159 type central stars (K1-16 and NGC 7094) have revealed an unexpected iron deficiency of at least 1 or 2 dex (Miksa et al. 2002). Here we present early results of FUSE spectroscopy of the CSPN Abell 78. It is shown that iron is strongly deficient in this star, too.

We compare the observed positions of post-AGB stars and planetary nebula nuclei in the log g and Teff diagram. We show that these positions and the resulting stellar masses are not fully consistent with theoretical expectations.

UV (IUE), far-UV (FUSE) and optical (INT) spectroscopy of four Galactic [WC]-type PN central stars are analysed by means of sophisticated model atmosphere codes which allow for detailed line blanketing and clumping, and make comparisons with earlier non-LTE models. Crucially, we find no systematic difference between carbon abundances amongst late and early-type [WC] stars, removing the main obstacle against evolution from [WCL] to [WCE] subtypes.

In Grosdidier et al. (2000, 2001), wind fluctuations were described for five [WC 8–10] stars. In this poster we present new results discussing the case of the hotter subtype [WO 4] (Grosdidier & Acker 2002). Specifically, we concentrate on the CIVλλ5801/12 emission-line variability observed for NGC 1501 and NGC 6751 (see also Acker & Durand, these proceedings). Main results: NGC 1501: The OVλ5590 and CIVλλ5801/12 emission lines as well as the CIV/CIII complex around 5690Å are variable at the 1% level. The amplitudes of the variations range from about 5% (OV), up to 7% (CIV) of the adjacent continuum flux. The HeIλ5876 is also found to be variable; NGC 6751: For this star, significant variability at the 1% level is detected for the CIVλλ5801/12 emission line only. Note that the variations are quite huge since they span 6–10% of the adjacent continuum flux. Small variations are seen around the line centre but they are essentially located in the red and blue wings of the line, the latter showing the largest level of variability. Generally, the amplitudes of the variations in [WO 4] central stars range up to 10% of the adjacent continuum flux, over timescales of hours, or days. This result is essentially the same than that found for [WC]-late type stars. We expect strong, hydrogen-deficient [WC] winds to be extreme examples for central stars of PN, so that any fine structure found in [WC] winds may apply to all winds of central stars of PN, much as one is finding now that weak, massive O-star winds also show the same fine structure as massive WR winds. The consequences of clumping in hot-star winds are manifold, including substantial constraints on the effective mass-loss rates, and their possible impact on the surrounding nebula itself (Acker et al. 2002). On the whole, the winds of all [WC] central stars are significantly stochastically variable on relatively short time-scales. This supports a turbulent origin.

The temperature of the central stars in planetary nebulae is generally obtained by the Zanstra method. This method provides two values for the temperature of a single star: one obtained from the H recombination lines, TZ(H), and another from the He recombination lines, TZ(He II). The ratio (ZR) of these two values can be different from unit, leading to the well-known “Zanstra discrepancy”. The discrepancy is higher for lower temperature stars and the method does not reproduce the high values of stellar temperatures suggested by stellar evolutionary models. In this work a careful analysis of the effect of the optical depth on the determination of the Zanstra temperature is made, using photoionization models. The effects due to deviations from a blackbody spectrum, as well as to the He abundance in the nebulae, are also discussed. We show, quantitatively, that the details of the distribution of the H and He II Zanstra temperatures are mainly explained by an optical depth effect; in particular, the fact that the discrepancy is larger for low stellar temperatures. The results also show that for high stellar temperatures both Zanstra temperatures underestimate the stellar temperature, even for high optical depths. The stellar temperature, as well as the optical depth, can be obtained from a plot of ZR vs. TZ(He II). Since for nebulae of very low optical depth and/or high stellar temperature this plot only provides lower limits for T*, we propose the use of the line intensity ratio He II/He I vs. TZ(He II) diagram for obtaining the stellar temperature, as well as the nebular optical depth. The results of this work has been published in ApJ 543, 889 (2000).

Photo-chemical processes in hot neutral gas are summarized that are likely responsible for the destruction and formation of observed molecules in planetary nebulae. According to the hot gas scenario, detected simple molecules such as CN, HCN, C2H, and HCO+ are destroyed in a matter of a week, but are constantly and quickly re-formed.

In this work we report the radial velocity field of the molecular hydrogen in five planetary nebulae, obtained from scanning Fabry-Perot interferometer observatins at the near-infrared vibrationally excited line H2 S(1) 1-0 at 2.122 μm. Direct images of the nebulae in both transitions of molecular hydrogen S(1) 1-0 and S(1) 2-1 are used in order to discriminate between shocks and fluorescence as the excitation mechanism of the H2. Finally, some physical parameters are derived.

We give a summary of radio molecular-line and infrared imaging observations of the newly found O-rich protoplanetary nebula, IRAS 19312+1950. This object exhibits a bipolar nebulosity of size ~ 30″ on the near-IR (JHK) images. A ring-like structure with a diameter of about 10″ is seen surrounding the central star. Toward this object, we detected thermal lines of CO, HCO+, SO, and SiO (O-bearing) molecules and CN, CS, HNC, NH3, N2H+, and HC3N (C- and N-bearing) molecules, as well as H2O and SiO masers lines. The line profiles of 12CO, HCN, SO, and HCO+ are composed of broad (Δv ~ 30–40 km s-1) and narrow (Δv < 5 km s-1) components. The SiO profile (J = 2—1 v = 0 thermal line) has only broad component, and the line profiles of non-O-bearing molecules (except HCN) have only a narrow component. Both components are spatially strongly peaked in intensity at the center of this object within a ~ 15″ telescope beam. We infer that both components originate from cool material surrounding the central star. This object is most likely an O-rich protoplanetary nebula with high mass loss rate and envelope chemistry similar to that of OH 231.8+0.4.

Water-vapour masers, typical of the envelopes in giant stars, are not expected to persist in planetary nebulae due to the ultraviolet radiation of the remnant star that progressively destroys the molecules. Recently, we have reported the first unambiguous detection of water maser emission in a planetary nebula, K 3–35 (Miranda et al. 2001). The water masers in K3–35 were detected at the center of the nebula, along the minor axis, at a radius of ~85 AU and also at the surprisingly large distance of 5000 AU from the star, at the tips of the bipolar lobes. The existence of these water molecules is puzzling, and probably we are observing the very moment of transformation of a giant star into a planetary nebula. Miranda et al. (2001) also report the presence of polarization in the OH 1665 MHz masers, which are distributed towards the central star in a torus-like structure. Here we review the main results on this source.