Measurements of the main far-infrared cooling lines from photodissociation regions in planetary nebulae were obtained with NASA's Kuiper Airborne Observatory, using a moderate-resolution far-infrared cooled grating spectrometer (Erickson et al. 1985). We surveyed about 20 nebulae in the [O I] 63 μm line, and detected it in most of the observed objects. We found that its strength correlates well with the total far-infrared power, with an average ratio of about 0.2%, as predicted by models of photodissociation regions (e.g. Tielens & Hollenbach 1985; Wolfire et al. 1990). Strong 63 μm emission is absent only for objects in which the ionization of the gas is just beginning and for a few evolved objects where the ionized nebula is probably matter-bounded.

We report the results of a near-infrared (mostly K-band) spectroscopic survey of planetary nebulae at McDonald Observatory during the period 1986-1993. These observations were made with a grating spectrometer based on a 1 × 32-element InSb array. Most of the K-band observations were taken with spectral resolving power R = λ/Δλ = 600 in order to resolve the v=1-0 S(1) 2.121 μm H2 line from the adjacent recombination line of He I at 2.113 μm. We also simultaneously measured the strengths of H I Br γ and He II 2.189 μm. The typical limiting line flux detected in our 3.8″ beam was 1-3 × 10–14 erg cm–2 s–1, corresponding to a surface brightness of 3 × 10–5 to 1 × 10–4 erg cm–2 s–1 ster–1. An early result of this study was the first conclusive proof that the UV-pumping or “fluorescence” mechanism, rather than thermal (shock) excitation, is responsible for the H2 emission in a planetary nebula, Hubble 12 (Dinerstein et al. 1988, ApJ, 327, L27). This was also one of the first demonstrated cases of UV-pumped H2 emission in any astronomical source, and Hubble 12 has become a template for the study of this emission mechanism.

TAURUS-II imaging Fabry-Perot data in the emission lines of Ha, He II, [O I], [O III] and [N II] have been obtained to study the kinematics of NGC 3242. By studying the kinematic structure in lines of a range of ionization, the expansion of the nebula from close to the central star to the low ionization outer regions can be explored.

The [O II]3726,3729Å doublet is sensitive to electron densities in the range 100 to 104 cm–3, typical of planetary nebulae, and thus provides an ideal tool for mapping the projected density structure. The first use of the imaging Fabry-Perot TAURUS-II to observe both the [O II] doublet lines, and hence map the electron density, is reported for NGC 6826. If sufficient spectral resolution is achieved both the [O II] lines can be resolved into separate components, opening the way to full 3-D density mapping of PN. Given the low finesse of the etalon and the low expansion velocity in NGC 6826 (10-15 kms–1), this original hope could not be fulfilled. However, a restricted aim of seeing-limited electron density mapping was accepted.

Planetary Nebulae (PNe) are formed by the interaction of the fast wind from a post-Asymptotic Giant Branch Star with the slow ambient wind from a previous epoch. If the two interacting winds have constant properties, the velocity of the PN shell tends towards a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. Using semi-analytical methods, complemented by hydrodynamic simulations, we have calculated the shapes of PNe in the self-similar stage (Dwarkadas et al. 1996). We have investigated the contribution of the ambient wind velocity to PN morphology, which has hitherto not received much attention since the work of Kahn & West (1985). We find that the nebular morphology is a consequence of the density contrast between pole and equator in the ambient medium, the steepness of the density profile and the velocity of the ambient wind; classification of PNe purely on the basis of the first two factors may be misleading. In particular, the ratio of ambient wind velocity to PN velocity is important in determining whether the nebula shows a bulge or a cusp at the equator. A high density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximum of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. As long as the external wind velocity is small compared to the expansion velocity of the nebula, the PNe tend to be more bipolar, even with a moderate density contrast. If the PN velocity is close to that of the external wind, the shape is relatively spherical. However, inclusion of an asymmetric velocity profile in the slow wind, with the velocity increasing towards the pole, can lead to a bipolar nebula if the equatorial velocity is sufficiently low. Preliminary results with a slow wind velocity increasing towards the equator (as is found in calculations of common envelope evolution) show that the nebulae tend to be more oblate, which is not often observed in nature. Representative results for shapes of PNe using various values of the relevant parameters are presented.

The general properties of elliptical planetary nebulae have been very successfully explained by a class of hydrodynamic models known as interacting stellar winds (ISW). PNs also contain a variety of microstructures (Anase,“FLIERs”) whose origins have remained puzzling. We (Frank, Balick, & Livio 1996) have shown that such flows will naturally occur in the ISW model in momentum-conserving PPN bubbles, and that they can naturally account for the formation of jets and ansae in a way consistent with extant observations.

We present hydrodynamical and magnetohydronynamical simulations for the formation and evolution of bipolar and elliptical planetary nebulae with two interacting winds. The models are performed under the hypothesis of a single central source, i.e. binary systems are not considered and a single initial wind function is used in our calculations. We explore various relevant parameters, including the effects of stellar rotation, ionizing radiation field and stellar magnetic field, and a catalogue of resulting shapes is generated.

For a nebula we construct a model, which is a spherical shell defined by inner and outer radii, density distribution and velocity field. The Teff and the luminosity of the central star are assumed to agree with observations. Then the photoionization structure is calculated and the emission lines are integrated. Having found the density from analysis of images the deduction of velocity field in order to fit the observed shapes of spectral lines is relatively easy. A detailed description of computer codes applied for the analysis of nebular spectra is presented in our earlier paper: Gesicki et al. (1996). See also Górny et al. in this volume.

A new code PAN (Photoionized Axially-symmetrical Nebula) for the self-consistent modelling of a cylindrical gaseous nebula photoionized by a central source of ionizing radiation is developed. All of the processes which play an important role in the ionization and thermal equilibrium of the nebular gas are included in the code.

We report on an investigation of the infrared properties of planetary nebulae (PNe) with H-rich central stars and with [WR]-type central stars ([WR] PNe) which certainly are H-poor. The infrared radiation comes mainly from the layers expelled at the AGB and can reveal the evolutionary history of the two groups.

The main aim of this work was to confirm that expansion of planetary nebulae surrounding Wolf-Rayet type central stars is characterized by turbulent motions or strong variations of velocity in the radial direction relative to the nucleus. Such properties have already been found in Ml-25, M3-15 and Pel-1 by Gesicki & Acker (1995). We have analyzed the photoionization structure and velocity field of the NGC 40 - a planetary nebula with late type ([WC 8]) Wolf-Rayet nucleus. The spectra of Hα and [NII] lines have been obtained with the 1.5m telescope at the Observatoire de Haute-Provence. The spectrograph Aurelie with dispersion of 5Å/mm and a 3″ circular entrance was used. The method and the details of the applied computer codes are published in Gesicki et al. (1996).

A three-dimensional (3D) self-consistent photoionization code is developed in order to build more realistic models for asymmetrical and/or inhomogeneous photoionized nebulae. With these models the assumption of spherical or plane-parallel symmetry can be dropped and models with various geometries can be treated. The gaseous region is divided into numberous cubic cells, and the physical conditions in each cell are obtained taking into account the effect of the other cells in the optical depth and their contribution into the diffuse radiation. A model for IC 4406, which is a typical example of bipolar planetary nebula is presented. The model assumes a torus of dense material around the central star, as suggested in the literature. Its presence is confirmed by the model, in particular by the shape of the theoretical Hα + [NII] isophotal map. The chemical abundances required to explain the observed line intensities indicate that the chemical properties of this bipolar nebula are not characteristic of type I planetaries. A detailed paper will be published in Ap.J. (FAPESP, CNPq)

There is a renewed interest in the study of the possible precession of the central sources of planetary nebulae. Three different morphological features are considered the effect of precession:

1. 1. Point-symmetric PNe: Objects whose morphological components are symmetrical with respect to reflection through the center.

2. 2. Quadrupolar PNe: Characterized by two well-defined pairs of lobes which are symmetric, in pairs, with respect to two different axes. These PNe are very likely the result of two episodic nebular ejection processes, produced at different positions of the symmetry axis.

3. 3. Bipolar, rotating episodic jets (or BRET's): Spectacular structures (Lopez, Meaburn, & Palmer 1994) due to the precession of a symmetrical, collimated episodic outflow.

We have carried out a comparative study of the chemical abundances and physical properties of the haloes and main nebulae on a sample of type I multiple shell PNe: M 1-46, NGC 2438, NGC 5882, NGC 6543, NGC 6720, NGC 6751, and NGC 6826.

Hydrogen-deficient planetary nebulae have central regions devoid of hydrogen. (See Harrington 1996 for a review of these nebulae.) They are characterized by exceptionally strong collisionally excited lines of [O III] and [Ne III], but relatively weak or undetected recombination lines of He or other elements. Such nebulae cannot be modeled successfully unless we include some source of heating in addition to photoionization by the central star.

We report on our project to re-evaluate carbon and other abundances in PNe spanning the expected PN progenitor mass range. The ultimate goal of this work is three-fold: (i) to determine the abundance of carbon in this sample; (ii) to assess the abundances of sulfur and argon as metallicity indicators in intermediate-mass stars; and (iii) to incorporate our metallicity results into stellar evolution models to predict nucleosynthesis yields as a function of mass and metallicity.

Spatial studies of the emission line regions in planetary nebulae (PN) can provide insight into the physical and chemical environments across the nebulae. In a collaborative effort by the coauthors, a K-band Fabry-Perot etalon has been coupled with an advanced 256 × 256 InSb focal plane array at the Wyoming Infrared Observatory 2.3m telescope. This system permits us to obtain spatially resolved, 0.24″/pixel, moderate spectral resolution (R ≈ 800), flux-density IR emission line images of astronomical sources. We obtained continuum-subtracted images of Br γ, HeI 2.06 μm, the 2-μm UIR features, and the 3.3 μm PAH dust feature in the PN NGC 6572, NGC 7027, and NGC 7662. One objective was to determine the spatial morphology of two unidentified emission lines, UIR1−2.199 μm, and UIR2−2.287 μm (Geballe et al. 1991). These UIR lines appear in the spectra of many PN (Hora et al. 1997) and in the Orion Nebula (Luhman & Rieke 1996). Geballe et al. suggested that the UIR lines are most likely forbidden transitions and showed that the parent ion ionization potential is ≈ 30–40 eV, while the ionization potential for the ions themselves is 40–60 eV. Here we directly compare the distribution of the UIR emitters to that of the gas (H+,He+) and dust (PAHs).

We have completed a near-infrared spectral survey of more than 40 planetary nebulae (PN). The data were obtained using the KSPEC spectrometer on the University of Hawaii 2.2m telescope on Mauna Kea. KSPEC is a cross-dispersed spectrograph that provides simultaneous sampling of the 1.1–2.4 μm range at a resolution of approximately 700. We used a 1 × 7 arcsec slit and a slit-viewing camera with a second NICMOS3 detector operating in the K-band for positioning and tracking of the source. The survey sample consists of compact IR-bright PN with a range of ages and morphological classifications. For many PN in the survey, spectra of several positions, such as the central star and one or more positions in the nebula, were obtained. There are many spectral features of interest within this wavelength range, such as HI recombination lines, emission lines of HeI, FeI, OI, and [FeII]; molecules such as H2, CN, C2, and CO; and continuum emission from the central star and hot dust in the nebula. A typical spectrum is shown in Figure 1. Emission from H2 was detected for the first time in several PN, including NGC 40, NGC 7026, M 1-92, and Vy 2-2. The survey data will be used to compare the properties of the sample PN, including H2 excitation mechanisms (shocks versus excitation by UV photons) and temperatures, and to correlate the properties with morphology class and age.

Progress in developing theories concerning the evolution of the central star and the surrounding planetary nebula requires a large, uniform set of data (monochromatic images, isophotes) which CCD imaging of PN can supply at present (Kaler, 1985; Balick 1987). One of the unknown parameters remains the mass budget of the (PN + central star) system. As a matter of fact, existing inventories of the measured ionised mass in PN reveal a shortfall as compared with theory. Nonetheless, since the major portion of the total mass loss occurs in the earlier ejection phases, a main objective was to detect the faint brightness peripheral nebular emissions and to provide quantitative measurement when possible of the global ionised mass.

We report the results of an extensive survey of molecular gas in planetary nebulae (PNe) using the millimeter lines of CO. The observations provide a range of information on the kinematics, the structure, and the mass of PN envelopes, which are important for understanding the formation and evolution of the ionized nebulae from the molecular envelopes ejected during the precursor AGB and proto-PNe phases.