The formation of a Planetary Nebula is determined by the star which lives and evolves in the middle of it. The star produces both the winds and the photons which determine the shape and appearance of the nebula. Here I study how the shape of the PN depends on the stellar properties.

The planetary nebula NGC 246 has a high degree of symmetry about its central star, and can be described most graphically as a filled disk. Direct images of NGC 246 reveal a relatively homogeneous distribution of gases, with an unusual morphological feature that appears to contain less of the nebular material. At the center of this roughly circular feature, in the southeast quadrant of the nebula, there is a star (hereafter referred to as “the program star”). The placement of the program star is very suggestive of a wind blown cavity in the PN. The question of whether this star actually is interacting with the nebula, or merely along the line-of-sight, is addressed here for the first time.

Recent observations of a number of molecular lines, among them the H2 2μm vibrational transitions, have clearly shown that in many planetary nebulae (PNe) a significant component of the eject mass is neutral.

We have observed a sample of 16 PNe of different morphological classes (from stellar to bipolar) in the mm-region, using the 15m Swedish-ESO Submillimetre Telescope (SEST). Continuum observations at 230 GHz were made with the SEST bolometer, and recombination line and continuum observations at 99 GHz (H40α) and 147 GHz (H35α) were made with SIS receivers.

The conventional interpretation of the “Wilson effect”is based on the fact that, in a simple photoionization model of a thick shell in free expansion, the elements with a high ionization potential are found in the innermost part of the shell, which move slower than the outer regions where the low ionization ions are located. A real PN is however a much more complex object than in the picture above. For these reasons, we are carrying on a project aimed at studying in detail the Wilson effect in a large number of objects of different types. We present here preliminary results for two PNe, the bipolar nebula Hu 1-2 and the elliptical NGC 7662. Observation have been secured with the Utrecht Echelle Spectrograph placed at 4.2m William Herschel Telescope, (La Palma, Canary Islands). The spatial resolution is 0.36 arcsec, and the resolving power R=46000. The results are presented in Table 1. The increase of expansion velocity with decreasing potential is clearly seen except for Hydrogen. This ion is a quite peculiar case: although its ionization potential is quite low, this element behaves also as a high excitation atom since it has only one possible ionized state. Futhermore, as we have spatial resolution we can study this relation between velocity and ionization potential in different points of the nebula.

The physico-chemical origin of the hydrogenated carbon clusters (cumulenes, PAHs, graphite or amorphous carbon) in space is still an open question. We have worked out a numerical simulation code in order to build up planar (graphite-like) carbon clusters. We assume that hydrogen atoms can fix on the carbon skeleton following a random process allowing for H2 formation. The structures we have found are very complex. In a given cluster, several molecular entities can simultaneously be present: (sp2) carbon chains, rings or compact formations (aromatic structures or small PAHs). We argue that these very contorted hydrogenated structures could be ubiquitous in the interstellar medium, in carbon-rich circumstellar regions and in PNe.

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, Stasińska 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).

We have obtained high spectral resolution, high signal-to-noise ratio longslit spectra of a sample of Planetary Nebulae with the purpose of studying their physical conditions, chemical composition and ionisation structure. In particular, we are interested in disentangling the effects of radiation and shock ionisation.

Imaging and spectroscopy are presented for four planetary nebulae known to contain close binary central stars resulting from a recent phase of common envelope evolution. These objects are Abell 41, Abell 46, Abell 63 and Abell 65. Determinations of the nebula abundances show that He is significantly enhanced in all of the objects. These results are in agreement with theoretical expectations. Uncertainties in the nebular electron temperature constrain other abundances less well. The line fluxes indicate that N is unexpectedly under-abundant. This effect is probably not real and may be an artifact of electron temperature fluctuations within the nebulae.

Two dimensional spectro-imaging of the planetary nebula NGC 40 was done to create spatially resolved intensity and electron density images. The CCD images, taken in Hβ, [S ii] λ6717, and [S ii] λλ6717, 6731, were calibrated, then correlated using previously published spectroscopic and photometric data of NGC 40 as a flux standard.

I have performed a statistical analysis on a group of emission line ratios of a sample of PNe. The optical data was taken from ELCAT2 Catalogue (http://www.stsci.edu/pub/elcat). Some observations of H–H objects were also included for comparison.

In order to study the putative enrichment within a PN, we have undertaken deep long-slit spectroscopic observations of selected targets in which we expected to find clear evidence of abundance gradients. The targets include NGC 3242: one of the PNs studied by Balick et al. (1994) in which they report N/H enhancements of ∼ 5 in each FLIER; M1-18, M1-8, M3-3, NGC 6537 and Hubble 5. The observations were obtained at the 5-m Hale Telescope of the Palomar Observatory.

NGC 7026 is one of the most remarkable bipolar planetary nebulae in the northern sky. There is an increasing interest in sources of this kind, as they indicate that anisotropic outflow phenomena play a significant role in the final evolutionary stages of massive stars. To investigate the spatial distribution of the excitation conditions in this nebula, and to get information about the structure of the progenitor's red giant wind, we started a multi-wawelength survey taking high spatial resolution line images in the visible, near and mid-infrared range using the Calar Alto and UKIRT telescopes. The instruments used are the STScI optical coronograph (Paresce & Burrows, ESO Messanger 47, 1987), the MAGIC IR camera (Herbst et al., SPIE Proc. N.1946, p.605, 1993), and the new MPIA thermal IR imager MAX. We present here some preliminary results, which allows us to estimate the main physical parameters of the central star, to find evidence for significant shock emission at the polar regions of the nebula, and to reveal an unexpected deficit of H2 emission.

Using a new photoionization code PAN (Yu. Malkov et al, this book) we have built a grid of 250 photoionization models for planetary nebulae (PN). The stellar evolutionary tracks for PN nuclei with M ∗ = 0.566, 0.598, 0.644 and 0.8M⊙ are taken from the computations of the Blöcker (A&A, 299, 1995). On the L ∗ – T eff diagram our grid covers whole region in which the PN nuclei are observed. The spectra of the central stars at λ ≤ 912 Å corresponded to non-LTE model atmospheres (R.E.S. Clegg and D. Middlemass, MNRAS, 228, 1987), corrected for presence of the stellar wind. The nebular shell was assumed to be spherically symmetric, and the profile of the radial gas density distribution in it was taken equal to the empirical approximate expression found from the analysis of isophotal maps of real PN (V. Golovaty and Yu. Malkov, Astron. Zh., 69, 1992). Each model was calculated for three choises of Mshell and each of them for two choises of shell expansion velosity −15 and 30 km/sec respectively. The relative elemental abundances were the same for all models: H:He:C:N:O:Ne:Mg:Si:S:Ar = 10000:1200:5.0:1.0:6.0:0.8:0.3:0.3:0.15:0.04 (by number of atoms).

Most of the existing flux data on galactic PN is based on measurements with scanners or photoelectric aperture photometers. Also, true global fluxes are not even available for many PNe in lines other than Hβ , and one has to rely on line intensities which have been derived from slit spectrometers. For extended, low surface brightness objects all of these instruments are not appropriate to derive reliable fluxes (see e.g. remark on NGC 7293 by O'Dell, this conference). As part of a PhD thesis a dedicated CCD camera for the Wendelstein Observatory 0.8m telescope has been developed (Roth 1990, 1993), optimized for flux-calibrated imaging through narrow-band interference filters with bandpasses down to 8å FWHM and a thermal control unit for central wavelength tuning. As a test, nebular and central star fluxes have been measured for NGC 2392, NGC 3242, NGC4361, and NGC 6210 in Hβ , HeII 4686, [OIII] 5007, and a continuum passband. The results for these bright objects are in agreement with the best references as compiled from the literature. A detailed comparison shows that the spatial extent of the nebula is now always considered correctly, based on the CCD image information and the curve-of-growth convergence of the surface photometry. The central star photometry is largely improved, in particular for high surface brightness PNe. Another advantage (which however was not important for the test objects here) is the technically easy removal of disturbing field stars within the radius of a faint, extended nebula. The use of very narrow bandwidth, thermally controlled filters proved to be beneficial in substantially reducing the sky and nebular continuum background contribution. From the nebular and central star fluxes, Zanstra temperatures have been derived. The cause of the observed Zanstra discrepancy (which is in accordance with several other determinations for the investigated objects) cannot be attributed to observational uncertainties. From the discussion of Unified NLTE model atmospheres (Gabler et al. 1991) and model fits to the central stars of NGC2392, NGC3242, NGC4361 (Méndez et al. 1988), and NGC6210 (McCarthy et al. 1990) the most likely explanation is a combination of two effects: EUV excess over currently predicted central star flux distributions, and leakage of UV photons from the nebula (see also Méndez et al. 1992).

We present new far-infrared line observations of the planetary nebulae (PNs) NGC 7027, NGC 7009, NGC 6210, NGC 6543, and IC 4997 obtained with the Kuiper Airborne Observatory (KAO). The bulk of our data are for NGC 7027 and NGC 7009, including [Ne V] 24 μm, [O IV] 26 μm, [O III] (52, 88μm), and [Nm] 57 μm. Our data for [O III] (52, 88) and [N III] 57 in NGC 7027 represent the first measurements of these lines in this source. The large [O III] 52/88 flux ratio implies an electron density (cm–3) of log Ne [O III] = 4.19, the largest Ne ever inferred from these lines. We derive N++/O++ = 0.394±0.062 for NGC 7027 and 0.179±0.043 for NGC 6210. We are able to infer the O+3/O++ ionic ratio from our data. As gauged by this ionic ratio, NGC 7027 is substantially higher ionization than is NGC 7009 – consistent with our observation that the former produces copious [Ne V] emission while the latter does not. These data help characterize the stellar ionizing radiation field.

Modern observational equipment makes it possible to identify extremely weak metal lines in deep surveys of the optical and near-IR region of the electromagnetic spectrum. In particular, collisionally excited lines from heavy ions (Z > 30) have been recently identified in the spectrum of NGC 7027 (Péquignot & Baluteau 1994). However, detailed quantitative analyses of the observed lines have not been feasible due to the lack of accurate collisional data for the heavy elements.

Since planetary nebulae(PNe) are defined as the expanding ionized gas surrounding hot central stars, the most important and fundamental subject is to study expansion characteristics. What and how can we determine a typical expansion velocity of individual nebula? In spite of great success of Perek and Kohoutek Catalog(1967) and a recent Strasbourg-ESO Catalogued 992), PNe researchers have suffered from the lack of sufficiently large samples of expansion measurements on various type of PNe.

The halo planetary nebulae are of special interest insofar as the sample is very limited and they show a wide range of nebular chemical properties. We are interested in deriving their detailed nebular properties and to try to determine the characteristics of their progenitor stars. We selected M2-29 and DDDM-1 since they are the most deficient in Ar and S of their group. During HST Cycle 3 we obtained WFC1 direct imagery in Hα of them to derive information on their morphology and surface brightness for performing FOS spectroscopy.

Long-slit optical spectroscopy and VLA-B radio continuum (λ = 3.6 cm) observations toward the compact planetary nebulae Cn 3-1 and M 3-27 are presented. Optical spectra were taken at different position angles (PAs) with the 2.2 m telescope at Calar Alto (Spain), covering the range from 6549 to 6751 Å. The radio and optical data show that the ionized shell of Cn 3-1 is an ellipsoid (size ≃ 6″ × 5″, PA ≃ 72°) containing a bright ring-like equatorial zone (size ≃ 2″.6, expansion velocity ≃ 14 km s–1) and two bright point-symmetric arcs, extending from the equator towards the polar regions of the ellipsoid (Fig. 1). These arcs seem to be filamentary structures embedded in the ellipsoid. An ionized stellar wind has been detected through faint extended wings in the Hα (≃ 660 km s–1) and [N II] (≃ 460 km s–1) emission lines. M 3-27 is unresolved at 3.6 cm (size ≤ 0″6). The detected [N II] and [S II] emission lines arise in a compact (≤ 1″4) probably non-spherical region which is identified with the ionized shell of M 3-27. The Hα emission from M 3-27 is dominated by strong emission from an ionized stellar wind and exhibits a Type III P Cygni profile with very extended wings (≃ 3000 km s–1). The estimated kinematic age and ionized mass of Cn 3-1 (≃ 1300 yr, 4 × 10–2 M⊙) and M 3-27 (≤ 530 yr, ≃ 3 × 10–4 M⊙) indicate that both objects are young planetary nebulae. Extended halos (size ≃ 36″ in Cn 3-1, ≃ 24″ in M 3-27) have been spectroscopically detected in both objects. An analysis of the kinematic and emission properties shows that both halos are reflection nebulosities and suggests that the distribution of neutral material in them probably is largely isotropic. The results suggest that the halos correspond to isotropic mass ejections occurred in the last ≃ 2 × 104 yr of the AGB phase of the Cn 3-1 and M 3-27 progenitors.