NGC 2440 is one of the most prominent butterfly- shaped nebula in the sky. It has a very rich spectrum up to high ionic species. Its central star is handled as one of the hottest central stars. We present a 2-dimensional cylindrically symmetric ionisation model of this nebula. Under the assumption that the main nebula axis lies perpendicular to the line of sight and achieving the inverse Abel∗∗∗transformation, the density distribution could be calculated using a monochromatic Hα-CCD-image. The gridsize of the model was chosen to 0.38 arcsec (=pixel size of the image). Due to the fact that in a cylindrically symmetric model only a half plane has to be calculated, the total grid has a size of (−100‥100, 0‥100). The procedures determining the ionisation state is principally the same we used for our 3D-model of NGC 3132 (Bässgen et al 1990). If the ionic densities and the electron temperatures in all volume elements are known, emission line strengths and artificial monochromatic images can be calculated. These can be compared with “real” monochromatic images.

He 2-119 is a bright, elliptical, planetary nebula of relatively large size (117 arcsec along the major axis and 74 arcsec along the minor one). Digital, unsharp masking CCD imaging of this object is presented, revealing a filamentary, nearly bipolar inner structure. In addition, the discovery of an extended, faint halo in this object is reported. The halo has a diameter of 208 arcsec and has a nearly circular form. He 2-119 thus becomes a new member of the group of planetary nebulae with halos. Its general characteristics are discussed.

We have obtained deep CCD images of 14 PN to search for and examine faint halos. These images were obtained with Hβ, [OIII], Hα, and [NII] narrowband interference filters on the Burrell Schmidt at Kitt Peak. Table 1 summarizes the observations. We have found interesting features around NGC 1360, NGC 3587 (The Owl), and NGC 6853 (The Dumbbell), and we have obtained new images of the very faint outer halo of NGC 7293 (The Helix). Two CCDs were used: TI6, an 800×800 chip, with 1.45″ /pix and a 19.3 arcmin square field., and ST2K, a 2048×2048 chip, of which only 1200×1200 pixels were read out, yielding 2.07″ /pix and a 40 arcmin square field.

We present high-resolution near- and mid-infrared images of the planetary nebula IC 418 at 1.2 (J), 1.6 (H), 2.2 (K), 9.8, and 11.7 μm. The near-IR images were obtained with a 64×64 pixel Hg:Cd:Te array camera, and the mid-IR images were obtained using the new 20×64 pixel Mid-Infrared Array Camera (MIRAC). The size of IC 418 in the near-IR is seen to vary with wavelength, being largest at K and smallest at J. Differences in the morphology of the nebula are seen between the J and K images. There is excess near-IR emission in the center of the nebula, after subtracting out the emission from the central star. Faint halo emission is detected at H and K, extending to a total diameter of approximately 40″. The 9.8 μm emission is distributed nonsymmetrically, with the peak in the NE lobe.

We present mid-IR (8–13μm) images of dust in six young planetary nebulae: IC 418, IRAS 21282+5050, NGC 6790, M4-18, M2-9 and IC 5117. The images were taken at UKIRT and the IRTF with the Berkeley mid-IR camera which was developed at the Space Sci. Lab. in UC Berkeley and is supported by IGPP and LEA, LLNL. In IC418, M2-9 and IRAS 21282, the spatial distributions of dust and of ionized gas are measurably different. In M4-18, IC5117 and NGC 6790 the spatial distributions are similar, so apparently the dust and the gas are well mixed. Spatial resolution is the key to discerning the differences in the gas and dust morphologies, and in 2 of the 3 cases where the spatial distributions appear similar, higher resolution may reveal differences. For example, we can discern that the [NeII] peaks further out than the SiC in IC 418 because it is so close and thus large in angular size compared to our ∼ 0.″ 8 resolution. In IRAS 21282+5050, we have compared the spatial distribution of the different features attributed to Polycyclic Aromatic Hydrocarbons to the dust continuum (Fig.1). Our data shows that while the 8.5 and 11.3 μm emission peaks outside the 10μm dust continuum, the 12.5μm emission is spatially coincident with it. Hence, not all PAH emission peaks outside of the dust continuum. The plateau emission, sampled by our 12.5μm band, arises from smaller PAHs than the size that causes the 11.3μm PAH feature. Thus, one interpretation of our observations is that the grain size distribution changes with radius: smaller PAHs in the center, increasing size with radius.

We have obtained Hubble Space Telescope (HST) Planetary Camera (PC) images of a number of Magellanic Cloud planetary nebulae. The objects, except for SMP 83 were observed as part of the Cycle I GO program. The observations were made in the [O III] λ5007Å line. The object SMP 83, was observed as part of the GTO program, and in this case observations were also made in the Hα line using the F650N filter. In order to characterise the point spread function, a star was placed at the same point on the chip as the PN. This allowed us to determine the diameters of barely resolved PN in an accurate manner, by convolving the PSF with a function until it matched the appearance of the PN image. The results are given in Table 1.

Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through narrow-band filters isolating [O III] λ5007 and Hβ, for a nominal exposure time of 1000 seconds in each filter. The f/96 optical chain of the FOC was used, yielding 512×512 0.022 arcsec square pixels. Considerable detail is evident on the raw images and after deconvolution using the Richardson-Lucy algorithm, structures as small as 0.06 arcsec are easily discernible. Figure 1 shows NS and EW intensity cross-cuts through the deconvolved [O III] λ5007 images of SMC N2 and SMC N5. SMC N2 is a slightly ellleptical ringlike nebula, with its greatest elongation in the EW direction. The peak-to-peak dimensions of the ring are 0.21×0.26 arcsec2. SMC N5 has a circular ring shape, with the [O III] λ5007 image showing a clearly defined, nearly uniform structure, apart from a bright patch at the northern edge. The peak-to-peak diameter of the ring is 0.26 arcsec and the ring itself is significantly narrower than that of SMC N2, with a width as small as 0.06 arcsec (FWHM) in some places. LMC N201 is very compact, with a FWHM of 0.21 arcsec in the Hβ image. The Type I PN LMC N66 is a multi-polar nebula, with the brightest part having an extent of about 2 arcsec. Its structure is extremely complex, with several bright knots and faint loops visible outside the two bright lobes. A full description of our results can be found in Blades et al., ApJ,398, L41–44.

Using the data from the catalogue of PNe images of Schwarz et al. (1992), we have classified 255 nebulae into 5 morphological groups. The images were taken through a filter centred on the Hα line and included the [NII]6583 line. Most of the observations were made with the 3.5m ESO NTT during commissioning time. The main groups are called: stellar (st), irregular (i), elliptical (e), bipolar (b), and point-symmetric (p). The ellipticals are subdivided into: simple (e), multiple event (em), and inner structure (es) types. The bipolars into: simple (b), and multiple event (bm). The point-symmetric objects into: simple (p), and multiple events (pm).

We developed a computer program, running on a PC which allows a quicklook of monochromatic PN-images. Until now the data base consists of about 300 images obtained by B. Balick, M. Grewing, L. Bianchi and ourselves. This data base can easily be enhanced. Four monochromatic images (Ha, NII, OIII and Hell, if available) are shown simultaneously. It is also possible to show up to six objects in one emission line simultaneously to compare special features. Different look-up-tables are possible. The program does not compete with reduction packages, its only intention is to do some ‘quick morphological studies’ in a comfortable and easy way. In the present version the program needs a PC equipped with a mouse, a TSENG based VGA graphics card, 640 K (EMS rec.) and about 15 MB free disk space (for the images).

We present narrow band images and spectra illustrating the morphological and kinematical characteristics of a new class of planetary nebulae. It consists of all those objects in the catalogue by Schwarz et al. (1992) whose morphology shows no other symmetries than point–reflection about the central source. This peculiar shape is often determined by pairs of ansae or blobs separated from the central body of the nebula. The kinematical data show both low (e.g. IC 4634) and high (He 2–186; Vexp > 135 km s−1) velocity outflows.

Some of the high luminosity stars in our Galaxy are surrounded by planetary-like nebulae formed by material ejected from the central star. The most interesting case is that of the ring nebula PK 289-0° 1 around the P Cygni star AG Car. Long slit spectroscopy shows that nitrogen is overabundant and oxygen underabundant in the nebula. The Hα/[NII] ratio is lower in the nebula with respect to the surrounding H II region, possibly as a result of the N overabundance in the stellar wind. The emission line peak separation confirms a model of a distorted spherical shell expanding at 66 km s−1. The scattered star's spectrum is observable near the star, suggesting the presence of circumstellar dust grains. A nebular mass of at least 2.7 M⊙ is derived. While the nebula in the Hα imagery reveals the ring-like shape with many structures, in the blue it is much fainter and smoother. No nebular emission was detected in the JHK bands, suggesting a low dust temperature.

As hydrodynamic models of planetary nebulae advance from 1D to 2D calculations, it becomes desirable to make the same step for reconstruction techniques, which aim at deriving from the 2D intensity distributions of PNe images their 3D structure. A basic step is the determination of a symmetry axis and its orientation in space which can be described by two angles, one measured in the plane of the sky, and one measured with respect to the tangential plane. While the first one can be determined from the images, e.g. by applying the criterion of maximum normalized correlation between the object halves, which we found to yield the best results, the second angle is treated as a free parameter (see below). The steps of the iterative reconstruction algorithm are the following (with image(x, y) = input image):

1. 1. Fill a 3D kartesian density grid(xyz) (random or continuous), observing the constraint ∫ grid(xyz)dz = image(x, y), where z is along the line of sight.

2. 2. Transform to cylindrical symmetry system (r, z', ϕ) and read out density (r, z') averaging over ϕ.

3. 3. Return density(r, z') into grid(xyz) and normalize the ∫ grid(xyz)dz to match the input image.

4. 4. Return to (2.) as long as two subsequent density(r, z') estimations differ by more than a specified limit.

Interference filter CCD images have been obtained in Hα and [O III] λ5007 for all population I WR stars in the LMC and SMC using the 2.4 m telescope at Siding Spring Observatory ANU. We have found new ring nebulae in the LMC around Br#13, 25, 31 and 56. Ring nebulae around Br 31 and Br 13 most probably represent stellar ejecta. Nebula around Br 56 is a filamentary wind-blown bubble type.

The photodissociation rate of H2 molecules by UV photons from PN central stars is generally several orders of magnitude larger than the rate produced by the average interstellar field (Sternberg 1988, Escalante et al. 1991). Thus, in neutral envelopes of PN's, H2 molecules are destroyed quickly, and a photodissociation region forms around ionization bounded nebulae. Observations of H2 in PN's reveal that not all the hydrogen is photodissociated, and it has been suggested that this is due to the existence of dense disks around the ionized region (Zuckerman and Gatley 1988).

A model of the neutral region of a planetary nebula has been constructed, building on an existing program (Abgrall et al. 1992, Astr. Astrophys. 253, 525). It incorporates a large set of equations governing the formation and destruction of molecular species and also covers photo-dissociation/ionization reactions and cosmic ray interactions. The radiation field impinging on the nebula is modelled as a 105 K diluted Planck spectrum, truncated below 91.2 nm, augmented by spectral emission lines from the ionized region (data from G. Stasinska, private communication) and the hydrogen (2s→1s) two-photon continuum. The chemical species involved in the reactions are composed of seven elements — H, He, C, O, N, S and Fe — with H and He dominating the elemental abundances. The model considers a chemical environment which is carbon-rich (i.e. C/O > 1).

Planetary nebulae (PNe) are believed to form when the envelope of gas and dust, ejected at the end of the AGB phase of stellar evolution, is heated by the hot stellar nucleus, left after mass loss due to the “superwind” is terminated. The presence of residual molecular gas in PNe should therefore be important for understanding the formation and subsequent evolution of the nebulae. Observations (Bachiller et al. 1988) of CO line radiation in proto-planetary nebulae (PPNe), the transition phase from AGB stars to PNe, allowed to set very low upper limits on the molecular gas mass and to predict almost complete dissociation of the molecular envelope at the end of the PPN stage. On the other hand, observations (Huggins & Healy 1989; Healy & Huggins 1990) of CO lines detected intense signals from several PNe, including some evolved sources.

We present CO (1−0) interferometer maps of carbon star, CIT 6, and carbon rich proto-planetary nebula, CRL618. Both objects were mapped with the Berekeley-Illinois-Maryland millimeter array (BIMA). The resulting resolution is ∼ 4″ and structure larger than ∼1′ is completely filtered out. Two velocity resolutions were employed; 0.4 km s−1 and 0.8 km s−1 permitting a velocity coverage of 52 and 104 km s−1. We find evidence for non-spherical expanding envelopes in both objects. The interferometer detected all the single dish CO flux in CRL618 (840 Jy km s−1), and 70% of the CO flux in CIT 6 (or 1030 Jy km s−1). For CIT 6, we obtained single dish maps at the NRAO 12m to measure the zero spacing flux distribution. We measure an envelope diameter of 90″ (2.6 × 1017 at 190 pc) for CIT 6 and 15″ (4.5 × 1017 at 2 kpc) for CRL 618 and expansion velocities of 17 km s−1 for both. The small scale structure seen by the interferometer in CIT 6 has a core and an elongation to the SW. We interpret this elongation as the beginning of an equatorial density enhancement and predict that that CIT 6 will evolve into a bipolar planetary nebula. In CRL 618, the elongated structure seen in CO is perpendicular to the optical reflection nebula, which has an east-west orientation. Hence the Asymptotic Giant Branch (AGB) wind appears as an expanding waist band around this bipolar nebula giving credence to the idea that equatorial density enhancements in AGB winds produce bipolar planetary nebulae (Balick 1987).

We report high angular resolution mapping of the CO (J=2→1 and 1→0) lines in three evolved planetary nebulae (PNe): NGC 6781, NGC 6772, and VV47. The CO 2→1 observations of the ring-like nebula NGC 6781 provide the most detailed map to date of the kinematic structure of a PN envelope. The data are well explained with a model consisting of a thin, clumpy, ellipsoidal shell, which is open at the ends and is expanding with a velocity proportional to distance from the star. The molecular shell of NGC 6772 appears similar, but the gas is more confined to an equatorial ring and is much more incomplete. The molecular gas in VV 47 is in two clumpy lobes, which are likely to be the only surviving molecular condensations from an earlier, more extended equatorial distribution of the same kind. The average CO excitation temperature of these PNe is found to be >23 K from the CO 2→1/1→0 line ratio, and the mass of molecular gas is estimated to be 0.1, 0.02, and 0.002 M ⊙ in NGC 6781, NGC 6772, and VV 47, respectively. It appears that the ring-like PNe are formed from the dissociation and ionization of neutral ellipsoidal shells; destruction of the envelope begins with the rapid ionization of the least dense polar caps, and continues until the densest molecular material at the nebular waist is fully ionized.

We have made aperture synthesis observations of 12CO(J=1−0) emission IRAS 21282+5050, CRL 618 and M 1–7 using the Nobeyama Millimeter Array (NMA). We observed with 3 or 2 configurations and obtained an angular resolution of 3″.2 × 3.1, 3″.6 × 3″.5 and 4″.3 × 3″.8.

We have recently obtained high resolution IR spectra (λ/δλ ≈ 1000) of the planetary nebula Hb 5, over the range 1.6–1.75 μm and 3.1–3.75 μm (Magazzù & Strazzulla 1992) at the European Southern Observatory (ESO). Emission bands have been detected the most prominent being at 3.3, usually attributed to PAH molecules, and 3.4 μm. For the predicted (de Muizon et al. 1986) first armonic (at 1.67 μm) of the 3.3 μm band we get an upper limit at least 45 times weaker than the 3.4 μm feature. This, together with the high ratio of fluxes F3.4/F3.3, challenges the hypothesis that the 3.4 μm band is the first hot band. We suggest that the first hot band may be identified with a small feature at 3.46 μm. In this case the first armonic would fall at 1.686 μm where we detect a small feature.