NGC7027 has been observed at the 193cm telescope of OHP in the range 6800 - 10500 Å, using the CARELEC spectrograph equiped with a RCA CCD. The dispersion corresponded to a resolution 1 Å/px.

With the Very Large Array it is now possible to make high resolution radio continuum maps with sensitivity less than a milliJansky in an observation of only 5 minutes. We have used this so-called snapshot capability to measure about 400 PN north of declination −35. Most of the measurements were carried out at 6 cm. Some of the stronger sources were observed at several frequencies. Most sources were detected, however many nebulae were too weak to map in detail. The resolution ranges from 1.5″ to 1′, depending on the size of the PN. The selected PN have sizes in the range from 4″ to 6′.

The object (α1950 = 18h04m.3; δ1950 = −8o56!4) was discovered in a 103a-E+RG 1 objective prism plate taken with the 92/67-cm Schmidt telescope of the Astrophysical Observatory of Asiago (Italy). It presents only the Hα emission and no stellar continuum; following Kohoutek (1965, 1969, 1972) it is a bona fide planetary nebula. This classification is confirmed by the appearance of the object in the red and infrared plates of the Near Infrared Photographic Survey of the galactic plane (Sabbadin, 1986): it is quite bright in the red plate and almost invisible in the infrared one.

An interesting object was found on the IIIaJ objective prism plate SP1270, taken on Jan. 12.6 UT, 1983 with the Beijing Observatory 60/90-cm Schmidt telescope plus 5°.3 objective prism with a dispersion of 580 A/mm at Hγ. The emission lines [O III]λλ4959+5007 and Hβ were extremely strong. The lines Hγ—Hδ and [O II]λ3727, all in emission, were broad and conspicuous. Two prominent emissions were tentatively identified as He II λ4686 and He II λ4542. Of all these lines none showed any noticeable redshift. It belongs to the Galaxy. The overall spectrum looked like that of a planetary nebula. But on the POSS overlay this object was designated as RNGC 2242 and ZWG 204.005. It was listed as a galaxy either in ZWG, or in A Master List of Nonstellar Optical Astronomical Objects, but it was absent from any previous catalogues of the planetary nebula.

A method is described for finding planetary nebulae. Use is made of the far infrared IRAS colors and radio continuum measurements. The method is applied here to a region within 15° of the galactic center. The first results are given, including 36 new PN. The characteristics of the nebulae are described. While they are generally similar to known nebulae, the method of selection gives an emphasis to younger objects. A substantial number of the new nebulae may be in the transition phase between OH/IR stars and PN.

We present the first results of a large scale infrared search for new planetary nebulae. More than 1000 unidentified sources were selected from the IRS PSC having infrared colours similar to those of known PN's. Subsequent near-infrared photometry and optical spectroscopy will be made to investigate their precise nature. We report here one to five microns photometry of 30 such sources obtained with the 1.5-m CSM telescope (Tenerife, Spain). The preliminary results indicate that many of the observed sources have near infrared colours of heavily reddened PN's (Av greater than 30 magnitudes in some cases), while a smaller fraction could represent obscured normal stars or giants surrounded by circumstellar envelopes.

Finding distances to planetary nebulae remains a frustrating undertaking, but significant progress has been made over the past several years. This review covers primarily work done on distances since 1980, with some references to earlier papers. Some interesting new methods have been tried recently and some methods that have been used for years have been refined. Missions such as the Hubble Space Telescope and Hipparcos may provide new data on distances. Advances in ground-based telescopes and instruments will make possible new studies of distances.

Since the discovery in 1779 of the first planetary nebula in the Lyra constellation by Antoine Darquier, the total number of objects known as PN has been steadily increasing. About 1600 PN have been identified in the Galaxy, although 10–20% are probably misclassified objects, which include H II regions, reflection nebulae, symbiotic stars, etc. (see for example Kohoutek, 1987; Acker et al., 1987; Stenholm and Acker, 1987).

One of the most striking attributes of planetary nebulae are their complex, yet highly symmetric shapes. The process(es) which shape planetaries are only beginning to be understood. It is proposed that the morphologies of most PNs can be understood within the context of the “interacting winds” wherein a fast but light wind driven by the nucleus rams into an older, slower, and more massive wind, or red giant envelope (“RGE”) ejected earlier.

In order to explain the shapes of noncircular PNs, it seems necessary to hypothesize that the slow wind was originally ejected with an enhanced density along an equatorial plane. The morphologies of nearly all PNs can be understood through two basic parameters: the equatorial density contrast in their RGEs, and the degree of interaction between the fast and slow winds.

An up-to-date account of expansion data and their interpretation is provided.- the importance of spatiokine-matical models is underlined; bipolar outflows appear to be characteristic of very young objects and prolate spheroids (including toroids and rings) seem to be a useful approximation for many PN.- High-velocity features are much more frequent than previously assumed.- Expansion velocities vs. linear radii diagrams for [OIII], HI, and [NII], based on a new catalogue show a broad, rather homogeneous distribution and thus are of limited value for studies of the dynamical evolution or formation mechanisms of PN - future investigations of these relations should be pursued separately for groups of PN with similar physical properties; a difference in the kinematical properties of B and C nebulae could, however, be confirmed.- Several recommendations for work in this area are added.

It has been shown in several independent investigations that the multiple-shell phenomenon is prevalent in planetary nebulae. Despite the common classification, the multiple shell planetary nebulae are a heterogeneous group of objects, as testified by the wide variety of their morphologies and physical structures. There are two types of double-shell structures that are seen frequently: one has an inner shell expanding supersonically into a faint, subsonically expanding halo, and the other has a bright attached envelope co-expanding with the inner shell. The physical structures and relative elemental abundances in the shells are reviewed, and their possible formation mechanisms are discussed.

The presence of dust in planetary nebulae can be deduced in several ways - from the observed depletions of condensable elements, internal extinction and, most directly, through the detection of infrared emission from the dust grains. We know that there is a substantial amount of dust in planetary nebulae, and that a significant fraction of the total luminosity emerges in the infrared through thermal emission in most objects. However, a number of questions still largely remain unsolved, and perhaps the most pressing of these are that we do not yet have a satisfactory understanding of the ultraviolet, optical or infrared properties of the dust grains and we also do not yet know exactly where the emitting grains are located within the nebulae; for example, are they mixed with the ionized gas, or in neutral inclusions or perhaps in a disk around the central star?

Molecules and/or neutral hydrogen have been detected in a modest number of planetary nebulae. However, when detected, these indicators of a significant neutral component can provide fundamental information on the total mass of the envelope, its chemistry and kinematics, and on the morphology and evolutionary status of the planetary nebula. A review of recent results is presented, giving emphasis to CO (carbon monoxide), H2 (molecular hydrogen), OH (hydroxil), and HI (neutral hydrogen). A major development of the last few years has been the capability to map with considerable angular resolution these species in planetary nebulae. In the best studied cases, the neutral component appears to be located surrounding the “waist” of a bipolar planetary nebulae. These is evidence suggesting that molecules and neutral hydrogen are not as uncommon in planetary nebula as the present statistics suggest. Indeed, the outer parts of a considerable fraction of the known planetary nebulae could be neutral. It is possible that a combination of good selection criteria and long integrations with the best telescopes could increase largely the number of known cases.

Good progress has been made since the last Symposium on the determination of planetary nebulae (PN) abundances. Notable features for modern abundance determinations include the availability of good collision strengths and transition probabilities (reviewed by C. Mendoza (1983) at the last meeting - IAU Symp.103), the use of the IUE & IRAS satellites to obtain UV & IR line fluxes, and the availability of modern sensitive detectors enabling measurements both of faint extra galactic nebulae and of very weak abundance-indicator lines in nearby bright nebulae. The impact of IUE on PN studies was described by Köppen & Aller (1987).

A recent comparison of the photoionization models generated by five independent codes run with the same density and stellar radiation shows substantial agreement. Problems are more likely to arise with the defining parameters: the density distribution should be based on observed images, and the ionizing radiation should be from model atmosphere calculations, which, however, are inadequate for stars with winds. Models can be improved by including dust and by incorporating, self-consistently, radiative transfer in optically thick lines. Future work may extend modeling to axially-symmetric objects, to the interface with the hot, shocked, stellar wind, and to the molecular component present around many nebulae.

Fifteen new PN have been discovered in the region of Baade's Windows using an objective prism technique. Absolute spectrophotometry, excitation classes, radii and radial velocities have been obtained. Radial velocities were also measured for eight other PN in this region. After correction for solar motion and the circular velocity at the sun, the radial velocities of bulge PN (Vc) with |b| < 5°.5 show good evidence for a rotation of the bulge. If Vc=α + βΔℓ then,

We present spectroscopic distances for 22 central stars of planetary nebulae. These distances have been determined using information provided by our non-LTE model atmosphere analyses of the stellar H and He absorption line profiles. In this way, no assumptions about nebular properties are necessary.

Our spectroscopic distances turn out to be larger than many other frequently cited values. We show that our distances are not in contradiction with the available information about the interstellar extinction, and we describe additional evidence supporting them.

We present the results of an investigation of M1-79 and K3-82. Physical parameters like expansion velocities, spatial shapes, Zanstrahydrogen-temperatures, etc. were obtained by use of high resolution spectroscopy and CCD-images.

The two PN are medium excitation and exhibit usual expansion velocities. To find out the spatial shapes we utilized the simple model of a truncated spherical shell. A comparison between the theoretical intensity ratios from this model and the measurements is leading to the conclusion that both PN have the structure of a ring. K3-82 is seen pole-on, Ml-79 is seen edge-on.

NGC 6369 is a remarkable object, especially in the light of structure and morphology. We studied this object by taking many red plates (103aE), coupled with red filters (F29), of varying exposures using the Schmidt Telescope of the INAOE. The structure brought out by the analysis of the plates indicate that the object consists of a prolate disk sphaped ring nebula with a central hole and featuring huge plumes emanating out of the ring which engulf an outer envelope having a diameter about twice that of the ring. The striking feature of the plumes is that they emanate almost symmetrically out of the two prolate ends of the ring and curve out almost symmetrically along opposite directions.

A comparison of the structures of this object with the temporal evolution of the gas density in the numerical simulations of a purely gaseous self-gravitating polytropic ring is conducted. Features resembling the plumes of this object are found at a certain stage of the simulations. A careful comparison of the observed and computer generated features indicate a marked similarity in the sense that both, the observed and simulated ring appear to be similar to the cross section of a prolate spheroid at the ends of which emanate the plumes. This seems to confirm that the evolution of this object is consistent with its being a planetary nebula having the appearance of a prolate spheroid with a central hole, which is a basic observational feature of most planetary nebulae.

We present infrared emission line images of the v = 1 → 0 S(1) transition of molecular hydrogen and Brγ recombination line of atomic hydrogen which cover the entire extent of NGC 6720, the Ring Nebula. The maps presented here are the highest angular resolution images of these transitions yet produced for this object, and have very low relative positional uncertainty. As a result, we clearly resolve the spatial stratification of the ionized and shocked molecular zones within the nebula discussed previously by Beckwith et al. (1978). The relative spatial distribution of molecular and ionized hydrogen we observe is typical of several planetaries which exhibit shocked H2 emission (eg. see Zuckerman and Gatley 1987), and is similar to that predicted by the interacting-stellar-winds model of planetary nebulae formation (see Volk and Kwok 1985 and references therein).