The spectra of gaseous nebulae differed strikingly from those of stars which were well understood since 1922 thanks to the work of Saha. Gaseous nebulae exhibited exotic bright line spectra characterized by strange emissions of unknown origin as well as familiar lines of hydrogen and helium. The strongest lines in most nebulae fell at 4959A and 5007A. They were originally attributed to an unknown element. First came the interpretation of the lines of H.

Basic data on planetary nebulae concern all the fields related to these objects. As an illustration of the increasing importance of planetary nebulae in large fields of contemporary science, let me note that, in a communication for a conference on “bibliometrics, informetrics and scientometrics”, Bassecoulard and Zitt (1994) chose planetary nebulae as the best example of a complicated network allowing and needing interesting cluster analysis.

We have carried out spectral classification of 65 [WC] stars, using spectra obtained at ESO in 1994-1995 with a spectral resolution of 1500 and high signal to noise ratio. We quantify the visual classification, by using the line ratios of CIII, CIV, OV, OVI in the 530-580 nm range, correlated with the blue CIII - IV lines. We measured the total strength of the above emission lines and derived the ratios of the emission line strengths. Using the stellar emission line ratios we classified about 32 CSPN as [WC] and about 30 as WELS which show only relatively weak CIV 5806 and CIV 4650 and He II 4686 stellar emission lines. The presence of CIV 5806 and the absence of CIII 5696 the WELS appear to belong to the [WC3] type. However the OV lines are very weak or absent. Some stars are reclassified, and 4 stars are found in the [WC5-7] gap. We classified 34 CSPN as [WC]. The [WC2] CSPN NGC 2867 and PB 6 show narrow and weak He II 5412 absorption feature. Based on the relative strengths of the stellar emission features NGC 2867 [WC 2], PB 6 [WC2] and M1-61 [WC4] appear to be related to WELS (Weak Emission Line Central Stars of Planetary Nebulae). The observed spectral characteristics of the central stars of these PN suggest that they are related to [WC] - PG 1159 type of objects.

We present a revised classification scheme for late WC-type stars based on new high quality optical observations of seven stars. For consistency with the usual WC scheme (Smith, ApJ 358 229 1990), our principal diagnostic is Cvi λ5801/Ciii λ5696, while Ciii λ5696/Cii λ4267, and He II λ4686/He I λ5876 serve as secondary criteria. Our quantitative scheme forms an natural extension to the existing WC scheme and provides an unambiguous definition of subtypes, with natural breaks found between subclasses.

Absolute emission line imaging photometry is often made difficult by the absence of good flux standards. Even bright PN often show as much as 25between different authors, reflecting the varying techniques of observation. In order to correct this situation, we have made slitless absolute spectrophotometric observations at high dispersion of compact (!5 arc sec. diameter) PN drawn from the Acker al. (1992) Catalogue. The complete results will appear in the Astrophysical Journal Supplement Series in early 1997. This paper gives absolute Hα , Hβ line fluxes, equivalent widths, accurate radial velocities, and relative fluxes of a number of other emission lines for some 50 PN in the southern sky between 7hr and 17hr in R.A.

The detailed line catalogue for the PN spectra is very useful for line identification. The first version of such catalogue was issued by Feklistova et al. (1994). Since the first edition the numerous weak lines belonging to the heavy elements (Z>30) have been identified in the spectra of NGC 7027 (Péquignot et al. 1994, Baluteau et al. 1995). Moreover, many newly identified lines were found in the spectra of other PN (e.g., Hyung and Aller 1996 and references given therein). This means that the PN line catalogue is needed to be extended and updated.

Our department has a long–standing tradition of discovery of planetary nebulae (PN), see e.g. Tamura & Weinberger (A&A 298, 204 (1995)) and Kerber et al. (A&AS in press (1996)) for the latest contributions.

This fifth supplement to the ‘Catalogue of Galactic Planetary Nebulae’ (CGPN - Perek, Kohoutek, 1967) covers the period 1991-1994 and contains four lists. In Table 1 we present 86 new PN, their PK designations, names and equatorial coordinates together with the references of their discovery as PN (!). The summary of the main properties of a PN and of a central star (Paper III) was used. We believe that the mean values given there are still valid, although some ‘limits’ (in parentheses) of the data have to be changed. It concerns mainly PN with very young central stars (stellar temperature down to ≈ 20000 K, gravity down to log g ≈ 3-4, variable spectrum) as well as old PN (diameter of the main nebular body up to ≈ 2.5 pc). Besides, large exp. velocity up to ≈ 300 km/s was measured for the nebular outer structure.

Planetary Nebulae (PNs) are highly representative of the late stages of intermediate mass stellar evolution. However, there are still many unresolved questions in their evolutionary scheme. Mass loss processes during the Asymptotic Giant Branch (AGB) are not fully understood. Binarity, rotation and magnetic fields may play an important role in PNs formation. The morphological study of PNs will help us to address those questions, and therefore a meaningful homogeneous database is needed.

In general, the methods for searching new PNe exploit one of their characteristics and typically introduce a bias in the sample extracted. It is therefore important to perform PN searches based on different selection criteria. Some years ago we started a new search for PN candidates on the plates of the Palomar Near Infrared Photographic Survey of the Galactic Plane. The selection criterion is based on the consideration that PNe have I(R) > I(NIR) up to AV ∼ 10, whereas normal field stars have I(R) < I(NIR). First the plates are examined directly using a binocular, with a medium magnification, searching for faint diffuse nebulosity. Hereafter the comparison between R and NIR images is used both to detect new compact PN candidate and to discard, among diffuse objects, reflection nebulae. Spectra and imaging of the new objects were obtained in dedicated program both at the ESO and Asiago Observatories. From a preliminary analysis of the data for the new PNe it appears that the sample contains objects with very different characteristics. They have different morphologies and spectral features, but in general only few of the new PNe have an IRAS counterpart and these show a small flux in the IR. In particular, in the IRAS color-color plot they do not seem confined to the area of the bona-fide PNe; this still preliminary evidence may indicate that our selection criteria is pointing to PNe which remain undiscovered using other methods.

The distances of planetary nebulae are discussed as derived from their angular expansions and radial expansion velocities. An assessment is given of distances derived by this method both at optical and radio wavelengths. The recent VLA radio data show promise in establishing a more accurate distance scale for planetary nebulae.

The accuracy of parallaxes obtained with ground-based CCD cameras now often reaches or exceeds 0.5 milliarcseconds. This improved accuracy permits us to measure significant parallaxes and determine distances for the nearest planetary nebulae. At present, the central stars of 11 planetary nebulae have been observed as part of the USNO parallax program. We now have determined distances with accuracies better than 20 percent for four central stars and better than 50 percent for five more. This paper gives the present status of the program, a brief interpretation of the results, and future prospects.

In the planetary nebulae (PNe) studies, their distance determination remains a confusing issue. The statistical distance scales cannot be regarded as reliable, and there are few PNe with individual distance determinations. In this work, we present a distance scale based on the method of individual distance determination by Méndez et al. (1988, A&A 190, 113).

We present deep narrow-band CCD images of four PNe obtained with the Palomar 5-m telescope in the light of [N II]λ6584 + Hα and [O III]λ5007. Several previously undetected structures are found, including faint multiple envelope structures. The inclusion of these sources with data for other multiple envelope PNe published in the literature permit an evaluation of the relationship between PNe ‘shells’ and the thermal pulses of the PN nucleus.

The distance determination to planetary nebulae (PNe) remains a serious problem as illustrated during the last IAU symposium in 1991 (Terzian, IAU 155, p.109). Since then the situation has not improved significantly. The number of stars for which reddening and spectral data are available, though, has increased tremendously over the last decade. Using data from the literature we have determined extinction distances for more than 50 PNe. The extinction distance method has been pioneered by Lutz (ApJ 181, 135 (1973)) and Acker (A&AS 33, 367 (1978)). The basic assumption of the extinction method is that a reddening vs distance relation (RDR) exists along the line of sight to a given object. Once this relation and the reddening of the object itself is known, a distance to the object can be derived. Gathier et al. (A&A 157, 171 (1986)) present a thorough discussion of the advantages and possible problems of the method. The most recent contributions are by Martin (A&A 281, 526 (1994)) and Saurer (A&A 297, 261 (1995)).

Recent work on the PN classification scheme initially proposed by Peimbert has shown that objects of types I, II, and III have markedly different properties such as central star mass, height distribution relative to the galactic plane, and kinematic behaviour. This fact can be used in order to determine distances, especially for the younger disk objects.