In this review lecture the increase of fundamental data for planetary nebulae is shortly reflected. Special attention is given to the new general catalogue of galactic planetary nebulae, and selection criteria for the entries are summarised. Some information on planetary nebula data in the Magellanic Clouds is also given.

This review paper gives an overview of many of the observational topics that will be covered during the symposium. Trends and new developments in planetary nebula observations will be highlighted.

Space astronomy has made major and ever increasing contributions to planetary nebula research. Three astronomical satellites – Rosat, Hubble, and EUVE – have been launched since our last meeting five years ago. In addition, SpaceLab experiments flying on the NASA Shuttle have now observed a planetary nebula. After fourteen years, the IUE satellite is still going strong, and IRAS data continue to provide new results on planetaries and their antecedents.

With such a large volume of space data and a broad range in research topics, it is impossible to describe all the results from these instruments. Fortunately, other reviews at this conference by Perinotto (IUE observations of stellar winds) and Zhang (broadband flux distributions) will cover some of these topics. I will limit this review to five topics: (1) the first far-UV spectrum of a planetary, (2) new observations concerning the interaction of a stellar wind and the nebula, (3) the first high-resolution pictures of planetaries made by Hubble, (4) new observational evidence on the masses of planetary nuclei, and (5) recent advances in UV spectroscopy of central stars.

A list of 1820 objects, each of them called at least once a planetary nebula, has been inspected; 1143 of them have been classified as true or probable planetary nebulae by the authors of the catalogue (Tables 1); 347 objects, the status of which is still unclear, were classified among the “possible” planetary nebulae (Table 2).; 330 objects have been rejected, on various grounds, from the community of planetary nebulae (Table 3).

While examining Palomar Observatory Sky Survey prints for various purposes, we came upon a number of hitherto uncatalogued nebulous objects, all of them of low surface brightness. Four of them are considered by us as new planetary nebula candidates due to their morphology. For the brightest one of them, spectroscopic observations were carried out with the Cassegrain spectrograph attached to the 74-inch telescope of the Okayama Astrophysical Observatory: this object (1 = 65.49°, b = +3.18°) is clearly confirmed as a planetary nebula and obviously is in an advanced stage in its evolution; in Fig. 1, a spectrum of it is shown.

As a complement to the “Strasbourg–ESO Catalogue of Galactic Planetary Nebulae” (Acker et al. 1992), we give the list of newly discovered planetary nebulae.

This fourth supplementary list to the CGPN (Perek, Kohoutek, 1967) contains 81 new objects (Table 1) which were published mainly between 1987 and 1990. We did not include as new PN those objects, which are in a transition phase between AGB and PN (no emission lines), and possible post-PN namely objects having central stars on the evolutionary way to WD and without nebulae. The possible pre–PN are summarized in a separate incomplete list as an Appendix to Table 1.

A catalogue of 388 new possible planetary nebulae was selected by Preite-Martinez (1988) from the IRAS Point Source Catalogue. These unidentified sources have IRAS colours in the range F(12)/F(25) ≤ 0.35 and F(25)/F(60) ≥ 0.35, and are located in the proximity of the galactic equator (|b| ≤ 15°). In order to identify these IRAS sources we have undertaken a programme of near-IR observations using an InSb photometer and a near-IR camera. We report here on results relative to four of these sources.

The IRAS Point Source Catalogue containing about 250,000 sources has yielded a large number of previously unknown planetary nebulae (PNe) and a smaller number of proto-planetary nebulae (PPNe). The spectral energy distributions for many of these objects peak at or close to 25μm. A program to optically identify sources in the complete IRAS Faint Source Database, which comprises about 750,000 sources, is currently under way (Wolstencroft et al. 1991), and in a related study Wolstencroft, Parker & Lonsdale are carrying out a spectroscopic survey of a small sample of the approximately 106,000 sources which either peak or are detected only at 25μm. So far spectra of 150 sources have been obtained: 3 of these sources are PNe and 1 is a PPNe. This suggests that this sample of 25μm emitters may be a rich source of new PNe and PPNe. In this note we discuss two of these four sources.

The near infrared light is important for the exploration of proto-planetary nebulae as well as for the planetary nebulae in early phases (Persi et. al. 1986, in Planetary and Proto-Planetary Nebulae: From IRAS to ISO, ed A. P. Martinez). Numerous work on the fluxes of the well known planetary nebulae was already done in the late 80's, but a sky survey will give a large sample of data to provide more detailed statistics.

The present work presents an overview of the data on planetary nebulae expected from the European project of a deep near infrared survey of the southern sky (denis) (IAP and DESPA Paris, Heidelberg, Leiden, IAC Tenerife, Grenoble, Lyon, Frascati, Innsbruck, Vienna) in the I, J and K band with a limiting magnitude of 14.5 to 15 for point sources and 17 mag arcsec−1 for the surface brightness. The angular resolution for identification of non–point source objects will be about 5″.

In an attempt to find new Planetary Nebulae we have short radio continuum observations at 6 cm and 3 cm of 90 PN candidates with the Australian Compact Array. We selected the unidentified objects from the IRAS Point Source Catalogue on basis of their PN colors. Detection of radio continuum emission at the IRAS position almost certainly confirms that these objects are PN, because it indicates the presence of ionized gas. Therefore the 18 detected sources are considered new PN. Because of their high brightness temperatures, they are probably young PN.

The first planetary nebula was discovered by Messier in 1794. But for some reasons it has not been studied detail for a long time, especially for the central star Of planetary nebula. The primary research for these objects showed that the lifetime of a planetary nebula is about 5 104 years, but in this period the luminosity of central star varies from 63 L ⊙ to nearly 3.5 104 L ⊙ and then decrease to 100 L ⊙; its temperature changes from 3.4 104 to 105 K and then begins to decrease (Seaton 1966). The radius of central stars also have fast varies in planetary nebula phase. For these reasons we consider that in the planetary nebula phase the activities of central star is very drastic and the result of these activities must cause some variation at the surface of central star witch may be detected on the earth, especially for the surface light variations. Some observers have been trying to find the luminosity variations in central stars. But until now no one has made systematical survey for these. Since the different authors used different instruments amd different processing methods at different places which may be caused a lot of uncertainty in the photometry of planetary nebulae and central stars. So it is hard to decide whether the differences between the authors or the essential variations of the objects is responsible of the observing differences. Therefore, we have selected over fifty planetary nebulae to observe for a long period at Beijing Observatory using the same instrument and the same processing method. From these observations we may determine the light variations and the brightness of the planetary nebulae and central stars more correctly.

During the past decade the achievements in the theory of stellar atmospheres of hot stars combined with improved spectrograph and detector technology at large telescopes have led to a significantly improved knowledge of PN nuclei properties (see Méndez et al. 1988, Kudritzki and Méndez 1989).

The “Astronomy and Astrophysics Abstracts”, edited twice a year by the “Astronomisches Recheninstitut” in Heidelberg, served as basis for the determination of some data concerning the development of planetary nebulae as a research field. From the numbered and unnumbered papers within the subject category 134 there it was, for example, possible to compare the development of the PN paper rate with that of the whole field of Astronomy; for the years 1986 to 1990, a list (including postal addresses) of all individuals (ca. 900!) who published at least one paper on PN was made. For these 5 years, we now know which scientist(s) published most, in how many countries research on PN is done, how the annual publication rate varies for a specific country etc. Below, we show two results of our statistics.

Intensities of the observed spectral lines, radio fluxes and Hβ fluxes are used for the classification of planetary nebulae by centroid method of taxonomical analysis. Two variants of classification are proposed. The first one– in the three–dimensional space of relation of intensity of spectral lines He II λ 4686/HeI λ 4471, [OIII] λ 4959+5007/[OII] λ 3726+29, [OIII] λ 4959+5007/[OIII] 4363. The second variants is the classification in the three-dimensional space with cooordinates being radio flux, Hβ flux and [OIII] λ 4959+5007 intensity. The membership of classes (taxons) are presented. In the diagram joining the planetary nebula descriptors pairwise there are regions of complete (or predominant) of nebulae belonging to the same taxon, but there are also some regions of overlap. The corresponding taxons are not isolated but merge continuously into one another.

We review the work done in this field since the time of the Mexico Symposium on PN, five years ago. Although substantial progress has been achieved, a lot of work is still needed, and we pay attention to some remaining problems. We briefly describe some recent results about stellar and nebular properties, obtained with NLTE model atmosphere techniques.

In the Introduction we recall the mass loss history of a progenitor of a planetary nebula (PN). Then we concentrate on the status of knowledge of fast winds in central stars of planetary nebulae (CSPN) : the detection and statistics, the observed edge velocities, relationships of the edge velocities with other stellar or nebular parameters. We then summarize the methods used to derive the mass loss rates associated to the fast winds, and review the determinations of the “observed” mass loss rates. The comparison with predictions from the radiation driven theory (RDT) is then discussed as well as possible lines for future improvements.