We present a study of the PNe systems of two nearby galaxies: the spirals M 33 and M 81. The luminosity functions (PNLFs) for the two PNe systems were built and the distances to both galaxies were given (0.84 ± 0.09 Mpc to M 33 and 3.84 ± 0.41 Mpc to M 81). The behavior of PNe excitation was examined across both galaxies, finding no evidence for substantial differences in excitation between bulge and disk PNe, nor for variations along the galaxian disks.

The Local Group Census is a narrowband survey of all the galaxies of the Local Group (LG) with Dec ≥ −30°, being carried out as part of the Isaac Newton Group's Wide Field Survey programme. Observations are being obtained with the Wide Field Camera at the 2.5m Isaac Newton telescope, equipped with a mosaic of four 2k x 4k EEV CCDs covering a field of view of 34′ x 34′.

Two planetary nebulae previously classified as Galactic were discovered, on the basis of their radial velocities, to be located in the Sagittarius Dwarf galaxy (Zijlstra & Walsh, 1996, A&A, 312, L21). At the distance of Sagittarius of ~25kpc, they are the closest extra-galactic PN. A detailed analysis based on ground-based spectra and radio continuum data was published (Dudziak et al. 2000, A&A, 363, 717); it was shown that the two nebulae are on the same evolutionary track with initial mass of 1.2M⊙ and almost identical light element abundances. One of the nebulae, Wray 16–423, underwent PN ejection about 1500yr before its twin He 2-436. On the basis of their similarity, a differential abundance analysis could be conducted. Third dredge-up carbon was found to be more abundant in He 2-436 and the first conclusive evidence for third-dredge-up oxygen enrichment was revealed (Péquignot et al. 2000, A&A, 361, L1).

The photoionization models (PhM) grid of the planetary nebulae (PN) and the HII regions in the blue compact dwarf galaxies (BCDG) was calculated. For grids modeling we used the CLOUDY94 code (Ferland G.J. 1999). Free parameters for PN grid were: (1) energy distribution, that corresponds to temperature of each of 15 chosen models (Clegg & Middlemass 1987); (2) chemical composition of nebular gas in models; (3) filling factor with its values, for every model, being equal to 0.1, 0.5 and 1. For HII regions the free parameters were: (1) energy distribution in the spectra of nuclei emission obtained for HII regions in BCDG by our method (Golovaty 1987, Melekh 2000) from high-quality observations (Izotov, Thuan, & Lipovetsky 1994, Izotov, Thuan, & Lipovetsky 1997, Thuan, Izotov, & Lipovetsky hys. J. 1995) of these objects (the method uses stellar atmosphere models of O-B stars (Schaerer et al. 1996, Schaerer & de Koter 1997)); (2) nebular gas filling factor with the values ranging from 0.0001 to 1; (3) the relative abundance of heavy elements; (4) the concentration of hydrogen atoms nH. All PhM were assumed to be spherically-symmetrical. As a result, 135 PN PhM and 270 HII regions PhM were calculated.

The expressions of new ionization-correction factors (ICF) (see these Proceedings) are employed for the determination of chemical composition of the 200 galactic planetary nebulae(PN) and 43 HII regions in blue compact dwarf galaxies (BCDG). We have used PN spectra from different papers published previously (> 100) and HII region spectra from (Izotov, Thuan, & Lipovetsky 1.994, Izotov, Thuan, & Lipovetsky 1997, Thuan, Izotov, & Lipovetsky hys. J. 1995). Code DIAGN (Holovatyy et al. 1999) developed at Astronomical Observatory of Lviv National University is also used. Atomic data for determination of ne, Te and the ionic abundances (A+i/H+) were modified to be compatible with the CLOUDY94 code (Ferland G.J. 1999).

This review contains: (1) the scientific motivations for studying Planetary Nebulae in the Magellanic Clouds; (2) a review of this field of study, from the origins to the most recent results, focusing on the papers that have been published since the last IAU Symposium on Planetary Nebulae; (3) a review of the Hubble contribution to the field, from the early results to our own Magellanic Cloud Planetary Nebula program.

The study of the formation and evolution of planetary nebulae (PNs) has been a subject of active investigation for several decades. In the past 15 years the relationship between nebular morphology and nebular/stellar evolution has been investigated in some detail. Although important insights have been gained, the connection between PN formation and even basic morphological features of the evolving nebula is far from clear. One of the most vexing problems to overcome is the difficulty of obtaining, at least for Galactic PNs where statistical distances must be adopted, reliable dimensions, ages, luminosities, and other physical quantities that are essential for understanding the evolutionary state of individual nebulae. Our emphasis of late has been to obtain high-resolution images of a large sample of PNs in the Magellanic Clouds, where uncertainties in the distances are minimal and selection effects due to, e. g., dust absorption in the Galactic plane do not apply.

HST UV and optical spectra of the early-type [WC] star SMP 61 in the LMC are analyzed by means of line blanketed non-LTE models for expanding atmospheres. The known distance to the LMC allows a reliable determination of the stellar parameters. The low iron surface abundance of the object possibly indicates a preceding evolution through a very late thermal pulse (VLTP).

LMC-N66 is an extraordinary planetary nebula whose central star underwent a violent mass loss event which has lasted for 10 years. The outburst reached its maximum in 1994. Since then the star has been slowly fading. During the stellar outburst, the nebular lines have shown no changes.

The nebula shows a complex morphology. Two very bright lobes at both sides of the central star, almost aligned in the E-W direction, constitute the main body of the nebula. Several knots and filaments are conspicuous over the surface lying preferentially on the S-E and N-W directions. A couple of faint, extended loops are also detected in the S-E and N-W directions at both sides of the star. The extension of these loops are larger than 0.5 pc at the LMC distance. A no emitting-zone in the S-W quadrant, seems to be part of a dusty toroid around the central star, although the central star is not obscured by such a dark material (see Blades et ale 1992 for a description of N66 morphology).

In this work, the chemical history of the SMC is described through an observed sample of planetary nebulae (PNe). Age-abundance relations were derived through the [α-elements/H] (oxygen, argon, neon and sulphur) ratios estimated from PNe of different progenitor masses. In particular, oxygen abundances seem do not decrease due to O-N cycle operation. (This work was supported by FAPESP)

Thanks to recent advances in instrumentation, metal abundances now can be measured routinely for PNe situated in galaxies beyond the Magellanic Clouds. Consequently, PNe are becoming a valuable tool for studying the chemical evolution of external galaxies, especially those which are not forming stars. Here we review problems and progress in this exciting nascent field of interdisciplinary research.

As the nearest large elliptical galaxy, NGC 5128 is ideal for planetary nebula studies. Its size, favourable aspect, small distance and reddening allow low mass stellar evolution in a whole galaxy to be surveyed. The surface density and properties of the PN can be compared with stars of various ages, metallicities and components (bulge, halo). The PN provide the α-element abundances whilst stellar photometry is calibrated against Fe/H; applied to the same stellar population, the PN abundances can be related to those of the stars. Gradients and non-radial trends in the abundance can be mapped using spectral observations of a large number of PN, allowing star formation history to be studied.

We present spectroscopy of planetary nebulae in M32, NGC 185, and NGC 205. With these new data, spectra exist for 14 planetary nebulae in M32, for 5 planetary nebulae in NGC 185, and 13 planetary nebulae in NGC 205. From these data, oxygen abundances based upon electron temperatures derived from detections of [O III]λ4363 may be derived for 11 planetary nebulae in M32, 5 in NGC 185, and 7 in NGC 205. The mean oxygen abundances and their dispersions based upon these [O III]λ4363 detections are 8.51 ± 0.20, 8.21 ± 0.27, and 8.20 ± 0.24 in M32, NGC 185, and NGC 205, respectively, in the usual 12 + log(O/H) format.

We confirm a previous finding that a significant fraction of the planetary nebulae in M32 have anomalously strong [N II] lines (Stasińska et al. 1998). Seven of the planetary nebulae for which there now exist spectra (half of the total) have I([N II]λ6584)/I(Hβ) > 1.5. These objects are concentrated towards the centre of M32, though less so than the light.

When we combine these new oxygen abundances with extant data, we find that the the same physical processes appear to control the chemical evolution of ellipticals, dwarf spheroidals, and the bulges of spirals. In addition, it is clear that dwarf spheroidals incorporated their metal production into stars much more efficiently than dwarf irregulars, casting more doubt upon an evolutionary link between these two types of dwarf galaxies.

PNG135.9+55.9 is a halo planetary nebula recently discovered among the objects from the Second Byurakan Survey. Based upon our first observations, a photoionization model analysis shows that the oxygen abundance in the nebula must be extremely low, probably 10-2–10-3 of the solar value. This finding has strong implications on our understanding of the formation of planetary nebulae, of mixing processes in the stellar progenitors and of the evolution of the Galactic halo.

We review the progress of research on intracluster planetary nebulae (IPN). In the past five years, hundreds of IPN candidates have been detected in the Virgo and Fornax galaxy clusters and searches are also underway in poorer galaxy groups. From the observations to date, and applying the known properties of extragalactic planetary nebulae, the intracluster light in Virgo and Fornax: 1) is significant, at least 20% of the total cluster stellar luminosity, 2) is elongated in Virgo along our line of sight, and 3) may derive from lower-luminosity galaxies, consistent with some models of intracluster star production. A fraction of IPN candidates are not true IPN, but emission-line sources of very large observed equivalent width (≥ 200 Å). The most likely source for these contaminating objects are Lyman-α galaxies at z ≈ 3.1. Follow-up spectroscopy of the IPN candidates will be crucial to discriminate against high red-shift galaxies and to derive the velocity field of the intracluster stellar population.

We present the initial results from an [O III] λ 5007 survey for intra-group planetary nebulae in the M 81 group of galaxies. A total of 0.36 square degrees of the survey have been analyzed thus far, and a total of four intra-group candidates have been detected. These data allow us to probe the physics of galaxy interactions in small groups, and give us an upper limit for the density of intracluster starlight. We find that the M 81 group has less than 3% of its stars in an intra-group component; this is much less than the fraction seen in richer galaxy clusters.

Planetary nebulae observed in our Milky Way galaxy and in the galaxies of the Local Group do impress us for their morphologies and complexities. But when we look at planetary nebulae outside the Local Group, all this must be forgotten, as they become unresolved and merely points of green light. This paper will review how these green spots of light can be used as probes of the mass distribution and dynamics of elliptical galaxies and nearby clusters.

The dynamics of the outer regions of elliptical galaxies is still poorly known. Their lack of gas means that it is not possible to use the usual optical and 21cm emission lines to determine the kinematics out to large radii, and the faintness of their stellar body means that data calculated using absorption lines are limited to the inner part of the galaxy. It is only by measuring the kinematics out to several optical scalelengths that one gets any unambiguous measure of the dark halo properties (Kent 1986).

The planetary nebula luminosity function (PNLF) plays a key role in the distance ladder, as it is the only general purpose standard candle that is applicable to both Pop I and Pop II systems. We review the physics underlying the method, and compare its distances to distances obtained from Cepheids and surface brightness fluctuations (SBF). We show that PNLF distances agree with the geometric distances to the LMC and NGC 4258, and that, on a galaxy-by-galaxy basis, the relative PNLF, Cepheid, and SBF distances are in excellent agreement with no systematic trends. However, even though the PNLF and SBF methods are both calibrated by Cepheids, the PNLF distance scale is ~17% smaller than the SBF scale. We discuss this offset, and examine the possible causes of the discrepancy.

Using the ESO 2.2m telescope with the 8K x 8K mosaic CCD, we surveyed 2.8 square degrees (~1.6° x 1.7°) of the SMC to search for faint planetary nebulae (PN). In this region, 34 PN were previously known; we identified 25 new objects. All of these are faint and have been spectroscopically confirmed. We estimate that there should be ~140 PN in the entire SMC to the limits of a survey like this one, which is complete to 6 mag down the planetary nebula luminosity function (PNLF). For a complete survey (8 mag down the PNLF), there should be ~220 PN. A strong new feature is evident in the PNLF as a deficiency at 4 mags below the brightest PN.

The survey spectra that were used to confirm the candidates as PN show that the fainter PN exhibit a higher incidence (~28%) of strong [N II] emission (where I([N II]/I(Hα) > 1) relative to the bright Sanduleak et al. (1978) sample (~6%). We propose that the very faint SMC PN are selectively biased toward the chemically enriched Type I objects derived from younger, more massive progenitors.