The Iron Project is an international consortium dedicated to the computation of atomic data for astrophysical applications. Although the project has been mainly concerned with ions in the iron group, the earlier papers gave priority to calculations of $A$-values and electron impact collision strengths for infrared transitions. In the present report we include a compilation of these data which will become useful in the spectral modelling of planetary nebulae.

In this talk, I describe methods for direct distance estimation to Planetary Nebulae (PNe). I review the foremost of these methods, the Expansion Parallax Distance, and present some recent results from this technique. In addition, I will discuss the major contributions to the systematic and random distance errors resulting from the method (including ionization front motions and deviations from spherical target morphologies), and show preliminary evidence quantifying these effects.

In this work we investigate the relation between wind momentum $\Pi$ and the luminosity of the CSPNs in the LMC taking advantage of the less uncertain distances to these objects. We show that these winds obey the same relation as the Galactic O stars and therefore have the same physics.

I review some of the main nucleosynthesis processes in Asymptotic Giant Branch (AGB) Stars. These include production of $^{12}$C, $^{19}$F, $^{22}$Ne and $s$-elements in the He-rich layers above the degenerate C-O core, and modifications in the abundances of intermediate-mass elements up to Mg-Al, due to proton captures above the H-burning shell. Emphasis is put on the uncertainties still affecting the yields (especially mixing processes and mass loss rates) and on the possible role of planetary nebulae as a source of information on the evolution and nucleosynthesis of the AGB progenitors

The formation and evolution of planetary nebulae (PNe) is largely attributed to the interaction of the fast stellar wind with the wind of the Asymptotic Giant Branch (AGB), and to the dynamical effects of the photo-ionization of the nebular material. The physical structure of a PN can be used to assess the relative importance of fast stellar winds and photo-ionization in its shaping and evolution, but there is little information on the hot gas content of PNe. Using our recent XMM-Newton observations of NGC 3242, we have made a comprehensive analysis of the physical structure of this nebula, combining the physical conditions of the shocked fast stellar wind in its interior and the spatio-dynamical structure and physical conditions of the photo-ionized material.

The results of longtime systematic UBV-observations of 6 hot protoplanetary nebulae (PPN) with early B spectra are given. Fast stochastic brightness variations in the range of 0.$^{m}$2-0.$^{m}$4 (in $V$-band) have been found. The minimal time scale of the oscillations is from several hours to one day. The repeated spectral observations of hot protoplanetary nebulae have shown obvious variability in the hydrogen emission lines. It is suggested that the stellar wind from the future planetary nebula nucleus with variable $\dot{M}$ is responsible for variations observed in hot PPNs.

The total number of Galactic planetary nebulae (GPNe) is highly uncertain; the most inclusive current catalog contains only $\sim$ 1,500. We will use the PRISM wide-field imager on the 1.83 m Perkins Telescope to conduct a pilot survey of the Galactic plane in search of [S III] emission from PNe obscured by dust and missed by surveys of H$\,\alpha$. We are employing the method of Jacoby & Van de Steene (JVS), who surveyed the bulge for [S III] $\lambda$9532. In addition to seeing through more of the extinction, use of the [S III] emission line will a priori reject the most troublesome catalog contaminants: ultracompact H II regions.

Planetary nebulae (PNe) have the potential to revolutionize our understanding of extragalactic stellar populations. Indeed, in many systems, bright PNe are the only individual objects identifiable from the ground, and, even more often, they are the only stars that are amenable to spectroscopy. We review the ways in which ensembles of PNe can be used to probe the metallicity, age, and history of a stellar population. In particular, we discuss three cases: the weak line spectroscopic regime, where one has knowledge of the line-strengths of faint forbidden lines such as [O III] $\lambda 4363$, a bright-line regime, where only the strongest emission lines are visible, and the photometric regime, where the only information available is the [O III] $\lambda 5007$ luminosity function. We show that each of these cases, when properly calibrated, can provide unique insights into the objects that make up a stellar population.

The shaping of Pre-planetary nebulae (PPN) and Planetary Nebulae (PN) is believed to result from the interaction of a fast, collimated post-AGB wind (CFW) plowing into the slow, dense wind emitted during the AGB phase, followed by an isotropic tenuous wind during the PN phase (Sahai & Trauger 1998). The expanding shell which forms the PPN and later the PN is expected to produce extended X-ray emission due to the large speed of the fast wind and resulting high temperatures in the shocked gas. X-ray emission was only detected in 3 of 60 PNs observed with ROSAT, followed by a few more from CHANDRA and XMM (e.g. Guerrero et al. 2005). In the case of PPNs, there is so far only one confirmed X-ray detection (Sahai et al. 2003), although many have been observed with CHANDRA. The general problem of understanding the formation and shaping of PNs has been addressed analytically and numerically (see Balick & Frank 2002, and references therein). X-ray emission is one of the most direct probes of the fast wind and the interaction process which drives PN formation. However, this probe has not been fully exploited in previous modeling studies. Very recently, Akashi et al. (2006, hereafter ASB06) used analytical, self-similar, spherically symmetric models to address this problem. We are performing numerical simulations with the hydrodynamics code FLASH varying the basic parameters of the fast and slow wind over an extensive parameter grid and computing the X-ray emission as a function of these parameters and the time history of the fast wind.

Accurate emission line fluxes from planetary nebulae (PNe) provide important constraints on the nature of the final phases of stellar evolution. Large, evolved PNe may trace the latest stages of PN evolution, where material from the AGB wind is returned to the interstellar medium. However, the low surface brightness and spatially extended emission of large PNe have made accurate measurements of line fluxes difficult with traditional long-slit spectroscopic techniques. Furthermore, distinguishing these nebulae from H II regions, supernova remnants, or interstellar gas ionized by a hot, evolved stellar core can be challenging. Here, we report on an ongoing survey of large Galactic PNe ($r > 5^\prime$) with the Wisconsin H-Alpha Mapper (WHAM), a Fabry-Perot spectrograph designed to detect faint diffuse optical emission lines with high sensitivity and spectral resolution. Our sample includes newly revealed $H\alpha$ enhancements from the AAO/UKST and WHAM $H\alpha$ surveys of Parker et al. and Haffner et al. We present accurate emission line fluxes of $H\alpha$, [N II]$\lambda$6583, and [O III]$\lambda$5007, and compare our data to other measurements. We use the emission line ratios and kinematics of the ionized gas to assess, or in some cases reassess, the identification of some nebulae.

The physical and abundance properties of the gaseous components of planetary nebulae have traditionally been studied using their rich, pan-chromatic emission line spectra. However, absorption lines produced within the column of nebular gas in front of the central star can provide complementary information, giving access to ions and energy levels that cannot be studied via emission lines and yielding new evidence on the presence and nature of internal inhomogeneities. The far ultraviolet (UV) spectral region, as studied with HST and FUSE, is particularly useful for probing species in the photodissociation region (PDR), such as H$_2$ and O I. Comparison of absorption-line and emission line results within the same nebula indicates strong spatial segregation of the molecular material – and possibly of the dust as well – globally and/or on small physical scales. Measurements of UV absorption lines from excited fine-structure levels of O I reveal that non-thermal (e.g. fluorescent) processes can have an important influence on the level populations, affecting common interpretations of the important infrared cooling lines at 63 and 145 $\mu$m. Unsaturated absorption lines usable for deriving column densities and their ratios can be seen from excited fine-structure levels of some ions abundant in the ionized zone, and in some cases from ions of rarer elements such as the neutron-capture element Ge, which can be self-enriched due to nuclear processing in the PN progenitor star.

We present observations of the dusty emission from the young planetary nebulae Hen 2-113 and CPD-56$^\circ$8032 obtained with VLT/NACO, VLTI/MIDI. Our NACO observations of Hen 2-113 reveals the presence of a diabolo-shaped structure. The L$\prime$ and M$\prime$ flux from the central source, show a strong infrared excess close to the central star and this source is resolved at a scale of about 150 mas. This infrared excess is explained by emission from a cocoon of hot dust with mass $\sim 10^{-9}$ M$_{\odot}$ at $\sim$900 K. The central source is no longer visible with MIDI in the N-band and the nebula is fully resolved by a 8m telescope in this band. The dusty environment of CPD-56$^\circ$8032 is much more compact, dominated by a bright, barely resolved, core whereas visible unpublished HST images shows that the nebula has an amazing complexity. From MIDI 8.7-$\mu$m acquisition images (dominated by PAH emission), the extension and geometry of the core have been estimated. Moreover, high SNR fringes at low level have been detected with projected baselines between 40 and 45 meters. This clear signal is interpreted in terms of the bright inner rim of a dusty disk exposed to the flux from the Wolf-Rayet star. The geometrical parameters of the N-band flux distribution are well constrained by means of simple geometrical models and a simple radiative transfer model has been developed to extract the physical parameters of the disc. The PA angle of the disk agrees well with the HST/STIS observations of De Marco et al. (2002), but the inferred inclination is much less (i$\,{\sim}\,30^\circ$).

The dwarf spheroidal galaxy NGC 147 is one of the companions of the Andromeda galaxy. In this contribution we show the first spectroscopic results for the PN population of NGC 147, obtained from the GEMINI Multi-Object Spectrograph (GMOS) in December 2005. We present our results on the physical and chemical properties of the planetary nebulae. At variance with the behaviour of the old stellar population of the galaxy, the metallicity of PNe is roughly constant through the galaxy. Moreover, if the $\pm$ 0.06 dex of the [Fe/H] to [O/H] conversion is considered, there is no difference between the RGB and the PNe metallicities. We also show that the PNe in NGC 147 are 1 to 10 Gyr-old. Therefore, these results suggest that NGC 147 had no significant enrichment for a long period of time.

We present the results of CLOUDY modeling of the central zone of the Helix Nebula. Our aim was to match the observed, excess far-infrared emission. Our best fit models fill the central zone with 1$\mu$m-sized grains, with a gas-to-dust ratio of 500, where precise composition is unimportant. We speculate on the origin of these grains.

The local planetary nebula (PN) census is dominated by extremely evolved examples, and until recently, was incomplete. New discoveries from the AAO/UKST H$\alpha$ Survey and SHASSA, have partially remedied this problem. In addition, we find that some currently accepted nearby PNe are in fact Strömgren spheres in the ISM ionised by a hot white dwarf. Distance estimates for a robust sample of calibrating PNe from the literature, plus new distances for a number of highly evolved PNe, have allowed a new H$\alpha$ surface brightness – radius relationship to be devised as a useful distance indicator. It covers $>$6 dex in SB, and while the spread in SB is $\sim$1 dex at a given radius, optically thick (mainly bipolar and bipolar-core) PNe tend to populate the upper bound of the trend, while common-envelope PNe and very high-excitation PNe form a sharp lower boundary. Hence, distances can be estimated for all remaining local PNe, allowing the definition of a relatively complete census of PNe in the solar neighbourhood within 1.0 kpc. This provides a first look at the faint end of the PN luminosity function, and new estimates of the space density, scale height, total number, and birth rate of Galactic PNe.

We report our discovery of 471 planetary nebulae (PNe) in the central 25~deg$^{2}$ region of the Large Magellanic Cloud (LMC) following confirmatory two-degree Field (2dF) spectroscopy on the Anglo-Australian Telescope (AAT). Candidate emission sources were discovered using deep, high resolution UKST stacked Short Red (SR) and H$\alpha$ images which go deeper than any previously available. The two digitized stacks were then merged to reveal emission sources. The new PNe have implications for the LMC PN luminosity function, kinematics, abundance gradients, chemical evolution and the initial to final mass relation for low to intermediate mass stars via the AGB halos revealed on the H$\alpha$ map. Excitation classes are presented.

Observations of molecular gas at 7 mm are made with the Green Bank Telescope (GBT) in a sample of planetary nebulae (PNe). PNe were selected to test stellar evolution models that include extra mixing processes induced by rotation by directly measuring the isotopic abundance ratios of processed material that has escaped the progenitor star. Moreover, these data are used to probe theories of chemical evolution through a sample of AGB stars, protoplanetary nebulae, and young and evolved PNe. One goal is to constrain the timelines and list of tracers for studying the molecular emission in these sources and examine the role of clumping for different species.

The assumption of spherical symmetry is not justified for the vast majority of PNe. The interpretation of spatially-resolved observations cannot rely solely on the application of 1D codes, which may yield incorrect abundances determinations resulting in misleading conclusions. The 3D photoionisation code MOCASSIN (Monte CArlo SimulationS of Ionised Nebulae) is designed to remedy these shortcomings. The 3D transfer of both primary and secondary radiation is treated self-consistently without the need of approximations. The code was benchmarked and has been applied to the study of several PNe. The current version includes a fully self-consistent radiative transfer treatment for dust grains mixed within the gas, taking into account the microphysics of dust-gas interactions within the geometry-independent Monte Carlo transfer. The new code provides an excellent tool for the self-consistent analysis of dusty ionised regions showing asymmetries and/or density and chemical inhomogeneities. Work is currently in progress to incorporate the processes that dominate the thermal balance of photo-dissociation regions (PDRs), as well as the formation and destruction processes for all the main molecular species.

PNe display a variety of large and small-scale structures which have been the object of a large number of observational and theoretical studies in the last two decades. This review contains a brief description of the different observational approaches used to determine the structure of PNe, and some critical discussion about the morphological components whose formation we believe we understand, and those which instead are still poorly understood.

We present non-LTE models of the wind for the central star in NGC 6543. The models suggest that the star is hydrogen-rich. The iron composition is solar, which, in turn, suggests that the hot X-ray emitting gas is of nebular origin.