A new assessment of the physics of the luminosity function of planetary nebulae is presented, based on our grid of nebular evolutionary sequences computed with a 1D radiation-hydrodynamics code. The nebular evolution is followed from the formation stage in the vicinity of the asymptotic-giant branch across the Hertzsprung-Russell diagram until the white-dwarf domain is reached, for various central-star models coupled to different initial envelope configurations. Along each sequence the relevant line luminosities of the nebulae are computed and analyzed. Our models predict that reasonably dense initial circumstellar envelopes with central stars of slightly above 0.6 $M$_{\odot}$$ will remain nearly optically thick and are able to provide the observed 5007 Å cutoff luminosity. We cannot support the claim of Marigo et al. (2004) according to which only planetary nebulae with central stars of $> 0.7$ $M_{\odot}$ are able to provide sufficient 5007 Å line emission to account for the bright end of the luminosity function.

Diffuse X-ray emission from hot gas in planetary nebulae (PNe) was hinted by ROSAT and ASCA, but only the improved sensitivity and spatial resolution of XMM-Newton and Chandra have allowed detailed studies of the hot gas in PNe. These studies are helping us to better assess the effects of fast stellar winds and collimated outflows in the shaping and evolution of individual PNe, but a comprehensive picture is lacking, because the X-ray analysis of different PNe is not homogeneous and, therefore, cannot be intercompared. Furthermore, a significant number of X-ray observations of PNe that did not detect X-ray emission have not been reported. We have undertaken a systematic study of all XMM-Newton and Chandra observations of PNe benefiting from a homogeneous analysis using the most up-to-date versions of SAS and CIAO, respectively, and the recently released calibration files with greater accuracy for energies below 1.0 keV. We present reprocessed event files, derived data products (X-ray images and spectra), supporting observations at other wavelengths, and analysis results in a database, the XPN Database, that can be accessed at http://www.iaa.csic.es/xpn

Mid-IR images of a small sample of post-AGB stars have been obtained with the mid-IR camera, OSCIR, mounted on the 8-m Gemini North Telescope. Model calculations, using a 2-D dust RT code, have been performed in order to constrain the physical and chemical properties of the dust in the envelopes, for each object. Studies of individual objects in this transitional phase can be used to investigate the final period of AGB mass loss and improve our current understanding of the evolution of PN. Mid-IR images and modelling results for IRAS 22223+4327 are presented here. The observed mid-IR structure, which shows two emission peaks, is interpreted as the detection of two limb brightened edges of a dust torus. The position of the dust torus is in agreement with the position of the outflows observed in the archived HST optical images. This object deviates from axisymmetry, in the same way as several other post-AGB stars, where one of these peaks is brighter than the other. From the modelling of the SED of this object, estimates for the mass of the dust in the envelope and the mass-loss rate are derived.

We present preliminary photometry of 122 PNs discovered in the elliptical galaxy NGC 821. We build the PN luminosity function (PNLF), which gives a distance modulus m - M = 31.9$\pm$0.3, in good agreement, within the uncertainties, with the SBF distance modulus 31.91$\pm$0.17 obtained by Tonry et al. (2001).

We present preliminary results of CTIO 4-m MOSAIC 2 imaging and Magellan and Gemini-South multi-object spectroscopy for NGC 6822. In our on-band off-band ([OIII] 5007, H$\alpha$) MOSAIC 2 data of the whole galaxy, we are searching for Planetary Nebula (PN) candidates and measuring their [OIII] 5007 fluxes. So far we have confirmed 13 of the 17 PN candidates reported previously and some other faint candidates. We obtained Magellan and Gemini-South multi-object spectroscopic data to derive simultaneously, the chemical abundances of some HII regions and PNe. The observed objects are distributed in different zones of the galaxy. Our aim is to obtain the chemical abundances of the present ISM (HII regions) and the corresponding values at the time of formation of the PNe. With these data the chemical homogeneity of NGC 6822 will be tested and the abundance pattern given by HII regions and PNe will be used as an observational constrain for computing chemical evolution models to infer the chemical history of NGC 6822.

Over the past 15 years the growth of detailed information about Planetary Nebulae in the Large and Small Magellanic Clouds (MCPN) has been explosive, to the point where these galactic laboratories are the preferred context for furthering and refining our understanding of this late phase of stellar evolution. Deep, photometrically uniform surveys have pushed the population of confirmed MCPN above 800, good-quality optical spectra exist for the bulk of these nebulae, infrared and satellite UV spectra of a few dozen PNe are archived or will become available soon, and high-resolution (HST) images have been archived for over 150 nebulae. In this paper I review the accumulated knowledge of MCPN: including physical and chemical properties of the nebulae and their relation to morphological characteristics; central star properties and what they tell us about the progenitor population; and what new insight has been gained from MCPN about the evolution of the combined PN+central star systems.

Some stellar maser sources at preplanetary stage have very thick circumstellar envelopes, for which no near-infrared identifications have been made. We investigated such stars at radio/NIR/MIR wavelengths using the NRO 45-m, ANU 2.2-m, UH 2.2-m, and SUBARU 8.2-m telescopes. Furthermore, using the Spitzer/Glimpse survey of the Galactic plane, we found counterparts in the 3.6 micron band for all of the OH/IR objects without previous NIR identification. One of the most interesting objects among these is IRAS 18450–0148 (W43A) with collimated outflows. Their spectra indicate that they have massive thick disks.

In this review we present a brief discussion on the observational evidence in favor of the presence of temperature variations, and conclude that many planetary nebulae show spatial temperature variations that are larger than those predicted by 1D static chemically homogeneous photoionization models. To determine accurate chemical abundances it is necessary to know the cause of these temperature variations and several possibilities are discussed. The importance of this problem is paramount to test the models of stellar evolution of low and intermediate mass stars and of the chemical evolution of galaxies. We conclude that the proper abundances for chemically homogeneous PNe are those derived from recombination lines, while for the two-abundance nebular model the proper heavy element abundances relative to hydrogen are those derived from visual and UV collisionally excited lines adopting the $t^2$ values derived from $T_e$([O III]) and $T_e$(Balmer).

Improved trigonometric parallaxes of 16 nearby planetary nebulae are presented. Continued observations now give reduced errors and additional nebulae since initial results were given in 1997. Twelve nebulae have parallax errors less than 20 percent. Comparisons with other distance estimates are discussed.

We have analyzed the [Fe II] and [Ni II] emission lines in the bipolar planetary nebula Mz 3. We find that the [Fe II] and [Ni II] lines arise exclusively from the central regions. Fluorescence excitation in the formation process of these lines is negligible for this low-excitation nebula. From the [Fe II]/[Ni II] ratio, we obtain a higher Fe/Ni abundance ratio than the solar value. The current result provides further supporting evidence for Mz 3 as a symbiotic Mira.

The radio astronomical approach is applied to 2D and 3D Doppler tomography for close binary central stars in planetary nebulae. It is more effective than the traditional one.

The formation and shaping of planetary nebulae (PNe) is probably the most exciting, yet least understood issue in the late evolution of (1–8) $M_{\odot}$ stars. PNe evolve from the envelopes of AGB stars through the supposedly very short ($\lesssim10^3$ yr) pre-PN (or PPN) phase (Balick & Frank 2002). In 1998, in a radical departure from the then long-standing theoretical paradigm for PN formation, Sahai & Trauger (1998) proposed that as most stars evolve off the AGB, they drive collimated fast winds that sweep up and shock the AGB circumstellar envelope, producing the observed dramatic changes in circumstellar geometry and kinematics from the AGB to the PN phase. Pre-Planetary Nebulae (PPNs) have traditionally been understood as rare objects that represent a transitory phase in the evolution of AGB stars to PNs. In recent years, mainly due to high-resolution imaging surveys with HST, it has become possible to start studying the detailed physical properties for a statistically significant number of these objects. Here we provide a brief report of results from our several large surveys of PPNs with HST (and supporting ground-based observations).

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.