We have acquired high spectral resolution observations (R=150,000) of the planetary nebulae NGC 7009 and NGC 6153, using bHROS on Gemini South. Observations of this type may provide a key to understanding why optical recombination lines (ORLs) yield systematically higher heavy element abundances for photoionized nebulae than do the classical forbidden collisionally excited lines (CELs) emitted by the same ions; NGC 7009 and NGC 6153 have notably high ORL/CEL abundance discrepancy factors (ADFs) of 5 and 10, respectively. Due to the opposite temperature dependences of ORLs and CELs, ORLs should be preferentially emitted by colder plasma. Our bHROS observations of NGC 7009 reveal that the [O III] 4363 Å CEL has a FWHM linewidth that is 1.5 times larger than that shown by O II ORLs in the same spectrum, despite the fact that all of these lines are emitted by the O$^{2+}$ ion. The bHROS spectra of NGC 6153 also show that its O II ORLs have significantly narrower linewidths than do the [O III] 4363 Å and 5007 Å lines but, in addition, the [O III] 4363 Å and 5007 Å lines show very different velocity profiles, implying the presence of large temperature variations in the nebula.

We describe a theoretical treatment of the recombination spectrum of O II. The ab initio calculations are carried out in intermediate coupling which allows the distribution of population among the 3P$_J$ ground levels of O$^{2+}$ to be correctly incorporated for the first time. The effects of dielectronic recombination due to states lying between the 3P$_J$ levels is also included. The new theory allows the strongest O II recombination lines to be used as a diagnostic of the temperature and density of the emitting region and illustrative examples are given.

Near-infared images from a NICMOS survey revealed the circumstellar matter around several proto-planetary nebulae (PPNe), including IRAS 18184–1623, AFGL 4106, and HD 179821 (=IRAS 19114+0002). The IRAS 18184 data was previously analyzed by O'Hara et al. (2003). Here we present the data on the other two objects.

The true nature of HD 179821 is still a subject of some debate. It could be a yellow hypergiant or a post-AGB star. Regardless, the NICMOS images show that it is surrounded by a nebula with a diameter of $\sim12^{\prime\prime}$. Until 1600 years ago, it was losing mass at a rate of 3 $\times 10^{-4}$ M$_{\odot}$ yr$^{-1}$. It now exhibits multiple concentric shells with small bipolar outer protuberances.

AFGL 4106 was known previously as a spectroscopic binary, consisting of a luminous F-type post-red-supergiant and an M-type red supergiant. It is surrounded by a faint nebula with a diameter of $\sim3^{\prime\prime}$. Here we present the first image that shows not only the nebula but also the binary companion. It appears at a position angle of $\sim270^{\circ}$ and a separation of 0.$^{\prime\prime}$3.

New Planetary Nebulae (PNe) were discovered through an [O III] 5007 Å emission line survey in the Galactic bulge region with $l >$ 0$^{\circ}$. We detected 240 objects, including 44 new PNe. Deep H$\alpha +$[N II] CCD images as well as low resolution spectra were obtained for the new PNe in order to study them in detail. Preliminary photo–ionization models of the new PNe with Cloudy resulted in first estimates of the physical parameters and abundances. They are compared to the abundances of Galactic PNe.

A byproduct of experiments designed to map the CMB is the detection of a new component of foreground galactic emission. The anomalous foreground at 10-30 GHz, unexplained by traditional emission mechanisms, correlates with 100$\mu$m dust emission, and is thus presumably due to dust. We present evidence obtained with the CBI and SIMBA+SEST supporting the existence of a 31GHz excess over free-free emission in PNe. Possible interpretations involve a spinning dust component or 1 mm extinction due to metallic needles.

The formation of planetary nebulae is a poorly understood phase of stellar evolution. In particular it is still not clear what mechanism leads to the complicated morphologies observed in such sources. We have started a systematic study of objects in transition from post-AGB to planetary nebula, and in this poster we show some preliminary results.

We have obtained new optical spectra with the ESO/VLT of the final helium flash star, V605 Aql. These spectra indicate that V605 Aql has evolved significantly in only 80 years. It now has a T$_{\rm eff}\sim$95,000 K and has abundances similar to those seen in [WC] central stars but not to those of a typical RCB star.

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.

The value of the $\alpha$ ratio, the number of PNe per unit bolometric luminosity in a galaxy, is computed using stellar population synthesis models covering the whole range of Hubble types of galaxies.

Model predictions are compared with the PNe counts in the Local Group, which indicate a fairly constant value of $\alpha$ – between 1 and 6 PNe per 10$^7$ solar luminosities – along the Hubble sequence.

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.

Bipolar planetary nebulae (BPNe) offer a unique opportunity to test models that aim to reproduce the PNe morphologies. In particular, kinematic studies of BPNe allow a reconstruction of the 3D structure of the nebula, otherwise hidden in imaging studies. With this aim in mind we have obtained long-slit echelle spectra of a sample of PNe which cover the full range of observed bipolar morphologies, from elliptical to highly collimated. The analysis of our kinematical data reveals equatorial expansion velocities in the low to medium range (3 to 16 km s$^{-1}$), while the polar expansion velocities range from 18 to 100 km s$^{-1}$. We find that the kinematics of the PN K 3-46 can only be explained by a decrease in the expansion velocity with time. The kinematical ages, calculated by using distances estimated from Galactic rotation curves, when available, or by using statistical values, show that the BPNe in our sample – even those which show non-extreme collimation – appear to be young. We have compared our results with the latest theoretical models of BPN formation, and find good agreement between the observed expansion velocities and the numerical models that use magnetic fields coupled with stellar rotation as the collimation mechanism.

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 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.

Relatives to Planetary Nebulae, such as barium stars or symbiotic systems, can shed light on the connection between Planetary Nebulae and binarity. Because of the observational selection effects against direct spectroscopic detection of binary PNe cores with orbital periods longer than a few dozen days, at present these “awkward relatives” are a critical source of our knowledge about the binary PNe population at longer periods. Below a few examples are discussed, posing constraints on the attempts to model nebula ejection process in a binary.

As an adjunct to the planetary nebula (PN) search from the AAO/UKST H$\alpha$ survey, a visual search was conducted for new emission nebulae from the SHASSA and VTSS surveys, outside a Galactic latitude of $\mid b\mid$ = 10°. Fifteen new objects were found from SHASSA and three from the available fields of VTSS. With one exception, all objects are $> 5^\prime$ across, as smaller nebulae are confused with large numbers of artifacts and compact emitters on these surveys. All previously known PNe larger than this size in the search area, as well as Hewett 1, PG 0108, and PG 0109 were recovered in this blind search. Candidates were selected as discrete, morphologically symmetric H$\alpha$ enhancements, to differentiate them from the ubiquitous diffuse emission structure of the ISM. These criteria were relaxed for the VTSS survey due to its poorer inherent resolution. Most of the new discoveries are probable Stromgren spheres in the ISM. Some show unusual line ratios (e.g. strong [O III] or [N II] emission) based on slit spectroscopy and WHAM data (see Madsen et al. 2006, this volume), suggesting these are ionised by a hot subdwarf or white dwarf star, and may be possible PNe. Our most interesting discovery is a rare bowshock nebula around a bright, previously unnoticed, nova-like cataclysmic variable.

We present Spitzer/IRS spectra of a small sample of galactic OHPNe. This is a rare class of transition sources displaying both radio continuum and OH maser emission at 1612 MHz. Our observations show that they are heavily obscured O-rich stars whose mid-infrared spectra are dominated by the simultaneous presence of strong and broad amorphous silicate absorption features together with crystalline silicate emission features which sometimes appear also in absorption. Three of the sources observed are non-variable, confirming their post-AGB status, while another two seem to be still strongly variable. We propose that OHPNe represent the youngest population of high-mass PNe in the Galaxy.

In this paper we explore the dynamics of ionization bounded planetary nebulae after the termination of the fast stellar wind. When the stellar wind becomes negligible, the hot, shocked bubble depressurizes and the thermal pressure of the photo-ionized region, at the inner edge of the swept-up shell, becomes dominant. At this stage the shell tends to fragment creating clumps with comet-like tails and long, photo-ionized trails in between, while the photo-ionized material expands back towards the central stars as a rarefaction wave. Once the photo-ionized gas fills the inner cavity, it develops a kinematical pattern of increasing velocity from the center outwards with a typical range of velocities starting from the systemic velocity to $\sim 50 {\mbox{ km s$^{-1}$}~}$ at the edges. The Helix nebula and the Dumbell nebula are clear examples of planetary nebulae at this late evolutionary stage.

The numerical experiment presented here (Figure 1) includes two phases: in the first phase, a typical two-wind model scenario (Kwok 1982) is considered, i. e., a fast wind with $v_{\infty}= 1000 \kms$ and $\dot{M} = 10^{-7} {\rm M}_{\odot} {\rm yr}^{-1}$ sweeps up a slow wind with $v_{\infty}= 10 \kms$ and $\dot{M} = 10^{-6} {\rm M}_{\odot} {\rm yr}^{-1}$. For simplicity, this phase lasts 1000 yr in the computation, but it could last longer or shorter depending on the particular track of stellar evolution. In the second phase, the fast wind is switched off, and the dynamical evolution is computed for a total of 8000 yr. In both phases the photo-ionization is considered following the approach of García-Segura & Franco 1996 with a central star that emits $10^{45}$ s$^{-1}$ ionizing photons. A simple expanding spherical morphology is adopted for simplicity (i.e., no rotation, magnetic field, or anisotropic mass-loss events).

The simulations are performed with the hydrodynamical code ZEUS-3D (version 3.4) (Stone & Norman 1992; Clarke 1996), and details about the set up can be found in García-Segura et al. (1999), and García-Segura et al. (2005) for the self-expanding grid technique.

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.

We present VLA (Very Large Array) observations of the 1720, 1667, 1665 and 1612 MHz OH maser emission from the central region of K 3–35. Circular polarization was found in the 1720, 1665, and 1612 MHz transitions. An estimate of the magnitude of the magnetic field, derived from the 1665 lines, toward this young planetary nebula is $\sim$ 0.14 mG at a radius of $\sim$ 250 AU.

We have recently (Gonçalves et al. 2006) shown that previously reported enhanced N abundances in fast, low-ionization emission regions (FLIERs) of PNe, particularly in NGC 7009, may be due to ionization effects. We reached this conclusion through the 3D MOCASSIN photoionization modeling of the bright inner rim of NGC 7009 and its pair of FLIERs, assuming homogeneous elemental abundances throughout the nebula, for N as well as other elements. The (N$^+$/N)/(O$^+$/O) ratio predicted by our models is 0.60 for the rim and 0.72 for the knots, clearly in disagreement with the N$^+$/N=O$^+$/O assumption of the ionization correction factors (ICF) method. Therefore the ICFs are underestimated in both components, rim and knots, but more so in the knots. This effect is partly responsible for the apparent N overabundance claimed for FLIERs.

Based on the above results we are also investigating what would be the effect of the N/O ICF overestimation on the definition of Type I PNe which do not have FLIERs-like structures.