The author presents the results of Berkeley-Illinois-Maryland (BIMA) array interferometric observations in the CO $J=1$–0 line toward X Her and EP Aqr, semiregular pulsating stars with a composite CO line profile, and also reports finding a disklike structure in X Her. In the CO spectrum both of X Her and EP Aqr, a composite profile including narrow and broad components is seen as reported by the previous single-dish observations. The spatial structure of the broad component region of X Her shows a bipolar shape, and that of the narrow component shows an elliptical/spherical shape. The blue- and red-shifted parts of the X Her narrow component show a systematic difference in the velocity integrated intensity map. The spatio-kinematic properties of the X Her narrow component are reminiscent of a Keplerian rotating disk with a central mass of 0.9 M$_{\odot}$. The spatial distributions of both the narrow and the broad components of EP Aqr appear to be roughly round with the same peak positions; no significant velocity gradient is seen. The spatio-kinematic properties of EP Aqr are reminiscent of a multiple-shell structure model rather than of a bipolar flow and disk model.

We present total element abundances based upon newly acquired spectrophotometry of a sample of $>$120 Galactic PNe. We continue to explore the use of the near-IR [S III] features to determine S$^{+2}$ abundances and to improve total extrapolated sulfur - a useful metallicity tracer. With this compilation we explore abundance patterns in PNe that reveal signatures of stellar evolution and nucleosynthesis as well as larger-scale galactic chemical evolution.

The progress over the last years in modelling the atmospheres and winds of PN central stars is reviewed. We discuss the effect of the inclusion of the blanketing by millions of metal lines in NLTE on the diagnostics of photospheric and stellar wind lines, which can be used to determine stellar parameters such as effective temperature, gravity, radius, mass loss rate and distance. We also refer to recent work on the winds of massive O-type stars, which indicates that their winds are possibly inhomogeneous and clumped. We investigate implications from this work on the spectral diagnostics of PN central stars and introduce a method to determine wind clumping factors from the relative strengths of H$_{\alpha}$ and He II 4686. Based on new results we discuss the wind properties of CSPN.

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.

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 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.

Based on existing hydrodynamical simulations, we review our present understanding of the formation and evolution of planetary nebulae (PNe) and discuss the relevant processes responsible for the development of the basic (1D) nebular structures.

From a survey of PNs in NGC 300 we obtain its PNLF. We use it to derive a distance estimate, and briefly discuss the PNLF shape.

We use H$_2$ as a marker to trace the interaction between the older and slower AGB wind and the newer fast wind. Integral field spectroscopy is a tool to probe the interactions of these winds. The measurement of the various line ratios makes it possible to differentiate between the excitation mechanisms. We have obtained $K$-band observations with UIST+IFU at UKIRT and SINFONI at VLT. The UKIRT observations enable us to locate the areas of emission over an area of $\sim 6 \times 3$ arcseconds, whilst SINFONI can provide high resolution sub-arcsecond observations. IRAS 19306+1407 is a B0/1 spectral type post-AGB/Young PN with a bipolar outflow and displays a mixture of shocks and fluorescence. It has emission lines that emanate from an elongated bipolar structure and bright arcs. The combination of H$_2$ and existing polarimetry enables us to analyse the gas and dust around this evolved star.

Using the VLBA, we have observed water maser emission in the pre-planetary nebula candidate, IRAS 19134+2131 (I1913), in which the water maser spectrum has two groups of emission features separated in radial velocity by $\sim$100${\rm km s}$^{-1}$. The morphology and 3-D kinematics indicate the existence of a fast collimated flow with a dynamical age of only $\sim$40 years. Such a “water fountain” source is a signature of the recent operation a stellar jet that may be responsible for the final shape of the planetary nebula into which I1913 is expected to evolve. We have also estimated the distance to I1913 on the basis of an annual parallax and the kinematics of IRAS 19134+2131 in our Galaxy. I1913 may be a component in the “thick disk” or the Galactic “warp”, whose kinematics are different from those of the Galactic “thin” disk.

Only a handful of binary central stars of planetary nebulae (PNe) are known today, due to the difficulty of detecting their companions. Preliminary results from radial velocity surveys, however, seem to indicate that binarity plays a fundamental, rather than marginal role in the evolution of PNe and that the close binary fraction might be much larger than the currently known value of 10-15%. In this review, we list all the known binary central stars, giving an updated census of their numbers and selected characteristics. A review is also given of the techniques used to detect binaries as well as selected characteristics of related stellar classes which might provide constraints (or additional puzzles) to the theory of PN evolution. Finally, we will formulate the conjecture that all PNe derive from binary interactions and suggest that this is not inconsistent with our current knowledge.

We present a systematic observational study of 32 PNe that present point-symmetric structures, multiple bipolar outflows or other related features.

Planetary nebulae (PNe) in the Magellanic Clouds (LMC, SMC) offer a unique opportunity to study both the population and evolution of low- and intermediate-mass stars in an environment which is free of the distance scale bias that hinders Galactic PN studies. The emission shown by PNe in the 5–40 $\mu$m range is characterized by the presence of a combination of solid state features (from the dust grains) and nebular emission lines superimposed on a strong dust continuum. We acquired low resolution IRS spectroscopy of a selected sample of LMC and SMC PNe whose morphology, size, central star brightness, and chemical composition are known. The data have been acquired and reduced, and the IRS spectra show outstanding quality as well as very interesting features. The preliminary analysis presented here allows to determine strong correlations between gas and dust composition, and nebular morphology. More detailed analysis in the future will deepen our knowledge of the mass-loss mechanism, its efficiency, and its relation to PN morphology.

We have observed the X-ray brightest planetary nebula BD +30° 3639 with the new Japanese astronomical satellite Suzaku. With its superior spectral resolution back-illuminated CCD camera, a blend of K-lines from highly ionized C, N, O elements are successfully resolved into individual species, and an extremely high relative abundance ratio of C/O $\sim$ 40 is obtained. This strongly suggests the direct measurement of the helium shell-burning products.

We are preparing a catalog of extragalactic planetary nebulae. The current number of entries is $\sim$8,000 objects, with the largest samples coming from the Local Group (SMC, LMC, M33, and M31), but with representation from over 55 galaxies. The catalog is expected to be complete in late 2007.

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 present the results of a small mid-infrared imaging survey of planetary nebulae. Of 21 objects observed 19 were resolved. Only in NGC 6210 was there a marked contrast between the dust morphology and the emission line morphology. For all the other objects the dust and the gas must be well mixed even in the faint lobes of bipolar objects such as Fg3, Pe1-7, and NGC 6881.

We report on our studies of the physical structure of the planetary nebula (PN) NGC 7662. Using (3D) Integral Field Spectroscopy we have been able to measure the electron temperature more accurately and at a larger number of radial locations than before. Here we briefly present our method by which we find a strong positive temperature gradient with increasing radius. According to hydrodynamic models a hot halo, when compared to the central star, can be the product of the passage of an ionization front (e.g. Marten 1993). Such a gradient is not found in equilibrium models, and this finding – when confirmed for other objects – strongly advocates the use of hydrodynamic models when modeling PN halos.

Here we are reporting the detection of HCO$^+$ ($J=1\rightarrow 0$) emission as well as weak emission of CO($J=1\rightarrow 0$) toward the planetary nebula (PN) K 3-35 as a result of a molecular emission survey carried out toward this source. K 3-35 is remarkable because it is one of the two PNe that are known to exhibit water maser emission. In this nebula, the emission is present in the central region as well as at a distance of $\simeq$ 5000 AU away from the center. The presence of molecular emission reveals some clues that could lead to the understanding of the persistence of water molecules in its envelope. We also report new spectra of the CO ($J=2\rightarrow 1$) transition. From the CO emission we have obtained a value for the excitation temperature of the molecular gas of $\simeq$ 20 K. Using this result, we have estimated a molecular mass for the envelope of $\simeq$0.017 $M_{\odot}$, and that the abundance for the HCO$^{+}$ is 6.1 $\times 10^{-7}$.

We present results of a quantitative spectral analysis of a sample comprising eleven hydrogen deficient post-AGB stars of the spectral type PG 1159 with state-of-the-art NLTE model atmospheres. For all objects high resolution spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) are available. The FUV spectra of PG 1159 stars are dominated by lines of helium, carbon and oxygen, and for the first time we also identified lines of several trace elements as sulfur and silicon which allow to determine the abundances of light metals in the atmospheres of these stars. As these stars show nuclear processed former intershell matter on their surface, the determined abundances also allow us to constrain the predictions of evolutionary models and element abundances in AGB stars.