We present the first direct measurements of the magnetic field strength and direction in a collimated jet from an evolved star on its way to become a planetary nebula. Very Long Baseline Array (VLBA) observations of the linear and circular polarization of the H$_2$O masers in the collimated jet of W43A reveal a strong toroidal magnetic field, indicating that the jet is magnetically collimated. The magnetic field strength in the jet extrapolated back to the stellar surface yields a surface field of several Gauss, consistent with the measurements of maser polarization in a large sample of evolved stars. The origin of the magnetic field is yet unknown, although the jet precession might point to the existence of a heavy planet or stellar companion. This is the first direct observational evidence for magnetic collimation in the jets, that likely plays an important role in shaping planetary nebulae.

We discuss the formation of globules in planetary nebulae, typified by those observed in the Helix Nebula. We show that the properties of the globules, their number, mass, separation, and overall geometry strongly support a scenario in which globules are formed by the fragmentation of a swept-up shell as opposed to models in which the knots form in the AGB wind. We show that the RT or other instabilities which lead to the break-up of shells formed in the nebulae by fast winds or ionization fronts can produce arrays of globules with the overall geometry and within the mass range observed. We also show that the presence of a magnetic field in the circumstellar gas may play an important role in controlling the fragmentation process. Using field strengths measured in the precursor AGB envelopes, we find that close to the central star where the fields are relatively strong, the wavelengths of unstable MRT modes are larger than the shell dimensions, and the fragmentation of the shell is suppressed. The wavelength of the most unstable MRT mode decreases with increasing distance from the star, and when it becomes comparable to the shell thickness, it can lead to the sudden, rapid break-up of an accelerating shell. For typical nebula parameters, the model results in numerous fragments with a mass scale and a separation scale similar to those observed. Our results provide a link between global models of PN shaping in which shells form via winds and ionization fronts, and the formation of small scale structures in the nebulae.

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.

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.

We review work on the evolution of planetary nebulae and proto-planetaries via magneto-rotational mechanisms showing that a dynamo generated magnetic field can produce the energy and momentum needed to drive pPN and PNe outflows. Angular momentum considerations lead to the conclusion that single stars can not support strong fields for long times. Thus we take the working hypothesis that most PN may form via binary stars. We propose that the grand challenge for PN studies is fully understanding the diverse physical processes at work in binary late stage evolution including the development of disks, fields and outflows.

Hydrodynamical simulations played an important role in understanding the dynamics and shaping of planetary nebulae in the past century. However, hydrodynamical simulations were just a first order approach. The new millennium arrived with the generalized understanding that the effects of magnetic fields were necessary to study the dynamics of planetary nebulae. Thus, B-fields introduced a whole new number of physical possibilities for the modeling. In this paper, we review observational work done in the last 5 years and several works on the magnetohydrodynamics of proto-planetary nebulae, since all the effort has been focused on that stage, and discuss different scenarios for the origin of magnetized winds, and the binary-bipolarity relation.

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.

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.

The properties of bright extragalactic planetary nebulae are reviewed based upon the results of low and high resolution spectroscopy. It is argued that bright extragalactic planetary nebulae from galaxies (or subsystems) with and without star formation have different distributions of central star temperature and ionization structure. As regards the chemical compositions, oxygen and neon are generally found to be unchanged as a result of the evolution of the stellar progenitors. Nitrogen enrichment may occur as a result of the evolution of the progenitors of bright planetary nebulae in all stellar populations, though this enrichment may be (more) random in old stellar populations. Helium abundances appear to be influenced by the chemical evolution of the host galaxy, with planetary nebulae in dwarf spheroidals having systematically elevated abundances. Neither the age nor the metallicity of the progenitor stellar population has a strong effect upon the kinematics observed for nebular shells. Both the range of expansion velocites, 8-28 km s$^{-1}$, and the typical expansion velocity, $\sim 18\,\mathrm{km\,s}^{-1}$, are found to be relatively constant in all galaxies. On the other hand, bright planetary nebulae in the bulge of M31 have systematically higher expansion velocities than their counterparts in M31's disk. The expansion velocities show no trend with nebular H$\beta$ luminosity, apart from a lack of large expansion velocities at the highest luminosities (the youngest objects), but appear to correlate with the $5007/\mathrm{H}\beta$ ratio, at least until this ratio saturates. These results suggest a link between the evolution of the nebular shells and central stars of bright extragalactic planetary nebulae.

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.

Planetary Nebula (PN) shells and AGB circumstellar envelopes evolve under a wide range of external conditions, from the high ISM densities found in the Galactic plane, to the rarefied and hot intracluster medium where the systemic velocity of the star can be as high as 2000 km $s^{-1}$. We explore the effects that the external pressure and/or stellar systemic velocity have on the observable properties of PNe. We investigate how the mass and size of the PN halos are reduced when the star is moving with respect to the external medium. We have studied as well how the mass of the circumstellar envelope is fed by ISM material when high ISM densities characteristic of the Galactic plane are considered. By studying the evolution of PNe in the intracluster medium in Virgo, we infer shorter PN lifetimes than what is usually adopted. This has important implications, since the assumed PN lifetime strongly affects the fraction of intracluster light derived from PN studies.

The Coma cluster is the richest and most compact of the nearby clusters, yet there is growing evidence that its formation is still on-going. A sensitive probe of this evolution is the dynamics of intracluster stars, which are unbound from galaxies while the cluster forms, according to cosmological simulations. With a new multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru telescope and FOCAS, we can now detect and measure the line-of-sight velocities of the intracluster planetary nebulae which are associated with the diffuse stellar population of stars, at 100 Mpc distance. We detect significant velocity substructures within a 6 arcmin diameter field, centred on the Coma X-ray cluster emission. One substructure is present at $\sim $5000 km s$^{-1}$, probably from infall of a galaxy group, while the main intracluster stellar component moves at $\sim $6500 km s$^{-1}$. Hence the ICPNs associated with the diffuse light at the position of the MSIS field are not bound to the nearby cD galaxy NGC 4874, whose radial velocity is $\sim $700 km s$^{-1}$ higher.

Planetary nebulae are useful kinematic tracers of the stars in all galaxy types. I review recent observationally-driven developments in the study of galaxy mass profiles. These have yielded surprising results on spiral galaxy disk masses and elliptical galaxy halo masses. A key remaining question is the coupling between PNe and the underlying stellar populations.

We describe the implementation and accuracy of slitless radial velocity measurements of extragalactic PNs with Subaru and the FOCAS spectrograph. As a first application of the method, we have extended a previous study of PNs in NGC 4697 to larger angular distances from its center, failing again to find evidence of dark matter in this elliptical galaxy.

About 500 MASH(Macquarie/AAO/Strasbourg H$\alpha$ planetary nebula project) PNe were discovered towards the galactic bulge (Parker et al. 2006). For 405 MASH PNe with a diameter $<$ 35 arcsec, we obtain surface brightness, diameter and dynamical age of the nebulae. From line intensity ratios of 133 GBPN observed with the 6dF device, we obtain their density and ionized mass, and their central star temperatures. We discover 15 bipolar and/or nitrogen-rich GBPNe having probably massive stellar progenitors (Peyaud, 2005).

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.

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 characterize the common properties of highly collimated bipolar outflows and identify the most plausible mechanisms that create and maintain them.

In this work we attempt to find Planetary Nebulae(PNe) belonging to the thick disk population of the Galaxy, based on the proper motion and radial velocity data of the objects available in literature, by using a simulation and Bayesian likelihood analysis. Making use of the established kinematical properties of the thick disk/thin disk/halo (TD/D/H) population of the Galaxy, we compute likelihoods of TD/D/H membership of 66 nebulae by fully taking into account the uncertainties associated with their proper motion and radial velocity data. We find 12 candidate PNe whose probability of belonging to the thick disc is 80% or greater, of which 9 PNe have a TD membership probability greater than 90%. Spectroscopy of the TD candidates is being planned and we hope this will shed light on the chemical characteristics of the TD population of the Galaxy, in the context of Planetary nebulae.

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.