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.

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.

From the sample of 613 PNe used in the paper ‘Revised Diagnostic Diagrams for Planetary Nebulae’ (Riesgo & López, 2006) we have isolated a subsample of 51 PNe defined by log [H$\alpha$/[N II]]$<0$ and log [H$\alpha$/[S II]] $<0.4$. These objects have extremely intense [N II] and [S II] lines with respect to H$\alpha$ and are indicative of either very low excitation and/or high optical depth conditions, abundance effects in the case of N or cooling effects in shock excited regions, such as those expected in high velocity, collimated outflows. We have undertaken an imaging and detailed kinematic study of all the members of the subsample visible from the northern hemisphere. In this work we discuss the results and some correlations found between the anomalous line ratios in these objects and their morphological and kinematic characteristics.

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.

Emission-line observations made with the Spitzer Space Telescope are used to test the predicted ionizing spectral energy distributions of various stellar atmosphere models.

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 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).

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.

HST multi-epoch images and VLT integral-field, high resolution spectroscopy allowed us a robust determination of the 3-D geometry and orientation of the nebula surrounding He 2-147, and to measure its apparent expansion in the plane of the sky. Applying the expansion parallax method results in a distance which is significantly shorter that the one obtained via the period-luminosity (P-L) relationship for the Mira component. We show how allowing for shock excitation of the nebula, as suggested by the extremely broad nebular line profiles, enables both distance derivations to be reconciled.

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.

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 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.

Despite many studies, the post-AGB phase is still not well understood. To make progress in this field, we searched for information about proto-planetary nebulae and built a catalogue of post-AGB objects. Based on collected data we were able to trace the evolution of stars in their late stages making a distinction between carbon and oxygen-rich objects. We focused our attention on spectral features seen in ISO data and clues for AGB nucleosynthesis. Together with the newest HST images of post-AGB objects we can study correlations between morphological types and chemical and physical properties of stars to improve our understanding of stellar evolution.

High-resolution 905-1187Å spectra of the central star of NGC 7009 obtained with the FUSE satellite provide new constraints on the mass loss and atmosphere parameters. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. The only other wind lines are S VI 933-44 (FUSE) and N V 1238-42 and O V 1371 from IUE spectra. C IV 1548-50 and P V 1118-28 are not present, indicating that the wind is very highly ionized. A lower limit on the mass loss rate ($\dot{M}>10^{-8} M_{\odot} $y$^{-1}, v_{\infty}=2450$ km s$^{-1}$) has been derived from an SEI analysis of these wind lines. Preliminary identification of several photospheric spectral features include several strong Fe VII and O VI lines between 1100 and 1170 Å.

We present Spitzer/MIPS far-infrared (FIR) mapping of O-rich AGB star, R Hya.

We present a powerful new tool to disentangle the 3-D geometry and kinematic structure of gaseous nebulae. The method consists of combining commercially available digital animation software to simulate the 3-D structure and expansion pattern of the nebula with a dedicated, purpose built rendering software and graphical user interface that produce the final images and long slit spectra which are compared to the real data.

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.

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 our recent results of the high dispersion spectroscopy of a Galactic halo planetary nebula, K 648, in the globular cluster M 15. The position-velocity diagrams of our spectra indicate the existence of collimated outflows in K 648. In the [N II$\lambda$6583 diagram, we found high velocity components with a velocity $\sim$60 km s$^{-1}$ in the central region of K648.

A better understanding of the nature of the molecular and ionized gas envelopes of planetary nebulae (PNe) is important both to our understanding of their contribution to the ISM and to the evolution of PNe themselves. Using HST's unprecedented resolution and sensitivity for near-IR observations, we are studying the distribution and intensity of molecular gas emission from PNe.