We studied Planetary Nebulae (PNe) metallicity gradients using Ar abundances. We compared them with H ii regions in the galaxies of the local universe M 31, M 33, NGC 300 and in the Milky Way. Galactocentric radio (RG) and chemical abundances were collected from the literature, carefully selecting an homogeneous sample for each galaxy. In these galaxies, metallicity gradients computed with PNe abundances are flatter than those of H ii regions.

In the last decade great strides have been made in understanding the role of binary stars in the evolution and shaping of planetary nebulæ (PNe). Observational efforts have mainly focused on finding close binaries with orbital periods of 1 day or less. Those close binary systems make up around 1 in 5 PNe, and constitute the youngest accessible window into the aftermath of the critical and unobserved common-envelope (CE) phase of binary-star evolution. The poster focused on our recent work with the High Resolution Spectrograph (HRS) on the Southern African Large Telescope (SALT) to search for long-period binaries in PNe. Considerably less is known about such long-period binaries with orbital periods of weeks to years, but they may be fundamental to improving CE population synthesis models and for determining the total binary fraction of PNe. The queue-mode operation of SALT and the excellent sensitivity and stability of HRS (which is enclosed in a vacuum tank) are ideally suited to detecting binaries with low radial-velocity amplitudes over the expected timescales of weeks to years. Many exciting new discoveries about binaries have already been made in this newly-accessible southern horizon in time-domain astronomy thanks to the many unique advantages of SALT.

Accurate measurements of the 4He/H abundance ratio are important in constraining Big Bang nucleosynthesis, models of stellar and Galactic evolution, and H ii region physics. We discuss observations of radio recombination lines using the Green Bank Telescope toward a small sample of H ii regions and planetary nebulae. We report 4He/H abundance ratio differences as high as 15–20% between optical and ratio data that are difficult to reconcile. Using the H ii regions S206 and M17 we determine 4He production in the Galaxy to be dY/dZ = 1.71 ± 0.86.

Helium abundances were derived for a sample of planetary nebulae of the Small Magellanic Cloud. These abundances were corrected from the chemical evolution of the galaxy as well as from stellar nucleosynthesis, and the primordial helium abundance then was estimated for the sample. Results indicate that the resulting average value for the sample is consistent with the expected values for primordial helium from SBBN and other values derived from HII regions in different stellar systems, even varying the enrichment ratio within its uncertainty range.

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.

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 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.