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Planetary Nebulae (PNe) are the result of heavy mass loss of the asymptotic giant branch (AGB) stars. They are understood in terms of Kwok's (1978) interacting-winds model as the product of the mass-loss history on the AGB and the central…
High quality spectrophotometric observations of 30 Planetary Nebulae in the Galactic Bulge have been made. Accurate reddenings, plasma parameters, and abundances of He,O,N,S,Ar,Cl are derived. We find the abundances of O,S,Ar in the…
Studying a range of old metal-poor stars provides information over cosmological timescales of our Galaxy. Such studies are indicative of the pristine gases and evolution of the Milky Way. Deriving stellar parameters and abundances from…
The correlations between planetary nebula (PN) morphology and the nature of their progenitors are explored by examining homogeneous PN samples in the Galaxy and the Magellanic Clouds. We selected PNe with reliable abundances from spectral…
A prerequisite for probing theortical evolutionary models for high-mass stars is the determination of stellar physical properties with a high accuracy. We do this for three binary systems containing components with masses above 10 Msun:…
The chemical abundance patterns of the oldest stars in the Galaxy are expected to contain residual signatures of the first stars in the early universe. Numerous studies attempt to explain the intrinsic abundance scatter observed in some…
The methods of abundance determinations in HII regions and planetary nebulae are described, with emphasis on the underlying assumptions and inherent problems. Recent results on abundances in Galactic HII regions and in Galactic and…
We study the relation between the chemical composition and the type of dust present in a group of 20 Galactic planetary nebulae (PNe) that have high quality optical and infrared spectra. The optical spectra are used, together with the best…
Chemical evolution models for the Galactic disk under an inside-out formation scenario are presented for seven sets of stellar yields, all of them metal dependent. In particular, the effects of yields from massive and…
We report on non-LTE Ne abundances for a sample of B-type stellar members of the Orion Association. The abundances were derived by means of non-LTE fully metal-blanketed model atmospheres and extensive model atoms with updated atomic data.…
Planetary Nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the Population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations…
We study the hypothesis of high metallicity clumps being responsible for the abundance discrepancy found in planetary nebulae between the values obtained from recombination and collisionaly excited lines. We generate grids of…
In view of their nature, planetary nebulae have very short lifetimes, and the chemical abundances derived so far have a natural bias favoring younger objects. In this work, we report physical parameters and abundances for a sample of old…
Planetary nebulae (PNe) have three main components: a central star (CS), ionised gas and dust in the nebula. Each of them contains critical chemical fingerprints of their evolution, serving as tracers of the evolution, nucleosynthesis and…
We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) models, with diffusive overshooting from all the convective borders, in the metallicity range Z/4 < Z < 2Zsun. They are compared to recent precise nebular…
The spectra of the planetary nebula NGC2392 is reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope. The aim is to determine the chemical composition of this object. We also make use of IUE and…
We present the results of a study aimed at determining the 12C/13C ratio in two samples of planetary nebuale (PNe) by means of mm-wave observations of 12CO and 13CO. The first group includes six PNe which have been observed in the 3He+…
It is now clear that abundance variations from star-to-star among the light elements, particularly C, N, O, Na and Al, are ubiquitous within galactic globular clusters; they appear seen whenever data of high quality is obtained for a…
Inhomogeneous chemical evolution models of galaxies which try to reproduce the scatter seen in element-to-iron ratios of metal-poor halo stars are heavily dependent on theoretical nucleosynthesis yields of core-collapse supernovae. Hence…
We present spectroscopic observations and chemical abundances of 16 planetary nebulae (PNe) in the outer disk of M31. The [O III] 4363 line is detected in all objects, allowing a direct measurement of the nebular temperature essential for…