Roberto D. D. Costa

• PhD
• Professor at University of São Paulo

High nitrogen abundance is characteristic of Type I planetary nebulae, as well as their highly filamentary structure. In the present work, we test the hypothesis of shocks as a relevant excitation mechanism for a Type I nebula, NGC 6302, using recently released diagnostic diagrams to distinguish shocks from photoexcitation. The construction of the...

High nitrogen abundance is characteristic of Type I planetary nebulae as well as their highly filamentary structure. In the present work we test the hypothesis of shocks as a relevant excitation mechanism for a Type-I nebula, NGC 6302, using recently released diagnostic diagrams to distinguish shocks from photoexcitation. The construction of diagra...

We study the evolution of oxygen abundance radial gradients as a function of time for the Milky Way Galaxy obtained with our MulChem chemical evolution model. We review the recent data of abundances for different objects observed in our Galactic disc. We analyse with our models the role of the growth of the stellar disc, as well as the effect of in...

We study the evolution of oxygen abundance radial gradients as a function of time for the Milky Way Galaxy obtained with our {\sc Mulchem} chemical evolution model. We review the recent data of abundances for different objects observed in our Galactic disc. We analyse with our models the role of the growth of the stellar disc, as well as the effect...

We investigate, in the light of new diagnostic diagrams, the role of shocks in the ionization profile of type-I planetary nebulae, and their relation to the empirical derivation of chemical abundances. We apply our technique to two well-known type-I objects: NGC 2440 and NGC 6302. Our results indicate that shocks play a very important role in the s...

A sample of AGB/RGB stars with an excess of Li abundances is considered in order to estimate their mass loss rates. Our method is based on a correlation between the Li abundances and the stellar luminosity, using a modified version of the Reimers formula. We have adopted a calibration based on an empirical correlation between the mass loss rate and...

A sample of AGB/RGB stars with an excess of Li abundances is considered in order to estimate their mass loss rates. Our method is based on a correlation between the Li abundances and the stellar luminosity, using a modified version of Reimers formula. We have adopted a calibration on the basis of an empirical correlation between the mass loss rate...

A sample of AGB/RGB stars with an excess of Li abundances is considered in order to estimate their mass loss rates. Our method is based on a correlation between the Li abundances and the stellar luminosity, using a modified version of Reimers formula. We have adopted a calibration on the basis of an empirical correlation between the mass loss rate...

We report new spectroscopic data on a sample constituted of 21 well observed planetary nebulae in the LMC. The observations were performed at the National Laboratory for Astrophysics (Brazópolis — Brasil) using the 1.6m telescope and a CCD detector. Extinction, electron temperature and densities were derived for all the planetaries and a comparison...

Some of the high luminosity stars in our Galaxy are surrounded by planetary-like nebulae formed by material ejected from the central star. The most interesting case is that of the ring nebula PK 289-0° 1 around the P Cygni star AG Car. Long slit spectroscopy shows that nitrogen is overabundant and oxygen underabundant in the nebula. The Hα/[NII] ra...

We report the results of our analysis of a well observed sample of southern planetary nebulae. The average S / O and Ar / O ratios are comparable to the solar value and to those observed in galactic H II regions. The He abundance correlates with the N / O ratio, confirming the trend found by previous studies, indicating the surface contamination of...

We present C / He ratios in the wind of a sample of 5 central stars of planetary nebulae having WC spectrum. The resulting values are comparable to those observed in population I WR stars.

Photoionized nebulae, comprising HII regions and planetary nebulae, are excellent laboratories to investigate the nucleosynthesis and chemical evolution of several elements in the Galaxy and other galaxies of the Local Group. Our purpose in this investigation is threefold: (i) compare the abundances of HII regions and planetary nebulae in each syst...

Photoionized nebulae, comprising HII regions and planetary nebulae, are excellent laboratories to investigate the nucleosynthesis and chemical evolution of several elements in the Galaxy and other galaxies of the Local Group. Our purpose in this investigation is threefold: (i) compare the abundances of HII regions and planetary nebulae in each syst...

Planetary nebulae (PNe) constitute an important tool to study the chemical evolution of the Milky Way and other galaxies, probing the nucleosynthesis processes, abundance gradients and the chemical enrichment of the interstellar medium. In particular, Galactic bulge PNe (GBPNe) have been extensively used in the literature to study the chemical prop...

Photoionized nebulae comprise basically HII regions and planetary nebulae, and their abundances give important clues on the nucleosynthesis and chemical evolution of their host galaxies. There is presently a large amount of data on these objects, especially for the elements He and N, which are strongly affected by the evolution of intermediate mass...

Planetary nebulae are the products of the evolution of low and intermediate mass stars. The chemical property studies of these objects give important information about the elemental abundances as He, O, Ne, Ar, S and their modifications associated with the evolution of the progenitor stars. The determination of accurate abundances in planetary nebu...

The aim of this work is to present our new series of chemical evolution models computed for spiral and low mass galaxies of different total masses and star formation efficiencies. We analyze the results of models, in particular the evolution of the radial gradient of oxygen abundance. Furthermore, we study the role of the infall rate and of the sta...

We review the state of our chemical evolution models for spiral and low mass galaxies. We analyze the consequences of using different stellar yields, infall rate laws and star formation prescriptions in the time/redshift evolution of the radial distributions of abundances, and other quantities as star formation rate or gas densities, in the Milky W...

We review the state of our chemical evolution models for spiral and low mass galaxies. We analyze the consequences of using different stellar yields, infall rate laws and star formation prescriptions in the time/redshift evolution of the radial distributions of abundances, and other quantities as star formation rate or gas densities, in the Milky W...

We analyze the evolution of oxygen abundance radial gradients resulting from our chemical evolution models calculated with different prescriptions for the star formation rate (SFR) and for the gas infall rate, in order to assess their respective roles in shaping gradients. We also compare with cosmological simulations and confront all with recent o...

In this work, we report physical parameters and abundances derived for a sample of 15 high extinction planetary nebulae located in the inner 2° of the Galactic bulge, based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman spectrograph. The new data allow us to extend our database including older, weaker objects that ar...

Most metal-rich AGB/RGB stars present strong Li underabundances, since this element is easily destroyed in the high temperatures of the stellar interiors. In spite of this fact, several of these stars are Li-rich, having Li abundances given by log (Li/H) + 12 > 1.5. In the present work, we extend our previous investigation on AGB/RGB stars to the e...

This work describes the modelling of the 3D structure and position-velocity (P-V) diagrams of NGC 2440, a well known planetary nebula, aiming to describe the morphology of this object, specially its core. We have used high resolution spectra and P-V diagrams to reproduce the 3D structure of the nebula using SHAPE, a software that allows 3D modellin...

We investigate the variations of the radial O/H abundance gradients from planetary nebulae (PN) located at different distances from the galactic plane. In particular, we determine the abundance gradients at different heights from the plane in order to investigate a possible gradient inversion for the objects at larger distances from the plane. We c...

Stars form, die and eject the elements created by stellar nucleosynthesis. Chemical evolution models are the tool used to interpret the elemental abundances in terms of star formation rate and of the gas dilution or enrichment processes in a region or galaxy. The evolutionary history gives the final state of the gas and stars. In this work we prese...

Planetary Nebulae have rich optical spectra, formed by recombination and collisional excitation lines. The use of these lines allows the derivation of several physical parameters such as density, electron temperature, ionization degree and the kinematic profile. These nebulae have typical expansion velocities between 20 and 40 km/s. Using high disp...

Planetary nebulae (PN) are excellent laboratories to study the chemical evolution of their host galaxies, especially concerning the radial abundance gradients and their time and spatial variations. Current chemical evolution models predict either some steepening or flattening of the abundance gradients with time, and PN can be useful in order to pr...

Structure, kinematics and physical parameters of planetary nebulae are related to their progenitor stars. A better understanding of these properties is essential to improve the knowledge of the late stages of evolution of intermediate-mass stars, as well as to better understand the chemical enrichment mechanisms that feed the interstellar medium wi...

In the absence of an interaction, central bars might be the most effective mechanism for radial motions of gas in barred spiral galaxies, which represent two-thirds of disc galaxies. The dynamical effects induced by bars in the first few kpc of discs might play an important role in the disc profiles in this region. In this work, a chemical evolutio...

The controversy on the time variation of the radial abundance gradients can in principle be settled by estimating the gradients from planetary nebulae (PN) ejected by central stars (CSPN) with different ages. In this work, we consider four samples of CSPN whose lifetimes have been estimated using three different methods and estimate the oxygen abun...

We have developed several methods to estimate the ages of central stars of planetary nebulae (CSPN), which are based either on observed nebular properties or on data from the stars themselves. Our goal is to derive the age distribution of these stars and compare the results with empirical distributions for CSPN and white dwarfs. We have initially d...

The present star formation rate (SFR) in the inner Galaxy is puzzling for the chemical evolution models (CEM). No static CEM is able to reproduce the peak of the SFR in the 4 kpc ring. The main reason is probably a shortage of gas, which could be due to the dynamical effects produced by the galactic bar, not considered by these models. We developed...

In this paper, a sample of planetary nebulae in the Galaxy's inner-disk and bulge is used to find the galactocentric distance that optimally separates these two populations in terms of their abundances. Statistical distance scales were used to investigate the distribution of abundances across the disk-bulge interface, while a Kolmogorov-Smirnov tes...

The star formation rate (SFR) is still a poorly known characteristic of the Milky Way, especially concerning the possibility of an irregular SFR, compared to a constant rate. Some recent results based on the distribution of dwarf stars with chromospheric ages suggest at least two major bursts in the past 10 Gyr, while other investigations are consi...

We discuss the effects on the time variation of the gradients resulting from our determinations of the age distributions of CSPN. The main conclusions are: (i) for most CSPN with accurate radial velocities the kinematic ages are usually under 3 Gyr, so that the differences between the gradients of these objects and of younger objects are expected t...

SOUTH POL will be a survey of the Southern sky in optical polarized light. It will use a newly designed polarimetric module at an 80cm Robotic Telescope. Telescope and polarimeter will be installed at CTIO, Chile, in late 2012. The initial goal is to cover the sky south of declination -15{\deg} in two years of observing time, aiming at a polarimetr...

Recent determinations of Li abundances in the Galaxy resulted in two important conclusions: first, there is a significant discrepancy between the predicted values by Standard Big Bang Nucleosynthesis (SBBN) and the observed values, reaching about 0.6 dex for the oldest, most metal-poor stars; second, for these stars there seems to exist an almost l...

We present the first results of a project aimed to derive physical parameters, chemical abundances and angular variations of spatially resolved planetary nebulae in the Galaxy that have bipolar structure. These results can be used as input and constraints into numerical simulations in order to reproduce their properties in the visual band of the sp...

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 PNe located in the galactic bulge, based on low dispersion spectroscopy secured at the SOAR telescope using the...

We discuss three methods to estimate the age distribution of central stars of planetary nebulae (CSPN) and their progenitor stars. These methods include the use of an age-metallicity relation that also depends on the galactocentric distance, an age-metallicity relation for the Galactic disk, and the determination of ages from the central star masse...

Se determina la distribución de edades de las estrellas centrales de nebulosas planetarias (CSPN) utilizando dos métodos basados en sus propiedades cinemáticas. En primer lugar, se comparan las velocidades de rotación de las nebulosas esperadas a partir de sus distancias galactocéntricas con los valores predichos por la curva de rotación, y las dif...

Bipolar nebulae constitute a large subset of the planetary nebulae population. In this work we report the first results of a program aimed to derive physical parameters and chemical abundances for a sample of Galactic bipolar planetary nebulae seen from the southern hemisphere. Observational data were gathered at the 1.60-m telescope of the Pico do...

In this work, a sample of planetary nebulae located in the inner-disk and bulge of the Galaxy is used in order to find the galactocentric distance which better separates these two populations, from the point of view of abundances. Statistical distance scales were used to study the distribution of abundances across the disk-bulge interface. A Kolmog...

Planetary nebulae (PN) are an excellent laboratory to investigate the nucleosynthesis and chemical evolution of intermediate mass stars. In these objects accurate abundances can be obtained for several chemical elements that are manufactured or contaminated by the PN progenitor stars, such as He, N, C, and also elements that were originally produce...

New helium abundances of planetary nebulae located towards the bulge of the Galaxy were derived, based on observations made at OPD (Brazil). We present accurate helium abundances for 56 PNe located towards the galactic bulge. The data show good agreement with other results in the literature, in the sense that the distribution of the abundances is s...

Abundance gradients are key parameters to constrain the chemical evolution of the galactic disk. In this review recent determinations for the radial gradient are described, including its slope as derived from different objects such as planetary nebulae, HII regions, cepheids, or B stars, and for different elements. Inner and outer limits for the ra...

We analyse a large sample of galactic planetary nebulae based on their chemical composition and morphology. A recent morphological classification system is adopted, and several elements are considered, namely He, N, O, S, Ar, Ne, and C in order to investigate the correlations involving these elements and the different PN types. Special emphasis is...

Context. Dwarf irregular galaxies are relatively simple unevolved objects where it is easy to test models of galactic chemical evolution. Aims: We attempt to determine the star formation and gas accretion history of IC 10, a local dwarf irregular for which abundance, gas, and mass determinations are available. Methods: We apply detailed chemical ev...

Context. The distribution of chemical abundances and their variation with time are important tools for understanding the chemical evolution of galaxies. In particular, the study of chemical evolution models can improve our understanding of the basic assumptions made when modelling our Galaxy and other spirals. Aims: We test a standard chemical evol...

We present the results of a medium-resolution spectroscopic survey of 43 field horizontal-branch (FHB) candidates carried out near the south galactic pole, selected from the original list of FHB candidates compiled by Beers et al. (2007). The observation list includes only stars classified as ``high-probability'' candidates, according to their 2MAS...

The results of the analysis of the spectra of comets 9P/Tempel 1, 37P/Forbes and C/2004 Q2 (Machholz) observed in 2004-2005 at Observatório do Pico dos Dias (Brazil), and at Mount Pastukhov (SAO, Russia) are presented.

Dwarf irregular galaxies are relatively simple unevolved objects where it is easy to test models of galactic chemical evolution. We attempt to determine the star formation and gas accretion history of IC10, a local dwarf irregular for which abundance, gas, and mass determinations are available. We apply detailed chemical evolution models to predict...

The distribution of chemical abundances and their variation in time are important tools to understand the chemical evolution of galaxies: in particular, the study of chemical evolution models can improve our understanding of the basic assumptions made for modelling our Galaxy and other spirals. To test a standard chemical evolution model for spiral...

The study of planetary nebulae in the inner-disk and bulge gives important information on the chemical abundances of elements such as He, N, O, Ar, Ne, and on the evolution of these abundances, which is associated with the evolution of intermediate-mass stars and the chemical evolution of the Galaxy. We present accurate abundances of the elements H...

Searches for field horizontal-branch (FHB) stars in the halo of the Galaxy in the past have been carried out by several techniques, such as objective-prism surveys and visual or infrared photometric surveys. By choosing adequate color criteria, it is possible to improve the efficiency of identifying bona fide FHB stars among the other objects that...

The determination of ages of central stars of planetary nebulae (CSPN) is a complex problem, and there is presently no single method that can be generally applied. We have developed several methods to estimate the ages of CSPN, based both on the observed nebular properties and in some properties of the stars themselves.Our aim is to estimate the ag...

New abundances of planetary nebulae located towards the bulge of the Galaxy are derived based on observations made at LNA (Brazil). We present accurate abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards the galactic bulge. The data shows a good agreement with other results in the literature, in the sense that the distribu...

Radial metallicity gradients are observed in the disks of the Milky Way and in several other spiral galaxies. In the case of the Milky Way, many objects can be used to determine the gradients, such as HII regions, B stars, Cepheids, open clusters and planetary nebulae. Several elements can be studied, such as oxygen, sulphur, neon, and argon in pho...

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...

We have obtained a large sample of PN with accurately determined helium abundances, as well as abundances of several heavy elements. The nebulae are located in the solar neighbourhood, in the galactic bulge, disk and anticentre, and in the Magellanic Clouds. The abundances are analyzed both in terms of the nucleosynthesis of intermediate mass stars...

The distribution of chemical abundances and their variation in space and time are important tools to understand the chemical evolution of disks in spiral galaxies. In this work we present an one infall chemical evolution model for the Galactic disk based on an updated version of the Trieste group model. We adopted a pre enriched gas (to take into a...

La determinaci n precisa de las abundancias qu micas en las nebulosas planetarias (PN) de diferentes galaxias nos permite obtener importantes l mites para los modelos de evoluci n qu mica en estos sistemas. Tenemos un programa a largo plazo para derivar abundancias en las galaxias del Grupo Local, en particular, la Nube Mayor y la Nube Menor de Mag...

Recent work has produced a wealth of data concerning the chemical evolution of the galactic bulge, both for stars and nebulae. Present theoretical models generally adopt a limited range of such constraints, frequently using a single chemical element (usually iron), which is not enough to describe it unambiguously. In this work, we take into account...

Planetary nebulae (PN) are an essential tool in the study of the chemical evolution of the Milky Way and galaxies of the Local Group, particularly the Magellanic Clouds. In this work, we present some recent results on the determination of chemical abundances from PN in the Large and Small Magellanic clouds, and compare these results with data from...

We report the discovery of the first known symbiotic star in IC10, a starburst galaxy belonging to the Local Group, at a distance of ∼750 kpc. The symbiotic star was identified during a survey of emission-line objects. It shines at V= 24.62 ± 0.04, V−RC= 2.77 ± 0.05 and RC−IC= 2.39 ± 0.02, and suffers from EB−V= 0.85 ± 0.05 reddening. The spectrum...

We report the spectrophotometric investigation of a planetary nebula sample located at the disk-bulge interface of the Milky Way. The main goal of this work was to determine the galactocentric distance where, according to the intermediate mass population, bulge and disk properties separate. In order to derive such distance, new abundances were deri...

Recent work on abundance gradients have focussed not only on their magnitudes, but also on their spatial and temporal variations. In this work, we analyze the behaviour of radial abundance gradients in the galactic disk giving special emphasis on these variations. The data used includes planetary nebulae and objects in different age brackets, namel...

Radiative wind theory applied to hot stars and central stars of planetary nebulae (CSPN) predicts a dependence of observed wind properties, such as the modified wind momentum, and basic stellar parameters, such as the stellar luminosity. Also, some dependence of this quantity is expected on the stellar metallicity, in view of the fact that the driv...

Recent investigations on the central stars of planetary nebulae (CSPN) indicate that the masses based on model atmospheres can be much larger than the masses derived from theoretical mass-luminosity relations. Also, the dispersion in the relation between the modified wind momentum and the luminosity depends on the mass spread of the CSPN, and is la...

We report the results of a spectroscopic survey of blue stars near the south Galactic pole, selected according to their color indices in the 2MASS database. The main scope of this work is to determine the nature of the objects that comprise the sample. Some characteristics of the Hβ, Hγ, and Hδ lines which are sensitive to temperature and gravity w...

The role of planetary nebulae (PN) as a key indicator of stellar populations both in the Milky Way and in galaxies of the Local Group has been emphasized in some recent publications (see for example Maciel et al. 2006, Planetary nebulae beyond the Milky Way, ed. L. Stanghellini, J.R. Walsh, N. G. Douglas, Springer, p.209; Richer and McCall 2006, ib...

We have used our dataset on the abundances of planetary nebulae (PN) to study the chemical evolution of the Galactic bulge. We have derived several relations involving the chemical abundances and computed three classes of models for the Galactic bulge: (i) one-zone, single-infall models, (ii) one-zone, double-infall models and (iii) multizone, doub...

We investigate the chemical evolution of the Small Magellanic Cloud (SMC) based on abundance data of planetary nebulae (PNe). The main goal is to investigate the time evolution of the oxygen abundance in this galaxy by deriving an age-metallicity relation. Such a relation is of fundamental importance as an observational constraint for chemical evol...

We investigate the chemical evolution of the Small Magellanic Cloud (SMC) based on abundance data of planetary nebulae (PNe). The main goal is to investigate the time evolution of the oxygen abundance in this galaxy by deriving an age-metallicity relation. Such a relation is of fundamental importance as an observational constraint of chemical evolu...

We investigate the electron temperature gradient in the galactic disk as measured by young HII regions on the basis of radio recombination lines and the corresponding gradient in planetary nebulae (PN) based on [OIII] electron temperatures. The main goal is to investigate the time evolution of the electron temperature gradient and of the radial abu...

We describe X-ray and optical observations of the symbiotic star RX Pup. From low resolution optical spectra, we obtain a reddening for RX Pup of E(B-V)=0.79. We use the neutral column density corresponding to this reddening as a lower limit for the X-ray spectra fits. The X-ray spectra can be fitted with either a two-temperarure thermal plasma mod...

Spectroscopic observations were performed in two runs at the National Laboratory for Astrophysics (Brasopolis, MG, Brazil) from 7-16 Jun., 2002, and from 23-26 Jun., 2003, using a Boller & Chivens Cassegrain spectrograph attached to the 1.60m telescope with a dispersion of 4.4{AA}/pixel. Some observations were made at ESO using the 1.52 m telescope...

An analysis is made of the abundances of planetary nebulae (PN) in the Galaxy (MW), the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). The data have been gathered by the IAG/USP group in a homogeneous procedure, involving observational techniques, data acquisition and reduction. Emphasis is placed on distance-independent correla...

The role of planetary nebulae as probes for the galactic chemical evolution is reviewed. Their abundances throughout the Galaxy are discussed for key elements, in particular oxygen and other alpha elements. The abundance distribution derived from planetary nebulae leads to the establishment of radial abundance gradients in the galactic disk that ar...

The time behaviour of the radial abundance gradients in the galactic disk is investigated on the basis of four different samples of planetary nebulae, comprising both smaller, homogeneous sets of data, and larger, albeit non-homogeneous samples. Four different chemical elements are considered, namely, oxygen, sulphur, argon and neon. Our analysis s...

New results on the time variation of the radial abundance gradients in the galactic disk are presented on the basis of four different samples of planetary nebulae. These comprise both smaller, homogeneous sets of data, and larger but non-homogeneous samples. Four different chemical elements are considered, namely, O, S, Ar, and Ne. Other objects su...

Abundance gradients and their variations constitute one of the main constraints of chemical evolution models for the Galaxy. The time evolution of the gradients, in particular, is essential to distinguish between models involving different physical processes and time scales (see for example [6] and [8]). The gradients can be derived from different...

We have estimated the magnitude and time variation of the radial abundance gradients using planetary nebulae, open clusters, cepheids and other young objects. We concluded that the gradients have flattened out in the last 8 Gyr, with important consequences for models of the chemical evolution of the Galaxy.

We describe X-ray and optical observations of the symbiotic star RX Pup. From low resolution optical spectra, we obtain a reddening for RX Pup of E(B − V) = 0.79. We use the neutral column density corresponding to this reddening as a lower limit for the X-ray spectra fits. The X-ray spectra can be fitted with either a two-temperature thermal plasma...

RT Cru is one of a subset of particularly active symbiotic stars (white dwarfs accreting from the winds of red giants) characterized by rapid optical flickering, and in some cases jets and recurrent nova explosions. The recent detection of RT Cru with INTEGRAL (ATels 519, 528, and 591) indicates that during outburst, it also produces the hardest X-...

In this work we obtain chemical diagrams for the Small Magellanic Cloud (SMC) using planetary nebulae (PNe) data. We collected a large number of measured spectral fluxes for a sample of SMC PNe, in order to derive accurate physical parameters and abundances. Here we present new spectral data for SMC PNe obtained between 1999 and 2002. These data ar...

We have studied the time variation of the radial abundance gradients using samples of planetary nebulae, open clusters, cepheids and other young objects. Based on the analysis of O/H and S/H abundances for planetary nebulae and metallicities of the remaining objects, we concluded that the gradients have been flattening out in the last 8 Gyr with an...

Electron temperatures, densities, ionic and elemental abundances of helium, nitrogen, oxygen, argon, sulfur and neon were derived for a sample of bulge planetary nebulae, representative of its intermediate mass population. Using these results as constraints, a model for the chemical evolution of the galactic bulge was developed. The results indicat...

We have calculated relative elemental abundances for a sample of 43 symbiotic stars. Helium abundances and the relative elemental abundances N/O, Ne/O, Ar/O were derived from new spectra collected in the optical range through low dispersion spectroscopy. The He ionic abundances were derived taking into account self-absorption effects in Balmer line...

The temporal behaviour of the radial abundance gradients has important consequences for models of the chemical evolution of the Galaxy. We present a comparison of the time variation of the abundance gradients in the Milky Way disk as determined from a sample of planetary nebulae, open clusters, cepheids and young objects, such as stars in OB associ...

We present new spectroscopic data (43 objects) and derived plasma diagnostics and abundances (164 objects) of a sample of planetary nebulae in the direction of the Galactic center. The spectra were obtained in July 2000 with the 1.9-m telescope at the South African Astronomical Observatory. The spectral coverage was 3500-7000Å with an average resol...

We have observed 44 planetary nebulae (PNe) in the direction of the Galactic bulge, and merged our data with published ones. We have distinguished, in the merged sample of 164 PNe, those PNe most likely to prtain physically to the Galactic bulge and those most likely to belong to the Galactic disk. We have determined the chemical composition of all...

An analysis is made of the abundances of planetary nebulae (PN) in the Galaxy (MW), the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). The data have been gathered by the IAG/USP group in a homogeneous procedure, involving observational techniques, data acquisition and reduction. Emphasis is placed on distance-independent correla...

In this paper we report new observations and derive chemical abundances for a sample of 26 planetary nebulae (PN) located in the anticenter direction. Most of these nebulae are far away objects, located at Galactocentric distances greater than about 8 kpc, so that they are particularly useful for the determination of the radial gradients at large d...