Roberto Costa - Academia.edu (original) (raw)
Papers by Roberto Costa
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Cornell University - arXiv, Oct 1, 1900
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Photoionized nebulae comprise basically HII regions and planetary nebulae, and their abundances g... more 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 stars, as well as O, Ne, S, and Ar, which are essentially synthesized in stars with larger masses. The abundances of these elements in several systems in the Local Group are discussed on the basis of distance-independent correlations.
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Journal of Physics: Conference Series, 2018
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Astronomische Nachrichten, 2018
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Monthly Notices of the Royal Astronomical Society, 2018
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The Astronomical Journal, 2007
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Proceedings of the International Astronomical Union, 2011
The star formation rate (SFR) is still a poorly known characteristic of the Milky Way, especially... more 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 consistent with an approximately constant SFR. The SFR also shows important spatial variations, particularly concerning the radial variations along the galactic disc. In this work, we investigate two different problems relative to the galactic SFR: (i) We estimate the star formation rate in the galactic disc based on the age distribution of the planetary nebula central stars (CSPN), and compare these results with previous investigations based on dwarf stars. The CSPN ages were derived on the basis of five different methods, involving the observed nebular metallicities and kinematical properties; (ii) We derive radial abundance gradients from se...
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Abstract. An analysis is made of the abundances of planetary nebulae (PN) in the Galaxy (MW), the... more Abstract. 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 has been gathered by the IAG/USP group in a homogeneous procedure, involving observational techniques, data acquisition and reduction. Emphasis is placed on distance-independent correlations, which are particularly important for PN in the galactic disk. It is shown that (i) our abundances are comparable to the accurate abundances of nebulae with ISO data, (ii) most abundance correlations hold for all three systems, taking into account the metallicity differences between the Galaxy and the Magellanic Clouds, and (iii) there is a good general agreement of our data with the predictions of recent theoretical models for PN progenitors. 1
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Abstract. Recent applications of PN to the study of galactic chemical evolution are reviewed, suc... more Abstract. Recent applications of PN to the study of galactic chemical evolution are reviewed, such as PN and stellar populations, abundance gradients, including their space and time variations, determination of the He/H radial gradient and of the helium-to-metals enrichment ratio, and the [O/Fe] × [Fe/H] relation in the solar neighbourhood and in the galactic bulge. 1.
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Astronomy and Astrophysics, 1996
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Astronomy and Astrophysics, 1993
CCD spectra for a sample of 8 type I planetary nebulae in the LMC were obtained in the wavelength... more CCD spectra for a sample of 8 type I planetary nebulae in the LMC were obtained in the wavelength region λλ 3800-8200 A. Electronic temperatures, densities and resulting abundances of He, N, O, S and Ar were obtained, where in particular the uncertainties in the He and O abundances are discussed. Using results from stellar nucleosynthesis we estimated from the S/O and Ar/O ratios that the relative number of type I supernovae in the LMC appear to be twice higher than in our Galaxy
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Astronomy and Astrophysics, 1993
Spectroscopic observations, plasma diagnostics and chemical composition of 15 non-type I planetar... more Spectroscopic observations, plasma diagnostics and chemical composition of 15 non-type I planetary nebulae in the Large Magellanic Cloud are reported. Abundances of He, O, N, S, and Ar are determined and compared with recently obtained data for nebulae both in the Magellanic Clouds and in the Galaxy
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Revista Mexicana De Astronomia Y Astrofisica, 2011
We present the first results of a project aimed to derive physical parameters, chemical abundance... more 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 spectrum. This provides a way to examine the non-homogeneity present in this kind of object, as well as a tool to derive their intrinsic properties, like tridimensional geometry and matter distribution, central star properties, distance, and other properties in a self-consistent way. Here we show our findings for two of these objects: IC 4406 and NGC 6572.
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We report new Cassegrain observation of the AG Car nebula, as well as long slit Coude spectra and... more We report new Cassegrain observation of the AG Car nebula, as well as long slit Coude spectra and imagery at Hα. From our data we derive an expansion velocity of 66 km s −1 for the nebula and a minimal mass of 2.7 M ○ .. Long slit data show Hα emission up to 45″ from the star, indicating a diffuse nebulosity surrounding the main nebula. We also find that nitrogen is overabundant by one order of magnitude and oxygen is deficient at least by a factor of 6 in the nebula. These results are consistent with the surface abundances of a 60 M ○ . star aged of 3.7×10 6 yr just beginning its LBV phase
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New optical data are reported on five symbiotic systems : AS 210, He2-38, RX Pup, RR Tel and HM S... more New optical data are reported on five symbiotic systems : AS 210, He2-38, RX Pup, RR Tel and HM Sge. Assuming that the wind of the red giant ionized by a hot source constitutes the emitting region, its chemical composition has been derived. Optical depth effects in both hydrogen and He I lines were taken into account. The resulting He abundances reveal that they are similar to those observed in planetary nebulae. Moreover, the helium abundance correlates with the N/O ratio, according to the expectations from contamination by dredge-up episodes
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Photoionized nebulae comprise basically HII regions and planetary nebulae, and their abundances g... more 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 stars, as well as O, Ne, S, and Ar, which are essentially synthesized in stars with larger masses. The abundances of these elements in several systems in the Local Group are discussed on the basis of distance-independent correlations.
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Symposium - International Astronomical Union
In this work, the chemical history of the SMC is described through an observed sample of planetar... more In this work, the chemical history of the SMC is described through an observed sample of planetary nebulae (PNe). Age-abundance relations were derived through the [α-elements/H] (oxygen, argon, neon and sulphur) ratios estimated from PNe of different progenitor masses. In particular, oxygen abundances seem do not decrease due to O-N cycle operation. (This work was supported by FAPESP)
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Cornell University - arXiv, Oct 1, 1900
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Photoionized nebulae comprise basically HII regions and planetary nebulae, and their abundances g... more 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 stars, as well as O, Ne, S, and Ar, which are essentially synthesized in stars with larger masses. The abundances of these elements in several systems in the Local Group are discussed on the basis of distance-independent correlations.
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Journal of Physics: Conference Series, 2018
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Astronomische Nachrichten, 2018
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Monthly Notices of the Royal Astronomical Society, 2018
Bookmarks Related papers MentionsView impact
The Astronomical Journal, 2007
Bookmarks Related papers MentionsView impact
Proceedings of the International Astronomical Union, 2011
The star formation rate (SFR) is still a poorly known characteristic of the Milky Way, especially... more 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 consistent with an approximately constant SFR. The SFR also shows important spatial variations, particularly concerning the radial variations along the galactic disc. In this work, we investigate two different problems relative to the galactic SFR: (i) We estimate the star formation rate in the galactic disc based on the age distribution of the planetary nebula central stars (CSPN), and compare these results with previous investigations based on dwarf stars. The CSPN ages were derived on the basis of five different methods, involving the observed nebular metallicities and kinematical properties; (ii) We derive radial abundance gradients from se...
Bookmarks Related papers MentionsView impact
Abstract. An analysis is made of the abundances of planetary nebulae (PN) in the Galaxy (MW), the... more Abstract. 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 has been gathered by the IAG/USP group in a homogeneous procedure, involving observational techniques, data acquisition and reduction. Emphasis is placed on distance-independent correlations, which are particularly important for PN in the galactic disk. It is shown that (i) our abundances are comparable to the accurate abundances of nebulae with ISO data, (ii) most abundance correlations hold for all three systems, taking into account the metallicity differences between the Galaxy and the Magellanic Clouds, and (iii) there is a good general agreement of our data with the predictions of recent theoretical models for PN progenitors. 1
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Abstract. Recent applications of PN to the study of galactic chemical evolution are reviewed, suc... more Abstract. Recent applications of PN to the study of galactic chemical evolution are reviewed, such as PN and stellar populations, abundance gradients, including their space and time variations, determination of the He/H radial gradient and of the helium-to-metals enrichment ratio, and the [O/Fe] × [Fe/H] relation in the solar neighbourhood and in the galactic bulge. 1.
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Bookmarks Related papers MentionsView impact
Astronomy and Astrophysics, 1996
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Astronomy and Astrophysics, 1993
CCD spectra for a sample of 8 type I planetary nebulae in the LMC were obtained in the wavelength... more CCD spectra for a sample of 8 type I planetary nebulae in the LMC were obtained in the wavelength region λλ 3800-8200 A. Electronic temperatures, densities and resulting abundances of He, N, O, S and Ar were obtained, where in particular the uncertainties in the He and O abundances are discussed. Using results from stellar nucleosynthesis we estimated from the S/O and Ar/O ratios that the relative number of type I supernovae in the LMC appear to be twice higher than in our Galaxy
Bookmarks Related papers MentionsView impact
Astronomy and Astrophysics, 1993
Spectroscopic observations, plasma diagnostics and chemical composition of 15 non-type I planetar... more Spectroscopic observations, plasma diagnostics and chemical composition of 15 non-type I planetary nebulae in the Large Magellanic Cloud are reported. Abundances of He, O, N, S, and Ar are determined and compared with recently obtained data for nebulae both in the Magellanic Clouds and in the Galaxy
Bookmarks Related papers MentionsView impact
Revista Mexicana De Astronomia Y Astrofisica, 2011
We present the first results of a project aimed to derive physical parameters, chemical abundance... more 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 spectrum. This provides a way to examine the non-homogeneity present in this kind of object, as well as a tool to derive their intrinsic properties, like tridimensional geometry and matter distribution, central star properties, distance, and other properties in a self-consistent way. Here we show our findings for two of these objects: IC 4406 and NGC 6572.
Bookmarks Related papers MentionsView impact
We report new Cassegrain observation of the AG Car nebula, as well as long slit Coude spectra and... more We report new Cassegrain observation of the AG Car nebula, as well as long slit Coude spectra and imagery at Hα. From our data we derive an expansion velocity of 66 km s −1 for the nebula and a minimal mass of 2.7 M ○ .. Long slit data show Hα emission up to 45″ from the star, indicating a diffuse nebulosity surrounding the main nebula. We also find that nitrogen is overabundant by one order of magnitude and oxygen is deficient at least by a factor of 6 in the nebula. These results are consistent with the surface abundances of a 60 M ○ . star aged of 3.7×10 6 yr just beginning its LBV phase
Bookmarks Related papers MentionsView impact
New optical data are reported on five symbiotic systems : AS 210, He2-38, RX Pup, RR Tel and HM S... more New optical data are reported on five symbiotic systems : AS 210, He2-38, RX Pup, RR Tel and HM Sge. Assuming that the wind of the red giant ionized by a hot source constitutes the emitting region, its chemical composition has been derived. Optical depth effects in both hydrogen and He I lines were taken into account. The resulting He abundances reveal that they are similar to those observed in planetary nebulae. Moreover, the helium abundance correlates with the N/O ratio, according to the expectations from contamination by dredge-up episodes
Bookmarks Related papers MentionsView impact
Photoionized nebulae comprise basically HII regions and planetary nebulae, and their abundances g... more 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 stars, as well as O, Ne, S, and Ar, which are essentially synthesized in stars with larger masses. The abundances of these elements in several systems in the Local Group are discussed on the basis of distance-independent correlations.
Bookmarks Related papers MentionsView impact
Symposium - International Astronomical Union
In this work, the chemical history of the SMC is described through an observed sample of planetar... more In this work, the chemical history of the SMC is described through an observed sample of planetary nebulae (PNe). Age-abundance relations were derived through the [α-elements/H] (oxygen, argon, neon and sulphur) ratios estimated from PNe of different progenitor masses. In particular, oxygen abundances seem do not decrease due to O-N cycle operation. (This work was supported by FAPESP)
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