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Papers by Ronaldo da Silva

Solar twins stars are, broadly, stars with the same mass, temperature, surface gravity, luminosit... more Solar twins stars are, broadly, stars with the same mass, temperature, surface gravity, luminosity, metal content and age as the Sun. Such objects are, presumably, privileged candidates to possess planetary systems similar to our own and also to be abodes for lifeforms based on carbon-chain chemistry and water oceans. They may also help answer the still lingering question of how typical the solar characteristics are with respect to the local galactic population of middle-aged G- type stars. The recent identification of the best ever solar twin (Porto de Mello & da Silva 1997, ApJ Letters, 476, L89) enabled a much better understanding of the strategies necessary to uncover stars that closely resemble the Sun. We present the preliminary results of a systematic survey to reveal all solar twin stars within 50 pc of the Sun. We have selected from the HIPPARCOS astrometric and photometric database 52 near main-sequence, G-type candidate stars with absolute magnitudes and color indices very closely approaching the Sun's. These stars are being spectroscopically studied with high-resolution, high S/N optical spectra, and with moderate resolution ultraviolet spectra. We aim at determining the atmospheric parameters, chemical abundances, evolutionary state and degree of chromospheric activity of these stars and to discuss their interest to the current search for planetary systems and SETI programs.

We present a determination of photospheric parameters and C abundances for a sample of 172 G and ... more We present a determination of photospheric parameters and C abundances for a sample of 172 G and K dwarfs, subgiants, and giants with and without detected planets in the solar neighbourhood. The analysis was based on high S/N and high resolution spectra observed with the ELODIE spectrograph, and for which the observational data was publicly available. We intend to contribute precise and homogeneous C abundances in studies that compare the behaviour of light elements in stars, hosting planets or not. This will bring new arguments to the discussion of possible anomalies that have been suggested and will contribute to a better understanding of different planetary formation process. The photospheric parameters were computed through the excitation potential, equivalent widths, and ionisation equilibrium of Fe lines selected in the spectra. C abundances were derived from spectral synthesis applied to prominent molecular head bands of C_2 Swan (5128 and 5165) and to a C atomic line (5380.3). The distribution of [C/Fe] vs. [Fe/H] shows no difference in the behaviour of planet-host stars in comparison with stars for which no planet was detected, for both dwarf and giant subsamples. This result is in agreement with the hypothesis of primordial origin for the chemical abundances presently observed instead of self-enrichment during the planetary system formation and evolution. Additionally, giants are clearly depleted in [C/Fe] (~0.14 dex) when compared with dwarfs, which is probably related to evolution-induced mixing of H-burning products in the envelope of evolved stars. Subgiants, although in small number, seems to follow the same C abundance distribution as dwarfs. We also analysed the kinematics of the sample stars that, in majority, are members of the Galaxy's thin disc. Finally, comparisons with other analogue studies were performed and, within the uncertainties, showed good agreement.

Proceedings of The International Astronomical Union, 2010

We have been analyzing a large sample of solar-like stars with and without planets in order to ho... more We have been analyzing a large sample of solar-like stars with and without planets in order to homogeneously measure their photospheric parameters and Carbon abundances. Our sample contains around 200 stars in the solar neighborhood observed with the ELODIE spectrograph, for which the observational data are publicly available. We performed spectral synthesis of prominent bands of C$_{2}$ and C I lines, aiming to accurately obtain the C abundances. We intend to contribute homogeneous results to studies that compare elemental abundances in stars with and without known planets. New arguments will be brought forward to the discussion of possible chemical anomalies that have been suggested in the literature, leading us to a better understanding of the planetary formation process. In this work we focus on the C abundances in both stellar groups of our sample.

We present a determination of photospheric parameters and C abundances for a sample of 172 G and ... more We present a determination of photospheric parameters and C abundances for a sample of 172 G and K dwarfs, subgiants, and giants with and without detected planets in the solar neighbourhood. The analysis was based on high S/N and high resolution spectra observed with the ELODIE spectrograph, and for which the observational data was publicly available. We intend to contribute precise and homogeneous C abundances in studies that compare the behaviour of light elements in stars, hosting planets or not. This will bring new arguments to the discussion of possible anomalies that have been suggested and will contribute to a better understanding of different planetary formation process. The photospheric parameters were computed through the excitation potential, equivalent widths, and ionisation equilibrium of Fe lines selected in the spectra. C abundances were derived from spectral synthesis applied to prominent molecular head bands of C_2 Swan (5128 and 5165) and to a C atomic line (5380.3). The distribution of [C/Fe] vs. [Fe/H] shows no difference in the behaviour of planet-host stars in comparison with stars for which no planet was detected, for both dwarf and giant subsamples. This result is in agreement with the hypothesis of primordial origin for the chemical abundances presently observed instead of self-enrichment during the planetary system formation and evolution. Additionally, giants are clearly depleted in [C/Fe] (~0.14 dex) when compared with dwarfs, which is probably related to evolution-induced mixing of H-burning products in the envelope of evolved stars. Subgiants, although in small number, seems to follow the same C abundance distribution as dwarfs. We also analysed the kinematics of the sample stars that, in majority, are members of the Galaxy's thin disc. Finally, comparisons with other analogue studies were performed and, within the uncertainties, showed good agreement.

Proceedings of The International Astronomical Union, 2010

We have been analyzing a large sample of solar-like stars with and without planets in order to ho... more We have been analyzing a large sample of solar-like stars with and without planets in order to homogeneously measure their photospheric parameters and Carbon abundances. Our sample contains around 200 stars in the solar neighborhood observed with the ELODIE spectrograph, for which the observational data are publicly available. We performed spectral synthesis of prominent bands of C$_{2}$ and C I lines, aiming to accurately obtain the C abundances. We intend to contribute homogeneous results to studies that compare elemental abundances in stars with and without known planets. New arguments will be brought forward to the discussion of possible chemical anomalies that have been suggested in the literature, leading us to a better understanding of the planetary formation process. In this work we focus on the C abundances in both stellar groups of our sample.

Sem dúvida, é enorme a necessidade de melhores motoristas. Embora impotente para resolver o probl... more Sem dúvida, é enorme a necessidade de melhores motoristas. Embora impotente para resolver o problema sozinho, você pode melhorar a situação se avaliar o seu próprio modo de dirigir, empregando a "Direção Defensiva" como padrão comparativo. "DIREÇÃO PERFEITA OU DIRIGIR COM PERFEIÇÃO, SIGNIFICA QUE VOCÊ REALIZA CADA VIAGEM SEM ACIDENTES, SEM INFRAÇÕES DE TRÂNSITO, SEM ABUSOS DO VEÍCULO, SEM ATRASOS HONORÁRIOS E SEM FALTAR COM A CORTESIA DEVIDA". Dirigir com perfeição inclui a habilidade em controlar o seu veículo, de maneira que você não seja envolvido em algum acidente. Os acidentes podem ser evitados. No caso de colisão entre dois veículos, geralmente o acidente pode ser evitado por qualquer um dos motoristas, ou por ambos. Sabendo que os acidentes podem ser evitados, como poderíamos definir um acidente evitável? "ACIDENTE EVITÁVEL É AQUELE EM QUE VOCÊ FEZ TUDO QUE RAZOAVELMENTE PODE FAZER PARA EVITÁ-LO".

Solar twins stars are, broadly, stars with the same mass, temperature, surface gravity, luminosit... more Solar twins stars are, broadly, stars with the same mass, temperature, surface gravity, luminosity, metal content and age as the Sun. Such objects are, presumably, privileged candidates to possess planetary systems similar to our own and also to be abodes for lifeforms based on carbon-chain chemistry and water oceans. They may also help answer the still lingering question of how typical the solar characteristics are with respect to the local galactic population of middle-aged G- type stars. The recent identification of the best ever solar twin (Porto de Mello & da Silva 1997, ApJ Letters, 476, L89) enabled a much better understanding of the strategies necessary to uncover stars that closely resemble the Sun. We present the preliminary results of a systematic survey to reveal all solar twin stars within 50 pc of the Sun. We have selected from the HIPPARCOS astrometric and photometric database 52 near main-sequence, G-type candidate stars with absolute magnitudes and color indices very closely approaching the Sun's. These stars are being spectroscopically studied with high-resolution, high S/N optical spectra, and with moderate resolution ultraviolet spectra. We aim at determining the atmospheric parameters, chemical abundances, evolutionary state and degree of chromospheric activity of these stars and to discuss their interest to the current search for planetary systems and SETI programs.

We present a determination of photospheric parameters and C abundances for a sample of 172 G and ... more We present a determination of photospheric parameters and C abundances for a sample of 172 G and K dwarfs, subgiants, and giants with and without detected planets in the solar neighbourhood. The analysis was based on high S/N and high resolution spectra observed with the ELODIE spectrograph, and for which the observational data was publicly available. We intend to contribute precise and homogeneous C abundances in studies that compare the behaviour of light elements in stars, hosting planets or not. This will bring new arguments to the discussion of possible anomalies that have been suggested and will contribute to a better understanding of different planetary formation process. The photospheric parameters were computed through the excitation potential, equivalent widths, and ionisation equilibrium of Fe lines selected in the spectra. C abundances were derived from spectral synthesis applied to prominent molecular head bands of C_2 Swan (5128 and 5165) and to a C atomic line (5380.3). The distribution of [C/Fe] vs. [Fe/H] shows no difference in the behaviour of planet-host stars in comparison with stars for which no planet was detected, for both dwarf and giant subsamples. This result is in agreement with the hypothesis of primordial origin for the chemical abundances presently observed instead of self-enrichment during the planetary system formation and evolution. Additionally, giants are clearly depleted in [C/Fe] (~0.14 dex) when compared with dwarfs, which is probably related to evolution-induced mixing of H-burning products in the envelope of evolved stars. Subgiants, although in small number, seems to follow the same C abundance distribution as dwarfs. We also analysed the kinematics of the sample stars that, in majority, are members of the Galaxy's thin disc. Finally, comparisons with other analogue studies were performed and, within the uncertainties, showed good agreement.

Proceedings of The International Astronomical Union, 2010

We have been analyzing a large sample of solar-like stars with and without planets in order to ho... more We have been analyzing a large sample of solar-like stars with and without planets in order to homogeneously measure their photospheric parameters and Carbon abundances. Our sample contains around 200 stars in the solar neighborhood observed with the ELODIE spectrograph, for which the observational data are publicly available. We performed spectral synthesis of prominent bands of C$_{2}$ and C I lines, aiming to accurately obtain the C abundances. We intend to contribute homogeneous results to studies that compare elemental abundances in stars with and without known planets. New arguments will be brought forward to the discussion of possible chemical anomalies that have been suggested in the literature, leading us to a better understanding of the planetary formation process. In this work we focus on the C abundances in both stellar groups of our sample.

We present a determination of photospheric parameters and C abundances for a sample of 172 G and ... more We present a determination of photospheric parameters and C abundances for a sample of 172 G and K dwarfs, subgiants, and giants with and without detected planets in the solar neighbourhood. The analysis was based on high S/N and high resolution spectra observed with the ELODIE spectrograph, and for which the observational data was publicly available. We intend to contribute precise and homogeneous C abundances in studies that compare the behaviour of light elements in stars, hosting planets or not. This will bring new arguments to the discussion of possible anomalies that have been suggested and will contribute to a better understanding of different planetary formation process. The photospheric parameters were computed through the excitation potential, equivalent widths, and ionisation equilibrium of Fe lines selected in the spectra. C abundances were derived from spectral synthesis applied to prominent molecular head bands of C_2 Swan (5128 and 5165) and to a C atomic line (5380.3). The distribution of [C/Fe] vs. [Fe/H] shows no difference in the behaviour of planet-host stars in comparison with stars for which no planet was detected, for both dwarf and giant subsamples. This result is in agreement with the hypothesis of primordial origin for the chemical abundances presently observed instead of self-enrichment during the planetary system formation and evolution. Additionally, giants are clearly depleted in [C/Fe] (~0.14 dex) when compared with dwarfs, which is probably related to evolution-induced mixing of H-burning products in the envelope of evolved stars. Subgiants, although in small number, seems to follow the same C abundance distribution as dwarfs. We also analysed the kinematics of the sample stars that, in majority, are members of the Galaxy's thin disc. Finally, comparisons with other analogue studies were performed and, within the uncertainties, showed good agreement.

Proceedings of The International Astronomical Union, 2010

We have been analyzing a large sample of solar-like stars with and without planets in order to ho... more We have been analyzing a large sample of solar-like stars with and without planets in order to homogeneously measure their photospheric parameters and Carbon abundances. Our sample contains around 200 stars in the solar neighborhood observed with the ELODIE spectrograph, for which the observational data are publicly available. We performed spectral synthesis of prominent bands of C$_{2}$ and C I lines, aiming to accurately obtain the C abundances. We intend to contribute homogeneous results to studies that compare elemental abundances in stars with and without known planets. New arguments will be brought forward to the discussion of possible chemical anomalies that have been suggested in the literature, leading us to a better understanding of the planetary formation process. In this work we focus on the C abundances in both stellar groups of our sample.

Sem dúvida, é enorme a necessidade de melhores motoristas. Embora impotente para resolver o probl... more Sem dúvida, é enorme a necessidade de melhores motoristas. Embora impotente para resolver o problema sozinho, você pode melhorar a situação se avaliar o seu próprio modo de dirigir, empregando a "Direção Defensiva" como padrão comparativo. "DIREÇÃO PERFEITA OU DIRIGIR COM PERFEIÇÃO, SIGNIFICA QUE VOCÊ REALIZA CADA VIAGEM SEM ACIDENTES, SEM INFRAÇÕES DE TRÂNSITO, SEM ABUSOS DO VEÍCULO, SEM ATRASOS HONORÁRIOS E SEM FALTAR COM A CORTESIA DEVIDA". Dirigir com perfeição inclui a habilidade em controlar o seu veículo, de maneira que você não seja envolvido em algum acidente. Os acidentes podem ser evitados. No caso de colisão entre dois veículos, geralmente o acidente pode ser evitado por qualquer um dos motoristas, ou por ambos. Sabendo que os acidentes podem ser evitados, como poderíamos definir um acidente evitável? "ACIDENTE EVITÁVEL É AQUELE EM QUE VOCÊ FEZ TUDO QUE RAZOAVELMENTE PODE FAZER PARA EVITÁ-LO".