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Elisson S. G. de Almeida

Publications and source records attributed to Elisson S. G. de Almeida.

2 recordsLinked to original sources

BRICS Southern Observatory (BRICS-SO) Project: Invitation to African countries to invest in Chile

Recently, the BRICS countries created a promising astronomy consortium (https://www.bricsastronomy.org/), which was joined last year by some emerging countries, including two African countries, namely: Egypt and Ethiopia. Certainly, other African countries will join BRICS+ in the years to come. Thus, by pooling their efforts, emerging countries (BRICS+) are sure to quickly catch up with their technological delay in the field of astronomy, particularly through ambitious and large-scale projects. Chile, due to the exceptional climatic conditions of its North, is recognized as the world capital of astronomy where all the largest consortia have settled there and applied all their know-how. The official launch of BRICS (and then its expansion to other countries; BRICS+) is welcomed as an excellent opportunity to think big in the development of astronomy. China has shown great determination in being the first country in the South to establish astronomical facilities in Chile, thus opening a possible opportunity for BRICS+ astronomers. Ambitious astronomical instrumentation is essential for the future of Astronomy and Astrophysics. Access to existing facilities is becoming more and more difficult because of saturation. Existing programs like the VLT-I/ELT and their instruments necessitated decades of collaboration between international institutions. It is therefore necessary for the BRICS+ astronomical community to collaborate together on ambitious projects without wasting time in order to offer a new pole with new opportunities for the researchers. This pole (BRICS-SO), in addition to attracting highly qualified people, will also help train new generations in all our countries, and encourage exchanges and collaborations.

astro-ph.IM↗

Unveiling the evolutionary state of three B supergiant stars: PU Gem, $ε$ CMa and $η$ CMa

We aim to combine asteroseismology, spectroscopy, and evolutionary models to establish a comprehensive picture of the evolution of Galactic blue supergiant stars (BSG). To start such an investigation, we selected three BSG candidates for our analysis: HD 42087 (PU Gem), HD 52089 ($ε$ CMa) and HD 58350 ($η$ CMa). These stars show pulsations and were suspected to be in an evolutionary stage either preceding or succeding the red supergiant (RSG) stage. For our analysis, we utilized the 2-min cadence TESS data to study the photometric variability and obtained new spectroscopic observations at the CASLEO observatory. We calculated CMFGEN non-LTE radiative transfer models and derived stellar and wind parameters using the iterative spectral analysis pipeline XTGRID. The spectral modeling was limited to changing only the effective temperature, surface gravity, CNO abundances, and mass-loss rates. Finally, we compared the derived metal abundances with predictions from Geneva stellar evolution models. The frequency spectra of all three stars show either stochastic oscillations, nonradial strange modes, or a rotational splitting. We conclude that the rather short sectoral observing windows of TESS prevent establishing a reliable mode identification of low frequencies connected to mass-loss variabilities. The spectral analysis confirmed gradual changes in the mass-loss rates and the derived CNO abundances comply with the values reported in the literature. We were able to achieve a quantitative match with stellar evolution models for the stellar masses and luminosities. However, the spectroscopic surface abundances turned out to be inconsistent with theoretical predictions. The stars show N enrichment, typical for CNO cycle processed material, but the abundance ratios do not reflect the associated levels of C and O depletion.

astro-ph.SR↗