Navegando por Autor "Costa, A. D. da"

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Debris disks among Kepler solar rotational analog stars
(American Astronomical Society, 2018-12-21) Martins, Bruno Leonardo Canto; Silva Sobrinho, R.; Costa, A. D. da; Leão, Izan de Castro; Silva, D. Freire da; Teixeira, M. A.; Souza, M. Gomes de; Freitas, D. Freire da; Bravo, J. P.; Chagas, M. L. das; Medeiros, José Renan de
Observations of circumstellar disks provide a powerful tool for our understanding of planetary system dynamics. Analogs to the solar system asteroid belts, debris disks result from the collision of the remaining solid material of the planet formation process. Even if the presence of disks is now reported for hundreds of stars, its detection around stars similar to the Sun is still very sparse. We report the results of a search for debris disks around Kepler stars with surface physical parameters close to solar values, including rotation period, using observations by the Wide-field infrared Survey Explorer. From the entire sample of Kepler stars, 881 targets were identified with these parameters and only six of them (KIC 1868785, 7267949, 7435796, 10533222, 11352643, and KIC 11666436) show unambiguous infrared excess, for which we determined as debris disk physical parameters. Interestingly, the present study reveals traces of debris disks much more massive and brighter than the solar system zodiacal dust, probably resulting from recent violent collisional events, orbiting stars with ages around the solar values.
On the incidence of wise infrared excess among solar analog, twin, and sibling stars
(The American Astronomical Society, 2017) Costa, A. D. da; Martins, Bruno Leonardo Canto; Leão, Izan Castro; Lima Jr, J. E.; Silva, D. Freire da; Freitas, D. B. de; Medeiros, José Renan de
This study presents a search for infrared (IR) excess in the 3.4, 4.6, 12, and 22 μm bands in a sample of 216 targets, composed of solar sibling, twin, and analog stars observed by the Wide-field Infrared Survey Explorer (WISE) mission. In general, an IR excess suggests the existence of warm dust around a star. We detected 12 μm and/or 22 μm excesses at the 3σ level of confidence in five solar analog stars, corresponding to a frequency of 4.1% of the entire sample of solar analogs analyzed, and in one out of 29 solar sibling candidates, confirming previous studies. The estimation of the dust properties shows that the sources with IR excesses possess circumstellar material with temperatures that, within the uncertainties, are similar to that of the material found in the asteroid belt in our solar system. No photospheric flux excess was identified at the W1 (3.4 μm) and W2 (4.6 μm) WISE bands, indicating that, in the majority of stars of the present sample, no detectable dust is generated. Interestingly, among the 60 solar twin stars analyzed in this work, no WISE photospheric flux excess was detected. However, a null-detection excess does not necessarily indicate the absence of dust around a star because different causes, including dynamic processes and instrument limitations, can mask its presence.
The variability behaviour of CoRoT M-giant stars
(EDP Sciences, 2015-11-04) Martins, Bruno Leonardo Canto; Lopes, C. E. Ferreira; Neves, V.; Leão, I. C.; Freitas, D. B de; Costa, A. D. da; Paz-Chinchón, F.; Chagas, M. L. das; Baglin, A.; Janot-Pacheco, E.; Medeiros, J. R. de
Context. For six years the Convection, Rotation, and planetary Transits (CoRoT) space mission has been acquiring photometric data from more than 100 000 point sources towards and directly opposite the inner and outer regions of the Galaxy. The high temporal resolution of the CoRoT data, combined with the wide time span of the observations, enabled the study of short- and long-time variations in unprecedented detail. Aims. The aim of this work is to study the variability and evolutionary behaviour of M-giant stars using CoRot data. Methods. From the initial sample of 2534 stars classified as M giants in the CoRoT databases, we selected 1428 targets that exhibit well defined variability, by visual inspection. Then, we defined three catalogues: C1 – stars with Teff < 4200 K and LCs displaying semi-sinusoidal signatures; C2 – rotating variable candidates with Teff > 4200 K; C3 – long-period variable candidates (with LCs showing a variability period up to the total time span of the observations). The variability period and amplitude of C1 stars were computed using Lomb-Scargle and harmonic fit methods. Finally, we used C1 and C3 stars to study the variability behaviour of M-giant stars. Results. The trends found in the V − I vs. J − K colour–colour diagram are in agreement with standard empirical calibrations for M giants. The sources located towards the inner regions of the Galaxy are distributed throughout the diagram, while the majority of the stars towards the outer regions of the Galaxy are spread between the calibrations of M giants and the predicted position for carbon stars. The stars classified as supergiants follow a different sequence from the one found for giant stars. We also performed a Kolmogorov-Smirnov (KS) test of the period and amplitude of stars towards the inner and outer regions of the Galaxy. We obtained a low probability that the two samples came from the same parent distribution. The observed behaviour of the period-amplitude and period-effective temperature (Teff) diagrams are, in general, in agreement with those found for Kepler sources and ground based photometry, with pulsation being the dominant cause responsible for the observed modulation. We also conclude that short-time variations on M-giant stars do not exist or are very rare, and the few cases we found are possibly related to biases or background stars.
The variability behaviour of CoRoT M-giant stars
(Astronomy & Astrophysics, 2015) Lopes, C. E. Ferreira; Neves, V.; Leão, I. C.; Freitas, D. B. de; Martins, B. L. Canto; Costa, A. D. da; Paz-Chinchón, F.; Chagas, M. L. das; Baglin, A.; Janot-Pacheco, E.; Medeiros, José Renan de
Context. For six years the Convection, Rotation, and planetary Transits (CoRoT) space mission has been acquiring photometric data from more than 100 000 point sources towards and directly opposite the inner and outer regions of the Galaxy. The high temporal resolution of the CoRoT data, combined with the wide time span of the observations, enabled the study of short- and long-time variations in unprecedented detail. Aims. The aim of this work is to study the variability and evolutionary behaviour of M-giant stars using CoRot data. Methods. From the initial sample of 2534 stars classified as M giants in the CoRoT databases, we selected 1428 targets that exhibit well defined variability, by visual inspection. Then, we defined three catalogues: C1 – stars with Teff< 4200 K and LCs displaying semi-sinusoidal signatures; C2 – rotating variable candidates with Teff> 4200 K; C3 – long-period variable candidates (with LCs showing a variability period up to the total time span of the observations). The variability period and amplitude of C1 stars were computed using Lomb-Scargle and harmonic fit methods. Finally, we used C1 and C3 stars to study the variability behaviour of M-giant stars. Results. The trends found in the V−I vs. J−K colour–colour diagram are in agreement with standard empirical calibrations for M giants. The sources located towards the inner regions of the Galaxy are distributed throughout the diagram, while the majority of the stars towards the outer regions of the Galaxy are spread between the calibrations of M giants and the predicted position for carbon stars. The stars classified as supergiants follow a different sequence from the one found for giant stars. We also performed a Kolmogorov-Smirnov (KS) test of the period and amplitude of stars towards the inner and outer regions of the Galaxy. We obtained a low probability that the two samples came from the same parent distribution. The observed behaviour of the period-amplitude and period-effective temperature (Teff) diagrams are, in general, in agreement with those found for Kepler sources and ground based photometry, with pulsation being the dominant cause responsible for the observed modulation. We also conclude that short-time variations on M-giant stars do not exist or are very rare, and the few cases we found are possibly related to biases or background stars.
A wavelet analysis of photometric variability in Kepler white dwarf stars
(Oxford University Press (OUP), 2019-01-12) Martins, Bruno Leonardo Canto; Lira, S. R. de; Bravo, J. P.; Leão, I. C.; Costa, A. D. da; Freitas, D. B. de; Medeiros, J. R. de
This work describes a wavelet analysis of 14 Kepler white dwarf stars, in order to confirm their photometric variability behaviour and to search for periodicities in these targets. From the observed Kepler light curves we obtained the wavelet local and global power spectra. Through this procedure, one can perform an analysis in the time–frequency domain rich in detail, and so obtain a new perspective on the time evolution of the periodicities present in these stars. We identified a photometric variability behaviour in 10 white dwarfs, corresponding to period variations of ∼2 h to 18 d: among these stars, three are new candidates and seven, earlier identified from other studies, are confirmed.

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Navegando por Autor "Costa, A. D. da"