Navegando por Autor "Garcia, R. A."
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Artigo Magnetic variability in the young solar analog KIC 10644253: observations from the Kepler satellite and the HERMES spectrograph(EDP Sciences, 2016-02-29) Salabert, D.; Régulo, C.; Garcia, R. A.; Beck, P. G.; Ballot, J.; Creevey, O. L.; Hernández, F. Pérez; Nascimento Júnior, José Dias do; Corsaro, E.; Egeland, R.; Marthur, S.; Metcalfe, T. S.; Bigot, L.; Ceillier, T.; Pallé, P. L.The continuous photometric observations collected by the Kepler satellite over 4 yr provide a wealth of data with an unequalled quantity and quality for the study of stellar evolution of more than 200 000 stars. Moreover, the length of the dataset provides a unique source of information for detecting magnetic activity and associated temporal variability in the acoustic oscillations. In this regards, the Kepler mission was awaited with great expectations. The search for the signature of magnetic activity variability in solar-like pulsations still remained unfruitful more than 2 yr after the end of the nominal mission. Here, however, we report the discovery of temporal variability in the low-degree acoustic frequencies of the young (1 Gyr-old) solar analog KIC 10644253 with a modulation of about 1.5 yr with significant temporal variations for the duration of the Kepler observations. The variations agree with the derived photometric activity. The frequency shifts extracted for KIC 10644253 are shown to result from the same physical mechanisms involved in the inner subsurface layers as in the Sun. In parallel, a detailed spectroscopic analysis of KIC 10644253 is performed based on complementary ground-based, high-resolution observations collected by the HERMES instrument mounted on the Mercator telescope. Its lithium abundance and chromospheric activity S index confirm that KIC 10644253 is a young and more active star than the SunArtigo Rotation periods and ages of solar analogs and solar twins revealed by the kepler mission(IOP Publishing, 2014-08-01) Costa, Jefferson Soares da; Nascimento, José Dias do; Garcia, R. A.; Mathur, S.; Anthony, F.; Barnes, S. A.; Meibom, S.; Castro, Matthieu Sebastien; Salabert, D.; Ceillier, T.A new sample of solar analogs and twin candidates has been constructed and studied, paying particular attention to their light curves from NASA’s Kepler mission. This Letter aims to assess their evolutionary status, derive their rotation and ages, and identify those which are solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days and averaging 19 days, allow us to assess their individual evolutionary states on the main sequence and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates