Navegando por Autor "Metcalfe, T. S."

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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 Sun
Rotation and magnetism of Kepler pulsating solar-like stars: towards asteroseismically calibrated age-rotation relations
(EDP Sciences, 2014-09-24) García, R. A.; Ceillier, T.; Salabert, D.; Mathur, S.; van Saders, J. L.; Pinsonneault, M.; Ballot, J.; Beck, P. G.; Bloemen, S.; Campante, T. L.; G. R., Davies; Nascimento Júnior, José Dias do; S., Mathis; Metcalfe, T. S.; M. B., Nielsen; J. C., Suárez; W. J., Chaplin; A., Jiménez
Kepler ultra-high precision photometry of long and continuous observations provides a unique dataset in which surface rotation and variability can be studied for thousands of stars. Because many of these old field stars also have independently measured asteroseismic ages, measurements of rotation and activity are particularly interesting in the context of age-rotation-activity relations. In particular, age-rotation relations generally lack good calibrators at old ages, a problem that this Kepler sample of old-field stars is uniquely suited to address. We study the surface rotation and photometric magnetic activity of a subset of 540 solar-like stars on the mainsequence and the subgiant branch for which stellar pulsations have been measured. The rotation period was determined by comparing the results from two di erent analysis methods: i) the projection onto the frequency domain of the time-period analysis, and ii) the autocorrelation function of the light curves. Reliable surface rotation rates were then extracted by comparing the results from two di erent sets of calibrated data and from the two complementary analyses. General photometric levels of magnetic activity in this sample of stars were also extracted by using a photometric activity index, which takes into account the rotation period of the stars.We report rotation periods for 310 out of 540 targets (excluding known binaries and candidate planet-host stars); our measurements span a range of 1 to 100 days. The photometric magnetic activity levels of these stars were computed, and for 61.5% of the dwarfs, this level is similar to the range, from minimum to maximum, of the solar magnetic activity.We demonstrate that hot dwarfs, cool dwarfs, and subgiants have very di erent rotation-age relationships, highlighting the importance of separating out distinct populations when interpreting stellar rotation periods. Our sample of cool dwarf stars with age and metallicity data of the highest quality is consistent with gyrochronology relations reported in the literature

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Navegando por Autor "Metcalfe, T. S."