Navegando por Autor "Mathur, S."
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Artigo 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., JiménezKepler 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 literatureArtigo 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