Navegando por Autor "Beck, P. G."

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Lithium abundance and rotation of seismic solar analogues: solar and stellar connection from Kepler and Hermes observations
(EDP Sciences, 2017-02-02) Beck, P. G.; Nascimento Júnior, José Dias do; Duarte, T.; Salabert, D.; Tkachenko, A.; Mathis, S.; Marthur, S.; García, R. A.; Castro, M.; Pallé, P. L.; Egeland, R.; Montes, D.; Creevey, O.; Andersen, M F.; Kamath, D.; van Winckel, H.
Context. Lithium abundance A(Li) and surface rotation are good diagnostic tools to probe the internal mixing and angular momentum transfer in stars. Aims. We explore the relation between surface rotation, A(Li), and age in a sample of seismic solar-analogue stars, and we study their possible binary nature. Methods. We selected a sample of 18 solar-analogue stars observed by the NASA Kepler satellite for an in-depth analysis. Their seismic properties and surface rotation rates are well constrained from previous studies. About 53 h of high-resolution spectroscopy were obtained to derive fundamental parameters from spectroscopy and A(Li). These values were combined and compared with seismic masses, radii, and ages, as well as with surface rotation periods measured from Kepler photometry. Results. Based on radial velocities, we identify and confirm a total of six binary star systems. For each star, a signal-to-noise ratio of 80 . S=N . 210 was typically achieved in the final spectrum around the lithium line. We report fundamental parameters and A(Li). Using the surface rotation period derived from Kepler photometry, we obtained a well-defined relation between A(Li) and rotation. The seismic radius translates the surface rotation period into surface velocity. With models constrained by the characterisation of the individual mode frequencies for single stars, we identify a sequence of three solar analogues with similar mass ( 1.1 M ) and stellar ages ranging between 1 to 9 Gyr.Within the realistic estimate of 7% for the mass uncertainty, we find a good agreement between the measured A(Li) and the predicted A(Li) evolution from a grid of models calculated with the Toulouse-Geneva stellar evolution code, which includes rotational internal mixing, calibrated to reproduce solar chemical properties. We found a scatter in ages inferred from the global seismic parameters that is too large when compared with A(Li). Conclusions.We present the Li-abundance for a consistent spectroscopic survey of solar-analogue stars with a mass of 1:00 0:15 M that are characterised through asteroseismology and surface rotation rates based on Kepler observations. The correlation between A(Li) and Prot supports the gyrochronological concept for stars younger than the Sun and becomes clearer when the confirmed binaries are excluded. The consensus between measured A(Li) for solar analogues with model grids, calibrated on the Sun’s chemical properties, suggests that these targets share the same internal physics. In this light, the solar Li and rotation rate appear to be normal for a star like the Sun
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
The HERMES solar atlas and the spectroscopic analysis of the seismic solar analogue KIC 3241581
(EDP Sciences, 2015-11-18) Beck, P. G.; Prieto, C. Allende; van Reeth, T.; Tkachenko, A.; Raskin, G.; van Winckel, H.; Nascimento Júnior, José Dias do; Salabert, D.; Corsaro, E.; García, R. A.
Context. Solar-analogue stars provide an excellent resource to study the Sun’s evolution, i.e. the changes with time in stellar structure, activity, or rotation for solar-like stars. The unparalleled photometric data from the NASA space telescope Kepler allows us to study and characterise solar-like stars through asteroseismology. Aims. We aim to spectroscopically investigate the fundamental parameter and chromospheric activity of solar analogues and twins, based on observations obtained with the HERMES spectrograph and combine them with asteroseismology. Therefore, we need to build a solar atlas for the spectrograph, to provide accurate calibrations of the spectroscopically determined abundances of solar- and late-type stars observed with this instrument and thus perform differential spectroscopic comparisons. Methods. We acquire high-resolution and high signal-to-noise (S/N) spectroscopy to construct three solar reference spectra by observing the reflected light of the asteroids Vesta and Victoria and the jovian moon Europa (100 <∼ S/N <∼ 450) with the HERMES spectrograph. We then observe the Kepler solar analogue KIC3241581 (S/N ∼ 170). For this star, the fundamental spectral parameters are extracted using a differential analysis. Sufficient S/N in the near ultraviolet allows us to investigate the chromospheric magnetic activity in both objects. Results. We constructed three solar spectrum atlases from 385 to 900 nm, obtained with the HERMES spectrograph from observations of two bright asteroids and a jovian moon. A comparison between our solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent agreement. KIC3241581 was found to be a long-periodic binary system. The fundamental parameter for the stellar primary component are Teff = 5689 ± 11 K, log g = 4.385 ± 0.005, [Fe/H] = +0.22 ± 0.01, being in agreement with the published global seismic values, which confirms its status as solar analogue. The chromospheric activity level is compatible with the solar magnetic activity observed during 2014 and 2015. Conclusions. Our solar atlas is an essential tool for the analysis of solar-like stars and to characterise solar analogues and twins with HERMES. The differential analysis, using the presented solar atlas from HERMES observations allows us to obtain the fundamental parameters with very high accuracy. KIC 3241581 is a metal-rich solar analogue with a solar-like activity level in a binary system of unknown period

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Navegando por Autor "Beck, P. G."