Magnetic activity and differential rotation in the very young star KIC 8429280

Frasca, A.; Fröhlich, H.‐E.; Bonanno, A.; Catanzaro, G.; Biazzo, K.; Molenda-Żakowicz, J.

doi:10.1051/0004-6361/201116980

Cited by 62 publications

(80 citation statements)

References 59 publications

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“…Lanza et al 2009a). Our spot rotation periods fall within the range found by Frasca et al (2011) for KIC 8429280, while they are close but slightly outside the ranges found for KIC 7765135 and KIC 7985370 by Fröhlich et al (2012). However, those models use seven to nine evolving spots to fit the whole time series instead of two fixed spots applied to fit a data interval.…”

Section: Dr In Our Sample Of Starssupporting

confidence: 68%

Measuring stellar differential rotation with high-precision space-borne photometry

Lanza

Chagas

Medeiros

2014

A&A

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Context. Stellar differential rotation is important for understanding hydromagnetic stellar dynamos, instabilities, and transport processes in stellar interiors, as well as for a better treatment of tides in close binary and star-planet systems. Aims. We introduce a method of measuring a lower limit to the amplitude of surface differential rotation from high-precision, evenly sampled photometric time series, such as those obtained by space-borne telescopes. It is designed to be applied to main-sequence late-type stars whose optical flux modulation is dominated by starspots.Methods. An autocorrelation of the time series was used to select stars that allow an accurate determination of starspot rotation periods. A simple two-spot model was applied together with a Bayesian information criterion to preliminarily select intervals of the time series showing evidence of differential rotation with starspots of almost constant area. Finally, the significance of the differential rotation detection and a measurement of its amplitude and uncertainty were obtained by an a posteriori Bayesian analysis based on a Monte Carlo Markov chain approach. We applied our method to the Sun and eight other stars for which previous spot modelling had been performed to compare our results with previous ones. Results. We find that autocorrelation is a simple method for selecting stars with a coherent rotational signal that is a prerequisite for successfully measuring differential rotation through spot modelling. For a proper Monte Carlo Markov chain analysis, it is necessary to take the strong correlations among different parameters that exist in spot modelling into account. For the planet-hosting star Kepler-30, we derive a lower limit to the relative amplitude of the differential rotation of ΔP/P = 0.0523± 0.0016. We confirm that the Sun as a star in the optical passband is not suitable for measuring differential rotation owing to the rapid evolution of its photospheric active regions. In general, our method performs well in comparison to more sophisticated and time-consuming approaches.

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Section: Dr In Our Sample Of Starssupporting

confidence: 68%

Measuring stellar differential rotation with high-precision space-borne photometry

Lanza

Chagas

Medeiros

2014

A&A

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“…McQuillan et al (2013) used the stability of the autocorrelation function to point out possible classical pulsators for which low-frequency modes are very stable, but this stability can also be due to longlived active regions or stable groups of starspots at a given active longitude on the star (e.g. Frasca et al 2011;Strassmeier 2009). These long-lived structures, if they are rotating at close rates (due to differential rotation), can produce a beating in the light curve that mimics the effect of activity cycles.…”

Section: Observations and Data Analysismentioning

confidence: 99%

Magnetic activity of F stars observed byKepler

Mathur

García

Ballot

et al. 2014

A&A

161

195

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Context. The study of stellar activity is important because it can provide new constraints for dynamo models when combined with surface rotation rates and the depth of the convection zone. We know that the dynamo mechanism, which is believed to be the main process that rules the magnetic cycle of solar-like stars, results from the interaction between (differential) rotation, convection, and magnetic field. The Kepler mission has already been collecting data for a large number of stars during four years allowing us to investigate magnetic stellar cycles. Aims. We investigated the Kepler light curves to look for magnetic activity or even hints of magnetic activity cycles. Based on the photometric data we also looked for new magnetic indexes to characterise the magnetic activity of the stars. Methods. We selected a sample of 22 solar-like F stars that have a rotation period shorter than 12 days. We performed a timefrequency analysis using the Morlet wavelet yielding a magnetic proxy for our sample of stars. We computed the magnetic index S ph as the standard deviation of the whole time series and the index S ph , which is the mean of standard deviations measured in subseries of length five times the rotation period of the star. We defined new indicators, such as the contrast between high and low activity, to take into account the fact that complete magnetic cycles are not observed for all the stars. We also inferred the Rossby number of the stars and studied their stellar background. Results. This analysis shows different types of behaviour in the 22 F stars. Two stars show behaviour very similar to magnetic activity cycles. Five stars show long-lived spots or active regions suggesting the existence of active longitudes. Two stars in our sample seem to have a decreasing or increasing trend in the temporal variation of the magnetic proxies. Finally, the last group of stars shows magnetic activity (with the presence of spots) but no sign of cycle.

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“…In principle, the spot-modeling procedure is as described in Frasca et al (2011) andFröhlich et al (2012). Central to this parameter estimation is the likelihood function.…”

Section: Some General Remarksmentioning

confidence: 99%

Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

Bonanno

Fröhlich

Karoff

et al. 2014

A&A

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We present photometric spot modeling of the nearly four-year long light-curve of the Kepler target KIC 5955122 in terms of persisting dark circular surface features. With a Bayesian technique, we produced a plausible surface map that shows dozens of small spots. After some artifacts are removed, the residuals are at ±0.16 mmag. The shortest rotational period found is P = 16.4 ± 0.2 days. The equator-to-pole extrapolated differential rotation is 0.25 ± 0.02 rad/d. The spots are roughly half as bright as the unperturbed stellar photosphere. Spot latitudes are restricted to the zone ±60 • latitude. There is no indication for any near-pole spots. In addition, the p-mode pulsations enabled us to determine the evolutionary status of the star, the extension of the convective zone, and its radius and mass. We discuss the possibility that the clear signature of active regions in the light curve of the F9IV star KIC 5955122 is produced by a flux-transport dynamo action at the base of the convection zone. In particular, we argue that this star has evolved from an active to a quiet status during the Q0-Q16 period of observation, and we predict, according to our dynamo model, that the characteristic activity cycle is of the order of the solar one.

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Magnetic activity and differential rotation in the very young star KIC 8429280

Cited by 62 publications

References 59 publications

Measuring stellar differential rotation with high-precision space-borne photometry

Measuring stellar differential rotation with high-precision space-borne photometry

Magnetic activity of F stars observed byKepler

Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

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