Magnetic Activity Analysis for a Sample of G-Type Main Sequence Kepler Targets

Mehrabi, Ahmad; He, Hongliang; Khosroshahi, Habib G.

doi:10.3847/1538-4357/834/2/207

Cited by 45 publications

(27 citation statements)

References 38 publications

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“…Kepler collected data in two cadence modes, a long cadence (LC) of 29.4 min and a short cadence (SC) of 58.85 s. LC data are well suited to the analysis of large-scale trends, such as the periodicity and amplitude of light curve modulation due to magnetic activity. For Kepler G-type mainsequence stars with rotation periods of 10-20 d, for example, the periodicity and amplitude of light curve variation show a positive correlation for approximately 80 per cent of sampled stars (Mehrabi et al 2017). The percentage of positive correlation stars is greatest for shorter stellar rotation periods and least for rotation periods longer than 20 d, inferring that magnetic activity decreases with age due to spin-down and decreasing T eff , though starspot stability increases as rotation slows.…”

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

“…The presence of starspots and faculae contribute to the overall stellar irradiance and light curve variance (Mehrabi, He & Khosroshahi 2017). The temporal change in starspot/facula coverage on the stellar surface is witnessed as periodic, sinusoidal trends in stellar light curves, with the degree of light curve modulation being indicative of magnetic activity level (Mehrabi et al 2017). Studies of modulation in light curves recorded by the Kepler mission (Borucki 2010) have produced a wealth of information on stellar rotation rates and activity trends (McQuillan, Mazeh & Aigrain 2013Reinhold, Reiners & Basri 2013;He, Wang & Yun 2015;Mehrabi, He & Khosroshahi 2017).…”

Section: Introductionmentioning

confidence: 99%

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Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots

Zaleski

Válio

Marsden

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Knowledge of dynamo evolution in solar-type stars is limited by the difficulty of using active region monitoring to measure stellar differential rotation, a key probe of stellar dynamo physics. This paper addresses the problem by presenting the first ever measurement of stellar differential rotation for a main-sequence solar-type star using starspots and faculae to provide complementary information. Our analysis uses modelling of light curves of multiple exoplanet transits for the young solar-type star Kepler-71, utilizing archival data from the Kepler mission. We estimate the physical characteristics of starspots and faculae on Kepler-71 from the characteristic amplitude variations they produce in the transit light curves and measure differential rotation from derived longitudes. Despite the higher contrast of faculae than those in the Sun, the bright features on Kepler-71 have similar properties such as increasing contrast towards the limb and larger sizes than sunspots. Adopting a solar-type differential rotation profile (faster rotation at the equator than the poles), the results from both starspot and facula analysis indicate a rotational shear less than about 0.005 rad d −1 , or a relative differential rotation less than 2 per cent, and hence almost rigid rotation. This rotational shear contrasts with the strong rotational shear of zero-age main-sequence stars and the modest but significant shear of the modern-day Sun. Various explanations for the likely rigid rotation are considered.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots

Zaleski

Válio

Marsden

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The results of the correlation analysis affirm that the two magnetic proxies are positively correlated for the three stars, with the correlation coefficients for the three stars being 0.77, 0.72, and 0.78, respectively. So all three stars being investigated in this paper belong to the positive-correlationstar category described in the work by Mehrabi et al (2017; see the introduction in Section 1). Table 2) among the 15 quarters of each plot; and the percentage value by the error bar is the ratio of the error bar height to the variation range of R eff or iAC (see the main text).…”

Section: Magnetic Feature Activitymentioning

confidence: 99%

Activity Analyses for Solar-type Stars Observed with Kepler. II. Magnetic Feature versus Flare Activity

Wang

Zhang

et al. 2018

ApJS

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The light curves of solar-type stars present both periodic fluctuation and flare spikes. The gradual periodic fluctuation is interpreted as the rotational modulation of magnetic features on the stellar surface and is used to deduce magnetic feature activity properties. The flare spikes in light curves are used to derive flare activity properties. In this paper, we analyze the light curve data of three solartype stars (KIC 6034120, KIC 3118883, and KIC 10528093) observed with Kepler space telescope and investigate the relationship between their magnetic feature activities and flare activities. The analysis shows that: (1) both the magnetic feature activity and the flare activity exhibit long-term variations as the Sun does; (2) unlike the Sun, the long-term variations of magnetic feature activity and flare activity are not in phase with each other; (3) the analysis of star KIC 6034120 suggests that the long-term variations of magnetic feature activity and flare activity have a similar cycle length. Our analysis and results indicate that the magnetic features that dominate rotational modulation and the flares possibly have different source regions, although they may be influenced by the magnetic field generated through a same dynamo process.

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“…Great care should thus be taken when claiming the detection of any cycles with only 4 years of Kepler observations. It is however, very interesting to compare the variability in such different activity indicators, as it can teach us something about the physical mechanisms responsible for generating the variability (Salabert et al 2016;Mehrabi et al 2017). Especially, it is interesting to compare magnetic activity indicators originating from the surface to indicators originating from the interior.…”

Section: Introductionmentioning

confidence: 99%

Sounding stellar cycles with Kepler – III. Comparative analysis of chromospheric, photometric, and asteroseismic variability

Karoff

Metcalfe

Montet

et al. 2019

Monthly Notices of the Royal Astronomical Society

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By combining ground-based spectrographic observations of variability in the chromospheric emission from Sun-like stars with the variability seen in their eigenmode frequencies, it is possible to relate the changes observed at the surfaces of these stars to the changes taking place in the interior. By further comparing this variability to changes in the relative flux from the stars, one can obtain an expression for how these activity indicators relate to the energy output from the stars. Such studies become very pertinent when the variability can be related to stellar cycles as they can then be used to improve our understanding of the solar cycle and its effect on the energy output from the Sun.Here we present observations of chromospheric emission in 20 Sun-like stars obtained over the course of the nominal 4-year Kepler mission. Even though 4 years is too short to detect stellar equivalents of the 11-year solar cycle, observations from the Kepler mission can still be used to analyse the variability of the different activity indicators thereby obtaining information of the physical mechanism generating the variability. The analysis reveals no strong correlation between the different activity indicators, except in very few cases. We suggest that this is due to the sparse sampling of our ground-based observations on the one hand and that we are likely not tracing cyclic variability on the other hand. We also discuss how to improve the situation.

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Magnetic Activity Analysis for a Sample of G-Type Main Sequence Kepler Targets

Cited by 45 publications

References 38 publications

Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots

Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots

Activity Analyses for Solar-type Stars Observed with Kepler. II. Magnetic Feature versus Flare Activity

Sounding stellar cycles with Kepler – III. Comparative analysis of chromospheric, photometric, and asteroseismic variability

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