Magnetic Activity Discrepancies of Solar-Type Stars Revealed by<i>Kepler</i>Light Curves

He, Hongliang; Wang, Huaning; Yan, Yan; Yun, Duo

doi:10.1017/s1743921317007670

Cited by 3 publications

(5 citation statements)

References 15 publications

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“…Furthermore, Shapiro et al (2017) showed that in the solar case, the superposition of bright facular and dark spot signatures might lead to a disappearance of the rotation peak from the power spectrum of solar brightness variations. This agrees with many studies (see Aigrain et al 2015;He et al 2015He et al , 2018 that have found that the rotation period of the Sun can be reliably determined only during the periods of low solar activity. We note that during these periods, the solar variability is caused by long-lived facular features, and the spot contribution is small.…”

Section: Methods For Determining Stellar Rotation Periodssupporting

confidence: 92%

“…Recently, He et al (2015He et al ( , 2018 analysed solar and stellar brightness using GLS and introduced two indicators: one describing the degree of periodicity in the light curve, and the other describing the amplitude of the photometric variability. They found that light curve periodicities of the Kepler stars are generally stronger during high-activity times.…”

Section: Methods For Determining Stellar Rotation Periodsmentioning

confidence: 99%

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Inflection point in the power spectrum of stellar brightness variations

Amazo-Gómez

Шапиро

Solanki

et al. 2020

A&A

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Context. Young and active stars generally have regular, almost sinusoidal, patterns of variability attributed to their rotation, while the majority of older and less active stars, including the Sun, have more complex and non-regular light curves, which do not have clear rotational-modulation signals. Consequently, the rotation periods have been successfully determined only for a small fraction of the Sun-like stars (mainly the active ones) observed by transit-based planet-hunting missions, such as CoRoT, Kepler, and TESS. This suggests that only a small fraction of such systems have been properly identified as solar-like analogues. Aims. We aim to apply a new method of determining rotation periods of low-activity stars, such as the Sun. The method is based on calculating the gradient of the power spectrum (GPS) of stellar brightness variations and identifying a tell-tale inflection point in the spectrum. The rotation frequency is then proportional to the frequency of that inflection point. In this paper, we compare this GPS method to already-available photometric records of the Sun. Methods. We applied GPS, auto-correlation functions, Lomb-Scargle periodograms, and wavelet analyses to the total solar irradiance (TSI) time series obtained from the Total Irradiance Monitor on the Solar Radiation and Climate Experiment and the Variability of solar IRradiance and Gravity Oscillations experiment on the SOlar and Heliospheric Observatory missions. We analysed the performance of all methods at various levels of solar activity. Results. We show that the GPS method returns accurate values of solar rotation independently of the level of solar activity. In particular, it performs well during periods of high solar activity, when TSI variability displays an irregular pattern, and other methods fail. Furthermore, we show that the GPS and light curve skewness can give constraints on facular and spot contributions to brightness variability. Conclusions. Our results suggest that the GPS method can successfully determine the rotational periods of stars with both regular and non-regular light curves.

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Section: Methods For Determining Stellar Rotation Periodssupporting

confidence: 92%

Section: Methods For Determining Stellar Rotation Periodsmentioning

confidence: 99%

Inflection point in the power spectrum of stellar brightness variations

Amazo-Gómez

Шапиро

Solanki

et al. 2020

A&A

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“…Furthermore, Shapiro et al (2017) showed that in the solar case, the superposition of bright facular and dark spot signatures might lead to a disappearance of the rotation peak from the power spectrum of solar brightness variations. This agrees with many studies (see Aigrain et al 2015;He et al 2015He et al , 2018 which have found that the rotation period of the Sun can be reliably determined only during the periods of low solar activity. We note that during these periods, the solar variability is caused by long-lived facular features, and the spot contribution is small.…”

Section: Methods For Determining Stellar-rotation Periodssupporting

confidence: 92%

“…In He et al (2015He et al ( , 2018 they analysed the solar and stellar activity using GLS and introducing two indicators, one by describing the degree of periodicity on the light-curve, i AC , and the other by the effective fluctuation range, R e f f , that describes the deep of the rotation modulation. They found that light-curves periodicities of the Kepler stars were generally stronger in maximum season of activity than the one of the Sun, where the highest periodicity was determined during low active seasons of activity.…”

Section: State Of the Artmentioning

confidence: 99%

Understanding the brightness variations of Sun-like stars on timescales of stellar rotation

Gomez¹,

Maritza²

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Twenty-four years after the discoveries of the first exoplanets, the radial-velocity (RV) method is still one of the most productive techniques to detect and confirm exoplanets. But stellar magnetic activity can induce RV variations large enough to make it difficult to disentangle planet signals from the stellar noise. In this context, HD41248 is an interesting planet-host candidate, with RV observations plagued by activity-induced signals. We report on ESPRESSO observations of HD41248 and analyse them together with previous observations from HARPS with the goal of evaluating the presence of orbiting planets. Using different noise models within a general Bayesian framework designed for planet detection in RV data, we test the significance of the various signals present in the HD41248 dataset. We use Gaussian processes as well as a first-order moving average component to try to correct for activity-induced signals. At the same time, we analyse photometry from the TESS mission, searching for transits and rotational modulation in the light curve. The number of significantly detected Keplerian signals depends on the noise model employed, which can range from 0 with the Gaussian process model to 3 with a white noise model. We find that the Gaussian process alone can explain the RV data while allowing for the stellar rotation period and active region evolution timescale to be constrained. The rotation period estimated from the RVs agrees with the value determined from the TESS light curve. Based on the data that is currently available, we conclude that the RV variations of HD41248 can be explained by stellar activity (using the Gaussian process model) in line with the evidence from activity indicators and the TESS photometry.

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“…The above results can be applied to the solar-terrestrial space weather studies and predictions (He et al 2008(He et al , 2012(He et al , 2018aWang et al 2009Wang et al , 2018Le et al 2011;Yang et al 2017). The magnetic configuration of solar flares can also provide useful implications for understanding the magnetic and flare activity properties of solar-type stars (He et al , 2018bYun et al 2016Yun et al , 2017Choudhuri 2017;Mehrabi et al 2017;Egeland 2018;Li et al 2018;Mehrabi & He 2019).…”

Section: Resultsmentioning

confidence: 89%

Chirality and magnetic configuration associated with two-ribbon solar flares: AR 10930 versus AR 11158

Wang

Yan

et al. 2020

Advances in Space Research

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The magnetic configuration of flare-bearing active regions (ARs) is one key aspect for understanding the initiation of solar flares. In this paper, we perform a comparative analysis on the chiral characteristics and the magnetic configurations of two X-class two-ribbon flares happening in AR 10930 and AR 11158, whose photospheric magnetic fields were observed by the Hinode and SDO satellites, respectively. The corresponding coronal magnetic fields were calculated based on the nonlinear forcefree field model. It is found that both the flares were initiated in local areas with extremely strong electric current density. The chirality of the magnetic field (indicated by the sign of force-free factor α) along the main polarity inversion line (PIL) is opposite for the two ARs, that is, left-handed (α < 0) for AR 10930 and right-handed (α > 0) for AR 11158. The analysis shows that, for both flare events, prominent magnetic connectivity (indicated by both high α and strong current distributions) was formed above the main PIL before the flare and was totally broken after the flare eruption. Yet the two branches of broken magnetic connectivity, combined with the isolated electric current at the magnetic connectivity breaking site, compose the opposite magnetic configurations for the two ARs owing to their opposite chiral characteristics. That is, Z-shaped configuration for AR 10930 with negative α and left-handed chirality, and inverse Z-shaped configuration for AR 11158 with positive α and right-handed chirality. We speculate that two-ribbon flares can be generally classified to these two magnetic configurations by chirality (α sign) of ARs.

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Magnetic Activity Discrepancies of Solar-Type Stars Revealed byKeplerLight Curves

Cited by 3 publications

References 15 publications

Inflection point in the power spectrum of stellar brightness variations

Inflection point in the power spectrum of stellar brightness variations

Understanding the brightness variations of Sun-like stars on timescales of stellar rotation

Chirality and magnetic configuration associated with two-ribbon solar flares: AR 10930 versus AR 11158

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