Stellar Magnetic Cycles in the Solar-Like Stars Kepler-17 and Kepler-63

Estrela, Raissa; Válio, Adriana

doi:10.3847/0004-637x/831/1/57

Cited by 48 publications

(39 citation statements)

References 33 publications

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“…A longterm change in the observed variance due to starspots would suggest additional evidence of magnetic cycles (Mathur et al 2014;Estrela & Valio 2016). A correlation or anti-correlation between the observed brightness of the star in the FFI photometry and variability from starspots would suggest that the brightness variations are dominated by faculae or starspots, respectively (Radick et al 1998).…”

Section: Information From Long Cadence Light Curvesmentioning

confidence: 99%

Long-term Photometric Variability in Kepler Full-frame Images: Magnetic Cycles of Sun–like Stars

Montet

Tovar

Foreman-Mackey

2017

ApJ

121

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Photometry from the Kepler mission is optimized to detect small, short duration signals like planet transits at the expense of long-term trends. This long-term variability can be recovered in photometry from the Full Frame Images (FFIs), a set of calibration data collected approximately monthly during the Kepler mission. Here, we present f3, an open-source package to perform photometry on the Kepler FFIs in order to detect changes in the brightness of stars in the Kepler field of view over long time baselines. We apply this package to a sample of 4,000 Sun-like stars with measured rotation periods. We find ≈ 10% of these targets have long-term variability in their observed flux. For the majority of targets we identify the luminosity variations are either correlated or anticorrelated with the short-term variability due to starspots on the stellar surface. We find a transition between anticorrelated (starspot-dominated) variability and correlated (facula-dominated) variability between rotation periods of 15 and 25 days, suggesting the transition between the two modes is complete for stars at the age of the Sun. We also identify a sample of stars with apparently complete cycles, as well as a collection of short-period binaries with extreme photometric variation over the Kepler mission.

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Section: Information From Long Cadence Light Curvesmentioning

confidence: 99%

Long-term Photometric Variability in Kepler Full-frame Images: Magnetic Cycles of Sun–like Stars

Montet

Tovar

Foreman-Mackey

2017

ApJ

121

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“…A Lomb-Scargle periodogram performed on the area data yield a maximum periodicity of 12.01 ± 0.05 d, that is smaller than the average rotation period of 12.4 d, and equals very closely 8 times the orbital period of the planet. For a detailed analysis of the periodogram and the presence of a magnetic cycle of 1.12 ± 0.16 yr, see Estrela and Valio (2016). Figure 7 shows the spots position (longitude), size, and intensity for each transit during the whole observing period.…”

Section: Spot Characteristicsmentioning

confidence: 99%

Activity and Rotation of Kepler-17

Válio

Estrela

Netto

et al. 2017

ApJ

Self Cite

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Magnetic activity on stars manifests itself in the form of dark spots on the stellar surface, that cause modulation of a few percent in the light curve of the star as it rotates. When a planet eclipses its host star, it might cross in front of one of these spots creating a "bump" in the transit light curve. By modelling these spot signatures, it is possible to determine the physical properties of the spots such as size, temperature, and location. In turn, the monitoring of the spots longitude provides estimates of the stellar rotation and differential rotation. This technique was applied to the star Kepler-17, a solar-type star orbited by a hot Jupiter. The model yields the following spot characteristics: average radius of 49 ± 10 Mm, temperatures of 5100 ± 300 K, and surface area coverage of 6 ± 4 %. The rotation period at the transit latitude, −5• , occulted by the planet was found to be 11.92 ± 0.05 d, slightly smaller than the out-of-transit average period of 12.4 ± 0.1 d. Adopting a solar like differential rotation, we estimated the differential rotation of Kepler-17 to be ∆Ω = 0.041 ± 0.005 rd/d, which is close to the solar value of 0.050 rd/d, and a relative differential rotation of ∆Ω/Ω = 8.0 ± 0.9 %. Since Kepler-17 is much more active than our Sun, it appears that for this star larger rotation rate is more effective in the generation of magnetic fields than shear.

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“…Other key ingredients related to dynamo models that can be inferred through the study of starspots are: butterfly diagram (Sanchis-Ojeda, & Winn 2011; Morris et al 2017;, period of magnetic cycle (Estrela & Valio 2016), and starspot lifetime (Berdyugina 2005). Thus by studying a sample of active stars we hope to be able to better understand the stellar dynamo.…”

Section: Introductionmentioning

confidence: 99%

Stellar magnetic activity and the butterfly diagram of Kepler-63

Netto

Válio

2020

A&A

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Context. The study of young solar type stars is fundamental for a better understanding of the magnetic activity of the Sun. Most commonly, this activity manifests itself in the form of spots and faculae. As a planet in transit crosses in front of its host star, a dark spot on the stellar surface may be occulted, causing a detectable variation in the light curve. Kepler-63 is a young solar-like star with an age of only 210 Myr that exhibit photometric variations compatible with spot signatures. Since its orbiting planet is in an almost polar orbit, different latitudes of the star can be probed by the method of spot transit mapping. Aims. The goal of this work is to characterise the spots of Kepler-63 and thus decipher the behaviour of the young Sun. Because of the high obliquity of the planetary orbit, the spots latitudinal distribution and thus its differential rotation may be determined. Methods. A total of 150 transits of Kepler-63b were observed in the short cadence light curve, corresponding to a total duration of about 4 years. Each transit light curve was fit by a model that simulates planetary transits and allows the inclusion of starspots on the surface of the host star. This enables the physical characterisation of the spots size, intensity, and location. We determine the spot position in a reference frame that rotates with the star, and thus obtain the latitudinal distribution of the spots. Results. A total of 297 spots were fit and their sizes, intensities, and positions determined. The spots longitude and latitude were calculated on a reference frame that rotates with the star. The latitude distribution of spots exhibits a bimodality with a lack of spots around 34 • . Moreover, the size of spots tend to be larger close to the equator, decreasing toward the latitude distribution gap, and then increasing again toward the poles. The high latitude spots dominate the magnetic cycle of Kepler-63. For a mean stellar rotation period of 5.400d, 59 spots were found at approximately the same longitude and latitude on a later transit. Some of these spots were detected 8 transits later, showing the existence of spots with lifetimes of at least 75d. Conclusions. Due to the geometry of the Kepler-63 system, we were able to build a starspot "butterfly diagram", similar to that of sunspots. It was also possible to infer Kepler-63 differential rotation from the presence of spots at different latitudes. This star was found to rotate almost rigidly with a period of 5.400d and relative shear close to 0.01% for latitudes less than 34 • , whereas the high latitudes do not follow a well behaved pattern.

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Stellar Magnetic Cycles in the Solar-Like Stars Kepler-17 and Kepler-63

Cited by 48 publications

References 33 publications

Long-term Photometric Variability in Kepler Full-frame Images: Magnetic Cycles of Sun–like Stars

Long-term Photometric Variability in Kepler Full-frame Images: Magnetic Cycles of Sun–like Stars

Activity and Rotation of Kepler-17

Stellar magnetic activity and the butterfly diagram of Kepler-63

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