Activity and rotation of Kepler-17

• Published in: arXiv.org
• Main Authors: Valio, A, Estrela, R, Netto, Y, Bravo, J P, de Medeiros, J R
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 07.02.2017
• Subjects: Differential rotation; Extrasolar planets; Gas giant planets; Light curve; Physical properties; Physics - Earth and Planetary Astrophysics; Physics - Solar and Stellar Astrophysics; Planetary rotation; Solar rotation; Spots; Stellar rotation; Stellar surfaces; Transit
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1702.02213

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 \(49 \pm 10\) Mm, temperatures of \(5100 \pm 300\) K, and surface area coverage of \(6 \pm 4\) \%. The rotation period at the transit latitude, \(-5^\circ\), occulted by the planet was found to be \(11.92 \pm 0.05\) d, slightly smaller than the out--of--transit average period of \(12.4 \pm 0.1\) d. Adopting a solar like differential rotation, we estimated the differential rotation of Kepler-17 to be \(\Delta\Omega = 0.041 \pm 0.005\) rd/d, which is close to the solar value of 0.050 rd/d, and a relative differential rotation of \(\Delta\Omega/\Omega=8.0 \pm 0.9\) \%. 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.