Timmi Grosen Jørgensen, MSc defense – University of Copenhagen

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Timmi Grosen Jørgensen, MSc defense

Title: Investigation of the Magnetically Active Detached Eclipsing Binary System V80 using New Photometric Observations from The Kepler Space Telescope

Supervisors: Anja C. Andersen (DARK), Karsten F. Brogaard (Aarhus University)

Abstract: This thesis investigates the magnetically active detached eclipsing binary system V80 by using new photometric data from the Kepler Space Telescope along with observations from Brogaard et al. (2011). Magnetically active stars are known to show discrepan- cies between observation and stellar models which predict stellar radii and temperatures which are ∼ 10% lower and ∼ 5% higher than what is observed, respectively. The stan- dard procedure to regain agreement is to decrease the mixing-length-parameter αMLT in order to mimick the expected reduction in convective efficiency due to starspots. This procedure is however highly likely to result in flawed estimates of the stellar parameters of such systems since it is assumed that the discrepancies can be explained solely by αMLT while keeping parameters such as helium abundance and [Fe/H] constant and dis- regarding their uncertanties. V80 is a member of the open cluster NGC 6791 which has an age constrained to be 8.3 ± 0.3 Gyr from two other longer period deatched eclipsing binaries that show no signs of magnetic activity. By knowing the mass-radius (MR) relation that V80 is expected to follow if it was unaffected by magnetic activity, we per- form light curve analysis to obtain the best estimate of the radii of the components. We determine the radii of V80 to lie in the range of 1.396±0.067R⊙ < Rp < 1.354±0.067R⊙ and 0.7595R⊙ < Rs < 0.8358R⊙ for the primary and secondary components, respec- tively. For the primary component this is 6.8 − 10.5% larger than what is expected for star which are not magnetically active.

V80 has high variability in its light curve which is caused by starspots generated by magnetic activity. Further signs of magnetic activty reveals itself by V80 being an X-ray source and by our identification of a superflare in its Kepler light curve. We present evidence indicating that the magnetic activity of V80 is originating from the primary component which also seems to be experiencing anti-solar differential rotation.

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