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Planets around giant stars: Two close-in transiting planets and one S-type planet in an eccentric binary system

Ortiz Álvarez, Mauricio

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Abstract

The study of planets around giant stars is an excellent way of probing the effects of stellar evolution on planetary systems. This is because as the star evolves from its main-sequence (MS) lifetime into the red giant branch (RGB) phase, it experiences important physical changes, like for example, significant mass loss, increase of the stellar radius and luminosity variability. These effects have the potential of influencing the whole architecture of planets that might have formed previously in the system. Additionally, as giant stars are generally more massive than MS stars, the effects of stellar mass on planet formation and migration theories can be tested. In this thesis, planets around evolved stars are studied from different perspectives. First, a comprehensive radial velocity (RV) follow-up of transiting planet candidates around evolved stars – observed by the Kepler telescope – was initiated to unveil a population of close-in planets (a < 0.5 au) that have been undetected by previous RV surveys. This effort led to the confirmation of the planetary nature of two close-in planets, Kepler-432 b and Kepler-91 b, providing evidence that short-period planets can exist around intermediate-mass evolved stars. These results suggest that gravitational interaction, with other planets or stars, is likely to be the preferred migration channel for close-in planets in intermediate-mass giant stars. Additionally, the findings in this thesis are in agreement with the view in which the scarcity of short-period planets around clump giants is explained by an increased planet-star tidal interaction during the RGB, subsequently leading to the tidal engulfment of giant planets. In the second part of this thesis, a very interesting binary system hosting a giant planet is analyzed. The planet, HD 59686 Ab, is orbiting the primary K-giant star at ~1 au, while the stellar companion is in a very eccentric orbit (e ~0.7) with a small semi-major axis of ~13.6 au. The existence of this planet in a tight eccentric binary system severely challenges the standard view in which gas giant planets form beyond the ice line of their hosts and then experience a migration phase to reach their current positions. The planet HD 59686 Ab presented in this thesis can become a benchmark object for the study of giant planets in close-separation binaries and might allow to shed light onto different planet formation theories in tight binaries.

Item Type: Dissertation
Supervisor: Quirrenbach, Prof. Dr. Andreas
Date of thesis defense: 14 December 2016
Date Deposited: 17 Jan 2017 12:47
Date: 2017
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
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