The Giants and their role in Ragnarök

University essay from Lunds universitet/Astronomi

Abstract: Observed population of giant planets around evolved stars shows a paucity of planets with semi-major axes below 0.5 au, in contrast to main sequence stars where those planets are present. This lack of close-in planets has been attributed to either planet engulfment due to tidal forces or substantially higher masses of evolved host stars implying dierent initial semi-major axis distributions, because of dierent parameters of planet formation and migration. However, there is recent evidence that the masses of evolved stars have been systematically overestimated and that they should not dier considerably from the main sequence sample, casting doubt on the latter hypothesis. In this project, to investigate the observed lack of close-in planets around evolved stars, I develop a tidal evolution code coupled with a population synthesis model which is based on probability distributions derived from observational data. I nd that the observed paucity of planets cannot be attributed to tidal engulfment alone. One possibility is that the lack of close-in planets is the combination of inherently dierent samples of stars, tidal engulfment, and a statistically insignicant sample of planets. However, further observations are necessary to reach any rm conclusion.

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