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One of the fundamental questions in astronomy is how planetary systems form and evolve. Measuring the planetary occurrence and architecture as a function of time directly addresses this question. In the fourth paper of the Planets Across Space and Time (PAST) series, we investigate the occurrence and architecture of Kepler planetary systems as a function of kinematic age by using the LAMOST-Gaia-Kepler sample. To isolate the age effect, other stellar properties (e.g., metallicity) have been controlled. We found the following results. (1) The fraction of stars with Kepler-like planets (FKep) is about 50% for all stars; no significant trend is found between FKep and age. (2) The average planet multiplicity (Np) exhibits a decreasing trend ( ∼2σ significance) with age, which decreases from Np ~ 2.6–2.7 for stars younger than 1 Gyr to Np ∼ 1.8–2.0 for stars older than 8 Gyrs. (3) The number of planets per star (η=FKep ×Np) shows a more pronounced decreasing trend (∼3σ significance), which decreases from η ∼ 1.4–1.5 for young stars to η ∼ 0.9–1.0 for old stars. (4) The median mutual orbital inclination of the planets (σi,k) increases from 2.2 to 3.9 as stars aging, and both the Solar System and the Kepler planetary systems fit such a trend. The nearly independence of FKep ∼ 50% on age implies that planet formation is robust and stable across the Galaxy history. The age dependence of Np and σi,k demonstrates that planetary architecture is evolving, and planetary systems generally become dynamically hotter with fewer planets as they age.
methods: statistical, planet–star interactions, planetary systems
methods: statistical, planet–star interactions, planetary systems
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