Statistical Trends in the Obliquity Distribution of Exoplanet Systems

Diego J. Munoz, Hagai B. Perets

Research output: Contribution to journalArticlepeer-review


Important clues to the formation and evolution of planetary systems can be inferred from the stellar obliquity . We study the distribution of obliquities using the California-Kepler Survey and the TEPCat Catalog of Rossiter- McLaughlin (RM) measurements, from which we extract, respectively, 275 and 118 targets. We infer a "best fit" obliquity distribution in with a single parameter κ. Large values of κ imply that is distributed narrowly around zero, while small values imply approximate isotropy. Our findings are as follows. (1) The distribution of in Kepler systems is narrower than found by previous studies and consistent with κ ∼ 15 (mean ayn ∼ 19 and spread ∼ 10°). (2) The value of κ in Kepler systems does not depend, at a statistically significant level, on planet multiplicity, stellar multiplicity, or stellar age; on the other hand, metal-rich hosts, small-planet hosts, and longperiod planet hosts tend to be more oblique than the general sample (at a ∼2.5σ significance level). (3) The obliquities of Hot Jupiter (HJ) systems with RM measurements are consistent with κ ∼ 2, which corresponds to a broader distribution than for the general Kepler population. (4) A separation of the RM sample into cooler (Teff 6250 K) and hotter (Teff 6250 K) HJ hosts results in two distinct distributions, κcooler ∼ 4 and κhotter ∼ 1 (4σ significance), both more oblique than the Kepler sample. We hypothesize that the total mass in planets may be behind the increasing obliquity with metallicity and planet radius, and that the dependence on period could be due to primordial disk alignment rather than tidal realignment of stellar spin.

Original languageEnglish
Article number253
JournalAstronomical Journal
Issue number6
StatePublished - 2018


  • methods: statistical
  • planet-star interactions
  • planetary systems
  • planets and satellites: general
  • stars: rotation

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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