Starspots and spin-orbit alignment for Kepler cool host stars

TL;DR

This paper introduces a novel method using starspot crossings to measure stellar obliquity in exoplanet systems, demonstrating its application on Kepler-30, which has a low obliquity, informing planet formation theories.

Contribution

It presents a new technique for measuring stellar obliquity via starspot crossings and applies it to a multi-planet system, providing insights into system alignment.

Findings

Kepler-30 has an obliquity smaller than 10 degrees.

Starspot crossing technique can effectively measure stellar obliquity.

Implications for hot-Jupiter formation and system evolution are discussed.

Abstract

The angle between the spin axis of the host star and the orbit of its planets (i.e., the stellar obliquity) is precious information about the formation and evolution of exoplanetary systems. Measurements of the Rossiter-McLaughlin effect revealed that many stars that host a hot-Jupiter have high obliquities, suggesting that hot-Jupiter formation involves excitation of orbital inclinations. In this contribution we show how the passage of the planet over starspots can be used to measure the obliquity of exoplanetary systems. This technique is used to obtain - for the first time - the obliquity of a system with several planets that lie in a disk, Kepler-30, with the result that the star has an obliquity smaller than 10 degrees. The implications for the formation of exoplanetary systems, in particular the hot-Jupiter population, are also discussed.