Using Transiting Planets to Model Starspot Evolution

TL;DR

This paper models starspot evolution using Kepler light curves, combining in- and out-of-transit data to understand stellar dynamos, differential rotation, and spot lifetimes across different stars.

Contribution

It introduces a novel approach that models both in- and out-of-transit light curves to break degeneracies in starspot property measurements.

Findings

Measured slow differential rotation rates in stars without transiting planets.

Constrained key physical parameters like rotation period and diffusion timescales.

Revealed long-term changes in starspot sizes and positions over four years.

Abstract

Photometry from Kepler has revealed the presence of cool starspots on the surfaces of thousands of stars, presenting a wide range of spot morphologies and lifetimes. Understanding the lifetime and evolution of starspots across the main sequence reveals critical information about the strength and nature of stellar dynamos. We probe the dynamo by modeling the starspot properties over time using Kepler light curves. In particular, we use planetary systems like Kepler 17 that show in-transit starspot crossing features. Spot-occulting transits probe smaller-scale starspot features on the stellar surface along a fixed latitude region. Our approach is novel in modeling both the in- and out-of transit light curve features, allowing us to break fundamental degeneracies between spot size, latitude, and contrast. With continuous monitoring from Kepler we are able to observe small changes in the positions and sizes of spots from many transits, spanning 4 years of data. Additionally, for stars without transiting planets like GJ 1243, we are able to recover subtle, long term changes in spot sizes and longitudes, leading to some of the slowest differential rotation rates yet measured. These studies constrain key physical parameters including rotation period, differential rotation, and diffusion timescales, and open the door to ensemble studies of detailed spot evolution in the future.