Estimating stellar rotation from starspot detection during planetary transits

TL;DR

This paper introduces a novel method to estimate stellar rotation periods by detecting starspots during planetary transits, validated on solar data and applied to HD 209458 to derive its rotation period.

Contribution

The paper presents a new technique for measuring stellar rotation using starspot detection during transits, demonstrated with simulations and real Hubble data.

Findings

Successfully estimated the solar rotation period from transit simulations.

Estimated the rotation period of HD 209458 as approximately 11.4 days.

Validated the method's effectiveness with real observational data.

Abstract

A new method for determining the stellar rotation period is proposed here, based on the detection of starspots during transits of an extra-solar planet orbiting its host star. As the planet eclipses the star, it may pass in front of a starspot which will then make itself known through small flux variations in the transit light curve. If we are lucky enough to catch the same spot on two consecutive transits, it is possible to estimate the stellar rotational period. This method is successfully tested on transit simulations on the Sun yielding the correct value for the solar period. By detecting two starspots on more than one transit of HD 209458 observed by the Hubble Space Telescope, it was possible to estimate a period of either 9.9 or 11.4 days for the star, depending on which spot is responsible for the signature in the light curve a few transits later. Comparison with period estimates of HD209458 reported in the literature indicates that 11.4 days is the most likely stellar rotation period.