Effect of stellar activity on the high precision transit light curve

M Oshagh,,I Boisse,,D Ehrenreich,,N C Santos,,P Figueira,,A Santerne,,G Boué,,X Dumusque,,N Haghighipour,

doi:10.1051/epjconf/201510105003

Abstract

Stellar activity features such as spots and plages can create difficulties in determining planetary parameters through spectroscopic and photometric observations. The overlap of a transiting planet and a stellar spot, for instance, can produce anomalies in the transit light curve that may lead to inaccurate estimation of the transit duration, depth, and timing. Such inaccuracies can affect the precise derivation of the planet’s radius. In this talk we will present the results of a quantitative study on the effects of stellar spots on high precision transit light curves. We show that spot anomalies can lead to the estimate of a planet radius that is 4% smaller than the real value. The effects on the transit duration can also be of the order of 4%, longer or shorter. Depending on the size and distribution of spots, anomalies can also produce transit timing variations with significant amplitudes. For instance, TTVs with signal amplitudes of 200 seconds can be produced by spots as large as the largest sunspot. Finally, we examine the impact of active regions on the transit depth measurements in different wavelengths, in order to probe the impact of this effect on transmission spectroscopy measurements. We show that significant (up to 10%) underestimation/overestimation of the planet-to-star radius ratio can be measured, especially in the short wavelength regime.

Highlights

The overlap of a transiting planet and stellar spots can produce anomalies in the transit light-curve that may lead to an incorrect determination of planetary parameters, such as the planet radius, orbital incliantion of planet and can cause offsets in the transit-timing measurement that can lead to a false-positive detection of a non-transiting planet by transit-timing variation (TTV) method (Oshagh et al 2012, Oshagh et al 2013a)
We examine the effect of stellar spots occultation on the transit light-curve and its corresponding planetary transit timing
We generated a large number of transit light-curves for a system with a spotted star, and to understand how the spot occultation affects the transit timing of the planet, we fit these light curves with the light curve of a system in which the effect of the spot-planet overlap was not taken into account

Summary

Introduction

EPJ Web of Conferences parameters such as its radius and the limb darkening coefficients of the host star (e.g, Czesla et al 2009, Csizmadia et al 2013 ). The overlap of a transiting planet and stellar spots can produce anomalies in the transit light-curve that may lead to an incorrect determination of planetary parameters, such as the planet radius, orbital incliantion of planet and can cause offsets in the transit-timing measurement that can lead to a false-positive detection of a non-transiting planet by transit-timing variation (TTV) method (Oshagh et al 2012, Oshagh et al 2013a)

Effect of the stellar spot occultation on the transit time

Impact of occultations of stellar active regions on transmission spectra

Findings

Reanalyzing HD 189733b