Revisiting KELT-19Ab, WASP-156b and WASP-121b in the TESS Era

TL;DR

This study re-analyzes transit data of three exoplanets using TESS observations, correcting for contamination, and investigates how sampling intervals affect derived planetary parameters, revealing potential atmospheric insights.

Contribution

It introduces a software tool for contamination correction and highlights the impact of sampling cadence on transit parameter estimation in TESS data.

Findings

All three exoplanets have larger inclinations than previously reported.

Sampling interval significantly biases radius ratio measurements, especially for small differences.

The radius ratio for KELT-19Ab is notably smaller in TESS data, suggesting possible atmospheric haze.

Abstract

We present a re-analysis of transit depths of KELT-19Ab, WASP-156b, and WASP-121b, including data from the Transiting Exoplanet Survey Satellite (TESS). The large $\sim$21$\arcsec$ TESS pixels and point spread function result in significant contamination of the stellar flux by nearby objects. We use Gaia data to fit for and remove this contribution, providing general-purpose software for this correction. We find all three sources have a larger inclination, compared to earlier work. For WASP-121b, we find significantly smaller values (13.5 degrees) of the inclination when using the 30 minutes cadence data compared to the 2 minutes cadence data. Using simulations, we demonstrate that the radius ratio of exoplanet to star ($R_{p}/R_{\ast}$) is biased small relative to data taken with a larger sampling interval although oversampling corrections mitigate the bias. This is particularly important for deriving sub-percent transit differences between bands. We find the radius ratio of exoplanet to star ($R_{p}/R_{\ast}$) in the TESS band is 7.5$\sigma$ smaller than previous work for KELT-19Ab, but consistent to within $\sim$2$\sigma$ for WASP-156b and WASP-121b. The difference could be due to specific choices in the analysis, not necessarily due to the presence of atmospheric features. The result for KELT-19Ab possibly favors a haze-dominated atmosphere. We do not find evidence for the $\sim$0.95\,$\mu$m water feature contaminating transit depths in the TESS band for these stars but show that with photometric precision of 500ppm and with a sampling of about 200 observations across the entire transit, this feature could be detectable in a more narrow $z-$band.