TraMoS project III: Improved physical parameters, timing analysis, and star-spot modelling of the WASP-4b exoplanet system from 38 transit observations

TL;DR

This study combines 38 transit observations of WASP-4b to refine its physical parameters, find no significant transit timing variations indicating no large nearby planets, and analyze star-spot activity suggesting a 34-day stellar rotation period.

Contribution

It provides an improved measurement of WASP-4b's radius, refines transit ephemerides, and conducts a comprehensive search for TTVs and stellar activity, with no significant variations detected.

Findings

No evidence of TTVs larger than 20 seconds over 4 years.

Rules out additional planets larger than 1-2.5 Earth masses near resonances.

Star's rotational period estimated at about 34 days.

Abstract

We report twelve new transit observations of the exoplanet WASP-4b from the Transit Monitoring in the South Project (TraMoS) project. These transits are combined with all previously published transit data for this planet to provide an improved radius measurement of Rp = 1.395 +- 0.022 Rjup and improved transit ephemerides. In a new homogeneous analysis in search for Transit Timing Variations (TTVs) we find no evidence of those with RMS amplitudes larger than 20 seconds over a 4-year time span. This lack of TTVs rules out the presence of additional planets in the system with masses larger than about 2.5 M_earth, 2.0 M_earth, and 1.0 M_earth around the 1:2, 5:3 and 2:1 orbital resonances. Our search for the variation of other parameters, such as orbital inclination and transit depth also yields negative results over the total time span of the transit observations. Finally we perform a simple study of stellar spots configurations of the system and conclude that the star rotational period is about 34 days.