Discarding orbital decay in WASP-19b after one decade of transit observations

TL;DR

This study analyzes 10 years of transit data for WASP-19b, finding no evidence of orbital decay, setting limits on the tidal quality factor, and constraining potential planetary companions, while also comparing stellar dissipation efficiencies.

Contribution

First direct empirical estimation of the stellar tidal quality factor $Q'_{\star}$ for WASP-19b using homogeneous transit timing data.

Findings

No evidence of orbital decay in WASP-19b over a decade.

Established upper limit for orbital period change rate, $\dot{P}$.

Disproved existence of planetary companions in key resonances within detection limits.

Abstract

We present a empirical study of orbital decay for the exoplanet WASP-19b, based on mid-time measurements of 74 complete transits (12 newly obtained by our team and 62 from the literature), covering a 10-year baseline. A linear ephemeris best represents the mid-transit times as a function of epoch. Thus, we detect no evidence of the shortening of WASP-19b's orbital period and establish an upper limit of its steady changing rate, $\dot{P}=-2.294$ ms $yr^{-1}$, and a lower limit for the modified tidal quality factor $Q'_{\star} = (1.23 \pm 0.231) \times 10^{6}$. Both are in agreement with previous works. This is the first estimation of $Q'_{\star}$ directly derived from the mid-times of WASP-19b obtained through homogeneously analyzed transit measurements. Additionally, we do not detect periodic variations in the transit timings within the measured uncertainties in the mid-times of transit. We are therefore able to discard the existence of planetary companions in the system down to a few $M_\mathrm{\oplus}$ in the first order mean-motion resonances 1:2 and 2:1 with WASP-19b, in the most conservative case of circular orbits. Finally, we measure the empirical $Q'_{\star}$ values of 15 exoplanet host stars which suggest that stars with $T_\mathrm{eff}$ $\lesssim$ 5600K dissipate tidal energy more efficiently than hotter stars. This tentative trend needs to be confirmed with a larger sample of empirically measured $Q'_{\star}$.