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

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 $y{r}^{-1}$, and a lower limit for the modified tidal quality factor $Q_{\star }^{\prime }=(1.23\pm 0.231)\times 10^6$. Both are in agreement with previous works. This is the first estimation of $Q_{\star }^{\prime }$ 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 $M_{\oplus }$ 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 $Q_{\star }^{\prime }$ 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 $Q_{\star }^{\prime }$.

Accepted for publication in MNRAS, 19 pages, 7 Figures, 9 Tables

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