Measuring the orbit shrinkage rate of hot Jupiters due to tides

Abstract

A tidal interaction between a star and a close-in exoplanet leads to shrinkage of the planetary orbit and eventual tidal disruption of the planet. Measuring the shrinkage of the orbits will allow for the tidal quality parameter of the star ($Q_{\star }^{\prime }$) to be measured, which is an important parameter to obtain information about stellar interiors. We analyse data from TESS for two targets known to host close-in hot Jupiters, WASP-18 and WASP-19, to measure the current limits on orbital period variation and provide new constrains on $Q_{\star }^{\prime }$. We modelled the transit shape using all the available TESS observations and fitted the individual transit times of each transit. We used previously published transit times together with our results to fit two models, a constant period model, and a quadratic orbital decay model, MCMC algorithms. We find period change rates of $(-0.11\pm 0.21)\times 10^{-10}$ for WASP-18b and $(-0.35\pm 0.22)\times 10^{-10}$ for WASP-19b and we do not find significant evidence of orbital decay in these targets. We obtain new lower limits for $Q_{\star }^{\prime }$ of $(1.42\pm 0.34)\times 10^7$ in WASP-18 and $(1.26\pm 0.10)\times 10^6$ in WASP-19, corresponding to upper limits of the orbital decay rate of $-0.45\times 10^{-10}$ and $-0.71\times 10^{-10}$, respectively, with a 95% confidence level. We compare our results with other relevant targets for tidal decay studies. We find that the orbital decay rate in both WASP-18b and WASP-19b appears to be smaller than the measured orbital decay of WASP-12b. We show that the minimum value of $Q_{\star }^{\prime }$ in WASP-18 is two orders of magnitude higher than that of WASP-12, while WASP-19 has a minimum value one order of magnitude higher, which is consistent with other similar targets. Further observations are required to constrain the orbital decay of WASP-18 and WASP-19.

10 pages plus 5-page appendix. To be published in Astronomy and Astrophysics

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• A close outer companion to the ultra-hot Jupiter TOI-2109 b?
• The Impact of Tidal Migration of Hot Jupiters on the Rotation of Sun-like Main-sequence Stars
• Planet-star interactions with precise transit timing. IV. Probing the regime of dynamical tides for GK host stars
• Precise characterisation of HD 15337 with CHEOPS: a laboratory for planet formation and evolution