VaTEST I: Validation of Sub-Saturn Exoplanet TOI-181b in Narrow Orbit from its Host Star

We present here a validation of sub-Saturn exoplanet TOI-181b orbiting a K-type star TOI-181 \((M_\star = 0.822 \pm 0.04\ M_\odot,\ R_\star = 0.745 \pm 0.02\ R_\odot,\ T_{\mathrm{eff}} = 4994 \pm 50\ \mathrm{K})\), as a part of the Validation of Transiting Exoplanets using Statistical Tools (VaTEST) project.

TOI-181b is a planet with radius \(R_p = 6.95 \pm 0.08\ R_\oplus\), mass \(M_p = 46.16 \pm 2.71\ M_\oplus\), orbiting in a slightly eccentric orbit with \(e = 0.15 \pm 0.06\), and a semi-major axis of \(a = 0.054 \pm 0.004\ \mathrm{AU}\), with an orbital period of \(P = 4.5320 \pm 0.000002\ \mathrm{days}\).

The transit photometry data was collected using the Transiting Exoplanet Survey Satellite (TESS), and the spectroscopic radial velocity (RV) data was collected using the ESO-HARPS (High Accuracy Radial velocity Planet Searcher) spectrograph. Based on the best-fit RV model, we measured an RV semi-amplitude of
\(K = 20.56 \pm 2.37\ \mathrm{m\ s^{-1}}\).

Additionally, we used VESPA and TRICERATOPS to compute the False Positive Probability (FPP), and the findings yielded FPP values of < 1% from both tools, significantly below the standard validation threshold.

The discovery of TOI-181b is significant in the context of understanding the formation and migration history of analogous planetary systems, especially given the rarity of warm sub-Saturns in the known exoplanet population.