The low density, hot Jupiter TOI-640 b is on a polar orbit

Abstract

TOI-640 b is a hot, puffy Jupiter with a mass of $0.57\pm 0.02$ M${}_{\mathrm{J}}$ and radius of $1.72\pm 0.05$ R${}_{\mathrm{J}}$, orbiting a slightly evolved F-type star with a separation of $6.33_{-0.06}^{+0.07}$ R${}_{\star }$. Through spectroscopic in-transit observations made with the HARPS spectrograph, we measured the Rossiter-McLaughlin effect, analysing both in-transit radial velocities and the distortion of the stellar spectral lines. From these observations, we find the host star to have a projected obliquity of $\hat{I}»=184\pm 3^{\circ }$. From the TESS light curve, we measured the stellar rotation period, allowing us to determine the stellar inclination, $i_{\star }=23_{-2}^{+3\circ }$, meaning we are viewing the star pole-on. Combining this with the orbital inclination allowed us to calculate the host star obliquity, $\ddot{I}ˆ=104\pm 2^{\circ }$. TOI-640 b joins a group of planets orbiting over stellar poles within the range $80^{\circ }-125^{\circ }$. The origin of this orbital configuration is not well understood.

15 pages, 12 figures, accepted for publication in A&A, in press