Orbital misalignment of the super-Earth π Men c with the spin of its star

Abstract

Planet-planet scattering events can leave an observable trace of a planet's migration history in the form of orbital misalignment with respect to the stellar spin axis, which is measurable from spectroscopic time-series taken during transit. We present high-resolution spectroscopic transits observed with ESPRESSO of the close-in super-Earth π Men c. The system also contains an outer giant planet on a wide, eccentric orbit, recently found to be inclined with respect to the inner planetary orbit. These characteristics are reminiscent of past dynamical interactions. We successfully retrieve the planet-occulted light during transit, and find evidence that the orbit of π Men c is moderately misaligned with the stellar spin axis with λ = - 24${_{.}^{\circ}}$0 ± 4${_{.}^{\circ}}$1 ($\psi = {26{_{.}^{\circ}} 9}^{+5{_{.}^{\circ}}8 }_{-4{_{.}^{\circ}}7 }$). This is consistent with the super-Earth π Men c having followed a high-eccentricity migration followed by tidal circularization, and hints that super-Earths can form at large distances from their star. We also detect clear signatures of solar-like oscillations within our ESPRESSO radial velocity time series, where we reach a radial velocity precision of ~20 cm s^-1. We model the oscillations using Gaussian processes (GPs) and retrieve a frequency of maximum oscillation, $\nu _\mathrm{max}{} = 2771^{+65}_{-60}\, \mu \mathrm{Hz}$. These oscillations make it challenging to detect the Rossiter-McLaughlin effect using traditional methods. We are, however, successful using the reloaded Rossiter-McLaughlin approach. Finally, in the appendix, we also present physical parameters and ephemerides for π Men c from a GP transit analysis of the full Transiting Exoplanet Survey Satellite Cycle 1 data.