Detecting the spin-orbit misalignment of the super-Earth 55 Cnc e

TL;DR

This study uses improved spectroscopic techniques to detect the smallest Rossiter-McLaughlin anomaly in an exoplanet, revealing a highly misaligned orbit of super-Earth 55 Cnc e, suggesting a tilted planetary system.

Contribution

Developed an empirical correction for the color effect in radial velocity data, enabling detection of the smallest Rossiter-McLaughlin anomaly and measuring the planet's high orbital obliquity.

Findings

Detected the smallest Rossiter-McLaughlin anomaly (~60 cm/s)

Measured the sky-projected obliquity at 72.4 degrees

Indicated a highly tilted, nearly polar orbit

Abstract

We present time-resolved spectroscopy of transits of the super-Earth 55 Cnc e using HARPS-N observations. We devised an empirical correction for the "color effect" affecting the radial velocity residuals from the Keplerian fit, which significantly improves their dispersion with respect to the HARPS-N pipeline standard data-reduction. Using our correction, we were able to detect the smallest Rossiter-McLaughlin anomaly amplitude of an exoplanet so far (~60 cm/s). The super-Earth 55 Cnc e is also the smallest exoplanet with a Rossiter-McLaughlin anomaly detection. We measured the sky-projected obliquity lambda = 72.4 (+12.7 -11.5 deg), indicating that the planet orbit is prograde, highly misaligned and nearly polar compared to the stellar equator. The entire 55 Cancri system may have been highly tilted by the presence of a stellar companion.