Radial velocity confirmation of Kepler-91 b. Additional evidence of its planetary nature using the Calar Alto/CAFE instrument

TL;DR

This study confirms Kepler-91b's planetary nature by measuring its radial velocity with high-resolution spectroscopy, providing independent evidence supporting its classification as a planet.

Contribution

It presents the first independent radial velocity confirmation of Kepler-91b using the CAFE instrument, validating previous light-curve based findings.

Findings

Mass of Kepler-91b is 1.09 ± 0.20 Jupiter masses.

Radial velocity measurements support planetary classification.

Results agree with previous brightness modulation estimates.

Abstract

The object transiting the star Kepler-91 was recently assessed as being of planetary nature. The confirmation was achieved by analysing the light-curve modulations observed in the Kepler data. However, quasi-simultaneous studies claimed a self-luminous nature for this object, thus rejecting it as a planet. In this work, we apply an {independent} approach to confirm the planetary mass of Kepler-91b by using multi-epoch high-resolution spectroscopy obtained with the Calar Alto Fiber-fed Echelle spectrograph (CAFE). We obtain the physical and orbital parameters with the radial velocity technique. In particular, we derive a value of $1.09 \pm 0.20\,M_{\mathrm{Jup}}$ for the mass of Kepler-91b, in excellent agreement with our previous estimate that was based on the orbital brightness modulation.