Analysis of combined radial velocities and activity of BD+20 1790: evidence supporting the existence of a planetary companion

TL;DR

This study uses Bayesian analysis to confirm a planetary companion around BD+20 1790, disentangling stellar activity from radial velocity signals and exploring magnetic interactions and flare origins.

Contribution

It introduces a new Bayesian method to separate stellar jitter components and provides the first magnetic field measurement of BD+20 1790.

Findings

Bayesian analysis supports the existence of a planetary companion.

New orbital parameters after removing stellar activity signals.

First detection of the star's magnetic field.

Abstract

This paper presents the simultaneous Bayesian analysis of the radial velocity and activity indices for the K5Ve active star BD+20 1790, that was proposed to host a close-in massive planet by Hern\'an-Obispo et al. (2010). The Bayesian analysis supports the hypothesis of a planetary companion. We present a new orbital solution after removing the two main contributions to the stellar jitter, one that varies with the photometric period and another that varies with the synodic period of the star+planet system. We use a new method to determine these jitter components, considering them as a second and third signals in the system. A discussion on possible magnetic star-planet-interaction is included, based on the Bayesian analysis of the activity indices. We propose two possible sources for flare events of this star: one related to the geometry of the system and the relative movement of the star+planet, and a second one purely stochastic source that is related to the evolution of stellar active regions. Also, we observe for the first time the magnetic field of the star, from spectropolarimetric data.