Distinguishing Between Stellar and Planetary Companions With Phase Monitoring

TL;DR

This paper explores how phase monitoring can distinguish stellar from planetary companions by analyzing changes in photometric signatures as the companion's mass and properties vary with orbital inclination.

Contribution

It introduces a method to identify the nature of companions by observing phase variations and their evolution across different mass regimes.

Findings

Phase variations reveal the transition from planetary to stellar companions.

Photometric signatures change significantly with inclination and companion mass.

Application to HD 114762 and HD 162020 demonstrates the method's potential.

Abstract

Exoplanets which are detected using the radial velocity technique have a well-known ambiguity of their true mass, caused by the unknown inclination of the planetary orbit with respect to the plane of the sky. Constraints on the inclination are aided by astrometric follow-up in rare cases or, in ideal situations, through subsequent detection of a planetary transit. As the predicted inclination decreases, the mass of the companion increases leading to a change in the predicted properties. Here we investigate the changes in the mass, radius, and atmospheric properties as the inclination pushes the companion from the planetary into the brown dwarf and finally low-mass star regimes. We determine the resulting detectable photometric signatures in the predicted phase variation as the companion changes properties and becomes self-luminous. We apply this to the HD 114762 and HD 162020 systems for which the minimum masses of the known companions places them at the deuterium-burning limit.