Substellar-mass companions to the K-dwarf BD +14 4559 and the K-giants HD 240210 and BD +20 2457

TL;DR

This paper reports the discovery of substellar companions, including potential brown dwarfs, around three evolved stars, providing insights into planetary system formation and the brown dwarf desert phenomenon.

Contribution

It presents new detections of substellar companions to three stars, including the first possible system with two brown dwarf-mass objects orbiting a giant star.

Findings

BD +14 4559 has a 1.5 M_J planet with a 269-day orbit.

HD 240210 shows radial velocity variations suggestive of a ~6.9 M_J planet.

BD +20 2457 hosts two companions with minimum masses of 21.4 and 12.5 M_J.

Abstract

We present the discovery of substellar-mass companions to three stars by the ongoing Penn State - Toru\' n Planet Search (PTPS) conducted with the 9.2-m Hobby-Eberly Telescope. The K2-dwarf, BD +14 4559, has a 1.5 M$_{J}$ companion with the orbital period of 269 days and shows a non-linear, long-term radial velocity trend, which indicates a possible presence of another planet-mass body in the system. The K3-giant, HD 240210, exhibits radial velocity variations that require modeling with multiple orbits, but the available data are not yet sufficient to do it unambiguously. A tentative, one-planet model calls for a 6.9 M$_J$ planet in a 502-day orbit around the star. The most massive of the three stars, the K2-giant, BD +20 2457, whose estimated mass is 2.8$\pm$1.5 M$_\odot$, has two companions with the respective minimum masses of 21.4 M$_J$ and 12.5 M$_J$ and orbital periods of 380 and 622 days. Depending on the unknown inclinations of the orbits, the currently very uncertain mass of the star, and the dynamical properties of the system, it may represent the first detection of two brown dwarf-mass companions orbiting a giant. The existence of such objects will have consequences for the interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars.