Planetary-mass companions to the K-giants BD+15 2940 and HD 233604

TL;DR

This paper reports the discovery of two planetary-mass companions orbiting red giants, highlighting their close orbits and potential for stellar engulfment, and discusses the observational methods used in the PTPS project.

Contribution

First detection of planetary-mass companions around two red giants using the PTPS survey, with detailed analysis of their orbits and stellar properties.

Findings

BD+15 2940 hosts a 1.1 Mj planet at 0.54 AU

HD 233604 hosts a 6.6 Mj planet at 0.75 AU

High lithium abundance in HD 233604 suggests recent planetary engulfment or early evolutionary stage

Abstract

We report the discovery of planetary-mass companions to two red giants by the ongoing Penn State - Torun Planet Search (PTPS) conducted with the 9.2-m Hobby-Eberly Telescope. The 1.1 Ms K0-giant, BD+15 2940, has a 1.1 Mj minimum mass companion orbiting the star at a 137.5-day period in a 0.54 AU orbit what makes it the closest - in planet around a giant and possible subject of engulfment as the consequence of stellar evolution. HD 233604, a 1.5 Ms K5-giant, is orbited by a 6.6 Mj minimum mass planet which has a period of 192 days and a semi-major axis of only 0.75 AU making it one of the least distant planets to a giant star. The chemical composition analysis of HD 233604 reveals a relatively high 7Li abundance which may be a sign of its early evolutionary stage or recent engulfment of another planet in the system. We also present independent detections of planetary-mass companions to HD 209458 and HD 88133, and stellar activity-induced RV variations in HD 166435, as part of the discussion of the observing and data analysis methods used in the PTPS project.