The Pan-Pacific Planet Search VI: Giant planets orbiting HD 86950 and HD 222076

TL;DR

This paper reports the discovery of two new giant planets orbiting evolved K giant stars using radial velocity measurements, and confirms the correlation between host-star metallicity and planet occurrence.

Contribution

It presents new planet detections around HD 86950 and HD 222076 and investigates the metallicity-planet occurrence relation in a sample of evolved stars.

Findings

Two new giant planets discovered orbiting K giants.

Confirmed the trend of increasing planet occurrence with higher stellar metallicity.

Identified stellar variability as the cause of a velocity signal in HD 29399.

Abstract

We report the detection of two new planets orbiting the K giants HD 86950 and HD 222076, based on precise radial velocities obtained with three instruments: AAT/UCLES, FEROS, and CHIRON. HD 86950b has a period of 1270$\pm$57 days at $a=2.72\pm$0.08 AU, and m sin $i=3.6\pm$0.7 Mjup. HD 222076b has $P=871\pm$19 days at $a=1.83\pm$0.03 AU, and m sin $i=1.56\pm$0.11 Mjup. These two giant planets are typical of the population of planets known to orbit evolved stars. In addition, we find a high-amplitude periodic velocity signal ($K\sim$50 m/s) in HD 29399, and show that it is due to stellar variability rather than Keplerian reflex motion. We also investigate the relation between planet occurrence and host-star metallicity for the 164-star Pan-Pacific Planet Search sample of evolved stars. In spite of the small sample of PPPS detections, we confirm the trend of increasing planet occurrence as a function of metallicity found by other studies of planets orbiting evolved stars.