A Giant Planet Around a Metal-poor Star of Extragalactic Origin

TL;DR

This paper reports the discovery of a Jupiter-mass planet orbiting a metal-poor Horizontal Branch star, suggesting planetary formation can occur in extragalactic environments and around evolved stars.

Contribution

First detection of a planet around a metal-poor Horizontal Branch star, indicating planetary formation in extragalactic and evolved stellar contexts.

Findings

Planet has a minimum mass of 1.25 Jupiter masses

Orbital semi-major axis is 0.116 AU

Star belongs to an extragalactic stellar population

Abstract

Stars in their late stage of evolution, such as Horizontal Branch stars, are still largely unexplored for planets. We report the detection of a planetary companion around HIP 13044, a very metal-poor star on the red Horizontal Branch, based on radial velocity observations with a high-resolution spectrograph at the 2.2-m MPG/ESO telescope. The star's periodic radial velocity variation of P=16.2 days caused by the planet can be distinguished from the periods of the stellar activity indicators. The minimum mass of the planet is 1.25 Jupiter masses and its orbital semi-major axis 0.116 AU. Because HIP 13044 belongs to a group of stars that have been accreted from a disrupted satellite galaxy of the Milky Way, the planet most likely has an extragalactic origin.