Korean-Japanese Planet Search Program: Substellar Companions around Intermediate-Mass Giants

TL;DR

This study reports the discovery of substellar companions around intermediate-mass giant stars through a collaborative Doppler survey, revealing potential gaps in companion mass distributions and supporting the trend of more massive companions orbiting more massive stars.

Contribution

It presents the first detections of a brown dwarf and a low-mass planet around intermediate-mass giants, highlighting unpopulated regions in companion mass versus stellar mass.

Findings

Discovered a brown dwarf-mass companion around a 3.9 solar mass giant.

Detected a 1.8 Jupiter-mass planet orbiting a 2.4 solar mass giant.

Identified potential unpopulated regions in companion mass-stellar mass diagram.

Abstract

A Korean-Japanese planet search program has been carried out using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea, and the 1.88m telescope at Okayama Astrophysical Observatory (OAO) in Japan to search for planets around intermediate-mass giant stars. The program aims to show the properties of planetary systems around such stars by precise Doppler survey of about 190 G or K type giants together with collaborative surveys of the East-Asian Planet Search Network. So far, we detected two substellar companions around massive intermediate-mass giants in the Korean-Japanese planet search program. One is a brown dwarf-mass companion with 37.6 $M_{\mathrm{J}}$ orbiting a giant HD 119445 with 3.9 $M_{\odot}$, which is the most massive brown dwarf companion among those found around intermediate-mass giants. The other is a planetary companion with 1.8 $M_{\mathrm{J}}$ orbiting a giant star with 2.4 $M_{\odot}$, which is the lowest-mass planetary companion among those detected around giant stars with $>$ 1.9 $M_{\odot}$. Plotting these systems on companion mass vs. stellar mass diagram, there seem to exist two unpopulated regions of substellar companions around giants with 1.5--3 $M_{\odot}$ and planetary companions orbiting giants with 2.4--4 $M_{\odot}$. The existence of these possible unpopulated regions supports a current characteristic view that more massive substellar companions tend to exist around more massive stars.