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

摘要

A Korean-Japanese planet search program has been carried out using the 1.8mtelescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea, and the1.88m telescope at Okayama Astrophysical Observatory (OAO) in Japan to searchfor planets around intermediate-mass giant stars. The program aims to show theproperties of planetary systems around such stars by precise Doppler survey ofabout 190 G or K type giants together with collaborative surveys of theEast-Asian Planet Search Network. So far, we detected two substellar companionsaround massive intermediate-mass giants in the Korean-Japanese planet searchprogram. 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 massivebrown dwarf companion among those found around intermediate-mass giants. Theother is a planetary companion with 1.8 $M_{\mathrm{J}}$ orbiting a giant starwith 2.4 $M_{\odot}$, which is the lowest-mass planetary companion among thosedetected around giant stars with $>$ 1.9 $M_{\odot}$. Plotting these systems oncompanion mass vs. stellar mass diagram, there seem to exist two unpopulatedregions of substellar companions around giants with 1.5--3 $M_{\odot}$ andplanetary companions orbiting giants with 2.4--4 $M_{\odot}$. The existence ofthese possible unpopulated regions supports a current characteristic view thatmore massive substellar companions tend to exist around more massive stars.