Four Jovian planets around low-luminosity giant stars observed by the EXPRESS and PPPS

Abstract

We report the discovery of planetary companions orbiting four low-luminosity giant stars with M⋆ between 1.04 and 1.39 M⊙. All four host stars have been independently observed by the EXoPlanets aRound Evolved StarS (EXPRESS) program and the Pan-Pacific Planet Search (PPPS). The companion signals were revealed by multi-epoch precision radial velocities obtained in nearly a decade. The planetary companions exhibit orbital periods between ~1.2 and 7.1 yr, minimum masses of mpsin i ~ 1.8–3.7 MJ, and eccentricities between 0.08 and 0.42. With these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets in the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets (mp ≳ 1– 2 MJ) orbiting within 5 AU from their parent star of f = 33.3−7.1+9.0%. This fraction is slightly higher than but consistent at the 1σ level with previous results obtained by different radial velocity surveys. Finally, this value is substantially higher than the fraction predicted by planet formation models of gas giants around stars more massive than the Sun.