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

TL;DR

This study reports the discovery of four new Jovian planets orbiting low-luminosity giant stars, increasing the known planetary fraction around such stars and challenging existing planet formation models.

Contribution

It presents four newly discovered Jovian planets around low-luminosity giant stars, expanding the sample and revealing a higher planetary occurrence rate than previously reported.

Findings

Detected planetary companions with periods 1.2-7.1 years.

Found a giant planet occurrence rate of 33.3%.

Results challenge existing planet formation models.

Abstract

We report the discovery of planetary companions orbiting four low-luminosity giant stars with M$_\star$ between 1.04 and 1.39 M$_\odot$. 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 during nearly a decade. The planetary companions exhibit orbital periods between $\sim$ 1.2 and 7.1 years, minimum masses of m$_{\rm p}$sini $\sim$ 1.8-3.7 M$_{jup}$ and eccentricities between 0.08 and 0.42. Including these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets between the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets (m$_{\rm p} \gtrsim$ 1-2 M$\_{jup}$) orbiting within 5 AU from their parent star of $f = 33.3^{+9.0}_{-7.1} \%$. This fraction is significantly higher than that previously reported in the literature by different radial velocity surveys. Similarly, planet formation models under predict the fraction of gas giant around stars more massive than the Sun.