Three massive planets discovered orbiting distant low luminosity red giant stars

Star system: HD 127195 | Distance from the Sun: 274 light years

Researchers have identified three massive planets orbiting two low luminosity red giant stars, marking a significant addition to our understanding of planetary systems around evolved stars. These stars, which have expanded and cooled after exhausting the hydrogen fuel in their cores, are a unique environment for planet formation and survival. The study, part of a long-term campaign using the CORALIE spectrograph, focused on observing changes in the light spectrum of stars to detect the gravitational influence of orbiting planets, a technique known as radial velocity.

The team analyzed data collected over a period of 15 to 18 years for the stars HD 125136, HD 127195, and HD 220218. By measuring these subtle wobbles in the stars caused by the gravitational pull of orbiting planets, they were able to detect signals matching the signature of planetary companions. They also developed and tested a new observing strategy to account for the intrinsic pulsations of these giant stars, which can otherwise mask the signals from planets.

For the star HD 125136, the team confirmed a single planetary companion with a minimum mass of 2.26 times that of Jupiter on an 850-day orbit. The system around HD 127195 was found to contain two planets with masses of 0.66 and 0.78 times the mass of Jupiter, orbiting every 535 and 834 days, respectively. While signals were also detected for HD 220218, these were attributed to stellar activity rather than a planet.

Key findings
- Identified one massive planet around HD 125136 with a minimum mass of 2.26 Jupiter masses.
- Identified two planets around HD 127195 with masses of 0.66 and 0.78 Jupiter masses.
- Demonstrated a successful observing method to mitigate the impact of stellar pulsations in low luminosity giant stars to below 5 meters per second.
- Confirmed that signals detected around HD 220218 were likely caused by stellar activity rather than a planet.

Scientific study

CORALIE radial-velocity search for companions around evolved stars (CASCADES) V. Three planetary companions and achievable precision (external link)