Astronomers Detect Three Planetary Companions Around Evolved Stars Using Radial Velocity Measurements
A team of astronomers has confirmed three planetary companions around two low-luminosity red giant stars — HD 125136 and HD 127195 — using 15–18 years of radial velocity data from the CORALIE spectrograph. The study, part of the CASCADES survey, also developed an observing strategy that successfully reduces the masking effect of stellar pulsations on planet detection signals. The findings help fill a sparsely populated region of parameter space concerning massive stars and long-period planetary orbits.
Using data spanning 15 to 18 years from the CORALIE spectrograph, researchers from the CASCADES survey identified three giant planets around two evolved, low-luminosity red giant stars. HD 125136 hosts one planet with a minimum mass of 2.26 Jupiter masses on an approximately 850-day orbit, while HD 127195 hosts a two-planet system with masses of 0.66 and 0.78 Jupiter masses on orbital periods of 535 and 834 days, respectively. A third target, HD 220218, showed a radial velocity signal that was ultimately attributed to stellar activity rather than a planetary companion. The team employed the Bayesian inference tool kima to evaluate planetary signals and derived stellar parameters through multiple methods for robust characterization. A dedicated observing strategy was designed and tested on HD 127195 to average out stellar pulsations, achieving residuals below 5 m/s — a meaningful precision benchmark for evolved stars. The discoveries populate a region of exoplanet parameter space that has been poorly sampled in terms of both host stellar mass and long planetary orbital periods. The paper has completed peer review and is accepted for publication in Astronomy and Astrophysics.
What's missing
The study reports minimum masses (m sin i) rather than true masses, as inclinations are unconstrained without additional observations such as astrometry or transit photometry. The long-term stability and dynamical interactions of the HD 127195 two-planet system are not fully characterized. The sample size of two confirmed planetary host stars limits statistical conclusions about planet occurrence rates around evolved massive stars.
What different sources said
- arXiv astro-phCenter
CORALIE radial-velocity search for companions around evolved stars (CASCADES) V. Three planetary companions and achievable precision
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