Astronomers have made a breakthrough in exoplanet research with the discovery of two giant planets orbiting evolved stars, HD 112570 and HD 154391. These findings are based on radial-velocity (RV) measurements from the Xinglong Station in China and Okayama Astrophysical Observatory in Japan.
HD 112570, a red-giant-branch star, has been found to host a Jovian planet, HD 112570 b. This planet, identified through combined radial-velocity and astrometry analyses, exhibits a unique orbital period and moderate eccentricity.
In a similar vein, HD 154391, a red-clump star, is home to the super-Jupiter HD 154391 b. This planet stands out for having one of the longest orbital periods ever discovered around evolved stars. Such a long period may offer valuable insights into planetary formation at wider orbits.
Interestingly, the discovery of HD 154391 b contributes to the ongoing debate about the mass distribution and metallicity of giant planets orbiting giant stars. A noted mass gap at around 4 Jupiter masses seems prevalent, yet no significant metallicity differences are observed across this threshold.
These discoveries challenge previous assumptions about planet survival and orbital dynamics around evolved stars. The detection of close-in giant planets around such stars, including the recently discovered HD 167768 b, provides a unique opportunity to study star-planet interactions and planetary orbit migration.
These findings also highlight a contrast in eccentricity distributions between short- and long-period planets around evolved stars, suggesting a relative dynamic inactivity in post-main-sequence systems at larger orbital separations.
The discoveries of HD 112570 b and HD 154391 b contribute to a growing list of over 5500 exoplanets discovered through various methods. They underscore the importance of evolved stars as targets for RV surveys, despite the challenges posed by their characteristics.
These discoveries, made possible by several RV surveys targeting giant stars, mark a significant step forward in our understanding of exoplanet diversity and the effects of stellar evolution on planetary systems.
Source
Xiao, GuangYao, et al. “Two Longperiod Giant Planets around Two Giant Stars: HD 112570 and HD 154391.” The Astronomical Journal, vol. 167, no. 2, 2024, p. 59, dx.doi.org/10.3847/15383881/ad11de, https://doi.org/10.3847/15383881/ad11de.
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