Red Giant Stars Hosting Close-In Jupiter-Like Planets
As a planet orbits its host star, it indices gravitational perturbations on its host star, causing its host star to wobble back and forth. If the planet is massive enough and/or if the planet is sufficiently close to its host star, the wobbling motion of the planet’s host star can be detected through radial velocity measurements. Radial velocity measurements of two red giant stars indicate that they harbour Jupiter-like planetary companions. Red giant stars are basically stars that have reached the end stages of their stellar evolution. Jupiter-like planets in close-in orbits seem to be very rare around red giant stars. One explanation is that such planets are ingested by their host stars due to tidal interactions.
HD 5583 is a red giant star with ~1.01 times the Sun’s mass, ~9.09 times the Sun’s radius, ~41 times the Sun’s luminosity, and it has an effective temperature of roughly 4830 K. It is located ~720 light years away and it hosts a gas giant planet identified as HD 5583 b. The planet has 5.78 ± 0.53 times the mass of Jupiter and it orbits in a near-circular orbit around its host star at 0.53 ± 0.02 AU. Its orbital period around its host star is ~139 days and the amount of wobbling it induces on its host star is ~226 m/s.
BD+15 2375 is a red giant star with ~1.08 times the Sun’s mass, ~8.95 times the Sun’s radius, ~37 times the Sun’s luminosity, and it has an effective temperature of roughly 4649 K. The star is located ~2520 light years away and circling it is a gas giant planet identified as BD+15 2375 b. Radial velocity measurements indicate the planet has ~1.06 times the mass of Jupiter and it is in an almost circular orbit around its host star at ~0.58 AU. The planet’s orbital period is ~153 days and it causes its host star to wobble by ~38.3 m/s. BD+15 2375 b is currently the lightest known planet around a red giant star.
Niedzielski et al. (2016), “Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. III. HD 5583 and BD+15 2375 - two cool giants with warm companions”, arXiv:1601.06832 [astro-ph.EP]