HD 38529
HD 38529 is a binary star system approximately 138 light-years away in the constellation of Orion.
HD 38529 A
HD 38529 A is a yellow subgiant star of spectral type G4IV, though it has also been classified as a main sequence dwarf of type G4V and a borderline giant star of type G8III/IV. It is about 48% more massive than the Sun.Two substellar companions are known in orbit around this star, including one with a mass near the deuterium fusion limit that is often used as the dividing line between giant planets and brown dwarfs. There is a debris disk located at least 86 astronomical units from the star. Its orbit is probably mildly misaligned with the planetary orbits, by 21−45°.
Planetary system
In 2001, the planet HD 38529 b was discovered orbiting the star HD 38529 A by Debra Fischer and collaborators who detected it using the Doppler spectroscopy technique. It has a mass at least 78% that of Jupiter and orbits very close to the star, just beyond the distance limit for hot Jupiters. It does not transit the star.In 2003, a massive superjovian HD 38529 c was found orbiting at 3.68 AU with a minimum mass of 12.7 Jupiter masses. Astrometric measurements from the Hipparcos satellite gave a best fit inclination of 160° and a true mass 37 times that of Jupiter, turning this planet into a brown dwarf.
Further study of the system using Hubble Space Telescope astrometry revised the mass of HD 38529 c downwards to 17.7 Jupiter masses and suggested the presence of an additional planet, orbiting in the gap between HD 38529 b and c. The possible third planet was refuted after additional radial velocity measurements were collected. Subsequent astrometric studies have found masses for HD 38529 c ranging from just to, with the most recent value as of 2025 being.