A University of Hawaiʻi team using the Keck Planet Finder on Maunakea has finally put a precise age on a nearby Sun‑like star and its long‑watched brown dwarf companion, turning a long‑standing cosmic curiosity into a gold‑standard reference for substellar physics. By tracking tiny, five‑minute oscillations in the star's light, the researchers dated the system to about 2.3 billion years old, giving theorists a sharp new test of how brown dwarfs cool and fade. The new age turns HR 7672B from an oddball outlier into a key benchmark for several competing models.
Precision asteroseismology on Maunakea
Over three nights of ultra‑precise radial‑velocity monitoring, the Keck Planet Finder picked up five‑minute stellar oscillations that allowed the team to run detailed asteroseismic models on the host star. The asteroseismic fit yielded an age of 1.87 ±0.65 Gyr, while an independent gyrochronology analysis gave 2.58 ±0.47 Gyr. Combining the two, the group arrived at a final age of 2.26 ±0.40 Gyr. The numbers and the method are laid out in the team's paper and preprint on arXiv.
HR 7672's two‑decade run as a test case
HR 7672B was first directly imaged in 2002 and since then has served as a touchstone for studies of substellar companions, in part because adaptive‑optics images revealed just how uncommon close brown‑dwarf companions are around Sun‑like stars. The new age estimate lets researchers combine the system's luminosity and dynamical mass to test brown dwarf cooling models against unusually precise data, according to Maui Now.
Mass, models and what fits
A joint orbital fit that blends new radial‑velocity measurements with astrometry yields a dynamical mass of 75.39 ±0.67 Jupiter masses for HR 7672B and 1.111 ±0.017 solar masses for the primary star. With both the precise age and mass in hand, the authors put six brown dwarf cooling models through their paces and found the best match with newer Chabrier et al. models, while some older frameworks struggle to reproduce the companion's luminosity. The results are documented in the paper and summarized in press coverage, including Phys.org.
The work also spotlights the Beatrice Watson Parrent Fellowship at UH's Institute for Astronomy and the long scientific arc from Michael Liu's discovery of HR 7672B to its new status as a precision benchmark. “This is like finally having a reliable clock for an object we've been trying to understand for years,” Parrent Fellow Yaguang Li said, as reported by Maui Now. The result underscores how instruments on Maunakea are turning decades of follow‑up work into decisive tests of substellar physics.
