Do the clues for imaging earth-like planets stare at us from the faint glow of the far-off companions? Astronomers on the roof of Maunakea have revealed two fantastic discoveries a huge exoplanet and an unusual brown dwarf whose finding not only contributes to the list of known substellar objects but also offers a necessary ground for testing the technologies of the future space telescopes.
This is a publication about the first scientific achievements of the Observing Accelerators with SCExAO Imaging Survey (OASIS), a program whose goal is to combine precise astrometric data from the ESA Hipparcos and Gaia missions with the high-contrast imaging powered by the Subaru Telescope’s Coronagraphic Extreme Adaptive Optics (SCExAO) system and the near-infrared instrumentation of the W. M. Keck Observatory. “accelerating stars”, i.e., those stars whose slight movement change is their trick to hide the gravitational pull of the unknown companions, are the targets of OASIS, thus the project avoids the problem of inefficient blind surveys and concentrates on the most probable candidates.
The first discovery, HIP 71618 B, is a brown dwarf with a mass of 60 times that of Jupiter which orbits a bright A-type star at 169 light-years distance in the constellation Boötes. Brown dwarfs originate the same way as stars but don’t have enough mass to start a permanent hydrogen fusion, so they emit mainly in the infrared region. The SCExAO CHARIS and Keck’s NIRC2 camera observations, which were done within a few days of each other, were able to catch the faint signal of the companion while the orbital parameters were determined through a year-long campaign. Spectral analysis places its effective temperature between 2600–2800 K, consistent with a low-gravity M6–M8 dwarf, and dynamical modeling suggests a highly eccentric orbit with a semimajor axis near 11 astronomical units.
What makes HIP 71618 B exceptional is its suitability for NASA’s Nancy Grace Roman Space Telescope coronagraph technology demonstration. Roman’s coronagraph aims to suppress starlight to detect planets ten billion times fainter than their host stars. Until now, no confirmed target met the stringent requirements for this test: a bright star, optimal angular separation, and a companion faint enough at visible wavelengths to challenge the instrument’s limits. “The discovery of HIP 71618 B is demonstrably suitable for the Roman Coronagraph Technology Demonstration,” said lead author Mona El Morsy. Projected to lie within Roman’s “dark-hole” region during the demonstration phase, HIP 71618 B offers a rare opportunity to validate performance metrics such as achieving 5σ contrast better than 10⁻⁷ at 575 nm in under ten hours.
The second discovery, HIP 54515 b, is an 18-Jupiter-mass superjovian planet orbiting a star 271 light-years away in Leo at roughly Neptune’s distance from the Sun. From Earth, its apparent separation is a mere 0.15 arcseconds comparable to a football seen from over 200 miles away demanding the extreme resolution of SCExAO’s adaptive optics. The Subaru system’s deformable mirror, operating at kilohertz rates, corrected atmospheric turbulence to deliver images sharp enough to resolve the planet against its star’s glare. Keck’s archival data spanning more than a decade provided essential calibration, enabling precise modeling of the planet’s moderately eccentric orbit and evolutionary history. Such eccentricities, increasingly observed among massive planets at Saturn-to-Neptune-like separations, hint at dynamic formation pathways distinct from those of Jupiter analogs.
The technological underpinnings of these achievements are as notable as the discoveries themselves. SCExAO integrates coronagraphy with advanced wavefront control to achieve high-contrast imaging at small angular separations, while Keck’s NIRC2 camera, paired with its upgraded adaptive optics including an infrared pyramid wavefront sensor delivers exquisite infrared detail. This sensor’s ability to use faint infrared sources as reference points expands the range of targets to cooler, dust-shrouded stars and young planets invisible in visible light, effectively adding “night-vision” capability to the observatory.
OASIS is a new model of exoplanet search that, along with the fusion of Gaia’s astrometric precision with ground-based extreme adaptive optics, not only increases the number of discoveries but also creates targets of high importance for the next missions. “These results show what happens when we combine Maunakea’s unmatched observing conditions with cutting-edge instrumentation,” said Thayne Currie, the principal investigator of OASIS.
The program, with more OASIS discoveries expected in 2026, is thus in a position to unravel the mysteries of the formation of planets and brown dwarfs, improve atmospheric models via infrared spectroscopy, and speed up the invention of the instruments necessary for the detection of habitable worlds outside our solar system.
