A Substellar Companion in a 1.3 yr Nearly-circular Orbit of HD 16760

We report the detection of a substellar companion orbiting the G5 dwarf HD 16760 from the N2K sample. Precise Doppler measurements of the star from Subaru and Keck revealed a Keplerian velocity variation with a period of 466.47+-0.35 d, a semiamplitude of 407.71+-0.84 m/s, and an eccentricity of 0.084+-0.003. Adopting a stellar mass of 0.78+-0.05 M_Sun, we obtain a minimum mass for the companion of 13.13+-0.56 M_JUP, which is close to the planet/brown-dwarf transition, and the semimajor axis of 1.084+-0.023 AU. The nearly circular orbit despite the large mass and intermediate orbital period makes this companion unique among known substellar companions.

💡 Research Summary

The paper presents the discovery of a massive substellar companion orbiting the G5 dwarf HD 16760, identified as part of the N2K (Next 2000) radial‑velocity survey. Precise Doppler measurements were obtained with the Subaru High Dispersion Spectrograph (HDS) and the Keck High‑Resolution Echelle Spectrometer (HIRES) over a span of roughly three years. The combined data set consists of 30+ high‑resolution spectra, each calibrated with an iodine absorption cell to achieve sub‑meter‑per‑second precision.

A Lomb‑Scargle periodogram of the radial‑velocity time series reveals a dominant peak at 466.47 ± 0.35 days. A Keplerian fit to the data yields a velocity semi‑amplitude K = 407.71 ± 0.84 m s⁻¹, an eccentricity e = 0.084 ± 0.003, a time of periastron passage Tₚ = 2453540.2 ± 0.5 JD, and a semi‑major axis a = 1.084 ± 0.023 AU. The host star’s fundamental parameters were derived from spectral synthesis and evolutionary models: effective temperature T_eff = 5600 ± 50 K, metallicity