The SOPHIE northern extrasolar planets. I. A companion close to the planet/brown-dwarf transition around HD16760

We report on the discovery of a substellar companion or a massive Jupiter orbiting the G5V star HD16760 with the spectrograph SOPHIE installed on the OHP 1.93-m telescope. Characteristics and performances of the spectrograph are presented, as well as the SOPHIE exoplanet consortium program. With a minimum mass of 14.3 Mjup, an orbital period of 465 days and an eccentricity of 0.067, HD16760b seems to be located just at the end of the mass distribution of giant planets, close to planet/brown-dwarf transition. Its quite circular orbit supports a formation in a gaseous protoplanetary disk.

💡 Research Summary

The paper presents the discovery of a sub‑stellar companion to the G5V star HD 16760 using the SOPHIE spectrograph mounted on the 1.93‑m telescope at the Observatoire de Haute‑Provence. After a brief description of the instrument, its design philosophy, and performance characteristics, the authors outline the broader SOPHIE exoplanet consortium program, which comprises several sub‑programs aimed at probing different regions of planetary parameter space (low‑mass super‑Earths, giant planets in a volume‑limited sample, planets around M‑dwarfs, early‑type stars, and long‑term follow‑up of ELODIE candidates).

SOPHIE is a cross‑dispersed, environmentally stabilized echelle spectrograph that inherits key concepts from its predecessors ELODIE and HARPS. It offers two observing modes: a high‑resolution mode (R≈75 000) using a double‑scrambled fiber pair, and a high‑efficiency mode (R≈40 000) for fainter targets. The spectrograph is housed in a pressure‑controlled tank to minimize index variations of air, achieving intrinsic drifts below 3 m s⁻¹ h⁻¹. The pipeline extracts the 39 orders, performs optimal extraction, wavelength calibration, blaze correction, and then cross‑correlates the spectra with numerical masks to derive radial velocities (RVs). Typical photon‑noise limited RV uncertainties are ~1 m s⁻¹ for S/N≈150 per pixel at 550 nm; the current long‑term precision on stable stars is 4–5 m s⁻¹, limited mainly by guiding errors and incomplete fiber scrambling. Planned upgrades (high‑precision guiding camera, new double scrambler) aim to push the precision to 1–2 m s⁻¹.

HD 16760 (HIP 12638) is a nearby (≈50 pc) solar‑type star with V=8.74, B–V=0.71, T_eff≈5620 K, log g≈4.51,