The HARPS search for southern extra-solar planets. III. Three Saturn-mass planets around HD 93083, HD 101930 and HD 102117

TL;DR

This paper reports the discovery of three Saturn-mass exoplanets around stars HD 93083, HD 101930, and HD 102117 using the HARPS instrument, demonstrating high radial velocity precision and contributing to understanding planet formation.

Contribution

First detection of multiple Saturn-mass planets with HARPS, highlighting the correlation between metallicity and planet occurrence and exploring planet formation in less-populated parameter space.

Findings

High RV precision achieved with HARPS (0.9-2.0 m/s residuals)

All three stars are metal-rich, supporting metallicity-planet occurrence link

Planets occupy a region challenging to explain with current formation theories

Abstract

We report on the detection of three Saturn-mass planets discovered with the HARPS instrument. HD 93083 shows radial-velocity (RV) variations best explained by the presence of a companion of 0.37 M_Jup orbiting in 143.6 days. HD 101930 b has an orbital period of 70.5 days and a minimum mass of 0.30 M_Jup. For HD 102117, we present the independent detection of a companion with m2sini = 0.14 M_Jup and orbital period P = 20.7 days. This planet was recently detected by Tinney et al. (2004). Activity and bisector indicators exclude any significant RV perturbations of stellar origin, reinforcing the planetary interpretation of the RV variations. The radial-velocity residuals around the Keplerian fits are 2.0, 1.8 and 0.9 m/s respectively, showing the unprecedented RV accuracy achieved with HARPS. A sample of stable stars observed with HARPS is also presented to illustrate the long-term precision of the instrument. All three stars are metal-rich, confirming the now well-established relation between planet occurrence and metallicity. The new planets are all in the Saturn-mass range, orbiting at moderate distance from their parent star, thereby occupying an area of the parameter space which seems difficult to populate according to planet formation theories. A systematic exploration of these regions will provide new constraints on formation scenarios in the near future.