New Planetary Systems from the Calan-Hertfordshire Extrasolar Planet Search and the Core Accretion Mass Limit

We report the discovery of eight new giant planets, and updated orbits for four known planets, orbiting dwarf and subgiant stars, using the CORALIE, HARPS, and MIKE instruments as part of the Calan-Hertfordshire Extrasolar Planet Search. We include radial velocity data prior- and post-2014 CORALIE upgrade and our Bayesian updating method returned a systematic offset of 19.2$\pm$4.8 m/s between the two velocity sets for our stars. The planets have masses in the range 1.1-5.4M$_{\rm{J}}$s, orbital periods from 40-2900 days, and eccentricities from 0.0-0.6. They include a double-planet system orbiting the most massive star in our sample (HD147873), two eccentric giant planets (HD128356$b$ and HD154672$b$), and a rare 14~Herculis analogue (HD224538$b$). We find that there is an over-abundance of Jupiter-mass objects compared to a simple power law fit to the mass function, with a steep increase in the planet frequency around 3M$_{\rm{J}}$, reflecting the increased efficiency of planet formation towards lower masses. We show that an exponential function provides a better fit to the data. This truncation of the mass function could provide the sought after upper limit of planetary-masses that can be formed by gas accretion onto a forming proto-planet, constraining future hydrodynamical models. We also confirm the growing body of evidence that low-mass planets tend to be found orbiting more metal-poor stars than giant planets, yet the functional form of the mass distribution does not change with metallicity. Finally, we observe a possible period-metallicity correlation and speculate on its origin.