2019/04/10 by Eric L. Nielsen, Robert J. De Rosa, Bruce Macintosh +62 · 1 voice
Physics and Astronomy · #astro-ph.EP
paper · pdf · doi:10.3847/1538-3881/ab16e9
We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey (GPIES). This subsample includes six detected planets and three brown dwarfs; from these detections and our contrast curves we infer the underlying distributions of substellar companions with respect to their mass, semi-major axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M > 1.5 M_\odot more likely to host planets with masses between 2-13 M\rm Jup and semi-major axes of 3-100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semi-major axis (a) for planet populations around high-mass stars (M > 1.5M_\odot) of the form (d2 N)/(dm da) ∝ mαaβ, finding α = -2.4 ± 0.8 and β = -2.0 ± 0.5, and an integrated occurrence rate of 9+5-4% between 5-13 M\rm Jup and 10-100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with 0.8+0.8-0.5% of stars hosting a brown dwarf companion between 13-80 M\rm Jup and 10-100 au. Brown dwarfs also appear to be distributed differently in mass and semi-major axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semi-major axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the RV method, our results are consistent with a peak in occurrence of giant planets between ~1-10 au. We discuss how these trends, including the preference of giant planets for high-mass host stars, point to formation of giant planets by core/pebble accretion, and formation of brown dwarfs by gravitational instability.