The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au

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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 more likely to host planets with masses between 2-13 MJup 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) of the form d2Ndmdamαaβ, finding α = -2.4 ± 0.8 and β = -2.0 ± 0.5, and an integrated occurrence rate of 9−4+5% between 5-13 MJup and 10-100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with 0.8−0.5+0.8% of stars hosting a brown dwarf companion between 13-80 MJup 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.

instrumentation: adaptive optics, planetary systems, planets and satellites: detection
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American Astronomical Society
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Science and Technology Facilities Council (ST/P000673/1)