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

July 2019 • 2019AJ....158...13N

Authors • Nielsen, Eric L. • De Rosa, Robert J. • Macintosh, Bruce • Wang, Jason J. • Ruffio, Jean-Baptiste • Chiang, Eugene • Marley, Mark S. • Saumon, Didier • Savransky, Dmitry • Ammons, S. Mark • Bailey, Vanessa P. • Barman, Travis • Blain, Célia • Bulger, Joanna • Burrows, Adam • Chilcote, Jeffrey • Cotten, Tara • Czekala, Ian • Doyon, Rene • Duchêne, Gaspard • Esposito, Thomas M. • Fabrycky, Daniel • Fitzgerald, Michael P. • Follette, Katherine B. • Fortney, Jonathan J. • Gerard, Benjamin L. • Goodsell, Stephen J. • Graham, James R. • Greenbaum, Alexandra Z. • Hibon, Pascale • Hinkley, Sasha • Hirsch, Lea A. • Hom, Justin • Hung, Li-Wei • Dawson, Rebekah Ilene • Ingraham, Patrick • Kalas, Paul • Konopacky, Quinn • Larkin, James E. • Lee, Eve J. • Lin, Jonathan W. • Maire, Jérôme • Marchis, Franck • Marois, Christian • Metchev, Stanimir • Millar-Blanchaer, Maxwell A. • Morzinski, Katie M. • Oppenheimer, Rebecca • Palmer, David • Patience, Jennifer • Perrin, Marshall • Poyneer, Lisa • Pueyo, Laurent • Rafikov, Roman R. • Rajan, Abhijith • Rameau, Julien • Rantakyrö, Fredrik T. • Ren, Bin • Schneider, Adam C. • Sivaramakrishnan, Anand • Song, Inseok • Soummer, Remi • Tallis, Melisa • Thomas, Sandrine • Ward-Duong, Kimberly • Wolff, Schuyler

Abstract • We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey. 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, semimajor 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 and 13M _Jup and semimajor axes of 3-100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semimajor axis (a) for planet populations around high-mass stars (M _* > 1.5 M _⊙) of the form {d}²N/({dm} {da})\propto {m}^α {a}^β, finding α = -2.4 ± 0.8 and β = -2.0 ± 0.5, and an integrated occurrence rate of {9}_-4⁺⁵% between 5-13M _Jup 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 13-80M _Jup and 10-100 au. Brown dwarfs also appear to be distributed differently in mass and semimajor axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semimajor axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the radial velocity method, our results are consistent with a peak in occurrence of giant planets between ∼1 and 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.

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Alexandra Greenbaum

Assistant Scientist