The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU

Abstract

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 * > 1.5M more likely to host planets with masses between 2-13M Jup and semi-major axes of 3-100au 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 d 2 N/(dm da)∝m α a β , finding α = −2.4 ± 0.8 and β = −2.0 ± 0.5, and an integrated occurrence rate of 9 +5 −4 % between 5-13M Jup and 10-100au. 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 13-80M Jup and 10-100au. 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 ∼1-10au. 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.

The origin of R CrA variability: A complex triple system hosting a disk

“…Observations suggest that giant planets form more frequently around intermediate mass stars than around solar-mass stars (see e.g. Johnson et al 2010;Nielsen et al 2019). Herbig AeBe (HAeBe) stars (Herbig 1960;Hillenbrand et al 1992) are still embedded in gasdust envelopes and are frequently surrounded by circumstellar disks (Perez & Grady 1997).…”

On the diversity of asymmetries in gapped protoplanetary disks

“…The occurrence rate of massive companions from direct imaging surveys in older systems argues against brown dwarf companions as a common explanation for transition disks. Super-Jovians (5-13 M Jup ) have an occurrence rate of 8.9% at 10-100 au for intermediate mass (1.5-5 M ) stars (Nielsen et al 2019), which is the stellar mass range of the majority of our sample. Above that mass treshold, the occurrence rate of brown dwarfs (13-80 M Jup ) at wide orbits is much lower (∼1% Nielsen et al 2019, also known as the 'brown dwarf desert'), but the occurrence of stellar companions (> 80M Jup ) or binarity rate at 10-100 au is again increased, with a fraction of ∼15% in the 1-2 M stellar mass range (Moe & Kratter 2019).…”

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. III. On-sky validation in VLT/SPHERE

“…Second-generation exoplanet imagers have already demonstrated great potential for studying close circumstellar environments, and for detecting new companions and helping to understand their physical properties. However, the current statistics derived from observations (e.g., Nielsen et al 2019) and the most recent planet population models (e.g., Mordasini et al 2017;Forgan et al 2018) respectively show and predict that giant planets are scarce in the regime of mass and separation probed by current instruments. In other words, we need to probe closer to the stars and at deeper contrasts.…”

“…These results begin to shed light on the architecture of planetary systems, planet formation and evolution, and atmospheric properties of young giant planets and brown dwarfs. In terms of planet demography, NIR surveys of hundreds of nearby stars have so far shown that giant gaseous planets on orbits wider than 10 AU remain rare, mostly due to inefficient formation of such companions at large distances (e.g., Bowler 2016;Uyama et al 2017;Vigan et al 2017;Chauvin et al 2017a;Nielsen et al 2019).…”