A Statistical Analysis of SEEDS and Other High-Contrast Exoplanet Surveys: Massive Planets or Low-Mass Brown Dwarfs?

2014/04/30 by Timothy D. Brandt, Michael W. McElwain, Edwin L. Turner +83 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.SR

paper · pdf · doi:10.1088/0004-637x/794/2/159

ApJ in press, replaced with accepted version. Methodology clarified, conclusions mostly unchanged

arxiv created 2014/09/25 · openalex publication_date 2014/10/07 · arxiv updated 2015/06/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01

Abstract

We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two ∼60 M_{\rm J} brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of ∼30--100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at ∼5 M_{\rm Jup}, with a single power law distribution. We find that p(M, a) ∝ M^-0.65±0.60 a^-0.85±0.39 (1σ errors) provides an adequate fit to our data, with 1.0--3.1% (68% confidence) of stars hosting 5--70 M_{\rm Jup} companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

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Cited by

• Exoplanet [wikipedia]