A statistical analysis of seeds and other high-contrast exoplanet surveys: Massive planets or low-mass brown dwarfs?

Timothy D. Brandt, Michael W. McElwain, Edwin L. Turner, Kyle Mede, David S. Spiegel, Masayuki Kuzuhara, Joshua E. Schlieder, John P. Wisniewski, L. Abe, B. Biller, W. Brandner, J. Carson, T. Currie, S. Egner, M. Feldt, T. Golota, M. Goto, C. A. Grady, O. Guyon, J. HashimotoY. Hayano, M. Hayashi, S. Hayashi, T. Henning, K. W. Hodapp, S. Inutsuka, M. Ishii, M. Iye, M. Janson, R. Kandori, G. R. Knapp, T. Kudo, N. Kusakabe, J. Kwon, T. Matsuo, S. Miyama, J. I. Morino, A. Moro-Martín, T. Nishimura, T. S. Pyo, E. Serabyn, H. Suto, R. Suzuki, M. Takami, N. Takato, H. Terada, C. Thalmann, D. Tomono, M. Watanabe, T. Yamada, H. Takami, T. Usuda, M. Tamura

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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, two60 M 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 For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B.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 of30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at5 M J, 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 J 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.

Original languageEnglish (US)
Article number159
JournalAstrophysical Journal
Volume794
Issue number2
DOIs
StatePublished - Oct 20 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • brown dwarfs
  • methods: statistical
  • open clusters and associations: general
  • planetary systems
  • stars: activity
  • stars: imaging

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    Brandt, T. D., McElwain, M. W., Turner, E. L., Mede, K., Spiegel, D. S., Kuzuhara, M., Schlieder, J. E., Wisniewski, J. P., Abe, L., Biller, B., Brandner, W., Carson, J., Currie, T., Egner, S., Feldt, M., Golota, T., Goto, M., Grady, C. A., Guyon, O., ... Tamura, M. (2014). A statistical analysis of seeds and other high-contrast exoplanet surveys: Massive planets or low-mass brown dwarfs? Astrophysical Journal, 794(2), [159]. https://doi.org/10.1088/0004-637X/794/2/159