An Analysis of the SEEDS High-Contrast Exoplanet Survey: Massive Planets or Low-Mass Brown Dwarfs?
We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars observed by HiCIAO on the Subaru Telescope, NIRI on Gemini North, and NICI on Gemini South. The stars cover a wide range of ages and spectral types, and include five detections (kap And b, two ~60 M_J brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722 B). We conduct a uniform, Bayesian analysis of the ages of our entire sample, using both membership in a kinematic moving group and activity/rotation age indicators, to obtain posterior age distributions.
We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most 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 beyond which the distribution function for radial-velocity planets cannot extend, finding model-dependent values of ~30–100 AU. Finally, we treat our entire substellar sample together, modeling it as a single power law distribution.
After including GJ 758 B and GJ 504 b, two other HiCIAO detections, a distribution p(M,a)∝ M −0.7±0.6 a −0.8±0.4 (1 sigma errors) from massive brown dwarfs to a theoretically motivated cutoff at ~5 M_J, provides an adequate fit to our data. 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.
Timothy D. Brandt, Michael W. McElwain, Edwin L. Turner, Kyle Mede, David S. Spiegel, Masayuki Kuzuhara, Joshua E. Schlieder, John P. Wisniewski, L. Abe, W. Brandner, J. Carson, T. Currie, S. Egner, M. Feldt, T. Golota, M. Goto, C. A. Grady, O. Guyon, J. Hashimoto, Y. 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 (Submitted on 21 Apr 2014)
Comments: 21 pages, 5 figures, submitted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1404.5335 [astro-ph.SR] (or arXiv:1404.5335v1 [astro-ph.SR] for this version)
Submission history From: Timothy Brandt [v1] Mon, 21 Apr 2014 21:16:13 GMT (1280kb)
