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

Journal Article · Mon Oct 20 00:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/794/2/159· OSTI ID:22370363

Brandt, Timothy D.; Spiegel, David S. ^[1]; McElwain, Michael W.; Grady, C. A. ^[2]; Turner, Edwin L. ^[3]; Mede, Kyle; Kuzuhara, Masayuki ^[4]; Schlieder, Joshua E.; Brandner, W.; Feldt, M. ^[5]; Wisniewski, John P. ^[6]; Abe, L. ^[7]; Biller, B. ^[8]; Carson, J. ^[9]; Currie, T. ^[10]; Egner, S.; Golota, T.; Guyon, O. ^[11]; Goto, M. ^[12]; Hashimoto, J. ^[13] ; others, and

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1. Institute for Advanced Study, Princeton, NJ (United States)
2. Exoplanets and Stellar Astrophysics Laboratory, Goddard Space Flight Center, Greenbelt, MD (United States)
3. Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States)
4. University of Tokyo, Tokyo (Japan)
5. Max Planck Institute for Astronomy, Heidelberg (Germany)
6. HL Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK (United States)
7. Laboratoire Hippolyte Fizeau, Nice (France)
8. University of Edinburgh, Edinburgh, Scotland (United Kingdom)
9. College of Charleston, Charleston, SC (United States)
10. Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON (Canada)
11. Subaru Telescope, Hilo, Hawai'i (United States)
12. Universitäts-Sternwarte München, Munich (Germany)
13. National Astronomical Observatory of Japan, Tokyo (Japan)

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 {sub 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 For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B.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 {sub J}, with a single power-law distribution. We find that p(M, a)∝M {sup –0.65} {sup ±} {sup 0.60} a {sup –0.85} {sup ±} {sup 0.39} (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M {sub 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.

• OSTI ID: 22370363
• Journal Information: Astrophysical Journal, Vol. 794, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CLOUDS
DETECTION
DISTRIBUTION
DISTRIBUTION FUNCTIONS
DWARF STARS
FRAGMENTATION
MASS
MONTE CARLO METHOD
PLANETS
RADIAL VELOCITY
ROTATION
STARS