An extrasolar giant planet in a close triple-star system

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Hot Jupiters are gas-giant planets orbiting with periods of 3–9 days around Sun-like stars. They are believed to form in a disk of gas and condensed matter at or beyond 2.7 astronomical units (au—the Sun–Earth distance) from their parent star1,2. At such distances, there exists a sufficient amount of solid material to produce a core capable of capturing enough gas to form a giant planet. Subsequently, they migrate inward to their present close orbits3. Here I report the detection of an unusual hot Jupiter orbiting the primary star of a triple stellar system, HD 188753. The planet has an orbital period of 3.35 days and a minimum mass of 1.14 times that of Jupiter. The primary star's mass is 1.06 times that of the Sun, 1.06 M. The secondary star, itself a binary stellar system, orbits the primary at an average distance of 12.3 au with an eccentricity of 0.50. The mass of the secondary pair is 1.63 M. Such a close and massive secondary would have truncated a disk around the primary to a radius of only 1.3 au (ref. 4) and might have heated it up to temperatures high enough to prohibit giant-planet formation5,6, leaving the origin of this planet unclear.

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Figure 1: Adaptive optics image of HD 188753.
Figure 2: Radial velocities as functions of orbital phase.
Figure 3: Spectroscopy and photometry of HD 188753.


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M.K. thanks S. Kulkarni for support and guidance, D. Sasselov for discussions, and C. Gelino for acquiring the NIRC2 data. The data presented here were obtained at the W. M. Keck Observatory (operated by the California Institute of Technology, University of California, and NASA), which was made possible by financial support from the W. M. Keck Foundation. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the NSF. M.K. acknowledges support from NASA.

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Correspondence to Maciej Konacki.

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Supplementary Methods

The file contains a detailed description of the novel method for precision radial velocity measurements with an iodine gas absorption cell of double-lined spectroscopic binary stars. (PDF 91 kb)

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Konacki, M. An extrasolar giant planet in a close triple-star system. Nature 436, 230–233 (2005) doi:10.1038/nature03856

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