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Published October 1, 2007 | Published
Journal Article Open

TrES-4: A Transiting Hot Jupiter of Very Low Density


We report the discovery of TrES-4, a hot Jupiter that transits the star GSC 02620-00648 every 3.55 days. From high-resolution spectroscopy of the star, we estimate a stellar effective temperature of T_(eff) = 6100 ± 150 K, and from high-precision z and B photometry of the transit we constrain the ratio of the semimajor axis a and the stellar radius R_* to be a/R_* = 6.03 ± 0.13. We compare these values to model stellar isochrones to constrain the stellar mass to be M_* = 1.22 ± 0.17 M_⊙. Based on this estimate and the photometric time series, we constrain the stellar radius to be R_* = 1.738 ± 0.092 R_⊙ and the planet radius to be R_p = 1.674 ± 0.094 R_(Jup). We model our radial velocity data assuming a circular orbit and find a planetary mass of 0.84 ± 0.10 M_(Jup). Our radial velocity observations rule out line-bisector variations that would indicate a specious detection resulting from a blend of an eclipsing binary system. TrES-4 has the largest radius and lowest density of any of the known transiting planets. It presents a challenge to current models of the physical structure of hot Jupiters and indicates that the diversity of physical properties among the members of this class of exoplanets has yet to be fully explored.

Additional Information

© 2007 The American Astronomical Society. Received 2007 June 18; accepted 2007 August 6; published 2007 September 14. We thank Travis Barman for useful discussions. This Letter is based on work supported in part by NASA grants NNG04GN74G, NNG04LG89G, NNG05GI57G, NNG05GJ29G, and NNH05AB88I through the Origins of Solar Systems Program, and NASA Planetary Major Equipment grant N4G5-12229.We acknowledge support from the NASA Kepler mission under cooperative agreement NCC2-1390. Work by G. A´. B. was supported by NASA through Hubble Fellowship grant HST-HF-01170.01-A. Observing time on Keck I was awarded by NASA.

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