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Published August 1, 2007 | Published
Journal Article Open

Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2


We report on a spectroscopic determination of the atmospheric parameters and chemical abundance of the parent star of the recently discovered transiting planet TrES-2. A detailed LTE analysis of a set of Fe I and Fe II lines from our Keck spectra yields T_(eff) = 5850 ± 50 K, log g = 4.4 ± 0.1, and [Fe/H] = -0.15 ± 0.10. Several independent checks (e.g., additional spectroscopy, line-depth ratios) confirm the reliability of our spectroscopic T_(eff) estimate. The mass and radius of the star, needed to determine the properties of the planet, are traditionally inferred by comparison with stellar evolution models using T_(eff) and some measure of the stellar luminosity, such as the spectroscopic surface gravity. We apply here a new method in which we use instead of log g the normalized separation a/R_* (related to the stellar density), directly measurabele from the light curves of transiting planets with much greater precision. With the a/R_* value from the light-curve analysis of Holman and coworkers and our T_(eff) estimate, we obtain M_* = 0.980 ± 0.062 M_☉ and R_* = 1.000^(+0.036)_(-0.033) R_☉, and an evolutionary age of 5.1^(+2.7)_(-2.3) Gyr, in good agreement with other constraints (Ca II H and K line cores, lithium abundance, and rotation). The new stellar parameters yield improved values for the planetary mass and radius of M_p = 1.198 ± 0.053 M_J and R_p = 1.220^(+0.045)_(-0.042) R_J, confirming that TrES-2 is the most massive among the currently known nearby (d ≲ 300 pc) transiting hot Jupiters. The surface gravity of the planet, log g_p = 3.299 ± 0.016, can be derived independently of the knowledge of the stellar parameters (i.e., directly from observations), and with a very high precision rivaling that of the best known double-lined eclipsing binaries.

Additional Information

© 2007 American Astronomical Society. Print publication: Issue 2 (2007 August 1); received 2007 March 12; accepted for publication 2007 April 21. We thank K. Biazzo (Catania Astrophysical Observatory) for providing the LDR calibrations in advance of publication, and A. Burrows and A. Spagna for helpful discussions. G. T. acknowledges partial support for this work from NASA Origins grant NNG04LG89G.D.C. is supported in part by NASA Origins grant NNG05GJ29G.A. S. gratefully acknowledges the Kepler mission for partial support under NASA cooperative agreement NCC 2-1390. J. B. L gratefully acknowledges support from NSF grant AST 03-07340. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M.Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research hasmade use of NASA's Astrophysics Data System Abstract Service and of the SIMBAD database, operated at CDS, Strasbourg, France.

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October 19, 2023