The GAPS programme with HARPS-N at TNG
VI. The curious case of TrES-4b

A. Sozzetti, A. S. Bonomo, K. Biazzo, L. Mancini, M. Damasso, S. Desidera, R. Gratton, A. F. Lanza, E. Poretti, M. Rainer, L. Malavolta, L. Affer, M. Barbieri, L. Bedin, C. Boccato, M. Bonavita, F. Borsa, S. Ciceri, R. Claudi, D. Gandolfi, P. Giacobbe, T. Henning, C. Knapic, D. W. Latham, G. Lodato, A. Maggio, J. Maldonado, F. Marzari, A. F. Martinez Fiorenziano, G. Micela, E. Molinari, C. Mordasini, V. Nascimbeni, I. Pagano, M. Pedani, F. Pepe, G. Piotto, N. C. Santos, G. Scandariato, E. Shkolnik, J. Southworth

Abstract
We update the TrES-4 system parameters using high-precision HARPS-N radial-velocity measurements and new photometric light curves. A combined spectroscopic and photometric analysis allows us to determine a spectroscopic orbit with a semi-amplitude K = 51 ± 3 m s^-1. The derived mass of TrES-4b is found to be M_p = 0.49 ± 0.04 M_Jup, significantly lower than previously reported. Combined with the large radius (R_p = 1.84_-0.09^+0.08 R_Jup) inferred from our analysis, TrES-4b becomes the transiting hot Jupiter with the second-lowest density known. We discuss several scenarios to explain the puzzling discrepancy in the mass of TrES-4b in the context of the exotic class of highly inflated transiting giant planets.

Keywords
stars: individual: TrES-4b – planetary systems – techniques: radial velocities – techniques: spectroscopic – techniques: photometric

Astronomy and Astrophysics
Volume 575, Page L15_1
March 2015

DOI: 10.1051/0004-6361/201425570
ADS Bibliographic code: 2015A%26A...575L..15S