The GAPS Programme with HARPS-N@TNG VI: The Curious Case of TrES-4b

Abstract

We revisit the TrES-4 system parameters based on 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 an amplitude $K=51\pm 3$ m s${}^{-1}$. The derived mass of TrES-4b is found to be $M_{\mathrm{p}}=0.49\pm 0.04{\mathrm{M}}_{\mathrm{Jup}}$, significantly lower than previously reported. Combined with the large radius ($R_{\mathrm{p}}=1.84_{-0.09}^{+0.08}{\mathrm{R}}_{\mathrm{Jup}}$) inferred from our analysis, TrES-4b becomes the second-lowest density transiting hot Jupiter 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.

5 pages, 4 figures, Letter accepted for publication in Astronomy and Astrophysics

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