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 $K=51\pm3$ m s$^{ -1}$. The derived mass of TrES-4b is found to be $M_{ \rm p} = 0.49\pm0.04 \rm M_{ Jup}$, significantly lower than previously reported. Combined with the large radius ($R_{ \rm p} = 1.84_{ -0.09}^{ +0.08} \rm R_{ Jup}$) 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.
Categories: astro-ph.EP