HD 137496 system discovery

We precisely estimate the stellar parameters, M*=1.035+/-0.022M_{sun}_, R*= 1.587+/-0.028R_{sun}_, Teff=5799+/-61K,together with the chemical composition (e.g. [Fe/H]=-0.027+/-0.040dex) of the slightly evolved star. We detect two planets orbiting HD 137496. The inner planet, HD 137496 b, is a super-Mercury (an Earth-sized planet with the density of Mercury) with a mass of Mb=4.04+/-0.55M_{sun}_), a radius of Rb=1.31^+0.06^_-0.05_R_{sun}_ and a density of {rho}b=10.49^+2.08^_-1.82_g/cm^3^.

From interior modeling analysis we find that the planet is composed mainly of iron, with the core representing over 70% of the planet's mass (Mcore/Mtotal=0.73^+0.11^_-0.12_). The outer planet, HD 137496 c, is an eccentric (e=0.477+/-0.004), long period (P=479.9^+1.0^_-1.1_days) giant planet (Mc*sinic=7.66+/-0.11M_{Jup}_) for which we do not detect a transit. HD 137496 b is one of the few super-Mercuries detected to date.

The accurate characterization reported here enhances its role as a key target to better understand the formation and evolution of planetary systems. The detection of an eccentric long period giant companion also reinforces the link between the presence of small transiting inner planets and long period gas giants.