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Description
We report the discovery of HAT-P-17b,c, a multi-planet system with an inner transiting planet in a short-period, eccentric orbit and an outer planet in a 4.4 yr, nearly circular orbit. The inner planet, HAT-P-17b, transits the bright V=10.54 early K dwarf star GSC 2717-00417, with an orbital period P=10.338523+/-0.000009 days, orbital eccentricity e=0.342+/-0.006, transit epoch T_c_=2454801.16943+/-0.00020 (BJD: barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time (UTC)), and transit duration 0.1690+/-0.0009 days. HAT-P-17b has a mass of 0.534+/-0.018M_J_ and radius of 1.010+/-0.029R_J_ yielding a mean density of 0.64+/-0.05g/cm3. This planet has a relatively low equilibrium temperature in the range 780-927K, making it an attractive target for follow-up spectroscopic studies. The outer planet, HAT-P-17c, has a significantly longer orbital period P_2_=1610+/-20d and a minimum mass m_2_sini_2_=1.31^+0.18^_-0.15_M_J_. The orbital inclination of HAT-P-17c is unknown as transits have not been observed and may not be present. The host star has a mass of 0.86+/-0.04M_{sun}_, radius of 0.84+/-0.02R_{sun}_, effective temperature 5246+/-80K, and metallicity [Fe/H]=0.00+/-0.08. HAT-P-17 is the second multi-planet system detected from ground-based transit surveys.
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