HAT-P-17b,c: A transiting, eccentric, hot saturn and a long-period, cold Jupiter

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 4.4yr, 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 ± 0.000009days, 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 ± 0.0009days. 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 cm^-3. 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 ± 20days and a minimum mass m ₂sin i 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, radius of 0.84 ± 0.02R, 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.