Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit

We report high-precision transit photometry for the recently detected planet HD 17156b. Using these new data with previously published transit photometry and radial velocity measurements, we perform a combined analysis based on a Markov Chain Monte Carlo approach. The resulting mass M[SUB]p[/SUB] = 3.09[SUP]+0.22[/SUP][SUB]-0.17[/SUB]~M_Jup and radius R[SUB]p[/SUB] = 1.23[SUP]+0.17[/SUP][SUB]-0.20[/SUB] R_Jup for the planet places it at the outer edge of the density distribution of known transiting planets with rho[SUB]p[/SUB] = 1.66[SUP]+1.37[/SUP][SUB]-0.60[/SUB] rho_Jup. The obtained transit ephemeris is T_Tr = 2 454 438.48271[SUP]+0.00077[/SUP][SUB]-0.00057[/SUB] + N × 21.21747[SUP]+0.00070[/SUP][SUB]-0.00067[/SUB] BJD. The derived plausible tidal circularization time scales for HD 17156b are larger than the age of the host star. The measured high orbital eccentricity e = 0.6719[SUP]+0.0052[/SUP][SUB]-0.0063[/SUB] can thus not be interpreted as the clear sign of the presence of another body in the system. Based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Photometric measurements are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/485/871