Solar-type stars with planetary companions: 51 Pegasi and 47 Ursae Majoris.

Accurate stellar parameters are presented for the solar-type stars 51 Peg and 47 UMa. The announcement of the detection of jovian planets around these objects has recently caused much attention to extrasolar planet research. From the analysis of high resolution spectrograms we obtain for 51 Peg: T_eff_=5793+/-70K, log(g)=4.33+/-0.1, [Fe/H]=+0.20+/-0.07 and for 47 UMa: T_eff_=5892+/-70K, log(g)=4.27+/-0.1, [Fe/H]=+0.00+/-0.07. Evolutionary tracks computed individually for both stars and with detailed model atmospheres as upper boundary condition, come up with stellar masses of 1.12+/-0.06 M_sun_ and 1.03+/-0.05 M_sun_ for 51 Peg and 47 UMa, respectively. The stellar ages inferred are 4.0+/-2.5 Gyr for 51 Peg, not significantly different from the age of the Sun, and 7.3+/-1.9 Gyr for 47 UMa. A comparison of the spectroscopic parallaxes with accurate distances available from the Hipparcos satellite shows good agreement, a result that primarily gives confidence in the values for the surface gravity parameter, which is derived here from the wings of the strong Mg Ib lines.