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 ar ound these objects has recently caused much attention to extrasolar pl anet research. From the analysis of high resolution spectrograms we ob tain for 51 Peg: T-eff = 5793 +/- 70 K, log g = 4.33 +/- 0.1, [Fe/H]= +0.20 +/- 0.07 and for 47 UMa: T-eff = 5892 +/- 70 K, log g = 4.27 +/- 0.1, [Fe/H]= +0.00 +/- 0.07. Evolutionary tracks computed individuall y for both stars and with detailed model atmospheres as upper boundary condition, come up with stellar masses of 1.12 +/- 0.05 M. and 1.03 /- 0.05 M. for 51 Peg and 47 UMa, respectively. The stellar ages infer red are 4.0 +/- 2.5 Gyr for 51 Peg, not significantly different from t he 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 H ipparcos 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.