Evidence for a planetary companion around a nearby young star

We report evidence for a planetary companion around the nearby young star HD 70573. The star is a G-type dwarf located at a distance of 46 pc. We carried out spectroscopic observations of this star with FEROS at the 2.2 m MPG/ESO telescope at La Silla. Our spectroscopic analysis yields a spectral type of G1 - 1.5 V and an age of about 100 Myr. Variations in stellar radial velocity ( RV) of HD 70573 were monitored from 2003 December until 2007 January. HD 70573 shows an RV variation with a period of 852(+/- 12) days and a semiamplitude of 149( +/- 6) m s(-1). The period of this variation is significantly longer than its rotational period. Based on the analysis of the Ca II K emission line, H alpha, and T-eff variation as stellar-activity indicators, as well as the lack of a correlation between the bisector velocity span and the RV, we can exclude rotational modulation and nonradial pulsations as the source of the long-period RV variation. Thus, the presence of a low-mass companion provides the best explanation for the observed RV variation. Assuming a primary mass m(1) = 1.0 +/- 0.1 M-., we calculated a minimum mass of the companion m(2) sin i of 6.1 M-Jup, which lies in the planetary-mass regime, and an orbital semimajor axis of 1.76 AU. The orbit's eccentricity is e = 0.4. The planet discovery around HD 70573 gives an important input for the study of debris disks around young stars and their relation to the presence of planets.