Evidence for a panetary 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, Halpha, and Teff 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 m1=1.0+/-0.1 Msolar, we calculated a minimum mass of the companion m2sini of 6.1 MJup, 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