Evidence for a Planetary Companion around a Nearby Young Star

Abstract

We report evidence for a planetary companion around the nearby young star HD\n70573. The star is a G type dwarf located at a distance of 46 pc with age\nestimation between 20 and 300 Myrs. We carried out spectroscopic observations\nof this star with FEROS at the 2.2 m MPG/ESO telescope at La Silla. Our\nspectroscopic analysis yields a spectral type of G1-1.5V and an age of about\n100 Myrs. Variations in stellar radial velocity of HD 70573 have been monitored\nsince December 2003 until January 2007. The velocity accuracy of FEROS within\nthis period is about 10 m/s. HD 70573 shows a radial velocity variation with a\nperiod of 852 +/- 12 days and a semi-amplitude of 149 +/- 6 m/s. The period of\nthis variation is significantly longer than its rotational period, which is 3.3\ndays. Based on the analysis of the Ca II K emission line, Halpha and Teff\nvariation as stellar activity indicators as well as the lack of a correlation\nbetween the bisector velocity span and the radial velocity, we can exclude the\nrotational modulation and non-radial pulsations as the source of the\nlong-period radial velocity variation. Thus, the presence of a low-mass\ncompanion around the star provides the best explanation for the observed radial\nvelocity variation. Assuming a primary mass m1=1.0 +/- 0.1 Msun for the host\nstar, we calculated a minimum mass of the companion m2sini of 6.1 Mjup, which\nlies in the planetary mass regime, and an orbital semi-major axis of 1.76 AU.\nThe orbit of the planet has an eccentricity of e=0.4. The planet discovery\naround the young star HD 70573 gives an important input for the study of debris\ndisks around young stars and their relation to the presence of planets.\n