SIMBAD references

Stellar activity influences radial velocity (RV) measurements and can also mimic the presence of orbiting planets. As part of the search for planets around the components of wide binaries performed with the SARG High Resolution Spectrograph at the TNG, it was discovered that HD 200466A shows strong variation in RV that is well correlated with the activity index based on H_α. We used SARG to study the H_α line variations in each component of the binaries and a few bright stars to test the capability of the H_α index of revealing the rotation period or activity cycle. We also analysed the relations between the average activity level and other physical properties of the stars. We finally tried to reveal signals in the RVs that are due to the activity. At least in some cases the variation in the observed RVs is due to the stellar activity. We confirm that H_α can be used as an activity indicator for solar-type stars and as an age indicator for stars younger than 1.5Gyr.