SIMBAD references

We present results of a study of the rotational periods of Post-T Tauri stars (PTTSs) in the Lupus star forming region. These stars have been discovered by spectroscopic follow-up observations of ROSAT x-ray sources. Photometric observations have allowed to determine their luminosity, and by comparison with theoretical evolutionary tracks they were found to be significantly older on average than typical T Tauri stars. 46 stars have been monitored photometrically, and for 34 of them photometric variations were found that are consistent with rotational brightness modulations caused by starspots. The large number of data on rotational periods of pre-main-sequence (PMS)/zero-age main-sequence (ZAMS) stars available by now allows us to study the impact of stellar mass on the evolution of angular momentum. For several different mass bins, we compare the available data on rotational periods with theoretical models, and find good agreement between theory and observations for the mass-dependency of the pre-main-sequence evolution of angular momentum. We also study the relation between activity, rotation, mass, and age of low mass stars, and demonstrate that activity is driven by rotation mainly, while it seems to be rather independent of mass and age.