Rotational evolution between 120 Myr and 1 Gyr

Abstract

In this work the rotational evolution and the lithium depletion of low -mass stars in young stellar system is investigated, taking advantage of extensive new data sets on rotational periods that have recently became available. The rotational evolution of slow-rotating stars between 100Myr and 1 Gyr have been examined in detail, outlining a complex behaviour that claim for improved modelling of the internal angular momentum transport and of the angular momentum loss via a magnetised wind. A puzzling change in the rotation distribution vs. mass takes place at 550 Myr, which seems to contradict current theoretical models. Previous assumptions on the factorisation of the rotational dependence on time and mass do not hold in the 100 Myr - 1 Gyr time interval, which complicates somewhat the age inference from rotation. Studies based on the distribution of rotational periods of solar-type stars suggest in addition a possible link between lithium depletion and the rotational history of stars. The dispersion of lithium abundance at a given color in the Pleiades member stars have been re-examined. Once removed the mass dependence from rotation and Li-depletion a soft correlation between lithium and rotational periods in K and M type stars has been found. On the other hand, a clear and solid correlation has been found in the 0.74<=(B-V)<1.15 color range. In this (B-V) range the slower a star is the larger is the lithium depletion. A comparison and an analysis of the rotation periods and lithium depletion in young stellar association AB Doradus and the Pleiades has allowed to confirm the coevality for these two systems. A group of slow-rotating stars in AB Dor, however, have Li abundance considerably higher that suggested by the general trend, which may be indicative of differences in the rotational histories of stars belonging to the young loose association. A young nearby cluster, gamma2 Velorum, has also been analyzed, using data from the Gaia-ESO survey. This latter has evidenced the presence of two possible different populations. These populations are kinematically different eventual differences in Li abundance are found below detectability.