The age decay of two indicators of the stellar magnetic activity (λ2800 Mg II emission flux and λ10830 He I equivalent width) have been studied for field solar-type stars. The Li abundance has been used, in most of the cases, as a stellar age indicator. A calibrated decay law for Mg II has been determined and compared with a similar one, recently

According to several properties, the active regions are divided in two groups whose limit is roughly set at 1021 Mx. A statistical analysis indicates that the small regions emerge almost exclusively in the remnant magnetic regions, resulting from the decay of previous active centers. According to these facts, a tentative picture is proposed, where

To investigate the location of the actual limit for the different behavior, the active regions with fluxes greater than 10 to the 20 Mx are investigated. After surveying the differences between large and small active regions reported in the literature, the birthplaces of the active regions are analyzed statistically. The analysis indicates that the

The temporal and spatial behavior of the K I 7699 line profile is investigated. In particular, the asymmetries of the line profile at several residual intensities have been measured using the bisector method. Similar shapes are found in the bisector of the mean line profile as those obtained before for different positions on the solar disk. However

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Observations from a sample of six regions of star formation in the 244 GHz, J = 5-4 rotational transition of CS, together with previous results for lower frequencies, indicate that the line temperatures for this transition in the cases of OMC-1, M17 SW, W3(OH) and Ori B are consistent with constant density, large velocity gradient models. This in