The broad components in the H line of very active stars : chromospheric micro aring ?

In our analysis of the H line, using the spectral subtraction technique , in chromospherically active binary systems and in weak-lined T Tauri stars (WTTS), we have found that in some stars the subtracted H emission line proole has very broad wings, and is not well matched using a single-Gaussian t. These prooles have therefore been tted using two Gaussian components: a narrow component having a FWHM of 45-90 km s ?1 and a broad component with a FWHM ranging from 133 to 470 km s ?1. This broad component could be interpreted as arising from microoar-ing that occurs in the chromosphere by similarity with the broad components also found by other authors in the chromospheric Mg ii h & k lines and in several transition region lines of active stars. The microoares are frequent, short-duration, energetically weak disturbances, i.e. they are the low-energy extension of ares, and therefore have large-scale motions associated that could explain the broad wings observed in these lines. A correlation between the contribution of the broad components and the degree of stellar activity seems to be present. In some cases the line is asymmetric and the t is better matched when the broad component is blue-shifted or red-shifted with respect to the narrow component. These asymmetries are also observed during the impulsive and gradual phases of solar and stellar ares, and favour the interpretation of the broad component as due to upward and downward motions produced by microoaring in the chromosphere.