Absolute fluxes of K chromospheric emission in main sequence stars.

Summary. From new observations ol the K emission line of Ca ii and additional data from various sources, absolute fluxes from the chromospheres of main sequence stars have been estimated. The analysis of these data leads to the following conclusions i) for stars with Teff < 5000 0K, the theoretical acoustic energy flux, which is commonly assumed as responsible for the heating of chromospheres and coronae, is ina dequate - by two orders of magnitude for the coolest stars - in accounting for the observed chromospheric emission flux; ii) the decay of the K emission line flux as the inverse roo square of star age (Skumanich, 1972) is proved to be valid in the range 4 x l0 + 1.5 x l0 years; the Sun as a whole does not fit in with this relation unless -only magnetically active regions are considered; iii) for stars of a given age, the K emission line flux, normalized to the star bolometric flux, has a maximum at the spectral type K 0. Key words: stellar chromospheres - K emission line flux - star age