Modelos cromosféricos de estrellas de tipo solar: Un estudio sobre el ``Vaughan-Preston gap"

VIEYTES, M. C.; MAUAS, P J D

Congreso; reunión Anual de la Asociación Argentina de Astronomía; 2001

Asociación Argentina de Astronomía

Areas of concentrated magnetic field on the Sun emit Ca II H (396.8 nm) and K (393.4 nm) more intensely than the non magnetic background. The intensity of this emission increases in response to the amount of non thermal heating of the chromosphere. By analogy with the Sun it is reasonable to suppose that Ca II emission in late type stellar atmospheres, which have physical properties and overall structure similar to the sun´s atmosphere, will also be associated with magnetic structures. A widely used indicator of chromospheric activity, the S index, is produced using the fluxes in these two lines. Up to the present, surveys of Ca II emission in the solar neighborhood seems to reveal a bimodal distribution in which most stars have weak chromospheric emission (CE), as the Sun does, some active ones have high levels of CE, and only a few have intermediate levels. This gap, called Vaughan - Preston gap, in CE exists for stars in the range 0.45 < (B-V) < 1. In this work, we compute different chromospheric models for stars with the same (B-V) as the Sun ((B-V) = 0.65) to investigate whether the Vaughan - Preston gap is due to the response of the Ca II lines to different changes in the chromospheric temperature with height.