Abstract
AbstractA modified index of the level of stellar chromospheric activity, A'Call, is proposed. It is calculated from the measured emission flux density in cores of Ca II H and K lines; however, unlike the other known indices, it is free from the influence of the colour of a star. Application of the new index leads to amodified activityrotation relationship in lower main‐sequence stars. It is shown that in the coordinate system log A'Call, log Ro (Ro being Rossby number) F‐M stars obey a common relationship corresponding to the parameter α = 1.6. The obtained curve shows no evidence for activity saturation for stars with small Rossby numbers, but in slowly rotating stars with thin convection zones the activity level tends to a constant value.
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