We compare schematic modeling of spots and plage on the surface of cool dwarfs with Pleiades data to assess effects of magnetic activity on the strengths of the L II and K I resonance lines in Pleiades spectra. Comprehensive L II and K I NLTE line formation computation is combined with comparatively well-established empirical solar spot and plage stratifications for solar-like stars. For other stars, we use theoretical constructs to model spots and plage that portray recipes commonly applied in stellar activity analyses. We find that - up to B-V = 1.1 | neither the L 670.8 nm nor the K I 769.9 nm line is sensitive to the presence of a chromosphere, in contrast to what is often supposed. Instead, both lines respond to the effects of activity on the stratification in the deep photosphere. They do so in similar fashion, making the K I line a valid proxy to study L II line formation without spread from abundance variations. The computed effects of activity on line strength are opposite between plage and spots, differ noticeably between the empirical and theoretical solar-like stratifications, and considerably affect stellar broad-band colors. Our results indicate that one can neither easily establish, nor easily exclude, magnetic activity as major provider of K I line strength variation in the Pleiades. Since L II line formation follows K I line formation closely, the same holds for L II and the apparent lithium abundance
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.