  In this work, we investigate the potassium excess absorption around 7699A of
the exoplanets HD189733b and HD209458b. For this purpose, we used high spectral
resolution transit observations acquired with the 2 x 8.4m Large Binocular
Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic
Instrument (PEPSI). For a bandwidth of 0.8A, we present a detection > 7-sigma
with an absorption level of 0.18% for HD189733b. Applying the same analysis to
HD209458b, we can set 3-sigma upper limit of 0.09%, even though we do not
detect a K- excess absorption. The investigation suggests that the K- feature
is less present in the atmosphere of HD209458b than in the one of HD189733b.
This comparison confirms previous claims that the atmospheres of these two
planets must have fundamentally different properties.
