Transmission spectrum of potassium (top) and lithium (bottom). The black dashed line marks the line position; the solid red line shows the no-atmosphere POLD model (top panel only) to illustrate the deformation scale; the red dashed line shows the continuum (bottom panel only). Gray data points indicate the full transmission spectrum, with black bins every 15 pixels. Potassium is contaminated by POLD effects, with no obvious atmospheric detection. Lithium shows no detection, even though it is not contaminated by POLD effects, as this species does not absorb in the stellar spectrum.