Stellar surface metallicity variation Δ[Fe/H] (≈ log(Z_surf/Z_ini); see text) resulting from planet formation as a function of effective temperature for stars in a cluster (same age, same metallicity). Three scenarios are considered: the dilution of the stellar surface due to the late accretion of 0.03 M_final of metal-free gas (solid red lines), the same dilution plus a pollution by the engulfment of 0.01 M_⊕ (dotted lines) or 1 M_⊕ (dashed lines) of planetesimals, respectively (see text). Observations of the 0.6-Gyr-old Hyades cluster (Takeda et al. 2013) are shown as blue crosses. All model values are evaluated at an age of 0.6 Gyr with X_D = 28 ppm. The first three panels show model ξ values of 0.5 (panel a), 0.1 (panel b) and 0 (panel c). The bottom panel d illustrates the possible range of Z_surf created only by the dilution scenario as a function of ξ.