[X/Fe] ratios (from carbon to zinc) vs. condensation temperature for different samples of solar twins and solar analogs. The solid line represents the mean trend found by Meléndez et al. (2009). upper-left (filled circles): Southern sample of solar twins by Meléndez et al. (2009); upper-right (open circles): Northern solar twin sample by Ramírez et al. (2009); middle-left (squares): average of six different literature samples of solar analogs (Ramírez et al. 2010); middle-right (pentagons): average of 15 solar twins in the HARPS sample of González Hernández et al. (2010), after a shift of  −0.004 dex; lower-left (triangles): average of the pair of solar analogs 16 Cyg A and B (Ramírez et al. 2011), after a shift of  − 0.015 dex; lower-right (stars): abundance pattern of the solar twin 18 Sco (Meléndez et al. 2012, in prep.), after a shift of  + 0.014 dex.