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HARPS spectra with S/N > 600 for 21 solar twin stars are used to determinevery precise (sigma ~ 0.01 dex) differential abundances of C, O, Na, Mg, Al,Si, S, Ca, Ti, Cr, Fe, Ni, Zn, and Y in order to see how well [X/Fe] iscorrelated with elemental condensation temperature, Tc. In addition, precise(sigma < 0.8 Gyr) stellar ages are obtained by interpolating betweenYonsei-Yale isochrones in the logg - Teff diagram. It is confirmed that theratio between refractory and volatile elements is lower in the Sun than in mostof the solar twins, but for many stars, the relation between [X/Fe] and Tc isnot well defined. For several elements there is, instead, an astonishinglytight correlation between [X/Fe] and stellar age with amplitudes up to 0.2 dexover an age interval of 8 Gyr in contrast to the lack of correlation between[Fe/H] and age. While [Mg/Fe] increases with age, the s-process element yttriumshows the opposite behavior so that [Y/Mg] can be used as a sensitivechronometer for Galactic evolution. [Na/Fe] and [Ni/Fe] are not well correlatedwith stellar age, but define a tight Ni-Na relation similar to that previouslyfound for more metal-poor stars. These results provide new constraints onsupernovae yields and Galactic evolution. Furthermore, it is found that the C/Oratio evolves very little with time, which is of interest for discussions ofthe composition of exoplanets.

High-precision abundances of elements in solar twin stars: Trends with stellar age and elemental condensation temperature