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Using data from the GALAH survey, we explore the dependence of elementalabundances on stellar age and metallicity among Galactic disc stars. We findthat the abundance of most elements can be predicted from age and [Fe/H] withan intrinsic scatter of about 0.03 dex. We discuss the possible causes for theexistence of the abundance-age-metallicity relations. Using a stochasticchemical enrichment scheme based on the size of Supernovae remnants, we showthe intrinsic scatter is expected to be small, about 0.05 dex or even smallerif there is additional mixing in the ISM. Elemental abundances show trends withboth age and metallicity and the relationship is well described by a simplemodel in which the dependence of abundance ([X/Fe]) on age and [Fe/H] areadditively separable. Elements can be grouped based on the direction of theirabundance gradient in the (age,[Fe/H]) plane and different groups can beroughly associated with three distinct nucleosynthetic production sites, theexploding massive stars, the exploding white dwarfs and the AGB stars. However,the abundances of some elements, like Co, La, and Li, show large scatter for agiven age and metallicity, suggesting processes other than simple Galacticchemical evolution are at play. We also compare the abundance trends ofmain-sequence turn-off stars against that of giants, whose ages were estimatedusing asteroseismic information from the K2 mission. For most elements, thetrends of main-sequence turn-off stars are similar to that of giants. Theexistence of abundance relations implies that we can estimate the age and birthradius of disc stars, which is important for studying the dynamic and chemicalevolution of the Galaxy.

The GALAH Survey: Dependence of elemental abundances on age and metallicity for stars in the Galactic disc