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

Abstract

Using data from the GALAH survey, we explore the dependence of elemental abundances on stellar age and metallicity among Galactic disc stars. We find that the abundance of most elements can be predicted from age and [Fe/H] with an intrinsic scatter of about 0.03 dex. We discuss the possible causes for the existence of the abundance-age-metallicity relations. Using a stochastic chemical enrichment scheme that takes the volume of supernovae remnants into account, we show the intrinsic scatter is expected to be small, about 0.05 dex or even smaller if there is additional mixing in the ISM. Elemental abundances show trends with both age and metallicity and the relationship is well described by a simple model in which the dependence of abundance ([X/Fe]) on age and [Fe/H] are additively separable. Elements can be grouped based on the direction of their abundance gradient in the (age,[Fe/H]) plane and different groups can be roughly associated with three distinct nucleosynthetic production sites, the exploding 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 a given age and metallicity, suggesting processes other than simple Galactic chemical evolution are at play. We also compare the abundance trends of main-sequence turn-off stars against that of giants, whose ages were estimated using asteroseismic information from the K2 mission. For most elements, the trends of main-sequence turn-off stars are similar to that of giants. The existence of abundance relations implies that we can estimate the age and birth radius of disc stars, which is important for studying the dynamic and chemical evolution of the Galaxy.

Residual Abundances in GALAH DR3: Implications for Nucleosynthesis and Identification of Unique Stellar Populations

“…(Sharma et al 2022) for O, K, Y, and Ba. The wings of the K residual abundance distribution increase to ∼0.8 dex at young ages, but the core of the distribution remains uncorrelated with age.…”

The Relationship between Age, Metallicity, and Abundances for Disk Stars in a Simulated Milky Way

“…First, we use the GALAH survey data release 3 (DR3; Buder et al 2021). This has an associated value added catalog from Sharma et al (2022) that contains ages from the BSTEP code (Sharma et al 2018), which makes use of stellar isochrones. In total, GALAH DR3 has abundances for 30 elements in 588,571 nearby stars in the Galactic disk measured in the optical.…”

“…It is important to further investigate these age-individual abundance, or age-[X/Fe], relations at a given [Fe/H] in the disk because the tightness of these relations illustrate that (1) by inverting the age-[X/Fe] relation, abundances can serve as chemical clocks providing ages for stars, and that (2) [Fe/H] and age capture majority of the crucial information about a star, e.g., [X/Fe], orbits, and birth location (Bedell et al 2018;Minchev et al 2018;Ness et al 2019;Hayden et al 2020;Jofré et al 2020;Casamiquela et al 2021;Espinoza-Rojas et al 2021;Ratcliffe et al 2022;Sharma et al 2022). Additionally, comparisons between the slope in the [Fe/H]-[X/Fe] relation and the slope in the age-[X/Fe] relation appear to group elements accordingly into three distinct nucleosynthetic sites: core-collapse supernova (SNe II), white dwarf explosion (SN Ia), and stellar winds (Sharma et al 2022). Furthermore, the slope in the age-[X/Fe] relation is sensitive to the location across the [Mg/Fe] versus [Fe/H] plane (Horta et al 2022;Yuxi et al 2022), but the scatter around these relations is consistently small.…”

“…Furthermore, the slope in the age-[X/Fe] relation is sensitive to the location across the [Mg/Fe] versus [Fe/H] plane (Horta et al 2022;Yuxi et al 2022), but the scatter around these relations is consistently small. Both the high-resolution studies at [Fe/H] = 0 dex from Nissen (2015) and Bedell et al (2018) as well as the larger samples exploring a wider range of metallicities (Ness et al 2019;Sharma et al 2022) have shown that the intrinsic scatter of stars around their age-[X/Fe] relations is on the order of <0.01-0.04 dex. The small intrinsic scatter in the age-[X/Fe] relations is also fairly insensitive to the current location of the stars in the disk (Ness et al 2019;Yuxi et al 2022), which is a natural consequence of radial redistribution or migration, whereby stars at any given radius, R, are from a wide range of initial radii (Frankel et al 2018(Frankel et al , 2019.…”

Ages of Main-sequence Turnoff Stars from the GALAH Survey

“…The original spatial distribution of stars is changed by the kinematic evolution of the galaxy; therefore, many works suggest that the stellar age rather than kinematics is a better parameter to study different disk populations (e.g., Haywood et al 2013;Bensby et al 2014;Delgado Mena et al 2019). The relations between abundances and stellar age, which can contribute to future models of the Galactic chemical evolution, are widely studied (Buder et al 2019;Delgado Mena et al 2019;Hayden et al 2020;Sharma et al 2022). The age structure of different disk populations are shown, providing clues for the formation history of the Galactic disk (Haywood et al 2013).…”