Traits for chemical evolution in solar twins

Abstract

The physical processes driving chemical evolution in the Milky Way can be probed using the distribution of abundances in low-mass FGK type stars in space phase at different times. During their final stages of evolution, stars experience nucleosynthesis several times, each at different timescales and producing different chemical elements. Finding abundance ratios that have simple variations across cosmic times therefore remains a challenge. Using the sample of 80 solar twins for which ages and abundances of 30 elements have been measured with high precision, we searched for all possible abundance ratio combinations that show linear trends with age. We found 55 such ratios, all combining an n-capture element and another element produced by different nucleosynthesis channels. We recovered the ratios of [Y/Mg], [Ba/Mg], and [Al/Y] that have been reported previously in the literature, and found that [C/Ba] depends most strongly on age, with a slope of 0.049 ± 0.003 dex Gyr −1 . This imposes constraints on the magnitude of the time dependency of abundance ratios in solar twins. Our results suggest that s-process elements, in lieu of Fe, should be used as a reference for constraining chemical evolution models of the solar neighbourhood. Our study illustrates that a wide variety of chemical elements measured in high-resolution spectra is key to meeting the current challenges in understanding the formation and evolution of our Galaxy.

Using heritability of stellar chemistry to reveal the history of the Milky Way

“…Since many chemical elements are produced at similar astrophysical sites, we have chosen traits that are evolutionary informative (Jofré et al 2020). Adding traits that do not evolve with time or that do not vary signicantly among stars only adds noise to any phylogenetic signal that may be in the data and therefore can be ignored.…”

“…Adding traits that do not evolve with time or that do not vary signicantly among stars only adds noise to any phylogenetic signal that may be in the data and therefore can be ignored. We select the abundance ratios presented in Jofré et al (2020) to produce our tree. These correspond to…”

“…Casali et al (2020), not all chemical clocks" hold for all stellar samples, and it is yet to be seen how their dependency with age changes accross the Galaxy and parameter space. The seemingly non-universality of these abundance ratios as a function of stellar age motivates us to treat them simply as heritable traits instead of a measure of time like a clock (see further discussions in Jofré et al 2020).…”

“…The chemical abundances are examined in four main nucleosynthesis channels (Jofré et al 2020) that represent dierent epochs after a given star formation episode and dierent rates of chemical enrichment. The α-capture elements of the top panel enrich the ISM through the death of massive stars during the rst 100 Myr after a star formation episode (Arnett 1978;Tinsley 1979).…”

Magnetic-buoyancy-induced mixing in AGB stars: a theoretical explanation of the non-universal relation of [Y/Mg] to age

“…Nissen (2015) attributed the trend to the different production mechanisms of the pair of elements considered in the ratios: Mg, Zn, and for example, Al and Ti (used in some subsequent works, as Delgado Mena et al 2019;Casali et al 2020) are also produced by massive stars on shorter timescales, while Y, Sr, and the other s-process elements are synthesised in lowand intermediate-mass stars and are released to the interstellar medium at later times. The value of their ratios therefore increases in the younger stellar populations, and it has been used as a sort of chemical clock to infer stellar ages, mainly in the solar neighbourhood (see e.g., Jofré et al 2020;Nissen et al 2020).…”