Browsing by Author "Hua, Xia"

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    Assembling a high-precision abundance catalogue of solar twins in GALAH for phylogenetic studies
    (2024) Walsen, Kurt; Jofre, Paula; Buder, Sven; Yaxley, Keaghan; Das, Payel; Yates, Robert M.; Hua, Xia; Signor, Theosamuele; Eldridge, Camilla; Rojas-Arriagada, Alvaro; Tissera, Patricia B.; Johnston, Evelyn; Aguilera-Gomez, Claudia; Zoccali, Manuela; Gilmore, Gerry; Foley, Robert
    Stellar chemical abundances have proved themselves a key source of information for understanding the evolution of the Milky Way, and the scale of major stellar surveys such as GALAH have massively increased the amount of chemical data available. However, progress is hampered by the level of precision in chemical abundance data as well as the visualization methods for comparing the multidimensional outputs of chemical evolution models to stellar abundance data. Machine learning methods have greatly improved the former; while the application of tree-building or phylogenetic methods borrowed from biology are beginning to show promise with the latter. Here, we analyse a sample of GALAH solar twins to address these issues. We apply The Cannon algorithm to generate a catalogue of about 40 000 solar twins with 14 high precision abundances which we use to perform a phylogenetic analysis on a selection of stars that have two different ranges of eccentricities. From our analyses, we are able to find a group with mostly stars on circular orbits and some old stars with eccentric orbits whose age-[Y/Mg] relation agrees remarkably well with the chemical clocks published by previous high precision abundance studies. Our results show the power of combining survey data with machine learning and phylogenetics to reconstruct the history of the Milky Way.
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    On the Evolutionary History of a Simulated Disk Galaxy as Seen by Phylogenetic Trees
    (2024) Silva, Danielle de Brito; Jofre, Paula; Tissera, Patricia B.; Yaxley, Keaghan J.; Jara, Jenny Gonzalez; Eldridge, Camilla J. L.; Sillero, Emanuel; Yates, Robert M.; Hua, Xia; Das, Payel; Aguilera-Gomez, Claudia; Johnston, Evelyn J.; Rojas-Arriagada, Alvaro; Foley, Robert; Gilmore, Gerard
    Phylogenetic methods have long been used in biology and more recently have been extended to other fields-for example, linguistics and technology-to study evolutionary histories. Galaxies also have an evolutionary history and fall within this broad phylogenetic framework. Under the hypothesis that chemical abundances can be used as a proxy for the interstellar medium's DNA, phylogenetic methods allow us to reconstruct hierarchical similarities and differences among stars-essentially, a tree of evolutionary relationships and thus history. In this work, we apply phylogenetic methods to a simulated disk galaxy obtained with a chemodynamical code to test the approach. We found that at least 100 stellar particles are required to reliably portray the evolutionary history of a selected stellar population in this simulation, and that the overall evolutionary history is reliably preserved when the typical uncertainties in the chemical abundances are smaller than 0.08 dex. The results show that the shapes of the trees are strongly affected by the age-metallicity relation, as well as the star formation history of the galaxy. We found that regions with low star formation rates produce shorter trees than regions with high star formation rates. Our analysis demonstrates that phylogenetic methods can shed light on the process of galaxy evolution.