Abundance ratios (X/H) of HE 2315−4240 (black-filled circles) as a function of atomic number. The best-fit population III nucleosynthesis model is overplotted in green. The mass and energy of the model are shown at the top right. Credit: Wang et al., 2024.
Based on data from the Magellan-Clay telescope in Chile, astronomers carried out a chemodynamic study of a very metal-poor star known as HE 2315−4240. Study results, published on the preprint server arXivprovide important information about the nature of this star.
Metal-poor stars are rare objects, as only a few thousand stars with an iron abundance (Fe/H) below -2.0 have been discovered to date. Expanding the still short list of metal-poor stars is of great importance to astronomers, because these objects have the potential to improve our knowledge of the chemical evolution of the universe.
With a metallicity of approximately -2.89 dex, HE 2315−4240 is a very metal-poor star located at an estimated distance of approximately 9,300 light-years from Earth. Since the star is poorly studied and very little is known about its properties, a team of astronomers led by Xinuo Wang of Cornell University in Ithaca, New York, decided to study it with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph mounted on the star. Magellan-Clay telescope.
“In this study, we present a spectrum of a very metal-poor star, HE 2315−4240, with (Fe/H) = −2.89, based on a high-resolution Magellan/MIKE visual light spectrum,” says the study.
In total, Wang’s team managed to obtain abundances of 19 elements. Alpha and iron peak elements were found to agree well with the abundance trend of other known metal-poor stars. This, according to astronomers, confirms that at least one supernova enhanced these elements in the gas cloud that formed HE 2315−4240.
Furthermore, observations revealed that HE 2315−4240 exhibits low strontium/barium and carbon/iron abundance ratios. These results indicate that the star accreted and formed in a dwarf galaxy. The effective temperature of HE 2315−4240 has been estimated to be 5181 K, making it a hot giant.
According to the study, the metallicity of HE 2315−4240, as well as its abundances of magnesium and silicon, suggest that the star formed from gas enriched by a Type II supernova explosion. Astronomers assume that the ancestor was most likely a massive (around 10 solar masses) population III star. The hypothetical Population III stars, composed almost entirely of primordial gas, would theoretically be the first stars to form after the Big Bang.
Based on the kinematic analysis performed, the researchers assume that HE 2315−4240 formed outside the galactic disk, probably in a small dwarf galaxy, and was subsequently absorbed by the growing Milky Way.
“The progenitor system likely accumulated before other systems, placing the star in the inner halo as we know it today,” the paper concludes.
More information:
Xinuo Wang, Chemodynamic analysis of the abundance of the very metal-poor halo star HE 2315-4240, arXiv (2024). DOI: 10.48550/arxiv.2410.02586
Journal information:
arXiv
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Quote: A study focuses on the very metal-poor star HE 2315−4240 (October 13, 2024) recovered on October 14, 2024 from
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