The evolving status of HD 1936. Credit: Çalışkan et al, 2024
Using the Ankara University Kreiken Observatory (AUKR) in Turkey, astronomers have made high-resolution spectroscopic observations of a metal-poor star known as HD 1936. Results of the campaign observations, published on February 15 on the preprint server. arXivallowed us to better understand the chemical composition of this star.
Metal-poor stars are rare objects since only a few thousand stars with iron abundance (Fe/H) less than -2.0 have been discovered to date. Expanding the still short list of metal-poor stars and studying these objects in detail is of great importance to astronomers, because these stars have the potential to improve our knowledge of the chemical evolution of the universe.
HD 1936 (also known as HIP 1873) is a very bright, metal-poor star of spectral type G5 located about 1,000 light-years away in the galactic halo. The star, around 10 billion years old, is estimated to be at least 10 times larger than the sun, while its mass is likely between 0.9 and 3.0 solar masses. Some studies suggest that the star has a substellar companion with a mass of about 18.35 Jupiter masses.
Although previous observations have determined the atmospheric parameters of HD 1936, a detailed chemical study of this star has not yet been conducted. This is why a team of Turkish astronomers led by Şeyma Çalışkan from Ankara University decided to study HD 1936 with the Whoppshel spectrograph mounted on AUKR’s 0.8m Berahitdin Albayrak telescope.
“We present the chemical abundances of the very bright, metal-poor star HD 1936 based on high-resolution and high SNR (signal-to-noise ratio) spectra of AUKR,” the researchers wrote.
The team managed to obtain the abundances of 29 atomic species for HD 1936. The metallicity of the star was determined to be -1.74, which is generally in agreement with previous estimates.
Observations revealed that HD 1936 is not carbon enhanced and has light and odd Z element abundance ratios primarily consistent with those of metal-poor field stars. The abundance ratio of sodium to iron appears to be subsolar, while the abundance ratio of aluminum to iron was found to be supersolar.
According to the article, the initial lithium abundance for HD 1936 was measured at approximately 1.01 dex. This is consistent with what is usually observed in lower red giant branch stars.
The determined abundance ratios of europium and barium suggest very little s-process contamination for the studied star. This allowed astronomers to classify HD 1936 as a moderately metal-poor star enhanced by the r process.
The results obtained also suggest that HD 1936 could be a second generation star formed in a multi-enriched environment. The measured abundance ratio of magnesium to carbon indicates enrichment due to more than one supernova.
More information:
Şeyma Çalışkan et al, On the chemical composition of the very bright and metal-poor evolved star HD 1936, arXiv (2024). DOI: 10.48550/arxiv.2402.09840
Journal information:
arXiv
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