Using the Gemini High-resolution Optical SpecTrograph (GHOST), which is attached to the 8.1-m Gemini South telescope at Cerro Pachón, Chile, astronomers have explored different scenarios to explain the chemical difference found in the remarkable giant-giant binary system HD 138202 + CD-30 12303.
It is estimated that up to 85% of stars exist in binary star systems, some even in systems with three or more stars.
These stellar pairs are born together out of the same molecular cloud from a shared abundance of chemical building blocks, so astronomers would expect to find that they have nearly identical compositions and planetary systems. However, for many binaries that isn’t the case.
While some proposed explanations attribute these dissimilarities to events occurring after the stars evolved, astronomers using the GHOST instrument confirmed that they can actually originate from before the stars even began to form.
“GHOST’s extremely high-quality spectra offered unprecedented resolution, allowing us to measure the stars’ stellar parameters and chemical abundances with the highest possible precision,” said Dr. Carlos Saffe, an astronomer at the Institute of Astronomical, Earth and Space Sciences (ICATE-CONICET).
“These measurements revealed that one star had higher abundances of heavy elements than the other.”
“To disentangle the origin of this discrepancy, we used a unique approach.”
Previous studies have proposed three possible explanations for observed chemical differences between binary stars.
Two of them involve processes that would occur well into the stars’ evolution: atomic diffusion, or the settling of chemical elements into gradient layers depending on each star’s temperature and surface gravity; and the engulfment of a small, rocky planet, which would introduce chemical variations in a star’s composition.
The third possible explanation looks back at the beginning of the stars’ formation, suggesting that the differences…
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