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Using the Gran Telescopio Canarias (GTC), astronomers from the Chinese Academy of Sciences (CAS) and elsewhere have discovered a new extremely r-process enhanced star in the Milky Way’s thin disk. The finding was reported in a research paper published July 16 on the preprint server arXiv.

Process-enhanced (RPE) stars are a small fraction of old, metal-poor stars that show large enhancements in elements (such as europium, thorium, or uranium) produced in the fast neutron capture process. These stars, which mainly populate the Milky Way’s halo and dwarf satellite galaxies, are excellent laboratories for studying the r-process and can help us better understand the assembly history of our galaxy.

Now a team of astronomers led by Xiao-Jin Xie of CAS reports the discovery of a new RPE star. They used the GTC’s High Optical Resolution Spectrograph (HORuS) to observe a star designated LAMOST J020623.21+494127.9 (or J 0206+4941 for short). The observing campaign led to the classification of this object as an extremely r-process enhanced star.

“It [J 0206+4941] was originally selected by the LAMOST Medium Resolution Survey as a candidate RPE star, based on its unusually strong europium lines,” the researchers wrote in the paper.

The observations found that J 0206+4941 is a bright star that belongs to the thin disk of the Milky Way. Based on the collected data, astronomers were able to deduce the abundances of 30 elements for this star and determine its kinematics.

According to the new findings, J 0206+4941 has a metallicity of -0.54, an effective temperature of approximately 4078 K, and a europium-to-hydrogen abundance ratio of 0.78. Overall, the light element abundances in this star were found to be comparable to other stars of similar metallicity and evolutionary phase, with a strong enhancement of europium and a moderate enhancement of barium.

The paper’s authors emphasize that J 0206+4941 is therefore the most metal-rich star with a highly enhanced r-process discovered to date. The age of the star is uncertain, probably around 12.3 billion years, and further research is needed to confirm this.

Trying to explain the origin of J 0206+4941, scientists do not rule out the possibility that it was born in situ in the thin disk of the Milky Way. They added that it may have formed from an interstellar medium (ISM) enriched in r-process elements by the merger of a single binary neutron star or core-collapse supernova (CCSNe).

In concluding remarks, the astronomers noted that in addition to J 0206+4941, they also identified several other metal-rich RPE candidates that are worth further investigation using instruments such as HORuS.

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