Chinese astronomers discover nine non-evolved super-rich lithium stars

(ORDO NEWS) — Using the Large Sky Area Multi-Object (LAMOST) Fiber Spectroscopic Telescope, astronomers from China have discovered nine new non-developing stars. These new stars are distinguished by an unusually high content of lithium. This is reported in an article published April 7 on the arXiv website.

Although the abundance of lithium in most stars is quite low, some of them contain a lot of lithium (Li) – more than the meteoritic value of 3.3 dex.

Astronomers speculate that stars with unusually high lithium abundances must have experienced lithium enrichment. However, current models for the mechanism of such enrichment are still being discussed, and none of them can explain these stars well.

In order to better understand the mechanism of lithium enrichment, it is necessary to study non-evolved super-rich lithium stars.

Given that only a few objects of this type have been discovered to date, a new study by Taisheng Yang of the University of the Chinese Academy of Sciences in Beijing, China, and colleagues, which presented the discovery of nine new stars of this class, could be a breakthrough in this area.

“We found nine superrich Li-undeveloped stars with Li A(Li) excesses above 3.8 dex from the LAMOST-MRS data, which is the largest sample of stars of this type,” the researchers write in their paper.

Nine of the newly discovered stars have unusually high levels of lithium, suggesting they must have experienced a history of lithium enrichment. Eight of them have almost solar metallicity (from -0.4 to 0.4 dex), and the poorest in metals is UCAC4 646-05072 with a metallicity of -0.69 dex.

In general, the stars presented in the study have radii from 0.89 to 2.51 solar radii, and their masses range from 0.78 to 1.6 solar masses. The effective temperatures of these stars have been measured in the range from 5100 K to 5800 K, with the exception of the hottest star UCAC4 629-030411, which has a temperature of 6807 K.

Four stars from this sample, namely UCAC4 440-009448, UCAC4 441-011058, UCAC4 451-011087, and UCAC4 606-009417, turned out to be young stellar objects. Their lithium abundances exceed 3.8 dex, about three times higher than the upper shell value for young stars reported in a study published in 2021.

Given that these four young stellar objects, as well as three other stars, are rapidly rotating, astronomers speculate that accretion of circumstellar matter may be a major factor contributing to the lithium increase.

“Given that they all rotate rapidly (v sini > 15 km/s), the most likely possibility is the accretion of lithium-rich circumstellar matter,” the researchers noted.

Further research is needed to confirm this scenario.” The authors hope that the ongoing LAMOST Medium-Resolution Spectroscopic Survey (MRS) will yield more discoveries of ultra-lithium-rich non-evolved stars.


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