We present the discovery of a super lithium-rich K giant star , G0928+73.2600 .
This red giant ( T _ { eff } = 4885 K and \log g = 2.65 ) is a fast rotator with a projected rotational velocity of 8.4 km s ^ { -1 } and an unusually high lithium abundance of A ( Li ) = 3.30 dex .
Although the lack of a measured parallax precludes knowing the exact evolutionary phase , an isochrone-derived estimate of its luminosity places the star on the Hertzsprung–Russell diagram in a location that is not consistent with either the red bump on the first ascent of the red giant branch or with the second ascent on the asymptotic giant branch , the two evolutionary stages where lithium-rich giant stars tend to cluster .
Thus , even among the already unusual group of lithium-rich giant stars , G0928+73.2600 is peculiar .
Using ^ { 12 } C/ ^ { 13 } C as a tracer for mixing—more mixing leads to lower ^ { 12 } C/ ^ { 13 } C—we find ^ { 12 } C/ ^ { 13 } C = 28 , which is near the expected value for standard first dredge-up mixing .
We can therefore conclude that “ extra ” deep mixing has not occurred .
Regardless of the ambiguity of the evolutionary stage , the extremely large lithium abundance and the rotational velocity of this star are unusual , and we speculate that G0928+73.2600 has been enriched in both lithium and angular momentum from a sub-stellar companion .