http://arxiv.org/abs/2209.03010
Current models of stellar evolution predict that stars more massive than $\sim6:$M${\odot}$ should have completely depleted all lithium (Li) in their atmospheres by the time when they reach the He core burning phase. Against this, a non-negligible number of red giants with masses $>6:$M${\odot}$ presenting strong Li lines have recently been reported. Motivated by this finding, we have carried out a spectroscopic survey of red supergiants (RSGs) in the Perseus Arm and a selection of young open clusters in the Magellanic Clouds to assess the presence of the Li I $\lambda$6708 doublet line. Based on a sample of >70 objects, close to one third of RSGs in the Perseus Arm display noticeable Li lines, with perhaps a trend towards a lower fraction among more luminous stars. The samples in the Magellanic Clouds are not as large, but hint at a metallicity dependence. Twenty one RSGs in 5 LMC clusters show a very high fraction of Li detection, around 40%. Conversely, 17 RSGs in 5 SMC clusters give only one secure detection. The interpretation of these observational results is not straightforward, but a mechanism for Li production seems most likely. Further characterisation work is ongoing, while theoretical studies into this matter are urgently needed.
I. Negueruela, J. Alonso-Santiago, R. Dorda, et. al.
Thu, 8 Sep 22
53/77
Comments: Accepted in proceedings for IAU Symposium 361: Massive Stars Near and Far, held in Ballyconnell, Ireland, 9-13 May 2022. N. St-Louis, J. S. Vink & J. Mackey, eds
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