Discovery of ubiquitous lithium production in low-mass stars. (arXiv:2007.07045v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kumar_Y/0/1/0/all/0/1">Yerra Bharat Kumar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reddy_B/0/1/0/all/0/1">Bacham E. Reddy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Campbell_S/0/1/0/all/0/1">Simon W. Campbell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maben_S/0/1/0/all/0/1">Sunayana Maben</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhao_G/0/1/0/all/0/1">Gang Zhao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ting_Y/0/1/0/all/0/1">Yuan-Sen Ting</a>
The vast majority of stars with mass similar to the Sun are expected to only
destroy lithium over the course of their lives, via low-temperature nuclear
burning. This has now been supported by observations of hundreds of thousands
of red giant stars (Brown et al. 1989, Kumar et al. 2011, Deepak et al. 2019,
Singh et al. 2019, Casey et al. 2019). Here we perform the first large-scale
systematic investigation into the Li content of stars in the red clump phase of
evolution, which directly follows the red giant branch phase. Surprisingly we
find that all red clump stars have high levels of lithium for their
evolutionary stage. On average the lithium content increases by a factor of 40
after the end of the red giant branch stage. This suggests that all low-mass
stars undergo a lithium production phase between the tip of the red giant
branch and the red clump. We demonstrate that our finding is not predicted by
stellar theory, revealing a stark tension between observations and models. We
also show that the heavily studied (Brown et al. 1989, Reddy et al. 2005, Kumar
et al. 2011, Singh et al. 2019, Casey et al. 2019) very Li-rich giants, with
A(Li) $> +1.5$ dex, represent only the extreme tail of the lithium enhancement
distribution, comprising 3% of red clump stars. Our findings suggest a new
definition limit for Li-richness in red clump stars, A(Li) $> -0.9$ dex, which
is much lower than the limit of A(Li) $> +1.5$ dex used over many decades
(Brown et al. 1989, Castilho et al. 1995, Reddy et al. 2005, Carlberg et al.
2016, Casey et al. 2019, Holanda et al. 2020).
The vast majority of stars with mass similar to the Sun are expected to only
destroy lithium over the course of their lives, via low-temperature nuclear
burning. This has now been supported by observations of hundreds of thousands
of red giant stars (Brown et al. 1989, Kumar et al. 2011, Deepak et al. 2019,
Singh et al. 2019, Casey et al. 2019). Here we perform the first large-scale
systematic investigation into the Li content of stars in the red clump phase of
evolution, which directly follows the red giant branch phase. Surprisingly we
find that all red clump stars have high levels of lithium for their
evolutionary stage. On average the lithium content increases by a factor of 40
after the end of the red giant branch stage. This suggests that all low-mass
stars undergo a lithium production phase between the tip of the red giant
branch and the red clump. We demonstrate that our finding is not predicted by
stellar theory, revealing a stark tension between observations and models. We
also show that the heavily studied (Brown et al. 1989, Reddy et al. 2005, Kumar
et al. 2011, Singh et al. 2019, Casey et al. 2019) very Li-rich giants, with
A(Li) $> +1.5$ dex, represent only the extreme tail of the lithium enhancement
distribution, comprising 3% of red clump stars. Our findings suggest a new
definition limit for Li-richness in red clump stars, A(Li) $> -0.9$ dex, which
is much lower than the limit of A(Li) $> +1.5$ dex used over many decades
(Brown et al. 1989, Castilho et al. 1995, Reddy et al. 2005, Carlberg et al.
2016, Casey et al. 2019, Holanda et al. 2020).
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