Lithium abundance of V404 Cygni’s tertiary companion

Determine whether the wide tertiary companion star in the V404 Cygni hierarchical triple exhibits enhanced lithium abundance relative to expectations for a 3–5 Gyr, approximately 1.2 solar mass star, by establishing the presence or absence of lithium enhancement in the tertiary’s spectrum.

Background

Several black hole low-mass X-ray binary donors have been reported to show enhanced lithium, with proposed origins including accretion-related processes or supernova nucleosynthesis. In V404 Cygni, the authors infer a system age of about 3–5 Gyr from the tertiary’s evolutionary state, ruling out recent formation as the cause of the donor’s lithium enrichment.

The authors attempted to assess whether the tertiary also shows lithium enhancement, but current spectroscopic data lack the signal-to-noise and resolution necessary. Clarifying the tertiary’s lithium abundance would inform the history of chemical enrichment in the system and the mechanisms responsible for lithium enhancement in BH LMXBs.