2021ApJ...916...44A

We report the new detection of ⁷Be II in the ultraviolet spectra of V5669 Sgr during its early decline phase (+24 and +28 d). We identified three blueshifted absorption systems in our spectra. The first two, referred to as low- and high-velocity components, were noticeably identified among H I Balmer, Na I D, and Fe II whose lower energies of transients are low (<4 eV). The third absorption component was identified among N II, He I, and C II lines whose lower energy levels are relatively high (9-21 eV). The absorption lines of ⁷Be II at 3130.583 Å and 3132.228 Å were identified as the first and second components in our observations. No evidence suggested the existence of Li I at 6708 Å in any velocity components. The estimated number density ratio of lithium relative to hydrogen, which was finally produced by this object using the equivalent widths of ⁷Be and Ca II K, N(⁷Li)/N(H)_final, is 4.0 ± 0.7 x 10^–6. This value is an order of magnitude lower than the average observed values for classical novae wherein ⁷Be has been detected, and is comparable to the most optimistic value of theoretical predictions.