We report spectroscopic observations of the resonance lines of singly ionized $^{ 7}$Be in the blue-shifted absorption line systems found in the post-outburst spectra of two classical novae -- V5668 Sgr (Nova Sagittarii 2015 No.2) and V2944 Oph (Nova Ophiuchi 2015). The unstable isotope, $^{ 7}$Be, should has been created during the thermonuclear runaway (TNR) of these novae and decays to form $^{ 7}$Li within a short period (a half-life of 53.22 days). Confirmations of $^{ 7}$Be are the second and the third ones following the first case found in V339 Del by Tajitsu et al. (2015). The blue-shifted absorption line systems in both novae are clearly divided into two velocity components, both of which contain $^{ 7}$Be. This means that the absorbing gases in both velocity components consist of products of TNR. We estimate amounts of $^{ 7}$Be produced during outbursts of both novae and conclude that significant $^{ 7}$Li should have been created. These findings strongly suggest that the explosive production of $^{ 7}$Li via the reaction $^{ 3}$He($\alpha$,$\gamma$)$^{ 7}$Be and subsequent decay to $^{ 7}$Li occurs frequently among classical novae and contributes to the process of the Galactic Li enrichment.
Categories: astro-ph.SR
