The ${}^7$Be II Resonance Lines in Two Classical Novae V5668 Sgr and V2944 Oph

Abstract

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.

8 pages, 6 figures, accepted for publication in ApJ

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