An evidencebased assumption that helps to reduce the discrepancy between the observed and predicted ^{7}Be abundances in novae
Abstract
Recent spectroscopic measurements of the equivalent widths of the resonant Be II doublet and Ca II K lines and their ratios in expanding nova ejecta indicate surprisingly high abundances of ^{7}Be with a typical mass fraction X_{obs}(^{7}Be) = 10^{4}. This is an order of magnitude larger than theoretically predicted values of X_{theor}(^{7}Be) ~ 10^{5} for novae. We use an analytical solution of the ^{7}Be production equations to demonstrate that X_{theor}(^{7}Be) is proportional to the ^{4}He mass fraction Y in the nova accreted envelope and then we perform computations of 1D hydrostatic evolution of the $1.15\, \mathrm{M}_\odot$ CO nova model that confirm our conclusion based on the analytical solution. Our assumption of enhanced ^{4}He abundances helps to reduce, although not completely eliminate, the discrepancy between X_{obs}(^{7}Be) and X_{theor}(^{7}Be). It is supported by ultraviolet, optical, and infrared spectroscopy data that reveal unusually high values of Y in nova ejecta. We also show that a significantly increased abundance of ^{3}He in nova accreted envelopes does not lead to higher values of X_{theor}(^{7}Be) because this assumption affects the evolution of nova models resulting in a decrease of both their peak temperatures and accreted masses and, as a consequence, in a reduced production of ^{7}Be.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 February 2021
 DOI:
 10.1093/mnrasl/slaa190
 arXiv:
 arXiv:2010.09825
 Bibcode:
 2021MNRAS.501L..33D
 Keywords:

 nuclear reactions;
 nucleosynthesis;
 abundances;
 stars: abundances;
 novae;
 cataclysmic variables;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 5 pages, 2 figures, accepted for publication in MNRAS Letters