2014ApJ...787..165O

We investigate the mechanism that reproduced notable spectral features at the ignition phase of the nova explosion observed for a super-Eddington X-ray transient source MAXI J0158-744 in the Small Magellanic Cloud. These features include a strong Ne IX emission line at 0.92 keV with large equivalent widths of 0.32 _–0.11^+0.21 keV and the absence of the Ne X line at 1.02 keV. In this paper, we calculate the radiative transfer using a Monte Carlo code, taking into account the line blanketing effect due to transitions of N, O, Ne, Mg, and Al ions in an accelerating wind emanating from a white dwarf with a structure based on a spherically symmetric stationary model. We found that the strong Ne IX line can be reproduced if the mass fraction of Ne is enhanced to 10^–3 or more and if that of O is reduced to ∼5x10^–9 or less and that the absence of other lines, including Ne X ions at higher energies, can be also reproduced by the line blanketing effect. This enhancement of the Ne mass fraction indicates that the ejecta are enriched by Ne dredged up from the surface of the white dwarf composed of O, Ne, and Mg rather than C and O, as already pointed out in previous work. We argue that the CNO cycle driving this nova explosion converted most of C and O into N and thus reduced the O mass fraction.