Speaker
Description
Classical novae are known to demonstrate a supersoft X-ray source (SSS) state following outbursts. This state is associated with residual thermonuclear burning on the white dwarf (WD) surface. We performed a spectral analysis of the supersoft X-ray phase of the classical nova AT 2018bej, which was observed in X-rays by the eROSITA and XMM-Newton telescopes. To describe the spectrum we calculated high-gravity hot LTE model atmospheres of hot WDs with chemical compositions typical for nova SSS phases, focusing specifically on carbon abundance. The code developed by Suleimanov et al. (2024) was used for this aim. The 0.3-0.6 keV analysis yields a WD temperature Teff ~ 600 kK, gravity $\log g \sim 8.3-8.4$ and a WD radius $R \sim 8000-8700$ km, which gives luminosity $L \sim 6-6.5 * 10^{37}$ erg/s. The derived WD mass is estimated to be $\sim 1.1*M_\odot$. We traced a minor evolution of the source on a half-year timescale accompanied by a decrease in carbon abundance, decrease in temperature and increase in radius, and concluded that LTE model atmospheres are applicable for analysing X-ray spectra of classical novae during their SSS stage.
