Observational Evidence for Expansion in the SSS spectra of Novae

TL;DR

This paper presents observational evidence that the ejecta in novae continue to expand during the Super Soft X-ray Source phase, challenging previous assumptions of halted mass loss at this stage.

Contribution

It demonstrates that all observed novae in the SSS phase exhibit significant expansion, requiring models to incorporate ongoing ejecta expansion.

Findings

All SSS phase novae show blue-shifted absorption lines.

Expansion persists throughout the SSS phase.

Models must account for continued ejecta expansion.

Abstract

For several novae, a bright X-ray source with a spectrum resembling the class of Super Soft X-ray Sources (SSS) has been observed a few weeks to months after outburst. Novae are powered by explosive nuclear burning on the surface of a white dwarf, and enough energy is produced to power a radiatively driven wind. Owing to the evolution of the opacity of the ejecta, the observable spectrum gradually shifts from optical to soft X-rays (SSS phase). It has sometimes been assumed that at the beginning of the SSS phase no more mass loss occurs. However, high-resolution X-ray spectra of some novae have shown highly blue-shifted absorption lines, indicating a significant expansion. In this paper, I show that all novae that have been observed with X-ray gratings during their SSS phase show significant blue shifts. I argue that all models that attempt to explain the X-ray bright SSS phase have to accommodate the continued expansion of the ejecta.