Mass-loss, composition and observational signatures of stellar winds from X-ray bursts

TL;DR

This study models the mass-loss and chemical composition of stellar winds from X-ray bursts on neutron stars, predicting observational signatures and ejected material characteristics.

Contribution

It applies a coupled wind and hydrodynamic model to multiple bursts, providing new insights into wind composition, mass-loss rates, and observational signatures during XRBs.

Findings

Approximately 0.1% of the envelope mass is ejected per burst.

Ejecta predominantly contain isotopes like $^{60}$Ni, $^{64}$Zn, and $^{68}$Ge.

Simulated NICER observations resemble real data from 4U 1820-40.

Abstract

X-Ray bursts (XRBs) are powerful thermonuclear events on the surface of accreting neutron stars (NSs), which can synthesize intermediate-mass elements. Although the high surface gravity prevents an explosive ejection, a small fraction of the envelope may be ejected by radiation-driven winds. In our previous works, we have developed a non-relativistic radiative wind model and coupled it to an XRB hydrodynamic simulation. We now apply this technique to another model featuring consecutive bursts. We determine the mass-loss and chemical composition of the wind ejecta. Results show that, for a representative XRB, about $0.1\%$ of the envelope mass is ejected per burst, at an average rate of $3.9 \times 10^{-12}\,M_\odot \texttt{yr}^{-1}$. Between $66\%$ and $76\%$ of the ejecta composition is $^{60}$Ni, $^{64}$Zn, $^{68}$Ge, $^{4}$He and $^{58}$Ni. We also report on the evolution of observational quantities during the wind phase and simulate NICER observations that resemble those of 4U 1820-40.