Influence of the gravitational darkening effect on the spectrum of a hot, rapidly rotating neutron star. II. Iron lines

TL;DR

This paper investigates how gravitational darkening affects the spectral lines of rapidly rotating neutron stars, emphasizing the importance of including this effect in realistic atmospheric models.

Contribution

It provides a detailed analysis of gravitational darkening's impact on iron line profiles, highlighting its significance in modeling neutron star spectra.

Findings

Gravitational darkening does not alter line central energies.

Spectral line profiles vary significantly with rotation frequency and inclination.

Including gravitational darkening is essential for accurate neutron star atmosphere models.

Abstract

Rapidly rotating neutron stars are similar to highly flattened ellipsoids. Observed spectra of flattened stars must exhibit effects of non spherical shape and the gravitational darkening. We examined in detail the influence of both effects on the observed central energies and profiles of lines of highly ionized iron, FeXXV and FeXXVI. We note that the gravitational darkening effect do not change the central energy of lines. What is important, spectra of neutron stars that rotate with different frequencies and are seen at various inclinations angles differ significantly. The appearance and the depth of lines strongly depends on the parameters like the inclination angle of the star or the frequency of the star rotation. In this paper we clearly show that the gravitational darkening effect should be included in realistic model of the atmospheres of the neutron stars.