A method to simulate inhomogeneously irradiated objects with a superposition of 1D models

TL;DR

This paper introduces a novel method to simulate inhomogeneously irradiated objects by combining multiple 1D models based on irradiation angles, improving accuracy over single-temperature approximations.

Contribution

It presents a geometry-based scheme to incorporate varying irradiation angles into stellar atmosphere models, independent of the physical mechanisms involved.

Findings

Different ionisation states are produced at various irradiation angles.

Single-angle models cannot accurately reproduce the spectrum of inhomogeneously irradiated objects.

The method effectively captures the dependence of spectral features on irradiation geometry.

Abstract

In close binary systems the atmosphere of one or both components can be significantly influenced by irradiation from the companion. Often the irradiated atmosphere is simulated with a single-temperature approximation for the entire half-sphere. We present a scheme to take the varying irradiation angle into account by combining several separate 1D models. This is independent of the actual code which provides the separate stellar spectra. We calculate the projected area of zones with given irradiation angle and use this geometrical factor to scale separate 1D models. As an example we calculate two different irradiation scenarios with the PHOENIX code. The scheme to calculate the projected area is applicable independent of the physical mechanism that forms these zones. In the case of irradiation by a primary with T=125000 K, the secondary forms ions at different ionisation states for different irradiation angles. No single irradiation angle exists which provides an accurate description of the spectrum. We show a similar simulation for weaker irradiation, where the profile of the H$\alpha$ line depends on the irradiation angle.