COBAIN: generalized 3D radiative transfer code for contact binary atmospheres

TL;DR

COBAIN is a new generalized 3D radiative transfer code designed to accurately model the complex atmospheres of contact binary stars, improving upon previous simplified methods.

Contribution

The paper introduces COBAIN, a novel radiative transfer code that addresses the limitations of traditional models by accurately simulating contact binary atmospheres with complex geometries.

Findings

Initial tests on various stellar models demonstrate COBAIN's capabilities.

The code can handle different geometries and rotational states.

It aims to produce accurate atmosphere tables for binary star analysis.

Abstract

Contact binary stars have been known to have a peculiar and somewhat mysterious hydro- and thermodynamical structure since their discovery, which directly affects the radiation distribution in their atmospheres. Over the past several decades, however, observational data of contact binaries have been modeled through a simplified approach, involving the artificial concatenation of the two components of the contact envelope and populating their respective surfaces with either blackbody atmospheres or plane-parallel model atmospheres of single stars. We show the implications this approach has on the reliability of the system parameter values and propose a method to overcome these issues with a new generalized radiative transfer code, COBAIN (COntact Binary Atmospheres with INterpolation). The basic principles of COBAIN are outlined and their application to different geometries and polytropic stellar structures is discussed. We present initial tests on single non-rotating, uniformly rotating and differentially rotating stars, as well as on simplified polytropic structural models of contact binaries. We briefly discuss the final goal of this ambitious project, which is the computation of model atmosphere tables under the correct assumptions for contact binary stars, to be used in modern binary star analysis codes.