An X-Ray and Optical Light Curv Model of the Eclipsing Symbiotic Binary SMC3

TL;DR

This paper models the light curves of the eclipsing symbiotic binary SMC3, revealing how the red giant's irradiation and the X-ray emitting region's occultation inform our understanding of symbiotic star evolution towards Type Ia supernovae.

Contribution

It provides a detailed eclipse and light curve model of SMC3, illustrating the mass transfer and X-ray emission characteristics in a rare symbiotic binary.

Findings

The red giant fills its Roche lobe and supplies matter to the white dwarf.

The X-ray emitting region is almost totally occulted during eclipse.

A spiral tail of neutral hydrogen surrounds the binary.

Abstract

Some binary evolution scenarios to Type Ia supernovae include long-period binaries that evolve to symbiotic supersoft X-ray sources in their late stage of evolution. However, symbiotic stars with steady hydrogen burning on the white dwarf's (WD) surface are very rare, and the X-ray characteristics are not well known. SMC3 is one such rare example and a key object for understanding the evolution of symbiotic stars to Type Ia supernovae. SMC3 is an eclipsing symbiotic binary, consisting of a massive WD and red giant (RG), with an orbital period of 4.5 years in the Small Magellanic Cloud. The long-term V light curve variations are reproduced as orbital variations in the irradiated RG, whose atmosphere fills its Roche lobe, thus supporting the idea that the RG supplies matter to the WD at rates high enough to maintain steady hydrogen burning on the WD. We also present an eclipse model in which an X-ray emitting region around the WD is almost totally occulted by the RG swelling over the Roche lobe on the trailing side, although it is always partly obscured by a long spiral tail of neutral hydrogen surrounding the binary in the orbital plane.