Taming the Invisible Monster: System Parameter Constraints for Epsilon Aurigae from the Far-Ultraviolet to the Mid-Infrared

TL;DR

This study constructs a detailed spectral energy distribution of Epsilon Aurigae, revealing the properties of its binary components and dusty disk, through multi-wavelength observations from ultraviolet to mid-infrared.

Contribution

It provides a comprehensive model of Epsilon Aurigae's binary system and circumstellar disk based on new and archival data, constraining physical parameters and disk composition.

Findings

The F star has a radius of approximately 135 solar radii.

The dusty disk is nearly edge-on with an inclination >87 degrees.

The disk contains predominantly large grains (>10 microns) and has a mass much less than one solar mass.

Abstract

We have assembled new Spitzer Space Telescope Infrared Array Camera observations of the mysterious binary star Epsilon Aurigae, along with archival far-ultraviolet to mid-infrared data, to form an unprecedented spectral energy distribution spanning three orders of magnitude in wavelength from 0.1 microns to 100 microns. The observed spectral energy distribution can be reproduced using a three component model consisting of a 2.2+0.9/-0.8 Msun F type post-asymptotic giant branch star, and a 5.9+/-0.8 Msun B5+/-1 type main sequence star that is surrounded by a geometrically thick, but partially transparent, disk of gas and dust. At the nominal HIPPARCOS parallax distance of 625 pc, the model normalization yields a radius of 135+/-5 Rsun for the F star, consistent with published interferometric observations. The dusty disk is constrained to be viewed at an inclination of i > 87 deg, and has effective temperature of 550+/-50 K with an outer radius of 3.8 AU and a thickness of 0.95 AU. The dust content of the disk must be largely confined to grains larger than ~10 microns in order to produce the observed gray optical-infrared eclipses and the lack of broad dust emission features in the archival Spitzer mid-infrared spectra. The total mass of the disk, even considering a potential gaseous contribution in addition to the dust that produces the observed infrared excess, is << 1 Msun. We discuss evolutionary scenarios for this system that could lead to the current status of the stellar components and suggests possibilities for its future evolution, as well as potential observational tests of our model.