Taming the Invisible Monster: System Parameter Constraints for epsilon Aurigae from the Far-ultraviolet to the Mid-infrared
We have assembled new Spitzer Space Telescope IRAC observations of the mysterious binary star epsilon Aurigae, along with archival far-ultraviolet to mid-infrared data, to form an unprecedented spectral energy distribution (SED) spanning 3 orders of magnitude in wavelength from 0.1 μm to 100 μm. The observed SED can be reproduced using a three-component model consisting of a 2.2+0.9 -0.8 M sun F-type post-asymptotic giant branch star, and a 5.9 ± 0.8 M sun 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 R sun for the F star, consistent with published interferometric observations. The dusty disk is constrained to be viewed at an inclination of i >~ 87°, and has an 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 μm 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 Lt1 M sun. We discuss evolutionary scenarios for this system that could lead to the current status of the stellar components and suggest possibilities for its future evolution, as well as potential observational tests of our model.
The Astrophysical Journal
- Pub Date:
- May 2010
- binaries: eclipsing;
- circumstellar matter;
- stars: AGB and post-AGB;
- stars: individual: Epsilon Aurigae;
- Astrophysics - Solar and Stellar Astrophysics
- 13 pages, 3 figures. Accepted for publication in The Astrophysical Journal.