Astronomy and Astrophysics – Astronomy
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...206.4005b&link_type=abstract
American Astronomical Society Meeting 206, #40.05; Bulletin of the American Astronomical Society, Vol. 37, p.495
Astronomy and Astrophysics
Astronomy
2
Scientific paper
Epsilon Aurigae, a bright third-magnitude star in the northern sky, has puzzled astronomers for most of the last century. The optical and ultraviolet spectrum longward of Lyman-α is that of an F supergiant. It is distinguished by having the longest known period, 27.1 years, of any eclipsing binary. The spectrum implies a massive primary (15--30 M&sun;) and the orbital solution implies a comparably massive companion. Although the two-year long primary eclipse is flat-bottomed, which should mean the primary star is totally occulted, no secondary stellar spectrum is seen. Shortward of 1600 Å and longward of 5 μ m, the eclipse is shallower. The most favored model for this system, which explains the optical light curve and excess infrared flux, is that the secondary object is a large, dark, cold disk (presumably with an optically-obscured star at its center), seen nearly edge-on, which partially occults the F star during eclipse.
Recent FUSE observations of the far ultraviolet spectrum of ɛ Aur show an emission line spectrum and scaled surface flux quite unlike that of the comparable supergiant α Car, suggesting the presence of a hot component. The rich emission line spectrum is reminiscent of ζ Aurigae stars in eclipse. The ζ Aur binaries are supergiant stars that eclipse their main-sequence companions. In these binaries, the emission line spectrum seen during totality is produced by scattering of hot star continuum photons in the wind of the cool supergiant. For ɛ Aur, the anomalous FUV spectrum and flux suggest a similar formation: continuum photons from a hot companion embedded in the occulting disk are scattered by the wind of the F supergiant. The presence of scattered photons down to 1050 Å implies the companion has a spectral type earlier than B5. We use a variety of multi-wavelength observations to constrain the parameters of the newly unveiled B-star in ɛ Aur.
Ake Thomas B.
Bennett David P.
Harper Graham M.
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