2018MNRAS.479.2161G

Worldwide interest in the recent eclipse of epsilon Aurigae resulted in the generation of several extensive data sets, including high-resolution spectroscopic data sets. This lead to the discovery, among other things, of the existence of a mass transfer stream, seen notably during third contact. We explored spectroscopic facets of the mass transfer stream during third contact, using high-resolution spectra obtained with the ARCES and TripleSpec instruments at Apache Point Observatory. One hundred and sixteen epochs of data were obtained between 2009 and 2012, and equivalent widths and line velocities of high- and low-eccentricity accretion disc lines were measured. These data sets also enabled greater detail to be measured of the mid-eclipse enhancement of the He I 10 830 Å line, and the discovery of the P Cygni shape of the Pa β line at the third contact. We found evidence of higher speed material, associated with the mass transfer stream, persisting between third and fourth eclipse contacts. We visualized the disc and stream interaction using SHAPE software, and used CLOUDY software to estimate that the source of the enhanced He I 10 830 Å absorption arises from a region with n_H = 10¹¹ cm^–3 and temperature of 20 000K, consistent with a mid-B-type central star. Van Rensbergen binary star evolutionary models are somewhat consistent with the current binary parameters for their case of a 9 plus 8 solar mass initial binary, evolving into a 2.3 and 14.11 solar mass end product after 35 Myr. With these results, it is possible to make predictions which suggest that continued monitoring prior to the next eclipse (2036) will help resolve standing questions about the mass and age of this binary.